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Sample records for high frequency quasi-periodic

  1. ON THE HIGH-FREQUENCY QUASI-PERIODIC OSCILLATIONS FROM BLACK HOLES

    SciTech Connect

    Erkut, M. Hakan

    2011-12-10

    We apply the global mode analysis, which has been recently developed for the modeling of kHz quasi-periodic oscillations (QPOs) from neutron stars, to the inner region of an accretion disk around a rotating black hole. Within a pseudo-Newtonian approach that keeps the ratio of the radial epicyclic frequency {kappa} to the orbital frequency {Omega} the same as the corresponding ratio for a Kerr black hole, we determine the innermost disk region where the hydrodynamic modes grow in amplitude. We find that the radiation flux emerging from the inner disk has the highest values within the same region. Using the flux-weighted averages of the frequency bands over this region we identify the growing modes with highest frequency branches {Omega} + {kappa} and {Omega} to be the plausible candidates for the high-frequency QPO pairs observed in black hole systems. The observed frequency ratio around 1.5 can therefore be understood naturally in terms of the global free oscillations in the innermost region of a viscous accretion disk around a black hole without invoking a particular resonance to produce black hole QPOs. Although the frequency ratio ({Omega} + {kappa})/({Omega}) is found to be not sensitive to the black hole's spin which is good for explaining the high-frequency QPOs, it may work as a limited diagnostic of the spin parameter to distinguish black holes with very large spin from the slowly rotating ones. Within our model we estimate the frequency ratio of a high-frequency QPO pair to be greater than 1.5 if the black hole is a slow rotator. For fast rotating black holes, we expect the same ratio to be less than 1.5.

  2. A model of the spectra and high-frequency quasi-periodic oscillations in black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Dexter, Jason

    2016-07-01

    High-frequency quasi-periodic oscillations (HFQPOs) in black hole X-ray binaries have frequencies comparable to the orbital frequency at the innermost stable circular orbit, and therefore may encode information about strong field general relativity. However, the origin of the oscillations and the associated X-ray spectra remain uncertain. I will discuss a new model for these spectra, which also acts to filter coherent QPOs from local accretion disk oscillations. This model explains many puzzling aspects of HFQPOs, makes predictions which are testable with archival and future X-ray data, and can in principle be used as a new method to measure black hole spin.

  3. High-Frequency Quasi-Periodic Oscillations in the Black Hole X-Ray Transient XTE J1650-500

    NASA Technical Reports Server (NTRS)

    Holman, Jeroen; Klein-Wolt, Marc; Rossi, Sabrina; Miller, Jon M.; Wijnands, Rudy; Belloni, Tomaso; VanDerKlis, Michiel; Lewin, Walter H. G.

    2003-01-01

    We report the detection of high-frequency variability in the black hole X-ray transient XTE 51650-500. A quasi-periodic oscillation (QPO) was found at 250 Hz during a transition from the hard to the soft state. We also detected less coherent variability around 50 Hz that disappeared when the 250 Hz QPO showed up. There are indications that when the energy spectrum hardened the QPO frequency increased from approx. 110 to approx. 270 Hz, although the observed frequencies are also consistent with being 1 : 2 : 3 harmonics of each other. Interpreting the 250 Hz as the orbital frequency at the innermost stable orbit around a Schwarzschild black hole leads to a mass estimate of 8.2 solar mass. The spectral results by Miller et al., which suggest considerable black hole spin, would imply a higher mass.

  4. DISCOVERY OF HIGH-FREQUENCY QUASI-PERIODIC OSCILLATIONS IN THE BLACK HOLE CANDIDATE IGR J17091-3624

    SciTech Connect

    Altamirano, D.; Belloni, T.

    2012-03-15

    We report the discovery of 8.5{sigma} high-frequency quasi-periodic oscillations (HFQPOs) at 66 Hz in the Rossi X-ray Timing Explorer data of the black hole candidate IGR J17091-3624, a system whose X-ray properties are very similar to those of microquasar GRS 1915+105. The centroid frequency of the strongest peak is {approx}66 Hz, its quality factor above five, and its rms is between 4% and 10%. We found a possible additional peak at 164 Hz when selecting a subset of the data; however, at the 4.5{sigma} level we consider this detection marginal. These QPOs have hard spectrum and are stronger in observations performed between 2011 September and October, during which IGR J17091-3624 displayed for the first time light curves that resemble those of the {gamma} variability class in GRS 1915+105. We find that the 66 Hz QPO is also present in previous observations (4.5{sigma}), but only when averaging {approx}235 ks of relatively high count rate data. The fact that the HFQPOs frequency in IGR J17091-3624 matches surprisingly well with that seen in GRS 1915+105 raises questions on the mass scaling of QPOs frequency in these two systems. We discuss some possible interpretations; however, they all strongly depend on the distance and mass of IGR J17091-3624, both completely unconstrained today.

  5. Studying X-Ray Binaries with High Energy Frequency Quasi-Periodic Oscillations

    NASA Technical Reports Server (NTRS)

    Kaaret, P.; West, Donald K. (Technical Monitor)

    2002-01-01

    The goal of this investigation is to further our understanding of the dynamics of secreting neutron stars and black holes in the hope of using these systems as probes of the physics of strong gravitational fetus. The main focus of this work has been a multi-year program of simultaneous millisecond X-ray timing and spectral observations carried out with the Rossi X-Ray Timing Explorer (RXTE) to perform the X-ray timing and one of the satellites Asca, BeppoSAX, or Chandra to perform X-ray spectral measurements. With the advent of Chandra, we have extended our work to incLude extragalactic X-ray binaries. We conducted a comprehensive study of the X-ray and radio behavior of the Black Hole Candidate (BHC) X-ray transient XTE J1550-564 using RXTE, Chandra, and the Australian Telescope Compact Array (ATCA). We showed that strong radio emission is associated with major X-ray outbursts involving an X-ray state transition, while a compact radio jet is seen in the low/hard X-ray state found in the outburst decay. Interesting, the total energy required to produce the compact jet may be a substantial fraction of the total accretion energy of the system in that state. We also performed a detailed study of the spectral and timing properties of the decay. In joint RXTE/BeppoSAX observations of the neutron-star X-ray binary Cyg X-2, we discovered a correlation between the timing properties (the frequency of the horizontal branch oscillations) and the properties of a soft, thermal component of the X-ray spectrum. d e showed that more det

  6. A GENERAL RELATIVISTIC MAGNETOHYDRODYNAMIC MODEL OF HIGH FREQUENCY QUASI-PERIODIC OSCILLATIONS IN BLACK HOLE LOW-MASS X-RAY BINARIES

    SciTech Connect

    Shi Changsheng; Li Xiangdong E-mail: lixd@nju.edu.c

    2010-05-10

    We suggest a possible explanation for the high frequency quasi-periodic oscillations (QPOs) in black hole (BH) low-mass X-ray binaries. By solving the perturbation general relativistic magnetohydrodynamic equations, we find two stable modes of the Alfven wave in the accretion disks with toroidal magnetic fields. We suggest that these two modes may lead to the double high frequency QPOs if they are produced in the transition region between the inner advection-dominated accretion flow and the outer thin disk. This model naturally accounts for the 3:2 relation for the upper and lower frequencies of the QPOs, and the relation between the BH mass and QPO frequency.

  7. Frequency variations of quasi-periodic ELF-VLF emissions: A possible new ground-based diagnostic of the outer high-latitude magnetosphere

    SciTech Connect

    Alford, J.; Engebretson, M.; Arnoldy, R.; Inan, U.

    1996-01-01

    Magnetic pulsations and quasi-periodic (QP) amplitude modulations of ELF-VLF waves at Pc 3-4 frequencies (15-50 mHz) are commonly observed simultaneously in cusp-latitude data. The naturally occurring ELF-VLF emissions are believed to be modulated within the magnetosphere by the compressional component of geomagnetic pulsations formed external to the magnetosphere. The authors have examined data from South Pole Station (L {approximately} 14) to determine the occurrence and characteristics of QP emissions. On the basis of 14 months of data during 1987 and 1988 they found that QP emissions typically appeared in both the 0.5-1 kHz and 1-2 kHz receiver channels at South Pole Station and ocassionally in the 2-4 kHz channel. The QP emission frequency appeared to depend on solar wind parameters and interplanetary magnetic field (IMF) direction, and the months near fall equinox in both 1987 and 1988 showed a significant increase in the percentage of QP emissions only in the lowest-frequency channel. The authors present a model consistent with these variations in which high-latitude (nonequatorial) magnetic field minima near the magnetopause play a major role, because the field magnitude governs both the frequency of ELF-VLF emissions and the whistler mode propagation cutoffs. Because the field in these regions will be strongly influenced by solar wind and IMF parameters, variations in the frequency of such emissions may be useful in providing ground-based diagnostics of the outer high-latitude magnetosphere. 32 refs., 13 figs.

  8. A model of the steep power-law spectra and high-frequency quasi-periodic oscillations in luminous black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Dexter, Jason; Blaes, Omer

    2014-03-01

    We propose a new model of the steep power-law state of luminous black hole X-ray binaries. The model uses the fact that at high luminosities, the inner radii of radiation pressure dominated accretion discs are expected to (i) become effectively optically thin and (ii) produce significant luminosities. The gas temperature therefore rises sharply inwards, producing local saturated Compton spectra with rapidly increasing peak energies. These spectra sum together to form a steep power-law tail to the spectrum. A given photon energy on this tail corresponds to a narrow range in radius, so that local vertical oscillations of the disc naturally produce high-quality high-frequency quasi-periodic oscillations (HFQPOs) in the hard X-ray band. The two lowest order modes have a robust frequency ratio of sqrt{7/3}˜eq 1.53. This model explains the appearance of steep power-law spectra and HFQPOs at high luminosity, the 3:2 HFQPO frequency ratios, and their association with the power-law spectral component. We predict an increase in QPO quality factor when the power spectrum is restricted to a narrower photon energy band, and an increase in HFQPO frequency at higher X-ray energies or lower luminosities. Future X-ray telescopes could detect additional HFQPOs from higher order modes. We demonstrate how this model could be used to measure black hole spin from HFQPOs, and qualitatively estimate the spin of GRO J1655-40 as a/M ˜ 0.4-0.7.

  9. Boundedness of solutions for non-linear quasi-periodic differential equations with Liouvillean frequency

    NASA Astrophysics Data System (ADS)

    Wang, Jing; You, Jiangong

    2016-07-01

    We study the boundedness of solutions for non-linear quasi-periodic differential equations with Liouvillean frequencies. We proved that if the forcing is quasi-periodic in time with two frequencies which is not super-Liouvillean, then all solutions of the equation are bounded. The proof is based on action-angle variables and modified KAM theory.

  10. Studies of the Origin of High-frequency Quasi-periodic Oscillations of Mass-accreting Black Holes in X-Ray Binaries with Next-generation X-Ray Telescopes

    NASA Astrophysics Data System (ADS)

    Beheshtipour, Banafsheh; Hoormann, Janie K.; Krawczynski, Henric

    2016-08-01

    Observations with RXTE (Rossi X-ray Timing Explorer) revealed the presence of high-frequency quasi-periodic oscillations (HFQPOs) of the X-ray flux from several accreting stellar-mass black holes. HFQPOs (and their counterparts at lower frequencies) may allow us to study general relativity in the regime of strong gravity. However, the observational evidence today does not yet allow us to distinguish between different HFQPO models. In this paper we use a general-relativistic ray-tracing code to investigate X-ray timing spectroscopy and polarization properties of HFQPOs in the orbiting Hotspot model. We study observational signatures for the particular case of the 166 Hz quasi-periodic oscillation (QPO) in the galactic binary GRS 1915+105. We conclude with a discussion of the observability of spectral signatures with a timing-spectroscopy experiment such as the LOFT (Large Observatory for X-ray Timing) and polarization signatures with space-borne X-ray polarimeters such as IXPE (Imaging X-ray Polarimetry Explorer), PolSTAR (Polarization Spectroscopic Telescope Array), PRAXyS(Polarimetry of Relativistic X-ray Sources), or XIPE (X-ray Imaging Polarimetry Explorer). A mission with high count rate such as LOFT would make it possible to get a QPO phase for each photon, enabling the study of the QPO-phase-resolved spectral shape and the correlation between this and the flux level. Owing to the short periods of the HFQPOs, first-generation X-ray polarimeters would not be able to assign a QPO phase to each photon. The study of QPO-phase-resolved polarization energy spectra would thus require simultaneous observations with a first-generation X-ray polarimeter and a LOFT-type mission.

  11. On The Low Frequency Quasi Periodic Oscillations Of X-Ray Sources

    NASA Astrophysics Data System (ADS)

    Zhang, C. M.

    2005-09-01

    Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) ascribed to the Keplerian and the periastron precession frequencies at the inner disk respectively, we ascribe the low frequency (0.1 10 Hz) Quasi Periodic Oscillations (LFQPO) and HBO (15 60 Hz QPO for Z sources or Atoll sources) to the periastron precession at some outer disk radius. It is assumed that both radii are correlated by a scaling factor of 0.4. The conclusions obtained include: All QPO frequencies increase with increasing accretion rate. The theoretical relations between HBO (LFQPO) frequency and the kHz QPO frequencies are similar to the measured empirical formula.

  12. Quasi-periodic solutions of nonlinear beam equation with prescribed frequencies

    NASA Astrophysics Data System (ADS)

    Chang, Jing; Gao, Yixian; Li, Yong

    2015-05-01

    Consider the one dimensional nonlinear beam equation utt + uxxxx + mu + u3 = 0 under Dirichlet boundary conditions. We show that for any m > 0 but a set of small Lebesgue measure, the above equation admits a family of small-amplitude quasi-periodic solutions with n-dimensional Diophantine frequencies. These Diophantine frequencies are the small dilation of a prescribed Diophantine vector. The proofs are based on an infinite dimensional Kolmogorov-Arnold-Moser iteration procedure and a partial Birkhoff normal form.

  13. Resonance tongues in the quasi-periodic Hill-Schrödinger equation with three frequencies

    NASA Astrophysics Data System (ADS)

    Puig, Joaquim; Simó, Carles

    2011-02-01

    In this paper we investigate numerically the following Hill's equation x″ + ( a + bq( t)) x = 0 where q(t) = \\cos t + \\cos sqrt {2t} + \\cos sqrt {3t} is a quasi-periodic forcing with three rationally independent frequencies. It appears, also, as the eigenvalue equation of a Schrödinger operator with quasi-periodic potential. Massive numerical computations were performed for the rotation number and the Lyapunov exponent in order to detect open and collapsed gaps, resonance tongues. Our results show that the quasi-periodic case with three independent frequencies is very different not only from the periodic analogs, but also from the case of two frequencies. Indeed, for large values of b the spectrum contains open intervals at the bottom. From a dynamical point of view we numerically give evidence of the existence of open intervals of a, for large b, where the system is nonuniformly hyperbolic: the system does not have an exponential dichotomy but the Lyapunov exponent is positive. In contrast with the region with zero Lyapunov exponents, both the rotation number and the Lyapunov exponent do not seem to have square root behavior at endpoints of gaps. The rate of convergence to the rotation number and the Lyapunov exponent in the nonuniformly hyperbolic case is also seen to be different from the reducible case.

  14. Quasi-periodic solutions of nonlinear beam equation with prescribed frequencies

    SciTech Connect

    Chang, Jing; Gao, Yixian Li, Yong

    2015-05-15

    Consider the one dimensional nonlinear beam equation u{sub tt} + u{sub xxxx} + mu + u{sup 3} = 0 under Dirichlet boundary conditions. We show that for any m > 0 but a set of small Lebesgue measure, the above equation admits a family of small-amplitude quasi-periodic solutions with n-dimensional Diophantine frequencies. These Diophantine frequencies are the small dilation of a prescribed Diophantine vector. The proofs are based on an infinite dimensional Kolmogorov-Arnold-Moser iteration procedure and a partial Birkhoff normal form. .

  15. Low-frequency quasi-periodic oscillations in black hole and neutron star LMXBs

    NASA Astrophysics Data System (ADS)

    Ingram, Adam

    2016-07-01

    Low-frequency quasi-periodic oscillations (QPOs) are routinely seen in the X-ray flux of accreting black holes and neutron stars. Since the QPO frequency correlates with the low frequency power spectral break in the same manner for both object classes, it is reasonable to believe that these oscillations have the same physical origin in neutron stars as they do in black holes. However, recent successes in modelling black hole low frequency QPOs as Lense-Thirring precession contrast sharply with failures of the same model in neutron stars. This could be attributable to the significant extra complexity, both in the physics and in the observed power spectra, of accreting neutron stars when compared with black holes. Alternatively, the QPO mechanism really is the same for the two object classes, but in that case, why does the Lense-Thirring model work so well for black holes? I will review the current state of this field.

  16. Radiation characteristics of quasi-periodic radio bursts in the Jovian high-latitude region

    NASA Astrophysics Data System (ADS)

    Kimura, Tomoki; Tsuchiya, Fuminori; Misawa, Hiroaki; Morioka, Akira; Nozawa, Hiromasa

    2008-12-01

    Ulysses had a "distant encounter" with Jupiter in February 2004. The spacecraft passed from north to south, and it observed Jovian radio waves from high to low latitudes (from +80° to +10°) for few months during its encounter. In this study, we present a statistical investigation of the occurrence characteristics of Jovian quasi-periodic bursts, using spectral data from the unified radio and plasma wave experiment (URAP) onboard Ulysses. The latitudinal distribution of quasi-periodic bursts is derived for the first time. The analysis suggested that the bursts can be roughly categorized into two types: one having periods shorter than 30 min and one with periods longer than 30 min, which is consistent with the results of the previous analysis of data from Ulysses' first Jovian flyby [MacDowall, R.J., Kaiser, M.L., Desch, M.D., Farrell, W.M., Hess, R.A., Stone, R.G., 1993. Quasi-periodic Jovian radio bursts: observations from the Ulysses radio and plasma wave. Experiment. Planet. Space Sci. 41, 1059-1072]. It is also suggested that the groups of quasi-periodic bursts showed a dependence on the Jovian longitude of the sub-solar point, which means that these burst groups are triggered during a particular rotational phase of the planet. Maps of the occurrence probability of these quasi-periodic bursts also showed a unique CML/MLAT dependence. We performed a 3D ray tracing analysis of the quasi-periodic burst emission to learn more about the source distribution. The results suggest that the longitudinal distribution of the occurrence probability depends on the rotational phase. The source region of quasi-periodic bursts seems to be located at an altitude between 0.4 and 1.4 Rj above the polar cap region ( L>30).

  17. Low-Frequency Quasi-Periodic Oscillations and Iron Line Variability of Discoseismic Corrugation Modes

    NASA Astrophysics Data System (ADS)

    Butsky, Iryna; Tsang, D.

    2013-01-01

    Using a fast semi-analytic raytracing code, we study the variability of iron lines due to discoseismic oscillations concentrated in the inner-most regions of accretion discs around black holes. The dependence of the relativistically broadened line profile on the oscillation-phase is studied for discoseismic corrugation modes. The corrugation mode, or c-mode, is of particular interest as their natural frequency corresponds well to the 0.1-10 Hz range observed for low-frequency quasi-periodic oscillations (LFQPOs) in X-ray binaries. Comparison of the oscillation phase dependent variability and QPO-phase stacked Fe-Kalpha line observations will allow such discoseismic models to be confirmed or ruled out as a source of LFQPOs.

  18. Viscosity profile and Quasi Periodic Oscillation frequency of few transient black hole candidates

    NASA Astrophysics Data System (ADS)

    Mondal, Santanu; Debnath, Dipak; Chakrabarti, Sandip Kumar; Jana, Arghajit; Chatterjee, Debjit; Molla, Aslam Ali

    2016-07-01

    Matters enter into the potential well formed by the compact objects due to the transport of angular momentum by viscosity. We compute the amount of viscosity during the outburst time of the transient sources. In the progressive days as the viscosity increases inner edge of the Keplerian disc moves closer to the black holes. Thus the size of the Compton cloud reduces and the frequency of the Quasi Periodic Oscillations increases. We also compute the Compton cooling day by day, which is responsible for the movement of the shock both in rising and declining phases of the outburst. Our viscosity value rises/decays monotonically during the rising/declining phases of the outburst, well within the range proposed by magneto-rotational instability. For that we solve the Rankine-Hugoniot conditions and derive the condition of shock formation in presence of Compton cooling.

  19. On the modulation of low-frequency quasi-periodic oscillations in black hole transients

    NASA Astrophysics Data System (ADS)

    Pawar, Devraj D.; Motta, Sara; Shanthi, K.; Bhattacharya, Dipankar; Belloni, Tomaso

    2015-04-01

    We studied the properties of the low-frequency quasi-periodic oscillations detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47, GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analysed the relation between the full width at half-maximum and the frequency of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a frequency modulation, while that of the sub-harmonic is independent of frequency, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.

  20. The quasi-periodic oscillations and very low frequency noise of Scorpius X-1 as transient chaos - A dripping handrail?

    NASA Technical Reports Server (NTRS)

    Scargle, Jeffrey D.; Steiman-Cameron, Thomas; Young, Karl; Donoho, David L.; Crutchfield, James P.; Imamura, James

    1993-01-01

    We present evidence that the quasi-periodic oscillations (QPO) and very low frequency noise (VLFN) characteristic of many accretion sources are different aspects of the same physical process. We analyzed a long, high time resolution EXOSAT observation of the low-mass X-ray binary (LMXB) Sco X-1. The X-ray luminosity varies stochastically on time scales from milliseconds to hours. The nature of this variability - as quantified with both power spectrum analysis and a new wavelet technique, the scalegram - agrees well with the dripping handrail accretion model, a simple dynamical system which exhibits transient chaos. In this model both the QPO and VLFN are produced by radiation from blobs with a wide size distribution, resulting from accretion and subsequent diffusion of hot gas, the density of which is limited by an unspecified instability to lie below a threshold.

  1. On the lack of correlation between X-ray flux and kHz quasi-periodic oscillation frequencies

    NASA Astrophysics Data System (ADS)

    Catmabacak, Onur; Hakan Erkut, M.

    2016-07-01

    We study the so-called "parallel tracks" phenomenon, which arises from the observation that kHz quasi-periodic oscillation (QPO) frequencies correlate with X-ray flux on short time scales (less than a day) while there seems to be no correlation at all on longer time scales (more than a day). The oscillatory modes with frequency bands determined by the radial epicyclic frequency in the magnetic boundary region between the disk and the neutron star magnetosphere are likely to be the origin of these high frequency QPOs. Within the boundary region model, we provide a possible explanation for the parallel track phenomenon taking into account the variation of the model parameters such as the rotation frequency of the innermost disk matter and the radial extension of the boundary region. In addition to the mass, radius, and magnetic field of the neutron star, the frequency bands of oscillatory modes depend on mass accretion rate through these model parameters as well. Using the aspect ratio of the disk, which actually depends on mass accretion rate, we estimate the radial width of the boundary region and its variation on long and short time scales to reproduce the parallel tracks in accordance with observations. We repeat the analysis for a wide range of neutron star masses, radii, and magnetic field strengths in order to understand the effects of these parameters on our results.

  2. UNIVERSAL SCALING OF THE 3:2 TWIN-PEAK QUASI-PERIODIC OSCILLATION FREQUENCIES WITH BLACK HOLE MASS AND SPIN REVISITED

    SciTech Connect

    Zhou, Xin-Lin; Yuan, Weimin; Pan, Hai-Wu; Liu, Zhu

    2015-01-01

    We discuss further observational support of an idea formulated a decade ago by Abramowicz, Kluźniak, McClintock and Remillard. They demonstrated that the 3:2 pairs of frequencies of the twin-peak black hole (BH) high-frequency quasi-periodic oscillations (QPOs) scale inversely with the BH masses and that the scaling covers the entire range from stellar to supermassive BHs. For this reason, they believed that the QPOs may be used for accurate measurements of masses and spins of BHs.

  3. Resonance condition and low-frequency quasi-periodic oscillations of the outbursting source H1743-322

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Sandip K.; Mondal, Santanu; Debnath, Dipak

    2015-10-01

    It has long been proposed that low-frequency quasi-periodic oscillations (QPOs) in stellar-mass black holes or their equivalents in supermassive black holes are the result of resonances between infall and cooling timescales. We explicitly compute these two timescales in a generic situation to show that resonances are easily achieved. During an outburst of a transient black hole candidate, the accretion rate of the Keplerian disc as well as the geometry of the Comptonizing cloud change very rapidly. During some period, a resonance condition between the cooling timescale (predominantly by Comptonization) and the infall timescale of the Comptonizing cloud is roughly satisfied. This leads to low-frequency quasi-periodic oscillations (LFQPOs) of the Compton cloud and the consequent oscillation of hard X-rays. In this paper, we explicitly follow black hole candidate H1743-322 during its 2010 outburst. We compute the Compton cooling time and infall time over several days and show that QPOs take place when these two roughly agree within ˜50 per cent, i.e., the resonance condition is generally satisfied. We also confirm that for the sharper LFQPOs (i.e. higher Q-factors) the ratio of the two timescales is very close to 1.

  4. STEREO observations of quasi-periodically driven high velocity outflows in polar plumes

    NASA Astrophysics Data System (ADS)

    McIntosh, S. W.; Innes, D. E.; de Pontieu, B.; Leamon, R. J.

    2010-02-01

    Context. Plumes are one of the most ubiquitous features seen at the limb in polar coronal holes and are considered to be a source of high density plasma streams to the fast solar wind. Aims: We analyze STEREO observations of plumes and aim to reinterpret and place observations with previous generations of EUV imagers within a new context that was recently developed from Hinode observations. Methods: We exploit the higher signal-to-noise, spatial and temporal resolution of the EUVI telescopes over that of SOHO/EIT to study the temporal variation of polar plumes in high detail. We employ recently developed insight from imaging (and spectral) diagnostics of active region, plage, and quiet Sun plasmas to identify the presence of apparent motions as high-speed upflows in magnetic regions as opposed to previous interpretations of propagating waves. Results: In almost all polar plumes observed at the limb in these STEREO sequences, in all coronal passbands, we observe high speed jets of plasma traveling along the structures with a mean velocity of 135 km s-1 at a range of temperatures from 0.5-1.5 MK. The jets have an apparent brightness enhancement of ~5% above that of the plumes they travel on and repeat quasi-periodically, with repeat-times ranging from five to twenty-five minutes. We also notice a very weak, fine scale, rapidly evolving, but ubiquitous companion of the plumes that covers the entire coronal hole limb. Conclusions: The observed jets are remarkably similar in intensity enhancement, periodicity and velocity to those observed in other magnetic regions of the solar atmosphere. They are multi-thermal in nature. We infer that the jets observed on the plumes are a source of heated mass to the fast solar wind. Further, based on the previous results that motivated this study, we suggest that these jets originated in the upper chromosphere. Five movies are only available in electronic form at http://www.aanda.org

  5. Dependence of kHz quasi-periodic oscillation frequencies on accretion-related parameters

    NASA Astrophysics Data System (ADS)

    Hakan Erkut, M.; Catmabacak, Onur; Duran, Sivan; Çatmabacak, Önder

    2016-07-01

    To study the possible dependence of kHz QPO frequencies on the parameters such as the mass accretion rate, the surface magnetic field strength, mass, and radius of the neutron star, we consider the up-to-date distribution of neutron star LMXBs in the kHz QPO frequency versus X-ray luminosity plane. We confirm the absence of any correlation between QPO frequencies and luminosity in the ensemble of LMXBs. Searching for the dependence of QPO data on accretion-related parameters, we find a correlation between the lower kHz QPO frequency and the parameter combining mass accretion rate with magnetic field strength. The correlation cannot be adequately described by a simple power law due to observed scattering of individual source data in the ensemble of Z and atoll sources. Based on disk-magnetosphere boundary region, the model function for QPO frequency can delineate the correlation taking into account the scattering of individual sources. In addition to mass accretion rate and magnetic field strength, the model function also depends on the radial width of the boundary region near the magnetopause. Modelling the variation of the width with mass accretion rate, we also provide an explanation for the parallel tracks phenomenon observed in the case of individual sources.

  6. High performance hybrid rGO/Ag quasi-periodic mesh transparent electrodes for flexible electrochromic devices

    NASA Astrophysics Data System (ADS)

    Voronin, A. S.; Ivanchenko, F. S.; Simunin, M. M.; Shiverskiy, A. V.; Aleksandrovsky, A. S.; Nemtsev, I. V.; Fadeev, Y. V.; Karpova, D. V.; Khartov, S. V.

    2016-02-01

    A possibility of creating a stable hybrid coating based on the hybrid of a reduced graphene oxide (rGO)/Ag quasi-periodic mesh (q-mesh) coating has been demonstrated. The main advantages of the suggested method are the low cost of the processes and the technology scalability. The Ag q-mesh coating is formed by means of the magnetron sputtering of silver on the original template obtained as a result of quasi-periodic cracking of a silica film. The protective rGO film is formed by low temperature reduction of a graphene oxide (GO) film, applied by the spray-deposition in the solution of NaBH4. The coatings have low sheet resistance (12.3 Ω/sq) and high optical transparency (82.2%). The hybrid coatings are characterized by high chemical stability, as well as they show high stability to deformation impacts. High performance of the hybrid coatings as electrodes in the sandwich-system «electrode-electrochromic composition-electrode» has been demonstrated. The hybrid electrodes allow the electrochromic sandwich to function without any visible degradation for a long time, while an unprotected mesh electrode does not allow performing even a single switching cycle.

  7. Quasi-periodic (~mHz) dayside auroral brightennings associated with high-speed solar wind

    NASA Astrophysics Data System (ADS)

    Liou, K.

    2013-12-01

    It has been reported that dayside auroral pulsations of a few mHz frequency can occur when variations of solar wind dynamic pressure at the same frequency appear. Magnetospheric compression/decompression is attributed to the auroral pulsations. Here we report another type of dayside auroral pulsations not associated with solar wind dynamic pressure changes by using global auroral images acquired from the Ultraviolet Imager (UVI) on board the Polar satellite. From one periodic (~2 - 8 mHz) auroral event that occurred on February 8, 2000, it is found that the auroral enhancements covered most of the day (~05 - 16 MLT) sector and did not show a latitudinal dependence. Based on in situ particle data from DMSP SSJ/4, the brightennings were associated mainly with enhanced particle precipitations from the central plasma sheet (i.e., diffuse aurora). There was no geomagnetic pulsation on the ground and in the dawn sector of the magnetosheath as indicated by the Geotail measurements. While the auroral pulsations occurred during high solar wind speed (> 600 km/s), they commenced when the interplanetary magnetic field turned northward, suggesting the Kelvin-Helmholtz instability being a source of the pulsations. We will present detail analysis results and discuss other possible mechanisms in the context of current theories.

  8. The energy dependence of the three types of low-frequency quasi-periodic oscillations in the black hole candidate H1743-322

    NASA Astrophysics Data System (ADS)

    Li, Z. B.; Zhang, S.; Qu, J. L.; Gao, H. Q.; Zhao, H. H.; Huang, C. P.; Song, L. M.

    2013-07-01

    We investigate the properties of the centroid frequency of low-frequency quasi-periodic oscillation (LF QPOs, 0.1-30 Hz) during the 2003 outburst of H1743-322, by using the observational data of the Rossi X-ray Timing Explorer. We find that the frequency shows different energy dependences for each of the sub-classes of LF QPOs: the QPO frequency is proportional to photon energy for the type C QPOs while it is ambiguous for the type A and B QPOs. For type C QPOs, the slope of the frequency-energy relation versus frequency plot can be well described by a power law with frequency till ˜7.5 Hz. Beyond ˜7.5 Hz the slope goes down. The LF QPO amplitude decreases monotonically with the frequency for the type C but increases for the other two types. These properties provide a joint diagnostic for discriminating the different types of LF QPO.

  9. Cluster observations of quasi-periodic impulsive signatures in the dayside northern lobe: High-latitude flux transfer events?

    NASA Technical Reports Server (NTRS)

    Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; Balogh, A.; Reme, H.; Fazakerley, A. N.; Kistler, L. M.

    2004-01-01

    We report on a series of quasi-periodic reversals in GSM B(sub Z) observed by the four Cluster spacecraft in the northern dayside lobe poleward of the cusp on 23 February 2001. During an interval of about 35 min, multiple reversals (negative to positive) in B(sub Z) of approximately 1-min duration with an approximate 8-min recurrence time were observed. The individual structures do not resemble low-latitude flux transfer events (FTE) [Russell and Elphic, 1979] but the 8-min recurrence frequency suggests that intermittent reconnection may be occurring .Measurements (appropriately lagged) of the solar wind at ACE show that the IMF was southward-oriented with a strong B(sub X) and that a modest dynamic pressure increased as the events started. The multi-point observations afforded by the Cluster spacecraft were used to infer the motion (direction and speed) of the observed magnetic field reversals. The associated currents were also calculated and they are consistent with the spatial confinement of the observed magnetic field reversals. We propose that the observed reversals are due to flux tubes reconnecting with closed field lines on the dayside. Ancillary data from the Cluster Ion Spectrometry (CIS) and Plasma Electron And Current Experiment (PEACE) instruments were used to develop a physical picture of the reversals.

  10. Comprehensive Analysis of RXTE Data from Cyg X-1. Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations

    NASA Technical Reports Server (NTRS)

    Shaposhnikov, Nickolai; Titarchuk, Lev

    2006-01-01

    We present timing and spectral analysis of approx. 2.2 Ms of Rossi X-ray Time Explorer (RXTE) archival data from Cyg X-1. Using the generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line. We find a strong correlation between 0.1-20 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral power-law index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and high values of QPO frequencies. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index- QPO frequency correlation shows a saturation of the photon index Gamma approx. 2.1 at high values of the low frequency upsilon(sub L). The saturation level of Gamma approx. 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index. We also show that Fe K(sub alpha) emission line strength (equivalent width, EW) correlates with the QPO frequency. EW increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state. The revealed observational correlations allow us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (the power-law index) evolution for eight years of Cyg X-1 observations by RXTE.

  11. Grouped and Multistep Nanoheteroepitaxy: Toward High-Quality GaN on Quasi-Periodic Nano-Mask.

    PubMed

    Feng, Xiaohui; Yu, Tongjun; Wei, Yang; Ji, Cheng; Cheng, Yutian; Zong, Hua; Wang, Kun; Yang, Zhijian; Kang, Xiangning; Zhang, Guoyi; Fan, Shoushan

    2016-07-20

    A novel nanoheteroepitaxy method, namely, the grouped and multistep nanoheteroepitaxy (GM-NHE), is proposed to attain a high-quality gallium nitride (GaN) epilayer by metal-organic vapor phase epitaxy. This method combines the effects of sub-100 nm nucleation and multistep lateral growth by using a low-cost but unique carbon nanotube mask, which consists of nanoscale growth windows with a quasi-periodic 2D fill factor. It is found that GM-NHE can facilely reduce threading dislocation density (TDD) and modulate residual stress on foreign substrate without any regrowth. As a result, high-quality GaN epilayer is produced with homogeneously low TDD of 4.51 × 10(7) cm(-2) and 2D-modulated stress, and the performance of the subsequent 410 nm near-ultraviolet light-emitting diode is greatly boosted. In this way, with the facile fabrication of nanomask and the one-off epitaxy procedure, GaN epilayer is prominently improved with the assistance of nanotechnology, which demonstrates great application potential for high-efficiency TDD-sensitive optoelectronic and electronic devices. PMID:27351723

  12. Studying Frequency Relationships of Kilohertz Quasi-periodic Oscillations for 4U 1636-53 and Sco X-1: Observations Confront Theories

    NASA Astrophysics Data System (ADS)

    Lin, Yong-Feng; Boutelier, Martin; Barret, Didier; Zhang, Shuang-Nan

    2011-01-01

    By fitting the frequencies of simultaneous lower and upper kilohertz quasi-periodic oscillations (kHz QPOs) in two prototype neutron star (NS) QPO sources (4U 1636-53 and Sco X-1), we test the predictive power of all currently proposed QPO models. Models predict a linear, power law, or other relationship between the two frequencies. We found that for plausible NS parameters (mass and angular momentum), no model can satisfactorily reproduce the data, leading to very large chi-square values in our fittings. For both 4U 1636-53 and Sco X-1, this is largely due to the fact that the data significantly differ from a linear relationship. Some models perform relatively better but still have their own problems. Such a detailed comparison of data from models enables identification of routes for improving those models further.

  13. STUDYING FREQUENCY RELATIONSHIPS OF KILOHERTZ QUASI-PERIODIC OSCILLATIONS FOR 4U 1636-53 AND Sco X-1: OBSERVATIONS CONFRONT THEORIES

    SciTech Connect

    Lin Yongfeng; Boutelier, Martin; Barret, Didier; Zhang Shuangnan

    2011-01-10

    By fitting the frequencies of simultaneous lower and upper kilohertz quasi-periodic oscillations (kHz QPOs) in two prototype neutron star (NS) QPO sources (4U 1636-53 and Sco X-1), we test the predictive power of all currently proposed QPO models. Models predict a linear, power law, or other relationship between the two frequencies. We found that for plausible NS parameters (mass and angular momentum), no model can satisfactorily reproduce the data, leading to very large chi-square values in our fittings. For both 4U 1636-53 and Sco X-1, this is largely due to the fact that the data significantly differ from a linear relationship. Some models perform relatively better but still have their own problems. Such a detailed comparison of data from models enables identification of routes for improving those models further.

  14. QUASI-PERIODIC PROPAGATING SIGNALS IN THE SOLAR CORONA: THE SIGNATURE OF MAGNETOACOUSTIC WAVES OR HIGH-VELOCITY UPFLOWS?

    SciTech Connect

    De Pontieu, Bart; McIntosh, Scott W. E-mail: mscott@ucar.ed

    2010-10-20

    Since the discovery of quasi-periodic propagating oscillations with periods of order 3-10 minutes in coronal loops with TRACE and SOHO/EIT (and later with STEREO/EUVI and Hinode/EIS), they have been almost universally interpreted as evidence for propagating slow-mode magnetoacoustic waves in the low plasma {beta} coronal environment. Here we show that this interpretation is not unique, and that for coronal loops associated with plage regions (as opposed to sunspots), the presence of magnetoacoustic waves may not be the only cause for the observed quasi-periodicities. We focus instead on the ubiquitous, faint upflows at 50-150 km s{sup -1} that were recently discovered as blueward asymmetries of spectral line profiles in footpoint regions of coronal loops, and as faint disturbances propagating along coronal loops in EUV/X-ray imaging time series. These faint upflows are most likely driven from below and have been associated with chromospheric jets that are (partially) rapidly heated to coronal temperatures at low heights. These two scenarios (waves versus flows) are difficult to differentiate using only imaging data, but careful analysis of spectral line profiles indicates that faint upflows are likely responsible for some of the observed quasi-periodic oscillatory signals in the corona. We show that recent EIS measurements of intensity and velocity oscillations of coronal lines (which had previously been interpreted as direct evidence for propagating waves) are actually accompanied by significant oscillations in the line width that are driven by a quasi-periodically varying component of emission in the blue wing of the line. This faint additional component of blue-shifted emission quasi-periodically modulates the peak intensity and line centroid of a single Gaussian fit to the spectral profile with the same small amplitudes (respectively a few percent of background intensity and a few km s{sup -1}) that were previously used to infer the presence of slow

  15. Correlations between Kilohertz Quasi-periodic Oscillations and Low-Frequency Features Attributed to Radial Oscillations and Diffusive Propagation in the Viscous Boundary Layer around a Neutron Star

    NASA Astrophysics Data System (ADS)

    Titarchuk, Lev; Osherovich, Vladimir

    1999-06-01

    We present a dimensional analysis of two characteristic timescales in the boundary layer where the disk adjusts to the rotating neutron star (NS). The boundary layer is treated as a transition region between the NS surface and the first Keplerian orbit. The radial transport of the angular momentum in this layer is controlled by a viscous force defined by the Reynolds number, which in turn is related to the mass accretion rate. We show that the observed low-Lorentzian frequency is associated with radial oscillations in the boundary layer, where the observed break frequency is determined by the characteristic diffusion time of the inward motion of the matter in the accretion flow. Predictions of our model regarding relations between those two frequencies and the frequencies of kilohertz quasi-periodic oscillations (kHz QPOs) compare favorably with recent observations of the source 4U 1728-34. This Letter contains a theoretical classification of kHz QPOs in NS binaries and the related low-frequency features. Thus, results concerning the relationship between the low-Lorentzian frequency of viscous oscillations and the break frequency are presented in the framework of our model of kHz QPOs viewed as Keplerian oscillations in a rotating frame of reference.

  16. Discovery of a low-frequency broad quasi-periodic oscillation peak in the power density spectrum of Cygnus X-1 with Granat/SIGMA

    NASA Astrophysics Data System (ADS)

    Vikhlinin, A.; Churazov, E.; Gilfanov, M.; Sunyaev, R.; Dyachkov, A.; Khavenson, N.; Kremnev, R.; Sukhanov, K.; Ballet, J.; Laurent, P.; Salotti, L.; Claret, A.; Olive, J. F.; Denis, M.; Mandrou, P.; Roques, J. P.

    1994-03-01

    A transient broad (delta(f)/f = 0.8 approximately 1) very low frequency (approximately 0.04-0.07 Hz) and strong (fractional rms variations are at the level of approximately 10-15% of total source intensity) quasi-periodic oscillations (QPO) feature was discovered by the SIGMA telescope onboard the Granat observatory in the power density spectra of Cygnus X-1; the source was during all the observations carried out in 1990-1992 in its standard (low or hard) spectral state (Sunyaev & Truemper 1979) with average 40-150 keV flux, corresponding appproximately to the 'nominal' gamma2 level of the source (Ling et al. 1979). The power density spectra, obtained in the 4 x 10-4-10 Hz frequency range, typically exhibit strong very low frequency noise below a few millihertz increasing toward lower frequencies, a nearly flat region from a few millihertz up to a break frequency fbr = 0.04 approximately 0.1 Hz and a power-law spectrum as f-1 above the break frequency. The QPO feature, when observed, was centered below or near the break frequency fbr.

  17. Spectral Index and Quasi-Periodic Oscillation Frequency Correlation in Black Hole Sources: Observational Evidence of Two Phases and Phase Transition in Black Holes

    NASA Technical Reports Server (NTRS)

    Titarchuk, Lev; Fiorito, Ralph

    2004-01-01

    Recent studies have shown that strong correlations are observed between the low frequencies (1-10 Hz) of quasi-periodic oscillations (QPOs) and the spectral power law index of several black hole (BH) candidate sources, in low (hard) states, steep power law (soft) states, and transitions between these states. The observations indicate that the X-ray spectra of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission, indicating the probable presence of a jet. Strong QPOs (>20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant (i.e., 60%90%). This evidence contradicts the dominant, long-standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model that identifies and explains the origin of the QPOs and how they are imprinted on the properties of the power-law flux component. We argue for the existence of a bounded compact coronal region that is a natural consequence of the adjustment of the Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) a hard state, in which the TL is optically thin and very hot (kT approximately greater than 50 keV), producing photon upscattering via thermal Comptonization (the photon spectrum index Gamma approximates 1.7 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius), and (2) a soft state that is optically thick and relatively cold (kT approximately less than 5 keV the index for this state, Gamma

  18. Relation between the quasi-periodic oscillations and the low-frequency noise of GX 5-1 in the horizontal branch

    NASA Technical Reports Server (NTRS)

    Mitsuda, Kazuhisa; Dotani, Tadayasu; Yoshida, Atsumasa; Vaughan, Brian; Norris, Jay P.

    1991-01-01

    Ginga observations of quasi-periodic oscillations (QPOs) and the low-frequency noise (LFN) from GX 5-1 in its horizontal-branch spectral state are presented. Power spectral fits were attempted using model functions based on simple oscillating shot models. A clear second-harmonic peak of QPO was detected. Variations in the powers of QPO and LFN on timescales of 8-256 s were also studied. These variations were significant for all of the timescales studied, and were uncorrelated with each other on timescales shorter than a few tens of seconds, and correlated on longer timescales. From simulations based on a simple shot model, it was found that the variation amplitude and the lack of correlation on short timescales are not inconsistent with the oscillating shot models. A more complex model is necessary to fully explain the observed properties.

  19. Accretion flow behaviour during the evolution of the quasi-periodic oscillation frequency of XTE J1550-564 in 1998 outburst

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Sandip K.; Dutta, Broja G.; Pal, P. S.

    2009-04-01

    Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs. Observational evidence of evolutions of QPOs would therefore be very important as they throw lights on the dynamics of the hotter region. Our aim is to find systems in which there is a well-defined correlation among the frequencies of the QPOs over a range of time so as to understand the physical picture. In this paper, we concentrate on the archival data of XTE J1550-564 obtained during 1998 outburst, and study the systematic drifts during the rising phase from the 1998 September 7 to the 1998 September 19, when the QPO frequency increased monotonically from 81mHz to 13.1Hz. Immediately after that, QPO frequency started to decrease and on the 1998 September 26, the QPO frequency became 2.62Hz. After that, its value remained almost constant. This frequency drift can be modelled satisfactorily with a propagatory oscillating shock solution where the post-shock region behaves as the Comptonized region. Comparing with the nature of a more recent 2005 outburst of another black hole candidate GRO 1655-40, where QPOs disappeared at the end of the rising phase, we conjecture that this so-called `outburst' may not be a full-fledged outburst.

  20. Quasi-periodic solutions of a quasi-periodically forced nonlinear beam equation

    NASA Astrophysics Data System (ADS)

    Wang, Yi

    2012-06-01

    In this paper, one quasi-periodically forced nonlinear beam equation utt+uxxxx+μu+ɛg(ωt,x)u3=0,μ>0,x∈[0,π] with hinged boundary conditions is considered. Here ɛ is a small positive parameter, g( ωt, x) is real analytic in all variables and quasi-periodic in t with a frequency vector ω = ( ω1, ω2, … , ωm). It is proved that the above equation admits small-amplitude quasi-periodic solutions.

  1. Rieger quasi-periodicity in solar indices

    NASA Astrophysics Data System (ADS)

    Akimov, L. A.; Belkina, I. L.

    2012-05-01

    Using wavelet analysis and Fourier analysis, the temporal behavior of ≈156-day quasi-periodicity (Rieger quasi-periodicity, RQ) is investigated for series of daily solar indices: Wolf numbers W for 161 years (from 1849), the flux F10.7 of the Sun's radio emission at a frequency of 2800 MHz for 63 years (from 1947), the number of X-ray flares N X for 29 years (from 1981), and the number of optical flares N α for 11 years in cycle 21. The N α series are studied for four quadrants of the solar disk. It is found for the W series that there is no stable dependence of the amplitude RQ on the cycle phase and the W value. It is associated with the fact that, corresponding to a period of around eight years, in the power spectrum changes in the amplitude of the Rieger quasiperiodicity of the index W are dominated by the peak. Moreover, the peaks corresponding to the 11-year cyclicity are also significant. The comparative study of the temporal behavior of the Rieger quasi-periodicity amplitude of the indices W, F10.7, and N X has shown that the quasi-periodicity covers the processes, occurring in active regions on the Sun at different altitudes, almost simultaneously. It is found that for N α, the lag of variations of the Rieger quasi-periodicity amplitude for series of the Sun's western hemisphere, relative to those for series of the eastern hemisphere, is on average less than for the flare series. Thus, if the flare occurrence is modulated by the Rieger quasi-periodicity process as a wave propagating over the Sun's disc, then the wave is not a retrograde one. Different interpretations of the nature of the Rieger quasi-periodicity are discussed including the hypothesis of Rossby waves.

  2. Detection of a 1258-Hz high-amplitude kilohertz quasi-periodic oscillation in the ultracompact X-ray binary 1A 1246-588

    NASA Astrophysics Data System (ADS)

    Jonker, P. G.; in't Zand, J. J. M.; Méndez, M.; van der Klis, M.

    2007-07-01

    We have observed the ultracompact low-mass X-ray binary (LMXB) 1A 1246-588 with the Rossi X-ray Timing Explorer (RXTE). In this paper we report the discovery of a kilohertz quasi-periodic oscillation (QPO) in 1A 1246-588. The kilohertz QPO was only detected when the source was in a soft high-flux state reminiscent of the lower banana branch in atoll sources. Only one kilohertz QPO peak is detected at a relatively high frequency of 1258 +/- 2 Hz and at a single trial significance of more than 7σ. Kilohertz QPOs with a higher frequency have only been found on two occasions in 4U 0614+09. Furthermore, the frequency is higher than that found for the lower kilohertz QPO in any source, strongly suggesting that the QPO is the upper of the kilohertz QPO pair often found in LMXBs. The full width at half-maximum is 25 +/- 4 Hz, making the coherence the highest found for an upper kilohertz QPO. From a distance estimate of ~6 kpc from a radius expansion burst we derive that 1A 1246-588 is at a persistent flux of ~0.2-0.3 per cent of the Eddington flux, hence 1A 1246-588 is one of the weakest LMXBs for which a kilohertz QPO has been detected. The rms amplitude in the 5-60 keV band is 27 +/- 3 per cent; this is the highest for any kilohertz QPO source so far, in line with the general anticorrelation between source luminosity and rms amplitude of the kilohertz QPO peak identified before. Using the X-ray spectral information we produce a colour-colour diagram. The source behaviour in this diagram provides further evidence for the atoll nature of the source.

  3. Discovery of a Variable-Frequency, 50--60 HZ Quasi-Periodic Oscillation on the Normal Branch of GX 17+2

    NASA Astrophysics Data System (ADS)

    Wijnands, R. A. D.; van der Klis, M.; Psaltis, D.; Lamb, F. K.; Kuulkers, E.; Dieters, S.; van Paradijs, J.; Lewin, W. H. G.

    1996-09-01

    We report the discovery, with the Rossi X-Ray Timing Explorer, of a 50--60 Hz quasi-periodic oscillation (QPO) in GX 17+2. The QPO is seen when GX 17+2 is on the normal branch in the X-ray color-color diagram. Its frequency initially increases from 59 to 62 Hz as the source moves down the normal branch, but below the middle of the normal branch it decreases to ~50 Hz. Together with this frequency decrease, the QPO peak becomes much broader, from ~4 Hz in the upper part of the normal branch to ~15 Hz in the lower normal branch. The rms amplitude remains approximately constant between 1% and 2% along the entire normal branch. From a comparison of the properties of this QPO with those of QPOs previously observed along the normal branch in other Z sources, we conclude that it is most likely the horizontal-branch QPO (HBO). However, this QPO displays a number of unusual characteristics. The decrease in the QPO frequency along the lower normal branch is not in agreement with the predictions of the beat-frequency model for the HBO unless the mass flux through the inner disk decreases as the source moves down the lower normal branch. We tentatively suggest that the required decrease in the mass flux through the inner disk is caused by an unusually rapid increase in the mass flux in the radial inflow as GX 17+2 moves down the normal branch. Assuming that this explanation is correct, we can derive an upper bound on the dipole component of the star's magnetic field at the magnetic equator of 5 x 109 G for a 1.4 Msolar neutron star with a radius of 106 cm.

  4. LOW-FREQUENCY (11 mHz) OSCILLATIONS IN H1743-322: A NEW CLASS OF BLACK HOLE QUASI-PERIODIC OSCILLATIONS?

    SciTech Connect

    Altamirano, D.; Strohmayer, T.

    2012-08-01

    We report the discovery of quasi-periodic oscillations (QPOs) at {approx}11 mHz in two RXTE and one Chandra observations of the black hole candidate H1743-322. The QPO is observed only at the beginning of the 2010 and 2011 outbursts at similar hard color and intensity, suggestive of an accretion state dependence for the QPO. Although its frequency appears to be correlated with X-ray intensity on timescales of a day, in successive outbursts eight months apart, we measure a QPO frequency that differs by less than Almost-Equal-To 2.2 mHz while the intensity had changed significantly. We show that this {approx}11 mHz QPO is different from the so-called Type C QPOs seen in black holes and that the mechanisms that produce the two flavors of variability are most probably independent. After comparing this QPO with other variability phenomena seen in accreting black holes and neutron stars, we conclude that it best resembles the so-called 1 Hz QPOs seen in dipping neutron star systems, although having a significantly lower (1-2 orders of magnitude) frequency. If confirmed, H1743-322 is the first black hole showing this type of variability. Given the unusual characteristics and the hard-state dependence of the {approx}11 mHz QPO, we also speculate whether these oscillations could instead be related to the radio jets observed in H1743-322. A systematic search for this type of low-frequency QPOs in similar systems is needed to test this speculation. In any case, it remains unexplained why these QPOs have only been seen in the last two outbursts of H1743-322.

  5. Quasi-periodicity in relative quasi-periodic tori

    NASA Astrophysics Data System (ADS)

    Fassò, Francesco; García-Naranjo, Luis C.; Giacobbe, Andrea

    2015-10-01

    At variance from the cases of relative equilibria and relative periodic orbits of dynamical systems with symmetry, the dynamics in relative quasi-periodic tori (namely, subsets of the phase space that project to an invariant torus of the reduced system on which the flow is quasi-periodic) is not yet completely understood. Even in the simplest situation of a free action of a compact and abelian connected group, the dynamics in a relative quasi-periodic torus is not necessarily quasi-periodic. It is known that quasi-periodicity of the unreduced dynamics is related to the reducibility of the reconstruction equation, and sufficient conditions for it are virtually known only in a perturbation context. We provide a different, though equivalent, approach to this subject, based on the hypothesis of the existence of commuting, group-invariant lifts of a set of generators of the reduced torus. Under this hypothesis, which is shown to be equivalent to the reducibility of the reconstruction equation, we give a complete description of the structure of the relative quasi-periodic torus, which is a principal torus bundle whose fibers are tori of a dimension which exceeds that of the reduced torus by at most the rank of the group. The construction can always be done in such a way that these tori have minimal dimension and carry ergodic flow.

  6. XMM-Newton discovery of mHz quasi-periodic oscillations in the high-mass X-ray binary IGR J19140+0951

    NASA Astrophysics Data System (ADS)

    Sidoli, L.; Esposito, P.; Motta, S. E.; Israel, G. L.; Rodríguez Castillo, G. A.

    2016-08-01

    We report on the discovery of mHz quasi-periodic oscillations (QPOs) from the high-mass X-ray binary (HMXB) IGR J19140+0951, during a 40 ks XMM-Newton observation performed in 2015, which caught the source in its faintest state ever observed. At the start of the observation, IGR J19140+0951 was at a low flux of 2 × 10-12 erg cm-2 s-1 (2-10 keV; LX = 3 × 1033 erg s-1 at 3.6 kpc), then its emission rose reaching a flux ˜10 times higher, in a flare-like activity. The investigation of the power spectrum reveals the presence of QPOs, detected only in the second part of the observation, with a strong peak at a frequency of 1.46 ± 0.07 mHz, together with higher harmonics. The X-ray spectrum is highly absorbed (NH = 1023 cm-2), well fitted by a power law with a photon index in the range 1.2-1.8. The re-analysis of a Chandra archival observation shows a modulation at ˜0.17 ± 0.05 mHz, very likely the neutron-star spin period (although a QPO cannot be excluded). We discuss the origin of the 1.46 mHz QPO in the framework of both disc-fed and wind-fed HMXBs, favouring the quasi-spherical accretion scenario. The low flux observed by XMM-Newton leads to about three orders of magnitude the source dynamic range, overlapping with the one observed from Supergiant Fast X-ray Transients (SFXTs). However, since its duty cycle is not as low as in SFXTs, IGR J19140+0951 is an intermediate system between persistent supergiant HMXBs and SFXTs, suggesting a smooth transition between these two sub-classes.

  7. Quasi-periodic solutions for the quasi-periodically forced cubic complex Ginzburg-Landau equation on {T}d

    NASA Astrophysics Data System (ADS)

    Cheng, Hongyu; Si, Jianguo

    2013-08-01

    In this paper, we discuss the existence of time quasi-periodic solutions for quasi-periodically forced cubic complex Ginzburg-Landau equation of higher spatial dimension with basic frequency vector ω = (ω1, ω2, …, ωm). By constructing a KAM (Kolmogorov-Arnold-Moser) theorem for a dissipative system which depends on time in a quasi-periodic way, we obtain a Cantorian branch of m + 2-dimensional invariant tori for the equation.

  8. Embedding of Analytic Quasi-Periodic Cocycles into Analytic Quasi-Periodic Linear Systems and its Applications

    NASA Astrophysics Data System (ADS)

    You, Jiangong; Zhou, Qi

    2013-11-01

    In this paper, we prove that any analytic quasi-periodic cocycle close to constant is the Poincaré map of an analytic quasi-periodic linear system close to constant, which bridges both methods and results in quasi-periodic linear systems and cocycles. We also show that the almost reducibility of an analytic quasi-periodic linear system is equivalent to the almost reducibility of its corresponding Poincaré cocycle. By the local embedding theorem and the equivalence, we transfer the recent local almost reducibility results of quasi-periodic linear systems (Hou and You, in Invent Math 190:209-260, 2012) to quasi-periodic cocycles, and the global reducibility results of quasi-periodic cocycles (Avila, in Almost reducibility and absolute continuity, 2010; Avila et al., in Geom Funct Anal 21:1001-1019, 2011) to quasi-periodic linear systems. Finally, we give a positive answer to a question of Avila et al. (Geom Funct Anal 21:1001-1019, 2011) and use it to study point spectrum of long-range quasi-periodic operator with Liouvillean frequency. The embedding also holds for some nonlinear systems.

  9. Quasi-periodicities at Year-like Timescales in Blazars

    NASA Astrophysics Data System (ADS)

    Sandrinelli, A.; Covino, S.; Dotti, M.; Treves, A.

    2016-03-01

    We searched for quasi-periodicities on year-like timescales in the light curves of six blazars in the optical—near-infrared bands and we made a comparison with the high energy emission. We obtained optical/NIR light curves from Rapid Eye Mounting photometry plus archival Small & Moderate Aperture Research Telescope System data and we accessed the Fermi light curves for the γ-ray data. The periodograms often show strong peaks in the optical and γ-ray bands, which in some cases may be inter-related. The significance of the revealed peaks is then discussed, taking into account that the noise is frequency dependent. Quasi-periodicities on a year-like timescale appear to occur often in blazars. No straightforward model describing these possible periodicities is yet available, but some plausible interpretations for the physical mechanisms causing periodic variabilities of these sources are examined.

  10. Quasi-periodic oscillations of perturbed tori

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Varadarajan; Manousakis, Antonios; Kluźniak, Włodzimierz

    2016-05-01

    We performed axisymmetric hydrodynamical simulations of oscillating tori orbiting a non-rotating black hole. The tori in equilibrium were constructed with a constant distribution of angular momentum in a pseudo-Newtonian potential (Kluźniak-Lee). Motions of the torus were triggered by adding subsonic velocity fields: radial, vertical and diagonal to the tori in equilibrium. As the perturbed tori evolved in time, we measured L2 norm of density and obtained the power spectrum of L2 norm which manifested eigenfrequencies of tori modes. The most prominent modes of oscillation excited in the torus by a quasi-random perturbation are the breathing mode and the radial and vertical epicyclic modes. The radial and the plus modes, as well as the vertical and the breathing modes will have frequencies in an approximate 3:2 ratio if the torus is several Schwarzschild radii away from the innermost stable circular orbit. Results of our simulations may be of interest in the context of high-frequency quasi-periodic oscillations observed in stellar-mass black hole binaries, as well as in supermassive black holes.

  11. Quasi periodic oscillations in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Alston, W.; Fabian, A.; Markevičiutė, J.; Parker, M.; Middleton, M.; Kara, E.

    2016-05-01

    Quasi-periodic oscillations (QPOs) are coherent peaks of variability power observed in the X-ray power spectra (PSDs) of stellar mass X-ray binaries (XRBs). A scale invariance of the accretion process implies they should be present in the active galactic nuclei. The first robust detection was a ∼ 1 h periodicity in the Seyfert galaxy RE J1034+396 from a ∼ 90 ks XMM-Newton observation; however, subsequent observations failed to detect the QPO in the 0.3-10.0 keV band. In this talk we present the recent detection of the ∼ 1 h periodicity in the 1.0-4.0 keV band of 4 further low-flux/spectrally-harder observations of RE J1034+396 (see Alston et al. 2014). We also present recent work on the discovery of a QPO in the Seyfert galaxy, MS 2254.9-3712, which again is only detected in energy bands associated with the primary power-law continuum emission (Alston et al. 2015). We conclude these features are most likely analogous to the high-frequency QPOs observed in XRBs. In both sources, we also see evidence for X-ray reverberation at the QPO frequency, where soft X-ray bands and Iron Kα emission lag the primary X-ray continuum. These time delays may provide another diagnostic for understanding the underlying QPO mechanism observed in accreting black holes.

  12. Quasi-periodic oscillations in superfluid magnetars

    NASA Astrophysics Data System (ADS)

    Passamonti, A.; Lander, S. K.

    2014-02-01

    We study the time evolution of axisymmetric oscillations of superfluid magnetars with a poloidal magnetic field and an elastic crust, working in Newtonian gravity. Extending earlier models, we study the effects of composition gradients and entrainment on the magneto-elastic wave spectrum and on the potential identification of the observed quasi-periodic oscillations (QPOs). We use two-fluid polytropic equations of state to construct our stellar models, which mimic realistic composition gradient configurations. The basic features of the axial axisymmetric spectrum of normal fluid stars are reproduced by our results and in addition we find several magneto-elastic waves with a mixed character. In the core, these oscillations mimic the shear mode pattern of the crust as a result of the strong dynamical coupling between these two regions. Incorporating the most recent entrainment configurations in our models, we find that they have a double effect on the spectrum: the magnetic oscillations of the core have a frequency enhancement, while the mixed magneto-elastic waves originating in the crust are moved towards the frequencies of the single-fluid case. The distribution of lower frequency magneto-elastic oscillations for our models is qualitatively similar to the observed magnetar QPOs with ν < 155 Hz. In particular, some of these QPOs could represent mixed magneto-elastic oscillations with frequencies not greatly different from the crustal modes of an unmagnetized star. We find that many QPOs could even be accounted for using a model with a relatively weak polar field of Bp ≃ 3 × 1014 G, because of the superfluid enhancement of magnetic oscillations. Finally, we discuss the possible identification of 625 and 1837 Hz QPOs either with non-axisymmetric modes or with high-frequency axisymmetric QPOs excited by crustal mode overtones.

  13. Multispacecraft observations of quasi-periodic emissions

    NASA Astrophysics Data System (ADS)

    Nemec, Frantisek; Picket, Jolene S.; Santolik, Ondrej

    2014-05-01

    Quasi-periodic (QP) emissions are VLF electromagnetic waves in the frequency range of about 0.5-5 kHz which exhibit a periodic time modulation of the wave intensity. The modulation period is usually on the order of a few tens of seconds. The generation mechanism of these emissions is still not understood, but at least in some cases it appears to be related to ULF magnetic field pulsations which result in periodic modifications of the resonant conditions in the source region. We use multipoint measurements of QP emissions by the 4 Cluster spacecraft. The observations are obtained close to the equatorial region at radial distances of about 4 Earth radii, i.e. close to a possible generation region. A combined analysis of the high resolution data obtained by the WBD instruments and the ULF magnetic field data obtained by the FGM instruments allows for a detailed case-study analysis of these unique emissions. The presented analysis benefits from the recent close-separation configuration of three of the Cluster spacecraft (≡20-100 km) and a related timing analysis, which would be impossible otherwise.

  14. Studying X-Ray Binaries with High Energy Frequency Quasi-Periodic Oscillations

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald J. (Technical Monitor); Kaaret, P.

    2003-01-01

    The goal of this investigation is to further our understanding of the dynamics of accreting neutron stars and black holes in the hope of using these systems as probes of the physics of strong gravitational fields. The main focus of this work has been a multi-year program of simultaneous millisecond x-ray timing and spectral observations carried out with the Rossi X-Ray Timing Explorer (RXTE) to perform the x-ray timing and one of the satellites Asca, BeppoSAX, or Chandra to perform x-ray spectral measurements. With the advent of Chandra, we have extended our work to include imaging of X-ray jets from binaries and the study of extragalactic X-ray binaries. Significant progress was made over the past year.

  15. Studying X-Ray Binaries with High Frequency Quasi-Periodic Oscillations

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald (Technical Monitor); Kaaret, Philip

    2004-01-01

    The goal of this investigation is to further our understanding of the dynamics of accreting neutron stars and black holes in the hope of using these systems as probes of the physics of strong gravitational fields. The main focus of this work has been a multi-year program of millisecond X-ray timing and spectral observations of accreting compact objects. include imaging of X-ray jets from binaries and the study of extragalactic X-ray binaries. past year. Nine papers were accepted and/or published, as listed below. Seven of these are new since our previous annual report. With the advent of Chandra, we have extended our work to Significant progress was made over the The presentation of several talks and posters at astronomical meetings were supported by this grant. The PI was the lead organizer of "X-Ray Timing 2003: Rossi and Beyond", a major conference held in Cambridge, MA, in November, 2003. A t the conference we reviewed the accomplishments of the Rossi X-Ray Timing Explorer and developed the scientific motivation for a future X-ray timing mission. This conference was well attended and generated a significant amount of interest.

  16. Spectral Index and Quasi-Periodic Oscillation Frequency Correlation in Black Hole (BH) Sources: Observational Evidence of Two Phases and Phase Transition in BHs

    NASA Technical Reports Server (NTRS)

    Titarchuk, Lev; Fiorito, Ralph

    2004-01-01

    -photon upscattering and photon trapping in converging flow into BH. In the TL model for corona the QPO frequency vnu(sub high) is related to the gravitational (close to Keplerian) frequency nu(sub K) at the outer (adjustment) radius and nu(sub low) is related to the TL s normal mode (magnetoacoustic) oscillation frequency nu(sub MA). The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

  17. How to Distinguish Neutron Star and Black Hole X-ray Binaries? Spectral Index and Quasi-Periodic Oscillation Frequency Correlation

    NASA Technical Reports Server (NTRS)

    Titarchuk, Lev; Shaposhnikov, Nickolai

    2005-01-01

    Recent studies have revealed strong correlations between 1-10 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral power law index of several Black Hole (BH) candidate sources when seen in the low/hard state, the steep power-law (soft) state, and in transition between these states. In the soft state these index-QPO frequency correlations show a saturation of the photon index GAMMA approximately equal to 2.7 at high values of the low frequency nu(sub L). This saturation effect was previously identified as a black hole signature. In this paper we argue that this saturation does not occur, at least for one neutron star (NS) source 4U 1728-34, for which the index GAMMA monotonically increases with nu(sub L) to the values of 6 and higher. We base this conclusion on our analysis of approximately 1.5 Msec of RXTE archival data for 4U 1728-34. We reveal the spectral evolution of the Comptonized blackbody spectra when the source transitions from the hard to soft states. The hard state spectrum is a typical thermal Comptonization spectrum of the soft photons which originate in the disk and the NS outer photospheric layers. The hard state photon index is GAMMA approximately 2. The soft state spectrum consists of two blackbody components which are only slightly Comptonized. Thus we can claim (as expected from theory) that in NS sources thermal equilibrium is established for the soft state. To the contrary in BH sources, the equilibrium is never established due to the presence of the BH horizon. The emergent BH spectrum, even in the high/soft state, has a power law component. We also identify the low QPO frequency nu(sub L) as a fundamental frequency of the quasi-spherical component of the transition layer (presumably related to the corona and the NS and disk magnetic closed field lines). The lower frequency nu(sub SL) is identified as the frequency of oscillations of a quasi-cylindrical configuration of the TL (presumably related to the NS and disk magnetic

  18. Energy dependence of r.m.s amplitude of low frequency broadband noise and kHz quasi periodic oscillations in 4U 1608-52

    NASA Astrophysics Data System (ADS)

    Mandal, Soma

    2016-07-01

    The neutron star low mass X-ray binary 4U 1608-52 is known to show kHz QPOs as well as low frequency broad band noise. The energy dependence of the fractional r.m.s of these variations reflect the underlying radiative mechanism responsible for the phenomena. In this work we compute the energy depedence for 26 instances of kHz QPO observed by RXTE. We typically find as reported before, that the r.m.s increases with energy with slope of ˜0.5. This indicates that the variation is in the hot thermal compotonization component and in particular the QPO is likely to be driven by variation in the thermal heating rate of the hot plasma. For the same data, we compute the energy dependent r.m.s variability of the low frequency broad band noise component by considering the light curves. In contrast to the behaviour seen for the kHz QPO, the energy dependence is nearly flat i.e. the r.m.s. is energy independent. This indicates that the driver here may be the soft photon source. Thus the radiative mechanism driving the low frequency broad band noise and the high frequency QPO are different in nature.

  19. On the Disappearance of Kilohertz Quasi-periodic Oscillations at a High Mass Accretion Rate in Low-Mass X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Cui, Wei

    2000-05-01

    For all sources in which the phenomenon of kilohertz quasi-periodic oscillation (kHz QPO) is observed, the QPOs disappear abruptly when the inferred mass accretion rate exceeds a certain threshold. Although the threshold cannot at present be accurately determined (or even quantified) observationally, it is clearly higher for bright Z sources than for faint atoll sources. Here we propose that the observational manifestation of kHz QPOs requires direct interaction between the neutron star magnetosphere and the Keplerian accretion disk and that the cessation of kHz QPOs at a high accretion rate is due to the lack of such an interaction when the Keplerian disk terminates at the last stable orbit and yet the magnetosphere is pushed farther inward. The threshold is therefore dependent on the magnetic field strength-the stronger the magnetic field, the higher the threshold. This is certainly in agreement with the atoll/Z paradigm, but we argue that it is also generally true, even for individual sources within each (atoll or Z) category. For atoll sources, the kHz QPOs also seem to vanish at a low accretion rate. Perhaps the ``disengagement'' between the magnetosphere and the Keplerian disk also takes place under such circumstances because of, for instance, the presence of quasi-spherical advection-dominated accretion flow (ADAF) close to the neutron star. Unfortunately, in this case, the estimation of the accretion rate threshold would require a knowledge of the physical mechanisms that cause the disengagement. If the ADAF is responsible, the threshold is likely dependent on the magnetic field of the neutron star.

  20. Quasi-periodic climate change on Mars

    NASA Technical Reports Server (NTRS)

    Kieffer, Hugh H.; Zent, Aaron P.

    1992-01-01

    The paper examines evidence that the Martian climate undergoes quasi-periodic variations, including the polar layered terrain, differences between the residual polar caps, and the current net southward flow of H2O. The driving functions for these variations are oscillations in the elements of the Martian orbit coupled with precession of the Martian spin axis. These 'astronomic variations' control the distribution of the insolation, which in turn influences the partition of volatiles between atmospheric and surface reservoirs. The major effects anticipated at low obliquity are growth of the polar caps, substantial decrease in surface pressure, cessation of duststorms, release of CO2 from the regolith, and poleward migration of H2O ground ice. At high obliquity, the mass of the perennial polar caps decreases and permanent CO2 frost disappears, CO2 desorbs from the regolith at high latitudes, the surface pressure may increase to several times its current value, and the atmospheric dust load increases.

  1. The Ten-Rotation Quasi-periodicity in Sunspot Areas

    NASA Astrophysics Data System (ADS)

    Getko, R.

    2014-06-01

    Sunspot-area fluctuations over an epoch of 12 solar cycles (12 - 23) are investigated in detail using wavelets. Getko ( Universal Heliophysical Processes, IAU Symp. 257, 169, 2009) found three significant quasi-periodicities at 10, 17, and 23 solar rotations, but two longer periods could be treated as subharmonics of the ten-rotation quasi-periodicity. Therefore we focused the analysis on the occurrence of this quasi-periodicity during the low- and high-activity periods of each solar cycle. Because of the N - S asymmetry, each solar hemisphere was considered separately. The skewness of each fluctuation-probability distribution suggests that the positive and negative fluctuations could be examined separately. To avoid the problem that occurs when a few strong fluctuations create a wavelet peak, we applied fluctuation transformations for which the amplitudes at the high- and the low-activity periods are almost the same. The wavelet analyses show that the ten-rotation quasi-periodicity is mainly detected during the high-activity periods, but it also exists during a few low-activity periods. The division of each solar hemisphere into 30∘-wide longitude bins and the wavelet calculations for the areas of sunspot clusters belonging to these 30∘ bins enable one to detect longitude zones in which the ten-rotation quasi-periodicity exists. These zones are present during the whole high-activity periods and dominate the integrated spectra.

  2. A result on quasi-periodic solutions of a nonlinear beam equation with a quasi-periodic forcing term

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Si, Jianguo

    2012-02-01

    In this paper, a quasi-periodically forced nonlinear beam equation {u_{tt}+u_{xxxx}+μ u+\\varepsilonφ(t)h(u)=0} with hinged boundary conditions is considered, where μ > 0, {\\varepsilon} is a small positive parameter, {φ} is a real analytic quasi-periodic function in t with a frequency vector ω = ( ω 1, ω 2 . . . , ω m ), and the nonlinearity h is a real analytic odd function of the form {h(u)=η_1u+η_{2bar{r}+1}u^{2bar{r}+1}+sum_{k≥ bar{r}+1}η_{2k+1}u^{2k+1},η_1,η_{2bar{r}+1} neq0, bar{r} in {mathbb {N}}.} The above equation admits a quasi-periodic solution.

  3. Quasi-periodic spatiotemporal filtering.

    PubMed

    Burghouts, Gertjan J; Geusebroek, Jan-Mark

    2006-06-01

    This paper presents the online estimation of temporal frequency to simultaneously detect and identify the quasiperiodic motion of an object. We introduce color to increase discriminative power of a reoccurring object and to provide robustness to appearance changes due to illumination changes. Spatial contextual information is incorporated by considering the object motion at different scales. We combined spatiospectral Gaussian filters and a temporal reparameterized Gabor filter to construct the online temporal frequency filter. We demonstrate the online filter to respond faster and decay faster than offline Gabor filters. Further, we show the online filter to be more selective to the tuned frequency than Gabor filters. We contribute to temporal frequency analysis in that we both identify ("what") and detect ("when") the frequency. In color video, we demonstrate the filter to detect and identify the periodicity of natural motion. The velocity of moving gratings is determined in a real world example. We consider periodic and quasiperiodic motion of both stationary and nonstationary objects. PMID:16764282

  4. Search for a correlation between kHz quasi-periodic oscillation frequencies and accretion-related parameters in the ensemble of neutron star low-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Çatmabacak, Önder; Hakan Erkut, M.; Catmabacak, Onur; Duran, Sivan

    2016-07-01

    The distribution of neutron star sources in the ensemble of low-mass X-ray binaries shows no evidence for a correlation between kHz quasi-periodic oscillation (QPO) frequencies and X-ray luminosity. Sources differing by orders of magnitude in luminosity can exhibit similar range of QPO frequencies. We study the possibility for the existence of a correlation between kHz QPO frequencies and accretion related parameters. The parameters such as the mass accretion rate and the size of the boundary region in the innermost disk are expected to be related to X-ray luminosity. Using the up-to-date data of neutron star low-mass X-ray binaries, we search for a possible correlation between lower kHz QPO frequencies and mass accretion rate through the mass and radius values predicted by different equations of state for the neutron star. The range of mass accretion rate for each source can be estimated if the accretion luminosity is assumed to be represented well by the X-ray luminosity of the source. Although we find no correlation between mass accretion rate and QPO frequencies, the source distribution seems to be in accordance with a correlation between kHz QPO frequencies and the parameter combining the neutron star magnetic field and the mas accretion rate. The model function we employ to descibe the correlation is able to account for the scattering of individual sources around a simple power law. The correlation argues disk-magnetosphere interaction as the origin of these millisecond oscillations.

  5. Broadband asymmetric acoustic transmission by a plate with quasi-periodic surface ridges

    SciTech Connect

    Li, Chunhui; Ke, Manzhu Ye, Yangtao; Xu, Shengjun; Qiu, Chunyin; Liu, Zhengyou

    2014-07-14

    In this paper, an acoustic system with broadband asymmetric transmission is designed and fabricated, which consists of a water-immersed aluminum plate engraved with quasi-periodically-patterned ridges on single surface. It demonstrates that when the acoustic waves are launched into the system from the structured side, they can couple into the Lamb modes in the plate efficiently and attain a high transmission; on the contrary, when the waves are incident from the opposite flat side, the coupling is weak, and the transmission is low. Superior to systems with periodic patterning, this quasi-periodically-patterned system has a broad working frequency range due to the collective contributions from the multiple diffractions specific to the structure.

  6. Aperiodic and Quasi-Periodic Variability in Scorpius X-1

    NASA Astrophysics Data System (ADS)

    Parker, Neil Ivan

    Low mass X-ray binary star systems (LMXBs) are among the brightest and most well-studied objects in the X-ray sky-indeed, the first extrasolar X-ray source discovered, Sco X-1, is an LMXB. But despite the wealth of available data, LMXBs remain enigmatic, in large part due to the fact that they show little or no coherent periodicity. LMXBs show aperiodic and quasi-periodic variability, for which the underlying mechanisms are poorly understood. Much information remains locked in archival data. Here we address this issue by re-analyzing archival EXOSAT data of Sco X-1 using modern time-series techniques, including multi-tapering, wavelet transforms and scalegrams, and nonlinear dynamical modelling, which are not yet commonly used in the analysis of astronomical data, with the goal of characterizing Sco X-1's variability and developing a formalism to take us from timing data to mathematical models to astrophysical models. The power spectra of Sco X-1 show several components: (i) very low frequency noise (VLFN), a colored noise component seen below ~0.25 Hz, (ii) high frequency noise (HFN), a colored noise component seen above ~30-40 Hz, and (iii) quasi-periodic oscillations (QPOs), localized excesses of Fourier power. The VLFN contains ~1.3% [1/over2]-peak-to-peak pulsed power on the average, can be described by a power law with an index of ~1.4, and is correlated with the 'flickeriness' of the source. QPOs contain ~4.6% [1/over2]-peak-to-peak pulsed power, have centroid frequencies of 6.7 Hz or 15 Hz, and are associated with extended 'quiescent' states and with brief gaps in 'flaring' states. HFN is difficult to characterize (though others have had success describing it as a damped power law), and is not strongly associated with any other source feature. It contains ~2.1% [1/over2]-peak-to-peak pulsed power. Several models have been proposed to explain the VLFN, QPOs, and HFN in Sco X-1, but none are completely satisfactory. Most models seek to explain only QPOs. Here

  7. Quasi-periodic quantum dot arrays produced by electrochemical synthesis

    SciTech Connect

    Bandyopadhyay, S.; Miller, A.E.; Yue, D.F.; Banerjee, G.; Ricker, R.E.; Jones, S.; Eastman, J.A.; Baugher, E.; Chandrasekhar, M.

    1994-06-01

    We discuss a ``gentle`` electrochemical technique for fabricating quasi-periodic quantum dot arrays. The technique exploits a self-organizing phenomenon to produce quasi-periodic arrangement of dots and provides excellent control over dot size and interdot spacing. Unlike conventional nanolithography, it does not cause radiation damage to the structures during exposure to pattern delineating beams (e-beam, ion-beam or x-ray). Moreover, it does not require harsh processing steps like reactive ion etching, offers a minimum feature size of {approximately}40 {angstrom}, allows the fabrication of structures on nonplanar surfaces (e.g. spherical or cylindrical substrates), is amenable to mass production (millions of wafers can be processed simultaneously) and is potentially orders of magnitude cheaper than conventional nanofabrication. In this paper, we describe our initial results and show the promise of this technique for low-cost and high-yield nanosynthesis.

  8. Quasi periodic oscillations in black hole binaries

    NASA Astrophysics Data System (ADS)

    Motta, S. E.

    2016-05-01

    Fast time variability is the most prominent characteristic of accreting systems and the presence of quasi periodic oscillations (QPOs) is a constant in all accreting systems, from cataclysmic variables to AGNs, passing through black hole and neutron star X-ray binaries and through the enigmatic ultra-luminous X-ray sources. In this paper, I will briefly review the current knowledge of QPOs in black hole X-ray binaries, mainly focussing on their observed properties, but also mentioning the most important models that have been proposed to explain the origin of QPOs over the last decades.

  9. Quasi-periodic transformations of nonlocal spatial solitons.

    PubMed

    Buccoliero, Daniel; Desyatnikov, Anton S

    2009-06-01

    We study quasi-periodic transformations between nonlocal spatial solitons of different symmetries triggered by modulational instability and resembling a self-induced mode converter. Transformation dynamics of solitons with zero angular momentum, e.g. the quadrupole-type soliton, reveal the equidistant spectrum of spatial field oscillations typical for the breather-type solutions. In contrast, the transformations of nonlocal solitons carrying orbital angular momentum, such as 2x3 soliton matrix, are accompanied by their spiralling and corresponding spectra of field oscillations show mixing of three characteristic spatial frequencies. PMID:19506609

  10. Pure Point Spectrum of the Floquet Hamiltonian for the Quantum Harmonic Oscillator Under Time Quasi-Periodic Perturbations

    NASA Astrophysics Data System (ADS)

    Wang, W.-M.

    2008-01-01

    We prove that the 1- d quantum harmonic oscillator is stable under spatially localized, time quasi-periodic perturbations on a set of Diophantine frequencies of positive measure. This proves a conjecture raised by Enss-Veselic in their 1983 paper [EV] in the general quasi-periodic setting. The motivation of the present paper also comes from construction of quasi-periodic solutions for the corresponding nonlinear equation.

  11. QUASI-PERIODIC OSCILLATIONS AND BROADBAND VARIABILITY IN SHORT MAGNETAR BURSTS

    SciTech Connect

    Huppenkothen, Daniela; Watts, Anna L.; Uttley, Phil; Van der Horst, Alexander J.; Van der Klis, Michiel; Kouveliotou, Chryssa; Goegues, Ersin; Granot, Jonathan; Vaughan, Simon; Finger, Mark H.

    2013-05-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and QPOs at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.

  12. Quasi-periodic Oscillations and Broadband Variability in Short Magnetar Bursts

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela; Watts, Anna L.; Uttley, Phil; van der Horst, Alexander J.; van der Klis, Michiel; Kouveliotou, Chryssa; Göǧüş, Ersin; Granot, Jonathan; Vaughan, Simon; Finger, Mark H.

    2013-05-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and QPOs at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.

  13. Tracking rhythmicity in nonstationary quasi-periodic biomedical signals using adaptive time-varying covariance.

    PubMed

    Li, Dan; Jung, Ranu

    2002-07-01

    A time-varying covariance method for detecting and quantifying the evolution of rhythmicity (frequency) in persistently varying quasi-periodic nonstationary signals is presented. The basic method, evaluated using chirp signals, utilizes a shifting window of fixed length. A substantial reduction in estimation bias and variability are obtained by utilizing an adaptive window whose length is dependent on past frequency estimates. The adaptive window yields estimates that are comparable in accuracy to those obtained using high-resolution time-frequency representation but with lower computation requirements and the potential for on-line application. Finally, an example of the application of the method for analyzing a neural recording is also illustrated. PMID:11931864

  14. Mid-term quasi-periodicities in the CaII-K plage index of the Sun and their implications

    NASA Astrophysics Data System (ADS)

    Chowdhury, Partha; Gokhale, M. H.; Singh, Jagdev; Moon, Y.-J.

    2016-02-01

    We present results of the fast Fourier transform (FFT), the MEM analysis, and the wavelet analysis (WA), of the temporal variation of the monthly disk integrated "CaII-K plage-area and enhanced network (EN) area" hereafter called `plage index' derived by Tlatov et al. (2009), from spectro-heliograms taken in Ca II K line at Kodaikanal Observatory, from February 1907 to April, 1998, In the range {>}3 months and < decade, the Fourier transform power spectra reveal solar cycle periodicity {˜}122 months, its sub-harmonic ˜61 months, two short quasi-periodicities ({>}2 and <4 months), and nine `intermediate-range' quasi-periodicities (≳ 4 mo and <11 yr), in the variation of the plage index. The quasi-periodicities include Rieger, Rieger type and quasi-biennial. The presence of quasi-periodicities and the mean values of the periods are confirmed by the maximum entropy method (MEM). The temporal spans of the quasi-periodicities during different solar cycles are determined from the complex Morlet-wavelet analyses. The Rieger quasi-periodicity (150-160 days) appeared during cycle 21 and cycle 22. Each of the quasi-periodicities in the studied range lies close to one or more planetary periodicities (orbital, or spring tidal, or heliocentric conjunction frequency). We discuss possible interpretations of our results, and those of similar results obtained earlier by other authors, towards understanding the mechanisms of excitation of various quasi-periodicities detected in solar variability parameters.

  15. Quasi-periodic modulation of equatorial noise intensity

    NASA Astrophysics Data System (ADS)

    Nemec, Frantisek; Santolik, Ondrej; Hrbackova, Zuzana; Pickett, Jolene S.; Cornilleau-Wehrlin, Nicole

    2015-04-01

    Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed routinely in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field. Although their harmonic structure, which is characteristic of the proton cyclotron frequency in the source region has been known for a couple of decades, they were generally believed to be continuous in time. The analysis of more than 2000 EN events observed by the STAFF-SA and WBD instruments on board the Cluster spacecraft reveals that this is not always the case, with about 5% of events exhibiting a clear quasi-periodic (QP) modulation of the wave intensity. We perform a systematic analysis of these events, and we discuss possible mechanisms of the QP intensity modulation. It is shown that the events occur usually in the noon-to-dawn magnetic local time sector, and their occurrence seems to be related to the periods of increased geomagnetic activity. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN were identified in about half of the events. These ULF pulsations might modulate the EN wave intensity, similarly as they modulate the intensity of formerly reported VLF whistler-mode QP events.

  16. Equatorial Noise Emissions and Their Quasi-Periodic Modulation

    NASA Astrophysics Data System (ADS)

    Nemec, F.; Santolik, O.; Hrbackova, Z.; Pickett, J. S.; Cornilleau-Wehrlin, N.; Parrot, M.; Hayosh, M.

    2015-12-01

    Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic structure related to the ion cyclotron frequency in the source region. We analyze more than 2000 EN events observed by the wave instruments on board the Cluster spacecraft, and we find that about 5% of EN events are not continuous in time, but exhibit a quasi-periodic (QP) modulation of the wave intensity. Typical modulation periods are on the order of minutes. The events predominantly occur in the noon-to-dawn local time sector, and their occurrence is related to the periods of increased geomagnetic activity and higher solar wind speeds. We suggest that the QP modulation of EN events may be due to compressional ULF pulsations, which periodically modulate the wave growth in the source region. These compressional ULF pulsations were identified in about half of the events. Finally, we demonstrate that EN emissions with QP modulation of the wave intensity can propagate down to altitudes as low as 700 km.

  17. Invariant tori for a derivative nonlinear Schrödinger equation with quasi-periodic forcing

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Si, Jianguo

    2015-03-01

    This paper is concerned with a one dimensional derivative nonlinear Schrödinger equation with quasi-periodic forcing under periodic boundary conditions i u t + u x x + i g ( β t ) ( f ( |u|2 ) u ) x = 0 , x ∈ T ≔ R / 2 π Z , where g(βt) is real analytic and quasi-periodic on t with frequency vector β = (β1, β2, …, βm). f is real analytic in some neighborhood of the origin in ℂ, f(0) = 0 and f'(0) ≠ 0. We show that the above equation admits Cantor families of smooth quasi-periodic solutions of small amplitude. The proof is based on an abstract infinite dimensional Kolmogorov-Arnold-Moser theorem for unbounded perturbation vector fields and partial Birkhoff normal form.

  18. Real analytic quasi-periodic solutions for the derivative nonlinear Schrödinger equations

    NASA Astrophysics Data System (ADS)

    Geng, Jiansheng; Wu, Jian

    2012-10-01

    In this paper, we show that one dimension derivative nonlinear Schrödinger equation admits a whitney smooth family of small amplitude, real analytic quasi-periodic solutions with two Diophantine frequencies. The proof is based on a partial Birkhoff normal form reduction and an abstract infinite dimensional Kolmogorov-Arnold-Moser (KAM) theorem.

  19. Concept of quasi-periodic undulator - control of radiation spectrum

    SciTech Connect

    Sasaki, Shigemi

    1995-02-01

    A new type of undulator, the quasi-periodic undulator (QPU) is considered which generates the irrational harmonics in the radiation spectrum. This undulator consists of the arrays of magnet blocks aligned in a quasi-periodic order, and consequentially lead to a quasi-periodic motion of electron. A combination of the QPU and a conventional crystal/grating monochromator provides pure monochromatic photon beam for synchrotron radiation users because the irrational harmonics do not be diffracted in the same direction by a monochromator. The radiation power and width of each radiation peak emitted from this undulator are expected to be comparable with those of the conventional periodic undulator.

  20. Hard apex transition in quasi-periodic oscillators - Closing of the accretion gap

    NASA Technical Reports Server (NTRS)

    Biehle, Garrett T.; Blandford, Roger D.

    1993-01-01

    We propose that the 'hard apex' transition in the X-ray two-color diagrams for low-mass X-ray binaries exhibiting quasi-periodic oscillation is associated with closure of a gap between the accretion disk and the star. At low accretion rates, gas crosses this gap intermittently. However, when the mass accretion rate increases, the disk thickens and its inner edge touches the star, thus forming a boundary layer through which the gas flows steadily. This explanation is viable provided that the equation of state of nuclear matter is not significantly harder than the Bethe-Johnson I prescription. Accretion gap scenarios are possibly distinguishable from models which invoke a small magnetosphere around the neutron star, in that they preclude large stellar magnetic fields and associate the high-frequency (horizontal-branch) oscillations with different sites.

  1. Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures

    NASA Astrophysics Data System (ADS)

    Lei, Yuxiong; Chen, Zheng; Li, Liangliang

    2015-05-01

    Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures were investigated in this study. The periodic and quasi-periodic structures were designed based on Fibonacci sequence and golden ratio. Ni nanowires arrays were electrodeposited in anodic aluminum oxide (AAO) templates with patterned Cu electrodes, and then the AAO templates were attached to the coplanar waveguide lines fabricated on quartz substrate for measurement. The S21 of both periodic and quasi-periodic structure-patterned Ni nanowire arrays showed an extra absorption peak besides the absorption peak due to the ferromagnetic resonance of Ni nanowires. The frequency of the absorption peak caused by the patterned structure could be higher than 40 GHz when the length and arrangement of the structural units were modified. In addition, the frequency of the absorption peak due to the quasi-periodic structure was calculated based on a simple analytical model, and the calculated value was consistent with the measured one. The experimental data showed that it could be a feasible approach to tune the performance of microwave devices by patterning ferromagnetic nanowires.

  2. Dripping handrails and the quasi-periodic oscillations of the AM Herculis objects

    NASA Technical Reports Server (NTRS)

    Steiman-Cameron, Thomas Y.; Young, Karl; Scargle, Jeffrey D.; Crutchfield, James P.; Imamura, James N.; Wolff, Michael T.; Wood, Kent S.

    1994-01-01

    AM Her objects exhibit periodic, quasi-periodic, and aperiodic variability on timescales ranging from seconds to years. Here, we investigate a process for the production of aperiodic and quasi-periodic accretion rate fluctuations. We consider the nonlinear dynamical model known as the dripping handrail (DHR). The DHR, basically a model for certain types of spatially extended systems and loosely based on water condensing on and dripping off a handrail, has recently been used as a model for the quasi-periodic oscillations (QPO) and very low frequency noise of the low-mass X-ray binary Sco X-1. Here, we show that (1) the DHR is a robust QPO generation process in that it leads to QPO production under a wide range of conditions and assumptions; (2) the phenomenology of the DHR is consistent with the observed aperiodic and quasi-periodic varibility of the AM Her QPO source VV Pup over timescales ranging from 16 ms to 20 s; and (3) a single DHR model can produce both broadband QPOs and features with quality Q greater than 20 as observed in several AM Her QPO sources.

  3. Pressure-driven reconnection and quasi periodical oscillations in plasmas

    SciTech Connect

    Paccagnella, R.

    2014-03-15

    This paper presents a model for an ohmically heated plasma in which a feedback exists between thermal conduction and transport, on one side, and the magneto-hydro-dynamical stability of the system, on the other side. In presence of a reconnection threshold for the magnetic field, a variety of periodical or quasi periodical oscillations for the physical quantities describing the system are evidenced. The model is employed to interpret the observed quasi periodical oscillations of electron temperature and perturbed magnetic field around the so called “Single Helical” state in the reversed field pinch, but its relevance for other periodical phenomena observed in magnetic confinement systems, especially in tokamaks, is suggested.

  4. MASS-ANGULAR-MOMENTUM RELATIONS IMPLIED BY MODELS OF TWIN PEAK QUASI-PERIODIC OSCILLATIONS

    SciTech Connect

    Toeroek, Gabriel; Bakala, Pavel; Sramkova, Eva; Stuchlik, Zdenek; Urbanec, Martin; Goluchova, Katerina E-mail: martin.urbanec@fpf.slu.cz E-mail: terek@volny.cz

    2012-12-01

    Twin peak quasi-periodic oscillations (QPOs) appear in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. Observations of the peculiar Z-source Circinus X-1 display unusually low QPO frequencies. Using these observations, we have previously considered the relativistic precession (RP) twin peak QPO model to estimate the mass of the central NS in Circinus X-1. We have shown that such an estimate results in a specific mass-angular-momentum (M - j) relation rather than a single preferred combination of M and j. Here we confront our previous results with another binary, the atoll source 4U 1636-53 that displays the twin peak QPOs at very high frequencies, and extend the consideration to various twin peak QPO models. In analogy to the RP model, we find that these imply their own specific M - j relations. We explore these relations for both sources and note differences in the {chi}{sup 2} behavior that represent a dichotomy between high- and low-frequency sources. Based on the RP model, we demonstrate that this dichotomy is related to a strong variability of the model predictive power across the frequency plane. This variability naturally comes from the radial dependence of characteristic frequencies of orbital motion. As a consequence, the restrictions on the models resulting from observations of low-frequency sources are weaker than those in the case of high-frequency sources. Finally we also discuss the need for a correction to the RP model and consider the removing of M - j degeneracies, based on the twin peak QPO-independent angular momentum estimates.

  5. Mass-Angular-momentum Relations Implied by Models of Twin Peak Quasi-periodic Oscillations

    NASA Astrophysics Data System (ADS)

    Török, Gabriel; Bakala, Pavel; Šrámková, Eva; Stuchlík, Zdeněk; Urbanec, Martin; Goluchová, Kateřina

    2012-12-01

    Twin peak quasi-periodic oscillations (QPOs) appear in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. Observations of the peculiar Z-source Circinus X-1 display unusually low QPO frequencies. Using these observations, we have previously considered the relativistic precession (RP) twin peak QPO model to estimate the mass of the central NS in Circinus X-1. We have shown that such an estimate results in a specific mass-angular-momentum (M - j) relation rather than a single preferred combination of M and j. Here we confront our previous results with another binary, the atoll source 4U 1636-53 that displays the twin peak QPOs at very high frequencies, and extend the consideration to various twin peak QPO models. In analogy to the RP model, we find that these imply their own specific M - j relations. We explore these relations for both sources and note differences in the χ2 behavior that represent a dichotomy between high- and low-frequency sources. Based on the RP model, we demonstrate that this dichotomy is related to a strong variability of the model predictive power across the frequency plane. This variability naturally comes from the radial dependence of characteristic frequencies of orbital motion. As a consequence, the restrictions on the models resulting from observations of low-frequency sources are weaker than those in the case of high-frequency sources. Finally we also discuss the need for a correction to the RP model and consider the removing of M - j degeneracies, based on the twin peak QPO-independent angular momentum estimates.

  6. Quasi-periodic solutions in a nonlinear Schrödinger equation

    NASA Astrophysics Data System (ADS)

    Geng, Jiansheng; Yi, Yingfei

    In this paper, one-dimensional (1D) nonlinear Schrödinger equation iu-u+mu+|u=0 with the periodic boundary condition is considered. It is proved that for each given constant potential m and each prescribed integer N>1, the equation admits a Whitney smooth family of small amplitude, time quasi-periodic solutions with N Diophantine frequencies. The proof is based on a partial Birkhoff normal form reduction and an improved KAM method.

  7. On quasi-periodic solutions for generalized Boussinesq equation with quadratic nonlinearity

    NASA Astrophysics Data System (ADS)

    Shi, Yanling; Xu, Junxiang; Xu, Xindong

    2015-02-01

    In this paper, one-dimensional generalized Boussinesq equation: utt - uxx + (u2 + uxx)xx = 0 with boundary conditions ux(0, t) = ux(π, t) = uxxx(0, t) = uxxx(π, t) = 0 is considered. It is proved that the equation admits a Whitney smooth family of small-amplitude quasi-periodic solutions with 2-dimensional Diophantine frequencies. The proof is based on an infinite dimensional Kolmogorov-Arnold-Moser theorem and Birkhoff normal form.

  8. Quasi-periodic oscillations of Jupiter's inner radiation belt

    NASA Astrophysics Data System (ADS)

    Soria, Roberto; Godfrey, Leith; Lou, Yu-Qing

    2014-04-01

    Radio and X-ray studies of Jupiter have detected quasi-periodic flux variability with timescales of ~20 min and ~45 min at some epochs but not others. Yu-Qing Lou and collaborators have suggested that this is caused by oscillations of the magnetosphere when it is buffeted by fast solar wind. We want to monitor Jupiter in the L-band with the ATCA: (1) to accurately characterise the variability over a wide bandwidth, during fast solar wind phases (v >~ 600 km/s); (2) to search for low-amplitude quasi-periodic variability during slow/intermediate wind phases or put an upper limit to the variability at those epochs; (3) to study the response of the characteristic oscillation timescales to different solar wind conditions. The induced magnetospheric oscillation model can be applied to broader astrophysical contexts, such as the Earth's magnetosphere, and quasi-periodic oscillations in accreting neutron-star and black holes. Jupiter provides a natural lab for our modelling of induced magnetospheric quasi-periodic oscillations.

  9. Ambarzumyan's theorem for the quasi-periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Kıraç, Alp Arslan

    2015-10-01

    We obtain the classical Ambarzumyan's theorem for the Sturm-Liouville operators Lt(q) with qin L1[0,1] and quasi-periodic boundary conditions, tin [0,2π ) , when there is not any additional condition on the potential q.

  10. Normal linear stability of quasi-periodic tori

    NASA Astrophysics Data System (ADS)

    Broer, H. W.; Hoo, J.; Naudot, V.

    We consider families of dynamical systems having invariant tori that carry quasi-periodic motions. Our interest is the persistence of such tori under small, nearly-integrable perturbations. This persistence problem is studied in the dissipative, the Hamiltonian and the reversible setting, as part of a more general KAM theory for classes of structure preserving dynamical systems. This concerns the parametrized KAM theory as initiated by Moser [J.K. Moser, On the theory of quasiperiodic motions, SIAM Rev. 8 (2) (1966)145-172; J.K. Moser, Convergent series expansions for quasi-periodic motions, Math. Ann. 169 (1967) 136-176] and further developed in [G.B. Huitema, Unfoldings of quasi-periodic tori, PhD thesis, University of Groningen, 1988; H.W. Broer, G.B. Huitema, F. Takens, Unfoldings of quasi-periodic tori, Mem. Amer. Math. Soc. 83 (421) (1990) 1-82; H.W. Broer, G.B. Huitema, Unfoldings of quasi-periodic tori in reversible systems, J. Dynam. Differential Equations 7 (1) (1995) 191-212]. The corresponding nondegeneracy condition involves certain (trans-)versality conditions on the normal linear, leading, part at the invariant tori. We show that as a consequence, a Cantor family of Diophantine tori with positive Hausdorff measure is persistent under nearly-integrable perturbations. This result extends the above references since presently the case of multiple Floquet exponents is included. Our leading example is the normal 1 :-1 resonance, which occurs a lot in applications, both Hamiltonian and reversible. As an illustration of this we briefly describe the Lagrange top coupled to an oscillator.

  11. Correlations between X-Ray Spectral Characteristics and Quasi-Periodic Oscillations in Scorpius X-1

    NASA Astrophysics Data System (ADS)

    Bradshaw, Charles F.; Titarchuk, Lev; Kuznetsov, Sergey

    2007-07-01

    Correlations between 1-10 Hz quasi-periodic oscillations (QPOs) and spectral power-law index have been reported for black hole (BH) candidate sources and one neutron star source, 4U 1728-34. An examination of QPO frequency and index relationships in Sco X-1 is reported here. We discover that Sco X-1, representing Z-source groups, can be adequately modeled by a simple two-component model of Compton up-scattering with a soft photon electron temperature of about 0.4 keV, plus an Iron K line. The results show a strong correlation between spectral power-law index and kHz QPOs. Because Sco X-1 radiates near the Eddington limit, one can infer that the geometrical configuration of the Compton cloud (CC) is quasi-spherical from high radiation pressure in the CC. Thus, we conclude that the high Thomson optical depth of the Compton cloud, in the range of ~5-6 from the best-fit model parameters, is consistent with the neutron star's surface being obscured by material. Moreover, a spin frequency of Sco X-1 is likely suppressed due to photon scattering off CC electrons. In addition, we demonstrate how the power spectrum evolves when Sco X-1 transitions from the horizontal branch to the normal branch.

  12. Discovery of quasi-periodic oscillations in the AM Herculis object BL Hydri

    SciTech Connect

    Middleditch, J.; Imamura, J.N.; Steiman-Cameron, T.Y.

    1997-11-01

    We obtained high-speed optical photometry of the AM Her object BL Hyi at the Las Campanas Observatory and the Cerro Tololo Inter-American Observatory during 1989{endash}1996. BL Hyi was in its faint-luminosity state in 1989; it subsequently brightened and was in its high-luminosity state for our 1994{endash}1996 observations. We discovered broad, 0.2{endash}0.8 Hz quasi-periodic oscillations (QPOs) and narrower QPOs superposed on the broad QPOs when BL Hyi was in its high-luminosity state. The broad QPOs had widths of {Delta}f/f{sub p}{approximately}0.5{endash}1 and runs pulsed amplitudes of {approximately}1{percent}{minus}4{percent}, where f{sub p} is the frequency of the QPO peak. The narrow QPOs had widths of {Delta}f/f{sub p}{lt}0.1{endash}1 and rms pulsed amplitudes of less than 1{percent}. BL Hyi showed stronger QPOs and was slightly brighter in 1994 than in 1995{endash}1996. The amplitudes of the broad and narrow QPOs were modulated on the orbital period of the system; they were strongest during the bright orbital phase. BL Hyi is the fifth AM Her system to show the short-period QPOs discovered by Middleditch. {copyright} {ital 1997} {ital The American Astronomical Society}

  13. Quasi-periodic continuation along a continuous symmetry

    NASA Astrophysics Data System (ADS)

    Salomone, Matthew David

    Given a system of differential equations which admits a continuous group of symmetries and possesses a periodic solution, we show that under certain nondegeneracy assumptions there always exists a continuous family containing infinitely many periodic and quasi-periodic trajectories. This generalizes the continuation method of Poincaré to orbits which are not necessarily periodic. We apply these results in the setting of the Lagrangian N -body problem of homogeneous potential to characterize an infinite family of rotating nonplanar "hip-hop" orbits in the four-body problem of equal masses, and show how some other trajectories in the N -body theory may be extended to infinite families of periodic and quasi-periodic trajectories.

  14. Quasi-periodic states in coupled rings of cells

    NASA Astrophysics Data System (ADS)

    Antoneli, Fernando; Dias, Ana Paula S.; Pinto, Carla M. A.

    2010-04-01

    We study some dynamical features of certain coupled cell networks that consist of two (unidirectional or bidirectional) rings of cells coupled through a 'buffer' cell. Depending on how the rings and the buffer cell are coupled, the full network may have a non-trivial group of symmetries or a non-trivial group of 'interior' symmetries. This group is Zp ×Zq in the unidirectional case and Dp ×Dq in the bidirectional case. We are interested in finding quasi-periodic motion in these networks, motivated by an example presented by Golubitsky, Nicol and Stewart (Some curious phenomena in coupled cell systems, J Nonlinear Sci 2004;14(2):207-36). In the examples considered here, we obtain quasi-periodic states through a sequence of Hopf bifurcations. Interestingly, we observe relaxation oscillation phenomena appearing further away from the last Hopf bifurcation point. We use XPPAUT and MATLAB to compute numerically the relevant states.

  15. SOFT LAGS IN NEUTRON STAR kHz QUASI-PERIODIC OSCILLATIONS: EVIDENCE FOR REVERBERATION?

    SciTech Connect

    Barret, Didier

    2013-06-10

    High frequency soft reverberation lags have now been detected from stellar mass and supermassive black holes. Their interpretation involves reflection of a hard source of photons onto an accretion disk, producing a delayed reflected emission, with a time lag consistent with the light travel time between the irradiating source and the disk. Independently of the location of the clock, the kHz quasi-periodic oscillation (QPO) emission is thought to arise from the neutron star boundary layer. Here, we search for the signature of reverberation of the kHz QPO emission, by measuring the soft lags and the lag energy spectrum of the lower kHz QPOs from 4U1608-522. Soft lags, ranging from {approx}15 to {approx}40 {mu}s, between the 3-8 keV and 8-30 keV modulated emissions are detected between 565 and 890 Hz. The soft lags are not constant with frequency and show a smooth decrease between 680 Hz and 890 Hz. The broad band X-ray spectrum is modeled as the sum of a disk and a thermal Comptonized component, plus a broad iron line, expected from reflection. The spectral parameters follow a smooth relationship with the QPO frequency, in particular the fitted inner disk radius decreases steadily with frequency. Both the bump around the iron line in the lag energy spectrum and the consistency between the lag changes and the inferred changes of the inner disk radius, from either spectral fitting or the QPO frequency, suggest that the soft lags may indeed involve reverberation of the hard pulsating QPO source on the disk.

  16. Explicit quasi-periodic solutions of the Vakhnenko equation

    NASA Astrophysics Data System (ADS)

    Zhai, Yunyun; Geng, Xianguo; He, Guoliang

    2014-05-01

    The trigonal curve associated with the Vakhnenko equation is introduced by using the Lax matrix for the nth stationary positive flow. Based on the theory of the trigonal curve and the properties of the three kinds of Abel differentials, the Riemann theta function representation for the Baker-Akhiezer function is derived, from which the straightening out of flows in the Jacobian variety is exactly given through the Abel maps. We finally arrive at quasi-periodic solutions of the Vakhnenko equation.

  17. QUASI-PERIODIC OSCILLATIONS IN LASCO CORONAL MASS EJECTION SPEEDS

    SciTech Connect

    Shanmugaraju, A.; Moon, Y.-J.; Cho, K.-S.; Bong, S. C.; Gopalswamy, N.; Akiyama, S.; Yashiro, S.; Umapathy, S.; Vrsnak, B. E-mail: moonyj@khu.ac.k

    2010-01-01

    Quasi-periodic oscillations in the speed profile of coronal mass ejections (CMEs) in the radial distance range 2-30 solar radii are studied. We considered the height-time data of the 307 CMEs recorded by the Large Angle and Spectrometric Coronagraph (LASCO) during 2005 January-March. In order to study the speed-distance profile of the CMEs, we have used only 116 events for which there are at least 10 height-time measurements made in the LASCO field of view. The instantaneous CME speed is estimated using a pair of height-time data points, providing the speed-distance profile. We found quasi-periodic patterns in at least 15 speed-distance profiles, where the speed amplitudes are larger than the speed errors. For these events we have determined the speed amplitude and period of oscillations. The periods of quasi-periodic oscillations are found in the range 48-240 minutes, tending to increase with height. The oscillations have similar properties as those reported by Krall et al., who interpreted them in terms of the flux-rope model. The nature of forces responsible for the motion of CMEs and their oscillations are discussed.

  18. Quasi-periodicities and Empirical Modes of the Heliospheric Magnetic Field

    NASA Astrophysics Data System (ADS)

    Smith, E. J.; Zhou, X.; Ruzmaikin, A.

    2006-12-01

    Quasi-periodicities in solar phenomena including variations in the heliospheric magnetic field have attracted attention in the past. Recently, such a periodicity near 140- 150 days has been of interest. In a recent analysis of solar cycle variations in the Sun's open magnetic flux, we found a quasi-periodicity of approximately one and one-half years in the radial component and the field magnitude that persists during the last four sunspot cycles. Inspection of the data revealed that this signal was variable in both amplitude and period. Power spectra having proved marginally useful in revealing the signal properties, we apply a new technique called Empirical Mode Decomposition (Huang et al., 1998) that treats both the frequency and amplitude as time-dependent. Application of this technique revealed several quasi-periodic modes including the mode near 1 and 1/2 years and the mode near 140 days that was not evident by inspection alone. The results of this analysis will be presented and the origin of the several periodicities will be discussed. Reference: Huang, N. E. Z. Shen, S. R. Long, M. C. Wu, H. H. Shih, Q. Zheng, N.-C. Yen, C. C. Tung, and H. H. Liu, Proc. R. Soc. Lond., A 454, 903-995, 1998.

  19. Downscaling climate variability associated with quasi-periodic climate signals: A new statistical approach using MSSA

    NASA Astrophysics Data System (ADS)

    Cañón, Julio; Domínguez, Francina; Valdés, Juan B.

    2011-02-01

    SummaryA statistical method is introduced to downscale hydroclimatic variables while incorporating the variability associated with quasi-periodic global climate signals. The method extracts statistical information of distributed variables from historic time series available at high resolution and uses Multichannel Singular Spectrum Analysis (MSSA) to reconstruct, on a cell-by-cell basis, specific frequency signatures associated with both the variable at a coarse scale and the global climate signals. Historical information is divided in two sets: a reconstruction set to identify the dominant modes of variability of the series for each cell and a validation set to compare the downscaling relative to the observed patterns. After validation, the coarse projections from Global Climate Models (GCMs) are disaggregated to higher spatial resolutions by using an iterative gap-filling MSSA algorithm to downscale the projected values of the variable, using the distributed series statistics and the MSSA analysis. The method is data adaptive and useful for downscaling short-term forecasts as well as long-term climate projections. The method is applied to the downscaling of temperature and precipitation from observed records and GCM projections over a region located in the US Southwest, taking into account the seasonal variability associated with ENSO.

  20. Relationship of Type III Radio Bursts with Quasi-periodic Pulsations in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Kupriyanova, E. G.; Kashapova, L. K.; Reid, H. A. S.; Myagkova, I. N.

    2016-08-01

    We studied a solar flare with pronounced quasi-periodic pulsations detected in the microwave, X-ray, and radio bands. We used correlation, Fourier, and wavelet analyses methods to examine the temporal fine structures and relationships between the time profiles in each wave band. We found that the time profiles of the microwaves, hard X-rays, and type III radio bursts vary quasi-periodically with a common period of 40 - 50 s. The average amplitude of the variations is high, above 30 % of the background flux level, and reaches 80 % after the flare maximum. We did not find this periodicity in either the thermal X-ray flux component or in the source size dynamics. Our findings indicate that the detected periodicity is probably associated with periodic dynamics in the injection of non-thermal electrons, which can be produced by periodic modulation of magnetic reconnection.

  1. Quasi-periodic Solutions to the K(-2, -2) Hierarchy

    NASA Astrophysics Data System (ADS)

    Wu, Lihua; Geng, Xianguo

    2016-07-01

    With the help of the characteristic polynomial of Lax matrix for the K(-2, -2) hierarchy, we define a hyperelliptic curve 𝒦n+1 of arithmetic genus n+1. By introducing the Baker-Akhiezer function and meromorphic function, the K(-2, -2) hierarchy is decomposed into Dubrovin-type differential equations. Based on the theory of hyperelliptic curve, the explicit Riemann theta function representation of meromorphic function is given, and from which the quasi-periodic solutions to the K(-2, -2) hierarchy are obtained.

  2. Analysis of stochastically forced quasi-periodic attractors

    SciTech Connect

    Ryashko, Lev

    2015-11-30

    A problem of the analysis of stochastically forced quasi-periodic auto-oscillations of nonlinear dynamic systems is considered. A stationary distribution of random trajectories in the neighborhood of the corresponding deterministic attractor (torus) is studied. A parametric description of quadratic approximation of the quasipotential based on the stochastic sensitivity functions (SSF) technique is given. Using this technique, we analyse a dispersion of stochastic flows near the torus. For the case of two-torus in three-dimensional space, the stochastic sensitivity function is constructed.

  3. Quasi-periodic pulsations in solar flares: new clues from the Fermi Gamma-Ray Burst Monitor

    NASA Astrophysics Data System (ADS)

    Gruber, D.; Lachowicz, P.; Bissaldi, E.; Briggs, M. S.; Connaughton, V.; Greiner, J.; van der Horst, A. J.; Kanbach, G.; Rau, A.; Bhat, P. N.; Diehl, R.; von Kienlin, A.; Kippen, R. M.; Meegan, C. A.; Paciesas, W. S.; Preece, R. D.; Wilson-Hodge, C.

    2011-09-01

    Aims: In the past four decades, it has been observed that solar flares display quasi-periodic pulsations (QPPs) from the lowest, i.e. radio, to the highest, i.e. gamma-ray, frequencies in the electromagnetic spectrum. It remains unclear which mechanism creates these QPPs. In this paper, we analyze four bright solar flares that display compelling signatures of quasi-periodic behavior and were observed with the Gamma-Ray Burst Monitor (GBM ) onboard the Fermi satellite. Because GBM covers over three decades in energy (8 keV to 40 MeV), it is regarded as a key instrument in our attempt to understand the physical processes that drive solar flares. Methods: We tested for periodicity in the time series of the solar flares observed by GBM by applying a classical periodogram analysis. However, in contrast to previous authors, we did not detrend the raw light curve before creating the power spectral density (PSD) spectrum. To assess the significance of the frequencies, we used a method that is commonly applied to X-ray binaries and Seyfert galaxies. This technique takes into account the underlying continuum of the PSD, which for all of these sources has a P(f) ~ f-α dependence and is typically labeled red-noise. Results: We checked the reliability of this technique by applying it to observations of a solar flare that had been observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI ). These data contain, besides any potential periodicity from the Sun, a 4 s rotational period caused by the rotation of the spacecraft about its axis. We were unable to identify any intrinsic solar quasi-periodic pulsation but we did manage to reproduce the instrumental periodicity. Moreover, with the method adopted here, we do not detect significant QPPs in the four bright solar flares observed by GBM. We stress that for this kind of analyses it is of utmost importance to account appropriately for the red-noise component in the PSD of these astrophysical sources.

  4. A search for quasi-periodic oscillations in 4U/MXB 1735-44

    NASA Technical Reports Server (NTRS)

    Penninx, Wim; Hasinger, Guenther; Lewin, Walter H. G.; Van Paradijs, Jan; Van Der Klis, Michiel

    1989-01-01

    A search for quasi-periodic oscillations (QPOs) in 4U/MXB 1735-44 was performed using Exosat observations during which the source was in a horizontal branch of the spectral hardness-intensity diagram for about 8 hr and in a normal branch type of behavior for about 46 hr. No QPOs or low-frequency noise was found in the horizontal branch state. It is suggested that this absence is due to either low luminosity or the fact that the companion in 1735-44 is a main-sequence star.

  5. Effect of temperature on terahertz photonic and omnidirectional band gaps in one-dimensional quasi-periodic photonic crystals composed of semiconductor InSb.

    PubMed

    Singh, Bipin K; Pandey, Praveen C

    2016-07-20

    Engineering of thermally tunable terahertz photonic and omnidirectional bandgaps has been demonstrated theoretically in one-dimensional quasi-periodic photonic crystals (PCs) containing semiconductor and dielectric materials. The considered quasi-periodic structures are taken in the form of Fibonacci, Thue-Morse, and double periodic sequences. We have shown that the photonic and omnidirectional bandgaps in the quasi-periodic structures with semiconductor constituents are strongly depend on the temperature, thickness of the constituted semiconductor and dielectric material layers, and generations of the quasi-periodic sequences. It has been found that the number of photonic bandgaps increases with layer thickness and generation of the quasi-periodic sequences. Omnidirectional bandgaps in the structures have also been obtained. Results show that the bandwidths of photonic and omnidirectional bandgaps are tunable by changing the temperature and lattice parameters of the structures. The generation of quasi-periodic sequences can also change the properties of photonic and omnidirectional bandgaps remarkably. The frequency range of the photonic and omnidirectional bandgaps can be tuned by the change of temperature and layer thickness of the considered quasi-periodic structures. This work will be useful to design tunable terahertz PC devices. PMID:27463924

  6. Quasi-Periodic Bifurcations of Higher-Dimensional Tori

    NASA Astrophysics Data System (ADS)

    Komuro, Motomasa; Kamiyama, Kyohei; Endo, Tetsuro; Aihara, Kazuyuki

    2016-06-01

    We classify the local bifurcations of quasi-periodic d-dimensional tori in maps (abbr. MTd) and in flows (abbr. FTd) for d ≥ 1. It is convenient to classify these bifurcations into normal bifurcations and resonance bifurcations. Normal bifurcations of MTd can be classified into four classes: namely, saddle-node, period doubling, double covering, and Neimark-Sacker bifurcations. Furthermore, normal bifurcations of FTd can be classified into three classes: saddle-node, double covering, and Neimark-Sacker bifurcations. These bifurcations are determined by the type of the dominant Lyapunov bundle. Resonance bifurcations are well known as phase locking of quasi-periodic solutions. These bifurcations are classified into two classes for both MTd and FTd: namely, saddle-node cycle and heteroclinic cycle bifurcations of the (d ‑ 1)-dimensional tori. The former is reversible, while the latter is irreversible. In addition, we propose a method for analyzing higher-dimensional tori, which uses one-dimensional tori in sections (abbr. ST1) and zero-dimensional tori in sections (abbr. ST0). The bifurcations of ST1 can be classified into five classes: saddle-node, period doubling, component doubling, double covering, and Neimark-Sacker bifurcations. The bifurcations of ST0 can be classified into four classes: saddle-node, period doubling, component doubling, and Neimark-Sacker bifurcations. Furthermore, we clarify the relationship between the bifurcations of ST1/ST0 and the bifurcations of MTd/FTd. We present examples of all of these bifurcations.

  7. The quasi-periodicity of the minority game revisited

    NASA Astrophysics Data System (ADS)

    Acosta, Gabriel; Caridi, Inés; Guala, Sebastián; Marenco, Javier

    2013-10-01

    We analyze two well-known related aspects regarding the sequence of minority sides from the Minority Game (MG) in its symmetric phase: period-two dynamics and quasi-periodic behavior. We also study the sequence of minority sides in a general way within a graph-theoretical framework. In order to analyze the outcome dynamics of the MG, it is useful to define the MG, namely an MG with a new choosing rule of the strategy to play, which takes into account both prior preferences and game information. In this way, each time an agent is undecided because two of her best strategies predict different choices while being equally successful so far, she selects her a priori favorite strategy to play, instead of performing a random tie-break as in the MG. This new choosing rule leaves the generic behavior of the model unaffected and simplifies the game analysis. Furthermore, interesting properties arise which are only partially present in the MG, like the quasi-periodic behavior of the sequence of minority sides, which turns out to be periodic for the MG.

  8. The quasi-periodical VLF/ELF emissions detected onboard the DEMETER spacecraft: statistical and theoretical analysis

    NASA Astrophysics Data System (ADS)

    Pasmanik, Dmitry; Hayosh, Mykhaylo; Demekhov, Andrei; Santolík, Ondřej; Nemec, František; Parrot, Michel

    2015-04-01

    We present a statistical study of the quasi-periodic (QP) ELF/VLF emissions measured by the DEMETER spacecraft. Events with modulation period larger than 10 s and frequency bandwidth more than 200 Hz were visually selected among the six year of measurements. Selected QP-emissions events occur mostly at frequencies from about 750 Hz to 2 kHz, but they may be observed at frequencies as low as 500 Hz and as high as 8 kHz. The statistical analysis clearly shows that QP events with larger modulation periods have lower frequency drift and smaller wave amplitude. Intense QP events have higher frequency drifts and larger values of the frequency bandwiths. Numerical simulation of the QP emissions based on the theoretical model of the flow cyclotron maser is performed. Calculations were made for wide range of plasma parameters (i.e. cold plasma density, L-shell, energetic electron flux and etc.) The numerical results are in good agreement with the observed relationship between different parameters of the QP emissions. The comparison between theoretical results and observations allow us to estimate the typical properties of the source of the QP emissions observed by the DEMETER satellite.

  9. Impact of inclination on quasi-periodic oscillations from spiral structures

    NASA Astrophysics Data System (ADS)

    Varniere, P.; Vincent, F. H.

    2016-06-01

    Context. Quasi-periodic oscillations (QPOs) are a common feature of the power spectrum of X-ray binaries. Currently it is not possible to unambiguously differentiate the large number of proposed models to explain these phenomena through existing observations. Aims: We investigate the observable predictions of a simple model that generates flux modulation: a spiral instability rotating in a thin accretion disk. This model is motivated by the accretion ejection instability (AEI) model for low-frequency QPOs (LFQPOs). We are particularly interested in the inclination dependence of the observables that are associated with this model. Methods: We develop a simple analytical model of an accretion disk, which features a spiral instability. The disk is assumed to emit blackbody radiation, which is ray-traced to a distant observer. We compute pulse profiles and power spectra as observed from infinity. Results: We show that the amplitude of the modulation associated with the spiral rotation is a strong function of inclination and frequency. The pulse profile is quasi-sinusoidal only at low inclination (face-on source). As a consequence, a higher-inclination geometry leads to a stronger and more diverse harmonic signature in the power spectrum. Conclusions: We present how the amplitude depends on the inclination when the flux modulation comes from a spiral in the disk. We also include new observables that could potentially differentiate between models, such as the pulse profile and the harmonic content of the power spectra of high-inclination sources that exhibit LFQPOs. These might be important observables to explore with existing and new instruments.

  10. Quasi-periodic Solutions of the Kaup-Kupershmidt Hierarchy

    NASA Astrophysics Data System (ADS)

    Geng, Xianguo; Wu, Lihua; He, Guoliang

    2013-08-01

    Based on solving the Lenard recursion equations and the zero-curvature equation, we derive the Kaup-Kupershmidt hierarchy associated with a 3×3 matrix spectral problem. Resorting to the characteristic polynomial of the Lax matrix for the Kaup-Kupershmidt hierarchy, we introduce a trigonal curve {K}_{m-1} and present the corresponding Baker-Akhiezer function and meromorphic function on it. The Abel map is introduced to straighten out the Kaup-Kupershmidt flows. With the aid of the properties of the Baker-Akhiezer function and the meromorphic function and their asymptotic expansions, we arrive at their explicit Riemann theta function representations. The Riemann-Jacobi inversion problem is achieved by comparing the asymptotic expansion of the Baker-Akhiezer function and its Riemann theta function representation, from which quasi-periodic solutions of the entire Kaup-Kupershmidt hierarchy are obtained in terms of the Riemann theta functions.

  11. Quasi-periodic oscillations in GX 17 + 2

    NASA Technical Reports Server (NTRS)

    Penninx, W.; Lewin, W. H. G.; Mitsuda, K.; Van Der Klis, M.; Van Paradijs, J.

    1990-01-01

    X-ray observations of GX 17 + 2 were made in March and April, 1988 with the Large Area Counter of the Ginga satellite. The source was observed in the flaring, normal, and horizontal branches. Quasi-periodic oscillations (QPOs) were oberved in all three of these branches. The relationship between QPO behavior and the X-ray spectral properties of GX 17 + 2 is examined. Continuous variation of QPO behavior is observed as GX 17 + 2 moves from the normal to flaring branch, indicating that the normal-branch QPO and the flaring-branch QPO are probably one physical phenomenon. This QPO behavior is similar to that observed in Sco X-1. Also, it is found that GX 17 + 2 is an example of the Z-type sources defined by Hasinger et al. (1989).

  12. Sources of Quasi-periodic Pulses in the Flare of 18 August 2012

    NASA Astrophysics Data System (ADS)

    Altyntsev, A.; Meshalkina, N.; Mészárosová, H.; Karlický, M.; Palshin, V.; Lesovoi, S.

    2016-02-01

    We analyzed spatial and spectral characteristics of quasi-periodic pulses (QPP) for the limb flare on 18 August 2012, using new data from a complex of spectral and imaging instruments developed by the Siberian Solar Radio Telescope team and the Wind/Konus γ-ray spectrometer. A sequence of broadband pulses with periods of approximately ten seconds were observed in X-rays at energies between 25 keV and 300 keV, and in microwaves at frequencies from a few GHz up to 34 GHz during an interval of one minute. The QPP X-ray source was located slightly above the limb where the southern legs of large and small EUV loop systems were close to each other. Before the QPPs occurred, the soft X-ray emission and the Ramaty High Energy Solar Spectroscopic Imager signal from the energy channels below 25 keV were gradually arising for several minutes at the same location. It was found that each X-ray pulse showed a soft-hard-soft behavior. The 17 and 34 GHz microwave sources were at the footpoints of the small loop system, the source emitting in the 4.2 - 7.4 GHz band in the large system. The QPPs were probably generated by modulated acceleration processes in the energy-release site. We determined the plasma parameters in the radio sources by analyzing the spectra. The microwave pulses might be explained by relatively weak variations of the spectral hardness of the emitting electrons.

  13. Phase-resolved spectroscopy of Type B quasi-periodic oscillations in GX 339-4

    NASA Astrophysics Data System (ADS)

    Stevens, Abigail L.; Uttley, Phil

    2016-08-01

    We present a new spectral-timing technique for phase-resolved spectroscopy and apply it to the low-frequency Type B quasi-periodic oscillation (QPO) from the black hole X-ray binary GX 339-4. We show that on the QPO time-scale the spectrum changes not only in normalization, but also in spectral shape. Using several different spectral models which parametrize the blackbody and power-law components seen in the time-averaged spectrum, we find that both components are required to vary, although the fractional rms amplitude of blackbody emission is small, ˜1.4 per cent compared to ˜25 per cent for the power-law emission. However, the blackbody variation leads the power-law variation by ˜0.3 in relative phase (˜110°), giving a significant break in the Fourier lag-energy spectrum that our phase-resolved spectral models are able to reproduce. Our results support a geometric interpretation for the QPO variations where the blackbody variation and its phase relation to the power-law are explained by quasi-periodic heating of the approaching and receding sides of the disc by a precessing Comptonizing region. The small amplitude of blackbody variations suggests that the Comptonizing region producing the QPO has a relatively large scaleheight, and may be linked to the base of the jet, as has previously been suggested to explain the binary orbit inclination-dependence of Type B QPO amplitudes.

  14. Phase-Resolved Spectroscopy of Type B Quasi-Periodic Oscillations in GX 339-4

    NASA Astrophysics Data System (ADS)

    Stevens, Abigail L.; Uttley, Phil

    2016-05-01

    We present a new spectral-timing technique for phase-resolved spectroscopy and apply it to the low-frequency Type B quasi-periodic oscillation (QPO) from the black hole X-ray binary GX 339-4. We show that on the QPO time-scale the spectrum changes not only in normalisation, but also in spectral shape. Using several different spectral models which parameterise the blackbody and power-law components seen in the time-averaged spectrum, we find that both components are required to vary, although the fractional rms amplitude of blackbody emission is small, ˜ 1.4 per cent compared to ˜ 25 per cent for the power-law emission. However the blackbody variation leads the power-law variation by ˜ 0.3 in relative phase (˜ 110 degrees), giving a significant break in the Fourier lag-energy spectrum that our phase-resolved spectral models are able to reproduce. Our results support a geometric interpretation for the QPO variations where the blackbody variation and its phase relation to the power-law are explained by quasi-periodic heating of the approaching and receding sides of the disk by a precessing Comptonising region. The small amplitude of blackbody variations suggests that the Comptonising region producing the QPO has a relatively large scale-height, and may be linked to the base of the jet, as has previously been suggested to explain the binary orbit inclination-dependence of Type B QPO amplitudes.

  15. Phase-resolved spectroscopy of Type B quasi-periodic oscillations in GX 339-4

    NASA Astrophysics Data System (ADS)

    Stevens, Abigail L.; Uttley, Phil

    2016-08-01

    We present a new spectral-timing technique for phase-resolved spectroscopy and apply it to the low-frequency Type B quasi-periodic oscillation (QPO) from the black hole X-ray binary GX 339-4. We show that on the QPO time-scale the spectrum changes not only in normalisation, but also in spectral shape. Using several different spectral models which parameterise the blackbody and power-law components seen in the time-averaged spectrum, we find that both components are required to vary, although the fractional rms amplitude of blackbody emission is small, ~1.4 per cent compared to ~25 per cent for the power-law emission. However the blackbody variation leads the power-law variation by ~0.3 in relative phase (~110 degrees), giving a significant break in the Fourier lag-energy spectrum that our phase-resolved spectral models are able to reproduce. Our results support a geometric interpretation for the QPO variations where the blackbody variation and its phase relation to the power-law are explained by quasi-periodic heating of the approaching and receding sides of the disc by a precessing Comptonising region. The small amplitude of blackbody variations suggests that the Comptonising region producing the QPO has a relatively large scale-height, and may be linked to the base of the jet, as has previously been suggested to explain the binary orbit inclination-dependence of Type B QPO amplitudes.

  16. Tunability of acoustic phonon transmission and thermal conductance in three dimensional quasi-periodically stubbed waveguides

    NASA Astrophysics Data System (ADS)

    Xie, Zhong-Xiang; Liu, Jing-Zhong; Yu, Xia; Wang, Hai-Bin; Deng, Yuan-Xiang; Li, Ke-Min; Zhang, Yong

    2015-03-01

    We investigate acoustic phonon transmission and thermal conductance in three dimensional (3D) quasi-periodically stubbed waveguides according to the Fibonacci sequence. Results show that the transmission coefficient exhibits the periodic oscillation upon varying the length of stub/waveguide at low frequency, and the period of such oscillation is tunably decreased with increasing the Fibonacci number N. Interestingly, there also exist some anti-resonant dips that gradually develop into wide stop-frequency gaps with increasing N. As the temperature goes up, a transition of the thermal conductance from the decrease to the increase occurs in these systems. When N is increased, the thermal conductance is approximately decreased with a linear trend. Moreover, the decreasing degree sensitively depends on the variation of temperature. A brief analysis of these results is given.

  17. Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

    NASA Astrophysics Data System (ADS)

    Li, T.; Zhang, J.

    2016-04-01

    Context. The new Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of UV spectra and slit-jaw images (SJIs). These data have become available for investigating the dynamic features in the transition region (TR) below the on-disk filaments. Aims: The driver of "counter-streaming" flows along the filament spine is still unknown yet. The magnetic structures and the upflows at the footpoints of the filaments and their relations with the filament mainbody have not been well understood. We study the dynamic evolution at the footpoints of filaments in order to find some clues for solving these questions. Methods: Using UV spectra and SJIs from the IRIS, along with coronal images and magnetograms from the Solar Dynamics Observatory (SDO), we present the new features in a quiescent filament channel: subarcsecond bright points (BPs) and quasi-periodic upflows. Results: The BPs in the TR have a spatial scale of about 350-580 km and lifetimes of more than several tens of minutes. They are located at stronger magnetic structures in the filament channel with a magnetic flux of about 1017-1018 Mx. Quasi-periodic brightenings and upflows are observed in the BPs, and the period is about 4-5 min. The BP and the associated jet-like upflow comprise a "tadpole-shaped" structure. The upflows move along bright filament threads, and their directions are almost parallel to the spine of the filament. The upflows initiated from the BPs with opposite polarity magnetic fields have opposite directions. The velocity of the upflows in the plane of sky is about 5-50 km s-1. The emission line of Si IV 1402.77 Å at the locations of upflows exhibits obvious blueshifts of about 5-30 km s-1, and the line profile is broadened with the width of more than 20 km s-1. Conclusions: The BPs seem to be the bases of filament threads, and the upflows are able to convey mass for the dynamic balance of the filament. The "counter-streaming" flows in previous observations

  18. Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

    NASA Astrophysics Data System (ADS)

    Li, T.; Zhang, J.

    2016-05-01

    Context. The new Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of UV spectra and slit-jaw images (SJIs). These data have become available for investigating the dynamic features in the transition region (TR) below the on-disk filaments. Aims: The driver of "counter-streaming" flows along the filament spine is still unknown yet. The magnetic structures and the upflows at the footpoints of the filaments and their relations with the filament mainbody have not been well understood. We study the dynamic evolution at the footpoints of filaments in order to find some clues for solving these questions. Methods: Using UV spectra and SJIs from the IRIS, along with coronal images and magnetograms from the Solar Dynamics Observatory (SDO), we present the new features in a quiescent filament channel: subarcsecond bright points (BPs) and quasi-periodic upflows. Results: The BPs in the TR have a spatial scale of about 350-580 km and lifetimes of more than several tens of minutes. They are located at stronger magnetic structures in the filament channel with a magnetic flux of about 1017-1018 Mx. Quasi-periodic brightenings and upflows are observed in the BPs, and the period is about 4-5 min. The BP and the associated jet-like upflow comprise a "tadpole-shaped" structure. The upflows move along bright filament threads, and their directions are almost parallel to the spine of the filament. The upflows initiated from the BPs with opposite polarity magnetic fields have opposite directions. The velocity of the upflows in the plane of sky is about 5-50 km s-1. The emission line of Si IV 1402.77 Å at the locations of upflows exhibits obvious blueshifts of about 5-30 km s-1, and the line profile is broadened with the width of more than 20 km s-1. Conclusions: The BPs seem to be the bases of filament threads, and the upflows are able to convey mass for the dynamic balance of the filament. The "counter-streaming" flows in previous observations

  19. The effect of a hot, spherical scattering cloud on quasi-periodic oscillation behavior. [of X-ray binaries

    NASA Technical Reports Server (NTRS)

    Bussard, R. W.; Weisskopf, M. C.; Elsner, R. F.; Shibazaki, N.

    1988-01-01

    A Monte Carlo technique is used to investigate the effects of a hot electron scattering cloud surrounding a time-dependent X-ray source. Results are presented for the time-averaged emergent energy spectra and the mean residence time in the cloud as a function of energy. Moreover, after Fourier transforming the scattering Green's function, it is shown how the cloud affects both the observed power spectrum of a time-dependent source and the cross spectrum (Fourier transform of a cross correlation between energy bands). It is found that the power spectra intrinsic to the source are related to those observed by a relatively simple frequency-dependent multiplicative factor (a transmission function). The cloud can severely attenuate high frequencies in the power spectra, depending on optical depth, and, at lower frequencies, the transmission function has roughly a Lorentzian shape. It is also found that if the intrinsic energy spectrum is constant in time, the phase of the cross spectrum is determined entirely by scattering. Finally, the implications of the results for studies of the X-ray quasi-periodic oscillators are discussed.

  20. The magnetohydrodynamical model of kilohertz quasi-periodic oscillations in neutron star low-mass X-ray binaries (II)

    SciTech Connect

    Shi, Chang-Sheng; Zhang, Shuang-Nan; Li, Xiang-Dong

    2014-08-10

    We study the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) with a new magnetohydrodynamics (MHD) model, in which the compressed magnetosphere is considered. The previous MHD model is reexamined and the relation between the frequencies of the kHz QPOs and the accretion rate in LMXBs is obtained. Our result agrees with the observations of six sources (4U 0614+09, 4U 1636-53, 4U 1608-52, 4U 1915-15, 4U 1728-34, and XTE 1807-294) with measured spins. In this model, the kHz QPOs originate from the MHD waves in the compressed magnetosphere. The single kHz QPOs and twin kHz QPOs are produced in two different parts of the accretion disk and the boundary is close to the corotation radius. The lower QPO frequency in a frequency-accretion rate diagram is cut off at a low accretion rate and the twin kHz QPOs encounter a top ceiling at a high accretion rate due to the restriction of the innermost stable circular orbit.

  1. The Magnetohydrodynamical Model of Kilohertz Quasi-periodic Oscillations in Neutron Star Low-mass X-Ray Binaries (II)

    NASA Astrophysics Data System (ADS)

    Shi, Chang-Sheng; Zhang, Shuang-Nan; Li, Xiang-Dong

    2014-08-01

    We study the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) with a new magnetohydrodynamics (MHD) model, in which the compressed magnetosphere is considered. The previous MHD model is reexamined and the relation between the frequencies of the kHz QPOs and the accretion rate in LMXBs is obtained. Our result agrees with the observations of six sources (4U 0614+09, 4U 1636-53, 4U 1608-52, 4U 1915-15, 4U 1728-34, and XTE 1807-294) with measured spins. In this model, the kHz QPOs originate from the MHD waves in the compressed magnetosphere. The single kHz QPOs and twin kHz QPOs are produced in two different parts of the accretion disk and the boundary is close to the corotation radius. The lower QPO frequency in a frequency-accretion rate diagram is cut off at a low accretion rate and the twin kHz QPOs encounter a top ceiling at a high accretion rate due to the restriction of the innermost stable circular orbit.

  2. Kilohertz Quasi-Periodic Oscillation Peak Separation Is Not Constant in Scorpius X-1

    NASA Astrophysics Data System (ADS)

    van der Klis, Michiel; Wijnands, Rudy A. D.; Horne, Keith; Chen, Wan

    1997-06-01

    We report on a series of 20, ~105 counts s-1, 0.125 ms time-resolution Rossi X-Ray Timing Explorer observations of the Z-source and low-mass X-ray binary Scorpius X-1. Twin kilohertz quasi-periodic oscillation (QPO) peaks are obvious in nearly all observations. We find that the peak separation is not constant, as expected in some beat-frequency models, but instead varies from ~310 to ~230 Hz when the centroid frequency of the higher frequency peak varies from ~875 to ~1085 Hz. We detect none of the additional QPO peaks at higher frequencies predicted in the photon bubble model (PBM), with best-case upper limits on the peaks' power ratio of 0.025. We do detect, simultaneously with the kilohertz QPO, additional QPO peaks near 45 and 90 Hz whose frequency increases with mass accretion rate. We interpret these as first and second harmonics of the so-called horizontal-branch oscillations that are well known from other Z-sources and usually interpreted in terms of the magnetospheric beat-frequency model (BFM). We conclude that the magnetospheric BFM and the PBM are now unlikely to explain the kilohertz QPO in Sco X-1. In order to succeed in doing so, any BFM involving the neutron star spin (unseen in Sco X-1) will have to postulate at least one additional unseen frequency, beating with the spin to produce one of the kilohertz peaks.

  3. Ergodic theory and visualization. II. Fourier mesochronic plots visualize (quasi)periodic sets

    SciTech Connect

    Levnajić, Zoran; Mezić, Igor

    2015-05-15

    We present an application and analysis of a visualization method for measure-preserving dynamical systems introduced by I. Mezić and A. Banaszuk [Physica D 197, 101 (2004)], based on frequency analysis and Koopman operator theory. This extends our earlier work on visualization of ergodic partition [Z. Levnajić and I. Mezić, Chaos 20, 033114 (2010)]. Our method employs the concept of Fourier time average [I. Mezić and A. Banaszuk, Physica D 197, 101 (2004)], and is realized as a computational algorithms for visualization of periodic and quasi-periodic sets in the phase space. The complement of periodic phase space partition contains chaotic zone, and we show how to identify it. The range of method's applicability is illustrated using well-known Chirikov standard map, while its potential in illuminating higher-dimensional dynamics is presented by studying the Froeschlé map and the Extended Standard Map.

  4. Ginga observations of quasi-periodic oscillations in type II bursts from the Rapid Burster

    NASA Technical Reports Server (NTRS)

    Dotani, T.; Mitsuda, K.; Inoue, H.; Tanaka, Y.; Kawai, N.

    1990-01-01

    During Ginga observations of the 'Rapid Burster' in August 1988, strong quasi-periodic oscillations (QPOs) were detected in its X-ray intensity. The QPOs had centroid frequencies of 5 and 2 Hz during type II X-ray bursts which lasted for 10 and 30 s, respectively. The presence of the QPOs is correlated with the time scale-invariant burst profile. They are very strong during the initial peak in the burst, absent in the second peak, and strong again at the onset of the third peak. From an analysis of the X-ray spectrum as observed during the maxima and minima of the oscillations, it is found that the oscillations can be described by changes of the temperature of a blackbody emitter of constant apparent area.

  5. Quasi-periodic oscillations in the Z source GX 5-1

    NASA Technical Reports Server (NTRS)

    Lewin, Walter H. G.; Lubin, Lori M.; Tan, Jianmin; Van Der Klis, Michiel; Van Paradijs, Jan; Penninx, Wim; Dotani, Tadayasu; Mitsuda, Kazuhisa

    1992-01-01

    A detailed study has been conducted of the time variability in the Z source GX 5-1 using Ginga, which observed the source in the horizontal and normal branches (HB, NB). Intensity-dependent HF, quasi-periodic oscillations (QPO) were observed in the HB, in which the source flux varied by a factor of 1.9. The QPO frequency in this portion of the HB ranges from about 13 to 17 Hz; this is lower than previously observed in any Z source. The HF and LF QPO were simultaneously observed in the NB. The strength of both forms of QPO and the strength of the LF noise increase rapidly with increasing photon energy.

  6. Ergodic theory and visualization. II. Fourier mesochronic plots visualize (quasi)periodic sets.

    PubMed

    Levnajić, Zoran; Mezić, Igor

    2015-05-01

    We present an application and analysis of a visualization method for measure-preserving dynamical systems introduced by I. Mezić and A. Banaszuk [Physica D 197, 101 (2004)], based on frequency analysis and Koopman operator theory. This extends our earlier work on visualization of ergodic partition [Z. Levnajić and I. Mezić, Chaos 20, 033114 (2010)]. Our method employs the concept of Fourier time average [I. Mezić and A. Banaszuk, Physica D 197, 101 (2004)], and is realized as a computational algorithms for visualization of periodic and quasi-periodic sets in the phase space. The complement of periodic phase space partition contains chaotic zone, and we show how to identify it. The range of method's applicability is illustrated using well-known Chirikov standard map, while its potential in illuminating higher-dimensional dynamics is presented by studying the Froeschlé map and the Extended Standard Map. PMID:26026317

  7. Growth of Sobolev Norms in Linear Schrödinger Equations with Quasi-Periodic Potential

    NASA Astrophysics Data System (ADS)

    Bourgain, J.

    In this paper, we consider the following problem. Let iut+Δu+V(x,t)u= 0 be a linear Schrödinger equation ( periodic boundary conditions) where V is a real, bounded, real analytic potential which is periodic in x and quasi periodic in t with diophantine frequency vector λ. Denote S(t) the corresponding flow map. Thus S(t) preserves the L2-norm and our aim is to study its behaviour on Hs(TD), s> 0. Our main result is the growth in time is at most logarithmic; thus if φ∈Hs, then More precisely, (*) is proven in 1D and 2D when V is small. We also exhibit examples showing that a growth of higher Sobolev norms may occur in this context and (*) is thus essentially best possible.

  8. Extracting multipole moments of neutron stars from quasi-periodic oscillations in low mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Boshkayev, Kuantay; Rueda, Jorge; Muccino, Marco

    2015-06-01

    We consider the kilohertz quasi-periodic oscillations of low-mass X-ray binaries within the Hartle-Thorne spacetime. We show that the interpretation of the epicyclic frequencies of this spacetime with the observed kilohertz quasi-periodic oscillations, within the Relativistic Precession Model, allows us to extract the total mass M, angular momentum J, and quadrupole moment Q of the compact object in a low-mass X-ray binary. We exemplify this fact by analyzing the data of the Z-source GX 5-1. We show that the extracted multipole structure of the compact component of this source deviates from the one expected from a Kerr black hole and instead it points to a neutron star explanation.

  9. Spectral variation during one quasi-periodic oscillation cycle in the black hole candidate H1743-322

    NASA Astrophysics Data System (ADS)

    Sarathi Pal, Partha; Debnath, Dipak; Chakrabarti, Sandip Kumar

    2016-07-01

    From the nature of energy dependence of the power density spectra, it is believed that the oscillation of the Compton cloud may be related to low frequency quasi-periodic oscillations (LFQPOs). In the context of two component advective flow (TCAF) solution, the centrifugal pressure supported boundary layer of a transonic flow acts as the Compton cloud. This region undergoes resonance oscillation when cooling time scale roughly agrees with infall time scale as matter crosses this region. By carefully separating photons emitted at different phases of a complete oscillation, we establish beyond reasonable doubt that such an oscillation is the cause of LFQPOs. We show that the degree of Comptonization and therefore the spectral properties of the flow oscillate systematically with the phase of LFQPOs. We analysis the properties of a 0.2Hz LFQPO exhibited by a black hole candidate H 1743-322 using the 3-80 keV data from NuSTAR satellite. This object was chosen because of availability of high quality data for a relatively low frequency oscillation, rendering easy phase-wise of separation of the light curve data.

  10. Quasi-periodic Oscillations Associated with Spectral Branches in Rossi X-Ray Timing Explorer Observations of Circinus X-1

    NASA Astrophysics Data System (ADS)

    Shirey, Robert E.; Bradt, Hale V.; Levine, Alan M.; Morgan, Edward H.

    1998-10-01

    We present Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor observations of the X-ray binary Circinus X-1 that illustrate the variety of intensity profiles associated with the 16.55 day flaring cycle of the source. We also present eight observations of Cir X-1 made with the RXTE Proportional Counter Array over the course of a cycle wherein the average intensity of the flaring state decreased gradually over ~12 days. Fourier power density spectra for these observations show a narrow quasi-periodic oscillation (QPO) peak that shifts in frequency between 6.8 and 32 Hz, as well as a broad QPO peak that remains roughly stationary at ~4 Hz. We identify these as Z-source horizontal and normal branch oscillations (HBOs/NBOs), respectively. Color-color and hardness-intensity diagrams (CDs/HIDs) show curvilinear tracks for each of the observations. The properties of the QPOs and very low frequency noise allow us to identify segments of these tracks with Z-source horizontal, normal, and flaring branches that shift location in the CDs and HIDs over the course of the 16.55 day cycle. These results contradict a previous prediction, based on the hypothesis that Cir X-1 is a high-Ṁ atoll source, that HBOs should never occur in this source.

  11. Possible identifications of newly observed magnetar quasi-periodic oscillations as crustal shear modes

    NASA Astrophysics Data System (ADS)

    Sotani, Hajime; Iida, Kei; Oyamatsu, Kazuhiro

    2016-02-01

    Quasi-periodic oscillations (QPOs) discovered in soft-gamma repeaters (SGRs) are expected to help us to study the properties of matter in neutron stars. In earlier investigations, we identified the QPOs of frequencies below ˜100 Hz observed in giant flares of SGR 1806 -20 and SGR 1900+14 as the crustal torsional oscillations. For this purpose, we calculated the frequencies of the fundamental torsional oscillations with various angular indices ℓ, by changing the stellar mass and radius. In this work, we try to explain the additional QPO frequencies recently reported by Huppenkothen et al. (2014a, 2014b) within the same framework as before except that we newly take into account the effect of electron screening, which acts to decrease the frequencies by a small amount. Those QPOs were discovered in two different SGRs, i.e., SGR 1806 -20 and SGR J1550 -5418. Then, we find that the newly observed QPO frequency in SGR 1806 -20 can be still identified as one of the frequencies of the fundamental torsional oscillations, while those in SGR J1550 -5418 can also be explained in terms of the torsional oscillations although the relevant angular indices are difficult to identify.

  12. Discovery of 800 HZ Quasi-Periodic Oscillations in 4U 1608-52

    NASA Astrophysics Data System (ADS)

    Berger, M.; van der Klis, M.; van Paradijs, J.; Lewin, W. H. G.; Lamb, F.; Vaughan, B.; Kuulkers, E.; Augusteijn, T.; Zhang, W.; Marshall, F. E.; Swank, J. H.; Lapidus, I.; Lochner, J. C.; Strohmayer, T. E.

    1996-09-01

    We present results of Rossi X-Ray Timing Explorer observations of the low-mass X-ray binary and atoll source 4U 1608-52 made over 9 days during the decline of an X-ray intensity outburst in 1996 March. A fast-timing analysis shows a strong and narrow quasi-periodic oscillation (QPO) peak at frequencies between 850 and 890 Hz on March 3 and 6, as well as a broad peak around 690 Hz on March 9. Observations on March 12 show no significant signal. On March 3, the X-ray spectrum of the QPO is quite hard; its strength increases steadily from 5% at ~2 keV to ~20% at ~12 keV. The QPO frequency varies between 850 and 890 Hz on that day, and the peak widens and its rms decreases with centroid frequency in a way very similar to the well-known horizontal branch oscillations (HBO) in Z sources. We apply the HBO beat frequency model to atoll sources and suggest that, whereas the model could produce QPOs at the observed frequencies, the lack of correlation we observe between QPO properties and X-ray count rate is hard to reconcile with this model.

  13. Quasi-Periodic Variability in NGC 5408 X-1

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Mushotzky, Richard F.; Winter, Lisa; Soria, Roberto; Uttley, Phil; Cropper, Mark

    2007-01-01

    We report the discovery with XMM-Newton of quasiperiodic variability in the 0.2 - 10 keV X-ray flux from the ultraluminous X-ray source NGC 5408 X-1. The average power spectrum of all EPIC-pn data reveals a strong 20 mHz QPO with an average amplitude (rms) of 9%, and a coherence, Q identical with nu(sub 0)/sigma approximately equal to 6. In a 33 ksec time interval when the 20 mHz QPO is strongest we also find evidence for a 2nd QPO peak at 15 mHz, the first indication for a close pair of QPOs in a ULX source. Interestingly, the frequency ratio of this QPO pair is inconsistent with 3:2 at the 3 sigma level, but is consistent with a 4:3 ratio. A powerlaw noise component with slope near 1.5 is also present below 0.1 Hz with evidence for a break to a flatter slope at about 3 mHz. The source shows substantial broadband variability, with a total amplitude (rms) of about 30% in the 0.1 - 100 mHz frequency band, and there is strong energy dependence to the variability. The power spectrum of hard X-ray photons (greater than 2 keV) shows a "classic" flat-topped continuum breaking to a power law with index 1.5 - 2. Both the break and 20 mHz QPO are detected in the hard band, and the 20 mHz QPO is essentially at the break. The QPO is both strong and narrow in this band, having an amplitude (rms) of 15%, and Q approx. equal to 25. The energy spectrum is well fit by three components, a "cool" disk with kT = 0.15 keV, a steep power law with index 2.56, and a thermal plasma at kT = 0.87 keV. The disk, power law, and thermal plasma components contribute 35, 60, and 5% of the 0.3 - 10 keV flux, respectively. Both the timing and spectral properties of NGC 5408 X-1 are strikingly reminiscent of Galactic black hole systems at high inferred accretion rates, but with its characteristic frequencies (QPO and break frequencies) scaled down by a factor of 10 - 100. We discuss the implications of these findings in the context of models for ULXs, and their implications for the object's mass.

  14. On quasi-periodic variations of low-energy cosmic rays observed near earth.

    PubMed

    Kudela, Karel; Langer, Ronald

    2015-06-01

    Cosmic ray (CR) may partially, especially at high altitudes, contribute to the dosimetric characteristics. Along with irregular CR variations as Forbush decreases and solar particle events are, the quasi-periodic variations may be of some relevance too. A very short review (with references to original papers) of the present knowledge of various types of such variations is presented, namely (i) diurnal wave, (ii) ~27 d variability due to the solar rotation, (iii) Rieger-type periodicity, and (iv) quasi-biennial oscillations as well as waves on longer time scales related to solar activity and to polarity of magnetic field of the Sun. Variability is illustrated in measurements of secondary CR on the ground including the high-altitude observations at Lomnický štít. PMID:25979741

  15. Uncovering the mechanism behind quasi-periodic oscillations in black holes

    NASA Astrophysics Data System (ADS)

    Ingram, Adam

    2012-10-01

    We propose a triggered 200ks XMM-Newton observation of a high inclination black hole binary in the hard intermediate state. This will allow us to constrain a characteristic shift in the iron line profile between the rising and falling phases of the quasi-periodic oscillations (QPOs) observed in these objects. Such a property is a necessary and sufficient condition of a QPO driven by precession in the inner regions of the accretion flow and is predicted by our model which invokes the relativistic effect of frame dragging. The model predicts the QPO phase dependence of the iron line to be stronger for high inclination sources displaying intermediate hardness ratios, leaving the hard intermediate state as the ideal configuration. We will trigger the observation from Swift monitoring throughout the outburst.

  16. Timing Studies of X Persei and the Discovery of Its Transient Quasi-periodic Oscillation Feature

    NASA Technical Reports Server (NTRS)

    Acuner, Z.; Inam,S. C.; Sahiner, S.; Serim, M. M.; Baykal, A.; Swank, J.

    2014-01-01

    We present a timing analysis of X Persei (X Per) using observations made between 1998 and 2010 with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) and with the INTEGRAL Soft Gamma-Ray Imager (ISGRI). All pulse arrival times obtained from the RXTE-PCA observations are phase-connected and a timing solution is obtained using these arrival times. We update the long-term pulse frequency history of the source by measuring its pulse frequencies using RXTE-PCA and ISGRI data. From the RXTEPCA data, the relation between the frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. However, the detection of a transient quasi-periodic oscillation feature, peaking at approximately 0.2 Hz, suggests the existence of an accretion disc. We find that doublebreak models fit the average power spectra well, which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectrum of frequency derivatives, we measure a power-law index of approximately - 1, which implies that, on short time-scales, disc accretion dominates over noise, while on time-scales longer than the viscous time-scales, the noise dominates. From pulse profiles, we find a correlation between the pulse fraction and the count rate of the source.

  17. Multiscale analysis in momentum space for quasi-periodic potential in dimension two

    NASA Astrophysics Data System (ADS)

    Karpeshina, Yulia; Shterenberg, Roman

    2013-07-01

    We consider a polyharmonic operator H=(-Δ)^l+V({x}) in dimension two with l ⩾ 2, l being an integer, and a quasi-periodic potential V({x}). We prove that the absolutely continuous spectrum of H contains a semiaxis and there is a family of generalized eigenfunctions at every point of this semiaxis with the following properties. First, the eigenfunctions are close to plane waves e^{i< {\\varkappa },{x}rangle } at the high energy region. Second, the isoenergetic curves in the space of momenta {\\varkappa } corresponding to these eigenfunctions have a form of slightly distorted circles with holes (Cantor type structure). A new method of multiscale analysis in the momentum space is developed to prove these results.

  18. QUASI-PERIODIC FORMALDEHYDE MASER FLARES IN THE MASSIVE PROTOSTELLAR OBJECT IRAS 18566+0408

    SciTech Connect

    Araya, E. D.; Hofner, P.; Goss, W. M.; Kurtz, S.; Richards, A. M. S.; Linz, H.; Olmi, L.; Sewilo, M.

    2010-07-10

    We report results of an extensive observational campaign of the 6 cm formaldehyde maser in the young massive stellar object IRAS 18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using the Arecibo Telescope, the Very Large Array, and the Green Bank Telescope, we discovered quasi-periodic formaldehyde flares (P {approx} 237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H{sub 2}CO) and methanol (CH{sub 3}OH) masers. The H{sub 2}CO and CH{sub 3}OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system.

  19. Casimir Effect Under Quasi-Periodic Boundary Condition Inspired by Nanotubes

    NASA Astrophysics Data System (ADS)

    Feng, Chao-Jun; Li, Xin-Zhou; Zhai, Xiang-Hua

    2014-01-01

    When one studies the Casimir effect, the periodic (anti-periodic) boundary condition is usually taken to mimic a periodic (anti-periodic) structure for a scalar field living in a flat space with a non-Euclidean topology. However, there could be an arbitrary phase difference between the value of the scalar field on one endpoint of the unit structure and that on the other endpoint, such as the structure of nanotubes. Then, in this paper, a periodic condition on the ends of the system with an additional phase factor, which is called the "quasi-periodic" condition, is imposed to investigate the corresponding Casimir effect. And an attractive or repulsive Casimir force is found, whose properties depend on the phase angle value. Especially, the Casimir effect disappears when the phase angle takes a particular value. High dimensional spacetime case is also investigated.

  20. QUASI-PERIODICITIES OF THE BL LACERTAE OBJECT PKS 2155–304

    SciTech Connect

    Sandrinelli, A.; Treves, A.; Covino, S.

    2014-09-20

    We have searched for periodicities in our VRIJHK photometry of PKS 2155–304, which covers the years 2005-2012. A peak of the Fourier spectrum with high significance is found at T ∼ 315 days, confirming the recent findings by Zhang et al. The examination of the gamma-ray light curves from the Fermi archives yields a significant signal at ∼2T, which, while nominally significant, involves data spanning only ∼6T. Assuming a black hole mass of 10{sup 9} M {sub ☉}, the Keplerian distance corresponding to the quasi-period T is ∼10{sup 16} cm, about 50 Schwarzschild radii.

  1. DISCOVERY OF QUASI-PERIODIC OSCILLATIONS IN THE RECURRENT BURST EMISSION FROM SGR 1806-20

    SciTech Connect

    El-Mezeini, Ahmed M.; Ibrahim, Alaa I. E-mail: ai@aucegypt.ed E-mail: ai@space.mit.ed

    2010-10-01

    We present evidence for quasi-periodic oscillations (QPOs) in the recurrent outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within {approx}1{sigma} from the 92 Hz QPO detected in the giant flare. The third QPO lies within {approx}9{sigma} from the 625 Hz QPO also detected in the same flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations, which set a lower limit confidence interval {>=}4.3{sigma}. We also find evidence for candidate QPOs at higher frequencies in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our finding against the available theoretical models and discuss the connection between the QPOs we report and those detected in the giant flares. The implications to the neutron star properties are also discussed.

  2. Lag variability associated with quasi periodic oscillations in GX 339-4 during outbursts

    NASA Astrophysics Data System (ADS)

    Dutta, Broja Gopal; Belloni, Tomaso; Motta, Sara

    The black hole transient GX 339-4 has exhibited four outbursts at a 2-3 years intervals. We have analyzed RXTE/PCA data of this source for the 2002/2003, 2004, 2007 and 2010 outbursts. The power density spectrum exhibits quasi-periodic oscillations (QPO) whose frequency varies from 0.2 Hz to 8 Hz in addition to band-limited noise. We measured the time/phase lags between soft (2-5 keV) and hard (5-13 keV) photons at the QPO centroid frequency and at the continuum noise. We find hard phase/time lags for both centroid frequency and continuum monotonically increasing from .01 at 0.2 Hz to 0.68 at 8 Hz. This correlation appears to be same for all outbursts. The single correlation picture of phase/time lag for all four outbursts suggests a general evolution scenario of the QPOs during the outbursts. We discuss the implications of these results on the basis of possible accretion models

  3. TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. III. QUASI-PERIODIC VARIABILITY

    SciTech Connect

    Johannsen, Tim; Psaltis, Dimitrios E-mail: dpsaltis@email.arizona.edu

    2011-01-01

    According to the no-hair theorem, astrophysical black holes are uniquely described by their masses and spins. An observational test of the no-hair theorem can be performed by measuring at least three different multipole moments of the spacetime of a black hole and verifying whether their values are consistent with the unique combinations of the Kerr solution. In this paper, we study quasi-periodic variability observed in the emission from black holes across the electromagnetic spectrum as a test of the no-hair theorem. We derive expressions for the Keplerian and epicyclic frequencies in a quasi-Kerr spacetime, in which the quadrupole moment is a free parameter in addition to mass and spin. We show that, for moderate spins, the Keplerian frequency is practically independent of small deviations of the quadrupole moment from the Kerr value, while the epicyclic frequencies exhibit significant variations. We apply this framework to quasi-periodic oscillations (QPOs) in black hole X-ray binaries in two different scenarios. In the case that a pair of QPOs can be identified as the fundamental g- and c-modes in the accretion disk, we show that the no-hair theorem can be tested in conjunction with an independent mass measurement. If pairs of oscillations are identified with non-parametric resonance of dynamical frequencies in the accretion disk, then testing the no-hair theorem also requires an independent measurement of the black hole spin. In addition, we argue that VLBI observations of Sgr A* may test the no-hair theorem through a combination of imaging observations and the detection of quasi-periodic variability.

  4. Negative permeability and subwavelength focusing of quasi-periodic dendritic cell metamaterials.

    PubMed

    Zhou, Xin; Fu, Quan H; Zhao, Jing; Yang, Yang; Zhao, Xiao P

    2006-08-01

    We present the design for a hexagonal cell made of quasi-periodic dendritic arranged collections of plasmonic metallic wires that may exhibit a resonant magnetic collective response. When such quasi-periodic dendritic cells are etched on a host medium, they may provide metamaterials with negative effective permeability. We also show that a clear point image is observed, as expected, with our left-handed metamaterials (LHMs) lens composed of metallic dendritic cells and wire strips. These prominent characteristics of quasi-periodic dendritic cells potentially enable us to prepare infrared or visible domain LHMs by using a general chemical method. PMID:19529087

  5. δ-Invariant for Quasi-periodic Oscillations and Physical Parameters of the 4U 0614+09 Binary

    NASA Astrophysics Data System (ADS)

    Titarchuk, Lev; Osherovich, Vladimir

    2000-07-01

    The recently formulated two-oscillator (TO) model interprets the lowest of the kilohertz frequencies of the twin-peak quasi-periodic oscillations in X-ray binaries as the Keplerian frequency νK. The high twin frequency νh in this model holds the upper hybrid frequency relation to the rotational frequency of the neutron star's magnetosphere Ω: ν2h=ν2K+4(Ω/ 2π)2. The vector Ω is assumed to have an angle δ with the normal to the disk. The first oscillator in the TO model allows one to interpret the horizontal branch observed below 100 Hz as the lower mode of the Keplerian oscillator under the influence of the Coriolis force, with frequency νL being dependent on νh, νK, and δ. For some stars such as 4U 0614+09, Scorpius X-1, and 4U 1702-42, νh, νK, and νL have been observed simultaneously, thus providing the opportunity to check the central prediction of the TO model, i.e., the constancy of δ for a particular source. Given the considerable variation of each of these three frequencies, the existence of an observational invariant with a clear physical interpretation as a global parameter of the neutron star magnetosphere is an important test of the TO model. Using the results of recent observations of 4U 0614+09, we verify the existence of this invariant and determine the angle δ=15.6d+/-0.5d for this star. The second oscillator in the model deals with both a radial (presumably sound) oscillation and a diffuse process in the viscous layer surrounding the neutron star. Our analysis of the viscous oscillation frequency νV and the break frequency νb of the diffusion shows that the spin value of the inner boundary of the transition layer for 4U 0614+09 is at least 2 times more than the values for 4U 1728-34 and Sco X-1.

  6. Observations of quasi-periodic scintillations and their possible relation to the dynamics of Es plasma blobs

    SciTech Connect

    Maruyama, Takashi )

    1991-06-01

    Quasi-periodic scintillations at a mid-latitude station, Wakkanai, Japan, are examined using 136-MHz geostationary satellite transmissions. Observations are compared with the ionospheric parameter obtained at the same station and random scintillation records. The results indicate that the quasi-periodic scintillations are most likely produced by plasma blobs within the sporadic E layers. Discussion focuses on characteristics of the ringing pattern which precedes and follows the primary deep fade-out, in field strength. In the majority of events the ringing pattern tends to develop after the distinct deep fade-out, i.e., the pattern is asymmetric. Quasi-periodic scintillation patterns are produced by the movement of plasma blobs in the case of geostationary satellite experiments. Thus the shape of the blob must be deformed so that a steep density gradient is attained on the backside. When the blob is highly deformed by the plasma instability which grows at the steep density gradient, burstlike random scintillations may be produced by the blob. 16 refs.

  7. Correlation between spectral state and quasi-periodic oscillation parameters in GX 5-1

    NASA Technical Reports Server (NTRS)

    Van Der Klis, M.; Jansen, F.; Van Paradijs, J.; Lewin, W. H. G.; Sztajno, M.

    1987-01-01

    In a series of seven Exosat observations, the bimodal spectral behavior and the quasi-periodic oscillation (QPO)/red noise properties of GX 5-1 show a strict correlation. In one of the two spectral states (characterized by a 'horizontal branch' in the hardness-intensity diagram), strong 20-40 Hz QPO and red noise below about 60 Hz were always present. In the other ('normal branch'), no QPO between 6 and 60 Hz or red noise above 1 Hz were detected, but there was an indication for weak QPO near 5 Hz. In both states 'very low frequency noise' (VLFN) is detected below 0.1 Hz which has a power-law shape and and which extends down to the lowest observed frequencies (0.0001 Hz). The VLFN is probably not directly related to the QPO. The results are compared to those on Sco X-1 and Cyg X-2 and it is concluded that, although all three sources show bimodal spectral and QPO/red noise behavior, there is a qualitative difference between GX 5-1 and Cyg X-2 on one hand and Sco X-1 on the other.

  8. Quasi-periodicity of spin motion in storage rings-a new look at spin tune

    NASA Astrophysics Data System (ADS)

    Barber, D. P.; Ellison, J.; Heinemann, K.

    2001-06-01

    We show how spin motion on the periodic closed orbit of a storage ring can be analyzed in terms of the Floquet theorem for equations of motion with periodic parameters. The spin tune on the closed orbit emerges as an extra frequency of the system which is contained in the Floquet exponent in analogy with the wave vector in Bloch wave functions for electrons in periodic atomic structures. We then show how to analyze spin motion on quasi-periodic synchro-betatron orbits in terms of a generalisation of the Floquet theorem and find that if small devisors are controlled by applying a Diophantine condition, a spin tune can again be defined and that it again emerges as an extra frequency in a Floquet-like exponent. We thereby obtain a deeper insight into the concept of ``spin tune'' and the conditions for its existence. The formalism suggests the use of Fourier analysis to ``measure'' spin tune during simulations of spin motion on synchro-betatron orbits. .

  9. On the development of quasi-periodic oscillations in Bondi-Hoyle accretion flows

    NASA Astrophysics Data System (ADS)

    Dönmez, O.; Zanotti, O.; Rezzolla, L.

    2011-04-01

    The numerical investigation of the Bondi-Hoyle accretion on to a moving black hole has a long history, both in Newtonian and in general-relativistic physics. By performing new two-dimensional and general-relativistic simulations on to a rotating black hole, we point out a novel feature, namely that quasi-periodic oscillations (QPOs) are naturally produced in the shock cone that develops in the downstream part of the flow. Because the shock cone in the downstream part of the flow acts as a cavity trapping pressure perturbations, modes with frequencies in the integer ratios of 2:1 and 3:1 are easily produced. The frequencies of these modes depend on the black hole spin and on the properties of the flow, and scale linearly with the inverse of the black hole mass. Our results may be relevant for explaining the detection of QPOs in Sagittarius A*, once such detection is confirmed by further observations. Finally, we report on the development of the flip-flop instability, which can affect the shock cone under suitable conditions; such an instability has been discussed before in Newtonian simulations but was never found in a relativistic regime.

  10. On the persistence of quasi-periodic invariant tori for double Hopf bifurcation of vector fields

    NASA Astrophysics Data System (ADS)

    Li, Xuemei

    2016-05-01

    We analyze the persistence of quasi-periodic invariant 2- and 3-tori for the double Hopf (Hopf-Hopf) bifurcation by using the KAM method. We prove that in a sufficiently small neighborhood of the bifurcation point, the full system has quasi-periodic 2-tori for most of the parameter sets where its truncated normal form possesses 2-tori. Under appropriate conditions we obtain that the full system also has quasi-periodic 3-tori for most parameters near the Hopf bifurcation curve of its truncated normal form and along the direction of the bifurcation, and these 3-tori bifurcate from invariant 2-tori. We also give concrete formulas on the existence of quasi-periodic invariant 2- and 3-tori, which are based on coefficients of the truncated normal form.

  11. The "Approximate 150 Day Quasi-Periodicity" in Interplanetary and Solar Phenomena During Cycle 23

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.

    2004-01-01

    A"quasi-periodicity" of approx. 150 days in various solar and interplanetary phenomena has been reported in earlier solar cycles. We suggest that variations in the occurrence of solar energetic particle events, inter-planetary coronal mass ejections, and geomagnetic storm sudden commenceents during solar cycle 23 show evidence of this quasi-periodicity, which is also present in the sunspot number, in particular in the northern solar hemisphere. It is not, however, prominent in the interplanetary magnetic field strength.

  12. Evidence from Quasi-Periodic Oscillations for a Millisecond Pulsar in the Low Mass X-Ray Binary 4U 0614+091

    NASA Technical Reports Server (NTRS)

    Ford, E.; Kaaret, P.; Tavani, M.; Barret, D.; Bloser, P.; Grindlay, J.; Harmon, B. A.; Paciesas, W. S.; Zhang, S. N.

    1997-01-01

    We have detected quasi-periodic oscillations (QPOs) near 1 kHz from the low mass X-ray binary 4U 0614+091 in observations with RXTE. The observations span several months and sample the source over a large range of X-ray luminosity. In every interval QPOs are present above 400 Hz with fractional RMS amplitudes from 3 to 12% over the full PCA band. At high count rates, two high frequency QPOs are detected simultaneously. The difference of their frequency centroids is consistent with a constant value of 323 Hz in all observations. During one interval a third signal is detected at 328 +/- 2 Hz. This suggests the system has a stable 'clock' which is most likely the neutron star with spin period 3.1 msec. Thus, our observations of 4U 0614+091 and those of 4U 1728-34 provide the first evidence for millisecond pulsars within low-mass X-ray binary systems and reveal the 'missing-link' between millisecond radiopulsars and the late stages of binary evolution in low mass X-ray binaries. The constant difference of the high frequency QPOs sug,,ests a beat-frequency interpretation. In this model, the high frequency QPO is associated with the Keplerian frequency of the inner accretion disk and the lower frequency QPO is a 'beat' between the differential rotation frequency of the inner disk and the spinning neutron star. Assuming the high frequency QPO is a Keplerian orbital frequency for the accretion disk, we find a maximum mass of 1.9 solar mass and a maximum radius of 17 km for the neutron star.

  13. Existence of quasi-periodic solutions of fast excited van der Pol-Mathieu-Duffing equation

    NASA Astrophysics Data System (ADS)

    Lu, Lin; Li, Xuemei

    2015-12-01

    The van der Pol-Mathieu-Duffing equation x ̈ + ( Ω0 2 + h 1 cos Ω 1 t + h 2 cos Ω 2 t ) x - ( α - β x 2 ) x ˙ - h 3 x 3 = h 4 Ω3 2 cos x cos Ω 3 t is considered in this paper, where α, β, h1, h2, h3, h4, Ω1, Ω2 are small parameters, α, β > 0, the frequency Ω3 is large compared to Ω1 and Ω2, the above parameters are real. For ∀α, β > 0, we use KAM (Kolmogorov-Arnold-Moser) theory to prove that the van der Pol-Mathieu-Duffing equation possesses quasi-periodic solutions for most of the parameters Ω0, Ω1, Ω2, Ω3, it verifies some phenomenon of Fahsi and Belhaq [Commun. Nonlinear Sci. 14, 244-253 (2009)] and can be regarded as a extension of Abouhazim et al. [Nonlinear Dyn. 39, 395-409 (2005)].

  14. Optical properties of one-dimensional Fibonacci quasi-periodic graphene photonic crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Yuping; Wu, Zhixin; Cao, Yanyan; Zhang, Huiyun

    2015-03-01

    We propose a novel type of one-dimensional photonic crystal called Fibonacci quasi-periodic graphene photonic crystal (FGPC), in which the structure in each dielectric cell follows the Fibonacci sequence and the graphene monolayers are embedded between adjacent dielectric layers. The transmission properties of FGPC are investigated using transfer matrix method in detail. It is shown that both photonic band gap induced by graphene (GIBPG) and the Bragg gap exist in the structure. We study the band gaps of TE and TM waves at different incident angles or chemical potentials. It is found that the band gaps can be tuned via a gate voltage and GIBPG is almost omnidirectional and insensitive to the polarization. In order to investigate difference between the GIPBG and Bragg gap, we plot the electromagnetic field profiles inside FGPC for some critical frequencies. The propagation loss of the structure caused by absorption of graphene is researched in detail. Also, the passing bands of Fibonacci sequences of different orders and their splitting behavior at higher order are investigated.

  15. Electrostatic and aerodynamic forced vibrations of a thin flexible electrode: Quasi-periodic vs. chaotic oscillations

    NASA Astrophysics Data System (ADS)

    Madanu, Sushma B.; Barbel, Stanley I.; Ward, Thomas

    2016-06-01

    In this paper, transverse vibrations of an electrostatically actuated thin flexible cantilever perturbed by low-speed air flow are studied using both experiments and numerical modeling. In the experiments, the dynamic characteristics of the cantilever are studied by supplying a DC voltage with an AC component for electrostatic forcing and a constant uniform air flow around the cantilever system for aerodynamic forcing. A range of control parameters leading to stable vibrations are established using a dimensionless operating parameter that is the ratio of the induced and the free stream velocities. Numerical results are validated with experimental data. Assuming the amplitude of vibrations are small, then a non-linear dynamic Euler-Bernoulli beam equation with viscous damping and gravitational effects is used to model the equation of motion. Aerodynamic forcing is modelled as a temporally sinusoidal and uniform force acting perpendicular to the beam length. The forcing amplitude is found to be proportional to the square of the air flow velocity. Numerical results strongly agree with the experiments predicting accurate vibration amplitude, displacement frequency, and quasi-periodic displacement of the cantilever tip.

  16. Quasi-periodic emissions and related electron precipitation observed by the low-altitude DEMETER spacecraft

    NASA Astrophysics Data System (ADS)

    Hayosh, M.; Nemec, F.; Pasmanik, D.; Santolik, O.; Demekhov, A. G.; Parrot, M.; Titova, L.

    2012-12-01

    We present a survey of quasi-periodic (QP) ELF/VLF emissions detected on board the DEMETER satellite (altitude of about 700 km, nearly Sun-synchronous orbit at 10:30/22:30 LT). Three years of data have been visually inspected for the presence of QP emissions. It is found that QP events occur in about 3 percents of daytime half-orbits, while they are basically absent during the night (note that we were likely to miss QP events with the modulation periods lower than about 10 s or the frequency bandwidth lower than about 400 Hz). The events occur predominantly during quiet geomagnetic conditions following the periods of enhanced geomagnetic activity. Their occurrence and properties are systematically analyzed. Three events with a simultaneous periodic modulation of wave intensity and energetic electron precipitation were analyzed in detail. All events are observed at quiet geomagnetic conditions. Most probably, they are not associated with geomagnetic pulsations. Energetic electron flux data measured by the NOAA-17 satellite are used to supplement DEMETER data in order to determine the spatial and temporal extent of the observed energetic electron precipitation events. Based on the observed correlation between bursts of wave intensity and energetic electron flux we estimate the location and the spatial extent of the source region of QP emissions.

  17. Electrostatic and aerodynamic forced vibrations of a thin flexible electrode: Quasi-periodic vs. chaotic oscillations.

    PubMed

    Madanu, Sushma B; Barbel, Stanley I; Ward, Thomas

    2016-06-01

    In this paper, transverse vibrations of an electrostatically actuated thin flexible cantilever perturbed by low-speed air flow are studied using both experiments and numerical modeling. In the experiments, the dynamic characteristics of the cantilever are studied by supplying a DC voltage with an AC component for electrostatic forcing and a constant uniform air flow around the cantilever system for aerodynamic forcing. A range of control parameters leading to stable vibrations are established using a dimensionless operating parameter that is the ratio of the induced and the free stream velocities. Numerical results are validated with experimental data. Assuming the amplitude of vibrations are small, then a non-linear dynamic Euler-Bernoulli beam equation with viscous damping and gravitational effects is used to model the equation of motion. Aerodynamic forcing is modelled as a temporally sinusoidal and uniform force acting perpendicular to the beam length. The forcing amplitude is found to be proportional to the square of the air flow velocity. Numerical results strongly agree with the experiments predicting accurate vibration amplitude, displacement frequency, and quasi-periodic displacement of the cantilever tip. PMID:27368778

  18. QUASI-PERIODIC WIGGLES OF MICROWAVE ZEBRA STRUCTURES IN A SOLAR FLARE

    SciTech Connect

    Yu, Sijie; Tan, Baolin; Yan, Yihua; Nakariakov, V. M.; Selzer, L. A.

    2013-11-10

    Quasi-periodic wiggles of microwave zebra pattern (ZP) structures with periods ranging from about 0.5 s to 1.5 s are found in an X-class solar flare on 2006 December 13 at the 2.6-3.8 GHz with the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou). Periodogram and correlation analysis show that the wiggles have two to three significant periodicities and are almost in phase between stripes at different frequencies. The Alfvén speed estimated from the ZP structures is about 700 km s{sup –1}. We find the spatial size of the wave-guiding plasma structure to be about 1 Mm with a detected period of about 1 s. This suggests that the ZP wiggles can be associated with the fast magnetoacoustic oscillations in the flaring active region. The lack of a significant phase shift between wiggles of different stripes suggests that the ZP wiggles are caused by a standing sausage oscillation.

  19. Effects of Resonance in Quasi-periodic Oscillators of Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Titarchuk, Lev

    2002-10-01

    Using a large quantity of Rossi X-Ray Timing Explorer data presented in the literature, I offer a detailed investigation into the accuracy of the quasi-periodic oscillation (QPO) frequency determination. The QPO phenomenon seen in X-ray binaries is possibly a result of the resonance of the intrinsic (eigen) oscillations and harmonic driving forces of the system. I show that the resonances, in the presence of the damping of oscillations, occur at frequencies that are systematically and randomly shifted with respect to the eigenfrequencies of the system. The shift value strongly depends on the damping rate that is measured by the half-width of the QPO feature. Taking into account this effect, I analyze the QPO data for four Z sources, Scorpius X-1, GX 340+0, GX 5-1, and GX 17+2, and two atoll sources, 4U 1728-34 and 4U 0614+09. The transition-layer model (TLM) predicts the existence of the invariant quantity δ, an inclination angle of the magnetospheric axis with respect to the normal to the disk. I calculate δ and the error bars of δ using the resonance shift, and I find that the inferred δ-values are consistent with constants for these four Z sources, in which horizontal-branch oscillation and kilohertz frequencies have been detected and correctly identified. It is shown that the inferred δ are in the range between 5.5d and 6.5d. I conclude that the TLM seems to be compatible with the data.

  20. FRACTIONAL AMPLITUDE OF KILOHERTZ QUASI-PERIODIC OSCILLATION FROM 4U 1728-34: EVIDENCE OF DECLINE AT HIGHER ENERGIES

    SciTech Connect

    Mukherjee, Arunava; Bhattacharyya, Sudip E-mail: sudip@tifr.res.in

    2012-09-01

    A kilohertz quasi-periodic oscillation (kHz QPO) is an observationally robust high-frequency timing feature detected from neutron star low-mass X-ray binaries (LMXBs). This feature can be very useful to probe the superdense core matter of neutron stars and the strong gravity regime. Although many models exist in the literature, the physical origin of kHz QPO is not known, and hence this feature cannot be used as a tool yet. The energy dependence of kHz QPO fractional rms amplitude is an important piece of the jigsaw puzzle to understand the physical origin of this timing feature. It is known that the fractional rms amplitude increases with energy at lower energies. At higher energies, the amplitude is usually believed to saturate, although this is not established. We combine tens of lower kHz QPOs from a neutron star LMXB 4U 1728-34 in order to improve the signal-to-noise ratio. Consequently, we, for the first time to the best of our knowledge, find a significant and systematic decrease of the fractional rms amplitude with energy at higher photon energies. Assuming an energy spectrum model, blackbody+powerlaw, we explore if the sinusoidal variation of a single spectral parameter can reproduce the above-mentioned fractional rms amplitude behavior. Our analysis suggests that the oscillation of any single blackbody parameter is favored over the oscillation of any single power-law parameter, in order to explain the measured amplitude behavior. We also find that the quality factor of a lower kHz QPO does not plausibly depend on photon energy.

  1. Discovery of Kilohertz Quasi-periodic Oscillations in the Z Source GX 340+0

    NASA Astrophysics Data System (ADS)

    Jonker, Peter G.; Wijnands, Rudy; van der Klis, Michiel; Psaltis, Dimitrios; Kuulkers, Erik; Lamb, Frederick K.

    1998-06-01

    We have discovered two simultaneous kHz quasi-periodic oscillations (QPOs) in the Z source GX 340+0 with the Rossi X-Ray Timing Explorer. The X-ray hardness-intensity and color-color diagrams each show a full Z track, with an extra limb branching off the flaring branch of the Z. Both peaks moved to higher frequencies when the mass accretion rate increased. The two peaks moved from 247+/-6 and 567+/-39 Hz at the left end of the horizontal branch to 625+/-18 and 820+/-19 Hz at its right end. The higher frequency peak's rms amplitude (5-60 keV) and FWHM decreased from ~5% and 383+/-135 Hz to ~2% and 145+/-62 Hz, respectively. The rms amplitude and FWHM of the lower peak were consistent with being constant near 2.5% and 100 Hz. The kHz QPO separation was consistent with being constant at 325+/-10 Hz. Simultaneous with the kHz QPOs, we detected the horizontal-branch oscillation (HBO) and its second harmonic, at frequencies between 20 and 50 Hz, and 38 and 69 Hz, respectively. The normal-branch oscillations were only detected on the upper and middle normal branch and became undetectable on the lower normal branch. The HBO frequencies do not fall within the range predicted for Lense-Thirring precession, unless either the ratio of the neutron star moment of inertia to neutron star mass is at least 4, 1045g cm2 M-1solar, the frequencies of the HBOs are in fact the second harmonic oscillations, or the observed kHz peak difference is half the spin frequency and not the spin frequency. During a 1.2 day gap between two observations, the Z track in the hardness-intensity diagram moved to higher count rates by about 3.5%. Comparing data before and after this shift, we find that the HBO properties are determined by position on the Z track and not directly by count rate or X-ray colors.

  2. Is Compton Cooling Sufficient to Explain Evolution of Observed Quasi-periodic Oscillations in Outburst Sources?

    NASA Astrophysics Data System (ADS)

    Mondal, Santanu; Chakrabarti, Sandip K.; Debnath, Dipak

    2015-01-01

    In outburst sources, quasi-periodic oscillation (QPO) frequency is known to evolve in a certain way: in the rising phase, it monotonically goes up until a soft intermediate state is achieved. In the propagating oscillatory shock model, oscillation of the Compton cloud is thought to cause QPOs. Thus, in order to increase QPO frequency, the Compton cloud must collapse steadily in the rising phase. In decline phases, the exact opposite should be true. We investigate cause of this evolution of the Compton cloud. The same viscosity parameter that increases the Keplerian disk rate also moves the inner edge of the Keplerian component, thereby reducing the size of the Compton cloud and reducing the cooling timescale. We show that cooling of the Compton cloud by inverse Comptonization is enough for it to collapse sufficiently so as to explain the QPO evolution. In the two-component advective flow configuration of Chakrabarti-Titarchuk, centrifugal force-induced shock represents the boundary of the Compton cloud. We take the rising phase of 2010 outburst of Galactic black hole candidate H 1743-322 and find an estimation of variation of the α parameter of the sub-Keplerian flow to be monotonically rising from 0.0001 to 0.02, well within the range suggested by magnetorotational instability. We also estimate the inward velocity of the Compton cloud to be a few meters per second, which is comparable to what is found in several earlier studies of our group by empirically fitting the shock locations with the time of observations.

  3. IS COMPTON COOLING SUFFICIENT TO EXPLAIN EVOLUTION OF OBSERVED QUASI-PERIODIC OSCILLATIONS IN OUTBURST SOURCES?

    SciTech Connect

    Mondal, Santanu; Chakrabarti, Sandip K.; Debnath, Dipak E-mail: chakraba@bose.res.in

    2015-01-01

    In outburst sources, quasi-periodic oscillation (QPO) frequency is known to evolve in a certain way: in the rising phase, it monotonically goes up until a soft intermediate state is achieved. In the propagating oscillatory shock model, oscillation of the Compton cloud is thought to cause QPOs. Thus, in order to increase QPO frequency, the Compton cloud must collapse steadily in the rising phase. In decline phases, the exact opposite should be true. We investigate cause of this evolution of the Compton cloud. The same viscosity parameter that increases the Keplerian disk rate also moves the inner edge of the Keplerian component, thereby reducing the size of the Compton cloud and reducing the cooling timescale. We show that cooling of the Compton cloud by inverse Comptonization is enough for it to collapse sufficiently so as to explain the QPO evolution. In the two-component advective flow configuration of Chakrabarti-Titarchuk, centrifugal force-induced shock represents the boundary of the Compton cloud. We take the rising phase of 2010 outburst of Galactic black hole candidate H 1743-322 and find an estimation of variation of the α parameter of the sub-Keplerian flow to be monotonically rising from 0.0001 to 0.02, well within the range suggested by magnetorotational instability. We also estimate the inward velocity of the Compton cloud to be a few meters per second, which is comparable to what is found in several earlier studies of our group by empirically fitting the shock locations with the time of observations.

  4. Probing the origin of quasi-periodic oscillations: the short-time-scale evolution of phase lags in GRS 1915+105

    NASA Astrophysics Data System (ADS)

    van den Eijnden, Jakob; Ingram, Adam; Uttley, Phil

    2016-06-01

    We present a model-independent analysis of the short-time-scale energy dependence of low-frequency quasi-periodic oscillations (QPOs) in the X-ray flux of GRS 1915+105. The QPO frequency in this source has previously been observed to depend on photon energy, with the frequency increasing with energy for observations with a high (≳2 Hz) QPO frequency, and decreasing with energy for observations with a low (≲2 Hz) QPO frequency. As this observed energy dependence is currently unexplained, we investigate if it is intrinsic to the QPO mechanism by tracking phase lags on (sub)second time-scales. We find that the phase lag between two broad energy bands systematically increases for 5-10 QPO cycles, after which the QPO becomes decoherent, the phase lag resets and the pattern repeats. This shows that the band with the higher QPO frequency is running away from the other band on short time-scales, providing strong evidence that the energy dependence of the QPO frequency is intrinsic. We also find that the faster the QPO decoheres, the faster the phase lag increases, suggesting that the intrinsic frequency difference contributes to the decoherence of the QPO. We interpret our results within a simple geometric QPO model, where different radii in the inner accretion flow experience Lense-Thirring precession at different frequencies, causing the decoherence of the oscillation. By varying the spectral shape of the inner accretion flow as a function of radius, we are able to qualitatively explain the energy-dependent behaviour of both QPO frequency and phase lag.

  5. Sensitivity of quasi-periodic outer rainband activity of tropical cyclones to the surface entropy flux

    NASA Astrophysics Data System (ADS)

    Li, Qingqing; Duan, Yihong

    2013-10-01

    The influence of outer-core surface entropy fluxes (SEFs) on tropical cyclone (TC) outer rainband activity is investigated in this study with a fully compressible, nonhydrostatic model. A control simulation and two sensitivity experiments with the outer-core SEF artificially increased and decreased by 20% respectively were conducted to examine the quasi-periodic outer rainband behavior. Larger negative horizontal advection due to the greater radial wind and the positive contribution by asymmetric eddies leads to a longer period of outerrainband activity in the SEF-enhanced experiment. The well-developed outer rainbands in the control and SEF-reduced simulations significantly limit the TC intensity, whereas such an intensity suppression influence is not pronounced in the SEF-enhanced experiment. As diabatic heating in outer rainbands strengthens the outer-core tangential wind, the quasi-periodic activity of outer rainbands contributes to the quasi-periodic variations of the inner-core size of the TCs.

  6. High frequency reference electrode

    DOEpatents

    Kronberg, J.W.

    1994-05-31

    A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or halo' at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes. 4 figs.

  7. [High frequency ultrasound].

    PubMed

    Sattler, E

    2015-07-01

    Diagnostic ultrasound has become a standard procedure in clinical dermatology. Devices with intermediate high frequencies of 7.5-15 MHz are used in dermato-oncology for the staging and postoperative care of skin tumor patients and in angiology for improved vessel diagnostics. In contrast, the high frequency ultrasound systems with 20-100 MHz probes offer a much higher resolution, yet with a lower penetration depth of about 1 cm. The main indications are the preoperative measurements of tumor thickness in malignant melanoma and other skin tumors and the assessment of inflammatory and soft tissue diseases, offering information on the course of these dermatoses and allowing therapy monitoring. This article gives an overview on technical principles, devices, mode of examination, influencing factors, interpretation of the images, indications but also limitations of this technique. PMID:25636803

  8. High frequency reference electrode

    DOEpatents

    Kronberg, James W.

    1994-01-01

    A high frequency reference electrode for electrochemical experiments comprises a mercury-calomel or silver-silver chloride reference electrode with a layer of platinum around it and a layer of a chemically and electrically resistant material such as TEFLON around the platinum covering all but a small ring or "halo" at the tip of the reference electrode, adjacent to the active portion of the reference electrode. The voltage output of the platinum layer, which serves as a redox electrode, and that of the reference electrode are coupled by a capacitor or a set of capacitors and the coupled output transmitted to a standard laboratory potentiostat. The platinum may be applied by thermal decomposition to the surface of the reference electrode. The electrode provides superior high-frequency response over conventional electrodes.

  9. Quasi-periodic Pulsations during the Impulsive and Decay phases of an X-class Flare

    NASA Astrophysics Data System (ADS)

    Hayes, L. A.; Gallagher, P. T.; Dennis, B. R.; Ireland, J.; Inglis, A. R.; Ryan, D. F.

    2016-08-01

    Quasi-periodic pulsations (QPPs) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 2013 October 28. We focus on the character of the fine structure pulsations evident in the soft X-ray (SXR) time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ∼20 s is observed in all channels and a second timescale of ∼55 s is observed in the non-thermal emissions. SXR pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ∼40 s up to ∼70 s. We interpret the bursty nature of the co-existing multi-wavelength QPPs during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPPs are most likely connected with compressive magnetohydrodynamic processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

  10. Probing Neutron Star Physics with Quasi-Periodic Oscillations in Magnetar Bursts

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela

    2015-04-01

    Neutron stars, the remnants of massive stellar explosions, are prime candidates for studying dense matter physics in conditions not accessible in the laboratory. Among the zoo of neutron star phenomena, magnetars, neutron stars with an extremely high magnetic field, are of particular interest for their spectacular bursting behaviour in X-rays and gamma-rays. They show thousands of recurrent short, bright bursts as well as some of the brightest gamma-ray events, called giant flares, ever observed on earth. The detection of quasi-periodic oscillations (QPOs) in giant flares and, more recently, in small recurrent bursts, is generally interpreted as the observable signature of global oscillations of the neutron star following a star quake. This detection has opened up the potential of neutron star seismology: probing the physical conditions in the interior of the star via the information conveyed in star quakes. In this talk, I will give an overview of observational studies of these sources, focusing on recent detections of QPOs in smaller bursts as well as results from the giant flares. I will then tie these observational results to theoretical models of the star quakes that tie observations to the neutron star interior and crust, and I will finish with an outlook of the future of magnetar seismology. DH is supported by the Moore-Sloan Data Science Environment at NYU.

  11. Case studies of quasi-periodic VLF emissions and related ULF fluctuations of the magnetic field

    NASA Astrophysics Data System (ADS)

    Hayosh, M.; Santolik, O.; Nemec, F.; Parrot, M.

    2014-12-01

    Quasi-periodic (QP) VLF emissions are observed in the inner magnetosphere mostly on the day-side. These waves exhibit a periodic time modulation of the wave intensity that is possibly a result of the whistler-mode wave growth being periodically modulated by compressional ULF magnetic field pulsations. We have analyzed 50 QP events measured by the DEMETER satellite at altitudes of about 700 km to verify their generation mechanism. The analyzed events have a modulation period between 15 s and 80 s, and they were observed during quiet geomagnetic conditions (Kp<3). Magnetometers of the CARISMA system were used for monitoring the ULF magnetic field pulsations in a wide spatial range. We have found that ULF magnetic field pulsations in the Pc3 - Pc5 range are well correlated with the occurrence of the QP emissions with modulation periods between about 40 and 80 s. At the same time, increased fluxes of high-energy electrons (E > 30 keV) were observed by DEMETER and by the NOAA-17 satellite. We analyze possible links between these electrons, QP emissions, and ULF magnetic field pulsations.

  12. Quasi-periodic Whistler Mode Waves Detected by the Van Allen Probes Spacecraft

    NASA Astrophysics Data System (ADS)

    Hospodarsky, G. B.; Santolik, O.; Nemec, F.; Kurth, W. S.; Kletzing, C.; Bounds, S. R.; Wygant, J. R.; Bonnell, J. W.

    2014-12-01

    Quasi-periodic (QP) whistler mode electromagnetic emissions have been detected in Earth's magnetosphere by the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) Waves instrument. These emissions typically consist of intervals of enhanced wave power between a few hundred Hz to a few kHz with modulation periods on the order of minutes. These emissions are primarily observed on the dayside and detected between L shells of 3 to 6, though some events are observed down to L shells of ~2. EMFISIS simultaneously measures the vector wave magnetic field and, with the support of the Electric Fields and Waves (EFW) instrument sensors, the vector wave electric field at two locations in Earth's magnetosphere in a continuous survey mode (typically with a 6 second cadence) along with a number of different burst modes to provide high time resolution waveforms (35000 samples per second). These two modes allow a systematic survey of the occurrence of these waves. By measuring all six wave components simultaneously, the wave propagation parameters, such as the wave normal angle and Poynting vector, of these plasma wave emissions are obtained. We will present a statistical survey of the properties of these waves as detected by the Van Allen Probes, examine their occurrence location and use burst data to examine the fine structure of individual events.

  13. Quasi-periodic Pulsations during the Impulsive and Decay phases of an X-class Flare

    NASA Astrophysics Data System (ADS)

    Hayes, L. A.; Gallagher, P. T.; Dennis, B. R.; Ireland, J.; Inglis, A. R.; Ryan, D. F.

    2016-08-01

    Quasi-periodic pulsations (QPPs) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 2013 October 28. We focus on the character of the fine structure pulsations evident in the soft X-ray (SXR) time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ˜20 s is observed in all channels and a second timescale of ˜55 s is observed in the non-thermal emissions. SXR pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ˜40 s up to ˜70 s. We interpret the bursty nature of the co-existing multi-wavelength QPPs during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPPs are most likely connected with compressive magnetohydrodynamic processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

  14. Detection of Quasi-Periodic Oscillations in the June 2015 Outburst of V404 Cygni

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela

    2016-04-01

    In June 2015, the black hole X-ray binary (BHXRB) V404 Cygni went into outburst for the first time in 26 years. The source is not only the closest known BHXRB, it is also known to undergo extreme variations in brightness, allowing us to study the source’s behaviour during flaring with the unprecedented detail afforded by modern space and ground-based instrumentation.Here we present a timing study and a comprehensive search for quasi-periodic oscillations (QPOs) of V404 Cygni during its most recent outburst, utilizing data from six instruments on board five different X-ray missions: Swift/XRT, Fermi/GBM, Chandra/ACIS, INTEGRAL’s IBIS/ISGRI and JEM-X, and NuSTAR.We find four previously unobserved, significant QPOs throughout the outburst. One QPO, at 18 mHz, is detected in simultaneous observations with both Fermi/GBM and Swift/XRT, and is a likely example of a rare, recently discovered class of mHz-QPOs in BHXRBs linked to high-inclination sources. We also find a broad structure in averaged periodograms of several Chandra/ACIS and INTEGRAL/JEM-X observations that contains significant variability, but is too broad to be called a QPO, reminiscent of a feature more commonly observed in Cygnus X-1. We discuss our results in the context of current models for QPO formation.

  15. Globally and locally attractive solutions for quasi-periodically forced systems

    NASA Astrophysics Data System (ADS)

    Bartuccelli, Michele V.; Deane, Jonathan H. B.; Gentile, Guido

    2007-04-01

    We consider a class of differential equations, , with , describing one-dimensional dissipative systems subject to a periodic or quasi-periodic (Diophantine) forcing. We study existence and properties of trajectories with the same quasi-periodicity as the forcing. For g(x)=x2p+1, , we show that, when the dissipation coefficient is large enough, there is only one such trajectory and that it describes a global attractor. In the case of more general nonlinearities, including g(x)=x2 (describing the varactor equation), we find that there is at least one trajectory which describes a local attractor.

  16. Exciton photoluminescence in resonant quasi-periodic Thue-Morse quantum wells.

    PubMed

    Hsueh, W J; Chang, C H; Lin, C T

    2014-02-01

    This Letter investigates exciton photoluminescence (PL) in resonant quasi-periodic Thue-Morse quantum wells (QWs). The results show that the PL properties of quasi-periodic Thue-Morse QWs are quite different from those of resonant Fibonacci QWs. The maximum and minimum PL intensities occur under the anti-Bragg and Bragg conditions, respectively. The maxima of the PL intensity gradually decline when the filling factor increases from 0.25 to 0.5. Accordingly, the squared electric field at the QWs decreases as the Thue-Morse QW deviates from the anti-Bragg condition. PMID:24487847

  17. MILLIHERTZ QUASI-PERIODIC OSCILLATIONS AND THERMONUCLEAR BURSTS FROM TERZAN 5: A SHOWCASE OF BURNING REGIMES

    SciTech Connect

    Linares, M.; Chakrabarty, D.; Altamirano, D.; Cumming, A.; Keek, L.

    2012-04-01

    We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480-2446, located in the globular cluster Terzan 5. The increase in burst rate that we found during its 2010 outburst, when persistent luminosity rose from 0.1 to 0.5 times the Eddington limit, is in qualitative agreement with thermonuclear burning theory yet contrary to all previous observations of thermonuclear bursts. Thermonuclear bursts gradually evolved into a mHz QPO when the accretion rate increased, and vice versa. The mHz QPOs from IGR J17480-2446 resemble those previously observed in other accreting NSs, yet they feature lower frequencies (by a factor {approx}3) and occur when the persistent luminosity is higher (by a factor 4-25). We find four distinct bursting regimes and a steep (close to inverse cubic) decrease of the burst recurrence time with increasing persistent luminosity. We compare these findings to nuclear burning models and find evidence for a transition between the pure helium and mixed hydrogen/helium ignition regimes when the persistent luminosity was about 0.3 times the Eddington limit. We also point out important discrepancies between the observed bursts and theory, which predicts brighter and less frequent bursts, and suggest that an additional source of heat in the NS envelope is required to reconcile the observed and expected burst properties. We discuss the impact of NS magnetic field and spin on the expected nuclear burning regimes, in the context of this particular pulsar.

  18. Multi-mode quasi-periodic pulsations in a solar flare

    NASA Astrophysics Data System (ADS)

    Kolotkov, D. Y.; Nakariakov, V. M.; Kupriyanova, E. G.; Ratcliffe, H.; Shibasaki, K.

    2015-02-01

    Context. Quasi-periodic pulsations (QPP) of the electromagnetic radiation emitted in solar and stellar flares are often detected in microwave, white light, X-ray, and gamma-ray bands. Mechanisms for QPP are intensively debated in the literature. Previous studies revealed that QPP may manifest non-linear, non-stationary and, perhaps, multi-modal processes operating in flares. Aims: We study QPP of the microwave emission generated in an X3.2-class solar flare on 14 May, 2013, observed with the Nobeyama Radioheliograph (NoRH), aiming to reveal signatures of the non-linear, non-stationary, and multi-modal processes in the signal. Methods: The NoRH correlation signal obtained at the 17 GHz intensity has a clear QPP pattern. The signal was analysed with the Hilbert-Huang transform (HHT) that allows one to determine its instant amplitude and frequency, and their time variation. Results: It was established that the QPP consists of at least three well-defined intrinsic modes, with the mean periods of 15, 45, and 100 s. All the modes have quasi-harmonic behaviour with different modulation patterns. The 100 s intrinsic mode is a decaying oscillation, with the decay time of 250 s. The 15 s intrinsic mode shows a similar behaviour, with the decay time of 90 s. The 45 s mode has a wave-train behaviour. Conclusions: Dynamical properties of detected intrinsic modes indicate that the 100 s and 15 s modes are likely to be associated with fundamental kink and sausage modes of the flaring loop, respectively. The 100 s oscillation could also be caused by the fundamental longitudinal mode, while this interpretation requires the plasma temperature of about 30 million K and hence is not likely. The 45 s mode could be the second standing harmonics of the kink mode.

  19. A delayed oscillator model for the quasi-periodic multidecadal variability of the NAO

    NASA Astrophysics Data System (ADS)

    Sun, Cheng; Li, Jianping; Jin, Fei-Fei

    2015-10-01

    Wavelet analysis of the annual North Atlantic Oscillation (NAO) index back to 1659 reveals a significant frequency band at about 60 years. Recent NAO decadal variations, including the increasing trend during 1960-1990 and decreasing trend since the mid-1990s, can be well explained by the approximate 60-year cycle. This quasi 60-year oscillation of the NAO is realistically reproduced in a long-term control simulation with version 4 of the Community Climate System Model, and the possible mechanisms are further investigated. The positive NAO forces the strengthening of the Atlantic meridional overturning circulation (AMOC) and induces a basin-wide uniform sea surface temperature (SST) warming that corresponds to the Atlantic multidecadal oscillation (AMO). The SST field exhibits a delayed response to the preceding enhanced AMOC, and shows a pattern similar to the North Atlantic tripole (NAT), with SST warming in the northern North Atlantic and cooling in the southern part. This SST pattern (negative NAT phase) may lead to an atmospheric response that resembles the negative NAO phase, and subsequently the oscillation proceeds, but in the opposite sense. Based on these mechanisms, a simple delayed oscillator model is established to explain the quasi-periodic multidecadal variability of the NAO. The magnitude of the NAO forcing of the AMOC/AMO and the time delay of the AMOC/AMO feedback are two key parameters of the delayed oscillator. For a given set of parameters, the quasi 60-year cycle of the NAO can be well predicted. This delayed oscillator model is useful for understanding of the oscillatory mechanism of the NAO, which has significant potential for decadal predictions as well as the interpretation of proxy data records.

  20. A Search for Periodic and Quasi-periodic Photometric Behavior in the Cataclysmic Variable TT ARIETIS

    NASA Astrophysics Data System (ADS)

    Andronov, I. L.; Arai, K.; Chinarova, L. L.; Dorokhov, N. I.; Dorokhova, T. N.; Dumitrescu, A.; Nogami, D.; Kolesnikov, S. V.; Lepardo, A.; Mason, P. A.; Matsumoto, K.; Oprescu, G.; Pajdosz, G.; Passuelo, R.; Patkos, L.; Senio, D. S.; Sostero, G.; Suleimanov, V. F.; Tremko, J.; Zhukov, G. V.; Zola, S.

    1999-01-01

    Observations of TT Ari obtained at 11 observatories (campaign TT Ari-94) during 258 hr were carried out to study optical variability on timescales from minutes to weeks. The best-fit primary photometric period determined from 16 nights of data obtained at the Dushak-Eregdag station of the Odessa State University is P=0.133160°+/-0.000004° with a mean amplitude of 0.0513+/-0.0008 mag. This new primary photometric period is larger than that obtained during the TT Ari-88 campaign and is well outside the range of estimates published since 1961. Contrary to previous findings, the ``5-7 hr'' secondary photometric period is not seen. Our observations do show evidence for periods of 2.916° and 0.3040° with amplitudes of 43 and 25 mmag, respectively. The beat period between the spectroscopic and photometric periods is not seen. No coherent oscillations in the range f=10-2500 cycles day^-1 are found. The highest peaks in the power spectrum cover the wide range of 24-139 cycles day^-1. In the mean periodogram, the highest peak corresponds to 21 and 30 minutes for the largest sets of observations, i.e., those obtained at Odessa and Krakow Universities, respectively. In the instrumental B system, variations with an amplitude exceeding 0.011 mag occur 8 times (from 33 runs) at 24 minutes. We conclude that quasi-periodic variations occur at a few preferred timescales rather than at a relatively stable period with a secular decrease. In the frequency range 90-900 cycles day^-1, the power spectrum obeys a power law with a slope ranging from gamma=1.3 to 2.6 for different runs.

  1. IMAGING OBSERVATIONS OF QUASI-PERIODIC PULSATIONS IN SOLAR FLARE LOOPS WITH SDO/AIA

    SciTech Connect

    Su, J. T.; Mao, X. J.; Shen, Y. D.; Liu, Y.

    2012-08-20

    Quasi-periodic pulsations (QPPs) of flaring emission with periods from a few seconds to tens of minutes have been widely detected from radio bands to {gamma}-ray emissions. However, in the past the spatial information of pulsations could not be utilized well due to the instrument limits. We report here imaging observations of the QPPs in three loop sections during a C1.7 flare with periods of P = 24 s-3 minutes by means of the extreme-ultraviolet 171 A channel of the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory. We confirm that the QPPs with the shortest period of 24 s were not of an artifact produced by the Nyquist frequency of the AIA 12 s cadence. The QPPs in the three loop sections were interconnected and closely associated with the flare. The detected perturbations propagated along the loops at speeds of 65-200 km s{sup -1}, close to those of acoustic waves in them. The loops were made up of many bright blobs arranged in alternating bright and dark changes in intensity (spatial periodical distribution) with the wavelengths 2.4-5 Mm (as if they were magnetohydrodynamic waves). Furthermore, in the time-distance diagrams, the detected perturbation wavelengths of the QPPs are estimated to be {approx}10 Mm, which evidently do not fit the above ones of the spatial periodic distributions and produce a difference of a factor of 2-4 with them. It is suggested that the short QPPs with periods P < 60 s were possibly sausage-mode oscillations and the long QPPs with periods P > 60 s were the higher (e.g., >2nd) harmonics of slow magnetoacoustic waves.

  2. Quasi-periodic oscillations in black-hole and neutron-star binaries

    NASA Astrophysics Data System (ADS)

    Mendez, Mariano; Motta, Sara Elisa

    2016-07-01

    Fast time variability is an important characteristic of black hole and neutron-star X-ray binaries and a key ingredient in understanding the physical processes in these systems. Black hole and neutron star X-ray binaries show a variety of X-ray spectral/variability states, representing different accretion regimes. It has been recently shown that the overall strength of the rapid variability is a good tracer of these states. Fast aperiodic variability is generally studied through the inspection of power density spectra. Most of the power spectral components are broad and can take the form of a wide power distribution over several decades of frequency or of a more localised peak (quasi-periodic oscillations, QPOs). It is now clear that QPOs are a common characteristic of accreting systems: they have been observed in accreting stellar mass black holes and neutron stars hosted in X-ray binaries, in cataclysmic variable, in the so-called ultra luminous X-ray sources and even in active galactic nuclei. Even though their origin and nature is still debated, the study of QPOs provides a way to explore the inner accretion flow around black holes and neutron stars. Various theoretical models have been proposed to explain the origin of QPOs in black hole and neutron star binaries, only a few have been proved to be promising so far, having shown good agreement with observations. I will describe how timing is done in X-rays and how QPOs are usually studied. I will briefly review some of the proposed models and I will finally show the most recent results obtained on QPOs.

  3. Structure-dependent localized surface plasmon resonance characteristics and surface enhanced Raman scattering performances of quasi-periodic nanoarrays: Measurements and analysis

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Zhou, Jun; Rippa, Massimo; Petti, Lucia

    2015-10-01

    A set of periodic and quasi-periodic Au nanoarrays with different morphologies have been fabricated by using electron beam lithography technique, and their optical properties have been examined experimentally and analyzed theoretically by scanning near-field optical microscope and finite element method, respectively. Results present that the localized surface plasmon resonance of the as-prepared Au nanoarrays exhibit the structure-depended characteristics. Comparing with the periodic nanoarrays, the quasi-periodic ones demonstrate stronger electric field enhancement, especially for Thue-Morse nanoarray. Meanwhile, the surface enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid molecular labeled nanoarrays show that the quasi-periodic nanoarrays exhibit distinct SERS enhancement, for example, a higher enhancement factor of ˜107 is obtained for the Thue-Morse nanoarray consisted of square pillars of 100 nm size. Therefore, it is significant to optimally design and fabricate the chip-scale quasi-periodic nanoarrays with high localized electric field enhancement for SERS applications in biosensing field.

  4. Structure-dependent localized surface plasmon resonance characteristics and surface enhanced Raman scattering performances of quasi-periodic nanoarrays: Measurements and analysis

    SciTech Connect

    Chen, Dong; Zhou, Jun; Rippa, Massimo; Petti, Lucia

    2015-10-28

    A set of periodic and quasi-periodic Au nanoarrays with different morphologies have been fabricated by using electron beam lithography technique, and their optical properties have been examined experimentally and analyzed theoretically by scanning near-field optical microscope and finite element method, respectively. Results present that the localized surface plasmon resonance of the as-prepared Au nanoarrays exhibit the structure-depended characteristics. Comparing with the periodic nanoarrays, the quasi-periodic ones demonstrate stronger electric field enhancement, especially for Thue-Morse nanoarray. Meanwhile, the surface enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid molecular labeled nanoarrays show that the quasi-periodic nanoarrays exhibit distinct SERS enhancement, for example, a higher enhancement factor of ∼10{sup 7} is obtained for the Thue-Morse nanoarray consisted of square pillars of 100 nm size. Therefore, it is significant to optimally design and fabricate the chip-scale quasi-periodic nanoarrays with high localized electric field enhancement for SERS applications in biosensing field.

  5. High Dynamic Range Observations of Solar Coronal Transients at Low Radio Frequencies with a Spectro-correlator

    NASA Astrophysics Data System (ADS)

    Hariharan, K.; Ramesh, R.; Kathiravan, C.; Abhilash, H. N.; Rajalingam, M.

    2016-02-01

    A new antenna system with a digital spectro-correlator that provides high temporal, spectral, and amplitude resolutions has been commissioned at the Gauribidanur Observatory near Bangalore in India. Presently, it is used for observations of the solar coronal transients in the scarcely explored frequency range ≈30-15 MHz. The details of the antenna system, the associated receiver setup, and the initial observational results are reported. Some of the observed transients exhibited quasi-periodicity in their time profiles at discrete frequencies. Estimates of the associated magnetic field strength (B) indicate that B ≈ 0.06-1 G at a typical frequency such as 19.5 MHz.

  6. High frequency electromagnetic tomography

    SciTech Connect

    Daily, W.; Ramirez, A.; Ueng, T.; Latorre, R.

    1989-09-01

    An experiment was conducted in G Tunnel at the Nevada Test Site to evaluate high frequency electromagnetic tomography as a candidate for in situ monitoring of hydrology in the near field of a heater placed in densely welded tuff. Tomographs of 200 MHz electromagnetic permittivity were made for several planes between boreholes. Data were taken before the heater was turned on, during heating and during cooldown of the rockmass. This data is interpreted to yield maps of changes in water content of the rockmass as a function of time. This interpretation is based on laboratory measurement of electromagnetic permittivity as a function of water content for densely welded tuff. 8 refs., 6 figs.

  7. High-frequency ventilation.

    PubMed

    Crawford, M R

    1986-08-01

    Over the last six years high-frequency ventilation has been extensively evaluated both in the clinical and laboratory settings. It is now no longer the great mystery it once was, and it is now no longer believed (as many had hoped), that it will solve all the problems associated with mechanical pulmonary ventilation. Although the technique is safe and appears to cause no harm even in the long term, it has not yet been shown to offer any major advantages over conventional mechanical ventilation. PMID:3530042

  8. Quasi-periodic pulsations in solar hard X-ray and microwave flares

    NASA Technical Reports Server (NTRS)

    Kosugi, Takeo; Kiplinger, Alan L.

    1986-01-01

    For more than a decade, various studies have pointed out that hard X-ray and microwave time profiles of some solar flares show quasi-periodic fluctuations or pulsations. Nevertheless, it was not until recently that a flare displaying large amplitude quasi-periodic pulsations in X-rays and microwaves was observed with good spectral coverage and with a sufficient time resolution. The event occurred on June 7, 1980, at approximately 0312 UT, and exhibits seven intense pulses with a quasi-periodicity of approximately 8 seconds in microwaves, hard X-rays, and gamma-ray lines. On May 12, 1983, at approximately 0253 UT, another good example of this type of flare was observed both in hard X-rays and in microwaves. Temporal and spectral characteristics of this flare are compared with the event of June 7, 1980. In order to further explore these observational results and theoretical scenarios, a study of nine additional quasi-periodic events were incorporated with the results from the two flares described. Analysis of these events are briefly summarized.

  9. High-frequency ECG

    NASA Technical Reports Server (NTRS)

    Tragardh, Elin; Schlegel, Todd T.

    2006-01-01

    The standard ECG is by convention limited to 0.05-150 Hz, but higher frequencies are also present in the ECG signal. With high-resolution technology, it is possible to record and analyze these higher frequencies. The highest amplitudes of the high-frequency components are found within the QRS complex. In past years, the term "high frequency", "high fidelity", and "wideband electrocardiography" have been used by several investigators to refer to the process of recording ECGs with an extended bandwidth of up to 1000 Hz. Several investigators have tried to analyze HF-QRS with the hope that additional features seen in the QRS complex would provide information enhancing the diagnostic value of the ECG. The development of computerized ECG-recording devices that made it possible to record ECG signals with high resolution in both time and amplitude, as well as better possibilities to store and process the signals digitally, offered new methods for analysis. Different techniques to extract the HF-QRS have been described. Several bandwidths and filter types have been applied for the extraction as well as different signal-averaging techniques for noise reduction. There is no standard method for acquiring and quantifying HF-QRS. The physiological mechanisms underlying HF-QRS are still not fully understood. One theory is that HF-QRS are related to the conduction velocity and the fragmentation of the depolarization wave in the myocardium. In a three-dimensional model of the ventricles with a fractal conduction system it was shown that high numbers of splitting branches are associated with HF-QRS. In this experiment, it was also shown that the changes seen in HF-QRS in patients with myocardial ischemia might be due to the slowing of the conduction velocity in the region of ischemia. This mechanism has been tested by Watanabe et al by infusing sodium channel blockers into the left anterior descending artery in dogs. In their study, 60 unipolar ECGs were recorded from the entire

  10. Radio Induced Fluorescence (RIF) Imaging Of E-region Quasi-periodic Structures

    NASA Astrophysics Data System (ADS)

    Bernhardt, P. A.

    The horizontal structure of sporadic-E layers has been imaged using artificial airglow excited by high power radio waves. In January 1998, the HF facility at Arecibo, Puerto Rico beamed a 80 MW signal upward at 3.175 MHz. The beam reflected in the E- region near 120 km altitude to excite green-line emissions at 557.7 nm. Ground based images showed quasi-periodic structures with periods near 2 and 10 km. These struc- tures been interpreted as being produced by Kelvin-Helmholtz (K-H) instabilities in the neutral atmosphere. The excitation of radio induced fluorescence (RIF) emissions has been studied with both one-dimensional and two-dimensional computer simulations of the conversion of electromagnetic waves into electron plasma waves. The steep gradients on the bottomside of the E-layer provide conditions for efficient mode conversion. The re- sulting Langmuir waves accelerate electrons to energies between 2 and 10 eV. These suprathermal electrons collide with oxygen atoms to produce green-line emissions. The optical glow only occurs in the parts of the E-region where the plamsa is dense enough to reflect the 3.175 MHz radio waves. Results of the E-layer observations using the RIF technique have shown horizontal stuctures that are most likely produced by the K-H instability. A numerical model has been generated to demonstrate the effects of neutral wind shears on the E-region structures. The model includes the effects of both speed-shear and turning shear dy- namics. The results of the numerical model are used to suggest future research using high-power radio wave to study the ion dynamics of the lower thermosphere.

  11. Coupled orbital angular momentum conversions in a quasi-periodically poled LiTaO_3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Xinyuan; Yang, Guang; Wei, Dunzhao; Wei, Dan; Ni, Rui; Ji, Wei; Zhang, Yong; Hu, Xiaopeng; Hu, Wei; Lu, Y. Q.; Zhu, S. N.; Xiao, Min

    2016-03-01

    We experimentally demonstrate the orbital angular momentum (OAM) conversion by the coupled nonlinear optical processes in a quasi-periodically poled LiTaO3 crystal. In such crystal, third-harmonic generation (THG) is realized by the coupled second-harmonic generation (SHG) and sum-frequency generation (SFG) processes, i.e., SHG is dependent on SFG and vice versa. The OAMs of the interacting waves are proved to be conserved in such coupled nonlinear optical processes. As increasing the input OAM in the experiment, the conversion efficiency decreases because of the reduced fundamental power intensity. Our results provide better understanding for the OAM conversions, which can be used to efficiently produce an optical OAM state at a short wavelength.

  12. Discovery of kHz Quasi-periodic Oscillations in the Z Source Cygnus X-2

    NASA Astrophysics Data System (ADS)

    Wijnands, Rudy; Homan, Jeroen; van der Klis, Michiel; Kuulkers, Erik; van Paradijs, Jan; Lewin, Walter H. G.; Lamb, Frederick K.; Psaltis, Dimitrios; Vaughan, Brian

    1998-02-01

    During observations with the Rossi X-Ray Timing Explorer from 1997 June 31 to July 3 we discovered two simultaneous kHz quasi-periodic oscillations (QPOs) near 500 and 860 Hz in the low-mass X-ray binary and Z source Cygnus X-2. In the X-ray color-color diagram and hardness-intensity diagram (HID), a clear Z track was traced out, which shifted in the HID within 1 day to higher count rates at the end of the observation. Z track shifts are well known to occur in Cyg X-2 our observation for the first time catches the source in the act. A single kHz QPO peak was detected at the left end of the horizontal branch (HB) of the Z track, with a frequency of 731+/-20 Hz and an amplitude of 4.7+0.8-0.6% rms in the energy band 5.0-60 keV. Further to the right on the HB, at somewhat higher count rates, an additional peak at 532+/-43 Hz was detected with an rms amplitude of 3.0+1.0-0.7%. When the source moved down the HB, thus when the inferred mass accretion rate increased, the frequency of the higher frequency QPO increased to 839+/-13 Hz, and its amplitude decreased to 3.5+0.4-0.3% rms. The higher frequency QPO was also detected on the upper normal branch (NB) with an rms amplitude of 1.8+0.6-0.4% and a frequency of 1007+/-15 Hz; its peak width did not show a clear correlation with inferred mass accretion rate. The lower frequency QPO was most of the time undetectable, with typical upper limits of 2% rms; no conclusion on how this QPO behaved with mass accretion rate can be drawn. If the peak separation between the QPOs is the neutron star spin frequency (as required in some beat-frequency models), then the neutron star spin period is 2.9+/-0.2 ms (346+/-29 Hz). This discovery makes Cyg X-2 the fourth Z source that displays kHz QPOs. The properties of the kHz QPOs in Cyg X-2 are similar to those of other Z sources. Simultaneous with the kHz QPOs, the well-known horizontal-branch QPOs (HBOs) were visible in the power spectra. At the left end of the HB, the second harmonic of

  13. Quasi-periodic injections of relativistic electrons in Saturn's outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Roussos, E.; Krupp, N.; Mitchell, D. G.; Paranicas, C.; Krimigis, S. M.; Andriopoulou, M.; Palmaerts, B.; Kurth, W. S.; Badman, S. V.; Masters, A.; Dougherty, M. K.

    2016-01-01

    Quasi-periodic, short-period injections of relativistic electrons have been observed in both Jupiter's and Saturn's magnetospheres, but understanding their origin or significance has been challenging, primarily due to the limited number of in-situ observations of such events by past flyby missions. Here we present the first survey of such injections in an outer planetary magnetosphere using almost nine years of energetic charged particle and magnetic field measurements at Saturn. We focus on events with a characteristic period of about 60-70 min (QP60, where QP stands for quasi-periodic). We find that the majority of QP60, which are very common in the outer magnetosphere, map outside Titan's orbit. QP60 are also observed over a very wide range of local times and latitudes. A local time asymmetry in their distribution is the most striking feature, with QP60 at dusk being between 5 and 25 times more frequent than at dawn. Field-line tracing and pitch angle distributions suggest that most events at dusk reside on closed field lines. They are distributed either near the magnetopause, or, in the case of the post-dusk (or pre-midnight) sector, up to about 30 RS inside it, along an area extending parallel to the dawn-dusk direction. QP60 at dawn map either on open field lines and/or near the magnetopause. Both the asymmetries and varying mapping characteristics as a function of local time indicate that generation of QP60 cannot be assigned to a single process. The locations of QP60 seem to trace sites that reconnection is expected to take place. In that respect, the subset of events observed post-dusk and deep inside the magnetopause may be directly or indirectly linked to the Vasyliunas reconnection cycle, while magnetopause reconnection/Kelvin-Helmholtz (KH) instability could be invoked to explain all other events at the duskside. Using similar arguments, injections at the dawnside magnetosphere may result from solar-wind induced storms and/or magnetopause reconnection

  14. B-Field Determination from Magnetoacoustic Oscillations in Kilohertz Quasi-periodic Oscillation Neutron Star Binaries: Theory and Observations

    NASA Astrophysics Data System (ADS)

    Titarchuk, L. G.; Bradshaw, C. F.; Wood, K. S.

    2001-10-01

    We present a method for determining the B-field around neutron stars based on observed kilohertz and viscous quasi-periodic oscillation (QPO) frequencies used in combination with the best-fit optical depth and temperature of a Comptonization model. In the framework of the transition layer QPO model, we analyze the magnetoacoustic wave (MAW) formation in the layer between a neutron star surface and the inner edge of a Keplerian disk. We derive formulas for the MAW frequencies for different regimes of radial transition layer oscillations. We demonstrate that our model can use the QPO as a new kind of probe to determine the magnetic field strengths for 4U 1728-42, GX 340+0, and Scorpius X-1 in the zone where the QPOs occur. Observations indicate that the dependence of the viscous frequency on the Keplerian frequency is closely related to the inferred dependence of the MAW frequency on the Keplerian frequency for a dipole magnetic field. The MAW dependence is based on a single parameter, the magnetic moment of the star as estimated from the field strength in the transition layer. The best-fit magnetic moment parameter is about (0.5-1)×1025 G cm3 for all studied sources. From observational data, the magnetic fields within distances less than 20 km from the neutron star for all three sources are strongly constrained to be dipole fields with the strengths of 107-108 G on the neutron star surface.

  15. Quasi Periodic Oscillations in X-ray Neutron Star and Probes of Perihelion Precession of General Relativity

    NASA Astrophysics Data System (ADS)

    Zhang, C. M.; Dolgov, A.

    We ascribe the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the pseudo-Newtonian Keplerian frequency and the apogee and perigee precession frequency of the same matter in the inner disk, and ascribe 15-60 ,Hz QPO (HBO) to the apogee (or perigee) precession and its second harmonic frequency to both apogee and perigee precession in the outer disk boundary of the neutron star (NS) magnetosphere. The radii of the inner and outer disks are correlated each other by a factor of two is assumed. The obtained conclusions include: all QPO frequencies increase and frequency difference of twin kHz QPOs decreases with increasing the accretion rate. The obtained theoretical relations between HBO frequency and twin kHz QPOs are simlilar to the measured empirical formula. Further, the theo-retical formula to calculate the NS mass by the twin kHz QPOs is proposed, and the resultant values are in the range of 1.4 to 1.8 Msolar. QPOs from LMXBs likely provide an accurate laboratory for a strong gravitational field, by which a new method to determine the NS masses of LMXBs is suggested.

  16. High-Frequency Gated Oscillator

    NASA Technical Reports Server (NTRS)

    Berard, C. A.

    1982-01-01

    New gated oscillator generates bursts of high-frequency sine waves, square waves, and triangular waves in response to control signals. Each burst starts at zero phase, with tight tolerances on signal amplitude and frequency. Frequencies in megahertz range are made possible by using high-speed comparators and high-speed flip-flop as fast-response threshold detector.

  17. The re-analysis of quasi-periodic oscillation of the blazar J1359+4011

    NASA Astrophysics Data System (ADS)

    Wang, Hongtao; Su, Yanping

    2016-05-01

    J1359+4011 is a flat spectral radio quasar monitored by the Owens Valley Radio Observatory 40 m radio telescope since 2008. The light curve of J1359+4011 in 15 GHz shows a possible quasi-periodic behavior by visual inspection. In order to confirm this quasi-periodic behavior, we utilize two classical methods: structure function method and discrete correlation function method, to investigate the possible time-scale of oscillation in the time series of J1359+4011. The analytical result shows a possible time-scale of oscillation of 120-130 days. The instabilities in the accretion flow could be a possible explanation for the modulation of the light curve; and global p-mode oscillations in a thick disc could be another possible reason for this behavior.

  18. Quasi-periodic oscillations in accreting magnetic white dwarfs. I. Observational constraints in X-ray and optical

    NASA Astrophysics Data System (ADS)

    Bonnet-Bidaud, J. M.; Mouchet, M.; Busschaert, C.; Falize, E.; Michaut, C.

    2015-07-01

    Quasi-periodic oscillations (QPOs) are observed in the optical flux of some polars with typical periods of 1 to 3 s but none have been observed yet in X-rays where a significant part of the accreting energy is released. QPOs are expected and predicted from shock oscillations. Most of the polars have been observed by the XMM-Newton satellite. We made use of the homogeneous set of observations of the polars by XMM-Newton to search for the presence of QPOs in the (0.5-10 keV) energy range and to set significant upper limits for the brightest X-ray polars. We extracted high time-resolution X-ray light curves by taking advantage of the 0.07 s resolution of the EPIC-PN camera. Among the 65 polars observed with XMM-Newton from 1998 to 2012, a sample of 24 sources was selected on the basis of their counting rate in the PN instrument to secure significant limits. We searched for QPOs using Fast Fourier Transform (FFT) methods and defined limits of detection using statistical tools. Among the sample surveyed, none shows QPOs at a significant level. Upper limits to the fractional flux in QPOs range from 7% to 71%. These negative results are compared to the detailed theoretical predictions of numerical simulations based on a 2D hydrodynamical code presented in Paper II. Cooling instabilities in the accretion column are expected to produce shock quasi-oscillations with a maximum amplitude reaching ~40% in the bremsstrahlung (0.5-10 keV) X-ray emission and ~20% in the optical cyclotron emission. The absence of X-ray QPOs imposes an upper limit of ~(5-10) g cm-2 s-1 on the specific accretion rate but this condition is found inconsistent with the value required to account for the amplitudes and frequencies of the observed optical QPOs. This contradiction outlines probable shortcomings with the shock instability model. Figures 1-3 are available in electronic form at http://www.aanda.org

  19. Discovery of Submillisecond Quasi-periodic Oscillations in the X-Ray Flux of Scorpius X-1

    NASA Astrophysics Data System (ADS)

    van der Klis, M.; Swank, J. H.; Zhang, W.; Jahoda, K.; Morgan, E. H.; Lewin, W. H. G.; Vaughan, B.; van Paradijs, J.

    1996-09-01

    We report the discovery, with NASA's Rossi X-Ray Timing Explorer (RXTE), of the first submillisecond oscillations found in a celestial X-ray source. The quasi-periodic oscillations (QPOs) come from Sco X-1 and have a frequency of ~1100 Hz and amplitudes of 0.6%--1.2% (rms) and are relatively coherent, with Q up to ~102. The frequency of the QPOs increases with accretion rate, rising from 1050 to 1130 Hz when the source moves from top to bottom along the normal branch in the X-ray color-color diagram, and shows a strong, approximately linear correlation with the frequency of the well-known 6--20 Hz normal/flaring-branch QPOs. We also report the discovery of QPOs with a frequency near 800 Hz that occur, simultaneously with the 1100 Hz QPOs, in the upper normal branch. We discuss several possible interpretations, one involving a millisecond X-ray pulsar whose pulses we see reflected off accretion flow inhomogeneities. Finally, we report the discovery of ~45 Hz QPOs, most prominent in the middle of the normal branch, which might be magnetospheric beat-frequency QPOs.

  20. Quasi-periodic variations in the Doppler shift of HF signals scattered by artificial ionospheric turbulence

    SciTech Connect

    Belenov, A.F.; Ponomarenko, P.V.; Sinitsyn, V.G.; Yampol`skii, Yu.M.

    1994-06-01

    The results of an experimental study of quasi-periodic variations of the Doppler shift (DS) of decimeter-wave signals scattered by artificial ionospheric turbulence are presented. It is suggested that ionospheric MHD waves of natural origin are a possible cause of such variations. The amplitude of the magnetic component of such waves that leads to observable values of DS variations is estimated to be 1{gamma}.

  1. Carleman linearization and normal forms for differential systems with quasi-periodic coefficients.

    PubMed

    Chermnykh, Sergey V

    2016-01-01

    We study the matrix representation of Poincaré normalization using the Carleman linearization technique for non-autonomous differential systems with quasi-periodic coefficients. We provide a rigorous proof of the validity of the matrix representation of the normalization and obtain a recursive algorithm for computing the normalizing transformation and the normal form of the differential systems. The algorithm provides explicit formulas for the coefficients of the normal form and the corresponding transformation. PMID:27588240

  2. Quasi-periodic variations in the Doppler shift of HF signals scattered by artificial ionospheric turbulence

    NASA Astrophysics Data System (ADS)

    Belenov, A. F.; Ponomarenko, P. V.; Sinitsyn, V. G.; Yampol'Skii, Yu. M.

    1993-12-01

    The results of an experimental study of quasi-periodic variations of the Doppler shift (DS) of decimeter-wave signals scattered by artificial ionospheric turbulence are presented. It is suggested that ionospheric MHD waves of natural origin are a possible cause of such variations. The amplitude of the magnetic component of such waves that leads to observable values of DS variations is estimated to be 1γ.

  3. Talbot interferometry with curved quasi-periodic gratings: towards large field of view X-ray phase-contrast imaging.

    PubMed

    Sun, Yangyang; Cong, Wenxiang; Xi, Yan; Wang, Ge; Pang, Shuo

    2015-10-01

    X-ray phase-contrast imaging based on grating interferometry has become a common method due to its superior contrast in biological soft tissue imaging. The high sensitivity relies on the high-aspect ratio structures of the planar gratings, which prohibit the large field of view applications with a diverging X-ray source. Curved gratings allow a high X-ray flux for a wider angular range, but the interference fringes are only visible within ~10° range due to the geometrical mismatch with the commonly used flat array detectors. In this paper, we propose a design using a curved quasi-periodic grating for large field of view imaging with a flat detector array. Our scheme is numerically verified in the X-ray regime and experimentally verified in the visible optical regime. The interference fringe pattern is observed over 25°, with less than 10% of decrease in visibility in our experiments. PMID:26480170

  4. Testing the Transition Layer Model of Quasi-periodic Oscillations in Neutron Star X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Wu, Xue-Bing

    2001-05-01

    We compare the theoretical predictions of the transition layer model with some observational features of quasi-periodic oscillations (QPOs) in neutron star X-ray binaries. We found that the correlation between horizontal branch oscillation (HBO) frequencies and kilohertz (kHz) QPO frequencies, the difference between the low-frequency QPOs in atoll sources and HBOs in Z sources, and the correlation between the frequencies of low-frequency QPOs and break frequencies can be well explained by the transition layer model, provided the neutron star mass is around 1.4 Msolar and the angle between magnetosphere equator and accretion disk plane is around 6°. The observed decrease of peak separation between the two kHz QPO frequencies with the increase of the kHz QPO frequencies and the increase of QPO frequencies with the increase of inferred mass accretion rate are also consistent with the theoretical predictions of the transition layer model. In addition, we derive a simple equation that can be adopted to estimate the angle (δ) between magnetosphere equator and accretion disk plane by use of the simultaneously observed QPO frequency data. We estimate this angle, in the range of 4°-8°, for five Z sources and two atoll sources. The nearly constant δ value for each source, derived from the different sets of simultaneously observed QPO frequency data, provides a strong test of the theoretical model. Finally, we suggest that similar transition layer oscillations may be responsible for the observed QPOs in accretion-powered millisecond X-ray pulsars and Galactic black hole candidates.

  5. Explicit error bounds for the α-quasi-periodic Helmholtz problem.

    PubMed

    Lord, Natacha H; Mulholland, Anthony J

    2013-10-01

    This paper considers a finite element approach to modeling electromagnetic waves in a periodic diffraction grating. In particular, an a priori error estimate associated with the α-quasi-periodic transformation is derived. This involves the solution of the associated Helmholtz problem being written as a product of e(iαx) and an unknown function called the α-quasi-periodic solution. To begin with, the well-posedness of the continuous problem is examined using a variational formulation. The problem is then discretized, and a rigorous a priori error estimate, which guarantees the uniqueness of this approximate solution, is derived. In previous studies, the continuity of the Dirichlet-to-Neumann map has simply been assumed and the dependency of the regularity constant on the system parameters, such as the wavenumber, has not been shown. To address this deficiency, in this paper an explicit dependence on the wavenumber and the degree of the polynomial basis in the a priori error estimate is obtained. Since the finite element method is well known for dealing with any geometries, comparison of numerical results obtained using the α-quasi-periodic transformation with a lattice sum technique is then presented. PMID:24322866

  6. Paleocene sea level movements with a 430,000 year quasi-periodic cyclicity

    SciTech Connect

    Briskin, M. ); Fluegeman, R. )

    1990-04-01

    Sea level movements with quasi-periodicity of 430,000 years are identified in the marine sedimentary units of the Eastern Gulf Coastal Plain of Mississippi, Alabama and Georgia which represent a 5.8 million year record of strandline displacement during Paleocene time. Principal component analysis of the benthic foraminiferal fauna yielded six assemblages which when combined with two other qualitatively derived assemblages provided paleoecologic information which clearly reflects the influence of paleocirculation and paleoclimatic regime of the Eastern Gulf Coastal Plain. The presence of the planktonic foraminiferal taxa Subbotina trinidadensis and Planorotalites pseudomenardii as well as paleolatitudes ranging from 15{degree} N (for the Campeche Shelf) to 25{degree} N (for the Coastal Plain) emphasizes a paleoclimatic regime which is dominantly tropical. A paleoceanographic model was derived which suggests that normal marine waters were brought into the Gulf of Mexico by two major currents. Strandline displacements are related to transgressive and regressive sea level movements in an ice free Paleocene world. The well delineated 430,000 year quasi-periodic cycle observed in the sea level curve is identified as being astronomical in character. These results support the view that changes in the Earth's orbit may trigger changes in the geometry of the Earth's surface in a way which causes sea level to oscillate with a quasi-periodicity of 430,000 years.

  7. Detection of a Possible X-Ray Quasi-periodic Oscillation in the Active Galactic Nucleus 1H 0707-495

    NASA Astrophysics Data System (ADS)

    Pan, Hai-Wu; Yuan, Weimin; Yao, Su; Zhou, Xin-Lin; Liu, Bifang; Zhou, Hongyan; Zhang, Shuang-Nan

    2016-03-01

    The quasi-periodic oscillation (QPO) detected in the X-ray radiation of black hole X-ray binaries (BHXBs) is thought to originate from dynamical processes in close vicinity of black holes (BHs), and thus carries important physical information therein. Such a feature is extremely rare in active galactic nuclei (AGNs) with supermassive BHs. Here we report on the detection of a possible X-ray QPO signal with a period of 3800 s at a confidence level >99.99% in the narrow-line Seyfert 1 galaxy (NLS1) 1H 0707-495 in one data set in 0.2-10 keV taken with XMM-Newton. The statistical significance is higher than that of most previously reported QPOs in AGNs. The QPO is highly coherent (quality factor Q=ν /{{Δ }}ν ≥slant 15) with a high rms fractional variability (˜15%). A comprehensive analysis of the optical spectra of this AGN is also performed, yielding a central BH mass of 5.2 × 106 M⊙ from the broad emission lines based on the scaling relation. The QPO follows the known frequency-BH mass relation closely, which spans from stellar-mass to supermassive BHs. The absence of QPOs in other observations of the object suggests that it is a transient phenomenon. We suggest that the (high-frequency) QPOs tend to occur in highly accreting BH systems, from BHXBs to supermassive BHs. Future precise estimation of the BH mass may be used to infer the BH spin from the QPO frequency.

  8. Dependence of Kilohertz Quasi-periodic Oscillation Properties on the Normal-Branch Oscillation Phase in Scorpius X-1

    NASA Astrophysics Data System (ADS)

    Yu, Wenfei; van der Klis, Michiel; Jonker, Peter G.

    2001-09-01

    We analyzed Rossi X-Ray Timing Explorer data of Scorpius X-1, which show kilohertz quasi-periodic oscillations (QPOs) and the ~6-8 Hz normal-branch oscillation (NBO) simultaneously. Using power spectra of 0.03-0.5 s data segments, we find that both the upper kilohertz QPO frequency ν2 and the ratio of lower to upper kilohertz QPO amplitude are anticorrelated to variations in the X-ray count rate taking place on the NBO timescale. The frequency dependence is similar to (but probably weaker than) that found on longer timescales, but the power ratio dependence is opposite to it. A model where radiative stresses on the disk material, modulated at the NBO frequency, lead to changes in ν2 can explain the data; this implies that some of the NBO flux changes originate from inside the inner disk radius. We discuss how these findings affect our understanding of kilohertz QPOs and of the low-frequency variability of low-mass X-ray binaries.

  9. Electronic Circuit Experiments and SPICE Simulation of Double Covering Bifurcation of 2-Torus Quasi-Periodic Flow in Phase-Locked Loop Circuit

    NASA Astrophysics Data System (ADS)

    Kamiyama, Kyohei; Endo, Tetsuro; Imai, Isao; Komuro, Motomasa

    2016-06-01

    Double covering (DC) bifurcation of a 2-torus quasi-periodic flow in a phase-locked loop circuit was experimentally investigated using an electronic circuit and via SPICE simulation; in the circuit, the input radio-frequency signal was frequency modulated by the sum of two asynchronous sinusoidal baseband signals. We observed both DC and period-doubling bifurcations of a discrete map on two Poincaré sections, which were realized by changing the sample timing from one baseband sinusoidal signal to the other. The results confirm the DC bifurcation of the original flow.

  10. Compton cooling and the signature of Quasi Periodic Oscillations for the transient black hole candidate H 1743-322

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Chakrabarti, S. K.; Debnath, D.; Jana, A.; Molla, A. A.

    In black hole accretion cooling of the Compton cloud has an enormous effect on the dynamics of post-shock flow. We demonstrate that the Compton cooling is highly responsible for the origin of Quasi Periodic Oscillations (QPOs) during the outburst time of the galactic black hole candidates (BHCs). Our study shows that the disk oscillation will take place when infall time from the shock roughly agrees with cooling time in the post-shock region i.e., the resonance condition. We believe that this oscillation is responsible for the origin of QPOs and will occur only when a particular disk condition (disk rate, halo rate and shock strength) satisfies. We also confirm that shock moves with an average velocity of a few meters/sec for the transient BHC H1743-322 due to the presence of Compton cooling.

  11. A 200-Second Quasi-Periodicity After the Tidal Disruption of a Star by a Dormant Black Hole

    NASA Technical Reports Server (NTRS)

    Reis, R. C.; Miller, J. M.; Reynolds, M. T.; Gueltkinm K.; Maitra, D.; King, A. L.; Strohmayer, T.

    2012-01-01

    Supermassive black holes are known to exist at the center of most galaxies with sufficient stellar mass, In the local Universe, it is possible to infer their properties from the surrounding stars or gas. However, at high redshifts we require active, continuous accretion to infer the presence of the SMBHs, often coming in the form of long term accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt stars orbiting nearby, resulting in bright flares from otherwise quiescent black holes. Here, we report on a approx.200-s X-ray quasi-periodicity around a previously dormant SMBH located in the center of a galaxy at redshift z = 0.3534. This result may open the possibility of probing general relativity beyond our local Universe.

  12. Driver of quasi-periodic modulation of pulsating aurora: Role of cold electron flux and electric field

    NASA Astrophysics Data System (ADS)

    Sato, N.; Kadokura, A.; Tanaka, Y.; Nishiyama, T.

    2013-12-01

    Pulsating auroras are common phenomena, which are observed universally during the recovery phase of substorm in the auroral and subauroral zones. But, even today, generation mechanism of fundamental characteristics of pulsating aurora, such as, their periodicity and shapes are still open to discussion. Simultaneous observations onboard satellites and on the ground are important method to examine such fundamental characteristics of pulsating aurora. In this study we examined some selected pulsating auroral events, which obtained onboard THEMIS spacecraft and the THEMIS ground-based all-sky camera network. THEMIS satellites were located in the post midnight sector near the equatorial plane in the magnetosphere. We found following signatures of particle, field and wave in the magnetosphere at the onset and during pulsating aurora; 1) All pulsating aurora associate with high-energy(>5 keV) electron flux enhancement, 2) There is no evidence to identify a quasi-periodic(QP) modulation of high-energy electron flux, which may be directly corresponding to pulsating aurora observed on the ground, 3) QP modulation of cold electron flux(<10 eV) and electric field often show one-to-one correspondence to QP modulation of ELF wave intensity, both type of electromagnetic lower-band chorus wave and electrostatic ECH(electron cyclotron harmonic) wave, which may be closely relating to visible pulsating aurora observed on the ground, 4) Not all pulsating aurora associate with ELF wave enhancement, 5) Pitch angle distribution of QP modulated cold electrons show field-aligned to ambient magnetic field. In this study we focus on the characteristics of QP modulation of cold electron flux and electric field, which may play the driver of quasi-periodic modulation of pulsating aurora.

  13. Above-the-loop-top Oscillation and Quasi-periodic Coronal Wave Generation in Solar Flares

    NASA Astrophysics Data System (ADS)

    Takasao, Shinsuke; Shibata, Kazunari

    2016-06-01

    Observations revealed that various kinds of oscillations are excited in solar flare regions. Quasi-periodic pulsations (QPPs) in flare emissions are commonly observed in a wide range of wavelengths. Recent observations have found that fast-mode magnetohydrodynamic (MHD) waves are quasi-periodically emitted from some flaring sites (quasi-periodic propagating fast-mode magnetoacoustic waves; QPFs). Both QPPs and QPFs imply a cyclic disturbance originating from the flaring sites. However, the physical mechanisms remain puzzling. By performing a set of two-dimensional MHD simulations of a solar flare, we discovered the local oscillation above the loops filled with evaporated plasma (above-the-loop-top region) and the generation of QPFs from such oscillating regions. Unlike all previous models for QPFs, our model includes essential physics for solar flares such as magnetic reconnection, heat conduction, and chromospheric evaporation. We revealed that QPFs can be spontaneously excited by the above-the-loop-top oscillation. We found that this oscillation is controlled by the backflow of the reconnection outflow. The new model revealed that flare loops and the above-the-loop-top region are full of shocks and waves, which is different from the previous expectations based on a standard flare model and previous simulations. In this paper, we show the QPF generation process based on our new picture of flare loops and will briefly discuss a possible relationship between QPFs and QPPs. Our findings will change the current view of solar flares to a new view in which they are a very dynamic phenomenon full of shocks and waves.

  14. Quasi-periodic solutions to the hierarchy of four-component Toda lattices

    NASA Astrophysics Data System (ADS)

    Wei, Jiao; Geng, Xianguo; Zeng, Xin

    2016-08-01

    Starting from a discrete 3×3 matrix spectral problem, the hierarchy of four-component Toda lattices is derived by using the stationary discrete zero-curvature equation. Resorting to the characteristic polynomial of the Lax matrix for the hierarchy, we introduce a trigonal curve Km-2 of genus m - 2 and present the related Baker-Akhiezer function and meromorphic function on it. Asymptotic expansions for the Baker-Akhiezer function and meromorphic function are given near three infinite points on the trigonal curve, from which explicit quasi-periodic solutions for the hierarchy of four-component Toda lattices are obtained in terms of the Riemann theta function.

  15. Analysis of quasi-periodic pore-network structure of centric marine diatom frustules

    NASA Astrophysics Data System (ADS)

    Cohoon, Gregory A.; Alvarez, Christine E.; Meyers, Keith; Deheyn, Dimitri D.; Hildebrand, Mark; Kieu, Khanh; Norwood, Robert A.

    2015-03-01

    Diatoms are a common type of phytoplankton characterized by their silica exoskeleton known as a frustule. The diatom frustule is composed of two valves and a series of connecting girdle bands. Each diatom species has a unique frustule shape and valves in particular species display an intricate pattern of pores resembling a photonic crystal structure. We used several numerical techniques to analyze the periodic and quasi-periodic valve pore-network structure in diatoms of the Coscinodiscophyceae order. We quantitatively identify defect locations and pore spacing in the valve and use this information to better understand the optical and biological properties of the diatom.

  16. Quasi-periodic Climate Teleconnections via the North Atlantic Oscillation: A New Perspective From Tree Rings

    NASA Astrophysics Data System (ADS)

    Meyers, S. R.; Pagani, M.

    2004-12-01

    Internal modes of climate variability such as the North Atlantic Oscillation (NAO) and the El Nino-Southern Oscillation (ENSO) significantly contribute to regional weather patterns on an inter-annual basis. Changes in the behavior of these modes over decadal and/or centennial timescales may represent an important driver of past climate events and future climate change. Importantly, if the internal modes express band-limited (periodic to quasi-periodic) variability, they provide a useful template for climate forecasting. Unfortunately, our ability to directly quantify the periodic/quasi-periodic nature of climate response to the internal modes is constrained by the limited temporal extent of instrumental records. In this study we present a novel approach toward recognition of band-limited climatic effects of the NAO in proxy records that span the past 400 years. The spatial climatic response of the NAO between northern and southern Europe provides a framework for detecting the influence of the NAO in proxy climate records. Specifically, if the NAO-forced climate signal is present it should be strongly correlated and anti-phased between the northern and southern regions of western Europe. To prospect for the NAO signal in paleoclimate data we employ independent networks of tree ring width series from Scandinavia and the Mediterranean. These locations were selected because modern instrumental records of the NAO and precipitation are significantly correlated in these regions, and tree ring width sensitivity to climate variability is maximized. The tree-ring width data from western Europe reveals a distinct 25-year quasi-periodic synchronization of climate change between Scandinavia and the Mediterranean during the 17th-20th centuries. Based on the dipole character of this signal, we propose that it is representative of climate forcing via the NAO. On this timescale of climate variability, dry/cold climate events in northern Europe are closely tied to wet events in

  17. Quasi-periodic solutions for d-dimensional beam equation with derivative nonlinear perturbation

    SciTech Connect

    Mi, Lufang; Cong, Hongzi

    2015-07-15

    In this paper, we consider the d-dimensional beam equation with convolution potential under periodic boundary conditions. We will apply the Kolmogorov-Arnold-Moser theorem in Eliasson and Kuksin [Ann. Math. 172, 371-435 (2010)] into this system and obtain that for sufficiently small ε, there is a large subset S′ of S such that for all s ∈ S′, the solution u of the unperturbed system persists as a time-quasi-periodic solution which has all Lyapunov exponents equal to zero and whose linearized equation is reducible to constant coefficients.

  18. KHz Quasi Periodic Oscillations in Low Mass X-ray Binaries as Probes of General Relativity in the Strong Field Regime

    NASA Astrophysics Data System (ADS)

    Stella, Luigi; Vietri, Mario

    1998-12-01

    The pair of kHz Quasi Periodic Oscillations (QPOs) in the Fourier spectra of two low mass X-ray binaries, Sco X-1 and 4U1608-52, hosting an old accreting neutron star, display a frequency difference that decreaseas for increasing QPO frequency. This is contrary to simple beat frequency models, which predict a constant frequency difference. We show that the behaviour of these QPOs is well matched in terms of the fundamental (radial and azimuthal) frequencies for test particle motion in the vicinity the neutron star, for reasonable star masses, and nearly independent of the star spin. The radial frequency must be much smaller than the azimuthal one, testifying that kHz QPOs originate from close to the innermost stable orbit. These results are not reproduced through the post-Newtonian approximation of General Relativity (GR). kHz QPOs from X-ray binaries likely provide an accurate laboratory for strong field GR.

  19. High frequency nanotube oscillator

    DOEpatents

    Peng, Haibing; Zettl, Alexander K.

    2012-02-21

    A tunable nanostructure such as a nanotube is used to make an electromechanical oscillator. The mechanically oscillating nanotube can be provided with inertial clamps in the form of metal beads. The metal beads serve to clamp the nanotube so that the fundamental resonance frequency is in the microwave range, i.e., greater than at least 1 GHz, and up to 4 GHz and beyond. An electric current can be run through the nanotube to cause the metal beads to move along the nanotube and changing the length of the intervening nanotube segments. The oscillator can operate at ambient temperature and in air without significant loss of resonance quality. The nanotube is can be fabricated in a semiconductor style process and the device can be provided with source, drain, and gate electrodes, which may be connected to appropriate circuitry for driving and measuring the oscillation. Novel driving and measuring circuits are also disclosed.

  20. Tracking the evolution of quasi-periodic oscillation in RE J1034+396 using the Hilbert-Huang transform

    SciTech Connect

    Hu, Chin-Ping; Chou, Yi; Yang, Ting-Chang; Su, Yi-Hao E-mail: yichou@astro.ncu.edu.tw

    2014-06-10

    RE J1034+396, a narrow-line Seyfert 1 active galactic nucleus (AGN), is the first example of AGNs that exhibited a nearly coherent quasi-periodic oscillation (QPO) for the data collected by XMM-Newton in 2007. The spectral behaviors and timing properties of the QPO have been studied since its discovery. We present an analysis of the QPO in RE J1034+396 based on the Hilbert-Huang transform. Comparing with other time-frequency analysis methods, the Hilbert spectrum reveals the variation of the QPO period in great detail. Furthermore, the empirical mode decomposition provides bandpass-filtered data that can be used in the O – C and correlation analysis. We suggest that it is better to divide the evolution of the QPO in this observation into three epochs according to their different periodicities. In addition to the periodicities, the correlations between the QPO periods and corresponding mean count rates are also different in these three epochs. Further examining the phase lags in these epochs, we found no significant phase lags between the soft and hard X-ray bands, which is also confirmed in the QPO phase-resolved spectral analysis. Finally, we discuss the indications of current models including a spotted accretion disk, diskoseismology, and oscillation of shock according to the observed time-frequency and spectral behaviors.

  1. DISCOVERY OF A 7 mHz X-RAY QUASI-PERIODIC OSCILLATION FROM THE MOST MASSIVE STELLAR-MASS BLACK HOLE IC 10 X-1

    SciTech Connect

    Pasham, Dheeraj R.; Mushotzky, Richard F.; Strohmayer, Tod E. E-mail: richard@astro.umd.edu

    2013-07-10

    We report the discovery with XMM-Newton of an Almost-Equal-To 7 mHz X-ray (0.3-10.0 keV) quasi-periodic oscillation (QPO) from the eclipsing, high-inclination black hole binary IC 10 X-1. The QPO is significant at >4.33{sigma} confidence level and has a fractional amplitude (% rms) and a quality factor, Q {identical_to} {nu}/{Delta}{nu}, of Almost-Equal-To 11 and 4, respectively. The overall X-ray (0.3-10.0 keV) power spectrum in the frequency range 0.0001-0.1 Hz can be described by a power-law with an index of Almost-Equal-To - 2, and a QPO at 7 mHz. At frequencies {approx}>0.02 Hz there is no evidence for significant variability. The fractional amplitude (rms) of the QPO is roughly energy-independent in the energy range of 0.3-1.5 keV. Above 1.5 keV the low signal-to-noise ratio of the data does not allow us to detect the QPO. By directly comparing these properties with the wide range of QPOs currently known from accreting black hole and neutron stars, we suggest that the 7 mHz QPO of IC 10 X-1 may be linked to one of the following three categories of QPOs: (1) the 'heartbeat' mHz QPOs of the black hole sources GRS 1915+105 and IGR J17091-3624, or (2) the 0.6-2.4 Hz 'dipper QPOs' of high-inclination neutron star systems, or (3) the mHz QPOs of Cygnus X-3.

  2. Discovery of a 7 mHz X-Ray Quasi-Periodic Oscillation from the Most Massive Stellar-Mass Black Hole IC 10 X-1

    NASA Technical Reports Server (NTRS)

    Pasham, Dheeraj R.; Strohmayer, Tod E.; Mushotzky, Richard F.

    2013-01-01

    We report the discovery with XMM-Newton of an approx.. = 7 mHz X-ray (0.3-10.0 keV) quasi-periodic oscillation (QPO) from the eclipsing, high-inclination black hole binary IC 10 X-1. The QPO is significant at >4.33 sigma confidence level and has a fractional amplitude (% rms) and a quality factor, Q is identical with nu/delta nu, of approx. = 11 and 4, respectively. The overall X-ray (0.3-10.0 keV) power spectrum in the frequency range 0.0001-0.1 Hz can be described by a power-law with an index of approx. = -2, and a QPO at 7 mHz. At frequencies approx. > 0.02 Hz there is no evidence for significant variability. The fractional amplitude (rms) of the QPO is roughly energy-independent in the energy range of 0.3-1.5 keV. Above 1.5 keV the low signal-to-noise ratio of the data does not allow us to detect the QPO. By directly comparing these properties with the wide range of QPOs currently known from accreting black hole and neutron stars, we suggest that the 7 mHz QPO of IC 10 X-1 may be linked to one of the following three categories of QPOs: (1) the "heartbeat" mHz QPOs of the black hole sources GRS 1915+105 and IGR J17091-3624, or (2) the 0.6-2.4 Hz "dipper QPOs" of high-inclination neutron star systems, or (3) the mHz QPOs of Cygnus X-3.

  3. Source of Quasi-Periodic Brightenings of Solar Coronal Bright Points: Waves or Repeated Reconnections

    NASA Astrophysics Data System (ADS)

    Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar

    2016-07-01

    Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.

  4. On the self-averaging of dispersion for transport in quasi-periodic random media

    NASA Astrophysics Data System (ADS)

    Eberhard, J. P.; Suciu, N.; Vamos, C.

    2007-01-01

    In this study we present a numerical analysis for the self-averaging of the longitudinal dispersion coefficient for transport in heterogeneous media. This is done by investigating the mean-square sample-to-sample fluctuations of the dispersion for finite times and finite numbers of modes for a random field using analytical arguments as well as numerical simulations. We consider transport of point-like injections in a quasi-periodic random field with a Gaussian correlation function. In particular, we focus on the asymptotic and pre-asymptotic behaviour of the fluctuations with the aid of a probability density function for the dispersion, and we verify the logarithmic growth of the sample-to-sample fluctuations as earlier reported in Eberhard (2004 J. Phys. A: Math. Gen. 37 2549-71). We also comment on the choice of the relevant parameters to generate quasi-periodic realizations with respect to the self-averaging of transport in statistically homogeneous Gaussian velocity fields.

  5. Stochastic Transients as a Source of Quasi-periodic Processes in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Yuan, Ding; Su, Jiangtao; Jiao, Fangran; Walsh, Robert W.

    2016-06-01

    Solar dynamics and turbulence occur at all heights of the solar atmosphere and could be described as stochastic processes. We propose that finite-lifetime transients recurring at a certain place could trigger quasi-periodic processes in the associated structures. In this study, we developed a mathematical model for finite-lifetime and randomly occurring transients, and found that quasi-periodic processes with periods longer than the timescale of the transients, are detectable intrinsically in the form of trains. We simulate their propagation in an empirical solar atmospheric model with chromosphere, transition region, and corona. We found that, due to the filtering effect of the chromospheric cavity, only the resonance period of the acoustic resonator is able to propagate to the upper atmosphere; such a scenario is applicable to slow magnetoacoustic waves in sunspots and active regions. If the thermal structure of the atmosphere is less wild and acoustic resonance does not take place, the long-period oscillations could propagate to the upper atmosphere. Such a case would be more likely to occur in polar plumes.

  6. Investigating the Connection between Quasi Periodic Oscillations and Spectral Components with NuSTAR Data of GRS 1915+105

    NASA Astrophysics Data System (ADS)

    Rao Jassal, Anjali; Vadawale, Santosh V.; Mithun, N. P. S.; Misra, Ranjeev

    2016-01-01

    Low-frequency quasi-periodic oscillations (QPOs) are commonly observed during the hard states of black hole binaries. Several studies have established various observational/empirical correlations between spectral parameters and QPO properties, indicating a close link between the two. However, the exact mechanism of generation of QPOs is not yet well understood. In this paper, we present our attempts to comprehend the connection between the spectral components and the low-frequency QPO (LFQPO) observed in GRS 1915+105 using the data from NuSTAR. Detailed spectral modeling as well as the presence of the LFQPO and its energy dependence during this observation have been reported by Miller et al. and Zhang et al., respectively. We investigate the compatibility of the spectral model and the energy dependence of the QPO by simulating light curves in various energy bands for small variation of the spectral parameters. The basic concept here is to establish the connection, if any, between the QPO and the variation of either a spectral component or a specific parameter, which in turn can shed some light on the origin of the QPO. We begin with the best-fit spectral model of Miller et al. and simulate the light curve by varying the spectral parameters at frequencies close to the observed QPO frequency in order to generate the simulated QPO. Furthermore we simulate similar light curves in various energy bands in order to reproduce the observed energy dependence of the rms amplitude of the QPO. We find that the observed trend of increasing rms amplitude with energy can be reproduced qualitatively if the spectral index is assumed to be varying with the phases of the QPO. Variation of any other spectral parameter does not reproduce the observed energy dependence.

  7. Quasi-periodic oscillations in short recurring bursts of the soft gamma repeater J1550–5418

    SciTech Connect

    Huppenkothen, D.; D'Angelo, C.; Watts, A. L.; Heil, L.; Van der Klis, M.; Van der Horst, A. J.; Kouveliotou, C.; Baring, M. G.; Göğüş, E.; Kaneko, Y.; Granot, J.; Lin, L.; Von Kienlin, A.; Younes, G.

    2014-06-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. The scarcity of giant flares makes a search for QPOs in the shorter, far more numerous bursts from soft gamma repeaters (SGRs) desirable. In Huppenkothen et al., we developed a Bayesian method for searching for QPOs in short magnetar bursts, taking into account the effects of the complicated burst structure, and have shown its feasibility on a small sample of bursts. Here we apply the same method to a much larger sample from a burst storm of 286 bursts from SGR J1550–5418. We report a candidate signal at 260 Hz in a search of the individual bursts, which is fairly broad. We also find two QPOs at ∼93 Hz, and one at 127 Hz, when averaging periodograms from a number of bursts in individual triggers, at frequencies close to QPOs previously observed in magnetar giant flares. Finally, for the first time, we explore the overall burst variability in the sample and report a weak anti-correlation between the power-law index of the broadband model characterizing aperiodic burst variability and the burst duration: shorter bursts have steeper power-law indices than longer bursts. This indicates that longer bursts vary over a broader range of timescales and are not simply longer versions of the short bursts.

  8. Quasi-periodic Oscillations in Short Recurring Bursts of the Soft Gamma Repeater J1550-5418

    NASA Astrophysics Data System (ADS)

    Huppenkothen, D.; D'Angelo, C.; Watts, A. L.; Heil, L.; van der Klis, M.; van der Horst, A. J.; Kouveliotou, C.; Baring, M. G.; Göğüş, E.; Granot, J.; Kaneko, Y.; Lin, L.; von Kienlin, A.; Younes, G.

    2014-06-01

    The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. The scarcity of giant flares makes a search for QPOs in the shorter, far more numerous bursts from soft gamma repeaters (SGRs) desirable. In Huppenkothen et al., we developed a Bayesian method for searching for QPOs in short magnetar bursts, taking into account the effects of the complicated burst structure, and have shown its feasibility on a small sample of bursts. Here we apply the same method to a much larger sample from a burst storm of 286 bursts from SGR J1550-5418. We report a candidate signal at 260 Hz in a search of the individual bursts, which is fairly broad. We also find two QPOs at ~93 Hz, and one at 127 Hz, when averaging periodograms from a number of bursts in individual triggers, at frequencies close to QPOs previously observed in magnetar giant flares. Finally, for the first time, we explore the overall burst variability in the sample and report a weak anti-correlation between the power-law index of the broadband model characterizing aperiodic burst variability and the burst duration: shorter bursts have steeper power-law indices than longer bursts. This indicates that longer bursts vary over a broader range of timescales and are not simply longer versions of the short bursts.

  9. Intermittency and lifetime of the 625 Hz quasi-periodic oscillation in the 2004 hyperflare from the magnetar SGR 1806-20 as evidence for magnetic coupling between the crust and the core

    SciTech Connect

    Huppenkothen, Daniela; Watts, Anna L.; Levin, Yuri

    2014-10-01

    Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR 1806-20 are often interpreted as global magneto-elastic oscillations of the neutron star. There is, however, a large discrepancy between theoretical models, which predict that the highest frequency oscillations should die out rapidly, and the observations, which suggested that the highest-frequency signals persisted for ∼100 s in X-ray data from two different spacecraft. This discrepancy is particularly important for the high-frequency QPO at ∼625 Hz. However, previous analyses did not systematically test whether the signal could also be present in much shorter data segments, more consistent with the theoretical predictions. Here, we test for the presence of the high-frequency QPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both in individual rotational cycles of the neutron star, as well as averaged over multiple successive rotational cycles at the same phase. We find that the QPO in the RXTE data is consistent with being only present in a single cycle, for a short duration of ∼0.5 s, whereas the RHESSI data are as consistent with a short-lived signal that appears and disappears as with a long-lived QPO. Taken together, this data provides evidence for strong magnetic interaction between the crust and the core.

  10. Intermittency and Lifetime of the 625 Hz Quasi-periodic Oscillation in the 2004 Hyperflare from the Magnetar SGR 1806-20 as Evidence for Magnetic Coupling between the Crust and the Core

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela; Watts, Anna L.; Levin, Yuri

    2014-10-01

    Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR 1806-20 are often interpreted as global magneto-elastic oscillations of the neutron star. There is, however, a large discrepancy between theoretical models, which predict that the highest frequency oscillations should die out rapidly, and the observations, which suggested that the highest-frequency signals persisted for ~100 s in X-ray data from two different spacecraft. This discrepancy is particularly important for the high-frequency QPO at ~625 Hz. However, previous analyses did not systematically test whether the signal could also be present in much shorter data segments, more consistent with the theoretical predictions. Here, we test for the presence of the high-frequency QPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both in individual rotational cycles of the neutron star, as well as averaged over multiple successive rotational cycles at the same phase. We find that the QPO in the RXTE data is consistent with being only present in a single cycle, for a short duration of ~0.5 s, whereas the RHESSI data are as consistent with a short-lived signal that appears and disappears as with a long-lived QPO. Taken together, this data provides evidence for strong magnetic interaction between the crust and the core.

  11. A possible imprint of quasi-periodic oscillations in the X-ray spectra of black hole binaries

    NASA Astrophysics Data System (ADS)

    Varniere, P.; Mignon-Risse, R.; Rodriguez, J.

    2016-02-01

    Context. While nobody would deny the presence of quasi-periodic oscillations in the power density spectrum of black hole binaries nor their importance in the understanding of the mechanisms powering the X-ray emissions, the possible impact on the time-averaged disk energy spectrum from the phenomenon responsible for quasi-periodic oscillations is largely ignored in models of sources emission. Aims: Here we investigate the potential impact of such a structure on the resultant energy spectrum. Methods: Using data from the well-documented outbursts of XTE J1550-564, we looked at possible hints that the presence of quasi-periodic oscillations actually impacts the energy spectrum emitted by the source. In particular, we look at the evolution of the relation between the inner disk radius and the inner disk temperature obtained from fits to the spectral data. We then test this further by developing a simple model to simulate the spectrum of a disk with a structure mimicking quasi-periodic oscillations that are increasing in strength simulated results to those obtained from real data. Results: We detect a similar departure in the inner radius - inner temperature curve coming from the standard fit of our simulated observations as is seen in XTE J1550-564 data. We interpret our results as evidence that the structure at the origin of the quasi-periodic oscillations impacts the energy spectrum. Conclusions: Furthermore, in states with significant disk emission the inaccuracy of the determination of the disk parameters increases with the strength of quasi-periodic oscillations, an increase that then renders the value given by the fit unreliable for strong quasi-periodic oscillations.

  12. Delayed feedback control and phase reduction of unstable quasi-periodic orbits.

    PubMed

    Ichinose, Natsuhiro; Komuro, Motomasa

    2014-09-01

    The delayed feedback control (DFC) is applied to stabilize unstable quasi-periodic orbits (QPOs) in discrete-time systems. The feedback input is given by the difference between the current state and a time-delayed state in the DFC. However, there is an inevitable time-delay mismatch in QPOs. To evaluate the influence of the time-delay mismatch on the DFC, we propose a phase reduction method for QPOs and construct a phase response curve (PRC) from unstable QPOs directly. Using the PRC, we estimate the rotation number of QPO stabilized by the DFC. We show that the orbit of the DFC is consistent with the unstable QPO perturbed by a small state difference resulting from the time-delay mismatch, implying that the DFC can certainly stabilize the unstable QPO. PMID:25273217

  13. Moment constraints on physical models for quasi-periodic oscillations from Galactic X-ray sources

    NASA Technical Reports Server (NTRS)

    Elsner, R. F.; Shibazaki, N.; Weisskopf, M. C.

    1988-01-01

    Shot-noise models provide a useful mathematical representation for some physical models for the quasi-periodic oscillations (QPOs) recently observed from several bright Galactic bulge and burst X-ray sources. Expressions are calculated for the first three moments for several versions of QPO shot-noise models that have appeared in the literature. It is shown that measurement of the third moment, together with measurement of the mean intensity and the power spectrum, can provide model-dependent constraints on important parameters of QPO shot-noise models, including the fraction of the X-ray intensity in shots and the shot rate. Under certain condtitions, a complete solution for all the shot-model parameters is possible.

  14. Quasi-periodic wave solutions with asymptotic analysis to the Saweda-Kotera-Kadomtsev-Petviashvili equation

    NASA Astrophysics Data System (ADS)

    Xu, Mei-Juan; Tian, Shou-Fu; Tu, Jian-Min; Ma, Pan-Li; Zhang, Tian-Tian

    2015-08-01

    In this paper, the (2+1)-dimensional Saweda-Kotera-Kadomtsev-Petviashvili (SK-KP) equation is investigated, which can be used to describe certain situations from the fluid mechanics, ocean dynamics and plasma physics. With the aid of generalized Bell's polynomials, the Hirota's bilinear equation and N-soliton solution are explicitly constructed to the SK-KP equation, respectively. Based on the Riemann theta function, a direct and lucid way is presented to explicitly construct quasi-periodic wave solutions for the SK-KP equation. The two-periodic waves admit two independent spatial periods in two independent horizontal directions, which are a direct generalization of one-periodic waves. Finally, the relationships between soliton solutions and periodic wave solutions are strictly established, which implies the asymptotic behaviors of the periodic waves under a limited procedure.

  15. Kinetic Simulation of Slow Magnetosonic Waves and Quasi-Periodic Upflows in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Ruan, Wenzhi; He, Jiansen; Zhang, Lei; Vocks, Christian; Marsch, Eckart; Tu, Chuanyi; Peter, Hardi; Wang, Linghua

    2016-07-01

    Quasi-periodic disturbances of emission-line parameters are frequently observed in the corona. These disturbances propagate upward along the magnetic field with speeds of ∼100 km s‑1. This phenomenon has been interpreted as evidence of the propagation of slow magnetosonic waves or has been argued to be a signature of intermittent outflows superposed on the background plasmas. Here we aim to present a new “wave + flow” model to interpret these observations. In our scenario, the oscillatory motion is a slow-mode wave, and the flow is associated with a beam created by the wave–particle interaction owing to Landau resonance. With the help of a kinetic model, we simulate the propagation of slow-mode waves and the generation of beam flows. We find that weak periodic beam flows can be generated by to Landau resonance in the solar corona, and the phase with the strongest blueward asymmetry is ahead of that with the strongest blueshift by about 1/4 period. We also find that the slow wave damps to the level of 1/e after the transit time of two wave periods, owing to Landau damping and Coulomb collisions in our simulation. This damping timescale is similar to that resulting from thermal conduction in the MHD regime. The beam flow is weakened/attenuated with increasing wave period and decreasing wave amplitude since Coulomb collisions become more and more dominant over the wave action. We suggest that this “wave + flow” kinetic model provides an alternative explanation for the observed quasi-periodic propagating perturbations in various parameters in the solar corona.

  16. The eight-vertex model with quasi-periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Niccoli, G.; Terras, V.

    2016-01-01

    We study the inhomogeneous eight-vertex model (or equivalently the XYZ Heisenberg spin-1/2 chain) with all kinds of integrable quasi-periodic boundary conditions: periodic, {σ }x-twisted, {σ }y-twisted or {σ }z-twisted. We show that in all these cases but the periodic one with an even number of sites {N}, the transfer matrix of the model is related, by the vertex-IRF transformation, to the transfer matrix of the dynamical six-vertex model with antiperiodic boundary conditions, which we have recently solved by means of Sklyanin's separation of variables approach. We show moreover that, in all the twisted cases, the vertex-IRF transformation is bijective. This allows us to completely characterize, from our previous results on the antiperiodic dynamical six-vertex model, the twisted eight-vertex transfer matrix spectrum (proving that it is simple) and eigenstates. We also consider the periodic case for {N} odd. In this case we can define two independent vertex-IRF transformations, both not bijective, and by using them we show that the eight-vertex transfer matrix spectrum is doubly degenerate, and that it can, as well as the corresponding eigenstates, also be completely characterized in terms of the spectrum and eigenstates of the dynamical six-vertex antiperiodic transfer matrix. In all these cases we can adapt to the eight-vertex case the reformulations of the dynamical six-vertex transfer matrix spectrum and eigenstates that had been obtained by T-Q functional equations, where the Q-functions are elliptic polynomials with twist-dependent quasi-periods. Such reformulations enable one to characterize the eight-vertex transfer matrix spectrum by the solutions of some Bethe-type equations, and to rewrite the corresponding eigenstates as the multiple action of some operators on a pseudo-vacuum state, in a similar way as in the algebraic Bethe ansatz framework.

  17. Energy Spectra and High Frequency Oscillations in 4U 0614+091

    NASA Technical Reports Server (NTRS)

    Ford, E. C.; Kaaret, P.; Chen, K.; Tavani, M.; Barret, D.; Bloser, P.; Grindlay, J.; Harmon, B. A.; Paciesas, W. S.; Zhang, S. N.

    1997-01-01

    We investigate the behavior of the high frequency quasi-periodic oscillations (QPOs) in 4U 0614+091, combining timing and spectral analysis of RXTE (Rossi X-ray Timing Explorer) observations. The energy spectrum of the source can be described by a power law plus a blackbody component. The blackbody has a variable temperature (kT approximately 0.8 to 1.4 keV) and accounts for 10 to 25% of the total energy flux. The power law flux and photon index also vary (F approximately 0.8 to 1.6 x 10(exp -9) erg/sq cm.s and alpha approximately 2.0 to 2.8 respectively). We find a robust correlation of the frequency of the higher frequency QPO with the flux of the blackbody. The source follows the same relation even in observations separated by several months. The QPO frequency does not have a similarly unique correlation with the total flux or the flux of the power law component. The RMS amplitudes of the higher frequency QPO rise with energy but are consistent with a constant for the lower frequency QPO. These results may be interpreted in terms of a beat frequency model for the production of the high frequency QPOs.

  18. High-frequency and type-C QPOs from oscillating, precessing hot, thick flow

    NASA Astrophysics Data System (ADS)

    Fragile, P. Chris; Straub, Odele; Blaes, Omer

    2016-09-01

    Motivated by recent studies showing an apparent correlation between the high-frequency quasi-periodic oscillations (QPOs) and the low-frequency, type-C QPO in black hole low-mass X-ray binaries (LMXBs), we explore a model that explains all three QPOs in terms of an oscillating, precessing hot flow in the truncated-disc geometry. Our model favours attributing the two high-frequency QPOs, often occurring in a near 3:2 frequency ratio, to the breathing and vertical epicyclic frequency modes of the hot, thick flow, although we cannot rule out the Keplerian and m = -1 radial epicyclic modes. In either case, the type-C QPO is attributed to precession. The correlation of the QPOs comes from the fact that all three frequencies are associated with the same geometrical structure. While the exact QPO frequencies are sensitive to the black hole mass and spin, their evolution over the course of an outburst is mainly tied to the truncation radius between the geometrically thin, optically thick disc and the inner, hot flow. We show that, in the case of the LMXB GRO J1655-40, this model can explain the one simultaneous observation of all three QPOs and that an extrapolation of the model appears to match lower frequency observations where only two of the three components are seen. Thus, this model may be able to unify multiple QPO observations using the properties of a single, simple, geometrical model.

  19. Statistical analysis and multi-instrument overview of the quasi-periodic 1-hour pulsations in Saturn's outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Palmaerts, B.; Roussos, E.; Krupp, N.; Kurth, W. S.; Mitchell, D. G.; Yates, J. N.

    2016-06-01

    The in-situ exploration of the magnetospheres of Jupiter and Saturn has revealed different periodic processes. In particular, in the Saturnian magnetosphere, several studies have reported pulsations in the outer magnetosphere with a periodicity of about 1 h in the measurements of charged particle fluxes, plasma wave, magnetic field strength and auroral emissions brightness. The Low-Energy Magnetospheric Measurement System detector of the Magnetospheric Imaging Instrument (MIMI/LEMMS) on board Cassini regularly detects 1-hour quasi-periodic enhancements in the intensities of electrons with an energy range from a hundred keV to several MeV. We extend an earlier survey of these relativistic electron injections using 10 years of LEMMS observations in addition to context measurements by several other Cassini magnetospheric experiments. The one-year extension of the data and a different method of detection of the injections do not lead to a discrepancy with the results of the previous survey, indicating an absence of a long-term temporal evolution of this phenomenon. We identified 720 pulsed events in the outer magnetosphere over a wide range of latitudes and local times, revealing that this phenomenon is common and frequent in Saturn's magnetosphere. However, the distribution of the injection events presents a strong local time asymmetry with ten times more events in the duskside than in the dawnside. In addition to the study of their topology, we present a first statistical analysis of the pulsed events properties. The morphology of the pulsations shows a weak local time dependence which could imply a high-latitude acceleration source. We provide some clues that the electron population associated with this pulsed phenomenon is distinct from the field-aligned electron beams previously observed in Saturn's magnetosphere, but both populations can be mixed. We have also investigated the signatures of each electron injection event in the observations acquired by the Radio

  20. Long-term quasi-periodicity of 4U 1636-536 resulting from accretion disc instability

    NASA Astrophysics Data System (ADS)

    Wisniewicz, Mateusz; Zdziarski, Andrzej; Janiuk, Agnieszka; Rosinska, Dorota; Slowikowska, Agnieszka

    2016-07-01

    We present the results of a study of the low-mass X-ray binary 4U 1636-536. We have performed temporal analysis of all available RXTE/ASM, RXTE/PCA, Swift/BAT and MAXI data. We have confirmed the previously discovered quasi-periodicity of ˜45 d present during ˜2004, however we found it continued to 2006. At other epochs, the quasi-periodicity is only transient, and the quasi-period, if present, drifts. We have then applied a time-dependent accretion disc model to the interval with the significant X-ray quasi-periodicity. For our best model, the period and the amplitude of the theoretical light curve agree well with that observed. The modelled quasi-periodicity is due to the hydrogen thermal-ionization instability occurring in outer regions of the accretion disc. The model parameters are the average mass accretion rate (estimated from the light curves), and the accretion disc viscosity parameters, α_{cold} and α_{hot}, for the hot and cold phases, respectively. Our best model gives relatively low values of α_{cold} and α_{hot}.

  1. The 2:3:6 quasi-periodic oscillation structure in GRS 1915+105 and cubic subharmonics in the context of relativistic discoseismology

    NASA Astrophysics Data System (ADS)

    Ortega-Rodríguez, M.; Solís-Sánchez, H.; López-Barquero, V.; Matamoros-Alvarado, B.; Venegas-Li, A.

    2014-06-01

    We propose a simple toy model to explain the 2:3:6 quasi-periodic oscillation (QPO) structure in GRS 1915+105 and, more generally, the 2:3 QPO structure in XTE J1550-564, GRO J1655-40 and H1743-322. The model exploits the onset of subharmonics in the context of discoseismology. We suggest that the observed frequencies may be the consequence of a resonance between a fundamental g mode and an unobservable p wave. The results include the prediction that, as better data become available, a QPO with a frequency of twice the higher twin frequency and a large quality factor will be observed in twin peak sources, as it might already have been observed in the especially active GRS 1915+105.

  2. Detection of the first infra-red quasi periodic oscillation in a black hole X-ray binary

    NASA Astrophysics Data System (ADS)

    Kalamkar, M.; Casella, P.; Uttley, P.; O'Brien, K.; Russell, D.; Maccarone, T.; van der Klis, M.; Vincentelli, F.

    2016-05-01

    We present analysis of fast variability of Very Large Telescope/ISAAC (infra-red), XMM-Newton/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its outburst in 2010. We report the first detection of a Quasi Periodic Oscillation (QPO) in the infra-red band (IR) of a black hole X-ray binary. The QPO is detected at 0.08 Hz in the IR as well as two optical bands (U and V). Interestingly, these QPOs are at half the X-ray QPO frequency at 0.16 Hz, which is classified as the type-C QPO; a weak sub-harmonic close to the IR and optical QPO frequency is also detected in X-rays. The band-limited sub-second time scale variability is strongly correlated in IR/X-ray bands, with X-rays leading the IR by over 120 ms. This short time delay, shape of the cross correlation function and spectral energy distribution strongly indicate that this band-limited variable IR emission is the synchrotron emission from the jet. A jet origin for the IR QPO is strongly favoured, but cannot be definitively established with the current data. The spectral energy distribution indicates a thermal disc origin for the bulk of the optical emission, but the origin of the optical QPO is unclear. We discuss our findings in the context of the existing models proposed to explain the origin of variability.

  3. Detection of the first infra-red quasi-periodic oscillation in a black hole X-ray binary

    NASA Astrophysics Data System (ADS)

    Kalamkar, M.; Casella, P.; Uttley, P.; O'Brien, K.; Russell, D.; Maccarone, T.; van der Klis, M.; Vincentelli, F.

    2016-08-01

    We present analysis of fast variability of Very Large Telescope/ISAAC (infra-red), \\textit{XMM-Newton}/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its outburst in 2010. We report the first detection of a Quasi Periodic Oscillation (QPO) in the infra-red band (IR) of a black hole X-ray binary. The QPO is detected at 0.08 Hz in the IR as well as two optical bands (U and V). Interestingly, these QPOs are at half the X-ray QPO frequency at 0.16 Hz, which is classified as the type-C QPO; a weak sub-harmonic close to the IR and optical QPO frequency is also detected in X-rays. The broad band sub-second time scale variability is strongly correlated in IR/X-ray bands, with X-rays leading the IR by over 100 ms. This short time delay, shape of the cross correlation function and spectral energy distribution strongly indicate that this broad band variable IR emission is the synchrotron emission from the jet. A jet origin for the IR QPO is strongly favoured, but cannot be definitively established with the current data. The spectral energy distribution indicates a thermal disc origin for the bulk of the optical emission, but the origin of the optical QPO is unclear. We discuss our findings in the context of the existing models proposed to explain the origin of variability.

  4. Detection of the first infra-red quasi-periodic oscillation in a black hole X-ray binary

    NASA Astrophysics Data System (ADS)

    Kalamkar, M.; Casella, P.; Uttley, P.; O'Brien, K.; Russell, D.; Maccarone, T.; van der Klis, M.; Vincentelli, F.

    2016-08-01

    We present the analysis of fast variability of Very Large Telescope/ISAAC (Infrared Spectrometer And Array Camera) (infra-red), XMM-Newton/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its outburst in 2010. We report the first detection of a quasi-periodic oscillation (QPO) in the infra-red band (IR) of a black hole X-ray binary. The QPO is detected at 0.08 Hz in the IR as well as two optical bands (U and V). Interestingly, these QPOs are at half the X-ray QPO frequency at 0.16 Hz, which is classified as the type-C QPO; a weak sub-harmonic close to the IR and optical QPO frequency is also detected in X-rays. The band-limited sub-second time-scale variability is strongly correlated in IR/X-ray bands, with X-rays leading the IR by over 120 ms. This short time delay, shape of the cross-correlation function and spectral energy distribution strongly indicate that this band-limited variable IR emission is the synchrotron emission from the jet. A jet origin for the IR QPO is strongly favoured, but cannot be definitively established with the current data. The spectral energy distribution indicates a thermal disc origin for the bulk of the optical emission, but the origin of the optical QPO is unclear. We discuss our findings in the context of the existing models proposed to explain the origin of variability.

  5. O VI 1032 Å intensity and Doppler shift oscillations above a coronal hole: Magnetosonic waves or quasi-periodic upflows?

    NASA Astrophysics Data System (ADS)

    Mancuso, S.; Raymond, J. C.; Rubinetti, S.; Taricco, C.

    2016-08-01

    On 1996 December 19, the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO) conducted a special high-cadence sit-and-stare observation in the O vi 1032 Å spectral line above a polar coronal hole at a heliocentric distance of 1.38 R⊙. The ~ 9-h dataset was analyzed by applying advanced spectral techniques to investigate the possible presence of propagating waves. Highly significant oscillations in O vi intensity (P = 19.5 min) and Doppler shift (P = 7.2 min) were detected over two different portions of the UVCS entrance slit. A cross-correlation analysis between the O vi intensity and Doppler shift fluctuations shows that the most powerful oscillations were in phase or anti-phase over the same portions of the slit, thus providing a possible signature of propagating magnetosonic waves. The episodic nature of the observed oscillations and the large amplitudes of the Doppler shift fluctuations detected in our observations, if not attributable to line-of-sight effects or inefficient damping, may indicate that the observed fluctuations were produced by quasi-periodic upflows.

  6. Optimizing light absorption in a thin-film p-i-n solar cell using a quasi-periodic grating

    NASA Astrophysics Data System (ADS)

    Atalla, Mahmoud R. M.

    2014-03-01

    A p-i-n solar cell is best suited for strong absorbers with poor collection capabilities. However, the absorption naturally decreases at photon energies close to the electronic bandgap of the semiconductor. We hypothesized that a quasi-periodic surface textures in the role of diffraction gratings at the back contact can efficiently scatter light increasing the optical path length inside the absorber layer. The effect of quasi-periodic corrugated backing metallic contact of various types was studied theoretically. To help optimizing the design of the quasi periodic grating the corresponding canonical problem was considered. The absorption of light was calculated using the rigorous coupled-wave approach. The n- and i-layers consist of isotropic nonhomogeneous multilayered semiconductor.

  7. Mobile high frequency vibrator system

    SciTech Connect

    Fair, D.W.; Buller, P.L.

    1985-01-08

    A carrier mounted seismic vibrator system that is primarily adapted for generation of high force, high frequency seismic energy into an earth medium. The apparatus includes first and second vibrators as supported by first and second lift systems disposed in tandem juxtaposition generally centrally in said vehicle, and the lift systems are designed to maintain equal hold-down force on the vibrator coupling baseplates without exceeding the weight of the carrier vehicle. The juxtaposed vibrators are then energized in synchronized relationship to propagate increased amounts of higher frequency seismic energy into an earth medium.

  8. Photometry of the 1991 Superoutburst of EF Pegasi: Super-Quasi-Periodic Oscillations with Rapidly Decaying Periods

    NASA Astrophysics Data System (ADS)

    Kato, Taichi

    2002-02-01

    We observed the 1991 October outburst of EF Peg. Prominent superhumps with a period of 0.08705(1)d were observed, qualifying EF Peg as being a long-period SU UMa-type dwarf nova. The superhump period showed a monotonic decrease during the superoutburst, which makes a contrast to the virtually zero period change observed during the 1997 superoutburst of the same object. Large-amplitude and highly coherent quasi-periodic oscillations (super-QPOs) were observed on October 18, when superhumps were still growing in amplitude. Most strikingly, the QPOs showed a rapid decrease in the period from 18min to 6.8min within the 3.2-hr observing run. Such a rapid change in the period has not been observed in any class of QPOs in cataclysmic variables. We propose a hypothesis that the rapid decrease of the QPO period reflects a rapid removal of the angular momentum from an orbiting blob in the accretion disk, via viscosity in a turbulent disk. A brief comparison is given with the QPOs in X-ray binaries, some of which are known to show a similar rapid decrease in the periods.

  9. Millihertz quasi-periodic oscillations in 4U 1636-53 associated with bursts with positive convexity only

    NASA Astrophysics Data System (ADS)

    Lyu, Ming; Méndez, Mariano; Altamirano, Diego; Zhang, Guobao

    2016-08-01

    We investigated the convexity of all type I X-ray bursts with millihertz quasi-periodic oscillations (mHz QPOs) in 4U 1636-53 using archival observations with the Rossi X-ray Timing Explorer. We found that, at a 3.5σ confidence level, in all 39 cases in which the mHz QPOs disappeared at the time of an X-ray burst, the convexity of the burst is positive. The convexity measures the shape of the rising part of the burst light curve and, according to recent models, it is related to the ignition site of bursts on the neutron-star surface. This finding suggests that in 4U 1636-53 these 39 bursts and the marginally-stable nuclear burning process responsible for the mHz QPOs take place at the neutron-star equator. This scenario could explain the inconsistency between the high accretion rate required for triggering mHz QPOs in theoretical models and the relatively low accretion rate derived from observations.

  10. Imaging observation of quasi-periodic disturbances' amplitudes increasing with height in the polar region of the solar corona

    SciTech Connect

    Su, J. T.; Priya, T. G.; Liu, Y.; Shen, Y. D.

    2014-08-01

    At present, there have been few extreme ultraviolet (EUV) imaging observations of spatial variations of the density perturbations due to the slow magnetoacoustic waves (SMWs) propagating along the solar coronal magnetic fields. In this paper, we present such observations taken from the polar region of the corona with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and investigate the amplitude of quasi-periodic propagating disturbances that increase with height in the lower corona (0-9 Mm over the solar limb). We statistically determined the following parameters associated with the disturbances: pressure scale height, period, and wavelength in AIA 171 Å, 193 Å, and 211 Å channels. The scale height and wavelength are dependent of temperature, while the period is independent of temperature. The acoustic velocities inferred from the scale height highly correlate with the ratios of wavelength to period, i.e., phase speeds. They provide evidence that the propagating disturbances in the lower corona are likely SMWs and the spatial variations in EUV intensity in the polar region likely reflects the density compressional effect by the propagating SMWs.

  11. Quasi-periodic Fibonacci and periodic one-dimensional hypersonic phononic crystals of porous silicon: Experiment and simulation

    SciTech Connect

    Aliev, Gazi N. Goller, Bernhard

    2014-09-07

    A one-dimensional Fibonacci phononic crystal and a distributed Bragg reflector were constructed from porous silicon. The structures had the same number of layers and similar acoustic impedance mismatch, and were electrochemically etched in highly boron doped silicon wafers. The thickness of the individual layers in the stacks was approximately 2 μm. Both types of hypersonic band gap structure were studied by direct measurement of the transmittance of longitudinal acoustic waves in the 0.1–2.6 GHz range. Acoustic band gaps deeper than 50 dB were detected in both structures. The experimental results were compared with model calculations employing the transfer matrix method. The acoustic properties of periodic and quasi-periodic structures in which half-wave retarding bi-layers do not consist of two quarter-wave retarding layers are discussed. The strong correlation between width and depth of gaps in the transmission spectra is demonstrated. The dominant mechanisms of acoustic losses in porous multilayer structures are discussed. The elastic constants remain proportional over our range of porosity, and hence, the Grüneisen parameter is constant. This simplifies the expression for the porosity dependence of the Akhiezer damping.

  12. A Model for Backscattering from Quasi Periodic Corn Canopies at L-Band

    NASA Technical Reports Server (NTRS)

    Lang, R.; Utku, C.; Zhao, Q.; O'Neill, P.

    2010-01-01

    In this study, a model for backscattering at L-band from a corn canopy is proposed. The canopy consists of a quasi-periodic distribution of stalks and a random distribution of leaves. The Distorted Born Approximation (DBA) is employed to calculate the single scattered return from the corn field. The new feature of the method is that the coherence of the stalks in the row direction is incorporated in the model in a systematic fashion. Since the wavelength is on the order of the distance between corn stalks in a row, grating lobe behavior is observed at certain azimuth angles of incidence. The results are compared with experimental values measured in Huntsville, Alabama in 1998. The mean field and the effective dielectric constant of the canopy are obtained by using the Foldy approximation. The stalks are placed in the effective medium in a two dimensional lattice to simulate the row structure of a corn field. In order to mimic a real corn field, a quasi-periodic stalk distribution is assumed where the stalks are given small random perturbations about their lattice locations. Corn leaves are also embedded in the effective medium and the backscattered field from the stalks and the leaves is computed. The backscattering coefficient is calculated and averaged over successive stalk position perturbations. It is assumed that soil erosion has smoothed the soil sufficiently so that it can be assumed flat. Corn field backscatter data was collected from cornfields during the Huntsville 98 experimental campaign held at Alabama A&M University Research Station, Huntsville, Alabama in 1998 using the NASA/GW truck mounted radar. Extensive ground truth data was collected. This included soil moisture measurements and corn plant architectural data to be used in the model. In particular, the distances between the stalks in a single row have been measured. The L-band radar backscatter data was collected for both H and V polarizations and for look angles of 15o and 45o over a two week

  13. High frequency integrated MOS filters

    NASA Technical Reports Server (NTRS)

    Peterson, C.

    1990-01-01

    Several techniques exist for implementing integrated MOS filters. These techniques fit into the general categories of sampled and tuned continuous-time filters. Advantages and limitations of each approach are discussed. This paper focuses primarily on the high frequency capabilities of MOS integrated filters.

  14. Relativistic simulation of flip-flop instabilities of Bondi-Hoyle accretion and quasi-periodic oscillations

    NASA Astrophysics Data System (ADS)

    Dönmez, O.

    2012-10-01

    It is known from recent numerical calculations that Bondi-Hoyle accretion creates a shock cone behind compact objects. This type of accretion leads to instabilities, which can explain certain astrophysical phenomena. In this paper, our main goal is to find the flip-flop behaviour of the shock cone in the relativistic region. In order to do so we have modelled the dynamics of a shock cone around non-rotating and rotating black holes at the equatorial plane in 2D. The effects of the various parameters on the shock cones and instabilities, such as the asymptotic velocity, sound speed, Mach number and adiabatic index, are studied. We have determined the mass accretion rate, shock opening angle, shock cone oscillation, quasi-periodic oscillations (QPOs), and growth rate of instabilities to reveal the disc properties and its radiation. We have discovered, for the first time, flip-flop instabilities around a black hole in the relativistic region by solving the general relativistic hydrodynamical equations. The flip-flop instabilities are found for sound speeds Cs, ∞ < 0.2 with moderate Mach numbers (˜M=3 and M=4 for Cs, ∞ = 0.1 or M=7 and M=8 for Cs, ∞ = 0.05). Our calculation clearly confirms that the shock cone should be detached from the black hole in the Bondi-Hoyle accretion flow with Γ ≥ 2 for non-rotating and rotating black holes. Results reveal that the flip-flopping shock cone not only creates a torque effect on the black hole but also produces continuous X-ray flares with a certain frequency. Furthermore, QPOs originate inside the shock cone and are stronger in regions that have a radius of a few gravitational radii away from the centre owing to the flip-flop oscillation. Finally, our results are compared with the results of numerical and theoretical calculations in Newtonian hydrodynamics, and it is found that they are in good agreement.

  15. ON THE NATURE OF QUASI-PERIODIC OSCILLATION PHASE LAGS IN BLACK HOLE CANDIDATES

    SciTech Connect

    Shaposhnikov, Nikolai E-mail: lev@milkyway.gsfc.nasa.gov

    2012-06-20

    Observations of quasi-periodic oscillations (QPOs) in X-ray binaries hold a key to understanding many aspects of these enigmatic systems. Complex appearance of the Fourier phase lags related to QPOs is one of the most puzzling observational effects in accreting black holes (BHs). In this Letter we show that QPO properties, including phase lags, can be explained in a framework of a simple scenario, where the oscillating media provide feedback on the emerging spectrum. We demonstrate that the QPO waveform is presented by the product of a perturbation and time-delayed response factors, where the response is energy dependent. The essential property of this effect is its nonlinear and multiplicative nature. Our multiplicative reverberation model successfully describes the QPO components in energy-dependent power spectra as well as the appearance of the phase lags between signals in different energy bands. We apply our model to QPOs observed by the Rossi X-Ray Timing Explorer in BH candidate XTE J1550-564. We briefly discuss the implications of the observed energy dependence of the QPO reverberation times and amplitudes on the nature of the power-law spectral component and its variability.

  16. Study of deformed quasi-periodic Fibonacci two dimensional photonic crystals

    NASA Astrophysics Data System (ADS)

    Ben Abdelaziz, K.; Bouazzi, Y.; Kanzari, M.

    2015-09-01

    Quasi-periodic photonic crystals are not periodic structures. These structures are generally obtained by the arrangement of layers according to a recursive rule. Properties of these structures make more attention the researchers especially in the case when applying defects. So, photonic crystals with defects present localized modes in the band gap leading to many potential applications such light localization. The objective of this work is to study by simulation the effect of the global deformation introduced in 2D quasiperiodic photonic crystals. Deformation was introduced by applying a power law, so that the coordinates y of the deformed object were determined through the coordinates x of the non-deformed structure in accordance with the following rule: y = x1+k. Here k is the coefficient defining the deformation. Therefore, the objective is to study the effect of this deformation on the optical properties of 2D quasiperiodic photonic crystals, constructed by Fibonacci generation. An omnidirectional mirror was obtained for optimization Fibonacci iteration in a part of visible spectra.

  17. Statistical properties of quasi-periodic pulsations in white-light flares observed with Kepler

    NASA Astrophysics Data System (ADS)

    Pugh, C. E.; Armstrong, D. J.; Nakariakov, V. M.; Broomhall, A.-M.

    2016-07-01

    We embark on a study of quasi-periodic pulsations (QPPs) in the decay phase of white-light stellar flares observed by Kepler. Out of the 1439 flares on 216 different stars detected in the short-cadence data using an automated search, 56 flares are found to have pronounced QPP-like signatures in the light curve, of which 11 have stable decaying oscillations. No correlation is found between the QPP period and the stellar temperature, radius, rotation period and surface gravity, suggesting that the QPPs are independent of global stellar parameters. Hence they are likely to be the result of processes occurring in the local environment. There is also no significant correlation between the QPP period and flare energy, however there is evidence that the period scales with the QPP decay time for the Gaussian damping scenario, but not to a significant degree for the exponentially damped case. This same scaling has been observed for MHD oscillations on the Sun, suggesting that they could be the cause of the QPPs in those flares. Scaling laws of the flare energy are also investigated, supporting previous reports of a strong correlation between the flare energy and stellar temperature/radius. A negative correlation between the flare energy and stellar surface gravity is also found.

  18. A Model for (Quasi-)Periodic Multiwavelength Photometric Variability in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Kesseli, Aurora Y.; Petkova, Maya A.; Wood, Kenneth; Whitney, Barbara A.; Hillenbrand, L. A.; Gregory, Scott G.; Stauffer, J. R.; Morales-Calderon, M.; Rebull, L.; Alencar, S. H. P.

    2016-09-01

    We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.

  19. Periodic, Quasi-periodic and Chaotic Dynamics in Simple Gene Elements with Time Delays

    PubMed Central

    Suzuki, Yoko; Lu, Mingyang; Ben-Jacob, Eshel; Onuchic, José N.

    2016-01-01

    Regulatory gene circuit motifs play crucial roles in performing and maintaining vital cellular functions. Frequently, theoretical studies of gene circuits focus on steady-state behaviors and do not include time delays. In this study, the inclusion of time delays is shown to entirely change the time-dependent dynamics for even the simplest possible circuits with one and two gene elements with self and cross regulations. These elements can give rise to rich behaviors including periodic, quasi-periodic, weak chaotic, strong chaotic and intermittent dynamics. We introduce a special power-spectrum-based method to characterize and discriminate these dynamical modes quantitatively. Our simulation results suggest that, while a single negative feedback loop of either one- or two-gene element can only have periodic dynamics, the elements with two positive/negative feedback loops are the minimalist elements to have chaotic dynamics. These elements typically have one negative feedback loop that generates oscillations, and another unit that allows frequent switches among multiple steady states or between oscillatory and non-oscillatory dynamics. Possible dynamical features of several simple one- and two-gene elements are presented in details. Discussion is presented for possible roles of the chaotic behavior in the robustness of cellular functions and diseases, for example, in the context of cancer. PMID:26876008

  20. Quasi-Periodic Stick-Slip of Glaciers and Ice Streams (Invited)

    NASA Astrophysics Data System (ADS)

    Anandakrishnan, S.; Christianson, K. A.; Zoet, L.; Winberry, J.

    2010-12-01

    Passive source seismology is an excellent tool for studying dynamic glaciological processes. The past decade has seen an explosion in interest in the field, with singing icebergs, galloping glaciers, pulsing ponds, and many other glaciological phenomena radiating seismic energy. Here I present results showing extraordinary regularity in basal seismicity associated with the sliding of glaciers that differ in almost every respect: size, temperature, location, etc. Engabreen Glacier in Norway and David Glacier in Antarctica both exhibit a near-metronomic seismicity associated with the sliding of the glaciers over their bases. These small events occur in one of two modes: either present and very regular (quasi-periodic) or absent (or very rare). The transition from the one state to the other is rapid. The stick-slip behavior of the glacier is analogous to slip on faults, and to the behavior observed on Whillans Ice Stream (though much more frequently occuring). We suggest that either basal sediment concentrations or water pressure fluctuations lead to the transition in behavior.

  1. Statistical Properties of Quasi-Periodic Pulsations in White-Light Flares Observed With Kepler

    NASA Astrophysics Data System (ADS)

    Pugh, C. E.; Armstrong, D. J.; Nakariakov, V. M.; Broomhall, A.-M.

    2016-04-01

    We embark on a study of quasi-periodic pulsations (QPPs) in the decay phase of white-light stellar flares observed by Kepler. Out of the 1439 flares on 216 different stars detected in the short-cadence data using an automated search, 56 flares are found to have pronounced QPP-like signatures in the light curve, of which 11 have stable decaying oscillations. No correlation is found between the QPP period and the stellar temperature, radius, rotation period and surface gravity, suggesting that the QPPs are independent of global stellar parameters. Hence they are likely to be the result of processes occurring in the local environment. There is also no significant correlation between the QPP period and flare energy, however there is evidence that the period scales with the QPP decay time for the Gaussian damping scenario, but not to a significant degree for the exponentially damped case. This same scaling has been observed for MHD oscillations on the Sun, suggesting that they could be the cause of the QPPs in those flares. Scaling laws of the flare energy are also investigated, supporting previous reports of a strong correlation between the flare energy and stellar temperature/radius. A negative correlation between the flare energy and stellar surface gravity is also found.

  2. Evidence for quasi-periodic modulation in the gamma-ray blazar PG 1553+113

    NASA Astrophysics Data System (ADS)

    Cutini, Sara; Ciprini, Stefano; Larsson, Stefan; Thompson, David John; Stamerra, Antonio; Fermi LAT Collaboration

    2016-01-01

    For the first time a gamma-ray and multiwavelength nearly-periodic oscillation in an active galactic nucleus is reported using the Fermi Large Area Telescope (LAT). A quasi-periodicity in the gamma-ray flux (E>100 MeV and E>1 GeV) is observed from the well-known GeV/TeV BL Lac object PG 1553+113 (Ackermann et al. submitted). The significance of the 2.18 +/- 0.08 year-period gamma-ray modulation, seen in 3.5 oscillation maxima observed, is supported by significant cross-correlated variations observed in radio and optical flux light curves, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle, appearing in about 10 years of data, has a similar period, while the radio-band oscillation observed at 15 GHz is less regular and coherent. The available X-ray flux data obtained by Swift XRT appears also to be linearly correlated with the gamma-ray flux. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this first evidence of periodicity.

  3. Strong Correlation between Quasi-periodic Echoes and Plasma Drift in E-region

    NASA Astrophysics Data System (ADS)

    Jin, H.; Chen, G.

    2015-12-01

    It is for the first time that the simultaneous observations of the quasi-periodic (QP) echoes and the plasma drift in the ionospheric E-region. This experiment was carried out in Fuke (19.5ºN, 109.1ºE), Hainan province, China. The Hainan VHF radar was used to observe the E-region field-aligned irregularities (FAIs) and the Hainan Digisonde was operated in the drift mode to record the drift velocities of the plasma blobs in the Es-layer. The QP echoes and the drift data of the whole year of 2013 were analyzed and compared. A surprising consistency between the striation tilt of the QP echoes and the drift direction of the plasma blobs was discovered. When the measured drift direction of the plasma blobs was southward, the negative echo striation of the QP FAIs was recorded, and vice versa. Furthermore, the phase of the echo trace was continuous, while the QP striation changed from negative to positive, or in contrary. Thus, a conclusion can be reached that the morphology of the QP echoes may be controlled by the background wind fields in the E-region. The northward/ southward drifting striated FAIs in the observing region of a coherent scatter radar possibly induce the positive/ negative QP echo striation in the range-time-intensity plots.

  4. Spherical accretion: the influence of inner boundary and quasi-periodic oscillations

    NASA Astrophysics Data System (ADS)

    Dhang, Prasun; Sharma, Prateek; Mukhopadhyay, Banibrata

    2016-09-01

    Bondi accretion assumes that there is a sink of mass at the centre - which in the case of a black hole (BH) corresponds to the advection of matter across the event horizon. Other stars, such as a neutron star (NS), have surfaces and hence the infalling matter has to slow down at the surface. We study the initial value problem in which the matter distribution is uniform and at rest at t = 0. We consider different inner boundary conditions for BHs and NSs: outflow boundary condition (mimicking mass sink at the centre) valid for BHs; and reflective and steady-shock (allowing gas to cross the inner boundary at subsonic speeds) boundary conditions for NSs. We also obtain a similarity solution for cold accretion on to BHs and NSs. 1D simulations show the formation of an outward-propagating and a standing shock in NSs for reflective and steady-shock boundary conditions, respectively. Entropy is the highest at the bottom of the subsonic region for reflective boundary conditions. In 2D this profile is convectively unstable. Using steady-shock inner boundary conditions, the flow is unstable to the standing accretion shock instability in 2D, which leads to global shock oscillations and may be responsible for quasi-periodic oscillations seen in the light curves of accreting systems. For steady accretion in the quiescent state, spherical accretion rate on to an NS can be suppressed by orders of magnitude compared to that on to a BH.

  5. Quasi-periodical variations of pulsars spin as mimicry of differential rotation

    NASA Astrophysics Data System (ADS)

    Kitiashvili, I.; Gusev, A.

    2008-09-01

    ABSTRACT Observation of pulsars is a powerful source of information for studying the dynamics and internal structure of neutron stars. Known about quasi-periodical fluctuations of the time-of-arrival of radiation(TOA) for some pulsars, which we explain as Chandler wobble, Free core nutation, Free inner core nutation and Inner core wobble in case three layer model. Using hamilton approximation to theory rotation of multilayer celestial bodies we estimate dynamical flattening for different layers for PSR B1828-11. It is known that an innate feature of pulsar radiation is high stability of the time-of-arrival (TOA) of pulses, and therefore the analysis of TOA fluctuations can reflect subtle effects of neutron stars dynamics. TOA variations of pulsars can be interpreted by three reasons: gravitational perturbation of pulsar by planetary bodies, peculiarities of a pulsar interior like Tkachenko oscillations and free precession motion, when axis of rotation do not coincide with vectors of the angular moment of solid crust, liquid outer core and crystal core. The radial velocity of a star is obtained by measuring the magnitude of the Doppler effect in its spectrum. Stars showing a small amplitude variation of the radial velocity can be interpreted as systems having planetary companions. Assuming that the pulsar PSR B1257+12 has a mass of 1:35M¯, the Keplerian orbital radii are 0.9, 1.4 and 2.1 AU and with masses are 3:1M©=sin(i), 10:2M©=sin(i), 4:6M©=sin(i), where i is the orbital inclination [7]. In 2000, Stairs, Lyne and Shemar reported about their discovery of long-term, highly-periodic and correlated variations of pulse shape and the rate of slow-down of the pulsar PSR B182811 with period variations approximately 1000, 500, 250 and 167 days, which may be a result of the spin axis caused by an asymmetry in the shape of the pulsar. The long-periodic precession phenomenon was also detected for a few pulsars: PSR 2217+47, PSR 0531+21, PSR B083345, PSR B182811, PSR B

  6. Construction of quasi-periodic solutions of state-dependent delay differential equations by the parameterization method II: Analytic case

    NASA Astrophysics Data System (ADS)

    He, Xiaolong; de la Llave, Rafael

    2016-08-01

    We construct analytic quasi-periodic solutions of a state-dependent delay differential equation with quasi-periodically forcing. We show that if we consider a family of problems that depends on one dimensional parameters (with some non-degeneracy conditions), there is a positive measure set Π of parameters for which the system admits analytic quasi-periodic solutions. The main difficulty to be overcome is the appearance of small divisors and this is the reason why we need to exclude parameters. Our main result is proved by a Nash-Moser fast convergent method and is formulated in the a-posteriori format of numerical analysis. That is, given an approximate solution of a functional equation which satisfies some non-degeneracy conditions, we can find a true solution close to it. This is in sharp contrast with the finite regularity theory developed in [18]. We conjecture that the exclusion of parameters is a real phenomenon and not a technical difficulty. More precisely, for generic families of perturbations, the quasi-periodic solutions are only finitely differentiable in open sets in the complement of parameters set Π.

  7. High frequency power distribution system

    NASA Technical Reports Server (NTRS)

    Patel, Mikund R.

    1986-01-01

    The objective of this project was to provide the technology of high frequency, high power transmission lines to the 100 kW power range at 20 kHz frequency. In addition to the necessary design studies, a 150 m long, 600 V, 60 A transmission line was built, tested and delivered for full vacuum tests. The configuration analysis on five alternative configurations resulted in the final selection of the three parallel Litz straps configuration, which gave a virtually concentric design in the electromagnetic sense. Low inductance, low EMI and flexibility in handling are the key features of this configuration. The final design was made after a parametric study to minimize the losses, weight and inductance. The construction of the cable was completed with no major difficulties. The R,L,C parameters measured on the cable agreed well with the calculated values. The corona tests on insulation samples showed a safety factor of 3.

  8. The energy dependence of quasi periodic oscillations in GRS 1915+105

    NASA Astrophysics Data System (ADS)

    Van Den Eijnden, Jakob; Ingram, Adam; Uttley, Phil

    2016-01-01

    Accreting stellar-mass black holes display quasi-periodic oscillations (QPOs) in their X-ray flux with a period that drifts from approximately 0.05 to 10 seconds. Since the oscillatory signal originates from the close proximity of the black hole, QPOs provide a diagnostic of the motion of matter in this region of extreme gravitational curvature. Here I present an analysis of the energy dependence of QPOs in the black hole binary GRS 1915+105. The QPO period in this black hole binary is known to be correlated with the observed energy band. To investigate this further, we extract light curves in two broad energy bands using archival data from the Rossi X-ray Timing Explorer, and apply a filter that separates the QPO from the coincident noise. The filtered light curves reveal that, in both energy bands, the modulation repeatedly rises and falls in amplitude in an envelope that typically lasts about five to ten QPO cycles. We find that, during each of these so-called coherence timescales, the phase difference between the two QPO light curves increases before resetting at the start of the next coherence time scale. This indicates that the oscillation in one energy band is genuinely faster than that in the other band, and puts interesting constraints on current QPO models. If the QPO originates from vertical general relativistic precession of the inner accretion flow, our result indicates that the inner regions of this flow precess slightly quicker than the outer regions, with the precession phase resetting after five to ten QPO cycles.

  9. A high-frequency Doppler feature in the power spectra of simulated GRMHD black hole accretion disks

    SciTech Connect

    Wellons, Sarah; Zhu, Yucong; Narayan, Ramesh; McClintock, Jeffrey E.; Psaltis, Dimitrios

    2014-04-20

    Black hole binaries exhibit a wide range of variability phenomena, from large-scale state changes to broadband noise and quasi-periodic oscillations, but the physical nature of much of this variability is poorly understood. We examine the variability properties of three GRMHD simulations of thin accretion disks around black holes of varying spin, producing light curves and power spectra as would be seen by observers. We find that the simulated power spectra show a broad feature at high frequency, which increases in amplitude with the inclination of the observer. We show that this high-frequency feature is a product of the Doppler effect and that its location is a function of the mass and spin of the black hole. This Doppler feature demonstrates that power spectral properties of the accretion disk can be tied to, and potentially used to determine, physical properties of the black hole.

  10. High-current, high-frequency capacitors

    NASA Technical Reports Server (NTRS)

    Renz, D. D.

    1983-01-01

    The NASA Lewis high-current, high-frequency capacitor development program was conducted under a contract with Maxwell Laboratories, Inc., San Diego, California. The program was started to develop power components for space power systems. One of the components lacking was a high-power, high-frequency capacitor. Some of the technology developed in this program may be directly usable in an all-electric airplane. The materials used in the capacitor included the following: the film is polypropylene, the impregnant is monoisopropyl biphenyl, the conductive epoxy is Emerson and Cuming Stycast 2850 KT, the foil is aluminum, the case is stainless steel (304), and the electrode is a modified copper-ceramic.

  11. TIME DELAYS IN QUASI-PERIODIC PULSATIONS OBSERVED DURING THE X2.2 SOLAR FLARE ON 2011 FEBRUARY 15

    SciTech Connect

    Dolla, L.; Marque, C.; Seaton, D. B.; Dominique, M.; Berghmans, D.; Cabanas, C.; De Groof, A.; Verdini, A.; West, M. J.; Zhukov, A. N.; Van Doorsselaere, T.; Schmutz, W.; Zender, J.

    2012-04-10

    We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 2011 February 15, observed simultaneously in several wavebands. We focus on fluctuations on timescale 1-30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager channels in the range 25-100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the extreme-ultraviolet (EUV) channels of the Euv SpectroPhotometer (ESP) on board the Solar Dynamic Observatory. The zirconium and aluminum filter channels of the Large Yield Radiometer on board the Project for On-Board Autonomy satellite and the soft X-ray (SXR) channel of ESP follow. The largest lags occur in observations from the Geostationary Operational Environmental Satellite, where the channel at 1-8 A leads the 0.5-4 A channel by several seconds. The time lags between the first and last channels is up to Almost-Equal-To 9 s. We identified at least two distinct time intervals during the flare impulsive phase, during which the QPPs were associated with two different sources in the Nobeyama RadioHeliograph at 17 GHz. The radio as well as the hard X-ray channels showed different lags during these two intervals. To our knowledge, this is the first time that time lags are reported between EUV and SXR fluctuations on these timescales. We discuss possible emission mechanisms and interpretations, including flare electron trapping.

  12. Frequency shifts of high frequency p-modes

    NASA Technical Reports Server (NTRS)

    Jain, Rekha

    1995-01-01

    Frequency shifts of high frequency p-modes during the solar cycle are calculated for a non-magnetic polytrope convection zone model. An isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field is correlated to this model. The relevant observations of such frequency changes are discussed. The calculated simultaneous changes in the field strength and chromospheric temperature result in the frequency shifts that are similar to those of the observations.

  13. High Frequency Stable Oscillate boiling

    NASA Astrophysics Data System (ADS)

    Li, Fenfang; Gonzalez-Avila, Silvestre Roberto; Ohl, Claus Dieter

    2015-11-01

    We present an unexpected regime of resonant bubble oscillations on a thin metal film submerged in water, which is continuously heated with a focused CW laser. The oscillatory bubble dynamics reveals a remarkably stable frequency of several 100 kHz and is resolved from the side using video recordings at 1 million frames per second. The emitted sound is measured simultaneously and shows higher harmonics. Once the laser is switched on the water in contact with the metal layer is superheated and an explosively expanding cavitation bubble is generated. However, after the collapse a microbubble is nucleated from the bubble remains which displays long lasting oscillations. Generally, pinch-off from of the upper part of the microbubble is observed generating a continuous stream of small gas bubbles rising upwards. The cavitation expansion, collapse, and the jetting of gas bubbles are detected by the hydrophone and are correlated to the high speed video. We find the bubble oscillation frequency is dependent on the bubble size and surface tension. A preliminary model based on Marangoni flow and heat transfer can explain the high flow velocities observed, yet the origin of bubble oscillation is currently not well understood.

  14. Classification of Bifurcations of Quasi-Periodic Solutions Using Lyapunov Bundles

    NASA Astrophysics Data System (ADS)

    Kamiyama, Kyohei; Komuro, Motomasa; Endo, Tetsuro; Aihara, Kazuyuki

    In continuous-time dynamical systems, a periodic orbit becomes a fixed point on a certain Poincaré section. The eigenvalues of the Jacobian matrix at this fixed point determine the local stability of the periodic orbit. Analogously, a quasi-periodic orbit (2-torus) becomes an invariant closed curve (ICC) on a Poincaré section. From the Lyapunov exponents of an ICC, we can determine the time average of the exponential divergence rate of the orbit, which corresponds to the eigenvalues of a fixed point. We denote the Lyapunov exponent with the smallest nonzero absolute value as the Dominant Lyapunov Exponent (DLE). A local bifurcation manifests as a crossing or touch of the DLE locus with zero. However, the type of bifurcation cannot be determined from the DLE. To overcome this problem, we define the Dominant Lyapunov Bundle (DLB), which corresponds to the dominant eigenvectors of a fixed point. We prove that the DLB of a 1-torus in a map can be classified into four types: A+ (annulus and orientation preserving), A- (annulus and orientation reversing), M (Möbius band), and F (focus). The DLB of a 2-torus in a flow can be classified into three types: A+ × A+, A- × M (equivalently M × A- and M × M), and F × F. From the results, we conjecture the possible local bifurcations in both cases. For the 1-torus in a map, we conjecture that type A+ and A- DLBs correspond to a saddle-node and period-doubling bifurcations, respectively, whereas a type M DLB denotes a double-covering bifurcation, and type F relates to a Neimark-Sacker bifurcation. Similarly, for the 2-torus in a flow, we conjecture that type A+ × A+ DLBs correspond to saddle-node bifurcations, type A- × M DLBs to double-covering bifurcations, and type F × F DLBs to the Neimark-Sacker bifurcations. After introducing the mathematical concepts, we provide a DLB-calculating algorithm and illustrate all of the above bifurcations by examples.

  15. Quasi-periodic processes in the flare loop generated by sudden temperature enhancements at loop footpoints

    NASA Astrophysics Data System (ADS)

    Karlický, M.; Jelínek, P.

    2016-05-01

    ~500 s the process with the periodically interacting shocks slowly changes to slow mode magnetosonic free oscillation. Furthermore, we detected quasi-periodic processes, even in the chromosphere under the location of the pressure perturbation. These processes can be observed in intensities and Doppler shifts of optical chromospheric lines. In the case with the asymmetric perturbations, we found that the processes are even more complex.

  16. Quasi-Periodic Long-Term Quadrature Light Variability in Early Type Interacting Binary Systems

    NASA Astrophysics Data System (ADS)

    Peters, Geraldine Joan

    2015-08-01

    Four years of Kepler observations have revealed a class of Algol-type binaries in which the relative brightness of the quadrature light varies from > 1 to <1 on a time scale of about 100-400 days. The behavior pattern is quasi-periodic. We call these systems L/T (leading hemisphere/ trailing hemisphere) variables. Although L/T inequality in eclipsing binaries has been noted from ground-based photometry by several observers since the early 1950s, the regular or quasi-regular switching between maxima is new. Twenty L/T systems have so far been found in the Kepler database and at least three classes of L/T behavior have been identified. In this presentation I will give an update on the L/T phenomenon gleaned from the Kepler and K2 databases. The Kepler and K2 light curves are being analyzed with the 2015 version of the Wilson-Devinney (WD) program that includes major improvements in modeling star spots (i.e. spot motions due to drift and stellar rotation and spot growth and decay). The prototype L/T variable is WX Draconis (A8V + K0IV, P=1.80 d) which shows L/ T light variations of 2-3%. The primary is a delta Scuti star with a dominant pulsation period of 41 m. Preliminary analysis of the WX Dra data suggests that the L/T variability can be fit with either an accretion hot spot on the primary (T = 2.3 Tphot) that jumps in longitude or a magnetic cool spotted region on the secondary. If the latter model is correct the dark region must occupy at least 20% of the surface of the facing hemisphere of the secondary if it is completely black, or a larger area if not completely black. In both hot and cool spot scenarios magnetic fields must play a role in the activity. Support from NASA grants NNX11AC78G and NNX12AE44G and USC’s Women in Science and Engineering (WiSE) program is greatly appreciated.

  17. New insights into the quasi-periodic X-ray burster GS 0836-429

    NASA Astrophysics Data System (ADS)

    Aranzana, E.; Sánchez-Fernández, C.; Kuulkers, E.

    2016-02-01

    GS 0836-429 is a neutron star X-ray transient that displays Type-I X-ray bursts. In 2003 and 2004 it experienced two outbursts in X-rays. We present here an analysis of the system's bursting properties during these outbursts. We studied the evolution of the 2003-2004 outbursts in soft X-rays using RXTE (2.5-12 keV; ASM) and in hard X-rays with INTEGRAL (17-80 keV, IBIS/ISGRI). Using data from the JEM-X monitor onboard INTEGRAL, we studied the bursting properties of the source. We detected 61 Type-I X-ray bursts during the 2004 outburst and confirm that the source displayed a quasi-periodic burst recurrence time of about 2.3 h. We improve the characterisation of the fuel composition, as well as the description of the typical burst durations and fluences. We estimate the average value of α to be 49 ± 3, which describes the ratio of the gravitational energy released between bursts to the nuclear energy released in an X-ray burst. Both this value and the observed burst profiles indicate a regime of a mixed He/H runaway triggered by unstable helium ignition. In addition, we report the detection of four series of double bursts, with burst recurrence times of ≤20 min. The secondary bursts are always shorter and less energetic than the primary and typical bursts from the source. The measured recurrence time in double bursts is too short to allow the accretion of enough fresh material, which is needed to trigger a Type-I X-ray burst. This suggests the presence of leftover, unburned material from the preceding burst, which gets ignited on a time scale of minutes. The energies and time scales of the secondary bursts suggest a lower fraction of hydrogen compared to that estimated for the primary bursts. The persistent emission was roughly constant during the period when the Type I X-ray bursts were detected. We derive an average accretion rate during our observations of ṁ ~ 8% ṁEdd. The spectrum of the persistent emission during these observations can be fit with a non

  18. High frequency dynamic nuclear polarization.

    PubMed

    Ni, Qing Zhe; Daviso, Eugenio; Can, Thach V; Markhasin, Evgeny; Jawla, Sudheer K; Swager, Timothy M; Temkin, Richard J; Herzfeld, Judith; Griffin, Robert G

    2013-09-17

    During the three decades 1980-2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical, and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-γ nuclei such as the I = 1/2 species (13)C or (15)N. The difficulty is still greater when quadrupolar nuclei, such as (17)O or (27)Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime, roughly 150-660 GHz, and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades, scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low

  19. High Frequency Dynamic Nuclear Polarization

    PubMed Central

    Ni, Qing Zhe; Daviso, Eugenio; Can, Thach V.; Markhasin, Evgeny; Jawla, Sudheer K.; Swager, Timothy M.; Temkin, Richard J.; Herzfeld, Judith; Griffin, Robert G.

    2013-01-01

    Conspectus During the three decades 1980–2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical and biological problems. In particular, a variety of dipolar recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-γ nuclei such as the I = ½ species 13C or 15N. The difficulty is still greater when quadrupolar nuclei, like 17O or 27Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime — roughly 150–660 GHz — and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low

  20. Phase-rectified signal averaging for the detection of quasi-periodicities and the prediction of cardiovascular risk

    NASA Astrophysics Data System (ADS)

    Kantelhardt, Jan W.; Bauer, Axel; Schumann, Aicko Y.; Barthel, Petra; Schneider, Raphael; Malik, Marek; Schmidt, Georg

    2007-03-01

    We present the phase-rectified signal averaging (PRSA) method as an efficient technique for the study of quasi-periodic oscillations in noisy, nonstationary signals. It allows the assessment of system dynamics despite phase resetting and noise and in relation with either increases or decreases of the considered signal. We employ the method to study the quasi-periodicities of the human heart rate based on long-term ECG recordings. The center deflection of the PRSA curve characterizes the average capacity of the heart to decelerate (or accelerate) the cardiac rhythm. It can be measured by a central wavelet coefficient which we denote as deceleration capacity (DC). We find that decreased DC is a more precise predictor of mortality in survivors of heart attack than left ventricular ejection fraction, the current "gold standard" risk predictor. In addition, we discuss the dependence of the DC parameter on age and on diabetes.

  1. Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-Ray Blazar PG 1553+113

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; Di Venere, L.; D´nguez, A.; Drell, P. S.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fuhrmann, L.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Harding, A. K.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Magill, J.; Maldera, S.; Manfreda, A.; Max-Moerbeck, W.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nuss, E.; Ohno, M.; Ohsugi, T.; Ojha, R.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Pearson, T. J.; Perkins, J. S.; Perri, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Suson, D. J.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Wood, K. S.; Wood, M.; Zimmer, S.; Berdyugin, A.; Corbet, R. H. D.; Hovatta, T.; Lindfors, E.; Nilsson, K.; Reinthal, R.; Sillanpää, A.; Stamerra, A.; Takalo, L. O.; Valtonen, M. J.

    2015-11-01

    We report for the first time a γ-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the γ-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 ± 0.08 year period γ-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in ˜10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

  2. High-Frequency Inductor Materials

    NASA Astrophysics Data System (ADS)

    Varga, L. K.

    2014-01-01

    The Finemet-type nanocrystalline alloy represents an advanced soft-magnetic metal-metal-type nanocomposite with an eddy-current-determined high- frequency limit. A survey of different heat treatments under tensile stress is presented to tailor the hysteresis loop by induced transversal anisotropy. The flattened loop having reduced effective permeability enhances the eddy- current limit in the MHz region; For example, continuous stress annealing in a tubular furnace of 1 m length at 650°C, pulling the ribbon with a velocity of 4 m/min under a tensile stress of 200 MPa, results in a wound core having a permeability of 120 and a frequency limit of 10 MHz. Careful annealing preserves the static coercivity below 10 A/m. The power loss at 0.1 T and 100 kHz is only 82 mW/cm3, which is an order of magnitude lower then the values obtained for Sendust™ cores in similar conditions.

  3. On quasi-periodic solutions of the 2+1 dimensional Caudrey-Dodd-Gibbon-Kotera-Sawada equation

    NASA Astrophysics Data System (ADS)

    Cao, Cewen; Wu, Yongtang; Geng, Xianguo

    1999-05-01

    The 2+1 dimensional Caudrey-Dodd-Gibbon-Kotera-Sawada equation is decomposed into systems of integrable ordinary differential equations resorting to the nonlinearization of Lax pairs. The Abel-Jacobi coordinates are introduced to straighten the flows, from which quasi-periodic solutions of the 2+1 dimensional Caudrey-Dodd-Gibbon-Kotera-Sawada equation are obtained in terms of Riemann theta functions.

  4. Pressurized high frequency thermoacoustic engines

    NASA Astrophysics Data System (ADS)

    Webb, Nicholas D.

    Acoustic heat engines show much promise for converting waste heat to electricity. Since most applications require high power levels, high frequency thermoacoustic engines can reach such performance by operating with a pressurized working gas. Results on a 3 kHz prime mover, consisting of a quarter-wave resonator and a random stack material between two heat exchangers, show that the acoustic power from such a device is raised substantially as the working gas is pressurized. At pressures up to approximately 10 bar, the increase in acoustic power is approximately linear to the increase in pressure, and thus is an effective way to increase the power output of thermoacoustic engines. Since the heat input was not changed during the experiments, the increases in acoustic power translate directly to increases in engine efficiency which is calculated as the output acoustic power divided by the input heat power. In most experiments run in this study, the engine efficiency increased by a factor of at least 4 as the pressure was increased from 2 bar up to about 10 bar. Further increases in pressure lead to acoustic power saturation and eventual attenuation. This is most likely due to a combination of several factors including the shrinking thermal penetration depth, and the fact that the losses increase faster with pressure in a random stack material than in traditional parallel plates. Pressurization also leads to a lower DeltaT for onset of oscillations in the range of 10 bar of mean pressure, potentially opening up even more heat sources that can power a thermoacoustic engine. Results from another 3 kHz engine, one that was pressurized itself as opposed to being placed in a pressurized chamber, are also presented. The configuration of this engine solves the problem of how to simultaneously pressurize the engine and inject heat into the hot heat exchanger. It was also noted that the geometry of the resonator cavity in the quarter wavelength pressurized engine plays an

  5. Evidence for High-frequency QPOs with a 3:2 Frequency Ratio from a 5000 Solar Mass Black Hole

    NASA Astrophysics Data System (ADS)

    Pasham, Dheeraj R.; Cenko, S. Bradley; Zoghbi, Abderahmen; Mushotzky, Richard F.; Miller, Jon; Tombesi, Francesco

    2015-09-01

    Following the discovery of 3:2 resonance quasi-periodic oscillations (QPOs) in M82X-1, we have constructed power density spectra (PDS) of all 15 (sufficiently long) XMM-Newton observations of the ultraluminous X-ray source NGC 1313 X-1 (LX ≈ 2 × 1040 erg s-1). We detect a strong QPO at a frequency of 0.29 ± 0.01 Hz in data obtained on 2012 December 16. Subsequent searching of all the remaining observations for a 3:2/2:3 frequency pair revealed a feature at 0.46 ± 0.02 Hz on 2003 December 13 (frequency ratio of 1.59 ± 0.09). The global significance of the 0.29 Hz feature considering all frequencies between 0.1 and 4 Hz is >3.5σ. The significance of the 0.46 ± 0.02 Hz QPO is >3.5σ for a search at 2/3 and 3/2 of 0.29 Hz. We also detect lower-frequency QPOs (32.9 ± 2.6 and 79.7 ± 1.2 mHz). All the QPOs are superimposed on a continuum consisting of flat-topped, band-limited noise, breaking into a power law at a frequency of 16 ± 3 mHz and white noise at ≳0.1 Hz. NGC 1313 X-1's PDS is analogous to stellar-mass black holes’ (StMBHs) PDS in the so-called steep power-law state, but with the respective frequencies (both QPOs and break frequencies) scaled down by a factor of ˜1000. Using the inverse mass-to-high-frequency QPO scaling of StMBHs, we estimate NGC 1313 X-1's black hole mass to be 5000 ± 1300 M⊙, consistent with an inference from the scaling of the break frequency. However, the implied Eddington ratio, LEdd > 0.03 ± 0.01, is significantly lower compared to that of StMBHs in the steep power-law state (LEdd ≳ 0.2).

  6. Damping and power spectra of quasi-periodic intensity disturbances above a solar polar coronal hole

    NASA Astrophysics Data System (ADS)

    Jiao, Fang-Ran; Xia, Li-Dong; Huang, Zheng-Hua; Li, Bo; Fu, Hui; Yuan, Ding; Chandrashekhar, Kalugodu

    2016-06-01

    We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 Å and 193 Å passbands, aiming to provide more insights into their physical nature. The damping and power spectra of the intensity disturbances with frequencies from 0.07 mHz to 10.5 mHz are investigated. The damping of the intensity disturbances tends to be stronger at lower frequencies, and their damping behavior below 980″ (for comparison, the limb is at 945″) is different from what happens above. No significant difference is found between the damping of the intensity disturbances in the AIA 171 Å and that in the AIA 193 Å. The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 Å than in the AIA 193 Å, but the difference is within one standard deviation. An additional enhanced component is present in the power spectra in a period range of 8–40 min at lower heights. The power spectra of a spicule is highly correlated with its associated intensity disturbance, which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities. We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities.

  7. High frequency, high power capacitor development

    NASA Technical Reports Server (NTRS)

    White, C. W.; Hoffman, P. S.

    1983-01-01

    A program to develop a special high energy density, high power transfer capacitor to operate at frequency of 40 kHz, 600 V rms at 125 A rms plus 600 V dc bias for space operation. The program included material evaluation and selection, a capacitor design was prepared, a thermal analysis performed on the design. Fifty capacitors were manufactured for testing at 10 kHz and 40 kHz for 50 hours at Industrial Electric Heating Co. of Columbus, Ohio. The vacuum endurance test used on environmental chamber and temperature plate furnished by Maxwell. The capacitors were energized with a special power conditioning apparatus developed by Industrial Electric Heating Co. Temperature conditions of the capacitors were monitored by IEHCo test equipment. Successful completion of the vacuum endurance test series confirmed achievement of the main goal of producing a capacitor or reliable operation at high frequency in an environment normally not hospitable to electrical and electronic components. The capacitor developed compared to a typical commercial capacitor at the 40 kHz level represents a decrease in size and weight by a factor of seven.

  8. High power, high frequency helix TWT's

    NASA Astrophysics Data System (ADS)

    Sloley, H. J.; Willard, J.; Paatz, S. R.; Keat, M. J.

    The design and performance characteristics of a 34-GHz pulse tube capable of 75 W peak power output at 30 percent duty cycle and a broadband CW tube are presented. Particular attention is given to the engineering problems encountered during the development of the tubes, including the suppression of backward wave oscillation, the design of electron guns for small-diameter high-current beams, and the thermal capability of small helix structures. The discussion also covers the effects of various design parameters and choice of engineering materials on the ultimate practical limit of power and gain at the operating frequencies. Measurements are presented for advanced experimental tubes.

  9. Special Aspects in Designing High - Frequency Betatron

    NASA Astrophysics Data System (ADS)

    Filimonov, A. A.; Kasyanov, S. V.; Kasyanov, V. A.

    2016-01-01

    The article is devoted to designing the high - frequency betatron. In high - frequency betatron most important problem is overheating of the elements of the body radiator unit. In an article some directions of solving this problem are shown.

  10. Atomic frequency standards for ultra-high-frequency stability

    NASA Technical Reports Server (NTRS)

    Maleki, L.; Prestage, J. D.; Dick, G. J.

    1987-01-01

    The general features of the Hg-199(+) trapped-ion frequency standard are outlined and compared to other atomic frequency standards, especially the hydrogen maser. The points discussed are those which make the trapped Hg-199(+) standard attractive: high line Q, reduced sensitivity to external magnetic fields, and simplicity of state selection, among others.

  11. High frequency-heated air turbojet

    NASA Technical Reports Server (NTRS)

    Miron, J. H. D.

    1986-01-01

    A description is given of a method to heat air coming from a turbojet compressor to a temperature necessary to produce required expansion without requiring fuel. This is done by high frequency heating, which heats the walls corresponding to the combustion chamber in existing jets, by mounting high frequency coils in them. The current transformer and high frequency generator to be used are discussed.

  12. High frequency testing of rubber mounts.

    PubMed

    Vahdati, Nader; Saunders, L Ken Lauderbaugh

    2002-04-01

    Rubber and fluid-filled rubber engine mounts are commonly used in automotive and aerospace applications to provide reduced cabin noise and vibration, and/or motion accommodations. In certain applications, the rubber mount may operate at frequencies as high as 5000 Hz. Therefore, dynamic stiffness of the mount needs to be known in this frequency range. Commercial high frequency test machines are practically nonexistent, and the best high frequency test machine on the market is only capable of frequencies as high as 1000 Hz. In this paper, a high frequency test machine is described that allows test engineers to study the high frequency performance of rubber mounts at frequencies up to 5000 Hz. PMID:12071247

  13. Phase lags of quasi-periodic oscillations across source states in the low-mass X-ray binary 4U 1636-53

    NASA Astrophysics Data System (ADS)

    de Avellar, Marcio G. B.; Méndez, Mariano; Altamirano, Diego; Sanna, Andrea; Zhang, Guobao

    2016-09-01

    While there are many dynamical mechanisms and models that try to explain the origin and phenomenology of the quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries, few of them address how the radiative processes occurring in these extreme environments give rise to the rich set of variability features actually observed in these light curves. A step towards this end comes from the study of the energy and frequency dependence of the phase lags of these QPOs. Here we used a methodology that allowed us to study, for the first time, the dependence of the phase lags of all QPOs in the range of 1-1300 Hz detected in the low-mass X-ray binary 4U 1636-53 upon energy and frequency as the source changes its states as it moves through the colour-colour diagram. Our results suggest that within the context of models of up-scattering Comptonization, the phase lags dependences upon frequency and energy can be used to extract size scales and physical conditions of the medium that produces the lags.

  14. High Frequency Electronic Packaging Technology

    NASA Technical Reports Server (NTRS)

    Herman, M.; Lowry, L.; Lee, K.; Kolawa, E.; Tulintseff, A.; Shalkhauser, K.; Whitaker, J.; Piket-May, M.

    1994-01-01

    Commercial and government communication, radar, and information systems face the challenge of cost and mass reduction via the application of advanced packaging technology. A majority of both government and industry support has been focused on low frequency digital electronics.

  15. Late Holocene shoreline behavior in embayments of Lake Michigan: Influence of quasi-periodic lake-level variations and sediment supply

    SciTech Connect

    Thompson, T.A.; Baedke, S.J. . Indiana Geological Survey)

    1994-04-01

    Lake Michigan contains numerous former embayments into glacial deposits or bedrock. Many of the embayments contain dunes, spits, and captured lakes, but others contain arcuate strandplains of beach ridges. The strandplains are a geologic record of shoreline behavior and lake-level variation throughout the late Holocene. The larger strandplains show similar long-term patterns of beach-ridge development. The similar patterns are expected because variations in lake level are a primary control on shoreline behavior, and all embayments would have experienced relatively the same lake-level changes. Some variations in the long-term pattern of shoreline development do occur between strandplains. These dissimilarities are primarily a function of different rates of sediment supply to the shoreline of each embayment. Beach-ridge development within embayments can be represented on a rate of water level change versus rate of sediment supply diagram (Curray diagram) as three superimposed ovals on the positive rate of sediment supply side of the diagram. The three stacked ovals represent the three quasi-periodic lake-level variations defined by Thompson (1992) and show the position of the shoreline for a given time within the Curray diagram fields. For shorelines with a high rate of sediment supply, only the 30-year quasi-periodic variation would reach the aggradation line. For shorelines having significantly less sediment supply, rising lake level on the 150- and 600-year variations would force the 30-year oval across the aggradation line and well into the depositional and possibly the erosional transgression fields. Under these conditions erosion would occur that may remove, stack, or at least prevent one or more beach ridges from being developed.

  16. High frequency gyrokinetic particle simulation

    SciTech Connect

    Kolesnikov, R. A.; Lee, W. W.; Qin, H.; Startsev, E.

    2007-07-15

    The gyrokinetic approach for arbitrary frequency dynamics in magnetized plasmas is explored, using the gyrocenter-gauge kinetic theory. Contrary to low-frequency gyrokinetics, which views each particle as a rigid charged ring, arbitrary frequency response of a particle is described by a quickly changing Kruskal ring. This approach allows the separation of gyrocenter and gyrophase responses and thus allows for, in many situations, larger time steps for the gyrocenter push than for the gyrophase push. The gyrophase response which determines the shape of Kruskal rings can be described by a Fourier series in gyrophase for some problems, thus allowing control over the cyclotron harmonics at which the plasma responds. A computational algorithm for particle-in-cell simulation based on this concept has been developed. An example of the ion Bernstein wave is used to illustrate its numerical properties, and comparison with a direct Lorentz-force approach is presented.

  17. Detection of quasi-periodic processes in repeated measurements: New approach for the fitting and clusterization of different data

    NASA Astrophysics Data System (ADS)

    Nigmatullin, R.; Rakhmatullin, R.

    2014-12-01

    Many experimentalists were accustomed to think that any independent measurement forms a non-correlated measurement that depends weakly from others. We are trying to reconsider this conventional point of view and prove that similar measurements form a strongly-correlated sequence of random functions with memory. In other words, successive measurements "remember" each other at least their nearest neighbors. This observation and justification on real data help to fit the wide set of data based on the Prony's function. The Prony's decomposition follows from the quasi-periodic (QP) properties of the measured functions and includes the Fourier transform as a partial case. New type of decomposition helps to obtain a specific amplitude-frequency response (AFR) of the measured (random) functions analyzed and each random function contains less number of the fitting parameters in comparison with its number of initial data points. Actually, the calculated AFR can be considered as the generalized Prony's spectrum (GPS), which will be extremely useful in cases where the simple model pretending on description of the measured data is absent but vital necessity of their quantitative description is remained. These possibilities open a new way for clusterization of the initial data and new information that is contained in these data gives a chance for their detailed analysis. The electron paramagnetic resonance (EPR) measurements realized for empty resonator (pure noise data) and resonator containing a sample (CeO2 in our case) confirmed the existence of the QP processes in reality. But we think that the detection of the QP processes is a common feature of many repeated measurements and this new property of successive measurements can attract an attention of many experimentalists. To formulate some general conditions that help to identify and then detect the presence of some QP process in the repeated experimental measurements. To find a functional equation and its solution that

  18. Quasi-periodic patterns (QPP): large-scale dynamics in resting state fMRI that correlate with local infraslow electrical activity.

    PubMed

    Thompson, Garth John; Pan, Wen-Ju; Magnuson, Matthew Evan; Jaeger, Dieter; Keilholz, Shella Dawn

    2014-01-01

    Functional connectivity measurements from resting state blood-oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) are proving a powerful tool to probe both normal brain function and neuropsychiatric disorders. However, the neural mechanisms that coordinate these large networks are poorly understood, particularly in the context of the growing interest in network dynamics. Recent work in anesthetized rats has shown that the spontaneous BOLD fluctuations are tightly linked to infraslow local field potentials (LFPs) that are seldom recorded but comparable in frequency to the slow BOLD fluctuations. These findings support the hypothesis that long-range coordination involves low frequency neural oscillations and establishes infraslow LFPs as an excellent candidate for probing the neural underpinnings of the BOLD spatiotemporal patterns observed in both rats and humans. To further examine the link between large-scale network dynamics and infraslow LFPs, simultaneous fMRI and microelectrode recording were performed in anesthetized rats. Using an optimized filter to isolate shared components of the signals, we found that time-lagged correlation between infraslow LFPs and BOLD is comparable in spatial extent and timing to a quasi-periodic pattern (QPP) found from BOLD alone, suggesting that fMRI-measured QPPs and the infraslow LFPs share a common mechanism. As fMRI allows spatial resolution and whole brain coverage not available with electroencephalography, QPPs can be used to better understand the role of infraslow oscillations in normal brain function and neurological or psychiatric disorders. PMID:24071524

  19. Confronting models for the high-frequency QPOs with Lense-Thirring precession

    NASA Astrophysics Data System (ADS)

    Stefanov, Ivan Zh.

    2014-11-01

    Quasi-periodic oscillations (QPOs) have been observed in the power-density spectra (PDS) of some low-mass X-ray binaries (LMXBs) containing a black hole. The two major groups of QPOs - low-frequency (LF) and high-frequency (HF) - have rather different properties. That is why they are usually studied separately. In the literature, one can find a large number of models for the HF QPOs but not so many for the LF ones. HF QPOs have attracted significant research efforts due to their potential to provide indispensable information for the properties of the black hole, for its accretion disc and for strong field gravity in general. However, in order to interpret the data for the HF QPOs of the observed objects, we have to fix a model. Here, we propose a simple test which could allow us to sift the models. The test is based on five rather general assumptions concerning the nature of the central object in black hole binaries and the mechanism for the generation of the LF QPOs observed in the PDS of such objects. In other words, we combine facts that we know about the LF and the HF QPOs of several objects and search for conflicts. As a result, we single out a model for the HF QPOs - the 3: 2 non-linear resonance model. As a byproduct of this study, we propose loose constraints on the mass of the LMXB H 1743-322.

  20. Can Any ``Invariants'' Be Revealed in Quasi-periodic Phenomena Observed from Scorpius X-1?

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Sergey; Titarchuk, Lev

    2002-06-01

    Using a large number of Rossi X-Ray Timing Explorer observations of Scorpius X-1, we present a detailed investigation of the transition layer and relativistic precession models (TLM and RPM, respectively). These models predict the existence of the invariant quantities: an inclination angle δ of the magnetospheric axis with the normal to the disk for the TLM and a neutron star (NS) mass MNS for the RPM. Theoretical predictions of both models are tested, and their self-consistency is checked. We establish the following: (1) The inferred δ-value is 5.56d+/-0.09d. Correlation of the δ-values with the horizontal-branch oscillation (HBO) frequency is rather weak. (2) There is a strong correlation between an inferred MNS and the HBO frequency in the RPM frameworks. (3) We infer MNS for different assumptions regarding the relations between the HBO frequency νHBO and the nodal frequency νnod. We find that the inferred MNS=2.7+/-0.1 Msolar cannot be consistent with any equation of state of NS matter. We conclude that the RPM fails to describe the data while the TLM seems to be compatible.

  1. Can Any Invariants Be Revealed in Quasi-periodic Phenomena Observed From Sco X-1?

    NASA Astrophysics Data System (ADS)

    Kuznetsov, S.; Titarchuk, L.

    Using large number of Rossi X-ray Time Explorer observations of Sco X-1 we present a detailed investigation of the transition layer and the relativistic precession models (TLM and RPM, respectively). These models predict the existence of the invariant quantities: an inclination angle delta of the magnetospheric axis with the normal to the disk for the TLM and a neutron star (NS) mass MN S for the RPM. Theoretical predictions of both models are tested and their self-consistency is checked. We establish that: (1) The inferred delta angle is 5.56 +/- 0.09 degrees. Correlation of the delta-values with the horizontal branch oscillation (HBO) frequency is rather weak. (2) There is a strong correlation between an inferred MN S and the HBO frequency in the RPM frameworks. (3) We infer MN S for different assumptions regarding the relations between the HBO frequency and the nodal frequency. We find that the inferred MN S = 2.7 +/- 0.1M cannot be consistent with any EOS of NS matter. We conclude that RPM fails to describe the data while TLM seems to be compatible.

  2. Transponder System for High-Frequency Ranging

    NASA Technical Reports Server (NTRS)

    Lichtenberg, C. L.; Shores, P. W.; Kobayashi, H. S.

    1986-01-01

    Transponder system uses phase difference between transmitted and reflected high-frequency radio waves to measure distance to target. To suppress spurious measurements of reflections from objects near target at transmitted frequency and its harmonics, transponder at target generates return signal at half transmitted frequency. System useful in such applications as surveying, docking of ships, and short-range navigation.

  3. Interpretations for Low- and High-Frequency QPO Correlations of X-Ray Sources among White Dwarfs, Neutron Stars, and Black Holes

    NASA Astrophysics Data System (ADS)

    Zhang, C. M.; Yin, H. X.; Zhao, Y. H.

    2007-04-01

    An empirical linear relation is found to exist between the high and low frequencieshigh, νlow) of quasi-periodic oscillations (QPOs) for black hole candidates (BHCs), neutron stars (NSs), and white dwarfs (WDs) in binary systems, spanning 5 orders of magnitude in frequency. For the NS Z (atoll) sources, νhigh and νlow are identified as the lower kHz QPO frequency and horizontal-branch oscillation (HBO) frequency νHBO (broad noise components); for the BHCs and low-luminosity NSs, they are the QPOs and broad noise components at frequencies between 1 and 10 Hz; for WDs, they are the ``dwarf nova oscillations'' (DNOs) and QPOs of cataclysmic variables (CVs). To interpret this relation, our model ascribes νhigh to the Alfvén wave oscillation frequency at a preferred radius, and νlow to the same mechanism at another radius. We can then obtain νlow=0.08νhigh and the relation between the upper kHz QPO frequency ν2 and the HBO frequency, νHBO~=(56 Hz)(ν2/kHz)2, which are in accordance with the observed empirical relations. Furthermore, some implications of the model are discussed, including why QPO frequencies of WDs and NSs span 5 orders of magnitude.

  4. High frequency oscillations in the intact brain

    PubMed Central

    Buzsáki, György; da Silva, Fernando Lopes

    2016-01-01

    High frequency oscillations (HFOs) constitute a novel trend in neurophysiology that is fascinating neuroscientists in general, and epileptologists in particular. But what are HFOs? What is the frequency range of HFOs? Are there different types of HFOs, physiological and pathological? How are HFOs generated? Can HFOs represent temporal codes for cognitive processes? These questions are pressing and this symposium volume attempts to give constructive answers. As a prelude to this exciting discussion, we summarize the physiological high frequency patterns in the intact brain, concentrating mainly on hippocampal patterns, where the mechanisms of high frequency oscillations are perhaps best understood. PMID:22449727

  5. Lightweight, high-frequency transformers

    NASA Technical Reports Server (NTRS)

    Schwarze, G. E.

    1983-01-01

    The 25-kVA space transformer was developed under contract by Thermal Technology Laboratory, Buffalo, N. Y. The NASA Lewis transformer technology program attempted to develop the baseline technology. For the 25-kVA transformer the input voltage was chosen as 200 V, the output voltage as 1500 V, the input voltage waveform as square wave, the duty cycle as continuous, the frequency range (within certain constraints) as 10 to 40 kHz, the operating temperatures as 85 deg. and 130 C, the baseplate temperature as 50 C, the equivalent leakage inductance as less than 10 micro-h, the operating environment as space, and the life expectancy as 10 years. Such a transformer can also be used for aircraft, ship and terrestrial applications.

  6. HIGH CURRENT RADIO FREQUENCY ION SOURCE

    DOEpatents

    Abdelaziz, M.E.

    1963-04-01

    This patent relates to a high current radio frequency ion source. A cylindrical plasma container has a coil disposed around the exterior surface thereof along the longitudinal axis. Means are provided for the injection of an unionized gas into the container and for applying a radio frequency signal to the coil whereby a radio frequency field is generated within the container parallel to the longitudinal axis thereof to ionize the injected gas. Cathode and anode means are provided for extracting transverse to the radio frequency field from an area midway between the ends of the container along the longitudinal axis thereof the ions created by said radio frequency field. (AEC)

  7. Quasi-periodic oscillations in short recurring bursts of magnetars SGR 1806–20 and SGR 1900+14 observed with RXTE

    SciTech Connect

    Huppenkothen, D.; Heil, L. M.; Watts, A. L.; Göğüş, E.

    2014-11-10

    Quasi-periodic oscillations (QPOs) observed in the giant flares of magnetars are of particular interest due to their potential to open up a window into the neutron star interior via neutron star asteroseismology. However, only three giant flares have been observed. We therefore make use of the much larger data set of shorter, less energetic recurrent bursts. Here, we report on a search for QPOs in a large data set of bursts from the two most burst-active magnetars, SGR 1806-20 and SGR 1900+14, observed with Rossi X-ray Timing Explorer. We find a single detection in an averaged periodogram comprising 30 bursts from SGR 1806–20, with a frequency of 57 Hz and a width of 5 Hz, remarkably similar to a giant flare QPO observed from SGR 1900+14. This QPO fits naturally within the framework of global magneto-elastic torsional oscillations employed to explain giant flare QPOs. Additionally, we uncover a limit on the applicability of Fourier analysis for light curves with low background count rates and strong variability on short timescales. In this regime, standard Fourier methodology and more sophisticated Fourier analyses fail in equal parts by yielding an unacceptably large number of false-positive detections. This problem is not straightforward to solve in the Fourier domain. Instead, we show how simulations of light curves can offer a viable solution for QPO searches in these light curves.

  8. Normal-Branch Quasi-periodic Oscillations in Scorpius X-1: Viscous Oscillations of a Spherical Shell Near the Neutron Star

    NASA Astrophysics Data System (ADS)

    Titarchuk, L. G.; Bradshaw, C. F.; Geldzahler, B. J.; Fomalont, E. B.

    2001-07-01

    We present a comprehensive classification of all observed quasi-periodic oscillations (QPOs) within the framework of the transition layer model using a large set of Rossi X-Ray Timing Explorer data for Scorpius X-1. The model assumes an optically thin material along the observer's line of sight in the horizontal branch and an increasingly optically thick material while in the other two branches that is consistent with X-ray and radio observations and the disk transition layer model of QPOs. We identify the ~6 Hz frequencies in the normal branch as acoustic oscillations of a spherical shell around the neutron star (NS) that is formed after radiation pressure near the Eddington accretion rate destroys the disk. The size of the shell is on the order of one NS radius from the NS. We also estimate the upper limit of Sco X-1's magnetic field to be 0.7×106 G at about one NS radius above the NS surface while in the horizontal X-ray branch.

  9. Time delay effect between long quasi-periodic oscillations of 37 GHz radio sources and the magnetic field of the nearest sunspots

    NASA Astrophysics Data System (ADS)

    Smirnova, V. V.; Riehokainen, A.; Solov'ev, A. A.; Kallunki, J.

    2015-06-01

    Measurements and the interpretation of the time delay effect between long quasi-periodic oscillations of sunspot magnetic fields and nearby millimeter radio sources observed at 37 GHz were the main goals of this work. Ground-based radio telescope operated by Metsähovi Radio Observatory, Aalto University, Finland was used to obtain time series variations of radio intensity at 37 GHz frequency, as well as, the Helioseismic and Magnetic Imager instrument on-board the Solar Dynamics Observatory spacecraft was used to obtain the magnetic field time series variations. Lags (time delays) in the interval of 15-35 minutes were obtained by cross-correlation analysis of time series and by direct geometrical measurements of distances between the radio sources and nearby sunspots. These distances were in the interval of 11-24 Mm. Corresponding time delays were defined as the relation of these distances to the sound speed. Time delays obtained by two different independent methods turned to be very close. This fact confirms the interpretation of the phenomenon under the study as a process of propagation of disturbances from the slowly oscillating sunspot to the radio source with the sound speed.

  10. Psychophysical tuning curves at very high frequencies

    NASA Astrophysics Data System (ADS)

    Yasin, Ifat; Plack, Christopher J.

    2005-10-01

    For most normal-hearing listeners, absolute thresholds increase rapidly above about 16 kHz. One hypothesis is that the high-frequency limit of the hearing-threshold curve is imposed by the transmission characteristics of the middle ear, which attenuates the sound input [Masterton et al., J. Acoust. Soc. Am. 45, 966-985 (1969)]. An alternative hypothesis is that the high-frequency limit of hearing is imposed by the tonotopicity of the cochlea [Ruggero and Temchin, Proc. Nat. Acad. Sci. U.S.A. 99, 13206-13210 (2002)]. The aim of this study was to test these hypotheses. Forward-masked psychophysical tuning curves (PTCs) were derived for signal frequencies of 12-17.5 kHz. For the highest signal frequencies, the high-frequency slopes of some PTCs were steeper than the slope of the hearing-threshold curve. The results also show that the human auditory system displays frequency selectivity for characteristic frequencies (CFs) as high as 17 kHz, above the frequency at which absolute thresholds begin to increase rapidly. The findings suggest that, for CFs up to 17 kHz, the high-frequency limitation in humans is imposed in part by the middle-ear attenuation, and not by the tonotopicity of the cochlea.

  11. Phase identification of quasi-periodic flow measured by particle image velocimetry with a low sampling rate

    NASA Astrophysics Data System (ADS)

    Pan, Chong; Wang, Hongping; Wang, Jinjun

    2013-05-01

    This work mainly deals with the proper orthogonal decomposition (POD) time coefficient method used for extracting phase information from quasi-periodic flow. The mathematical equivalence between this method and the traditional cross-correlation method is firstly proved. A two-dimensional circular cylinder wake flow measured by time-resolved particle image velocimetry within a range of Reynolds numbers is then used to evaluate the reliability of this method. The effect of both the sampling rate and Reynolds number on the identification accuracy is finally discussed. It is found that the POD time coefficient method provides a convenient alternative for phase identification, whose feasibility in low-sampling-rate measurement has additional advantages for experimentalists.

  12. Noise-driven radiative shocks - A new model for the optical quasi-periodic oscillations of the AM Herculis objects

    NASA Technical Reports Server (NTRS)

    Wolff, Michael T.; Wood, Kent S.; Imamura, James N.

    1991-01-01

    A model for the 0.3-1.2 Hz optical quasi-periodic oscillations (QPOs) observed in a number of AM Her-type binary systems has been developed. It is suggested that the observed optical modulation is the result of shock oscillations induced by nonsteady accretion flows. It is shown that time-dependent models of radiative shock waves in nonsteady accretion flows onto magnetic white dwarfs with mass 0.6 solar mass and magnetic field strength of 30 MG can produce optical QPOs similar to those observed in the AM Her objects. Theoretical calculations have shown that oscillations cannot be sustained for these white dwarf parameters when the accretion rate is constant.

  13. Anomalous magnetic response of a quasi-periodic mesoscopic ring in presence of Rashba and Dresselhaus spin-orbit interactions

    NASA Astrophysics Data System (ADS)

    Patra, Moumita; Maiti, Santanu K.

    2016-04-01

    We investigate the properties of persistent charge current driven by magnetic flux in a quasi-periodic mesoscopic Fibonacci ring with Rashba and Dresselhaus spin-orbit interactions. Within a tight-binding framework we work out individual state currents together with net current based on second-quantized approach. A significant enhancement of current is observed in presence of spin-orbit coupling and sometimes it becomes orders of magnitude higher compared to the spin-orbit interaction free Fibonacci ring. We also establish a scaling relation of persistent current with ring size, associated with the Fibonacci generation, from which one can directly estimate current for any arbitrary flux, even in presence of spin-orbit interaction, without doing numerical simulation. The present analysis indeed gives a unique opportunity of determining persistent current and has not been discussed so far.

  14. Optical filters using Cantor quasi-periodic one dimensional photonic crystal based on Si/SiO2

    NASA Astrophysics Data System (ADS)

    Sahel, S.; Amri, R.; Bouaziz, L.; Gamra, D.; Lejeune, M.; Benlahsen, M.; Zellama, K.; Bouchriha, H.

    2016-09-01

    Quasi-periodic one-dimensional Cantor photonic crystals are elaborated by depositing alternating silicon and silica Si/SiO2 layers by radiofrequency magnetron sputtering technique with cold plasma. Transmittance and reflectance spectra of these quasi crystals exhibit a large photonic band gap in the infrared range at normal incidence which is well reproduced by a theoretical model based on the transfer matrix method. The obtained wide photonic band gap reveals the existence of permitted modes depending on the nature and characteristics of the built in system which can constitute optical windows. This effect can be a good alternative for the design of flexible filters used in many areas of applications such as telecommunication and optoelectronic devices.

  15. Quasi-periodic fast-mode magnetosonic wave trains within coronal waveguides associated with flares and CMEs

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Ofman, Leon; Broder, Brittany; Karlický, Marian; Downs, Cooper

    2016-03-01

    Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new observational phenomenon recently discovered in the solar corona by the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging observations. They originate from flares and propagate at speeds up to ˜2000 km s-1 within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry suffcient energy fluxes required for coronal heating during their occurr ences. They can provide new diagnostics for the solar corona and their associated flares. We present recent observations of QFPs focusing on their spatio-temporal properties, temperature dependence, and statistical correlation with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2 flare with correlated QFPs and drifting zebra and fiber radio bursts, which might be different manifestations of the same fast-mode wave trains. We also discuss the potential roles of QFPs in accelerating and/or modulating the solar wind.

  16. Quasi-periodic pulsations with varying period in multi-wavelength observations of an X-class flare

    SciTech Connect

    Huang, Jing; Tan, Baolin; Zhang, Yin; Karlický, Marian; Mészárosová, Hana

    2014-08-10

    This work presents an interesting phenomenon of the period variation in quasi-periodic pulsations (QPPs) observed during the impulsive phase of a coronal mass ejection-related X1.1 class flare on 2012 July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR) to 22-23 s at microwaves, to ∼24 s at extreme ultraviolet emissions (EUV), and to 27-32 s at metric-decimetric waves. The microwave, EUV, and SXR QPPs, emitted from flare loops of different heights, were oscillating in phase. Fast kink mode oscillations were proposed to be the modulation mechanism, which may exist in a wide region in the solar atmosphere from the chromosphere to the upper corona or even to the interplanetary space. Changed parameters of flare loops through the solar atmosphere could result in the varying period of QPPs at different wavelengths. The first appearing microwave QPPs and quasi-periodic metric-decimetric type III bursts were generated by energetic electrons. This may imply that particle acceleration or magnetic reconnection were located between these two non-thermal emission sources. Thermal QPPs (in SXR and EUV emissions) occurred later than the nonthermal ones, which would suggest a some time for plasma heating or energy dissipation in flare loops during burst processes. At the beginning of flare, a sudden collapse and expansion of two separated flare loop structures occurred simultaneously with the multi-wavelength QPPs. An implosion in the corona, including both collapse and expansion of flare loops, could be a trigger of loop oscillations in a very large region in the solar atmosphere.

  17. Apparatus for measuring high frequency currents

    NASA Technical Reports Server (NTRS)

    Hagmann, Mark J. (Inventor); Sutton, John F. (Inventor)

    2003-01-01

    An apparatus for measuring high frequency currents includes a non-ferrous core current probe that is coupled to a wide-band transimpedance amplifier. The current probe has a secondary winding with a winding resistance that is substantially smaller than the reactance of the winding. The sensitivity of the current probe is substantially flat over a wide band of frequencies. The apparatus is particularly useful for measuring exposure of humans to radio frequency currents.

  18. Ultra-High-Frequency Capacitive Displacement Sensor

    NASA Technical Reports Server (NTRS)

    Vanzandt, Thomas R.; Kenny, Thomas W.; Kaiser, William J.

    1994-01-01

    Improved class of compact, high-resolution capacitive displacement sensors operates at excitation frequency of 915 MHz and measures about 7.5 by 4 by 2 centimeters. Contains commercially available 915-MHz oscillator and transmission-line resonator. Resonator contains stripline inductor in addition to variable capacitor. Ultrahigh excitation frequency offers advantages of resolution and frequency response. Not deleteriously affected by mechanical overdriving, or contact between electrodes.

  19. High frequency pressure oscillator for microcryocoolers.

    PubMed

    Vanapalli, S; ter Brake, H J M; Jansen, H V; Zhao, Y; Holland, H J; Burger, J F; Elwenspoek, M C

    2008-04-01

    Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80 K, delivering a cooling power of 10 mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5 MPa and compression volume of about 22.6 mm(3) when operating the actuator with a peak-to-peak sinusoidal voltage of 100 V at a frequency of 1 kHz. The electrical power input was 2.73 W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers. PMID:18447548

  20. Characterizing quasi-periodic disturbances in GPS TEC data and their drivers

    NASA Astrophysics Data System (ADS)

    Wurtz, J.; Coster, A. J.; Goncharenko, L.; Zhang, S.

    2012-12-01

    We examine a large data set (2003-2009) of total electron content (TEC) values derived from a global network of differential GPS receivers that was downloaded from the Madrigal database. We report on TEC oscillations at multiple periods ranging from 5 to ~30 days. A significant portion of oscillations with 9-day and 13.5-day periods is driven by the recurrent geomagnetic activity, as evident from the analysis of geomagnetic indices. The TEC disturbances in response to the recurrent geomagnetic activity are stronger at middle and high latitudes, and are less pronounced at lower latitudes (< 30 degrees). We also observe a correlation between TEC and the 28-day lunar cycle that is more evident at lower (equatorial) latitudes in both northern and southern hemispheres. The TEC disturbances associated with the lunar cycle are well pronounced during the northern hemisphere winter and equinox seasons.

  1. Turbulence in unsteady flow at high frequencies

    NASA Technical Reports Server (NTRS)

    Kuhn, Gary D.

    1990-01-01

    Turbulent flows subjected to oscillations of the mean flow were simulated using a large-eddy simulation computer code for flow in a channel. The objective of the simulations was to provide better understanding of the effects of time-dependent disturbances on the turbulence of a boundary layer and of the underlying physical phenomena regarding the basic interaction between the turbulence and external disturbances. The results confirmed that turbulence is sensitive to certain ranges of frequencies of disturbances. However, no direct connection was found between the frequency of imposed disturbances and the characteristic 'burst' frequency of turbulence. New insight into the nature of turbulence at high frequencies was found. Viscous phenomena near solid walls were found to be the dominant influence for high-frequency perturbations.

  2. Real-time, high frequency QRS electrocardiograph

    NASA Technical Reports Server (NTRS)

    Schlegel, Todd T. (Inventor); DePalma, Jude L. (Inventor); Moradi, Saeed (Inventor)

    2006-01-01

    Real time cardiac electrical data are received from a patient, manipulated to determine various useful aspects of the ECG signal, and displayed in real time in a useful form on a computer screen or monitor. The monitor displays the high frequency data from the QRS complex in units of microvolts, juxtaposed with a display of conventional ECG data in units of millivolts or microvolts. The high frequency data are analyzed for their root mean square (RMS) voltage values and the discrete RMS values and related parameters are displayed in real time. The high frequency data from the QRS complex are analyzed with imbedded algorithms to determine the presence or absence of reduced amplitude zones, referred to herein as RAZs. RAZs are displayed as go, no-go signals on the computer monitor. The RMS and related values of the high frequency components are displayed as time varying signals, and the presence or absence of RAZs may be similarly displayed over time.

  3. Overview of the Advanced High Frequency Branch

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.

    2015-01-01

    This presentation provides an overview of the competencies, selected areas of research and technology development activities, and current external collaborative efforts of the NASA Glenn Research Center's Advanced High Frequency Branch.

  4. Low-altitude quasi-periodic echoes studied using a large database of Gadanki radar observations

    NASA Astrophysics Data System (ADS)

    Venkateswara Rao, N.; Patra, A. K.; Rao, S. V. B.

    2009-01-01

    In this paper we present studies on low-altitude quasiperiodic (LQP) echoes based on a large database of Gadanki radar observations. LQP echoes have been observed 33% of the time during daytime and 39% during nighttime. Their occurrence is found to be maximum in the summer (daytime, 58% nighttime, 57%), followed by the September equinox (daytime, 32% nighttime, 48%), the March equinox (daytime, 26% nighttime, 36%), and minimum in the winter (daytime, 25% nighttime, 26%). Height-time occurrence of LQP echoes shows two local time maxima: one in the morning (0700-1100 LT) and another in the evening (1900-0000 LT). The most significant results not reported earlier are the large occurrence rate of LQP echoes and the height-time occurrence maps showing a descending pattern with close resemblance to tidal wind behavior. The Doppler velocities are upward-northward (downward-southward) for positive- (negative-) sloped LQP echoes. Also, we find the Doppler spread as high as 200 m s-1 at times underlining the presence of strong plasma turbulence in the collision-dominated lower E region. These results are discussed in the light of the current understanding of the LQP echoes.

  5. Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables - VIII. VW Hyi in outburst observed with the Southern African Large Telescope

    NASA Astrophysics Data System (ADS)

    Woudt, P. A.; Warner, B.; O'Donoghue, D.; Buckley, D. A. H.; Still, M.; Romero-Colemero, E.; Väisänen, P.

    2010-01-01

    We analyse four light curves obtained at high time resolution (~0.1s) with the 11-m Southern African Large Telescope, at the ends of two normal outbursts and one superoutburst of the dwarf nova VW Hyi. All of these contain at least some Dwarf Nova Oscillations (DNOs), which, when at their highest amplitudes, are seen in unprecedented detail. In addition to the expected DNOs with periods >20 s, we find a previously unknown modulation at 13.39s, but none at shorter periods. The various DNOs and their interaction with the longer period quasi-periodic oscillations are interpreted in terms of the model of magnetically controlled flow from an accretion disc proposed earlier in this series of papers. Our observations include rare DNOs very late in outburst; we find that the fundamental period does not increase beyond ~90 s, which is the same value that the independent `longer period DNOs' converge on. Based on observations made with the Southern African Large Telescope (SALT). E-mail: Patrick.Woudt@uct.ac.za

  6. Extremely high frequency RF effects on electronics.

    SciTech Connect

    Loubriel, Guillermo Manuel; Vigliano, David; Coleman, Phillip Dale; Williams, Jeffery Thomas; Wouters, Gregg A.; Bacon, Larry Donald; Mar, Alan

    2012-01-01

    The objective of this work was to understand the fundamental physics of extremely high frequency RF effects on electronics. To accomplish this objective, we produced models, conducted simulations, and performed measurements to identify the mechanisms of effects as frequency increases into the millimeter-wave regime. Our purpose was to answer the questions, 'What are the tradeoffs between coupling, transmission losses, and device responses as frequency increases?', and, 'How high in frequency do effects on electronic systems continue to occur?' Using full wave electromagnetics codes and a transmission-line/circuit code, we investigated how extremely high-frequency RF propagates on wires and printed circuit board traces. We investigated both field-to-wire coupling and direct illumination of printed circuit boards to determine the significant mechanisms for inducing currents at device terminals. We measured coupling to wires and attenuation along wires for comparison to the simulations, looking at plane-wave coupling as it launches modes onto single and multiconductor structures. We simulated the response of discrete and integrated circuit semiconductor devices to those high-frequency currents and voltages, using SGFramework, the open-source General-purpose Semiconductor Simulator (gss), and Sandia's Charon semiconductor device physics codes. This report documents our findings.

  7. High power radio frequency attenuation device

    DOEpatents

    Kerns, Quentin A.; Miller, Harold W.

    1984-01-01

    A resistor device for attenuating radio frequency power includes a radio frequency conductor connected to a series of fins formed of high relative magnetic permeability material. The fins are dimensional to accommodate the skin depth of the current conduction therethrough, as well as an inner heat conducting portion where current does not travel. Thermal connections for air or water cooling are provided for the inner heat conducting portions of each fin. Also disclosed is a resistor device to selectively alternate unwanted radio frequency energy in a resonant cavity.

  8. High power, high frequency, vacuum flange

    DOEpatents

    Felker, B.; McDaniel, M.R.

    1993-03-23

    An improved waveguide flange is disclosed for high power operation that helps prevent arcs from being initiated at the junctions between waveguide sections. The flanges at the end of the waveguide sections have counter bores surrounding the waveguide tubes. When the sections are bolted together the counter bores form a groove that holds a fully annealed copper gasket. Each counterbore has a beveled step that is specially configured to insure the gasket forms a metal-to-metal vacuum seal without gaps or sharp edges. The resultant inner surface of the waveguide is smooth across the junctions between waveguide sections, and arcing is prevented.

  9. High power, high frequency, vacuum flange

    DOEpatents

    Felker, Brian; McDaniel, Michael R.

    1993-01-01

    An improved waveguide flange is disclosed for high power operation that helps prevent arcs from being initiated at the junctions between waveguide sections. The flanges at the end of the waveguide sections have counterbores surrounding the waveguide tubes. When the sections are bolted together the counterbores form a groove that holds a fully annealed copper gasket. Each counterbore has a beveled step that is specially configured to insure the gasket forms a metal-to-metal vacuum seal without gaps or sharp edges. The resultant inner surface of the waveguide is smooth across the junctions between waveguide sections, and arcing is prevented.

  10. Construction of invariant whiskered tori by a parameterization method. Part II: Quasi-periodic and almost periodic breathers in coupled map lattices

    NASA Astrophysics Data System (ADS)

    Fontich, Ernest; de la Llave, Rafael; Sire, Yannick

    2015-09-01

    We construct quasi-periodic and almost periodic solutions for coupled Hamiltonian systems on an infinite lattice which is translation invariant. The couplings can be long range, provided that they decay moderately fast with respect to the distance. For the solutions we construct, most of the sites are moving in a neighborhood of a hyperbolic fixed point, but there are oscillating sites clustered around a sequence of nodes. The amplitude of these oscillations does not need to tend to zero. In particular, the almost periodic solutions do not decay at infinity. The main result is an a posteriori theorem. We formulate an invariance equation. Solutions of this equation are embeddings of an invariant torus on which the motion is conjugate to a rotation. We show that, if there is an approximate solution of the invariance equation that satisfies some non-degeneracy conditions, there is a true solution close by. This does not require that the system is close to integrable, hence it can be used to validate numerical calculations or formal expansions. The proof of this a posteriori theorem is based on a Nash-Moser iteration, which does not use transformation theory. Simpler versions of the scheme were developed in [28]. One technical tool, important for our purposes, is the use of weighted spaces that capture the idea that the maps under consideration are local interactions. Using these weighted spaces, the estimates of iterative steps are similar to those in finite dimensional spaces. In particular, the estimates are independent of the number of nodes that get excited. Using these techniques, given two breathers, we can place them apart and obtain an approximate solution, which leads to a true solution nearby. By repeating the process infinitely often, we can get solutions with infinitely many frequencies which do not tend to zero at infinity.

  11. Spike-Interval Triggered Averaging Reveals a Quasi-Periodic Spiking Alternative for Stochastic Resonance in Catfish Electroreceptors

    PubMed Central

    Lankheet, Martin J. M.; Klink, P. Christiaan; Borghuis, Bart G.; Noest, André J.

    2012-01-01

    Catfish detect and identify invisible prey by sensing their ultra-weak electric fields with electroreceptors. Any neuron that deals with small-amplitude input has to overcome sensitivity limitations arising from inherent threshold non-linearities in spike-generation mechanisms. Many sensory cells solve this issue with stochastic resonance, in which a moderate amount of intrinsic noise causes irregular spontaneous spiking activity with a probability that is modulated by the input signal. Here we show that catfish electroreceptors have adopted a fundamentally different strategy. Using a reverse correlation technique in which we take spike interval durations into account, we show that the electroreceptors generate a supra-threshold bias current that results in quasi-periodically produced spikes. In this regime stimuli modulate the interval between successive spikes rather than the instantaneous probability for a spike. This alternative for stochastic resonance combines threshold-free sensitivity for weak stimuli with similar sensitivity for excitations and inhibitions based on single interspike intervals. PMID:22403709

  12. A composite study of the quasi-periodic subtropical wind maxima over the South Pacific during November 1984-April 1985

    NASA Technical Reports Server (NTRS)

    Ko, Ken-Chung; Vincent, Dayton G.

    1995-01-01

    A composite of 10 cases of zonal wind maxima at 200 hPa over the subtropical region stretching from Australia to the central Pacific is examined for the six-month period, November 1984-April 1985. This region is unique in that distinct westerly jets frequently form and propagate eastward at latitudes between 20 deg and 35 deg S in the summer season. Some statistical tests were applied and suggest that the flow patterns are quasi periodic, consisting of a tendency for new jet streaks to develop over the eastern Australian region approximately every one to two weeks. These jets then take about 10 days to propagate across the western Pacific before dissipating or, perhaps, moving toward higher latitudes. Their average propagation speed is approximately 4 m/s. An examination of the case-to-case variability of the jets provides additional evidence that they are significant features. A diagnosis of the trough/ridge systems at 200 and 850 hPa, together with calculations of the vertically integrated mean and shear kinetic energies suggests that baroclinic processes dominate in the entrance and center regions of the jet, whereas barotropic processes dominate in the exit and downstream regions.

  13. Energy dependence of normal branch quasi-periodic intensity oscillations in low-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Miller, Guy S.; Lamb, Frederick K.

    1992-04-01

    The properties of the approximately 6 Hz quasi-periodic X-ray intensity oscillations observed in the low-mass X-ray binary Cyg X-2 when it is on the normal spectral branch are shown to be consistent with a model in which photons from a central source with a fixed spectrum are Comptonized by an oscillating radial inflow. As the electron scattering optical depth of the flow varies, the spectrum of the escaping X-rays appears to rotate about a pivot energy that depends mainly on the electron temperature in the flow. The temperature derived from the observed energy dependence of the Cyg X-2 normal branch oscillations is approximately 1 keV, in good agreement with the estimated Compton temperature of its X-ray spectrum. The mean optical depth tau of the Comptonizing flow is inferred to be about 10, while the change in tau over an oscillation is estimated to be about 1; both values are in good agreement with radiation hydrodcode simulations of the radial flow.

  14. Energy dependence of normal branch quasi-periodic intensity oscillations in low-mass X-ray binaries

    NASA Technical Reports Server (NTRS)

    Miller, Guy S.; Lamb, Frederick K.

    1992-01-01

    The properties of the approximately 6 Hz quasi-periodic X-ray intensity oscillations observed in the low-mass X-ray binary Cyg X-2 when it is on the normal spectral branch are shown to be consistent with a model in which photons from a central source with a fixed spectrum are Comptonized by an oscillating radial inflow. As the electron scattering optical depth of the flow varies, the spectrum of the escaping X-rays appears to rotate about a pivot energy that depends mainly on the electron temperature in the flow. The temperature derived from the observed energy dependence of the Cyg X-2 normal branch oscillations is approximately 1 keV, in good agreement with the estimated Compton temperature of its X-ray spectrum. The mean optical depth tau of the Comptonizing flow is inferred to be about 10, while the change in tau over an oscillation is estimated to be about 1; both values are in good agreement with radiation hydrodcode simulations of the radial flow.

  15. Quasi-periodic transverse plasma flow associated with an evolving MHD vortex street in the outer heliosphere

    NASA Technical Reports Server (NTRS)

    Siregar, Edouard; Roberts, D. A.; Goldstein, Melvyn L.

    1993-01-01

    We study a transverse plasma flow induced by the evolution of a Karman vortex street using a Chebyshev-Fourier spectral algorithm to solve both the compressible Navier-Stokes and MHD equations. The evolving vortex street is formed by the nonlinear interaction of two vortex sheets initially in equilibrium. We study spatial profiles of the total plasma velocity, the density, the meridional flow angle and the location of sector boundaries and find generally good agreement with Voyager 2 measurements of quasi-periodic transverse flow in the outer heliosphere. The pressure pulses associated with the meridional flows in the simulation are too small, although they are correctly located, and this may be due to the lack of any 'warp' in the current sheet in this model. A strong, flow-aligned magnetic field, such as would occur in the inner heliosphere, is shown to lead to weak effects that would be masked by the background interplanetary turbulence. We also study the plasma and magnetic transport resulting from the meridional flow and find that deficits of magnetic quantities do occur near the ecliptic. While the effect is relatively small, it is in general agreement with the most recent analysis of 'flux deficit' in the outer heliosphere.

  16. Periodic and quasi-periodic motions of a solar sail close to SL 1 in the Earth-Sun system

    NASA Astrophysics Data System (ADS)

    Farrés, Ariadna; Jorba, Àngel

    2010-06-01

    Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to propel a satellite taking advantage of the solar radiation pressure. To model the dynamics of a solar sail we have considered the Earth-Sun Restricted Three Body Problem including the Solar radiation pressure (RTBPS). This model has a 2D surface of equilibrium points parametrised by the two angles that define the sail orientation. In this paper we study the non-linear dynamics close to an equilibrium point, with special interest in the bounded motion. We focus on the region of equilibria close to SL 1, a collinear equilibrium point that lies between the Earth and the Sun when the sail is perpendicular to the Sun-sail direction. For different fixed sail orientations we find families of planar, vertical and Halo-type orbits. We have also computed the centre manifold around different equilibria and used it to describe the quasi-periodic motion around them. We also show how the geometry of the phase space varies with the sail orientation. These kind of studies can be very useful for future mission applications.

  17. Spike-interval triggered averaging reveals a quasi-periodic spiking alternative for stochastic resonance in catfish electroreceptors.

    PubMed

    Lankheet, Martin J M; Klink, P Christiaan; Borghuis, Bart G; Noest, André J

    2012-01-01

    Catfish detect and identify invisible prey by sensing their ultra-weak electric fields with electroreceptors. Any neuron that deals with small-amplitude input has to overcome sensitivity limitations arising from inherent threshold non-linearities in spike-generation mechanisms. Many sensory cells solve this issue with stochastic resonance, in which a moderate amount of intrinsic noise causes irregular spontaneous spiking activity with a probability that is modulated by the input signal. Here we show that catfish electroreceptors have adopted a fundamentally different strategy. Using a reverse correlation technique in which we take spike interval durations into account, we show that the electroreceptors generate a supra-threshold bias current that results in quasi-periodically produced spikes. In this regime stimuli modulate the interval between successive spikes rather than the instantaneous probability for a spike. This alternative for stochastic resonance combines threshold-free sensitivity for weak stimuli with similar sensitivity for excitations and inhibitions based on single interspike intervals. PMID:22403709

  18. A quasi-periodic modulation of the iron line centroid energy in the black hole binary H1743-322

    NASA Astrophysics Data System (ADS)

    Ingram, Adam; van der Klis, Michiel; Middleton, Matthew; Done, Chris; Altamirano, Diego; Heil, Lucy; Uttley, Phil; Axelsson, Magnus

    2016-09-01

    Accreting stellar-mass black holes often show a `Type-C' quasi-periodic oscillation (QPO) in their X-ray flux and an iron emission line in their X-ray spectrum. The iron line is generated through continuum photons reflecting off the accretion disc, and its shape is distorted by relativistic motion of the orbiting plasma and the gravitational pull of the black hole. The physical origin of the QPO has long been debated, but is often attributed to Lense-Thirring precession, a General Relativistic effect causing the inner flow to precess as the spinning black hole twists up the surrounding space-time. This predicts a characteristic rocking of the iron line between red- and blueshift as the receding and approaching sides of the disc are respectively illuminated. Here we report on XMM-Newton and NuSTAR observations of the black hole binary H1743-322 in which the line energy varies systematically over the ˜4 s QPO cycle (3.70σ significance), as predicted. This provides strong evidence that the QPO is produced by Lense-Thirring precession, constituting the first detection of this effect in the strong gravitation regime. There are however elements of our results harder to explain, with one section of data behaving differently than all the others. Our result enables the future application of tomographic techniques to map the inner regions of black hole accretion discs.

  19. Quasi-periodic radar echoes from midlatitude sporadic E and role of the 5-day planetary wave

    NASA Astrophysics Data System (ADS)

    Tsunoda, Roland T.; Yamamoto, Mamoru; Igarashi, Kiyoshi; Hocke, Klemens; Fukao, Shoichiro

    Using measurements of magnetic-aspect-sensitive radar echoes from midlatitude sporadic E collected over a two-month period from Tanegashima, Japan, we show that while their occurrence duration from night to night did not exhibit any systematic variation, that of the so-called quasi-periodic (QP) echoes varied sinusoidally with a period of 5 days. We have interpreted this behavior in terms of effects produced by a planetary wave and identified its presence through neutral-wind measurements made with a partial-reflection drift radar located nearby at Yamagawa. We propose that the occurrence of QP echoes is affected both by a contribution of the wind to the dynamo electric field and by the direction of the neutral wind. We argue that because the wind vector of the planetary wave is elliptically polarized at midlatitudes, a preferred wind direction conducive to the generation of QP echoes occurs once every 5 days. On the other hand, this wave is linearly polarized and directed zonally over the geographic equator. The fact that QP echoes are most fully developed at midlatitudes and less so at lower latitudes suggests that zonal flow is not particularly favorable for QP echo production.

  20. Swift-XRT observations of Quasi-periodic oscillations seen in the Super Soft Source emission from Classical and Recurrent Novae

    NASA Astrophysics Data System (ADS)

    Beardmore, Andrew

    2016-07-01

    We report short timescale, soft X-ray flux quasi-periodic oscillations that have been seen by the Swift X-ray Telescope (XRT) during the super soft source (SSS) emission phase from novae. A periodogram analysis revealed oscillations were visible in the 0.3-10 keV XRT light curves obtained from RS Oph (period, P=35.0 s), KT Eri (P=34.9s), V339 Del (P=54.0s), and V5668 Sgr (P=69.7s), with fractional rms variabilities ranging from 1-8 per cent. During day 32-59 of the RS Oph outburst, the oscillation central frequency appeared quite variable, ranging from 26.2-31.1 mHz, caused by a lower coherence at this time. However, after day 50 the oscillation became more coherent, with a frequency that slowly increased from 28.3-28.9 mHz over 9 days, before the trend reversed. The oscillation frequency was less variable in KT Eri and V339 Del. No other correlations, such as between the oscillation frequency or amplitude with source intensity, were seen. A wavelet analysis of the variability seen in RS Oph, KT Eri and V339 Del revealed the oscillations were sometimes visible for entire XRT snapshots lasting 1.0-1.5 ks, yet on other occasions, they were detected for only ˜120 s (i.e. ˜2-4 cycles). The modulation fractional amplitude was variable, occasionally reaching values of 15-20 per cent for a few cycles. During times when the coherence was low, the oscillation phase was seen to jump by ˜0.4-0.6 cycles in RS Oph, then remain stable for ˜10 cycles. KT Eri showed smaller phase jumps of ˜0.2 cycles. We detect a significant spectral variation through the 35s oscillation seen in RS~Oph, with the spectrum becoming harder at the time of the modulation maximum. Fits to the oscillation maximum and minima spectra suggest the increased flux between 0.6-0.75 keV in the former is caused by a 25 per cent reduction in the neutral oxygen column density at this phase. We discuss the possible origins behind the oscillations.

  1. High frequency electromagnetic response of the moon

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Schwartz, K.

    1971-01-01

    It is shown that the contribution of higher harmonics to the lunar transfer functions for the tangential components of the surface magnetic field is significant at frequencies greater than 0.01 Hz. The inclusion of the higher harmonics shows that there are two distinct transfer functions corresponding to the components of the tangential surface magnetic field perpendicular and parallel to the direction of the wave vector of the external disturbance forcing the lunar induction. The dependences of these transfer functions on frequency and location are determined. The effects of the higher harmonics can: (1) account for a hitherto unexplained feature in the Apollo 12-Explorer 35 transfer functions, namely the rolloff at high frequencies; and (2) offer a possible explanation for the frequency dependence of the difference between the transfer functions for the two orthogonal components of the surface magnetic field. The harmonic response of a simple current layer model of the moon is derived.

  2. A High Power Frequency Doubled Fiber Laser

    NASA Technical Reports Server (NTRS)

    Thompson, Robert J.; Tu, Meirong; Aveline, Dave; Lundblad, Nathan; Maleki, Lute

    2003-01-01

    This viewgraph presentation reports on the development of a high power 780 nm laser suitable for space applications of laser cooling. A possible solution is to use frequency doubling of high power 1560 nm telecom lasers. The presentation shows a diagram of the frequency conversion, and a graph of the second harmonic generation in one crystal, and the use of the cascading crystals. Graphs show the second harmonic power as a function of distance between crystals, second harmonic power vs. pump power, tunability of laser systems.

  3. A numerical method for computing initial conditions of Lagrangian invariant tori using the frequency map

    NASA Astrophysics Data System (ADS)

    Luque, Alejandro; Villanueva, Jordi

    2016-06-01

    We present a numerical method for computing initial conditions of Lagrangian quasi-periodic invariant tori of Hamiltonian systems and symplectic maps. Such initial conditions are found by solving, using the Newton method, a nonlinear system obtained by imposing suitable conditions on the frequency map. The basic tool is a newly developed methodology to perform the frequency analysis of a discrete quasi-periodic signal, allowing to compute frequencies and their derivatives with respect to parameters. Roughly speaking, this method consists in computing suitable weighted averages of the iterates of the signal and using the Richardson extrapolation method. The proposed approach performs with high accuracy at a moderate computational cost. We illustrate the method by considering a discrete FPU model and the vicinity of the point L4 in a RTBP.

  4. High frequency inductive lamp and power oscillator

    DOEpatents

    MacLennan, Donald A.; Turner, Brian P.; Dolan, James T.; Kirkpatrick, Douglas A.; Leng, Yongzhang

    2000-01-01

    A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and/or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to match the driving frequency of the oscillator to a plurality of tuning states of the lamp.

  5. High frequency inductive lamp and power oscillator

    DOEpatents

    MacLennan, Donald A.; Dymond, Jr., Lauren E.; Gitsevich, Aleksandr; Grimm, William G.; Kipling, Kent; Kirkpatrick, Douglas A.; Ola, Samuel A.; Simpson, James E.; Trimble, William C.; Tsai, Peter; Turner, Brian P.

    2001-01-01

    A high frequency inductively coupled electrodeless lamp includes an excitation coil with an effective electrical length which is less than one half wavelength of a driving frequency applied thereto, preferably much less. The driving frequency may be greater than 100 MHz and is preferably as high as 915 MHz. Preferably, the excitation coil is configured as a non-helical, semi-cylindrical conductive surface having less than one turn, in the general shape of a wedding ring. At high frequencies, the current in the coil forms two loops which are spaced apart and parallel to each other. Configured appropriately, the coil approximates a Helmholtz configuration. The lamp preferably utilizes an bulb encased in a reflective ceramic cup with a pre-formed aperture defined therethrough. The ceramic cup may include structural features to aid in alignment and I or a flanged face to aid in thermal management. The lamp head is preferably an integrated lamp head comprising a metal matrix composite surrounding an insulating ceramic with the excitation integrally formed on the ceramic. A novel solid-state oscillator preferably provides RF power to the lamp. The oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to adjust the driving frequency of the oscillator.

  6. Investigation of Quasi-periodic Variations in Hard X-Rays of Solar Flares. II. Further Investigation of Oscillating Magnetic Traps

    NASA Astrophysics Data System (ADS)

    Jakimiec, J.; Tomczak, M.

    2012-06-01

    In our recent paper (Jakimiec and Tomczak, Solar Physics 261, 233, 2010) we investigated quasi-periodic oscillations of hard X-rays during the impulsive phase of solar flares. We have come to the conclusion that they are caused by magnetosonic oscillations of magnetic traps within the volume of hard-X-ray (HXR) loop-top sources. In the present paper we investigate four flares that show clear quasi-periodic sequences of the HXR pulses. We also describe our phenomenological model of oscillating magnetic traps to show that it can explain the observed properties of the HXR oscillations. The main results are the following: i) Low-amplitude quasi-periodic oscillations occur before the impulsive phase of some flares. ii) The quasi-periodicity of the oscillations can change in some flares. We interpret this as being due to changes of the length of oscillating magnetic traps. iii) During the impulsive phase a significant part of the energy of accelerated (non-thermal) electrons is deposited within a HXR loop-top source. iv) The quick development of the impulsive phase is due to feedback between the pressure pulses by accelerated electrons and the amplitude of the magnetic-trap oscillation. v) The electron number density and magnetic field strength values obtained for the HXR loop-top sources in several flares fall within the limits of N≈(2 - 15)×1010 cm-3, B≈(45 - 130) gauss. These results show that the HXR quasi-periodic oscillations contain important information about the energy release in solar flares.

  7. High spectral purity Kerr frequency comb radio frequency photonic oscillator.

    PubMed

    Liang, W; Eliyahu, D; Ilchenko, V S; Savchenkov, A A; Matsko, A B; Seidel, D; Maleki, L

    2015-01-01

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10 GHz radio frequency photonic oscillator characterized with phase noise better than -60 dBc Hz(-1) at 10 Hz, -90 dBc Hz(-1) at 100 Hz and -170 dBc Hz(-1) at 10 MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10(-10) at 1-100 s integration time-orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption. PMID:26260955

  8. High spectral purity Kerr frequency comb radio frequency photonic oscillator

    PubMed Central

    Liang, W.; Eliyahu, D.; Ilchenko, V. S.; Savchenkov, A. A.; Matsko, A. B.; Seidel, D.; Maleki, L.

    2015-01-01

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10 GHz radio frequency photonic oscillator characterized with phase noise better than −60 dBc Hz−1 at 10 Hz, −90 dBc Hz−1 at 100 Hz and −170 dBc Hz−1 at 10 MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10−10 at 1–100 s integration time—orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption. PMID:26260955

  9. High spectral purity Kerr frequency comb radio frequency photonic oscillator

    NASA Astrophysics Data System (ADS)

    Liang, W.; Eliyahu, D.; Ilchenko, V. S.; Savchenkov, A. A.; Matsko, A. B.; Seidel, D.; Maleki, L.

    2015-08-01

    Femtosecond laser-based generation of radio frequency signals has produced astonishing improvements in achievable spectral purity, one of the basic features characterizing the performance of an radio frequency oscillator. Kerr frequency combs hold promise for transforming these lab-scale oscillators to chip-scale level. In this work we demonstrate a miniature 10 GHz radio frequency photonic oscillator characterized with phase noise better than -60 dBc Hz-1 at 10 Hz, -90 dBc Hz-1 at 100 Hz and -170 dBc Hz-1 at 10 MHz. The frequency stability of this device, as represented by Allan deviation measurements, is at the level of 10-10 at 1-100 s integration time--orders of magnitude better than existing radio frequency photonic devices of similar size, weight and power consumption.

  10. Evidence For Quasi-Periodic X-ray Dips From An Ultraluminous X-ray Source: Implications for the Binary Motion

    NASA Technical Reports Server (NTRS)

    Pasham, Dheeraj R.; Strohmayer, Tod E.

    2013-01-01

    We report results from long-term (approx.1240 days) X-ray (0.3-8.0 keV) monitoring of the ultraluminous X-ray source NGC 5408 X-1 with the Swift/X-Ray Telescope. Here we expand on earlier work by Strohmayer (2009) who used only a part of the present data set. Our primary results are: (1) the discovery of sharp, quasi-periodic, energy-independent dips in the X-ray intensity that recur on average every 243 days, (2) the detection of an energy dependent (variability amplitude decreases with increasing energy), quasi-sinusoidal X-ray modulation with a period of 112.6 +/- 4 days, the amplitude of which weakens during the second half of the light curve, and (3) spectral evidence for an increase in photoelectric absorption during the last continuous segment of the data. We interpret the X-ray modulations within the context of binary motion in analogy to that seen in high-inclination accreting X-ray binaries. If correct, this implies that NGC 5408 X-1 is in a binary with an orbital period of 243 +/- 23 days, in contrast to the 115.5 day quasi-sinusoidal period previously reported by Strohmayer (2009). We discuss the overall X-ray modulation within the framework of accretion via Roche-lobe overflow of the donor star. In addition, if the X-ray modulation is caused by vertically structured obscuring material in the accretion disk, this would imply a high value for the inclination of the orbit. A comparison with estimates from accreting X-ray binaries suggests an inclination > or approx.70deg. We note that, in principle, a precessing accretion disk could also produce the observed X-ray modulations.

  11. Evidence for Quasi-Periodic X-ray Dips from an ULX: Implications for the Binary Motion and the Orbital Inclination

    NASA Technical Reports Server (NTRS)

    Pasham, Dheeraj R.; Strohmayer, Tod E.

    2012-01-01

    We report results from long-term X-ray (0.3-8.0 keY) monitoring of the ultraluminous X-ray source NGC 5408 X-1 with the Swift/X-Ray Telescope. Our primary results are: (1) the discovery of quasi-periodic dips in the X-ray intensity that recur on average every 243 days, (2) the detection of an energy-dependent (variability amplitude decreases with increasing energy), quasi-sinusoidal X-ray modulation with a period of 112.6 +/- 4 days the amplitude of which decreases during the second half of the light curve and (3) energy spectral evidence for an increase in photoelectric absorption during the last continuous segment of the data, possibly due to a change in the ionization state of the circumbinary material. We interpret the X-ray modulations in the context of binary motion in analogy to that seen in high-inclination low-mass X-ray binaries. If correct, this implies that NGC 5408 X-1 is in a binary with an orbital period of 243 +/- 23 days in contrast to the 115.5 day quasi-sinusoidal period previously reported. In addition, if the X-ray modulation is caused by vertically structured obscuring material in the accretion disk (similar to the phenomenon of dipping LMXBs), this would imply a high value for the inclination of the orbit. A comparison with estimates from accreting X-ray binaries suggests an inclination approx > 60 deg. We note that, in principle, a precessing accretion disk could also produce the observed X-ray modulations.

  12. [High-frequency oscillatory ventilation in neonates].

    PubMed

    2002-09-01

    High-frequency oscillatory ventilation (HFOV) may be considered as an alternative in the management of severe neonatal respiratory failure requiring mechanical ventilation. In patients with diffuse pulmonary disease, HFOV can applied as a rescue therapy with a high lung volume strategy to obtain adequate alveolar recruitment. We review the mechanisms of gas exchange, as well as the indications, monitoring and special features of the use HVOF in the neonatal period. PMID:12199947

  13. Ionospheric modifications in high frequency heating experiments

    SciTech Connect

    Kuo, Spencer P.

    2015-01-15

    Featured observations in high-frequency (HF) heating experiments conducted at Arecibo, EISCAT, and high frequency active auroral research program are discussed. These phenomena appearing in the F region of the ionosphere include high-frequency heater enhanced plasma lines, airglow enhancement, energetic electron flux, artificial ionization layers, artificial spread-F, ionization enhancement, artificial cusp, wideband absorption, short-scale (meters) density irregularities, and stimulated electromagnetic emissions, which were observed when the O-mode HF heater waves with frequencies below foF2 were applied. The implication and associated physical mechanism of each observation are discussed and explained. It is shown that these phenomena caused by the HF heating are all ascribed directly or indirectly to the excitation of parametric instabilities which instigate anomalous heating. Formulation and analysis of parametric instabilities are presented. The results show that oscillating two stream instability and parametric decay instability can be excited by the O-mode HF heater waves, transmitted from all three heating facilities, in the regions near the HF reflection height and near the upper hybrid resonance layer. The excited Langmuir waves, upper hybrid waves, ion acoustic waves, lower hybrid waves, and field-aligned density irregularities set off subsequent wave-wave and wave-electron interactions, giving rise to the observed phenomena.

  14. The LASI high-frequency ellipticity system

    SciTech Connect

    Sternberg, B.K.; Poulton, M.M.

    1995-10-01

    A high-frequency, high-resolution, electromagnetic (EM) imaging system has been developed for environmental geophysics surveys. Some key features of this system include: (1) rapid surveying to allow dense spatial sampling over a large area, (2) high-accuracy measurements which are used to produce a high-resolution image of the subsurface, (3) measurements which have excellent signal-to-noise ratio over a wide bandwidth (31 kHz to 32 MHz), (4) large-scale physical modeling to produce accurate theoretical responses over targets of interest in environmental geophysics surveys, (5) rapid neural network interpretation at the field site, and (6) visualization of complex structures during the survey.

  15. The LASI high-frequency ellipticity system

    SciTech Connect

    Sternberg, B.K.; Poulton, M.M.

    1995-12-31

    A high-frequency, high-resolution, electromagnetic (EM) imaging system has been developed for environmental geophysics surveys. Some key features of this system include: (1) rapid surveying to allow dense spatial sampling over a large area, (2) high-accuracy measurements which are used to produce a high-resolution image of the subsurface, (3) measurements which have excellent signal-to-noise ratio over a wide bandwidth (31 kHz to 32 MHz), (4) large-scale physical modeling to produce accurate theoretical responses over targets of interest in environmental geophysics surveys, (5) rapid neural network interpretation at the field site, and (6) visualization of complex structures during the survey.

  16. High-frequency resonant-tunneling oscillators

    NASA Technical Reports Server (NTRS)

    Brown, E. R.; Parker, C. D.; Calawa, A. R.; Manfra, M. J.; Chen, C. L.

    1991-01-01

    Advances in high-frequency resonant-tunneling-diode (RTD) oscillators are described. Oscillations up to a frequency of 420 GHz have been achieved in the GaAs/AlAs system. Recent results obtained with In0.53Ga0.47As/AlAs and InAs/AlSb RTDs show a greatly increased power density and indicate the potential for fundamental oscillations up to about 1 THz. These results are consistent with a lumped-element equivalent circuit model of the RTD. The model shows that the maximum oscillation frequency of the GaAs/AlAs RTDs is limited primarily by series resistance, and that the power density is limited by low peak-to-valley current ratio.

  17. High Frequency Laser-Based Ultrasound

    SciTech Connect

    Huber, R; Chinn, D; Balogun, O; Murray, T

    2005-09-12

    To obtain micrometer resolution of materials using acoustics requires frequencies around 1 GHz. Attenuation of such frequencies is high, limiting the thickness of the parts that can be characterized. Although acoustic microscopes can operate up to several GHz in frequency, they are used primarily as a surface characterization tool. The use of a pulsed laser for acoustic generation allows generation directly in the part, eliminating the loss of energy associated with coupling the energy from a piezoelectric transducer to the part of interest. The use of pulsed laser acoustic generation in combination with optical detection is investigated for the non-contact characterization of materials with features that must be characterized to micrometer resolution.

  18. Discovery of a Soft Spectral Component and Transient 22.7 Second Quasi-periodic Oscillations of SAX J2103.5+4545

    NASA Astrophysics Data System (ADS)

    İnam, S. Ç.; Baykal, A.; Swank, J.; Stark, M. J.

    2004-11-01

    XMM-Newton observed SAX J2103.5+4545 on 2003 January 6, while the Rossi X-Ray Timing Explorer (RXTE) was also monitoring the source. Using the RXTE Proportional Counter Array data set between 2002 December 3 and 2003 January 29, the spin period and average spin-up rate during the XMM-Newton observations were found to be 354.7940+/-0.0008 s and (7.4+/-0.9)×10-13 Hz s-1, respectively. In the power spectrum of the 0.9-11 keV EPIC PN light curve, we found quasi-periodic oscillations (QPOs) around 0.044 Hz (22.7 s) with an rms fractional amplitude of ~6.6%. We interpreted this QPO feature as the Keplerian motion of inhomogeneities through the inner disk. In the X-ray spectrum, in addition to the power-law component with high-energy cutoff and the ~6.4 keV fluorescent iron emission line, we discovered a soft component consistent with blackbody emission with kT~1.9 keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius of ~0.3 km, suggesting the polar cap on the neutron star surface as the source of the blackbody emission. The flux of the iron emission line at ~6.42 keV was shown to peak at the off-pulse phase, supporting the idea that this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap.

  19. EVIDENCE OF A WARM ABSORBER THAT VARIES WITH QUASI-PERIODIC OSCILLATION PHASE IN THE ACTIVE GALACTIC NUCLEUS RE J1034+396

    SciTech Connect

    Maitra, Dipankar; Miller, Jon M. E-mail: jonmm@umich.ed

    2010-07-20

    A recent observation of the nearby (z = 0.042) narrow-line Seyfert 1 galaxy RE J1034+396 on 2007 May 31 showed strong quasi-periodic oscillations (QPOs) in the 0.3-10 keV X-ray flux. We present phase-resolved spectroscopy of this observation, using data obtained by the EPIC PN detector on board XMM-Newton. The 'low' phase spectrum, associated with the troughs in the light curve, shows (at >4{sigma} confidence level) an absorption edge at 0.86 {+-} 0.05 keV with an absorption depth of 0.3 {+-} 0.1. Ionized oxygen edges are hallmarks of X-ray warm absorbers in Seyfert active galactic nuclei; the observed edge is consistent with H-like O VIII and implies a column density of N{sub OVIII} {approx} 3 x 10{sup 18} cm{sup -2}. The edge is not seen in the 'high' phase spectrum associated with the crests in the light curve, suggesting the presence of a warm absorber in the immediate vicinity of the supermassive black hole that periodically obscures the continuum emission. If the QPO arises due to Keplerian orbital motion around the central black hole, the periodic appearance of the O VIII edge would imply a radius of {approx}9.4(M/[4x10{sup 6}M{sub sun}]){sup -2/3}(P/[1 hr]){sup 2/3} r{sub g} for the size of the warm absorber.

  20. Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545

    NASA Technical Reports Server (NTRS)

    Inam, S. C.; Baykal, A.; Swank, J.; Stark, M. J.

    2003-01-01

    XMM-Newton observed SAX J2103.5+4545 on January 6, 2003, while RXTE was monitoring the source. Using RXTE-PCA dataset between December 3, 2002 and January 29, 2003, the spin period and average spin-up rate during the XMM-Newton observations were found to be 354.7940+/-0.0008 s and (7.4 +/- 0.9) x 10(exp -13) Hz/s respectively. In the power spectrum of the 0.9-11 keV EPIC-PN lightcurve, we found quasi periodic oscillations around 0.044 Hz (22.7 s) with an rms fractional amplitude approx. 6.6 %. We interpreted this QPO feature as the Keplerian motion of inhomogeneities through the inner disk. In the X-ray spectrum, in addition to the power law component with high energy cutoff and approx. 6.4 keV fluorescent iron emission line, we discovered a soft component consistent with a blackbody emission with kT approx. 1.9 keV. The pulse phase spectroscopy of the source revealed that the blackbody flux peaked at the peak of the pulse with an emission radius approx. 0.3 km, suggesting the polar cap on the neutron star approx. 6.42 keV was shown to peak at the off-pulse phase, supporting the idea that this feature arises from fluorescent emission of the circumstellar material around the neutron star rather than the hot region in the vicinity of the neutron star polar cap.

  1. High Frequency Plasma Generators for Ion Thrusters

    NASA Technical Reports Server (NTRS)

    Divergilio, W. F.; Goede, H.; Fosnight, V. V.

    1981-01-01

    The results of a one year program to experimentally adapt two new types of high frequency plasma generators to Argon ion thrusters and to analytically study a third high frequency source concept are presented. Conventional 30 cm two grid ion extraction was utilized or proposed for all three sources. The two plasma generating methods selected for experimental study were a radio frequency induction (RFI) source, operating at about 1 MHz, and an electron cyclotron heated (ECH) plasma source operating at about 5 GHz. Both sources utilize multi-linecusp permanent magnet configurations for plasma confinement. The plasma characteristics, plasma loading of the rf antenna, and the rf frequency dependence of source efficiency and antenna circuit efficiency are described for the RFI Multi-cusp source. In a series of tests of this source at Lewis Research Center, minimum discharge losses of 220+/-10 eV/ion were obtained with propellant utilization of .45 at a beam current of 3 amperes. Possible improvement modifications are discussed.

  2. Noise temperature in graphene at high frequencies

    NASA Astrophysics Data System (ADS)

    Rengel, Raúl; Iglesias, José M.; Pascual, Elena; Martín, María J.

    2016-07-01

    A numerical method for obtaining the frequency-dependent noise temperature in monolayer graphene is presented. From the mobility and diffusion coefficient values provided by Monte Carlo simulation, the noise temperature in graphene is studied up to the THz range, considering also the influence of different substrate types. The influence of the applied electric field is investigated: the noise temperature is found to increase with the applied field, dropping down at high frequencies (in the sub-THz range). The results show that the low-frequency value of the noise temperature in graphene on a substrate tends to be reduced as compared to the case of suspended graphene due to the important effect of remote polar phonon interactions, thus indicating a reduced emitted noise power; however, at very high frequencies the influence of the substrate tends to be significantly reduced, and the differences between the suspended and on-substrate cases tend to be minimized. The values obtained are comparable to those observed in GaAs and semiconductor nitrides.

  3. High-frequency Rayleigh-wave method

    USGS Publications Warehouse

    Xia, J.; Miller, R.D.; Xu, Y.; Luo, Y.; Chen, C.; Liu, J.; Ivanov, J.; Zeng, C.

    2009-01-01

    High-frequency (???2 Hz) Rayleigh-wave data acquired with a multichannel recording system have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave techniques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a non-invasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

  4. Statistical analysis and multi-instrument overview of the quasi-periodic 1-hour pulsations in Saturn's outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Palmaerts, B.; Roussos, E.; Krupp, N.; Kurth, W. S.; Mitchell, D. G.; Dougherty, M. K.

    2015-10-01

    The in-situ exploration of the magnetospheres of Jupiter and Saturn has revealed different periodic processes. In particular, in the Saturnian magnetosphere, several studies have reported pulsations in the outer magnetosphere with a periodicity of about 1 hour in the measurements of charged particle fluxes, plasma wave, magnetic field strength and auroral emissions brightness. The Low- Energy Magnetospheric Measurement System detector of the Magnetospheric Imaging Instrument (MIMI/LEMMS) on board Cassini regularly detects 1-hour quasi-periodic enhancements in the intensities of electrons with an energy range from a hundred keV to several MeV. We extend an earlier survey of these relativistic electron injections, using 10 years of LEMMS observations in addition to context measurements by several other Cassini magnetospheric experiments. During this period, we identified 720 pulsed events in the outer magnetosphere over a wide range of latitudes and local times, revealing that this phenomenon is common and frequent in Saturn's magnetosphere. However, the distribution of the injection events presents a strong local time asymmetry with ten times more events in the duskside than in the dawnside. In addition to the study of their topology, we present a first statistical analysis of these pulsed events to investigate their properties. This analysis reveals that the mean interpulse period is 68 ± 10 minutes and that the events are made up of less than 9 pulses in general, but they can include up to 19 pulses. The most common shape of these pulses is a fast rise followed by a slow decay. Moreover, the ratio between the rise rate and the decay rate increases with the energy. We have also investigated the signatures of each electron injection event in the observations acquired by the Radio and Plasma Wave Science (RPWS) instrument and the magnetometer (MAG). Correlated pulsed signatures are observed in the plasma wave emissions, especially in the auroral hiss, for 12% of the

  5. Performance of annular high frequency thermoacoustic engines

    NASA Astrophysics Data System (ADS)

    Rodriguez, Ivan A.

    This thesis presents studies of the behavior of miniature annular thermoacoustic prime movers and the imaging of the complex sound fields using PIV inside the small acoustic wave guides when driven by a temperature gradient. Thermoacoustic engines operating in the standing wave mode are limited in their acoustic efficiency by a high degree of irreversibility that is inherent in how they work. Better performance can be achieved by using traveling waves in the thermoacoustic devices. This has led to the development of an annular high frequency thermoacoustic prime mover consisting of a regenerator, which is a random stack in-between a hot and cold heat exchanger, inside an annular waveguide. Miniature devices were developed and studied with operating frequencies in the range of 2-4 kHz. This corresponds to an average ring circumference of 11 cm for the 3 kHz device, the resonator bore being 6 mm. A similar device of 11 mm bore, length of 18 cm was also investigated; its resonant frequency was 2 kHz. Sound intensities as high as 166.8 dB were generated with limited heat input. Sound power was extracted from the annular structure by an impedance-matching side arm. The nature of the acoustic wave generated by heat was investigated using a high speed PIV instrument. Although the acoustic device appears symmetric, its performance is characterized by a broken symmetry and by perturbations that exist in its structure. Effects of these are observed in the PIV imaging; images show axial and radial components. Moreover, PIV studies show effects of streaming and instabilities which affect the devices' acoustic efficiency. The acoustic efficiency is high, being of 40% of Carnot. This type of device shows much promise as a high efficiency energy converter; it can be reduced in size for microcircuit applications.

  6. Inverter design for high frequency power distribution

    NASA Technical Reports Server (NTRS)

    King, R. J.

    1985-01-01

    A class of simple resonantly commutated inverters are investigated for use in a high power (100 KW - 1000 KW) high frequency (10 KHz - 20 KHz) AC power distribution system. The Mapham inverter is found to provide a unique combination of large thyristor turn-off angle and good utilization factor, much better than an alternate 'current-fed' inverter. The effects of loading the Mapham inverter entirely with rectifier loads are investigated by simulation and with an experimental 3 KW 20 KHz inverter. This inverter is found to be well suited to a power system with heavy rectifier loading.

  7. High frequency stimulation can block axonal conduction.

    PubMed

    Jensen, Alicia L; Durand, Dominique M

    2009-11-01

    High frequency stimulation (HFS) is used to control abnormal neuronal activity associated with movement, seizure, and psychiatric disorders. Yet, the mechanisms of its therapeutic action are not known. Although experimental results have shown that HFS suppresses somatic activity, other data has suggested that HFS could generate excitation of axons. Moreover it is unclear what effect the stimulation has on tissue surrounding the stimulation electrode. Electrophysiological and computational modeling literature suggests that HFS can drive axons at the stimulus frequency. Therefore, we tested the hypothesis that unlike cell bodies, axons are driven by pulse train HFS. This hypothesis was tested in fibers of the hippocampus both in-vivo and in-vitro. Our results indicate that although electrical stimulation could activate and drive axons at low frequencies (0.5-25 Hz), as the stimulus frequency increased, electrical stimulation failed to continuously excite axonal activity. Fiber tracts were unable to follow extracellular pulse trains above 50 Hz in-vitro and above 125 Hz in-vivo. The number of cycles required for failure was frequency dependent but independent of stimulus amplitude. A novel in-vitro preparation was developed, in which, the alveus was isolated from the remainder of the hippocampus slice. The isolated fiber tract was unable to follow pulse trains above 75 Hz. Reversible conduction block occurred at much higher stimulus amplitudes, with pulse train HFS (>150 Hz) preventing propagation through the site of stimulation. This study shows that pulse train HFS affects axonal activity by: (1) disrupting HFS evoked excitation leading to partial conduction block of activity through the site of HFS; and (2) generating complete conduction block of secondary evoked activity, as HFS amplitude is increased. These results are relevant for the interpretation of the effects of HFS for the control of abnormal neural activity such as epilepsy and Parkinson's disease. PMID

  8. An Abstract Nash-Moser Theorem and Quasi-Periodic Solutions for NLW and NLS on Compact Lie Groups and Homogeneous Manifolds

    NASA Astrophysics Data System (ADS)

    Berti, Massimiliano; Corsi, Livia; Procesi, Michela

    2015-03-01

    We prove an abstract implicit function theorem with parameters for smooth operators defined on scales of sequence spaces, modeled for the search of quasi-periodic solutions of PDEs. The tame estimates required for the inverse linearised operators at each step of the iterative scheme are deduced via a multiscale inductive argument. The Cantor-like set of parameters where the solution exists is defined in a non inductive way. This formulation completely decouples the iterative scheme from the measure theoretical analysis of the parameters where the small divisors non-resonance conditions are verified. As an application, we deduce the existence of quasi-periodic solutions for forced NLW and NLS equations on any compact Lie group or manifold which is homogeneous with respect to a compact Lie group, extending previous results valid only for tori. A basic tool of harmonic analysis is the highest weight theory for the irreducible representations of compact Lie groups.

  9. High-frequency plasma-heating apparatus

    DOEpatents

    Brambilla, Marco; Lallia, Pascal

    1978-01-01

    An array of adjacent wave guides feed high-frequency energy into a vacuum chamber in which a toroidal plasma is confined by a magnetic field, the wave guide array being located between two toroidal current windings. Waves are excited in the wave guide at a frequency substantially equal to the lower frequency hybrid wave of the plasma and a substantially equal phase shift is provided from one guide to the next between the waves therein. For plasmas of low peripheral density gradient, the guides are excited in the TE.sub.01 mode and the output electric field is parallel to the direction of the toroidal magnetic field. For exciting waves in plasmas of high peripheral density gradient, the guides are excited in the TM.sub.01 mode and the magnetic field at the wave guide outlets is parallel to the direction of the toroidal magnetic field. The wave excited at the outlet of the wave guide array is a progressive wave propagating in the direction opposite to that of the toroidal current and is, therefore, not absorbed by so-called "runaway" electrons.

  10. High power and high SFDR frequency conversion using sum frequency generation in KTP waveguides.

    PubMed

    Barbour, Russell J; Brewer, Tyler; Barber, Zeb W

    2016-08-01

    We characterize the intermodulation distortion of high power and efficient frequency conversion of modulated optical signals based on sum frequency generation (SFG) in a periodically poled potassium titanyl phosphate (KTP) waveguide. Unwanted frequency two-tone spurs are generated near the converted signal via a three-step cascaded three-wave mixing process. Computer simulations describing the process are presented along with the experimental measurements. High-conversion efficiencies and large spur-free dynamic range of the converted optical signal are demonstrated. PMID:27472638

  11. A high frequency electromagnetic impedance imaging system

    SciTech Connect

    Tseng, Hung-Wen; Lee, Ki Ha; Becker, Alex

    2003-01-15

    Non-invasive, high resolution geophysical mapping of the shallow subsurface is necessary for delineation of buried hazardous wastes, detecting unexploded ordinance, verifying and monitoring of containment or moisture contents, and other environmental applications. Electromagnetic (EM) techniques can be used for this purpose since electrical conductivity and dielectric permittivity are representative of the subsurface media. Measurements in the EM frequency band between 1 and 100 MHz are very important for such applications, because the induction number of many targets is small and the ability to determine the subsurface distribution of both electrical properties is required. Earlier workers were successful in developing systems for detecting anomalous areas, but quantitative interpretation of the data was difficult. Accurate measurements are necessary, but difficult to achieve for high-resolution imaging of the subsurface. We are developing a broadband non-invasive method for accurately mapping the electrical conductivity and dielectric permittivity of the shallow subsurface using an EM impedance approach similar to the MT exploration technique. Electric and magnetic sensors were tested to ensure that stray EM scattering is minimized and the quality of the data collected with the high-frequency impedance (HFI) system is good enough to allow high-resolution, multi-dimensional imaging of hidden targets. Additional efforts are being made to modify and further develop existing sensors and transmitters to improve the imaging capability and data acquisition efficiency.

  12. DIRECT IMAGING OF QUASI-PERIODIC FAST PROPAGATING WAVES OF {approx}2000 km s{sup -1} IN THE LOW SOLAR CORONA BY THE SOLAR DYNAMICS OBSERVATORY ATMOSPHERIC IMAGING ASSEMBLY

    SciTech Connect

    Liu Wei; Title, Alan M.; Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart; Tarbell, Theodore D.; Zhao Junwei; Ofman, Leon

    2011-07-20

    Quasi-periodic propagating fast mode magnetosonic waves in the solar corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2 flare/coronal mass ejection event, we find arc-shaped wave trains of 1%-5% intensity variations (lifetime {approx}200 s) that emanate near the flare kernel and propagate outward up to {approx}400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 {+-} 130 km s{sup -1}. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-{omega} diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-{omega} ridge shows a broad frequency distribution with power peaks at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of (0.1-2.6) x 10{sup 7} erg cm{sup -2} s{sup -1} estimated at the coronal base is comparable to the steady-state heating requirement of active region loops.

  13. Rapid trajectory design in the Earth-Moon ephemeris system via an interactive catalog of periodic and quasi-periodic orbits

    NASA Astrophysics Data System (ADS)

    Guzzetti, Davide; Bosanac, Natasha; Haapala, Amanda; Howell, Kathleen C.; Folta, David C.

    2016-09-01

    Upcoming missions and prospective design concepts in the Earth-Moon system extensively leverage multi-body dynamics that may facilitate access to strategic locations or reduce propellant usage. To incorporate these dynamical structures into the mission design process, Purdue University and the NASA Goddard Flight Space Center have initiated the construction of a trajectory design framework to rapidly access and compare solutions from the circular restricted three-body problem. This framework, based upon a 'dynamic' catalog of periodic and quasi-periodic orbits within the Earth-Moon system, can guide an end-to-end trajectory design in an ephemeris model. In particular, the inclusion of quasi-periodic orbits further expands the design space, potentially enabling the detection of additional orbit options. To demonstrate the concept of a 'dynamic' catalog, a prototype graphical interface is developed. Strategies to characterize and represent periodic and quasi-periodic information for interactive trajectory comparison and selection are discussed. Two sample applications for formation flying near the Earth-Moon L2 point and lunar space infrastructures are explored to demonstrate the efficacy of a 'dynamic' catalog for rapid trajectory design and validity in higher-fidelity models.

  14. Quasi-periodic Variations in X-Ray Emission and Long-term Radio Observations: Evidence for a Two-component Jet in Sw J1644+57

    NASA Astrophysics Data System (ADS)

    Wang, Jiu-Zhou; Lei, Wei-Hua; Wang, Ding-Xiong; Zou, Yuan-Chuan; Zhang, Bing; Gao, He; Huang, Chang-Yin

    2014-06-01

    The continued observations of Sw J1644+57 in X-ray and radio bands accumulated a rich data set to study the relativistic jet launched in this tidal disruption event. The X-ray light curve of Sw J1644+57 from 5-30 days presents two kinds of quasi-periodic variations: a 200 s quasi-periodic oscillation (QPO) and a 2.7 day quasi-periodic variation. The latter has been interpreted by a precessing jet launched near the Bardeen-Petterson radius of a warped disk. Here we suggest that the ~200 s QPO could be associated with a second, narrower jet sweeping the observer line-of-sight periodically, which is launched from a spinning black hole in the misaligned direction with respect to the black hole's angular momentum. In addition, we show that this two-component jet model can interpret the radio light curve of the event, especially the re-brightening feature starting ~100 days after the trigger. From the data we infer that inner jet may have a Lorentz factor of Γj ~ 5.5 and a kinetic energy of E k, iso ~ 3.0 × 1052 erg, while the outer jet may have a Lorentz factor of Γj ~ 2.5 and a kinetic energy of E k, iso ~ 3.0 × 1053 erg.

  15. High frequency plasma generator for ion thrusters

    NASA Technical Reports Server (NTRS)

    Goede, H.; Divergilio, W. F.; Fosnight, V. V.; Komatsu, G.

    1984-01-01

    The results of a program to experimentally develop two new types of plasma generators for 30 cm electrostatic argon ion thrusters are presented. The two plasma generating methods selected for this study were by radio frequency induction (RFI), operating at an input power frequency of 1 MHz, and by electron cyclotron heating (ECH) at an operating frequency of 5.0 GHz. Both of these generators utilize multiline cusp permanent magnet configurations for plasma confinement and beam profile optimization. The program goals were to develop a plasma generator possessing the characteristics of high electrical efficiency (low eV/ion) and simplicity of operation while maintaining the reliability and durability of the conventional hollow cathode plasma sources. The RFI plasma generator has achieved minimum discharge losses of 120 eV/ion while the ECH generator has obtained 145 eV/ion, assuming a 90% ion optical transparency of the electrostatic acceleration system. Details of experimental tests with a variety of magnet configurations are presented.

  16. High-frequency graphene voltage amplifier.

    PubMed

    Han, Shu-Jen; Jenkins, Keith A; Valdes Garcia, Alberto; Franklin, Aaron D; Bol, Ageeth A; Haensch, Wilfried

    2011-09-14

    While graphene transistors have proven capable of delivering gigahertz-range cutoff frequencies, applying the devices to RF circuits has been largely hindered by the lack of current saturation in the zero band gap graphene. Herein, the first high-frequency voltage amplifier is demonstrated using large-area chemical vapor deposition grown graphene. The graphene field-effect transistor (GFET) has a 6-finger gate design with gate length of 500 nm. The graphene common-source amplifier exhibits ∼5 dB low frequency gain with the 3 dB bandwidth greater than 6 GHz. This first AC voltage gain demonstration of a GFET is attributed to the clear current saturation in the device, which is enabled by an ultrathin gate dielectric (4 nm HfO(2)) of the embedded gate structures. The device also shows extrinsic transconductance of 1.2 mS/μm at 1 V drain bias, the highest for graphene FETs using large-scale graphene reported to date. PMID:21805988

  17. Aerodynamics of high frequency flapping wings

    NASA Astrophysics Data System (ADS)

    Hu, Zheng; Roll, Jesse; Cheng, Bo; Deng, Xinyan

    2010-11-01

    We investigated the aerodynamic performance of high frequency flapping wings using a 2.5 gram robotic insect mechanism developed in our lab. The mechanism flaps up to 65Hz with a pair of man-made wing mounted with 10cm wingtip-to-wingtip span. The mean aerodynamic lift force was measured by a lever platform, and the flow velocity and vorticity were measured using a stereo DPIV system in the frontal, parasagittal, and horizontal planes. Both near field (leading edge vortex) and far field flow (induced flow) were measured with instantaneous and phase-averaged results. Systematic experiments were performed on the man-made wings, cicada and hawk moth wings due to their similar size, frequency and Reynolds number. For insect wings, we used both dry and freshly-cut wings. The aerodynamic force increase with flapping frequency and the man-made wing generates more than 4 grams of lift at 35Hz with 3 volt input. Here we present the experimental results and the major differences in their aerodynamic performances.

  18. High Frequency Self-pulsing Microplasmas

    NASA Astrophysics Data System (ADS)

    Lassalle, John; Pollard, William; Staack, David

    2014-10-01

    Pulsing behavior in high-pressure microplasmas was studied. Microplasmas are of interest because of potential application in plasma switches for robust electronics. These devices require fast switching. Self-pulsing microplasmas were generated in a variable-length spark gap at pressures between 0 and 220 psig in Air, Ar, N2, H2, and He for spark gap lengths from 15 to 1810 μm. Resulting breakdown voltages varied between 90 and 1500 V. Voltage measurements show pulse frequencies as high as 8.9 MHz in argon at 100 psig. These findings demonstrate the potential for fast switching of plasma switches that incorporate high-pressure microplasmas. Work was supported by the National Science Foundation, Grant #1057175, and the Department of Defense, ARO Grant #W911NF1210007.

  19. High frequency ultrasonic mitigation of microbial corrosion

    NASA Astrophysics Data System (ADS)

    Almahamedh, Hussain H.; Meegan, G. Douglas; Mishra, Brajendra; Olson, David L.; Spear, John R.

    2012-05-01

    Microbiologically Influenced Corrosion (MIC) is a major problem in oil industry facilities, and considerable effort has been spent to mitigate this costly issue. More environmentally benign methods are under consideration as alternatives to biocides, among which are ultrasonic techniques. In this study, a high frequency ultrasonic technique (HFUT) was used as a mitigation method for MIC. The killing percentages of the HFUT were higher than 99.8 percent and their corrosivity on steel was reduced by more than 50 percent. The practice and result will be discussed.

  20. Inviscid fluid in high frequency excitation field

    NASA Technical Reports Server (NTRS)

    Zak, M.

    1984-01-01

    The influence of high frequency excitations (HFE) on a fluid is investigated. The response to these excitations is decomposed in two parts: 'slow' motion, which practically remains unchanged during the vanishingly small period tau, and 'fast' motion whose value during this period is negligible in terms of displacements, but is essential in terms of the kinetic energy. After such a decomposition the 'slow' and 'fast' motions become nonlinearly coupled by the corresponding governing equations. This coupling leads to an 'effective' potential energy which imparts some 'elastic' properties to the fluid and stabilizes laminar flows.

  1. Anisotropic Transport of Electrons in a Novel FET Channel with Chains of InGaAs Nano-Islands Embedded along Quasi-Periodic Multi-Atomic Steps on Vicinal (111)B GaAs

    SciTech Connect

    Akiyama, Y.; Kawazu, T.; Noda, T.; Sakaki, H.

    2010-01-04

    We have studied electron transport in n-AlGaAs/GaAs heterojunction FET channels, in which chains of InGaAs nano-islands are embedded along quasi-periodic steps. By using two samples, conductance G{sub para}(V{sub g}) parallel to the steps and G{sub perp}(V{sub g}) perpendicular to them were measured at 80 K as functions of gate voltage V{sub g}. At sufficiently high V{sub g}, G{sub para} at 80 K is several times as high as G{sub perp}, which manifests the anisotropic two-dimensional transport of electrons. When V{sub g} is reduced to -0.7 V, G{sub perp} almost vanishes, while {sub Gpara} stays sizable unless V{sub g} is set below -0.8 V. These results indicate that 'inter-chain' barriers play stronger roles than 'intra-chain' barriers.

  2. High frequency homogenization for structural mechanics

    NASA Astrophysics Data System (ADS)

    Nolde, E.; Craster, R. V.; Kaplunov, J.

    2011-03-01

    We consider a net created from elastic strings as a model structure to investigate the propagation of waves through semi-discrete media. We are particularly interested in the development of continuum models, valid at high frequencies, when the wavelength and each cell of the net are of similar order. Net structures are chosen as these form a general two-dimensional example, encapsulating the essential physics involved in the two-dimensional excitation of a lattice structure whilst retaining the simplicity of dealing with elastic strings. Homogenization techniques are developed here for wavelengths commensurate with the cellular scale. Unlike previous theories, these techniques are not limited to low frequency or static regimes, and lead to effective continuum equations valid on a macroscale with the details of the cellular structure encapsulated only through integrated quantities. The asymptotic procedure is based upon a two-scale approach and the physical observation that there are frequencies that give standing waves, periodic with the period or double-period of the cell. A specific example of a net created by a lattice of elastic strings is constructed, the theory is general and not reliant upon the net being infinite, none the less the infinite net is a useful special case for which Bloch theory can be applied. This special case is explored in detail allowing for verification of the theory, and highlights the importance of degenerate cases; the specific example of a square net is treated in detail. An additional illustration of the versatility of the method is the response to point forcing which provides a stringent test of the homogenized equations; an exact Green's function for the net is deduced and compared to the asymptotics.

  3. High-frequency laser sonar system

    NASA Astrophysics Data System (ADS)

    Cray, Benjamin A.; Sarma, Ashwin; Kirsteins, Ivars P.

    2002-11-01

    A set of measurements recently completed at the Naval Undersea Warfare Center (NUWC) demonstrated that a laser-based sonar system can be used to detect acoustic particle velocity on the surface of a thin acoustically-compliant plate embedded beneath a standard acoustic window. The theoretical acoustic and measured surface particle velocity varied by less than 1 dB (reference m/s) over a wide frequency band (10 kHz to 100 kHz). However, the Polytec Model PSV-100 Scanning Laser Vibrometer System (SLVS) used in the experiments had relatively poor acoustic sensitivity, presumably due to high electronic noise, speckle noise, stand-off distance, and drifting laser focus. The laser's acoustic sensitivity appears to be inversely proportional to the backscatter signal level. The existing SLVS can sample a grid of 512 by 512 points, with each grid point having a spot size of approximately 10 mm (0.0004 in.). Such fine sampling may be used to create essentially a continuous aperture, eliminating acoustic grating lobes at all frequencies of practical sonar interest.

  4. Frequency metrology using highly charged ions

    NASA Astrophysics Data System (ADS)

    Crespo López-Urrutia, J. R.

    2016-06-01

    Due to the scaling laws of relativistic fine structure splitting, many forbidden optical transitions appear within the ground state configurations of highly charged ions (HCI). In some hydrogen-like ions, even the hyperfine splitting of the 1s ground state gives rise to optical transitions. Given the very low polarizability of HCI, such laser-accessible transitions are extremely impervious to external perturbations and systematics that limit optical clock performance and arise from AC and DC Stark effects, such as black-body radiation and light shifts. Moreover, AC and DC Zeeman splitting are symmetric due to the much larger relativistic spin-orbit coupling and corresponding fine-structure splitting. Appropriate choice of states or magnetic sub-states with suitable total angular momentum and magnetic quantum numbers can lead to a cancellation of residual quadrupolar shifts. All these properties are very advantageous for the proposed use of HCI forbidden lines as optical frequency standards. Extremely magnified relativistic, quantum electrodynamic, and nuclear size contributions to the binding energies of the optically active electrons make HCI ideal tools for fundamental research, as in proposed studies of a possible time variation of the fine structure constant. Beyond this, HCI that cannot be photoionized by vacuum-ultraviolet photons could also provide frequency standards for future lasers operating in that range.

  5. Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

    SciTech Connect

    Liqiu, Wei E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang; Jing, Li; Yong, Cao; Daren, Yu; Jianhua, Du

    2015-02-07

    It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

  6. Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

    NASA Astrophysics Data System (ADS)

    Liqiu, Wei; Liang, Han; Ziyi, Yang; Jing, Li; Yong, Cao; Daren, Yu; Jianhua, Du

    2015-02-01

    It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

  7. Inline high frequency ultrasonic particle sizer

    NASA Astrophysics Data System (ADS)

    Lefebvre, F.; Petit, J.; Nassar, G.; Debreyne, P.; Delaplace, G.; Nongaillard, B.

    2013-07-01

    This paper reports the development of a new method of particle sizing in a liquid. This method uses high frequency focused ultrasounds to detect particles crossing the focal zone of an ultrasonic sensor and to determine their size distribution by processing the reflected echoes. The major advantage of this technique compared to optical sizing methods is its ability to measure the size of particles suspended in an opaque liquid without any dedicated sample preparation. Validations of ultrasonic measurements were achieved on suspensions of polymethyl methacrylate beads in a size range extending from a few micrometer to several hundred micrometer with a temporal resolution of 1 s. The inline detection of aggregate formation was also demonstrated.

  8. High frequency oscillators for chaotic radar

    NASA Astrophysics Data System (ADS)

    Beal, A. N.; Blakely, J. N.; Corron, N. J.; Dean, R. N.

    2016-05-01

    This work focuses on implementing a class of exactly solvable chaotic oscillators at speeds that allow real world radar applications. The implementation of a chaotic radar using a solvable system has many advantages due to the generation of aperiodic, random-like waveforms with an analytic representation. These advantages include high range resolution, no range ambiguity, and spread spectrum characteristics. These systems allow for optimal detection of a noise-like signal by the means of a linear matched filter using simple and inexpensive methods. This paper outlines the use of exactly solvable chaos in ranging systems, while addressing electronic design issues related to the frequency dependence of the system's stretching function introduced by the use of negative impedance converters (NICs).

  9. Plasma effects in high frequency radiative transfer

    SciTech Connect

    Alonso, C.T.

    1981-02-08

    This paper is intended as a survey of collective plasma processes which can affect the transfer of high frequency radiation in a hot dense plasma. We are rapidly approaching an era when this subject will become important in the laboratory. For pedagogical reasons we have chosen to examine plasma processes by relating them to a particular reference plasma which will consist of fully ionized carbon at a temperature kT=1 KeV (10/sup 70/K) and an electron density N = 3 x 10/sup 23/cm/sup -3/, (which corresponds to a mass density rho = 1 gm/cm/sup 3/ and an ion density N/sub i/ = 5 x 10/sup 22/ cm/sup -3/). We will consider the transport in such a plasma of photons ranging from 1 eV to 1 KeV in energy. Such photons will probably be frequently used as diagnostic probes of hot dense laboratory plasmas.

  10. High Power Third Gyroharmonic Frequency Multiplier

    NASA Astrophysics Data System (ADS)

    Lapointe, M. A.; Ganguly, A. K.; Hirshfield, J. L.; Wang, Changbiao; Yoder, R. B.; Wang, Mei

    1998-11-01

    A high power freqeuncy multplier which uses a cyclotron autoresonance accelerator (CARA)(M.A. LaPointe, R.B. Yoder, Changbiao Wang, A.K. Ganguly and J.L. Hirshfield, Phys. Rev. Lett., 76), 2718 (1996) and a third harmonic, TE_311 cavity is being tested. Primary power at 2.856 GHz is used to accelerate a 20--30 A, 75--96kV electron beam up to 320 kV in a CARA. The prepared beam interacts with the TE_311 cavity tuned to the third harmonic of the drive frequency. Simulations show that conversion efficiencies from beam power to microwave power can be as high as 48% producing up to 4.5 MW of 8.568 GHz power. Experiments to date have shown under certain conditions only third harmonic radiation has been generated with a FWHM of 350 kHz, the Fourier limit for the length of the radiation pulse. High power experiments are underway to measure the efficiency of the device.

  11. High frequency of tumours in Mulibrey nanism.

    PubMed

    Karlberg, Niklas; Karlberg, Susann; Karikoski, Riitta; Mikkola, Sakari; Lipsanen-Nyman, Marita; Jalanko, Hannu

    2009-06-01

    Mulibrey nanism (MUL) is a monogenic disorder with prenatal-onset growth failure, typical clinical characteristics, cardiopathy and tendency for a metabolic syndrome. It is caused by recessive mutations in the TRIM37 gene encoding for the peroxisomal TRIM37 protein with ubiquitin-ligase activity. In this work, the frequency and pathology of malignant and benign tumours were analysed in a national cohort of 89 Finnish MUL patients aged 0.7-76 years. The subjects had a clinical and radiological evaluation, and histological and immunohistocemical analyses on specimens obtained from biopsy, surgery or autopsy, were performed. The results show that the MUL patients have disturbed architecture with ectopic tissues and a high frequency of both benign and malignant tumours detectable in several internal organs. A total of 210 tumorous lesions were detected in 66/89 patients (74%). Fifteen malignancies occurred in 13 patients (15%), seven of them in the kidney (five Wilms' tumours), three in the thyroid gland, two gynaecological cancers, one gastrointestinal carcinoid tumour, one neuropituitary Langerhans cell histiocytosis and one case of acute lymphoblastic leukaemia (ALL). Tumours detected by radiology in the liver and other organs mainly comprised strongly dilated blood vessels (peliosis), vascularized cysts and nodular lesions. The lesions showed strong expression of the endothelial cell markers CD34 and CD31 as well as the myocyte marker alpha-smooth muscle actin (alpha-SMA). Our findings show that MUL is associated with frequent malignant tumours and benign adenomatous and vascular lesions, as well as disturbed organ development. PMID:19334051

  12. Plant Responses to High Frequency Electromagnetic Fields

    PubMed Central

    Vian, Alain; Davies, Eric; Gendraud, Michel; Bonnet, Pierre

    2016-01-01

    High frequency nonionizing electromagnetic fields (HF-EMF) that are increasingly present in the environment constitute a genuine environmental stimulus able to evoke specific responses in plants that share many similarities with those observed after a stressful treatment. Plants constitute an outstanding model to study such interactions since their architecture (high surface area to volume ratio) optimizes their interaction with the environment. In the present review, after identifying the main exposure devices (transverse and gigahertz electromagnetic cells, wave guide, and mode stirred reverberating chamber) and general physics laws that govern EMF interactions with plants, we illustrate some of the observed responses after exposure to HF-EMF at the cellular, molecular, and whole plant scale. Indeed, numerous metabolic activities (reactive oxygen species metabolism, α- and β-amylase, Krebs cycle, pentose phosphate pathway, chlorophyll content, terpene emission, etc.) are modified, gene expression altered (calmodulin, calcium-dependent protein kinase, and proteinase inhibitor), and growth reduced (stem elongation and dry weight) after low power (i.e., nonthermal) HF-EMF exposure. These changes occur not only in the tissues directly exposed but also systemically in distant tissues. While the long-term impact of these metabolic changes remains largely unknown, we propose to consider nonionizing HF-EMF radiation as a noninjurious, genuine environmental factor that readily evokes changes in plant metabolism. PMID:26981524

  13. Plant Responses to High Frequency Electromagnetic Fields.

    PubMed

    Vian, Alain; Davies, Eric; Gendraud, Michel; Bonnet, Pierre

    2016-01-01

    High frequency nonionizing electromagnetic fields (HF-EMF) that are increasingly present in the environment constitute a genuine environmental stimulus able to evoke specific responses in plants that share many similarities with those observed after a stressful treatment. Plants constitute an outstanding model to study such interactions since their architecture (high surface area to volume ratio) optimizes their interaction with the environment. In the present review, after identifying the main exposure devices (transverse and gigahertz electromagnetic cells, wave guide, and mode stirred reverberating chamber) and general physics laws that govern EMF interactions with plants, we illustrate some of the observed responses after exposure to HF-EMF at the cellular, molecular, and whole plant scale. Indeed, numerous metabolic activities (reactive oxygen species metabolism, α- and β-amylase, Krebs cycle, pentose phosphate pathway, chlorophyll content, terpene emission, etc.) are modified, gene expression altered (calmodulin, calcium-dependent protein kinase, and proteinase inhibitor), and growth reduced (stem elongation and dry weight) after low power (i.e., nonthermal) HF-EMF exposure. These changes occur not only in the tissues directly exposed but also systemically in distant tissues. While the long-term impact of these metabolic changes remains largely unknown, we propose to consider nonionizing HF-EMF radiation as a noninjurious, genuine environmental factor that readily evokes changes in plant metabolism. PMID:26981524

  14. Quasi-periodic self-assembled sub-micrometer ferroelectric bulk domain gratings in Rb-doped KTiOPO4

    NASA Astrophysics Data System (ADS)

    Zukauskas, Andrius; Pasiskevicius, Valdas; Canalias, Carlota

    2013-12-01

    We present a simple technique for fabricating quasi-periodic bulk sub-μm ferroelectric domain gratings in Rb-doped KTiOPO4 (RKTP) based on self-organized ferroelectric domain formation. One-dimensional ferroelectric domain structures, with an average periodicity of 650 ± 200 nm and extending throughout 1 mm thick crystals, are obtained by etching and subsequent electric field poling using planar electrodes. The sub-μm structures in RKTP were used to demonstrate 5th order non-collinear quasi-phase matched backward second harmonic generation.

  15. ENGLISH WORDS OF VERY HIGH FREQUENCY.

    ERIC Educational Resources Information Center

    CARD, WILLIAM; MCDAVID, VIRGINIA

    THE BIAS OF THE FREQUENCY OF THE 122 MOST COMMONLY USED ENGLISH WORDS WAS STUDIED. THE METHOD USED TO ASSEMBLE THESE DATA IS DESCRIBED FULLY. THE MOST FREQUENTLY USED WORDS WERE TAKEN FROM A DISSERTATION BY GEORGE K. MONROE, "PHONEMIC TRANSCRIPTION OF GRAPHIC POSTBASE AFFIXES IN ENGLISH," GODFREY DEWEY, "RELATIVE FREQUENCY OF ENGLISH SPEECH…

  16. Laser for high frequency modulated interferometry

    DOEpatents

    Mansfield, D.K.; Vocaturo, M.; Guttadora, L.J.

    1991-07-23

    A Stark-tuned laser operating in the 119 micron line of CH[sub 3]OH has an output power of several tens of milliwatts at 30 Watts of pump power while exhibiting a doublet splitting of about ten MHz with the application of a Stark field on the order of 500 volts/cm. This output power allows for use of the laser in a multi-channel interferometer, while its high operating frequency permits the interferometer to measure rapid electron density changes in a pellet injected or otherwise fueled plasma such as encountered in magnetic fusion devices. The laser includes a long far-infrared (FIR) pyrex resonator tube disposed within a cylindrical water jacket and incorporating charged electrodes for applying the Stark field to a gas confined therein. With the electrodes located within the resonator tube, the resonator tube walls are cooled by a flowing coolant without electrical breakdown in the coolant liquid during application of the Stark field. Wall cooling allows for substantially increased FIR output powers. Provision is made for introducing a buffer gas into the resonator tube for increasing laser output power and its operating bandwidth. 10 figures.

  17. Laser for high frequency modulated interferometry

    DOEpatents

    Mansfield, Dennis K.; Vocaturo, Michael; Guttadora, Lawrence J.

    1991-01-01

    A Stark-tuned laser operating in the 119 micron line of CH.sub.3 OH has an output power of several tens of milliwatts at 30 Watts of pump power while exhibiting a doublet splitting of about ten MHz with the application of a Stark field on the order of 500 volts/cm. This output power allows for use of the laser in a multi-channel interferometer, while its high operating frequency permits the interferometer to measure rapid electron density changes in a pellet injected or otherwise fueled plasma such as encountered in magnetic fusion devices. The laser includes a long far-infrared (FIR) pyrex resonator tube disposed within a cylindrical water jacket and incorporating charged electrodes for applying the Stark field to a gas confined therein. With the electrodes located within the resonator tube, the resonator tube walls are cooled by a flowing coolant without electrical breakdown in the coolant liquid during application of the Stark field. Wall cooling allows for substantially increased FIR output powers. Provision is made for introducing a buffer gas into the resonator tube for increasing laser output power and its operating bandwidth.

  18. A High Frequency Model of Cascade Noise

    NASA Technical Reports Server (NTRS)

    Envia, Edmane

    1998-01-01

    Closed form asymptotic expressions for computing high frequency noise generated by an annular cascade in an infinite duct containing a uniform flow are presented. There are two new elements in this work. First, the annular duct mode representation does not rely on the often-used Bessel function expansion resulting in simpler expressions for both the radial eigenvalues and eigenfunctions of the duct. In particular, the new representation provides an explicit approximate formula for the radial eigenvalues obviating the need for solutions of the transcendental annular duct eigenvalue equation. Also, the radial eigenfunctions are represented in terms of exponentials eliminating the numerical problems associated with generating the Bessel functions on a computer. The second new element is the construction of an unsteady response model for an annular cascade. The new construction satisfies the boundary conditions on both the cascade and duct walls simultaneously adding a new level of realism to the noise calculations. Preliminary results which demonstrate the effectiveness of the new elements are presented. A discussion of the utility of the asymptotic formulas for calculating cascade discrete tone as well as broadband noise is also included.

  19. High-Frequency Observations of Blazars

    NASA Technical Reports Server (NTRS)

    Marscher, A. P.; Marchenko-Jorstad, S. G.; Mattox, J. R.; Wehrle, A. E.; Aller, M. F.

    2000-01-01

    We report on the results of high-frequency VLBA observations of 42 gamma-ray bright blazars monitored at 22 and 43 GHz between 1993.9 and 1997.6. In 1997 the observations included polarization-sensitive imaging. The cores of gamma-ray blazars are only weakly polarized, with EVPAs (electric-vector position angles) usually within 40 deg of the local direction of the jet. The EVPAs of the jet components are usually within 20 deg of the local jet direction. The apparent speeds of the gamma-ray bright blazars are considerably faster than in the general population of bright compact radio sources. Two X-ray flares (observed with RXTE) of the quasar PKS 1510-089 appear to be related to radio flares, but with the radio leading the X-ray variations by about 2 weeks. This can be explained either by synchrotron self-Compton emission in a component whose variations are limited by light travel time or by the Mirror Compton model.

  20. Reversible tobramycin-induced bilateral high-frequency vestibular toxicity.

    PubMed

    Walsh, R M; Bath, A P; Bance, M L

    2000-01-01

    We report an unusual case of tobramycin-induced bilateral high-frequency vestibular toxicity with subsequent clinical and objective evidence of functional recovery. In those patients with a clinical presentation suggestive of aminoglycoside-induced bilateral vestibular toxicity (ataxia and oscillopsia) and normal low-frequency (ENG-caloric) responses, high-frequency rotation chair testing should be performed to exclude a high-frequency vestibular deficit. PMID:10810261

  1. Hydrothermal Synthesis Au-Bi2Te3 Nanocomposite Thermoelectric Film with a Hierarchical Sub-Micron Antireflection Quasi-Periodic Structure

    PubMed Central

    Tian, Junlong; Zhang, Wang; Zhang, Yuan; Xue, Ruiyang; Wang, Yuhua; Zhang, Zhijian; Zhang, Di

    2015-01-01

    In this work, Au-Bi2Te3 nanocomposite thermoelectric film with a hierarchical sub-micron antireflection quasi-periodic structure was synthesized via a low-temperature chemical route using Troides helena (Linnaeus) forewing (T_FW) as the biomimetic template. This method combines chemosynthesis with biomimetic techniques, without the requirement of expensive equipment and energy intensive processes. The microstructure and the morphology of the Au-Bi2Te3 nanocomposite thermoelectric film was analyzed by X-ray diffraction (XRD), field-emission scanning-electron microscopy (FESEM), and transmission electron microscopy (TEM). Coupled the plasmon resonances of the Au nanoparticles with the hierarchical sub-micron antireflection quasi-periodic structure, the Au-Bi2Te3 nanocomposite thermoelectric film possesses an effective infrared absorption and infrared photothermal conversion performance. Based on the finite difference time domain method and the Joule effect, the heat generation and the heat source density distribution of the Au-Bi2Te3 nanocomposite thermoelectric film were studied. The heterogeneity of heat source density distribution of the Au-Bi2Te3 nanocomposite thermoelectric film opens up a novel promising technique for generating thermoelectric power under illumination. PMID:26047340

  2. Hydrothermal Synthesis Au-Bi2Te3 Nanocomposite Thermoelectric Film with a Hierarchical Sub-Micron Antireflection Quasi-Periodic Structure.

    PubMed

    Tian, Junlong; Zhang, Wang; Zhang, Yuan; Xue, Ruiyang; Wang, Yuhua; Zhang, Zhijian; Zhang, Di

    2015-01-01

    In this work, Au-Bi(2)Te(3) nanocomposite thermoelectric film with a hierarchical sub-micron antireflection quasi-periodic structure was synthesized via a low-temperature chemical route using Troides helena (Linnaeus) forewing (T_FW) as the biomimetic template. This method combines chemosynthesis with biomimetic techniques, without the requirement of expensive equipment and energy intensive processes. The microstructure and the morphology of the Au-Bi(2)Te(3) nanocomposite thermoelectric film was analyzed by X-ray diffraction (XRD), field-emission scanning-electron microscopy (FESEM), and transmission electron microscopy (TEM). Coupled the plasmon resonances of the Au nanoparticles with the hierarchical sub-micron antireflection quasi-periodic structure, the Au-Bi(2)Te(3) nanocomposite thermoelectric film possesses an effective infrared absorption and infrared photothermal conversion performance. Based on the finite difference time domain method and the Joule effect, the heat generation and the heat source density distribution of the Au-Bi(2)Te(3) nanocomposite thermoelectric film were studied. The heterogeneity of heat source density distribution of the Au-Bi(2)Te(3) nanocomposite thermoelectric film opens up a novel promising technique for generating thermoelectric power under illumination. PMID:26047340

  3. A High Power Frequency Doubled Fiber Laser

    NASA Technical Reports Server (NTRS)

    Thompson, Rob; Tu, Meirong; Aveline, Dave; Lundblad, Nathan; Maleki, Lute

    2003-01-01

    This slide presentation reviews the power frequencies for the doubled fiber laser. It includes information on the 780 nm laser, second harmonic generation in one crystal, cascading crystals, the tenability of laser systems, laser cooling, and directions for future work.

  4. Light Echos in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Fukumura, K.; Kazanas, D.

    2008-01-01

    We propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are affected significantly by the black hole's dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct 'bunches' separated by a roughly constant time lag of t/M approximately equal to 14, regardless of the bursts' azimuthal position. We argue that every other such 'bunch' represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon 'echo'). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M=0.99 and mass of M=10*Msun the QPO is expected at a frequency of approximately 1.3-1.4 kHz. We discuss the plausibility and observational implications of our model/results as well as its limitations.

  5. High Frequency QRS ECG Accurately Detects Cardiomyopathy

    NASA Technical Reports Server (NTRS)

    Schlegel, Todd T.; Arenare, Brian; Poulin, Gregory; Moser, Daniel R.; Delgado, Reynolds

    2005-01-01

    High frequency (HF, 150-250 Hz) analysis over the entire QRS interval of the ECG is more sensitive than conventional ECG for detecting myocardial ischemia. However, the accuracy of HF QRS ECG for detecting cardiomyopathy is unknown. We obtained simultaneous resting conventional and HF QRS 12-lead ECGs in 66 patients with cardiomyopathy (EF = 23.2 plus or minus 6.l%, mean plus or minus SD) and in 66 age- and gender-matched healthy controls using PC-based ECG software recently developed at NASA. The single most accurate ECG parameter for detecting cardiomyopathy was an HF QRS morphological score that takes into consideration the total number and severity of reduced amplitude zones (RAZs) present plus the clustering of RAZs together in contiguous leads. This RAZ score had an area under the receiver operator curve (ROC) of 0.91, and was 88% sensitive, 82% specific and 85% accurate for identifying cardiomyopathy at optimum score cut-off of 140 points. Although conventional ECG parameters such as the QRS and QTc intervals were also significantly longer in patients than controls (P less than 0.001, BBBs excluded), these conventional parameters were less accurate (area under the ROC = 0.77 and 0.77, respectively) than HF QRS morphological parameters for identifying underlying cardiomyopathy. The total amplitude of the HF QRS complexes, as measured by summed root mean square voltages (RMSVs), also differed between patients and controls (33.8 plus or minus 11.5 vs. 41.5 plus or minus 13.6 mV, respectively, P less than 0.003), but this parameter was even less accurate in distinguishing the two groups (area under ROC = 0.67) than the HF QRS morphologic and conventional ECG parameters. Diagnostic accuracy was optimal (86%) when the RAZ score from the HF QRS ECG and the QTc interval from the conventional ECG were used simultaneously with cut-offs of greater than or equal to 40 points and greater than or equal to 445 ms, respectively. In conclusion 12-lead HF QRS ECG employing

  6. An inkjet vision measurement technique for high-frequency jetting

    SciTech Connect

    Kwon, Kye-Si Jang, Min-Hyuck; Park, Ha Yeong; Ko, Hyun-Seok

    2014-06-15

    Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance.

  7. An inkjet vision measurement technique for high-frequency jetting

    NASA Astrophysics Data System (ADS)

    Kwon, Kye-Si; Jang, Min-Hyuck; Park, Ha Yeong; Ko, Hyun-Seok

    2014-06-01

    Inkjet technology has been used as manufacturing a tool for printed electronics. To increase the productivity, the jetting frequency needs to be increased. When using high-frequency jetting, the printed pattern quality could be non-uniform since the jetting performance characteristics including the jetting speed and droplet volume could vary significantly with increases in jet frequency. Therefore, high-frequency jetting behavior must be evaluated properly for improvement. However, it is difficult to measure high-frequency jetting behavior using previous vision analysis methods, because subsequent droplets are close or even merged. In this paper, we present vision measurement techniques to evaluate the drop formation of high-frequency jetting. The proposed method is based on tracking target droplets such that subsequent droplets can be excluded in the image analysis by focusing on the target droplet. Finally, a frequency sweeping method for jetting speed and droplet volume is presented to understand the overall jetting frequency effects on jetting performance.

  8. Near infrared frequency dependence of high-order sideband generation

    SciTech Connect

    Zaks, Benjamin; Banks, Hunter; Sherwin, Mark; Liu, Ren-Bao

    2013-12-04

    The near infrared frequency dependence of high order sideband generation in InGaAs quantum wells is discussed. The NIR frequency dependence of the sidebands indicates that the HSG phenomenon is excitonic in nature.

  9. High-performance iodine fiber frequency standard.

    PubMed

    Lurie, Anna; Baynes, Fred N; Anstie, James D; Light, Philip S; Benabid, Fetah; Stace, Thomas M; Luiten, Andre N

    2011-12-15

    We have constructed a compact and robust optical frequency standard based around iodine vapor loaded into the core of a hollow-core photonic crystal fiber (HC-PCF). A 532 nm laser was frequency locked to one hyperfine component of the R(56) 32-0 (127)I(2) transition using modulation transfer spectroscopy. The stabilized laser demonstrated a frequency stability of 2.3×10(-12) at 1 s, almost an order of magnitude better than previously reported for a laser stabilized to a gas-filled HC-PCF. This limit is set by the shot noise in the detection system. We present a discussion of the current limitations to the performance and a route to improve the performance by more than an order of magnitude. PMID:22179880

  10. ON THE NATURE OF THE mHz X-RAY QUASI-PERIODIC OSCILLATIONS FROM ULTRALUMINOUS X-RAY SOURCE M82 X-1: SEARCH FOR TIMING-SPECTRAL CORRELATIONS

    SciTech Connect

    Pasham, Dheeraj R.; Strohmayer, Tod E. E-mail: tod.strohmayer@nasa.gov

    2013-07-10

    Using all the archival XMM-Newton X-ray (3-10 keV) observations of the ultraluminous X-ray source (ULX) M82 X-1, we searched for a correlation between its variable mHz quasi-periodic oscillation (QPO) frequency and its hardness ratio (5-10 keV/3-5 keV), an indicator of the energy spectral power-law index. When stellar-mass black holes (StMBHs) exhibit type-C low-frequency QPOs ({approx}0.2-15 Hz), the centroid frequency of the QPO is known to correlate with the energy spectral index. The detection of such a correlation would strengthen the identification of M82 X-1's mHz QPOs as type-C and enable a more reliable mass estimate by scaling its QPO frequencies to those of type-C QPOs in StMBHs of known mass. We resolved the count rates and the hardness ratios of M82 X-1 and a nearby bright ULX (source 5/X42.3+59) through surface brightness modeling. We detected QPOs in the frequency range of 36-210 mHz during which M82 X-1's hardness ratio varied from 0.42 to 0.47. Our primary results are (1) that we do not detect any correlation between the mHz QPO frequency and the hardness ratio (a substitute for the energy spectral power-law index) and (2) similar to some accreting X-ray binaries, we find that M82 X-1's mHz QPO frequency increases with its X-ray count rate (Pearson's correlation coefficient = +0.97). The apparent lack of a correlation between the QPO centroid frequency and the hardness ratio poses a challenge to the earlier claims that the mHz QPOs of M82 X-1 are the analogs of the type-C low-frequency QPOs of StMBHs. On the other hand, it is possible that the observed relation between the hardness ratio and the QPO frequency represents the saturated portion of the correlation seen in type-C QPOs of StMBHs-in which case M82 X-1's mHz QPOs can still be analogous to type-C QPOs.

  11. On the Nature of the mHz X-ray Quasi-Periodic Oscillations from Ultraluminous X-ray source M82 X-1: Search for Timing-Spectral Correlations

    NASA Technical Reports Server (NTRS)

    Pasham, Dheeraj R.; Strohmayer, Tod E.

    2013-01-01

    Using all the archival XMM-Newton X-ray (3-10 keV) observations of the ultraluminous X-ray source (ULX) M82 X-1, we searched for a correlation between its variable mHz quasi-periodic oscillation (QPO) frequency and its hardness ratio (5-10 keV/3-5 keV), an indicator of the energy spectral power-law index. When stellar-mass black holes (StMBHs) exhibit type-C low-frequency QPOs (0.2-15 Hz), the centroid frequency of the QPO is known to correlate with the energy spectral index. The detection of such a correlation would strengthen the identification of M82 X-1's mHz QPOs as type-C and enable a more reliable mass estimate by scaling its QPO frequencies to those of type-C QPOs in StMBHs of known mass.We resolved the count rates and the hardness ratios of M82 X-1 and a nearby bright ULX (source 5/X42.3+59) through surface brightness modeling.We detected QPOs in the frequency range of 36-210 mHz during which M82 X-1's hardness ratio varied from 0.42 to 0.47. Our primary results are (1) that we do not detect any correlation between the mHz QPO frequency and the hardness ratio (a substitute for the energy spectral power-law index) and (2) similar to some accreting X-ray binaries, we find that M82 X-1's mHz QPO frequency increases with its X-ray count rate (Pearson's correlation coefficient = +0.97). The apparent lack of a correlation between the QPO centroid frequency and the hardness ratio poses a challenge to the earlier claims that the mHz QPOs of M82 X-1 are the analogs of the type-C low-frequency QPOs of StMBHs. On the other hand, it is possible that the observed relation between the hardness ratio and the QPO frequency represents the saturated portion of the correlation seen in type-C QPOs of StMBHs-in which case M82 X-1's mHz QPOs can still be analogous to type-C QPOs.

  12. On the Nature of the mHz X-Ray Quasi-periodic Oscillations from Ultraluminous X-Ray Source M82 X-1: Search for Timing-Spectral Correlations

    NASA Astrophysics Data System (ADS)

    Pasham, Dheeraj R.; Strohmayer, Tod E.

    2013-07-01

    Using all the archival XMM-Newton X-ray (3-10 keV) observations of the ultraluminous X-ray source (ULX) M82 X-1, we searched for a correlation between its variable mHz quasi-periodic oscillation (QPO) frequency and its hardness ratio (5-10 keV/3-5 keV), an indicator of the energy spectral power-law index. When stellar-mass black holes (StMBHs) exhibit type-C low-frequency QPOs (~0.2-15 Hz), the centroid frequency of the QPO is known to correlate with the energy spectral index. The detection of such a correlation would strengthen the identification of M82 X-1's mHz QPOs as type-C and enable a more reliable mass estimate by scaling its QPO frequencies to those of type-C QPOs in StMBHs of known mass. We resolved the count rates and the hardness ratios of M82 X-1 and a nearby bright ULX (source 5/X42.3+59) through surface brightness modeling. We detected QPOs in the frequency range of 36-210 mHz during which M82 X-1's hardness ratio varied from 0.42 to 0.47. Our primary results are (1) that we do not detect any correlation between the mHz QPO frequency and the hardness ratio (a substitute for the energy spectral power-law index) and (2) similar to some accreting X-ray binaries, we find that M82 X-1's mHz QPO frequency increases with its X-ray count rate (Pearson's correlation coefficient = +0.97). The apparent lack of a correlation between the QPO centroid frequency and the hardness ratio poses a challenge to the earlier claims that the mHz QPOs of M82 X-1 are the analogs of the type-C low-frequency QPOs of StMBHs. On the other hand, it is possible that the observed relation between the hardness ratio and the QPO frequency represents the saturated portion of the correlation seen in type-C QPOs of StMBHs—in which case M82 X-1's mHz QPOs can still be analogous to type-C QPOs.

  13. Study of Quasi-Periodic Variations in Drag of Artificial Satellite during 23-24 Solar Cycles

    NASA Astrophysics Data System (ADS)

    Komendant, V. H.; Ryabov, M. I.; Sukharev, A. L.

    Apply of the method of time-frequency analysis allows to reveal the detailed structure of the manifestations of the influence of the state space weather on the upper atmosphere of the Earth. Sensitive indicators of such changes are low-orbit satellites. The dynamics of drag of nineteen low-orbit satellites was viewed. The study period includes phases of declining and a long minimum of 23rd solar cycle, phases of rise and maximum of 24th solar cycle. In dynamic of inhibition of all the analyzed satellite pronounced regular inhibition effects with extended periods of 2 - 6 years and short-period effects with periods less than one year. In the satellites: 00063, 00165, 25064, 00932 and 00746 - detected periods with trend from 25 - 28 days to 1 - 1.7 months.

  14. Quasi-periodic VLF emissions with short-period modulation and their relationship to whistlers: a case study

    NASA Astrophysics Data System (ADS)

    Titova, Elena; Demekhov, Andrei; Kozlovsky, Alexander; Manninen, Jyrki; Pasmanik, Dmitry

    We study properties of quasiperiodic (QP) VLF emissions recorded on December 24, 2011 during the VLF campaign in Northern Finland. The main attention is paid to interrelationships between different characteristic periods in the QP spectra. In particular, we analyze regular variations in the QP repetition intervals (1 - 10 min) during the event from 15:30 to 22 UT, their changes during substorms, and short periodic (several-second) modulation observed within separate QP elements. We explained the variations of periods of QP emissions in terms of the model of auto-oscillation regime of the cyclotron instability in the magnetosphere. During the considered event lasting about 7 hours we observed a regular increase in the time intervals between the QP elements. We relate this increase with weakening of the magnetospheric source of energetic electrons. Significant variations in the QP period occurred during substorms. These variations can be due to a substorm-related increase in the energetic-electron flux and/or due to the precipitation of these electrons into the ionosphere which changes the reflection coefficient of VLF waves. We analyze the fine structure of QP element spectra and reveal the periods related to the time scales of guided propagation of whistler-mode waves along the magnetic field line, which suggests that ducted propagation regime took place for the QP emissions. The periods were about 6--9 s for frequencies 3.5--1.2 kHz respectively, which was similar to the period of almost simultaneously observed two-hop whistlers In the low-frequency part of QP spectra periodic emissions with меньшими periods of about 3 s were observed. Analysis of fine structure of QP elements shows that their formation is affected by both linear effects (i.e., group-velocity dispersion) and nonlinear effects related

  15. High-Frequency, High-Temperature Fretting Experiments

    NASA Technical Reports Server (NTRS)

    Matlik, J. F.; Farris, T. N.; Haake, F. K.; Swanson, G. R.; Duke, G. C.

    2005-01-01

    Fretting is a structural damage mechanism observed when two nominally clamped surfaces are subjected to an oscillatory loading. A critical location for fretting induced damage has been identified at the blade/disk and blade/damper interfaces of gas turbine engine turbomachinery and space propulsion components. The high-temperature, high-frequency loading environment seen by these components lead to severe stress gradients at the edge-of-contact. These contact stresses drive crack nucleation and propagation in fretting and are very sensitive to the geometry of the contacting bodies, the contact loads, materials, temperature, and contact surface tribology (friction). To diagnose the threat that small and relatively undetectable fretting cracks pose to damage tolerance and structural integrity of in-service components, the objective of this work is to develop a well-characterized experimental fretting rig capable of investigating fretting behavior of advanced aerospace alloys subjected to load and temperature conditions representative of such turbomachinery components.

  16. Detection With Rhessi of High Frequency X-ray Oscillations in the Tail of the 2004 Hyperflare From SGR 1806-20

    NASA Technical Reports Server (NTRS)

    Watts, Anna L.; Strohmayer, Tod E.

    2005-01-01

    The recent discovery of high frequency oscillations in giant flares from SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. Using timing data from RHESSI, we have confirmed the detection of a 92.5 Hz Quasi-Periodic Oscillation (QPO) in the tail of the SGR 1806-20 giant flare. We also find another, stronger, QPO at higher energies, at 626.5 Hz. Both QPOs are visible only at particular (but different) rotational phases, implying an association with a specific area of the neutron star surface or magnetosphere. At lower frequencies we confirm the detection of an 18 Hz QPO, at the same rotational phase as the 92.5 Hz QPO, and report the additional presence of a broad 26 Hz QPO. We are however unable to make a robust confirmation of the presence of a 30 Hz QPO, despite higher count rates. We discuss our results in the light of neutron star vibration models.

  17. The High Frequency Stabilization of a Magnetoplasmadynamic Thruster

    NASA Astrophysics Data System (ADS)

    Kirdyashev, K.

    2004-10-01

    Experimental data on the high-frequency stabilization of the MPD thruster and the suppression of low-frequency oscillations in the frequency range from 20 to 100 kHz are presented. Conditions for the stabilizing effect of a high-frequency magnetic field at the frequency of 40 MHz on the plasma jet produced by the thruster are determined, and the efficiency of this action is evaluated. The action of high frequency field on the MPD thruster consists in the contention of two processes - the stabilization of the plasma drift instability by the magnetic component of high frequency field and the energy conversion of natural plasma oscillations excited by the external field to the ion-sound wave energy.

  18. Electromagnetic inhibition of high frequency thermal bonding machine

    NASA Astrophysics Data System (ADS)

    He, Hong; Zhang, Qing-qing; Li, Hang; Zhang, Da-jian; Hou, Ming-feng; Zhu, Xian-wei

    2011-12-01

    The traditional high frequency thermal bonding machine had serious radiation problems at dominant frequency, two times frequency and three times frequency. Combining with its working principle, the problems of electromagnetic compatibility were studied, three following measures were adopted: 1.At the head part of the high frequency thermal bonding machine, resonant circuit attenuator was designed. The notch groove and reaction field can make the radiation being undermined or absorbed; 2.The electromagnetic radiation shielding was made for the high frequency copper power feeder; 3.Redesigned the high-frequency oscillator circuit to reduce the output of harmonic oscillator. The test results showed that these measures can make the output according with the national standard of electromagnetic compatibility (GB4824-2004-2A), the problems of electromagnetic radiation leakage can be solved, and good social, environmental and economic benefits would be brought.

  19. Mechanisms of high-frequency song generation in brachypterous crickets and the role of ghost frequencies.

    PubMed

    Robillard, Tony; Montealegre-Z, Fernando; Desutter-Grandcolas, Laure; Grandcolas, Philippe; Robert, Daniel

    2013-06-01

    Sound production in crickets relies on stridulation, the well-understood rubbing together of a pair of specialised wings. As the file of one wing slides over the scraper of the other, a series of rhythmic impacts causes harmonic oscillations, usually resulting in the radiation of pure tones delivered at low frequencies (2-8 kHz). In the short-winged crickets of the Lebinthini tribe, acoustic communication relies on signals with remarkably high frequencies (>8 kHz) and rich harmonic content. Using several species of the subfamily Eneopterinae, we characterised the morphological and mechanical specialisations supporting the production of high frequencies, and demonstrated that higher harmonics are exploited as dominant frequencies. These specialisations affect the structure of the stridulatory file, the motor control of stridulation and the resonance of the sound radiator. We placed these specialisations in a phylogenetic framework and show that they serve to exploit high-frequency vibrational modes pre-existing in the phylogenetic ancestor. In Eneopterinae, the lower frequency components are harmonically related to the dominant peak, suggesting they are relicts of ancestral carrier frequencies. Yet, such ghost frequencies still occur in the wings' free resonances, highlighting the fundamental mechanical constraints of sound radiation. These results support the hypothesis that such high-frequency songs evolved stepwise, by a form of punctuated evolution that could be related to functional constraints, rather than by only the progressive increase of the ancestral fundamental frequency. PMID:23430987

  20. Processing of superconductive materials and high frequency

    SciTech Connect

    Smith, J.L.

    1987-01-01

    We do not know yet if superconductivity will become useful without refrigeration. Now, the superconductors are so different from copper that it is difficult to imagine replacing copper with such a brittle material. Superconductors conduct dc with no loss, ac with small losses, and microwaves in co-axial lines with almost no loss and with no dispersion from dc to the highest frequencies. They will probably allow us to close the gap between radio frequency and infrared optical transmission. Clearly your industry should know some things about where superconductivity may lead us and must consider whether the greater risk is to develop them or to let others try it. There are no easy answers yet.

  1. High-Frequency Radiation and Tritium Channel

    NASA Astrophysics Data System (ADS)

    Afonichev, D. D.

    2005-12-01

    In the process of deformation of titanium alloy samples preliminarily saturated by deuterium (at a temperature T = 710°C) radiation, which is not a neutron flux, was detected. Electromagnetic radiation in the range of radio frequencies was detected in titanium alloy samples in the process of their saturation by deuterium. The probable mechanism of its occurrence may be the retardation of charged particles in the metallic matrix.

  2. Coplanar stripline components for high frequency application

    NASA Technical Reports Server (NTRS)

    Goverdhanam, Kavita; Simons, Rainee N.; Dib, Nihad; Katehi, Linda P. B.

    1996-01-01

    In this paper, coplanar stripline discontinuities such as a slit, a right angle bend and a T-junction are characterized and their performance is parameterized with respect to frequency and geometry. Lumped equivalent circuits are presented for some of them. The element values are obtained from the measured discontinuity scattering (S) parameters. The experimental results are compared with theoretical data obtained using the Finite Difference Time Domain (FD-TD) technique for validation and show very good agreement.

  3. High-Frequency, Conformable Organic Amplifiers.

    PubMed

    Reuveny, Amir; Lee, Sunghoon; Yokota, Tomoyuki; Fuketa, Hiroshi; Siket, Christian M; Lee, Sungwon; Sekitani, Tsuyoshi; Sakurai, Takayasu; Bauer, Siegfried; Someya, Takao

    2016-05-01

    Large-bandwidth, low-operation-voltage, and uniform organic amplifiers are fabricated on ultrathin foils. By the integration of short-channel OTFTs and AlOx capacitors, organic amplifiers with a bandwidth of 25 kHz are realized, demonstrating the highest gain-bandwidth product (GBWP) reported to date. Owing to material and process advancements, closed-loop architectures operate at frequencies of several kilohertz with an area smaller than 30 mm(2) . PMID:26922899

  4. High Precision Noise Measurements at Microwave Frequencies

    SciTech Connect

    Ivanov, Eugene; Tobar, Michael

    2009-04-23

    We describe microwave noise measurement system capable of detecting the phase fluctuations of rms amplitude of 2{center_dot}10{sup -11} rad/{radical}(Hz). Such resolution allows the study of intrinsic fluctuations in various microwave components and materials, as well as precise tests of fundamental physics. Employing this system we discovered a previously unknown phenomenon of down-conversion of pump oscillator phase noise into the low-frequency voltage fluctuations.

  5. On quasi-periodic wave solutions and asymptotic behaviors to a (2 + 1)-dimensional generalized variable-coefficient Sawada-Kotera equation

    NASA Astrophysics Data System (ADS)

    Tu, Jian-Min; Tian, Shou-Fu; Xu, Mei-Juan; Ma, Pan-Li

    2015-07-01

    In this paper, a (2 + 1)-dimensional generalized variable-coefficient Sawada-Kotera (gvcSK) equation is investigated, which describes many nonlinear phenomena in fluid dynamics and plasma physics. Based on the properties of binary Bell polynomials, we present a Hirota’s bilinear equation to the gvcSK equation. By virtue of the Hirota’s bilinear equation, we obtain the N-soliton solutions and the quasi-periodic wave solutions of the gvcSK equation, which can be reduced to the ones of several integrable equations such as Sawada-Kotera, modified Caudrey-Dodd-Gibbon-Sawada-Kotera, isospectral BKP equations and etc. Furthermore, we obtain the relationship between the soliton solutions and periodic solutions by considering the asymptotic properties of the periodic solutions.

  6. How are the VLF quasi-periodic emissions controlled by harmonics of field line oscillations? - The results of a comparison between ground and GEOS satellites measurements

    NASA Astrophysics Data System (ADS)

    Tixier, M.; Cornilleau-Wehrlin, N.

    1986-06-01

    Data on VLF and UHF waves observed in situ for the first time by the GEOS 1 and 2 satellites close to the equatorial plane are compared with ground-based measurements. The results permit a more complete explanation of quasi-periodic (QP) modulation. The data are described, and a general ground-satellite comparison of occurrence and spectra of simultaneous emission is given. A detailed study of some selected events shows that, when the GEOS data are taken into account, it is sometimes difficult to classify QP emissions as either type I or type II. It is suggested that QPs may be due to the same mechanism involving compressional harmonics of a standing fundamental ULF wave.

  7. High-frequency Probing Diagnostic for Hall Current Plasma Thrusters

    SciTech Connect

    A.A. Litvak; Y. Raitses; N.J. Fisch

    2001-10-25

    High-frequency oscillations (1-100 MHz) in Hall thrusters have apparently eluded significant experimental scrutiny. A diagnostic setup, consisting of a single Langmuir probe, a special shielded probe connector-positioner, and an electronic impedance-matching circuit, was successfully built and calibrated. Through simultaneous high-frequency probing of the Hall thruster plasma at multiple locations, high-frequency plasma waves have been identified and characterized for various thruster operating conditions.

  8. On-clip high frequency reliability and failure test structures

    DOEpatents

    Snyder, E.S.; Campbell, D.V.

    1997-04-29

    Self-stressing test structures for realistic high frequency reliability characterizations. An on-chip high frequency oscillator, controlled by DC signals from off-chip, provides a range of high frequency pulses to test structures. The test structures provide information with regard to a variety of reliability failure mechanisms, including hot-carriers, electromigration, and oxide breakdown. The system is normally integrated at the wafer level to predict the failure mechanisms of the production integrated circuits on the same wafer. 22 figs.

  9. On-clip high frequency reliability and failure test structures

    DOEpatents

    Snyder, Eric S.; Campbell, David V.

    1997-01-01

    Self-stressing test structures for realistic high frequency reliability characterizations. An on-chip high frequency oscillator, controlled by DC signals from off-chip, provides a range of high frequency pulses to test structures. The test structures provide information with regard to a variety of reliability failure mechanisms, including hot-carriers, electromigration, and oxide breakdown. The system is normally integrated at the wafer level to predict the failure mechanisms of the production integrated circuits on the same wafer.

  10. High-resolution observation of field-aligned irregularities in the ionosphere using multi-frequency range imaging of VHF atmospheric radar

    NASA Astrophysics Data System (ADS)

    Chen, Jenn-Shyong; Furumoto, Jun-ichi; Su, Ching-Lun; Chu, Yen-Hsyang

    Field-aligned irregularity (FAI) in the ionosphere is a topic of interest to atmospheric radar community. In addition to the field-aligned characteristic, quasi-periodic (QP) appearance of FAI echoes has been observed frequently by very-high-frequency (VHF) atmospheric radar. The occurrence range of QP FAI echoes changes with time, and the slope of range versus time can be positive or negative, depending on occurrence time of the echoes. Several mechanisms responsible for the QP FAI echoes have been proposed, e.g., modulation in altitude by a passing atmospheric gravity wave, semidiurnal neutral-wind variation, and so on. Owing to the finite pulse length of radar in observation, the range resolution of measurement is limited within hundreds of meters. In view of this, the range imaging (RIM) using multiple frequencies has been employed to improve the range resolution of measurement. The multi-frequency technique transmits a set of slightly different frequencies sequentially during each radar pulse, and the radar returns at different transmitting frequencies are received, respectively. With adaptive retrieval algorithms for these radar returns, it is capable of resolving the echo structures at meter scale in the range direction. RIM has been employed in the lower atmosphere successfully. In this study, the performance of RIM for FAI was first carried out with the Middle and Upper atmosphere Radar (46 MHz; 34.85(°) N, 136.10(°) N; Japan) and the Chung-Li VHF radar (52 MHz; 24.9(°) N, 121.1(°) E; Taiwan). Some initial results of high-resolution FAI echoes within the range gate will be shown.

  11. Phoneme categorization relying solely on high-frequency energy.

    PubMed

    Vitela, A Davi; Monson, Brian B; Lotto, Andrew J

    2015-01-01

    Speech perception studies generally focus on the acoustic information present in the frequency regions below 6 kHz. Recent evidence suggests that there is perceptually relevant information in the higher frequencies, including information affecting speech intelligibility. This experiment examined whether listeners are able to accurately identify a subset of vowels and consonants in CV-context when only high-frequency (above 5 kHz) acoustic information is available (through high-pass filtering and masking of lower frequency energy). The findings reveal that listeners are capable of extracting information from these higher frequency regions to accurately identify certain consonants and vowels. PMID:25618101

  12. Phoneme categorization relying solely on high-frequency energy

    PubMed Central

    Vitela, A. Davi; Monson, Brian B.; Lotto, Andrew J.

    2015-01-01

    Speech perception studies generally focus on the acoustic information present in the frequency regions below 6 kHz. Recent evidence suggests that there is perceptually relevant information in the higher frequencies, including information affecting speech intelligibility. This experiment examined whether listeners are able to accurately identify a subset of vowels and consonants in CV-context when only high-frequency (above 5 kHz) acoustic information is available (through high-pass filtering and masking of lower frequency energy). The findings reveal that listeners are capable of extracting information from these higher frequency regions to accurately identify certain consonants and vowels. PMID:25618101

  13. A high frequency resonance gravity gradiometer

    SciTech Connect

    Bagaev, S. N.; Kvashnin, N. L.; Skvortsov, M. N.; Bezrukov, L. B.; Krysanov, V. A.; Oreshkin, S. I.; Motylev, A. M.; Popov, S. M.; Samoilenko, A. A.; Yudin, I. S.; Rudenko, V. N.

    2014-06-15

    A new setup OGRAN—the large scale opto-acoustical gravitational detector is described. As distinguished from known gravitational bar detectors it uses the optical interferometrical readout for registering weak variations of gravity gradient at the kilohetz frequency region. At room temperature, its sensitivity is limited only by the bar Brownian noise at the bandwidth close to 100 Hz. It is destined for a search for rare events—gravitational pulses coincident with signals of neutrino scintillator (BUST) in the deep underground of Baksan Neutrino Observatory of INR RAS.

  14. Self isolating high frequency saturable reactor

    DOEpatents

    Moore, James A.

    1998-06-23

    The present invention discloses a saturable reactor and a method for decoupling the interwinding capacitance from the frequency limitations of the reactor so that the equivalent electrical circuit of the saturable reactor comprises a variable inductor. The saturable reactor comprises a plurality of physically symmetrical magnetic cores with closed loop magnetic paths and a novel method of wiring a control winding and a RF winding. The present invention additionally discloses a matching network and method for matching the impedances of a RF generator to a load. The matching network comprises a matching transformer and a saturable reactor.

  15. A high frequency resonance gravity gradiometer.

    PubMed

    Bagaev, S N; Bezrukov, L B; Kvashnin, N L; Krysanov, V A; Oreshkin, S I; Motylev, A M; Popov, S M; Rudenko, V N; Samoilenko, A A; Skvortsov, M N; Yudin, I S

    2014-06-01

    A new setup OGRAN--the large scale opto-acoustical gravitational detector is described. As distinguished from known gravitational bar detectors it uses the optical interferometrical readout for registering weak variations of gravity gradient at the kilohetz frequency region. At room temperature, its sensitivity is limited only by the bar Brownian noise at the bandwidth close to 100 Hz. It is destined for a search for rare events--gravitational pulses coincident with signals of neutrino scintillator (BUST) in the deep underground of Baksan Neutrino Observatory of INR RAS. PMID:24985859

  16. High efficiency, oxidation resistant radio frequency susceptor

    DOEpatents

    Besmann, Theodore M.; Klett, James W.

    2004-10-26

    An article and method of producing an article for converting energy from one form to another having a pitch-derived graphitic foam carbon foam substrate and a single layer coating applied to all exposed surfaces wherein the coating is either silicon carbide or carbides formed from a Group IVA metal. The article is used as fully coated carbon foam susceptors that more effectively absorb radio frequency (RF) band energy and more effectively convert the RF energy into thermal band energy or sensible heat. The essentially non-permeable coatings also serve as corrosion or oxidation resistant barriers.

  17. Calibration of High Frequency MEMS Microphones

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Humphreys, William M.; Bartram, Scott M.; Zuckewar, Allan J.

    2007-01-01

    Understanding and controlling aircraft noise is one of the major research topics of the NASA Fundamental Aeronautics Program. One of the measurement technologies used to acquire noise data is the microphone directional array (DA). Traditional direction array hardware, consisting of commercially available condenser microphones and preamplifiers can be too expensive and their installation in hard-walled wind tunnel test sections too complicated. An emerging micro-machining technology coupled with the latest cutting edge technologies for smaller and faster systems have opened the way for development of MEMS microphones. The MEMS microphone devices are available in the market but suffer from certain important shortcomings. Based on early experiments with array prototypes, it has been found that both the bandwidth and the sound pressure level dynamic range of the microphones should be increased significantly to improve the performance and flexibility of the overall array. Thus, in collaboration with an outside MEMS design vendor, NASA Langley modified commercially available MEMS microphone as shown in Figure 1 to meet the new requirements. Coupled with the design of the enhanced MEMS microphones was the development of a new calibration method for simultaneously obtaining the sensitivity and phase response of the devices over their entire broadband frequency range. Over the years, several methods have been used for microphone calibration. Some of the common methods of microphone calibration are Coupler (Reciprocity, Substitution, and Simultaneous), Pistonphone, Electrostatic actuator, and Free-field calibration (Reciprocity, Substitution, and Simultaneous). Traditionally, electrostatic actuators (EA) have been used to characterize air-condenser microphones for wideband frequency ranges; however, MEMS microphones are not adaptable to the EA method due to their construction and very small diaphragm size. Hence a substitution-based, free-field method was developed to

  18. Coherence Effects in L-Band Active and Passive Remote Sensing of Quasi-Periodic Corn Canopies

    NASA Technical Reports Server (NTRS)

    Utku, Cuneyt; Lang, Roger H.

    2011-01-01

    Due to their highly random nature, vegetation canopies can be modeled using the incoherent transport theory for active and passive remote sensing applications. Agricultural vegetation canopies however are generally more structured than natural vegetation. The inherent row structure in agricultural canopies induces coherence effects disregarded by the transport theory. The objective of this study is to demonstrate, via Monte-Carlo simulations, these coherence effects on L-band scattering and thermal emission from corn canopies consisting of only stalks.

  19. High power single-frequency Innoslab amplifier.

    PubMed

    Han, Ke-Zhen; Ning, Jian; Zhang, Bai-Tao; Wang, Yi-Ran; Zhang, Hai-Kun; Nie, Hong-Kun; Sun, Xiao-Li; He, Jing-Liang

    2016-07-10

    A laser diode array (LDA) end-pumped continuous-wave single-frequency Innoslab amplifier has been demonstrated. The Gaussian ray bundle method was used to model the light propagation in the Innoslab amplifier for the first time to the best of our knowledge. With discrete reflectors, the maximum output of 60 W with a linewidth of 44 MHz was achieved under the pump power of 245 W, corresponding to the optical-optical efficiency of 24.5%. The beam quality factor M2 at the output power of 51 W in the horizontal and vertical direction was measured to be 1.4 and 1.3, respectively. The long-term power instability in 2 h was less than 0.25%. PMID:27409308

  20. Effects of high frequency current in welding aluminum alloy 6061

    NASA Technical Reports Server (NTRS)

    Fish, R. E.

    1968-01-01

    Uncontrolled high frequency current causes cracking in the heat-affected zone of aluminum alloy 6061 weldments during tungsten inert gas ac welding. Cracking developed when an improperly adjusted superimposed high frequency current was agitating the semimolten metal in the areas of grain boundary.

  1. Beach-ridge development in Lake Michigan: Shoreline behavior in response to quasi-periodic lake-level events

    USGS Publications Warehouse

    Thompson, T.A.; Baedke, S.J.

    1996-01-01

    Strandplains of arcuate beach ridges are common in coastal embayments in parts of the Great Lakes. Similarities in beach-ridge development and geomorphology are recognizable in many of the embayments in the Lake Michigan basin despite differences in size and shape, available sediment type and supply, predepositional slope and topography, and hydrographic regime between the embayments. These similarities are primarily a product of three scales of quasiperiodic lake-level variation ranging in time from 30 to 600 years and in water level change from 0.5 to 3.7 m. The interaction of these three lake-level variations can be represented on a Curray (1964) diagram (rate of water level change versus rate of sediment supply). The position of any shoreline on the diagram and the type of behavior the shoreline is experiencing is a product of the interaction of the three variations. Two large Strandplains of late Holocene beach ridges occur at opposite ends of Lake Michigan (Toleston Beach and Thompson embayment). The two areas exhibit similar patterns of beach-ridge development for the past 2600 calendar years. That is, both areas form beach ridges about every 30 years. Groups of 4 to 6 beach ridges reflect a longer-term lake-level variation of about 150 years. Only during the largest variation of about 600 years in duration do the two areas differ. The rise to the 1700 cal yr B.P. high caused the erosion of beach ridges back to 2800 cal yrs B.P. in northern Lake Michigan. In southern Lake Michigan, no erosion occurred during this lake level high. Differences in shoreline development between the two areas are related to the rate of sediment supply to the shorelines. As the sediment sink for the southern half of Lake Michigan, the southern strandplain received a greater sediment flux than the northern strandplain during the latter part of the late Holocene and produced a continuous record of beach-ridge development. ?? 1995 Elsevier Science B.V. All rights reserved.

  2. Monitoring method and apparatus using high-frequency carrier

    DOEpatents

    Haynes, H.D.

    1996-04-30

    A method and apparatus for monitoring an electrical-motor-driven device by injecting a high frequency carrier signal onto the power line current. The method is accomplished by injecting a high frequency carrier signal onto an AC power line current. The AC power line current supplies the electrical-motor-driven device with electrical energy. As a result, electrical and mechanical characteristics of the electrical-motor-driven device modulate the high frequency carrier signal and the AC power line current. The high frequency carrier signal is then monitored, conditioned and demodulated. Finally, the modulated high frequency carrier signal is analyzed to ascertain the operating condition of the electrical-motor-driven device. 6 figs.

  3. Monitoring method and apparatus using high-frequency carrier

    DOEpatents

    Haynes, Howard D.

    1996-01-01

    A method and apparatus for monitoring an electrical-motor-driven device by injecting a high frequency carrier signal onto the power line current. The method is accomplished by injecting a high frequency carrier signal onto an AC power line current. The AC power line current supplies the electrical-motor-driven device with electrical energy. As a result, electrical and mechanical characteristics of the electrical-motor-driven device modulate the high frequency carrier signal and the AC power line current. The high frequency carrier signal is then monitored, conditioned and demodulated. Finally, the modulated high frequency carrier signal is analyzed to ascertain the operating condition of the electrical-motor-driven device.

  4. Real-Time, High-Frequency QRS Electrocardiograph

    NASA Technical Reports Server (NTRS)

    Schlegel, Todd T.; DePalma, Jude L.; Moradi, Saeed

    2003-01-01

    An electronic system that performs real-time analysis of the low-amplitude, high-frequency, ordinarily invisible components of the QRS portion of an electrocardiographic signal in real time has been developed. Whereas the signals readily visible on a conventional electrocardiogram (ECG) have amplitudes of the order of a millivolt and are characterized by frequencies <100 Hz, the ordinarily invisible components have amplitudes in the microvolt range and are characterized by frequencies from about 150 to about 250 Hz. Deviations of these high-frequency components from a normal pattern can be indicative of myocardial ischemia or myocardial infarction

  5. Condenser Microphone Protective Grid Correction for High Frequency Measurements

    NASA Technical Reports Server (NTRS)

    Lee, Erik; Bennett, Reginald

    2010-01-01

    Use of a protective grid on small diameter microphones can prolong the lifetime of the unit, but the high frequency effects can complicate data interpretation. Analytical methods have been developed to correct for the grid effect at high frequencies. Specifically, the analysis pertains to quantifying the microphone protective grid response characteristics in the acoustic near field of a rocket plume noise source. A frequency response function computation using two microphones will be explained. Experimental and instrumentation setup details will be provided. The resulting frequency response function for a B&K 4944 condenser microphone protective grid will be presented, along with associated uncertainties

  6. High frequency microbubble-switched oscillations modulated by microfluidic transistors

    NASA Astrophysics Data System (ADS)

    Yang, Fanghao; Dai, Xianming; Li, Chen

    2012-08-01

    Creating high frequency two-phase oscillations (HF-TPOs) remains an important goal in advancing microscale fluidic logic devices, micro-mixers, micro-actuators, and flow controls. However, thermally driven TPO frequency has been hindered by confinements of compressible vapor bubbles and low thermal diffusivity in microfluidic systems. In this study, a mechanism creating high frequency microbubbles growth/collapse cycle has been developed to achieve HF-TPOs. A "microfluidic transistor" was conceptualized and fabricated to passively sustain and modulate HF-TPOs. Three orders of magnitude higher TPO frequency has been achieved compared to TPOs reported in literatures under similar working conditions.

  7. Time lags of the kilohertz quasi-periodic oscillations in the low-mass X-ray binaries 4U 1608-52 and 4U 1636-53

    NASA Astrophysics Data System (ADS)

    de Avellar, Marcio G. B.; Méndez, Mariano; Sanna, Andrea; Horvath, Jorge E.

    2013-08-01

    We studied the energy and frequency dependence of the Fourier time lags and intrinsic coherence of the kilohertz quasi-periodic oscillations (kHz QPOs) in the neutron-star low-mass X-ray binaries 4U 1608-52 and 4U 1636-53, using a large data set obtained with the Rossi X-ray Timing Explorer. We confirmed that, in both sources, the time lags of the lower kHz QPO are soft and their magnitude increases with energy. We also found that: (i) In 4U 1636-53, the soft lags of the lower kHz QPO remain constant at ˜ 30 μs in the QPO frequency range 500-850 Hz, and decrease to ˜ 10 μs when the QPO frequency increases further. In 4U 1608-52, the soft lags of the lower kHz QPO remain constant at 40 μs up to 800 Hz, the highest frequency reached by this QPO in our data. (ii) In both sources, the time lags of the upper kHz QPO are hard, independent of energy or frequency and inconsistent with the soft lags of the lower kHz QPO. (iii) In both sources the intrinsic coherence of the lower kHz QPO remains constant at ˜0.6 between 5 and 12 keV, and drops to zero above that energy. The intrinsic coherence of the upper kHz QPO is consistent with being zero across the full energy range. (iv) In 4U 1636-53, the intrinsic coherence of the lower kHz QPO increases from ˜0 at ˜600 Hz to ˜1, and it decreases to ˜0.5 at 920 Hz; in 4U 1608-52, the intrinsic coherence is consistent with the same trend. (v) In both sources the intrinsic coherence of the upper kHz QPO is consistent with zero over the full frequency range of the QPO, except in 4U 1636-53 between 700 and 900 Hz where the intrinsic coherence marginally increases. We discuss our results in the context of scenarios in which the soft lags are either due to reflection off the accretion disc or up-/down-scattering in a hot medium close to the neutron star. We finally explore the connection between, on one hand the time lags and the intrinsic coherence of the kHz QPOs, and on the other the QPOs' amplitude and quality factor in

  8. Responses of a two degree-of-freedom system coupled to a nonlinear damper under multi-forcing frequencies

    NASA Astrophysics Data System (ADS)

    Bellizzi, Sergio; Côte, Renaud; Pachebat, Marc

    2013-04-01

    In this paper, forced responses are investigated in a two degree-of-freedom linear system with a linear coupling to a Non-linear Energy Sink (NES) subjected to quasi-periodic excitation. The quasi-periodic regimes associated to quasi-periodic forcing in the regime of 1:1-1:1 are studied analytically using the complexification method combined to the averaging method in terms of multi-time parameter. Local bifurcations of the quasi-periodic regimes are also analyzed using the excitation frequencies as control parameters. The nonlinear differential system is also solved numerically in time domain and the responses are analyzed in view of the analytical results. Stable and unstable quasi-periodic responses are found in good agreement with the analytical study, and strongly modulated responses are noticed. We observe that a single NES can be efficient for the reduction of two resonance peaks even if they are well separated, incommensurable, and excited simultaneously.

  9. High-frequency filtering of strong-motion records

    USGS Publications Warehouse

    Douglas, J.; Boore, D.M.

    2011-01-01

    The influence of noise in strong-motion records is most problematic at low and high frequencies where the signal to noise ratio is commonly low compared to that in the mid-spectrum. The impact of low-frequency noise (5 Hz) on computed pseudo-absolute response spectral accelerations (PSAs). In contrast to the case of low-frequency noise our analysis shows that filtering to remove high-frequency noise is only necessary in certain situations and that PSAs can often be used up to 100 Hz even if much lower high-cut corner frequencies are required to remove the noise. This apparent contradiction can be explained by the fact that PSAs are often controlled by ground accelerations associated with much lower frequencies than the natural frequency of the oscillator because path and site attenuation (often modelled by Q and κ, respectively) have removed the highest frequencies. We demonstrate that if high-cut filters are to be used, then their corner frequencies should be selected on an individual basis, as has been done in a few recent studies.

  10. Schlieren metrology for high frequency medical ultrasound.

    PubMed

    Zanelli, Claudio I; Howard, Samuel M

    2006-12-22

    The increased use of medical ultrasound above 40 MHz poses the challenge of measuring beam features that may be less than 40 microm. We have successfully used the optical Schlieren technique for transducers operating as high as 110 MHz. After a brief discussion of the technique, results are presented, including comparisons to state-of-the-art hydrophones and wire targets. PMID:16949117

  11. Gyrotron: A high-frequency microwave amplifier

    NASA Technical Reports Server (NTRS)

    Kupiszewski, A.

    1979-01-01

    A proposed microwave amplifier mechanism for future generations of millimeter high power uplinks to spacecraft and planetary radar transmitters is introduced. Basic electron-electromagnetic field interaction theory for RF power gain is explained. The starting point for general analytical methods leading to detailed design results is presented.

  12. High temperature pressurized high frequency testing rig and test method

    DOEpatents

    De La Cruz, Jose; Lacey, Paul

    2003-04-15

    An apparatus is described which permits the lubricity of fuel compositions at or near temperatures and pressures experienced by compression ignition fuel injector components during operation in a running engine. The apparatus consists of means to apply a measured force between two surfaces and oscillate them at high frequency while wetted with a sample of the fuel composition heated to an operator selected temperature. Provision is made to permit operation at or near the flash point of the fuel compositions. Additionally a method of using the subject apparatus to simulate ASTM Testing Method D6079 is disclosed, said method involving using the disclosed apparatus to contact the faces of prepared workpieces under a measured load, sealing the workface contact point into the disclosed apparatus while immersing said contact point between said workfaces in a lubricating media to be tested, pressurizing and heating the chamber and thereby the fluid and workfaces therewithin, using the disclosed apparatus to impart a differential linear motion between the workpieces at their contact point until a measurable scar is imparted to at least one workpiece workface, and then evaluating the workface scar.

  13. High-frequency energy in singing and speech

    NASA Astrophysics Data System (ADS)

    Monson, Brian Bruce

    While human speech and the human voice generate acoustical energy up to (and beyond) 20 kHz, the energy above approximately 5 kHz has been largely neglected. Evidence is accruing that this high-frequency energy contains perceptual information relevant to speech and voice, including percepts of quality, localization, and intelligibility. The present research was an initial step in the long-range goal of characterizing high-frequency energy in singing voice and speech, with particular regard for its perceptual role and its potential for modification during voice and speech production. In this study, a database of high-fidelity recordings of talkers was created and used for a broad acoustical analysis and general characterization of high-frequency energy, as well as specific characterization of phoneme category, voice and speech intensity level, and mode of production (speech versus singing) by high-frequency energy content. Directionality of radiation of high-frequency energy from the mouth was also examined. The recordings were used for perceptual experiments wherein listeners were asked to discriminate between speech and voice samples that differed only in high-frequency energy content. Listeners were also subjected to gender discrimination tasks, mode-of-production discrimination tasks, and transcription tasks with samples of speech and singing that contained only high-frequency content. The combination of these experiments has revealed that (1) human listeners are able to detect very subtle level changes in high-frequency energy, and (2) human listeners are able to extract significant perceptual information from high-frequency energy.

  14. Advanced high frequency partial discharge measuring system

    NASA Technical Reports Server (NTRS)

    Karady, George G.

    1994-01-01

    This report explains the Advanced Partial Discharge Measuring System in ASU's High Voltage Laboratory and presents some of the results obtained using the setup. While in operation an insulation is subjected to wide ranging temperature and voltage stresses. Hence, it is necessary to study the effect of temperature on the behavior of partial discharges in an insulation. The setup described in this report can be used to test samples at temperatures ranging from -50 C to 200 C. The aim of conducting the tests described herein is to be able to predict the behavior of an insulation under different operating conditions in addition to being able to predict the possibility of failure.

  15. High frequency single mode traveling wave structure for particle acceleration

    NASA Astrophysics Data System (ADS)

    Ivanyan, M. I.; Danielyan, V. A.; Grigoryan, B. A.; Grigoryan, A. H.; Tsakanian, A. V.; Tsakanov, V. M.; Vardanyan, A. S.; Zakaryan, S. V.

    2016-09-01

    The development of the new high frequency slow traveling wave structures is one of the promising directions in accomplishment of charged particles high acceleration gradient. The disc and dielectric loaded structures are the most known structures with slowly propagating modes. In this paper a large aperture high frequency metallic two-layer accelerating structure is studied. The electrodynamical properties of the slowly propagating TM01 mode in a metallic tube with internally coated low conductive thin layer are examined.

  16. The Influence of High-Frequency Envelope Information on Low-Frequency Vowel Identification in Noise.

    PubMed

    Schubotz, Wiebke; Brand, Thomas; Kollmeier, Birger; Ewert, Stephan D

    2016-01-01

    Vowel identification in noise using consonant-vowel-consonant (CVC) logatomes was used to investigate a possible interplay of speech information from different frequency regions. It was hypothesized that the periodicity conveyed by the temporal envelope of a high frequency stimulus can enhance the use of the information carried by auditory channels in the low-frequency region that share the same periodicity. It was further hypothesized that this acts as a strobe-like mechanism and would increase the signal-to-noise ratio for the voiced parts of the CVCs. In a first experiment, different high-frequency cues were provided to test this hypothesis, whereas a second experiment examined more closely the role of amplitude modulations and intact phase information within the high-frequency region (4-8 kHz). CVCs were either natural or vocoded speech (both limited to a low-pass cutoff-frequency of 2.5 kHz) and were presented in stationary 3-kHz low-pass filtered masking noise. The experimental results did not support the hypothesized use of periodicity information for aiding low-frequency perception. PMID:26730702

  17. The Influence of High-Frequency Envelope Information on Low-Frequency Vowel Identification in Noise

    PubMed Central

    2016-01-01

    Vowel identification in noise using consonant-vowel-consonant (CVC) logatomes was used to investigate a possible interplay of speech information from different frequency regions. It was hypothesized that the periodicity conveyed by the temporal envelope of a high frequency stimulus can enhance the use of the information carried by auditory channels in the low-frequency region that share the same periodicity. It was further hypothesized that this acts as a strobe-like mechanism and would increase the signal-to-noise ratio for the voiced parts of the CVCs. In a first experiment, different high-frequency cues were provided to test this hypothesis, whereas a second experiment examined more closely the role of amplitude modulations and intact phase information within the high-frequency region (4–8 kHz). CVCs were either natural or vocoded speech (both limited to a low-pass cutoff-frequency of 2.5 kHz) and were presented in stationary 3-kHz low-pass filtered masking noise. The experimental results did not support the hypothesized use of periodicity information for aiding low-frequency perception. PMID:26730702

  18. High-frequency Broadband Modulations of Electroencephalographic Spectra

    PubMed Central

    Onton, Julie; Makeig, Scott

    2009-01-01

    High-frequency cortical potentials in electroencephalographic (EEG) scalp recordings have low amplitudes and may be confounded with scalp muscle activities. EEG data from an eyes-closed emotion imagination task were linearly decomposed using independent component analysis (ICA) into maximally independent component (IC) processes. Joint decomposition of IC log spectrograms into source- and frequency-independent modulator (IM) processes revealed three distinct classes of IMs that separately modulated broadband high-frequency (∼15–200 Hz) power of brain, scalp muscle, and likely ocular motor IC processes. Multi-dimensional scaling revealed significant but spatially complex relationships between mean broadband brain IM effects and the valence of the imagined emotions. Thus, contrary to prevalent assumption, unitary modes of spectral modulation of frequencies encompassing the beta, gamma, and high gamma frequency ranges can be isolated from scalp-recorded EEG data and may be differentially associated with brain sources and cognitive activities. PMID:20076775

  19. Interface Strategy To Achieve Tunable High Frequency Attenuation.

    PubMed

    Lv, Hualiang; Zhang, Haiqian; Ji, Guangbin; Xu, Zhichuan J

    2016-03-16

    Among all polarizations, the interface polarization effect is the most effective, especially at high frequency. The design of various ferrite/iron interfaces can significantly enhance the materials' dielectric loss ability at high frequency. This paper presents a simple method to generate ferrite/iron interfaces to enhance the microwave attenuation at high frequency. The ferrites were coated onto carbonyl iron and could be varied to ZnFe2O4, CoFe2O4, Fe3O4, and NiFe2O4. Due to the ferrite/iron interface inducing a stronger dielectric loss effect, all of these materials achieved broad effective frequency width at a coating layer as thin as 1.5 mm. In particular, an effective frequency width of 6.2 GHz could be gained from the Fe@NiFe2O4 composite. PMID:26918285

  20. Radio-frequency electromagnetic emissions from materials under high-frequency mechanical excitation

    NASA Astrophysics Data System (ADS)

    Sorensen, Christian; Moore, David

    2015-06-01

    Direct contact piezoelectric transducers were used to excite compacted polycrystalline dielectric material samples with high amplitude but short duration ultrasound through a frequency range of 50 kHz to 10 MHz, while near field RF emissions were measured in 12 frequency bands from 18 to 750 GHz using a suite of detectors. Emissions were observed only in three detectors, covering the 40-75 GHz, 110-170 GHz, and 170-260 GHz frequency ranges. Emission amplitudes appear to rise nonlinearly with applied ultrasound amplitude, and the emission amplitudes versus ultrasound frequency are different than the thermal responses of these samples. Data comparing thermal responses and electromagnetic emissions versus ultrasound frequency and amplitude for several sample types (oxidizers and energetic materials) will be presented. LA-UR-15-20605.

  1. High frequency energy cascades in inviscid hydrodynamics

    NASA Astrophysics Data System (ADS)

    Costa, Adam Smith N.; de Araújo, J. M.; Cohen, Nir; Lucena, Liacir S.; Viswanathan, G. M.

    2014-04-01

    With the aim of gaining insight into the notoriously difficult problem of energy and vorticity cascades in high dimensional incompressible flows, we take a simpler and very well understood low dimensional analog and approach it from a new perspective, using the Fourier transform. Specifically, we study, numerically and analytically, how kinetic energy moves from one scale to another in solutions of the hyperbolic or inviscid Burgers equation in one spatial dimension (1D). We restrict our attention to initial conditions which go to zero as x→±∞. The main result we report here is a Fourier analytic way of describing the cascade process. We find that the cascade proceeds by rapid growth of a crossover scale below which there is asymptotic power law decay of the magnitude of the Fourier transform.

  2. High-frequency multimodal atomic force microscopy

    PubMed Central

    Nievergelt, Adrian P; Adams, Jonathan D; Odermatt, Pascal D

    2014-01-01

    Summary Multifrequency atomic force microscopy imaging has been recently demonstrated as a powerful technique for quickly obtaining information about the mechanical properties of a sample. Combining this development with recent gains in imaging speed through small cantilevers holds the promise of a convenient, high-speed method for obtaining nanoscale topography as well as mechanical properties. Nevertheless, instrument bandwidth limitations on cantilever excitation and readout have restricted the ability of multifrequency techniques to fully benefit from small cantilevers. We present an approach for cantilever excitation and deflection readout with a bandwidth of 20 MHz, enabling multifrequency techniques extended beyond 2 MHz for obtaining materials contrast in liquid and air, as well as soft imaging of delicate biological samples. PMID:25671141

  3. High-frequency hearing in seals and sea lions.

    PubMed

    Cunningham, Kane A; Reichmuth, Colleen

    2016-01-01

    Existing evidence suggests that some pinnipeds (seals, sea lions, and walruses) can detect underwater sound at frequencies well above the traditional high-frequency hearing limits for their species. This phenomenon, however, is not well studied: Sensitivity patterns at frequencies beyond traditional high-frequency limits are poorly resolved, and the nature of the auditory mechanism mediating hearing at these frequencies is unknown. In the first portion of this study, auditory sensitivity patterns in the 50-180 kHz range were measured for one California sea lion (Zalophus californianus), one harbor seal (Phoca vitulina), and one spotted seal (Phoca largha). Results show the presence of two distinct slope-regions at the high-frequency ends of the audiograms of all three subjects. The first region is characterized by a rapid decrease in sensitivity with increasing frequency-i.e. a steep slope-followed by a region of much less rapid sensitivity decrease-i.e. a shallower slope. In the second portion of this study, a masking experiment was conducted to investigate how the basilar membrane of a harbor seal subject responded to acoustic energy from a narrowband masking noise centered at 140 kHz. The measured masking pattern suggests that the initial, rapid decrease in sensitivity on the high-frequency end of the subject's audiogram is not due to cochlear constraints, as has been previously hypothesized, but rather to constraints on the conductive mechanism. PMID:26519092

  4. Factors Affecting the Benefits of High-Frequency Amplification

    ERIC Educational Resources Information Center

    Horwitz, Amy R.; Ahlstrom, Jayne B.; Dubno, Judy R.

    2008-01-01

    Purpose: This study was designed to determine the extent to which high-frequency amplification helped or hindered speech recognition as a function of hearing loss, gain-frequency response, and background noise. Method: Speech recognition was measured monaurally under headphones for nonsense syllables low-pass filtered in one-third-octave steps…

  5. High frequency eddy current device for near surface material characterizations

    NASA Astrophysics Data System (ADS)

    Hillmann, S.; Heuer, H.; Meyendorf, N.

    2009-03-01

    For near surface characterization a new high frequency eddy current device was been developed. By using a measurement frequency up to 100 MHz information of near surface areas can be acquired. Depending on the investigated material high resolution depth profiles can be derived. The obtained data with the new device were compared to those obtained with a high precision impedance analyser. It could be demonstrated that the new device measures the eddy current conductivity signal in the high frequencies much better than the impedance analyser. By sweeping the frequency from 100 kHz up to 100 MHz the technique delivers a depth profile of the electrical conductivity of the material. This kind of high frequency eddy current technique can be used for quality assurance, surface contamination control or near surface material characterization e.g. microstructure and cold work influences. It can be a powerful tool to obtain information for process control or a good / bad decision in mass production processes like for example rolling, coating, and surface treatments. The big advantage of the high frequency eddy current method is that it is fast und precise. This paper presents results with a new developed prototype Eddy-Current-Device for measurement frequencies up to 100 MHz which is first time suitable in rough industrial environment and makes expensive lab network analysers unnecessary for this kind of investigations.

  6. Residual absorption of high temperature superconductors at THz frequencies

    SciTech Connect

    Keller, P.; Barowski, H.S.; Prenninger, M.; Pechen, E.V.; Renk, K.F.

    1996-12-31

    The authors report on a study of the residual absorption of high temperature superconductors (HTS) at THz frequencies. Using transmission Fabry-Perot interferometry, they determined both, real and imaginary part of the conductivity. They especially studied YBCO thin films. They found that the dynamical conductivity varied strongly from sample to sample. As a main result, they find that the absorptivity increases at frequencies above 1 THz much weaker than quadratically, i.e., the {omega}{sup 2} behavior of the absorptivity at microwave frequencies is not continued in the THz frequency range.

  7. High performance vapour-cell frequency standards

    NASA Astrophysics Data System (ADS)

    Gharavipour, M.; Affolderbach, C.; Kang, S.; Bandi, T.; Gruet, F.; Pellaton, M.; Mileti, G.

    2016-06-01

    We report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10-13 τ-1/2 and 2.4×10-13 τ-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.

  8. Pigeons use high spatial frequencies when memorizing pictures.

    PubMed

    Murphy, Matthew S; Brooks, Daniel I; Cook, Robert G

    2015-07-01

    The ability of animals to visually memorize and categorize a large number of pictures is well established. Determining the kinds of information animals use to accomplish these goals has been more difficult. This experiment examined the contribution of spatial frequency information to picture memorization by pigeons. A series of grayscale pictures were notch-filtered to eliminate different portions of the spatial frequency spectrum of memorized pictures. The results indicated that the higher spatial frequencies in the pictures were most important to accurate recognition, suggesting that the detection of fine detail at the high range of pigeon visual acuity was a critical component to their memorized representations. Subsequent tests with band-pass and hybrid conflict stimuli confirmed this conclusion. It is suggested that cognitive and task demands may determine how spatial frequency is used by pigeons, with higher frequencies more important to item memorization, while lower spatial frequencies may contribute to categorization in other types of discrimination tasks. PMID:25915753

  9. ON MASS CONSTRAINTS IMPLIED BY THE RELATIVISTIC PRECESSION MODEL OF TWIN-PEAK QUASI-PERIODIC OSCILLATIONS IN CIRCINUS X-1

    SciTech Connect

    Toeroek, Gabriel; Bakala, Pavel; Sramkova, Eva; StuchlIk, Zdenek; Urbanec, Martin E-mail: pavel.bakala@fpf.slu.c E-mail: zdenek.stuchlik@fpf.slu.c

    2010-05-01

    Boutloukos et al. discovered twin-peak quasi-periodic oscillations (QPOs) in 11 observations of the peculiar Z-source Circinus X-1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M{sub 0} = 2.2 {+-} 0.3 M{sub sun}. We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j = cJ/GM {sup 2}. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M {approx} M{sub 0}[1 + 0.55(j + j {sup 2})]. It is therefore impossible to estimate the mass without independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M{sub sun}. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.

  10. Interaction between ELF-VLF emission and magnetic pulsations: quasi-periodic ELF-VLF emissions associated with Pc 3--4 magnetic pulsations and their geomagnetic conjugacy

    SciTech Connect

    Sato, N.; Kokubun, S.

    1980-01-01

    The characteristics of quasi-periodic (QP) ELF-VLF emissions with periods of 10--150 s and their relationships to magnetic pulsations are studied by using data obtained from Syowa and Mizuho Stations in Antarctica and at Husafell in Iceland, which is located near the geomagnetic conjugate point of Syowa. From the coherency analysis between QP emissions and Pc 3--4 magnetic pulsations it is found that the coherency between the D component of magnetic pulsations and the intensity fluctuations of QP's is much higher than that between the H component of magnetic pulsations and QP's. It is also found that the propagation time of magnetic pulsations (HM waves) from the interaction region between magnetic pulsations and QP's in the magnetosphere to the ground is 20--30 s. These properties are observed at conjugate-pair stations with good conjugacy. The results strongly suggest that QP emissions are modulated by compressional mode Pc 3--4 magnetic pulsations near the equatorial plane in the outer magnetosphere.

  11. A stable quasi-periodic 4.18-d oscillation and mysterious occultations in the 2011 MOST light-curve of TW Hya

    NASA Astrophysics Data System (ADS)

    Siwak, Michal; Rucinski, Slavek M.; Matthews, Jaymie M.; Guenther, David B.; Kuschnig, Rainer; Moffat, Anthony F. J.; Rowe, Jason F.; Sasselov, Dimitar; Weiss, Werner W.

    2014-10-01

    We present an analysis of the 2011 photometric observations of TW Hya by the MOST satellite; this is the fourth continuous series of this type. The large-scale light variations are dominated by a strong, quasi-periodic 4.18-d oscillation with superimposed, apparently chaotic flaring activity. The former is probably produced by stellar rotation with one large hotspot created by a stable accretion funnel, while the latter may be produced by small hotspots, created at moderate latitudes by unstable accretion tongues. A new, previously unnoticed feature is a series of semiperiodic, well-defined brightness dips of unknown nature, of which 19 were observed during 43 d of our nearly continuous observations. Re-analysis of the 2009 MOST light-curve revealed the presence of three similar dips. On the basis of recent theoretical results, we tentatively conclude that the dips may represent occultations of the small hotspots created by unstable accretion tongues by hypothetical optically thick clumps of dust.

  12. On Mass Constraints Implied by the Relativistic Precession Model of Twin-peak Quasi-periodic Oscillations in Circinus X-1

    NASA Astrophysics Data System (ADS)

    Török, Gabriel; Bakala, Pavel; Šrámková, Eva; Stuchlík, Zdeněk; Urbanec, Martin

    2010-05-01

    Boutloukos et al. discovered twin-peak quasi-periodic oscillations (QPOs) in 11 observations of the peculiar Z-source Circinus X-1. Among several other conjunctions the authors briefly discussed the related estimate of the compact object mass following from the geodesic relativistic precession model for kHz QPOs. Neglecting the neutron star rotation they reported the inferred mass M 0 = 2.2 ± 0.3 M sun. We present a more detailed analysis of the estimate which involves the frame-dragging effects associated with rotating spacetimes. For a free mass we find acceptable fits of the model to data for (any) small dimensionless compact object angular momentum j = cJ/GM 2. Moreover, quality of the fit tends to increase very gently with rising j. Good fits are reached when M ~ M 0[1 + 0.55(j + j 2)]. It is therefore impossible to estimate the mass without independent knowledge of the angular momentum and vice versa. Considering j up to 0.3 the range of the feasible values of mass extends up to 3 M sun. We suggest that similar increase of estimated mass due to rotational effects can be relevant for several other sources.

  13. High-Frequency Subband Compressed Sensing MRI Using Quadruplet Sampling

    PubMed Central

    Sung, Kyunghyun; Hargreaves, Brian A

    2013-01-01

    Purpose To presents and validates a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data. Theory and Methods High- and low-spatial-frequency regions are defined in k-space based on the separation of wavelet subbands, and the conventional compressed sensing (CS) problem is transformed into one of localized k-space estimation. To better exploit wavelet-domain sparsity, CS can be used for high-spatial-frequency regions while parallel imaging can be used for low-spatial-frequency regions. Fourier undersampling is also customized to better accommodate each reconstruction method: random undersampling for CS and regular undersampling for parallel imaging. Results Examples using the proposed method demonstrate successful reconstruction of both low-spatial-frequency content and fine structures in high-resolution 3D breast imaging with a net acceleration of 11 to 12. Conclusion The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size. PMID:23280540

  14. High density terahertz frequency comb produced by coherent synchrotron radiation

    PubMed Central

    Tammaro, S.; Pirali, O.; Roy, P.; Lampin, J.-F.; Ducournau, G.; Cuisset, A.; Hindle, F.; Mouret, G.

    2015-01-01

    Frequency combs have enabled significant progress in frequency metrology and high-resolution spectroscopy extending the achievable resolution while increasing the signal-to-noise ratio. In its coherent mode, synchrotron radiation is accepted to provide an intense terahertz continuum covering a wide spectral range from about 0.1 to 1 THz. Using a dedicated heterodyne receiver, we reveal the purely discrete nature of this emission. A phase relationship between the light pulses leads to a powerful frequency comb spanning over one decade in frequency. The comb has a mode spacing of 846 kHz, a linewidth of about 200 Hz, a fractional precision of about 2 × 10−10 and no frequency offset. The unprecedented potential of the comb for high-resolution spectroscopy is demonstrated by the accurate determination of pure rotation transitions of acetonitrile. PMID:26190043

  15. Disruption of microalgal cells using high-frequency focused ultrasound.

    PubMed

    Wang, Meng; Yuan, Wenqiao; Jiang, Xiaoning; Jing, Yun; Wang, Zhuochen

    2014-02-01

    The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated. PMID:24374364

  16. High-frequency matrix converter with square wave input

    SciTech Connect

    Carr, Joseph Alexander; Balda, Juan Carlos

    2015-03-31

    A device for producing an alternating current output voltage from a high-frequency, square-wave input voltage comprising, high-frequency, square-wave input a matrix converter and a control system. The matrix converter comprises a plurality of electrical switches. The high-frequency input and the matrix converter are electrically connected to each other. The control system is connected to each switch of the matrix converter. The control system is electrically connected to the input of the matrix converter. The control system is configured to operate each electrical switch of the matrix converter converting a high-frequency, square-wave input voltage across the first input port of the matrix converter and the second input port of the matrix converter to an alternating current output voltage at the output of the matrix converter.

  17. High frequency jet ventilation in fat embolism syndrome.

    PubMed

    Lee, A; Simpson, D

    1986-11-01

    The use of high frequency jet ventilation in the management of a patient with fat embolism syndrome is described. Its principal advantage over conventional intermittent positive pressure ventilation is a reduction in the amount of sedation necessary. PMID:3789371

  18. Shift of the shadow boundary in high frequency scattering

    NASA Astrophysics Data System (ADS)

    Zworski, Maciej

    1991-02-01

    The microlocal theory of diffraction is used to establish the conjecture of Keller and Rubinow relating the shift of the shadow boundary in high frequency scattering to the directional curvatures of a strictly convex obstacle.

  19. LOW-FREQUENCY OSCILLATIONS IN XTE J1550-564

    SciTech Connect

    Rao Fengyun; Belloni, Tomaso; Stella, Luigi; Zhang Shuangnan; Li Tipei E-mail: tomaso.belloni@brera.inaf.i

    2010-05-10

    We present the results of a timing analysis of the low-frequency quasi-periodic oscillation (QPO) in the Rossi X-Ray Timing Explorer data of the black hole binary XTE J1550-564 during its 1998 outburst. The QPO frequency is observed to vary on timescales between {approx}100 s and days, correlated with the count rate contribution from the optically thick accretion disk: we studied this correlation and discuss its influence on the QPO width. In all observations, the quality factors ({nu}{sub 0}/FWHM) of the fundamental and second harmonic peaks were observed to be consistent, suggesting that the quasi-periodic nature of the oscillation is due to frequency modulation. In addition to the QPO and its harmonic peaks, a new 1.5{nu} component was detected in the power spectra. This component is broad, with a quality factor of {approx}0.6. From this, we argue that the peak observed at half the QPO frequency, usually referred to as 'sub-harmonic', could be the fundamental frequency, leading to the sequence 1:2:3:4. We also studied the energy dependence of the timing features and conclude that the two continuum components observed in the power spectrum, although both more intense at high energies, show a different dependence on energy. At low energies, the lowest-frequency component dominates, while at high energies the higher-frequency one has a higher fractional rms. An interplay between these two components was also observed as a function of their characteristic frequency. In this source, the transition between the low/hard state and the hard-intermediate state appears to be a smooth process.

  20. High frequency, small signal MH loops of ferromagnetic thin films

    NASA Technical Reports Server (NTRS)

    Grimes, C. A.; Ong, K. G.

    2000-01-01

    A method is presented for transforming the high frequency bias susceptibility measurements of ferromagnetic thin films into the form of a MH loop with, depending upon the measurement geometry, the y-axis zero crossing giving a measure of the coercive force or anisotropy field. The loops provide a measure of the quantitative and qualitative high frequency switching properties of ferromagnetic thin films. c2000 American Institute of Physics.

  1. SEPP-ZVS High Frequency Inverter Incorporating Auxiliary Switch

    NASA Astrophysics Data System (ADS)

    Ogiwara, Hiroyuki; Itoi, Misao; Nakaoka, Mutsuo

    This paper presents a novel circuit topology to attain ZVS operation of a high frequency inverter over a wide range output power regulation using a PWM control technique by connecting an auxiliary switch to the conventional single ended push-pull (SEPP) ZVS high frequency inverter. A switching current is injected into the main switches via the auxiliary switch only during the short period between its turn-on and off times to supply a current required for its ZVS operation.

  2. Soft Switching SEPP High Frequency Inverter for Induction Heating

    NASA Astrophysics Data System (ADS)

    Ogiwara, Hiroyuki; Nakaoka, Mutsuo

    This paper presents a novel circuit topology to attain soft switching operation of a high frequency inverter. Its output power is regulated over a wide range using a PWM control technique by connecting an auxiliary resonant circuit to the conventional single ended push pull (SEPP) high frequency inverter for induction heating. All switching devices in the proposed inverter are operated soft switching mode. This paper describes its circuit constitution and obtained experimental results from a practical point of view.

  3. High-flow frequencies for selected streams in Oklahoma

    USGS Publications Warehouse

    Huntzinger, Thomas L.

    1978-01-01

    Streamflow records are analyzed statistically to determine high-flow characteristics of selected streams in Oklahoma. Tables are included which show the 2-, 5-, 10-, 25-, 50-, and 100-year high-flow frequencies for durations of 1, 3, 7, 30, 90, and 365 days. The log-Pearson Type III frequency distribution was used in the computations. Streamflow records used include data extending from 1903 to 1974.

  4. High frequency ultrasound with color Doppler in dermatology*

    PubMed Central

    Barcaui, Elisa de Oliveira; Carvalho, Antonio Carlos Pires; Lopes, Flavia Paiva Proença Lobo; Piñeiro-Maceira, Juan; Barcaui, Carlos Baptista

    2016-01-01

    Ultrasonography is a method of imaging that classically is used in dermatology to study changes in the hypoderma, as nodules and infectious and inflammatory processes. The introduction of high frequency and resolution equipments enabled the observation of superficial structures, allowing differentiation between skin layers and providing details for the analysis of the skin and its appendages. This paper aims to review the basic principles of high frequency ultrasound and its applications in different areas of dermatology. PMID:27438191

  5. Characterizing Earthquake Rupture Properties Using Peak High-Frequency Offset

    NASA Astrophysics Data System (ADS)

    Wen, L.; Meng, L.

    2014-12-01

    Teleseismic array back-projection (BP) of high frequency (~1Hz) seismic waves has been recently applied to image the aftershock sequence of the Tohoku-Oki earthquake. The BP method proves to be effective in capturing early aftershocks that are difficult to be detected due to the contamination of the mainshock coda wave. Furthermore, since the event detection is based on the identification of the local peaks in time series of the BP power, the resulting event location corresponds to the peak high-frequency energy rather than the hypocenter. In this work, we show that the comparison between the BP-determined catalog and conventional phase-picking catalog provides estimates of the spatial and temporal offset between the hypocenter and the peak high-frequency radiation. We propose to measure this peak high-frequency shift of global earthquakes between M4.0 to M7.0. We average the BP locations calibrated by multiple reference events to minimize the uncertainty due to the variation of 3D path effects. In our initial effort focusing on the foreshock and aftershock sequence of the 2014 Iquique earthquake, we find systematic shifts of the peak high-frequency energy towards the down-dip direction. We find that the amount of the shift is a good indication of rupture length, which scales with the earthquake magnitude. Further investigations of the peak high frequency offset may provide constraints on earthquake source properties such as rupture directivity, rupture duration, rupture speed, and stress drop.

  6. High-frequency homogenization of zero-frequency stop band photonic and phononic crystals

    NASA Astrophysics Data System (ADS)

    Antonakakis, T.; Craster, R. V.; Guenneau, S.

    2013-10-01

    We present an accurate methodology for representing the physics of waves, in periodic structures, through effective properties for a replacement bulk medium: this is valid even for media with zero-frequency stop bands and where high-frequency phenomena dominate. Since the work of Lord Rayleigh in 1892, low-frequency (or quasi-static) behaviour has been neatly encapsulated in effective anisotropic media; the various parameters come from asymptotic analysis relying upon the ratio of the array pitch to the wavelength being sufficiently small. However, such classical homogenization theories break down in the high-frequency or stop band regime whereby the wavelength to pitch ratio is of order one. Furthermore, arrays of inclusions with Dirichlet data lead to a zero-frequency stop band, with the salient consequence that classical homogenization is invalid. Higher-frequency phenomena are of significant importance in photonics (transverse magnetic waves propagating in infinite conducting parallel fibres), phononics (anti-plane shear waves propagating in isotropic elastic materials with inclusions) and platonics (flexural waves propagating in thin-elastic plates with holes). Fortunately, the recently proposed high-frequency homogenization (HFH) theory is only constrained by the knowledge of standing waves in order to asymptotically reconstruct dispersion curves and associated Floquet-Bloch eigenfields: it is capable of accurately representing zero-frequency stop band structures. The homogenized equations are partial differential equations with a dispersive anisotropic homogenized tensor that characterizes the effective medium. We apply HFH to metamaterials, exploiting the subtle features of Bloch dispersion curves such as Dirac-like cones, as well as zero and negative group velocity near stop bands in order to achieve exciting physical phenomena such as cloaking, lensing and endoscope effects. These are simulated numerically using finite elements and compared to predictions

  7. Frequencies of Inaudible High-Frequency Sounds Differentially Affect Brain Activity: Positive and Negative Hypersonic Effects

    PubMed Central

    Fukushima, Ariko; Yagi, Reiko; Kawai, Norie; Honda, Manabu; Nishina, Emi; Oohashi, Tsutomu

    2014-01-01

    The hypersonic effect is a phenomenon in which sounds containing significant quantities of non-stationary high-frequency components (HFCs) above the human audible range (max. 20 kHz) activate the midbrain and diencephalon and evoke various physiological, psychological and behavioral responses. Yet important issues remain unverified, especially the relationship existing between the frequency of HFCs and the emergence of the hypersonic effect. In this study, to investigate the relationship between the hypersonic effect and HFC frequencies, we divided an HFC (above 16 kHz) of recorded gamelan music into 12 band components and applied them to subjects along with an audible component (below 16 kHz) to observe changes in the alpha2 frequency component (10–13 Hz) of spontaneous EEGs measured from centro-parieto-occipital regions (Alpha-2 EEG), which we previously reported as an index of the hypersonic effect. Our results showed reciprocal directional changes in Alpha-2 EEGs depending on the frequency of the HFCs presented with audible low-frequency component (LFC). When an HFC above approximately 32 kHz was applied, Alpha-2 EEG increased significantly compared to when only audible sound was applied (positive hypersonic effect), while, when an HFC below approximately 32 kHz was applied, the Alpha-2 EEG decreased (negative hypersonic effect). These findings suggest that the emergence of the hypersonic effect depends on the frequencies of inaudible HFC. PMID:24788141

  8. High frequency source localization in a shallow ocean sound channel using frequency difference matched field processing.

    PubMed

    Worthmann, Brian M; Song, H C; Dowling, David R

    2015-12-01

    Matched field processing (MFP) is an established technique for source localization in known multipath acoustic environments. Unfortunately, in many situations, particularly those involving high frequency signals, imperfect knowledge of the actual propagation environment prevents accurate propagation modeling and source localization via MFP fails. For beamforming applications, this actual-to-model mismatch problem was mitigated through a frequency downshift, made possible by a nonlinear array-signal-processing technique called frequency difference beamforming [Abadi, Song, and Dowling (2012). J. Acoust. Soc. Am. 132, 3018-3029]. Here, this technique is extended to conventional (Bartlett) MFP using simulations and measurements from the 2011 Kauai Acoustic Communications MURI experiment (KAM11) to produce ambiguity surfaces at frequencies well below the signal bandwidth where the detrimental effects of mismatch are reduced. Both the simulation and experimental results suggest that frequency difference MFP can be more robust against environmental mismatch than conventional MFP. In particular, signals of frequency 11.2 kHz-32.8 kHz were broadcast 3 km through a 106-m-deep shallow ocean sound channel to a sparse 16-element vertical receiving array. Frequency difference MFP unambiguously localized the source in several experimental data sets with average peak-to-side-lobe ratio of 0.9 dB, average absolute-value range error of 170 m, and average absolute-value depth error of 10 m. PMID:26723312

  9. Frequencies of inaudible high-frequency sounds differentially affect brain activity: positive and negative hypersonic effects.

    PubMed

    Fukushima, Ariko; Yagi, Reiko; Kawai, Norie; Honda, Manabu; Nishina, Emi; Oohashi, Tsutomu

    2014-01-01

    The hypersonic effect is a phenomenon in which sounds containing significant quantities of non-stationary high-frequency components (HFCs) above the human audible range (max. 20 kHz) activate the midbrain and diencephalon and evoke various physiological, psychological and behavioral responses. Yet important issues remain unverified, especially the relationship existing between the frequency of HFCs and the emergence of the hypersonic effect. In this study, to investigate the relationship between the hypersonic effect and HFC frequencies, we divided an HFC (above 16 kHz) of recorded gamelan music into 12 band components and applied them to subjects along with an audible component (below 16 kHz) to observe changes in the alpha2 frequency component (10-13 Hz) of spontaneous EEGs measured from centro-parieto-occipital regions (Alpha-2 EEG), which we previously reported as an index of the hypersonic effect. Our results showed reciprocal directional changes in Alpha-2 EEGs depending on the frequency of the HFCs presented with audible low-frequency component (LFC). When an HFC above approximately 32 kHz was applied, Alpha-2 EEG increased significantly compared to when only audible sound was applied (positive hypersonic effect), while, when an HFC below approximately 32 kHz was applied, the Alpha-2 EEG decreased (negative hypersonic effect). These findings suggest that the emergence of the hypersonic effect depends on the frequencies of inaudible HFC. PMID:24788141

  10. Effect of temperature on the shape of spatial quasi-periodic oscillations of the refractive index of alkali atoms in an optically dense medium with a closed excitation contour of Δ type

    SciTech Connect

    Barantsev, K A; Litvinov, A N

    2014-10-31

    A theory of a closed excitation contour (Δ system) of a three-level atom in an optically dense medium is constructed with allowance for temperature. The spatial quasi-periodic oscillations of the refractive index in the system under study are shown to damp with increasing temperature. The range of temperatures at which these oscillations are most pronounced is found. (quantum optics)

  11. Switch over to the high frequency rf systems near transition

    SciTech Connect

    Brennan, J.M.; Wei, J.

    1988-01-01

    The purpose of this note is to point out that since bunch narrowing naturally occurs in the acceleration process in the vicinity of transition, it should be possible to switch over to the high frequency system close to transition when the bunch has narrowed enough to fit directly into the high frequency bucket. The advantage of this approach is the simplicity, no extra components or gymnastics are required of the low frequency system. The disadvantage, of course, is for protons which do not go through transition. But on the other hand, there is no shortage of intensity for protons and so it should be possible to keep the phase space area low for protons, and then matching to the high frequency bucket should be easily accomplished by adiabatic compression. 3 refs., 7 figs.

  12. Parametric Study of High Frequency Pulse Detonation Tubes

    NASA Technical Reports Server (NTRS)

    Cutler, Anderw D.

    2008-01-01

    This paper describes development of high frequency pulse detonation tubes similar to a small pulse detonation engine (PDE). A high-speed valve injects a charge of a mixture of fuel and air at rates of up to 1000 Hz into a constant area tube closed at one end. The reactants detonate in the tube and the products exit as a pulsed jet. High frequency pressure transducers are used to monitor the pressure fluctuations in the device and thrust is measured with a balance. The effects of injection frequency, fuel and air flow rates, tube length, and injection location are considered. Both H2 and C2H4 fuels are considered. Optimum (maximum specific thrust) fuel-air compositions and resonant frequencies are identified. Results are compared to PDE calculations. Design rules are postulated and applications to aerodynamic flow control and propulsion are discussed.

  13. Advanced waveforms and frequency with spinal cord stimulation: burst and high-frequency energy delivery.

    PubMed

    Pope, Jason E; Falowski, Steven; Deer, Tim R

    2015-07-01

    In recent years, software development has been key to the next generation of neuromodulation devices. In this review, we will describe the new strategies for electrical waveform delivery for spinal cord stimulation. A systematic literature review was performed using bibliographic databases, limited to the English language and human data, between 2010 and 2014. The literature search yielded three articles on burst stimulation and four articles on high-frequency stimulation. High-frequency and burst stimulation may offer advantages over tonic stimulation, as data suggest improved patient tolerance, comparable increase in function and possible success with a subset of patients refractory to tonic spinal cord stimulation. High-frequency and burst stimulation are new ways to deliver energy to the spinal cord that may offer advantages over tonic stimulation. These may offer new salvage strategies to mitigate spinal cord stimulation failure and improve cost-effectiveness by reducing explant rate. PMID:25846152

  14. Dynamic high-resolution spectroscopic frequency referencing for frequency sweeping interferometry

    NASA Astrophysics Data System (ADS)

    Prellinger, Günther; Meiners-Hagen, Karl; Pollinger, Florian

    2016-06-01

    A spectroscopic reference for the intrinsic frequency calibration of a ranging system based on frequency-sweeping interferometry (FSI) is presented. Saturation spectroscopy of iodine transitions at 636.8 nm is used to generate well-defined frequency markers. The experimental and analytic implementation is shown to enable in principle a frequency determination with an uncertainty of 0.17 MHz for a coverage factor k = 1. This corresponds to a relative standard uncertainty of 1.5× {10}-7 as contribution to the combined measurement uncertainty of the FSI-based length measurement. But the analysis also reveals the high sensitivity of the actually achievable measurement uncertainty to the quality of the spectroscopic reference data.

  15. Broadband high-resolution X-ray frequency combs

    NASA Astrophysics Data System (ADS)

    Cavaletto, Stefano M.; Harman, Zoltán; Ott, Christian; Buth, Christian; Pfeifer, Thomas; Keitel, Christoph H.

    2014-07-01

    Optical frequency combs have had a remarkable impact on precision spectroscopy. Enabling this technology in the X-ray domain is expected to result in wide-ranging applications, such as stringent tests of astrophysical models and quantum electrodynamics, a more sensitive search for the variability of fundamental constants, and precision studies of nuclear structure. Ultraprecise X-ray atomic clocks may also be envisaged. In this work, an X-ray pulse-shaping method is proposed to generate a comb in the absorption spectrum of an ultrashort high-frequency pulse. The method employs an optical-frequency-comb laser, manipulating the system's dipole response to imprint a comb on an excited transition with a high photon energy. The described scheme provides higher comb frequencies and requires lower optical-comb peak intensities than currently explored methods, preserves the overall width of the optical comb, and may be implemented using currently available X-ray technology.

  16. Combination frequencies in high-amplitude δ Scuti stars

    NASA Astrophysics Data System (ADS)

    Balona, L. A.

    2016-06-01

    Short-cadence observations of δ Scuti stars in the Kepler field are used to investigate the physical nature of high-amplitude δ Scuti stars (HADS). Although it is often mentioned that HADS are transition objects between classical Cepheids and δ Scuti stars, neither ground-based or space-based observations support this view. It is found that HADS occur randomly within the instability strip. The possibility that HADS may be defined by the presence of combination frequencies is discussed. There is a weak tendency for the number of combination frequencies to increase with increasing amplitude of the parent frequencies. However, even stars with very low amplitudes may have detectable combination frequencies. Very few parent modes have a period ratio appropriate to first-overtone and fundamental radial modes. It appears that a high amplitude, in itself, is not useful as a distinguishing feature of δ Scuti stars.

  17. A high frequency transformer model for the EMTP

    SciTech Connect

    Morched, A.; Marti, L.; Ottevangers, J. )

    1993-07-01

    A model to simulate the high frequency behavior of a power transformer is presented. This model is based on the frequency characteristics of the transformer admittance matrix between its terminals over a given range of frequencies. The transformer admittance characteristics can be obtained from measurements or from detailed internal models based on the physical layout of the transformer. The elements of the nodal admittance matrix are approximated with rational functions consisting of real as well as complex conjugate poles and zeros. These approximations are realized in the form of an RLC network in a format suitable for direct use with EMTP. The high frequency transformer model can be used as a stand-alone linear model or as an add-on module of a more comprehensive model where iron core nonlinearities are represented in detail.

  18. Gravitational wave detection with high frequency phonon trapping acoustic cavities

    NASA Astrophysics Data System (ADS)

    Goryachev, Maxim; Tobar, Michael E.

    2014-11-01

    There are a number of theoretical predictions for astrophysical and cosmological objects, which emit high frequency (1 06-1 09 Hz ) gravitation waves (GW) or contribute somehow to the stochastic high frequency GW background. Here we propose a new sensitive detector in this frequency band, which is based on existing cryogenic ultrahigh quality factor quartz bulk acoustic wave cavity technology, coupled to near-quantum-limited SQUID amplifiers at 20 mK. We show that spectral strain sensitivities reaching 1 0-22 per √{Hz } per mode is possible, which in principle can cover the frequency range with multiple (>100 ) modes with quality factors varying between 1 06 and 1 010 allowing wide bandwidth detection. Due to its compactness and well-established manufacturing process, the system is easily scalable into arrays and distributed networks that can also impact the overall sensitivity and introduce coincidence analysis to ensure no false detections.

  19. Frequency and time domain modeling of high speed amplifier

    NASA Astrophysics Data System (ADS)

    Opalska, Katarzyna

    2015-09-01

    The paper presents the lumped model of high speed amplifier useful for frequency and time domain (also large signal) simulation. Model is constructed on the basis of two-domain device measurements, namely small signal frequency parameters and time response to the input step of varying amplitude. Rational approximation of frequency domain data leads to small signal model composed of RLC subcircuits and controlled sources. Next, the model is complimented with the nonlinearities identified from time-domain measurements, including those taken for large input signals. Final amplifier model implemented in SPICE simulator is shown to correctly render the behavior of the device over the wide variety of operating conditions.

  20. High-power radio-frequency attenuation device

    DOEpatents

    Kerns, Q.A.; Miller, H.W.

    1981-12-30

    A resistor device for attenuating radio frequency power includes a radio frequency conductor connected to a series of fins formed of high relative magnetic permeability material. The fins are dimensional to accommodate the skin depth of the current conduction therethrough, as well as an inner heat conducting portion where current does not travel. Thermal connections for air or water cooling are provided for the inner heat conducting portions of each fin. Also disclosed is a resistor device to selectively alternate unwanted radio frequency energy in a resonant cavity.