For comprehensive and current results, perform a real-time search at Science.gov.

1

Quasi Periodic Oscillations in Blazars

NASA Astrophysics Data System (ADS)

Here we report our recent discoveries of Quasi-Periodic Oscillations (QPOs) in blazars time series data in X-ray and optical electromagnetic bands. Any such detection can give important clue of the location and nature of the processes of emission mechanism. In the case of radio-quiet AGN, the detected QPOs are very likely to be associated with the accretion disk. But in the case of blazars, it may be associated with jets in the high and outburst states, and in the low-state, it is probably associated with the accretion disk. In this brief review, I summarize the recent QPOs detections in blazars. There is one strong evidence of QPO detection in XMM-Newton time series data of narrow line Seyfert 1 galaxy RE J1034 +396 about which we will also discuss briefly.

Gupta, Alok C.

2014-12-01

2

Talbot effect of quasi-periodic grating.

Theoretic and experimental studies of the Talbot effect of quasi-periodic gratings are performed in this paper. The diffractions of periodic and quasi-periodic square aperture arrays in Fresnel fields are analyzed according to the scalar diffraction theory. The expressions of the diffraction intensities of two types of quasi-periodic gratings are deduced. Talbot images of the quasi-periodic gratings are predicted to appear at multiple certain distances. The quasi-periodic square aperture arrays are produced with the aid of a liquid crystal light modulator, and the self-images of the quasi-periodic gratings are measured successfully in the experiment. This study indicates that even a structure in short-range disorder may take on the self-imaging effect in a Fresnel field. PMID:23872752

Zhang, Chong; Zhang, Wei; Li, Furui; Wang, Junhong; Teng, Shuyun

2013-07-20

3

NASA Astrophysics Data System (ADS)

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.

You, Jiangong; Zhou, Qi

2013-11-01

4

Pressure-driven reconnection and quasi periodical oscillations in plasmas

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.

Paccagnella, R., E-mail: roberto.paccagnella@igi.cnr.it [Consorzio RFX and Istituto Gas Ionizzati del Consiglio Nazionale delle Ricerche (CNR), Padova (Italy)

2014-03-15

5

Quasi-periodic solutions for modified Toda lattice equation

Based on a spectral problem and the Lenard operator pairs, we derive in this paper a modified Toda lattice hierarchy. The modified Toda lattice equation is first decomposed into systems of integrable ordinary differential equations. A hyper-elliptic Riemann surface and Abel–Jacobi coordinates are then introduced to linearize the associated flow, from which some quasi-periodic solutions of the modified Toda lattice

Y. C. Hon; E. G. Fan

2009-01-01

6

QUASI-PERIODIC OSCILLATIONS IN LASCO CORONAL MASS EJECTION SPEEDS

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.

Shanmugaraju, A. [Department of Physics, Arul Anandar College, Karumathur-625 514 (India); Moon, Y.-J. [School of Space Research, Kyung Hee University, Yongin 446-701 (Korea, Republic of); Cho, K.-S.; Bong, S. C. [Korea Astronomy and Space Science Institute (KASI), Whaamdong, Yuseong-gu, Daejeon, 305-348 (Korea, Republic of); Gopalswamy, N.; Akiyama, S.; Yashiro, S. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Umapathy, S. [School of Physics, Madurai Kamaraj University, Madurai (India); Vrsnak, B., E-mail: shanmugaraju_a@yahoo.co, E-mail: moonyj@khu.ac.k [Hvar Observatory, Faculty of Geodesy, Zagreb (Croatia)

2010-01-01

7

Forced Oscillations in Fluid Tori and Quasi-Periodic Oscillations

The kilo-Hertz Quasi--Periodic Oscillations in X-ray binaries could originate within the accretion flow, and be a signature of non--linear fluid oscillations and mode coupling in strong gravity. The possibility to decipher these systems will impact our knowledge of fundamental parameters such as the neutron star mass, radius, and spin. Thus they offer the possibility to constrain the nuclear equation of state and the rotation parameter of stellar--mass black holes. We review the general properties of these oscillations from a hydrodynamical point of view, when the accretion flow is subject to external perturbations and summarize recent results.

William H. Lee

2005-10-19

8

Quantum phase transitions in the quasi-periodic kicked rotor

We present a microscopic theory of transport in quasi-periodically driven environments (`kicked rotors'), as realized in recent atom optic experiments. We find that the behavior of these systems depends sensitively on the value of Planck's constant $\\tilde h$: for irrational values of $\\tilde h/(4\\pi)$ they fall into the universality class of disordered electronic systems and we derive the microscopic theory of the ensuing localization phenomena. In contrast, for rational values the rotor-Anderson insulator acquires an infinite (static) conductivity and turns into a `super-metal'. Signatures of the corresponding metal/super-metal transition are discussed.

Chushun Tian; Alexander Altland; Markus Garst

2011-01-17

9

Development of a Quasi-Periodic Undulator for the HLS

China's first quasi-periodic undulator (QPU) has been developed for the Hefei Light Source (HLS). It uses a magnetic configuration with varied thicknesses of NdFeB blocks, based on the QPU of European Synchrotron Radiation Facility (ESRF). Depression of 3rd harmonic radiation is significantly improved over the ESRF QPU, as deduced from the measured magnetic fields. A method of configuring shims of different geometries and sizes, based on a symmetric principle to correct multi-pole field integrals, was demonstrated.

Yang, Yufeng; Chen, Wan; Jia, Qika; Sun, Shuchen; Li, Zhiqiang

2014-01-01

10

Development of a quasi-periodic undulator for the HLS

NASA Astrophysics Data System (ADS)

China's first quasi-periodic undulator (QPU) has been developed for the Hefei Light Source (HLS). It uses a magnetic configuration with varied thicknesses of NdFeB blocks, which is based on the QPU of European Synchrotron Radiation Facility (ESRF). The depression of 3rd harmonic radiation is significantly improved over the ESRF QPU, as deduced from the measured magnetic fields. A method of configuring shims of different geometries and sizes, based on a symmetric principle to correct multi-pole field integrals, is demonstrated.

Yang, Yu-Feng; Lu, Hui-Hua; Chen, Wan; Jia, Qi-Ka; Sun, Shu-Chen; Li, Zhi-Qiang

2014-07-01

11

Development of a Quasi-Periodic Undulator for the HLS

China's first quasi-periodic undulator (QPU) has been developed for the Hefei Light Source (HLS). It uses a magnetic configuration with varied thicknesses of NdFeB blocks, based on the QPU of European Synchrotron Radiation Facility (ESRF). Depression of 3rd harmonic radiation is significantly improved over the ESRF QPU, as deduced from the measured magnetic fields. A method of configuring shims of different geometries and sizes, based on a symmetric principle to correct multi-pole field integrals, was demonstrated.

Yufeng Yang; Huihua Lu; Wan Chen; Qika Jia; Shuchen Sun; Zhiqiang Li

2014-03-11

12

Quasi-periodic pulsations and diagnostics of flaring plasma

NASA Astrophysics Data System (ADS)

Two approaches in the interpretation of quasi-periodic pulsations in solar and stellar flares are presented. The first presents flaring loops as resonators for magneto-hydrodynamic (MHD) oscillations. Leaky and non-leaky modes are discussed. The second approach is based on Alfvén's idea of the flaring loop as an equivalent electric circuit. This approach naturally explains high-quality pulsations. It is shown that coronal seismology provides an efficient diagnostic tool for flare plasma on the Sun, red dwarfs, and in giant flares on neutron stars.

Stepanov, A. V.; Zaitsev, V. V.

2014-12-01

13

Overall ultimate yield strength of a quasi-periodic masonry

NASA Astrophysics Data System (ADS)

The purpose of this Note is the determination of the in-plane homogenized strength domain of a "quasi-periodic" masonry under the assumption of infinitely resistant blocks connected by cohesionless Mohr-Coulomb interfaces. This masonry is obtained by introducing a random perturbation on the horizontal width of the blocks of a periodic running bond masonry. It is found that in some non-trivial cases the strength domain coincides exactly with that of the initial periodic masonry. To cite this article: K. Sab, C. R. Mecanique 337 (2009).

Sab, Karam

2009-08-01

14

Electrochemically assembled quasi-periodic quantum dot arrays

NASA Astrophysics Data System (ADS)

We describe two electrochemical self-assembly processes for producing highly ordered quasi-periodic arrays of quantum dots on a surface. The advantages of these techniques are: (i) they are `gentle' and do not cause radiation damage to nanostructures unlike beam lithography, (ii) they have high throughput and are amenable to mass production unlike direct-write lithography, (iii) structures can be delineated on non-planar substrates, and (iv) the techniques are potentially orders of magnitude cheaper to implement than conventional nanosynthesis. Samples produced by these techniques have been characterized by microscopy, optical and transport measurements, Auger and x-ray. These measurements reveal intriguing properties of the nanostructures. In this paper, we describe our initial results and show the promise of such techniques for low-cost and high-yield nanosynthesis.

Bandyopadhyay, S.; Miller, A. E.; Chang, H. C.; Banerjee, G.; Yuzhakov, V.; Yue, D.-F.; Ricker, R. E.; Jones, S.; Eastman, J. A.; Baugher, E.; Chandrasekhar, M.

1996-12-01

15

Quasi-Periodic Pulsations in a Solar Microwave Burst

NASA Technical Reports Server (NTRS)

We studied a microwave burst that showed deep quasi-periodic pulsations using imaging observations at 17 and 34 GHz. Strongly modulated pul sations appear in radio images from the eastern end of a long loop an d in hard X-rays from the western end of the loop. Radio modulations are seen at the western end of the loop but at a level some 20 times weaker than at the eastern end; these radio modulations at the western end of the loop, like the hard X-ray modulations at the same locatio n, appear to lead the modulations at the eastern end by about 0.5 s, but all have the same period. The period of the modulation can be exp lained by MHD oscillations of the loop approximately 120" long connecting the sources.

Kundu, Mukul R.; Grechnev, V. V.; White, S. M.

2003-01-01

16

NASA Astrophysics Data System (ADS)

A microwave quasi-periodic pulsation with zigzag pattern (Z-QPP) in a solar flare on 2005-01-15 is observed by the Chinese Solar Broadband Spectrometer in Huairou (SBRS/Huairou) at 1.10-1.34 GHz. The zigzag pulsation occurred just in the early rising phase of the flare with weakly right-handed circular polarization. Its period is only several decades millisecond. Particularly, before and after the pulsation, there are many spectral fine structures, such as zebra patterns, fibers, and millisecond spikes. The microwave Z-QPP can provide some kinematic information of the source region in the early rising phase of the flare, and the source width changes from ~1000 km to 3300 km, even if we have no imaging observations. The abundant spectral fine structures possibly reflect the dynamic features of non-thermal particles.

Tan, Baolin

2013-07-01

17

Omnidirectional reflection from Fibonacci quasi-periodic one-dimensional photonic crystal

NASA Astrophysics Data System (ADS)

It is shown that omnidirectional reflection (ODR) is possible from quasi-periodic isotropic dielectric stacks following a Fibonacci sequence (FS). The transition from truly periodic to fully quasi-periodic structure is investigated by building periodic structures having unit cells made of FS of order j. The number of periods required to achieve ODR decreases as j increases until only a single period is required at which the structure is fully quasi-periodic. As compared to the periodic case, for the quasi-periodic structure the spectral range is wider, the thickness of the single layers is smaller and the tolerance on the layer thicknesses is smaller.

Lusk, D.; Abdulhalim, I.; Placido, F.

2001-11-01

18

Bifurcations of quasi-periodic dynamics: torus breakdown

NASA Astrophysics Data System (ADS)

To study the dynamics of quasi-periodic bifurcations, we consider a system of two nonlinearly coupled oscillators using averaging, continuation and numerical bifurcation techniques. This relatively simple system displays considerable complexity. Assuming the internal resonance to be 1:2, we find a 2 ?-periodic solution which undergoes a supercritical Neimark-Sacker bifurcation, yielding a stable torus. Choosing a route in parameter space, we show by numerical bifurcation techniques how the torus gets destroyed by dynamical and topological changes in the involved manifolds (Krauskopf and Osinga in J Comput Phys 146:404-419, 1998). The 1:6 resonance turns out to be prominent in parameter space, and we detected a cascade of period doublings within the corresponding resonance tongue yielding a strange attractor. The phenomena agree with the Ruelle-Takens (Commun. Math. Phys. 20:167-192, 1971, Commun. Math. Phys. 23:343-344, 1971) scenario leading to strange attractors. Other periodic regimes are present in this system, and there is interesting evidence that two different regimes interact with each other, yielding yet another type of strange attractor. In this context, certain ?-periodic solutions emerge that are studied by continuation following the Poincaré-Lindstedt method using Mathieu functions; when the implicit function theorem breaks down, the analysis is supplemented by numerical bifurcation techniques.

Bakri, Taoufik; Verhulst, Ferdinand

2014-12-01

19

Quasi-periodic variations in Doppler velocities of H ? spicules

NASA Astrophysics Data System (ADS)

New series of CCD spectral observations of spicules were obtained using 53-cm Lyot coronagraph of Abastumani Astrophysical Observatory (Georgia) at 5500 km height above the solar limb on October 17, 2012 in H ? spectral line. The line-of-sight Doppler velocities of 34 spicules were measured with the cadence of 4.5 s and standard error equal to ±0.3 km/s. Life times of almost all measured spicules were 5-6 min (and longer), therefore they resemble the type I spicules. No short lived structures (similar to type II spicules) were identified during the time series neither inside nor outside the observed spicules. The Doppler velocity time series were processed using Lomb Periodogram Algorithm revealing 4 types of dominating period intervals centered around: 254 s, 136 s, 94 s and 65 s having confidence levels over 95 %. The oscillations with periods around 254 s can be caused by quasi-periodic rebound shocks after the propagation of photospheric pulses. The oscillations with periods around 136 s can be caused by the oscillation of spicules axis at the kink cut-off frequency in gravitationally stratified magnetic tubes. In this case, seismological estimations give the density scale height as 380-540 km for the kink wave speed of 70-100 km/s in spicules. Shorter period oscillations are probably caused by propagating kink waves in spicules.

Khutshishvili, E.; Kulidzanishvili, V.; Kvernadze, T.; Zaqarashvili, T. V.; Kakhiani, V.; Khutsishvili, D.; Sikharulidze, M.

2014-12-01

20

Omnidirectional reflection from Fibonacci quasi-periodic one-dimensional photonic crystal

It is shown that omnidirectional reflection (ODR) is possible from quasi-periodic isotropic dielectric stacks following a Fibonacci sequence (FS). The transition from truly periodic to fully quasi-periodic structure is investigated by building periodic structures having unit cells made of FS of order j. The number of periods required to achieve ODR decreases as j increases until only a single period

D. Lusk; I. Abdulhalim; F. Placido

2001-01-01

21

Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP

Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP F. Gabern1 `A. Jorba1 Abstract We make a local semi-analytical study of a quasi-periodic perturbation of the Sun-Jupiter RTBP particle near the triangular points of the Sun-Jupiter system. In order to perform this study, we use

Barcelona, Universitat de

22

Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP

Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP F. Gabern 1 #18; A. Jorba 1 Abstract We make a local semi-analytical study of a quasi-periodic perturbation of the Sun-Jupiter RTBP of a small particle near the triangular points of the Sun-Jupiter system. In order to perform this study, we

Barcelona, Universitat de

23

Dynamical behavior of nonlinear ionization waves excited in positive columns of glow discharge is investigated with external modulation. It is well known that competition of two frequencies leads the system into a state of chaotic motion via quasi-periodicity as mentioned in Ruelle and Takens scenario (D. Ruelle and F. Takens, Commun. Math. Phys. 20, 167 (1971)). Here, quasi-periodic route to

FUKUYAMA Takao; KOZAKOV Ruslan; TESTRICH Holger; WILKE Christian; KAWAI Yoshinobu

2004-01-01

24

Quasi-Periodic Pulsations with Varying Period in Multi-Wavelength Observations of an X-class Flare

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

25

New Anomalous Lieb-Robinson Bounds in Quasi-Periodic XY Chains

We announce and sketch the rigorous proof of a new kind of anomalous (or sub-ballistic) Lieb-Robinson bound for an isotropic XY chain in a quasi-periodic transversal magnetic field. By "anomalous", we mean that the usual effective light cone defined by $|x|\\leq v|t|$ is replaced by the region $|x|\\leq v|t|^\\alpha$ for some $0law type if one replaces the quasi-periodic field by a random dimer field.

David Damanik; Marius Lemm; Milivoje Lukic; William Yessen

2014-08-28

26

THE SPECTROSCOPIC SIGNATURE OF QUASI-PERIODIC UPFLOWS IN ACTIVE REGION TIMESERIES

Quasi-periodic propagating disturbances are frequently observed in coronal intensity image sequences. These disturbances have historically been interpreted as being the signature of slow-mode magnetoacoustic waves propagating into the corona. The detailed analysis of Hinode EUV Imaging Spectrometer (EIS) timeseries observations of an active region (known to contain propagating disturbances) shows strongly correlated, quasi-periodic, oscillations in intensity, Doppler shift, and line width. No frequency doubling is visible in the latter. The enhancements in the moments of the line profile are generally accompanied by a faint, quasi-periodically occurring, excess emission at {approx}100 km s{sup -1} in the blue wing of coronal emission lines. The correspondence of quasi-periodic excess wing emission and the moments of the line profile indicates that repetitive high-velocity upflows are responsible for the oscillatory behavior observed. Furthermore, we show that the same quasi-periodic upflows can be directly identified in a simultaneous image sequence obtained by the Hinode X-Ray Telescope. These results are consistent with the recent assertion of De Pontieu and McIntosh that the wave interpretation of the data is not unique. Indeed, given that several instances are seen to propagate along the direction of the EIS slit that clearly shows in-phase, quasi-periodic variations of intensity, velocity, width (without frequency doubling), and blue wing enhanced emission, this data set would appear to provide a compelling example that upflows are more likely to be the main cause of the quasi-periodicities observed here, as such correspondences are hard to reconcile in the wave paradigm.

Tian Hui; McIntosh, Scott W. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 8037 (United States); De Pontieu, Bart, E-mail: htian@ucar.edu, E-mail: mscott@ucar.edu, E-mail: bdp@lmsal.com [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. ADBS, Bldg. 252, Palo Alto, CA 94304 (United States)

2011-02-01

27

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

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

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

2014-02-01

28

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 \\cite{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.

W. -M. Wang

2008-05-24

29

In this chapter we review the current theoretical state of the art of small black holes at the LHC. We discuss the production mechanism for small non thermal black holes at the LHC and discuss new signatures due to a possible discrete mass spectrum of these black holes.

Xavier Calmet; Dionysios Fragkakis; Nina Gausmann

2012-01-21

30

Dominated splittings and the spectrum of quasi-periodic Jacobi operators

NASA Astrophysics Data System (ADS)

We prove that the resolvent set of any, possibly singular, quasi- periodic Jacobi operator is characterized as the set of all energies whose associated Jacobi cocycles induce a dominated splitting. This extends a well-known result by Johnson for Schrödinger operators.

Marx, C. A.

2014-12-01

31

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 ...

Linares, M.

32

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

33

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

NASA Technical Reports Server (NTRS)

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.

Kosugi, Takeo; Kiplinger, Alan L.

1986-01-01

34

Quasi-periodic Green's functions of the Helmholtz and Laplace equations

A classical problem of free-space Green's function $G_{0\\Lambda}$ representations of the Helmholtz equation is studied in various quasi-periodic cases, i.e., when an underlying periodicity is imposed in less dimensions than is the dimension of an embedding space. Exponentially convergent series for the free-space quasi-periodic $G_{0\\Lambda}$ and for the expansion coefficients $D_{L}$ of $G_{0\\Lambda}$ in the basis of regular (cylindrical in two dimensions and spherical in three dimension (3D)) waves, or lattice sums, are reviewed and new results for the case of a one-dimensional (1D) periodicity in 3D are derived. From a mathematical point of view, a derivation of exponentially convergent representations for Schl\\"{o}milch series of cylindrical and spherical Hankel functions of any integer order is accomplished. The quasi-periodic Green's functions of the Laplace equation are obtained from the corresponding representations of $G_{0\\Lambda}$ of the Helmholtz equation by taking the limit of the wave vector magnitude going to zero. The derivation of relevant results in the case of a 1D periodicity in 3D highlights the common part which is universally applicable to any of remaining quasi-periodic cases. The results obtained can be useful for numerical solution of boundary integral equations for potential flows in fluid mechanics, remote sensing of periodic surfaces, periodic gratings, in many contexts of simulating systems of charged particles, in molecular dynamics, for the description of quasi-periodic arrays of point interactions in quantum mechanics, and in various ab-initio first-principle multiple-scattering theories for the analysis of diffraction of classical and quantum waves.

Alexander Moroz

2006-02-08

35

Quasi-periodic Green's functions of the Helmholtz and Laplace equations

NASA Astrophysics Data System (ADS)

A classical problem of free-space Green's function G0? representations of the Helmholtz equation is studied in various quasi-periodic cases, i.e., when an underlying periodicity is imposed in less dimensions than is the dimension of an embedding space. Exponentially convergent series for the free-space quasi-periodic G0? and for the expansion coefficients DL of G0? in the basis of regular (cylindrical in two dimensions and spherical in three dimension (3D)) waves, or lattice sums, are reviewed and new results for the case of a one-dimensional (1D) periodicity in 3D are derived. From a mathematical point of view, a derivation of exponentially convergent representations for Schlömilch series of cylindrical and spherical Hankel functions of any integer order is accomplished. Exponentially convergent series for G0? and lattice sums DL hold for any value of the Bloch momentum and allow G0? to be efficiently evaluated also in the periodicity plane. The quasi-periodic Green's functions of the Laplace equation are obtained from the corresponding representations of G0? of the Helmholtz equation by taking the limit of the wave vector magnitude going to zero. The derivation of relevant results in the case of a 1D periodicity in 3D highlights the common part which is universally applicable to any of remaining quasi-periodic cases. The results obtained can be useful for the numerical solution of boundary integral equations for potential flows in fluid mechanics, remote sensing of periodic surfaces, periodic gratings, and infinite arrays of resonators coupled to a waveguide, in many contexts of simulating systems of charged particles, in molecular dynamics, for the description of quasi-periodic arrays of point interactions in quantum mechanics, and in various ab initio first-principle multiple-scattering theories for the analysis of diffraction of classical and quantum waves.

Moroz, Alexander

2006-09-01

36

LOW-FREQUENCY OBSERVATIONS OF TRANSIENT QUASI-PERIODIC RADIO EMISSION FROM THE SOLAR ATMOSPHERE

We report low-frequency observations of quasi-periodic, circularly polarized, harmonic type III radio bursts whose associated sunspot active regions were located close to the solar limb. The measured periodicity of the bursts at 80 MHz was ?5.2 s, and their average degree of circular polarization (dcp) was ?0.12. We calculated the associated magnetic field B (1) using the empirical relationship between the dcp and B for the harmonic type III emission, and (2) from the observed quasi-periodicity of the bursts. Both the methods result in B ? 4.2 G at the location of the 80 MHz plasma level (radial distance r ? 1.3 R{sub ?}) in the active region corona.

Sasikumar Raja, K.; Ramesh, R., E-mail: sasikumar@iiap.res.in [Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560 034 (India)

2013-09-20

37

The localization of light in a 2D quasi-periodic coherently prepared atomic medium

NASA Astrophysics Data System (ADS)

We study the localization of light in two-dimensional (2D) atomic systems. The system proposed in this paper is a resonant cold atomic ensemble with N configuration, which is coherently prepared by four pairs of control fields. Under the condition of the electromagnetically induced transparency, the propagation of the signal field is modelled as a system that is uniform along the propagating direction (z) but shows quasi-periodic structure on the transverse plane (x - y plane). Through numerical simulations, we find that the 2D quasi-periodic coherently prepared atomic medium can make the signal field anisotropic localized transversely during the propagation, and the localization direction can be manipulated by the phase of the control field.

Wang, C. F.; Cheng, J.; Chen, B.

2015-02-01

38

Narrowband DWDM filters based on Fibonacci-class quasi-periodic structures.

In this paper, we propose a narrowband DWDM filter structure, whose reflection band characteristics, meets the ITU-T standard. The proposed filter structure is based on Fibonacci quasi-periodic structures composed of multilayers with large index differences. Studying the effects of the optical and geometrical parameters of Fibonacci quasi-periodic structures on its filtering properties, we have realized that to achieve the ITU-T standard, we need to cascade two successive structures both with the same generation numbers j=4 and orders n=25 and apodized refractive indices. The apodization process helps to minimize the stop band sidelobes. We have also demonstrated that beside Fibonacci's order, n, the layers dimensions, and their refractive index ratios are the main design parameters. PMID:19547405

Golmohammadi, S; Moravvej-Farshi, M K; Rostami, A; Zarifkar, A

2007-08-20

39

Exact quasi-periodic solutions of the Konno-Oono equations

NASA Astrophysics Data System (ADS)

On the basis of the Lax matrix and elliptic variables, the Konno-Oono equations are decomposed into solvable ordinary differential equations. The Konno-Oono flows are straightened with the aid of the theory of algebraic curves and the Abel-Jacobi coordinates. The asymptotic properties of the meromorphic function at infinite points and its algebro-geometric characteristics are studied, from which exact quasi-periodic solutions of the Konno-Oono equations are obtained.

Guan, Liang; Geng, Xianguo; Li, Zhu

2014-07-01

40

Quasi-periodic variations of gamma-ray intensity in the atmosphere and atmospheric buoyancy waves

High-altitude balloons have been used to measure gamma rays with energies above 40 MeV in the stratosphere near the equator and at midlatitudes. Quasi-periodic fluctuations (QPF) of the gamma rays were observed which can be explained in terms of atmospheric buoyancy waves: in propagating, these waves modulate the amount of matter in the residual atmosphere above the instrument and thus

A. M. Galper; L. P. Gorbachev; L. V. Kurnosova; N. G. Leikov; B. I. Luchkov

1985-01-01

41

Evidence for quasi-periodic July drought in the Hudson Valley, New York

July Palmer Drought Severity Indices1 (PDSI) have been reconstructed2 for the Hudson Valley region of New York State from the annual ring-width variations of local old trees. Using additional, subsequently developed tree-ring chronologies, we have developed a new July drought reconstruction that extends back to 1694. Variance spectra of the new PDSI series reveal statistically significant quasi-periodicities of 11.4 and

Edward R. Cook; Gordon C. Jacoby

1979-01-01

42

Temporal Super Resolution from a Single Quasi-periodic Image Sequence Based on Phase Registration

\\u000a This paper describes a method for temporal super resolution from a single quasi-periodic image sequence. A so-called reconstruction-based\\u000a method is applied to construct a one period image sequence with high frame-rate based on phase registration data in sub-frame\\u000a order among multiple periods of the image sequence. First, the periodic image sequence to be reconstructed is expressed as\\u000a a manifold in

Yasushi Makihara; Atsushi Mori; Yasushi Yagi

2010-01-01

43

Quasi-periodical components in the radial distributions of cosmologically remote objects

NASA Astrophysics Data System (ADS)

A statistical analysis of radial (line-of-sight) 1D-distributions of brightest cluster galaxies (BCGs) within the redshift interval 0.044 ? z ? 0.78 and Mg II absorption-line systems (0.37 ? z ? 2.28) is carried out. Power spectra and two-point radial correlation functions are calculated. It is found that both radial distributions of spectroscopic redshifts of 52 683 BCGs and 32 840 Mg II absorption systems incorporate similar quasi-periodical components relatively to the comoving distance. Significance of the components exceeds 4?-level and admits an increase ( ? 5?) for some broad subsamples. For the ? cold dark matter cosmological model the periodicities correspond to spatial comoving scales (98 ± 3) and (101 ± 2) h-1 Mpc, respectively. These quasi-periods turn out to be close to the characteristic scale (101 ± 6) h-1 Mpc of the quasi-periodical component obtained earlier for the radial distribution of luminous red galaxies (LRGs). On the other hand, the scales are close to the spatial scale corresponding to the baryon acoustic oscillations (BAOs) revealed by many authors at the last decade. Fourier transform phases obtained for the BCGs and LRGs are found to be close, while the phases calculated for the Mg II absorption systems and LRGs are opposite. Discussions of the results in a context of the BAO and large-scale structure characteristic scales are outlined.

Ryabinkov, A. I.; Kaminker, A. D.

2014-05-01

44

We performed 1.5-dimensional general relativistic hydrodynamic simulations with a Kerr metric to construct a model for high-frequency quasi-periodic oscillations (QPOs) in microquasars. The simulations were performed assuming an initial accretion disk without viscosity rotating around a Kerr black hole at sub-Keplerian velocity (sub-Keplerian case), which induces various wave modes everywhere in the disk. We found that quasi-periodic inward shock waves

Seiichiro I. Aoki; Shinji Koide; Takahiro Kudoh; Kunji Nakayama; Kazunari Shibata

2004-01-01

45

Quasi-periodic behavior of ion acoustic solitary waves in electron-ion quantum plasma

The ion acoustic solitary waves are investigated in an unmagnetized electron-ion quantum plasmas. The one dimensional quantum hydrodynamic model is used to study small as well as arbitrary amplitude ion acoustic waves in quantum plasmas. It is shown that ion temperature plays a critical role in the dynamics of quantum electron ion plasma, especially for arbitrary amplitude nonlinear waves. In the small amplitude region Korteweg-de Vries equation describes the solitonic nature of the waves. However, for arbitrary amplitude waves, in the fully nonlinear regime, the system exhibits possible existence of quasi-periodic behavior for small values of ion temperature.

Sahu, Biswajit [Department of Mathematics, West Bengal State University Barasat, Kolkata-700126 (India); Poria, Swarup [Department of Applied Mathematics, University of Calcutta Kolkata-700009 (India); Narayan Ghosh, Uday [Department of Mathematics, Siksha Bhavana, Visva Bharati University Santiniketan (India); Roychoudhury, Rajkumar [Physics and Applied Mathematics Unit, Indian Statistical Institute Kolkata-700108 (India)

2012-05-15

46

Quasi-periodicities of the BL Lacertae Object PKS 2155-304

NASA Astrophysics Data System (ADS)

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 109 M ?, the Keplerian distance corresponding to the quasi-period T is ~1016 cm, about 50 Schwarzschild radii.

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

2014-09-01

47

NASA Astrophysics Data System (ADS)

The Kadometsev-Petviashvili (KP) and modified KP (mKP) equations are retrieved from the first two soliton equations of coupled Korteweg-de Vries (cKdV) hierarchy. Based on the nonlinearization of Lax pairs, the KP and mKP equations are ultimately reduced to integrable finite-dimensional Hamiltonian systems in view of the r-matrix theory. Finally, the resulting Hamiltonian flows are linearized in Abel-Jacobi coordinates, such that some specially explicit quasi-periodic solutions to the KP and mKP equations are synchronously given in terms of theta functions through the Jacobi inversion.

Chen, J.; Geng, X.

2006-04-01

48

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

49

THz laser based on quasi-periodic AlGaAs superlattices

The use of quasi-periodic AlGaAs superlattices as an active element of a quantum cascade laser of terahertz range is proposed and theoretically investigated. A multi-colour emission, having from three to six peaks of optical gain, is found in Fibonacci, Thue-Morse, and figurate superlattices in electric fields of intensity F = 11 - 13 kV cm{sup -1} in the frequency range f = 2 - 4 THz. The peaks depend linearly on the electric field, retain the height of 20 cm{sup -1}, and strongly depend on the thickness of the AlGaAs-layers. (lasers)

Malyshev, K V [N.E. Bauman Moscow State Technical University, Moscow (Russian Federation)

2013-06-30

50

Application of the multiband kp-models to quantum transport in quasi-periodic crystals

NASA Astrophysics Data System (ADS)

We consider the quantum transport of a particle in a crystal where the global three-dimensional translation symmetry is removed. Our analysis concerns solid state structures where the microscopic potential of the ions is no longer periodic. This includes materials with variable chemical composition, intergrowth compounds and abrupt junctions. The application of the kp multiband envelope function models to the description of the quantum mechanical motion in such a quasi-periodic structure is investigated. By using a spectral decomposition technique, we show that when the interatomic distance is asymptotically small, the particle probability density can be obtained by the envelope kp model with variable coefficients.

Morandi, O.

2014-12-01

51

The synchronisation of periodic self-modulation oscillations in a ring Nd:YAG chip laser under an external periodic signal modulating the pump power has been experimentally investigated. A new quasi-periodic regime of synchronisation of self-modulation oscillations is found. The characteristic features of the behaviour of spectral and temporal structures of synchronised quasi-periodic oscillations with a change in the external signal frequency are studied. (control of laser radiation parameters)

Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N [D.V. Skobel'tsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2011-06-30

52

QUASI-PERIODIC OSCILLATIONS AND BROADBAND VARIABILITY IN SHORT MAGNETAR BURSTS

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.

Huppenkothen, Daniela; Watts, Anna L.; Uttley, Phil; Van der Horst, Alexander J.; Van der Klis, Michiel [Astronomical Institute ''Anton Pannekoek'', University of Amsterdam, Postbus 94249, 1090-GE Amsterdam (Netherlands); Kouveliotou, Chryssa [Office of Science and Technology, ZP12, NASA Marshall Space Flight Center, Huntsville, AL 35812 (United States); Goegues, Ersin [Sabanc Latin-Small-Letter-Dotless-I University, Orhanl Latin-Small-Letter-Dotless-I -Tuzla, Istanbul 34956 (Turkey); Granot, Jonathan [The Open University of Israel, 1 University Road, P.O. Box 808, Ra'anana 43537 (Israel); Vaughan, Simon [X-Ray and Observational Astronomy Group, University of Leicester, Leicester LE1 7RH (United Kingdom); Finger, Mark H., E-mail: D.Huppenkothen@uva.nl [Universities Space Research Association, Huntsville, AL 35805 (United States)

2013-05-01

53

GENERATION OF QUASI-PERIODIC WAVES AND FLOWS IN THE SOLAR ATMOSPHERE BY OSCILLATORY RECONNECTION

We investigate the long-term evolution of an initially buoyant magnetic flux tube emerging into a gravitationally stratified coronal hole environment and report on the resulting oscillations and outflows. We perform 2.5-dimensional nonlinear numerical simulations, generalizing the models of McLaughlin et al. and Murray et al. We find that the physical mechanism of oscillatory reconnection naturally generates quasi-periodic vertical outflows, with a transverse/swaying aspect. The vertical outflows consist of both a periodic aspect and evidence of a positively directed flow. The speed of the vertical outflow (20-60 km s{sup -1}) is comparable to those reported in the observational literature. We also perform a parametric study varying the magnetic strength of the buoyant flux tube and find a range of associated periodicities: 1.75-3.5 minutes. Thus, the mechanism of oscillatory reconnection may provide a physical explanation to some of the high-speed, quasi-periodic, transverse outflows/jets recently reported by a multitude of authors and instruments.

McLaughlin, J. A.; Verth, G. [School of Computing, Engineering and Information Sciences, Northumbria University, Newcastle Upon Tyne, NE1 8ST (United Kingdom); Fedun, V.; Erdelyi, R., E-mail: james.a.mclaughlin@northumbria.ac.uk, E-mail: gary.verth@northumbria.ac.uk, E-mail: v.fedun@sheffield.ac.uk, E-mail: robertus@sheffield.ac.uk [Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hounsfield Road, Hicks Building, Sheffield, S3 7RH (United Kingdom)

2012-04-10

54

Quasi-periodic Wiggles of Microwave Zebra Structures in a Solar Flare

NASA Astrophysics Data System (ADS)

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-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.

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

2013-11-01

55

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

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.

Araya, E. D. [Physics Department, Western Illinois University, 1 University Circle, Macomb, IL 61455 (United States); Hofner, P.; Goss, W. M. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Kurtz, S. [Centro de RadioastronomIa y Astrofisica, Universidad Nacional Autonoma de Mexico, Apdo. Postal 3-72, 58089 Morelia, Michoacan (Mexico); Richards, A. M. S. [Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Linz, H. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Olmi, L. [University of Puerto Rico at Rio Piedras, Physics Department, P.O. Box 23343, San Juan, PR 00931 (Puerto Rico); Sewilo, M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-07-10

56

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

NASA Technical Reports Server (NTRS)

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.

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

57

From archived and recent high speed photometry of VW Hyi we find Dwarf Nova Oscillations (DNOs) occasionally present throughout outburst, evolving from 14.06 s period at maximum to > 40 s near the end of outburst. A relatively slow increase of period is followed by rapid increase and subsequent decrease. Quasi-periodic Oscillations (QPOs) are seen at periods of hundreds of seconds. For the first time, an evolution of QPO period is seen, steadily increasing during the final decline of an outburst. The occasional presence of two DNOs, separated in frequency by the QPO frequency, suggests reprocessing of the rotating DNO beam by a `wall' rotating progradely in the disc at the QPO period.

Woudt, P A; Woudt, Patrick A.; Warner, Brian

2002-01-01

58

Wideband absorption in fibonacci quasi-periodic graphene-based hyperbolic metamaterials

NASA Astrophysics Data System (ADS)

A heterostructure containing a Fibonacci quasi-periodic layer and a resonant metal back reflector is proposed, which can realize wideband absorption. The Fibonacci layer is composed of graphene-based hyperbolic metamaterials and isotropic media to obtain wideband absorption. To enhance absorption, an impedance-matching layer is put on top of the Fibonacci layer. It is shown to absorb roughly 90% of all available electromagnetic waves in an 11 terahertz absorption bandwidth for a transverse magnetic mode at normal angle incidence. The absorption bandwidth is affected by the reflection band gap. Compared with some previous designs, our proposed structure has a larger absorption bandwidth and higher absorption in the mid-infrared range. The results should be valuable in the design of infrared stealth and broadband optoelectronic devices.

Ning, Renxia; Liu, Shaobin; Zhang, Haifeng; Kong, Xiangkun; Bian, Borui; Bao, Jie

2014-12-01

59

Singular Density of States Measure for Subshift and Quasi-Periodic Schrödinger Operators

NASA Astrophysics Data System (ADS)

Simon's subshift conjecture states that for every aperiodic minimal subshift of Verblunsky coefficients, the common essential support of the associated measures has zero Lebesgue measure. We disprove this conjecture in this paper, both in the form stated and in the analogous formulation of it for discrete Schrödinger operators. In addition we prove a weak version of the conjecture in the Schrödinger setting. Namely, under some additional assumptions on the subshift, we show that the density of states measure, a natural measure associated with the operator family and whose topological support is equal to the spectrum, is singular. We also consider one-frequency quasi-periodic Schrödinger operators with continuous sampling functions and show that generically, the density of states measure is singular as well.

Avila, Artur; Damanik, David; Zhang, Zhenghe

2014-09-01

60

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

We present a new method of analysis of measure-preserving dynamical systems, based on frequency analysis and ergodic theory, which extends our earlier work [1]. Our method employs the novel concept of harmonic time average [2], and is realized as a computational algorithms for visualization of periodic and quasi-periodic sets or arbitrary periodicity in the phase space. Besides identifying all periodic sets, our method is useful in detecting chaotic phase space regions with a good precision. The range of method's applicability is illustrated using well-known Chirikov standard map, while its full potential is presented by studying higher-dimensional measure-preserving systems, in particular Froeschl\\'e map and extended standard map.

Zoran Levnaji?; Igor Mezi?

2014-07-26

61

Quasi-periodic frequency fluctuations observed during coronal radio sounding experiments 1991-2009

NASA Astrophysics Data System (ADS)

Coronal radio sounding experiments were carried out using the dual-frequency signals of the spacecraft Ulysses, Galileo, Mars Express, Venus Express, and Rosetta. The change in differential frequency recorded at the NASA and ESA ground stations, a quantity sensitive only to the plasma along the radio ray path from spacecraft to receiver, has been analyzed in this work. This large volume of observational data provides evidence for the occasional presence of a quasi-periodic component (QPC) in the derived frequency fluctuation spectra. First seen in data from the Mars Express conjunction in 2004, further evidence for the QPC has now been found in data recorded at other solar conjunction opportunities from 1991 to 2009, thereby better defining the statistical characteristics of the QPC. The level of QPC spectral density is a factor of three higher than the expected power-law background level. The characteristic frequency of the spectral density maximum is roughly 4 mHz, corresponding to a QPC fluctuation period of about 4 min. The bandwidth of the spectral line is comparable to the maximum frequency. The QPC are observed at heliocentric distances between 3 and 40 solar radii, both in equatorial regions and at high heliolatitudes. The QPC is detected with an occurrence frequency of about 20% and is occasionally accompanied by its second harmonic. The most likely progenitors of the QPC are quasi-periodic electron density fluctuations associated with magnetosonic waves, which are generated locally from nonlinear interactions of 5-min band Alfvén waves propagating from the coronal base.

Efimov, A. I.; Lukanina, L. A.; Samoznaev, L. N.; Rudash, V. K.; Chashei, I. V.; Bird, M. K.; Pätzold, M.; MEX, VEX, ROS Radio Science Team

2012-02-01

62

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

NASA Technical Reports Server (NTRS)

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 period under varying soil moisture conditions. These measured backscattering values will be compared with the model backscattering values and a discussion of the results will be presented.

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

2010-01-01

63

In this paper, we consider one dimensional adiabatic quasi-periodic Schr\\"{o}dinger operators in the regime of strong resonant tunneling. We show the emergence of a level repulsion phenomenon which is seen to be very naturally related to the local spectral type of the operator: the more singular the spectrum, the weaker the repulsion.

Alexander Fedotov; Frédéric Klopp

2005-02-13

64

monotone circle maps J. STARK*, U. FEUDEL{, P. A. GLENDINNING{ and A. PIKOVSKY} * Centre for Nonlinear numbers have played a central role in the study of (unforced) monotone circle maps. In such a case Herman has proved that quasi-periodically forced circle maps also possess a well-deÂ®ned rotation number

Pikovsky, Arkady

65

Periodic and Quasi -Periodic Motions of a Solar Sail Close to SL1 in the Earth -Sun System

Periodic and Quasi - Periodic Motions of a Solar Sail Close to SL1 in the Earth - Sun System with the Sun - sail direction) the system has five equilibrium points. When we add the effect of the solar sail Abstract Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to propel

Barcelona, Universitat de

66

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

67

Quasi-periodic oscillations discovered in the X-ray pulsar XTE J1858+034

NASA Astrophysics Data System (ADS)

We have discovered low frequency quasi-periodic oscillations at 0.11 Hz in the 221 s X-ray pulsar XTE J1858+034. Among about 30 known transient X-ray pulsars this is the sixth source in which QPOs have been observed. If the QPOs are produced because of inhomogeneities in the accretion disk at the magnetospheric boundary, the low frequency of the QPOs indicate a large magnetosphere for this pulsar. Both the Keplerian frequency model and the beat frequency model are applicable for production of QPOs in this source. The QPOs and regular pulsations are found to be stronger at higher energy which favours the beat frequency model. A detailed analysis, of the QPO feature as a function of pulse phase and energy will be presented which will help in firmly deciding one of the two alternatives for the QPO phenomenon. The spectrum is hard, consisting of two components, a cut-off power law and an iron fluorescence line.

Paul, B.; Rao, A. R.

1998-12-01

68

NASA Astrophysics Data System (ADS)

It has been shown that in reality at least two general scenarios of data structuring are possible: (a) a self-similar (SS) scenario when the measured data form an SS structure and (b) a quasi-periodic (QP) scenario when the repeated (strongly correlated) data form random sequences that are almost periodic with respect to each other. In the second case it becomes possible to describe their behavior and express a part of their randomness quantitatively in terms of the deterministic amplitude-frequency response belonging to the generalized Prony spectrum. This possibility allows us to re-examine the conventional concept of measurements and opens a new way for the description of a wide set of different data. In particular, it concerns different complex systems when the ‘best-fit’ model pretending to be the description of the data measured is absent but the barest necessity of description of these data in terms of the reduced number of quantitative parameters exists. The possibilities of the proposed approach and detection algorithm of the QP processes were demonstrated on actual data: spectroscopic data recorded for pure water and acoustic data for a test hole. The suggested methodology allows revising the accepted classification of different incommensurable and self-affine spatial structures and finding accurate interpretation of the generalized Prony spectroscopy that includes the Fourier spectroscopy as a partial case.

Nigmatullin, Raoul R.; Khamzin, Airat A.; Tenreiro Machado, J.

2014-01-01

69

Drift-Free Position Estimation of Periodic or Quasi-Periodic Motion Using Inertial Sensors

Position sensing with inertial sensors such as accelerometers and gyroscopes usually requires other aided sensors or prior knowledge of motion characteristics to remove position drift resulting from integration of acceleration or velocity so as to obtain accurate position estimation. A method based on analytical integration has previously been developed to obtain accurate position estimate of periodic or quasi-periodic motion from inertial sensors using prior knowledge of the motion but without using aided sensors. In this paper, a new method is proposed which employs linear filtering stage coupled with adaptive filtering stage to remove drift and attenuation. The prior knowledge of the motion the proposed method requires is only approximate band of frequencies of the motion. Existing adaptive filtering methods based on Fourier series such as weighted-frequency Fourier linear combiner (WFLC), and band-limited multiple Fourier linear combiner (BMFLC) are modified to combine with the proposed method. To validate and compare the performance of the proposed method with the method based on analytical integration, simulation study is performed using periodic signals as well as real physiological tremor data, and real-time experiments are conducted using an ADXL-203 accelerometer. Results demonstrate that the performance of the proposed method outperforms the existing analytical integration method. PMID:22163935

Latt, Win Tun; Veluvolu, Kalyana Chakravarthy; Ang, Wei Tech

2011-01-01

70

Drift-free position estimation of periodic or quasi-periodic motion using inertial sensors.

Position sensing with inertial sensors such as accelerometers and gyroscopes usually requires other aided sensors or prior knowledge of motion characteristics to remove position drift resulting from integration of acceleration or velocity so as to obtain accurate position estimation. A method based on analytical integration has previously been developed to obtain accurate position estimate of periodic or quasi-periodic motion from inertial sensors using prior knowledge of the motion but without using aided sensors. In this paper, a new method is proposed which employs linear filtering stage coupled with adaptive filtering stage to remove drift and attenuation. The prior knowledge of the motion the proposed method requires is only approximate band of frequencies of the motion. Existing adaptive filtering methods based on Fourier series such as weighted-frequency Fourier linear combiner (WFLC), and band-limited multiple Fourier linear combiner (BMFLC) are modified to combine with the proposed method. To validate and compare the performance of the proposed method with the method based on analytical integration, simulation study is performed using periodic signals as well as real physiological tremor data, and real-time experiments are conducted using an ADXL-203 accelerometer. Results demonstrate that the performance of the proposed method outperforms the existing analytical integration method. PMID:22163935

Latt, Win Tun; Veluvolu, Kalyana Chakravarthy; Ang, Wei Tech

2011-01-01

71

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

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.

Shaposhnikov, Nikolai, E-mail: nikolai.v.shaposhnikov@nasa.gov, E-mail: lev@milkyway.gsfc.nasa.gov [Department of Astronomy, CRESST/University of Maryland, College Park, MD 20742 (United States)

2012-06-20

72

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

73

SUBMILLIMETER QUASI-PERIODIC OSCILLATIONS IN MAGNETICALLY CHOKED ACCRETION FLOW MODELS OF SgrA*

High-frequency quasi-periodic oscillations (QPOs) appear in general-relativistic magnetohydrodynamic simulations of magnetically choked accretion flows around rapidly rotating black holes (BHs). We perform polarized radiative transfer calculations with the ASTRORAY code to explore the manifestations of these QPOs for SgrA*. We construct a simulation-based model of a radiatively inefficient accretion flow and find model parameters by fitting the mean polarized source spectrum. The simulated QPOs have a total submillimeter flux amplitude up to 5% and a linearly polarized flux amplitude up to 2%. The oscillations reach high levels of significance 10{sigma}-30{sigma} and high-quality factors Q Almost-Equal-To 5. The oscillation period T Almost-Equal-To 100 M Almost-Equal-To 35 minutes corresponds to the rotation period of the BH magnetosphere that produces a trailing spiral in resolved disk images. The total flux signal is significant over noise for all tested frequencies 87 GHz, 230 GHz, and 857 GHz and inclination angles 10 Degree-Sign , 37 Degree-Sign , and 80 Degree-Sign . The non-detection in the 230 GHz SubMillimeter Array light curve is consistent with a low signal level and a low sampling rate. The presence of submillimeter QPOs in SgrA* will be better tested with the Atacama Large Millimeter Array.

Shcherbakov, Roman V. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); McKinney, Jonathan C., E-mail: roman@astro.umd.edu [Joint Space Science Institute, University of Maryland, College Park, MD 20742 (United States)

2013-09-10

74

Keck II spectroscopy of mHz quasi-periodic oscillations in Hercules X-1

We present Keck II spectroscopy of an optical mHz quasi-periodic oscillations (QPOs) in the lightcurve of the X-ray pulsar binary Her X-1. In the power spectrum it appears as `peaked noise', with a coherency $\\sim$2, a central frequency of 35 mHz and a peak-to-peak amplitude of 5%. However, the dynamic power spectrum shows it to be an intermittent QPO, with a lifetime of $\\sim$hundred seconds, as expected if the lifetime of the orbiting material is equal to the thermal timescale of the inner disk. We have decomposed the spectral time series into constant and variable components and used blackbody fits to the resulting spectra to characterise the spectrum of the QPO variability and constrain possible production sites. We find that the spectrum of the QPO is best-fit by a small hot region, possibly the inner regions of the accretion disk, where the ballistic accretion stream impacts onto the disk. The lack of any excess power around the QPO frequency in the X-ray power spectrum, created using simultaneous lightcurves from XTE, implies that the QPO is not simply reprocessed X-ray variability.

K O'Brien; Keith Horne; B Boroson; M Still; R Gomer; JB Oke; P Boyd; S Vrtilek

2001-05-10

75

Quasi-periodic Fluctuations Detected in Mars Express Coronal Radio Sounding Observations

NASA Astrophysics Data System (ADS)

Spectral analysis of the high-quality dual-frequency data obtained with the radio sounding experiment MaRS on the ESA spacecraft Mars Express has revealed a quasi-periodic component (QPC) at heliocentric distances from 4 to 10 solar radii. The QPC typically appears as a broad maximum in the temporal frequency fluctuation spectrum centered at a frequency in the range 3.7 mHz

Efimov, A. I.; Lukanina, L. A.; Samoznaev, L. N.; Rudash, V. K.; Chashei, I. V.; Bird, M. K.; Pätzold, M.; Tellmann, S.

2010-03-01

76

Discovery of High Frequency Quasi-Periodic Oscillations in 4u1915-05

The type I X-ray burster and dipper 4U1915-05 (also known as XB1916-053) was monitored by the Rossi X-ray Timing Explorer between February and October, 1996. The source was observed in various spectral states; the highest luminosity state (LX ~ 1.5 10^37 ergs/s, 10 kpc, 1-20 keV) is associated with a soft spectrum, whereas for the lower luminosity state (down to ~5 10^36 ergs/s) the spectrum is significantly harder. Using the high time resolution data provided by the Proportional Counter Array (PCA), we have discovered High-Frequency Quasi-Periodic Oscillations (HFQPOs) in the persistent X-ray emission of 4U1915-05 while its luminosity was ~8 10^36 ergs/s. The QPO frequency ranges from 600 Hz up to ~1000 Hz, with typical Full Width at Half Maximum (FWHM) ~50-100 Hz and Root Mean Squared (RMS) values 15%. In addition, by using the ``shift and add'' technique, we have detected a twin HFQPO (5.5 sigma level) separated from the main peak by ~355 Hz. 4U1915-05 is the eighth Atoll source displaying simultaneous twi...

Barret, D; Olive, J F; Grindlay, J E; Bloser, P F; Swank, J H; Smale, A P

1998-01-01

77

On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients

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 analyzed the relation between the full width 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.

Pawar, Devraj D; Shanthi, K; Bhattacharya, Dipankar; Belloni, Tomaso

2015-01-01

78

Quasi-periodic components of solar microwave emission preceded CME's onset

NASA Astrophysics Data System (ADS)

The results of observations at the radio-astronomical station NIRFI "Zimenki" are examined. Pre-eruption manifestations can be detected over different time scales: from several days, which is typical to the evolution of active region in whole, to several hours and tens of minutes, which leads to the formation of conditions for CME initiation and propagation. Primarily this process is developed as wave motion. For example, a study of the evolution of radio emission in January 2005 discovered the growth of amplitude of long-period pulsations with a period of more than 20 minutes in centimetre solar radio emission three days before coronal mass ejections. During the time intervals of 25 to 15 minutes prior to CMEs registration the oscillations of substantially smaller period (t 6-22 s) occurred, which were apparently connected to waves in coronal loops. The obtained result is close to the results of other authors, based on the observations of solar radio emission with the high spatial resolution. Thus, it is shown that the use of patrol multi wave observational data with the high sensitivity and a sufficient time resolution is possible for the analysis of the quasi-periodic components of radio emission and their dynamics.

Sheyner, Olga; Fridman, Vladimir

79

Timing studies of X Persei and the discovery of its transient quasi-periodic oscillation feature

NASA Astrophysics Data System (ADS)

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 RXTE-PCA 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 ˜0.2 Hz, suggests the existence of an accretion disc. We find that double-break 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 ˜- 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.

Acuner, Z.; ?nam, S. Ç.; ?ahiner, ?.; Serim, M. M.; Baykal, A.; Swank, J.

2014-10-01

80

Non-thermal cellular effects of ultrasound.

The cellular effects of ultrasound can be grouped into those which are predominantly thermal in origin and those which are, at least in part, non-thermal. Cellular effects of ultrasound generally acknowledged to be essentially non-thermal include changes associated with standing waves, acoustic streaming, microstreaming and cavitation; they have been demonstrated in vitro and may, in many instances, also occur in vivo. While some stimulate cell activity and can be exploited in ultrasonic therapy, others are potentially hazardous and must be avoided. Examples of experimentally-demonstrated cellular effects in which non-thermal, ultrasonically-induced events are involved are described, together with the mechanisms considered to be involved in producing them. The relevance of such effects to the safe and beneficial use of ultrasound in diagnosis and therapy is considered. Images Fig. 1 Fig. 3 Fig. 4 Fig. 5 PMID:6950755

Dyson, M.

1982-01-01

81

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.

Linares, M.; Chakrabarty, D. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Altamirano, D. [Astronomical Institute 'Anton Pannekoek', University of Amsterdam and Center for High-Energy Astrophysics, P.O. BOX 94249, 1090 GE Amsterdam (Netherlands); Cumming, A. [Department of Physics, McGill University, 3600 Rue University, Montreal, QC H3A 2T8 (Canada); Keek, L. [School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States)

2012-04-01

82

NASA Astrophysics Data System (ADS)

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 ? 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.

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

2015-01-01

83

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

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.

Barret, Didier, E-mail: didier.barret@irap.omp.eu [Universite de Toulouse, UPS-OMP, IRAP, F-31400 Toulouse (France); CNRS, Institut de Recherche en Astrophysique et Planetologie, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France)

2013-06-10

84

Quasi-periodic perturbation of unimodal maps exhibiting an attracting 3-cycle

NASA Astrophysics Data System (ADS)

We study a class of smooth maps \\Phi:{T}\\times [0,1]\\to {T}\\times [0,1] of the form \\[ \\begin{eqnarray*} \\theta&\\mapsto \\theta+\\omega \\\\ x&\\mapsto c(\\theta)h(x) \\end{eqnarray*} \\] where h : [0, 1] ? [0, 1] is a unimodal map exhibiting an attracting periodic point of prime period 3, and ? is irrational ( {T}={R}/{Z} ). We show that the following phenomenon can occur for certain h and c:{T}\\to{R} : There exists a single measurable function \\psi:{T}\\to[0,1] whose graph attracts (exponentially fast) a.e. (\\theta,x)\\in {T}\\times [0,1] under forward iterations of the map ?. Moreover, the graph of ? is dense in a cylinder M\\subset {T}\\times [0,1] . Furthermore, for every integer n >= 1 there exists n distinct repelling continuous curves \\Gamma_k:(\\theta,\\phi_k(\\theta))_{\\theta\\in{T}} , all lying in M , such that ?(?k) = ?k+1 (k < n) and ?(?n) = ?1. We give concrete examples where both c(?) and h(x) are real-analytic, but in the analysis we only need that they are C1. In our setting the function c(?) will be very close to 1 for all ? outside a tiny interval; on the interval c(?) > 1 makes a small bump. Thus we cause the perturbation of h by rare quasi-periodic kicking. Research supported by grant KAW 2005.0098 from the Knut and Alice Wallenberg Foundation, and by grant 0906B from the Göran Gustafsson Foundation.

Bjerklöv, Kristian

2012-03-01

85

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

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.

Erkut, M. Hakan, E-mail: m.erkut@iku.edu.tr [Department of Physics, Istanbul Kueltuer University, Atakoey Campus, Bak Latin-Small-Letter-Dotless-I rkoey 34156, Istanbul (Turkey)

2011-12-10

86

Multi-mode quasi-periodic pulsations in a solar flare

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

87

Conjugate observations of quasi-periodic emissions by Cluster and DEMETER spacecraft

NASA Astrophysics Data System (ADS)