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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.

2014-09-01

2

Quasi-periodic planar metamaterial substrates

We report our experimental and theoretical studies on a metamaterial substrate consisting of a quasi-periodic metallic planr pattern and a flat metal sheet, interconnected through metallic vias. We show that this structure possesses multiple in-phase reflection frequency regimes and spectral gaps for transverse-magnetic surface waves, whereas the transverse-electric surface waves are suppressed in all frequencies. In particular, an antenna put

Hongqiang Li; Zhihong Hang; Yaqin Qin; Zeyong Wei; Lei Zhou; Yewen Zhang; Hong Chen; C. T. Chan

2005-01-01

3

Quasi-periodic planar metamaterial substrates

NASA Astrophysics Data System (ADS)

We report our experimental and theoretical studies on a metamaterial substrate consisting of a quasi-periodic metallic planr pattern and a flat metal sheet, interconnected through metallic vias. We show that this structure possesses multiple in-phase reflection frequency regimes and spectral gaps for transverse-magnetic surface waves, whereas the transverse-electric surface waves are suppressed in all frequencies. In particular, an antenna put on top of this planar structure radiates with very high directivity (D=240) at some frequencies. This phenomenon is mainly governed by the inhomogeneity of the structure, which is a collective effect of perfect magnetic and electric conductors operating simultaneously at the frequency.

Li, Hongqiang; Hang, Zhihong; Qin, Yaqin; Wei, Zeyong; Zhou, Lei; Zhang, Yewen; Chen, Hong; Chan, C. T.

2005-03-01

4

Quasi-periodic climate change on Mars

NASA Technical Reports Server (NTRS)

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

Kieffer, Hugh H.; Zent, Aaron P.

1992-01-01

5

Multispacecraft observations of quasi-periodic emissions

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

6

NASA Astrophysics Data System (ADS)

In this paper, we discuss the existence of time quasi-periodic solutions for quasi-periodically forced cubic complex Ginzburg-Landau equation of higher spatial dimension with basic frequency vector ? = (?1, ?2, …, ?m). By constructing a KAM (Kolmogorov-Arnold-Moser) theorem for a dissipative system which depends on time in a quasi-periodic way, we obtain a Cantorian branch of m + 2-dimensional invariant tori for the equation.

Cheng, Hongyu; Si, Jianguo

2013-08-01

7

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

8

Band nonparabolicity in quasi-periodic Fibonacci heterostructures

Nonparabolic dispersion relations of electrons in the reformulated Schrödinger equation and a 2 × 2 transfer matrix approach are applied to the study of quasi-periodic Fibonacci semiconductor heterostructures. Energy minibands and resonant tunneling amplitudes are investigated and compared with the parabolic case to show the importance of nonparabolic deviations in AlxGa1?xAsGaAs superlattices.

M. Palomino-Ovando; Gregorio H. Cocoletzi; C. Pérez-López

1996-01-01

9

Quasi-periodic structure of a turbulent jet

The instantaneous near field pressure fluctuations of an axisymmetric subsonic jet were measured by using a longitudinal and an azimuthal microphone arrays in order to qualitatively determine the behaviors of the quasi-periodic structure within the flow. Statistical analysis is used to explain the characteristic of the pressure signals. In addition to the information obtained by forming the power spectral density,

L. Maestrello; Y.-T. Fung

1979-01-01

10

Pulsatory magma supply to a phonolite lava lake Clive Oppenheimer a,

Pulsatory magma supply to a phonolite lava lake Clive Oppenheimer a, , Alexandra S. Lomakina b processes (Tazieff, 1997; Oppenheimer et al., 2004). The decadal persistence of some lava lakes, with no net, though it may well have existed for a century or more (Oppenheimer and Kyle, 2008). Since 2001, the lake

Kingsbury, Nick

11

High directive antenna using quasi-periodic planar metamaterial substrates

We report our experimental and theoretical studies on a metamaterial substrate consisting of a quasi-periodic metallic planar pattern and a flat metal sheet, interconnected through metallic vias. We show that this structure possesses multiple in-phase reflection frequency regimes and spectral gaps for transverse-magnetic surface waves, whereas the transverse-electric surface waves are suppressed in all frequencies. In particular, an antenna put

Hongqiang Li; Z. H. Hang; Yaqin Qin; Lei Zhou; Yewen Zhang; Hong Chen; C. T. Chan

2005-01-01

12

Quasi-periodic compressive waves in polar plumes

NASA Technical Reports Server (NTRS)

The observation of polar plumes in the south polar coronal hole, carried out on 7 March 1996 by the Solar and Heliospheric Observatory (SOHO), are analyzed. These polar plumes are cool density structures that arise from morphologically unipolar magnetic footpoints. Data from the extreme ultraviolet imaging telescope show quasi-periodic perturbations in the brightness of the Fe IX and X line emissions at 171 A from polar plumes. The perturbations have periods of 10 to 15 min, and repeat for several cycles suggesting that they are compressive waves propagating through the plume at or near the Alfven speed. Possible explanations for the observed phenomenon are proposed.

DeForest, C. E.; Gurman, J. B.

1997-01-01

13

Quasi-periodicities of PKS 2155-304

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$\\sim$315 days, confirming the recent findings by \\cite{Zhang2014}. The examination of the gamma-ray light curves from the\\textit{ Fermi} archives yields a significant signal at $\\sim$ 2T, which, while nominally significant, involves data spanning only $\\sim$ 6T. Assuming a black hole mass of $10^{9}\\ M_{\\odot}$ the Keplerian distance corresponding to the quasi-period T is $\\sim10^{16}$ cm, about 50 Schwarzschild radii.

Sandrinelli, Angela; Treves, Aldo

2014-01-01

14

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

15

On repellers in quasi-periodically forced logistic map system

We propose a method to identify and to locate "repellers'' in quasi-periodically forced logistic map (QPLM), using a kind of Morse decomposition of nested attracting invariant sets. In order to obtain the invariant sets, we use an auxiliary 1+2-dimensional skew-product map system describing the evolution of a line segment in the phase space of QPLM. With this method, detailed structure of repellers can be visualized, and the emergence of a repeller in QPLM can be detected as an easily observable bifurcation in the auxiliary system. In addition to the method to detect the repellers, we propose a new numerical method for distinguishing a strange non-chaotic attractor (SNA) from a smooth torus attractor, using a correspondence between SNAs in QPLM and attractors with riddled basin in the auxiliary system.

Tsuyoshi Chawanya; Takafumi Sakai

2014-03-03

16

Dynamics of a classical particle in a quasi periodic potential

NASA Astrophysics Data System (ADS)

We study the dynamics of a one-dimensional classical particle in a space and time dependent potential with randomly chosen parameters. The focus of this work is a quasi-periodic potential, which only includes a finite number of Fourier components. The momentum is calculated analytically for short time within a self-consistent approximation, under certain conditions. We find that the dynamics can be described by a model of a random walk between the Chirikov resonances, which are resonances between the particle momentum and the Fourier components of the potential. We use numerical methods to test these results and to evaluate the important properties, such as the characteristic hopping time between the resonances. This work sheds light on the short time dynamics induced by potentials which are relevant for optics and atom optics.

Tenenbaum Katan, Yaniv; Kachman, Tal; Fishman, Shmuel; Soffer, Avy

2015-03-01

17

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.

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

2014-12-01

18

Models of Kilohertz Quasi-Periodic Brightness Oscillations

The remarkable discovery of kilohertz quasi-periodic brightness oscillations (QPOs) in the accretion-powered emission from some sixteen neutron-star low-mass X-ray binary systems has led to much speculation about and theoretical modeling of the origin of these oscillations. It has also led to intense study of the implications that these QPOs have for the properties of neutron stars and of the accretion flow onto them. In this review we describe the strengths and weaknesses of the models that have been proposed for the kilohertz QPOs observed in the accretion-powered emission. We conclude that beat-frequency models, and in particular the sonic-point model, are currently the most promising. If these models are correct, the kilohertz QPOs provide the strongest constraints to date on the masses and radii of neutron stars in low-mass X-ray binaries, and on the equation of state of the dense matter in all neutron stars.

M. Coleman Miller

1997-12-18

19

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

20

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

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

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

23

Quasi-periodic regimes in the transition to unstable Lagrange dynamics

The appearance of a narrow band of quasi-periodic regimes between the regions of periodic (stable) and unstable (in the Lagrange\\u000a sense) dynamics in the space of parameters of a dynamical system has been studied in the case of a model two-dimensional Hnon\\u000a map. It is established that fast breakage of a quasi-periodic regime proceeds via nonlocal bifurcation, whereby an attractor

A. P. Kuznetsov; A. V. Savin

2006-01-01

24

Quasi-periodic signal analysis using harmonic transform with application to voiced speech processing

A new method for quasi-periodic signal analysis and modelling with application to speech processing is proposed in this paper. The model of quasi-periodic signal treats the signal as a composition the two components. Periodic component is modelled as a sum of harmonically related sinusoidal partials with slowly time-varying amplitudes and frequencies, aperiodic component is modulated white noise. Fundamental frequency, amplitudes

Piotr Zubrycki; Alexander A. Petrovsky

2010-01-01

25

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

26

A renormalization operator for 1D maps under quasi-periodic perturbations

NASA Astrophysics Data System (ADS)

This paper concerns the reducibility loss of (periodic) invariant curves of quasi-periodically forced one-dimensional maps and its relationship with the renormalization operator. Let g? be a one-parametric family of one-dimensional maps with a cascade of period doubling bifurcations. Between each of these bifurcations, there exists a parameter value ?n such that g?_n has a superstable periodic orbit of period 2n. Consider a quasi-periodic perturbation (with only one frequency) of the one-dimensional family of maps, and let us call ? the perturbing parameter. For ? small enough, the superstable periodic orbits of the unperturbed map become attracting invariant curves (depending on ? and ?) of the perturbed system. Under a suitable hypothesis, it is known that there exist two reducibility loss bifurcation curves around each parameter value (?n, 0), which can be locally expressed as (?_n^+(\\varepsilon), \\varepsilon) and (?_n^-(\\varepsilon), \\varepsilon) . We propose an extension of the classic one-dimensional (doubling) renormalization operator to the quasi-periodic case. We show that this extension is well defined and the operator is differentiable. Moreover, we show that the slopes of reducibility loss bifurcation \\frac{d}{d\\varepsilon} ?_n^+/-(0) can be written in terms of the tangent map of the new quasi-periodic renormalization operator. In particular, our result applies to the families of quasi-periodic forced perturbations of the Logistic Map typically encountered in the literature. We also present a numerical study that demonstrates that the asymptotic behaviour of \\{\\frac{d}{d\\varepsilon} ?_n^+/-(0)\\}n? 0 is governed by the dynamics of the proposed quasi-periodic renormalization operator.

Jorba, À.; Rabassa, P.; Tatjer, J. C.

2015-04-01

27

The quasi-periodic nature of wall slip for molten plastics in large amplitude oscillatory shear

THE QUASI-PERIODIC NATURE OF WALL SLIP FOR MOLTEN PLASTICS IN LARGE AMPLITUDE OSCILLATORY SHEAR A Thesis by DAVID WARREN ADRIAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE May 1992 Major Subject: Mechanical Engineering THE QUASI-PERIODIC NATURE OF WALL SLIP FOR MOLTEN PLASTICS IN LARGE AMPLITUDE OSCILLATORY SHEAR A Thesis by DAVID WARREN ADRIAN Approved as to style and content by: A. J...

Adrian, David Warren

1992-01-01

28

Phase Registration of a Single Quasi-Periodic Signal Using Self Dynamic Time Warping

\\u000a This paper proposes a method for phase registration of a single non-parametric quasi-periodic signal. After a short-term period\\u000a has been detected for each sample by normalized autocorrelation, Self Dynamic Time Warping (Self DTW) between a quasi-periodic\\u000a signal and that with multiple-period shifts is applied to obtain corresponding samples of the same phase. A phase sequence\\u000a is finally estimated by the

Yasushi Makihara; Trung Ngo Thanh; Hajime Nagahara; Ryusuke Sagawa; Yasuhiro Mukaigawa; Yasushi Yagi

2010-01-01

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

Observation and removal of daily quasi-periodic components in soil radon data

We report (quasi) periodic oscillations observed in soil radon emanation data especially during summer period. Soil radon has been continuously monitored in the Marmara region of Turkey over the past nine years to reveal possible relationships between soil radon and seismic activities. This long term monitoring has clearly demonstrated that soil radon concentrations are affected by various parameters such as

S. Baykut; T. Akgül; S. ?nan; C. Seyis

2010-01-01

31

Period doubling and reducibility in the quasi-periodically forced logistic map

Period doubling and reducibility in the quasi-periodically forced logistic map Angel Jorba1 , Pau of Groningen, Groningen, The Netherlands July 19, 2011 Abstract We study the dynamics of the Forced Logistic;3 The Forced Logistic Map 6 3.1 Basic study of the dynamics

Barcelona, Universitat de

32

A Two-Component Generalization of Burgers' Equation with Quasi-Periodic Solution

NASA Astrophysics Data System (ADS)

In this paper, we aim for the theta function representation of quasi-periodic solution and related crucial quantities for a two-component generalization of Burgers' equation. Our tools include the theory of algebraic curves, meromorphic functions, Baker-Akhiezer functions and the Dubrovin-type equations for auxiliary divisor. Eith these tools, the explicit representations for above quantities are obtained.

Pan, Hongfei; Xia, Tiecheng; Chen, Dengyuan

2014-10-01

33

Quasi-periodic oscillations in a network of four Rossler chaotic oscillators

We consider a network of four non-identical chaotic Rossler oscillators. The possibility is shown of appearance of two-, three- and four-frequency invariant tori resulting from secondary quasi-periodic Hopf bifurcations and saddle-node homoclinic bifurcations of tori.

Alexander P. Kuznetsov; Igor R. Sataev; Yuliya V. Sedova; Ludmila V. Turukina

2014-10-29

34

A FAST DIRECT SOLVER FOR QUASI-PERIODIC SCATTERING A. GILLMAN, A. BARNETT

-kind), rendering fast multipole-based iterative schemes also inefficient. We present an integral equation based incident angle than a fast multipole based iterative solution, and 600 times faster when incident anglesA FAST DIRECT SOLVER FOR QUASI-PERIODIC SCATTERING PROBLEMS A. GILLMAN, A. BARNETT Abstract. We

Barnett, Alex

35

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

36

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

2006-04-24

37

NASA Astrophysics Data System (ADS)

This presentation starts with Karl Jansky's discovery of cosmic radio emission in 1933 and notes the striking similarities to Hess's discovery of cosmic-rays in 1912. At first it was assumed that this radio emission was thermal but in 1939 Grote Reber discovered that it was stronger at longer wavelengths, requiring a non-thermal emission process. These discoveries had a revolutionary impact on astronomy and radio astronomy was born. The interpretation of this non-thermal radiation as synchrotron emission from high energy particles in the interstellar medium did not occur until the late 1940s but then it provided the link between radio astronomy and cosmic-ray research. Ginzburg, in particular, saw that cosmic-ray astrophysics was now possible using radio waves to trace sources of cosmic-rays. We discuss the discovery of extragalactic active galactic nuclei leading to the discovery of quasars and the first evidence for black holes in the nuclei of galaxies. We summarise the present status and future of some of the main radio telescopes used to image the non-thermal emission from external galaxies. Finally, we include a short description of the use of radio signals for the direct detection of cosmic-rays and UHE neutrinos.

Ekers, R. D.

2014-01-01

38

On The Low Frequency Quasi Periodic Oscillations of X-ray Sources

Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the Keplerian and the periastron precession frequencies at the magnetosphere-disk of X-ray neutron star (NS) respectively, we ascribe the low frequency Quasi Periodic Oscillations (LFQPO) and HBO (15-60 Hz QPO for Z sources or Atoll sources) to the periastron precession at some outer disk radius. The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The obtained theoretical relations between HBO (LFQPO) frequency and the kHz QPO frequency are similar to the measured empirical formula. Further, the possible dynamical mechanism for QPO production is discussed.

C. M. Zhang

2005-07-25

39

Quasi-periodic oscillations of the magnetopause during northward sheath magnetic field

NASA Technical Reports Server (NTRS)

The Geotail satellite quasi-periodically crossed the dawn flank of magnetopause more than ten times during an interval of 1.5 hours on November 4, 1992. Magnetopause crossings were characterized by quasi-periodic pulses of a sawtooth wave form in the magnetic field and the plasma flow components tangential to the magnetopause. The magnetic field strength in the magnetosheath was larger than that in the magnetosphere. The direction of magnetic field outside the magnetopause current layer was northward with antisunward tilt, indicating the draping of magnetic field on the magnetopause. Boundary normals of wavy magnetopause systematically incline sunward on the upstream side, while they tend to incline antisunward with considerable deviation on the downstream side. Comparison with other multiple crossing events suggests that the November 4 event exhibits wavy structure of the dawn flank magnetopause associated with the northward interplanetary magnetic field (IMF).

Kokubun, S.; Kawano, H.; Nakamura, M.; Yamamoto, T.; Tsuruda, K.; Hayakawa, H.; Matsuoka, A.; Frank, L. A.

1994-01-01

40

Towards modeling quasi-periodic oscillations of microquasars with oscillating slender tori

Context. One of the often discussed models for X-ray binaries high-frequency quasi-periodic oscillations is the oscillating torus model that considers oscillation modes of slender accretion tori. Aims. Here, we aim at developing this model by considering the observable signature of an optically thick slender accretion torus subject to simple periodic deformations. Methods. We compute light curves and power spectra of a slender accretion torus subject to simple periodic deformations: vertical or radial translation, rotation, expansion and shear. Results. We show that different types of deformations lead to very different Fourier power spectra and therefore could be observationally distinguished. Conclusions. This work is a first step in a longer-term study of the observable characteristics of the oscillating torus model. It gives promising perspectives on the possibility to constrain this model by studying the observed power spectra of quasi-periodic oscillations.

Mazur, G P; Johansson, M; Sramkova, E; Torok, G; Bakala, P; Abramowicz, M A

2013-01-01

41

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

42

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

43

We have found that quasi-periodic (QP) echoes in the E region were well defined when medium scale traveling ionospheric disturbances (MSTIDs) in the F region were present. The appearance and disappearance of the MSTIDs observed with the dense GPS receiver network are well correlated with the development and decay of QP echoes observed with the Middle-and-Upper atmosphere (MU) radar. Interferometric

S. Saito; M. Yamamoto; H. Hashiguchi; A. Maegawa; A. Saito

2007-01-01

44

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

NASA Astrophysics Data System (ADS)

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

Shi, Yanling; Xu, Junxiang; Xu, Xindong

2015-02-01

45

Order determination and optimum harmonic reconstruction of quasi-periodic signals in noise

This article proposes a new method for determining the order of wide-band quasi-periodic signals from frequency estimates provided either by their short-time Fourier or linear prediction (LP) spectra. The method consists in the search for harmonic patterns in the signal spectrum that minimize an error sum of the estimated frequencies. This error can be thought of as an extension to

Christos Malliopoulos; Stelios Bakamidis; George Carayannis

1999-01-01

46

Design broadband Fabry-Perot resonator antenna using quasi-periodic structure

The broadband Fabry-Perot (FP) resonator antenna composed of single-layer quasi-periodic FSS superstrate with tapered size square patch fed by U-slotted patch is proposed, whose common bandwidth for -3 dB directivity-drop and -10 dB returned loss increases by 7.99% to 12.2% for two different cases, as compared to that of previously single layer uniform FSS. Furthermore, FP resonator antenna can be

Zhen-Guo Liu

2008-01-01

47

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

48

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

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

Briskin, M. (Univ. of Cincinnati, OH (USA)); Fluegeman, R. (Ball State Univ., Muncie, IN (USA))

1990-04-01

49

NASA Astrophysics Data System (ADS)

We investigate the lifetime distribution functions of spontaneous emission from line antennas embedded in finite-size two-dimensional 12-fold quasi-periodic photonic crystals. Our calculations indicate that two-dimensional quasi-periodic crystals lead to the coexistence of both accelerated and inhibited decay processes. The decay behaviors of line antennas are drastically changed as the locations of the antennas are varied from the center to the edge in quasi-periodic photonic crystals and the location of transition frequency is varied.

Xu, Xingsheng; Hu, Haiyang; Yamada, Toshiki; Chen, Hongda; Wang, Yiquan

2008-03-01

50

September1995, accepted 18 October 1995) PACS.47.20.-k Hydrodynamic stability PACS.03.40.Gc Fluid dynamics-dimensional periodic and quasi-periodic patterns, such as rectangular pattern, skewed varicose pattern, undulations

Boyer, Edmond

51

NASA Astrophysics Data System (ADS)

We study evolution of quasi-periodic oscillation (QPO) frequencies using the oscillating properties of the Compton cloud which constitute the inner puffed-up region (the so-called CENBOL) of the transonic, low-angular momentum flow. As the CENBOL is cooled down by inverse Compton effect, the oscillating centrifugal pressure supported shock moves inward, while trying to satisfy Rankine-Hugoniot shock condition. We show that the low frequency QPOs do indeed originate from these oscillating shocks and their frequencies evolve on a daily basis in a predictable way.

Mondal, Santanu; Debnath, Dipak; Chakrabarti, Sandip Kumar

52

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

53

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

54

We investigate the lifetime distribution functions of spontaneous emission from line antennas embedded in finite-size two-dimensional 12-fold quasi-periodic photonic crystals. Our calculations indicate that two-dimensional quasi-periodic crystals lead to the coexistence of both accelerated and inhibited decay processes. The decay behaviors of line antennas are drastically changed as the locations of the antennas are varied from the center to the

Xingsheng Xu; Haiyang Hu; Toshiki Yamada; Hongda Chen; Yiquan Wang

2008-01-01

55

In this paper, the monodromy variant of Newton's method is applied to locate periodic or quasi-periodic relative satellite motion. Advantages of using Newton's method to search for periodic or quasi-periodic relative satellite motion include simplicity of im- plementation, ability to deal with nonlinear dynamics, repeatability of the solutions due to its non-random nature, and fast convergence. A nonlinear Hamiltonian model

V. M. Becerra; J. D. Biggs; S. J. Nasuto; V. F. Ruiz; W. Holderbaum; D. Izzo

56

Topological incommensurate magnetization plateaus in quasi-periodic quantum spin chains

NASA Astrophysics Data System (ADS)

Uncovering topologically nontrivial states in nature is an intriguing and important issue in recent years. While most studies are based on the topological band insulators, the topological state in strongly correlated low-dimensional systems has not been extensively explored due to the failure of direct explanation from the topological band insulator theory on such systems and the origin of the topological property is unclear. Here we report the theoretical discovery of strongly correlated topological states in quasi-periodic Heisenberg spin chain systems corresponding to a series of incommensurate magnetization plateaus under the presence of the magnetic field, which are uniquely determined by the quasi-periodic structure of exchange couplings. The topological features of plateau states are demonstrated by the existence of non-trivial spin-flip edge excitations, which can be well characterized by nonzero topological invariants defined in a two-dimensional parameter space. Furthermore, we demonstrate that the topological invariant of the plateau state can be read out from a generalized Streda formula and the spin-flip excitation spectrum exhibits a similar structure of the Hofstadter's butterfly spectrum for the two-dimensional quantum Hall system on a lattice.

Hu, Hai-Ping; Cheng, Chen; Luo, Hong-Gang; Chen, Shu

2015-02-01

57

We show how one can estimate the multipole moments of the space-time, assuming that the quasi-periodic modulations of the X-ray flux (quasi-periodic oscillations), observed from accreting neutron stars or black holes, are due to orbital and precession frequencies (relativistic precession model). The precession frequencies $\\Omega_{\\rho}$ and $\\Omega_z$ can be expressed as expansions on the orbital frequency $\\Omega$, in which the moments enter the coefficients in a prescribed form. Thus, observations can be fitted to these expressions in order to evaluate the moments. If the compact object is a neutron star, constrains can be imposed on the equation of state. The same analysis can be used for black holes as a test for the validity of the no-hair theorem. Alternatively, instead of fitting for the moments, observations can be matched to frequencies calculated from analytic models that are produced so as to correspond to realistic neutron stars described by various equations of state. Observations can thus be used to constrain the equation of state and possibly other physical parameters (mass, rotation, quadrupole, etc.) Some distinctive features of the frequencies, which become evident by using the analytic models, are discussed.

George Pappas

2012-04-16

58

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 $0values of $\\alpha$ for which this holds as those exceeding the upper transport exponent $\\alpha_u^+$ of an appropriate one-body discrete Schr\\"odinger operator. Previous study has produced a good amount of quantitative information on $\\alpha_u^+$. The result is obtained by mapping to free fermions, obtaining good dynamical bounds on the one-body level by adapting techniques developed by Damanik, Gorodetski, Tcheremchantsev, and Yessen and then "pulling back" these bounds through the non-local Jordan-Wigner transformation, following an idea of Hamza, Sims, and Stolz. To our knowledge, this is the first rigorous derivation of anomalous many-body transport. We also explain why our method does not extend to yield anomalous LR bounds of power-law type if one replaces the quasi-periodic field by a random dimer field.

David Damanik; Marius Lemm; Milivoje Lukic; William Yessen

2014-08-28

59

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

60

The geometric origin of low frequency quasi-periodic oscillations in black hole binaries

NASA Astrophysics Data System (ADS)

X-ray radiation from accreting black holes displays quasi-periodic oscillations (QPOs). This was discovered 30 years ago and the potential of the signal to provide insight into accretion physics was immediately recognised, however the QPO origin was not understood. Perhaps the most promising model to date associates the QPO with Lense-Thirring (LT) precession of the inner accretion flow. In general relativity, a spinning black hole drags the surrounding spacetime with it (frame dragging), causing LT precession in any particle orbit misaligned with the black hole equatorial plane. Determining the QPO phase dependence of the spectrum provides a powerful diagnostic tool to test this model against alternative interpretations. However, this poses a technical challenge because the QPO is quasi-periodic rather than purely periodic and so existing techniques are not suitable. I will describe a method designed to circumvent these problems and present the results of the first QPO phase resolved spectral analyses using archival data from the Rossi X-ray Timing Explorer (RXTE). We find, through variations in the equivalent width of the iron K alpha emission line, strong evidence that the accretion geometry changes on the QPO period, consistent with the predictions of the precession model.

Ingram, A.; van der Klis, M.; Done, C.

2014-07-01

61

Topological incommensurate magnetization plateaus in quasi-periodic quantum spin chains

Uncovering topologically nontrivial states in nature is an intriguing and important issue in recent years. While most studies are based on the topological band insulators, the topological state in strongly correlated low-dimensional systems has not been extensively explored due to the failure of direct explanation from the topological band insulator theory on such systems and the origin of the topological property is unclear. Here we report the theoretical discovery of strongly correlated topological states in quasi-periodic Heisenberg spin chain systems corresponding to a series of incommensurate magnetization plateaus under the presence of the magnetic field, which are uniquely determined by the quasi-periodic structure of exchange couplings. The topological features of plateau states are demonstrated by the existence of non-trivial spin-flip edge excitations, which can be well characterized by nonzero topological invariants defined in a two-dimensional parameter space. Furthermore, we demonstrate that the topological invariant of the plateau state can be read out from a generalized Streda formula and the spin-flip excitation spectrum exhibits a similar structure of the Hofstadter's butterfly spectrum for the two-dimensional quantum Hall system on a lattice. PMID:25678145

Hu, Hai-Ping; Cheng, Chen; Luo, Hong-Gang; Chen, Shu

2015-01-01

62

Topological incommensurate magnetization plateaus in quasi-periodic quantum spin chains.

Uncovering topologically nontrivial states in nature is an intriguing and important issue in recent years. While most studies are based on the topological band insulators, the topological state in strongly correlated low-dimensional systems has not been extensively explored due to the failure of direct explanation from the topological band insulator theory on such systems and the origin of the topological property is unclear. Here we report the theoretical discovery of strongly correlated topological states in quasi-periodic Heisenberg spin chain systems corresponding to a series of incommensurate magnetization plateaus under the presence of the magnetic field, which are uniquely determined by the quasi-periodic structure of exchange couplings. The topological features of plateau states are demonstrated by the existence of non-trivial spin-flip edge excitations, which can be well characterized by nonzero topological invariants defined in a two-dimensional parameter space. Furthermore, we demonstrate that the topological invariant of the plateau state can be read out from a generalized Streda formula and the spin-flip excitation spectrum exhibits a similar structure of the Hofstadter's butterfly spectrum for the two-dimensional quantum Hall system on a lattice. PMID:25678145

Hu, Hai-Ping; Cheng, Chen; Luo, Hong-Gang; Chen, Shu

2015-01-01

63

NASA Astrophysics Data System (ADS)

This report presents an extensive investigation of bifurcations of quasi-periodic oscillations based on an analysis of a coupled delayed logistic map. This map generates an invariant two-torus (IT>2) that corresponds to a three-torus in vector fields. We illustrate detailed Lyapunov diagrams and, by observing attractors, derive a quasi-periodic saddle-node (QSN) bifurcation boundary with a precision of 10-9. We derive a stable invariant one-torus (IT>1) and a saddle IT>1, which correspond to a stable two-torus and a saddle two-torus in vector fields, respectively. We confirmed that the QSN bifurcation boundary coincides with a saddle-node bifurcation point of a stable IT>1 and a saddle IT>1. Our major concern in this study is whether the qualitative transition from an IT>1 to an IT>2 via QSN bifurcations includes phase-locking. We prove with a precision of 10-9 that there is no resonance at the bifurcation point.

Kamiyama, Kyohei; Inaba, Naohiko; Sekikawa, Munehisa; Endo, Tetsuro

2014-12-01

64

Non-thermal plasma treatment of textiles

This article attempts to give an overview of the literature on the treatment of textiles with non-thermal plasmas. Because of the enormous amount of potential uses of non-thermal plasmas for the modification of textile products, categorizing the applications is difficult, and therefore a review is given on plasma treatment effects or results rather than on the textile applications that benefit

R. Morent; N. De Geyter; J. Verschuren; K. De Clerck; P. Kiekens; C. Leys

2008-01-01

65

An evolving MHD vortex street model for quasi-periodic solar wind fluctuations

NASA Technical Reports Server (NTRS)

Magnetohydrodynamic (MHD) simulation are used to provide a dynamical basis for the 'vortex street' model of the quasi-periodic meridional flow observed by Voyager 2 in the outer heliosphere. Various observations suggest the existence near the current sheet at solar minimum, of a vorticity distribution of two opposite shear layers with an antisymmetric staggered velocity pattern due to structured high-speed wind surrounding low-speed equatorial flow. It is shown that this flow pattern leads to the formation of a highly stable vortex street through the nonlinear interaction of the two shear layers. Spatial profiles of various simulated parameters (velocity, density, meridional flow angle and the location of magnetic sector boundaries) and their relative locations in the quasi-steady vortex street are generally in good agreement with the observations.

Siregar, Edouard; Roberts, D. A.; Goldstein, Melvyn L.

1992-01-01

66

Strong-field general relativity and quasi-periodic oscillations in x-ray binaries

Quasi-periodic oscillations (QPOs) at frequencies near 1000 Hz were recently discovered in several x-ray binaries containing neutron stars. Two sources show no correlation between QPO frequency and source count rate (Berger et al. 1996, Zhang et al. 1996). We suggest that the QPO frequency is determined by the Keplerian orbital frequency near the marginally stable orbit predicted by general relativity in strong gravitational fields (Muchotrzeb-Czerny 1986, Paczynski 1987, Kluzniak et al. 1990). The QPO frequencies observed from 4U 1636-536 imply that the mass of the neutron star is 2.02 +/- 0.12 solar masses. Interpretation of the 4.1 keV absorption line observed from 4U 1636-536 (Waki et al. 1984) as due to Fe XXV ions then implies a neutron star radius of 9.6 +/-0.6 km.

Philip Kaaret; Eric Ford; Kaiyou Chen

1997-01-16

67

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

68

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

69

Modelling the energy dependencies of X-ray quasi-periodic oscillations in accreting compact objects

We have constructed models of quasi-periodic variability of X-ray emission from accreting compact objects. Assuming a general scenario of a propagation model of variability, with inverse Compton upscatering as the emission mechanism, we have considered a number of cases for the periodic modulation: modulation of the plasma heating rate, cooling rate by external soft photons, and the amplitude of the reprocessed component. We have computed various observational characteristics which can be compared to good quality data.These include Fourier-frequency resolved spectra and results of cross-correlation analysis between light-curves at different energies. Each model of modulation predicts specific observational signatures, which help in identifying the physical processes driving QPO emission in accreting sources.

P. T. Zycki; M. Sobolewska

2005-09-08

70

Synchronizations of Quasi-period and Hyperchaos in Injected Two-section Semiconductor Lasers

NASA Astrophysics Data System (ADS)

A novel hyperchaos synchronization system is presented. Hyperchaos synchronization in injection two-section semiconductor lasers was achieved for its application in secure communication. We found also a route from single-period to hyperchaos after passing quasi-period and chaos with increasing frequency detuning while the receiver synchronized with the transmitter in these dynamical regions. All optical private data communication encoded by a rate of 0.16 Gbit/s on/off phase shift key and a rate of 0.16 Gbit/s amplitude modulation and photoelectric private data communication encoded by a rate of 0.2 Gbit/s on/off current shift key and a current modulation of 0.12 GHz frequency, respectively, are simulated via this hyperchaos synchronization system. Decoding has been numerically demonstrated to achieve successfully.

Yan, Sen-lin

2013-03-01

71

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

72

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

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

Yu, Sijie; Tan, Baolin; Yan, Yihua [Key Laboratory of Solar Activity, National Astronomical Observatories Chinese Academy of Sciences, Beijing 100012 (China); Nakariakov, V. M.; Selzer, L. A., E-mail: sjyu@nao.cas.cn [Centre for Fusion, Space and Astrophysics, Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom)

2013-11-10

73

Extended states for polyharmonic operators with quasi-periodic potentials in dimension two

NASA Astrophysics Data System (ADS)

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

Karpeshina, Yulia; Shterenberg, Roman

2012-10-01

74

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

NASA Astrophysics Data System (ADS)

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

Karpeshina, Yulia; Shterenberg, Roman

2013-07-01

75

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

76

GB6 J1058+5628: A NEW QUASI-PERIODIC BL LAC OBJECT FROM THE ASIAGO PLATE ARCHIVE

We present the historic photographic light curves of three little known blazars (two BL Lac objects and one FSRQ), GB6 J1058+5628, GB6 J1148+5254, and GB6 J1209+4119, spanning a time interval of about 50 years, mostly built using the Asiago plate archive. All objects show evident long-term variability, over which short-term variations are superposed. One source, GB6 J1058+5628, showed a marked quasi-periodic variability of 1 mag on timescale of about 6.3 years, making it one of the few BL Lac objects with a quasi-periodic behavior.

Nesci, R., E-mail: roberto.nesci@uniroma1.i [Physics Department, University of Roma La Sapienza, Piazzale A. Moro 2, I-00185 Roma (Italy)

2010-06-15

77

Multi-splitting and self-similarity of band gap structures in quasi-periodic plates of Cantor series

NASA Astrophysics Data System (ADS)

The authors have demonstrated the multi-splitting and self-similarity of the band gap structures in quasi-periodic plates of Cantor series. The splitting peaks give the regularity of tri-branching. A semi-quantitative explanation is proposed in which the inherent cavity-like structure is proven to play the essential role in the phenomena of multi-splitting and self-similarity, which gives a reliable way to predict where and how the band gap is splitting in the quasi-periodic systems. Possible applications are discussed.

Ding, Hong-Xing; Shen, Zhong-Hua; Ni, Xiao-Wu; Zhu, Xue-Feng

2012-02-01

78

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

79

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

80

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

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

El-Mezeini, Ahmed M.; Ibrahim, Alaa I., E-mail: amezeini@aucegypt.ed, E-mail: ai@aucegypt.ed, E-mail: amiae2@cam.ac.u, E-mail: ai@space.mit.ed [Department of Physics, American University in Cairo, New Cairo 11835 (Egypt)

2010-10-01

81

Reprocessing model for the optical quasi-periodic oscillations in black hole binaries

NASA Astrophysics Data System (ADS)

A number of black hole X-ray transients show quasi-periodic oscillations (QPOs) in the optical (ultraviolet) and X-ray bands at the same frequency, which challenge models for production of radiation at these wavelengths. We propose a model where the optical radiation is modulated by the oscillating X-ray flux resulting in varying irradiation of the outer parts of the accretion disc. The proposed QPO mechanism inevitably takes place in the systems with sufficiently small ratio of the outer disc radius to the QPO period. We show that, unlike in the case of the aperiodic variability, it is not possible to obtain the optical QPO profiles from those observed in the X-rays through the transfer function, because of different X-ray signals seen by the disc and by the observer. We demonstrate that with the increasing QPO frequency, occurring at the rising phase of the X-ray outburst, the rms should be constant for sufficiently low frequencies, then to increase reaching the peak and finally to drop substantially when the QPO period becomes comparable to the light-crossing time to the outer disc. We predict that the QPO rms in this model should increase towards shorter wavelengths and this fact can be used to distinguish it from other QPO mechanisms.

Veledina, Alexandra; Poutanen, Juri

2015-03-01

82

Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri

Our photometric monitoring revealed that DW Cnc, which was originally classified as a dwarf nova (V=15--17.5), remained at a bright state of Rc=14.68+/-0.07 for 61 days. In conjunction with optical spectra lacking a strong He II emission line, we propose that the object is not a dwarf nova, but a non-magnetic nova-like variable. Throughout our monitoring, the object showed strong quasi-periodic oscillations (QPOs) with amplitudes reaching about 0.3 mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose center periods are 37.5+/-0.1 and 73.4+/-0.4 min and, furthermore, with a significant power in frequencies lower than the QPOs. DW Cnc is a unique cataclysmic variable in which kilo-second QPOs were continuously detected for 61 days. We propose two possible interpretations of DW Cnc: (i) A permanent superhumper below the period minimum of hydrogen-rich cataclysmic variables. (ii) A nova-like variable having an orbital period over 3 hours. In this case, the QPOs may be caused by trapped disk oscillations.

M. Uemura; T. Kato; R. Ishioka; R. Novak; J. Pietz

2002-03-15

83

Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri

NASA Astrophysics Data System (ADS)

Our photometric monitoring revealed that DWCnc, which was originally classified as a dwarf nova (V=15 - 17.5) remained at a bright state of Rc=14.68 +/- 0.07 for 61days. In conjunction with optical spectra lacking a strong He II emission line, we propose that the object is not a dwarf nova, but a non-magnetic nova-like variable. Throughout our monitoring, the object showed strong quasi-periodic oscillations (QPOs) with amplitudes reaching about 0.3mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose center periods are 37.5 +/- 0.1 and 73.4 +/- 0.4 min and, furthermore, with a significant power in frequencies lower than the QPOs. DWCnc is a unique cataclysmic variable in which kilo-second QPOs were continuously detected for 61days. We propose two possible interpretations of DWCnc: (i) A permanent superhumper below the period minimum of hydrogen-rich cataclysmic variab les. (ii) A nova-like variable having an orbital period over 3hours. In this case, the QPOs may be caused by trapped disk oscillations.

Uemura, Makoto; Kato, Taichi; Ishioka, Ryoko; Novak, Rudolf; Pietz, Jochen

2002-04-01

84

Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri

Our photometric monitoring revealed that DW Cnc, which was originally classified as a dwarf nova (V=15--17.5), remained at a bright state of Rc=14.68+/-0.07 for 61 days. In conjunction with optical spectra lacking a strong He II emission line, we propose that the object is not a dwarf nova, but a non-magnetic nova-like variable. Throughout our monitoring, the object showed strong quasi-periodic oscillations (QPOs) with amplitudes reaching about 0.3 mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose center periods are 37.5+/-0.1 and 73.4+/-0.4 min and, furthermore, with a significant power in frequencies lower than the QPOs. DW Cnc is a unique cataclysmic variable in which kilo-second QPOs were continuously detected for 61 days. We propose two possible interpretations of DW Cnc: (i) A permanent superhumper below the period minimum of hydrogen-rich cataclysmic variables. (ii) A nova-like variable having an orbital period over 3 hours. In this case, the QPOs may be caused by trapped ...

Uemura, M; Ishioka, R; Novak, R; Pietz, J

2002-01-01

85

Quasi-periodic recurrence of large earthquakes on the southern San Andreas fault

It has been 153 yr since the last large earthquake on the southern San Andreas fault (California, United States), but the average interseismic interval is only ~100 yr. If the recurrence of large earthquakes is periodic, rather than random or clustered, the length of this period is notable and would generally increase the risk estimated in probabilistic seismic hazard analyses. Unfortunately, robust characterization of a distribution describing earthquake recurrence on a single fault is limited by the brevity of most earthquake records. Here we use statistical tests on a 3000 yr combined record of 29 ground-rupturing earthquakes from Wrightwood, California. We show that earthquake recurrence there is more regular than expected from a Poisson distribution and is not clustered, leading us to conclude that recurrence is quasi-periodic. The observation of unimodal time dependence is persistent across an observationally based sensitivity analysis that critically examines alternative interpretations of the geologic record. The results support formal forecast efforts that use renewal models to estimate probabilities of future earthquakes on the southern San Andreas fault. Only four intervals (15%) from the record are longer than the present open interval, highlighting the current hazard posed by this fault.

Scharer, Katherine M.; Biasi, Glenn P.; Weldon, Ray J., II; Fumal, Tom E.

2010-01-01

86

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

87

On the Inverse Spectral Problem for the Quasi-Periodic Schrödinger Equation

We study the quasi-periodic Schr\\"odinger equation $$ -\\psi"(x) + V(x) \\psi(x) = E \\psi(x), \\qquad x \\in \\IR $$ in the regime of "small" $V$. Let $(E_m',E"_m)$, $m \\in \\zv$, be the standard labeled gaps in the spectrum. Our main result says that if $E"_m - E'_m \\le \\ve \\exp(-\\kappa_0 |m|)$ for all $m \\in \\zv$, with $\\ve$ being small enough, depending on $\\kappa_0 > 0$ and the frequency vector involved, then the Fourier coefficients of $V$ obey $|c(m)| \\le \\ve^{1/2} \\exp(-\\frac{\\kappa_0}{2} |m|)$ for all $m \\in \\zv$. On the other hand we prove that if $|c(m)| \\le \\ve \\exp(-\\kappa_0 |m|)$ with $\\ve$ being small enough, depending on $\\kappa_0 > 0$ and the frequency vector involved, then $E"_m - E'_m \\le 2 \\ve \\exp(-\\frac{\\kappa_0}{2} |m|)$.

David Damanik; Michael Goldstein

2014-09-28

88

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

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

89

Millihertz quasi-periodic oscillations and broad iron line from LMC X-1

NASA Astrophysics Data System (ADS)

We study the temporal and energy spectral characteristics of the persistent black hole X-ray binary LMC X-1 using two XMM-Newton and a Suzaku observation. We report the discovery of low-frequency (˜26-29 m Hz) quasi-periodic oscillations (QPOs). We also report the variability of the broad iron K? line studied earlier with Suzaku. The QPOs are found to be weak with fractional rms amplitude in the ˜1-2 per cent range and quality factor Q ˜ 2-10. They are accompanied by weak red noise or zero-centred Lorentzian components with rms variability at the ˜1-3 per cent level. The energy spectra consist of three varying components - multicolour disc blackbody (kTin ˜ 0.7-0.9 keV), high-energy power-law tail (? ˜ 2.4-3.3) and a broad iron line at 6.4-6.9 keV. The broad iron line, the QPO and the strong power-law component are not always present. The QPOs and the broad iron line appear to be clearly detected in the presence of a strong power-law component. The broad iron line is found to be weaker when the disc is likely truncated and absent when the power-law component almost vanished. These results suggest that the QPO and the broad iron line together can be used to probe the dynamics of the accretion disc and the corona.

Alam, Md. Shah; Dewangan, G. C.; Belloni, T.; Mukherjee, D.; Jhingan, S.

2014-12-01

90

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

91

Entrainment in nerve by a ferroelectric model (II): Quasi-periodic oscillation and the phase locking

NASA Astrophysics Data System (ADS)

A nonlinear state equation for membrane excitation can be simplified by Leuchtag's ferroelectric model which is applied to a chemical network theory. A dissipative structure of such a membrane is described by an equilibrium space, ? 3 + a? + b = 0, giving a cusp catastrophe, and the membrane is self-organized in the resting state under the condition, a < 0( T < Tc), where ? corresponds to the membrane potential, and a and b imply dipole-dipole and dipole-ion interactions of channel proteins embedded in the membrane, respectively. As well known, a specific characteristic of nonlinear electrical phenomena in the membrane is a limit cycle arising through the entrainment by periodical stimuli or chaos. A phase transition between the equilibrium and the non-equilibrium states (a dissipative structure without the resting state) is described by a parameter giving the difference from thermal equilibrium. In this dynamic system, quasi-periodic oscillations which arise in periodic external fields and the phase locking, that is, entrainment, caused by changing I0 at ? ? ? n (? n - the natural frequency of the membrane) are studied with parameters introduced into Zeeman's formulas of ? and ?.

Shirane, Kotaro; Tokimoto, Takayuki; Kushibe, Hiroyuki

1997-09-01

92

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

93

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

94

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

95

Quasi-Periodic Oscillations from Random X-Ray Bursts Around Rotating Black Holes

NASA Astrophysics Data System (ADS)

We continue our earlier studies of quasi-periodic oscillations (QPOs) in the power spectra of accreting, rapidly rotating black holes that originate from the geometric "light echoes" of X-ray flares occurring within the black hole ergosphere. Our present work extends our previous treatment to three-dimensional photon emission and orbits to allow for arbitrary latitudes in the positions of the distant observers and the X-ray sources in place of the mainly equatorial positions and photon orbits of the earlier consideration. Following the trajectories of a large number of photons, we calculate the response functions of a given geometry and use them to produce model light curves which we subsequently analyze to compute their power spectra and autocorrelation functions. In the case of an optically thin environment, relevant to advection-dominated accretion flows, we consistently find QPOs at frequencies on the order of ~kHz for stellar-mass black hole candidates, while on the order of ~mHz for typical active galactic nuclei (~107 M sun) for a wide range of viewing angles (30°-80°) from X-ray sources predominantly concentrated toward the equator within the ergosphere. As in our previous treatment, here too, the QPO signal is produced by the frame-dragging of the photons by the rapidly rotating black hole, which results in photon "bunches" separated by constant time lags, the result of multiple photon orbits around the hole. Our model predicts for various source/observer configurations the robust presence of a new class of QPOs, which is inevitably generic to a curved spacetime structure in rotating black hole systems.

Fukumura, Keigo; Kazanas, Demosthenes; Stephenson, Gordon

2009-04-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

97

Effects of Resonance in Quasi-Periodic Oscillators of Neutron Star Binaries

NASA Technical Reports Server (NTRS)

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

Titarchuk, Lev; White, Nicholas E. (Technical Monitor)

2002-01-01

98

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

99

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

100

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

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

Toeroek, Gabriel; Bakala, Pavel; Sramkova, Eva; Stuchlik, Zdenek; Urbanec, Martin; Goluchova, Katerina, E-mail: pavel.bakala@fpf.slu.cz, E-mail: martin.urbanec@fpf.slu.cz, E-mail: zdenek.stuchlik@fpf.slu.cz, E-mail: terek@volny.cz, E-mail: sram_eva@centrum.cz [Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava, Bezrucovo nam. 13, CZ-746 01 Opava (Czech Republic)

2012-12-01

101

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

NASA Astrophysics Data System (ADS)