EQUILIBRIUM QUASI-PERIODIC CONFIGURATIONS WITH RESONANT FREQUENCIES IN QUASI-PERIODIC MEDIA II
EQUILIBRIUM QUASI-PERIODIC CONFIGURATIONS WITH RESONANT FREQUENCIES IN QUASI-PERIODIC MEDIA II: KAM the frequency of the solutions resonates with the frequen- cies of the substratum. The KAM theory we develop the quasi-periodic solutions. Quasi-periodic Frenkel-Kontorova models, resonant frequencies, equi- libria
Quasi-periodic solutions of a quasi-periodically forced nonlinear beam equation
NASA Astrophysics Data System (ADS)
Wang, Yi
2012-06-01
In this paper, one quasi-periodically forced nonlinear beam equation utt+uxxxx+?u+?g(?t,x)u3=0,?>0,x?[0,?] with hinged boundary conditions is considered. Here ? is a small positive parameter, g( ?t, x) is real analytic in all variables and quasi-periodic in t with a frequency vector ? = ( ?1, ?2, … , ?m). It is proved that the above equation admits small-amplitude quasi-periodic solutions.
EQUILIBRIUM QUASI-PERIODIC CONFIGURATIONS WITH RESONANT FREQUENCIES IN QUASI-PERIODIC MEDIA I
EQUILIBRIUM QUASI-PERIODIC CONFIGURATIONS WITH RESONANT FREQUENCIES IN QUASI-PERIODIC MEDIA I of deposited material) is resonant with the frequencies of the substratum. We study perturbation theory-periodic equilibria with resonant frequencies. Under very general conditions, we show that there are at least two
Xifeng Su; Lei Zhang; Rafael de la Llave
2015-03-11
We consider 1-D quasi-periodic Frenkel-Kontorova models (describing, for example, deposition of materials in a quasi-periodic substratum). We study the existence of equilibria whose frequency (i.e. the inverse of the density of deposited material) is resonant with the frequencies of the substratum. We study perturbation theory for small potential. We show that there are perturbative expansions to all orders for the quasi-periodic equilibria with resonant frequencies. Under very general conditions, we show that there are at least two such perturbative expansions for equilibria for small values of the parameter. We also develop a dynamical interpretation of the equilibria in these quasi-periodic media. We show that the dynamical system has very unusual properties. Using these, we obtain results on the Lyapunov exponents of the resonant quasi-periodic solutions. In a companion paper, we develop a rather unusual KAM theory (requiring new considerations) which establishes that the perturbative expansions converge when the perturbing potentials satisfy a one-dimensional constraint.
Lei Zhang; Xifeng Su; Rafael de la Llave
2015-03-11
We develop an a-posteriori KAM theory for the equilibrium equations for quasi-periodic solutions in a quasi-periodic Frenkel-Kontorova model when the frequency of the solutions resonates with the frequencies of the substratum. The KAM theory we develop is very different both in the methods and in the conclusions from the more customary KAM theory for Hamiltonian systems or from the KAM theory in quasi-periodic media for solutions with frequencies Diophantine with respect to the frequencies of the media. The main difficulty is that we cannot use transformations (as in the Hamiltonian case) nor Ward identities (as in the case of frequencies Diophantine with those of the media). The technique we use is to add an extra equation to make the linearization of the equilibrium equation factorize. This requires an extra counterterm. We compare this phenomenon with other phenomena in KAM theory. It seems that this technique could be used in several other problems. As a conclusion, we obtain that the perturbation expansions developed in the previous paper \\cite{SuZL14} converge when the potentials are in a codimension one manifold in a space of potentials. The method of proof also leads to efficient (low storage requirements and low operation count) algorithms to compute the quasi-periodic solutions.
Quasi-periodic motions in strongly dissipative forced systems
Quasi-periodic motions in strongly dissipative forced systems Guido Gentile Dipartimento di], that is the existence of quasi- periodic motions in strongly dissipative forced systems, with the aim of removing as far-periodic forcing term and in the presence of large damping. We discuss the conditions to be assumed
Imaging and Spectral Observations of Quasi-periodic Pulsations in a Solar Flare
NASA Astrophysics Data System (ADS)
Li, D.; Ning, Z. J.; Zhang, Q. M.
2015-07-01
We explore the quasi-periodic pulsations (QPPs) in a solar flare observed by Fermi Gamma-ray Burst Monitor, Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Interface Region Imaging Spectrograph (IRIS) on 2014 September 10. QPPs are identified as the regular and periodic peaks on the rapidly varying components, which are the light curves after removing the slowly varying components. The QPPs display only three peaks at the beginning on the hard X-ray emissions, but 10 peaks on the chromospheric and coronal line emissions, and more than seven peaks (each peak corresponds to a type III burst on the dynamic spectra) at the radio emissions. A uniform quasi-period of about 4 minutes is detected among them. AIA imaging observations exhibit that the 4-minute QPPs originate from the flare ribbon and tend to appear on the ribbon front. IRIS spectral observations show that each peak of the QPPs tends to a broad line width and a red Doppler velocity at C i, O iv, Si iv, and Fe xxi lines. Our findings indicate that the QPPs are produced by the non-thermal electrons that are accelerated by the induced quasi-periodic magnetic reconnections in this flare.
Characteristics of quasi-periodic scintillations observed at low latitude
NASA Astrophysics Data System (ADS)
Patel, Kalpana; Singh, Ashutosh K.; Singh, A. K.; Singh, R. P.
2009-12-01
Quasi-periodic scintillations are characterized as primary deep fadeout in field strength, associated with regular ringing patterns before and after it. In this paper, observations of quasi-periodic scintillations using geostationary satellite (FLEETSAT) transmissions operating at frequency 250 MHz at low-latitude ground station, Varanasi (geomagnetic latitude 14°55'N, longitude 153°59'E), are reported. The results indicate that the quasi-periodic scintillations are most likely produced by plasma blobs/bubbles present in the E and F regions of the ionosphere which are helpful in identifying the generation mechanism of the associated irregularities. The various characteristic features of the different types of quasi-periodic scintillations observed at low latitude are discussed for the first time in detail based on a highly comprehensive analysis of longer data sets using autocorrelation, power spectrum, and scintillation index analysis. The computed horizontal scale size of the quasi-periodic scintillations producing irregularity varies from 100 to 1300 m which shows that the irregularities are of intermediate-scale sizes. The spectral index obtained from the slopes of power spectrum varies from -2 to -8. All of these observed results are important for identifying the generation mechanism of ionospheric irregularities associated with quasi-periodic scintillations. The observed fading patterns, especially the modulation of the diffraction patterns (fading envelopes), can be explained by considering an obstacle called radio lens in the ionosphere elongated in one direction. For the first time, we have successfully simulated the amplitude versus time plots of almost all types of quasi-periodic scintillation patches and found that our modeled and observed characteristics of quasi-periodic scintillation patches compare well with each other.
The Ten-Rotation Quasi-periodicity in Sunspot Areas
NASA Astrophysics Data System (ADS)
Getko, R.
2014-06-01
Sunspot-area fluctuations over an epoch of 12 solar cycles (12 - 23) are investigated in detail using wavelets. Getko ( Universal Heliophysical Processes, IAU Symp. 257, 169, 2009) found three significant quasi-periodicities at 10, 17, and 23 solar rotations, but two longer periods could be treated as subharmonics of the ten-rotation quasi-periodicity. Therefore we focused the analysis on the occurrence of this quasi-periodicity during the low- and high-activity periods of each solar cycle. Because of the N - S asymmetry, each solar hemisphere was considered separately. The skewness of each fluctuation-probability distribution suggests that the positive and negative fluctuations could be examined separately. To avoid the problem that occurs when a few strong fluctuations create a wavelet peak, we applied fluctuation transformations for which the amplitudes at the high- and the low-activity periods are almost the same. The wavelet analyses show that the ten-rotation quasi-periodicity is mainly detected during the high-activity periods, but it also exists during a few low-activity periods. The division of each solar hemisphere into 30?-wide longitude bins and the wavelet calculations for the areas of sunspot clusters belonging to these 30? bins enable one to detect longitude zones in which the ten-rotation quasi-periodicity exists. These zones are present during the whole high-activity periods and dominate the integrated spectra.
Pressure-driven reconnection and quasi periodical oscillations in plasmas
Paccagnella, R.
2014-03-15
This paper presents a model for an ohmically heated plasma in which a feedback exists between thermal conduction and transport, on one side, and the magneto-hydro-dynamical stability of the system, on the other side. In presence of a reconnection threshold for the magnetic field, a variety of periodical or quasi periodical oscillations for the physical quantities describing the system are evidenced. The model is employed to interpret the observed quasi periodical oscillations of electron temperature and perturbed magnetic field around the so called “Single Helical” state in the reversed field pinch, but its relevance for other periodical phenomena observed in magnetic confinement systems, especially in tokamaks, is suggested.
A result on quasi-periodic solutions of a nonlinear beam equation with a quasi-periodic forcing term
NASA Astrophysics Data System (ADS)
Wang, Yi; Si, Jianguo
2012-02-01
In this paper, a quasi-periodically forced nonlinear beam equation {u_{tt}+u_{xxxx}+? u+\\varepsilon?(t)h(u)=0} with hinged boundary conditions is considered, where ? > 0, {\\varepsilon} is a small positive parameter, {?} is a real analytic quasi-periodic function in t with a frequency vector ? = ( ? 1, ? 2 . . . , ? m ), and the nonlinearity h is a real analytic odd function of the form {h(u)=?_1u+?_{2bar{r}+1}u^{2bar{r}+1}+sum_{k? bar{r}+1}?_{2k+1}u^{2k+1},?_1,?_{2bar{r}+1} neq0, bar{r} in {mathbb {N}}.} The above equation admits a quasi-periodic solution.
TT Ari and its Quasi-Periodic Oscillations
NASA Astrophysics Data System (ADS)
Smak, J.
2014-06-01
Quasi-periodic oscillation (QPO) of TT Ari are transient, short-lived phenomena. They appear and disappear and their periods and amplitudes vary on a time scale as short as 1 hour. Consequently the periodograms covering longer intervals of time are generally meaningless.
Explicit error bounds for the ?-quasi-periodic Helmholtz problem.
Lord, Natacha H; Mulholland, Anthony J
2013-10-01
This paper considers a finite element approach to modeling electromagnetic waves in a periodic diffraction grating. In particular, an a priori error estimate associated with the ?-quasi-periodic transformation is derived. This involves the solution of the associated Helmholtz problem being written as a product of e(i?x) and an unknown function called the ?-quasi-periodic solution. To begin with, the well-posedness of the continuous problem is examined using a variational formulation. The problem is then discretized, and a rigorous a priori error estimate, which guarantees the uniqueness of this approximate solution, is derived. In previous studies, the continuity of the Dirichlet-to-Neumann map has simply been assumed and the dependency of the regularity constant on the system parameters, such as the wavenumber, has not been shown. To address this deficiency, in this paper an explicit dependence on the wavenumber and the degree of the polynomial basis in the a priori error estimate is obtained. Since the finite element method is well known for dealing with any geometries, comparison of numerical results obtained using the ?-quasi-periodic transformation with a lattice sum technique is then presented. PMID:24322866
Cassini and Galileo Observations of Quasi-periodic Radio Bursts
NASA Astrophysics Data System (ADS)
Hospodarsky, G. B.; Kurth, W. S.; Gurnett, D. A.; Kaiser, M. L.; Zarka, P.; Krupp, N.; Waite, J. H.
Simultaneous measurements of many Jovian plasma and radio emissions were ob- tained by the Cassini and Galileo spacecraft during the Cassini flyby of Jupiter (clos- est approach was on December 30, 2000). Jovian type III radio emissions, also known as quasi-periodic (QP) emissions, were often detected by both spacecraft. This type of emission has been detected by Voyager, Ulysses, Galileo, and Cassini, with pe- riodicities ranging from about a minute to many tens of minutes (often around 40 minutes). Other quasi-periodic events have been detected in the energetic particle data of Ulysses, Galileo and Cassini and in the x-ray spectrum obtained by the Chandra spacecraft, usually with periodicities around 40 minutes. The multiple observations of similar quasi-periodic events suggests that there may be a common source for these phenomena. Many examples of simultaneous detection of the QP radio emissions were obtained by the Cassini and Galileo plasma wave and radio instruments. The charac- teristics of the QP emissions observed by each spacecraft are very similar, and when the difference in the travel time of a radio emission from Jupiter to each spacecraft is taken into account, the QP bursts are observed to occur simultaneously at each space- craft. These similar characteristics of the emissions, even when the two spacecraft are separated by many hours in local time and many degrees of system III longitude, sug- gest a broadly beamed 'strobe light' source for the emission, and not a narrow beam which rotates with the planet. The implications of these simultaneous observations will be discussed.
Quasi-periodic transformations of nonlocal spatial solitons.
Buccoliero, Daniel; Desyatnikov, Anton S
2009-06-01
We study quasi-periodic transformations between nonlocal spatial solitons of different symmetries triggered by modulational instability and resembling a self-induced mode converter. Transformation dynamics of solitons with zero angular momentum, e.g. the quadrupole-type soliton, reveal the equidistant spectrum of spatial field oscillations typical for the breather-type solutions. In contrast, the transformations of nonlocal solitons carrying orbital angular momentum, such as 2x3 soliton matrix, are accompanied by their spiralling and corresponding spectra of field oscillations show mixing of three characteristic spatial frequencies. PMID:19506609
Quasi-periodic oscillations, charge and the gravitomagnetic theory
Biemond, Jacob
2007-01-01
A new model for the explanation of the high frequency quasi-periodic oscillations (QPOs) in pulsars, black holes and white dwarfs is presented. Three circular tori are assumed to be present around the star: an inner torus with charge $Q_i$, an outer torus with charge $Q_o$ and a torus with electrically neutral mass $m_m$ in the middle, whereas the star bears a charge $Q_s$ ($Q_o$ and $Q_s$ have the same sign, $Q_i$ the opposite one). The frequency $\
Quasi-periodic oscillations, charge and the gravitomagnetic theory
Jacob Biemond
2009-03-20
A new model for the explanation of the high frequency quasi-periodic oscillations (QPOs) in pulsars, black holes and white dwarfs is presented. Three circular tori are assumed to be present around the star: an inner torus with charge $Q_i$, an outer torus with charge $Q_o$ and a torus with electrically neutral mass $m_m$ in the middle, whereas the star bears a charge $Q_s$ ($Q_o$ and $Q_s$ have the same sign, $Q_i$ the opposite one). The frequency $\
Forced Oscillations in Fluid Tori and Quasi-Periodic Oscillations
William H. Lee
2005-10-19
The kilo-Hertz Quasi--Periodic Oscillations in X-ray binaries could originate within the accretion flow, and be a signature of non--linear fluid oscillations and mode coupling in strong gravity. The possibility to decipher these systems will impact our knowledge of fundamental parameters such as the neutron star mass, radius, and spin. Thus they offer the possibility to constrain the nuclear equation of state and the rotation parameter of stellar--mass black holes. We review the general properties of these oscillations from a hydrodynamical point of view, when the accretion flow is subject to external perturbations and summarize recent results.
Quasi-periodicities of PKS 2155-304
Sandrinelli, Angela; Treves, Aldo
2014-01-01
We have searched for periodicities in our VRIJHK photometry of PKS 2155-304, which covers the years 2005-2012. A peak of the Fourier spectrum with high significance is found at T$\\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.
Overall ultimate yield strength of a quasi-periodic masonry
NASA Astrophysics Data System (ADS)
Sab, Karam
2009-08-01
The purpose of this Note is the determination of the in-plane homogenized strength domain of a "quasi-periodic" masonry under the assumption of infinitely resistant blocks connected by cohesionless Mohr-Coulomb interfaces. This masonry is obtained by introducing a random perturbation on the horizontal width of the blocks of a periodic running bond masonry. It is found that in some non-trivial cases the strength domain coincides exactly with that of the initial periodic masonry. To cite this article: K. Sab, C. R. Mecanique 337 (2009).
Quasi-Periodic Orbits of the Restricted Three-Body Problem Egemen Kolemen
Quasi-Periodic Orbits of the Restricted Three-Body Problem Made Easy Egemen Kolemen , N. Jeremy is presented which employs multiple Poincaré sections to find quasi-periodic orbits. The main advantages chaotic regions that leads to full convergence for given family of quasi-periodic orbits and the minimal
Quasi-periodic Oscillation of a Coronal Bright Point
NASA Astrophysics Data System (ADS)
Samanta, Tanmoy; Banerjee, Dipankar; Tian, Hui
2015-06-01
Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.
Quasi-Periodic Oscillation of a Coronal Bright Point
Samanta, Tanmoy; Tian, Hui
2015-01-01
Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underneath magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly (AIA) images, the Helioseismic and Magnetic Imager (HMI) magnetogram on board the Solar Dynamics Observatory (SDO) and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and FUV images. With highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit and stare observation provided a unique opportunity to study the time evolution of one foot point of the BP as the slit position crossed it. We noticed enhanced line prof...
Quasi-Periodic Pulsations in a Solar Microwave Burst
NASA Technical Reports Server (NTRS)
Kundu, Mukul R.; Grechnev, V. V.; White, S. M.
2003-01-01
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.
Quasi-periodic oscillations in GX 17 + 2
NASA Technical Reports Server (NTRS)
Penninx, W.; Lewin, W. H. G.; Mitsuda, K.; Van Der Klis, M.; Van Paradijs, J.
1990-01-01
X-ray observations of GX 17 + 2 were made in March and April, 1988 with the Large Area Counter of the Ginga satellite. The source was observed in the flaring, normal, and horizontal branches. Quasi-periodic oscillations (QPOs) were oberved in all three of these branches. The relationship between QPO behavior and the X-ray spectral properties of GX 17 + 2 is examined. Continuous variation of QPO behavior is observed as GX 17 + 2 moves from the normal to flaring branch, indicating that the normal-branch QPO and the flaring-branch QPO are probably one physical phenomenon. This QPO behavior is similar to that observed in Sco X-1. Also, it is found that GX 17 + 2 is an example of the Z-type sources defined by Hasinger et al. (1989).
NASA Astrophysics Data System (ADS)
Jakimiec, J.; Tomczak, M.
2012-06-01
In our recent paper (Jakimiec and Tomczak, Solar Physics 261, 233, 2010) we investigated quasi-periodic oscillations of hard X-rays during the impulsive phase of solar flares. We have come to the conclusion that they are caused by magnetosonic oscillations of magnetic traps within the volume of hard-X-ray (HXR) loop-top sources. In the present paper we investigate four flares that show clear quasi-periodic sequences of the HXR pulses. We also describe our phenomenological model of oscillating magnetic traps to show that it can explain the observed properties of the HXR oscillations. The main results are the following: i) Low-amplitude quasi-periodic oscillations occur before the impulsive phase of some flares. ii) The quasi-periodicity of the oscillations can change in some flares. We interpret this as being due to changes of the length of oscillating magnetic traps. iii) During the impulsive phase a significant part of the energy of accelerated (non-thermal) electrons is deposited within a HXR loop-top source. iv) The quick development of the impulsive phase is due to feedback between the pressure pulses by accelerated electrons and the amplitude of the magnetic-trap oscillation. v) The electron number density and magnetic field strength values obtained for the HXR loop-top sources in several flares fall within the limits of N?(2 - 15)×1010 cm-3, B?(45 - 130) gauss. These results show that the HXR quasi-periodic oscillations contain important information about the energy release in solar flares.
Quasi-periodic modulation of equatorial noise intensity
NASA Astrophysics Data System (ADS)
Nemec, Frantisek; Santolik, Ondrej; Hrbackova, Zuzana; Pickett, Jolene S.; Cornilleau-Wehrlin, Nicole
2015-04-01
Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed routinely in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field. Although their harmonic structure, which is characteristic of the proton cyclotron frequency in the source region has been known for a couple of decades, they were generally believed to be continuous in time. The analysis of more than 2000 EN events observed by the STAFF-SA and WBD instruments on board the Cluster spacecraft reveals that this is not always the case, with about 5% of events exhibiting a clear quasi-periodic (QP) modulation of the wave intensity. We perform a systematic analysis of these events, and we discuss possible mechanisms of the QP intensity modulation. It is shown that the events occur usually in the noon-to-dawn magnetic local time sector, and their occurrence seems to be related to the periods of increased geomagnetic activity. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN were identified in about half of the events. These ULF pulsations might modulate the EN wave intensity, similarly as they modulate the intensity of formerly reported VLF whistler-mode QP events.
Quasi-Periodic Variably Polarizing Undulator at HiSOR
NASA Astrophysics Data System (ADS)
Sasaki, S.; Miyamoto, A.; Goto, K.; Arita, M.; Okuda, T.; Mitsuyasu, T.; Fujioka, K.; Namatame, H.; Taniguchi, M.
2013-03-01
A 1.8-m-long 78-mm-period quasi-periodic APLPE-II undulator was installed in the 700-MeV HiSOR storage ring of Hiroshima Synchrotron Radiation Center. At the minimum gap, achievable lowest photon energies are 3.1 eV, 6.5 eV, and 4.8 eV for horizontal linear, vertical linear, and circular polarization, respectively. Observed photon energies of fundamental and higher harmonic radiations are in good agreement with those of model calculations using measured magnetic field of undulator and the HiSOR beam parameters. Also, observed flux through a slit and a grating monochromator was more than twice larger than that from previously installed 100-mm-period helical undulator for the whole range of radiation spectra. The feedforward COD correction was done to avoid the intensity fluctuation of photon beam in other beamlines due to the gap and phase motion of undulator. No fatal effect on the stored electron beam by installing the undulator was observed though a slight beam size change was observed at the minimum gap.
Large deviations for quasi-periodic cocycles with singularities
Pedro Duarte; Silvius Klein
2015-07-10
We derive large deviations type (LDT) estimates for linear cocycles over an ergodic multifrequency torus translation. These models are called quasi-periodic cocycles. We make the following assumptions on the model: the translation vector satisfies a generic Diophantine condition, and the fiber action is given by a matrix valued analytic function of several variables which is not identically singular. The LDT estimates obtained here depend on some uniform measurements on the cocycle. Our general results derived in [9] regarding the continuity properties of the Lyapunov exponents (LE) and of the Oseledets filtration and decompositions are then applicable, and we obtain local weak-Holder continuity of these quantities in the presence of gaps in the Lyapunov spectrum. The main new feature of this work is allowing a cocycle depending on several variables to have singularities, i.e. points of non invertibility. This requires a careful analysis of the set of zeros of certain analytic functions of several variables and of the singularities (i.e. negative infinity values) of pluri-subharmonic functions related to the iterates of the cocycle. A refinement of this method in the one variable case leads to a stronger LDT estimate and in turn to a stronger, nearly-Holder modulus of continuity of the LE, Oseledets filtration and Oseledets decomposition. This is a draft of a chapter in our forthcoming research monograph [9].
Quasi-periodic variations in Doppler velocities of H ? spicules
NASA Astrophysics Data System (ADS)
Khutsishvili, E.; Kulidzanishvili, V.; Kvernadze, T.; Zaqarashvili, T. V.; Kakhiani, V.; Khutsishvili, D.; Sikharulidze, M.
2014-12-01
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.
Are Flare Quasi-periodic Pulsations Signatures of Intermittent Reconnection?
NASA Astrophysics Data System (ADS)
Guidoni, Silvina; Karpen, J. T.; DeVore, C. R.
2013-07-01
Flare quasi-periodic pulsations (QPPs) have been observed over a vast energy spectrum, from radio to hard x-rays. The periodicities of these fine structures range from tens of milliseconds to tens of seconds and suggest highly structured but intermittent energy release. In some cases, the sources of microwaves and thermal hard x-rays are situated near the apex of the flare loop arcades and are not stationary. Although it is unclear whether all the observed varieties of QPPs can be explained via a single, unified process, our recent high-resolution simulations of a breakout eruptive flare (Karpen et al. 2012) indicate that spatially and temporally localized reconnection is a plausible candidate for these bursts of radiation. With our null-tracking capabilities, we follow the creation and evolution of X- and O-type nulls in the flare current sheet and characterize their periodicity. QPPs located at the apex of the flare arcade may result from the interaction of downward-moving islands in the sheet with the arcade below. Each island is composed of highly twisted magnetic field lines that comprise a single reconnected flux tube. Upon arrival at the top of the flare loops, secondary reconnection events between the island and the arcade produce discrete energy release events that could be related to observed QPPs in that region. Different regimes of current-sheet reconnection (slow/fast), island sizes, rates of island coalescence, and rates of reconnection between islands and arcades may all help to explain the variety of energy and time scales exhibited by the flare QPPs.Abstract (2,250 Maximum Characters): Flare quasi-periodic pulsations (QPPs) have been observed over a vast energy spectrum, from radio to hard x-rays. The periodicities of these fine structures range from tens of milliseconds to tens of seconds and suggest highly structured but intermittent energy release. In some cases, the sources of microwaves and thermal hard x-rays are situated near the apex of the flare loop arcades and are not stationary. Although it is unclear whether all the observed varieties of QPPs can be explained via a single, unified process, our recent high-resolution simulations of a breakout eruptive flare (Karpen et al. 2012) indicate that spatially and temporally localized reconnection is a plausible candidate for these bursts of radiation. With our null-tracking capabilities, we follow the creation and evolution of X- and O-type nulls in the flare current sheet and characterize their periodicity. QPPs located at the apex of the flare arcade may result from the interaction of downward-moving islands in the sheet with the arcade below. Each island is composed of highly twisted magnetic field lines that comprise a single reconnected flux tube. Upon arrival at the top of the flare loops, secondary reconnection events between the island and the arcade produce discrete energy release events that could be related to observed QPPs in that region. Different regimes of current-sheet reconnection (slow/fast), island sizes, rates of island coalescence, and rates of reconnection between islands and arcades may all help to explain the variety of energy and time scales exhibited by the flare QPPs.
On the Quasi-Periodic Oscillations of Magnetars
A. Colaiuda; H. Beyer; K. D. Kokkotas
2009-02-11
We study torsional Alfv\\'en oscillations of magnetars, i.e., neutron stars with a strong magnetic field. We consider the poloidal and toroidal components of the magnetic field and a wide range of equilibrium stellar models. We use a new coordinate system (X,Y), where $X=\\sqrt{a_1} \\sin \\theta$, $Y=\\sqrt{a_1}\\cos \\theta$ and $a_1$ is the radial component of the magnetic field. In this coordinate system, the 1+2-dimensional evolution equation describing the quasi-periodic oscillations, QPOs, see Sotani et al. (2007), is reduced to a 1+1-dimensional equation, where the perturbations propagate only along the Y-axis. We solve the 1+1-dimensional equation for different boundary conditions and open magnetic field lines, i.e., magnetic field lines that reach the surface and there match up with the exterior dipole magnetic field, as well as closed magnetic lines, i.e., magnetic lines that never reach the stellar surface. For the open field lines, we find two families of QPOs frequencies; a family of "lower" QPOs frequencies which is located near the X-axis and a family of "upper" frequencies located near the Y-axis. According to Levin (2007), the fundamental frequencies of these two families can be interpreted as the turning points of a continuous spectrum. We find that the upper frequencies are constant multiples of the lower frequencies with a constant equaling 2n+1. For the closed lines, the corresponding factor is n+1 . By these relations, we can explain both the lower and the higher observed frequencies in SGR 1806-20 and SGR 1900+14.
Modelling of quasi-periodic oscillations with wave packets
NASA Astrophysics Data System (ADS)
Alpar, M. A.; Yilmaz, A.
1997-08-01
Model dispersion relations are introduced to explore power spectra of the normal-branch (NB) and horizontal-branch (HB) quasi-periodic oscillations (QPOs; for reviews see Van der Klis (1989)[ARA&A, 27, 517], (1992) [Proc. of NATO ASI X-Ray Binaries and Recycled Pulsars, eds. E.P.J. Van den Heuvel & S.A. Rappaport, Kluwer, Dordrecht], (1995)[Proc. of NATO ASI The Lives of the Neutron Stars, eds. M.A. Alpar, Ümit Kizilo?lu, & J. van Paradijs, Kluwer, Dordrecht]) of low mass X-ray binaries (LMXBs) in terms of wave packets and to illustrate the presence of frequency bands around the Kepler and beat frequencies. For the NB QPOs wave packets of sound waves in a thick middle disk state, with frequencies determined by the rotation frequency, have wavelengths comparable to the size of the middle disk. For Z-sources on the HB, the wave packets result from disturbances in the inner disk induced by the neutron star magnetic field which rotates at the beat frequency with respect to the inner disk. For both the NB and the HB QPOs, we construct simple model dispersion relations, and show that the QPO peaks in the observed power spectra correspond to reasonable wavelengths and system parameters. The kilohertz QPOs, which were discovered after the original version of this paper was submitted, are also discussed as a possible realization of the Kepler and beat frequency bands. Problems of integrating the kHz and HB QPOs in a disk model are briefly noted. It is tentatively suggested that supersonic and wave propagation regions of the inner disk have complementary functions for the origin of kHz and HB QPOs respectively.
Quasi-Periodicity in Medieval and Islamic architecture and ornament , Helmer Aslaksen2
Aslaksen, Helmer
Quasi-Periodicity in Medieval and Islamic architecture and ornament Ser Zheng1 , Helmer Aslaksen2 1 Medieval Islamic tilings are examples of aperiodic and quasiperiodic tilings. The tilings have five- or ten regarding quasi-periodicity in Medieval Islamic tilings. We will focus on three properties: the method
Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP
Barcelona, Universitat de
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
Normal form for a quasi-periodic perturbation of the Sun-Jupiter RTBP
Barcelona, Universitat de
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
Quasi-periodic electron bursts in the Jovian magnetosphere
NASA Astrophysics Data System (ADS)
Steffl, A. J.; Shinn, A. B.
2012-12-01
In early 2007, the New Horizons spacecraft flew through the Jovian magnetosphere on the dusk side. During the flyby, the Alice FUV spectrograph proved that in addition to detecting FUV photons, it was also quite effective at detecting MeV electrons, which can penetrate the relatively thin instrument housing and interact with the microchannel plate detector. Radiation modeling shows that Alice is sensitive primarily to electrons with energies between 1-8 MeV. Alice cannot determine the spatial distribution of these MeV electrons, nor does it have any energy resolution, but it does have large count rates (up to 15000 counts/s) and a time resolution of 1s—the highest of any electron detector yet flown to Jupiter. Along New Horizons' trajectory from 60 R_J upstream of Jupiter to closest approach at 32 R_J on the dusk side to 60 R_J downstream of Jupiter, we find the flux of MeV electrons to be highly variable on timescales of minutes to hours. There are numerous factor of two changes in electron flux (both increases and decreases) that occur over 50-100s. Frequently, though not always, the MeV electron flux exhibits quasi-periodic variations with timescales of 1-3 minutes. The amplitude of these bursts can vary, sometimes abruptly, from a few percent to factors of several. We also see evidence of larger amplitude 20-45 minute QP bursts with smaller amplitude 1-3 minute bursts superimposed. During two incidences of particularly strong 1-3 minute QP bursts, we find the magnetic field lines passing through the spacecraft map back to Jupiter's ionosphere just inside the main auroral oval to the same location where 1-3 minute QP flares have been seen in the FUV aurora. We therefore suggest that these auroral flares are not caused by pulsed reconnection at the dayside magnetopause, as has been proposed, but rather by some acceleration mechanism internal to the magnetosphere.
Quasi-Periodic Pulsations with Varying Period in Multi-Wavelength Observations of an X-class Flare
NASA Astrophysics Data System (ADS)
Huang, Jing; Tan, Baolin; Zhang, Yin; Karlický, Marian; Mészárosová, Hana
2014-08-01
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.
Quasi-periodic pulsations with varying period in multi-wavelength observations of an X-class flare
Huang, Jing; Tan, Baolin; Zhang, Yin [Key Laboratory of Solar Activities, National Astronomical Observatories Chinese Academy of Sciences, Beijing 100012 (China); Karlický, Marian; Mészárosová, Hana, E-mail: huangj@nao.cas.cn [Astronomical Institute of the Academy of Sciences of the Czech Republic, CZ-25165 Ond?ejov (Czech Republic)
2014-08-10
This work presents an interesting phenomenon of the period variation in quasi-periodic pulsations (QPPs) observed during the impulsive phase of a coronal mass ejection-related X1.1 class flare on 2012 July 6. The period of QPPs was changed from 21 s at soft X-rays (SXR) to 22-23 s at microwaves, to ?24 s at extreme ultraviolet emissions (EUV), and to 27-32 s at metric-decimetric waves. The microwave, EUV, and SXR QPPs, emitted from flare loops of different heights, were oscillating in phase. Fast kink mode oscillations were proposed to be the modulation mechanism, which may exist in a wide region in the solar atmosphere from the chromosphere to the upper corona or even to the interplanetary space. Changed parameters of flare loops through the solar atmosphere could result in the varying period of QPPs at different wavelengths. The first appearing microwave QPPs and quasi-periodic metric-decimetric type III bursts were generated by energetic electrons. This may imply that particle acceleration or magnetic reconnection were located between these two non-thermal emission sources. Thermal QPPs (in SXR and EUV emissions) occurred later than the nonthermal ones, which would suggest a some time for plasma heating or energy dissipation in flare loops during burst processes. At the beginning of flare, a sudden collapse and expansion of two separated flare loop structures occurred simultaneously with the multi-wavelength QPPs. An implosion in the corona, including both collapse and expansion of flare loops, could be a trigger of loop oscillations in a very large region in the solar atmosphere.
Normal--internal resonances in quasi--periodically forced oscillators: a conservative approach
is a skew--product flow with a quasi--periodic driving with n basic frequencies. The dynamics of the forced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 Reduction to an autonomous system on a covering space
All optical Schmitt trigger based on nonlinear quasi periodic photonic crystals
NASA Astrophysics Data System (ADS)
Teimourpour, Mohammad Hosain
2011-11-01
All optical Schmitt trigger based on Kerr bistability in quasi periodic Thue-Morse photonic crystals is investigated. Finite difference time domain is used to investigate the Schmitt trigger operation in one dimensional nonlinear Thue-Morse Photonic crystals.
All optical Schmitt trigger based on nonlinear quasi periodic photonic crystals
NASA Astrophysics Data System (ADS)
Teimourpour, Mohammad Hosain
2012-02-01
All optical Schmitt trigger based on Kerr bistability in quasi periodic Thue-Morse photonic crystals is investigated. Finite difference time domain is used to investigate the Schmitt trigger operation in one dimensional nonlinear Thue-Morse Photonic crystals.
Quasi-periodic Green's functions of the Helmholtz and Laplace equations
Alexander Moroz
2006-01-01
A classical problem of free-space Green's function G0Lambda 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 G0Lambda and for the expansion coefficients DL of G0Lambda in the basis of regular (cylindrical in
Shell Collision Induced Kilo-Hertz Quasi-Periodic Oscillation in X-Ray Binaries
Gong, Bi-Ping
2013-01-01
Twin kilo-Hertz Quasi-periodic oscillation with ratio 3/2 has been found in some compact sources, which is believed to be related with their innermost regions of accretion disks, and hence carrying information of gravity in strong regime. However, more complicated phenomena have been revealed, e.g., the twin kilo-Hertz Quasi-periodic oscillation of 4U 1820-20 start increasing at certain spectral state and then saturate upon reaching certain level. Moreover, such quasi-periodic oscillation is not uniform and has multiple peaks, which displays random feature. This letter suggests that these challenges could be easy to understand if the quasi-periodic oscillation originates in jets of compact objects. With a seed periodicity originating in either neutron star spin or accretion, shell collision develops in jet. The corresponding twin kilo-Hertz quasi-periodic oscillations automatically carry random feature, vary in frequency; and couple with luminosity, spectral properties, which well account for the observation ...
Dipolar mode localization and spectral gaps in quasi-periodic arrays of ferromagnetic nanoparticles
NASA Astrophysics Data System (ADS)
Forestiere, Carlo; Miano, Giovanni; Serpico, Claudio; D'Aquino, Massimiliano; Dal Negro, Luca
2009-06-01
In this paper we study the spectral, localization, and dispersion properties of the ferromagnetic dipolar modes around a stable, saturated, and spatially uniform equilibrium in quasi-periodically modulated arrays of ferromagnetic nanoparticles based on the Fibonacci sequence. The Fibonacci sequence is the chief example of deterministic quasi-periodic order. The problem is reduced to the study of a linear-generalized eigenvalue equation for a suitable Hermitian operator connected to the micromagnetic effective field, which accounts for the magnetostatic, anisotropy, and Zeeman interactions. The coupling with a weak applied magnetic field, varying sinusoidally in time, is dealt with and the role of the losses is highlighted. By calculating the resonance frequencies and eigenmodes of the Fibonacci arrays we demonstrate the presence of large spectral gaps and strongly localized modes and we evaluate the pseudodispersion diagrams. The magnetization oscillation modes in quasi-periodic arrays of magnetic nanoparticles show, at microwave frequencies, behaviors that are very similar to those shown, at optical frequencies, by plasmon modes in quasi-periodic arrays of metal nanoparticles. The presence of band gaps and strongly localized states in magnetic nanoparticle arrays based on quasi-periodic order may have an impact in the design and fabrication of new microwave nanodevices and magnetic nanosensors.
Exciton photoluminescence in resonant quasi-periodic Thue-Morse quantum wells.
Hsueh, W J; Chang, C H; Lin, C T
2014-02-01
This Letter investigates exciton photoluminescence (PL) in resonant quasi-periodic Thue-Morse quantum wells (QWs). The results show that the PL properties of quasi-periodic Thue-Morse QWs are quite different from those of resonant Fibonacci QWs. The maximum and minimum PL intensities occur under the anti-Bragg and Bragg conditions, respectively. The maxima of the PL intensity gradually decline when the filling factor increases from 0.25 to 0.5. Accordingly, the squared electric field at the QWs decreases as the Thue-Morse QW deviates from the anti-Bragg condition. PMID:24487847
Xavier Calmet; Dionysios Fragkakis; Nina Gausmann
2012-01-21
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.
W. -M. Wang
2008-05-24
We prove that the $1-d$ quantum harmonic oscillator is stable under spatially localized, time quasi-periodic perturbations on a set of Diophantine frequencies of positive measure. This proves a conjecture raised by Enss-Veselic in their 1983 paper \\cite{EV} in the general quasi-periodic setting. The motivation of the present paper also comes from construction of quasi-periodic solutions for the corresponding nonlinear equation.
Dripping handrails and the quasi-periodic oscillations of the AM Herculis objects
NASA Technical Reports Server (NTRS)
Steiman-Cameron, Thomas Y.; Young, Karl; Scargle, Jeffrey D.; Crutchfield, James P.; Imamura, James N.; Wolff, Michael T.; Wood, Kent S.
1994-01-01
AM Her objects exhibit periodic, quasi-periodic, and aperiodic variability on timescales ranging from seconds to years. Here, we investigate a process for the production of aperiodic and quasi-periodic accretion rate fluctuations. We consider the nonlinear dynamical model known as the dripping handrail (DHR). The DHR, basically a model for certain types of spatially extended systems and loosely based on water condensing on and dripping off a handrail, has recently been used as a model for the quasi-periodic oscillations (QPO) and very low frequency noise of the low-mass X-ray binary Sco X-1. Here, we show that (1) the DHR is a robust QPO generation process in that it leads to QPO production under a wide range of conditions and assumptions; (2) the phenomenology of the DHR is consistent with the observed aperiodic and quasi-periodic varibility of the AM Her QPO source VV Pup over timescales ranging from 16 ms to 20 s; and (3) a single DHR model can produce both broadband QPOs and features with quality Q greater than 20 as observed in several AM Her QPO sources.
Quasi-Periodic Brightness Oscillations from Accreting Neutron Stars and Black Holes
Miller, Cole
of quasiperiodic brightness oscillations (QPOs) from black holes and weakly magnetic neutron stars, and what we canQuasi-Periodic Brightness Oscillations from Accreting Neutron Stars and Black Holes M. Coleman frequencies of variation in the X-ray emission from accreting neutron stars and black holes. These frequencies
RESONANCE TONGUES AND SPECTRAL GAPS IN QUASI-PERIODIC SCHRODINGER OPERATORS WITH ONE
Puig. Joaquim
RESONANCE TONGUES AND SPECTRAL GAPS IN QUASI-PERIODIC SCHRÂ¨ODINGER OPERATORS WITH ONE OR MORE and the Lyapunov exponent to detect open and collapsed gaps, resonance tongues and the measure of the spectrum. We-Periodic Cocycles and Skew-products, Spectral Gaps, Resonance Tongues, Rotation number, Lyapunov exponent, Nu
RESONANCE TONGUES IN THE QUASI-PERIODIC HILL-SCHRODINGER EQUATION WITH THREE
PolitÃ¨cnica de Catalunya, Universitat
RESONANCE TONGUES IN THE QUASI-PERIODIC HILL-SCHRÂ¨ODINGER EQUATION WITH THREE FREQUENCIES JOAQUIM number and the Lyapunov exponent in order to detect open and collapsed gaps, res- onance tongues. Our tongues get out of control. They are restless and evil, and always spreading deadly poison". (James 3, 6
Resonance tongues and instability pockets in the quasi--periodic Hill--Schr odinger equation
Puig. Joaquim
Resonance tongues and instability pockets in the quasi--periodic Hill--SchrË? odinger equation Henk the following. The resonance `tongues' with rotation number 1 2 hk; !i; k 2 Z d have C 1 Âboundary curves. Our results are obtained with respect to the geometry of the tongues. One result reÂ gards transversality
Resonance tongues and instability pockets in the quasi{periodic Hill{Schrodinger equation
Barcelona, Universitat de
Resonance tongues and instability pockets in the quasi{periodic Hill{Schrodinger equation Henk values of jbj the following holds. The `tongues' with rotation number 1 2 hk; !i; k 2 Z d ; have C 1, such as a criterion for transversality of the tongue boundaries at b = 0, the occurrence of instability pockets in R p
Linares, M.
We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480–2446, located in the globular cluster ...
NASA Astrophysics Data System (ADS)
Lei, Yuxiong; Chen, Zheng; Li, Liangliang
2015-05-01
Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures were investigated in this study. The periodic and quasi-periodic structures were designed based on Fibonacci sequence and golden ratio. Ni nanowires arrays were electrodeposited in anodic aluminum oxide (AAO) templates with patterned Cu electrodes, and then the AAO templates were attached to the coplanar waveguide lines fabricated on quartz substrate for measurement. The S21 of both periodic and quasi-periodic structure-patterned Ni nanowire arrays showed an extra absorption peak besides the absorption peak due to the ferromagnetic resonance of Ni nanowires. The frequency of the absorption peak caused by the patterned structure could be higher than 40 GHz when the length and arrangement of the structural units were modified. In addition, the frequency of the absorption peak due to the quasi-periodic structure was calculated based on a simple analytical model, and the calculated value was consistent with the measured one. The experimental data showed that it could be a feasible approach to tune the performance of microwave devices by patterning ferromagnetic nanowires.
Quasi-periodic oscillations in a network of four Rossler chaotic oscillators
Alexander P. Kuznetsov; Igor R. Sataev; Yuliya V. Sedova; Ludmila V. Turukina
2014-10-29
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.
Period doubling and reducibility in the quasi-periodically forced logistic map
Barcelona, Universitat de
Period doubling and reducibility in the quasi-periodically forced logistic map Angel Jorba1 , Pau of having a periodic invariant curve, its period and its reducibility. This reveals that the parameter values for which the invariant curve doubles its period are contained in regions of the parameter space
A MODEL FOR QUASI-PERIODIC SIGNALS WITH APPLICATION TO RAIN ESTIMATION FROM MICROWAVE LINK GAIN
Loeliger, Hans-Andrea
A MODEL FOR QUASI-PERIODIC SIGNALS WITH APPLICATION TO RAIN ESTIMATION FROM MICROWAVE LINK GAIN (for a single microwave link), which is based on a dynamical model of the attenuation with- out rain from attenuation due to rain [1]. From this observation, it has been suggested to estimate rain- fall
WEAKLY CONNECTED QUASI-PERIODIC OSCILLATORS, FM INTERACTIONS, AND MULTIPLEXING IN THE BRAIN
Izhikevich, Eugene
WEAKLY CONNECTED QUASI-PERIODIC OSCILLATORS, FM INTERACTIONS, AND MULTIPLEXING IN THE BRAIN EUGENE interact via phase deviations. This mechanism resembles that of the FM radio, with a shared feature--multiplexing, multiplexing, oscillatory neurocomputer, thalamo- cortical system AMS subject classifications. 92B20, 34C, 34D
Quasi-periodic pulsations in solar hard X-ray and microwave flares
NASA Technical Reports Server (NTRS)
Kosugi, Takeo; Kiplinger, Alan L.
1986-01-01
For more than a decade, various studies have pointed out that hard X-ray and microwave time profiles of some solar flares show quasi-periodic fluctuations or pulsations. Nevertheless, it was not until recently that a flare displaying large amplitude quasi-periodic pulsations in X-rays and microwaves was observed with good spectral coverage and with a sufficient time resolution. The event occurred on June 7, 1980, at approximately 0312 UT, and exhibits seven intense pulses with a quasi-periodicity of approximately 8 seconds in microwaves, hard X-rays, and gamma-ray lines. On May 12, 1983, at approximately 0253 UT, another good example of this type of flare was observed both in hard X-rays and in microwaves. Temporal and spectral characteristics of this flare are compared with the event of June 7, 1980. In order to further explore these observational results and theoretical scenarios, a study of nine additional quasi-periodic events were incorporated with the results from the two flares described. Analysis of these events are briefly summarized.
NASA Astrophysics Data System (ADS)
Li, Q.; Wang, Y.
2012-04-01
The formation and quasi-periodic behavior of outer spiral rainbands in a tropical cyclone simulated in the cloud-resolving tropical cyclone model version 4 (TCM4) are analyzed. The outer spiral rainbands in the simulation are preferably initiated near the 60-km radius, or roughly about three times the radius of maximum wind (RMW). After initiation, they generally propagate radially outward with a mean speed of ~5 m s-1. They are reinitiated quasi-periodically with a period between 22 h and 26 h in the simulation. While the inner spiral rainbands, which form within a radius of about three times the RMW, are characterized by the convectively coupled vortex Rossby waves (VRWs), the formation of outer spiral rainbands, namely, rainbands formed outside a radius of about three times the RMW, is much more complicated. It is shown that outer spiral rainbands are triggered by the inner-rainband remnants immediately outside the rapid filamentation zone and inertial instability in the upper troposphere. The preferred radial location of initiation of outer spiral rainbands is understood as a balance between the suppression of deep convection by rapid filamentation and the favorable dynamical and thermodynamic conditions for initiation of deep convection. The quasi-periodic occurrence of outer spiral rainbands is found to be associated with the boundary layer recovery from the effect of convective downdrafts and the consumption of convective available potential energy (CAPE) by convection in the previous outer spiral rainbands. Specifically, once convection is initiated and organized in the form of outer spiral rainbands, it will produce strong downdrafts and consume CAPE. These effects weaken convection near its initiation location. As the rainband propagates outward further, the boundary layer air near the original location of convection initiation takes about 10 h to recover by extracting energy from the underlying ocean. Convection and thus new outer spiral rainbands will be initiated near a radius of about three times the RMW. This will be followed by a similar outward propagation and the subsequent boundary layer recovery, leading to a quasi-periodic occurrence of outer spiral rainbands. In response to the quasi-periodic appearance of outer spiral rainbands, the storm intensity experiences a similar quasi-periodic oscillation with its intensity or intensification rate starting to decrease after about 4 h of the initiation of an outer spiral rainband. The results provide an alternative explanation or one of the mechanisms that are responsible for the quasi-periodic (quasi-diurnal) variation in the intensity and in the area of outflow-layer cloud canopy of observed tropical cyclones.
Quasi-periodic Green's functions of the Helmholtz and Laplace equations
NASA Astrophysics Data System (ADS)
Moroz, Alexander
2006-09-01
A classical problem of free-space Green's function G0? representations of the Helmholtz equation is studied in various quasi-periodic cases, i.e., when an underlying periodicity is imposed in less dimensions than is the dimension of an embedding space. Exponentially convergent series for the free-space quasi-periodic G0? and for the expansion coefficients DL of G0? in the basis of regular (cylindrical in two dimensions and spherical in three dimension (3D)) waves, or lattice sums, are reviewed and new results for the case of a one-dimensional (1D) periodicity in 3D are derived. From a mathematical point of view, a derivation of exponentially convergent representations for Schlömilch series of cylindrical and spherical Hankel functions of any integer order is accomplished. Exponentially convergent series for G0? and lattice sums DL hold for any value of the Bloch momentum and allow G0? to be efficiently evaluated also in the periodicity plane. The quasi-periodic Green's functions of the Laplace equation are obtained from the corresponding representations of G0? of the Helmholtz equation by taking the limit of the wave vector magnitude going to zero. The derivation of relevant results in the case of a 1D periodicity in 3D highlights the common part which is universally applicable to any of remaining quasi-periodic cases. The results obtained can be useful for the numerical solution of boundary integral equations for potential flows in fluid mechanics, remote sensing of periodic surfaces, periodic gratings, and infinite arrays of resonators coupled to a waveguide, in many contexts of simulating systems of charged particles, in molecular dynamics, for the description of quasi-periodic arrays of point interactions in quantum mechanics, and in various ab initio first-principle multiple-scattering theories for the analysis of diffraction of classical and quantum waves.
Quasi-periodic Green's functions of the Helmholtz and Laplace equations
Alexander Moroz
2006-04-24
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.
Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113
Ackermann, M; Albert, A; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Gonzalez, J Becerra; Bellazzini, R; Bissaldi, E; Blandford, R D; Bloom, E D; Bonino, R; Bottacini, E; Bregeon, J; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caputo, R; Caragiulo, M; Caraveo, P A; Cavazzuti, E; Cecchi, C; Chekhtman, A; Chiang, J; Chiaro, G; Ciprini, S; Cohen-Tanugi, J; Conrad, J; Cutini, S; D'Ammando, F; De Angelis, A; De Palma, F; Desiante, R; Di Venere, L; Dominguez, A; Drell, P S; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Fuhrmann, L; Fukazawa, Y; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giommi, P; Giordano, F; Giroletti, M; Godfrey, G; Green, D; Grenier, I A; Grove, J E; Guiriec, S; Harding, A K; Hays, E; Hewitt, J W; Hill, A B; Horan, D; Jogler, T; Johannesson, G; Johnson, A S; Kamae, T; Kuss, M; Larsson, S; Latronico, L; Li, J; Li, L; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Magill, J; Maldera, S; Manfreda, A; Max-Moerbeck, W; Mayer, M; Mazziotta, M N; Mcenery, J E; Michelson, P F; Mizuno, T; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nuss, E; Ohno, M; Ohsugi, T; Ojha, R; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Pearson, T J; Perkins, J S; Perri, M; Pesce-Rollins, M; Petrosian, V; Piron, F; Pivato, G; Porter, T A; Raino', S; Rando, R; Razzano, M; Readhead, A; Reimer, A; Reimer, O; Schulz, A; Sgro', C; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Suson, D J; Takahashi, H; Thayer, J B; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Troja, E; Uchiyama, Y; Vianello, G; Wood, K S; Wood, M; Zimmer, S; Berdyugin, A; Corbet, R H D; Hovatta, T; Lindfors, E; Nilsson, K; Reinthal, R; Sillanpaa, A; Stamerra, A; Takalo, L O; Valtonen, M J
2015-01-01
We report for the first time a gamma-ray and multiwavelength nearly-periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope (LAT) we have discovered an apparent quasi-periodicity in the gamma-ray flux (E>100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/- 0.08 year-period gamma-ray cycle, seen in 3.5 oscillation maxima observed, is corroborated by correlated oscillations observed in radio and optical fluxes, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle appearing in sim 10 years of data has a similar period, while the 15 GHz oscillation is less regular. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.
Towards modeling quasi-periodic oscillations of microquasars with oscillating slender tori
Mazur, G P; Johansson, M; Sramkova, E; Torok, G; Bakala, P; Abramowicz, M A
2013-01-01
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.
Broadband asymmetric acoustic transmission by a plate with quasi-periodic surface ridges
Li, Chunhui; Ke, Manzhu Ye, Yangtao; Xu, Shengjun; Qiu, Chunyin; Liu, Zhengyou
2014-07-14
In this paper, an acoustic system with broadband asymmetric transmission is designed and fabricated, which consists of a water-immersed aluminum plate engraved with quasi-periodically-patterned ridges on single surface. It demonstrates that when the acoustic waves are launched into the system from the structured side, they can couple into the Lamb modes in the plate efficiently and attain a high transmission; on the contrary, when the waves are incident from the opposite flat side, the coupling is weak, and the transmission is low. Superior to systems with periodic patterning, this quasi-periodically-patterned system has a broad working frequency range due to the collective contributions from the multiple diffractions specific to the structure.
The localization of light in a 2D quasi-periodic coherently prepared atomic medium
NASA Astrophysics Data System (ADS)
Wang, C. F.; Cheng, J.; Chen, B.
2015-02-01
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.
Quasi-Periodicity in global solar radio flux at metric wavelengths during Noise Storms
NASA Astrophysics Data System (ADS)
Sundaram, G. A. Shanmugha; Subramanian, K. R.
2004-08-01
We present observational results from studying the quasi-periodicities in global solar radio flux during periods of enhanced noise storm activity, over durations of ~4 hr a day (`intra-day' variations), observed at 77.5 MHz with the newly commissioned log-periodic array tracking system at the Gauribidanur Radio Observatory. Positional information on the storm centers was obtained with the radio imaging data from the Nan\\c cay Radio Heliograph (NRH), while their active region counterparts on the photosphere (and the overlying chromosphere ) were located from the H? images of the Big Bear Solar Observatory. The quasi-periodicity in flux was found to be 110 min, with the fluctuation in flux being 3(+/-1.5) solar flux units (s.f.u.). The results of such pulsations are interpreted qualitatively as evidence for coronal seismology.
Quasi-periodic oscillations of the magnetopause during northward sheath magnetic field
NASA Technical Reports Server (NTRS)
Kokubun, S.; Kawano, H.; Nakamura, M.; Yamamoto, T.; Tsuruda, K.; Hayakawa, H.; Matsuoka, A.; Frank, L. A.
1994-01-01
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).
Wave propagation in one-dimensional solid-fluid quasi-periodic and aperiodic phononic crystals
NASA Astrophysics Data System (ADS)
Chen, A.-Li; Wang, Yue-Sheng; Zhang, Chuanzeng
2012-02-01
The propagation of the elastic waves in one-dimensional (1D) solid-fluid quasi-periodic phononic crystals is studied by employing the concept of the localization factor, which is calculated by the transfer matrix method. The solid-fluid interaction effect at the interfaces between the solid and the fluid components is considered. For comparison, the periodic systems and aperiodic Thue-Morse sequence are also analyzed in this paper. The splitting phenomenon of the pass bands and bandgaps are discussed for these 1D solid-fluid systems. At last the influences of the material impedance ratios on the band structures of the 1D solid-fluid quasi-periodic phononic crystals arranged as Fibonacci sequence are discussed.
Belenov, A.F.; Ponomarenko, P.V.; Sinitsyn, V.G.; Yampol`skii, Yu.M.
1994-06-01
The results of an experimental study of quasi-periodic variations of the Doppler shift (DS) of decimeter-wave signals scattered by artificial ionospheric turbulence are presented. It is suggested that ionospheric MHD waves of natural origin are a possible cause of such variations. The amplitude of the magnetic component of such waves that leads to observable values of DS variations is estimated to be 1{gamma}.
Quasi-periodic solutions of nonlinear beam equation with prescribed frequencies
NASA Astrophysics Data System (ADS)
Chang, Jing; Gao, Yixian; Li, Yong
2015-05-01
Consider the one dimensional nonlinear beam equation utt + uxxxx + mu + u3 = 0 under Dirichlet boundary conditions. We show that for any m > 0 but a set of small Lebesgue measure, the above equation admits a family of small-amplitude quasi-periodic solutions with n-dimensional Diophantine frequencies. These Diophantine frequencies are the small dilation of a prescribed Diophantine vector. The proofs are based on an infinite dimensional Kolmogorov-Arnold-Moser iteration procedure and a partial Birkhoff normal form.
Quasi-periodic oscillations in the bright Galactic bulge X-ray source GX 340 + 0
NASA Technical Reports Server (NTRS)
Van Paradijs, J.; Hasinger, G.; Sztajno, M.; Lewin, W. H. G.; Van Der Klis, M.
1988-01-01
Quasi-periodic oscillations (QPOs) have been detected in the X-ray flux of the bright Galactic bulge X-ray source GX 340+0. The QPO, the associated red noise, and their relation to the spectral state of the source are described. The QPO behavior is found to be similar to that seen in Cyg X-2 and GX 5-1.
Periodic and quasi-periodic solutions for multi-instabilities involved in brake squeal
N. Coudeyras; S. Nacivet; J.-J. Sinou
2009-01-01
This paper is devoted to the computation of nonlinear dynamic steady-state solutions of autonomous systems subjected to multi-instabilities and proposes a new nonlinear method for predicting periodic and quasi-periodic solutions intended for application to the disc brake squeal phenomenon. Firstly, finite element models of a pad and a disc are reduced to include only their contact nodes by using a
On quasi-periodic solutions for generalized Boussinesq equation with quadratic nonlinearity
NASA Astrophysics Data System (ADS)
Shi, Yanling; Xu, Junxiang; Xu, Xindong
2015-02-01
In this paper, one-dimensional generalized Boussinesq equation: utt - uxx + (u2 + uxx)xx = 0 with boundary conditions ux(0, t) = ux(?, 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.
Band, D.L.
1986-12-01
The infrared, optical and x-ray continua from radio quiet active galactic nuclei (AGN) are explained by a compact non-thermal source surrounding a thermal ultraviolet emitter, presumably the accretion disk around a supermassive black hole. The ultraviolet source is observed as the ''big blue bump.'' The flat (..cap alpha.. approx. = .7) hard x-ray spectrum results from the scattering of thermal ultraviolet photons by the flat, low energy end of an electron distribution ''broken'' by Compton losses; the infrared through soft x-ray continuum is the synchrotron radiation of the steep, high energy end of the electron distribution. Quantitative fits to specific AGN result in models which satisfy the variability constraints but require electron (re)acceleration throughout the source. 11 refs., 1 fig.
Quasi-Periodic Solutions of (3+1) Generalized BKP Equation By Using Riemann Theta Functions
Seçil Demiray; Filiz Ta?can Güney
2014-09-24
This paper is focused on quasi-periodic wave solutions of (3+1) generalized BKP equation. Because of some difficulties in calculations of N=3 periodic solutions, hardly ever has there been a study on these solutions by using Rieamann theta function. In this study, we obtain one and two periodic wave solutions as well as three periodic wave solutions for (3+1) generalized BKP equation. Moreover we analyse the asymptotic behavior of the periodic wave solutions tend to the known soliton solutions under a small amplitude limit.
THz laser based on quasi-periodic AlGaAs superlattices
Malyshev, K V
2013-06-30
The use of quasi-periodic AlGaAs superlattices as an active element of a quantum cascade laser of terahertz range is proposed and theoretically investigated. A multi-colour emission, having from three to six peaks of optical gain, is found in Fibonacci, Thue-Morse, and figurate superlattices in electric fields of intensity F = 11 - 13 kV cm{sup -1} in the frequency range f = 2 - 4 THz. The peaks depend linearly on the electric field, retain the height of 20 cm{sup -1}, and strongly depend on the thickness of the AlGaAs-layers. (lasers)
QUASI-PERIODICITIES OF THE BL LACERTAE OBJECT PKS 2155–304
Sandrinelli, A.; Treves, A. [Università degli Studi dell' Insubria, Via Valleggio 11, I-22100 Como (Italy); Covino, S., E-mail: asandrinelli@yahoo.it [INAF-Osservatorio Astronomico di Brera, Via Emilio Bianchi 46, I-23807 Merate (Italy)
2014-09-20
We have searched for periodicities in our VRIJHK photometry of PKS 2155–304, which covers the years 2005-2012. A peak of the Fourier spectrum with high significance is found at T ? 315 days, confirming the recent findings by Zhang et al. The examination of the gamma-ray light curves from the Fermi archives yields a significant signal at ?2T, which, while nominally significant, involves data spanning only ?6T. Assuming a black hole mass of 10{sup 9} M {sub ?}, the Keplerian distance corresponding to the quasi-period T is ?10{sup 16} cm, about 50 Schwarzschild radii.
Analysis of quasi-periodic pore-network structure of centric marine diatom frustules
NASA Astrophysics Data System (ADS)
Cohoon, Gregory A.; Alvarez, Christine E.; Meyers, Keith; Deheyn, Dimitri D.; Hildebrand, Mark; Kieu, Khanh; Norwood, Robert A.
2015-03-01
Diatoms are a common type of phytoplankton characterized by their silica exoskeleton known as a frustule. The diatom frustule is composed of two valves and a series of connecting girdle bands. Each diatom species has a unique frustule shape and valves in particular species display an intricate pattern of pores resembling a photonic crystal structure. We used several numerical techniques to analyze the periodic and quasi-periodic valve pore-network structure in diatoms of the Coscinodiscophyceae order. We quantitatively identify defect locations and pore spacing in the valve and use this information to better understand the optical and biological properties of the diatom.
Quasi-periodic oscillations in low-mass x ray binaries
NASA Technical Reports Server (NTRS)
Lewin, Walter H. G.; Vanparadijs, J.; Vanderklis, M.
1991-01-01
Variability on short time scales in the x-ray flux is a very general property of binary x-ray sources. Not until after the discovery of intensity-dependent quasi-periodic oscillations (QPO) and associated red noise form luminous low-mass x-ray binaries were systematic studies of the shape of the power-spectral components made. A brief account is given of the main developments since this discovery which have led to a new picture of the properties of low-mass x-ray binaries.
A search for quasi-periodic oscillations in 4U/MXB 1735-44
NASA Technical Reports Server (NTRS)
Penninx, Wim; Hasinger, Guenther; Lewin, Walter H. G.; Van Paradijs, Jan; Van Der Klis, Michiel
1989-01-01
A search for quasi-periodic oscillations (QPOs) in 4U/MXB 1735-44 was performed using Exosat observations during which the source was in a horizontal branch of the spectral hardness-intensity diagram for about 8 hr and in a normal branch type of behavior for about 46 hr. No QPOs or low-frequency noise was found in the horizontal branch state. It is suggested that this absence is due to either low luminosity or the fact that the companion in 1735-44 is a main-sequence star.
A review of quasi-periodic oscillations in low-mass X-ray binaries
NASA Technical Reports Server (NTRS)
Lewin, Walter H. G.; Van Paradijs, Jan; Van Der Klis, Michiel
1988-01-01
A review of the quasi-periodic oscillations (QPO) observed in the X-ray flux of low-mass X-ray binaries is presented. In Section 1 a general background is given on galactic populations of accretion-driven X-ray sources. Section 2 contains a description of the methods that have been used to analyze these QPO. In Section 3 the QPO observations are described in some detail. Models for the QPO are considered in Section 4. In Section 5 the time lags observed between QPO at different photon energies and their possible implications for X-ray spectral models are discussed. Conclusions are summarized in Section 6.
Sources of quasi-periodic propagating disturbances above a solar polar coronal hole
Jiao, Fang-Ran; Li, Bo; Huang, Zheng-Hua; Li, Xing; Chandrashekhar, Kalugodu; Mou, Chao-Zhou; Fu, Hui
2015-01-01
Quasi-periodic propagating disturbances (PDs) are ubiquitous in polar coronal holes on the Sun. It remains unclear as to what generates PDs. In this work, we investigate how the PDs are generated in the solar atmosphere by analyzing a fourhour dataset taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We find convincing evidence that spicular activities in the solar transition region as seen in the AIA 304 {\\AA} passband are responsible for PDs in the corona as revealed in the AIA 171 {\\AA} images. We conclude that spicules are an important source that triggers coronal PDs.
Sources of Quasi-periodic Propagating Disturbances above a Solar Polar Coronal Hole
NASA Astrophysics Data System (ADS)
Jiao, Fangran; Xia, Lidong; Li, Bo; Huang, Zhenghua; Li, Xing; Chandrashekhar, Kalugodu; Mou, Chaozhou; Fu, Hui
2015-08-01
Quasi-periodic propagating disturbances (PDs) are ubiquitous in polar coronal holes on the Sun. It remains unclear as to what generates PDs. In this work, we investigate how the PDs are generated in the solar atmosphere by analyzing a four-hour data set taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We find convincing evidence that spicular activities in the solar transition region, as seen in the AIA 304 Å passband, are responsible for PDs in the corona as revealed in the AIA 171 Å images. We conclude that spicules are an important source that triggers coronal PDs.
Electronic band gap and transport in Fibonacci quasi-periodic graphene superlattice
NASA Astrophysics Data System (ADS)
Zhao, Pei-Liang; Chen, Xi
2011-10-01
We investigate electronic band gap and transport in Fibonacci quasi-periodic graphene superlattice. It is found that such structure can possess a zero-k¯ gap which exists in all Fibonacci sequences. Different from Bragg gap, zero-k¯ gap associated with Dirac point is less sensitive to the incidence angle and lattice constants. The defect mode appeared inside the zero-k¯ gap has a great effect on transmission, conductance, and shot noise, which can be applicable to control the electron transport.
Aulova, T V; Kravtsov, Nikolai V; Lariontsev, E G; Chekina, S N
2011-06-30
The synchronisation of periodic self-modulation oscillations in a ring Nd:YAG chip laser under an external periodic signal modulating the pump power has been experimentally investigated. A new quasi-periodic regime of synchronisation of self-modulation oscillations is found. The characteristic features of the behaviour of spectral and temporal structures of synchronised quasi-periodic oscillations with a change in the external signal frequency are studied. (control of laser radiation parameters)
NASA Astrophysics Data System (ADS)
Kamiyama, Kyohei; Inaba, Naohiko; Sekikawa, Munehisa; Endo, Tetsuro
2014-12-01
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.
QUASI-PERIODIC OSCILLATIONS AND BROADBAND VARIABILITY IN SHORT MAGNETAR BURSTS
Huppenkothen, Daniela; Watts, Anna L.; Uttley, Phil; Van der Horst, Alexander J.; Van der Klis, Michiel; Kouveliotou, Chryssa; Goegues, Ersin; Granot, Jonathan; Vaughan, Simon; Finger, Mark H.
2013-05-01
The discovery of quasi-periodic oscillations (QPOs) in magnetar giant flares has opened up prospects for neutron star asteroseismology. However, with only three giant flares ever recorded, and only two with data of sufficient quality to search for QPOs, such analysis is seriously data limited. We set out a procedure for doing QPO searches in the far more numerous, short, less energetic magnetar bursts. The short, transient nature of these bursts requires the implementation of sophisticated statistical techniques to make reliable inferences. Using Bayesian statistics, we model the periodogram as a combination of red noise at low frequencies and white noise at high frequencies, which we show is a conservative approach to the problem. We use empirical models to make inferences about the potential signature of periodic and QPOs at these frequencies. We compare our method with previously used techniques and find that although it is on the whole more conservative, it is also more reliable in ruling out false positives. We illustrate our Bayesian method by applying it to a sample of 27 bursts from the magnetar SGR J0501+4516 observed by the Fermi Gamma-ray Burst Monitor, and we find no evidence for the presence of QPOs in any of the bursts in the unbinned spectra, but do find a candidate detection in the binned spectra of one burst. However, whether this signal is due to a genuine quasi-periodic process, or can be attributed to unmodeled effects in the noise is at this point a matter of interpretation.
Dynamics and spectral theory of quasi-periodic Schrödinger-type operators
S. Jitomirskaya; C. A. Marx
2015-03-19
Quasi-periodic Schr\\"odinger-type operators naturally arise in solid state physics, describing the influence of an external magnetic field on the electrons of a crystal. In the late 1970s, numerical studies for the most prominent model, the almost Mathieu operator (AMO), produced the first example of a fractal in physics known as "Hofstadter's butterfly," marking the starting point for the ongoing strong interest in such operators in both mathematics (several of B. Simon's problems) and physics (e.g. Graphene, quantum Hall effect). Whereas research in the first three decades was focused mainly on unraveling the unusual properties of the AMO and operators with similar structure of potential, in recent years a combination of techniques from dynamical systems with those from spectral theory has allowed for a more "global," model-independent point of view. Intriguing phenomena first encountered for the AMO, notably the appearance of criticality corresponding to purely singular continuous spectrum for a measure theoretically typical realization of the phase, could be tested for prevalence in general models. The intention of this article is to survey the theory of quasi-periodic Schr\\"odinger-type operators attaining this "global" view-point with an emphasis on dynamical aspects of the spectral theory of such operators.
Imaging and Spectral Observations of Quasi-Periodic Pulsations in a Solar Flare
Li, D; Zhang, Q M
2015-01-01
We explore the Quasi-Periodic Pulsations (QPPs) in a solar flare observed by Fermi Gamma-ray Burst Monitor (GBM), Solar Dynamics Observatory (SDO), Solar Terrestrial Relations Observatory (STEREO), and Interface Region Imaging Spectrograph (IRIS) on 2014 September 10. QPPs are identified as the regular and periodic peaks on the rapidly-varying components, which are the light curves after removing the slowly-varying components. The QPPs display only three peaks at the beginning on the hard X-ray (HXR) emissions, but ten peaks on the chromospheric and coronal line emissions, and more than seven peaks (each peak is corresponding to a type III burst on the dynamic spectra) at the radio emissions. An uniform quasi-period about 4 minutes are detected among them. AIA imaging observations exhibit that the 4-min QPPs originate from the flare ribbon, and tend to appear on the ribbon front. IRIS spectral observations show that each peak of the QPPs tends to a broad line width and a red Doppler velocity at C I, O IV, Si ...
New Anomalous Lieb-Robinson Bounds in Quasi-Periodic XY Chains
David Damanik; Marius Lemm; Milivoje Lukic; William Yessen
2014-08-28
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.
Long-term quasi-periodicity of 4U 1636-536 resulting from accretion disc instability
Wisniewicz, Mateusz; Gondek-Rosinska, Dorota; Zdziarski, Andrzej A; Janiuk, Agnieszka
2015-01-01
We present the results of a study of the low-mass X-ray binary 4U 1636-536. We have performed temporal analysis of all available RXTE/ASM, Swift/BAT and MAXI data. We have confirmed the previously discovered quasi-periodicity of ~45 d present during ~2004, however we found it continued to 2006. At other epochs, the quasi-periodicity is only transient, and the quasi-period, if present, drifts. We have then applied a time-dependent accretion disc model to the interval with the significant X-ray quasi-periodicity. For our best model, the period and the amplitude of the theoretical light curve agree well with that observed. The modelled quasi-periodicity is due to the hydrogen thermal-ionization instability occurring in outer regions of the accretion disc. The model parameters are the average mass accretion rate (estimated from the light curves), and the accretion disc viscosity parameters, for the hot and cold phases. Our best model gives relatively low values of viscosity parameter for cold phase 0.01 and for h...
Long quasi-periodic oscillations of sunspots and nearby magnetic structures
NASA Astrophysics Data System (ADS)
Smirnova, V.; Riehokainen, A.; Solov'ev, A.; Kallunki, J.; Zhiltsov, A.; Ryzhov, V.
2013-04-01
Aims: Simultaneous study of long quasi-periodic oscillations in sunspots (using line-of-sight magnetic field data) and nearby magnetic structures located above them (using radio emission data at 37 GHz) was the basic aim of this work. Methods: Data from the ground-based radio-telescope (Metsähovi Radio Observatory, Aalto University, Finland) and the Helioseismic and Magnetic Imager instrument on-board the Solar Dynamics Observatory spacecraft were obtained and analyzed. We used the wavelet (Morlet) analysis and the fast Fourier transform (FFT) method to obtain the oscillation periods. Results: Long-period oscillations in intervals of 200-400 min were found both in radio and in magnetic field data. The interpretation of these oscillations and their propagation to higher levels of the solar atmosphere are discussed in the context of a "shallow sunspot" model.
Models for quasi-periodic electric fields and associated electron precipitation in the auroral zone
NASA Technical Reports Server (NTRS)
Petelski, E. F.; Fahleson, U.; Shawhan, S. D.
1978-01-01
Quasi-periodic electric fields observed in the nighttime auroral oval and in the polar cleft had periods of between 0.5 and 3 s and amplitudes from 2 to 30 mV/m and exhibited left-hand and right-hand elliptical polarization. The events in the auroral oval were associated with substorms and visual auroral activity, and the spectral and polarization properties of the observed fields suggest that they represented the electric components of Pc 1 or Pi 1 micropulsations. One possibility is that the micropulsations result from Birkeland current chopping by an unstable double layer located at an altitude of approximately one earth radius. In this interpretation, the double layer is assumed to accelerate the observed electrons, the electron flux variations being due either to the inherent variations of the double layer or to its interaction with the micropulsations.
Singular Density of States Measure for Subshift and Quasi-Periodic Schrödinger Operators
Artur Avila; David Damanik; Zhenghe Zhang
2014-09-28
Simon's subshift conjecture states that for every aperiodic minimal subshift of Verblunsky coefficients, the common essential support of the associated measures has zero Lebesgue measure. We disprove this conjecture in this paper, both in the form stated and in the analogous formulation of it for discrete Schr\\"odinger operators. In addition we prove a weak version of the conjecture in the Schr\\"odinger setting. Namely, under some additional assumptions on the subshift, we show that the density of states measure, a natural measure associated with the operator family and whose topological support is equal to the spectrum, is singular. We also consider one-frequency quasi-periodic Schr\\"odinger operators with continuous sampling functions and show that generically, the density of states measure is singular as well.
Transient and quasi-periodic (5-15 Min) events in the outer magnetosphere
NASA Astrophysics Data System (ADS)
Sibeck, David G.
This article reviews and summarizes the expected characteristics of transient (˜1-2 min) and quasi-periodic (T ˜ 5-15 min) events in the outer magnetosphere driven by sudden changes in solar wind dynamic pressure; impulsive penetration; the Kelvin-Helmholtz instability; or patchy, sporadic, merging on the magnetopause. The review emphasizes tests that might be used in case and statistical studies to distinguish between the various competing mechanisms. A well-known case study which has received several contradictory interpretations is reexarnined. The conflicting results suggest a need for further theoretical refinements and more extensive observational studies. Until such time as those tasks are completed, it does not seem possible to rule out any mechanism or combination of mechanisms.
Large and Tunable Optical Absorption in Quasi-Periodically Corrugated Graphene
NASA Astrophysics Data System (ADS)
Ni, Guang-Xin; Ma, De Lima Ferreira Rodrigues; Andersen, Henrik; Baeck, Seung-Jae; Ahn, Jong-Hyun; Jose Carlos, Viana-Gomes; Pereira, Vitor M.; Antonio Helio, Castro Neto; Özyilmaz, Barbaros
2014-03-01
Graphene is currently one of the notable players in the intense drive towards bendable, thin, and portable electronic displays. Given that the intrinsic transparency of a graphene monolayer is 97.7%, any reproducible and controllable modulation of transparency can have a significant impact for graphene as a viable transparent conducting electrode. Here we demonstrate a large and tunable optical aborption modulation in large-scale CVD graphene by introducing quasi-periodic ripples using functional elastomer substrates. We find that the optical modulation is more than 15% at visible wavelengths and moreover such optical modulation can be simultaneously tuned on and off by controlling the elastomer status. The simple device configuration and large tunability optical response of graphene demonstrated in this study can be very important towards novel ultra-thin optical polarizer devices applications.
Different Regimes of Stick-slip In Granular Matter: From Quasi-periodicity To Randomness
NASA Astrophysics Data System (ADS)
Adjémian, F.; Evesque, P.
Using granular materials and a geothecnical test (Triaxial), stick-slips are generated: we observe deviatoric stress drops, whose distribution changes of behaviour with the sample size. When the sample is small (< 10 000 000 grains), the system exhibits numerous fluctuations (exponential distribution) with a large amount of small events and fewer larger, similarly to seismic behaviours that produces very few large ground motions but many small events. When the sample is larger, (> 10 000 000 grains), the distribution is more regular (Gaussian-like) and a quasi-periodic stress drop is observed. These behaviours are observed with glass spheres of 0.3 or/and 0.7 mm di- ameter; smoother behaviours are observed with sand or larger glass spheres, whose fluctuation amplitudes decreases inversely to sample size. This last effect is inter- preted.
NASA Astrophysics Data System (ADS)
Xie, Zhong-Xiang; Liu, Jing-Zhong; Yu, Xia; Wang, Hai-Bin; Deng, Yuan-Xiang; Li, Ke-Min; Zhang, Yong
2015-03-01
We investigate acoustic phonon transmission and thermal conductance in three dimensional (3D) quasi-periodically stubbed waveguides according to the Fibonacci sequence. Results show that the transmission coefficient exhibits the periodic oscillation upon varying the length of stub/waveguide at low frequency, and the period of such oscillation is tunably decreased with increasing the Fibonacci number N. Interestingly, there also exist some anti-resonant dips that gradually develop into wide stop-frequency gaps with increasing N. As the temperature goes up, a transition of the thermal conductance from the decrease to the increase occurs in these systems. When N is increased, the thermal conductance is approximately decreased with a linear trend. Moreover, the decreasing degree sensitively depends on the variation of temperature. A brief analysis of these results is given.
Wideband absorption in fibonacci quasi-periodic graphene-based hyperbolic metamaterials
NASA Astrophysics Data System (ADS)
Ning, Renxia; Liu, Shaobin; Zhang, Haifeng; Kong, Xiangkun; Bian, Borui; Bao, Jie
2014-12-01
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.
Quasi-periodic brightness oscillations of the dwarf nova SS Cyg and their magnetic origin
NASA Astrophysics Data System (ADS)
Gnedin, Yu. N.; Nagovitsyn, Yu. A.; Natsvlishvili, T. M.
1999-07-01
Observations are analyzed of rapid variability of the cataclysmic variable SS Cyg during a peculiar flare in August 1993. The observations were made using the AZT-11 telescope of Abastumani Observatory, Republic of Georgia. The main time scales for the quasi-periodic brightness oscillations (QPOs) are determined using wavelet analysis. The brightness oscillations reveal for the first time the effect of a low-dimension strange attractor with a characteristic time scale of one to ten minutes. This phenomenon can be explained qualitatively by an "impact oscillator" model (shocks in a freely oscillating accretion disk). One possible physical mechanism for the QPOs is a nonlinear current-sheet oscillation regime in a magnetized accretion disk.
Quasi-periodic oscillations in the Z source GX 5-1
NASA Technical Reports Server (NTRS)
Lewin, Walter H. G.; Lubin, Lori M.; Tan, Jianmin; Van Der Klis, Michiel; Van Paradijs, Jan; Penninx, Wim; Dotani, Tadayasu; Mitsuda, Kazuhisa
1992-01-01
A detailed study has been conducted of the time variability in the Z source GX 5-1 using Ginga, which observed the source in the horizontal and normal branches (HB, NB). Intensity-dependent HF, quasi-periodic oscillations (QPO) were observed in the HB, in which the source flux varied by a factor of 1.9. The QPO frequency in this portion of the HB ranges from about 13 to 17 Hz; this is lower than previously observed in any Z source. The HF and LF QPO were simultaneously observed in the NB. The strength of both forms of QPO and the strength of the LF noise increase rapidly with increasing photon energy.
Ergodic theory and visualization. II. Fourier mesochronic plots visualize (quasi)periodic sets
NASA Astrophysics Data System (ADS)
Levnaji?, Zoran; Mezi?, Igor
2015-05-01
We present an application and analysis of a visualization method for measure-preserving dynamical systems introduced by I. Mezi? and A. Banaszuk [Physica D 197, 101 (2004)], based on frequency analysis and Koopman operator theory. This extends our earlier work on visualization of ergodic partition [Z. Levnaji? and I. Mezi?, Chaos 20, 033114 (2010)]. Our method employs the concept of Fourier time average [I. Mezi? and A. Banaszuk, Physica D 197, 101 (2004)], and is realized as a computational algorithms for visualization of periodic and quasi-periodic sets in the phase space. The complement of periodic phase space partition contains chaotic zone, and we show how to identify it. The range of method's applicability is illustrated using well-known Chirikov standard map, while its potential in illuminating higher-dimensional dynamics is presented by studying the Froeschlé map and the Extended Standard Map.
QUASI-PERIODIC WIGGLES OF MICROWAVE ZEBRA STRUCTURES IN A SOLAR FLARE
Yu, Sijie; Tan, Baolin; Yan, Yihua; Nakariakov, V. M.; Selzer, L. A.
2013-11-10
Quasi-periodic wiggles of microwave zebra pattern (ZP) structures with periods ranging from about 0.5 s to 1.5 s are found in an X-class solar flare on 2006 December 13 at the 2.6-3.8 GHz with the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou). Periodogram and correlation analysis show that the wiggles have two to three significant periodicities and are almost in phase between stripes at different frequencies. The Alfvén speed estimated from the ZP structures is about 700 km s{sup –1}. We find the spatial size of the wave-guiding plasma structure to be about 1 Mm with a detected period of about 1 s. This suggests that the ZP wiggles can be associated with the fast magnetoacoustic oscillations in the flaring active region. The lack of a significant phase shift between wiggles of different stripes suggests that the ZP wiggles are caused by a standing sausage oscillation.
Periodic and quasi-periodic solutions for multi-instabilities involved in brake squeal
NASA Astrophysics Data System (ADS)
Coudeyras, N.; Nacivet, S.; Sinou, J.-J.
2009-12-01
This paper is devoted to the computation of nonlinear dynamic steady-state solutions of autonomous systems subjected to multi-instabilities and proposes a new nonlinear method for predicting periodic and quasi-periodic solutions intended for application to the disc brake squeal phenomenon. Firstly, finite element models of a pad and a disc are reduced to include only their contact nodes by using a Craig and Bampton strategy. Secondly, a complex eigenvalue analysis is performed showing two unstable modes for a wide range of friction coefficients, after which a Generalized Constrained Harmonic Balance Method (GCHBM) is presented. This method can compute nonlinear periodic or pseudo-periodic responses depending on the number of unstable frequencies. The numerical results are in good agreement with those of time marching methods.
Hard apex transition in quasi-periodic oscillators - Closing of the accretion gap
NASA Technical Reports Server (NTRS)
Biehle, Garrett T.; Blandford, Roger D.
1993-01-01
We propose that the 'hard apex' transition in the X-ray two-color diagrams for low-mass X-ray binaries exhibiting quasi-periodic oscillation is associated with closure of a gap between the accretion disk and the star. At low accretion rates, gas crosses this gap intermittently. However, when the mass accretion rate increases, the disk thickens and its inner edge touches the star, thus forming a boundary layer through which the gas flows steadily. This explanation is viable provided that the equation of state of nuclear matter is not significantly harder than the Bethe-Johnson I prescription. Accretion gap scenarios are possibly distinguishable from models which invoke a small magnetosphere around the neutron star, in that they preclude large stellar magnetic fields and associate the high-frequency (horizontal-branch) oscillations with different sites.
Ginga observations of quasi-periodic oscillations in type II bursts from the Rapid Burster
NASA Technical Reports Server (NTRS)
Dotani, T.; Mitsuda, K.; Inoue, H.; Tanaka, Y.; Kawai, N.
1990-01-01
During Ginga observations of the 'Rapid Burster' in August 1988, strong quasi-periodic oscillations (QPOs) were detected in its X-ray intensity. The QPOs had centroid frequencies of 5 and 2 Hz during type II X-ray bursts which lasted for 10 and 30 s, respectively. The presence of the QPOs is correlated with the time scale-invariant burst profile. They are very strong during the initial peak in the burst, absent in the second peak, and strong again at the onset of the third peak. From an analysis of the X-ray spectrum as observed during the maxima and minima of the oscillations, it is found that the oscillations can be described by changes of the temperature of a blackbody emitter of constant apparent area.
QUASI-PERIODIC FORMALDEHYDE MASER FLARES IN THE MASSIVE PROTOSTELLAR OBJECT IRAS 18566+0408
Araya, E. D.; Hofner, P.; Goss, W. M.; Kurtz, S.; Richards, A. M. S.; Linz, H.; Olmi, L.; Sewilo, M.
2010-07-10
We report results of an extensive observational campaign of the 6 cm formaldehyde maser in the young massive stellar object IRAS 18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using the Arecibo Telescope, the Very Large Array, and the Green Bank Telescope, we discovered quasi-periodic formaldehyde flares (P {approx} 237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H{sub 2}CO) and methanol (CH{sub 3}OH) masers. The H{sub 2}CO and CH{sub 3}OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system.
Quasi-periodic Fluctuations and Chromospheric Evaporation in a Solar Flare Ribbon Observed by IRIS
NASA Astrophysics Data System (ADS)
Brosius, Jeffrey W.; Daw, Adrian N.
2015-09-01
The Interface Region Imaging Spectrograph (IRIS) satellite obtained rapid cadence (9.4 s) stare spectra of an M7 flare ribbon in AR 12036 on 2014 April 18. Chromospheric and transition region line emission exhibited quasi-periodic intensity and velocity fluctuations in the ribbon prior to the appearance of Fe xxi emission. Seven intensity peaks were observed in light curves from small (0\\buildrel{\\prime\\prime}\\over{.} 333× 0\\buildrel{\\prime\\prime}\\over{.} 333) tracked spatial locations in the ribbon, the first four of which show variable time separations around 3 minutes, and the last four of which show variable time separations about half that value, i.e., the frequency appears to have doubled. The Fe xxi intensity increased rapidly and impulsively after the quasi-periodic fluctuations in chromospheric and transition region lines. The entire Fe xxi line profile was blueshifted when the line first appeared, corresponding to an upward velocity around ?100 km s?1. This upward velocity increased to a maximum of about ?150 km s?1 before diminishing to zero around the time of maximum intensity. Simultaneous, cospatial velocities observed with Si iv line emission were directed downward, consistent with explosive chromospheric evaporation. During this flare the Fe xxi line’s profile is well fit with only one Gaussian component that is either wholly blueshifted or wholly at rest; no significant secondary blueshifted or redshifted components are observed. This suggests that IRIS may have sufficient spatial resolution to resolve loop strands in these flare observations. Under the assumption that the Fe xxi line is at rest when its width is thermal, we derive a rest wavelength of 1354.0714 ± 0.0108 Å for this forbidden line.
GB6 J1058+5628: A NEW QUASI-PERIODIC BL LAC OBJECT FROM THE ASIAGO PLATE ARCHIVE
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
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.
A Model for Backscattering from Quasi Periodic Corn Canopies at L-Band
NASA Technical Reports Server (NTRS)
Lang, R.; Utku, C.; Zhao, Q.; O'Neill, P.
2010-01-01
In this study, a model for backscattering at L-band from a corn canopy is proposed. The canopy consists of a quasi-periodic distribution of stalks and a random distribution of leaves. The Distorted Born Approximation (DBA) is employed to calculate the single scattered return from the corn field. The new feature of the method is that the coherence of the stalks in the row direction is incorporated in the model in a systematic fashion. Since the wavelength is on the order of the distance between corn stalks in a row, grating lobe behavior is observed at certain azimuth angles of incidence. The results are compared with experimental values measured in Huntsville, Alabama in 1998. The mean field and the effective dielectric constant of the canopy are obtained by using the Foldy approximation. The stalks are placed in the effective medium in a two dimensional lattice to simulate the row structure of a corn field. In order to mimic a real corn field, a quasi-periodic stalk distribution is assumed where the stalks are given small random perturbations about their lattice locations. Corn leaves are also embedded in the effective medium and the backscattered field from the stalks and the leaves is computed. The backscattering coefficient is calculated and averaged over successive stalk position perturbations. It is assumed that soil erosion has smoothed the soil sufficiently so that it can be assumed flat. Corn field backscatter data was collected from cornfields during the Huntsville 98 experimental campaign held at Alabama A&M University Research Station, Huntsville, Alabama in 1998 using the NASA/GW truck mounted radar. Extensive ground truth data was collected. This included soil moisture measurements and corn plant architectural data to be used in the model. In particular, the distances between the stalks in a single row have been measured. The L-band radar backscatter data was collected for both H and V polarizations and for look angles of 15o and 45o over a two week 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.
New quasi-periodic waves of the (2+1)-dimensional sine-Gordon system [rapid communication
NASA Astrophysics Data System (ADS)
Hu, H. C.; Lou, S. Y.
2005-06-01
New exact solutions of the well-known (2+1)-dimensional sine-Gordon system are studied by introducing the modified mapping relations between the cubic nonlinear Klein Gordon and sine-Gordon equations. Two arbitrary functions are included into the Jacobi elliptic function solutions. By proper selections of the arbitrary functions, new quasi-periodic wave solutions are obtained and displayed graphically.
Chakrabarti, Sandip K; Debnath, Dipak
2015-01-01
It has long been proposed that low frequency QPOs in stellar mass black holes or their equivalents in super massive black holes are results of resonances between infall and cooling time scales. We explicitly compute these two time scales in a generic situation to show that resonances are easily achieved. During an outburst of a transient black hole candidate (BHC), the accretion rate of the Keplerian disk as well as the geometry of the Comptonizing cloud change very rapidly. During some period, resonance condition between the cooling time scale (predominantly by Comptonization) and the infall time scale of the Comptonizing cloud is roughly satisfied. This leads to low frequency quasi-periodic oscillations (LFQPOs) of the Compton cloud and the consequent oscillation of hard X-rays. In this paper, we explicitly follow the BHC H 1743-322 during its 2010 outburst. We compute Compton cooling time and infall time on several days and show that QPOs take place when these two roughly agree within ~50%, i.e., the reson...
Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri
M. Uemura; T. Kato; R. Ishioka; R. Novak; J. Pietz
2002-03-15
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.
ON THE NATURE OF QUASI-PERIODIC OSCILLATION PHASE LAGS IN BLACK HOLE CANDIDATES
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
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.
Quasi-periodic Variations in the Hard X-ray Emission of a Large Arcade Flare
NASA Astrophysics Data System (ADS)
Jakimiec, J.; Tomczak, M.
2013-09-01
We investigated the quasi-periodic oscillations of the hard X-ray (HXR) emission of the large flare of 2 November 1991 using HXR light curves and soft X-ray and HXR images recorded with the Yohkoh X-ray telescopes. We analysed these observations and report five main results: i) The observations confirm that electrons are accelerated in oscillating magnetic traps that are contained within the cusp magnetic structure. ii) The chromospheric upflow increases the density within the magnetic traps, which in turn together with the higher amplitude of the trap oscillations increases the amplitude of the HXR pulses. iii) This increase stops when the density inside the traps increases progressively and inhibits the acceleration of electrons. iv) The model of oscillating magnetic traps is able to explain the time variation of the electron precipitation, the strong asymmetry in the precipitation of the accelerated electrons, and the systematic differences in the precipitation of 15 and 25 keV electrons. v) We have obtained direct observational evidence that strong HXR pulses are the result of the inflow into the accelerated volume of dense plasma from chromospheric evaporation.
SGR1806-20: evidence for a superstrong Magnetic Field from Quasi Periodic Oscillations
M. Vietri; L. Stella; G. Israel
2007-02-22
Fast Quasi-Periodic Oscillations (QPOs, frequencies of $\\sim 20 - 1840$ Hz) have been recently discovered in the ringing tail of giant flares from Soft Gamma Repeaters (SGRs), when the luminosity was of order $10^{41}-10^{41.5}$ erg/s. These oscillations persisted for many tens of seconds, remained coherent for up to hundreds of cycles and were observed over a wide range of rotational phases of the neutron stars believed to host SGRs. Therefore these QPOs must have originated from a compact, virtually non-expanding region inside the star's magnetosphere, emitting with a very moderate degree of beaming (if at all). The fastest QPOs imply a luminosity variation of $\\Delta L/\\Delta t \\simeq 6 \\times 10^{43}$ erg s$^{-2}$, the largest luminosity variation ever observed from a compact source. It exceeds by over an order of magnitude the usual Cavallo-Fabian-Rees (CFR) luminosity variability limit for a matter-to-radiation conversion efficiency of 100%. We show that such an extreme variability can be reconciled with the CFR limit if the emitting region is immersed in a magnetic field $\\gtrsim 10^{15}$ G at the star surface, providing independent evidence for the superstrong magnetic fields of magnetars.
Optical properties of one-dimensional Fibonacci quasi-periodic graphene photonic crystal
NASA Astrophysics Data System (ADS)
Zhang, Yuping; Wu, Zhixin; Cao, Yanyan; Zhang, Huiyun
2015-03-01
We propose a novel type of one-dimensional photonic crystal called Fibonacci quasi-periodic graphene photonic crystal (FGPC), in which the structure in each dielectric cell follows the Fibonacci sequence and the graphene monolayers are embedded between adjacent dielectric layers. The transmission properties of FGPC are investigated using transfer matrix method in detail. It is shown that both photonic band gap induced by graphene (GIBPG) and the Bragg gap exist in the structure. We study the band gaps of TE and TM waves at different incident angles or chemical potentials. It is found that the band gaps can be tuned via a gate voltage and GIBPG is almost omnidirectional and insensitive to the polarization. In order to investigate difference between the GIPBG and Bragg gap, we plot the electromagnetic field profiles inside FGPC for some critical frequencies. The propagation loss of the structure caused by absorption of graphene is researched in detail. Also, the passing bands of Fibonacci sequences of different orders and their splitting behavior at higher order are investigated.
Strong gravity effects of rotating black holes: quasi-periodic oscillations
NASA Astrophysics Data System (ADS)
Aliev, Alikram N.; Daylan Esmer, Göksel; Talazan, Pamir
2013-02-01
We explore strong gravity effects of the geodesic motion in the spacetime of rotating black holes in general relativity and braneworld gravity. We focus on the description of the motion in terms of three fundamental frequencies: the orbital frequency, the radial and vertical epicyclic frequencies. For a Kerr black hole, we perform a detailed numerical analysis of these frequencies at the innermost stable circular orbits and beyond them as well as at the characteristic stable orbits, at which the radial epicyclic frequency attains its highest value. We find that the values of the epicyclic frequencies for a class of stable orbits exhibit good qualitative agreement with the observed frequencies of the twin peaks quasi-periodic oscillations (QPOs) in some black hole binaries. We also find that at the characteristic stable circular orbits, where the radial (or the vertical) epicyclic frequency has maxima, the vertical and radial epicyclic frequencies exhibit an approximate 2:1 ratio even in the case of near-extreme rotation of the black hole. Next, we perform a similar analysis of the fundamental frequencies for a rotating braneworld black hole and argue that the existence of such a black hole with a negative tidal charge, whose angular momentum exceeds the Kerr bound in general relativity, does not confront with the observations of high-frequency QPOs.
Correlation between spectral state and quasi-periodic oscillation parameters in GX 5-1
NASA Technical Reports Server (NTRS)
Van Der Klis, M.; Jansen, F.; Van Paradijs, J.; Lewin, W. H. G.; Sztajno, M.
1987-01-01
In a series of seven Exosat observations, the bimodal spectral behavior and the quasi-periodic oscillation (QPO)/red noise properties of GX 5-1 show a strict correlation. In one of the two spectral states (characterized by a 'horizontal branch' in the hardness-intensity diagram), strong 20-40 Hz QPO and red noise below about 60 Hz were always present. In the other ('normal branch'), no QPO between 6 and 60 Hz or red noise above 1 Hz were detected, but there was an indication for weak QPO near 5 Hz. In both states 'very low frequency noise' (VLFN) is detected below 0.1 Hz which has a power-law shape and and which extends down to the lowest observed frequencies (0.0001 Hz). The VLFN is probably not directly related to the QPO. The results are compared to those on Sco X-1 and Cyg X-2 and it is concluded that, although all three sources show bimodal spectral and QPO/red noise behavior, there is a qualitative difference between GX 5-1 and Cyg X-2 on one hand and Sco X-1 on the other.
Kilohertz quasi-periodic oscillations in low-mass X-ray binaries
M. van der Klis
1997-04-28
In early 1996 a series of discoveries begun with NASA's Rossi X-ray Timing Explorer of a new, up to then unknown astrophysical phenomenon. It turned out that accreting low magnetic-field neutron stars show quasi-periodic oscillations in their X-ray flux at rates of up to more than a kilohertz. These kHz QPO, now reported from eleven different systems, are among the fastest phenomena in the sky and can provide us with new information about the fundamental properties of neutron stars and help testing general relativity in the strong-field regime. If, for example, their frequencies can be identified with the Keplerian frequencies of matter in orbit around a 1.4 Solar-mass neutron star, then the radius of the star would have to be less than 15 km, which directly constrains the equation of state of bulk nuclear-density matter, and for an only slightly tighter orbit or slightly more massive neutron star the orbital radius would equal the Schwarzschild-geometry general-relativistic marginally stable orbit (12.5 km for a 1.4 Solar mass object). So far all models that have been put forward for explaining the new phenomenon have encountered problems. In this paper I review the relatively simple and highly suggestive phenomenology as it has emerged from the data up to now, and discuss some of the proposed models.
OBSERVABLE QUASI-PERIODIC OSCILLATIONS PRODUCED BY STEEP PULSE PROFILES IN MAGNETAR FLARES
D'Angelo, C. R.; Watts, A. L., E-mail: c.r.dangelo@uva.nl [Instituut Anton Pannekoek, University of Amsterdam, Amsterdam 1098 XH (Netherlands)
2012-06-01
Strong quasi-periodic oscillations (QPOs) in the tails of the giant gamma-ray flares seen in SGR 1806-20 and SGR 1900+14 are thought to be produced by starquakes in the flaring magnetar. However, the large fractional amplitudes (up to {approx}20%) observed are difficult to reconcile with predicted amplitudes of starquakes. Here, we demonstrate that the steeply pulsed emission profile in the tail of the giant flare can enhance the observed amplitude of the underlying oscillation, analogous to a beam of light oscillating in and out of the line of sight. This mechanism will also broaden the feature in the power spectrum and introduce power at harmonics of the oscillation. The observed strength of the oscillation depends on the amplitude of the underlying starquake, the orientation and location of the emission on the surface of the star, and the gradient of the light curve profile. While the amplification of the signal can be significant, we demonstrate that, even with uncertainties in the emission geometry, this effect is not sufficient to produce the observed QPOs. This result excludes the direct observation of a starquake and suggests that the observed variations come from modulations in the intensity of the emission.
Case studies of quasi-periodic VLF emissions and related ULF fluctuations of the magnetic field
NASA Astrophysics Data System (ADS)
Hayosh, M.; Santolik, O.; Nemec, F.; Parrot, M.
2014-12-01
Quasi-periodic (QP) VLF emissions are observed in the inner magnetosphere mostly on the day-side. These waves exhibit a periodic time modulation of the wave intensity that is possibly a result of the whistler-mode wave growth being periodically modulated by compressional ULF magnetic field pulsations. We have analyzed 50 QP events measured by the DEMETER satellite at altitudes of about 700 km to verify their generation mechanism. The analyzed events have a modulation period between 15 s and 80 s, and they were observed during quiet geomagnetic conditions (Kp<3). Magnetometers of the CARISMA system were used for monitoring the ULF magnetic field pulsations in a wide spatial range. We have found that ULF magnetic field pulsations in the Pc3 - Pc5 range are well correlated with the occurrence of the QP emissions with modulation periods between about 40 and 80 s. At the same time, increased fluxes of high-energy electrons (E > 30 keV) were observed by DEMETER and by the NOAA-17 satellite. We analyze possible links between these electrons, QP emissions, and ULF magnetic field pulsations.
On the modulation of low-frequency quasi-periodic oscillations in black hole transients
NASA Astrophysics Data System (ADS)
Pawar, Devraj D.; Motta, Sara; Shanthi, K.; Bhattacharya, Dipankar; Belloni, Tomaso
2015-04-01
We studied the properties of the low-frequency quasi-periodic oscillations detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47, GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analysed the relation between the full width at half-maximum and the frequency of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a frequency modulation, while that of the sub-harmonic is independent of frequency, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.
Coronal Quasi-Periodic Fast-Propagating Magnetosonic Waves Observed by SDO/AIA
NASA Astrophysics Data System (ADS)
Shen, Yuandeng
2015-08-01
The observations of coronal quasi-periodic fast-propagating (QFP) magnetosonic waves are scare in previous articles due to the low temporal and spatial resolution of the past solar telescopes. Recently, it was detected by the high temporal and spatial resolution observations taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Here we present two cases of such kind of QFP waves. In Case I (May 30, 2011), we analysis the periodicity of the QFP wave and the accompanying flare. It is found that almost all of the frequencies of the flare are included in the frequency spectrum of the QFP wave, suggesting their common origin. In Case II (April 23, 2012), we study the multi-wavelengths observations of the QFP wave and its interaction with a perpendicular loop system on the path. The period of the QFP wave and the accompanying flare are the same (80 seconds). Based on our observations, we propose the possible interpretations of the wave trains observed in 193 Å observations.
Quasi-periodic Whistler Mode Waves Detected by the Van Allen Probes Spacecraft
NASA Astrophysics Data System (ADS)
Hospodarsky, G. B.; Santolik, O.; Nemec, F.; Kurth, W. S.; Kletzing, C.; Bounds, S. R.; Wygant, J. R.; Bonnell, J. W.
2014-12-01
Quasi-periodic (QP) whistler mode electromagnetic emissions have been detected in Earth's magnetosphere by the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) Waves instrument. These emissions typically consist of intervals of enhanced wave power between a few hundred Hz to a few kHz with modulation periods on the order of minutes. These emissions are primarily observed on the dayside and detected between L shells of 3 to 6, though some events are observed down to L shells of ~2. EMFISIS simultaneously measures the vector wave magnetic field and, with the support of the Electric Fields and Waves (EFW) instrument sensors, the vector wave electric field at two locations in Earth's magnetosphere in a continuous survey mode (typically with a 6 second cadence) along with a number of different burst modes to provide high time resolution waveforms (35000 samples per second). These two modes allow a systematic survey of the occurrence of these waves. By measuring all six wave components simultaneously, the wave propagation parameters, such as the wave normal angle and Poynting vector, of these plasma wave emissions are obtained. We will present a statistical survey of the properties of these waves as detected by the Van Allen Probes, examine their occurrence location and use burst data to examine the fine structure of individual events.
Mass-angular-momentum relations implied by models of twin peak quasi-periodic oscillations
Torok, Gabriel; Sramkova, Eva; Stuchlik, Zdenek; Urbanec, Martin; Goluchova, Katerina
2014-01-01
Twin peak quasi-periodic oscillations (QPOs) appear in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. Observations of the peculiar Z-source Circinus X-1 display unusually low QPO frequencies. Using these observations, we have previously considered the relativistic precession (RP) twin peak QPO model to estimate the mass of 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-square behavior that represent a dichotomy between high- and low-frequency sources. Based on the RP model, ...
Timing studies of X Persei and the discovery of its transient quasi-periodic oscillation feature
NASA Astrophysics Data System (ADS)
Acuner, Z.; ?nam, S. Ç.; ?ahiner, ?.; Serim, M. M.; Baykal, A.; Swank, J.
2014-10-01
We present a timing analysis of X Persei (X Per) using observations made between 1998 and 2010 with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) and with the INTEGRAL Soft Gamma-Ray Imager (ISGRI). All pulse arrival times obtained from the RXTE-PCA observations are phase-connected and a timing solution is obtained using these arrival times. We update the long-term pulse frequency history of the source by measuring its pulse frequencies using RXTE-PCA and ISGRI data. From the RXTE-PCA data, the relation between the frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. However, the detection of a transient quasi-periodic oscillation feature, peaking at ˜0.2 Hz, suggests the existence of an accretion disc. We find that double-break models fit the average power spectra well, which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectrum of frequency derivatives, we measure a power-law index of ˜- 1, which implies that, on short time-scales, disc accretion dominates over noise, while on time-scales longer than the viscous time-scales, the noise dominates. From pulse profiles, we find a correlation between the pulse fraction and the count rate of the source.
Broadband Quasi-Periodic Radio and X-ray Pulsations in a Solar Flare
G. D. Fleishman; T. S. Bastian; D. E. Gary
2008-04-25
We describe microwave and hard X-ray observations of strong quasiperiodic pulsations from the GOES X1.3 solar flare on 15 June 2003. The radio observations were made jointly by the Owens Valley Solar Array (OVSA), the Nobeyama Polarimeter (NoRP), and the Nobeyama Radioheliograph (NoRH). Hard X-ray observations were made by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Using Fourier analysis, we study the frequency- and energy-dependent oscillation periods, differential phase, and modulation amplitudes of the radio and X-ray pulsations. Focusing on the more complete radio observations, we also examine the modulation of the degree of circular polarization and of the radio spectral index. The observed properties of the oscillations are compared with those derived from two simple models for the radio emission. In particular, we explicitly fit the observed modulation amplitude data to the two competing models. The first model considers the effects of MHD oscillations on the radio emission. The second model considers the quasi-periodic injection of fast electrons. We demonstrate that quasiperiodic acceleration and injection of fast electrons is the more likely cause of the quasiperiodic oscillations observed in the radio and hard X-ray emission, which has important implications for particle acceleration and transport in the flaring sources.
Quasi-periodic Occultation by a Precessing Accretion Disk and Other Variabilities of SMC X-1
NASA Astrophysics Data System (ADS)
Wojdowski, Patrick; Clark, George W.; Levine, Alan M.; Woo, Jonathan W.; Zhang, Shuang Nan
1998-07-01
We have investigated the variability of the binary X-ray pulsar SMC X-1 in data from several X-ray observatories. We confirm the ~60 day cyclic variation of the X-ray flux in the long-term monitoring data from the RXTE and CGRO observatories. X-ray light curves and spectra from the ROSAT, Ginga, and ASCA observatories show that the uneclipsed flux varies by as much as a factor of 20 between a high-flux state when 0.71 s pulses are present and a low-flux state when pulses are absent. In contrast, during eclipses when the X-rays consist of radiation scattered from circumsource matter, the fluxes and spectra in the high and low states are approximately the same. These observations prove that the low state of SMC X-1 is not caused by a reduction in the intrinsic luminosity of the source or a spectral redistribution thereof, but rather by a quasi-periodic blockage of the line of sight, most likely by a precessing tilted accretion disk. In each of two observations in the midst of low states a brief increase in the X-ray flux and reappearance of 0.71 s pulses occurred near orbital phase 0.2. A similar brief flux increase near orbital phase 0.2 was observed during a low-state observation that did not have sufficient time resolution to detect 0.71 s pulses. These brief increases result from an opening of the line of sight to the pulsar that may be caused by wobble in the precessing accretion disk. The records of spin-up of the neutron star and decay of the binary orbit are extended during 1991-1996 by pulse-timing analysis of ROSAT, ASCA, and RXTE PCA data. The pulse profiles in various energy ranges from 0.1 to greater than 21 keV are well represented as a combination of a pencil beam and a fan beam. Finally, there is a marked difference between the power spectra of random fluctuations in the high-state data from the RXTE PCA below and above 3.4 keV. In the higher energy range the spectrum has a sharp break at 3.3 Hz, with fitted power-law indices of 0.45 and 1.76 below and above the break. No break is evident in the power spectrum below 3.4 keV, and the fitted power-law index is 0.51. In both spectra there is a positive deviation from the fitted power law around 0.06 Hz that may be quasi-periodic oscillation.
The time derivative of the kilohertz quasi-periodic oscillations in 4U 1636-53
NASA Astrophysics Data System (ADS)
Sanna, Andrea; Méndez, Mariano; Belloni, Tomaso; Altamirano, Diego
2012-08-01
We analysed all archival Rossi X-ray Timing Explorer (RXTE) observations of the neutron star low-mass X-ray binary 4U 1636-53 up to 2010 May. In 528 out of 1280 observations we detected kilohertz quasi-periodic oscillations (kHz QPOs), with ˜65 per cent of these detections corresponding to the so-called lower kHz QPO. Using this QPO we measured, for the first time, the rate at which the QPO frequency changes as a function of QPO frequency. For this we used the spread of the QPO frequency over groups of 10 consecutive measurements, sampling time-scales between 320 and 1600 s and the time derivative of the QPO frequency, ?\\dot QPO , over time-scales of 32-160 s. We found that (i) both the QPO-frequency spread and ?\\dot QPO decrease by a factor of ˜3 as the QPO frequency increases. (ii) The average value of ?\\dot QPO decreases by a factor of ˜2 as the time-scale over which the derivative is measured increases from less than 64 to 160 s. (iii) The relation between the absolute value of ?\\dot QPO and the QPO frequency is consistent with being the same both for the positive and negative QPO-frequency derivatives. We show that, if either the lower or the upper kHz QPO reflects the Keplerian frequency at the inner edge of the accretion disc, these results support a scenario in which the inner part of the accretion disc is truncated at a radius that is set by the combined effect of viscosity and radiation drag.
Conjugate observations of quasi-periodic emissions by Cluster and DEMETER spacecraft
NASA Astrophysics Data System (ADS)
N?Mec, F.; SantolíK, O.; Parrot, M.; Pickett, J. S.; Hayosh, M.; Cornilleau-Wehrlin, N.
2013-01-01