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1

NASA Astrophysics Data System (ADS)

In this paper, it is shown that there exist many small amplitude quasi-periodic solutions for non-autonomous, quasi-periodically forced in time nonlinear Schrödinger equations with quasi-periodic inhomogeneous terms, under periodic spatial boundary conditions, via KAM theory.

Rui, Jie; Si, Jianguo

2014-10-01

2

Quasi-periodic bifurcations in reversible systems

NASA Astrophysics Data System (ADS)

Invariant tori of integrable dynamical systems occur both in the dissipative and in the conservative context, but only in the latter the tori are parameterized by phase space variables. This allows for quasi-periodic bifurcations within a single given system, induced by changes of the normal behavior of the tori. It turns out that in a non-degenerate reversible system all semi-local bifurcations of co-dimension 1 persist, under small non-integrable perturbations, on large Cantor sets.

Hanßmann, Heinz

2011-02-01

3

Quasi-periodic quantum dot arrays produced by electrochemical synthesis.

National Technical Information Service (NTIS)

We discuss a ''gentle'' electrochemical technique for fabricating quasi-periodic quantum dot arrays. The technique exploits a self-organizing phenomenon to produce quasi-periodic arrangement of dots and provides excellent control over dot size and interdo...

S. Bandyopadhyay, A. E. Miller, D. F. Yue, G. Banerjee, R. E. Ricker

1994-01-01

4

Quasi-periodicities in Chinese precipitation time series

NASA Astrophysics Data System (ADS)

Although climate change deeply affects China, climatic time series are expected to show quasi-periodic behavior. This hypothesis has been tested by means of Autocorrelation Spectral Analysis (ASA) to detect quasi-periodicities in precipitation time series of 132 climate stations spread over China for the period from 1951 to 2002. A Continuous Wavelet Transform (CWT) has also been applied in order to examine if these quasi-periods are stable in time. Finally, it has been tested whether precipitation series recorded at neighboring stations show similar spectral behavior and can thus be grouped. All in all, our hypothesis regarding quasi-periodicities has been verified. Most of the time series show significant quasi-periods. A 2-3 year quasi-periodicity is predominant in many different regions of China. The result of ASA is that precipitation series from neighboring stations often show similar quasi-periods and therefore a grouping seems to be justified. However, the outcome of CWT provides more detailed information. In north-eastern China several series show similar quasi-periods which are statistically significant at different times; here, a grouping would be incorrect. In addition, the results of CWT show a less uniform pattern of quasi-periods in the southern inland regions. Whereas ASA shows a relatively uniform pattern of 2-3 year quasi-periods, CWT detects 2-3, 4-5 and 6-7 year quasi-periods. Nevertheless, although the quasi-periods are detected as being unstable, time series from neighboring stations sometimes show analogous significant quasi-periods within the same time frame and can thus be grouped. This can be seen in the northern part of central China, near the border to North Korea and along the coast of the South China Sea.

Hartmann, H.; Becker, S.; King, L.

2008-05-01

5

Quasi-Periodic Solutions and Stability for a Weakly Damped Nonlinear Quasi-Periodic Mathieu Equation

Quasi-Periodic (QP) solutions are investigated for a weakly dampednonlinear QP Mathieu equation. A double parametric primary resonance(1:2, 1:2) is considered. To approximate QP solutions, a double multiple-scales method is applied to transform the original QP oscillator to anautonomous system performing two successive reductions. In a first step,the multiple-scales method is applied to the original equation to derive afirst reduced differential

K. Guennoun; M. Houssni; M. Belhaq

2002-01-01

6

Multispacecraft observations of quasi-periodic emissions

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

7

Quasi-periodic oscillations in superfluid magnetars

NASA Astrophysics Data System (ADS)

We study the time evolution of axisymmetric oscillations of superfluid magnetars with a poloidal magnetic field and an elastic crust, working in Newtonian gravity. Extending earlier models, we study the effects of composition gradients and entrainment on the magneto-elastic wave spectrum and on the potential identification of the observed quasi-periodic oscillations (QPOs). We use two-fluid polytropic equations of state to construct our stellar models, which mimic realistic composition gradient configurations. The basic features of the axial axisymmetric spectrum of normal fluid stars are reproduced by our results and in addition we find several magneto-elastic waves with a mixed character. In the core, these oscillations mimic the shear mode pattern of the crust as a result of the strong dynamical coupling between these two regions. Incorporating the most recent entrainment configurations in our models, we find that they have a double effect on the spectrum: the magnetic oscillations of the core have a frequency enhancement, while the mixed magneto-elastic waves originating in the crust are moved towards the frequencies of the single-fluid case. The distribution of lower frequency magneto-elastic oscillations for our models is qualitatively similar to the observed magnetar QPOs with ? < 155 Hz.

Passamonti, A.; Lander, S. K.

2014-02-01

8

NASA Astrophysics Data System (ADS)

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

Cheng, Hongyu; Si, Jianguo

2013-08-01

9

Phase Equations for Quasi-Periodic Oscillators Alper Demir

Phase Equations for Quasi-Periodic Oscillators Alper Demir Chenjie Gu Jaijeet Roychowdhury KocÂ¸ University Istanbul, Turkey University of California Berkeley, CA, USA Abstract--Oscillations and rhythmic activity are seen in natural and man-made systems. Dynamics of oscillators can be compactly described

Roychowdhury, Jaijeet

10

Cassini and Galileo Observations of Quasi-periodic Radio Bursts

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,

G. B. Hospodarsky; W. S. Kurth; D. A. Gurnett; M. L. Kaiser; P. Zarka; N. Krupp; J. H. Waite

2002-01-01

11

Stability for quasi-periodically perturbed Hill's equations

's equation of the form Â¨ + (p0(t) + p1(t)) = 0, where p0 is real analytic and periodic, p1 is real analytic than analyticity, we prove that quasi-periodic solutions of the unperturbed equation can be continued as a solution of a generalized Riccati equation associated to Hill's problem. 1 Introduction In the present work

Gentile, Guido

12

Transition Curves for the Quasi-Periodic Mathieu Equation

In this work we investigate an extension of Mathieu's equation, the quasi-periodic(QP) Mathieu equation given by # +[# + # (cos t + cos #t)] # =0for small # and irrational #. Of interest is the generation of stability diagrams that identify thepoints or regions in the #-# parameter plane (for fixed #) for which all solutions of the QP

Randolph S. Zounes; Richard H. Rand

1998-01-01

13

Explicit quasi-periodic solutions of the Vakhnenko equation

NASA Astrophysics Data System (ADS)

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

Zhai, Yunyun; Geng, Xianguo; He, Guoliang

2014-05-01

14

Cassini and Galileo Observations of Quasi-periodic Radio Bursts

NASA Astrophysics Data System (ADS)

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.

Hospodarsky, G. B.; Kurth, W. S.; Gurnett, D. A.; Kaiser, M. L.; Zarka, P.; Krupp, N.; Waite, J. H.

15

Development of a quasi-periodic undulator for the HLS

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

16

Development of a Quasi-Periodic Undulator for the HLS

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

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

2014-03-11

17

Quasi-periodic oscillations in GX 17 + 2

NASA Technical Reports Server (NTRS)

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).

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

1990-01-01

18

Quasi-periodic fluctuations in climate due to sea ice

NASA Astrophysics Data System (ADS)

A new mechanism behind the occurrence of Dansgaard-Oeschger (D-O) events is proposed. Paleo-proxy observations suggests that these quasi-periodic fluctuations occurred during the last glacial period, and similar fluctuations are also observed in the present interglacial (Bond events). The persistent occurrence of a quasi-periodic fluctuation under different background climates is explained by the interaction between deep water formation and sea ice in the North Atlantic. A simple ocean circulation model coupled to a thermodynamic sea ice model is shown to exhibit self-sustained oscillations in the overturning circulation strength. The physical mechanism behind the oscillations is the insulating property of sea ice in cutting off ocean-atmosphere heat exchange. During periods of extended sea ice, heat builds up in the top layers of the polar ocean which subsequently contributes to the retreat of sea ice and the loss of heat. The dynamics of the system is such that there is a net loss of heat in each cycle of sea ice advance and retreat. Gradually over several cycles, a convective situation results with the top oceanic layers reaching the same density as the bottom layers, and the system abruptly switches to an enhanced circulation mode for a brief period of time before returning to its preferred state from where the cycle repeats. The periodic relaxation oscillations can be modulated by external freshwater or solar forcing. A pulsed freshwater injection mimicking Heinrich events produces packets of fluctuations with similar characteristics to D-O events. Numerical experiments with the model suggests that the volume of the ocean that comes under sea ice is an important parameter in determining the periodicity of oscillations. In this respect, the geometry of the ocean basin could be the determinant of the natural oscillation time-scale of the sea ice-circulation system. When subjected to freshwater pulses mimicking Heinrich events, the model produces packets of progressively weaker fluctuations (top). This pattern resembles D-O events between 30 and 50 ky before present (bottom).

Saha, R.

2013-12-01

19

Quasi-Periodicities, Magnetic Clusters and Solar Activity

NASA Astrophysics Data System (ADS)

To investigate quasi-periodicities, 12 hour averages of the radial component of the interplanetary magnetic field and the solar wind speed, covering ~ 42 (1963-2005) years were analyzed. A Lomb periodogram for data up to 1998 showed a dominant period of 27.03 days as fpund in earlier results. Including cycle 23, a dominant period of 27.06 days was identified. Analysis of the solar cycles independently showed a dominant period of 27.03 days in solar cycle 20, but not in the other cycles. To investigate the degree of persistency of a particular signal, the technique of complex demodulation was applied since it permits the determination of continuous changes in time of the amplitude and frequency of the signal relative to the test signal. It was found that a period of ~27.6 days gave an overall flat phase function in time, while other periods < ~0.5 day shorter and longer, with comparable but lesser amplitude, come and go. To investigate the solar sources of these periods, the method of principal component analysis (PCA) was applied to ~ 27 years (1976-2003) of synoptic maps obtained with the NSO Kitt Peak Vaccum Telescope. Before the analysis, the original synoptic maps were shifted relative to the previous maps using the period under investigation. Using PCA the Empirical Orthogonal Functions (EOFs) and Pricipal Components (PCs) were found for the set of synoptic maps rescaled to the rotation rate 27.03 days in 1999-2003. The patterns characterized by EOFs 1 and 2 are mostly axisymmetric and PCs 1 and 2 show solar cycle variability. EOF3 shows only one well-localized pattern in the Southern Hemisphere which is markedly non-axisymmetric and PC3 has peaks at times when fast CMEs occur.

Cadavid, A. C.; Lawrence, J. K.; Sandor, C.; Ruzmaikin, A.

2006-12-01

20

Quasi-periodic emissions observed by Cluster and DEMETER spacecraft

NASA Astrophysics Data System (ADS)

Quasi-periodic (QP) emissions are electromagnetic emissions in the frequency range of about 0.5-4 kHz that are characterized by a periodic modulation of wave intensity. Typical periods of this modulation are on the order of minutes. Although there are many observations of these events by ground-based instruments, satellite observations are still rather sparse. Nevertheless, these are of great importance, as they allow us to analyze wave properties in situ, close to the probable generation region, and, moreover, they are not affected by the wave propagation in the Earth-ionosphere waveguide. We present a survey of QP events observed by the WBD instruments on board the four Cluster spacecraft during their perigee passes at radial distances of about 4 RE. Moreover, a conjugate observation of a QP event by Cluster spacecraft and by the low-altitude DEMETER spacecraft has been identified. Simultaneous observations of the same event by several different spacecraft enable us to distinguish between spatial and temporal variations of the phenomenon. It is shown that during a QP event, the same modulation is observed at the same time at very different locations of the inner magnetosphere. The results of a detailed wave analysis based on multi-component measurements by the STAFF-SA instruments indicate that the emissions propagate unducted, with oblique wave normal angles at larger geomagnetic latitudes. Finally, ULF magnetic field data are inspected for the presence of magnetic field fluctuations with a period corresponding to the period of modulation and a possible generation mechanism of the events is discussed.

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

2012-12-01

21

Quasi-periodic solutions for two-level systems Guido Gentile

generalized Riccati equation. We prove the existence of quasi-periodic solutions of the latter equation are the Pauli matrices and f(t) is a real analytic quasi-periodic function with frequency vector ; the real of a generalized Riccati equation (see next section). In particular in [1] it was found that quasi

Gentile, Guido

22

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

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

Barcelona, Universitat de

23

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

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

Barcelona, Universitat de

24

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

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

D. Lusk; I. Abdulhalim; F. Placido

2001-01-01

25

Quasi-Periodicity in Medieval and Islamic architecture and ornament , Helmer Aslaksen2

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

Aslaksen, Helmer

26

POINTWISE EXISTENCE OF THE LYAPUNOV EXPONENT FOR A QUASI-PERIODIC EQUATION

understood only for a few models, most prominently, for the almost Mathieu equation when v(x) = 2 cos(x)). 0POINTWISE EXISTENCE OF THE LYAPUNOV EXPONENT FOR A QUASI-PERIODIC EQUATION ALEXANDER FEDOTOV AND FRÂ´EDÂ´ERIC KLOPP 0. Introduction 0.1. Quasi-periodic finite difference equations. Consider the finite difference

Boyer, Edmond

27

POINTWISE EXISTENCE OF THE LYAPUNOV EXPONENT FOR A QUASI-PERIODIC EQUATION

understood only for a few models, most prominently, for the almost Mathieu equation when v(x) = 2#21; cosPOINTWISE EXISTENCE OF THE LYAPUNOV EXPONENT FOR A QUASI-PERIODIC EQUATION ALEXANDER FEDOTOV AND FR #19; ED #19; ERIC KLOPP 0. Introduction 0.1. Quasi-periodic #12;nite di#11;erence equations. Consider

Recanati, Catherine

28

TRANSITION CURVES FOR THE QUASI-PERIODIC MATHIEU RANDOLPH S. ZOUNES AND RICHARD H. RAND

TRANSITION CURVES FOR THE QUASI-PERIODIC MATHIEU EQUATION RANDOLPH S. ZOUNES AND RICHARD H. RANDÂ1115, August 1998 004 Abstract. In this work we investigate an extension of Mathieu's equation, the quasi-periodic (QP) Mathieu equation given by Â¨ + [ + (cos t + cos t)] = 0 for small and irrational . Of interest

Rand, Richard H.

29

On Quasi-Periodic Variations of Cosmic Rays Observed at Earth: Direct Measurements

NASA Astrophysics Data System (ADS)

Important role in space weather related studies play cosmic rays (CR). Their temporal variability, both of quasi-periodic character as well as of irregular one, is studied on the ground from direct measurements as well as from cosmogenic nuclides, over long time. We attempt to describe the current knowledge on selected quasi-periodicities in CR flux, especially in energy range above the atmospheric threshold, from direct measurement. Quasi-periodicities in relativistic electron flux near Earth is discussed shortly too. The power spectrum density (PSD) of the CR time series at a single station has rather complicated character. Along with the shape (slope) of PSD the knowledge of contribution of quasi-periodic variations to the CR signal is of importance for the modulation as well as for the checking the links of CR to space weather and/or space climate effects. Rotation of the Earth and solar rotation cause two types of mechanisms behind the certain quasi-periodicities observed in secondary CR on the Earth's surface. Solar activity and solar magnetic field cyclicities contribute to the quasi-periodic signals in CR if studied over longer time periods. The complexity of spatial structure of IMF and its evolution within the heliosphere as well as the changes in the geomagnetic field cause variability in contributions of the quasi-periodicities in CR. Wavelet spectra are useful tool for checking the fine strucure of quasi-periodicities and their temporal behaviour. Over long time the neutron monitors and muon telescopes provide the informations about quasi-periodicities in CR. In addition to that, in recent years there are new installations on the ground from which the unique information about CR variability can be deduced (higher statistical accuracy, different response function to primaries). The unsolved questions and few tasks for the future studies are listed.

Kudela, K.; Perez-Peraza, J. A.

2013-05-01

30

Assisted Coronary Artery Bypass Graft Surgery by Jason Rotella Submitted in partial fulfillment Bypass Graft Surgery . . . . . . . . . . . . . 6 1.4 Robotic Surgical SolutionsPredictive Tracking of Quasi Periodic Signals for Active Relative Motion Cancellation in Robotic

Cavusoglu, Cenk

31

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

-Periodicity Experimental LLDPE XU4R (Mw= 116000) . Strain Amplitude and Onset of Quasi-Periodicity Effect of Molecular Weight . . V. CONCLUSION VI. RECOMMENDATIONS . . 53 , , 67 67 70 . . 77 77 . 77 . . 83 88 88 . . 96 96 . 99 101 REFERENCES 102...-Periodicity Experimental LLDPE XU4R (Mw= 116000) . Strain Amplitude and Onset of Quasi-Periodicity Effect of Molecular Weight . . V. CONCLUSION VI. RECOMMENDATIONS . . 53 , , 67 67 70 . . 77 77 . 77 . . 83 88 88 . . 96 96 . 99 101 REFERENCES 102...

Adrian, David Warren

2012-06-07

32

of the quasi-periodic Mathieu equation Â¨x + ( + cos t + cos t)x = 0 in the neighborhood of the point = 0 equation 1. Introduction The following quasi-periodic Mathieu equation, Â¨x + ( + cos t + cos t)x = 0 (1 which relate their relative sizes. #12;Quasi-Periodic Mathieu Equation 197 The title of this paper

Rand, Richard H.

33

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

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

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

2014-02-01

34

A MODEL FOR QUASI-PERIODIC SIGNALS WITH APPLICATION TO RAIN ESTIMATION FROM MICROWAVE LINK GAIN

A MODEL FOR QUASI-PERIODIC SIGNALS WITH APPLICATION TO RAIN ESTIMATION FROM MICROWAVE LINK GAIN from attenuation due to rain [1]. From this observation, it has been suggested to estimate rain- fall in this way would be a welcome complement to rain gauges and rain radar mea- surements [2,3]. However

Loeliger, Hans-Andrea

35

Quasi-periodic intermediate orbits for major planets and zero-order resonances

Particular quasi-periodic solutions of the equations of motion of the major planets in rectangular heliocentric coordinates have been constructed by means of successive iterations with respect to the planetary masses. These solutions are presented as exponential series in multiples of the mean longitudes of the planets, the sum of all exponential indices in every term being equal to zero. The

V. A. Brumberg; L. S. Evdokimova; V. I. Skripnichenko

1975-01-01

36

Quasi-periodic solutions for two-level systems Guido Gentile

of a related generalized Riccati equation. We prove the existence of quasi-periodic solutions of the latter:1) where #27; 1 ; #27; 2 ; #27; 3 are the Pauli matrices and f(t) is a real analytic quasiodinger equation (1.2) were shown to be expressible in terms of particular solutions of a generalized Riccati

Roma "La Sapienza", UniversitÃ di

37

Quasi-periodic solutions for two-level systems Guido Gentile

, and that they are not analytic in ", according to the conjecture proposed in [1]; in fact they are de#12;ned on a set of values.1) was shown in [1] to be expressible in terms of a particular solution of a generalized Riccati equation (see which is quasi-periodic in time and non-analytic in the p

38

Asymptotic solutions for a damped non-linear quasi-periodic Mathieu equation

Quasi-periodic (QP) solutions of a weakly damped non-linear QP Mathieu equation are investigated near a double primary parametric resonance. A double multiple scales method is applied to reduce the original QP oscillator to an autonomous system performing two successive reduction. The problem for approximating QP solutions of the original system is then transformed to the study of stationary regimes of

Mohamed Belhaq; Kamar Guennoun; Mohamed Houssni

2002-01-01

39

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

NASA Technical Reports Server (NTRS)

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

Kosugi, Takeo; Kiplinger, Alan L.

1986-01-01

40

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

Xavier Calmet; Dionysios Fragkakis; Nina Gausmann

2012-01-21

41

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

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

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

2007-08-20

42

Quasi-Periodicity in global solar radio flux at metric wavelengths during Noise Storms

NASA Astrophysics Data System (ADS)

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.

Sundaram, G. A. Shanmugha; Subramanian, K. R.

2004-08-01

43

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

44

Pure point spectrum for two-level systems in a strong quasi-periodic eld

that if the #12;eld is an analytic function with zero average, then for a large set of values of its frequency and f(t) is assumed to be a real analytic quasi-periodic function with frequency (or rotation) vector particular solution g of the generalized Riccati equation dG dt iG 2 2if(t) G+ i" 2 = 0: (1:5) To come back

Roma "La Sapienza", UniversitÃ di

45

2:1:1 Resonance in the Quasi-Periodic Mathieu Equation

We present a small e perturbation analysis of the quasi-periodic Mathieu equation\\u000a$$\\u000a\\\\ddot x + (\\\\delta + \\\\epsilon \\\\cos t + \\\\epsilon \\\\cos \\\\omega t) x=0\\u000a$$\\u000ain the neighborhood of the point d = 0.25 and ? = 0.5. We use multiple scales including terms of O(e2) with three time scales. We obtain an asymptotic expansion for an

Richard Rand; Tina Morrison

2005-01-01

46

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

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

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

1985-01-01

47

Long-lived quasi-periodic Bloch oscillations by spatially selective photoexcitation

NASA Astrophysics Data System (ADS)

We show, through accurate numerical simulations, that long-lived, large-amplitude quasi-periodic Bloch oscillations can be achieved through a spatially selective photoexcitation process in semiconductor superlattices. Specifically, by doping a single interior well of a GaAs/Al_xGa_1-xAs superlattice with a low level (typically less than 2%) of In, it becomes possible to photoexcite electrons to a small number of In-perturbed Wannier-Stark levels. This procedure circumvents the dephasing effects of interface roughness that is associated with conventional photoexcitation methods, where electrons are excited to Wannier-Stark levels essentially over the entire superlattice.

Reynolds, Joseph P.; Luban, Marshall; Luscombe, James H.

1997-03-01

48

Quasi-periodic oscillations in low-mass x ray binaries

NASA Technical Reports Server (NTRS)

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.

Lewin, Walter H. G.; Vanparadijs, J.; Vanderklis, M.

1991-01-01

49

Quasi-Periodic Solutions of (3+1) Generalized BKP Equation By Using Riemann Theta Functions

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.

Seçil Demiray; Filiz Ta?can Güney

2014-09-24

50

THz laser based on quasi-periodic AlGaAs superlattices

NASA Astrophysics Data System (ADS)

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-1 in the frequency range f = 2 - 4 THz. The peaks depend linearly on the electric field, retain the height of 20 cm-1, and strongly depend on the thickness of the AlGaAs-layers.

Malyshev, K. V.

2013-06-01

51

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

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

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

2012-05-15

52

THz laser based on quasi-periodic AlGaAs superlattices

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

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

2013-06-30

53

A Resonance Model of Quasi-Periodic Oscillations of Low-Mass X-Ray Binaries

We try to understand the quasi-periodic oscillations (QPOs) in low-mass neutron-star and black-hole X-ray binaries by a resonance model in warped disks with precession. Our main concern is high-frequency QPOs, hectohertz QPOs, and horizontal-branch QPOs in the z sources and the atoll sources, and the correponding QPOs in black-hole X-ray binaries. Our resonance model can qualitatively, but systematically, explain these QPOs by regarding hectohertz QPOs as a precession of warp.

Shoji Kato

2005-05-11

54

We propose an extension of the one dimensional (doubling) renormalization operator to the case of maps on the cylinder. The kind of maps considered are commonly referred as quasi-periodic forced one dimensional maps. We prove that the fixed point of the one dimensional renormalization operator extends to a fixed point of the quasi-periodic forced renormalization operator. We also prove that the operator is differentiable around the fixed point and we study its derivative. Then we consider a two parametric family of quasi-periodically forced maps which is a unimodal one dimensional map with a full cascade of period doubling bifurcations plus a quasi-periodic perturbation. For one dimensional maps it is well known that between one period doubling and the next one there exists a parameter value where the $2^n$-periodic orbit is superatracting. Under appropriate hypotheses, we prove that the two parameter family has two curves of reducibility loss bifurcation around these points.

Rabassa, Pau; Tatjer, Joan Carles

2011-01-01

55

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

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

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

2012-04-10

56

Generation of Quasi-periodic Waves and Flows in the Solar Atmosphere by Oscillatory Reconnection

NASA Astrophysics Data System (ADS)

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

McLaughlin, J. A.; Verth, G.; Fedun, V.; Erdélyi, R.

2012-04-01

57

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

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

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

2013-11-10

58

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

59

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

NASA Astrophysics Data System (ADS)

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

Karpeshina, Yulia; Shterenberg, Roman

2012-10-01

60

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

NASA Astrophysics Data System (ADS)

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

Karpeshina, Yulia; Shterenberg, Roman

2013-07-01

61

Casimir Effect Under Quasi-Periodic Boundary Condition Inspired by Nanotubes

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

62

NASA Astrophysics Data System (ADS)

Quasi-periodic (QP) VLF emissions are wideband emissions which are observed inside or near the plasmapause. They are characterized by a periodic modulation of the wave intensity with typical periods from several seconds up to a few minutes. The source region of QP emissions is probably located close to the geomagnetic equatorial plane. We have systematically analyzed six years of measurements from the Demeter spacecraft in order to determine the direction of propagation of QP emissions as a function of geomagnetic latitude, magnetic local time, L-parameter, and frequency. A large database of time-frequency structured QP emissions in the range from 0.1 to 1200 Hz has been used for our analysis.

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

2013-12-01

63

Statistical investigation of the VLF quasi-periodic emissions measured by the DEMETER spacecraft

NASA Astrophysics Data System (ADS)

We present a survey of quasi-periodic (QP) ELF/VLF emissions detected on board the DEMETER satellite (altitude of about 700 km, nearly Sun-synchronous orbit at 10:30/22:30 LT). Five years of data have been visually inspected for the presence of QP emissions. It is found that QP events occur in about 3 percents of daytime half-orbits, while they are basically absent during the night (note that we were likely to miss QP events with the modulation periods lower than about 10 s or the frequency bandwidth lower than about 400 Hz). The events occur predominantly during quiet geomagnetic conditions following the periods of enhanced geomagnetic activity. Their occurrence and properties are systematically analyzed.

Hayosh, Mykhaylo; Nemec, František; Santolík, Ond?ej; Pasmanik, Dmitry; Parrot, Michel

2013-04-01

64

Casimir Effect under Quasi-Periodic Boundary Condition Inspired by Nanotubes

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

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

2013-12-06

65

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

66

Long Term Simulations Of Astrophysical Jets; Energy Structure and Quasi-Periodic Ejection

We have performed self-consistent 2.5-dimensional nonsteady MHD numerical simulations of jet formation as long as possible, including the dynamics of accretion disks. Although the previous nonsteady MHD simulations for astrophysical jets revealed that the characteristics of nonsteady jets are similar to those of steady jets, the calculation time of these simulations is very short compared with the time scale of observed jets. Thus we have investigated long term evolutions of mass accretion rate, mass outflow rate, jet velocity, and various energy flux. We found that the ejection of jet is quasi-periodic. The period of the ejection is related to the time needed for the initial magnetic filed to be twisted to generate toroidal filed. We compare our results with both the steady state theory and previous 2.5-dimensional nonsteady MHD simulations.

Ahmed Ibrahim; Kazunari Shibata

2007-04-23

67

Long Term Simulations Of Astrophysical Jets; Energy Structure and Quasi-Periodic Ejection

We have performed self-consistent 2.5-dimensional nonsteady MHD numerical simulations of jet formation as long as possible, including the dynamics of accretion disks. Although the previous nonsteady MHD simulations for astrophysical jets revealed that the characteristics of nonsteady jets are similar to those of steady jets, the calculation time of these simulations is very short compared with the time scale of observed jets. Thus we have investigated long term evolutions of mass accretion rate, mass outflow rate, jet velocity, and various energy flux. We found that the ejection of jet is quasi-periodic. The period of the ejection is related to the time needed for the initial magnetic filed to be twisted to generate toroidal filed. We compare our results with both the steady state theory and previous 2.5-dimensional nonsteady MHD simulations.

Ibrahim, Ahmed

2007-01-01

68

Phase-resolved spectroscopy of low frequency quasi-periodic oscillations in GRS 1915+105

X-ray radiation from black hole binary (BHB) systems regularly displays quasi-periodic oscillations (QPOs). In principle, a number of suggested physical mechanisms can reproduce their power spectral properties, thus more powerful diagnostics which preserve phase are required to discern between different models. In this paper, we first find for two Rossi X-ray Timing Explorer (RXTE) observations of the BHB GRS 1915+105 that the QPO has a well defined average waveform. That is, the phase difference and amplitude ratios between the first two harmonics vary tightly around a well defined mean. This enables us to reconstruct QPO waveforms in each energy channel, in order to constrain QPO phase-resolved spectra. We fit these phase resolved spectra across 16 phases with a model including Comptonisation and reflection (Gaussian and smeared edge components) to find strong spectral pivoting and a modulation in the iron line equivalent width. The latter indicates the observed reflection fraction is changing throughout th...

Ingram, Adam

2014-01-01

69

Non-thermal plasma treatment of textiles

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

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

2008-01-01

70

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

NASA Astrophysics Data System (ADS)

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

Atalla, Mahmoud R. M.

2014-03-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

72

Experimental realization of broadband parametric generation in a quasi-periodically poled LiTaO3.

We have achieved broadband parametric generation by using a quasi-periodically poled LiTaO(3) crystal as frequency converter. Tuning wavelength rang from 0.609 microm to 5.208 microm, which covered three quasi-phase-matching processes, was obtained by means of changing the pump wavelength from 0.530 microm to 1.184 microm. The experiment results are in good agreement with theory. The maximum conversion efficiency is 62% with a 10 Hz-5 ns pump source, at the average pump power of 0.5 mW. Our results exhibit a possible application of quasi-periodic superlattice in laser technology. PMID:19581947

Pan, S D; Yuan, Y; Zhao, L N; Lv, X J; Zhu, S N

2008-11-10

73

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

74

OBSERVABLE QUASI-PERIODIC OSCILLATIONS PRODUCED BY STEEP PULSE PROFILES IN MAGNETAR FLARES

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.

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

75

Kilohertz quasi-periodic oscillations in low-mass X-ray binaries

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.

M. van der Klis

1997-04-28

76

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

77

Correlations between X-ray Spectral Characteristics and Quasi-Periodic Oscillations in Sco X-1

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

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

2007-01-01

78

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

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

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

2010-10-01

79

Correlations between X-ray Spectral Characteristics and Quasi-Periodic Oscillations in Sco X-1

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

Charles F. Bradshaw; Lev Titarchuk; Sergey Kuznetsov

2007-03-16

80

Extended States for the Schrödinger Operator with Quasi-periodic Potential in Dimension Two

We consider a Schr\\"odinger operator $H=-\\Delta+V(\\vec x)$ in dimension two with a quasi-periodic potential $V(\\vec x)$. We prove that the absolutely continuous spectrum of $H$ contains a semiaxis and there is a family of generalized eigenfunctions at every point of this semiaxis with the following properties. First, the eigenfunctions are close to plane waves $e^{i\\langle \\vec \\varkappa,\\vec x\\rangle}$ at the high energy region. Second, the isoenergetic curves in the space of momenta $\\vec \\varkappa$ corresponding to these eigenfunctions have a form of slightly distorted circles with holes (Cantor type structure). A new method of multiscale analysis in the momentum space is developed to prove these results. The result is based on the previous paper [1] on quasiperiodic polyharmonic operator $(-\\Delta)^l+V(\\vec x)$, $l>1$. We address here technical complications arising in the case $l=1$. However, this text is self-contained and can be read without familiarity with [1].

Yulia Karpeshina; Roman Shterenberg

2014-08-25

81

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

82

The observational characteristics of quasi-periodic oscillations (QPOs) from accreting neutron stars strongly indicate the oscillatory modes in the innermost regions of accretion disks as a likely source of the QPOs. The inner regions of accretion disks around neutron stars can harbor very high frequency modes related to the radial epicyclic frequency $\\kappa $. The degeneracy of $\\kappa $ with the orbital frequency $\\Omega $ is removed in a non-Keplerian boundary or transition zone near the magnetopause between the disk and the compact object. We show, by analyzing the global hydrodynamic modes of long wavelength in the boundary layers of viscous accretion disks, that the fastest growing mode frequencies are associated with frequency bands around $\\kappa $ and $\\kappa \\pm \\Omega $. The maximum growth rates are achieved near the radius where the orbital frequency $\\Omega $ is maximum. The global hydrodynamic parameters such as the surface density profile and the radial drift velocity determine which modes of free oscillations will grow at a given particular radius in the boundary layer. In accordance with the peak separation between kHz QPOs observed in neutron-star sources, the difference frequency between two consecutive bands of the fastest growing modes is always related to the spin frequency of the neutron star. This is a natural outcome of the boundary condition imposed by the rotating magnetosphere on the boundary region of the inner disk.

M. Hakan Erkut; Dimitrios Psaltis; M. Ali Alpar

2008-07-05

83

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure.

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%. PMID:14719672

Xu, Ping; Li, Kun; Zhao, Gang; Zhu, Shi-ning; Du, Yan; Ji, Shuai-hua; Zhu, Yong-yuan; Ming, Nai-ben; Luo, L; Li, K F; Cheah, K W

2004-01-01

84

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

NASA Astrophysics Data System (ADS)

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

Sheyner, Olga; Fridman, Vladimir

85

NASA Astrophysics Data System (ADS)

It has been known that high-speed solar wind streams associated with coronal holes lead to quasi-periodic substorms that occur approximately every 2˜4 hours. In this paper we examined 222 repetitive substorms that occurred during high-speed stream periods in July through December in 2003 to quantitatively determine a range of energy input from the solar wind into the magnetosphere between two consecutive substorms. For this study, we have used the Akasofu \\varepsilon-parameter to time-integrate it for the interval between two consecutive substorms, and have applied this method to the 222 substorms. We find that the average amount of solar wind input energy between two adjacent substorms is 1.28×10^{14}J and about 85% out of the 222 substorms occur after an energy input of 2×10^{13}˜2.3×10^{14}J. Based on these results, we suggest that it is not practical to predict when a substorm will occur after a previous one occurs purely based on the solar wind-magnetosphere energy coupling. We provide discussion on several possible factors that may affect determining substorm onset times during high-speed streams.

Park, M. Y.; Lee, D.-Y.; Kim, K. C.; Choi, C. R.; Park, K. S.

2008-06-01

86

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

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

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

2013-09-10

87

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

88

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

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

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

2011-01-01

89

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

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

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

2011-01-01

90

Light trapping has been an important issue for thin film silicon solar cells because of the low absorption coefficient in the near infrared range. In this paper, we present a photonic structure which combines anodic aluminum oxide (AAO) and a distributed Bragg reflector (DBR) in the backside of thin film silicon. Simulation results show that this quasi-periodic AAO structure has

Xing Sheng; Jifeng Liu; Jurgen Michel; Anuradha M. Agarwal; Lionel C. Kimerling

2009-01-01

91

In this paper we are concerned with quasi-periodic forced one dimensional maps. We consider a two parametric family of quasi-periodically forced maps such that the one dimensional map (before forcing) is unimodal and it has a full cascade of period doubling bifurcations. Between one period doubling and the next one it is known that there exist a parameter value where the $2^n$-periodic orbit is superatracting. In a previous work we proposed an extension of the one-dimensional (doubling) renormalization operator to the quasi-periodic case. We proved that, if the family satisfies suitable hypotheses, the two parameter family has two curves of reducibility loss bifurcation around these parameter values. In the present work we study the asymptotic behavior of these bifurcations when $n$ grows to infinity. We show that the asymptotic behavior depends on the Fourier expansion of the quasi-periodic coupling of the family. The theory developed here provides a theoretical explanation to the behavior that can be observ...

Rabassa, Pau; Tatjer, Joan Carles

2011-01-01

92

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

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

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

2013-06-10

93

Entrainment, instability, quasi-periodicity, and chaos in a compound neural oscillator.

We studied the dynamical behavior of a class of compound central pattern generator (CPG) models consisting of a simple neural network oscillator driven by both constant and periodic inputs of varying amplitudes, frequencies, and phases. We focused on a specific oscillator composed of two mutually inhibiting types of neuron (inspiratory and expiratory neurons) that may be considered as a minimal model of the mammalian respiratory rhythm generator. The simulation results demonstrated how a simple CPG model--with a minimum number of neurons and mild nonlinearities--may reproduce a host of complex dynamical behaviors under various periodic inputs. In particular, the network oscillated spontaneously only when both neurons received adequate and proportionate constant excitations. In the presence of a periodic source, the spontaneous rhythm was overridden by an entrained oscillation of varying forms depending on the nature of the source. Stable entrained oscillations were inducible by two types of inputs: (1) anti-phase periodic inputs with alternating agonist-antagonist drives to both neurons and (2) a single periodic drive to only one of the neurons. In-phase inputs, which exert periodic drives of similar magnitude and phase relationships to both neurons, resulted in varying disruptions of the entrained oscillations including magnitude attenuation, harmonic and phase distortions, and quasi-periodic interference. In the absence of significant phasic feedback, chaotic motion developed only when the CPG was driven by multiple periodic inputs. Apneic episodes with repetitive alternation of active (intrinsic oscillation) and inactive (cessation of oscillation) states developed when the network was driven by a moderate periodic input of low frequency. Similar results were demonstrated in other, more complex oscillator models (that is, half-center oscillator and three-phase respiratory network model). These theoretical results may have important implications in elucidating the mechanisms of rhythmogenesis in the mature and developing respiratory CPG as well as other compound CPGs in mammalian and invertebrate nervous systems. PMID:9540048

Matsugu, M; Duffin, J; Poon, C S

1998-03-01

94

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

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

2012-04-01

95

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

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

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

2011-12-10

96

Imaging Observations of Quasi-periodic Pulsations in Solar Flare Loops with SDO/AIA

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

97

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

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

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

2012-12-01

98

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

NASA Astrophysics Data System (ADS)