Noise Oscillations Research Articles

A HIGH-FREQUENCY DOPPLER FEATURE IN THE POWER SPECTRA OF SIMULATED GRMHD BLACK HOLE ACCRETION DISKS

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

Load Position Estimation for Crane Anti-Sway Control Systems

A rising number of modern cranes are equipped with anti-sway control systems to facilitate crane operation, improve positioning accuracy, and increase turnover. Commonly, these industrial crane control systems require pendulum state information for feedback control. Therefore, a pendulum sway sensor (e.g., a rope-mounted gyroscope) and a signal processing algorithm are required. Such a signal processing algorithm needs to filter out disturbances from both the sensor and the crane, e.g., signal noise and string oscillations of a long rope. Typically, these signal processing algorithms require the knowledge of the acceleration of the rope suspension point. This acceleration signal is often estimated from drive models. When drive models are uncertain, the pendulum state estimation accuracy suffers from drive model inaccuracy. In this contribution, an improved estimation algorithm is presented which estimates the load position without relying on the rope suspension point acceleration. The developed Extended Kalman Filter is implemented on a Liebherr mobile harbor crane and its effectiveness is validated with multiple test rides and GPS load position reference measurements.

Pulse shape analysis of a two fold clover detector with an EMD based new algorithm: A comparison

An investigation of Empirical Mode Decomposition (EMD) based noise filtering algorithm has been carried out on a mirror signal from a two fold germanium clover detector. EMD technique can decompose linear as well as nonlinear and chaotic signals with a precise frequency resolution. It allows to decompose the preamplifier signal (charge pulse) on an event-by-event basis. The filtering algorithm provides the information about the Intrinsic Mode Functions (IMFs) mainly dominated by the noise. It preserves the signal information and separates the overriding noise oscillations from the signals. The identification of noise structure is based on the frequency distributions of different IMFs. The preamplifier noise components which distort the azimuthal co-ordinates information have been extracted on the basis of the correlation between the different IMFs and the mirror signal. The correlation studies have been carried out both in frequency and time domain. The extracted correlation coefficient provides an important information regarding the pulse shape of the γ-ray interaction in the detector. A comparison between the EMD based and state-of-the-art wavelet based denoising techniques has also been made and discussed. It has been observed that the fractional noise strength distribution varies with the position of the collimated gamma-ray source. Above trend has been reproduced by both the denoising techniques.

TRACE OF PHASE-SPACE NONCOMMUTATIVITY IN RESPONSE OF A FREE PARTICLE TO LINEARIZED GRAVITATIONAL WAVES

Interaction of linearized gravitational waves with a otherwise free particle has been studied quantum mechanically in a noncommutative (NC) phase-space to examine whether the particle's response to the gravitational wave gets modified due to spatial and/or momentum noncommutativity. The result shows that momentum noncommutativity introduces a oscillatory noise with a specific frequency determined by the fundamental momentum scale and particle mass. Because of the global nature of the phase-space noncommutativity such noise will have similar characteristics for all detector sites and thus will stand out in a data cross-correlation procedure. If detected, this noise will provide evidence of momentum noncommutativity and also an estimation of the relevant noncommutative parameter.

МоделюваннЯ алгоритмУ генеруваннЯ ключА шифруваннЯ інформаціЇ нА основІ динамічниХ систеМ

The modern state of telecommunications requires the development of new digital communication systems. The paper presents and investigates the scheme of digital transmission of information with the usage of chaotic masking. Recovery signal is based on diagnostication of the chaotic regime of synchronous response of the slave system to the synchrosignal of the driving system in their unidirection coupled communication. Chua’s circuit has been selected as chaos generator. The essence of the proposed changes to the classical scheme of transmission with the usage of chaotic masking is the introduction of additional generator of harmonic, chaotic or noise oscillations which initially modulates digital information signal, and then additionally is added in adder to the carrying signal. The research has shown that the hiding increases with decrease of the amplitude of harmonic signal, and increase of its frequency to a value that does not exceed the practical width of the spectrum of carrying signal. The power of the signal of desynchronization at low frequency of informational signal increases almost linearly with increasing amplitude at frequencies close to the limited frequency spectrum of a chaotic signal, the power of the desynchronization signal practically does not depend on the amplitude. The results can be used for the construction of communication systems which use a chaotic signal as a carrying one. The suitability of the proposed scheme for digital data exchange has been demonstrated and the conditions of reestablishment of the information in the receiver have been determined

ENERGY-DEPENDENT POWER SPECTRAL STATES AND ORIGIN OF APERIODIC VARIABILITY IN BLACK HOLE BINARIES

We found the black hole candidate MAXI J1659-152 showed distinct power spectra, i.e., a power-law noise (PLN) vs. band-limited noise (BLN) plus quasi-periodic oscillations (QPOs), below and above about 2 keV respectively, in the observations with the Swift and the RXTE during the 2010 outburst, indicating a high energy cut-off of the PLN and a low energy cut-off of the BLN and the QPOs around 2 keV. The emergence of the PLN and the fading of the BLN and the QPOs initially took place from below 2 keV when the source entered the hard intermediate state and finally settled in the soft state three weeks later. The evolution was accompanied by the emergence of the disk spectral component and decreases in the amplitudes of variability in the soft X-ray and the hard X-ray bands. Our results indicate that the PLN is associated with the optically thick disk in both hard and intermediate states, and power spectral state is independent of the X-ray energy spectral state in a broadband view. We suggest that in the hard and the intermediate state, the BLN and the QPOs emerge from the innermost hot flow subjected to Comptonization, while the PLN originates from the optically thick disk further out. The energy cut-offs of the PLN and the BLN or QPOs then follow the temperature of the seed photons from the inner edge of the optically thick disk, while the high frequency cut-off of the PLN follows the orbital frequency at the inner edge of the optically thick disk as well.

АдаптаціЯ методУ хаОтичнОгО маскуваннЯ длЯ цифрОвОгО передаваннЯ інформаціЇ

The modern state of telecommunications requires the development of new digital communication systems. The paper presents and investigates the scheme of digital transmission of information with the usage of chaotic masking. Recovery signal is based on diagnostication of the chaotic regime of synchronous response of the slave system to the synchrosignal of the driving system in their unidirection coupled communication. Chua’s circuit has been selected as chaos generator. The essence of the proposed changes to the classical scheme of transmission with the usage of chaotic masking is the introduction of additional generator of harmonic, chaotic or noise oscillations which initially modulates digital information signal, and then additionally is added in adder to the carrying signal. The research has shown that the hiding increases with decrease of the amplitude of harmonic signal, and increase of its frequency to a value that does not exceed the practical width of the spectrum of carrying signal. The power of the signal of desynchronization at low frequency of informational signal increases almost linearly with increasing amplitude at frequencies close to the limited frequency spectrum of a chaotic signal, the power of the desynchronization signal practically does not depend on the amplitude. The results can be used for the construction of communication systems which use a chaotic signal as a carrying one. The suitability of the proposed scheme for digital data exchange has been demonstrated and the conditions of reestablishment of the information in the receiver have been determined

Effect of Body Mass Index on Intrafraction Prostate Displacement Monitored by Real-Time Electromagnetic Tracking

To evaluate, using real-time monitoring of implanted radiofrequency transponders, the intrafraction prostate displacement of patients as a function of body mass index (BMI). The motions of Beacon radiofrequency transponders (Calypso Medical Technologies, Seattle, WA) implanted in the prostate glands of 66 men were monitored throughout the course of intensity modulated radiation therapy. Data were acquired at 10 Hz from setup to the end of treatment, but only the 1.7 million data points with a "beam on" tag were used in the analysis. There were 21 obese patients, with BMI ≥ 30 and 45 nonobese patients in the study. Mean displacements were least in the left-right lateral direction (0.56 ± 0.24 mm) and approximately twice that magnitude in the superior-inferior and anterior-posterior directions. The net vector displacement was larger still, 1.95 ± 0.47 mm. Stratified by BMI cohort, the mean displacements per patient in the 3 Cartesian axes as well as the net vector for patients with BMI ≥ 30 were slightly less (<0.2 mm) but not significantly different than the corresponding values for patients with lower BMIs. As a surrogate for the magnitude of oscillatory noise, the standard deviation for displacements in all measured planes showed no significant differences in the prostate positional variability between the lower and higher BMI groups. Histograms of prostate displacements showed a lower frequency of large displacements in obese patients, and there were no significant differences in short-term and long-term velocity distributions. After patients were positioned accurately using implanted radiofrequency transponders, the intrafractional displacements in the lateral, superior-inferior, and anterior-posterior directions as well as the net vector displacements were smaller, but not significantly so, for obese men than for those with lower BMI.

A Data-Driven Noise Reduction Method and Its Application for the Enhancement of Stress Wave Signals

Ensemble empirical mode decomposition (EEMD) has been recently used to recover a signal from observed noisy data. Typically this is performed by partial reconstruction or thresholding operation. In this paper we describe an efficient noise reduction method. EEMD is used to decompose a signal into several intrinsic mode functions (IMFs). The time intervals between two adjacent zero-crossings within the IMF, called instantaneous half period (IHP), are used as a criterion to detect and classify the noise oscillations. The undesirable waveforms with a larger IHP are set to zero. Furthermore, the optimum threshold in this approach can be derived from the signal itself using the consecutive mean square error (CMSE). The method is fully data driven, and it requires no prior knowledge of the target signals. This method can be verified with the simulative program by using Matlab. The denoising results are proper. In comparison with other EEMD based methods, it is concluded that the means adopted in this paper is suitable to preprocess the stress wave signals in the wood nondestructive testing.

Electrostatic force between rings and discs of charge inside a grounded metallic pipe using the Green’s function technique

Abstract We derive analytic formulae for the electrostatic force between ring and disc charge distributions inside a grounded metallic pipe using the Green’s function technique. These distribution models are useful in the modeling of electron beams commonly employed in microwave tubes. We analyze the electric force between two discs, between two rings, and between a disc and a ring and we compare the results for the electric potential, field, and force to numerical ones obtained from a 3D electrostatic solver. Present expressions were developed to avoid an oscillatory noise when the field diverges by axial proximity between source and observer.

Modelling variability in black hole binaries: linking simulations to observations

Black hole accretion flows show rapid X-ray variability. The Power Spectral Density (PSD) of this is typically fit by a phenomenological model of multiple Lorentzians for both the broad band noise and Quasi-Periodic Oscillations (QPOs). Our previous paper (Ingram & Done 2011) developed the first physical model for the PSD and fit this to observational data. This was based on the same truncated disc/hot inner flow geometry which can explain the correlated properties of the energy spectra. This assumes that the broad band noise is from propagating fluctuations in mass accretion rate within the hot flow, while the QPO is produced by global Lense-Thirring precession of the same hot flow. Here we develop this model, making some significant improvements. Firstly we specify that the viscous frequency (equivalently, surface density) in the hot flow has the same form as that measured from numerical simulations of precessing, tilted accretion flows. Secondly, we refine the statistical techniques which we use to fit the model to the data. We re-analyse the PSD from the 1998 rise to outburst of XTE J1550-564 with our new model in order to assess the impact of these changes. We find that the derived outer radii of the hot flow (set by the inner radius of the truncated disc) are rather similar, changing from ~68-13 Rg throughout the outburst rise. However, the more physical assumptions of our new model also allow us to constrain the scale height of the flow. This decreases as the outer radius of the flow decreases, as expected from the spectral evolution. The spectrum steepens in response to the increased cooling as the as the truncation radius sweeps in, so gas pressure support for the flow decreases. The new model, propfluc, is publically available within the xspec spectral fitting package.

Stress wave signal denoising using ensemble empirical mode decomposition and an instantaneous half period model.

Stress-wave-based techniques have been proven to be an accurate nondestructive test means for determining the quality of wood based materials and they been widely used for this purpose. However, the results are usually inconsistent, partially due to the significant difficulties in processing the nonlinear, non-stationary stress wave signals which are often corrupted by noise. In this paper, an ensemble empirical mode decomposition (EEMD) based approach with the aim of signal denoising was proposed and applied to stress wave signals. The method defined the time interval between two adjacent zero-crossings within the intrinsic mode function (IMF) as the instantaneous half period (IHP) and used it as a criterion to detect and classify the noise oscillations. The waveform between the two adjacent zero-crossings was retained when the IHP was larger than the predefined threshold, whereas the waveforms with smaller IHP were set to zero. Finally the estimated signal was obtained by reconstructing the processed IMFs. The details of threshold choosing rules were also discussed in the paper. Additive Gaussian white noise was embedded into real stress wave signals to test the proposed method. Butterworth low pass filter, EEMD-based low pass filter and EEMD-based thresholding filter were used to compare filtering performance. Mean square error between clean and filtered stress waves was used as filtering performance indexes. The results demonstrated the excellent efficiency of the proposed method.

Dynamic characterization of complex bridge structures with passive control systems

The article focuses on dynamic identification strategies for complex bridge structures equipped with passive vibration control systems. In detail, a recently built curved twin-deck cable-stayed footbridge was analysed, whose structural complexity required wind tunnel tests and a specific design for vibration reduction. A passive control system was deemed necessary in order to: (i) meet wind safety requirements owing to premature aeroelastic instability, and (ii) mitigate pedestrian vibrations. Uncertainties in numerical modelling and changes during its construction suggested a modal testing campaign in order to check the effectiveness of the vibration absorption system. Different excitation sources related to output-only techniques were exploited, including ambient noise and free-decay oscillations through released masses. Several sensor set-ups were deemed necessary in the view of the structure complexity that exhibits numerous close modes and modal couplings between the two decks. The effect of the dampers was analysed by performing the testing campaign for two distinct configurations: (i) disconnected dampers, and (ii) connected dampers. The dynamic properties of the cables were also investigated in order to complete the whole dynamic characterization of the structure. Two time-domain techniques were applied and compared under different excitations. The dynamic identification procedure provided consistent results and highlighted that full functionality of the damping system was realized only for high vibration levels. Finally, time–frequency instantaneous estimators were applied in order to analyse both the modal frequency and the damping time-variation. These results revealed amplitude dependent behaviours as well as dynamic deck-cable interactions. Copyright © 2011 John Wiley & Sons, Ltd.

A Model of the Surface Electromyogram in Pathological Tremor

The study developed a novel multi-scale model for simulating the surface electromyogram (EMG) of an antagonistic pair of muscles during pathological tremor. By combining and expanding mathematical descriptions from motor units to limb kinematics, the model constitutes the first attempt to simulate the surface EMG and the individual motor unit activity under the influence of descending voluntary command, oscillatory noise in the descending signal, and afferent feedback when controlling a freely moving limb to achieve a predefined angular trajectory. The oscillatory noise was adjusted to simulate various types of pathological tremor. The simulations replicated previously reported experimental results for the power spectral density of the surface EMG, the angular velocity of the limb, and single motor unit activity. The model provides a powerful tool for extracting information about how the surface EMG can be used to describe tremor in various conditions, including different tremor frequencies and intensities, that cannot be achieved solely with experimental approaches.

Synaptic Noise and Physiological Coupling Generate High-Frequency Oscillations in a Hippocampal Computational Model

There is great interest in the role of coherent oscillations in the brain. In some cases, high-frequency oscillations (HFOs) are integral to normal brain function, whereas at other times they are implicated as markers of epileptic tissue. Mechanisms underlying HFO generation, especially in abnormal tissue, are not well understood. Using a physiological computer model of hippocampus, we investigate random synaptic activity (noise) as a potential initiator of HFOs. We explore parameters necessary to produce these oscillations and quantify the response using the tools of stochastic resonance (SR) and coherence resonance (CR). As predicted by SR, when noise was added to the network the model was able to detect a subthreshold periodic signal. Addition of basket cell interneurons produced two novel SR effects: 1) improved signal detection at low noise levels and 2) formation of coherent oscillations at high noise that were entrained to harmonics of the signal frequency. The periodic signal was then removed to study oscillations generated only by noise. The combined effects of network coupling and synaptic noise produced coherent, periodic oscillations within the network, an example of CR. Our results show that, under normal coupling conditions, synaptic noise was able to produce gamma (30-100 Hz) frequency oscillations. Synaptic noise generated HFOs in the ripple range (100-200 Hz) when the network had parameters similar to pathological findings in epilepsy: increased gap junctions or recurrent synaptic connections, loss of inhibitory interneurons such as basket cells, and increased synaptic noise. The model parameters that generated these effects are comparable with published experimental data. We propose that increased synaptic noise and physiological coupling mechanisms are sufficient to generate gamma oscillations and that pathologic changes in noise and coupling similar to those in epilepsy can produce abnormal ripples.

Coherence resonance in a unijunction transistor relaxation oscillator

The phenomenon of coherence resonance is investigated in an unijunction transistor relaxation oscillator and quantified by estimating the normal variance (NV). Depending on the measuring points, two types of NV curves have been obtained. We have observed that the degradations in coherency at higher noise amplitudes in our system is probably the result of direct interference of coherent oscillations and the stochastic perturbation. Degradation of coherency may be minimal if this direct interference of noise and coherent oscillations is eliminated.

Aggregation Bias in Traffic Flow Time Series: The Effects of Ignoring It

Current ITS infrastructure provides the ability to simultaneously capture and monitor a variety of transportation data in very fine intervals. However, in order for the data to be analyzed and integrated to the different intelligent traffic management and traveler information systems, the optimum data resolution should be selected. In many transportation studies it is suggested that data should be aggregated in order to avoid the effects of noise and spurious oscillations. In the present paper, we analyze the effect of data aggregation on the fractional dynamics of traffic volume and occupancy, as well as the information degradation between the original and the aggregated data. Results indicate that aggregation may suppress the long memory characteristics of traffic flow. Moreover, uncertainty associated with the aggregated data with respect to the original data series increases with coarser data resolutions.

Image Decomposition and Texture Segmentation via Sparse Representation

Decomposing an image into a texture part and a non-texture (cartoon) part, as well as grouping the texture part into several homogeneous subparts, is studied in this letter. The so-called texture part is composed of both the self-similar structure and the oscillatory noise. The self-similar structure of each homogenous subtexture is captured in its principal subspace. Both the segmentation and the decomposition are essentially related to sparse representation and are united to a framework.

Ground Chamber Measurements of the Electromagnetic Emissions from the Hayabusa Ion Engine

DOI: 10.2514/1.19473 Radiated electric field emissions from the prototype model of the ion engine system of the asteroid explorer Hayabusa (MUSES-C) were measured in approximate accordance to MIL-STD-461C. The typical noise level exceeded the narrowband specification at frequencies less than 5 MHz. The microwave discharge neutralizer generates broadband noise and narrowband oscillations that have a fundamental frequency of about 160 kHz and are accompanied by its harmonics up to the fifth. Leakage of 4.25 GHz microwaves for plasma production and its second harmonic were 65 dB and 35 dB above specifications, respectively. The X-band receiver onboard Hayabusa measured the noise from the ion engine system at the uplink frequency of 7.16 GHz through a horn antenna. This susceptibility test showed that the microwave discharge ion thruster is unlikely to interfere with deep space microwave communication. Nomenclature d = neutralizer orifice diameter ID = electron emission current of the neutralizer l = anode distance from the neutralizer _ m = xenon flow rate P� = microwave power for plasma discharge of the neutralizer VD = voltage between the neutralizer and the anode in diode mode operation

Letter by Selvaraj and Chauhan Regarding Article, “Upsurge in T-Wave Alternans and Nonalternating Repolarization Instability Precedes Spontaneous Initiation of Ventricular Tachyarrhythmias in Humans”

HomeCirculationVol. 115, No. 1Letter by Selvaraj and Chauhan Regarding Article, “Upsurge in T-Wave Alternans and Nonalternating Repolarization Instability Precedes Spontaneous Initiation of Ventricular Tachyarrhythmias in Humans” Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessLetterPDF/EPUBLetter by Selvaraj and Chauhan Regarding Article, “Upsurge in T-Wave Alternans and Nonalternating Repolarization Instability Precedes Spontaneous Initiation of Ventricular Tachyarrhythmias in Humans” Raja J. Selvaraj and Vijay S. Chauhan Raja J. SelvarajRaja J. Selvaraj Division of Cardiology, University Health Network, Toronto, Canada Search for more papers by this author and Vijay S. ChauhanVijay S. Chauhan Division of Cardiology, University Health Network, Toronto, Canada Search for more papers by this author Originally published2 Jan 2007https://doi.org/10.1161/CIRCULATIONAHA.106.650952Circulation. 2007;115:e9To the Editor:We read with interest the article by Shusterman et al1 concerning repolarization dynamics preceding spontaneous initiation of ventricular tachyarrhythmias in humans. Two related time-domain methods measured a larger magnitude of “alternans” at 30 minutes compared with 60 to 120 minutes preceding arrhythmia onset. Spectral analysis of T-wave amplitude showed a nonuniform increase in power in all frequency ranges. The authors interpret these findings as a surge in alternans and nonalternating repolarization complexity preceding the arrhythmia.An increase in sympathetic activity preceding the onset of ventricular arrhythmia was reported by the authors in the same population.2 This can lead to increased noise in the ECG recordings from perspiration and an increase in motion and respiratory artifact.3The modified moving average and, to a larger extent, the intrabeat average measurements are affected by noise that cannot be completely removed by preprocessing.3 Using these time-domain methods, the authors have previously emphasized the need to measure surrogate alternans in the isoelectric T end to P onset segment to show that an increase in T-wave alternans magnitude is not artifactually attributable to noise.3 It is unclear why the authors did not use a similar analysis of surrogate alternans in the present study1 to ensure that noise was not a confounder.Using the spectral method, white noise can spuriously increase the spectral power in the alternans frequency, and subtraction of the spectral power in a “noise band” is required to measure true alternans.4 Therefore, the increase in spectral power seen in all frequency ranges could be explained by an increase in noise rather than an increase in “nonalternating repolarization complexity.” The possibility of subharmonics influencing the measured power in the alternans range is another important confounder, particularly respiratory subharmonics (0.15 to 0.25 cpb), which increase in spectral power before the tachyarrhythmia. The authors feel the contribution of respiratory subharmonics is improbable because the increase in T-wave alternans magnitude has been confirmed by 3 independent methods. However, the concordant findings do not exclude the confounding effects of subharmonics, because these methods are all inherently influenced by subharmonics.3 Although the increase in alternans may not be accounted for entirely by respiratory subharmonics, this is likely an important contribution and is not unexpected, because respiratory excursions that influence T-wave amplitude can increase during sympathetic surges preceding tachyarrhythmia. Thus, we feel that white noise and respiratory oscillations may significantly contribute to the apparent increase in alternating and nonalternating repolarization instability.DisclosuresNone.1 Shusterman V, Goldberg A, London B. Upsurge in T-wave alternans and nonalternating repolarization instability precedes spontaneous initiation of ventricular tachyarrhythmias in humans. Circulation. 2006; 113: 2880–2887.LinkGoogle Scholar2 Shusterman V, Aysin B, Gottipaty V, Weiss R, Brode S, Schwartzman D, Anderson KP. Autonomic nervous system activity and the spontaneous initiation of ventricular tachycardia. ESVEM Investigators. Electrophysiologic Study Versus Electrocardiographic Monitoring Trial. J Am Coll Cardiol. 1998; 32: 1891–1899.CrossrefMedlineGoogle Scholar3 Shusterman V, Goldberg A. Tracking repolarization dynamics in real-life data. J Electrocardiol. 2004; 37 (suppl): 180–186.CrossrefMedlineGoogle Scholar4 Bloomfield DM, Hohnloser SH, Cohen RJ. Interpretation and classification of microvolt T wave alternans tests. J Cardiovasc Electrophysiol. 2002; 13: 502–512.CrossrefMedlineGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetails January 2, 2007Vol 115, Issue 1 Advertisement Article InformationMetrics https://doi.org/10.1161/CIRCULATIONAHA.106.650952PMID: 17200449 Originally publishedJanuary 2, 2007 PDF download Advertisement SubjectsArrhythmias