Direct Cross-correlation Research Articles

Diagnostic aspects of laboratory research of amniotic fluid are at premature births

The objective: to learn a diagnostic value clinical-and-laboratory research of amniotic fluid atpremature births. Materials and methods. Under our supervision in clinical terms was 142 puerpera which actedon births to maternity establishments of different level. All the inspected acted with beginning ofchildbirth. From an incurrence there were eliminated puerpera with a multifetation, pelvic fetal presentation, anomalies of development of fetus and antenatal fetal death. Most inspected was inactive reproductive age. Middle age of inspected made 24,9±0,3 year.A complex clinical inspection was conducted all pregnant at a receipt in permanentestablishment. The clinical inspection of women was included by the study of anamnesisof life, including also to anamnesis of disease, the features of motion of pregnancy werestudied, the generally accepted laboratory and functional methods of research wereconducted. To the complex of additional methods researches were included echographic,cardiotocographic and Doppler. Results. The study of hormonal status of amniotic fluid rotined in births, that content ofestradiol during a childbirth had hesitated within the limits of 30–180 ng/ml. Found out areliable difference between maintenance of this hormone in a amniotic fluid at birth of boysand girls. So at birth of girls the index of estradiol arrived at 21,4±2,3 ng/ml, while at birthof boys a middle index of estradiol was at the level of 16,5±2,3 ng/ml. Although found out adifference and did not carry reliable character (р>0,05), this fact specifies on participating offetus in making a amniotic fluid.Meantime, level of estradiol in a amniotic fluid at birth of boys and girls identically for certainrose at presence of obstetric pathology, such as a weakness of childbirth in combination withfetal distress (p<0,05). An analogical picture is marked in maintenance of cortisol in a amnioticfluid. Indexes of cortisol in a amniotic fluid in births were within the limits of 200–450 nmol/ml.Thus at birth of girls the middle level of cortisol made 180,4±8,4 nmol/ml and at birth of boys –265,4±10,2 nmol/ml, that also testifies to participating of fetus in making of amniotic fluid.Between two hormones found out direct cross-correlation connection (r=0,64; p<0,05). Atpathological motion of births index of estradiol, as well as to the cortisol, rose for certain, thathad testified to the intrauterine fetal distress (p<0,01). The found out intercommunication oflevels of estradiol and cortisol is with other parameters of amniotic fluid and state of fetus inbirths. An index of estradiol was in direct dependence on the indexes of resistance of bloodstream at dopplerometry, namely – systolic-diastolic ratio and index of resistance (r=0,64).The indexes of estradiol and cortisol appropriately rose at the decline of pH in a amnioticfluid (r=-0,71; p<0,01) and at the decline of basale rhythm of cardiac activity of fetus oncardiotocogram (r=-0,69). Conclusion. The results of the conducted researches rotined that the physical and chemicaland biochemical parameters of amniotic fluid are inclined statistically to the reliable changesdepending on the term of births and intrauterine fetal distress in births. A most model are changesof concentration of kreatinine and urea in a amniotic fluid at births which were late, that canhave a diagnostic value. Combination of the indicated signs with the decline of acidity by theincrease of closeness of amniotic fluid at births which were late, and also a presence in it ofmeconium specifies on violation of metabolism of fetus and necessity of timely correction of foundout violations.The clinical use of the transferred parameters of amniotic fluid in births has an important diagnosticvalue at physiology and pathological motion of pregnancy and births.

Robustness measures for molecular detections using high-resolution transmission spectroscopy of exoplanets

ABSTRACT Ground-based high-resolution transmission spectroscopy has emerged as a promising technique for detecting chemicals in transiting exoplanetary atmospheres. Despite chemical inferences in several exoplanets and previous robustness studies, a robust and consistent detrending method to remove telluric and stellar features from transmission spectra has yet to be agreed upon. In this work, we investigate the robustness of metrics used to optimize principle component analysis (PCA)-based detrending for high-resolution transmission spectra of exoplanets in the near-infrared. As a case study, we consider observations of the hot Jupiter HD 189733 b obtained using the CARMENES spectrograph on the 3.5 m CAHA telescope. We confirm that optimizing the detrending parameters to maximize the signal-to-noise ratio (S/N) of a cross-correlation signal in the presence of noise has the potential to bias the detection significance at the planetary velocity of optimization. However, we find that optimization using the difference between a signal-injected cross-correlation function and the direct cross-correlation function (CCF) is more robust against over-optimization of noise and spurious signals. We additionally examine the robustness of weighting the contribution of each order to the final CCF, and of S/N calculations. Using a prescribed robust methodology, we confirm H2O in the atmosphere of HD 189733 b (S/N = 6.1). We then investigate two further case studies, of exoplanets HD 209458 b and WASP-76 b, confirming OH in the atmosphere of WASP-76 b (S/N = 4.7), and demonstrating how non-robust methods may induce false positive or inflated detections. Our findings pave the way towards a robust framework for homogeneous characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy in the near-infrared.

A lightweight convolutional neural network to reconstruct deformation in BOS recordings

We introduce a Convolutional Neural Network (CNN) that is specifically designed and trained to post-process recordings obtained by Background Oriented Schlieren (BOS), a popular technique to visualize compressible and convective flows. To reconstruct BOS image deformation, we devised a lightweight network (LIMA) that has comparatively fewer parameters to train than the CNNs that have been previously proposed for optical flow. To train LIMA, we introduce a novel strategy based on the generation of synthetic images from random-irrotational deformation fields, which are intended to mimic those provided by real BOS recordings. This allows us to generate a large number of training examples at minimal computational cost. To assess the accuracy of the reconstructed displacements, we consider test cases consisting of synthetic images with sinusoidal displacement as well as images obtained in the experimental studies of a hot plume in air and a flow past and inside a heated hollow hemisphere. By comparing the reconstructed deformation fields using the LIMA or conventional post-processing techniques used in Direct Image Correlation (DIC) or conventional image cross-correlation, we show that LIMA is more accurate and robust in the synthetic test case. When applied to experimental BOS recordings, all methods provide similar and consistent deformation fields. As LIMA is capable of achieving a comparable or better accuracy at a fraction of the computational costs, it represents a valuable alternative to conventional post-processing techniques for BOS experiments.

Flow measurement in open channels using imaging techniques in conjunction with a convolutional neural network

Data related to river velocity and discharge are important for water resource management. Non-intrusive image measurement techniques based on direct cross-correlation (DCC) algorithms, such as particle image velocimetry (PIV), are widely used to measure velocity and discharge in the field. However, environmental noise is highly complex and uncontrollable in the field, significantly reducing the accuracy of DCC-based methods. Convolutional neural networks (CNNs) are commonly used in image recognition because of their outstanding accuracy, which far exceeds that of conventional imaging methods. However, these accuracy levels cannot be directly extrapolated for flow movement estimation. Therefore, in this study, we developed an innovative sub-pixel correction technique that allows CNN-based methods to obtain stable measurements in the PIV framework. This is the first study that successfully applied the concept of CNN to measure velocity data using images. The Hamel-Oseen vortex-flow, uniform steady-flow, and plane laminar jet-flow models are established as benchmark vector fields. Non-uniform illumination and Gaussian noise with varying degrees of interference are added to the synthetic data to evaluate the performance of the CNN-based method in PIV. For noiseless images, the DCC-based and CNN-based methods achieve lower measurement errors than benchmark errors. For noisy images, the DCC suffers a fold error increase ranging from 2.77 to 31.13, whereas the CNN suffers only a fold error increase ranging from 1.25 to 1.68. A 30-m-long flume is then used in an uncontrolled environment to mimic real-world flow measurement. The dispersion of the instantaneous velocity measurements for the CNN is more concentrated than that for the DCC. The acoustic Doppler velocimetry yields an error of only 7.87% in discharge estimation using CNN. These results indicate that the CNN-based method is more robust than conventional methods and has the potential to be effectively applied to measurements in the field.

Mechano-Transduction Boosts the Aging Effects in Human Erythrocytes Submitted to Mechanical Stimulation.

Erythrocytes’ aging and mechano-transduction are fundamental cellular pathways that determine the red blood cells’ (RBCs) behavior and function. The aging pattern can be influenced, in morphological, biochemical, and metabolic terms by the environmental conditions. In this paper, we studied the effect of a moderate mechanical stimulation applied through external shaking during the RBCs aging and revealed a strong acceleration of the aging pattern induced by such stimulation. Moreover, we evaluated the behavior of the main cellular effectors and resources in the presence of drugs (diamide) or of specific inhibitors of the mechano-transduction (probenecid, carbenoxolone, and glibenclamide). This approach provided the first evidence of a direct cross-correlation between aging and mechano-transduction and permitted an evaluation of the overall metabolic regulation and of the insurgence of specific morphological features, such as micro-vesicles and roughness alterations. Overall, for the first time the present data provided a schematic to understand the integration of distinct complex patterns in a comprehensive view of the cell and of its interactions with the environment. Mechano-transduction produces structural effects that are correlated with the stimulation and the strength of the environmental stimulation is paramount to effectively activate and trigger the biological cascades initiated by the mechano-sensing.

A nonlinear beamforming for enhanced spatiotemporal sensitivity in high frame rate ultrasound flow imaging

Typically, an ultrasound flow imaging system employs the conventional delay and sum (DAS) beamformer due to its inherent low complexity. But the conventional DAS technique offers poor contrast, low imaging resolution, and limited spatiotemporal sensitivity. This article attempts to improve the spatiotemporal sensitivity of the conventional flow imaging with a novel multiply and sum based nonlinear high-resolution (NLHR) beamforming approach. The major advantages of the proposed beamformer are the harmonic generation and the enhanced coherence in beamformed signals that improve the spatiotemporal sensitivity towards flow transients. We demonstrate the proposed beamformer for a directional cross-correlation as well as an autocorrelation based velocity estimator with simulated parabolic flow profiles of different velocities and flow directions, an in-vitro rotating disk dataset, and pulsatile flow experiments. The sensitivity of NLHR beamforming towards the flow transients is validated in-vitro with a sudden reversal of flow direction and air bubble tracking experiments. The comparison between the time–frequency plots of DAS and NLHR beamforming indicates that the impulsive spatiotemporal changes induced by the flow of air bubbles are clearly characterized by nonlinear beamforming than that of DAS beamforming. Furthermore, better spatiotemporal velocity tracking of a single air bubble and a clear distinguishability between the tracking of two proximal air bubbles are observed in-vitro. Preliminary studies on the in-vivo carotid data also show comparable, if not better, results than that of the DAS algorithm. Detailed results for each test case in simulation, phantom, and in-vivo studies are available as movies with the supplementary material and online [Online Link].

Time Synchronization of Multimodal Physiological Signals through Alignment of Common Signal Types and Its Technical Considerations in Digital Health

Background: Despite advancements in digital health, it remains challenging to obtain precise time synchronization of multimodal physiological signals collected through different devices. Existing algorithms mainly rely on specific physiological features that restrict the use cases to certain signal types. The present study aims to complement previous algorithms and solve a niche time alignment problem when a common signal type is available across different devices. Methods: We proposed a simple time alignment approach based on the direct cross-correlation of temporal amplitudes, making it agnostic and thus generalizable to different signal types. The approach was tested on a public electrocardiographic (ECG) dataset to simulate the synchronization of signals collected from an ECG watch and an ECG patch. The algorithm was evaluated considering key practical factors, including sample durations, signal quality index (SQI), resilience to noise, and varying sampling rates. Results: The proposed approach requires a short sample duration (30 s) to operate, and demonstrates stable performance across varying sampling rates and resilience to common noise. The lowest synchronization delay achieved by the algorithm is 0.13 s with the integration of SQI thresholding. Conclusions: Our findings help improve the time alignment of multimodal signals in digital health and advance healthcare toward precise remote monitoring and disease prevention.

Wideband Channel Sounding Simulation Tool and Sounding Sequences Evaluation

This work presents the Base-Band Sounding Tool (BSOT), a wideband channel sounding simulator with different scenarios and configurations, providing the channels characterization in terms of delay and Doppler spreading. BSOT follows COST 207 statistical channel model and the pulse compression technique with direct cross-correlation at the receiver. Besides its validation results, the paper presentes a performance evaluation of 6 types of sounding sequences (Random, Kasami, Gold, m-Sequence, Zadoff-Chu and Golay), including a robustness evaluation with different lengths, sampling rates, and SNR values. The simulated outputs are coherent with the theoretical modeling, and the investigation of sounding sequences reveals a better sounding performance obtained with the Zadoff-Chu and Golay sequences.

Performance Assessment of Row-Column Transverse Oscillation Tensor Velocity Imaging Using Computational Fluid Dynamics Simulation of Carotid Bifurcation Flow.

In this work, the accuracy of row-column tensor velocity imaging (TVI), i.e., 3-D vector flow imaging (VFI) in 3-D space over time, is quantified on a complex, clinically relevant flow. The quantification is achieved by transferring the flow simulated using computational fluid dynamics (CFD) to a Field II simulation environment, and this allows for a direct comparison between the actual and estimated velocities. The carotid bifurcation flow simulations were performed with a peak inlet velocity of 80 cm/s, nonrigid vessel walls, and a flow cycle duration of 1.2 s. The flow was simulated from two observation angles, and it was acquired using a 3-MHz 62+62 row-column addressed array (RCA) at a pulse repetition frequency ( fprf ) of 10 and 20 kHz. The tensor velocities were obtained at a frame rate of 208.3 Hz, at fprf = 10 kHz , and the results from two velocity estimators were compared. The two estimators were the directional transverse oscillation (TO) cross correlation estimator and the proposed autocorrelation estimator. Linear regression between the actual and estimated velocity components yielded, for the cross correlation estimator, an R 2 value in the range of 0.89-0.91, 0.46-0.77, and 0.91-0.97 for the x -, y -, and z -components, and 0.87-0.89, 0.40-0.83, and 0.91-0.96 when using the autocorrelation estimator. The results demonstrate that an RCA can, with just 62 receive channels, measure complex 3-D flow fields at a high volume rate.

Leak location procedure based on the complex-valued FastICA blind deconvolution algorithm for water-filled branch pipe

Abstract Water pipe networks have a large number of branch joints. Branch joint shunting generates vortices in the fluid, which excite the pipe wall to produce a type of branch noise. The branch noise is coupled with the leak source signal through the pipe. Here, a novel leak location protocol based on the complex-valued FastICA method (C-FastICA) is proposed to address the leak location problem under the branch noise interference. The C-FastICA, a complex-value domain blind deconvolution algorithm, effectively extended the cost function, constraint function, and iteration rules of the instantaneous linear FastICA into the complex-valued domain. The C-FastICA method was used to realize the separation of branch noise and leak source signal. The experimental results showed that the separation efficiency of the C-FastICA was higher than that of time-domain blind convolution separation (T-BCS). Furthermore, the relative location error of the C-FastICA method to the leak point was less than 14.238%, which was significantly lower than in traditional T-BCS and direct cross-correlation (DCC) technology.

High-precision nonlocal temporal correlation identification of entangled photon pairs for quantum clock synchronization.

High-precision nonlocal temporal correlation identification in entangled photon pairs is critical to measure the time offset between remote independent time scales for many quantum information applications. The first nonlocal correlation identification was reported in 2009, which extracts the time offset via the algorithm of iterative fast Fourier transformations and their inverse. The best identification resolution is restricted by the peak identification threshold of the algorithm, and thus the time offset calculation precision is limited. In this paper, an improvement for the identification is presented both in resolution and precision via a modified algorithm of direct cross correlation extraction. A flexible resolution down to 1 ps is realized, which is only dependent on the least significant bit resolution of the time-tagging device. The attainable precision is shown to be mainly determined by the inherent timing jitter of single photon detectors, the acquired pair rate, and acquisition time, and a sub-picosecond precision (0.72 ps) has been achieved at an acquisition time of 4.5 s. This high-precision nonlocal measurement realization provides a solid foundation for the field applications of entanglement-based quantum clock synchronization, ranging, and communications.

Leakage Signal Analysis of Urban Gas Pipeline Based on Improved Variational Mode Decomposition

Aiming at problems of multipoint leakage source detection and low positioning accuracy in urban gas pipelines, a multipoint leak location method base on improved variational mode decomposition (VMD) was proposed. By improving the VMD decomposition of the original leakage signal, the parameters of the VMD were optimized to reduce the influence of noise and weak correlation signals on the leak location. Then the multi-point leakage location model of pipeline was established, and the sensitive modal component Intrinsic mode function (IMF) with the most leakage information was selected by multiscale entropy. According to the characteristics of the blind source separation method, the relevant time delays of the simultaneous leakage of multiple points on the pipeline and the frequency of the signal are extracted. Finally, The location of the leak source is determined according to the principle of cross-correlation. The experimental results show that compared with the direct cross-correlation method and the VMD-based method, the proposed multipoint leak diagnosis method has less error, the minimum relative error is 1.61%, and the positioning accuracy is higher.

Electrostatic induced charge signal extraction based on waveform characteristic in time domain

The measurement signal from the inner flush-mounted electrostatic sensor includes both induced charge signal and transferred charge signal. The extraction of induced charge signal from the mixed signals is of great significance to the solid phase velocity measurement. In this paper, a method of extracting induced charge signal based on the waveform characteristic in time domain is proposed. In the calibration experiment of the belt-style electrostatic velocity measurement rig, the mean absolute percentage error and the mean relative standard deviation (1.30%/1.01%) are lower than the direct cross-correlation method (4.81%/5.71%) and the Empirical Mode Decomposition (EMD-based) method (2.55%/2.38%), moreover, the average signal-to-noise ratio (SNR) of the proposed method is the greatest. In the experiment of gas-solid two-phase flow rig, the average correlation coefficient and the mean relative standard deviation are 0.77 and 2.46%, which are better than the direct cross-correlation (0.48/2.87%) and the Discrete Wavelet Transform (DWT) (0.74/2.69%).

Effect of fluid injection on turbulence and noise reduction of a supersonic jet.

Supersonic jets, such as the ones used in high-performance military aircraft, have both downstream and upstream noise components due to the large-scale turbulent structures and the presence of shock cells in the jet plume. The fluid insert technology is a noise reduction method that has been shown to effectively reduce both these noise components. This paper analyses the unsteady flow changes associated with different fluid insert configurations with a goal of helping to understand the detailed noise reduction mechanisms. Using direct cross-correlations of the near-field data with the far-field microphone signals, it is found that even the use of a single injector as a fluid insert helps break up the large-scale structures of the flow. However, a more azimuthally distributed blowing is required to reduce the upstream broadband shock-associated noise (BBSAN). Addition of upstream injectors at each azimuthal location further enhances the BBSAN reduction. Decomposition of the jet flow-field into hydrodynamic and acoustic modes shows that fluid insert nozzles reduce the amplitude and convection speed of the coherent acoustic mode in the plane of highest noise reduction. This article is part of the theme issue 'Frontiers of aeroacoustics research: theory, computation and experiment'.

A Signal Processing Algorithm Proposed for OFDR Distributed Sensing System to Enhance Its Performance

A novel OFDR processing algorithm is proposed to improve the measurable range. The high local similarity found between the reference and measurement Rayleigh scattering spectrum (ReS and MeS). The spectrum shift of the Rayleigh backscatter which is the function of strain is measured using an improved optical frequency-domain reflectometry (OFDR). This method is improved by matching local ReS on MeS rather than a direct cross-correlation between whole ReS and MeS in conventional OFDR methods. By this method, a larger measurable range (0∼3000µε) OFDR method with a high level spatial resolution (3mm gauge) is experimentally achieved comparing to conventional OFDR methods.

Influence of meteorological factors on the secondary contamination of atmospheric air by formaldehyde ( on the example of the city of Kyiv).

Many authors on the basis of researches give information that motor transport is the basic source of contamination of atmospheric air of cities of Ukraine. This work touches on the estimation of the level and dynamics of contamination of m. Kyiv extras from a motor transport and influence of meteorological factors of locality on the degree of atmospheric contamination (including secondary one as a result of actinic transformations). Authors set connections between the components of SO, Nox, CHOH, and ambient temperature, on the basis of the analysis of the last five years of statistical information of basic components contaminations from motor transport, which take part in the formation of actinic transformations. The authors found out close cross-correlation connection between the molecules of Nox, CHOH, and average monthly values of temperature on the basis of the analysis of these monitoring supervisions. Also, there were investigational processes of the formation of molecules of SNON depending on other climatic factors of the city of Kyiv, namely: the humidity of the air, speed of the wind, and index of acidity of the atmosphere (pH). It is well-proven that formation of formaldehyde in mid-air above motor transport ways the degree of acidification of atmospheric fallouts influences mediated. However, have a direct cross-correlation connection between the relative humidity of air and the speed of the wind. Temperature terms play a key role in forming the secondary contamination formaldehyde above motor transport overpasses and he takes into account other climatic factors of locality mediated. Speed of reaction of the transformation of hydrocarbons in formaldehyde at neutral meteorological terms is considered on the example of the motor-car upshot of the Darnicka square. The decision of equalization of the speed of transformation of extras of hydrocarbons is found in formaldehyde by the decision of equalization of Arreniusa. This method can be applied to other cities of Ukraine. The conducted researches will allow to promote ecological strength security on the urbanized territories by the improvement of questions of acceptance of administrative decisions at building and reconstruction of motor-car overpasses of the city, and also at forming of strategic plans of ecological development of city and setting of nature protection measures.

Effect of Magnetic Field Strength on Solar Differential Rotation and Meridional Circulation

Abstract We studied the solar surface flows (differential rotation and meridional circulation) using a magnetic element feature tracking technique by which the surface velocity is obtained using magnetic field data. We used the line-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory from 2010 May 01 to 2017 August 16 (Carrington rotations 2096 to 2193) and tracked the magnetic element features every hour. Using our method, we estimated the differential rotation velocity profile. We found rotation velocities of ∼30 and −170 m s−1 at latitudes of 0° and 60° in the Carrington rotation frame, respectively. Our results are consistent with previous results obtained by other methods, such as direct Doppler, time-distance helioseismology, or cross-correlation analyses. We also estimated the meridional circulation velocity profile and found that it peaked at ∼12 m s−1 at a latitude of 45°, which is also consistent with previous results. The dependence of the surface flow velocity on the magnetic field strength was also studied. In our analysis, the magnetic elements with stronger and weaker magnetic fields largely represent the characteristics of the active region remnants and solar magnetic networks, respectively. We found that magnetic elements with a strong (weak) magnetic field show a faster (slower) rotation speed. On the other hand, magnetic elements with a strong (weak) magnetic field show slower (faster) meridional circulation velocity. These results might be related to the Sun’s internal dynamics.

Pregravid preparation as the main method of preventing undeveloped pregnancy

How to make a pregravid women with the stood pregnancy in the anamnesis is the key to success in the fight against miscarriage. The testing outside of pregnancy, the identification of reasons for stopping a previous gestation, adherence to medical recommendations in the programme of preparation for future conception and implantation is a required step in the management of women who have had non-developing pregnancy. Periconceptional prevention is effective only at its beginning 3 months before conception and in the early stages of development of the embryo and fetus (12 weeks).The purpose of the study was improvement profilakticheskih activities based on identified pathogenetic mechanisms of occurrence of missed abortion. Aim of the study: to perfect the features of pregravid preparation for pregnant with undeveloping pregnancy in anamnesis on the basis of the educed nosotropic mechanisms of origin of this pathology, her intercommunication with a folats deficit. Materials and methods. Research was conducted in a few stages. On the first stage retrospectively on the basis of analysis 90 hospital charts are educed the supposed risk factors. On the second stage the exposure of reliable risk and development of algorithms of prognostication of undeveloping pregnancy (factors was conducted in 2 groups - basic (90 pregnant with stopping beating pregnancy) and control (30 pregnant with normally aleak pregnancy). The methods of prophylaxis of this pathology offered in high-risk of origin of stopping beating pregnancy groups. One of them was application of folates, namely vitamin-mineral complex before and after conception. Results. On the basis of undertaken studies multifactor genesis of missed miscarriage was confirmed, and the basic etiologic factors of origin of this pathology are educed. Stopping beating of pregnancy at anomalous karyotype takes place for certain before (6.2±0.8 weeks) what at normal karyotype (8.7±1.2 weeks). Cross-correlation connection was set between frequency of development of chromosomal anomalies and level of homocysteine from МТНFR677ТТ, level correlation of Spirmena equaled 0.84 - direct cross-correlation connection. As a result of undertaken a study one of methods of preparation application of folates offered in a kind vitamin-mineral complex for 16 weeks to conception and 12 weeks after conception. Conclusion. High-frequency of МТНFR677ТТ of heterogeneous or homozygous carriers educed for women with undeveloping pregnancy. Application of folates is in a vitamin-mineral complex, can be one of the most effective methods in the prophylaxis of early reproductive losses.

Application of conditional averaging to time delay estimation of random signals

Abstract The article presents the possibilities of using the function of conditional average value of a delayed signal (CAV) and the function of conditional average value of a delayed signal absolute value (CAAV) to determine the time delay estimation (TDE) of random signals. For discrete CAV and CAAV estimators, the standard uncertainties of the estimation of function values at extreme points and the standard uncertainties of the TDE were given and compared with the corresponding uncertainties for the direct discrete cross-correlation function (CCF) estimator. It was found that the standard uncertainty of TDE for CAV is lower than for CCF independent of signal-to-noise ratio (SNR) for parameter values of α ≥ 2 and M/N ≥ 0.25 (where: α - relative threshold value, M/N - quotient of number of averaging and number of samples). The standard uncertainty of TDE for CAAV will be lower than for CCF for SNR values greater than 0.35 (for N/M = 1).

Signature of Two-Component Advective Flow in several Black Hole candidates obtained through time-of-arrival analysis of RXTE/ASM Data

We study several Galactic black hole candidates using long-time RXTE/ASM X-ray data to search for telltale signatures of differences in viscous timescales in the two components used in the Two-Component Advective Flow (TCAF) paradigm. In high-mass X-ray binaries (HMXBs) mainly winds are accreted. This nearly inviscid and dominant sub-Keplerian flow falls almost freely towards the black hole. A standard Keplerian disc can form out of this sub-Keplerian matter in presence of a significant viscosity and could be small in size. However, in low-mass X-ray binaries (LMXBs), highly viscous and larger Keplerian accretion disc is expected to form inside the sub-Keplerian disc due to the Roche-lobe overflow. Due to two viscous timescales in these two components, it is expected to have a larger lag between the times-of-arrival of these components in LMXBs than that in HMXBs. Direct cross-correlation between the photon fluxes will not reveal this lag/delay since they lack linear dependence; however, they are coupled through the viscous processes which bring in both matter. To quantify the aforesaid time lag, we introduce an index ({\Theta}), which is a proxy of the usual photon index ({\Gamma}). Thus, when {\Theta}, being dynamically responsive to both fluxes, is considered as a reference, the arrival time lag between the two fluxes in LMXBs is found to be much larger than that in HMXBs. Our result establishes the presence of two dynamical components in accretion and shows that the Keplerian disc size indeed is smaller in HMXBs as compared to that in LMXBs.