Fluctuations Of Phase Difference Research Articles

Study of turbulence intermittency in unstable atmospheric surface layer and its effect on saltation sand motion based on wavelet transform

Turbulence in the atmospheric surface layer, especially in deserts and semi-arid regions, significantly affects sand movement. In unstable stratification, turbulence exhibits complex intermittency, complicating its impact on saltation. This study uses wavelet transform analysis to examine the effects of turbulence intermittency in unstable stratification on saltation. Our analysis reveals that in unstable stratification, the energy distribution of turbulence is more dispersed, the intermittent characteristics are more significant, and the intermittent burst duration of streamwise turbulence is longer, while the vertical intermittent burst duration is shorter. The fitting formulas of the energy ratio and stratification stability of the streamwise wind speed, vertical wind speed, and temperature at different frequencies are given. In addition, there is a complex nonlinear relationship between stratification stability and friction velocity on saltation. In unstable stratification, the critical wind speed required for saltation is higher than that of near-neutral, and the jumping speed and horizontal transport are weakened. Moreover, the coherence between wind speed and saltation flux increases significantly at low frequency with the increase in instability, indicating that large-scale motion plays a key role in saltation under these conditions. The more unstable the stratification is, the more obvious the phase difference fluctuation of the low frequency part is, and the more unfavorable the formation of stable saltation sand conditions. This study reveals the turbulence intermittently and its complex effects on sand particle movement in unstable stratification, which is of great significance for predicting and controlling dust storms, land desertification, and soil erosion.

Mechanism Analysis of the Effect of Wake Vortex on Cylinder Vibration in Flow Induced Motion

Abstract Unsteady Reynolds-averaged Navier–Stokes (RANS) method combined with Spalart–Allmaras turbulence model and dynamic mesh technology was used to investigate the impact of wake vortex on the vibration response of a cylinder. By analyzing the phase difference between the wake vortex force and the displacement under different mass parameters in flow-induced vibration (FIV), the study reveals that the influence of wake vortex on the cylinder varies significantly in different vibration branches. The wake vortex of the initial branch enhances the cylinder's vibration, whereas the wake vortices of the upper, lower, and desynchronized branches suppress the vibration. At the critical point between the initial branch and the upper branch of vortex-induced vibration (VIV), there is a 90 degree phase jump, and the instantaneous phase difference fluctuation between the wake vortex force and displacement of the VIV branch remains relatively constant. In the galloping branch, there are wake vortices in different directions that affect the cylinder's vibration every quarter of the vibration period, and the phase difference undergoes periodic large fluctuations (either in-phase or out-of-phase), with the result that the wake vortex force periodically promotes or restrains the cylinder's vibration, which can serve as a novel criterion for identifying the occurrence of galloping. Furthermore, when varying the mass parameters at a constant reduced velocity, the impact of the wake vortex in the initial branch is relatively insignificant. However, as the mass ratio increases in other vibration branches, the suppressive effect increases, and the wake vortex force can prevent VIV induced galloping phenomenon by affecting the vibration intensity.

A Fine-grained Channel State Information-based Deep Learning System for Dynamic Gesture Recognition

Indoor gesture recognition technology is concerned with making the machine accurately recognize dynamic gestures within a certain range. Remarkably, most of this technology is based on passive recognition methods. This is quite striking because the high cost is a crucial factor in active recognition methods and ignoring this aspect can increase the reality gap. In this paper, we tend to use the fine-grained channel state information (CSI) in Wi-Fi to build a dynamic CNN-GRU-Attention (CGA) model to implement a gesture recognition system and thus alleviate this problem. Firstly, we study the influence of gestures on the amplitude and phase difference in CSI, and prove the feasibility of proposed method by analyzing the fluctuation of amplitude and phase difference under different conditions. Then, we use data processing methods such as phase correction and unwrapping with a new proposed adaptive gesture action truncation algorithm to extract the phase difference and remove redundant information, thus ensuring the validity of data. Finally, we propose to segment gesture fragment into 3-channel CSI images as input information of model. Extensive comparison experiments are conducted under the influence of different people, different indoor environments, and different sampling rates. The results show that the system has high accuracy.

Design of Wideband Filtering Quadrature Coupler Consisting of Inductor-Loaded Coupled Line With Three-Coupled-Lines

In this brief, the design of a wideband filtering quadrature coupler is presented. It is composed of an inductor-loaded coupled line (I-CL), two open-ended stubs, four short-ended stepped impedance resonators, and four three- coupled-lines (TCLs). Wideband operation with three resonant points is generated by using the I-CL with the TCLs. Due to the utilization of short-ended resonators combined with the open stubs, wide stopband is also obtained. Design formulas are derived using the even-odd decomposition technique and optimization process is given for guidance. For demonstration, a 3-dB prototype is designed, fabricated and measured. Measurement results show that a bandpass bandwidth (BPBW) of 43% is realized under the criterions of 15-dB return loss and isolation. While the BPBWs for 0.5-dB amplitude imbalance and 5° phase difference fluctuation are 40.3% and 48%, respectively. Besides, wide stopband extends to 2.64 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{0}$ </tex-math></inline-formula> is realized with more than 10 dB rejection level.

Absolutely Consistent Fiber-Optic Phase Synchronization Based On Fixed-Phase-Reference Optical Active Compensation

An absolutely consistent fiber-optic phase synchronization scheme based on fixed-phase-reference optical active compensation is proposed. By measuring the time interval of time pulse and the phase difference of frequency signal, and then using the optical delay line to compensate the phase change in real time according to a fixed phase reference, the phase period ambiguity and the phase-lock control initial randomness are eliminated, realizing a stable and repeatable fixed phase difference between different sites. Then the phase synchronization performances of stability and absolute consistence have been demonstrated through experiments in different scenarios. The phase difference fluctuation within 10000 s is only ±0.0006 rad, showing an ultra-high stability. Under the total of 5 different operations, including the signal source restart, system restart, adding 20 m additional fiber, adding 1 km additional fiber, and adding 2 km additional fiber, the maximum inconsistency of the mean phase difference is about 1% of one full cycle. The proposed and verified absolutely consistent phase synchronization method can well maintain the coherence in transferring frequency signal, having important application prospects in radar network and other time-frequency-phase synchronization-based coherent detection.

Tone detection thresholds in interaurally delayed noise of different bandwidths

Differences between the interaural phase of a noise and a target tone improve detection thresholds. The maximum masking release is obtained for detecting an antiphasic tone (Sπ) in diotic noise (N0). It has been shown in several studies that this benefit gradually declines as an interaural time delay (ITD) is applied to the noise. This decline has been attributed to the reduced interaural coherence of the noise. Here, we report detection thresholds for a 500 Hz tone in masking noise with ITDs up to 8 ms and bandwidths from 25 to 1000 Hz. Reducing the noise bandwidth from 100 to 50 and 25 Hz increased the masking release for 8-ms ITD, as expected for increasing temporal coherence with decreasing bandwidth. For bandwidths of 100–1000 Hz no significant difference in masking release was observed. Detection thresholds with these wider-band noises had an ITD dependence that is fully described by the temporal coherence imposed by the typical monaurally determined auditory-filter bandwidth. A binaural model based on interaural phase-difference fluctuations accounts for the data without using delay lines.

Effect of non-uniform asymmetric heating on the thermal and entropy generation characteristics for flow of Al2O3-water nanofluid in a micro-channel

Purpose The purpose of this study is to numerically analyze the thermal and entropy generation characteristics on two-dimensional, incompressible, laminar single-phase flow of Al2O3-water nanofluid in a micro-channel subjected to asymmetric sinusoidal wall heating with varying amplitude, length of fluctuation period and phase difference of applied heat flux for Reynolds number in the range of 25-1000. Design/methodology/approach The numerical computation is based on the Finite Element Method and the Lagrange finite element technique is used for approximating the flow variables within the computational domain. Findings The average Nusselt number increases with increasing Reynolds number (Re) for all the volume fractions of nanofluid. However, the total entropy generation decreases up to a critical value of Re and increases thereafter. Increase in volume fraction shifts the critical Re towards the lower Re regime. The average Nusselt number and total entropy generation increase with amplitude and length of fluctuation period of heat flux. The optimal choice of volume fraction for lesser entropy generation and higher heat transfer is found to be 3 per cent independent of the value of amplitude, length of fluctuation period and phase difference of the heat flux. Originality/value To the best of authors’ knowledge, the interplay of various parameters concerning non-uniform heating in achieving the maximum heat transfer with minimum irreversibility has not been investigated. Focusing on this agenda, the results of this study would benefit the industrial sector in achieving the maximum heat transfer at the cost of minimum irreversibilities with an optimal choice of inlet Reynolds number, volume fraction of nanofluid, amplitude, length of the period of fluctuation of heat flux and phase difference of applied heat flux.

Численное моделирование колебаний элементов трубы с потоком несжимаемой жидкости

Monitoring of fluid flow in pipelines is an actual and practically significant task. The control is carried out by means of Coriolis flowmeters, the principle of which is based on the phase difference fluctuations of the pipe sections. Of particular interest is the process of transverse vibrations of a straight pipe through which the flow of an incompressible fluid moves. This paper presents a mathematical model of the vibration of a straight section of a pipe with an incompressible fluid flow subjected to external impulse action. Numerical simulation is based on the finite difference analogue. Computational experiments were carried out to determine the transverse vibrations of the elements of a straight pipe on the results of dynamic measurements. According to the results of computational experiments, graphical dependencies for deviations of straight pipe elements with rigid fastening at the ends are presented. The influence on the fluctuations of the fluid flow pipe (velocity, mass), the pulse action, as well as the parameters of the pipe are studied.

Investigation of the phase stability of an X-band long pulse multibeam relativistic klystron amplifier

To realize coherent high power microwave combining, an X-band long pulse multibeam relativistic klystron amplifier is designed, and the relative phase stability is investigated by three dimensions particle in cell simulation and high power microwave experiment. The simulation shows that the relative phase difference can be stabilized at gigawatt level radiation power. But the relative phase jitter increases in the experiment, then some measures are proposed to improve the stability of relative phase difference and avoid pulse shortening. A 0.98 GW radiation power with pulse duration of 160 ns is obtained in the experiment, the pulse shortening is avoided. The relative phase difference fluctuation between output microwave and input RF signal is less than ±25° in a single shot with duration of 100 ns. Then, the experiment of pulse repetition is carried out, and an output microwave with 0.98 GW radiation power at 25 Hz repetition rate is obtained. The power conversion efficiency is about 35% with pulse duration of 160 ns. The relative phase difference is less than ±30° at 25 Hz repetition rate in 100 ns.

Particle-in-cell simulation of a new X-band low-impedance high power microwave source

High power microwave (HPM) source is attractive in generating gigawatt (GW) class microwaves based on the beam-wave interaction. Generally, HPM source with a high beam-wave conversion efficiency has a higher impedance. To improve the single-tube output power of HPM source, reducing the impedance of the device and increasing its power capacity are necessary. In this paper, a new low-impedance HPM source is proposed and proved to be capable of generating two phase-locked high power microwaves, which makes it promising to realize a higher combined power in a single HPM device.The new low-impedance HPM device consists of a two-cavity TKA (denoting the outer sub-source in the following) and a multiwave Cerenkov generator (referring to the inner sub-source below) inserted in the TKA inner conductor. These two sub-sources are connected in parallel and share a common magnetic field. A dual-concentric annular cathode is used in this microwave source, which is capable of emitting two concentric annular electron beams and driving the internal and external sub-source simultaneously. The advantages of this device are reducing the impedance and improving the injection electric power. When a voltage pulse is applied to the diode, part of microwaves generated in the inner subsource will leak into the outer sub-source (i.e., TKA) through the A-K gap. By amplifying the leakage microwaves, the TKA will be easily locked by the inner sub-source. Considering the fact that the microwave source consists of two sub-sources, the power capacity will also be greatly improved.As a result, particle-in-cell simulation indicates that when the diode voltage is 687 kV and the axial magnetic field is 0.8 T, two microwave beams that have a nearly identical frequency of 9.72 GHz and output powers of 1.20 GW and 2.58 GW respectively, are generated. The corresponding power conversion efficiencies are 28% and 30%, respectively. The frequency difference between these two microwaves fluctuates within 3 MHz and their phase difference is not in excess of 3. When the diode voltage changes from 665 kV to 709 kV, frequency difference between the two sub-sources fluctuates within 3 MHz and their phase difference fluctuation is within 5 in one voltage burst; the phase difference changes 10 in this voltage range. The impedance of this HPM source is as low as 36 .To sum up, the new HPM source proposed in this paper has a lower impedance and higher power capacity. The phase difference between the inner sub-source and the outer sub-source is very stable and favorable for the coherent power combination, which indicates that the new HPM source promises to realize a higher output power in a single-tube device.

Resting state MEG oscillations show long-range temporal correlations of phase synchrony that break down during finger movement.

The capacity of the human brain to interpret and respond to multiple temporal scales in its surroundings suggests that its internal interactions must also be able to operate over a broad temporal range. In this paper, we utilize a recently introduced method for characterizing the rate of change of the phase difference between MEG signals and use it to study the temporal structure of the phase interactions between MEG recordings from the left and right motor cortices during rest and during a finger-tapping task. We use the Hilbert transform to estimate moment-to-moment fluctuations of the phase difference between signals. After confirming the presence of scale-invariance we estimate the Hurst exponent using detrended fluctuation analysis (DFA). An exponent of >0.5 is indicative of long-range temporal correlations (LRTCs) in the signal. We find that LRTCs are present in the α/μ and β frequency bands of resting state MEG data. We demonstrate that finger movement disrupts LRTCs correlations, producing a phase relationship with a structure similar to that of Gaussian white noise. The results are validated by applying the same analysis to data with Gaussian white noise phase difference, recordings from an empty scanner and phase-shuffled time series. We interpret the findings through comparison of the results with those we obtained from an earlier study during which we adopted this method to characterize phase relationships within a Kuramoto model of oscillators in its sub-critical, critical, and super-critical synchronization states. We find that the resting state MEG from left and right motor cortices shows moment-to-moment fluctuations of phase difference with a similar temporal structure to that of a system of Kuramoto oscillators just prior to its critical level of coupling, and that finger tapping moves the system away from this pre-critical state toward a more random state.

A new compact self-coherent high power microwave source based on dual beams

In this paper, a compact self-coherent high power microwave source based on dual beams is presented. It consists of a two-cavity triaxial klystron amplifier (TKA) (noted as the outer sub-source below) and a multiwave Cerenkov generators (noted as the inner sub-source) inserted in the TKA's inner conductor. These two sub-sources share a common cathode and the magnetic field. The injected signals to the outer sub-source are leakage microwaves from the inner sub-source through the anode-cathode gap (A-K gap). Particle-in-cell simulation shows that when the diode voltage is 687 kV and the axial magnetic field is 0.8 T, two microwaves with power of 1.02 GW and 2.65 GW and the same frequency of 9.72 GHz are generated in the inner and the outer sub-source, respectively; the corresponding power efficiencies are 24% and 31%. Two sub-sources reach the phase locking at 23 ns with a phase difference fluctuation within ±3°. The fast and stable phase locking in the voltage ranging from 665 kV to 709 kV further suggests that the proposed source is promising for coherent power combination and to export a higher power of combined microwaves.

Simulation and experimental study of phase characteristics in high-gain relativistic klystron amplifier

In order to realize the combination of the coherent high power microwave, an S-band high gain relativistic klystron amplifier with high phase stability is presented and studied theoretically and experimentally. The phase characteristics of the output microwave are explored in particle-in-cell code and experiment. The experimental results accord well with the simulation results, which indicates that the parasitic oscillation excited by retrograde electrons is the main cause of phase variation in the development of high-gain relativistic klystron with high phase stability. When the input RF power is 10 kW, a microwave pulse with about ± 10° in relative phase difference fluctuation between output and input is obtained in experiment. And the corresponding locking duration is about 90 ns. Accordingly, the expectation of power combination efficiency of 10 high-gain relativistic klystron amplifiers can be achieved to be 99% with continuous uniform distribution of random relative phase difference.

An S-band high gain relativistic klystron amplifier with high phase stability

For the purpose of coherent high power microwave combining, an S-band high gain relativistic klystron amplifier with high phase stability is presented and studied. By the aid of 3D particle-in-cell code and circuit simulation software, the mechanism of parasitic oscillation in the device is investigated. And the RF lossy material is adopted in the simulation and experiment to suppress the oscillation. The experimental results show that with an input RF power of 10 kW, a microwave pulse with power of 1.8 GW is generated with a gain of 52.6 dB. And the relative phase difference fluctuation between output microwave and input RF signal is less than ±10° in 90 ns.

Phase fluctuation in multi-band superconductors

Abstract The positive interband Josephson interaction leads to emergence of non-trivial order parameters such as a sign-reversal one for a two-band superconductor, a frustrated superconductivity for a three-band superconductor. The frustrated superconductivity appears on the way to fully incoherent state due to the Coulomb interaction. The physical background of the frustrated superconductivity is transparent and the effect can be directly examined in the fluctuation of the interband phase difference. To understand the relationship between the phase fluctuation and an emergence of the chiral superconductivity, we examine a simple situation, which is almost degenerated system using Ginzburg-Landau theory. The frustration retains the interband phase difference fluctuation and this fluctuation becomes a seed of a chiral domain.

88 W 05 mJ femtosecond laser pulses from two coherently combined fiber amplifiers

The generation of 0.5 mJ femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of 175 kHz producing 88 W of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach-Zehnder interferometer, which has been stabilized with a Hänsch-Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as λ/70 rad at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.

Frequency Spectra Fluctuations in the Radio Interferometry of Polarized Radiation

The presence of a longitudinal magnetic field is shown to lead to the appearance of an additional component of the frequency spectrum of the linearly polarized emission. This component is proportional to the spectrum of normal waves phase difference fluctuations. The fluctuations spectra baseline dependence of a linear polarized radiation is periodical near zero frequency, one is absent in the high frequency ranges and such dependence has different character in magnetoactive plasma with electron density irregularities and in plasma with a random magnetic field.

Number-phase properties of correlated chaotic fields

We study the arrangement of two down-conversion crystals with aligned and partially aligned idler beams in the quasimonochromatic approximation. Treating the signal fields as correlated chaotic modes, we arrive at a detailed description and illustration of their mathematically well defined state in terms of number and phase properties. We show it to be a mixed partial phase-difference state. We derive the closed formulae for the phase-difference distributions in this state derived from the phase-space distributions related to the normal, symmetrical and antinormal orderings of field operators and show that such distributions depend exclusively on measures of correlation which are variants of the modulus of the familiar degree of coherence. Quantum correlation influences fluctuations of photon-number sum, photon-number difference and quantum phase difference. Starting from a quasidistribution which carries the same information as the statistical operator, we arrive at the joint distributions of number sum and phase difference and the quasidistribution of number difference and phase difference.

Ground-based spatial interferometers and atmospheric turbulence

The asymptotic and numerical analysis of the phase difference spectrum for stellar interferometers has been performed based on the development of models of atmospheric turbulence. Peculiarities of phase difference spectra as well as for a `small' and `large' baseline of interferometers are investigated. The influence of the outer scale of turbulence is under study. Different models of turbulence intensity, the outer scale of turbulence and wind velocity are used. The results of the fields measurements, carried out using stellar interferometers in different parts of the world, are analysed on the basis of the data available from the literature. In order for the results of measurements of phase difference fluctuations to become the basis for improving the model of a turbulent atmosphere the following parameters are required to be measured: initial altitude, value and direction of wind velocity relative to the orientation of the interferometer measuring baseline, as well as the value of contrast of the interference pattern (for estimating the Fried radius value at the operation wavelength).

Estimation of time characteristics of millimeter-band signals on sea path at small grazing angles

Result are presented for an experimental study of fluctuations of signal arrival angle and intensity and the crosscorrelation of fluctuations of signal amplitude and phase difference at a wavelength of 8.3 mm at spatially separated antennas for two versions of a 14.5-km sea path.