Integrated Power Spectrum Research Articles

Development Of A Spatio-Temporal Acoustic Pressure Measurement Technique Utilizing Background Oriented Schlieren Technique

We developed an image and optical-based technique to measure spatio-temporal acoustic pressure fields using BOS instead of a hydrophone. Fast checker demodulation (FCD) and vector tomography (VT) were employed for displacement detection and axisymmetric tomography, respectively. In experiments, BOS and hydrophones of different diameters measured focused ultrasound, revealing BOS's higher spatial resolution and ability to capture temporal evolution at 4.554 MHz. However, BOS showed systematic errors under amplified pressure. Using synthetic data, we identified that FCD's underestimation issues could be defined by the integrated power spectra of distorted images. Thus, BOS with FCD and VT provides high-resolution measurements but requires criteria to avoid displacement underestimation.

TPS Fast Orbit Feedback Upgrade

The orbit feedback system for the Taiwan Photon Source (TPS) was delivered in 2014. With the installation of an increasing number of insertion devices, a variety of wide-band disturbances are produced. In 2019, a proposal was put forth to enhance the stability of the orbit through the implementation of the fast orbit feedback (FOFB) system upgrade. The upgrade plan encompasses the revision of the power supply controller and an increase in the feedback computation rate from 10 kHz to 30 kHz. Following the upgrade, the bandwidth of the TPS fast orbit feedback system has been expanded from 250 Hz to 400 Hz in the vertical plane and from 200 Hz to 250 Hz in the horizontal plane. The integrated power spectrum density of the orbit could be reduced by approximately 20% with effective measures.

Validity of Single Fluorescent Molecule to Report Local Dynamics of a Polymer Matrix: The Effect of Molecular Architecture

AbstractThe influence of van der Waals volume as well as molecular configuration of the probe on its rotation is investigated by defocused single molecule fluorescence microscopy. The results show that the probe with a larger van der Waals volume has lower integrated power spectra density and the fraction of rotational molecules at each temperature. However, the asymmetric configuration of probe can make the integrated power spectra density and the fraction of rotational molecules larger. Therefore, the van der Waals volume of probe is the most dominating factor to determine the length scales and frequency of reported local dynamics while the asymmetric configuration of probe can bring about additional effect.

The Noise Behavior of Gap-Type Amorphous Silicon TFT Under Illumination

Gap-type amorphous silicon (a-Si) thin-film transistor (TFT) used as photo sensor has been reported in previous literature. However, the noise behavior of gap-type a-Si TFT is not inspected yet. Therefore, we investigate the noise response of the gap-type a-Si TFT under illumination in this paper. We compare the difference between the results of the gap-type and the conventional-type TFTs. In addition, we analyze it including the perspectives of power spectrum, integral power spectrum, Hooge parameter, fluctuate slope. Finally, we explain the reason for its fluctuate slope transition and review the correlation between noise behavior and photo effect mechanism.

The Effects of Turbulence Intensity and Tip Speed Ratio on the Coherent Structure of Horizontal-Axis Wind Turbine Wake: A Wind Tunnel Experiment

The evolution laws of the large-eddy coherent structure of the wind turbine wake have been evaluated via wind tunnel experiments under uniform and turbulent inflow conditions. The spatial correlation coefficients, the turbulence integral scales and power spectrum are obtained at different tip speed ratios (TSRs) based on the time-resolved particle image velocity (TR-PIV) technique. The results indicate that the large-eddy coherent structures are more likely to dissipate with an increase in turbulence intensity and TSR. Furthermore, the spatial correlation of the longitudinal pulsation velocity is greater than its axial counterpart, resulting into a wake turbulence dominated by the longitudinal pulsation. With an increase of turbulence intensity, the integral scale of the axial turbulence increases, meanwhile, its longitudinal counterpart decreases. Owing to an increase in TSR, the integral scale of axial turbulence decreases, whereas, that of the longitudinal turbulence increases. By analyzing the wake power spectrum, it is found that the turbulent pulsation kinetic energy of the wake structure is mainly concentrated in the low-frequency vortex region. The dissipation rate of turbulent kinetic energy increases with an increase of turbulence intensity and the turbulence is transported and dissipated on a smaller scale vortex, thus promoting the recovery of wake.

Full-Scale Measurements of Wind Characteristics on a High-Rise Building during Typhoon Sarika

A full-scale measurement of wind characteristics atop a high-rise building (with a height of 115 m) was conducted during the passage of Typhoon Sarika on 18 October 2016. Wind field characteristics, wind speed, and wind direction atop the building were recorded synchronously, and turbulence intensity, turbulence integral scale, gust factor, and power spectrum were investigated. Meanwhile, the time and frequency domain characteristics of the wind field were analyzed. The stationarity test results of Typhoon Sarika at different time steps are researched in a runs test. And the time-frequency analysis of non-stationary samples of fluctuating wind speed are conducted by wavelet transform, the measured data are valuable for the wind-resistant design of high-rise buildings in typhoon-prone regions.

BOUNDARY LAYER WIND PROFILE MEASUREMENT BASED ON A SIX-ROTOR UAV ANEMOMETER

They studied the feasibility of boundary layer wind field measurement based on a six-rotor drone equipped with an anemometer, and analyzed the measured wind characteristics including average wind speed, wind direction, turbulence intensity, gust factor, the turbulence integral length and power spectrum. The results are compared with the measured results of anemometers fixed on a wind tower. The results show that the wind speed and wind direction values measured by the UAV are basically the same as the measured values on the wind tower after correction, and the error between the two is within ±3%. The accuracy of fitted wind profile by the UAV is high. The wind profile is close to the B-type geomorphic wind profile specified by the Chinese standard. The average ground roughness calculated by data fitting is 0.148. The various fluctuating wind characteristic parameters measured by the UAV are close to the measured values on the wind tower, and the error between the two is within ±5%. There is an exponential correlation between the turbulence intensity and the gust factor. The wind power spectrum measured by the UAV is basically consistent with that measured on the wind tower and is consistent with the Karman spectrum.

Subspace-Based Blood Power Spectral Capon Combined with Wiener Postfilter to Provide a High-Quality Velocity Waveform with Low Mathematical Complexity

In Doppler analysis, the power spectral density (PSD), which accounts for the axial velocity distribution of the blood scatterers, is estimated. The conventional spectral estimator is Welch's method, which suffers from frequency leakage at small observation window length. The performance of adaptive techniques such as blood power Capon (BPC) has been promising at the cost of higher computation complexity. Reducing the computational complexity while retaining the benefits of BPC would be necessary for real-time implementation. The purpose of the work described here was to investigate whether it is possible to decrease the computation load in BPC and still obtain acceptable results. The computation complexity in BPC is owing primarily to the matrix inversion required for computing the PSD estimate. We here propose the subspace blood power Capon technique, which employs a data covariance matrix with reduced number of rows in estimation of the weight vector. In maximum velocity estimation in the spectra, the signal noise slope intersection envelop estimator that makes use of the integrated power spectrum is employed. The evaluations are made based on both simulated and in vivo data. The results indicate that it is possible to reduce the order of complexity to almost 12.25% at the cost of 2.31% and 2.24% increases in the relative standard deviation and relative bias of the estimates. Moreover, the Wiener post-filter as a post-weighting factor, which will be multiplied by the final weight vector of the spectral estimator, estimates the power of the desired signal and the power of the interference plus noise to improve the contrast. The proposed estimator has exhibited a promising performance at beam-to-flow angles of 45°, 60° and 75°. Furthermore, the robust performance of the proposed estimator against variation in the flow rate is also documented.

Normal and typhoon wind loadings on a large cooling tower: A comparative study

Large cooling towers are sensitive to wind effects with their increasing heights and flexibilities. Unlike traditional approaches, which employed Code-defined normal winds to check the loading characteristics, this paper developed a framework for checking the typhoon-induced wind loading on a large cooling tower using Monte Carlo simulations and multi-fan wind tunnel tests. Some distinct characteristics of typhoon winds were compared with those of Code-defined normal winds. Furthermore, wind characteristics of incoming normal and typhoon winds in terms of vertical profile of mean wind speed, turbulence intensity, turbulence integral length scale and power spectrum density of fluctuating winds were well reproduced by a feedback control process of a multi-fan actively controlled wind tunnel. The surface wind pressure distributions of a large cooling tower under these conditions were then investigated by testing a 1:600 reduced scale model. Mean and fluctuating external wind pressures along the circumferential direction under various incoming winds were discussed and quantitatively formulated with eight-term trigonometric equations. Moreover, the cross correlations of wind pressures in the circumferential and meridian directions and correlations with structure base forces, i.e. integral drag and lift forces, were investigated. Non-Gaussian characteristics in terms of skewness and kurtosis of fluctuating wind pressures were also analyzed under two wind climates. Peak factors for modeling extreme wind pressures were examined and compared with those of various models. Finally, the extreme wind loads on a large cooling tower obtained from different wind pressure combinations were compared with peak-factor-theory-based results to identify an appropriate combination for structural design.

Deep multiredshift limits on Epoch of Reionization 21 cm power spectra from four seasons of Murchison Widefield Array observations

Abstract We compute the spherically averaged power spectrum from four seasons of data obtained for the Epoch of Reionization (EoR) project observed with the Murchison Widefield Array (MWA). We measure the EoR power spectrum over k = 0.07–3.0 h Mpc−1 at redshifts $z$ = 6.5–8.7. The largest aggregation of 110 h on EoR0 high band (3340 observations), yields a lowest measurement of (43 mK)2 = 1.8 × 103 mK2 at k = 0.14 h Mpc−1 and $z$ = 6.5 (2σ thermal noise plus sample variance). Using the Real-Time System to calibrate and the CHIPS pipeline to estimate power spectra, we select the best observations from the central five pointings within the 2013–2016 observing seasons, observing three independent fields and in two frequency bands. This yields 13 591 2-min snapshots (453 h), based on a quality assurance metric that measures ionospheric activity. We perform another cut to remove poorly calibrated data, based on power in the foreground-dominated and EoR-dominated regions of the two-dimensional power spectrum, reducing the set to 12 569 observations (419 h). These data are processed in groups of 20 observations, to retain the capacity to identify poor data, and used to analyse the evolution and structure of the data over field, frequency, and data quality. We subsequently choose the cleanest 8935 observations (298 h of data) to form integrated power spectra over the different fields, pointings, and redshift ranges.

Evaluation of Temporally Correlated Noise in Global Navigation Satellite System Time Series: Geodetic Monument Performance

AbstractEstimates of background noise of Global Positioning System‐derived time series of positions for 740 sites in the western United States are examined. These data consist of daily epochs of three components of displacements that are at least 9.75 years long within the interval between 2000 and 2018. We find that these time series have significant temporal correlations that could be represented as a combination of white, flicker, random‐walk, and band‐pass filtered noise. From this noise model, two other metrics are computed: the root‐mean‐square of seasonal noise, that is, the integrated power spectrum between 0.5 and 2 cycles per year, and the standard error in position rate for a 10‐year‐long time series. These two metrics are used to evaluate potential correlations with different geographic regions and with different methods of construction of monuments used to attach the Global Positioning System antenna to the Earth's surface. The sites with the lowest noise, both in terms of rate error and seasonal root‐mean‐square, are located in semiarid regions east of the rain shadow provided by the Cascade and Sierra Nevada mountain ranges. In addition, according to statistical rank tests, monuments known as drilled‐braced monuments perform 30% to 50% better than other monument types (buildings, boreholes, piers, etc.) in terms of having smaller rate errors and lower seasonal noise.

Investigation of radio pulsar emission features using power spectra

Since 2013, round-the-clock monitoring of the sky has been carried out simultaneously in 96 beams using a high-sensitivity radio telescope called the Large Phased Array (LPA) at the frequency 110.25 MHz. These observations are made under the program of interplanetary plasma investigation. The same data are used to search for pulsars by means of power spectra. To increase the sensitivity of the pulsar search, 500–600 power spectra corresponding to different days of observations are summed. In the integrated spectra of known pulsars, besides expected improvement in signal-to-noise (S/N) ratio for the frequency harmonics, some features are explored in this paper. We present the 27 strongest pulsars which are in a field with declination 21° − 42°. The observable details in the integrated power spectra are connected with the presence of pulsar periods of the second (P2) and third (P3) class, which have been identified. Empirical relations for calculating these periods are obtained. The value P2 is estimated for 26 pulsars, and for 15 sources it is made for the first time. The value P3 is estimated for 13 pulsars, among them these values are given for five sources for the first time.

Investigation of driving forces of cerebrospinal fluid motion by power and frequency mapping based on asynchronous phase contrast technique.

To classify the cardiac- and respiratory-driven cerebrospinal fluid (CSF) motions, asynchronous 2D phase contrast (PC) of magnetic resonance imaging (MRI) with 217 ms time resolution in conjunction with power and frequency mapping was performed for 7 healthy subjects under respiration guidance. In the frequency domain, the cardiac-driven motion was at around 1.29±0.21 Hz and respiratory-driven motion was at 0.16±0.01 Hz under 6 sec respiratory cycle. Two different techniques were proposed for characterizing the motions; one was power-map (P-map) depicting integrated power spectrum in a selected band, and the other was frequency-map (F-map) delineating the frequency of maximum peak in power spectral density (PSD). These maps visualized the anatomical distributions of the two motions. Portions of the cardiac- and respiratory-driven CSF motions in the spinal subarachnoid space were 58.1±22.2 and 9.50±3.83 %, respectively. Power and frequency mapping clearly classified the cardiac-driven and respiratory-driven CSF motions.

Extragalactic gamma-ray signal from dark matter annihilation: an appraisal

We re-evaluate the extragalactic gamma-ray flux prediction from dark matter annihilation in the approach of integrating over the non-linear matter power spectrum, extrapolated to the free-streaming scale. We provide an estimate of the uncertainty based entirely on available N-body simulation results and minimal theoretical assumptions. We illustrate how an improvement in the simulation resolution, exemplified by the comparison between the Millennium and Millennium II simulations, affects our estimate of the flux uncertainty and we provide a ‘best guess’ value for the flux multiplier, based on the assumption of stable clustering for the dark matter perturbations described as a collision-less fluid. We achieve results comparable to traditional halo model calculations, but with a much simpler procedure and a more general approach, as it relies only on one, directly measurable quantity. In addition, we discuss the extension of our calculation to include baryonic effects as modelled in hydrodynamical cosmological simulations and other possible sources of uncertainty that would in turn affect indirect dark matter signals. Upper limits on the integrated power spectrum from supernovae lensing magnification are also derived and compared with theoretical expectations.

Statistical characteristics of sustained wind environment for a long-span bridge based on long-term field measurement data

The fluctuating wind induced vibration is one of the most important factors which has been taken into account in the design of long-span bridge due to the low stiffness and low natural frequency. Field measurement characteristics of sustained wind on structure site can provide accurate wind load parameters for wind field simulation and structural wind resistance design. As a suspension bridge with 1490 m main span, the Runyang Suspension Bridge (RSB) has high sensitivity to fluctuating wind. The simultaneous and continuously wind environment field measurement both in mid-span and on tower top is executed from 2005 up to now by the structural health monitoring system installed on this bridge. Based on the recorded data, the wind characteristic parameters, including mean wind speed, wind direction, the turbulence intensity, the gust factors, the turbulence integral length, power spectrum and spatial correlation, are analyzed in detail and the coherence functions of those parameters are evaluated using statistical method in this paper. The results indicate that, the turbulence component of sustain wind is larger than extremely strong winds although its mean wind speed is smaller; the correlation between turbulence parameters is obvious; the power spectrum is special and not accord with the Simiu spectrum and von Karman spectrum. Results obtained in this study can be used to evaluate the long term reliability of the Runyang Suspension Bridge and provide reference values for wind resistant design of other structures in this region.

Comparative Spectral Analysis and Correlation Properties of Observed and Simulated Total Column Ozone Records

We present a statistical analysis of total column ozone records obtained from satellite measurements and from two global climate chemistry models on global scale. Firstly, a spectral weight analysis is performed where the relative strength of semiannual, annual and quasi-biennial oscillations are determined with respect to the integrated power spectra. The comparison reveals some anomalies in the model representations at each spectral component. The tails of the spectra demonstrate that both models underestimate high frequency (daily) ozone variability, which might have a complex origin, since several dynamical processes affect short time changes of the ozone level at a given location. Secondly, detrended fluctuation analysis is exploited to analyze two-point correlations of anomaly time series. Both models reproduce the characteristic geographic dependence of correlation strength over the overlapping area with empirical observations (latitude band between 60°S and 60°N). The values of precise correlation exponents are hard to obtain over regions where quasi-biennial oscillations or other strong nonstationarities (ozone hole) are present. In spite of all the numerical difficulties, significant long range correlations are detected for total ozone over all geographic locations.

造影タイミングの変化におけるパワースペクトル解析の試み

Frequency analysis is a method of measuring the spatial frequency component in images. We attempted to analyze and assess frequency analyses of images of various contrast medium injection timings using a normalized integral power spectrum. In magnetic resonance imaging, the k-space order was linear and sequential. During the twenty-second scanning time, we injected contrast medium at 3 ml/s and varied the duration of the injection from zero to four seconds, four to eight seconds, eight to twelve seconds, twelve to sixteen seconds, and sixteen to twenty seconds. We then analyzed the images. The rates of change and area values were calculated, and a dendrogram of area value by cluster analysis was made. The element of high frequency area's power values rose when the contrast medium was in the high-frequency area, and the element of low frequency area's power values rose when the contrast medium was in the low-frequency area. These data lines crossed at 0.092-0.115 cycles/mm. Five time durations were identified: these were a function of rate of change and area value. Frequency analysis of injection timing for contrast medium using the normalized integral power spectrum can thus be applied; this method can thus be employed as a method of examining injection timing for contrast medium and choosing a k-space order of optimization.

An ex vivo Study of the Correlation Between Acoustic Emission and Microvascular Damage

The objective of this study was to conduct an ex vivo examination of correlation between acoustic emission and tissue damage. Intravital microscopy was employed in conjunction with ultrasound exposure in cremaster muscle of male Wistar rats. Definity microbubbles were administered intravenously through the tail vein (80 μL.kg −1.min −1infusion rate) with the aid of a syringe pump. For the pulse repetition frequency (PRF) study, exposures were performed at four locations of the cremaster at a PRF of 1000, 500, 100 and 10 Hz (one location per PRF per rat). The 100-pulse exposures were implemented at a peak rarefactional pressure (P r) of 2 MPa, frequency of 2.25 MHz with 46 cycle pulses. For the pressure amplitude threshold study, 100-pulse exposures (46 cycle pulses) were conducted at various peak rarefactional pressures from 0.5 MPa to 2 MPa at a frequency of 2.25 MHz and PRF of 100 Hz. Photomicrographs were captured before and 2-min postexposure. On a pulse-to-pulse basis, the 10 Hz acoustic emission was considerably higher and more sustained than those at other PRFs (1000, 500, and 100 Hz) ( p < 0.05). Damage, measured as area of extravasation of red blood cells (RBCs), was also significantly higher at 10 Hz PRF than at 1000, 500 and 100 Hz ( p < 0.01). The correlation of acoustic emission to tissue damage showed a trend of increasing damage with increasing cumulative function of the relative integrated power spectrum (CRIPS; R 2 = 0.75). No visible damage was present at P r ≤ 0.85 MPa. Damage, however, was observed at P r ≥ 1.0 MPa and it increased with increasing acoustic pressure. (E-mail: ssamuel@umich.edu)

Estimating 2-D vector velocities using multidimensional spectrum analysis

Wilson (1991) presented an ultrasonic wideband estimator for axial blood flow velocity estimation through the use of the 2-D Fourier transform. It was shown how a single velocity component was concentrated along a line in the 2-D Fourier space, where the slope was given by the axial velocity. Later, it was shown that this approach could also be used for finding the lateral velocity component by also including a lateral sampling. A single velocity component would then be concentrated along a plane in the 3-D Fourier space, tilted according to the 2 velocity components. This paper presents 2 new velocity estimators for finding both the axial and lateral velocity components. The estimators essentially search for the plane in the 3- D Fourier space, where the integrated power spectrum is largest. The first uses the 3-D Fourier transform to find the power spectrum, while the second uses a minimum variance approach. Based on this plane, the axial and lateral velocity components are estimated. Several phantom measurements, for flow-to-depth angles of 60, 75, and 90 degrees, were performed. Multiple parallel lines were beamformed simultaneously, and 2 different receive apodization schemes were tried. The 2 estimators were then applied to the data. The axial velocity component was estimated with an average standard deviation below 2.8% of the peak velocity, while the average standard deviation of the lateral velocity estimates was between 2.0% and 16.4%. The 2 estimators were also tested on in vivo data from a transverse scan of the common carotid artery, showing the potential of the vector velocity estimation method under in vivo conditions.

Determination of Reaction Rate Constants andT2Relaxation Times Using Integrated NMR Power Spectra

An alternative method of evaluating chemical rate constants from NMR measurements is proposed. The integral over the NMR power spectrum depends on the life times of reacting species in contrast to the integral over the conventional phase sensitive NMR spectrum. Using this effect the range of measurable rates can be increased by about two orders of magnitude as compared to those obtained with the line shape method. From integrated power spectra also the ratio of T2 to a precisely known reference T ref 2 can be determined. Inhomogeneous magnets do not deteriorate T2, thus obtained.