Amplitude Correction Factors Research Articles

An Enhanced Current Differential Protection for AC Transmission Lines Connecting MMC-HVDC Stations

The peculiar fault current signatures of modular multilevel converter-based high voltage dc transmission (MMC-HVdc) system degenerate the operating performance of conventional current differential protection (CDP). CDP may incur low sensitivity or maloperations, especially when MMC-HVdc stations operate in rectifier mode. The performance problem of CDP in the presence of MMC-HVdc stations is analyzed. To address this issue, an enhanced CDP (ECDP) based on amplitude and phase correction factors is presented. The basic principle of ECDP is illustrated and the performance comparison between CDP and ECDP is provided. Furthermore, to avoid unwanted operations caused by abnormal data under external faults, abnormal data index is designed to identify abnormal data. Saturation index is proposed to improve the security of ECDP in the case of CT saturation. Compared with CDP, ECDP has a faster respond speed for internal faults. ECDP can perform well under different operation modes of MMC-HVdc station and various fault conditions. Therefore, ECDP is a promising candidate to protect transmission lines connecting MMC-based converter stations. The performance of ECDP is evaluated using PSCAD/EMTDC and RTDS.

Insights on the Hydrodynamics of Chiari Malformation.

Background: We propose that the appearance of a ptosis of the cerebellar tonsils and syringomyelia is linked to its own hemohydrodynamic mechanisms. We aimed to quantify cerebrospinal fluid (CSF) and cerebral blood flow to highlight how neurofluid is affected by Chiari malformations type 1(CMI) and its surgery. Methods: We retrospectively included 21 adult patients with CMI who underwent pre- and postoperative phase contrast MRI (PCMRI) during the period from 2001 to 2017. We analyzed intraventricular CSF, subarachnoid spaces CSF, blood, and tonsils pulsatilities. Results: In preoperative period, jugular venous drainage seems to be less preponderant in patients with syringomyelia than other patients (venous correction factor: 1.49 ± 0.4 vs. 1.19 ± 0.1, p = 0.05). After surgery, tonsils pulsatility decreased significantly (323 ± 175 μL/cardiac cycle (CC) vs. 194 ± 130 μL/CC, p = 0.008) and subarachnoid CSF pulsatility at the foramen magnum increased significantly (201 ± 124 μL/CC vs. 363 ± 231 μL/CC, p = 0.02). After surgery, we found a decrease in venous flow amplitude (5578 ± 2469 mm3/s vs. 4576 ± 2084 mm3/s, p = 0.008) and venous correction factor (1.98 ± 0.3 vs. 1.20 ± 0.3 mm3/s, p = 0.004). Conclusions: Phase-contrast MRI could be a useful additional tool for postoperative evaluation and follow-up, and is complementary to morphological imaging.

Compensating Method of Equivalent Current Sources of LSI-Core Macromodel Considering Voltage Fluctuations in On-Chip Power Distribution Network

Electro-magnetic compatibility (EMC) macromodels of a large-scale integrated (LSI) circuit core have been proposed to predict conducted RF emission and power integrity issues not only on a printed circuit board but also inside an LSI. They are equivalent circuit models that consist of lumped element impedance blocks of an LSI-core and equivalent current sources expressing internal switching activities. In conventional macromodeling, equivalent current sources have been extracted under ideal power supply conditions, i.e., with constant supply voltage. However, there exists transient supply voltage fluctuations in an actual on-chip power distribution network (PDN), and the operating current and its equivalent current sources are expected to vary with such fluctuations. Such issues with transient supply voltage fluctuations have not been extensively investigated. We propose a method of compensating the equivalent current sources of a macromodel by introducing amplitude and time correction factors, taking into account the voltage fluctuations in an on-chip PDN.

Cascaded Least Square Algorithm for Strong Clutter Removal in Airborne Passive Radar

Owing to the continuous random and nonperiodic characteristics of the passive signal, the random range sidelobe coupling (RRSC) effects of the strong clutter (i.e., the direct path signal and the strong multipath signal) will exacerbate the performance of space-time adaptive processing (STAP) algorithm in airborne passive radar (APR). This article analyzes the influence of RRSC caused by strong clutter on detection range cell of interest and illustrates that strong clutter should be suppressed before applying the STAP algorithm. A cascaded least square (CLS) algorithm based on the directional dependence of clutter Doppler frequency is proposed for side-looking APR, where the first least square (LS) algorithm is performed to achieve the amplitude estimation of the Doppler-shift echo signal, and the channel amplitude and phase error correction factor can be obtained by the estimated amplitude information of the direct patch signal and the APR geometric configuration. The second LS is employed to further estimate the amplitude information of the strong clutter, and the resulting weight vector can be utilized for clutter cancelation. To make the CLS algorithm more practical, a batch version of the CLS (CLS-B) algorithm is proposed in this article. The advantage of the method is that it cannot only cancel clutter along the clutter ridge but also effectively prevent the suppression of targets falling in the clutter Doppler band. In addition, the proposed CLS algorithm performs well in the presence of the channel amplitude and phase error. A series of simulations are conducted to test the proposed algorithms.

Calibrating the 2016 IRIS Wavefields Experiment Nodal Sensors for Amplitude Statics and Orientation Errors

ABSTRACTWe used teleseismic P and S waves recorded in the course of the 2016 Incorporated Research Institutions for Seismology (IRIS) community-planned experiment in northern Oklahoma, to estimate amplitude correction factors (ACFs) and orientation correction factors (OCFs) for the gradiometer’s three-component Fairfield nodal sensors and two other gradiometer-styled subarray nodal sensors. These subarrays were embedded in the 13 km aperture nodal array that was also fielded during the 2016 IRIS experiment. The array calibration method we used in this study is based on the premise that a common wavefield should be recorded over a small-aperture array using teleseismic observation. In situ estimates of ACF for the gradiometer vary by 2.3% (standard deviation) for the vertical components and, typically, variability is less than 4.3% for the horizontal components; associated OCFs generally dispersed by 3°. For the two subarrays, the vertical-component ACF usually vary up to 2.4%; their horizontal-component ACFs largely spread up to 3.6%. OCFs for the subarrays generally disperse by 6.5°. ACF and OCF estimates for the gradiometer are seen to be stable across frequency bands having high signal coherence and/or signal-to-noise ratio. Gradiometry analyses of calibrated and uncalibrated gradiometer records from a local event revealed notable improvements in accuracy of attributes obtained from analyzing the calibrated horizontal-component waveforms in the light of catalog epicenter-derived azimuth. The improved waveform relative amplitudes after calibration, coupled with the enhanced wave attribute accuracy, suggests that instrument calibration for amplitude statics and orientation errors should be encouraged prior to doing gradiometry analysis in future studies.

Analysis of Wave Patterns Under the Region of Macro-Fiber Composite Transducer to Improve the Analytical Modelling for Directivity Calculation in Isotropic Medium

Analytical modelling is an efficient approach to estimate the directivity of a transducer generating guided waves in the research field of ultrasonic non-destructive testing of the large and complex structures due to its short processing time as compared to the numerical modelling and experimental techniques. The wave patterns or the amplitude variations along the region of ultrasonic transducer itself depend on its behavior, excitation frequency, and the type of propagating wave mode. Depending on the wave-pattern of a propagating wave mode, the appropriate value of the amplitude correction factor must be multiplied to the amplitudes of the excitation signal for the accurate evaluation of directivity pattern of the ultrasonic transducers generating guided waves in analytical modelling. The objective of this work is to analyse the wave patterns under the region of macro-fiber composite (MFC) transducer to improve the accuracy of a previously developed analytical model for the prediction of directivity patterns. Firstly, the amplitude correction factor based on the wave patterns under the region of P1-type MFC (MFC-2814) transducer at two different frequencies (80 kHz, 3 periods and 220 kHz, 3 period) glued on 2 mm Al alloy plate has been estimated analytically in the case of an asymmetric (A0) guided Lamb wave. The validation of analytically estimated amplitude correction factor is performed by a proposed experimental method that allows analyzing the behaviour of MFC transducer under its region by gluing MFC on bottom surface and scanning the receiver on the top surface of the sample. Later on, the estimated amplitude correction factor is included in the previously developed 2D analytical model for the improvement in the directivity patterns of the A0 mode. The modified analytical model shows a significant improvement in the directivity pattern of the A0 wave mode in comparison to the results obtained by the previous model without considering the proper wave patterns. The results reveal that errors between the directivity estimated by the present modified 2D analytical model and experimental investigation are reduced by more than 58% in comparison to the previously developed analytical model.

A High Precision Lumped Parameter Model for Piezoelectric Energy Harvesters

We present a high precision lumped parameter model for efficient prediction of the resonant frequencies and coupling of cantilevered piezoelectric energy harvesters in absence of tip mass. Correction factors for the existing lumped parameter model are derived by comparing with the highly accurate distributed parameter model of cantilevered harvesters. First, a correction factor is defined for uncoupled lumped parameter model to predict the natural frequencies. Finally, the coupled lumped parameter model is subjected to a unified correction factor to accurately predict both the resonant frequencies and electrical outputs. The unified correction factor is derived by unifying the frequency and amplitude correction factors. The calculated outputs are in good agreement with the experimental results available in the literature.

AMPLITUDE CORRECTION FACTORS OF KOREAN VLBI NETWORK OBSERVATIONS

We report results of investigation of amplitude calibration for very long baseline interferometry (VLBI) observations with Korean VLBI Network (KVN). Amplitude correction factors are estimated based on comparison of KVN observations at 22~GHz correlated by Daejeon hardware correlator and DiFX software correlator in Korea Astronomy and Space Science Institute (KASI) with Very Long Baseline Array (VLBA) observations at 22~GHz by DiFX software correlator in National Radio Astronomy Observatory (NRAO). We used the observations for compact radio sources, 3C 454.3, NRAO 512, OJ 287, BL Lac, 3C 279, 1633+382, and 1510-089, which are almost unresolved for baselines in a range of 350-477 km. Visibility data of the sources obtained with similar baselines at KVN and VLBA are selected, fringe-fitted, calibrated, and compared for their amplitudes. We found that visibility amplitudes of KVN observations should be corrected by factors of 1.10 and 1.35 when correlated by DiFX and Daejeon correlators, respectively. These correction factors are attributed to the combination of two steps of 2-bit quantization in KVN observing systems and characteristics of Daejeon correlator.

Acquisition aperture correction in the angle domain toward true-reflection reverse time migration

Due to incomplete aperture coverage and complex overburden structures, the migration process cannot provide a true-amplitude image even though a true-amplitude propagator is used. Amplitude compensation based on source-side illumination ignores the aperture effects on the receiver side, and it may fail to recover the true-reflection/scattering strength of a geologic structure from the image. The structural dip largely controls if the wave incident on the structure can be reflected back and received by the acquisition aperture, so it should be taken into account in removing the acquisition effects from the migration image. We derived a dip-angle domain amplitude correctionfrom the resolution theory. The stacked migration image created by reverse time migration was decomposed into common dip images, which were compensated individually by the corresponding amplitude correction factor. Then, we summed up the corrected images to form a final image. To construct the amplitude correction factor, we generated a monofrequency Green’s function at the shot/geophone location and further decomposed it into incident/scattered plane waves. They were combined based on Snell’s law to construct correction factors for different dips. The final amplitude correction factor was formed by visiting all the shot-geophone pairs in the observation system. We devised efficient algorithms to make the amplitude correction more practical. We evaluated two numerical experiments, a five-layer model and the SEG/EAGE salt model, in which the amplitude correction led to a scalar/pressure image with an amplitude better matching the true impedance contrasts of subsurface structures, especially in areas with steep dips and in subsalt regions.

Two Dimensional Array Imaging With Beam Steered Data

This paper discusses different approaches used for millimeter wave imaging of 2D objects. Imaging of a 2D object requires reflected wave data to be collected across two distinct dimensions. In this paper, we propose a reconstruction method that uses narrowband waveforms along with 2D beam steering. The beam is steered in azimuthal and elevation direction, which forms the two distinct dimensions required for the reconstruction. The reconstruction technique uses inverse Fourier transform along with amplitude and phase correction factors. In addition, this reconstruction technique does not require interpolation of the data in either wavenumber or spatial domain. Use of the 2D beam steering offers better performance in the presence of noise compared with the existing methods, such as switched array imaging system. Effects of radio-frequency impairments such as quantization of the phase of beam steering weights and timing jitter, which add to phase noise, are analyzed.

TISSUE ABERRATION CORRECTIONS IN ULTRASOUND THERAPY

A system for focusing ultrasonic energy through intervening tissue into a target site within a tissue region includes a transducer array including transducer element, an imager for imaging the tissue region, a processor receiving images from the imager to determine boundaries between different tissue types within the intervening tissue and generate correction factors for the transducer elements to compensate for refraction occurring at the boundaries between the tissue types and/or for variations in speed of sound. A controller is coupled to the processor and the transducer array to receive the correction factors and provide excitation signals to the transducer elements based upon the correction factors. The correction factors may include phase and/or amplitude correction factors, and the phases and/or amplitudes of excitation signals provided to the transducer elements may be adjusted based upon the phase correction factors to focus the ultrasonic energy to treat tissue at the target site.

Joining multiple AEM datasets to improve accuracy, cross calibration and derived products: The Spiritwood VTEM and AeroTEM case study

ABSTRACTAirborne time‐domain electromagnetic methods (AEM) are useful for hydrogeological mapping due to their rapid and extensive spatial coverage and high correlation between measured magnetic fields, electrical conductivity, and relevant hydrogeological parameters. However, AEM data, preprocessing and modelling procedures can suffer from inaccuracies that may dramatically affect the final interpretation. We demonstrate the importance and the benefits of advanced data processing for two AEM datasets (AeroTEM III and VTEM) collected over the Spiritwood buried valley aquifer in southern Manitoba, Canada. Early‐time data gates are identified as having significant flight‐dependent signal bias that reflects survey flights and flight lines. These data are removed from inversions along with late time data gates contaminated by apparently random noise. In conjunction with supporting information, the less‐extensive, but broader‐band VTEM data are used to construct an electrical reference model. The reference model is subsequently used to calibrate the AeroTEM dataset via forward modelling for coincident soundings. The procedure produces calibration factors that we apply to AeroTEM data over the entire survey domain. Inversion of the calibrated data results in improved data fits, particularly at early times, but some flight‐line artefacts remain. Residual striping between adjacent flights is corrected by including a mean empirical amplitude correction factor within the spatially constrained inversion scheme. Finally, the AeroTEM and VTEM data are combined in a joint inversion. Results confirm consistency between the two different AEM datasets and the recovered models. On the contrary, joint inversion of unprocessed or uncalibrated AEM datasets results in erroneous resistivity models which, in turn, can result in an inappropriate hydrogeological interpretation of the study area.

Fast acquisition aperture correction in prestack depth migration using beamlet decomposition

Wave-equation-based acquisition aperture correction in the local angle domain can improve image amplitude significantly in prestack depth migration. However, its original implementation is inefficient because the wavefield decomposition uses the local slant stack (LSS), which is demanding computationally. We propose a faster method to obtain the image and amplitude correction factor in the local angle domain using beamlet decomposition in the local wavenumber domain. For a given frequency, the image matrix in the local wavenumber domain for all shots can be calculated efficiently. We then transform the shot-summed image matrix from the local wavenumber domain to the local angle domain (LAD). The LAD amplitude correction factor can be obtained with a similar strategy. Having a calculated image and correction factor, one can apply similar acquisition aperture corrections to the original LSS-based method. For the new implementation, we compare the accuracy and efficiency of two beamlet decompositions: Gabor-Daubechies frame (GDF) and local exponential frame (LEF). With both decompositions, our method produces results similar to the original LSS-based method. However, our method can be more than twice as fast as LSS and cost only twice the computation time of traditional one-way wave-equation-based migrations. The results from GDF decomposition are superior to those from LEF decomposition in terms of artifacts, although GDF requires a little more computing time.

Comment on “Measuring the transverse magnetization of rotating ferrofluids”

Contrary to the main conclusion of Embs [Phys. Rev. E 73, 036302 (2006)], we demonstrate with amplitude correction factors that the predictions of the magnetization model proposed by Shliomis [Sov. Phys. JETP 34, 1291 (1972)] are well consistent with the experimental data for weakly nonequilibrium states and that the model proposed by Shliomis [Phys. Rev. E 64, 063501 (2001)] is valid even far from equilibrium. A model on the basis of the weak-field magnetization equation of Müller and Liu [Phys. Res. E 64, 061405 (2001)] with a "structure" modification is also shown to reproduce a wide range of experimental data. Our statement is confirmed by a more exact insight into the hydrodynamic problem of rotating ferrofluids.

Using Interstation Amplitude Correction Factors to Predict Regional Phase Amplitudes

Abstract Developing regional discriminants at any given seismic station requires a ground truth database of waveforms from both earthquakes and explosions. Recently installed stations used for seismic monitoring have no single-charge explosions on which to base discriminants. We have developed a procedure to map regional seismic amplitudes from surrogate stations, which have a long recording history, to newly installed operational stations. This procedure uses an interstation amplitude correction factor (IACF), computed using a set of commonly recorded calibration earthquakes between the surrogate and operational station pair, to predict seismic amplitudes at the new station using the IACF and historical explosion amplitudes from the surrogate station. We tested the method using an earthquake aftershock sequence in Pakistan recorded at the Kyrgyzstan broadband seismic network. The aftershocks had a range of depths and were clustered in a linear trend defining the fault rupture plane of the mainshock. We computed IACFs for all possible station combinations at KNET (45 combinations) for all events and then computed a mean IACF value for each station pair. Using the mean IACF values, we calculated predicted phase amplitudes at each station and compared the predictions to the actual values. The observed-predicted relationship performed well ( r 2 -values>0.8) for all phases and frequency bands. At frequencies above 6 Hz, the observed-predicted relationship showed more scatter, a trend not due to interstation distance, source depth, or spatial location of the calibration earthquakes. We were able to reduce scatter in the observed-predicted relationship by applying path corrections to the data, suggesting that sensitivities in differing paths between certain surrogate-operational station combinations do play a role in the effectiveness of the method. We used this methodology to predict explosion values at the Lop Nor nuclear test site in China using a suite of nearby calibration earthquakes to calculate IACF values. The results indicate good correlation between the observed and predicted amplitudes, suggesting that the method can be used to simulate explosion characteristics at stations that have never recorded explosions. Comparing the IACF values from the calibration dataset near Lop Nor to those calculated for the earthquakes in Pakistan, we see some similarity for certain station combinations; however, on the whole, there are differences that suggest that IACFs have a spatial variance and must be tuned to the region and path of interest for the method to be successful.

Correction factor for strongly reflecting U-path RACs

An equation from the literature describing multiple reflections in a U-path surface-acoustic-wave (SAW) reflective array compressor (RAC) is simplified for RACs with a large time-bandwidth product, yielding a very convenient expression consisting of the relation for weakly reflecting RACs plus phase and amplitude correction factors. The quantitative effect of multiple reflections is immediately apparent, so that the designer has a better understanding of how various parameters affect the final performance. A down-chirp, which is more common in practical devices, is described. Empirical extensions to higher-order and variable weighing are deduced and verified numerically, while the possibility of variable chirp is discussed.

Least-squares methods for the extraction of surface currents from CODAR crossed-loop data: Application at ARSLOE

Least-squares methods are demonstrated that extract surface current radial velocities from first-order Coastal Ocean Dynamics Applications Radar (CODAR) sea-echo Doppler spectra for the compact crossed-loop/monopole antenna system. Based on the known physics of first-order sea scatter at HF, these techniques, implemented as software, are objective and automatic in that they: a) determine from the sea-echo phase and amplitude correction factors for the antenna elements; b) separate the first-order spectrum from the surrounding continuum for arbitrarily varying current conditions; c) using statistical hypothesis testing, select and use either a single or dual-angle model for radial current patterns, whichever best fits the data; d) calculate angles associated with given radial velocities; e) combine the data into a polar-coordinate map of radial velocity versus position; and f) calculate radial velocity uncertainties at each point on the map. In addition, as interpretive aids, two methods are evaluated and compared that provide total current vectors from single-site CODAR data, along with their uncertainties: model fitting and the application of the equation of continuity. It is shown how these methods can be applied to the older, CODAR 4-element antenna system, however, the following advantages of the crossed-loop/monopole system are discussed: it is physically more compact; analysis procedures are more efficient; resulting current velocities are more accurate, because there are no side-lobe problems; and finally, it also gives the ocean wave-height directional spectrum. These methods are tested and optimized against data taken during the Atlantic Remote Sensing Land Ocean Experiment (ARSLOE) storm (October 23-27, 1980), when surface currents varied in speed between 0-50 cm/s and over nearly 300° in angle. Current velocities were measured to a range of 36 km from the radar. Standard deviations in angle are typically 1°-3°; these translate to 2-3 cm/s rms radial velocity uncertainties over most of the coverage area, with decreased accuracy in angular sectors nearest the coast. Total current velocity vectors in strips parallel to shore obtained from model fitting have typical speed and angle uncertainties of 4 cm/s and 12°, respectively. Of the several formulations for the equation of continuity evaluated here, the best gave uncertainties of 5 cm/s, 12° at the closest range cells; these values increase rapidly with range to exceed 20 cm/s, 30° for distances greater than 20 km. The surface currents were observed to follow the wind throughout most of the storm at ARSLOE, but the current was almost always more closely parallel to the shore than the wind. An interesting exception occurred when the onshore storm wind that had prevailed for two days ceased; there was a rush of surface current directly offshore as the storm-surge sea level dropped. The surface current speed measured by CODAR in the upper meter of the ocean was, on the average, 2.1 percent of the windspeed.

Correction of fan noise for effects of forward flight

When acoustic measurements are made on a static engine test stand, the data must be corrected for the effects of forward flight to predict correctly the noise characteristics of the engine in flight. A ray tracing approach is used here to relate the static test case to the flight case. The assumptions of isentropic irrotational flow into the fan inlet and a cylindrical shear layer at the fan exhaust lead to slightly different methods for correcting inlet noise and exhaust noise. The forward flight correction method generally involves both an angle and an amplitude correction. The amplitude correction factors for inlet and exhaust noise are the same as that for a dipole and can be as much as 6 dB for a flight Mach number of 0·3. The angle correction for the inlet noise differs from that of the exhaust noise, and both differ from the generally used correction to retarded angle.

ChemInform Abstract: THE GAS‐PHASE MOLECULAR STRUCTURE OF SILYL(METHYL)ACETYLENE (1‐SILABUT‐2‐YNE), DETERMINED BY ELECTRON DIFFRACTION

Abstract The molecular structure of CH3C  CSiH3 in the gas phase has been investigated using electron diffraction. Mean amplitudes of vibration and perpendicular amplitude correction factors calculated from spectroscopic data enabled refinements of both ra and rαo structures to be carried out, allowing a comparison with the B rotation constant, corrected to Bz. Ths r0α refinement leads to a linear skeleton, with parameters: r(Si-C), 180.2(4) pm; r(CC), 121.9(4) pm; r(C-C), 145-0(5) pm; r(Si-H), 150.6(10) pm; r(C-H), 105.3(7) pm; ∠-HSiC, 110.7(10)°; ∠HCC, 110.9(12)°. The ra structure shows the usual apparent bends in the skeleton due to shrinkage.

ChemInform Abstract: THE GAS‐PHASE MOLECULAR STRUCTURE OF SILYL CHLOROACETYLENE, DETERMINED BY ELECTRON DIFFRACTION

Abstract The molecular structure of SiH 3 CCCl in the gas phase has been investigated using electron diffraction. Mean amplitudes of vibration and perpendicular amplitude correction factors calculated from spectroscopic data enabled refinement of both r a and r α structures to be carried out. The r α refinement leads to a linear skeleton, with r α parameters: r (Si-C) 181.2(5) pm, r (CC) 123.4(6) pm, r (C-Cl) 162.0(5) pm, r (Si-H) 148.8(12) pm, ∠HSiC 109.4(20)°. The r a structure shows an apparent angle in the skeleton of 172(3)° (∠CCCl) owing to shrinkage.