Calculation Of Transfer Function Research Articles

Assessment of temporal resolution and detectability of moving objects in CT: A task-based image quality study

The metrics used for assessing image quality in computed tomography (CT) do not integrate the influence of temporal resolution. A shortcoming in the assessment of image quality for imaging protocols where motion blur can therefore occur. We developed a method to calculate the temporal resolution of standard CT protocols and introduced a specific spatiotemporal formulation of the non-prewhitening with eye filter (NPWE) model observer to assess the detectability of moving objects as a function of their speed. We scanned a cubic water phantom with a plexiglass cylindrical insert (120 HU) using a large panel of acquisition parameters (rotation times, pitch factors and collimation widths) on two systems (GE Revolution Apex and Siemens SOMATOM Force) to determine the in-plane task-based transfer functions (TTF) and noise power spectra (NPS). The phantom set in a uniform rectilinear motion in the transverse plane allowed the temporal modulation transfer function (MTF) calculation. The temporal MTF appropriately compared the temporal resolution of the various acquisition protocols. The longitudinal TTF was measured using a thin tungsten wire. The detectability index showed the advantage of applying high rotation speed, wide collimations and high pitch for object detection in the presence of motion. No counterpart to the increase in these three parameters was found in the in-plane and longitudinal image quality.

Revisit Impedance-Based Stability Analysis of VSC-HVDC System

According to different partitioning styles, there exist different impedance-based stability analysis methods for complex systems such as voltage source converter (VSC)-based high-voltage direct current (HVDC) systems. Thus, the determination of the partitioning method is of importance in impedance-based stability analysis. However, how to partition a complex system is not paid much attention in the past. In this paper, the partitioning problems are revisited and a set of practical partitioning principles are proposed. Based on the principles, the VSC-HVDC system is partitioned into five parts, satisfying simplicity and integrity. In addition, the methods to form the equivalent circuits of the sub-systems are given and the equivalent circuits of the sub-systems are built, which is helpful to obtain the input-output models of the sub-systems. Furthermore, a stability criterion by directly applying the argument principle is used instead of the generalized Nyquist criterion (GNC), which could avoid the calculation of eigenvalue transfer functions, especially when a large number of sub-systems are involved. Finally, the correctness of the impedance-based stability analysis method is verified by control hardware-in-loop (CHIL) experimental results.

Sketches of chimpanzee (Pan troglodytes) hoo’s: vowels by any other name?

In human speech, the close back rounded vowel /u/ (the vowel in “boot”) is articulated with the tongue arched toward the dorsal boundary of the hard palate, with the pharyngeal cavity open. Acoustic and perceptual properties of chimpanzee (Pan troglodytes) hoo’s are similar to those of the human vowel /u/. However, the vocal tract morphology of chimpanzees likely limits their phonetic capabilities, so that it is unlikely, or even impossible, that their articulation is comparable to that of a human. To determine how qualities of the vowel /u/ may be achieved given the chimpanzee vocal tract, we calculated transfer functions of the vocal tract area for tube models of vocal tract configurations in which vocal tract length, length and area of a laryngeal air sac simulacrum, length of lip protrusion, and area of lip opening were systematically varied. The method described is principally acoustic; we make no claim as to the actual shape of the chimpanzee vocal tract during call production. Nonetheless, we demonstrate that it may be possible to achieve the acoustic and perceptual qualities of back vowels without a reconfigured human vocal tract. The results, while tentative, suggest that the production of hoo’s by chimpanzees, while achieving comparable vowel-like qualities to the human /u/, may involve articulatory gestures that are beyond the range of the human articulators. The purpose of this study was to (1) stimulate further simulation research on great ape articulation, and (2) show that apparently vowel-like phenomena in nature are not necessarily indicative of evolutionary continuity per se.

InFluence: An Open-Source Python Package to Model Images Captured with Direct Electron Detectors.

The high detection efficiencies of direct electron detectors facilitate the routine collection of low fluence electron micrographs and diffraction patterns. Low dose and low fluence electron microscopy experiments are the only practical way to acquire useful data from beam sensitive pharmaceutical and biological materials. Appropriate modeling of low fluence images acquired using direct electron detectors is, therefore, paramount for quantitative analysis of the experimental images. We have developed a new open-source Python package to accurately model any single layer direct electron detector for low and high fluence imaging conditions, including a means to validate against experimental data through computation of modulation transfer function and detective quantum efficiency.

Comparative analysis of closed-form expressions and other commonly used seakeeping methods

Closed-form expressions (CFE) are semi-analytical transfer functions for ship wave-induced responses based only on main ship particulars. They are useful in an early stage of ship design and situations when hull lines for seakeeping analysis are not available. As the accuracy of CFE remains an open subject, the aim of the present study is to quantify the frequency independent model error (FIME) of CFE. Measured transfer functions of the heave, pitch, and vertical wave bending moment at midship for 13 ships are acquired from literature, together with calculated transfer functions using the strip theory and the 3D panel method, where several speeds and heading angles are available. FIME is determined by comparing transfer functions calculated by CFE, strip theory, and 3D panel codes with model-scale experiments. Multivariate linear regression analysis is performed for three seakeeping methods to indicate a dependence of FIME on the main parameters of the analysis. Dispersion of the FIME around the regression line is determined, enabling a relative comparison of the uncertainty of seakeeping methods of different complexity. The results of this study may improve the practical applicability of CFE and provide an uncertainty quantification of commonly used seakeeping methods, which is important for probability-based applications.

A New Model Uncertainty Measure of Wave-Induced Motions and Loads on a Container Ship with Forward Speed

A new uncertainty quantifier is presented for linear transfer functions of wave-induced ship motions and loads obtained by various seakeeping codes. The numerical simulations are conducted for the high-speed Flokstra container ship in regular waves at various heading angles, and the results are compared with existing experimental data. The study employs five numerical codes that are based on three different seakeeping theories, namely strip theory, 3D frequency-domain method, and 3D time-domain method. Multiple measures are applied to quantify the uncertainty in the calculated transfer functions, such as frequency-independent model error, coefficient of determination, and the total difference. In addition, a new measure of uncertainty, termed modified total difference, is proposed for determining the uncertainty of individual seakeeping codes based on experimental data rather than the mean of results obtained by numerical codes. Results show that the uncertainty measures can identify differences between the codes. The predicted wave-induced loads have higher uncertainties compared to motions. The uncertainty assessment shows that none of the applied codes can produce accurate estimates for all wave-induced motions and loads at all heading angles at the same time.

Growth and Saturation of the Electron Drift Instability in a Crossed Field Plasma.

The linear growth and nonlinear energy transfer of the electron drift instability (EDI) are experimentally measured in the plume of a low-temperature, Hall effect discharge. A frequency-based bispectral analysis technique applied to fast ion density fluctuation measurements shows a growth rate function that is qualitatively similar to predictions from the linear instability dispersion relation, but an order of magnitude smaller. Calculation of the nonlinear transfer function indicates multiple three-wave interactions between high-frequency resonances of the instability in addition to an inverse energy cascade toward lower-frequency modes. These results are discussed in the context of recent theoretical, numerical, and experimental efforts on the EDI in Hall effect discharges and how the EDI may impact anomalous cross field transport.

Theoretical and Practical Investigation of Stability Performance for Power Regulation in Hydroelectric Power Plants

Hydroelectric power plants are the insurance of the interconnected system in order to provide fast energy to the system compared to other fossil fueled power plants. Hydroelectric power plants control the balance between the energy it supplies to the interconnected system and the pressurized water it uses with a system based on the fully automatic control principle. The quality of the energy supplied to the interconnected system depends entirely on this automatic control mechanism. In this study, mathematical models of the mechanisms that affect the automatic control system during the generation of energy in hydroelectric power plants are formed. Transfer functions of the obtained mathematical models are calculated by laplace transform. With the calculated transfer functions, the responses of the units of a hydroelectric power plant to the change of the amount of energy produced under different operating conditions are determined. The obtained data are compared with the actual conditions in a 1330 MW hydroelectric power plant with 8 Francis turbines. It is seen that the mathematical model and the turbine responses in real conditions are similar. In the calculations made at 115, 125, 135, 145 m. net head, the best stability conditions were obtained at 135 m. In addition, as a result of the calculations obtained under different operating conditions, ideal operating conditions are determined to minimize the fluctuations in energy production.

Far-Field Radiation Prediction and Analysis of a Power Converter With V-Shaped Flat Cables Based on PEEC

The far-field radiation generated by a power electronic converter with V-shaped cables is a key theoretical problem with engineering application significance. The irregular V-shaped antenna is very difficult to calculate analytically, making a precise prediction of the power converter's far-field radiation very challenging. In this work, the far-field radiation of a power converter with flat shielded cables is modeled and predicted using the retarded partial element equivalent circuit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathbf{\tau}}$</tex-math></inline-formula> PEEC) theory. The τPEEC modified node analysis circuit model of a metal radiator is introduced first, and then the radiator's input impedance formula is deduced. The τPEEC computation model of the V-shaped radiator, which includes the ground plane reflection effect, is developed for the typical far-field radiation test configuration, and the numerical calculation of the far-field radiation transfer function is obtained using the field strength sensor method. To test the suggested τPEEC approach, a 30-MHz low-side buck converter with flat shielded cables is built, and its 10-m far-field radiation strength is predicted. The V-shaped radiator's radiation characteristics are also investigated, and a design for suppression is proposed and demonstrated.

Transfer function calculation for the Poincaré-Steklov operator in the case of a functionally gradient elastic strip

Рассматривается краевая задача для функционально-градиентной упругой полосы. Получено трехчленное асимптотическое разложение передаточной функции оператора Пуанкаре-Стеклова, отображающего на части границы полосы нормальные напряжения в нормальные перемещения. Построены аппроксимации Паде полученного асимптотического ряда. Предложен подход к вычислению передаточной функции с использованием асимптотического ряда и аппроксимаций Паде, сокращающий вычислительные затраты.

Fast SEMS size distribution measurements under down-scan operation

Particle size distributions obtained with a Scanning Electrical-Mobility Spectrometer (SEMS) are based on the response of charged particles in an applied electric field. A complete operation of SEMS instrument for particle sizing involves the exposure of charged particles to an exponentially increasing voltage (up-scan) followed by an exponentially decreasing voltage (down-scan). Accurate calculation of particle size distributions from SEMS measurements requires knowledge of the instrument transfer function or Kernel as a function of its operating conditions and subsequently, the inversion of an integral equation. A semi-theoretical transfer function calculation approach based on particle arrival-times was shown to accurately characterize fast up-scan SEMS operation. In this paper, we extend the arrival-time calculation approach for SEMS down-scan operation. The combination of a decreasing voltage over time and a parabolic velocity field results in particle trajectories that are fundamentally different from the up-scan operation. However, when smearing due to downstream transport of particles to the detector is considered, the down-scan transfer functions are seen to be a mirror image of the up-scan transfer functions in the mobility space. This suggests that the inversion algorithms optimized for fast up-scan operation could also be applicable for fast down-scan operation. The combination of near real-time up-scan and down-scan transfer functions should enable fast, and accurate size distribution measurements under a range of operating conditions.

Efficient computation of modal transfer function in mode composition beamforming for rotating broadband source localization.

For rotating sound source localization, there are mainly two types of frequency-domain beamforming methods, the virtual rotating array (VRA) method and mode composition beamforming (MCB). Compared with the VRA method, MCB overcomes the constraint of microphone array configuration and avoids error introduced by interpolation. In order to obtain the MCB result, modal transfer functions, which are the modal coefficients in the analytical solution of the sound field of rotating source, should be pre-calculated. However, the computation of modal transfer functions takes a long time, especially under a large number of considered frequencies. Therefore, the computational efficiency of MCB is limited by the computation of modal transfer functions. In this paper, an expression of modal transfer functions at multiple considered frequencies is derived first. According to this expression, intermediate variables independent of frequency are computed in a fast way, then modal transfer functions at each considered frequency are calculated through these intermediate variables. This expression is successfully applied to improve the computational efficiency of MCB for rotating broadband source localization.

Application of matrices for transfer function values calculation in mechanical systems

The paper describes the formalism and methodology that can be employed for calculation of transfer function in distributed parameter elastic mechanical systems. Generalized formalism for derivation of transfer function matrices is presented as developed in accordance with the Hilbert-Schmidt theorem. Matrix-based method to determine elastic mechanical system transfer function is offered. The solution of the problem of forced harmonic oscillations of an elastic body of a mechanical system with the presence of friction is considered. The described technique can be applied to find the transfer functions of technological equipment in order to determine the dynamic characteristics of the system.

Research on acoustic reconstruction methods of the hull vibration based on the limited vibration monitor data

The prediction of hull vibration response is the basis for the quantitative control of cabin noise and underwater radiated noise, which has an important engineering value to obtain vibration characteristics accurately. In this paper, a new method is proposed to reconstruct hull vibration by some monitoring data in low frequencies. The hull vibration response is reconstructed by the monitoring data and the transfer function, and the ill-posed problem of inversion for the transfer function matrix is solved by the total least-squares regularization. A P-GRU (Peak-based Gated Recurrent Unit) neural network correction model is proposed to improve the prediction accuracy of vibration response. Taking a certain cabin structure as an example, some research such as the hull vibration data monitoring, the vibration transfer function calculation, vibration response reconstruction, and correction based on experimental data were carried out, and the simulation calculations and verification of experiment models were obtained. The multi-parameter comprehensive method is adopted to quantitatively evaluate the results between the simulation and the experiment. The results show that the acoustic reconstruction results are in good agreement with the experimental data. The overall level error is within 3 dB, the main peak value correlation coefficient is above 0.9, and the main peak difference is within 4 dB. The mechanism of the rapid and accurate prediction of the low-frequency vibration for the hull based on limited monitoring data is discussed by using a semi-physical simulation method combining the simulation calculation, vibration monitoring, and machine learning. The problem of phase asynchrony was solved, and strong support was provided for the construction of the ship's acoustic digital twin.

A Pair of Coupled Waveguides as a Classical Analogue for a Solid-State Qubit.

We have determined conditions when a pair of coupled waveguides, a common element for integrated room-temperature photonics, can act as a qubit based on a system with a double-well potential. Moreover, we have used slow-varying amplitude approximation (SVA) for the "classical" wave equation to study the propagation of electromagnetic beams in a couple of dielectric waveguides both analytically and numerically. As a part of an extension of the optical-mechanical analogy, we have considered examples of "quantum operations" on the electromagnetic wave state in a pair of waveguides. Furthermore, we have provided examples of "quantum-mechanical" calculations of nonlinear transfer functions for the implementation of the considered element in optical neural networks.

Adaptive Linearization for the Sub-Nyquist Photonic Receiver Based on Deep Learning

Due to the nonlinear and aliasing effects, the sub-Nyquist photonic receiver for radio frequency (RF) signals with large instantaneous bandwidth suffers limited dynamic range and noise performance. We designated a deep residual network (Resnet) to realize adaptive linearization across 40 GHz bandwidth. In contrast to conventional linearization methods, the deep learning method achieves the suppression of multifactorial spurious distortions and the noise floor simultaneously. It does not require an accurate calculation of the nonlinear transfer function or prior signal information. The experiments demonstrated that the proposed Resnet could improve the spur-free dynamic range (SFDR) and the signal-to-noise ratio (SNR) significantly by testing with single-tone signals, dual-tone signals, wireless communication signals, and modulated radar signals.

A generalized analysis of high‐order N‐path filters

AbstractIn N‐path filter analysis, assumptions are used to simplify their analysis to avoid the complexity of the calculations. These assumptions limit the number of examinable circuits. This paper analyzes a general system including an arbitrary number of N‐path filters to generalize the analysis. In the proposed method, due to the calculation of harmonic transfer functions for each independent capacitor in each time interval, it is possible to examine N‐path filters in the presence of common capacitors between multiple branches, leakage resistors, and branches with asymmetric switching. The absence of discontinuous jumps during the switching moments and switching operation in a non‐overlapping fashion with a specified periodicity are the only assumptions of the proposed method. As a result, more LPTV (linear periodically time‐varying) systems can be analyzed using the calculations provided. After presenting the method, we show the proposed method's ability by analyzing a recently published impedance‐transforming N‐path filter and examining its details.

Cerebral Autoregulation Assessment Using the Near Infrared Spectroscopy 'NIRS-Only' High Frequency Methodology in Critically Ill Patients: A Prospective Cross-Sectional Study.

Impairments in cerebral autoregulation (CA) are related to poor clinical outcome. Near infrared spectroscopy (NIRS) is a non-invasive technique applied to estimate CA. Our general purpose was to study the clinical feasibility of a previously published ‘NIRS-only’ CA methodology in a critically ill intensive care unit (ICU) population and determine its relationship with clinical outcome. Bilateral NIRS measurements were performed for 1–2 h. Data segments of ten-minutes were used to calculate transfer function analyses (TFA) CA estimates between high frequency oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb) signals. The phase shift was corrected for serial time shifts. Criteria were defined to select TFA phase plot segments (segments) with ‘high-pass filter’ characteristics. In 54 patients, 490 out of 729 segments were automatically selected (67%). In 34 primary neurology patients the median (q1–q3) low frequency (LF) phase shift was higher in 19 survivors compared to 15 non-survivors (13° (6.3–35) versus 0.83° (−2.8–13), p = 0.0167). CA estimation using the NIRS-only methodology seems feasible in an ICU population using segment selection for more robust and consistent CA estimations. The ‘NIRS-only’ methodology needs further validation, but has the advantage of being non-invasive without the need for arterial blood pressure monitoring.

DOE-ANOVA for Identifying the Effect of Extreme Sea-States over the Structural Dynamic Parameters of a Floating Structure

Sea extreme events affect the integrity and operation of the offshore structures, then, it is important to analyze wind-waves-currents loads over the structural dynamics. Traditional offshore designing identifies structural parameters with certain limitations: physical modeling involves using shaking tables in dry conditions; numerical simulations have not sufficiently considered the effects of combined extreme waves-wind-current loads over the structure and the significance of the near and far hydrodynamic field over the structure. The non-linear interactions in the near hydrodynamic field generate viscous damping that modifies the dynamic structural parameters of the offshore structures. The traditional determination of structural parameters considers the hydrodynamic forces computed from wave records, omitting fluid-structure interactions that could generate unexpected damped periods and amplification peaks. This study applied physical modeling to determine floating structural parameters, considering combined loads and the effect of far and near hydrodynamic field in the fluid-structure interaction. The calculated transfer functions in the near hydrodynamic field revealed the highest amplification of the structural accelerations, and the transfer functions in the far field did not evidence structural resonance. Finally, this study recommends measuring the near hydrodynamic field and applying DOE-ANOVA for offshore designing to assess the viscous damping that may provoke dangerous structural amplifications.

Simulation of a double-circuit subordinated coordinate regulation system of the active po wer factor corrector for the electric locomotive auxiliary electric drive

Introduction. The object of this study is an auxiliary frequency-controlled electric drive of an AC locomotive, or more specifically, the structure and parameters of the system for regulating the coordinates of the active power factor corrector, which is a part of the electric drive and a unit that ensures the energy efficiency of the electric drive as well as its electromagnetic compatibility with other equipment on board the electric locomotive and the power network. The purpose of the study is to substantiate the structure of the system for regulating the coordinates of an active power factor corrector, the choice of types of regulators and the calculation of their parameters.Materials and methods. The author has chosen as the research method the calculation of transfer functions of regulators of the subordinated regulation system, followed by computer simulation of the processes in electrical circuits using the OrCAD computer-aided design system.Results. The author made a conclusion about the expediency of using a two-circuit system of subordinated coordinate regulation containing a voltage control circuit and a current control circuit. The researcher presented and analytically compares the results of modelling of a two-circuit coordinate regulation system for the active power factor corrector for various types of regulators. The models with an aperiodic current regulator and a proportional-integral voltage regulator showed the best results.Discussion and conclusion. The obtained data serve as the basis for further improvement of the active power factor corrector operation by improving and optimising the settings, structure and algorithms of the control system, which, with the selected hardware components of the power unit, will enable it to perform its functions with a high degree of reliability in the entire range of disturbing and controlling actions on board of an electric locomotive.