Transfer Function Parameters Research Articles

Reflection Assisted Sound Source Localization Through a Harmonic Domain MUSIC Framework

This work presents a method that persuades acoustic reflections to be a favorable property for sound source localization. Whilst most real world spatial audio applications utilize prior knowledge of sound source position, estimating such positions in reverberant environments is still considered to be a difficult problem due to acoustic reflections. This article presents a novel MUSIC framework for multiple sound source localization (range, elevation, azimuth) in reverberant rooms by incorporating a recently proposed region-to-region room transfer model. The method is built upon the received signals of a higher order microphone and a spherical harmonic representation of the room transfer function. We demonstrate the method's general applicability and multiple source localization performance through a simulation study across an assortment of reverberant conditions. Additionally, we investigate robustness against various system modeling errors to gauge implementation viability. Finally, we prove the method in a practical experiment inside a real-world room with measured region-to-region transfer function parameters.

Parametric inverse impulse response based on reduced order modeling and randomized excitations

This paper is concerned with the computation of the inverse impulse response of a parametrized structural dynamics problem using reduced-order modeling and randomized excitations. A two-stages approach is proposed, involving the solution of both direct and inverse problems. In the first stage, the parametrized structural dynamics problem is formulated in the frequency domain, and solved using a reduced-order modeling approach. As a result, the parametric transfer function of the structure is obtained, and then readily transformed into a parametric direct impulse response (DIR). In the second stage, the parametric inverse impulse response (IIR) is computed. We use randomized excitations to generate synthetic samples inexpensively from the parametric DIR. Based on these, the parametric IIR is computed by minimizing the mean square error between the estimate and the samples. Most importantly, we show that the randomized excitations can be generated by sampling the frequency domain only. Hence, the parametric domain does not need to be sampled, which makes the computation of the parametric IIR very efficient.

Parametric electromagnetic transfer function estimation at USArray Site MNF34

We propose a new parametric approach to electromagnetic transfer function (EMTF) estimation which has attributes not found in the nonparametric approach most extensively used by the magentotelluric (MT) community. Firstly, parametric EMTFs are smooth by construction, which is consistent with the underlying physics. Secondly, fewer parameters are generally required to represent an EMTF by parametric means. Thirdly, our parametric approach can simplify data quality control and editing of time series because of the direct operation in the time domain. Our approach is based on the mature discipline of system identification which is concerned with parametric transfer function determination given system input and output. In this study, MT data from one USArray site are analyzed, showing a statistical advantage in reproducing measured geoelectric field time series using a parametric model EMTF versus the standard EMTF approach.

The Dead Time Characterization Method of Quartz Flexure Accelerometers Using Monotonicity Number.

Dead time estimation is important in the design process of quartz flexure accelerometers. However, to the authors’ knowledge, the dead time existing in quartz flexure accelerometers is not well investigated in conventional identification studies. In this paper, the dead time, together with the open-loop transfer function of quartz flexure accelerometers, is identified from step excitation experiments using two steps. Firstly, a monotonicity number was proposed to estimate the dead time. Analysis showed that the monotonicity number was robust enough to measurement noise and sensitive to step excitation. Secondly, parameters of the open-loop transfer function were identified using the least mean squares algorithm. A simulation example was applied to demonstrate the validity of the proposed method. The verified method was used to test a quartz flexure accelerometer. The experimental result shows that the dead time was 500 μs.

Model parameter identification of indoor temperature lag characteristic based on hysteresis relay feedback control in VAV systems

The dynamic regulation process of variable air volume (VAV) systems is a typical nonlinear process, which has characteristics of multi-variable, strong coupling, and large lag. Due to the lag response characteristics of indoor temperature versus system regulation variables, it is difficult to accurately describe indoor temperature dynamic regulation characteristics based on a conventional open-loop step response test. Taking indoor temperature lag characteristic of the air conditioning system as the study object, this paper brings hysteresis relay feedback control (HRFC) into the model parameter identification of indoor temperature lag characteristic, and provides a novel method for indoor temperature lag characteristic identification of the air conditioning system. This study provides the detail implementation process of the proposed identification method. Supported by the comparative experimental study, the effectiveness and practicability of the proposed method is validated in an integrated control test rig for a VAV system. Under the condition of no prior knowledge, model parameters of indoor temperature first-order inertia plus lag link transfer function could be identified based on HRFC accurately. Results indicate that inertial time coefficients and pure lag time coefficients are convergent. The key contribution of this paper is to propose an online identification method for indoor temperature lag characteristic in dynamic regulation process of VAV system. It's worth noting that the proposed method may be invalid if the indoor temperature changes greatly due to some uncertainty large disturbances, however it is useful for new-built VAV system during the commissioning process.

Research on system identification based on hydraulic pump-motor of HMCVT

In order to study the speed ratio regulation and dynamic change of hydraulic mechanical continuously variable speed tractor, it is necessary to comprehend the dynamic characteristics of the hydraulic circuit. The identification method was adopted to study the pump-motor system of transmission. Firstly, the typical identification method of combination modeling was selected to establish the model, and then the corresponding experiments were designed to determine the transfer function parameters and models of the combined modeling. Based on these, through further simplification and indirect methods, with the help of MATLAB toolbox, a fast system identification method was established by calculating the transmission ratio of the pump motor system through the output speed of the gearbox, the engine speed and the drive ratio of the front gear of the pump, as well as the transmission ratio of the gearbox. Filter was used to remove the influence of noise during the experiment. Compared with the test data, the models established by the two identification methods have higher accuracy. The positive and negative fitting rates of the fast identification method are 91.85 and 91.13, respectively, which can meet the needs of subsequent research. This study can be used as a reference for the subsequent control design of transmission and the study on the quality of the transmission.

Amplitude modulation detection and temporal modulation cutoff frequency in normal hearing infants.

The goal of this study was to determine if temporal modulation cutoff frequency was mature in three-month-old infants. Normal-hearing infants and young adults were tested in a single-interval forced-choice observer-based psychoacoustic procedure. Two parameters of the temporal modulation transfer function (TMTF) were estimated to separate temporal resolution from amplitude modulation sensitivity. The modulation detection threshold (MDT) of a broadband noise amplitude modulated at 10 Hz estimated the y-intercept of the TMTF. The cutoff frequency of the TMTF, measured at a modulation depth 4 dB greater than the MDT, provided an estimate of temporal resolution. MDT was obtained in 27 of 33 infants while both MDT and cutoff frequency was obtained in 15 infants and in 16 of 16 adults. Mean MDT was approximately 10 dB poorer in infants compared to adults. In contrast, mean temporal modulation cutoff frequency did not differ significantly between age groups. These results suggest that temporal resolution is mature, on average, by three months of age in normal hearing children despite immature sensitivity to amplitude modulation. The temporal modulation cutoff frequency approach used here may be a feasible way to examine development of temporal resolution in young listeners with markedly immature sensitivity to amplitude modulation.

A Modified Just Noticeable Depth Difference Model Built in Perceived Depth Space

This paper proposes a modified just noticeable depth difference (JNDD) (JNDiD) model in perceived depth space. The JNDiD model improves the accuracy of current JNDD models by also taking into account the blurriness caused by the change in accommodation when a 3-D object is perceived far from the screen. This change in accommodation is a result of the convergence-accommodation conflict, in which convergence plays a leading role. In the JNDiD model described in this paper, the JNDD threshold is the addition between a base threshold and an additional threshold. Adapted to different blurring effects in three depth regions, the additional threshold is defined as a three-piecewise linear function. The proposed model also attempts to separate the JNDD modeling from the display modeling and viewing conditions in perceived depth space, making it applicable for different types of displays given their specific model parameters. With the help of model parameter transfer functions, the JNDiD model in perceived depth space and the corresponding one in any specific stimulated depth space can be easily transformed to each other. Experimental results demonstrate the effectiveness and superiority of the JNDiD model in perceived depth space.

MPC Inspired Dynamical Output Feedback and Adaptive Feedforward Control Applied to Piezo-Actuated Positioning Systems

It has been shown that the closed-loop transfer function representation of the unconstrained model predictive control (MPC) for single input single output systems is similar to a two-degree-of-freedom controller, which is capable of improving the tracking performance of positioning systems. Conventionally, the optimal parameters of the above-mentioned transfer function are result of a quite complicated MPC tuning. This paper proposes a new approach to obtain the parameters directly instead, where the input/output constraints are not considered. The method combines conventional feedback and adaptive feedforward techniques to minimize the tracking error as well as mitigate the influence of the load disturbance. Experiments on an ultra precision positioning system actuated by piezoelectric actuator show that the proposed method achieves much better tracking performance over a well-tuned conventional MPC.

SENSITIVITY OF CHARACTERISTICS OF MODEL OF THE ELECTRIC ARC TO CHANGE OF PARAMETERS OF ELEMENTS

Purpose. Consideration of the quantitative assessment of the sensitivity of certain properties of the automatic system to changes in the parameters of elements of only a part of the controlled object - the welding arc.Methodology. When solving practical problems of regulation by electric arc and plasma technological processes, it is important to solve the problem of determining the optimal settings or parametric optimization of automatic control systems, among the methods of which are non-exploratory methods based on the use of the sensitivity apparatus.Findings. The sensitivity to changes in the parameters of the nominal transfer function of the arc was analyzed, expressions for the sensitivity functions were obtained, and graphs of the corresponding functions were plotted. For more precision, it is assumed that changes in parameters are caused by changes in capacity, which always takes place in circuits with an arc.Originality. The problem of finding an acceptable compromise between the requirements of a small value of the stabilization error without a significant increase in the value of the input variable is formulated and solved.Practical value. Various rules have been developed to reduce the sensitivity of the transfer function of an object with respect to possible, unexpected changes in the parameters of a controlled object, which can be used in the design of high-quality transistor current sources for arc loads. To illustrate the sensitivity of the transfer function of the arc, the model shows the response to a stepwise change in input for different cases. Unfortunately, the article does not consider the characteristics of the disturbance and noise suppression, but only some options for reducing the sensitivity function are studied.

Formula omitted] Divergence for robust colour transfer

Optimal Transport (OT) is a very popular framework for performing colour transfer in images and videos. We have proposed an alternative framework where the cost function used for inferring a parametric transfer function is defined as the robust L2 divergence between two probability density functions (Grogan and Dahyot, 2015). In this paper, we show that our approach combines many advantages of state of the art techniques and outperforms many recent algorithms as measured quantitatively with standard quality metrics, and qualitatively using perceptual studies (Grogan and Dahyot, 2017). Mathematically, our formulation is presented in contrast to the OT cost function that shares similarities with our cost function. Our formulation, however, is more flexible as it allows colour correspondences that may be available to be taken into account and performs well despite potential occurrences of correspondence outlier pairs. Our algorithm is shown to be fast, robust and it easily allows for user interaction providing freedom for artists to fine tune the recoloured images and videos (Grogan et al., 2017).

A Numerical Study of Lithium-ion Battery Degradation Feature Extraction based on Transfer Function

Lithium-ion battery has been widely applied in various industrial fields including electrical vehicles (EVs), portable electronics and spacecraft. As the key part of the power supply system, the health state of the battery directly influence the reliability and safety of the host system. The degradation feature extraction approach is the vital part for battery state of health (SOH) estimation. The lithium-ion battery can be equalized as an electric circuit consists of a current source and several capacitances and resistances. These parameters varies based on the battery state of charge (SOC) and SOH. In other words, the battery performance degradation leads to the variation of the parameters in battery equivalent circuit model (ECM) which will directly influence the battery transfer function. Thus, this paper quantitative analysis of degradation characterization capability of parameters in battery equations. For the first-order ECM, the transfer function is established and the parameters are identified based on the battery hybrid pulse power characteristic test. Three different kinds of correlation analysis methods are applied in to evaluate the effectiveness of the parameters in transfer function for degradation representation.

Relay Feedback Identification with Additional Integrator

Abstract This paper presents a relay feedback technique for identification of dynamical systems for control purposes. The proposed technique uses a biased relay test with an added integration to determine three frequency response points for a phase lag in the range from 0 to 180° from a single experiment. This approach is based on a recently published method called “shifting method”. The additional integrator helps to improve the position of the frequency points obtained by the shifting method. The three frequency response points can be used for fitting up to five parameters of a process transfer function with various structures. The paper provides explicit formulas for determining the parameters of the second order model with a time delay from the obtained frequency response points. This approach can be used for the purpose of the controller design. The method is demonstrated on lag dominated, balanced and delay dominated processes. Matlab/Simulink programming environment was used for all experiments.

Control-Oriented Modelling of a 3D-Printed Soft Actuator.

A new type of soft actuator was developed by using hydrogel materials and three-dimensional (3D) printing technology, attracting the attention of researchers in the soft robotics field. Due to parametric uncertainties of such actuators, which originate in both a custom design nature of 3D printing as well as time and voltage variant characteristics of polyelectrolyte actuators, a sophisticated model to estimate their behaviour is required. This paper presents a practical modeling approach for the deflection of a 3D printed soft actuator. The suggested model is composed of electrical and mechanical dynamic models while the earlier version describes the actuator as a resistive-capacitive (RC) circuit. The latter model relates the ionic charges to the bending of an actuator. The experimental results were acquired to estimate the transfer function parameters of the developed model incorporating Takagi-Sugeno (T-S) fuzzy sets. The proposed model was successful in estimating the end-point trajectory of the actuator, especially in response to a broad range of input voltage variation. With some modifications in the electromechanical aspects of the model, the proposed modelling method can be used with other 3D printed soft actuators.

GoCTF: Geometrically optimized CTF determination for single-particle cryo-EM

Preferred particle orientation represents a recurring problem in single-particle cryogenic electron microcopy (cryo-EM). A specimen-independent approach through tilting has been attempted to increase particle orientation coverage, thus minimizing anisotropic three-dimensional (3D) reconstruction. However, focus gradient is a critical issue hindering tilt applications from being a general practice in single-particle cryo-EM. The present study describes a newly developed geometrically optimized approach, goCTF, to reliably determine the global focus gradient. A novel strategy of determining contrast transfer function (CTF) parameters from a sector of the signal preserved power spectrum is applied to increase reliability. Subsequently, per-particle based local focus refinement is conducted in an iterative manner to further improve the defocus accuracy. Novel diagnosis methods using a standard deviation defocus plot and goodness of fit heatmap have also been proposed to evaluate CTF fitting quality prior to 3D refinement. In a benchmark study, goCTF processed a published single-particle cryo-EM dataset for influenza hemagglutinin trimer collected at a 40-degree specimen tilt. The resulting 3D reconstruction map was improved from 4.1 Å to 3.7 Å resolution. The goCTF program is built on the open-source code of CTFFIND4, which adopts a consistent user interface for ease of use.

Impact of Load Dynamics on Electromechanical Oscillations of Power Systems

In this paper, the impact of load dynamics on the oscillatory stability of power systems is studied. The well-known composite load model is linearized to yield third order transfer functions for active and reactive power dynamics of loads. It is shown that the third order model exhibits a recovery response that is accompanied by damped oscillations. In studying the impact of loads’ transfer function parameters on the small signal stability of power systems, a resonance is observed between the load and the electromechanical modes of the system that significantly alters the electromechanical modes’ damping. The role of the active and reactive power dynamics, as well as the operating condition of the system on the impact from a dynamic load on electromechanical modes are investigated. For preliminary insights, a single machine infinite bus system (SMIB) is used initially to avoid the unnecessary complexities associated with large grids. The general conclusions drawn from the SMIB studies are then confirmed on a 14 generator model of the Australian grid.

Cerebral autoregulation in migraine with aura: A case control study.

Migraine with aura is independently associated with increased risk of ischemic stroke, especially in younger subjects. This association might be related to an impairment of cerebral autoregulation, which normally maintains cerebral blood flow independent of arterial blood pressure variations. Patients aged 30-55, fulfilling ICHD-3 beta criteria for migraine with aura, were prospectively enrolled and compared with gender- and age-matched healthy controls without a history of migraine. Patients and controls with a history of stroke or any disease potentially impairing cerebral autoregulation were excluded. We assessed cerebral autoregulation with two different methods: Transfer function analysis, and the correlation coefficient index Mx. The transfer function phase and gain reflect responses of cerebral blood flow velocities to relatively fast fluctuations of arterial blood pressure, whereas Mx also reflects responses to slower arterial blood pressure fluctuations. A total of 22 migraine with aura patients (median age [IQR]: 39.5 [12.5] years) and 22 controls (39 [9.75] years) were included. Transfer function parameters and Mx were not different between patients and controls. However, Mx was inversely correlated with age in patients (ρ = -0.567, p = 0.006) and not in controls (ρ = -0.084, p = 0.509). Mx was also inversely correlated with migraine with aura duration (ρ = -0.617, p = 0.002), suggesting improvement of cerebral autoregulation efficiency with disease duration. Cerebral autoregulation did not differ between patients and controls aged 30-55. However, cerebral autoregulation efficiency was strongly correlated with migraine with aura duration. Further studies in younger patients are needed to determine whether cerebral autoregulation is impaired early in the course of disease. NCT02708797.

Efficient parameterisation of nonlinear system models: a comment on Nöel and Schoukens (2018)

Nöel, J. P., & Schoukens, J. [2018. Grey-box state-space identification of nonlinear mechanical vibrations. International Journal of Control, 91, 1–22] discuss a methodology for the discrete-time state-space identification of nonlinear systems and apply this to experimental data from the well known Silverbox nonlinear circuit, producing a model characterised by 13 parameters. This model explains the data very well but the parameter estimates are not well defined in the optimisation results, with the very large confidence bounds suggesting that the model is over-parameterised. This comment shows that this is indeed the case and that the data can be explained equally well by an alternative continuous-time, State-Dependent Parameter (SDP) transfer function model with only 6 parameters, the estimates of which are well defined with very tight confidence bounds. The comment also raises questions about how the model form for nonlinear systems such as the Silverbox should be identified and suggests that the Data-Based Mechanistic (DBM) approach to modelling has some advantages in this regard.

On the application of curve reparameterization in isogeometric vibration analysis of free-from curved beams

In the present paper, an innovative approach based on a curve reparameterization technique is developed to solve the natural frequency problem of free-form Euler–Bernoulli curved beams using isogeometric analysis (IGA). The method is beneficial in modifying the probably inappropriate initial parameterization of input geometries. For this purpose, a transformation from the initial parametric domain to a new reparameterized one is adopted, creating a pseudo arc-length parameterization that is suitable for IGA. An auxiliary one-dimensional B-spline curve is utilized as the parametric transfer function (PTF). A combination of curve rectification and B-spline approximation techniques is implemented to construct the PTF. The number of elements in the proposed approach is based on the knot vector of the PTF that is not dependent on the knot vector of the input NURBS curve defining the geometry. The method is tested on different numerical examples that prove the validity and applicability of the formulations.

Exceptional points in the thermoacoustic spectrum

Exceptional points are found in the spectrum of a prototypical thermoacoustic system as the parameters of the flame transfer function are varied. At these points, two eigenvalues and the associated eigenfunctions coalesce. The system's sensitivity to changes in the parameters becomes infinite. Two eigenvalue branches collide at the exceptional point as the interaction index is increased. One branch originates from a purely acoustic mode, whereas the other branch originates from an intrinsic thermoacoustic mode. The existence of exceptional points in thermoacoustic systems has implications for physical understanding, computing, modeling and control.