Time Domain Research Papers - Academia.edu (original) (raw)

Fruit thinning has been practised for thousand of years, and serves a number of purposes. Too many fruits per tree can result in small fruit size and poor quality, breakage of limbs, exhaustion of tree reserves, and can also partially o completely inhibit bud initiation. Hand thinning of the peaches is the most common thinning practice adopted, but it is

- by
- •
- Profitability, Laboratory experiment, Field Experiment, Low Power

By using an approach based on the full nonlinear Barkhausen criterion, it is possible to describe oscillator behavior under the form of a nonlinear characteristic polynomial whose coefficients are functions of the circuit components and of the oscillation amplitude. Solving the polynomial in the frequency domain leads to the steady state oscillation amplitude and frequency. In the time domain, the characteristic polynomial represents a nonlinear differential equation whose solution gives the oscillator signal transient. It is shown how symbolic manipulation capabilities of commercially available softwares can be used to automatically generate the coding of the oscillator characteristic polynomial from the SPICE description netlist. The numerical processing of such an equation in the time domain leads to unacceptable computer time because of the high quality factor of the oscillator circuits involved. Nevertheless, by using the slowly varying amplitude and phase method, it is possible to transform the initial nonlinear differential equation into a nonlinear first order differential equation system in the amplitude and phase variables. The solution of this system directly gives the designer the most relevant features of the oscillation; that is, the amplitude, phase, or frequency transients which can be accurately obtained within a short computer time by using classical numerical algorithms.

- by Ndya A
- •
- Engineering, Quality Factor, Physical sciences, Oscillations
- by Greg Watts
- •
- Mechanical Engineering, Architecture, Classical Physics, Road Traffic

The reproducibility of heart rate variability (HRV) measures during graded lower body negative pressure (LBNP) have not been studied in sufficient detail. Active college age men (n=14) underwent an orientation exposure and two trials of graded LBNP to presyncope or)100 mmHg, separated by 1 week. Heart rate, stroke volume (impedance cardiography), blood pressure (Finapres), and forearm blood flow were assessed, as was HRV in both time and frequency domains. The trial-to-trial responses to LBNP common to all subjects (LBNP £)60 mmHg and at test termination) showed parallel changes, suggesting similar responses between both trials. Good reproducibility estimates were found for the resting HRV data (lowest: R=0.62 for low frequency/high frequency ratio; highest: R=0.94 for standard deviation of normal R-R intervals). During LBNP, reproducibility estimates varied but were generally similar to that seen at rest. At test termination, they were unacceptably low (R<0.41) for the HRV data assessed in the frequency domain and expressed in absolute units. LBNP tolerance was lower in the first trial [LBNP tolerance index: 404 (21) versus 437 (15) mmHg min)1 ; P<0.05] but the intraclass correlation coefficient was high (R=0.87). These data suggest that (1) HRV responses to submaximal LBNP up to)60 mmHg are consistent across trials, (2) the considerable variability seen in the HRV parameters at maximal LBNP can be reduced by expressing these data in either the time domain or using normalized units in the frequency domain, and (3) cardiovascular responses to sub-and maximal LBNP are reproducible. Data are presented as mean (SEM) unless otherwise stated.

- by Warren Franke
- •
- Medicine, Low Frequency, Electrocardiography, High Frequency

The mid-Pleistocene transition (MPT) from obliquity-to eccentricity-forced climate variations has been extensively documented within the oceanic realm. Using a collection of orbitally tuned records of palaeoclimatic change from the loess sequences of northern China, we have analysed terrestrial palaeomonsoon behaviour since 1.5 Ma and characterised the structure of the MPT. Wavelet analysis of a stacked magnetic susceptibility record from the loess sequences indicates that the onset of 100-kyr cyclicity was synchronous in both global ice volume and the East Asian monsoon system. However, analysis in the time domain reveals that during the MPT 'interim' period the East Asian winter monsoon appears to have weakened whilst global ice volume was increasing, indicating that the palaeomonsoon was not the primary forcing mechanism responsible for driving the global climatic change.

- by D Heslop
- •
- Evolutionary Biology, Palaeogeography, Geology, Ecology

The numerical implementation of the Direct Boundary Element formulation for time-domain transient analysis of three-dimensional solids is presented in a most general and complete manner. The present formulation employs the space and time dependent fundamental solution (Stokes' solution) and Graffi's dynamic reciprocal theorem to derive the boundary integral equations in the time domain. A time-stepping scheme is then used to solve the boundary initial value problem by marching forward in time. Higher order shape functions are used to approximate the field quantities in space as well as in time, and a combination of analytical (time-integration) and numerical (spatial-integration) integration is carried out to form a system of linear equations. At the end of each time step, these equations are solved to obtain the unknown field quantities at that time.Finally, the accuracy and reliability of this algorithm is demonstrated by solving a number of example problems and comparing the results against the available analytical and numerical solution.

- by Shahid Ahmad
- •
- Engineering, Civil Engineering, Boundary Element Method, Time Domain

We propose the audio inpainting framework that recovers portions of audio data distorted due to impairments such as impulsive noise, clipping, and packet loss. In this framework, the distorted data are treated as missing and their location is assumed to be known. The signal is decomposed into overlapping time-domain frames and the restoration problem is then formulated as an inverse problem per audio frame. Sparse representation modeling is employed per frame, and each inverse problem is solved using the Orthogonal Matching Pursuit algorithm together with a discrete cosine or a Gabor dictionary. The Signal-to-Noise Ratio performance of this algorithm is shown to be comparable or better than state-of-the-art methods when blocks of samples of variable durations are missing. We also demonstrate that the size of the block of missing samples, rather than the overall number of missing samples, is a crucial parameter for high quality signal restoration. We further introduce a constrained Matching Pursuit approach for the special case of audio declipping that exploits the sign pattern of clipped audio samples and their maximal absolute value, as well as allowing the user to specify the maximum amplitude of the signal. This approach is shown to outperform state-of-the-art and commercially available methods for audio declipping in terms of Signal-to-Noise Ratio.

- by Amir Adler
- •
- Engineering, Image Restoration, Impulse Noise, Time Frequency Analysis

Machine condition monitoring plays an important role in industry to ensure the continuity of the process. This work presents a simple and yet, fast approach to detect simultaneous machinery faults using sound mixture emitted by machines. We developed a microphone array as the sensor. By exploiting the independency of each individual signal, we estimated the mixture of the signals and compared time-domain independent component analysis (TDICA), frequency-domain independent component analysis (FDICA) and Multi-stage ICA. In this research, four fault conditions commonly occurred in industry were evaluated, namely normal (as baseline), unbalance, misalignment and bearing fault. The results showed that the best separation process by SNR criterion was time-domain ICA. At the final stage, the separated signal was analyzed using Instantaneous Frequency technique to determine the exact location of the frequency at the specific time better than spectrogram.

Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare recombination rate of quasiparticles, the Cooper pair-breaking rate and the electron-phonon coupling constant, lambda=1.1pm0.1,\lambda=1.1\pm0.1,lambda=1.1pm0.1, which is in excellent agreement with theoretical estimates.

- by Paul Leiderer
- •
- Superconductors, Terahertz, Density dependence, Time Domain

Vehicle classification is a demanding application of Wireless Sensor Networks. In many cases, sensor nodes detect and classify vehicles from their acoustic and/or seismic signature using spectral or wavelet based feature extraction methods. Such methods, while providing good results are quite demanding in computational power and energy and are difficult to implement on low-cost sensor nodes with limited resources. In this work, we investigate the use of a time-domain encoding and feature extraction method, to produce simple, fixedsize matrices from complex acoustic and seismic signatures of vehicles for classification purposes. Classification is accomplished using an Artificial Neural Network and a basic, L1 distance, archetype classifier. Hardware implementation issues on a prototype sensor node, based on an 8-bit microcontroller, are also discussed. For evaluation purposes we use real data from DARPA's SensIt project, which contains various acoustic and seismic signatures from two different vehicle types, a tracked vehicle and a heavy truck.

- by buthina Qatatsheh
- •
- Signal Processing, Wireless Sensor Networks, Neural Networks, Computer Hardware

A time-domain formulation for sound propagation in rigid-frame porous media, including waveform attenuation and dispersion, is developed. The new formulation is based on inversion of the relaxation functions from a previous model [Wilson DK, Ostashev VE, Collier SL. J Acoust Soc Am 2004;116:1889-92], thereby casting the convolution integrals in a form amenable to numerical implementation. Numerical techniques are developed that accurately implement the relaxational equations and transparently reduce to previous results in low-and high-frequency limits. The techniques are demonstrated on calculations of outdoor sound propagation involving hills, barriers, and ground surfaces with various material properties. We also compare the relaxation formulation to a widely applied phenomenological model developed by Zwikker and Kosten. The two models can be made equivalent if the resistance constant, structure constant, and compression modulus in the ZK model are allowed to be weakly frequency dependent. But if the ZK parameters are taken to be constant, as is typically the case, the relaxation model provides more accurate calculations of attenuation by acoustically soft porous materials such as snow, gravel, and forest litter.

- by David Marlin
- •
- Mechanical Engineering, Architecture, Turbulence, Interaction

There is currently no method for detecting corrosion under Shuttle tiles except for the expensive process of tile removal and replacement; hence NASA is investigating new NDE methods for detecting hidden corrosion. Time domain terahertz radiation has been applied to corrosion detection under tiles in samples ranging from small lab samples to a Shuttle with positive results. Terahertz imaging methods have been able to detect corrosion at thicknesses of 5 mils or greater under 1" thick Shuttle tiles and 7-12 mils or greater under 2" thick Shuttle tiles.

Electrothermal impedance spectroscopy (ETIS), is introduced as a new measurement method and thermal parameters derived from a pouch-type lithium-ion cell are presented. ETIS is a valuable tool for (i) the determination of the thermal impedance and (ii) the validation of thermal models. The excitation signal applied to the cell during measurement does not cause a change in entropy, thus facilitating the parameter identification of a thermal model for heat conduction and thermal capacity.

- by Dino Klotz and +1
- •
- Engineering, Impedance Spectroscopy, Parameter Identification, Lancet

With the introduction of spectral-domain optical coherence tomography (OCT), much larger image datasets are routinely acquired compared to what was possible using the previous generation of time-domain OCT. Thus, the need for 3-D segmentation methods for processing such data is becoming increasingly important. We report a graph-theoretic segmentation method for the simultaneous segmentation of multiple 3-D surfaces that is guaranteed to be optimal with respect to the cost function and that is directly applicable to the segmentation of 3-D spectral OCT image data. We present two extensions to the general layered graph segmentation method: the ability to incorporate varying feasibility constraints and the ability to incorporate true regional information. Appropriate feasibility constraints and cost functions were learned from a training set of 13 spectral-domain OCT images from 13 subjects. After training, our approach was tested on a test set of 28 images from 14 subjects. An overall mean unsigned border positioning error of 5 69 2 41 m was achieved when segmenting seven surfaces (six layers) and using the average of the manual tracings of two ophthalmologists as the reference standard. This result is very comparable to the measured interobserver variability of 5 71 1 98 m.

- by Stephen Russell
- •
- Engineering, Algorithms, Medical Imaging, Optical coherence tomography

One critical task in any wind power interconnection study involves the modelling of wind turbines. This paper provides the most basic yet comprehensive timedomain wind turbine model upon which more sophisticated models along with their... more

- by Ha Thu Le and +1
- •
- Mechanical Engineering, Renewable Energy, Wind Power, Wind turbine

This paper deals with load frequency control of an interconnected reheat thermal system considering battery energy storage (BES) system. Area control error (ACE) is used for the control of BES system. Time domain simulations are used to study the performance of the power system and BES system. Results reveal that BES meets sudden requirements of real power load and very effective in reducing the peak deviations of frequency and tie-power and also reduces the steady state values of time error and inadvertent interchange accumulations.

Purpose: In the present work was made the comparative analysis in time domain and frequency domain to the acoustical pressure generate by the electric arc to determinate which of the two analysis methods is better to evaluates the stability in GMAW process. Design/methodology/approach: Welds had been made with the parameters adjusted to get the highest stability. In these conditions, were

- by Evelin Cayo
- •
- Comparative Study, Acoustic Emission, Frequency-domain analysis, Process Design

A simple non-quasi-static small-signal equivalent circuit model is derived for the ideal MOSFET wave equation under the gradual channel approximation. This equivalent circuit represents each Y-parameter by its DC small-signal value shunted by a (trans) capacitor in series with a charging (trans) resistor. A large-signal model for the intrinsic MOSFET is derived by first implementing this RC topology in the

The linkages between the space-time variability of observed clouds, rainfall, large-circulation patterns and topography in northern India and the Himalayas were investigated using remote sensing data. The research purpose was to test the hypothesis that cloudiness patterns are dynamic tracers of rainstorms, and therefore their temporal and spatial evolution can be used as a proxy of the spatial and temporal organization of precipitation and precipitation processes in the Himalayan range during the monsoon. The results suggest that the space-time distribution of precipitation, the spatial variability of the diurnal cycle of convective activity, and the terrain (landform and altitudinal gradients) are intertwined at spatial scales ranging from the order of a few kms (1-5 km) up to the continental-scale. Furthermore, this relationship is equally strong in the time domain with respect to the onset and intra-seasonal variability of the monsoon. Infrared and microwave imagery of cloud fields were analyzed to characterize the spatial and temporal evolution of mesoscale convective weather systems and short-lived convection in Northern India, the Himalayan range, and in the Tibetan Plateau during three monsoon seasons (1999, 2000 and 2001). The life cycle of convective systems suggests landform and orographic controls consistent with a convergence zone constrained to the valley of the Ganges and the Himalayan range, bounded in the west by the Aravalli range and the Garhwal mountains and in the East by the Khasi Hills and the Bay of Bengal, which we call the Northern India Convergence Zone (NICZ). The NICZ exhibits strong nighttime activity along the south-facing slopes of the Himalayan range, which is characterized by the development of shortlived convection (1-3 h) aligned with protruding ridges between 1:00 and 3:00 AM. The intra-annual and inter-annual variability of convective activity in the NICZ were assessed with respect to large-scale synoptic conditions, monsoon activity in the Bay of Bengal, and the modulating role of orography. Empirical orthogonal function (EOF) and canoni

- by Ana Barros
- •
- Geology, Natural Hazards, Seasonality, Altitudinal gradient

In this article, we demonstrate an energy efficient convolutional neural network (CNN) engine by performing the multiply-and-accumulate (MAC) operations in the time domain. The multi-bit inputs are compactly represented as a single pulse width encoded input. This translates into reduced switching capacitance (CDYN), compared to baseline digital implementation, and can enable low power neural network computing in an edge device. The time-domain CNN engine employs a novel bi-directional memory delay line (MDL) unit to perform signed accumulation of input and weight products. The proposed MDL design leverages standard digital circuits and does not require any capacitors and complex analog-to-digital converters (ADCs) to realize the convolution operation, thereby enabling easy scaling across the process technology nodes. Four speed-up modes and a configurable MDL length are supported to address throughput versus accuracy trade-off of the time-domain computing approach. Delay calibration units have been accommodated to mitigate the process variation induced delay mismatch among concurrently operating MDL units. The proposed time-domain MDL design implements a LeNet-5 CNN engine in a commercial 40-nm CMOS process achieving energy efficiency of 12.08 TOPS/W, a throughput of 0.365 GOPS at 537 mV in the 16× speed-up mode. 40-nm CMOS test-chip measurements over 100 MNIST images show 97% classification accuracy. Simulation results over the entire 10000 MNIST validation dataset images taking into account the circuit non-ideal effects of the MDL-based time-domain approach show a classification accuracy of 98.42%. The test-chip is operational down to the near-threshold voltage (up to 375 mV) while maintaining the classification accuracy over 90% in the 1× speed-up mode. Furthermore, two methods of scaling MDLs to multi-bit weights are proposed. Simulation results for 1000-class AlexNet over 50000 ImageNet validation dataset images show classification accuracy loss within 1% when compared with software implementation.

- by Aseem Sayal
- •
- Machine Learning, Accelerators, Time Domain, Convolutional Neural Network [CNN]

Synthesis and photophysical studies of (O-methyl)-ß-tyrosine (ß-tyrosine; an analogue of tyrosine, in which the amino group is moved from the a-to the ß-carbon, closer to the phenol ring) and its derivatives with a blocked amino and/or... more

We consider the problem of the gravitational waves produced by a particle of negligible mass orbiting a Kerr black hole. We treat the Teukolsky perturbation equation in the time domain numerically as a 2+1 partial differential equation. We model the particle by smearing the singularities in the source term by the use of narrow Gaussian distributions. We have been able to reproduce earlier results for equatorial circular orbits that were computed using the frequency domain formalism. The time domain approach is however geared for a more general evolution, for instance of nearly geodesic orbits under the effects of radiation reaction.

Abstruct-Carrier transport plays an important role and can significantly affect the ultra-fast properties of quantum-well (QW) lasers. We present a detailed multi-mode time-domain large-signal dynamic model including the effects of carrier transport, suitable for the high-speed QW lasers. It is based on the well-proven transmission-line laser modelling technique with the addition of a multilevel system of coupled rateequations. Simulated results from studies of both the static and small-signal properties are compared with measurements from another laboratory. Our model can accurately predict the modulation-bandwidth discontinuity in QW laser structures with large separate-confinement-heterostructure (SCH) regions. We use large-signal simulations to predict increased damping of transient responses and larger turn-on delays caused by the effects of carrier transport. Our large-signal simulations also show that an increase in the turn-on delay times is expected in QW structures with large carrier transport times across the SCH region, whereas the inter-well transport times do not affect the turn-on delay times significantly. 1077-26013/95$04.00 0 1995 IEEE

- by Dalma Novak
- •
- Quantum Physics, Time-Delay Systems, Damping, Predictive models

An algorithm is developed to define, from the data samples themselves, a frequency weighted norm to use in minimum weighted norm extrapolation. Normally, the weight would be chosen to incorporate apriori knowledge of the bandwidth and shape of the spectrum of the signal to be estimated. The iterative procedure developed in this paper uses a periodogram spectrum estimate obtained from some samples of the signal estimatelextrapolation found at one iteration to define the weight that is used to estimate at the next iteration. This algorithm usually converges in less than 10 iterations to an extrapolation which is characterized as a nonparametric frequency-stationary extension of the data.

- by Thomas Parkes
- •
- A Priori Knowledge, Multidisciplinary, Spectrum, Spectral Estimation

IC switching current is the main noise source of many power integrity issues in printed circuit boards. Accurate measurement of the current waveforms is critical for an effective power distribution network design. In this paper, using a giant magnetoimpedance (GMI) probe for this purpose is studied. A side-band detection and demodulation system is built up to measure various time-domain waveforms using an oscilloscope. It is found that the GMI probes are potentially suitable for this kind of time-domain measurements, but probe designs and measurement setups need further improvements for this application.

- by David Pommerenke
- •
- Power Systems, Giant Magnetoresistance, Printed Circuit Board, Circuit Switching

This work addresses the problem of estimating the conduction velocity (CV) of single motor unit (MU) action potentials from surface EMG signals detected with linear electrode arrays during voluntary muscle contractions. In idea/conditions, that is without shape or scale changes of the propagating signals and with additive white Gaussian noise, the maximum likelihood (ML) is the optimum estimator of delay. Nevertheless, other methods with computational advantages can be proposed; among them, a modified version of the beamforming algorithm is presented and compared with the ML estimator. In real cases, the resolution in delay estimation in the time domain is limited because of the sampling process. Transformation to the frequency

- by Roberto Merletti and +1
- •
- Biomedical Engineering, Standard Deviation, Maximum Likelihood, Statistical Significance

The time-harmonic solution for the anomnalous vector potential due to a conducting permeable sphere in the field of a currentcarrying loop is used to derive the corresponding step response. The step response is then used to obtain analytical expressions for the voltage induced in a second loop due to a chosen exciting current pulse train. The voltage induced in an actual system of coils is obtained by superposition. The effect of the measurement system is included in the analysis in order to experimentally verify the model. Measured responses of a number of aluminum and steel spheres at various distances from the coils are compared with theoretical predictions. The agreement between the two is generally good.

- by John McFee
- •
- Geophysics, Geomatic Engineering, Time Domain, Electrical And Electronic Engineering

This paper introduces and evaluates the use of Gaussian mixture models (GMMs) for multiple limb motion classification using continuous myoelectric signals. The focus of this work is to optimize the configuration of this classification scheme. To that end, a complete experimental evaluation of this system is conducted on a 12 subject database. The experiments examine the GMMs algorithmic issues including the model order selection and variance limiting, the segmentation of the data, and various feature sets including time-domain features and autoregressive features. The benefits of postprocessing the results using a majority vote rule are demonstrated. The performance of the GMM is compared to three commonly used classifiers: a linear discriminant analysis, a linear perceptron network, and a multilayer perceptron neural network. The GMM-based limb motion classification system demonstrates exceptional classification accuracy and results in a robust method of motion classification with low computational load.

- by B. Hudgins
- •
- Algorithms, Artificial Intelligence, Biomedical Engineering, Pattern Recognition

This work proposes a methodology of identifying linear parameter varying (LPV) models for nonlinear systems. First, linear local models in some operating points, by applying standard identifications procedures for linear systems in time domain, are obtained. Next, a LPV model with linear fractional dependence (LFR) with respect to measured variables is fitted with the condition of containing all the linear models identified in previous step (differential inclusion). The fit is carried out using nonlinear least squares algorithms. Finally, this identification methodology will then be applied to a nonlinear turbocharged diesel engine.

- by Miguel Martínez
- •
- Mathematics, Applied Mathematics, Linear Model, Identification

In many physical insulation systems it is often necessary to establish the approximate estimate of the breakdown voltage for nonstandard impulse voltages. The disruptive effect method, which is an analytical method, has some success in such estimations. However, it does not cater to waveforms that are of the bidirectionally oscillating impulse type. Such voltages occur frequently within transformer windings. A new method called unconditionally sequential approach is proposed in order to serve as a measure of insulation strength under bidirectionally oscillating voltages. The method is validated by experiments on test specimens. The utility of the method is shown by an assessment of tap stresses in a 50/25 MVA power transformer. Abstract: The Bayesian network is a probabilistic graphical model in which a problem is structured as a set of variables (parameters) and probabilistic relationships among them. The Bayesian network has been effectively used to incorporate expert knowledge and historical data for revising the prior belief in the light of new evidence in many fields. However, little research has been done to apply the Bayesian network for fault location in power delivery systems. We construct a Bayesian network on the basis of expert knowledge and historical data for fault diagnosis on a distribution feeder in Taiwan. The experimental results validate the practical viability of the proposed approach.

- by Masoud Karimi Ghartemani
- •
- Power Systems, Signal Processing, Power Quality, Power System

As far as we are concerned, the implementation of the finite differences in the time domain (FDTD) method requires, for the solutions of several practical problems in electromagnetism, a long process time and a large amount of memory, what makes it impracticable in various cases, principally when the serial process is used. The current work deals with the conception of a Beowulf cluster and it aims to implement the FDTD method using parallel process for the study of antennas. The obtained system efficiency is then tested in the analysis of a monopole antenna, what is done by comparing the time spent in the parallel and serial processing.

- by Regiane Kawasaki
- •
- Electromagnetism, Parallel Processing, Finite Difference, Beowulf Cluster

Within linearized perturbation theory, black holes decay to their final stationary state through the well-known spectrum of quasinormal modes. Here we numerically study whether nonlinearities change this picture. For that purpose we study the ringdown frequencies of gauge-invariant second-order gravitational perturbations induced by self-coupling of linearized perturbations of Schwarzschild black holes. We do so through high-accuracy simulations in the time domain of first and second-order Regge-Wheeler-Zerilli type equations, for a variety of initial data sets. We consider first-order even-parity (ell=2,m=pm2)(\ell=2,m=\pm 2)(ell=2,m=pm2) perturbations and odd-parity (ell=2,m=0)(\ell=2,m=0)(ell=2,m=0) ones, and all the multipoles that they generate through self-coupling. For all of them and all the initial data sets considered we find that ---in contrast to previous predictions in the literature--- the numerical decay frequencies of second-order perturbations are the same ones of linearized theory, and we explain the observe...

- by J. Martin-Garcia and +1
- •
- Quantum Physics, Structural Stability, Relativity and Gravitation, Gravitational Wave Detectors

A time domain model of scattering from small discrete particles embedded in a sediment volume is presented here with an experimental validation. The model is implemented on the backbone of the BORIS-3D model which originally included only surface scattering and volume scattering from small perturbations of the volume density and sound speed. The proposed model adds discrete volume scatterers and simulates both monostatic and bistatic configurations. The experimental data for validation were collected in a tank using a silicon plate (with a flat upper interface) in which 10% of the volume is occupied by spherical glass beads 1 mm in diameter. This work is focused on the time domain evolution of the scattered echo. The results shows a very good agreement between simulated and experimental data in both amplitude and shape.

- by Alessandra Tesei and +2
- •
- Multidisciplinary, Time Domain

Terahertz time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of polycrystalline quartz, amorphous silica, Pyrex and BK7 glasses. The results were analyzed in terms of the power-law model of far-infrared absorption. Evidence of the Boson peak was seen in the absorption spectra. Relationships were observed between THz absorption and refractive indices on the one hand, and glass structure and properties on the other. THz TDS is demonstrated to be a useful tool in the study of far-infrared transmission properties of glasses, producing low-noise, high resolution measurements of absorption coefficients and refractive indices.

- by Mira Naftaly
- •
- Materials Engineering, Terahertz time-domain spectroscopy, Silica, Power Law

In this paper we report directivity enhancement by a short-focal-length plano-concave lens engineered by stacked subwavelength hole arrays (fishnet-like stack) with an effective negative index of refraction close to zero, n → 0, that arises from ε and μ near-zero extreme values. The plano-concave lens frequency response shows two enhancement peaks, one at the wavelength corresponding to n = −1 and, prominent in this configuration, another unexpected peak when n → 0 that comes as a result of the similar low values of ε and μ. The frequency-dependent negative refractive index and beam-forming properties of the lens are supported by finite-integration-frequencyand time-domain simulations and experimental results. This near-zero metamaterial lens can find applications in terahertz and even optics since the building block, stacked extraordinary optical transmission layers, has already been reported for those regimes under the name of fishnet structure.

- by Miguel Navarro-Cía
- •
- Extreme Value Theory, Physical sciences, Terahertz, CHEMICAL SCIENCES

This paper deals with an application of the Wigner-Ville distribution (WVD) and with usual digitalprocessing techniques, such as the short-time Fourier transform (STET), used in dedicated instrumentation for measuring nonstationary signals. The processed real signals are made analytic by means of Hilbert transformations; then suitable implementations of the windowed STFT and of the pseudo Wigner-Ville distribution (PWVD) in the time domain have been performed. Particularly, the fast Hartley transform (FHT) is used to evaluate the PWVD in the real domain. Furthermore, the use of an efficient interpolation algorithm and of a suitable flat-top windowing function is proposed in order to give accurate real-time frequency and amplitude measurements, respectively.

- by Gregorio Andria
- •
- Hilbert transform, Digital Systems, Real Time, Fourier transform

In a Text-to-Speech system based on time-domain techniques that employ pitch-synchronous manipulation of the speech waveforms, one of the most important issues that affect the output quality is the way the analysis points of the speech signal are estimated and the actual points, i.e. the analysis pitchmarks. In this paper we present our methodology for calculating the pitchmarks of a speech waveform, a pitchmark detection algorithm, which after thorough experimentation and in comparison with other algorithms, proves to behave better with our TD-PSOLA-based Text-to-Speech synthesizer (Time-Domain Pitch-Synchronous Overlap Add Text to Speech System).

- by Aimilios Chalamandaris and +2
- •
- Text to Speech, Edge Detection Algorithm, Time Domain

The objective of this work is to characterize certain important features of excitation of speech, namely, detecting the regions of glottal activity and estimating the strength of excitation in each glottal cycle. The proposed method is based on the assumption that the excitation to the vocal-tract system can be approximated by a sequence of impulses of varying strengths. The effect due to an impulse in the time-domain is spread uniformly across the frequency-domain including at zero-frequency. We propose the use of a zero-frequency resonator to extract the characteristics of excitation source from speech signals by filtering out most of the time-varying vocal-tract information. The regions of glottal activity and the strengths of excitation estimated from the speech signal are in close agreement with those observed from the simultaneously recorded electro-glotto-graph signals. The performance of the proposed glottal activity detection is evaluated under different noisy environments at varying levels of degradation.

- by Sri Anand
- •
- Vocal Tract, Time Domain, Electrical And Electronic Engineering, Time varying

Measures of postural steadiness -known as posturography -are commonly used for balance assessment during quiet standing. Although quiet sitting balance may be studied via posturography as well, this has not been done to date. As such, the purpose of this study was to characterize the posturography during quiet sitting in comparison with quiet standing and to provide a benchmark for future studies investigating differences in balance regulation and execution. Twelve young and healthy people agreed to quietly sit and stand on a force platform with their eyes open and closed. For each condition, one trial of 2 min was executed and the anterior-posterior, medial-lateral, and resultant distance fluctuations of the body's center of pressure (COP) were calculated. Finally, time-domain, frequency-domain, and stabilogram diffusion function (SDF) measures were identified and compared for all COP time series. The results consistently indicate that, for quiet sitting, the body sway size and velocity were smaller and the power-weighted average frequency larger than for quiet standing. Moreover, the SDF analysis revealed that quiet sitting shows fewer drifts over short time intervals, but also fewer controlled adjustments in the longer term to bring the system back to equilibrium. The observed differences can be partially explained by biomechanical and dynamic differences of the body portions that are in motion during quiet sitting and standing. The SDF analysis suggests, however, that also the balance control strategies are not identical. These findings may be especially useful for the assessment of sitting balance and the development of novel balance rehabilitation techniques and assistive devices.

- by Kei Masani
- •
- Engineering, Biomechanics, Time Series, Comparative Study

Al~traet-Detection of tool failure is very important in automated manufacturing. In this study, tool failure detection was conducted in two steps by using Wavelet Transformations and Neural Networks (WT-NN). In the first step, data were compressed by using wavelet transformations and unnecessary details were eliminated. In the second step, the estimated parameters of the wavelet transformations were classified by using Adaptive Resonance Theory (ART2)-type self-learning neural networks. Wavelet transformations represent transitionary data and complex patterns in a more compact form than time-series methods (frequency and time-domain) by using a family of the most suitable wave forms. Wavelet transformations can also be implemented on parallel processors and require less computations than Fast Fourier Transformation (FFT). The training of ART2-type neural networks is faster than backpropagation-type neural networks and ART2 is capable of updating its experience with the help of an operator while it is monitoring the sensory signals. The proposed approach was tested in over 171 cases and all the presented cases were accurately classified. The proposed system can be easily trained to inspect data during transition and/or any complex cutting conditions. The system will indicate failure instantaneously by creating a new category, thus alerting the operator.

- by Ibrahim Tansel
- •
- Engineering, Time Series, Neural Network, Wavelet Transform

In this paper, the potential benefits of a Wide Area Control System for coordinated power oscillation damping control is investigated for the Nordic power system, with an overall motivation to facilitate increased power transfer limits. Several approaches to the design of power system stabilizers making use of phasor measurements from a wide area monitoring system are presented and compared with conventional stabilizers using locally measured control feedback signals. Linear analysis and time domain simulations illustrate the performance of these PSS designs when applied to selected SVCs in the Norwegian power transmission grid. Utilizing remote signals available recently through wide area monitoring systems enables selection of the best feedback control signal with highest modal observability of the modes of interest. Preliminary conclusions indicate that this leads to a higher performance and robustness of the power system stabilizer control.

- by Petr Korba
- •
- Power System, Control system, Power Transmission, Power system stability

The paper describes a horizontal axis wind turbine time domain simulation and fatigue estimation program written using the Delphi2+ language. The program models the #apwise motion of a single rotor blade to determine the blade-root fatigue damage of a medium size wind turbine. The e!ects of turbulence intensity, mean wind speed, wind shear, vertical wind component, dynamic stall, stall hysteresis, and blade sti!ness were examined. When all these e!ects were simulated it is found that a reduction in life of about 2 occurs between a low wind speed low turbulence intensity site, compared to a high wind speed high turbulence intensity site.

- by Richard Flay
- •
- Mechanical Engineering, Civil Engineering, Computer Simulation, Wind turbine

From a comparison of the photoresponses and membrane properties of photoreceptors from 20 species of Diptera, we conclude that coding in the time domain is matched to the dictates of visual ecology. This matching involves the dynamics of phototransduction and the use of an appropriate mix of potassium conductances to tune the photoreceptor membrane. Rapidly flying, manoeuvrable diurnal Diptera from several families have fast photoreceptors, with corner frequencies (the frequency at which signal power falls by a half) of between 50 and 107 Hz. The ponderous and predominantly nocturnal tipulids have slow photoreceptors with fully light adapted corner frequencies of 16 to 19 Hz. Dark adapted fast photoreceptors have a lower gain (as indicated by lower noise levels), a lower sensitivity, and light adapt more rapidly than dark adapted slow photoreceptors. Fast cells also have much lower input resistances and shorter time constants. Fast photoreceptors rectify more strongly in the steady state because of a weakly inactivating delayed rectifier potassium conductance with fast and slow components of activation. Slow photoreceptors rectify less strongly in the steady state because their membrane properties are dominated by strongly inactivating outward currents with reversal potentials in the range — 80 to -90 mV. The differences between potassium conductances match the differing functional requirements of fast and slow photoreceptors. The non-inactivating delayed rectifier promotes the rapid response of fast cells by reducing the membrane time constant. This is an expensive strategy, involving large conductances and currents. Slowly flying nocturnal insects do not require a high speed of response. The potassium conductances in their slow photoreceptors inactivate to avoid costly and unnecessary ion fluxes. Both the dynamics of the photoresponse and photoreceptor membrane properties exhibit sexual dimorphism. Light adapted photoreceptors in the enlarged male dorsal eye of Bibio markii have a corner frequency of 42 Hz, compared with 27 Hz for cells in the smaller female eye. This difference in frequency response correlates with the male's higher spatial acuity and is accompanied by consistent differences in potassium conductance activation rate. We conclude that the divison between fast and slow cells is the product of cellular constraints, metabolic costs and the requirements of coding efficiency at different light levels and retinal image velocities.

- by Matti Weckstrom
- •
- Electrophysiology, Comparative Physiology, Sexual dimorphism, Biological Sciences

Orthonormal vector fitting is a robust method for broadband macromodeling of frequency domain responses. The use of orthonormal rational basis functions makes the conditioning of the system equations less sensitive to the initial pole specification when compared with the classical Vector Fitting procedure. This paper presents a time domain generalization of the technique to compute broadband rational macromodels from transient input-output port responses. The efficacy of the approach is illustrated by two numerical examples.

- by Tom Dhaene
- •
- Numerical, Time Domain, Transient Responses, Transfer Functions

Recently, joint Spectral and Time domain Optical Coherence Tomography (joint STdOCT) has been proposed to measure ocular blood flow velocity. Limitations of CCD technology allowed only for twodimensional imaging at that time. In this paper we demonstrate fast threedimensional STdOCT based on ultrahigh speed CMOS camera. Proposed method is straightforward, fully automatic and does not require any advanced image processing techniques. Three-dimensional distributions of axial velocity components of the blood in human eye vasculature are presented: in retinal and, for the first time, in choroidal layer. Different factors that affect quality of velocity images are discussed. Additionally, the quantitative measurement allows to observe a new interesting optical phenomenon -random Doppler shift in OCT signals that forms a vascular pattern at the depth of sclera.

- by Maciej Wojtkowski and +1
- •
- Optical coherence tomography, Fourier Analysis, Automation, Lasers

This paper reports the first use of terahertz time domain reflection imaging involving textiles on part of a complete human mummy, still in original wrapping. X-ray technique has been used extensively to investigate anatomical features, since X-ray pass through the wrapping. Terahertz waves, on the other hand, can penetrate into non-metallic materials and its reflection depends on the refractive index of materials at the interface, such as textiles and the air. The mummy of Kharushere (ca. 945-712 B.C.) was examined by using Terahertz time domain reflection imaging in the Egyptian galleries of The Metropolitan Museum of Art. Experimental results suggest that the Terahetz imaging is a promising technique for probing the fabric layers surrounding Egyptian mummies, although it is still very limited in its current state. In the future it could become a useful complement to CT scanning when materials with low radiographic density and contrast are being investigated.

- by Irl Duling
- •
- Terahertz, Refractive Index, Time Domain

A6stract-Frequency-domain adaptive filters have long been recognized as an attractive alternative to time-domain algorithms when dealing with systems with large impulse response and/or correlated input. Recently, new frequency-domain LMS adaptive schemes have been proposed. These algorithms essentially retain the attractive features of frequency-domain implementations, while requiring a processing delay considerably smaller than the length of the impulse response. The first purpose of this contribution is to show that these algorithms can be seen as particular implementations of a more general scheme, the generalized multidelay filter (GMDF). Within this general class of algorithms, we focus on implementations based on the weighted overlap and add reconstruction algorithms; these variants, overlooked in previous contributions, provide an independent control of the overall processing delay and of the rate of update of the filter coefficients, allowing a trade-off between the computational complexity and the rate of convergence. The second purpose of this work is to present a comprehensive analysis of the performance of this new scheme and to provide insight into the influence of impulse response segmentation on the behavior of the adaptive algorithm. Exact analytical expressions for the steady-state mean-square error are first derived. Necessary and sufficient conditions for the convergence of the algorithm to the optimal solution within finite variance are then obtained, and are translated into bounds for the stepsize parameter. Simulations are presented to support our analysis and to demonstrate the practical usefulness of the GMDF algorithm in applications where large impulse response has to be processed. 'Making use of the CCITT recommendations for evaluation of echocanceller in ISDN hands-free terminal [29].

- by omar AIT AMRANE
- •
- Computational Complexity, Multidisciplinary, Mean square error, Impulse response

In this work, an efficient numerical method is introduced for solving one-dimensional batch crystallization models with size-dependent growth rates. The proposed method consist of two parts. In the first part, a coupled system of ordinary differential equations (ODEs) for the moments and the solute concentration is numerically solved to obtain their discrete values in the time domain of interest. These discrete values are also used to get growth and nucleation rates in the same time domain. To overcome the issue of closure, a Gaussian quadrature method based on orthogonal polynomials is employed for approximating integrals appearing in the ODE system. In the second part, the discrete growth and nucleation rates along with the initial crystal size distribution (CSD) are used to construct the final CSD. The expression for CSD is obtained by applying the method of characteristics and Duhamel's principle on the given population balance model (PBM). The proposed method is efficient, accurate, and easy to implement in the computer. Several numerical test problems of batch crystallization processes are considered. For a validation, the results of the proposed technique are compared with those obtained using a high resolution finite volume scheme.

- by Nagaraj Shivaramaiah
- •
- Time Domain, Frequency Domain

The continuous rotation speed variation is demonstrated to be an efficient method to avoid regenerative chatter in different machining processes. This paper presents a time-domain dynamic model for throughfeed centerless grinding process that can predict chatter by means of part roundness error evolution. Continuous workpiece speed variation (CWSV) has been implemented in this model to analyze the influence of this disturbing method on the dynamic instability. Experimental results have validated the model and verified the effectiveness of CWSV for chatter avoidance and surface finish and dimensional tolerances improvement. It has been demonstrated that the selection of the optimal variation parameters is an important factor not only for chatter avoidance, but also for the stability of surface finish and dimensional tolerances since workpiece speed variation has a direct influence on throughfeed rate and grinding forces.

- by Inigo Bediaga
- •
- Manufacturing Engineering, Machine, Dynamic Model of WSN, Time Domain