Showing papers by "Iran University of Science and Technology published in 1998"

A window-based image processing technique for quantitative and qualitative analysis of road traffic parameters

Abstract: Traffic information is an important tool in the planning, maintenance, and control of any modern transport system. Of special interest to traffic engineers are parameters of traffic flow such as volume, speed, type of vehicle, queue parameters, traffic movements at junctions, etc. Various algorithms, mainly based on background differencing techniques, have been applied for this purpose. Since background-based algorithms are very sensitive to ambient lighting conditions, they have not yielded the expectative results. In this paper, we describe a novel approach to measure traffic parameters. This approach is based on applying edge-detection techniques to the key regions or windows. This method of measuring road traffic parameters eliminates the need of a background frame, which is an essential, but unreliable technique for background-based image-detection methods. A dynamic threshold selection technique has also been introduced to select the threshold value automatically. The image process algorithm has been applied to measure basic traffic parameters such a traffic volume, types of vehicles, as well as the complex traffic parameters such as queue parameters and movements of vehicles at a traffic junction.

Combining Subset Selection and Parameter Constraints in Model Updating

Abstract: Model updating often produces sets of equations whose solution are ill-conditioned and extra information must be used to produce a well-conditioned estimation problem. One possibility is to change all the parameters, but to introduce extra constraints, for example by taking the minimum norm solution. This paper takes a different approach, by considering only a subset of the parameters to be in error. The critical decision is then the choice of parameters to include in the subset. The methods of subset selection are outlined and extended to the selection of groups of parameters. The incorporation of side constraints is considered and demonstrated using an experimental example.

Using evoked EMG as a synthetic force sensor of isometric electrically stimulated muscle

Abstract: A method for the estimation of the force generated by electrically stimulated muscle during isometric contraction is developed here. It is based upon measurements of the evoked electromyogram (EMG) [EEMG] signal. Muscle stimulation is provided to the quadriceps muscle of a paralyzed human subject using percutaneous intramuscular electrodes, and EEMG signals are collected using surface electrodes. Through the use of novel signal acquisition and processing techniques, as well, as a mathematical model that reflects both the excitation and activation phenomena involved in isometric muscle force generation, accurate prediction of stimulated muscle forces is obtained for large time horizons. This approach yields synthetic muscle force estimates for both unfatigued and fatigued states of the stimulated muscle. In addition, a method is developed that accomplishes automatic recalibration of the model to account for day-to-day changes in pickup electrode mounting as well as other factors contributing to EEMG gain variations. It is demonstrated that the use of the measured EEMG as the input to a predictive model of muscle torque generation is superior to the use of the electrical stimulation signal as the model input. This is because the measured EEMG signal captures all of the neural excitation, whereas stimulation-to-torque models only reflect that portion of the neural excitation that results directly from stimulation. The time-varying properties of the excitation process cannot be captured by existing stimulation-to-torque models, but they are tracked by the EEMG-to-torque models that are developed here. This work represents a promising approach to the real-time estimation of stimulated muscle force in functional neuromuscular stimulation applications.

Optimum design of multihole directional couplers with arbitrary aperture spacing

Abstract: A numerical procedure based on the method of least squares is presented for the optimum design of multihole directional couplers with a specified number of apertures and their arbitrary spacing in a desired frequency band for a given coupling coefficient (C) together with maximization of the mean value of isolation (I) or equivalently directivity (D) across the band and also specified values of (C) and (D) (or equivalently isolation I). An error function is constructed in the band for optimization of C and D or I, which after minimization gives the best values of the hole radii and spacing. The proposed method is quite suitable for computer-aided design (CAD) and has several advantages over common design methods for multihole directional couplers, such as simplicity of analysis and development of the numerical algorithm, flexibility of hole spacing, specification of the desired values of C and D or I, and actual optimization of the coupler design in the desired frequency band. The proposed method is potentially applicable to the design of other couplers.

On the decomposition method to the heat equation with non‐linear and non‐local boundary conditions

Abstract: The Adomian decomposition method is used and applied to the mathematical model of a biosensor This model consists of a heat equation with non‐linear and non‐local boundary conditions To obtain a canonical form of Adomian, an equivalent non‐linear Volterra integral equation with a weakly singular kernel is set up In addition, the asymptotic behaviour of the solution as t → 0 and t → • by asymptotic decomposition is obtained Finally, numerical results are given which support the theoretical results

The modified autocorrelation technique for parameter estimation of random FH signals

Abstract: Multiple-hop autocorrelation (MHAC) processing is used for estimating the parameter of frequency-hopping (FH) signals in the presence of broadband thermal noise. The dependence on hopping frequency carrier phase and hop timing is suppressed by power sampling in the MHAC domain, while maintaining signal power and hop-rate information. We propose and analyze a joint recursive signal power and hop-rate estimator, based on maximum likelihood arguments. The conditional mean and variance of the estimator are derived and compared to a similar method assuming a priori knowledge of signal power.

Incremental communication for multilayer neural networks: error analysis

Abstract: Artificial neural networks (ANNs) involve a large amount of internode communications. To reduce the communication cost as well as the time of learning process in ANNs, we earlier proposed (1995) an incremental internode communication method. In the incremental communication method, instead of communicating the full magnitude of the output value of a node, only the increment or decrement to its previous value is sent to a communication link. In this paper, the effects of the limited precision incremental communication method on the convergence behavior and performance of multilayer neural networks are investigated. The nonlinear aspects of representing the incremental values with reduced (limited) precision for the commonly used error backpropagation training algorithm are analyzed. It is shown that the nonlinear effect of small perturbations in the input(s)/output of a node does not cause instability. The analysis is supported by simulation studies of two problems. The simulation results demonstrate that the limited precision errors are bounded and do not seriously affect the convergence of multilayer neural networks.

Multiresolution adaptive filter for estimating brainstem auditory evoked potential

Abstract: This paper presents a Multiresolution Adaptive Filter (MAF) for estimating brainstem auditory evoked potential (BAEP). Multiresolution Adaptive Filter is implemented simply by the orthonormal wavelet transforming (WT) the reference and primary signals, adaptive filtering of each independent, frequency channel separately, and then inverse wavelet transforming (IWT). Multiresolution adaptive processing can be employed as adaptive noise cancellation, adaptive line enhancer, and adaptive averaging. In this paper, we apply the MAF for BAEP estimation. The method is evaluated by using simulation and human data. A comparison of the proposed scheme with ensemble averaging and time-invariant adaptive filter (TIAF) is presented. It is observed that a significant improvement in waveform estimation, compared with the ensemble averaging and TIAF, can be achieved by multiresolution adaptive processing.

The Influence of Urban Network Features on the Quality of Traffic Service (RESEARCH NOTE)

Abstract: The work reported here presents a methodology based on a two-fluid model to assess the degree of influence of various geometric and control features of an urban network on the quality of traffic service. The two-fluid model gives a curvilinear relation between the trip time and stop time per unit distance and its parameters characterize the quality of traffic service in urban networks. Any Change in geometric and control features of a network would alter these parameters and the relationships permit the engineer to predict and evaluate traffic impacts of a given modification in advance.

Chaotic radial basis function network with application to dynamic modeling of chaotic time series

Abstract: Introduces a novel algorithm for adjusting the structure of a Radial Basis Function Network (RBFN). It has been shown that Radial Basis Function Networks (RBFNs) are capable of universal approximation. This suggests the possibility of using these neural models to identify the chaotic systems. However, when one deals with the observable from some process (e.g., biological systems) whose mathematical formulation and the total number of variables may not be known exactly, structure construction and adjustment of the artificial neural network remain as an open question. In this work, the authors introduce the chaotic dynamics in the structure construction of the RBFN. It can be seen that the radial basis functions establish a partition of the embedding space into regions in each of which it is possible to approximate the dynamics with a basis function. On account of the fact that the attractor of the chaotic systems is a fractal object, the authors use the fractal scaling process for partitioning the strange attractor into self-similar structures. Accordingly, the number of input variables, the number of basis function, and the scaling parameter of the basis function can be specified by the fractal scaling process. This work represents a promising approach to the modeling and prediction of chaotic time series.

A new thrust estimation method for online control of thrust and flux of a LIM using a fuzzy space-vector controller

Abstract: A new method is proposed for estimating the thrust of linear induction motors (LIMs) which has a suitable performance in a wide range of thrust variations. This eliminates the thrust control problems encountered in low frequency and thrust levels. A new formula is proved showing the high flexibility of multi-level inverters. A fuzzy space-vector controller is adapted for decoupling control of thrust and flux of a LIM. The main objective in the new thrust estimation method and the fuzzy controller is realizing an online and efficient controller for a LIM. A simulation program is provided for investigation of the LIM transient behavior which shows a suitable performance of the proposed method.

Time-domain analysis of transmission lines with stochastic input and general load

Abstract: In this paper an exact solution for the wave equation in lossy or lossless transmission lines when the input is a stochastic process, or when some of its characteristics are unknown, is presented. In this approach the input stochastic process may be nonstationary. In the first step, the general principles of the time domain approach for transmission lines with stochastic inputs are presented, and then as an example white noise is applied to the input of the transmission line. In this paper there is no restriction on the nature of the load, so it may be a nonlinear or time dependent load.

Effect of Induced Dipole-Induced Dipole Potential and the Size of Colliding Particles on Ion-Quadrupolar Molecule Collision Rate Constants

Abstract: Classical trajectory (Monte Carlo) calculation is used to calculate collision rate constants of ion-quadrupolar molecule interactions for the H¯+C2H2 system. The method presented here takes into account the effect of the induced dipole-induced dipole potential on ion-quadrupolar molecule collision rate constants. It is also assumed that the colliding particles have a definite size. The thermal energy collision rate constants are calculated at 300-3000 K temperature range and the kinetic energy dependence of rate constants is examined at a relative kinetic energy of the colliding particles in the range from thermal energy up to ~1.3 eV. It is suggested that the induced dipole-induced dipole potential term and the particles size are important factors and should not be ignored when calculating collision rate constants of ion-quadrupolar molecule system.

Optimum design of radar pulses for stealth targets (time-domain approach)

Abstract: The principles of an optimum design method of radar nonsinusoidal pulses for stealth targets are presented. To extract the principles of the method, first we have to obtain time-domain performance of the special absorber which is used on the target. Using the results of this time-domain approach, we can design an optimum pulse figure to maximise the reflected wave energy from the surface of the stealth target. This optimum pulse figure is not necessarily unique. We use a single layer model for the absorbing material but this method also can be generalized for multiple layer absorbing materials. Then we show, for the same absorbing material structure and the same reflected energy used by Mohamed (see IEEE Trans. on EMC, vol.37, no.2, 1995), one can use nonsinusoidal radar pulses with larger time-width (narrow-band pulses). So it is not necessary for the time-width of the pulse to be less than the propagation delay time in the absorbing material (as was stated by Mohamed). Finally, some optimum nonsinusoidal radar pulses are presented for some special applications of stealth targets.

Spectral coding of speech based on generalized sorted codebook vector quantization

Abstract: Sorted codebook vector quantization (SCVQ) is shown to be a very efficient vector quantization method. Generalization of SCVQ is suggested and its application to the spectral coding of speech using the quantization of line spectral frequencies (LSF), which are the most popular parameters to represent the linear prediction model for spectrum quantization in speech coders, is described. Computer simulations are conducted to evaluate the performance of the new method. We demonstrate that the new method achieves superior quality and has low implementation costs.

Transient analysis of transmission lines with time-dependent terminations and general input

Abstract: In this paper an exact time-domain solution for the wave equation in lossless TEM transmission lines with time-dependent boundary conditions in the input and output terminals will be presented. First a mathematical closed form time-domain solution for the wave equation in lossless TEM transmissions lines subject to arbitrary terminations will be presented, then this general solution will be specialized for some time dependent resistive terminations. Fundamentals of transient analysis of transmission lines with random inputs such as white noise was also briefly considered in this paper. In the latter situation the results are in the form of some statistical parameters, such as, correlation function, mean, variance and spectral density of the voltage or current stochastic processes, in the line as a function of time and distance.

Optimum design of radar pulses for stealth targets (time domain approach)

Abstract: Summary form only given. The principles of an optimum design method of radar nonsinusoidal pulses for stealth targets are presented. First we obtain the time-domain performance of the special absorber, which is used on the target. Using the results of this time-domain approach, we design an optimum pulse figure to maximize the reflected wave energy from the surface of the stealth target. This optimum pulse figure is not necessarily unique. We use a single-layer model of absorbing material, but this method can be generalized for multiple-layer absorbing materials. Also we assume that there is only attenuation during pulse propagation in absorbing material (there is no dispersion). We also show, for the same absorbing material structure and the same reflected energy as used by Mohamed (see IEEE Trans. EMC, vol.37, no.2, 1995), one can use nonsinusoidal radar pulses with larger time-width (narrow-band pulses). It is therefore necessary for time-width of the pulse to be less than the propagation delay time in the absorbing material. Finally, some optimum nonsinusoidal radar pulses are presented for some special applications of stealth targets.

Fabrication of reflection gratings by aluminum coating on holographic transmission gratings

Abstract: The fabrication of holographic reflection gratings can be done either directly or by first making a phase transmission relief grating and then metalizing its surface by an appropriate metal. In this paper, the fabrication of reflection gratings with different spatial frequencies, from 100 L/mm to 1200 L/mm registered dissimetrically are reported and the curves of diffraction efficiency versus the slope angle are illustrated and finally the results are interpreted.