Mean Square Value Research Articles

Fuzzy error diffusion

Quantization errors are generally hidden by performing a dithering operation on the image. A common method is to utilize error diffusion. However, this method is prone to error accumulation, resulting in color impulses and streaks. This paper presents a new approach to error diffusion dithering through a fuzzy error diffusion algorithm. In this method, the amount of error to be diffused is determined by considering the relative location of the pixel not only to the closest codebook vector, but to all other palette entries. The goal is to hide the quantization errors by error diffusion, while preventing the excess accumulation of errors. This is achieved through an attraction-repulsion schema according to a fuzzy membership function. We also explored methods to speed up the fuzzy error diffusion process through a L-filter approach by determining a fixed set of membership values. We have implemented the fuzzy error diffusion algorithm for color images and achieved drastic improvements, resulting in superior quality dithered images and significantly lower mean squared error values. A different error measure modeling the characteristic of the human visual system also indicates the superiority of our method.

Mean-square magnitude of all orders of polarization mode dispersion and the relation with the bandwidth of the principal states

Using the retarded plate model, we derive the correlations and the mean-square values of all orders of polarization mode dispersion (PMD) as well as the autocorrelation function of the PMD vector. Our results provide the signal bandwidth below which the first-order approximation of the principal states of polarization is valid. We show that this bandwidth depends only on the mean value of the differential group delay. Our theoretical results are supported by simulations and experiments.

Simulation of self-diffusion of point-like and finite-size tracers in stochastically reconstructed Vycor porous glasses

Aim of the present study is to simulate self-diffusion in three-dimensional images of reconstructed Vycor porous glass, which have the same statistical content as the actual material in terms of porosity and autocorrelation function. Effective diffusivities are determined from a step-by-step random walk process at different porosities and diffusion regimes. In all cases, the effective diffusivity curves show a sharp decrease below 20% porosity and drop to zero below a porosity of about 15%, a value suggested independently from the theory of spinodal decomposition. Comparison between the computed and experimental diffusivity values obtained in the Knudsen regime, shows a relative difference of less than 6%. Additional simulations in the molecular diffusion regime are performed using inert tracers of finite size. In these simulations, a transition is found in the value of diffusivity from a high value at small time scales, to a lower constant value achieved at large times. The time at which this crossover takes place corresponds to a mean-square displacement value whose square root is roughly equal to the average pore radius of the material. Comparison between computed and experimental results taken from the literature, shows very good agreement, as in the case of point-like tracer diffusion. Thus, the reconstructed Vycor is shown to represent properly not only structural properties such as porosity and correlation function, but also dynamic properties such as effective diffusivity of inert gas molecules of various sizes.

Um algoritmo prático para determinação da variância do estimador de um contraste de parâmetros

Testes de significância de contrastes de efeitos de níveis de um fator ou de combinações de níveis de dois ou mais fatores requerem o conhecimento das estimativas das variâncias dos estimadores desses contrastes. As expressões dessas estimativas para experimentos com delineamentos complexos, em geral, não são disponíveis em textos. Sua derivação algébrica a partir da equação do modelo estatístico é trabalhosa. Expõe-se um algoritmo prático para a obtenção da variância do estimador de qualquer contraste de parâmetros para delineamentos completos balanceados. O algoritmo baseia-se nos valores esperados dos quadrados médios.

Assessment of right atrial mapping and P wave—triggered signal-average in patients with paroxysmal atrial fibrillation

To assess right atrial mapping and P wave—triggered signal-averaged electrocardiogram (ECG) in patients with paroxysmal atrial fibrillation (PAF), this study examined right atrial electrograms using atrial mapping and parameters by P wave—triggered signal-averaged ECG in 39 patients without sick sinus syndrome. Subjects were divided into those with PAF (n = 13; 60 ± 13 years old) and a control group (n = 26; 49 ± 19 years old). The total number of abnormal right atrial electrograms per patient was significantly greater in the PAF group (3.2 ± 1.9) than in the control group (1.1 ± 0.9; P < .001). The longest duration of right atrial electrogram in the PAF group tended to be greater than that in the control group ( P = .06). The filtered P wave duration was significantly longer in the PAF group than in the control group (144 ± 21 vs 125 ± 14 ms [ P < .002]). The values of the root mean square of P wave—triggered signal-averaged ECG 15 ms from the onset (RMSi 15) and 20 ms from the offset (RMSe 20) were significantly lower in the PAF group (1.1 ± 0.4 μV, 1.4 ± 0.5 μV) than in the control group (1.9 ± 1.1 μV [ P < .021, 2.1 ± 0.9 μV [ P < .011). The total number of right atrial electrograms in patients with RMSi 15 of ≤ 1.5 μV was significantly greater than in patients with RMSi 15 of >1.5 μV (2.2 ± 1.8 vs 1.3 ± 1.3 [ P < .05]). Thus, the total number of abnormal right atrial electrograms per patient, the total filtered P wave duration, RMSi 15, and RMSe 20 may be good indices of PAF in patients without sick sinus syndrome. RMSi 15 may reflect the total number of the abnormal right atrial electrograms per patient.

Liquid Flow Characteristics in an Air-Water Bubbling Wall Jet Rising Along a Vertical Flat Plate.

An air-water bubbling jet was generated vertically upward along a vertical fiat plate. The liquid flow characteristics represented by the axial mean velocity and the root mean-square value of the axial turbulence component, designated by u^- and u'rms, were measured with a two-channel laser Doppler velocimeter. The horizontal distributions of u^- and u'rms followed their respective similar distributions in the vertical region where the buoyancy force acting on bubbles governs the flow field just like the distributions of bubble frequency and void fraction. An empirical equation was proposed for the horizontal distribution of u^-. The skewness and flatness factors for the axial turbulence component were also discussed to describe the structure of turbulence in more detail.

A study of turbulent flow of solutions of a polymer and a surface-active substance

We give the results of laser doppler anemometer measurements of the velocity profiles and mean-square values of the longitudinal velocity pulses in the flow of solutions of a polymer (polyacrylamides) or a surface-active substance (undustrial “metaupon” paste) that lower hydrodynamic frictional resistance and mixtures of such substances. It is shown that a solution of a mixture has a significantly greater effect on the turbulence of the flow than the polymers or surface-active substances do individually.

FILTERED REFERENCE AND FILTERED ERROR LMS ALGORITHMS FOR ADAPTIVE FEEDFORWARD CONTROL

A unified and consistent formulation is developed for both filtered reference and filtered error forms of the instantaneous steepest decent, or LMS, algorithm when used to adapt FIR feedforward controllers. Both algorithms minimise the mean-square value of the same, output, error function. The two algorithms are first formulated for single-input single-output linear plants. It is argued that since the behaviour of the two algorithms is equivalent in the case of slow adaption, the conditions on the accuracy of the plant model for stability should also be the same in both cases. This is expressed as a bound on the unstructured multiplicative uncertainty of the plant. Filtered reference and filtered error algorithms are also derived for multiple-input multiple-output (MIMO) linear systems, although the filtered reference algorithm is found not to have a simple block diagram interpretation. In the MIMO case, the filtered error form of the algorithm can have considerable computational advantages over the filtered reference form. Finally the two algorithms are extended to the case of non-linear plants and/or controllers which are modelled as feedforward neural networks. In the non-linear case the two formulations of the LMS algorithm reduce to two forms of the widely used backpropagation algorithm.

Partial control for wide-band interference suppression using eigen approach

This paper presents a simple and efficient array pattern synthesis technique for multiple wideband interference suppression using only the edge elements of linear arrays. By minimizing the mean-square value of the pattern in the directions of interference, the eigenvector that corresponds to the minimum eigenvalue is computed to obtain the required current excitation of the edge elements, the number of computations is greatly reduced since partial amplitude control of the edge elements is used.

Design of a mega-sub-controlled building system under stochastic wind loads

Vibration control of high-rise buildings under wind loads with application of the mega-sub-control method is studied in this paper. A building with a megasub-configuration consists of two major structural components - a megastructure as the main structural frame and several sub-structures for residential and/or commercial usage. The authors have previously proposed a ‘megasub-control method’ in which the sub-structures are designed to serve as vibration control dampers. The control objective is to suppress certain critical building responses such as inter-story drifts of the mega-structure for the purpose of structural safety and acceleration response of the sub-structures for the purpose of protecting contents and improving human comfort. The feasibility of this method has been explored by the authors in previous publications. In this study, the procedure of optimally designing dynamic parameters of a megasub-controlled building under stochastic wind loads is developed, together with two possible structural configurations which provide a mega-sub-control mechanism. The mega-structure of a mega-sub-building is modeled as a cantilever beam to retain the dominant bending mode characteristics of highrise buildings, and the sub-structure as a shear building to retain the shear mode. The fluctuating wind speed is modeled as a non-white random process in both time and space domains. The power spectral density (PSD) of critical building responses is obtained using the random vibration theory. The mean square value (MSV) of those responses, as functions of the dynamic parameters including the stiffness and damping ratio of the sub-structures, are evaluated from their PSD by numerical integration in the frequency domain. The optimal values of the dynamic parameters are determined by minimizing the MSV of certain critical building responses. An example building is used to demonstrate the design procedure and the numerical simulation of the response quantities in the time domain is carried out to verify the MSV of the building responses obtained from the random vibration theory in the frequency domain. The results show that the proposed design procedure is suitable to apply to a mega-sub-building with different sub-structural configurations. The MSV obtained from the random vibration theory in the frequency domain and from the numerical simulation in the time domain exhibit an excellent agreement. It is also found that the megasub-control method is robust in the sense that slight change in the dynamic parameters affects the building's performance very little. With the design procedure developed, and the corresponding favorable building response demonstrated, this paper has enhanced the feasibility of application of the mega-sub-control method to actual high-rise buildings for wind vibration suppression.

Complex spreading sequences with a wide range of correlation properties

This paper presents a new family of complex valued pseudo-random sequences for use in coded multiple access communication systems. The family offers a very wide range of values for both auto-correlation (AC) and cross-correlation (CC) functions, allowing great flexibility in the selection of characteristics of sequence sets. Based on the measure described in this paper for the mean-square aperiodic AC and CC values of a set of sequences, the correlation properties of sets of these sequences are compared to well-known sequence sets, and it is shown that sets from the new family of sequences have superior qualities. Tables of parameters for various sequence sets are presented to enable the construction and comparison of sets from this new family.

Delay-spread considerations of same-frequency repeaters in wideband channels

In current analog cellular systems, same-frequency repeaters are very often used as gap fillers. With digital wideband systems, the use of a repeater, with its inherent group delay added to the differential propagation delay, may yield a degradation in the performance in view of the resulting delay spread. An approach to estimate the statistics of the delay spread when each link is subjected to lognormal shadowing and each channel's power-delay profile follows an exponential decay is presented. Expressions for the cumulative density function (CDF), mean value, mean-square value, and standard deviation for the RMS delay spread are derived, and their accuracy is verified through simulation.

The Theory of ESR Hyperfine-Structure Narrowing as Applied to Wide-Gap Semimagnetic Semiconductors

The theory of ESR hyperfine-structure exchange narrowing is developed. The kinetic equations describing the nonequilibrium magnetization dynamics of hyperfine components of ESR spectra are derived by using the nonequilibrium statistical-operator method. Numerical solution of these general equations is applied to the simulation of the experimental spectra of (Cd, Mn)Te crystals with a Mn2+ ion content of between 0.05 and 0.5%. The hyperfine-splitting constant, homogeneous ESR linewidth, and mean-square value of the exchange fluctuation frequency are obtained from the fitting of the spectra for different concentrations of manganese ions. The concentration dependence of the latter quantity is discussed in relation to the spatial dependence of magnetic-ion exchange interaction and the gap value in the band structure of semimagnetic semiconductors.

Austenite content and dislocation density in electron-beam welds of a stainless maraging steel

The volume fraction of austenite and dislocation density in electron beam weld joints of a martensitic-austenitic age-hardenable CrNiMoTiAl stainless steel were investigated using neutron diffraction. Experiments were performed on a high-resolution diffractometer which resolved microstrains of the order of 10 −4. The effect of post-weld heat treatment on austenite content and dislocation density was investigated. As in other maraging steels, the maximum volume fraction of austenite was obtained after quenching and intercritical annealing. Dislocation densities computed on the base of mean-square microstrain values were about 10 11 cm −2. These densities were systematically higher in martensite than in austenite, with very small differences between the weld metal and base metal.

Classification of cardiac arrhythmias using fuzzy ARTMAP.

We have investigated the QRS complex, extracted from electrocardiogram (ECG) data, using fuzzy adaptive resonance theory mapping (ARTMAP) to classify cardiac arrhythmias. Two different conditions have been analyzed: normal and abnormal premature ventricular contraction (PVC). Based on MIT/BIH database annotations, cardiac beats for normal and abnormal QRS complexes were extracted from this database, scaled, and Hamming windowed, after bandpass filtering, to yield a sequence of 100 samples for each ORS segment. From each of these sequences, two linear predictive coding (LPC) coefficients were generated using Burg's maximum entropy method. The two LPC coefficients, along with the mean-square value of the QRS complex segment, were utilized as features for each condition to train and test a fuzzy ARTMAP neural network for classification of normal and abnormal PVC conditions. The test results show that the fuzzy ARTMAP neural network can classify cardiac arrhythmias with greater than 99% specificity and 97% sensitivity.

A new approach for evaluating the performance of a symbol timing recovery system employing a general type of nonlinearity

A new technique is presented for evaluating the jitter performance of a symbol timing recovery (STR) subsystem for digital data transmission systems. The STR system consists of any even-symmetric zero-memory nonlinear device followed by a narrowband filter tuned to the pulse repetition frequency. Exact analytical expressions are derived for the mean and the mean-square values of the timing wave, based on iterative computations of high-order moments of the input signal. Then, the root mean-square (RMS) jitter performance is determined as a function of various system parameters such as the power series expansion of the zero-memory nonlinear device, the rolloff factor of the input pulse shape, and the postfiltering. Finally, the numerical results obtained from some specific examples serve to illustrate several aspects of the timing recovery problem.

Performance evaluation of DS-CDMA system with M-ary orthogonal signaling

The effects of signature sequence on the performance of direct-sequence code-division multiple-access (DS-CDMA) systems employing Walsh M-ary orthogonal signaling are considered. The mean-squared value of multiple access interference (MAI) is derived by treating the signature sequence as deterministic. The numerical results show that Walsh orthogonal signaling changes the original properties of signature sequences, and a different choice of signature sequence results in significant performance difference. These results can be used as guides in selecting signature sequences for systems that employ Walsh M-ary orthogonal signaling.

Evaluation of reverberation times using a nonlinear regression approach

Reverberation decay curves can be obtained by the backward integration of room impulse responses proposed by M. R. Schroeder. The evaluation of reverberation times is often achieved by a linear regression line fitting the reverberation decay curves. However, under noisy conditions, the successful application of this method requires either a careful choice of the integration limit or a precise estimate of the mean-square value of the background noise. In the present paper, an alternative method using a nonlinear iterative regression approach for evaluating reverberation times from Schroeder’s decay curves is proposed. A nonlinear model of the decay curves, established according to the nature of Schroeder’s decay curves, is used for the regression process rather than the linear model used in linear regression. The regression process is based on the generalized least-squares error principle in which a rapid convergence can be observed. Preliminary experiments show a slight dependence of the reverberation time T30 dB on both the integration limit and the background noise. Using this approach, a high precision of reverberation time evaluations can be achieved without either careful selection of the integration limit or precise estimation of the mean square value of the background noise.

Remarks on the mean-square values of the geomagnetic field and its components

When considering functions on the Earth's (spherical) surface, mean-square values are often used to indicate their (relative) magnitude. If a function is separated into it, (essentially) spherical harmonic components then, provided these individual harmonic components are orthogonal over the surface, the concept of spatial power spectrum can be introduced, with each harmonic contributing separately to the total mean square value; this is true for the geomagnetic field vector B, its horizontal component vector H, and its vertical component z. However, because of the lack of orthogonality this concept is not applicable to the horizontal X and y components individually; problems which arise from this are discussed.

Design of FIR filters using quadratic programming approach

The paper presents a simple computer-aided design approach for designing FIR digital filters. The design problem is formulated as a quadratic programming problem with quadratic constraint. Two design methods are considered. One method involves minimizing the mean-square error between a desired response and the filter response over a passband subject to a mean-square stopband constraint. The other method involves minimizing the mean-square value of the filter response in the stopband subject to a mean-square error constraint over the passband. Numerical techniques based on matrix factorization are proposed to reduce the computational complexity. Relationship of the approach with the eigenfilter method is established. Numerical results are presented to illustrate the performance achievable. >