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Closed-form Expressions (closed-form + expression)

Distribution by Scientific Domains

Engineering	48%
Business, Economics, Finance and Accounting	15%
Mathematics and Statistics	13%
Chemistry	8%
Medical Sciences	6%
3 Other Domains	10%

Distribution within Engineering

Communication Technology	58%
General & Introductory Electrical & Electronics Engineering	8%
5 Other Subdomains	26%

Selected Abstracts

Closed-form expression for the BER of m-QAM-OFDM systems over time- and frequency-selective wireless channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2006
F. Castells
Abstract The broadcast DVB-T system is an m-QAM-OFDM communication system that includes pilot-symbol-assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB-T suitable for a mobile reception, over time- and frequency-selective wireless channels. In this work, a closed-form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB-T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Closed-form expression of asymmetric stripline open-end and its applications for analysis of LTCC components and circuits

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2009
Wanchun Tang
Abstract In this article, we have obtained simple excess capacitance formula for asymmetric stripline open-end. The average error of the formula is less than 2%. On the basis of this formula and the field-based equivalent circuit model obtained by the authors before, a low-pass filter and an edge coupled stripline band-pass filter are analyzed by the field-based equivalent circuit together with the excess capacitance formula of this article. Compared with numerical results, the average errors of S parameters are less than 2%. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 406,408, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24072 [source]

Performance analysis of system with L-branch selection combining over correlated Weibull fading channels in the presence of cochannel interference

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2010
. Stefanovi, Mihajlo
Abstract In this paper, the performance of L-branch selection combining receiver over correlated Weibull fading channels in the presence of correlated Weibull-distributed cochannel interference is analyzed. Closed-form expressions for probability density function and cumulative distribution function of the signal-to-interference ratio at the output of the selection combining receiver present main contribution of this paper. Numerical results are also presented to show the effects of various parameters as the fading severity, correlation and number of branches on outage probability. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Design and optimization of multi-band Wilkinson power divider

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2008
Nihad Dib
Abstract In this paper, a general and easy procedure for designing the symmetrical Wilkinson power divider that achieves equal-power split at N arbitrary frequencies is introduced. Each quarter-wave branch in the conventional Wilkinson divider is replaced by N sections of transmission lines, and the isolation between the output ports is achieved by using N resistors. The design parameters are the characteristic impedances and lengths of the N transmission line sections, and the N isolation resistors. The even,odd modes of analysis are used to derive the design equations. Closed-form expressions, which are suitable for CAD purposes, are derived for the dual-band divider. For N , 3, closed-form expressions are not available, and therefore, the powerful particle swarm optimization method is used to obtain the design parameters. Examples of the dual-, triple-, and quad-band dividers are presented to validate the proposed design procedure, and the results are compared, wherever possible, with published results using other methods. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008. [source]

Closed-form physical optics expressions for the radar cross section of perfectly conducting plane angular sectors

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2008
Andrea Vallecchi
Abstract Closed-form expressions for the physical optics (PO) field scattered in the far zone by perfectly electrically conducting (PEC) plane angular sectors with a conical-section boundary are derived in terms of incomplete cylindrical functions (ICFs). The developed representations are very efficient from a computational point of view and constitute a useful tool to analytically predict the radar cross section (RCS) of metal plates with both convex and concave curved edges. The correctness of the proposed scattered field formulas is demonstrated through comparisons with the results obtained by an accurate completely numerical PO approach. A sample analysis of the scattering from a more elaborate geometry, which can be seen as a juxtaposition of angular sectors, is also presented. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 160,165, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22989 [source]

The statistics of refractive error maps: managing wavefront aberration analysis without Zernike polynomials

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2009
D. Robert Iskander
Abstract The refractive error of a human eye varies across the pupil and therefore may be treated as a random variable. The probability distribution of this random variable provides a means for assessing the main refractive properties of the eye without the necessity of traditional functional representation of wavefront aberrations. To demonstrate this approach, the statistical properties of refractive error maps are investigated. Closed-form expressions are derived for the probability density function (PDF) and its statistical moments for the general case of rotationally-symmetric aberrations. A closed-form expression for a PDF for a general non-rotationally symmetric wavefront aberration is difficult to derive. However, for specific cases, such as astigmatism, a closed-form expression of the PDF can be obtained. Further, interpretation of the distribution of the refractive error map as well as its moments is provided for a range of wavefront aberrations measured in real eyes. These are evaluated using a kernel density and sample moments estimators. It is concluded that the refractive error domain allows non-functional analysis of wavefront aberrations based on simple statistics in the form of its sample moments. Clinicians may find this approach to wavefront analysis easier to interpret due to the clinical familiarity and intuitive appeal of refractive error maps. [source]

A two-mean reverting-factor model of the term structure of interest rates

THE JOURNAL OF FUTURES MARKETS, Issue 11 2003
Manuel Moreno
This article presents a two-factor model of the term structure of interest rates. It is assumed that default-free discount bond prices are determined by the time to maturity and two factors, the long-term interest rate, and the spread (i.e., the difference) between the short-term (instantaneous) risk-free rate of interest and the long-term rate. Assuming that both factors follow a joint Ornstein-Uhlenbeck process, a general bond pricing equation is derived. Closed-form expressions for prices of bonds and interest rate derivatives are obtained. The analytical formula for derivatives is applied to price European options on discount bonds and more complex types of options. Finally, empirical evidence of the model's performance in comparison with an alternative two-factor (Vasicek-CIR) model is presented. The findings show that both models exhibit a similar behavior for the shortest maturities. However, importantly, the results demonstrate that modeling the volatility in the long-term rate process can help to fit the observed data, and can improve the prediction of the future movements in medium- and long-term interest rates. So it is not so clear which is the best model to be used. © 2003 Wiley Periodicals, Inc. Jrl Fut Mark 23: 1075,1105, 2003 [source]

Kinematic response functions and dynamic stiffnesses of bridge embankments

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2002
Jian Zhang
Abstract Recognizing that soil,structure interaction affects appreciably the earthquake response of highway overcrossings, this paper compares approximate analytical solutions and finite element results to conclude on a simple procedure that allows for the estimation of the kinematic response functions and dynamic stiffnesses of approach embankments. It is shown that the shear-wedge model yields realistic estimates for the amplification functions of typical embankments and reveals the appropriate levels of dynamic strains which are subsequently used to estimate the stiffness and damping coefficients of embankments. The shear-wedge model is extended to a two-dimensional model in order to calculate the transverse static stiffness of an approach embankment loaded at one end. The formulation leads to a sound closed-form expression for the critical length, Lc, that is the ratio of the transverse static stiffness of an approach embankment and the transverse static stiffness of a unit-width wedge. It is shown through two case studies that the transverse dynamic stiffness (,spring' and ,dashpot') of the approach embankment can be estimated with confidence by multiplying the dynamic stiffness of the unit-width wedge with the critical length, Lc. The paper concludes that the values obtained for the transverse kinematic response function and dynamic stiffness can also be used with confidence to represent the longitudinal kinematic response function and dynamic stiffness, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Bond Price and Impulse Response Function for the Balduzzi, Das, Foresi and Sundaram (1996) Model

ECONOMIC NOTES, Issue 3 2004
Martino Grasselli
In this paper, we analyse the Affine Term Structure Model (ATSM) proposed by Balduzzi, Das, Foresi and Sundaram (BDFS, 1996) and provide the closed-form expression of the bond price. In addition, we extend the notion of Impulse Response Function to the class of ATSM. We show that it is closely related to the duration measure, and we compute it explicitly in the BDFS model. [source]

A Simple Engineering Estimate of the Fatigue Notch Factor of Arbitrary Stress Concentrators

ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Hans-Peter Gaenser
In fatigue life estimates, the fatigue stress endured at the hot spot is usually higher than what is predicted by the elastic stress concentration factor. Recently, Neuber's and Novozhilov's approaches of introducing an effective stress by averaging the actual stress field over a characteristic microstructural length have experienced a reappraisal. The present contribution aims at complementing these recent proposals by a mathematically simple engineering assessment of arbitrarily shaped notches, resulting in a closed-form expression for the fatigue notch factor. The limits of validity of the solution are discussed. [source]

An accurate scheme for mixed-mode fracture analysis of functionally graded materials using the interaction integral and micromechanics models

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2003
Jeong-Ho Kim
Abstract The interaction integral is a conservation integral that relies on two admissible mechanical states for evaluating mixed-mode stress intensity factors (SIFs). The present paper extends this integral to functionally graded materials in which the material properties are determined by means of either continuum functions (e.g. exponentially graded materials) or micromechanics models (e.g. self-consistent, Mori,Tanaka, or three-phase model). In the latter case, there is no closed-form expression for the material-property variation, and thus several quantities, such as the explicit derivative of the strain energy density, need to be evaluated numerically (this leads to several implications in the numerical implementation). The SIFs are determined using conservation integrals involving known auxiliary solutions. The choice of such auxiliary fields and their implications on the solution procedure are discussed in detail. The computational implementation is done using the finite element method and thus the interaction energy contour integral is converted to an equivalent domain integral over a finite region surrounding the crack tip. Several examples are given which show that the proposed method is convenient, accurate, and computationally efficient. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Dynamic model of one-cycle control for converters operating in continuous and discontinuous conduction modes,

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 5 2009
N. Femia
Abstract In this paper a new dynamic model of one-cycle-controlled converters operating either in continuous or in discontinuous conduction mode (DCM) is introduced. The static and dynamic behaviour is analysed by using sampled-data modelling combined with the small-signal linearization of the average model of the converter's power stage. The proposed model is valid for frequencies up to half the switching frequency and, while the other dynamic models presented in the literature cover continuous conduction mode only, it also gives an accurate prediction of the system's dynamic behaviour in the DCM. The model allows to determine the closed-form expression of the reference-to-output transfer function G of the system, which is a fundamental prerequisite for the design of a conventional output feedback control circuit aimed at improving the dynamic behaviour of the system in response to load variations. In this paper it is also shown that one-cycle control does not work properly in switching converters operating in deep DCM if some specific design constraints are not fulfilled. The theoretical predictions are confirmed by the results of suitable numerical simulations and laboratory experiments on a one-cycle-controlled buck-switching converter. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On the error probability of quasi-orthogonal space,time block codes

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2008
Jae-Dong Yang
Abstract In this paper, we derive the exact pairwise error probabilities (PEPs) of various quasi-orthogonal space,time block codes (QO-STBCs) using the moment generating function. By classifying the exact PEPs of QO-STBCs into three types, we derive the closed-form expression for each type of PEP. Based on these closed-form expressions, we obtain the union bounds on the symbol error probability and bit error probability for QPSK modulation. Through simulation, it is shown that these union bounds are quite tight. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Performance analysis of wireless multihop diversity systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2008
Diomidis S. Michalopoulos
Abstract We study the performance of multihop diversity systems with non-regenerative relays over independent and non-identical Rayleigh fading channels. The analysis is based on the evaluation of the instantaneous end-to-end signal-to-noise ratio (SNR), depending on the type of the relay and the diversity scheme used. A closed-form expression is derived for the average end-to-end SNR, when fixed-gain relays and a maximal ratio combiner are used; also, an analytical expression formula for the average symbol-error rate (ASER) for the above case is presented. The results show that, as expected, multihop diversity systems outperform conventional telecommunication systems in terms of ASER when the same amount of energy is assumed to be consumed in both cases. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On the application of forking nodes to product-form queueing networks,

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2008
Essia H. Elhafsi
Abstract We define a ,forking node' as a service centre with one input feeding two outputs (each served by its own queue) under the control of an internal path-selection (PS) policy. We assume that both outputs lead to paths through which a packet reaches its final destination. However, the mean downstream delays on the two paths may be different and the PS policy should favour the path with the lower downstream delay. Using simulation, we compare the performance of this system under a variety of random, deterministic, state-dependent PS policies, including threshold-based and join-shortest-queue with bias (JSQ + b). We show that JSQ + b has better performance than the other alternatives. Moreover, if the input process to the forking node is Poisson, standard time series analysis techniques show that its two outputs are very close to being independent Poisson processes. Thus, if we find an accurate and efficient ,offline' analytical performance model for JSQ + b forking node, we can extend the applicability of product-form queueing networks to include such forking nodes. For this reason, we present several ways of modelling the performance of a JSQ + b node, using bounds, and compare their results on example networks. We establish a closed-form expression relating the bias b and the delays of the downstream paths. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Closed-form expression for the BER of m-QAM-OFDM systems over time- and frequency-selective wireless channels

Perceptual denoising of color images

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 3 2010
Ilka A. Netravali
Abstract Denoising of color images is a trade-off between sharpness of an image and perceived noise. We formulate a novel optimization problem that can maximize sharpness of an image while limiting the perceived noise under a model of visibility of additive random noise. We derive a closed-form expression for an optimal two-dimensional finite impulse response filter, show its uniqueness and existence, and present simulation results for black and white as well as color images. Simulation results show remarkable reduction in perceptibility of noise, while preserving sharpness. The computational burden required for the optimal filter is reduced by a new adhoc filter which is simple but has near optimal performance. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 215,222, 2010. [source]

A new multi-state fading model for mobile satellite channels based upon AFD and LCR data,

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2004
David W. Matolak
Abstract Using measured data on average fade duration (AFD) and level crossing rate (LCR), we obtain new analytical expressions for the probability density function (pdf) of received signal envelope in a mobile satellite channel, via a new method. The measured data for an urban environment comes from Kanatas et al. Proceedings of the 1997 International Mobile Satellite Conference, Pasadena, CA, 16,18 June, 1997; 169,175, but the new method is general in nature and can be applied to other environments. The method is less direct than curve-fitting to a histogram of the ,raw' measured fading amplitude data, but is comparable in complexity and yields good results. Our new model is a composite one, similar to other composite models given in the literature, e.g. the Loo and Lutz models, but in contrast to these, the new model affords a completely closed-form expression for the pdf. As with these other composite models, the new model is amenable to the development of computer simulations of mobile satellite channel amplitude time series realizations, and can be combined with state transition models to provide a complete multi-state fading model. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Integer programming solution approach for inventory-production,distribution problems with direct shipments

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2008
Miguel A. Lejeune
Abstract We construct an integrated multi-period inventory,production,distribution replenishment plan for three-stage supply chains. The supply chain maintains close relationships with a small group of suppliers, and the nature of the products (bulk, chemical, etc.) makes it more economical to rely upon a direct shipment, full-truck load distribution policy between supply chain nodes. In this paper, we formulate the problem as an integer linear program that proves challenging to solve due to the general integer variables associated with the distribution requirements. We propose new families of valid cover inequalities, and we derive a practical closed-form expression for generating them, upon the determination of a single parameter. We study their performances through benchmarking several branch-and-bound and branch-and-cut approaches. Computational testing is performed using a large-scale planning problem faced by a North American company. [source]

The statistics of refractive error maps: managing wavefront aberration analysis without Zernike polynomials

Heterogeneity in dynamic discrete choice models

THE ECONOMETRICS JOURNAL, Issue 1 2010
Martin Browning
Summary, We consider dynamic discrete choice models with heterogeneity in both the levels parameter and the state dependence parameter. We first present an empirical analysis that motivates the theoretical analysis which follows. The theoretical analysis considers a simple two-state, first-order Markov chain model without covariates in which both transition probabilities are heterogeneous. Using such a model we are able to derive exact small sample results for bias and mean squared error (MSE). We discuss the maximum likelihood approach and derive two novel estimators. The first is a bias corrected version of the Maximum Likelihood Estimator (MLE) although the second, which we term MIMSE, minimizes the integrated mean square error. The MIMSE estimator is always well defined, has a closed-form expression and inherits the desirable large sample properties of the MLE. Our main finding is that in almost all short panel contexts the MIMSE significantly outperforms the other two estimators in terms of MSE. A final section extends the MIMSE estimator to allow for exogenous covariates. [source]

Granger's representation theorem: A closed-form expression for I(1) processes

THE ECONOMETRICS JOURNAL, Issue 1 2005
Peter Reinhard Hansen
Summary, The Granger representation theorem states that a cointegrated vector autoregressive process can be decomposed into four components: a random walk, a stationary process, a deterministic part, and a term that depends on the initial values. In this paper, we present a new proof of the theorem. This proof enables us to derive closed-form expressions of all terms of the representation and allows a unified treatment of models with different deterministic specifications. The applicability of our results is illustrated by examples. For example, the closed-form expressions are useful for impulse response analyses and facilitate the analysis of cointegration models with structural changes. [source]

New Powerful Approaches for Family-based Association Tests with Longitudinal Measurements

ANNALS OF HUMAN GENETICS, Issue 1 2009
Xiao Ding
Summary We discuss several new powerful family-based approaches for testing genetic association when the traits are obtained from longitudinal or repeated measurement studies. The popular approach FBAT-PC is based on a linear combination of the individual traits. We propose a one-sided modification, FBAT-PCM, which has a closed-form expression and is always more powerful. We also present two approaches FBAT-LC and FBAT-LCC based on linear combination of the univariate test statistics. Furthermore, all three approaches are shown to be unified to a general form. Through simulation studies, we compare the power of these tests under different models of genetic effect sizes. Compared to original FBAT-PC, our modification achieves a power gain of up to 50%. In addition, all three new approaches gain substantial power compared to the ordinary approach of Bonferroni correction, with the relative performance depending upon the underlying model. Application of these approaches for testing an association between Body Mass Index and a previously reported candidate SNP confirms our results. [source]

On a class of renewal risk model with random income

APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 6 2009
Hu Yang
Abstract In this paper, we consider a renewal risk process with random premium income based on a Poisson process. Generating function for the discounted penalty function is obtained. We show that the discounted penalty function satisfies a defective renewal equation and the corresponding explicit expression can be obtained via a compound geometric tail. Finally, we consider the Laplace transform of the time to ruin, and derive the closed-form expression for it when the claims have a discrete Km distribution (i.e. the generating function of the distribution function is a ratio of two polynomials of order m,,+). Copyright © 2008 John Wiley & Sons, Ltd. [source]

Optimal investment problem with stochastic interest rate and stochastic volatility: Maximizing a power utility

APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 3 2009
Jinzhu Li
Abstract In this paper, we assume that an investor can invest his/her wealth in a bond and a stock. In our wealth model, the stochastic interest rate is described by a Cox,Ingersoll,Ross (CIR) model, and the volatility of the stock is proportional to another CIR process. We obtain a closed-form expression of the optimal policy that maximizes a power utility. Moreover, a verification theorem without the usual Lipschitz assumptions is proved, and the relationships between the optimal policy and various parameters are given. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Optimal design of added viscoelastic dampers and supporting braces

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2004
Ji-Hun Park
Abstract This paper presents a simultaneous optimization procedure for both viscoelastic dampers (VEDs) and supporting braces installed in a structure. The effect of supporting braces on the control efficiency of VEDs is also investigated. To apply a general gradient-based optimization algorithm, closed-form expressions for the gradients of objective function and constraints are derived. Also, the constraint on the dynamic behavior of a structure is embedded in the gradient computation procedure to reduce the number of variables in the optimization. From numerical analysis of an example structure, it was found that when sufficient stiffness cannot be provided for the supporting braces, the flexibility of the brace should be taken into account in the design of the VED to achieve the desired performance of the structure. It was also observed that, as a result of the proposed optimization process, the size of the supporting brace could be reduced while the additional VED size (to compensate for the loss of the control effect) was insignificant. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Opportunistic multiuser scheduling with reduced feedback load

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2010
Yahya S. Al-HarthiArticle first published online: 27 MAY 2010
In this paper, we propose a reduced feedback opportunistic scheduling (RFOS) algorithm that reduces the feedback load while preserving the performance of opportunistic scheduling (OS). The RFOS algorithm is a modified version of our previously proposed algorithm, the DSMUDiv algorithm. The main difference is that RFOS consists of a probing process (search process) and a requesting feedback process based on a threshold. The threshold value is variable, and it depends on the probing process. To reduce the feedback rate, a quantised value indicating the modulation level is fed back, instead of the full value of the signal-to-noise ratio (SNR), which we call quantised SNR. The paper includes the closed-form expressions of the probing load, feedback load and spectral efficiency. In addition, we investigate the effect of the scheduling delay on the system throughput (STH). Under slow Rayleigh fading assumption, we compare RFOS algorithm with the DSMUDiv and optimal (full feedback load) selective diversity scheduling algorithms. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Determination of Transverse Dispersion Coefficients from Reactive Plume Lengths

GROUND WATER, Issue 2 2006
Olaf A. Cirpka
With most existing methods, transverse dispersion coefficients are difficult to determine. We present a new, simple, and robust approach based on steady-state transport of a reacting agent, introduced over a certain height into the porous medium of interest. The agent reacts with compounds in the ambient water. In our application, we use an alkaline solution injected into acidic ambient water. Threshold values of pH are visualized by adding standard pH indicators. Since aqueous-phase acid-base reactions can be considered practically instantaneous and the only process leading to mixing of the reactants is transverse dispersion, the length of the plume is controlled by the ratio of transverse dispersion to advection. We use existing closed-form expressions for multidimensional steady-state transport of conservative compounds in order to evaluate the concentration distributions of the reacting compounds. Based on these results, we derive an easy-to-use expression for the length of the reactive plume; it is proportional to the injection height squared, times the velocity, and inversely proportional to the transverse dispersion coefficient. Solving this expression for the transverse dispersion coefficient, we can estimate its value from the length of the alkaline plume. We apply the method to two experimental setups of different dimension. The computed transverse dispersion coefficients are rather small. We conclude that at slow but realistic ground water velocities, the contribution of effective molecular diffusion to transverse dispersion cannot be neglected. This results in plume lengths that increase with increasing velocity. [source]

Optimal time integration parameters for elastodynamic contact problems

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2001
A. Czekanski
Abstract In this paper, we employ the generalized- , time integration scheme for treating elastodynamic contact problems. The criteria invoked for the selection of the four time integration parameters are motivated by our desire to ensure that the solution is unconditionally stable, second-order accurate, provides optimal high-frequency dissipation and preserves the energy and momentum transfer in dynamic rigid impact problems. New closed-form expressions for the time integration parameters are determined in terms of user-specified high-frequency spectral radius. The selected parameters help in avoiding the spurious high-frequency modes, which are present in the traditional Newmark method. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Performance evaluation for asynchronous MC-CDMA systems with a symbol timing offset

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2009
Myonghee Park
Abstract This paper models a symbol timing offset (STO) with respect to the guard period and the maximum access delay time for asynchronous multicarrier-code division multiple access systems over frequency-selective multipath fading channels. Analytical derivation shows that STO causes desired signal power degradation and generates self-interferences. This effect of the STO on the average bit error rate (BER) and the effective signal-to-noise ratio (SNR) is evaluated using the semi-analytical method, and the approximated BER and the SNR loss caused by STO are then obtained as closed-form expressions. The tightness between the semi-analytical result and the approximated one is verified for the different STOs and SNRs. Furthermore, the derived analytical results are verified via Monte Carlo simulations. Copyright © 2008 John Wiley & Sons, Ltd. [source]