a new approach to multipath correction of constant modulus signals an adaptive digital filtering algorithm that can compensate for both frequency selective multipath and interference on constant envelope modulated signals is presented the method exploits the fact that multipath reception and various interference sources generate incidental amplitude modulation on the received signal a class of so called constant modulus performance functions is developed which sense this am term but are insensitive to the angle modulation simple adaptive algorithms for finite impulse response fir digital filters are developed which employ a gradient search of the performance function one of the resulting algorithms is simulated for the example of an fm signal degraded by specular multipath propagation substantial improvements in noise power ratio npr are observed e g 25 db with moderately rapid convergence time these results are then extended to include tonal interference on a fm signal and intersymbol interference on a qpsk data signal

blind constant modulus equalization via convex optimization in this paper we formulate the problem of blind equalization of constant modulus cm signals as a convex optimization problem the convex formulation is obtained by performing an algebraic transformation on the direct formulation of the cm equalization problem using this transformation the original nonconvex cm equalization formulation is turned into a convex semidefinite program sdp that can be efficiently solved using interior point methods our sdp formulation is applicable to baud spaced equalization as well as fractionally spaced equalization performance analysis shows that the expected distance between the equalizer obtained by the sdp approach and the optimal equalizer in the noise free case converges to zero exponentially as the signal to noise ratio snr increases in addition simulations suggest that our method performs better than standard methods while requiring significantly fewer data samples

on the non existence of undesirable equilibria of godard blind equalizers existing results in the literature have proved that particular blind equalization algorithms including godard algorithms are globally convergent in an ideal and nonimplementable setting where a doubly infinite dimensional equalizer is available for adaptation contrary to popular conjectures it is shown that implementable finite dimensional equalizers which attempt to approximate the ideal setting generally fail to have global convergence to acceptable equalizer parameter settings without the use of special remedial measures a theory based on the channel convolution matrix nullspace is proposed to explain the failure of godard algorithms for such practical blind equalization situations this nullspace theory is supported by a simple example showing ill convergence of the godard algorithm

high friction limit for euler korteweg and navier stokes korteweg models via relative entropy approach abstract the aim of this paper is to investigate the singular relaxation limits for the euler korteweg and the navier stokes korteweg system in the high friction regime we shall prove that the viscosity term is present only in higher orders in the proposed scaling and therefore it does not affect the limiting dynamics and the two models share the same equilibrium equation the analysis of the limit is carried out using the relative entropy techniques in the framework of weak finite energy solutions of the relaxation models converging toward smooth solutions of the equilibrium the results proved here take advantage of the enlarged formulation of the models in terms of the drift velocity introduced in 6 generalizing in this way the ones proved in 15 for the euler korteweg model

hyperbolic conservation laws with relaxation the effect of relaxation is important in many physical situations it is present in the kinetic theory of gases elasticity with memory gas flow with thermo non equilibrium water waves etc the governing equations often take the form of hyperbolic conservation laws with lower order terms in this article we present and analyze a simple model of hyperbolic conservation laws with relaxation effects dynamic subcharacteristics governing the propagation of disturbances over strong wave forms are identified stability criteria for diffusion waves expansion waves and traveling waves are found and justified nonlinearly time asymptotic expansion and the energy method are used in the analysis for dissipative waves the expansion is similar in spirit to the chapman enskog expansion in the kinetic theory for shock waves however a different approach is needed

l 1 convergence to the barenblatt solution for compressible euler equations with damping we study the asymptotic behavior of compressible isentropic flow through a porous medium when the initial mass is finite the model system is the compressible euler equation with frictional damping as t the density is conjectured to obey the well known porous medium equation and the momentum is expected to be formulated by darcy s law in this paper we prove that any l weak entropy solution to the cauchy problem of damped euler equations with finite initial mass converges strongly in the natural l1 topology with decay rates to the barenblatt profile of the porous medium equation the density function tends to the barenblatt solution of the porous medium equation while the momentum is described by darcy s law the results are achieved through a comprehensive entropy analysis capturing the dissipative character of the problem

best asymptotic profile for linear damped p system with boundary effect abstract this paper is devoted to the study of the 2 2 linear damped p system with boundary effect by a heuristic analysis we realize that the best asymptotic profile for the original solution is the parabolic solution of the ibvp for the corresponding porous media equation with a specified initial data in particular we further show the convergence rates of the original solution to its best asymptotic profile which are much better than the existing rates obtained in the previous works the approach adopted in the paper is the elementary weighted energy method with green function method together

on the initial boundary value problem for the bipolar hydrodynamic model for semiconductors abstract the global existence and zero relaxation limit results of weak solutions of the initial boundary value problem to the bipolar hydrodynamic model for semiconductors are established by the theory of compensated compactness the boundary conditions of weak solutions in the sense of traces are discussed

the relaxation of the hydrodynamic model for semiconductors to the drift diffusion equations abstract we establish the convergence and consistency of approximate solutions derived by the modified godunov scheme for the initial boundary value problem to a simplified one dimensional hydrodynamic model for semiconductors using the compensated compactness method the traces of weak solutions are introduced and then the weak solutions are proved to satisfy the natural boundary conditions the zero relaxation limit of the hydrodynamic model to the drift diffusion model is proved when the momentum relaxation time tends to zero

frequency localization duhamel principle and its application to the optimal decay of dissipative systems in low dimensions abstract recently a time decay framework l 2 r n b 2 s r n s 0 has been given by 49 for linearized dissipative hyperbolic systems which allows to pay less attention to the traditional spectral analysis however owing to interpolation techniques those decay results for nonlinear hyperbolic systems hold true only in higher dimensions n 3 and the analysis in low dimensions say n 1 2 was left open we try to give a satisfactory answer in the current work first of all we develop new time decay properties on the frequency localization duhamel principle and then it is shown that the classical solution and its derivatives of fractional order decay at the optimal algebraic rate in dimensions n 1 2 by using a new technique which is the so called piecewise duhamel principle in localized time weighted energy approaches compared to 49 finally as direct applications explicit decay statements are worked out for some relevant examples subjected to the same dissipative structure for instance damped compressible euler equations the thermoelasticity with second sound and timoshenko systems with equal wave speeds

the strong relaxation limit of the multidimensional isothermal euler equations we construct global smooth solutions to the multidimensional isothermal euler equations with a strong relaxation when the relaxation time tends to zero we show that the density converges towards the solution to the heat equation

nonlinear camera response functions and image deblurring theoretical analysis and practice this paper investigates the role that nonlinear camera response functions crfs have on image deblurring we present a comprehensive study to analyze the effects of crfs on motion deblurring in particular we show how nonlinear crfs can cause a spatially invariant blur to behave as a spatially varying blur we prove that such nonlinearity can cause large errors around edges when directly applying deconvolution to a motion blurred image without crf correction these errors are inevitable even with a known point spread function psf and with state of the art regularization based deconvolution algorithms in addition we show how crfs can adversely affect psf estimation algorithms in the case of blind deconvolution to help counter these effects we introduce two methods to estimate the crf directly from one or more blurred images when the psf is known or unknown our experimental results on synthetic and real images validate our analysis and demonstrate the robustness and accuracy of our approaches

an analytical constant modulus algorithm iterative constant modulus algorithms such as godard 1980 and cma have been used to blindly separate a superposition of cochannel constant modulus cm signals impinging on an antenna array these algorithms have certain deficiencies in the context of convergence to local minima and the retrieval of all individual cm signals that are present in the channel we show that the underlying constant modulus factorization problem is in fact a generalized eigenvalue problem and may be solved via a simultaneous diagonalization of a set of matrices with this new analytical approach it is possible to detect the number of cm signals present in the channel and to retrieve all of them exactly rejecting other non cm signals only a modest amount of samples is required the algorithm is robust in the presence of noise and is tested on measured data collected from an experimental set up

convergence of the viscosity method for isentropic gas dynamics a convergence theorem for the method of artificial viscosity applied to the isentropic equations of gas dynamics is established convergence of a subsequence in the strong topology is proved without uniform estimates on the derivatives using the theory of compensated compactness and an analysis of progressing entropy waves

l1 convergence rates to the barenblatt solution for the damped compressible euler equations abstract in our previous work 17 it is shown that any l weak entropy solution of damped compressible euler equation converges to the barrenblatt s solution with finite mass in l 1 norm with a convergence rate for 1 3 in this paper by introducing an elaborate iterative method and using the intensive entropy analysis we prove the l 1 convergence to the barrenblatt s solution for any large 3 furthermore we get better l 1 convergence rate for 2 3

the bipolar hydrodynamic model for semiconductors and the drift diffusion equations we establish the existence of entropy solutions for a bipolar hydrodynamic model for semiconductors we show also that the limit as the relaxation time goes to zero of an appropriate scaled sequence of entropy solutions is a solution of the classical drift diffusion equations

oscillations and concentrations in weak solutions of the incompressible fluid equations the authors introduce a new concept of measure valued solution for the 3 d incompressible euler equations in order to incorporate the complex phenomena present in limits of approximate solutions of these equations one application of the concepts developed here is the following important result a sequence of leray hopf weak solutions of the navier stokes equations converges in the high reynolds number limit to a measure valued solution of 3 d euler defined for all positive times the authors present several explicit examples of solution sequences for 3 d incompressible euler with uniformly bounded local kinetic energy which exhibit complex phenomena involving both persistence of oscillations and development of concentrations an extensions of the concept of young measure is developed to incorporate these complex phenomena in the measure valued solutions constructed here

diffusive relaxation limit of classical solutions to the damped compressible euler equations abstract we construct uniform global classical solutions to the damped compressible euler equations on the framework of general besov spaces which includes both the usual sobolev spaces h s r d s 1 d 2 and the critical besov space b 2 1 1 d 2 r d such extension heavily depends on a revision of commutator estimates and an elementary fact that indicates the connection between homogeneous and inhomogeneous chemin lerner spaces furthermore we obtain the diffusive relaxation limit of euler equations towards the porous medium equation by means of aubin lions compactness argument

large time behavior of solutions for compressible euler equations with damping in r 3 we consider the long time behavior and optimal decay rates of global strong solutions for the isentropic compressible euler equations with damping in r3 in the present paper when the regular initial data belong to some sobolev space hl r3 b 1 s r3 with l 4 and s 0 1 we show that the density of the system converges to its equilibrium state at the rates 1 t 34 s2 in the l2 norm or 1 t 32 s2 in the l norm respectively the momentum of the system decays at the rates 1 t 54 s2 in the l2 norm or 1 t 2 s2 in the l norm respectively which are shown to be optimal for the compressible euler equations with damping

zero relaxation time limits to a hydrodynamic model of two carrier types for semiconductors in this paper we study the zero relaxation time limits to a one dimensional hydrodynamic model of two carrier types for semiconductors first we introduce the flux approximation coupled with the classical viscosity method to obtain the uniform l loc p p ge 1 bound of the approximation solutions rho i varepsilon delta and other estimates of u i varepsilon delta e varepsilon delta with the help of the high energy estimates jungel and peng comm partial differ equ 58 1007 1033 1999 then we apply the compensated compactness method coupled with the scaled variables technique marcati and natalini arch ration mech anal 129 129 145 1995 to prove the zero relaxation time limits with arbitrarily large initial data and arbitrary adiabatic exponents gamma i 1

upwinding of the source term at interfaces for euler equations with high friction we consider euler equations with a friction term that describe an isentropic gas flow in a porous domain more precisely we consider the transition between low and high friction regions in the high friction region the system is reduced to a parabolic equation the porous media equation in this paper we present a hyperbolic approach based on a finite volume technique to compute numerical solutions for the system in both regimes the upwind source at interfaces usi scheme that we propose satisfies the following properties firstly it preserves the nonnegativity of gas density secondly and this is the motivation the scheme is asymptotically consistent with the limit model porous media equation when the friction coefficient goes to infinity we show analytically and through numerical results that the above properties are satisfied we shall also compare results given with the use of usi hyperbolic parabolic coupling and classical centered sources schemes

numerical schemes for hyperbolic systems of conservation laws with stiff diffusive relaxation hyperbolic systems of conservation laws often have diffusive relaxation terms that lead to a small relaxation limit governed by reduced systems of a parabolic or hyperbolic type in such systems the understanding of basic wave pattern is difficult to achieve and standard high resolution methods fail to describe the right asymptotic behavior unless the small relaxation rate is numerically resolved we develop high resolution underresolved numerical schemes that possess the discrete analogue of the continuous asymptotic limit which are thus able to approximate the equilibrium system with high order accuracy even if the limiting equations may change type

a spectral bundle method for semidefinite programming a central drawback of primal dual interior point methods for semidefinite programs is their lack of ability to exploit problem structure in cost and coefficient matrices this restricts applicability to problems of small dimension typically semidefinite relaxations arising in combinatorial applications have sparse and well structured cost and coefficient matrices of huge order we present a method that allows us to compute acceptable approximations to the optimal solution of large problems within reasonable time semidefinite programming problems with constant trace on the primal feasible set are equivalent to eigenvalue optimization problems these are convex nonsmooth programming problems and can be solved by bundle methods we propose replacing the traditional polyhedral cutting plane model constructed from subgradient information by a semidefinite model that is tailored to eigenvalue problems convergence follows from the traditional approach but a proof is included for completeness we present numerical examples demonstrating the efficiency of the approach on combinatorial examples

length and cost dependent local minima of unconstrained blind channel equalizers baud rate linear blind equalizers may converge to undesirable stable equilibria due to different mechanisms one such mechanism is the use of linear fir filters as equalizers it is shown that this type of local minima exist for all unconstrained blind equalizers whose cost functions satisfy two general conditions the local minima generated by this mechanism are thus called length dependent local minima another mechanism is generated by the cost function adopted by the blind algorithm itself this type of local minima are called cost dependent local minima it is shown that several well designed algorithms do not have cost dependent local minimum whereas other algorithms such as the decision directed equalizer and the stop and go algorithm sga do unlike many existing convergence analysis the convergence of the godard 1980 algorithms gas and standard cumulant algorithms scas under gaussian noise is also presented computer simulations are used to verify the analytical results

pointwise estimates and lp convergence rates to diffusion waves for p system with damping abstract by introducing a new approximate green function we obtain the pointwise estimates on the solutions of euler equations with linear frictional damping from which we can deduce the optimal l p 1 p convergence rates to the nonlinear diffusion waves the pointwise estimates and l p 1 p convergence rates given in this paper are new

singularity formation for the 1d compressible euler equations with variable damping coefficient abstract in this paper we consider some blow up problems for the 1d euler equations with time and space dependent damping we investigate sufficient conditions on initial data and the rate of spatial or time like decay of the coefficient of damping for the occurrence of the finite time blow up in particular our sufficient conditions ensure that the derivative blow up occurs in finite time with the solution itself and the pressure bounded our method is based on simple estimates with riemann invariant furthermore we give sharp lower and upper estimates of the lifespan of solutions when initial data are small perturbations of constant states

convergence to equilibrium in wasserstein distance for damped euler equations with interaction forces we develop tools to construct lyapunov functionals on the space of probability measures in order to investigate the convergence to global equilibrium of a damped euler system under the influence of external and interaction potential forces with respect to the 2 wasserstein distance we also discuss the overdamped limit to a nonlocal equation used in the modelling of granular media with respect to the 2 wasserstein distance and provide rigorous proofs for particular examples in one spatial dimension

asymptotic preserving scheme for the shallow water equations with source terms on unstructured meshes the following work is devoted to the construction and validation of a numerical scheme for the 2d shallow water system on unstructured meshes supplemented by topography and friction source terms approximate solutions of frictionless flows are obtained considering a suitable formulation of the conservation laws involving the water free surface and some fractions of water accounting for the topography variations the discretization of the friction source terms relies on the use of a modified riemann solver for the flux computation the resulting scheme is then corrected in order to achieve an asymptotic regime preservation a muscl reconstruction is also performed to increase the space order of accuracy the overall numerical approach is shown to be consistent well balanced and to satisfy a domain invariant principle these results are assessed through several benchmark tests involving complex geometry and varying bathymetry in the presence of dry areas special interest is given to the wave front speed computation highlighting the stability of the method even when implementing the asymptotic preserving correction

hyperbolic to parabolic relaxation theory for quasilinear first order systems abstract in this paper we study the limiting behavior of nonhomogeneous hyperbolic systems of balance laws when the relaxed equilibria are described by means of systems of parabolic type in particular we obtain a complete theory for the 2 2 systems of genuinely nonlinear hyperbolic balance laws in 1 d with a strong dissipative term a different method which combines the div curl lemma with accretive operators is then applied to study the limiting profiles in the case of nonhomogeneous isentropic gas dynamics we also investigate relaxation results for some 2 d cases which include the cattaneo model for nonlinear heat conduction and the compressible euler flow moreover convergence result is also obtained for general semilinear systems in 1 d

uniform global existence and parabolic limit for partially dissipative hyperbolic systems abstract this work concerns smooth solutions to the cauchy problem for first order partially dissipative hyperbolic systems with a small parameter the systems are written in non conservative form in several space variables we introduce algebraic conditions on the structure of the systems under these conditions together with a partial dissipation condition and the shizuta kawashima stability condition we prove three main results around constant equilibrium states these results are uniform global existence with respect to the parameter global in time convergence of the systems to second order nonlinear parabolic systems in a slow time variable and global existence when the parameter is fixed we also give examples of physical models to which the above results can be applied

reduced hausdorff dimension and concentration cancellation for two dimensional incompressible flow where v t v1 v2 is the fluid velocity p is the scalar pressure dv dt av at v v v and vo is an initial incompressible velocity field i e div vo 0 in this paper we study the detailed limiting behavior of approximate solution sequences for 2 d euler with vortex sheet initial data a sequence of smooth velocity fields v8 x t is an approximate solution sequence for 2 d euler provided that v is incompressible i e div v 0 and satisfies the following properties 1 the velocity fields v6 have uniformly bounded local kinetic energy i e

weak solutions to a hydrodynamic model for semiconductors and relaxation to the drift diffusion equation we investigate the relaxation problem for the hydrodynamic isentropic euler poisson system when the momentum relaxation time tends to zero very sharp estimates on the solutions independent of the relaxation time are obtained and used to establish compactness

non linear diffusions as limit of kinetic equations with relaxation collision kernels kinetic transport equations with a given confining potential and non linear relaxation type collision operators are considered general monotone energy dependent equilibrium distributions are allowed with a chemical potential ensuring mass conservation existence and uniqueness of solutions is proved for initial data bounded by equilibrium distributions the diffusive macroscopic limit is carried out using compensated compactness theory the results are drift diffusion equations with non linear diffusion the most notable examples are of the form partial t rho nabla cdot nabla rho m rho nabla v ranging from porous medium equations to fast diffusion with the exponent satisfying 0 m 5 3 in mathbb r 3

convergence to the barenblatt solution for the compressible euler equations with damping and vacuum we study the asymptotic behavior of a compressible isentropic flow through a porous medium when the initial mass is finite the model system is the compressible euler equation with frictional damping as t the density is conjectured to obey the well known porous medium equation and the momentum is expected to be formulated by darcy s law in this paper we give a definite answer to this conjecture without any assumption on smallness or regularity for the initial data we prove that any l weak entropy solution to the cauchy problem of damped euler equations with finite initial mass converges strongly in lp with decay rates to matching barenblatt s profile of the porous medium equation the density function tends to the barenblatt s solution of the porous medium equation while the momentum is described by darcy s law

global existence and large time behavior for the system of compressible adiabatic flow through porous media in r 3 abstract the system of compressible adiabatic flow through porous media is considered in r 3 in the present paper the global existence and uniqueness of classical solutions are obtained when the initial data is near its equilibrium we also show that the pressure of the system converges to its equilibrium state at the same l 2 rate 1 t 3 4 as the navier stokes equations without heat conductivity but the velocity of the system decays at the l 2 rate 1 t 5 4 which is faster than the l 2 rate 1 t 3 4 for the navier stokes equations without heat conductivity duan and ma 2008 3

asymptotic behavior of the solutions to the damped compressible euler equations with vacuum abstract the asymptotic behavior of solutions of the damped compressible euler equations is conjectured to obey to the famous porous media equations pmes the previous works on this topic concern the case away from vacuum where the system is strictly hyperbolic in present paper we prove that the l entropy weak solution with vacuum obtained by the compensated compactness theory converges strongly in l loc p 1 p space to the unique similarity solution of the related pme as time goes to infinity

solving large scale sparse semidefinite programs for combinatorial optimization we present a dual scaling interior point algorithm and show how it exploits the structure and sparsity of some large scale problems we solve the positive semidefinite relaxation of combinatorial and quadratic optimization problems subject to boolean constraints we report the first computational results of interior point algorithms for approximating maximum cut semidefinite programs with dimension up to 3 000

analytical method for blind binary signal separation the blind separation of multiple co channel binary digital signals using an antenna array involves finding a factorization of a data matrix x into x as where all entries of s are 1 or 1 it is shown that this problem can be solved exactly and noniteratively via a certain generalized eigenvalue decomposition as indicated by simulations the algorithm is robust in the presence of noise an interesting implication is that certain cluster segmentation problems can be solved using eigenvalue techniques

long time existence and singular perturbation results for quasilinear hyperbolic equations with small parameter and dissipation term iii on considere des solutions lisses du probleme aux valeurs initiales hyperbolique quasilineaire eu tt u t ij 1 n a ij i j u 0 u 0 u 0 u t 0 u 1 ou e 0 0 u u x t r x r n on etudie l existence de solutions globales correspondant a des donnees arbitrairement grandes initiales u 0 et u 1 et a leur convergence quand e 0 vers la solution du probleme parabolique correspondant

an admissibility and asymptotic preserving scheme for systems of conservation laws with source term on 2d unstructured meshes the objective of this work is to design explicit finite volumes schemes for specific systems of conservations laws with stiff source terms which degenerate into diffusion equations we propose a general framework to design an asymptotic preserving scheme that is stable and consistent under a classical hyperbolic cfl condition in both hyperbolic and diffusive regime for any two dimensional unstructured mesh moreover the scheme developed also preserves the set of admissible states which is mandatory to keep physical solutions in stiff configurations this construction is achieved by using a non linear scheme as a target scheme for the diffusive equation which gives the form of the global scheme for the complete system of conservation laws numerical results are provided to validate the scheme in both regimes

space localization and well balanced schemes for discrete kinetic models in diffusive regimes we derive and study well balanced schemes for quasi monotone discrete kinetic models by means of a rigorous localization procedure we reformulate the collision terms as nonconservative products and solve the resulting riemann problem whose solution is self similar the construction of an asymptotic preserving ap godunov scheme is straightforward and various compactness properties are established within different scalings finally some computational results are supplied to show that this approach is realizable and efficient on concrete 2 2 models

an analysis of constant modulus receivers this paper investigates connections between non blind wiener receivers and blind receivers designed by minimizing the constant modulus cm cost applicable to both t spaced and fractionally spaced fir equalization the main results include 1 a test for the existence of cm local minima near wiener receivers 2 an analytical description of cm receivers in the neighborhood of wiener receivers 3 mean square error mse bounds for cm receivers when the channel matrix is invertible we also show that the cm receiver is approximately colinear with the wiener receiver and provide a quantitative measure of the size of neighborhoods that contain the cm receivers and the accuracy of the mse bounds

half space problem of the system of compressible adiabatic flow through porous media in multi d abstract in this paper we consider the half space problem for the system of compressible adiabatic flow through porous media in 2 d and 3 d combining energy method green s function method and bootstrap method one establishes the decaying energy estimates which lead to global existence and optimal l 2 decaying rate of the solution finally for more large time information especially in spatial variables one applies green s function solution representation obtained by duhamel s principle and a priori estimate from energy method to obtain the space time pointwise structure of the solution

new criteria for blind deconvolution of nonminimum phase systems channels a necessary and sufficient condition for blind deconvolution without observing the input of nonminimum phase linear time invariant systems channels is derived based on this condition several optimization criteria are proposed and their solution is shown to correspond to the desired response these criteria involve the computation only of second and fourth order moments implying a simple tap update procedure the proposed methods are universal in the sense that they do not impose any restrictions on the probability distribution of the unobserved input sequence it is shown that in several important cases e g when the additive noise is gaussian the proposed criteria are essentially unaffected

global and blow up solutions for compressible euler equations with time dependent damping abstract this paper deals with the cauchy problem for the compressible euler equations with time dependent damping where the time vanishing damping in the form of 1 t makes some fantastic variety of the dynamic system for 0 1 and 0 or 1 but 2 the solutions are proved to exist globally in time when the derivatives of the initial data are small but the initial data themselves can be arbitrarily large this is the so called challenging case of global solutions with large initial data while when the initial riemann invariants are monotonic and their derivatives with absolute value are large at least at one point then the solutions are still bounded but their derivatives will blow up at finite time somewhat like the singularity formed by shock waves for 1 and 0 or 1 but 0 1 the derivatives of solutions will blow up even for all initial data including the interesting case of blow up solutions with small initial data here the initial riemann invariants are monotonic in fact such a blow up phenomenon is determined by the mechanism of the dynamic system itself in order to prove the global existence of solutions with large initial data we introduce a new energy functional related to the riemann invariants which crucially enables us to build up the maximum principle for the corresponding riemann invariants and the uniform boundedness for the local solutions finally numerical simulations in different cases are carried out which further confirm our theoretical results

non monotonic traveling wave and computational solutions for gas dynamics euler equations with stiff relaxation source terms abstract we study the existence of non monotone traveling wave solutions and its properties for an isothermal euler system with relaxation describing the perfect gas flow in order to confront our results we first apply a mollification approach as an effective regularization method for solving an ill posed problem for an associated reduced system for the euler model under consideration which in turn is solved by using the method of characteristics next we developed a cheap unsplitting finite volume scheme that reproduces the same traveling wave asymptotic structure as that of the euler solutions of the continuous system at the discrete level the method is conservative by construction and relatively easy to understand and implement although we do not have a mathematical proof that our designed scheme enjoys the asymptotic preserving and well balanced properties we were able to reproduce consistent solutions for the more general euler equations with gravity and friction recently published in the specialized literature which in turn are procedures based on a godunov type scheme and based on an asymptotic preserving scheme yielding good verification and performance to our method

blind separation of synchronous co channel digital signals using an antenna array i algorithms we propose a maximum likelihood ml approach for separating and estimating multiple synchronous digital signals arriving at an antenna array at a cell site the spatial response of the array is assumed to be known imprecisely or unknown we exploit the finite alphabet property of digital signals to simultaneously estimate the array response and the symbol sequence for each signal uniqueness of the estimates is established for bpsk signals we introduce a signal detection technique based on the finite alphabet property that is different from a standard linear combiner computationally efficient algorithms for both block and recursive estimation of the signals are presented this new approach is applicable to an unknown array geometry and propagation environment which is particularly useful in wireless communication systems simulation results demonstrate its promising performance

fractionally spaced equalization using cma robustness to channel noise and lack of disparity in the noise free case the fractionally spaced equalization using constant modulus fse cm criterion has been studied previously its minima were shown to achieve perfect equalization when zero forcing zf conditions are satisfied and to be able to still achieve fair equalization when there is lack of disparity however to our best knowledge the effect of additive channel noise on the fse cm cost function minima has not been studied in this paper we show that the noisy fse cm cost function is subject to a smoothing effect with respect to the noise free cost function the result of which is a tradeoff between achieving zero forcing and noise enhancement furthermore we give an analytical closed form expression for the loss of performance due to the noise in terms of input output mean square error mse under the zf conditions the fse cm mse is shown to be mostly due to output noise enhancement and not to residual intersymbol interference isi when there is lack of disparity an irreducible amount of isi appears independently of the algorithm it is the lower equalizability bound for given channel conditions and equalizer length the so called minimum mse mmse the mmse lower bound is the sum of the mmse and of additional mse mostly due to noise enhancement finally we compare the fse cm mse to this lower bound

convergence of singular limits for multi d semilinear hyperbolic systems to parabolic systems in this paper we investigate the diffusive zero relaxation limit of the following multi d semilinear hyperbolic system in pseudodifferential form w t x t 1 ea x d w x t 1 e 2 b x w x t 1 e d w x t e w x t we analyze the singular convergence as e 0 in the case which leads to a limit system of parabolic type the analysis is carried out by using the following steps i we single out algebraic structure conditions on the full system motivated by formal asymptotics by some examples of discrete velocity models in kinetic theories ii we deduce energy estimates uniformly in e by assuming the existence of a symmetrizer having the so called block structure and by assuming dissipativity conditions on b iii we assume a kawashima type condition and perform the convergence analysis by using generalizations of compensated compactness due to tartar and gerard finally we include examples that show how to use our theory to approximate any quasilinear parabolic systems satisfying the petrowski parabolicity condition or general reaction diffusion systems including chemotaxis and brusselator type systems