accurate projection methods for the incompressible navier stokes equations abstract this paper considers the accuracy of projection method approximations to the initial boundary value problem for the incompressible navier stokes equations the issue of how to correctly specify numerical boundary conditions for these methods has been outstanding since the birth of the second order methodology a decade and a half ago it has been observed that while the velocity can be reliably computed to second order accuracy in time and space the pressure is typically only first order accurate in the l norm this paper identifies the source of this problem in the interplay of the global pressure update formula with the numerical boundary conditions and presents an improved projection algorithm which is fully second order accurate as demonstrated by a normal mode analysis and numerical experiments in addition a numerical method based on a gauge variable formulation of the incompressible navier stokes equations which provides another option for obtaining fully second order convergence in both velocity and pressure is discussed the connection between the boundary conditions for projection methods and the gauge method is explained in detail

the timoshenko system with history and cattaneo law in this paper we study a fully hyperbolic thermoelastic timoshenko system with past history where the thermal effects are given by cattaneo s law we obtain exponential stability of solutions if and only if a new condition on the wave speed of propagation is verified otherwise when that condition fails we obtain polynomial stability of solutions in this case optimal rates of decay are established

a new class of truly consistent splitting schemes for incompressible flows a new class of splitting schemes for incompressible flows is introduced the new schemes are based on a weak form of the pressure poisson equation and at each time step only require to solve a set of helmholtz type equations for the velocity and a poisson equation in the weak form for the pressure just as pressure correction and velocity correction schemes however unlike pressure correction and velocity correction schemes the new splitting schemes are free of splitting errors and deliver full accuracy on the vorticity and the pressure

energy decay for timoshenko systems of memory type abstract linear systems of timoshenko type equations for beams including a memory term are studied the exponential decay is proved for exponential kernels while polynomial kernels are shown to lead to a polynomial decay the optimality of the results is also investigated

application of a fractional step method to incompressible navier stokes equations a numerical method for computing three dimensional time dependent incompressible flows is presented the method is based on a fractional step or time splitting scheme in conjunction with the approximate factorization technique it is shown that the use of velocity boundary conditions for the intermediate velocity field can lead to inconsistent numerical solutions appropriate boundary conditions for the intermediate velocity field are derived and tested numerical solutions for flows inside a driven cavity and over a backward facing step are presented and compared with experimental data and other numerical results

stable and accurate pressure approximation for unsteady incompressible viscous flow how to properly specify boundary conditions for pressure is a longstanding problem for the incompressible navier stokes equations with no slip boundary conditions an analytical resolution of this issue stems from a recently developed formula for the pressure in terms of the commutator of the laplacian and leray projection operators here we make use of this formula to a improve the accuracy of computing pressure in two kinds of existing time discrete projection methods implicit in viscosity only and b devise new higher order accurate time discrete projection methods that extend a slip correction idea behind the well known finite difference scheme of kim and moin we test these schemes for stability and accuracy using various combinations of c 0 finite elements for all three kinds of time discretization one can obtain third order accuracy for both pressure and velocity without a time step stability restriction of diffusive type furthermore two kinds of projection methods are found stable using piecewise linear elements for both velocity and pressure

long time numerical solution of the navier stokes equations based on a sequential regularization formulation the sequential regularization method is a reformulation of the unsteady navier stokes equations from the viewpoint of constrained dynamical systems or the approximate helmholtz hodge projection in this paper we study the long time behavior of the sequential regularization formulation we give a uniform in time estimate between the solution of the reformulated system and that of the navier stokes equations we also conduct an error analysis for the temporal discrete system and show that the error bound is independent of time a couple of long time flow examples are computed to demonstrate this method

diffusion on multifractals abstract we introduce a class of random fields with variable mean square regularity order defined on multifractal domains the local singularity order of these random fields then depends on the initial variable mean square regularity order and on the variable local singularity exponent of the multifractal measure defining the local dimension of the domain considered the theory is developed in a generalized framework through the covariance factorization using the tools of reproducing kernel hilbert spaces and fractional sobolev spaces of variable order

open and traction boundary conditions for the incompressible navier stokes equations we present numerical schemes for the incompressible navier stokes equations nse with open and traction boundary conditions we use pressure poisson equation ppe formulation and propose new boundary conditions for the pressure on the open or traction boundaries after replacing the divergence free constraint by this pressure poisson equation we obtain an unconstrained nse for stokes equation with open boundary condition on a simple domain we prove unconditional stability of a first order semi implicit scheme where the pressure is treated explicitly and hence is decoupled from the computation of velocity using either boundary condition the schemes for the full nse that treat both convection and pressure terms explicitly work well with various spatial discretizations including spectral collocation and c 0 finite elements moreover when reynolds number is of o 1 and when the first order semi implicit time stepping is used time step size of o 1 is allowed in benchmark computations for the full nse besides standard stability and accuracy check various numerical results including flow over a backward facing step flow past a cylinder and flow in a bifurcated tube are reported numerically we have observed that using ppe formulation enables us to use the velocity pressure pairs that do not satisfy the standard inf sup compatibility condition our results extend that of johnston and liu h johnston j g liu accurate stable and efficient navier stokes solvers based on explicit treatment of the pressure term j comp phys 199 1 2004 221 259 which deals with no slip boundary conditions only

dynamical model for dna sequences we address the problem of dna sequences developing a dynamical method based on the assumption that the statistical properties of dna paths are determined by the joint action of two processes one deterministic with long range correlations and the other random and ensuremath delta function correlated the generator of the deterministic evolution is a nonlinear map belonging to a class of maps recently tailored to mimic the processes of weak chaos that are responsible for the birth of anomalous diffusion it is assumed that the deterministic process corresponds to unknown biological rules that determine the dna path whereas the noise mimics the influence of an infinite dimensional environment on the biological process under study we prove that the resulting diffusion process if the effect of the random process is neglected is an ensuremath alpha stable l evy process with 12 we also show that if the diffusion process is determined by the joint action of the deterministic and the random process the correlation effects of the deterministic dynamics are cancelled on the short range scale but show up in the long range one we denote our prescription to generate statistical sequences as the copying mistake map cmm we carry out our analysis of several dna sequences and their cmm realizations with a variety of techniques and we especially focus on a method of regression to equilibrium which we call the onsager analysis with these techniques we establish the statistical equivalence of the real dna sequences with their cmm realizations we show that long range correlations are present in exons as well as in introns but are difficult to detect since the exon dynamics is shown to be determined by the entanglement of three distinct and independent cmm s

multifractal characterization of complete genomes this paper develops a theory for characterization of dna sequences based on their measure representation the measures are shown to be random cascades generated by an infinitely divisible distribution this probability distribution is uniquely determined by the exponent function in the multifractal theory of random cascades curve fitting to a large number of complete genomes of bacteria indicates that the gamma density function provides an excellent fit to the exponent function and hence to the probability distribution of the complete genomes

boundary control of the timoshenko beam it is shown that the timoshenko beam can be uniformly stabilized by means of a boundary control a numerical study on the spectrum is also presented

trace theorems for three dimensional time dependent solenoidal vector fields and their applications we study trace theorems for three dimensional time dependent solenoidal vector fields the interior function spaces we consider are natural for solving unsteady boundary value problems for the navier stokes system and other systems of partial differential equations we describe the space of restrictions of such vector fields to the boundary of the space time cylinder and construct extension operators from this space of restrictions defined on the boundary into the interior only for two exceptional but useful values of the spatial smoothness index the spaces for which we construct extension operators is narrower than the spaces in which we seek restrictions the trace spaces are characterized by vector fields having different smoothnesses in directions tangential and normal to the boundary this is a consequence of the solenoidal nature of the fields these results are fundamental in the study of inhomogeneous boundary value problems for systems involving solenoidal vector fields in particular we use the trace theorems in a study of inhomogeneous boundary value problems for the navier stokes system of viscous incompressible flows

a pressure correction scheme for generalized form of energy stable open boundary conditions for incompressible flows we present a generalized form of open boundary conditions and an associated numerical algorithm for simulating incompressible flows involving open or outflow boundaries the generalized form represents a family of open boundary conditions which all ensure the energy stability of the system even in situations where strong vortices or backflows occur at the open outflow boundaries our numerical algorithm for treating these open boundary conditions is based on a rotational pressure correction type strategy with a formulation suitable for c 0 spectral element spatial discretizations we have introduced a discrete equation and associated boundary conditions for an auxiliary variable the algorithm contains constructions that prevent a numerical locking at the open outflow boundary in addition we have developed a scheme with a provable unconditional stability for a sub class of the open boundary conditions extensive numerical experiments have been presented to demonstrate the performance of our method for several flow problems involving open outflow boundaries we compare simulation results with the experimental data to demonstrate the accuracy of our algorithm long time simulations have been performed for a range of reynolds numbers at which strong vortices or backflows occur at the open outflow boundaries we show that the open boundary conditions and the numerical algorithm developed herein produce stable simulations in such situations

on pressure approximation via projection methods for nonstationary incompressible navier stokes equations projection methods are an efficient tool to approximate strong solutions of the incompressible navier stokes equations as a major deficiency these methods often suffer from reduced accuracy for pressure iterates caused by nonphysical boundary data going along with suboptimal error estimates for pressure iterates we verify a rigorous bound for arising boundary layers in chorin s scheme under realistic regularity assumptions in a second step the new chorin penalty method is proposed where optimal rate of convergence for pressure iterates is shown

the stability number of the timoshenko system with second sound abstract in this work we consider the timoshenko beam model with second sound we introduce a new number 0 that characterizes the exponential decay we prove that the corresponding semigroup associated to the system is exponentially stable if and only if 0 0 otherwise there is a lack of exponential stability in this case we prove that the semigroup decays as t 1 2 moreover we show that the rate is optimal

multifractal analysis and topological properties of a new family of weighted koch networks abstract weighted complex networks especially scale free networks which characterize real life systems better than non weighted networks have attracted considerable interest in recent years studies on the multifractality of weighted complex networks are still to be undertaken in this paper inspired by the concepts of koch networks and koch island we propose a new family of weighted koch networks and investigate their multifractal behavior and topological properties we find some key topological properties of the new networks their vertex cumulative strength has a power law distribution there is a power law relationship between their topological degree and weight strength the networks have a high weighted clustering coefficient of 0 41004 which is independent of the scaling factor c in the limit of large generation t the second smallest eigenvalue 2 and the maximum eigenvalue n are approximated by quartic polynomials of the scaling factor c for the general laplacian operator while 2 is approximately a quartic polynomial of c and n 1 5 for the normalized laplacian operator then we find that weighted koch networks are both fractal and multifractal their fractal dimension is influenced by the scaling factor c we also apply these analyses to six real world networks and find that the multifractality in three of them are strong

recognition of an organism from fragments of its complete genome this paper considers the problem of matching a fragment to an organism using its complete genome our method is based on the probability measure representation of a genome we first demonstrate that these probability measures can be modeled as recurrent iterated function systems rifs consisting of four contractive similarities our hypothesis is that the multifractal characteristics of the probability measure of a complete genome as captured by the rifs is preserved in its reasonably long fragments we compute the rifs of fragments of various lengths and random starting points and compare with that of the original sequence for recognition using the euclidean distance a demonstration on five randomly selected organisms supports the above hypothesis

a taxonomy of consistently stabilized finite element methods for the stokes problem stabilized mixed methods can circumvent the restrictive inf sup condition without introducing penalty errors for properly chosen stabilization parameters these methods are well posed for all conforming velocity pressure pairs however their variational forms have widely varying properties first stabilization offers a choice between weakly or strongly coercive bilinear forms that give rise to linear systems with identical solutions but very different matrix properties second coercivity may be conditional upon a proper choice of a stabilizing parameter here we focus on how these two aspects of stabilized methods affect their accuracy and efficient iterative solution we present results that indicate a preference of krylov subspace solvers for strongly coercive formulations stability criteria obtained by finite element and algebraic analyses are compared with numerical experiments while for two popular classes of stabilized methods sufficient stability bounds correlate well with numerical stability our experiments indicate the intriguing possibility that the pressure stabilized galerkin method is unconditionally stable

a split step finite element method for incompressible navier stokes equations with high order accuracy up to the boundary abstract an efficient and accurate finite element algorithm is described for the numerical solution of the incompressible navier stokes ins equations the new algorithm that solves the ins equations in a velocity pressure reformulation is based on a split step scheme in conjunction with the standard finite element method the split step scheme employed for the temporal discretization of our algorithm completely separates the pressure updates from the solution of velocity variables when the pressure equation is formed explicitly the algorithm avoids solving a saddle point problem therefore our algorithm has more flexibility in choosing finite element spaces in contrast popular mixed finite element methods that solve the ins equations in the primitive variables or velocity divergence formulation lead to discrete saddle point problems whose solution depends on the choice of finite element spaces for velocity and pressure that is subject to the well known ladyzenskaja babuska brezzi lbb or inf sup condition for efficiency and robustness lagrange piecewise polynomial finite elements of equal order for both velocity and pressure are used accurate numerical boundary condition for the pressure equation is also investigated motivated by a post processing technique that calculates derivatives of a finite element solution with super convergent error estimates an alternative numerical boundary condition is proposed for the pressure equation at the discrete level the new numerical pressure boundary condition that can be regarded as a better implementation of the compatibility boundary condition improves the boundary layer errors of the pressure solution a normal mode analysis is performed using a simplified model problem on a uniform mesh to demonstrate the numerical properties of our methods convergence studies using p 1 elements support the analytical results and demonstrates that our algorithm with the new numerical boundary condition achieves the optimal second order accuracy for both velocity and pressure up to the boundary benchmark problems are also computed and carefully compared with existing studies finally as an example to illustrate that our approach can be easily adapted for higher order finite elements we solve the classical flow past a cylinder problem using p n finite elements with n 1

an energy stable scheme for incompressible navier stokes equations with periodically updated coefficient matrix abstract we present an energy stable scheme for simulating the incompressible navier stokes equations based on the generalized positive auxiliary variable gpav framework in the gpav reformulated system the original nonlinear term is replaced by a linear term plus a correction term where the correction term is put under control by an auxiliary variable the proposed scheme incorporates a pressure correction type strategy into the gpav procedure and it satisfies a discrete energy stability property the scheme entails the computation of two copies of the velocity and pressure within a time step by solving an individual de coupled linear equation for each of these field variables upon discretization the pressure linear system involves a constant coefficient matrix that can be pre computed while the velocity linear system involves a coefficient matrix that is updated periodically once every k 0 time steps in the current work where k 0 is a user specified integer the auxiliary variable being a scalar valued number is computed by a well defined explicit formula which guarantees the positivity of its computed values it is observed that the current method can produce accurate simulation results at large or fairly large time step sizes for the incompressible navier stokes equations the impact of the periodic coefficient matrix update on the overall cost of the method is observed to be small in typical numerical simulations several flow problems have been simulated to demonstrate the accuracy and performance of the method developed herein

a compatible high order meshless method for the stokes equations with applications to suspension flows abstract a stable numerical solution of the steady stokes problem requires compatibility between the choice of velocity and pressure approximation that has traditionally proven problematic for meshless methods in this work we present a discretization that couples a staggered scheme for pressure approximation with a divergence free velocity reconstruction to obtain an adaptive high order finite difference like discretization that can be efficiently solved with conventional algebraic multigrid techniques we use analytic benchmarks to demonstrate equal order convergence for both velocity and pressure when solving problems with curvilinear geometries in order to study problems in dense suspensions we couple the solution for the flow to the equations of motion for freely suspended particles in an implicit monolithic scheme the combination of high order accuracy with fully implicit schemes allows the accurate resolution of stiff lubrication forces directly from the solution of the stokes problem without the need to introduce sub grid lubrication models

multifractality in time series we apply the concepts of multifractal physics to financial time series in order to characterize the onset of crash for the standard poor 500 s p500 stock index x t it is found that within the framework of multifractality the analogous specific heat of the s p500 discrete price index displays a shoulder to the right of the main peak for low time lag values for decreasing t the presence of the shoulder is a consequence of the peaked temporal x t t x t fluctuations in this regime for large time lags t 80 we have found that cq displays typical features of a classical phase transition at a critical point an example of such dynamic phase transition in a simple economic model system based on a mapping with multifractality phenomena in random multiplicative processes is also presented by applying former results obtained with a continuous probability theory for describing scaling measures

stability of pressure boundary conditions for stokes and navier stokes equations abstract the stability of a finite difference discretization of the time dependent incompressible navier stokes equations in velocity pressure formulation is studied in paticular we compare the stability for different pressure boundary conditions in a semiimplicit time integration scheme where only the viscous term is treated implicitly the stability is studied in three different ways by a normal mode analysis by numerical computation of the amplification factors and by direct numerical simulation of the governing equations all three approaches identify the same pressure boundary condition as the best alternative this condition implicitly enforces the normal derivative of the divergence to be zero on the boundary by coupling the normal derivative of the pressure to the normal component of the curl of the vorticity using this boundary condition we demonstrate that the time step is determined only by the convective term

coercivity and stability results for an extended navier stokes system in this paper we study a system of equations that is known to extend navier stokes dynamicsinawell posedmannertovelocityfieldsthatarenotnecessarilydivergencefree ouraimistocontributetoanunderstandingoftheroleofdivergenceandpressure in developing energy estimates capable of both controlling the nonlinear terms and being useful at the time discrete level we address questions of global existence and stability in bounded domains with no slip boundary conditions through use of new h 1 coercivity estimates for the linear equations we establish a number of global existence and stability results including results for small divergence and a timediscrete scheme we also prove global existence in 2d for any initial data provided sufficient divergence damping is included c 2012 american institute of physics

mildly dissipative nonlinear timoshenko systems global existence and exponential stability we consider nonlinear systems of timoshenko type in a one dimensional bounded domain the system has a dissipative mechanism being present only in the equation for the rotation angle it is a damping effect through heat conduction the global existence of small smooth solutions as well as the exponential stability are investigated

boundary stabilization of solutions of a nonlinear system of timoshenko type in this paper we are concerned with a multidimensional timoshenko system subjected to boundary conditions of memory type we establish general rate decay results the usual exponential and polynomial decay rates are only special cases

analysis of a sequential regularization method for the unsteady navier stokes equations the incompressibility constraint makes navier stokes equations difficult a reformulation to a better posed problem is needed before solving it numerically the sequential regularization method srm is a reformulation which combines the penalty method with a stabilization method in the context of constrained dynamical systems and has the benefit of both methods in the paper we study the existence and uniqueness for the solution of the srm and provide a simple proof of the convergence of the solution of the srm to the solution of the navier stokes equations we also give error estimates for the time discretized srm formulation

stability and convergence of efficient navier stokes solvers via a commutator estimate for strong solutions of the incompressible navier stokes equations in bounded domains with velocity specified at the boundary we establish the unconditional stability and convergence of discretization schemes that decouple the updates of pressure and velocity through explicit time stepping for pressure these schemes require no solution of stationary stokes systems nor any compatibility between velocity and pressure spaces to ensure an inf sup condition and are representative of a class of highly efficient computational methods that have recently emerged the proofs are simple based upon a new sharp estimate for the commutator of the laplacian and helmholtz projection operators this allows us to treat an unconstrained formulation of the navier stokes equations as a perturbed diffusion equation c 2006 wiley periodicals inc

an efficient numerical method for the equations of steady and unsteady flows of homogeneous incompressible newtonian fluid in the present paper we present some numerical methods to solve the equations of steady and unsteady flows such as those in the microcirculatory bed and large blood vessels arteries and veins respectively in the case of steady flows the method does not need neither any boundary conditions on pressure nor any small parameter and the main computation consists of solving some poisson equations in the case of unsteady flows the scheme uses a consistent neumann boundary condition for the pressure poisson equation at each time step a poisson and heat equation are solved for the pressure and each velocity component respectively the accuracy and efficiency of scheme are checked by a set of numerical tests

an unconditionally stable rotational velocity correction scheme for incompressible flows we present an unconditionally stable splitting scheme for incompressible navier stokes equations based on the rotational velocity correction formulation the main advantages of the scheme are i it allows the use of time step sizes considerably larger than the widely used semi implicit type schemes the time step size is only constrained by accuracy ii it does not require the velocity and pressure approximation spaces to satisfy the usual inf sup condition in particular the equal order finite element spectral element approximation spaces can be used iii it only requires solving a pressure poisson equation and a linear convection diffusion equation at each time step numerical tests indicate that the computational cost of the new scheme for each time step under identical time step sizes is even less expensive than the semi implicit scheme with low element orders therefore the total computational cost of the new scheme can be significantly less than the usual semi implicit scheme

iterated function systems and the global construction of fractals iterated function systems i f ss are introduced as a unified way of generating a broad class of fractals these fractals are often attractors for i f ss and occur as the supports of probability measures associated with functional equations the existence of certain p balanced measures for i f ss is established and these measures are uniquely characterized for hyperbolic i f ss the hausdorff besicovitch dimension for some attrac tors of hyperbolic i f ss is estimated with the aid of p balanced measures what appears to be the broadest framework for the exactly computable moment theory of p balanced measures that of linear i f ss and of probabilistic mixtures of iterated riemann surfaces is presented this extensively generalizes earlier work on orthogonal polynomials on julia sets an example is given of fractal reconstruction with the use of linear i f ss and moment theory

factorial moments analyses show a characteristic length scale in dna sequences a unique feature of most of the dna sequences found through the factorial moments analysis is the existence of a characteristic length scale around which the density distribution is nearly poissonian above this point the dna sequences irrespective of their intron contents show long range correlations with a significant deviation from the gaussian statistics while below this point the dna statistics are essentially gaussian the famous dna walk representation is also shown to be a special case of the present analysis

uniform decay in a timoshenko type system with past history abstract fernandez sare and rivera h d fernandez sare j e munoz rivera stability of timoshenko systems with past history j math anal appl 339 1 2008 482 502 considered the following timoshenko type system 1 t t k x x 0 2 t t b x x 0 g t x x t s d s k x 0 where g is a positive differentiable exponentially decaying function they established an exponential decay result in the case of equal wave speed propagation and a polynomial decay result in the case of nonequal wave speed propagation in this paper we study the same system for g decaying polynomially and prove polynomial stability results for the equal and nonequal wave speed propagation our results are established under conditions on the relaxation function weaker than those in h d fernandez sare j e munoz rivera stability of timoshenko systems with past history j math anal appl 339 1 2008 482 502

fractal analysis of measure representation of large proteins based on the detailed hp model abstract the notion of measure representation of protein sequences is introduced based on the detailed hp model multifractal analysis and detrended fluctuation analysis are then performed on the measure representations of a large number of long protein sequences it is concluded that these protein sequences are not completely random sequences through the measure representations and the values of the d q spectra and related c q curves the values of the exponent from the detrended fluctuation analysis show that the k strings with the ordering in the measure representation exhibit strong long range correlation for substrings with length k 5 the d q spectra of all proteins studied are multifractal like and sufficiently smooth for the c q curves to be meaningful the c q curves of all proteins resemble a classical phase transition at a critical point an ifs model is found to simulate the measure representation of protein sequences very well from the estimated values of parameters in the ifs model we think the non polar residues and uncharged polar residues play a more important role than other kinds of residues in the protein folding process

on the stability of damped timoshenko systems cattaneo versus fourier law we consider hyperbolic timoshenko type vibrating systems that are coupled to a heat equation modeling an expectedly dissipative effect through heat conduction while exponential stability under the fourier law of heat conduction holds it turns out that the coupling via the cattaneo law does not yield an exponentially stable system this seems to be the first example that a removal of the paradox of infinite propagation speed inherent in fourier s law by changing to the cattaneo law causes a loss of the exponential stability property actually for systems with history the fourier law keeps the exponential stability known for the pure timoshenko system without heat conduction but introducing the cattaneo coupling even destroys this property

long range correlation properties of coding and noncoding dna sequences genbank analysis an open question in computational molecular biology is whether long range correlations are present in both coding and noncoding dna or only in the latter to answer this question we consider all 33301 coding and all 29453 noncoding eukaryotic sequences each of length larger than 512 base pairs bp in the present release of the genbank to dtermine whether there is any statistically significant distinction in their long range correlation properties standard fast fourier transform fft analysis indicates that coding sequences have practically no correlations in the range from 10 bp to 100 bp spectral exponent beta 0 00 0 04 where the uncertainty is two standard deviations in contrast for noncoding sequences the average value of the spectral exponent beta is positive 0 16 0 05 which unambiguously shows the presence of long range correlations we also separately analyze the 874 coding and the 1157 noncoding sequences that have more than 4096 bp and find a larger region of power law behavior we calculate the probability that these two data sets coding and noncoding were drawn from the same distribution and we find that it is less than 10 10 we obtain independent confirmation of these findings using the method of detrended fluctuation analysis dfa which is designed to treat sequences with statistical heterogeneity such as dna s known mosaic structure patchiness arising from the nonstationarity of nucleotide concentration the near perfect agreement between the two independent analysis methods fft and dfa increases the confidence in the reliability of our conclusion

numerical approximation of incompressible navier stokes equations based on an auxiliary energy variable abstract we present a numerical scheme for approximating the incompressible navier stokes equations based on an auxiliary variable associated with the total system energy by introducing a dynamic equation for the auxiliary variable and reformulating the navier stokes equations into an equivalent system the scheme satisfies a discrete energy stability property in terms of a modified energy and it allows for an efficient solution algorithm and implementation within each time step the algorithm involves the computations of two pressure fields and two velocity fields by solving several de coupled individual linear algebraic systems with constant coefficient matrices together with the solution of a nonlinear algebraic equation about a scalar number involving a negligible cost a number of numerical experiments are presented to demonstrate the accuracy and the performance of the presented algorithm

accurate stable and efficient navier stokes solvers based on explicit treatment of the pressure term we present numerical schemes for the incompressible navier stokes equations based on a primitive variable formulation in which the incompressibility constraint has been replaced by a pressure poisson equation the pressure is treated explicitly in time completely decoupling the computation of the momentum and kinematic equations the result is a class of extremely efficient navier stokes solvers full time accuracy is achieved for all flow variables the key to the schemes is a neumann boundary condition for the pressure poisson equation which enforces the incompressibility condition for the velocity field irrespective of explicit or implicit time discretization of the viscous term in the momentum equation the explicit time discretization of the pressure term does not affect the time step constraint indeed we prove unconditional stability of the new formulation for the stokes equation with explicit treatment of the pressure term and first or second order implicit treatment of the viscous term systematic numerical experiments for the full navier stokes equations indicate that a second order implicit time discretization of the viscous term with the pressure and convective terms treated explicitly is stable under the standard cfl condition additionally various numerical examples are presented including both implicit and explicit time discretizations using spectral and finite difference spatial discretizations demonstrating the accuracy flexibility and efficiency of this class of schemes in particular a galerkin formulation is presented requiring only c0 elements to implement

multifractal measures and a weak separation condition abstract we define a new separation property on the family of contractive similitudes that allows certain overlappings this property is weaker than the open set condition of hutchinson it includes the well known class of infinite bernoulli convolutions associated with the p v numbers and the solutions of the two scale dilation equations our main purpose in this paper is to prove the multifractal formalism under such condition

order of convergence of splitting schemes for both deterministic and stochastic nonlinear schrodinger equations we first prove the second order convergence of the strang type splitting scheme for the nonlinear schrodinger equation the proof does not require commutator estimates but crucially relies on an integral representation of the scheme it reveals the connection between strang type splitting and the midpoint rule we then show that the integral representation idea can also be used to study the stochastic nonlinear schrodinger equation with multiplicative noise of stratonovich type even though the nonlinear term there is not globally lipschitz we prove the first order convergence of a splitting scheme of it both schemes preserve the mass they are very efficient because they use explicit formulas to solve the subproblems containing the nonlinear or the nonlinear plus stochastic terms

a two level finite element discretization of the streamfunction formulation of the stationary quasi geostrophic equations of the ocean in this paper we proposed a two level finite element discretization of the nonlinear stationary quasi geostrophic equations which model the wind driven large scale ocean circulation optimal error estimates for the two level finite element discretization were derived numerical experiments for the two level algorithm with the argyris finite element were also carried out the numerical results verified the theoretical error estimates and showed that for the appropriate scaling between the coarse and fine mesh sizes the two level algorithm significantly decreases the computational time of the standard one level algorithm

a finite element pressure correction scheme for the navier stokes equations with traction boundary condition abstract we consider the popular pressure correction scheme for the solution of the time dependent navier stokes equations with traction boundary condition a finite element based method to improve the performance of the classical approach is proposed the improvement is achieved by modifying the traction boundary condition for the provisional velocity u n 1 in each time step the corresponding term consists of a simple boundary functional involving the normal derivative of the pressure correction that can be evaluated in a natural and easy way in the context of finite elements computational results show a significant improvement of the solution in particular for the pressure in the case of smooth domains

the optimal convergence rate of a c1 finite element method for non smooth domains we establish optimal up to arbitrary e 0 convergence rates for a finite element formulation of a model second order elliptic boundary value problem in a weightedh 2 sobolev space with 5th degree argyris elements this formulation arises while generalizing to the case of non smooth domains an unconditionally stable scheme developed by liu et al j g liu j liu r l pego stability and convergence of efficient navier stokes solvers via a commutator estimate comm pure appl math 60 2007 pp 1443 1487 for the navier stokes equations we prove the optimality for both quasiuniform and graded mesh refinements and provide numerical results that agree with our theoretical predictions

factorizable language from dynamics to bacterial complete genomes symbolic sequences generated by symbolic dynamics of a dynamical system belong to a special class of language in which any admissible word is factorisable as well as prolongable from a complete genome sequence of an organism one may also define a factorizable language a factorizable language enjoys the nice property that it is entirely determined by the set of minimal fobidden words or distinct excluded blocks debs we use this property to calculate the fractal dimension of patterns related to a visualisation scheme of under represented strings in bacterial complete genomes within the limit of infinitely long strings the same problem may be solved by using a purely combinatorial approach the methods described in this paper may be applied to other regular fractals with self similar and self overlapping structure c 2000 elsevier science b v all rights reserved

an overview of projection methods for incompressible flows a series of numerical issues related to the analysis and implementation of fractional step methods for incompressible flows are addressed in this paper these methods are often referred to in the literature as projection methods and can be classified into three classes namely the pressure correction methods the velocity correction methods and the consistent splitting methods for each class of schemes theoretical and numerical convergence results available in the literature are reviewed and open questions are discussed the essential results are summarized in a table which could serve as a useful reference to numerical analysts and practitioners published by elsevier b v msc 65n35 65n22 65f05 35j05

on the existence of traveling waves in the 3d boussinesq system we extend earlier work on traveling waves in premixed flames in a gravitationally stratified medium subject to the boussinesq approximation for three dimensional channels not aligned with the gravity direction and under the dirichlet boundary conditions in the fluid velocity it is shown that a non planar traveling wave corresponding to a non zero reaction exists under an explicit condition relating the geometry of the crossection of the channel to the magnitude of the prandtl and rayleigh numbers or when the advection term in the flow equations is neglected

measure representation and multifractal analysis of complete genomes this paper introduces the notion of measure representation of dna sequences spectral analysis and multifractal analysis are then performed on the measure representations of a large number of complete genomes the main aim of this paper is to discuss the multifractal property of the measure representation and the classification of bacteria from the measure representations and the values of the dq spectra and related cq curves it is concluded that these complete genomes are not random sequences in fact spectral analyses performed indicate that these measure representations considered as time series exhibit strong long range correlation here the long range correlation is for the k strings with dictionary ordering and it is different from the base pair correlations introduced by other people for substrings with length k58 the dq spectra of all organisms studied are multifractal like and sufficiently smooth for the cq curves to be meaningful with the decreasing value of k the multifractality lessens the cq curves of all bacteria resemble a classical phase transition at a critical point but the analogous phase transitions of chromosomes of nonbacteria organisms are different apart from chromosome 1 of c elegans they exhibit the shape of double peaked specific heat function a classification of genomes of bacteria by assigning to each sequence a point in two dimensional space d21 d1 and in three dimensional space d21 d1 d22 was given bacteria that are close phylogenetically are almost close in the spaces d21 d1 and d21 d1 d22

multifractal characterisation of length sequences of coding and noncoding segments in a complete genome the coding and noncoding length sequences constructed from a complete genome are characterised by multifractal analysis the dimension spectrum dq and its derivative the analogous specific heat cq are calculated for the coding and noncoding length sequences of bacteria where q is the moment order of the partition sum of the sequences from the shape of the dq and cq curves it is seen that there exists a clear difference between the coding noncoding length sequences of all organisms considered and a completely random sequence the complexity of noncoding length sequences is higher than that of coding length sequences for bacteria almost all dq curves for coding length sequences are flat so their multifractality is small whereas almost all dq curves for noncoding length sequences are multifractal like it is seen that the analogous specific heats of noncoding length sequences of bacteria have a rich variety of behaviour which is much more complex than that of coding length sequences we propose to characterise the bacteria according to the types of the cq curves of their noncoding length sequences this new type of classification allows a better understanding of the relationship among bacteria at the global gene level instead of nucleotide sequence level

a sequential regularization method for time dependent incompressible navier stokes equations the objective of the paper is to present a method called the sequential regularization method srm for the nonstationary incompressible navier stokes equations from the viewpoint of regularization of differential algebraic equations daes and to provide a way to apply a dae method to partial differential algebraic equations pdaes the srm is a functional iterative procedure it is proved that its convergence rate is o epsilon m where m is the number of the srm iterations and epsilon is the regularization parameter the discretization and implementation issues of the method are considered in particular a simple explicit difference scheme is analyzed and its stability is proved under the usual step size condition of explicit schemes it appears that the srm formulation is new in the navier stokes context unlike other regularizations or pseudocompressibility methods in the navier stokes context the regularization parameter epsilon in the srm need not be very small and the regularized problem in the sequence may be essentially nonstiff in time direction for any epsilon hence the stability condition is independent of epsilon even for explicit time discretization numerical experiments are given to verify our theoretical results

stabilization of the nonuniform timoshenko beam in this paper we consider a timoshenko beam with variable physical parameters we prove that the model can be stabilize by one control force for both internal and boundary cases

convergence of gauge method for incompressible flow a new formulation a gauge formulation of the incompressible navier stokes equations in terms of an auxiliary field a and a gauge variable u a was proposed recently by e and liu this paper provides a theoretical analysis of their formulation and verifies the computational advantages we discuss the implicit gauge method which uses backward euler or crank nicolson in time discretization however the boundary conditions for the auxiliary field a are implemented explicitly vertical extrapolation the resulting momentum equation is decoupled from the kinematic equation and the computational cost is reduced to solving a standard heat and poisson equation moreover such explicit boundary conditions for the auxiliary field a will be shown to be unconditionally stable for stokes equations for the full nonlinear navier stokes equations the time stepping constraint is reduced to the standard cfl constraint t x c we also prove first order convergence of the gauge method when we use mac grids as our spatial discretization the optimal error estimate for the velocity field is also obtained

statistics of dna sequences a low frequency analysis we study statistical properties of dna chains of thirteen microbial complete genomes we find that the power spectrum of several of the sequences studied flattens off in the low frequency limit this implies the correlation length in those sequences is much smaller than the entire dna chain consequently in contradiction with previous studies we show that the fractal behavior of dna chains does not always prevail through the entire dna molecule

a gpav based unconditionally energy stable scheme for incompressible flows with outflow open boundaries abstract we present an unconditionally energy stable scheme for approximating the incompressible navier stokes equations on domains with outflow open boundaries the scheme combines the generalized positive auxiliary variable gpav approach and a rotational velocity correction type strategy and the adoption of the auxiliary variable simplifies the numerical treatment for the open boundary conditions the discrete energy stability of the proposed scheme has been proven irrespective of the time step sizes within each time step the scheme entails the computation of two velocity fields and two pressure fields by solving an individual de coupled helmholtz including poisson type equation with a constant pre computable coefficient matrix for each of these field variables the auxiliary variable being a scalar number is given by a well defined explicit formula within a time step which ensures the positivity of its computed values extensive numerical experiments with several flows involving outflow open boundaries in regimes where the backflow instability becomes severe have been presented to test the performance of the proposed method and to demonstrate its stability at large time step sizes

energy decay in a timoshenko type system of thermoelasticity of type iii in this paper we consider a one dimensional linear thermoelastic system of timoshenko type where the heat conduction is given by green and naghdi theories we prove the exponential stability by using the energy method

a basic inequality for the stokes operator related to the navier boundary condition we show that au u l2 e c e u l2 e u l2 e where e is a thin domain in r3 of depth e the vector field u belongs to the domain of a which is the stokes operator for divergence free vector fields on e satisfying the navier boundary condition

continuous alignment of vorticity direction prevents the blow up of the navier stokes flow under the no slip boundary condition abstract this paper is concerned with a regularity criterion based on vorticity direction for navier stokes equations in a three dimensional bounded domain under the no slip boundary condition it asserts that if the vorticity direction is uniformly continuous in space uniformly in time there is no type i blow up a similar result has been proved for a half space by y maekawa and the first and the last authors 2014 the result of this paper is its natural but non trivial extension based on l theory of the stokes and the navier stokes equations recently developed by k abe and the first author

a generalized mac scheme on curvilinear domains we propose a simple finite difference scheme for navier stokes equations in primitive formulation on curvilinear domains with proper boundary treatment and interplay between covariant and contravariant components the spatial discretization admits exact hodge decomposition and energy identity as a result the pressure can be decoupled from the momentum equation with explicit time stepping no artificial pressure boundary condition is needed in addition it can be shown that this spatially compatible discretization leads to uniform inf sup condition which plays a crucial role in the pressure approximation of both dynamic and steady state calculations numerical experiments demonstrate the robustness and efficiency of our scheme

optimal polynomial decay of functions and operator semigroups we characterize the polynomial decay of orbits of hilbert space c 0 semigroups in resolvent terms we also show that results of the same type for general banach space semigroups and functions obtained recently in batty and duyckaerts j evol eq 8 765 780 2008 are sharp this settles a conjecture posed in batty and duyckaerts 2008

stability of timoshenko systems with past history we consider vibrating systems of timoshenko type with past history acting only in one equation we show that the dissipation given by the history term is strong enough to produce exponential stability if and only if the equations have the same wave speeds otherwise the corresponding system does not decay exponentially as time goes to infinity in the case that the wave speeds of the equations are different which is more realistic from the physical point of view we show that the solution decays polynomially to zero with rates that can be improved depending on the regularity of the initial data

high order galerkin convergence and boundary characteristics of the 3 d navier stokes equations on intervals of regularity abstract we consider the 3 d navier stokes equations nse on a bounded domain r 3 with zero boundary data let p denote the leray projection and let a p denote the stokes operator for a natural number 2 assume that the forcing data satisfies f c 0 t d a 1 2 and let 0 t be an interval over which the h 1 norms of galerkin solutions u m are uniformly bounded then on any subinterval t we show that sup t t a 2 u m t u t 2 0 as m where u is the unique regular strong solution of the nse on 0 t from this convergence result we show that if f c 0 t d a 1 2 then a 2 u t 0 on the boundary of for any t 0 when 2 applications of this boundary result include boundary data specification for the nse pressure within the framework developed in 19 20 and corroboration for the choice of boundary values in 22 for the ns equation