rate distortion optimal fast thresholding with complete jpeg mpeg decoder compatibility we show a rate distortion optimal way to threshold or drop the dct coefficients of the jpeg and mpeg compression standards our optimal algorithm uses a fast dynamic programming recursive structure the primary advantage of our approach lies in its complete compatibility with standard jpeg and mpeg decoders

on the eisenstein cohomology of arithmetic groups the cohomology h gamma e of an arithmetic subgroup gamma of a connected reductive algebraic group g defined over some algebraic number field f can be interpreted in terms of the automorphic spectrum of gamma with this framework in place there is a sum decomposition of the cohomology into the cuspidal cohomology i e classes represented by cuspidal automorphic forms for g and the so called eisenstein cohomology constructed as the span of appropriate residues or derivatives of eisenstein series attached to cuspidal automorphic forms on the levi components of proper parabolic f subgroups of g the main objective of this paper is to isolate a specific structural part in the eisenstein cohomology this pertains to regular eisenstein cohomology classes attached to cuspidal automorphic representations whose archimedean component is tempered it is shown that the cohomological degree of these classes is bounded from below by the constant q 0 g mathbb r 1 2 dim x g mathbb r rk g mathbb r rk k mathbb r where k mathbb r denotes a maximal compact subgroup of the real lie group g mathbb r where x g mathbb r is the associated symmetric space this investigation has various applications one of these is a vanishing result for the cohomology in the generic case i e where the representation determining the coefficient system e has regular highest weight in degrees below q 0 g mathbb r this is a sharp bound depending only on the underlying real lie group g mathbb r corollary 5 6 proposition 5 8 this result is supplemented by a qualitative structural result in the description of the cohomology in higher degrees by means of regular eisenstein cohomology classes

on the cuspidal cohomology of arithmetic groups it is the main objective of this paper to show a vanishing result for cuspidal cohomology of arithmetic groups in classical groups g defined over some number field k our approach relies on the fact that cuspidal automorphic forms are nonsingular in the sense of howe this result puts a strong constraint on the archimedean components of irreducible cuspidal automorphic representations of g that can possibly contribute to the cuspidal cohomology combining this with the classification of vogan zuckerman of unitary representations with nonzero cohomology provides a constant r 0 g k only depending on g k below which the cuspidal cohomology vanishes we will give a formula for this constant for each classical group of type i in the classification scheme due to weil we conclude with making this result explicit for some split classical groups over a totally real algebraic number field

some groups of transformations defined by jordan algebras ii groups of type f4 the principal objective of this paper is the study of one of the types of linear groups defined in i 15 the groups of automorphisms of central simple exceptional jordan algebras this can also be considered as the second step in a program of studying exceptional linear groups analogous to the exceptional simple lie groups via non associative algebras the first step in this program has been taken in another paper 13 in which we studied the counterparts of the lie groups of type g 2 as groups of automorphisms of cayley algebras in an analogous fashion the present paper deals with the counterparts of the lie group f 4 as groups of automorphisms of exceptional jordan algebras

geometry of integral binary hermitian forms abstract we generalize conway s approach to integral binary quadratic forms to study integral binary hermitian forms over quadratic imaginary extensions of q we show that every indefinite anisotropic form determines a plane ocean in mendoza s spine associated to the corresponding bianchi group in the hyperbolic 3 space the ocean can be used to compute the group of integral transformations preserving the hermitian form

some uniserial representations of certain special linear groups abstract in an earlier paper a construction was given for an infinite dimensional uniserial module over q for sl 2 z whose composition factors are all isomorphic to the standard two dimensional module in this note we consider generalizations of this construction to other composition factors and to other rings of algebraic integers

microwave imaging of nonsparse domains using born iterative method with wavelet transform and block sparse bayesian learning a microwave technique utilizing the combination of wavelet transform block sparse bayesian learning bsbl and born iterative method bim is proposed to image nonsparse domains the wavelet transform is implemented to convert the nonsparse domain into a sparse domain then bsbl framework based on expectation maximization em algorithm is applied on the bim model to reconstruct the original profile of the nonsparse domain the presented imaging results of a nonsparse model indicate that the proposed technique in comparison with traditional microwave imaging or compressive sensing cs algorithms achieve very low normalized error rate ner at a short computational time using only small number of antennas the accuracy robustness and effectiveness of the proposed method are further assessed by employing it to detect a hemorrhagic brain stroke in a realistic numerical head model which is a nonsparse domain the obtained results indicate the capability for the technique to detect an early stroke in the realistic nonsparse environment of the human head using only six antennas

the homological torsion of psl_2 of the imaginary quadratic integers denote by q sqrt m with m a square free positive integer an imaginary quadratic number field and by a its ring of integers the bianchi groups are the groups sl 2 a we reveal a correspondence between the homological torsion of the bianchi groups and new geometric invariants which are effectively computable thanks to their action on hyperbolic space we expose a novel technique the torsion subcomplex reduction to obtain these invariants we use it to explicitly compute the integral group homology of the bianchi groups furthermore this correspondence facilitates the computation of the equivariant k homology of the bianchi groups by the baum connes conjecture which is verified by the bianchi groups we obtain the k theory of their reduced c algebras in terms of isomorphic images of their equivariant k homology

joint optimization of run length coding huffman coding and quantization table with complete baseline jpeg decoder compatibility to maximize rate distortion performance while remaining faithful to the jpeg syntax the joint optimization of the huffman tables quantization step sizes and dct indices of a jpeg encoder is investigated given huffman tables and quantization step sizes an efficient graph based algorithm is first proposed to find the optimal dct indices in the form of run size pairs based on this graph based algorithm an iterative algorithm is then presented to jointly optimize run length coding huffman coding and quantization table selection the proposed iterative algorithm not only results in a compressed bitstream completely compatible with existing jpeg and mpeg decoders but is also computationally efficient furthermore when tested over standard test images it achieves the best jpeg compression results to the extent that its own jpeg compression performance even exceeds the quoted psnr results of some state of the art wavelet based image coders such as shapiro s embedded zerotree wavelet algorithm at the common bit rates under comparison both the graph based algorithm and the iterative algorithm can be applied to application areas such as web image acceleration digital camera image compression mpeg frame optimization and transcoding etc

on the growth of torsion in the cohomology of arithmetic groups in this paper we consider certain families of arithmetic subgroups of mathrm so 0 p q and mathrm sl 3 mathbb r respectively we study the cohomology of such arithmetic groups with coefficients in arithmetically defined modules we show that for natural sequences of such modules the torsion in the cohomology grows exponentially

an efficient algorithm for optimizing dct quantization we describe the rd opt algorithm for dct quantization optimization which can be used as an efficient tool for near optimal rate control in dct based compression techniques such as jpeg and mpeg rd opt measures dct coefficient statistics for the given image data to construct rate distortion specific quantization tables with nearly optimal tradeoffs

accessing the cohomology of discrete groups above their virtual cohomological dimension abstract we introduce a method to explicitly determine the farrell tate cohomology of discrete groups we apply this method to the coxeter triangle and tetrahedral groups as well as to the bianchi groups i e psl 2 o for o the ring of integers in an imaginary quadratic number field and to their finite index subgroups we show that the farrell tate cohomology of the bianchi groups is completely determined by the numbers of conjugacy classes of finite subgroups in fact our access to farrell tate cohomology allows us to detach the information about it from geometric models for the bianchi groups and to express it only with the group structure formulae for the numbers of conjugacy classes of finite subgroups have been determined in a thesis of kramer in terms of elementary number theoretic information on o an evaluation of these formulae for a large number of bianchi groups is provided numerically in the electronically released appendix to this paper our new insights about their homological torsion allow us to give a conceptual description of the cohomology ring structure of the bianchi groups

entropy constrained vector quantization an iterative descent algorithm based on a lagrangian formulation for designing vector quantizers having minimum distortion subject to an entropy constraint is discussed these entropy constrained vector quantizers ecvqs can be used in tandem with variable rate noiseless coding systems to provide locally optimal variable rate block source coding with respect to a fidelity criterion experiments on sampled speech and on synthetic sources with memory indicate that for waveform coding at low rates about 1 bit sample under the squared error distortion measure about 1 6 db improvement in the signal to noise ratio can be expected over the best scalar and lattice quantizers when block entropy coded with block length 4 even greater gains are made over other forms of entropy coded vector quantizers for pattern recognition it is shown that the ecvq algorithm is a generalization of the k means and related algorithms for estimating cluster means in that the ecvq algorithm estimates the prior cluster probabilities as well experiments on multivariate gaussian distributions show that for clustering problems involving classes with widely different priors the ecvq outperforms the k means algorithm in both likelihood and probability of error

integrality in the steinberg module and the top dimensional cohomology of sln ok we prove a new structural result for the spherical tits building attached to glnk for many number fields k and more generally for the fraction fields of many dedekind domains o the steinberg module stn k is generated by integral apartments if and only if the ideal class group cl o is trivial we deduce this integrality by proving that the complex of partial bases of o is cohen macaulay we apply this to prove new vanishing and nonvanishing results for h glnok q where ok is the ring of integers in a number field and n is the virtual cohomological dimension of glnok the non vanishing depends on the non triviality of the class group of ok we also obtain a vanishing theorem for the cohomology h glnok v with twisted coefficients v the same results hold for slnok as well

on the effect of support estimation and of a new model in 2 d inverse scattering problems starting from the concept of degree of non linearity of the relationship amongst unknown parameters and scattered fields we discuss how knowledge of the geometrical features of the targets favorably affects the solution of inverse scattering problems the same concept is also exploited to optimize the contrast source extended born cs eb model resulting in the optimized cs eb o cs eb inversion approach which remarkably reduces false solutions occurrence then a two steps approach is proposed as a reliable and effective inversion strategy the first step consists in retrieving the shape of the targets using the linear sampling method while in the second step the estimated shapes and the o cs eb are exploited to reconstruct the permittivity profile the approach has been tested against experimental data showing that very accurate reconstructions are achieved from monochromatic data

link complements and the bianchi modular groups we determine the values of m for which the bianchi modular group psl2 om contains a link group

some groups of transformations defined by jordan algebras i it is well known that the lie algebra of derivations of the exceptional jordan algebra m 3 8 over an algebraically closed field of characteristic 0 or over the field of reals is the exceptional lie algebra f 4 of killing cartan and that the lie algebra of linear transformations in m 3 8 leaving a certain cubic norm form defined on m 3 8 invariant is the exceptional lie algebra e 6 chevalley schafer 7 freudenthal 11 the program envisaged in the present series of papers is the extension of these results and their group analogues to arbitrary central simple jordan algebras the present paper gives the definition of the groups and lie algebras in the general case and gives their determination for special jordan algebras with some restrictions on the base field in a second paper we plan to consider the groups of automorphisms of arbitrary reduced exceptional simple jordan algebras and in a third paper we hope to study the generalized groups of types e 6 which arise from these jordan algebras

all principal congruence link groups abstract we enumerate all the principal congruence link complements in s 3 thereby answering a question of w thurston

on the non vanishing of the first betti number of hyperbolic three manifolds we show the non vanishing of cohomology groups of sufficiently small congruence lattices in sl 1 d where d is a quaternion division algebra defined over a number field e contained inside a solvable extension of a totally real number field as a corollary we obtain new examples of compact arithmetic hyperbolic three manifolds with non torsion first homology group confirming a conjecture of waldhausen the proof uses the characterisation of the image of solvable base change by the author and the construction of cusp forms with non zero cusp cohomology by labesse and schwermer

bounds for eigenforms on arithmetic hyperbolic 3 manifolds on a family of arithmetic hyperbolic 3 manifolds of square free level we prove an upper bound for the sup norm of hecke maas cusp forms with a power saving over the local geometric bound simultaneously in the laplacian eigenvalue and the volume by a novel combination of diophantine and geometric arguments in a noncommutative setting we obtain bounds as strong as the best corresponding results on arithmetic surfaces

electromagnetic inverse scattering of multiple perfectly conducting cylinders by differential evolution strategy with individuals in groups gdes the differential evolution strategy with individuals in groups gdes is proposed to solve the electromagnetic inverse scattering of multiple perfectly conducting cylinders with transverse magnetic wave incidence the inverse problem is to locate the cylinders and reconstruct their contours besides the determination on the number of cylinders the governing electric field integral equations for the scattering problem are expressed as surface integrals over the cylinder contours the scattering problem is solved using point matching method with pulse basis and dirac test functions the inverse problem is cast into an optimization problem and solved using the gdes numerical reconstruction results show that both the quality of the reconstructed profile and the convergence performance are significantly improved as compared to the original des

fuchsian groups finite simple groups and representation varieties let be a fuchsian group of genus at least 2 at least 3 if is non oriented we study the spaces of homomorphisms from to finite simple groups g and derive a number of applications concerning random generation and representation varieties precise asymptotic estimates for hom g are given implying in particular that as the rank of g tends to infinity this is of the form g 1 o 1 where is the measure of we then prove that a randomly chosen homomorphism from to g is surjective with probability tending to 1 as g combining our results with lang weil estimates from algebraic geometry we obtain the dimensions of the representation varieties text hom gamma bar g where bar g is gl n k or a simple algebraic group over k an algebraically closed field of arbitrary characteristic a key ingredient of our approach is character theory involving the study of the zeta function g s 1 s where the sum is over all irreducible complex characters of g

the mod 2 cohomology of the bianchi groups the bianchi groups are a family of discrete subgroups of psl2 c which have group theoretic descriptions as amalgamated products and hnn extensions using bass serre theory we show how the cohomology of these two constructions relates to the cohomology of their pieces we then apply these results to calculate the mod 2 cohomology ring for various bianchi groups

the integral cohomology of the bianchi groups we calculate the integral cohomology ring structure for various members of the bianchi group family the main tools we use are the bockstein spectral sequence and a long exact sequence derived from bass serre theory

two dimensional microwave imaging based on hybrid scatterer representation and differential evolution a hybrid method for solving two dimensional inverse scattering problems is proposed the method utilizes differential evolution as a global optimizer and is based on two alternative representations of the unknown scatterer initially the scatterer properties are represented by means of truncated cosine fourier series expansion that involves limited number of unknown expansion coefficients then the reconstructed profile obtained is used as an initial estimate and the differential evolution is further applied to a scatterer representation based on pulse function expansion in this representation the scatterer region is subdivided by a fine grid and the scatterer properties are considered constant within each cell when the truncated cosine fourier expansion representation is adopted the dimension of the solution space can be reduced and the instabilities caused by the ill posedness of the problem are suppressed in the second step of the hybrid method where the pulse functions representation is considered the scatterer reconstruction is finer and more accurate due to its quite accurate initial estimate numerical results show that the hybrid method results in lower reconstruction error compared to above mentioned representations also the hybrid method outperforms the other two representations even in the presence of noisy field measurements

on the torsion in the cohomology of arithmetic hyperbolic 3 manifolds in this paper we consider the cohomology of a closed arithmetic hyperbolic 3 manifold with coefficients in the local system defined by the even symmetric powers of the standard representation of sl 2 c the cohomology is defined over the integers and is a finite abelian group we show that the order of the 2nd cohomology grows exponentially as the local system grows we also consider the twisted ruelle zeta function of a closed arithmetic hyperbolic 3 manifold and we express the leading coefficient of its laurent expansion at the origin in terms of the orders of the torsion subgroups of the cohomology

subgroups of bianchi groups and arithmetic quotients of hyperbolic 3 space let o be the ring of integers in an imaginary quadratic number field the group psl 2 o acts discontinuously on hyperbolic 3 space h if psl 2 o is a torsionfree subgroup of finite index then the manifold h can be compactified to a manifold m so that the inclusion h m is a homotopy equivalence m is a compact with boundary the boundary being a union of finitely many 2 tori this paper contains a computer aided study of subgroups of low index in psl 2 o for various o the explicit description of these subgroups leads to a study of the homeomorphism types of the m

joint thresholding and quantizer selection for transform image coding entropy constrained analysis and applications to baseline jpeg striving to maximize baseline joint photographers expert group jpeg image quality without compromising compatibility of current jpeg decoders we develop an image adaptive jpeg encoding algorithm that jointly optimizes quantizer selection coefficient thresholding and huffman coding within a rate distortion r d framework practically speaking our algorithm unifies two previous approaches to image adaptive jpeg encoding r d optimized quantizer selection and r d optimal thresholding conceptually speaking our algorithm is a logical consequence of entropy constrained vector quantization ecvq design principles in the severely constrained instance of jpeg compatible encoding we explore both viewpoints the practical to concretely derive our algorithm and the conceptual to justify the claim that our algorithm approaches the best performance that a jpeg encoder can achieve this performance includes significant objective peak signal to noise ratio psnr improvement over previous work and at high rates gives results comparable to state of the art image coders for example coding the lena image at 1 0 b pixel our jpeg encoder achieves a psnr performance of 39 6 db that slightly exceeds the quoted psnr results of shapiro s wavelet based zero tree coder using a visually based distortion metric we can achieve noticeable subjective improvement as well furthermore our algorithm may be applied to other systems that use run length encoding including intraframe mpeg and subband or wavelet coding

stochastic optimization methods applied to microwave imaging a review stochastic methods are now very common in electromagnetics among the various applications they have been recently proposed for solving inverse problems arising in radio frequency and microwave imaging some of the recently proposed stochastic inversion procedures are critically discussed e g genetic algorithms differential evolution methods memetic algorithms particle swarm optimizations hybrid techniques etc and the way they have been applied in this area the use of the ant colony optimization method which is a relatively new method in electromagnetics is also proposed various imaging modalities are considered tomography buried object detection and borehole sensing finally the main features making these approaches useful for imaging purposes are discussed and the currently considered strategies to reduce the computational load associated with stochastic optimization procedures delineated

cohomology of the symplectic group i the odd torsion case let h 2 be the degree two siegel space and sp 4 z the symplectic group the quotient sp 4 z h 2 can be interpreted as the moduli space of stable riemann surfaces of genus 2 this moduli space can be decomposed into two pieces corresponding to the moduli of degenerate and nondegenerate surfaces of genus 2 the decomposition leads to a mayer vietoris sequence in cohomology relating the cohomology of sp 4 z to the cohomology of the genus two mapping class group 2 0 using this tool the 3 and 5 primary pieces of the integral cohomology of sp 4 z are computed

parallel ga based approach for microwave imaging applications genetic algorithms gas are well known optimization strategies able to deal with nonlinear functions as those arising in inverse scattering problems however they are computationally expensive thus offering poor performances in terms of general efficiency when compared with inversion techniques based on deterministic optimization methods in this paper a parallel implementation of an inverse scattering procedure based on a suitable hybrid genetic algorithm is presented the proposed strategy is aimed at reducing the overall clock time in order to make the approach competitive with gradient based methods in terms of runtime but preserving the capabilities of escaping from local minima this result is achieved by exploiting the natural parallelism of evolutionary techniques and the searching capabilities of the hybrid approach the effectiveness of the proposed implementation is demonstrated by considering a selected numerical benchmark related to two dimensional scattering geometries

solving inverse scattering problems based on truncated cosine fourier and cubic b spline expansions in this paper a comparison between truncated cosine fourier expansion tcfe and cubic b spline expansion cbse for representation of the unknown scatterer properties in solving inverse scattering problems is presented in this comparison the efficiency of both aforementioned expansion techniques is examined for permittivity and conductivity profile reconstruction problems the study is carried out by converting the reconstruction problem to an optimization one and using the finite difference time domain fdtd method as forward electromagnetic em solver and the differential evolution de technique as global optimizer the main benefit of the expansion representations of the unknown properties is the reduction of the ill posedness which is achieved by decreasing the number of unknowns of the inverse problem the comparison is done under the same conditions of the number of population and optimization iterations numerical results related to the reconstruction of one dimensional 1d and two dimensional 2d scatterers indicate that both expansion methods are reliable tools for inverse scattering applications it is shown that the use of the cbse results in faster convergence of the reconstruction process compared to the tcfe however the tcfe gives more accurate reconstruction especially in the edges of scatterers both expansion techniques are robust against the presence of noise in the measurements

electromagnetic inverse scattering of multiple two dimensional perfectly conducting objects by the differential evolution strategy electromagnetic inverse scattering of multiple two dimensional 2 d perfectly conducting objects with transverse magnetic tm wave incidence by the differential evolution strategy des is presented the governing electric field integral equations for the scattering problem are expressed as surface integral over the cylinder contours the cylinder contours are approximately represented by closed cubic b splines local shape functions in local polar coordinate system the inverse problem is to locate the cylinders and to reconstruct their shape with or without a priori knowledge of the number of cylinders it is cast into an optimization problem and is solved using the des both synthetic and real reconstructions are carried out the reconstruction results agree with the true profiles very well comparison with the real coded genetic algorithm has been carried out it has been observed that the des outperforms the real coded genetic algorithm

intersection numbers of special cycles let g q be a connected semisimple algebraic group defined over q and let a r be two q rational automorphisms of finite order of g which commute with each other we assume that the group g r of real points of g is noncompact let i be a torsionfree arithmetic subgroup of g q which is stable under the group a r generated by a and r then a and r act on the space x of maximal compact subgroups of g r and on the locally symmetric space x i in a natural way if g f l denotes the reductive algebraic q group of fixed points of f l a r acting on g then the corresponding symmetric space x f l is acted upon by the arithmetic group 1 f l of fixed points of f l acting on i these give rise to nonempty closed immersed submanifolds c a x a 1 a and c r x r 1 r of x i they are called special cycles we assume that x i c a and c r are oriented and that the intersection c a n c r is compact then if dim c a dim c r dim x the intersection number

a generalized hermite constant for imaginary quadratic fields we introduce the projective hermite constant for positive definite binary hermitian forms associated with an imaginary quadratic number field k it is a lower bound for the classical hermite constant and these two constants coincide when k has class number one using the geometric tools developed by mendoza 6 and vogtmann 15 for their study of the homology of the bianchi groups we compute the projective hermite constants for those k whose absolute discriminants are less than 70 and determine the hermitian forms that attain the projective hermite constants in these cases a comparison of the projective hermitian constant with some other generalizations of the classical hermite constant is also given

cycles with local coefficients for orthogonal groups and vector valued siegel modular forms the purpose of this paper is to generalize the relation between intersection numbers of cycles in locally symmetric spaces of orthogonal type and fourier coefficients of siegel modular forms to the case where the cycles have local coefficients now the correspondence will involve vector valued siegel modular forms

iterative forward and inverse algorithms based on domain integral equations for three dimensional electric and magnetic objects an iterative approach to full vector three dimensional inverse scattering problems where the unknown objects can have conductivity permittivity and permeability different from the known background medium is discussed since this problem involves a large number of unknowns it has to be solved effectively and efficiently so that the results can be obtained in timely manner the forward modeling is based on a domain integral equation approach formulated in terms of the electric and magnetic contrast sources normalized with the characteristic impedance of the background medium our numerical tests indicate that this formulation is prerequisite in order to arrive at a forward solution within an acceptable number of iterations and hence it is also of significant importance in the optimization process of the inverse problem the inverse scattering problem is attacked using the multiplicative regularized contrast source inversion method as known in the literature the complexity of this inverse method is approximately equal to the complexity of two equivalent forward algorithms of the conjugate gradient type furthermore this inverse method has been armed with a weighted l2 norm regularizer which has been included as a multiplicative constraint some representative numerical testings will be presented to illustrate the ability of the our numerical algorithms

on the cuspidal cohomology of arithmetic subgroups of mathrm sl 2n and the first betti number of arithmetic 3 manifolds

appendix to the paper some uniserial representations of certain special linear groups by p sin and j g thompson abstract this appendix collects some material on the cohomology of discrete subgroups of lie groups and the theory of their representation varieties to provide background for the results of sin and thompson 2010 2013 in 22 23

rate distortion optimization for h 264 interframe coding a general framework and algorithms rate distortion rd optimization for h 264 interframe coding with complete baseline decoding compatibility is investigated on a frame basis using soft decision quantization sdq rather than the standard hard decision quantization we first establish a general framework in which motion estimation quantization and entropy coding in h 264 for the current frame can be jointly designed to minimize a true rd cost given previously coded reference frames we then propose three rd optimization algorithms a graph based algorithm for near optimal sdq in h 264 baseline encoding given motion estimation and quantization step sizes an algorithm for near optimal residual coding in h 264 baseline encoding given motion estimation and an iterative overall algorithm to optimize h 264 baseline encoding for each individual frame given previously coded reference frames with them embedded in the indicated order the graph based algorithm for near optimal sdq is the core given motion estimation and quantization step sizes it is guaranteed to perform optimal sdq if the weak adjacent block dependency utilized in the context adaptive variable length coding of h 264 is ignored for optimization the proposed algorithms have been implemented based on the reference encoder jm82 of h 264 with complete compatibility to the baseline profile experiments show that for a set of typical video testing sequences the graph based algorithm for near optimal sdq the algorithm for near optimal residual coding and the overall algorithm achieve on average 6 8 and 12 respectively rate reduction at the same psnr ranging from 30 to 38 db when compared with the rd optimization method implemented in the h 264 reference software

image compression with adaptive local cosines a comparative study the goal of this work is twofold first we demonstrate that an advantage can be gained by using local cosine bases over wavelets to encode images that contain periodic textures we designed a coder that outperforms one of the best wavelet coders on a large number of images the coder finds the optimal segmentation of the image in terms of local cosine bases the coefficients are encoded using a scalar quantizer optimized for laplacian distributions this new coder constitutes the first concrete contribution of the paper second we used our coder to perform an extensive comparison of several optimized bells in terms of rate distortion and visual quality for a large collection of images this study provides for the first time a rigorous evaluation in realistic conditions of these bells our experiments show that bells that are designed to reproduce exactly polynomials of degree 1 resulted in the worst performance in terms of the psnr however a visual inspection of the compressed images indicates that these bells often provide reconstructed images with very few visual artifacts even at low bit rates the bell with the most narrow fourier transform gave the best results in terms of the psnr on most images this bell tends however to create annoying visual artifacts in very smooth regions at low bit rate

improved microwave imaging procedure for nondestructive evaluations of two dimensional structures an improved microwave procedure for detecting defects in dielectric structures is proposed the procedure is based on the integral equations of the inverse scattering problem a hybrid genetic algorithm ga is applied in order to minimize the obtained nonlinear functional since in nondestructive evaluations the unperturbed object is completely known it is possible off line to numerically compute the green s function for the configuration without defects consequently a very significant computation saving is obtained since the chromosome of the ga codes only the parameters describing the unknown defect