binary convexities and distributive lattices a convex structure is binary if every finite family of pairwise intersecting convex sets has a non empty intersection distributive lattices with the convexity of all order convex sublattices are a prominent type of example because they correspond exactly to the intervals of a binary convex structure which has a certain separation property in one direction this result relies on a study of so called base point orders induced by a convex structure these orderings are used to construct an intrinsic topology for binary convexities certain basic questions are answered with the aid of some results on completely distributive lattices several applications are given dimension problems are studied in a subsequent paper 0 introduction a convex structure consists of a set x together with a collection of subsets of x henceforth called convex sets such that 1 1 the empty set and the set x are convex 1 2 the intersection of convex sets is convex 1 3 the union of an updirected collection of convex sets is convex the collection itself is called a convexity on x axiom 1 2 allows the construction of an associated convex hull operator usually denoted by h in the obvious way the hull of a finite set is called a polytope and the hull of a two point set is also called an interval a half space is a convex set with a convex complement the following separation axioms comparable with the axioms tl 5 t4 in topology are used frequently sx singletons are convex which we will assume throughout s2 two distinct points are in complementary half spaces s3 a convex set is an intersection of half spaces s4 two disjoint convex sets extend to complementary half spaces in this paper we will concentrate largely on a particular though fundamental class of convexities with the following binarity property each finite collection of pairwise intersecting convex sets has a non empty intersection the basic types of examples are described in 1 many of these examples arise in a topological context for other examples a natural topology can be constructed binary convex structures on a topological space have been studied extensively in the past years 15 17 19 22 29 34 38 the topology and the convexity are always assumed to be compatible in the sense that polytopes are closed a triple consisting of a set x a convexity and a compatible topology st is called a topological convex proc london math soc 3 48 1984 1 33 5388 3 48 a

finite element methods for active contour models and balloons for 2 d and 3 d images the use of energy minimizing curves known as snakes to extract features of interest in images has been introduced by kass witkin and terzopoulos 1987 a balloon model was introduced by cohen 1991 as a way to generalize and solve some of the problems encountered with the original method a 3 d generalization of the balloon model as a 3 d deformable surface which evolves in 3 d images is presented it is deformed under the action of internal and external forces attracting the surface toward detected edgels by means of an attraction potential we also show properties of energy minimizing surfaces concerning their relationship with 3 d edge points to solve the minimization problem for a surface two simplified approaches are shown first defining a 3 d surface as a series of 2 d planar curves then after comparing finite element method and finite difference method in the 2 d problem we solve the 3 d model using the finite element method yielding greater stability and faster convergence this model is applied for segmenting magnetic resonance images

on the distribution of the peak to average power ratio in ofdm signals the distribution of the peak to average power ratio papr in strictly band limited orthogonal frequency division multiplexing ofdm signals is studied assuming that the base band ofdm signal is characterized as a band limited complex gaussian process we first attempt to derive the exact distribution of the papr in the band limited ofdm signals since this distribution cannot be expressed in a closed form we further develop a simple closed form approximation based on the level crossing rate analysis comparisons of the proposed distributions with those obtained by computer simulations show good agreement and convergence with an increase in the number of subcarriers

multi block joint optimization for the peak to average power ratio reduction of fbmc oqam signals recently the filter bank multicarrier with offset quadrature amplitude modulation fbmc oqam has attracted increasing attention however most peak to average power ratio papr reduction schemes developed for orthogonal frequency division multiplexing ofdm signals are not effective for fbmc oqam signals due to the overlapping structure of fbmc oqam signals in this paper we propose an improved partial transmit sequence pts scheme by employing multi block joint optimization mbjo for the papr reduction of fbmc oqam signals called as mbjo pts scheme in pts scheme one data block is divided into several subblocks and each subblock is multiplied by a phase rotation factor for the subblock the pts scheme searches over all combinations of allowed phase factors to lower the papr unlike existing papr reduction schemes of independently optimizing the data blocks the mbjo based scheme exploits the overlapping structure of the fbmc oqam signal and jointly optimizes multiple data blocks moreover we develop two algorithms for the optimization problem in the mbjo pts scheme including a dynamic programming dp algorithm to guarantee the optimal solution and avoid exhaustive search theoretical analysis and simulations show that the proposed mbjo pts scheme could provide a significant papr reduction in the fbmc oqam system by exploiting the overlapping structure of the fbmc oqam signal employing the proposed dp algorithm the fbmc oqam system with the proposed mbjo pts scheme even outperforms the ofdm system with the conventional pts scheme by 0 9 db at ccdf of 10 3 in papr reduction under the same number of subcarriers modulation type and pts parameters given in section v

discrete and continuous maxima in multicarrier communication the ratio between the discrete and continuous maxima of signals used in multicarrier communications is analyzed an exact expression up to an additive term is obtained for the considered ratio when the number of uniformly distributed samples is equal to the number of carriers a more accurate upper estimate on the continuous maximum from discrete samples of the signal and its derivative is suggested finally a tight upper bound is given for the value of the continuous maximum via discrete values of samples when the number of samples is greater than the number of carriers

active contours without edges we propose a new model for active contours to detect objects in a given image based on techniques of curve evolution mumford shah 1989 functional for segmentation and level sets our model can detect objects whose boundaries are not necessarily defined by the gradient we minimize an energy which can be seen as a particular case of the minimal partition problem in the level set formulation the problem becomes a mean curvature flow like evolving the active contour which will stop on the desired boundary however the stopping term does not depend on the gradient of the image as in the classical active contour models but is instead related to a particular segmentation of the image we give a numerical algorithm using finite differences finally we present various experimental results and in particular some examples for which the classical snakes methods based on the gradient are not applicable also the initial curve can be anywhere in the image and interior contours are automatically detected

reduction of peak factor in orthogonal multicarrier modulation by amplitude limiting and coding a main disadvantage of orthogonal multicarrier modulation is that it exhibits a high peak to average power ratio papr because of this all circuits between the output of the modulator and the input of the demodulator must be linear within a large dynamic range to avoid distortions and spectral spreading it is therefore desirable to limit the papr of the multicarrier signal a method based on amplitude limiting and forward error correcting al fec coding is proposed for reduction of the papr the performance of the al fec is compared to two methods based on block coding specially constructed to reduce the papr the al fec is superior as compared to the existing methods moreover its practical realization is very simple for any number of carriers

a balancing method for pmepr reduction in ofdm signals a relation is established between the strength of a binary code over the alphabet 1 1 and its ability to reduce peak to mean envelope power ratio pmepr in n subcarrier ofdm signals based on this relation a method is proposed to deterministically bound pmepr of such signals using coordinate wise multiplication by a balancing vector bv chosen from a code of given strength a practical probabilistic scheme considering a small number of candidate codewords is devised for this scheme estimates on the pmepr reduction achievable with arbitrary high probability are derived in particular the scheme provides for large n pmepr of lnn 2 01lnlnn with ln2 middot log2n 2 1 bits of redundancy the failure probability at most e n and testing n lnlnn candidate bvs finally several practical settings are considered for example for quaternary phase shift keying n 128 the scheme with 36 bits of redundancy 18 redundant subcarriers by testing only 4 bvs provides over 2 db pmepr reduction for any failure rate below 10 2 5

peak value estimation of bandlimited signals from their samples noise enhancement and a local characterization in the neighborhood of an extremum the paper addresses the problem of estimating the peak value of bandlimited signals from their samples with and without oversampling this problem has significant relevance to orthogonal frequency division multiplexing ofdm signal processing and system design in particular an upper bound on the peak value is established given the peak value of the samples and the oversampling rate moreover it is shown that the bounds are sharp for all practical rates by constructing bandlimited signals taking on this bound the proof also provides a local characterization of bandlimited signals in the neighborhood of an extremum a different analysis examines the effect of small errors in the samples it is shown that oversampling can provide robust recovery in the sense that small errors in the samples lead to small errors in the reconstructed signal again an upper bound is derived relating the peak error in the samples and the peak error in the signals furthermore both problems are shown to be coupled and put in a unifying context the bounds are compared and applied to problems concerning ofdm

fuzzifying interval operators fuzzifying convex structures and fuzzy pre orders abstract the paper presents essential connections between fuzzifying convexities fuzzifying interval operators and fuzzy pre orders firstly we study the relationship between fuzzifying convex structures and fuzzifying interval operators on a universal set secondly we show that there exists a connection between based point fuzzy orders and geometric fuzzifying interval operators on fuzzy partially ordered sets finally we establish a connection between fuzzifying convexities and fuzzy pre orders

a systematic method for constructing sparse gaussian integer sequences with ideal periodic autocorrelation functions a gaussian integer is a complex number whose real and imaginary parts are both integers meanwhile a sequence is defined as perfect if and only if it has an ideal periodic auto correlation function this paper proposes a method for constructing sparse perfect gaussian integer sequences spgiss in which most of the sequence elements are zero the proposed spgiss are obtained by linearly combining four base sequences or their cyclic shift equivalents using nonzero gaussian integer coefficients of equal magnitudes each base sequence contains four nonzero elements belonging to the set pm 1 pm j the number of nonzero elements of the constructed spgiss depends on the choice of complex coefficients and cyclic shifts however each spgis has at most 16 nonzero elements irrespective of the sequence length a systematic investigation is performed into the properties of the spgiss and their fourier dual equivalents finally a general expression is derived for a perfect gaussian integer sequence pgis of length 4n where n is any positive integer and most of the sequence elements are nonzero

perfect gaussian integer sequences of arbitrary composite length a composite number can be factored into either n mp or n 2 n where p is an odd prime and m n geq 2 are integers this paper proposes a method for constructing degree 3 and degree 4 perfect gaussian integer sequences pgiss of an arbitrary composite length utilizing an upsampling technique and the base sequence concept proposed by hu wang and li in constructing the pgiss the degree of the sequence is defined as the number of distinct nonzero elements within one period of the sequence this paper commences by constructing degree 3 pgiss of odd prime length followed by degree 2 pgiss of odd prime length the proposed method is then extended to the construction of degree 3 and degree 4 pgiss of composite length n mp finally degree 3 and degree 4 pgiss of length n 4 are built to facilitate the construction of degree 3 and degree 4 pgiss of length n 2 n where n geq 3

constraints on deformable models recovering 3d shape and nongrid motion abstract inferring the 3d structures of nonrigidly moving objects from images is a difficult yet basic problem in computational vision our approach makes use of dynamic elastically deformable object models that offer the geometric flexibility to satisfy a diversity of real world visual constraints we specialize these models to include intrinsic forces inducing a preference for axisymmetry image based constraints are applied as extrinsic forces that mold the symmetry seeking model into shapes consistent with image data we describe an extrinsic force that applies constraints derived from profiles of monocularly viewed objects we generalize this constraint force to incorporate profile information from multiple views and use it to exploit binocular image data for time varying images the force becomes dynamic and the model is able to infer not only depth but nonrigid motion as well we demonstrate the recovery of 3d shape and nonrigid motion from natural imagery

low complexity selected mapping schemes for peak to average power ratio reduction in ofdm systems orthogonal frequency division multiplexing ofdm is an attractive transmission technique for high bit rate communication systems one major drawback of ofdm is the high peak to average power ratio papr of the transmitter s output signal the selected mapping slm approach provides good performance for papr reduction but it requires a bank of inverse fast fourier transforms iffts to generate a set of candidate transmission signals and this requirement usually results in high computational complexity in this paper we propose a kind of low complexity conversions to replace the ifft blocks in the conventional slm method based on the proposed conversions we develop two novel slm schemes with much lower complexity than the conventional one the first method uses only one ifft block to generate the set of candidate signals while the second one uses two ifft blocks computer simulation results show that as compared to the conventional slm scheme the first proposed approach has slightly worse papr reduction performance and the second proposed one reaches almost the same papr reduction performance

automatic active model initialization via poisson inverse gradient active models have been widely used in image processing applications a crucial stage that affects the ultimate active model performance is initialization this paper proposes a novel automatic initialization approach for parametric active models in both 2 d and 3 d the pig initialization method exploits a novel technique that essentially estimates the external energy field from the external force field and determines the most likely initial segmentation examples and comparisons with two state of the art automatic initialization methods are presented to illustrate the advantages of this innovation including the ability to choose the number of active models deployed rapid convergence accommodation of broken edges superior noise robustness and segmentation accuracy

segmentation of external force field for automatic initialization and splitting of snakes active contours or snakes have been extensively utilized in handling image segmentation and classification problems in traditional active contour models snake initialization is performed manually by users and topological changes such as splitting of the snake cannot be automatically handled in this paper we introduce a new method to solve the snake initialization and splitting problem based on an area segmentation approach the external force field is segmented first and then the snake initialization and splitting can be automatically performed by using the segmented external force field such initialization and splitting produces multiple snakes each of which is within the capture range associated to an object and will be evolved to the object boundary the external force used in this paper is a gradient vector flow with an edge preserving property epgvf which can prevent the snakes from passing over weak boundaries to segment the external force field we represent it with a graph and a graph theory approach can be taken to determine the membership of each pixel experimental results establish the effectiveness of the proposed approach

on the computation and reduction of the peak to average power ratio in multicarrier communications for any code c defined over an equal energy constellation it is first shown that at any time instance the problem of determining codewords of c with high peak to average power ratios papr in a multicarrier communication system is intimately related to the problem of minimum distance decoding of c subsequently a method is proposed for computing the papr by minimum distance decoding of c at many points of time moreover an upper bound on the error between this computed value and the true one is derived analogous results are established for codes defined over arbitrary signal constellations as an application of this computational method an approach for reducing the papr of c proposed by jones and wilkinson 1996 is revisited this approach is based on introducing a specific phase shift to each coordinate of all the codewords where phase shifts are independent of the codewords and known both to the transmitter and the receiver we optimize the phase shifts offline by applying our method for computing the papr for the coding scenario proposed by the etsi bran standardization committee reductions of order 4 5 db can be freely obtained using the computed phase shifts examples are provided showing that most of the gain is preserved when the computed optimal phase shifts are rounded to quantenary phase shift keying psk 8 psk and 16 psk type phase shifts

characterizations of l convex spaces via domain theory abstract we provide some new characterizations of l convex spaces by using the way below relation in domain theory for this purpose we first study the notion of domain finiteness in the lattice valued case and then introduce three kinds of spaces algebraic l closure spaces restricted l hull spaces and l entailment spaces these three spaces are shown to be categorically isomorphic to l convex spaces additionally we introduce the notion of l polytopes and prove that a subcollection of a dense l convex structure is a base if and only if it contains all l polytopes these results indicate that in the study of the theory of fuzzy convex spaces fuzzy domain theory has important applications

reed solomon and simplex codes for peak to average power ratio reduction in ofdm new schemes for peak to average power ratio reduction in orthogonal frequency division multiplexing ofdm systems are proposed reed solomon rs and simplex codes are employed to create a number of candidates from which the best are selected thereby in contrast to existing approaches the codes are arranged over a number of ofdm frames rather than over the carriers hence a combination of the principles of multiple signal representation with selection as done in selected mapping and the use of channel coding is present in particular in multiple antenna transmission the proposed schemes do not cause any additional delay but due to the utilization of the dimension space additional gains can be achieved moreover the schemes are very flexible due to the selection step any criterion of optimality can be taken into account besides multiple antenna transmission packet transmission is briefly considered which moreover covers the appealing similarities with incremental redundancy check schemes in automatic repeat request arq applications and with decoding of codes transmitted over the erasure channel the performance of the schemes is using some approximations derived analytically and is covered by numerical results that are in very good agreement with the theory significant gains can be achieved with these very flexible and versatile methods

speckle reducing anisotropic diffusion this paper provides the derivation of speckle reducing anisotropic diffusion srad a diffusion method tailored to ultrasonic and radar imaging applications srad is the edge sensitive diffusion for speckled images in the same way that conventional anisotropic diffusion is the edge sensitive diffusion for images corrupted with additive noise we first show that the lee and frost filters can be cast as partial differential equations and then we derive srad by allowing edge sensitive anisotropic diffusion within this context just as the lee 1980 1981 1986 and frost 1982 filters utilize the coefficient of variation in adaptive filtering srad exploits the instantaneous coefficient of variation which is shown to be a function of the local gradient magnitude and laplacian operators we validate the new algorithm using both synthetic and real linear scan ultrasonic imagery of the carotid artery we also demonstrate the algorithm performance with real sar data the performance measures obtained by means of computer simulation of carotid artery images are compared with three existing speckle reduction schemes in the presence of speckle noise speckle reducing anisotropic diffusion excels over the traditional speckle removal filters and over the conventional anisotropic diffusion method in terms of mean preservation variance reduction and edge localization

an axiomatic approach to bases and subbases in l convex spaces and their applications abstract considering a continuous lattice l as the lattice background an axiomatic approach to bases and subbases in the framework of l convex spaces is provided firstly the concepts of bases and subbases in l convex spaces are introduced and then l convexity base axioms and l convexity subbase axioms are proposed by abstracting the properties of bases and subbases respectively secondly some applications of l convexity base axioms and l convexity subbase axioms are investigated it is shown that l convexity base axioms can be used to demonstrate some relationship between spatial structures with respect to l convex structures and l convexity subbase axioms can be applied to define the join space and the product space of l convex spaces

snakes active contour models a snake is an energy minimizing spline guided by external constraint forces and influenced by image forces that pull it toward features such as lines and edges snakes are active contour models they lock onto nearby edges localizing them accurately scale space continuation can be used to enlarge the capture region surrounding a feature snakes provide a unified account of a number of visual problems including detection of edges lines and subjective contours motion tracking and stereo matching we have used snakes successfully for interactive interpretation in which user imposed constraint forces guide the snake near features of interest

fast constrained surface extraction by minimal paths in this paper we consider a new approach for single object segmentation in 3d images our method improves the classical geodesic active surface model it greatly simplifies the model initialization and naturally avoids local minima by incorporating user extra information into the segmentation process the initialization procedure is reduced to introducing 3d curves into the image these curves are supposed to belong to the surface to extract and thus also constitute user given information hence our model finds a surface that has these curves as boundary conditions and that minimizes the integral of a potential function that corresponds to the image features our goal is achieved by using globally minimal paths we approximate the surface to extract by a discrete network of paths furthermore an interpolation method is used to build a mesh or an implicit representation based on the information retrieved from the network of paths our paper describes a fast construction obtained by exploiting the fast marching algorithm and a fast analytical interpolation method moreover a level set method can be used to refine the segmentation when higher accuracy is required the algorithm has been successfully applied to 3d medical images and synthetic images

asymptotic performance analysis and successive selected mapping for par reduction in ofdm one major drawback of orthogonal frequency division multiplexing ofdm systems is the high peak to average power ratio par of the transmit signal in order to overcome this problem selected mapping slm is a well known method for par reduction in this paper asymptotic performance analysis of slm is carried out and a bound on the maximum tolerable par values is derived starting with the analysis of gaussian signalling at nyquist rate it is also shown that these theoretic results can be applied for qam signalling at any oversampling rate based on the idea to distinguish between tolerable and nontolerable par values a novel variant of slm is derived namely successive slm sslm with this approach it is possible to significantly decrease the average number of assessed signal candidates and the average number of required side information bits per ofdm frame as long as the threshold of tolerable par values is larger than the critical par for nyquist sampled signals as a rule of thumb less than 2 71 euler s number candidates and less than 2 57 bits of side information are required on average

subcategories of the category of l convex spaces abstract in this paper several types of l convex spaces are introduced including stratified l convex spaces convex generated l convex spaces weakly induced l convex spaces and induced l convex spaces their relations are discussed category theoretically firstly it is shown that there is a galois correspondence between the category sl cs of stratified l convex spaces resp the category wil cs of weakly induced l convex spaces and the category l cs of l convex spaces in particular sl cs and wil cs are both coreflective subcategories of l cs secondly it is proved that there is a galois correspondence between the category cs of convex spaces and the category sl cs resp wil cs specially cs can be embedded into sl cs and wil cs as a coreflective subcategory finally it is shown that the category cgl cs of convex generated l convex spaces the category il cs of induced l convex spaces and cs are isomorphic

peak power reduction of ofdm signals with sign adjustment it has recently been shown that significant reduction in the peak to mean envelope power pmepr can be obtained by altering the sign of each subcarrier in a multicarrier system with n subcarriers however finding the best sign not only requires a search over 2n possible signs but also may lead to a substantial rate loss for small size constellations in this paper we first propose a greedy algorithm to choose the signs based on p norm minimization and prove that the resulting pmepr is guaranteed to be less than c log n where c is a constant independent of n for any n this approach has lower complexity in each iteration compared to the derandomization approach of while achieving similar pmepr reduction we further improve the performance of the proposed algorithm by enlarging the search space using pruning simulation results show that pmepr of a multicarrier signal with 128 subcarriers can be reduced to within 1 6 db of the pmepr of a single carrier system in the second part of the paper we address the rate loss by proposing a block coding scheme in which only one sign vector is chosen for k different modulating vectors the sign vector can be computed using the greedy algorithm in n iterations we show that the multi symbol encoding approach can reduce the rate loss by a factor of k while achieving the pmepr of c logkn i e only logarithmic growth in k simulation results show that the rate loss can be made smaller than 10 at the cost of only 1 db increase in the resulting pmepr for a system with 128 subcarriers

generalized bounds on the crest factor distribution of ofdm signals with applications to code design in this paper generalized bounds on the crest factor cf distribution in orthogonal frequency division multiplexing ofdm transmission for both independent and dependent subcarriers are derived here the latter situation represents the coded case for independent subcarriers a general path for bounding practical constellations is provided moreover a complete characterization of their asymptotic behavior is devised and discussed the results are shown to carry over to the spherical constellations improving on recent results for dependent subcarriers the focus is mainly on binary codes where bounds on the cf distribution are obtained in terms of the distance distributions and their duals the asymptotic behavior of codes is analyzed and it is shown that the upper bound on the effective crest factor of a large class of bose chaudhuri hocquenghem bch codes behaves asymptotically as radiclogn finally two applications of the results to code design are presented first fixed phase shifts on the subcarriers for all codewords are used and an algorithm to calculate the phase shifts is designed that way it is proved that the effective cf of any binary code can be scaled to be of order radiclogn for large n without sacrificing on rate furthermore the same approach is applied to calculation of the phases of redundant subcarriers for each codeword it is shown by simulations that the values can be effectively chosen so that the cf is significantly reduced with nonexponential complexity

a novel low complexity precoded ofdm system with reduced papr the computational complexity and peak to average power ratio papr of conventional precoded orthogonal frequency division multiplexing ofdm systems can be reduced using a t ofdm precoded system based on the walsh hadamard matrix the present paper proposes a novel precoding scheme for further reducing the computational complexity and papr of t ofdm in the proposed scheme the precoding matrix is combined with an inverse discrete fourier transform to construct a new transform matrix at the transmitter notably the transform matrix is both unitary and circulant with each column being a perfect gaussian integer sequence containing just four non zero elements of pm 1 pm j a low complexity receiver is additionally constructed for the proposed precoding scheme a closed form expression is derived for the bit error rate ber in t ofdm and the proposed precoding scheme under frequency selective fading channels the simulation results for the ber are shown to be in good agreement with the mathematical derivations in addition it is demonstrated that t ofdm and the proposed scheme have an equivalent ber performance when their precoding matrices are designed in such a way as to obtain full frequency diversity however the proposed scheme has a better papr performance and a lower computational complexity than t ofdm

on fuzzy topology fuzzy convexity spaces and fuzzy local convexity abstract in this paper we consider a fuzzy topology together with a fuzzy convexity on the same underlying set x and introduce fuzzy topology convexity spaces ftfcs we also introduce the notion on fuzzy local convexity we also study certain related topics in this context like subspace product and quotient the special case when the fuzzy topology is compatible with a fuzzy convexity is discussed in a separate paper

dynamic directional gradient vector flow for snakes snakes or active contour models have been widely used in image segmentation however most present snake models do not discern between positive and negative step edges in this paper a new type of dynamic external force for snakes named dynamic directional gradient vector flow ddgvf is proposed that uses this information for better performance it makes use of the gradients in both x and y directions and deals with the external force field for the two directions separately in snake deformation the ddgvf field is utilized dynamically according to the orientation of snake in each iteration experimental results demonstrate that the ddgvf snake provides a much better segmentation than gvf snake in situations when edges of different directions are present which pose confusion for segmentation

gaussian integer sequences with ideal periodic autocorrelation functions a gaussian integer is a complex number whose real and imaginary parts are both integers meanwhile a sequence is defined as perfect if and only if the out of phase value of the periodic autocorrelation function is equal to zero this paper presents two novel classes of perfect sequences constructed using two groups of base sequences the nonzero elements of these base sequences belong to the set 1 j a perfect sequence can be obtained by linearly combining these base sequences or their cyclic shift equivalents with arbitrary nonzero complex coefficients of equal magnitudes in general the elements of the constructed sequences are not gaussian integers however if the complex coefficients are gaussian integers then the resulting perfect sequences will be gaussian integer perfect sequences gipss in addition a periodic cross correlation function is derived which has the same mathematical expression as the investigated sequences finally the maximal energy efficiency of the proposed gipss is investigated

second fundamental measure of geometric sets and local approximation of curvatures using the theory of normal cycles we associate with each geometric subset of a riemannian manifold a tensor valued curvature measure which we call its second fundamental measure this measure provides a finer description of the geometry of singular sets than the standard curvature measures moreover we deal with approximation of curvature measures we get a local quantitative estimate of the difference between curvature measures of two geometric subsets when one of them is a smooth hypersurface

novel low complexity slm schemes for papr reduction in ofdm systems selected mapping slm schemes are commonly employed to reduce the peak to average power ratio papr in orthogonal frequency division multiplexing ofdm systems it has been shown that the computational complexity of the traditional slm scheme can be substantially reduced by adopting conversion vectors obtained by using the inverse fast fourier transform ifft of the phase rotation vectors in place of the conventional ifft operations c l wang and y ouyang low complexity selected mapping schemes for peak to average power ratio reduction in ofdm systems ieee trans signal process vol 53 no 12 pp 4652 4660 dec 2005 to ensure that the elements of these phase rotation vectors have an equal magnitude conversion vectors should have the form of a perfect sequence this paper presents three novel classes of perfect sequence each of which comprises certain base vectors and their cyclically shifted versions three novel low complexity slm schemes are then proposed based upon the unique structures of these perfect sequences it is shown that while the papr reduction performances of the proposed schemes are marginally poorer than that of the traditional slm scheme the three schemes achieve a substantially lower computational complexity

on multicarrier signals where the pmepr of a random codeword is asymptotically logn multicarrier signals exhibit a large peak to mean envelope power ratio pmepr in this correspondence without using a gaussian assumption we derive lower and upper probability bounds for the pmepr distribution when the number of subcarriers n is large even though the worst case pmepr is of the order of n the main result is that the pmepr of a random codeword c c sub 1 c sub n is logn with probability approaching one asymptotically for the following three general cases i c sub i s are independent and identically distributed i i d chosen from a complex quadrature amplitude modulation qam constellation in which the real and imaginary part of c sub i each has i i d and even distribution not necessarily uniform ii c sub i s are i i d chosen from a phase shift keying psk constellation where the distribution over the constellation points is invariant under spl pi 2 rotation and iii c is chosen uniformly from a complex sphere of dimension n based on this result it is proved that asymptotically the varshamov gilbert vg bound remains the same for codes with pmepr of less than logn chosen from qam psk constellations

constraining active contour evolution via lie groups of transformation we present a novel approach to constraining the evolution of active contours used in image analysis the proposed approach constrains the final curve obtained at convergence of curve evolution to be related to the initial curve from which evolution begins through an element of a desired lie group of plane transformations constraining curve evolution in such a way is important in numerous tracking applications where the contour being tracked in a certain frame is known to be related to the contour in the previous frame through a geometric transformation such as translation rotation or affine transformation for example it is also of importance in segmentation applications where the region to be segmented is known up to a geometric transformation our approach is based on suitably modifying the euler lagrange descent equations by using the correspondence between lie groups of plane actions and their lie algebras of infinitesimal generators and thereby ensures that curve evolution takes place on an orbit of the chosen transformation group while remaining a descent equation of the original functional the main advantage of our approach is that it does not necessitate any knowledge of nor any modification to the original curve functional and is extremely straightforward to implement our approach therefore stands in sharp contrast to other approaches where the curve functional is modified by the addition of geometric penalty terms we illustrate our algorithm on numerous real and synthetic examples

upper bounds on the statistical distribution of the crest factor in ofdm transmission this article analyzes the crest factor behavior of an orthogonal frequency division multiplexing ofdm modem the behavior is characterized in terms of the complementary distribution function of the crest factor cdfc the cdfc is a key parameter of ofdm systems for example it provides limits on achievable information rates several approximations have been developed in the literature so far but no true upper bounds dependent on the different constellations that are used in ofdm modulation have been derived a new approach is given providing upper bounds that substitute for time consuming simulations

multigrid geometric active contour models geometric active contour models are very popular partial differential equation based tools in image analysis and computer vision we present a new multigrid algorithm for the fast evolution of level set based geometric active contours and compare it with other established numerical schemes we overcome the main bottleneck associated with most numerical implementations of geometric active contours namely the need for very small time steps to avoid instability by employing a very stable fully 2 d implicit explicit time integration numerical scheme the proposed scheme is more accurate and has improved rotational invariance properties compared with alternative split schemes particularly when big time steps are utilized we then apply properly designed multigrid methods to efficiently solve the occurring sparse linear system the combined algorithm allows for the rapid evolution of the contour and convergence to its final configuration after very few iterations image segmentation experiments demonstrate the efficiency and accuracy of the method

a general discrete contour model in two three and four dimensions for topology adaptive multichannel segmentation we present a discrete contour model for the segmentation of image data with any dimension of image domain and value range the model consists of a representation using simplex meshes and a mechanical formulation of influences that drive an iterative segmentation the object s representation as well as the influences are valid for any dimension of the image domain the image influences introduced here can combine information from independent channels of higher dimensional value ranges additionally the topology of the model automatically adapts to objects contained in images noncontextual tests have validated the ability of the model to reproducibly delineate synthetic objects in particular images with a signal to noise ratio of snr spl les 0 5 are delineated within two pixels of their ground truth contour contextual validations have shown the applicability of the model for medical image analysis in image domains of two three and four dimensions in single as well as multichannel value ranges

on simple oversampled a d conversion in l sup 2 r the accuracy of oversampled analog to digital a d conversion the dependence of accuracy on the sampling interval spl tau and on the bit rate r are characteristics fundamental to a d conversion but not completely understood these characteristics are studied for oversampled a d conversion of band limited signals in l sup 2 r we show that the digital sequence obtained in the process of oversampled a d conversion describes the corresponding analog signal with an error which tends to zero as spl tau sup 2 in energy provided that the quantization threshold crossings of the signal constitute a sequence of stable sampling in the respective space of band limited functions further we show that the sequence of quantized samples can be represented in a manner which requires only a logarithmic increase in the bit rate with the sampling frequency r o log spl tau and hence that the error of oversampled a d conversion actually exhibits an exponential decay in the bit rate as the sampling interval tends to zero

image segmentation based on the poincare map method active contour models acms integrated with various kinds of external force fields to pull the contours to the exact boundaries have shown their powerful abilities in object segmentation however local minimum problems still exist within these models particularly the vector field s equilibrium issues different from traditional acms within this paper the task of object segmentation is achieved in a novel manner by the poincare map method in a defined vector field in view of dynamical systems an interpolated swirling and attracting flow isaf vector field is first generated for the observed image then the states on the limit cycles of the isaf are located by the convergence of newton raphson sequences on the given poincare sections meanwhile the periods of limit cycles are determined consequently the objects boundaries are represented by integral equations with the corresponding converged states and periods experiments and comparisons with some traditional external force field methods are done to exhibit the superiority of the proposed method in cases of complex concave boundary segmentation multiple object segmentation and initialization flexibility in addition it is more computationally efficient than traditional acms by solving the problem in some lower dimensional subspace without using level set methods

theory of topological molecular lattices abstract the aim of this paper is to bring the theories of point set topology fuzzy topology and l fuzzy topology into a unified theory the theory of topological molecular lattices for this purpose we first introduce the concepts of molecule for completely distributive complete lattice molecular lattice for short the cotopology on it and the concept of remote neighborhoods of molecules therefrom we develop the theory of pointwise topology on molecular lattices

active appearance models we describe a new method of matching statistical models of appearance to images a set of model parameters control modes of shape and gray level variation learned from a training set we construct an efficient iterative matching algorithm by learning the relationship between perturbations in the model parameters and the induced image errors

fuzzy counterparts of hull operators and interval operators in the framework of l convex spaces abstract for fuzzy counterparts of hull operators and interval operators two types of fuzzy hull operators and one type of fuzzy interval operators are proposed firstly the concept of l hull operators is introduced and the resulting category is shown to be isomorphic to that of l convex spaces secondly considering the graded inclusions of l subsets the notion of l ordered hull operators is presented which is shown to be categorically isomorphic to strong l convex structures finally the concept of l interval operators is introduced and it is shown that there is a galois correspondence between the category of l interval spaces and that of l convex spaces in particular the category of arity 2 l convex spaces can be reflectively embedded into that of l interval spaces

snakes shapes and gradient vector flow snakes or active contours are used extensively in computer vision and image processing applications particularly to locate object boundaries problems associated with initialization and poor convergence to boundary concavities however have limited their utility this paper presents a new external force for active contours largely solving both problems this external force which we call gradient vector flow gvf is computed as a diffusion of the gradient vectors of a gray level or binary edge map derived from the image it differs fundamentally from traditional snake external forces in that it cannot be written as the negative gradient of a potential function and the corresponding snake is formulated directly from a force balance condition rather than a variational formulation using several two dimensional 2 d examples and one three dimensional 3 d example we show that gvf has a large capture range and is able to move snakes into boundary concavities

l metric on the space of l fuzzy numbers abstract in this article a natural l topology is constructed on the set of l fuzzy numbers which is called the standard l topology it is proved that the standard l topology can be induced by an l metric the space of trapezoidal fuzzy numbers can be regarded as a subspace of the space of l fuzzy numbers an l metric on the set of trapezoidal fuzzy numbers is presented

some properties of m fuzzifying convexities induced by m orders abstract in this paper the notions of geometric interval spaces convex geometries and base point orders in the theory of convexity spaces are generalized to m fuzzifying convexity spaces using m fuzzifying restricted hull operators the m fuzzifying convexity spaces induced by m orders are defined conveniently then it is shown that m fuzzifying convexity spaces induced by m orders are m fuzzifying jhc and arity 2 and if the m order is strongly anti symmetric then the m fuzzifying convexity space is an m fuzzifying convex geometry and its segment operator is an m fuzzifying geometric interval operator

geodesic active contours and level sets for the detection and tracking of moving objects this paper presents a new variational framework for detecting and tracking multiple moving objects in image sequences motion detection is performed using a statistical framework for which the observed interframe difference density function is approximated using a mixture model this model is composed of two components namely the static background and the mobile moving objects one both components are zero mean and obey laplacian or gaussian law this statistical framework is used to provide the motion detection boundaries additionally the original frame is used to provide the moving object boundaries then the detection and the tracking problem are addressed in a common framework that employs a geodesic active contour objective function this function is minimized using a gradient descent method a new approach named hermes is proposed which exploits aspects from the well known front propagation algorithms and compares favorably to them very promising experimental results are provided using real video sequences

fundamental duality of abstract categories and its applications given an abstract category c c m l spaces that are categorical generalization of fixed basis fuzzy topological spaces in c and their category c m l top are introduced it is pointed out as one of the main contributions of this paper that c is dually adjoint to c m l top by defining l spatiality in c and l sobriety in c m l top this adjunction induces a dual equivalence between the full subcategory of c of all l spatial objects and the full subcategory of c m l top of all l sober objects the present adjunction and duality are fruitful categorical extensions of the classical top loc adjunction and sobtop spatloc duality to abstract categories with a great deal of applications in particular their applications to q categories quasivarieties and augmented posets are given

simplified approach to optimized iterative clipping and filtering for papr reduction of ofdm signals iterative clipping and filtering icf is a well known technique to reduce the peak to average power ratio papr of orthogonal frequency division multiplexing ofdm signals recently wang and luo investigated the clipped signal and proposed a modified algorithm called optimized icf oicf this is an optimal algorithm since it can achieve the required papr reduction with minimum in band distortion and far fewer iterations however oicf needs to solve a convex optimization problem with o n3 complexity where n represents the number of subcarriers in this paper instead of analyzing the clipped signal we study the clipping noise and propose a simplified oicf algorithm in the new algorithm solving the convex optimization problem is approximated by some simple algebraic operations and the computational complexity reduces to o n simulation results show that after three iterations the original oicf algorithm can achieve the desired papr while the simplified one exhibits almost the same performance for a 128 subcarrier and quadrature phase shift keying qpsk modulated ofdm system the papr reduction performance difference between the two algorithms are 5 10 3db at a 10 4 clipping probability and the bit error rate performance difference is 6 10 3 db at a 10 7 error probability

on the reflective and coreflective subcategory of stratified l cech closure spaces abstract in this paper it is shown that the category of cech closure spaces can be embedded in the category of stratified l cech closure spaces as a coreflective full subcategory furthermore if the underlying lattice of the complete residuated lattice l is completely distributive the embedding is also reflective finally some related commutative diagrams are obtained

variational segmentation of vector valued images with gradient vector flow in this paper we extend the gradient vector flow field for robust variational segmentation of vector valued images rather than using scalar edge information we define a vectorial edge map derived from a weighted local structure tensor of the image that enables the diffusion of the gradient vectors in accurate directions through the 4d gradient vector flow equation to reduce the contribution of noise in the structure tensor image channels are weighted according to a blind estimator of contrast the method is applied to biological volume delineation in dynamic pet imaging and validated on realistic monte carlo simulations of numerical phantoms as well as on real images

generation and correlation architectures of multilevel complementary sets of sequences complementary sets of sequences css are used extensively in many applications as channel estimation and synchronization preamble or as a basic block for the generation of generalized orthogonal go sequences nevertheless binary css exist for very limited lengths while for multilevel css there are fewer limitations in the sequence length this paper presents two modular architectures for the generation and correlation of k multilevel css an algorithm for k 2k k n 0 multilevel css and another for k 3 4 multilevel css in contrast to previous generation algorithms the proposed architectures reduce the number of computations needed to perform the correlation of k multilevel css when compared to those required with a straightforward architecture furthermore these architectures can be used as a starting point for the search of multilevel css with low peak to average power ratio papr and flexible length

active contour external force using vector field convolution for image segmentation snakes or active contours have been widely used in image processing applications typical roadblocks to consistent performance include limited capture range noise sensitivity and poor convergence to concavities this paper proposes a new external force for active contours called vector field convolution vfc to address these problems vfc is calculated by convolving the edge map generated from the image with the user defined vector field kernel we propose two structures for the magnitude function of the vector field kernel and we provide an analytical method to estimate the parameter of the magnitude function mixed vfc is introduced to alleviate the possible leakage problem caused by choosing inappropriate parameters we also demonstrate that the standard external force and the gradient vector flow gvf external force are special cases of vfc in certain scenarios examples and comparisons with gvf are presented in this paper to show the advantages of this innovation including superior noise robustness reduced computational cost and the flexibility of tailoring the force field

l fuzzy numbers and their properties in this paper the notions of l fuzzy convex sets and l fuzzy numbers are introduced where l is a completely distributive lattice the notions of 0 1 fuzzy convex sets and 0 1 fuzzy numbers are generalized furthermore their properties and characterizations are presented in terms of cut sets of l fuzzy sets

average power reduction for msm optical signals via sparsity and uncertainty principle multiple subcarrier modulation is an appealing scheme for high data rate optical communication however a major drawback is its low average power efficiency while subcarrier reservation is a common approach to combat this problem little is known about the performance of algorithms that utilize subcarrier reservation by combining properties of sparse signals with an abstract form of the uncertainty principle related to multiple subcarrier signals we design an effective iterative method for constructing average power efficient multicarrier signals unlike most existing subcarrier reservation methods our method provides a guaranteed bound for the achievable average power reduction as well as guaranteed rates of convergence numerical simulations demonstrate the performance of the proposed method

amplitude and sign adjustment for peak to average power reduction in this letter we propose a method to reduce the peak to mean envelope power ratio pmepr of multicarrier signals by modifying the constellation for m ary phase shift keying constellations we minimize the maximum of the multicarrier signal over the sign and amplitude of each subcarrier in order to find an efficient solution to the aforementioned nonconvex optimization problem we present a suboptimal solution by first optimizing over the signs and then optimizing over the amplitudes given the signs we prove that the minimization of the maximum of a continuous multicarrier signal over the amplitude of each subcarrier can be written as a convex optimization problem with linear matrix inequality constraints we also generalize the idea to other constellations such as 16 quadrature amplitude modulation simulation results show that by an average power increase of 0 21 db and not sending information over the sign of each subcarrier pmepr can be decreased by 5 1 db for a system with 128 subcarriers

existence of codes with constant pmepr and related design recently several coding methods have been proposed to reduce the high peak to mean envelope ratio pmepr of multicarrier signals it has also been shown that with probability one the pmepr of any random codeword chosen from a symmetric quadrature amplitude modulation phase shift keying qam psk constellation is logn for large n where n is the number of subcarriers therefore the question is how much reduction beyond logn can one asymptotically achieve with coding and what is the price in terms of the rate loss in this paper by optimally choosing the sign of each subcarrier we prove the existence of q ary codes of constant pmepr for sufficiently large n and with a rate loss of at most log sub q 2 we also obtain a varsharmov gilbert type upper bound on the rate of a code given its minimum hamming distance with constant pmepr for large n since ours is an existence result we also study the problem of designing signs for pmepr reduction motivated by a derandomization algorithm suggested by spencer we propose a deterministic and efficient algorithm to design signs such that the pmepr of the resulting codeword is less than clogn for any n where c is a constant independent of n for symmetric q ary constellations this algorithm constructs a code with rate 1 log sub q 2 and with pmepr of clogn with simple encoding and decoding simulation results for our algorithm are presented

a computational approach to edge detection this paper describes a computational approach to edge detection the success of the approach depends on the definition of a comprehensive set of goals for the computation of edge points these goals must be precise enough to delimit the desired behavior of the detector while making minimal assumptions about the form of the solution we define detection and localization criteria for a class of edges and present mathematical forms for these criteria as functionals on the operator impulse response a third criterion is then added to ensure that the detector has only one response to a single edge we use the criteria in numerical optimization to derive detectors for several common image features including step edges on specializing the analysis to step edges we find that there is a natural uncertainty principle between detection and localization performance which are the two main goals with this principle we derive a single operator shape which is optimal at any scale the optimal detector has a simple approximate implementation in which edges are marked at maxima in gradient magnitude of a gaussian smoothed image we extend this simple detector using operators of several widths to cope with different signal to noise ratios in the image we present a general method called feature synthesis for the fine to coarse integration of information from operators at different scales finally we show that step edge detector performance improves considerably as the operator point spread function is extended along the edge

the continuous time peak to average power ratio of ofdm signals using complex modulation schemes computing the continuous time peak to average power ratio papr of ofdm signals is computationally challenging the pioneering work by tellambura applies only to ofdm signals using real valued modulation schemes in this paper a practical technique for evaluating the continuous time papr of ofdm signals using complex modulation is presented using the proposed scheme it is confirmed that the four time oversampled discrete time papr is a good approximation of the continuous time papr even for complex ofdm signals furthermore the proposed scheme is employed to verify some existing analytical bounds on continuous papr in the literature

low complexity transmitter architectures for sfbc mimo ofdm systems multiple input multiple output mimo orthogonal frequency division multiplexing ofdm systems with space frequency block coding sfbc have a high computational complexity since the number of inverse fast fourier transforms iffts required scales in direct proportion to the number of antennas at the transmitter this paper proposes to generate the sfbc encoded signals of the various antennas in time domain by exploiting the time domain signal properties and signal correlations among the various transmitter antennas achieving a significant reduction in computational complexity in particular it is demonstrated that the time domain sfbc encoded signals of the various antennas can be obtained from the time domain signal of the first antenna therefore the proposed scheme requires only one ifft irrespective of the number of transmission antennas in addition a low complexity peak to average power ratio papr reduction scheme is presented based on the proposed transmitter architectures

the shortest path problem on a fuzzy time dependent network in this study we introduce a fuzzy time dependent network ftdn and analyze its shortest path problem the ftdn is a network in which travel times are represented as fuzzy sets and are also time dependent under these circumstances the shortest path problem on the ftdn is far more complex in comparison with the shortest path problem on the existing networks to highlight the complexity we show that on the ftdn standard shortest path algorithms e g the well known dijkstra algorithm are not able to come up with solutions subsequently we construct a suitable method which is suitable to deal with the shortest problem a fuzzy programming model is presented for finding the shortest path on the ftdn the proposed model is handled through the techniques which combine mechanisms of fuzzy simulation and genetic optimization in this particular setting fuzzy simulation is exploited to estimate the value of uncertain functions which do not exist in the general networks the proposed model is evaluated with the use of numerical experimentation a comparative analysis demonstrates that the proposed model leads to the shortest path while standard algorithms are not capable of finding the path when dealing with the shortest path problem on the ftdn

there exists no globally uniformly convergent reconstruction for the paley wiener space cal pw _ pi 1 of bandlimited functions sampled at nyquist rate the bandlimited interpolation of signals and the convergence behavior of the shannon sampling series are discussed in order to show that it is desirable to have a uniformly convergent reconstruction for as large a space of signals as possible in this paper general sampling series are analyzed for the frequently utilized paley wiener space pw pi 1 which is the largest space in the scale of paley wiener spaces the analysis is done not only for the shannon sampling series but for a whole class of axiomatically defined reconstruction processes it is shown that for this very general class which contains all common sampling series including the shannon sampling series a uniformly convergent reconstruction is not possible for the space pw pi 1 moreover a universal signal is identified that causes the divergence behavior for all sampling series finally a lower and an upper bound are derived and used to describe the asymptotic behavior of the peak value of the finite sampling series

cross entropy based sign selection algorithms for peak to average power ratio reduction of ofdm systems sign selection uses a set of subcarrier signs to reduce the peak to average power ratio par of orthogonal frequency division multiplexing ofdm however the computational complexity worst case is exponential in n the number of subcarriers suboptimal sign selection algorithms achieving different tradeoffs between the par reduction and complexity have thus been developed for example the derandomization method achieves high par reduction of o log n with relatively high complexity of o n2 on the other hand selective mapping slm and partial transmit sequences pts sacrifice the achievable par reduction for lower complexity in this paper we develop two new cross entropy ce based sign selection algorithms our algorithms simultaneously updates the probabilities of the signs of all subcarriers the first algorithm obtains a par lower than the above methods with a complexity level of o n2 however if the number of iterations is fixed this algorithm obtains the same par reduction as derandomization but with o n log n complexity practical par reduction algorithms require that the extra cost of par reduction must be small therefore we propose the second algorithm which adaptively adjusts the probability of elite samples and stops whenever a par threshold is reached our second algorithm achieves up to 95 complexity savings over the first with only a 0 4 db par reduction loss the simulations confirm the complexity advantages of the proposed algorithms compared to slm and derandomization

dynamic programming for detecting tracking and matching deformable contours the problem of segmenting an image into separate regions and tracking them over time is one of the most significant problems in vision terzopoulos et al 1987 proposed an approach to detect the contour regions of complex shapes assuming a user selected initial contour not very far from the desired solution we propose to further explore the information provided by the user s selected points and apply an optimal method to detect contours which allows a segmentation of the image the method is based on dynamic programming dp and applies to a wide variety of shapes it is exact and not iterative we also consider a multiscale approach capable of speeding up the algorithm by a factor of 20 although at the expense of losing the guaranteed optimality characteristic the problem of tracking and matching these contours is addressed for tracking the final contour obtained at one frame is sampled and used as initial points for the next frame then the same dp process is applied for matching a novel strategy is proposed where the solution is a smooth displacement field in which unmatched regions are allowed while cross vectors are not the algorithm is again based on dp and the optimal solution is guaranteed we have demonstrated the algorithms on natural objects in a large spectrum of applications including interactive segmentation and automatic tracking of the regions of interest in medical images

global minimum for active contour models a minimal path approach a new boundary detection approach for shape modeling is presented it detects the global minimum of an active contour model s energy between two end points initialization is made easier and the curve is not trapped at a local minimum by spurious edges we modify the snake energy by including the internal regularization term in the external potential term our method is based on finding a path of minimal length in a riemannian metric we then make use of a new efficient numerical method to find this shortest path it is shown that the proposed energy though based only on a potential integrated along the curve imposes a regularization effect like snakes we explore the relation between the maximum curvature along the resulting contour and the potential generated from the image the method is capable to close contours given only one point on the objects boundary by using a topology based saddle search routine we show examples of our method applied to real aerial and medical images

stratified categorical fixed basis fuzzy topological spaces and their duality abstract for an abstract category c a class m of c monomorphisms and a fixed c object l we introduce stratified c m l spaces to be categorical counterparts of stratified fixed basis fuzzy topological spaces in c and consider their category sc m l top as two main results of this paper it is shown that sc m l top is dually adjoint to the comma category l c and this adjunction can be restricted to a dual equivalence between the full category of l c with comma spatial objects and the full category of sc m l top with comma sober objects the present paper also describes applications and relationships of these results to stratified fixed basis fuzzy topological spaces in this respect a considerable part of this paper is devoted to stratified l quasi topological spaces and their duality

novel conversion matrices for simplifying the ifft computation of an slm based papr reduction scheme for ofdm systems there have been a set of conversion matrices proposed recently by wang and ouyang to simplify the inverse fast fourier transform ifft computation involved in the selected mapping slm scheme for reduction of the peak to average power ratio papr in orthogonal frequency division multiplexing ofdm systems as compared to the conventional slm scheme the modified approach achieves close papr reduction with much lower complexity but degraded bit error rate ber performance in this paper we propose a new set of conversion matrices for the slm scheme such that the complexity can be reduced without sacrificing the ber performance it is shown that the improved slm method has better ber performance and lower complexity than the previous work by wang and ouyang at the cost of a slight papr reduction loss

rags region aided geometric snake an enhanced region aided geometric active contour that is more tolerant toward weak edges and noise in images is introduced the proposed method integrates gradient flow forces with region constraints composed of image region vector flow forces obtained through the diffusion of the region segmentation map we refer to this as the region aided geometric snake or rags the diffused region forces can be generated from any reliable region segmentation technique greylevel or color this extra region force gives the snake a global complementary view of the boundary information within the image which along with the local gradient flow helps detect fuzzy boundaries and overcome noisy regions the partial differential equation pde resulting from this integration of image gradient flow and diffused region flow is implemented using a level set approach we present various examples and also evaluate and compare the performance of rags on weak boundaries and noisy images

high rate codes with bounded pmepr for bpsk and other symmetric constellations in this letter we consider the problem of constructing high rate codes with low peak to mean envelope power ratio pmepr for multicarrier signals assuming coefficients of the multicarrier signal are chosen from a symmetric q ary constellation we construct codes with rate 1 1 r logq2 and pmepr of less than crlogn for any r and n where n is the number of subcarriers and c is a constant independent of n and r the construction is based on dividing n subcarriers into n r groups of r subcarriers and choosing a sign for each group to minimize the pmepr the signs are chosen using a variation of the algorithm proposed by the authors in previous papers for large n we can in fact construct a code with a rate of 1 o 1 logn and pmepr of less than clog2n for binary phase shift keying modulated signals this partially solves the problem posed by litsyn and implies a construction of 2n 2 codewords with pmepr less than 2clogn