from one cell to the whole froth a dynamical map we investigate two and three dimensional shell structured inflatable froths which can be constructed by a recursion procedure adding successive layers of cells around a germ cell we prove that any froth can be reduced into a system of concentric shells there is only a restricted set of local configurations for which the recursive inflation transformation is not applicable these configurations are inclusions between successive layers and can be treated as vertices and edges decorations of a shell structured inflatable skeleton the recursion procedure is described by a logistic map which provides a natural classification into euclidean hyperbolic and elliptic froths froths tiling manifolds with different curvatures can be classified simply by distinguishing between those with a bounded or unbounded number of elements per shell without any a priori knowledge on their curvature a result associated with maximal orientational entropy is obtained on topological properties of natural cellular systems the topological characteristics of all experimentally known tetrahedrally close packed structures are retrieved

twenty five years of multifractals in fully developed turbulence a tribute to giovanni paladin the paper on the multifractal nature of fully developed turbulence and chaotic systems by benzi et al 1984 j phys a math gen 17 3521 has been a starting point of many investigations on the different faces of self similarity and intermittency in turbulent phenomena since then the multifractal model has become a useful tool for the study of small scale turbulence in particular for detailed predictions of different eulerian and lagrangian statistical properties on the occasion of the 50th birthday of our unforgettable friend and colleague giovanni paladin 1958 1996 we review here the basic concepts and some applications of the multifractal model for turbulence

exact location of the multicritical point for finite dimensional spin glasses a conjecture we present a conjecture on the exact location of the multicritical point in the phase diagram of spin glass models in finite dimensions by generalizing our previous work we combine duality and gauge symmetry for replicated random systems to derive formulae which make it possible to understand all the relevant available numerical results in a unified way the method applies to non self dual lattices as well as to self dual cases in the former case of which we derive a relation for a pair of values of multicritical points for mutually dual lattices the examples include the j and gaussian ising spin glasses on the square hexagonal and triangular lattices the potts and zq models with chiral randomness on these lattices and the three dimensional j ising spin glass and the random plaquette gauge model

fluctuation response relation in turbulent systems we address the problem of measuring time properties of response functions green functions in gaussian models orszag mclaughin and strongly non gaussian models shell models for turbulence we introduce the concept of halving time statistics to have a statistically stable tool to quantify the time decay of response functions and generalized response functions of high order we show numerically that in shell models for three dimensional turbulence response functions are inertial range quantities this is a strong indication that the invariant measure describing the shell velocity fluctuations is characterized by short range interactions between neighboring shells

two point two time closures applied to forced isotropic turbulence abstract the direct interaction approximation and the local energy transfer theory were used to calculate freely decaying turbulence for a range of initial taylor reynolds numbers 3 r t 0 129 and forced turbulence for evolved taylor reynolds numbers r t evolved 88 and r t evolved 232 in the case of the freely decaying turbulence the new feature of the work as compared to mccomb et al j fluid mech 245 1992 279 was the ability to make comparisons with a direct numerical simulation at the same initial conditions we were also able to obtain experimental results from the simulation with an estimate of the experimental error we present a small sample of results from an extensive investigation sufficient to confirm that both closures agree with the simulation to within the experimental error in broad agreement with our earlier investigations however the main motivation of the work was to study the application of the closures to stationary turbulence and here we faced new problems such as how to force the closures or the need to compute the time history integrals of the closures over the long transient period during which the numerical simulation settles down for this reason our results should be seen as rather preliminary and tentative in nature essentially we found that agreement between the closures and the simulation was not as good as for free decay for low wavenumber behaviour but was quite good for high wavenumber spectra and quantities determined by this region such as the taylor microscale we conclude that further work is needed to establish just what is a fair comparison between forced closure calculations and the analogous direct numerical simulation

dynamics and topological aspects of a reconstructed two dimensional foam time series using potts model on a pinned lattice we discuss a method to reconstruct an approximate two dimensional foam structure from an incomplete image using the extended potts model on a pinned lattice the initial information consists of the positions of the vertices only we locate the centers of the bubbles using the euclidean distance map construction and assign at each vertex position a continuous pinning field with a potential falling off as 1 r we nucleate a bubble at each center using the extended potts model and let the structure evolve under the constraint of scaled target areas until the bubbles contact each other the target area constraint and pinning centers prevent further coarsening we then turn the area constraint off and let the edges relax to a minimum energy configuration the result is a reconstructed structure very close to the simulation we repeated this procedure for various stages of the coarsening of the same simulated foam and investigated the simulation and reconstruction dynamics topology and area distribution finding that they agreed to good accuracy

asymptotic freedom non gaussian perturbation theory and the application of renormalization group theory to isotropic turbulence a model equation with an extended range of asymptotic freedom is used as the basis of a non gaussian perturbation expansion in powers of the control parameter of the conditional average re expansion in the local reynolds number allows the systematic rederivation of an earlier heuristic theory w d mccomb and a g watt phys rev lett 65 3281 1990

multicritical dynamics for the j ising model exact dynamical properties are discussed for the j ising model around the multicritical point mcp it is found that the relation of relaxations between the non equilibrium remanent magnetization m t and the equilibrium autocorrelation function q t at the mcp is different from that at the pure critical point the dynamic critical exponent for the ferromagnetic ordering defined by and that for the spin glass ordering defined by become identical at the mcp accurate numerical calculations for them are performed in two and three dimensions using the non equilibrium relaxation analysis the mcp is located at and the exponent is estimated as for the square lattice they are estimated as and for the simple cubic lattice

direct numerical simulation based measurement of the mean impulse response of homogeneous isotropic turbulence a technique for measuring the mean impulse response function of stationary homogeneous isotropic turbulence is proposed such a measurement is carried out here on the basis of direct numerical simulation dns a zero mean white noise volume forcing is used to probe the turbulent flow and the response function is obtained by accumulating the space time correlation between the white forcing and the velocity field this technique to measure the turbulent response in a dns numerical experiment is a research tool in that field of spectral closures where the linear response concept is invoked either by resorting to renormalized perturbations theories or by introducing the well known fluctuation dissipation relation fdr although the results obtained in the present work are limited to relatively low values of the reynolds number a preliminary analysis is possible both the characteristic form and the time scaling properties of the response function are investigated in the universal subrange of dissipative wave numbers a comparison with the response approximation given by the fdr is proposed through the independent dns measurement of the correlation function very good agreement is found between the measured response and kraichnan s description of random energy range advection effects

on the universality of the kolmogorov constant in numerical simulations of turbulence motivated by a recent survey of experimental data k r sreenivasan phys fluids 2778 1995 we examine data on the kolmogorov spectrum constant in numerical simulations of isotropic turbulence using results both from previous studies and from new direct numerical simulations over a range of reynolds numbers up to 240 on the taylor scale at grid resolutions up to 5123 it is noted that in addition to k 5 3 scaling identification of a true inertial range requires spectral isotropy in the same wavenumber range we found that a plateau in the compensated three dimensional energy spectrum at k eta 0 1 0 2 commonly used to infer the kolmogorov constant from the compensated three dimensional energy spectrum actually does not represent proper inertial range behavior rather a proper if still approximate inertial range emerges at k eta 0 02 0 05 when r sub sub sub sub sub sub sub sub 0 53 for c 1 62 in excellent agreement with experiments however the one and three dimensional estimates are not fully consistent because of departures due to numerical and statistical limitations from isotropy of the computed spectra at low wavenumbers the inertial scaling of structure functions in physical space is briefly addressed since dns is still restricted to moderate reynolds numbers an accurate evaluation of the kolmogorov constant is very difficult we focus on providing new insights on the interpretation of kolmogorov 1941 similarity in the dns literature and do not consider issues pertaining to the refined similarity hypotheses of kolmogorov

new perspectives in turbulence scaling laws asymptotics and intermittency intermittency a basic property of fully developed turbulent flow decreases with growing viscosity therefore classical relationships obtained in the limit of vanishing viscosity must be corrected when the reynolds number is finite but large these corrections are the main subject of the present paper they lead to a new scaling law for wall bounded turbulence which is of key importance in engineering and to a reinterpretation of the kolmogorov obukhov scaling for the local structure of turbulence which has been of paramount interest in both theory and applications the background of these results is reviewed in similarity methods in the statistical theory of vortex motion and in intermediate asymptotics and relevant experimental data are summarized

eulerian spectral closures for isotropic turbulence using a time ordered fluctuation dissipation relation in a previous paper 1 the kraichnan wyld perturbation expansion 2 3 was used to justify the introduction of a renormalized response function connecting two point covariances at different times the resulting relationship was specialized by suitable choice of initial conditions to the form of a fluctuation dissipation relation fdr this was further developed to reconcile the time symmetry of the covariance with the causality of the response function by the introduction of time ordering along with a counter term we pointed out that this formulation provides a solution to an old problem in turbulence theory that of representing the time dependence of the covariance and response by exponential forms 4 5 we showed that the derivative with respect to difference time of the covariance with this time ordering now vanishes at the origin this allows one to study the relationships between two time spectral closures and time independent theories such as the fokker planck theory of edwards 6 or the more recent renormalization group approaches we also showed that the renormalized response function is transitive with respect to intermediate times and reported a new langevin type equation for turbulence in this paper we interpret the second order response function as a mean field propagator and show that in addition to propagating two time covariances it also links single time covariances we then make use of its newly established properties to re derive the local energy transfer let response equation 7 and show that it now contains a counter term which removes the singularity of previous propagator equations at t t we also introduce a partial propagator representation and hence reformulate the let statistical equations furthermore we specialize the two time equations to time independent form by introducing exponential time dependences and

closure approach to high order structure functions of turbulence let t p be the structure function of order p of turbulence first t2 is determined then t3 is derived from t2 and finally t p p 3 are derived from t2 and t3 this closure scheme is realized by a non gaussian statistical model we use it to study the scaling law of t p and we find that the available data on scaling exponents favor kolmogorov s 1941 theory rather than his 1962 theory we also predict the high order universal constants of inertial range scaling

efficient multiple range random walk algorithm to calculate the density of states we present a new monte carlo algorithm that produces results of high accuracy with reduced simulational effort independent random walks are performed concurrently or serially in different restricted ranges of energy and the resultant density of states is modified continuously to produce locally flat histograms this method permits us to directly access the free energy and entropy is independent of temperature and is efficient for the study of both 1st order and 2nd order phase transitions it should also be useful for the study of complex systems with a rough energy landscape

a formal derivation of the local energy transfer let theory of homogeneous turbulence a statistical closure of the navier stokes hierarchy which leads to equations for the two point two time covariance of the velocity field for stationary homogeneous isotropic turbulence is presented it is a generalisation of the self consistent field method due to edwards 1964 for the stationary single time velocity covariance the probability distribution functional p u t is obtained in the form of a series from the liouville equation by means of a perturbation expansion about a gaussian distribution which is chosen to give the exact two point two time covariance the triple moment is calculated in terms of an ensemble averaged infinitesimal velocity field propagator and shown to yield the edwards result as a special case the use of a gaussian zero order distribution has been found to justify the introduction of a fluctuation response relation which is in accord with modern dynamical theories in a sense this work completes the analogy drawn by edwards between turbulence and brownian motion originally edwards had shown that the noise input was determined by the correlation of the velocity field with the externally applied stirring forces but was unable to determine the system response now we find that the system response is determined by the correlation of the velocity field with internal quasi entropic forces this analysis is valid to all orders of perturbation theory and allows the recovery of the local energy transfer let theory which had previously been derived by more heuristical methods the let theory is known to be in good agreement with experimental results it is also unique among two point statistical closures in displaying an acceptable i e non markovian relationship between the transfer spectrum and the system response in accordance with experimental results as a result of the latter property it is compatible with the kolmogorov k41 spectral phenomenology

spectral analysis of structure functions and their scaling exponents in forced isotropic turbulence the pseudospectral method in conjunction with a technique for obtaining scaling exponents n from the structure functions sn r is presented as an alternative to the extended self similarity ess method and the use of generalized structure functions we propose plotting the ratio sn r s3 r against the separation r in accordance with a standard technique for analyzing experimental data this method differs from the ess technique which plots sn r against s3 r with the assumption s3 r r using our method for the particular case of s2 r we obtain the result that the exponent 2 decreases as the taylor reynolds number increases with 2 0 679 0 013 as r this supports the idea of finite viscosity corrections to the k41 prediction for s2 and is the opposite of the result obtained by ess the pseudospectral method also permits the forcing to be taken into account exactly through the calculation of the energy input in real space from the work spectrum of the stirring forces

solution of functional equations and reduction of dimension in the local energy transfer theory of incompressible three dimensional turbulence it is shown that the set of integrodifferential and algebraic functional equations of the local energy transfer theory may be considerably reduced in dimension for the case of isotropic turbulence this is achieved without restricting the solution space the basis for this is a complete analytical solution to the functional equations q k t t h k t t q k t t and h k t s h k s t h k t t the solution is proved to depend only on a single function straight phi k t solely determining q and h hence the dimension of both the dependent and the independent variables is reduced by one from the latter the corresponding two integrodifferential equations are lowered to a single integrodifferential equation for straight phi k t extended by an integral side condition on the k dependence of straight phi k t in the limit nu 0 a partial solution to the reduced set of equations is presented in the appendix

multicritical nishimori point in the phase diagram of the j ising model on a square lattice we investigate the critical behavior of the random bond j ising model on a square lattice at the multicritical nishimori point in the t p phase diagram where t is the temperature and p is the disorder parameter p 1 corresponds to the pure ising model we perform a finite size scaling analysis of high statistics monte carlo simulations along the nishimori line defined by 2p 1 tanh 1 t along which the multicritical point lies the multicritical nishimori point is located at p 0 890 81 7 t 0 9528 4 and the renormalization group dimensions of the operators that control the multicritical behavior are y 1 0 655 15 and y 2 0 250 2 they correspond to the thermal exponent nu identical with1 y 2 4 00 3 and to the crossover exponent phi identical withy 1 y 2 2 62 6

parallel tempering cluster algorithm for computer simulations of critical phenomena in finite size scaling analyses of monte carlo simulations of second order phase transitions one often needs an extended temperature range around the critical point by combining the parallel tempering algorithm with cluster updates and an adaptive routine to find the temperature window of interest we introduce a flexible and powerful method for systematic investigations of critical phenomena as a result we gain one to two orders of magnitude in the performance for two and three dimensional ising models in comparison with the recently proposed wang landau recursion for cluster algorithms based on the multibondic algorithm which is already a great improvement over the standard multicanonical variant

self noise and contrast controlled thinning of gray images homotopic grayscale thinning leads to bushy skeleton when applied on noisy images one way to reduce this phenomenon is the use of the parametric thinning approach it consists in relaxing the initial constraint by lowering low contrast crests peaks and ends according to a manually selected parameter and under the constraint of ascendant gray level processing in this work we propose to control the thinning parameter by considering the lowering decision as a hypothesis testing of a statistical framework a unitary hypothesis test based on the minimum test statistic is used for the elimination of noise related peaks and extremities while a fusion of multiple tests is performed for the insignificant crest lowering decision this statistical control is first detailed under the assumption of additive gaussian noise and then is generalized for noise distributions with known pivotal quantity the proposed statistical control leads to a local adjustment and a standardization of the parametric thinning process that depends on both the test significance level which is linked to image contrast and to noise standard deviation the proposed method is tested on synthetic and real images and compared to two skeletonization methods with proven efficiency highlightsreview of thinning methods including gray parametric thinning ability to separate self image noise and contrast impact on parametric thinning setting standardization of the setting through the use of statistical test framework assessment protocol of gray thinning methods based on mandatory properties high performance of our method regarding homotopy and extremity preservation properties

strong disorder paramagnetic ferromagnetic fixed point in the square lattice j ising model we consider the random bond j ising model on a square lattice as a function of the temperature t and of the disorder parameter p p 1 corresponds to the pure ising model we investigate the critical behavior along the paramagnetic ferromagnetic transition line at low temperatures below the temperature of the multicritical nishimori point at t 0 9527 1 p 0 89083 3 we present finite size scaling analyses of monte carlo results at two temperature values t 0 645 and t 0 5 the results show that the paramagnetic ferromagnetic transition line is reentrant for t t that the transitions are continuous and controlled by a strong disorder fixed point with critical exponents 1 50 4 0 128 8 and 0 095 5 this fixed point is definitely different from the ising fixed point controlling the paramagnetic ferromagnetic transitions for t t our results for the critical exponents are consistent with the hyperscaling relation 2 d 2 0

non equilibrium critical relaxation of the three dimensional ising model abstract the non equilibrium relaxation process at the critical point is studied using monte carlo simulation for the ferromagnetic ising model on a cubic lattice it was observed that the time dependent magnetization decayed following a power law t from the all up initial condition three kinds of single spin flip dynamics were studied for several lattices up to 1536 3 the system size dependences are also studied the value of was estimated to be 0 250 2 this value of leads to the estimation of the dynamical exponent z to be 2 06 2 if we assume z where and denote the critical exponents for spontaneous magnetization and correlation length in equilibrium state respectively and 0 515 the result of the non equilibrium relaxation in the ordered phase is also given

extension of the momentum transfer model to time dependent pipe turbulence we analyze a possible extension of gioia and chakraborty s momentum transfer model of friction in steady turbulent pipe flows phys rev lett 96 044502 2006 to the case of time and or space dependent turbulent flows the end result is an expression for the stress at the wall as the sum of a steady and a dynamic component the steady part is obtained by using the instantaneous velocity in the expression for the stress at the wall of a stationary flow the unsteady part is a weighted average over the history of the flow acceleration with a weighting function similar to that proposed by vardy and brown j sound vibr 259 1011 2003 j sound vibr 270 233 2004 but naturally including the effect of spatial derivatives of the mean flow as in the brunone model brunone et al j water res plan manage 126 236 2000

energy transfer and dissipation in forced isotropic turbulence a model for the reynolds number dependence of the dimensionless dissipation rate ce was derived from the dimensionless karman howarth equation resulting in ce ce c rl o 1 rl where rl is the integral scale reynolds number the coefficients c and ce arise from asymptotic expansions of the dimensionless second and third order structure functions this theoretical work was supplemented by direct numerical simulations dns of forced isotropic turbulence for integral scale reynolds numbers up to rl 5875 r 435 which were used to establish that the decay of dimensionless dissipation with increasing reynolds number took the form of a power law rln with exponent value n 1 000 0 009 and that this decay of ce was actually due to the increase in the taylor surrogate u3 l the model equation was fitted to data from the dns which resulted in the value c 18 9 1 3 and in an asymptotic value for ce in the infinite reynolds number limit of ce 0 468 0 006

a fluctuation relaxation relation for homogeneous isotropic turbulence a liouville type equation is solved perturbatively for the exact pdf of fluctuating velocities by expansion about an invariant gaussian measure which is an approximation to the symmetric part of the pdf and is constrained to give the correct covariance the antisymmetric part of the pdf is calculated to the lowest nontrivial order and leads to closed equations for the covariance in terms of a response function which arises from the liouville operator averaged against the ground state distribution as the latter is a stationary gaussian pdf we obtain an expression for the system response which is linear in the covariance

non equilibrium relaxation and interface energy of the ising model abstract from the non equilibrium critical relaxation study of the two dimensional ising model the dynamical critical exponent z is estimated to be 2 165 0 010 for this model the relaxation in the ordered phase of this model is consistent with exp t behavior the interface energy of the three dimensional ising model is studied and the critical exponent of the correlation length and the critical amplitude of the surface tension 0 are estimated to be 0 6250 0 0025 and 1 42 0 04 respectively a dynamic monte carlo renormalization group method is successfully applied to the equilibrium properties of the three dimensional ising model

evaluation of ridge seeking operators for multimodality medical image matching ridge like structures in digital images may be extracted by convolving the images with derivatives of gaussians the choice of the convolution operator and of the parameters involved defines a specific ridge image in this paper various ridge measures related to isophote curvature are constructed reviewed and evaluated with respect to their usability in ct mri matching of human brain scans construction is initially done using heuristics in two dimensional images and then established firmly in a mathematical framework attention is paid to the necessity of operator invariance scale of the operator extension to three dimensional images and relations to isophote and principal curvature it is shown that one of the ridge measures appears well suited for the purpose of matching despite the fact that the measure fails to detect ridges in a number of stylized scenes

detection of curvilinear structures and reconstruction of their regions in gray scale images in this paper we present a new method for detecting curvilinear structures and reconstructing their regions in gray scale images the concept of skeleton extraction is introduced to detect more general structures such as tapering structures a candidate skeleton is extracted from the euclidean distance map that is constructed based on the edge map of an input image the extracted skeleton is usually noisy due to small protrusions and gaps existing on edge contours unnecessary skeletal points are e6ectively removed with a method combining previously proposed and our own methods then each skeletal point is classi7ed as one of three types ridge ravine o rstair and connected points of the same type are grouped to form a skeletal segment finally the reconstruction of curvilinear structure regions is performed based on the skeletal segment classi7cation result experimental results show that our detector contains many of the desirable properties required of a curvilinear structure detector furthermore since the range of widths that our detector can detect at one time is wide it is very useful for example when an input image includes curvilinear structures of various widths or tapering structures whose width varies greatly our algorithm for reconstructing curvilinear structure regions enables us to decompose an image into several types of regions the reconstruction result together with the skeleton extraction result is expected to be useful to make a simpli7ed scene description of an image 2002 pattern recognition society published by elsevier science ltd all rights reserved

new prospects in line detection by dynamic programming the detection of lines in satellite images has drawn a lot of attention within the last 15 years problems of resolution noise and image understanding are involved and one of the best methods developed so far is the f algorithm of fischler which achieves robustness rightness and rapidity like other methods of dynamic programming it consists of defining a cost which depends on local information then a summation minimization process in the image is performed the authors present herein a mathematical formalization of the f algorithm which allows them to extend the cost both to cliques of more than two points to deal with the contrast and to neighborhoods of size larger than one to take into account the curvature thus all the needed information contrast grey level curvature is synthesized in a unique cost function defined on the digital original image this cost is used to detect roads and valleys in satellite images spot

topology of slightly polydisperse real foams the topology of slightly polydisperse meta stable real foams was investigated by means of optical tomography associated with a numerical reconstruction procedure the values of the mean numbers of faces per bubble and edges per face were very close to matzke s data 1946 the real foams were essentially disordered and possessed a noncentered symmetry and ideal structures also could not be observed the disorder was quantified by the second moment of the edge per face and face per bubble distributions and also by a statistical correlation coefficient between the numbers of edges of adjacent faces it was found that the edge distributions of the internal bubbles and not of the external ones were significantly anticorrelated even during foam aging which provided a measure of the disorder in the foam no obvious relationship could be deduced between the isoperimetric quotient and the face combination in an individual bubble eventually it was shown that the physical boundaries of the foam sample had no influence on the foam topology beyond a single bubble layer

eulerian field theoretic closure formalisms for fluid turbulence the formalisms of wyld ann phys 14 143 1961 and martin siggia and rose msr phys rev a 8 423 1973 address the closure problem of a statistical treatment of homogeneous isotropic turbulence hit based on techniques primarily developed for quantum field theory in the wyld formalism there is a well known double counting problem for which an ad hoc solution was suggested by lee ann phys 32 292 1965 we show how to implement this correction in a more natural way from the basic equations of the formalism this leads to what we call the improved wyld lee renormalized perturbation theory msr had noted that their formalism had more vertex functions than wyld s formalism and based on this felt wyld s formalism was incorrect however a careful comparison of both formalisms here shows that the wyld formalism follows a different procedure to that of the msr formalism and so the treatment of vertex corrections appears in different ways in the two formalisms taking that into account along with clarifications made to both formalisms we find that they are equivalent and we demonstrate this up to fourth order

scale invariance and the inertial range spectrum in three dimensional stationary isotropic turbulence the assumption of scale invariance when taken in conjunction with the symmetries of the navier stokes equation is shown to lead to the energy spectrum e k e2 3tk 5 3 in the limit of infinite reynolds number here et is the flux of energy due to inertial transfer while the prefactor is determined by an integral over triple correlations of the phases of the system it is argued that this form of the prefactor provides an answer to the landau kraichnan criticism of the original kolmogorov 1941 theory k41

response function of turbulence computed via fluctuation response relation of a langevin system with vanishing noise for a shell model of the fully developed turbulence and the incompressible navier stokes equations in the fourier space when a gaussian white noise is artificially added to the equation of each mode an expression of the mean linear response function in terms of the velocity correlation functions is derived by applying the method developed for nonequilibrium langevin systems harada and sasa phys rev lett 95 130602 2005 we verify numerically for the shell model case that the derived expression of the response function as the noise tends to zero converges to the response function of the noiseless shell model

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

duality and multicritical point of two dimensional spin glasses abstract we present a conjecture on the exact location of the multicritical point of models of spin glasses on the two dimensional square lattice using duality transformation the results not only agree very well with numerical estimates but also conform excellently to the existing knowledge on annealed systems and to the arguments using gauge symmetry

comparative study of selected parallel tempering methods we review several parallel tempering schemes and examine their main ingredients for accuracy and efficiency the present study covers two selection methods of temperatures and several choices for the exchange of replicas including a recent novel all pair exchange method we compare the resulting schemes and measure specific heat errors and efficiency using the two dimensional 2d ising model our tests suggest that an earlier proposal for using numbers of local moves related to the canonical correlation times is one of the key ingredients for increasing efficiency and protocols using cluster algorithms are found to be very effective some of the protocols are also tested for efficiency and ground state production in 3d spin glass models where we find that a simple nearest neighbor approach using a local n fold way algorithm is the most effective finally we present evidence that the asymptotic limits of the ground state energy for the isotropic case and for an anisotropic case of the 3d spin glass model are very close and may even coincide

dynamic exponent of the 3d ising spin glass the nonequilibrium critical dynamics of the 3d ising spin glass following a quench to the critical temperature from t infinity are used to measure both the dynamical exponent z and the static exponent eta the results for z and eta are quite sensitive to the value assumed for tc although the ratio 2 eta z is rather insensitive and close to the value 0 39 obtained by huse 1989 taking tc 1 18 gives z 5 85 or 0 3 and eta 0 29 or 0 07

universality of the ising and the s 1 model on archimedean lattices a monte carlo determination the ising models s 1 2 and s 1 are studied by efficient monte carlo schemes on the 3 4 6 4 and the 3 3 3 3 6 archimedean lattices the algorithms used a hybrid metropolis wolff algorithm and a parallel tempering protocol are briefly described and compared with the simple metropolis algorithm accurate monte carlo data are produced at the exact critical temperatures of the ising model for these lattices their finite size analysis provide with high accuracy all critical exponents which as expected are the same with the well known 2d ising model exact values a detailed finite size scaling analysis of our monte carlo data for the s 1 model on the same lattices provides very clear evidence that this model obeys also very well the 2d ising model critical exponents as a result we find that recent monte carlo simulations and attempts to define effective dimensionality for the s 1 model on these lattices are misleading accurate estimates are obtained for the critical amplitudes of the logarithmic expansions of the specific heat for both models on the two archimedean lattices

lagrangian statistical mechanics applied to non linear stochastic field equations abstract we consider non linear stochastic field equations such as the kpz equation for deposition and the noise driven navier stokes equation for hydrodynamics we focus on the fourier transform of the time dependent two point field correlation k t we employ a lagrangian method aimed at obtaining the distribution function of the possible histories of the system in a way that fits naturally with our previous work on the static distribution our main result is a non linear integro differential equation for k t which is derived from a peierls boltzmann type transport equation for its fourier transform in time k that transport equation is a natural extension of the steady state transport equation we previously derived for k 0 we find a new and remarkable result which applies to all the non linear systems studied here the long time decay of k t is described by k t exp a k t where a is a constant and is system dependent

local symmetry detection in natural images using a particle filtering approach in this paper we propose an algorithm to detect smooth local symmetries and contours of ribbon like objects in natural images the detection is formulated as a spatial tracking task using a particle filtering approach extracting one part of a structure at a time using an adaptive local geometric model the method can detect straight reflection symmetries in perfectly symmetrical objects as well as smooth local symmetries in curved elongated objects in addition the proposed approach jointly estimates spine and contours making it possible to generate back ribbon objects experiments for local symmetry detection have been conducted on a recent extension of the berkeley segmentation data sets we also show that it is possible to retrieve specific geometrical objects using intuitive prior structural information

nonequilibrium relaxation study on spin glass model ferromagnetic fm transition point and universality class of the j ising model on cubic lattice are studied by computer simulation using the nonequilibrium relaxation ner method at fm bond density p between multicritical one pmc and 1 static exponents take universal values which are different from those of p 1 or p pmc and they are consistent with the values of the random fixed point and of the simulations and experiments for diluted ising systems the dynamical exponent however seems to depend on p and not to be universal although it may be due to finite time correction the estimation of pmc on square lattice is also refined to be 0 8894 9 which is consistent with the nishimori and nemoto s conjecture 0 889972