advantages of the mixed format in geometrically nonlinear analysis of beams and shells using solid finite elements summary the paper deals with two main advantages in the analysis of slender elastic structures both achieved through the mixed stress and displacement format with respect to the more commonly used displacement one i the smaller error in the extrapolations usually employed in the solution strategies of nonlinear problems and ii the lower polynomial dependence of the problem equations on the finite element degrees of freedom when solid finite elements are used the smaller extrapolation error produces a lower number of iterations and larger step length in path following analysis and a greater accuracy in koiter asymptotic method to focus on the origin of the phenomenon the two formats are derived for the same finite element interpolation the reduced polynomial dependence improves the koiter asymptotic strategy in terms of both computational efficiency accuracy and simplicity copyright 2016 john wiley sons ltd

element formulation and numerical techniques for stability problems in shells in the context of instability problems in shells or shell like structures the objective of the present paper is twofold primarily the paper describes how quasi static conservative instability problems can be considered in a multi parametric context where generalized path following procedures for augmented equilibrium problems are used as computational tools these allow systematic treatment of the higher dimensional solution sets generated under the variations of certain parameters deemed relevant for the given problem the efficient implementation of the above mentioned procedures requires however as an essential ingredient a non linear finite element which is not only accurate but also inexpensive to this end a systematic view on a corotational total lagrangian formulation is described the tric element of argyris and coworkers is slightly modified and introduced as core element formulation special emphasis is given to the alternative methods for treatment of finite three dimensional rotations with reference to both the element definition and solution algorithms numerical examples verify the element capabilities and the possibility to completely describe instability phenomena of large discretized models

total variation structured total least squares method for image restoration in this paper we study the total variation structured total least squares method for image restoration in the image restoration problem the point spread function is corrupted by errors in the model we study the objective function by minimizing two variables the restored image and the estimated error of the point spread function the proposed objective function consists of the data fitting term containing these two variables the magnitude of error and the total variation regularization of the restored image by making use of the structure of the objective function an efficient alternating minimization scheme is developed to solve the proposed model numerical examples are also presented to demonstrate the effectiveness of the proposed model and the efficiency of the numerical scheme

the estimation of the mean squared error of small area estimators abstract small area estimation has received considerable attention in recent years because of a growing demand for reliable small area statistics the direct survey estimators based only on the data from a given small area or small domain are likely to yield unacceptably large standard errors because of small sample size in the domain therefore alternative estimators that borrow strength from other related small areas have been proposed in the literature to improve the efficiency these estimators use models either implicitly or explicitly that connect the small areas through supplementary e g census and administrative data for example simple synthetic estimators are based on implicit modeling in this article three small area models of battese harter and fuller 1988 dempster rubin and tsutakawa 1981 and fay and herriot 1979 are investigated these models are all special cases of a general mixed linear model involving fixed and random effects and a small area mean can be expr

numerical analysis of complex instability behaviour using incremental iterative strategies the paper describes how quasi static conservative instability problems can be analysed in a multi parametric space using generalised path following procedures for augmented equilibrium problems

extrapolation locking and its sanitization in koiter s asymptotic analysis abstract this paper shows that the fem implementation of koiter s asymptotic method w t koiter on the stability of elastic equilibrium 1970 ph d thesis delft 1945 english transl nasa tt f10 883 1967 affdl tr70 25 outlined by casciaro et al finite element asymptotic analysis of slender elastic structures a simple approach int j num meth eng 35 1992 1397 1426 provides accurate and reliable results in the critical and post critical analysis of non linear elastic structures care however does have to be taken in implementing apparently minor details to avoid locking effects which adversely affect accuracy and which can destroy the method reliability as the effects related to the finite element interpolation have been discussed before this paper focuses on the non linear locking due to the use implicit in the method of finite distance extrapolations within this scope it is shown that perturbation algorithms based on compatible formulations can imply a strong critical and post critical locking when analysing structures characterized by high stiffness ratios in the presence of moderate pre critical rotations on the contrary perturbation algorithms based on independent extrapolations of displacements and stresses furnish reliable results in excellent agreement with those provided by step by step analysis at a small fraction of its computational cost

finite element analysis of post buckling dynamics in plates part i an asymptotic approach abstract various static and dynamic aspects of post buckled thin plates including the transition of buckled patterns post buckling dynamics secondary bifurcation and dynamic snapping mode jumping phenomenon are investigated systematically using asymptotical and non stationary finite element methods in part i the secondary dynamic instability and the local post secondary buckling behavior of thin rectangular plates under generalized mechanical and thermal loading is investigated using an asymptotic numerical method which combines koiter s nonlinear instability theory with the finite element technique a dynamic multi mode reduction method similar to its static single mode counterpart liapunov schmidt reduction is developed in this perturbation approach post secondary buckling equilibrium branches are obtained by solving the reduced low dimensional parametric equations and their stability properties are determined directly by checking the eigenvalues of the resulting jacobian matrix typical post secondary buckling forms transcritical supercritical and subcritical bifurcations are observed according to different combinations of boundary conditions and load types geometric imperfection analysis shows that not only the secondary bifurcation load but also changes in the fundamental post secondary buckling behavior are affected the post buckling dynamics and the global analysis of mode jumping of the plates are addressed in part ii

mixed formulation and locking in path following nonlinear analysis abstract the arc length riks strategy has rapidly become a standard tool for path following analysis of nonlinear structures due to its theoretical ability to surpass limit points the aim of this paper is to show that the failures in convergence that are occasionally experienced are not related to proper defects of the algorithm but come from a subtle locking effect intrinsic to the nonlinear nature of the problem as a consequence its sanitization has to be pursued within a reformulation of the structural model the use of a mixed stress displacement variant of the algorithm in particular appears very promising in this respect the topic is discussed with reference to the analysis of nonlinear frames using a mixed version of the nonlinear beam model discussed in 39 it is shown that with no extra computational cost and only a minor modification in coding with respect to a purely compatible formulation it is possible to achieve a noticeable improvement in convergence and a real gain in both computational time and overall robustness of the algorithm

estimation in covariance components models abstract estimation techniques for linear covariance components models are developed and illustrated with special emphasis on explaining computational processes the estimation of fixed and random effects when the variances and covariances are known is presented in bayesian terms point estimates of the unknown variances and covariances are computed using the em algorithm for maximum likelihood estimation from incomplete data the techniques are illustrated with data on law schools field mice and professional football teams

inexact alternating direction methods for image recovery in the image processing community there have recently been many restoration and reconstruction problems that can be reformulated into linearly constrained convex programming models whose objective functions have separable structures these favorable reformulations have promoted impressive applications of the alternating direction method adm in the field of image processing at each iteration the computation of adm is dominated by solving two subproblems exactly however in many restoration and reconstruction applications it is either impossible or extremely expensive to obtain exact solutions of these adm subproblems this fact urges the development on inexact versions of adm which allow the generated adm subproblems to be solved approximately subject to certain inexactness criteria in this paper we develop some truly implementable inexact adms whose inexactness criteria controlling the accuracy of the adm subproblems are easily implementable the convergence of the new inexact adms will be proved numerical results on several image processing problems will be given to illustrate the effectiveness of the proposed inexact adms

a numerical analysis of infinitesimal mechanisms the paper presents a numerical algorithm based on koiter s theory of the elastic stability for detecting the order of infinitesimal mechanisms i e kinematically indeterminate systems of pin jointed bars in cases of one degree of indeterminacy the algorithm improves in terms of computational simplicity and efficiency an analogous algorithm proposed by salerno in 1992 this is shown to be due to the vanishing of the terms higher than the third order of the asymptotic expressions of the energy owing to the use of the green strain measure and a mixed displacement and stress formulation of the problem moreover the proposed algorithm is able to provide a correct definition of mechanism in cases of several degrees of indeterminacy mainly for structures like those first studied by connelly and servatius in 1994 which the paper will treat in depth

best linear recursive estimation for mixed linear models abstract recursive estimation techniques for fixed and completely random models are extended to mixed linear models the kalman filter is used to obtain recursive estimators for a two part random model where the second random factor obeys a generalized autoregressive process by passing to the limit in an appropriate way recursions for the mixed model are derived

the koiter newton approach using von karman kinematics for buckling analyses of imperfection sensitive structures the koiter newton approach is a reduced basis method for nonlinear structural analyses the method combines koiter s approach as a predictor step and the newton arc length technique as a corrector step to trace the entire load displacement equilibrium path of a structure in a step by step manner this computationally highly efficient and accurate solution method has recently demonstrated a superior performance in nonlinear analyses compared to standard techniques in this paper we propose an extension to buckling imperfection sensitivity analyses exploiting the method s stability and reliability we present two different modeling techniques for imperfection loads that both profit from the koiter newton approach reducing the initial computation steps to a small fraction thereof we introduce von karman kinematics which neglect some nonlinear terms of the green strain displacement relations to further increase the computational efficiency of the analysis by an essential reduction of the computation effort required to obtain higher order derivatives of the strain energy using various numerical examples and benchmark tests we demonstrate the overall high quality and performance of the proposed method

a nonlinear beam finite element for the post buckling analysis of plane frames by koiter s perturbation approach abstract a nonlinear finite element of plane beam oriented to koiter s perturbation analysis of frames is presented the locking problem arising in the calculation of the post critical curvature is thoroughly examined and solved at the continuum level by means of a suitable definition of the kinematic settings the proposed strain measures are lagrangian and rationally founded geometrically exact the exact solutions of the critical problem have been chosen as shape functions of the finite element so obtaining an immediately convergent finite element in the calculation of the critical load and of the post critical slope

asymptotic post buckling fem analysis using corotational formulation finite element asymptotic post buckling analysis being based on fourth order expansions of the strain energy requires that nonlinear structural modeling be accurate to same order at least with respect to the rigid motions of the elements a corotational description is proposed here as a general tool to satisfy this requirement of objectivity by referring each element to a local frame which moves rotates with the element so filtering its rigid motion in this description nonlinearity of the problem derives essentially from the change of reference from the global fixed frame to the local one the strain energy being governed by their relative rotations in finite kinematics this noticeably complicates the algebra for obtaining exact expressions of its variations quite simple basic expressions for the first four corotational derivatives of the strain energy are provided allowing the set up of a fourth order accurate asymptotic analysis starting from standard finite elements based on linear or simplified nonlinear local modelings the formulation is implemented for the analysis of 3d beam assemblages and several numerical results are presented and discussed showing the effectiveness and robustness of the proposed approach in reproducing the nonlinear equilibrium path in both cases of monomodal and coupled multimodal buckling

comparison of different methods for decision making in bioequivalence assessment if the regulatory requirements are symmetrical the use of symmetrical confidence intervals as a decision rule for bioequivalence assessment leads as shown by simulations to better level properties and an inferior power compared to a rule based on shortest confidence intervals a choice between these two approaches will have to depend on a loss function for asymmetric regulatory requirements symmetrical confidence intervals should not be used however a decision can still be based on posterior probabilities pr theta epsilon r1 r2 x or shortest confidence intervals for purposes of inference presentation and interpretation of results we think that the use of symmetrical confidence intervals alone can be misleading and we therefore recommend that the posterior probabilities and densities or at least the shortest confidence intervals be given

finite element asymptotic analysis of slender elastic structures a simple approach an asymptotic method directly derived from koiter s theory and suitable for the solution of elastic buckling problems and its natural adaptation to a numerical solution by means of a finite element technique are presented here the order of the extrapolation of the equilibrium equations has been intentionally kept very low because attention has been entirely devoted to all those features theoretical definitions eigenproblem numerical techniques suitable fem implementation which make such an approach competitive with respect to the classic step by step methods for plane frames and 3d pin jointed trusses the performances of the algorithm numerical accuracy and computational cost are compared with those of riks are length method

an efficient inexact symmetric gauss seidel based majorized admm for high dimensional convex composite conic programming in this paper we propose an inexact multi block admm type first order method for solving a class of high dimensional convex composite conic optimization problems to moderate accuracy the design of this method combines an inexact 2 block majorized semi proximal admm and the recent advances in the inexact symmetric gauss seidel sgs technique for solving a multi block convex composite quadratic programming whose objective contains a nonsmooth term involving only the first block variable one distinctive feature of our proposed method the sgs imspadmm is that it only needs one cycle of an inexact sgs method instead of an unknown number of cycles to solve each of the subproblems involved with some simple and implementable error tolerance criteria the cost for solving the subproblems can be greatly reduced and many steps in the forward sweep of each sgs cycle can often be skipped which further contributes to the efficiency of the proposed method global convergence as well as the iteration complexity in the non ergodic sense is established preliminary numerical experiments on some high dimensional linear and convex quadratic sdp problems with a large number of linear equality and inequality constraints are also provided the results show that for the vast majority of the tested problems the sgs imspadmm is 2 3 times faster than the directly extended multi block admm with the aggressive step length of 1 618 which is currently the benchmark among first order methods for solving multi block linear and quadratic sdp problems though its convergence is not guaranteed

imperfection sensitivity due to coupled local instability a non convex qp solution algorithm the paper deals with the collapse safety of slender elastic structures subjected to local buckling interaction using koiter s asymptotic approach the mechanical problem is reduced to the search for all the local minima of an indefinite quadratic form over the unit simplex an efficient recursive branch and cut algorithm is proposed for solving this non convex qp problem allowing a numerical procedure providing statistical information about the collapse load for a given distribution of random imperfections to be set up copyright 2006 john wiley sons ltd

planning and monitoring of equivalence studies demonstrating therapeutic equivalence of two treatments is the goal of many clinical trials for instance when the toxicity of an effective standard treatment is of concern much effort is devoted to developing new therapies that would be both as effective and less toxic in this paper we review the special characteristics of these trials and describe sequential monitoring of equivalence studies using repeated confidence intervals we show how sequential monitoring may be of particular value in this setting and critically discuss the choice of some important design parameters we also provide tables for use when planning a sequential equivalence trial

koiter s analysis of thin walled structures by a finite element approach summary this paper refers to the analysis of the postbuckling behaviour of thin walled structures by means of an asymptotic approach based on a finite element implementation of koiter s non linear theory of instability the analysis has been accomplished by using the following assumptions i the structure is described as an assemblage of flat slender rectangular panels ii a non linear kirchhoff type plate theory is used to model each panel iii hc finite elements discretization is used iv linear and quadratic extrapolations are assumed for the fundamental and the postbuckling paths respectively v multimodal buckling is considered and vi imperfection sensitivity analysis is performed in both multimodal and monomodal form based on the steepest descent path criterion several numerical results are presented and discussed comparisons with numerical solution obtained by standard incremental codes are given which show the accuracy and reliability of the proposed approach

an improvement of commonly used tests in bioequivalence assessment if equivalence of two treatments has to be proved by an experiment with normally distributed observations and fixed sample size there are two usual methods on the one hand there is the double t test and on the other hand a test procedure suggested by anderson hauck which is uniformly more powerful than the first one but only capable of keeping asymptotically to the nominal level based on these two methods a new test is presented which is uniformly more powerful than the double t test and also keeps the preassigned level

simultaneous image fusion and denoising by using fractional order gradient information abstract image fusion and denoising are significant in image processing because of the availability of multi sensor and the presence of the noise the first order and second order gradient information have been effectively applied to deal with fusing the noise free source images in this paper we utilize the fractional order derivatives to represent image features and propose two new convex variational models for fusing noisy source images furthermore we apply an alternating direction method of multiplier admm to solve the minimization problems in the proposed models numerical experiments show that the proposed methods outperform the conventional total variation methods for simultaneously fusing and denoising

parametric empirical bayes inference theory and applications abstract this article reviews the state of multiparameter shrinkage estimators with emphasis on the empirical bayes viewpoint particularly in the case of parametric prior distributions some successful applications of major importance are considered recent results concerning estimates of error and confidence intervals are described and illustrated with data

efficient algorithms for solving condition number constrained matrix minimization problems abstract well conditioned matrices are often required in science and engineering such as signal processing and finance problem to find the nearest positive definite matrix by explicitly imposing a constraint on the condition number are considered in this paper a new algorithm based on geometric perspective is proposed for getting the required well conditioned matrix based on these a condition number constrained matrix minimization problem is further considered where the constraints are imposed for avoiding degenerate solutions in which parameter matrices become rank deficient an inexact version of alternating direction method with truly implementable inexactness criteria is proposed for solving this problem numerical experiments including comparison with some existing methods are performed to illustrate the efficiency of the proposed algorithms

empirical bayes estimation in finite population sampling abstract empirical bayes methods are becoming increasingly popular in statistics robbins 1955 introduced the method in the context of nonparametric estimation of a completely unspecified prior distribution subsequently the method has been explored very successfully in a series of articles by efron and morris 1973 1975 1977 in a parametric framework in the efron morris setup a family of parametric distributions is used as possible priors but only when one or more of the parameters of the family of prior distributions is estimated from the data morris 1983 listed a number of areas where empirical bayes methods are used one of the main features of empirical bayes analysis is to borrow strength from the ensemble that is use information from similar sources in constructing estimators and predictors in addition to the most directly available source of information there are some situations in finite population sampling where such methods might be suitable for instance in many repetitive surve

convergence rate analysis for the alternating direction method of multipliers with a substitution procedure for separable convex programming recently in he et al he bs tao m yuan xm 2012 alternating direction method with gaussian back substitution for separable convex programming siam j optim 22 2 313 340 we have showed the first possibility of combining the douglas rachford alternating direction method of multipliers admm with a gaussian back substitution procedure for solving a convex minimization model with a general separable structure this paper is a further study on this theme we first derive a general algorithmic framework to combine admm with either a forward or backward substitution procedure then we show that convergence of this framework can be easily proved from the contraction perspective and its local linear convergence rate is provable if certain error bound condition is assumed without such an error bound assumption we can estimate its worst case convergence rate measured by the iteration complexity

a customized douglas rachford splitting algorithm for separable convex minimization with linear constraints we consider applying the douglas rachford splitting method drsm to the convex minimization problem with linear constraints and a separable objective function the dual application of drsm has been well studied in the literature resulting in the well known alternating direction method of multipliers admm in this paper we show that the primal application of drsm in combination with an appropriate decomposition can yield an efficient structure exploiting algorithm for the model under consideration whose subproblems could be easier than those of admm both the exact and inexact versions of this customized drsm are studied and their numerical efficiency is demonstrated by some preliminary numerical results

multiplicative noise and blur removal by framelet decomposition and l_ 1 based l curve method this paper proposes a framelet based convex optimization model for multiplicative noise and blur removal problem the main idea is to employ framelet expansion to represent the original image and use the variable decomposition to solve the problem because of the nature of multiplicative noise we decompose the observed data into the original image variable and the noise variable to obtain the resulting model the original image variable is represented by framelet and it is determined by using l 1 norm in the selection and shrinkage of framelet coefficients the noise variable is measured by using the mean and the variance of the underlying probability distribution this framelet setting can be applied to analysis synthesis and balanced approaches and the resulting optimization models are convex such that they can be solved very efficiently by the alternating direction of a multiplier method an another contribution of this paper is to propose to select the regularization parameter by using the l 1 based l curve method for these framelet based models numerical examples are presented to illustrate the effectiveness of these models and show that the performance of the proposed method is better than that by the existing methods

on the o 1 t convergence rate of alternating direction method with logarithmic quadratic proximal regularization it was shown recently that the douglas rachford alternating direction method of multipliers can be combined with the logarithmic quadratic proximal regularization for solving a class of variational inequalities with separable structures this paper further shows a worst case o 1 t convergence rate for this algorithm where a general glowinski relaxation factor is used

dlm decentralized linearized alternating direction method of multipliers this paper develops the decentralized linearized alternating direction method of multipliers dlm that minimizes a sum of local cost functions in a multiagent network the algorithm mimics operation of the decentralized alternating direction method of multipliers dadmm except that it linearizes the optimization objective at each iteration this results in iterations that instead of successive minimizations implement steps whose cost is akin to the much lower cost of the gradient descent step used in the distributed gradient method dgm the algorithm is proven to converge to the optimal solution when the local cost functions have lipschitz continuous gradients its rate of convergence is shown to be linear if the local cost functions are further assumed to be strongly convex numerical experiments in least squares and logistic regression problems show that the number of iterations to achieve equivalent optimality gaps are similar for dlm and admm and both much smaller than those of dgm in that sense dlm combines the rapid convergence of admm with the low computational burden of dgm

decomposition of prediction error abstract the problem considered is that of predicting the value of an unobservable random variable w from the value of an observable random vector y this problem is considered under each of four states of knowledge about the joint distribution of w and y ranging from complete knowledge to no knowledge a point predictor or predictors are presented for each case prediction error is decomposed so that each component reflects an absence of information under certain conditions these components are uncorrelated and have zero means an exact or approximate expression is given for the variance of each component

a variational method for multiple image blending the main aim of this paper is to develop an algorithm for blending of multiple images in the image stitching process our idea is to propose a variational method containing an energy functional to determine both a stitched image and weighting mask functions of multiple input images for image blending the existence of the solution of the proposed energy functional is shown we also present an alternative minimizing algorithm to solve the proposed model numerically and show the convergence of this algorithm experimental results show that the proposed model works effectively and efficiently and that the proposed method is competitive with the tested existing methods under noisy conditions

1 α equivariant confidence rules for convex alternatives are α 2 level tests with applications to the multivariate assessment of bioequivalence abstract in general a 1 confidence region c x for a parameter yields a test at level a for h h versus k c h whenever we reject if c x h we show under certain equivariance properties of c x that for the case of convex alternatives c h the level of the resulting test is in fact 2 this extends recent findings for hyperrectangular alternatives as they occur in the multivariate bioequivalence problem furthermore we apply the suggested test to ellipsoid type alternatives instead of hyperrectangulars in the multivariate bioequivalence problem and to a problem occurring in neurophysiology finally we compare our test numerically with existing methods

a simplified kirchhoff love large deformation model for elastic shells and its effective isogeometric formulation abstract isogeometric kirchhoff love elements have received an increasing attention in geometrically nonlinear analysis of elastic shells nevertheless some difficulties still remain among the others the highly nonlinear expression of the strain measure which leads to a complicated and costly computation of the discrete operators and the existence of locking which prevents the use of coarse meshes for slender shells and low order nurbs are key issues that need to be addressed in this work exploiting the hypothesis of small membrane strains we propose a simplified strain measure with a third order polynomial dependence on the displacement variables which allows an efficient evaluation of the discrete quantities numerical results show practically no difference to the original model even for very large displacements and composite structures patch wise reduced integrations are then investigated to deal with membrane locking in large deformation problems an optimal integration scheme for third order c 2 nurbs in terms of accuracy and efficiency is identified finally the recently proposed newton method with mixed integration points is used for the solution of the discrete nonlinear equations with a great reduction of the iterative burden with respect to the standard newton scheme

an extension of welch s approximate t solution to comparative bioequivalence trials summary we consider the problem of proving statistically the equivalence of two treatments with normally distributed observations the size and the power of the commonly used test procedures which assume equality of the variances are investigated when this assumption is violated on the one hand the preassigned level is considerably exceeded and on the other hand the power if no treatment difference exists drops heavily for differing sample sizes we propose an extension of welch s approximate t solution for the behrens fisher problem in bioequivalence assessment which is asymptotically optimal in a certain subclass of tests the behaviour of the proposed test is investigated in various finite sample situations the results show that the extension of welch s approximate t solution should be preferred for testing bioequivalence of two treatments whenever the population variances cannot be assumed equal and the sample sizes are different sometimes the experimenter knows which sample has the larger variance in this case the larger sample size should always be assigned to that group with the larger variance in order to optimize the actual level and power of the test

an efficient model reduction method for buckling analyses of thin shells based on iga abstract an efficient reduced basis method is proposed for buckling analyses of thin shells subject to large deformations and strains the thin shells are modeled with the classical kirchhoff love kinematics under the framework of iga isogeometric analysis which makes it possible to satisfy the requirement of c 1 continuity the analytically defined geometry of thin shells can be exactly represented by the nurbs non uniform rational b splines basis functions in addition the critical buckling point can be better pin pointed due to the exact geometric description for efficient structural analyses a simplified rom reduced order model is presented by combining the koiter perturbation technique and the finite element method fem alternative perturbation forces based on nonlinear eigenvalue analyses are also proposed embedding three strategies including arc length control accompanying eigenvalue analysis and mode injection into the analysis procedure the proposed method is extended to be applicable to nonlinear buckling analyses furthermore imperfection sensitivity analyses can be conveniently performed with the proposed method finally the effectiveness and efficiency of the proposed method are validated via three benchmark problems

an unbiased test for the bioequivalence problem it is shown that the standard two one sided tests procedure for bioequivalence is a biased test better tests exist in this paper an unbiased level test and other tests which are uniformly more powerful than the two one sided tests procedure are constructed its power can be noticeably larger than that of the level two one sided tests procedure

mixed formulation in koiter analysis of thin walled beams abstract the paper extends the asymptotic mixed formulation proposed in g garcea g salerno sanitizing of locking in koiter perturbation analysis through mixed formulation fourth world congress on computational mechanics buenos aires argentina 1988 g garcea g salerno r casciaro comput methods appl mech engrg 180 1 2 1999 137 167 to structures composed of an assemblage of flat slender elastic panels the same type of structure has already been investigated in a d lanzo g garcea r casciaro int j numer methods engrg 38 1995 2325 2345 a d lanzo g garcea int j numer methods engrg 39 1996 3007 3031 with a compatible formulation and using the usual hypothesis of negligible precritical rotations in order to avoid the extrapolation locking see also g garcea g a trunfio r casciaro comput methods appl mech engrg 165 1 4 1998 137 167 produced by the high axial to flexural stiffness ratio of the panels the use of a mixed formulation provides a consistent way of eliminating the extrapolation locking without introducing ad hoc approximations it is thus both reliable and accurate when combined with a quadratic strain displacement relationship as presented here it gives zero fourth order energy variations further computational simplifications and a natural linearization of the eigenvalue problem required by the buckling analysis an extensive numerical testing shows the effectiveness and robustness of the proposed approach

koiter analysis of folded structures using a corotational approach the paper deals with geometrically nonlinear finite element analysis of folded plate and shell structures a koiter asymptotic approach is proposed based on the reuse of a linear element in the nonlinear context through a corotational formulation the corotational approach represents a simple and effective way to satisfy the basic requirement of koiter analysis i e full objectivity in the finite element modeling in fact starting simply from a suitable linear finite element and implementing the corotational algebra proposed in garcea et al 2009 zagari 2009 lead to objective explicit expressions for the first four variations of the strain energy which are needed by asymptotic analysis the shell element used here is the flat shell quadrangular element with 4 nodes and 6 dofs per node proposed in madeo et al 2012 and called miss 4 a mixed element based on the reissner mindlin plate theory with an allman like quadratic interpolation for displacements and an equilibrated isostatic interpolation for the stress resultants the element is free from locking and spurious zero energy modes so it appears a suitable candidate for nonlinear corotational analysis the results of the numerical validation show the effectiveness and accuracy of the proposed approach and its excellent overall robustness for both mono and multi modal buckling problems also in the presence of strong nonlinear pre critical behavior

on testing for bioequivalence a number of methods have been proposed for statistical analysis of bioequivalence trials a new method is proposed and compared to three previously suggested techniques this comparison clarifies the relationship among the four methods and yields practical suggestions regarding statistical tests

asymptotic post buckling analysis of rectangular plates by hc finite elements the present paper extends the finite element perturbation approach already presented for pin jointed and framed structures15 to rectangular thin plates koiter s asymptotic strategy2 is coupled with a high continuity finite element discretization of the plate 22 the consistency of the discrete model is discussed from the kinematical and numerical points of view and several numerical tests are reported it appears that use of the hc elements makes the perturbation algorithm insensitive to the locking phenomenon occurring in the evaluation of the postbuckling behaviour it also allows the use of very fine discretization meshes at low computational cost

some bayesian and non bayesian procedures for the analysis of comparative experiments and for small area estimation computational aspects frequentist properties and relationships abstract the estimation of a treatment contrast from experimental data and the estimation of a small area mean are special cases of the prediction of the realization of a linear combination of fixed and random effects in a possibly unbalanced two part mixed linear model in this article a bayesian approach to point and interval prediction is presented and its computational requirements are examined differences between the bayesian approach and the traditional classical approach are discussed in general terms and in addition in terms of two examples taken from the literature 1 the comparison of drug formulations in a bioavailability trial westlake and 2 the estimation of corn crop areas using satellite data battese harter and fuller some deficiencies in the classical approach are pointed out and the bayesian approach is considered from a frequentist perspective it is shown via a monte carlo study that for certain noninformative choices of the prior distribution the frequentist prop

image restoration based on the minimized surface regularization abstract we propose an image restoration model based on the minimized surface regularization the proposed model closely relates to the classical smoothing rof model rudin et al 1992 we deduce two different conjugation forms via coupling the gradient operator with the smoothing parameter or not and then provide the existence of the minimizer in the continuous setting in order to efficiently solving the proposed model we employ the primal dual method by reformulating the proposed model as a min max problem relying on the convex conjugation the convergence of the algorithm is provided as well numerical implementations mainly emphasize the effectiveness of the proposed method by comparing it to other two well known methods in terms of the cpu time and restoration quality

interactive buckling in thin walled beams i theory abstract a method is derived for the analysis of mode interaction in thin walled elastic beams a nonlinear plate theory is employed for the plate segments of the beam in which the exact nonlinear expressions are used for the middle surface strain measures but the bending measures are linearized the beam is subjected to a combination of axial compression and a constant bending moment and it is assumed to be simply supported at the ends in the calculation of the total potential energy the influence of the prebuckling deformations is neglected the finite strip method is used with the transverse variation of all three displacement components described by cubic polynomials in the arc length the nonlinear mode interaction is analysed by means of koiter s asymptotic theory of stability some applications of the method to representative problems are presented in a subsequent paper by the authors this shows that significant mode interaction and imperfection sensitivity occur in these structures

direct evaluation of the worst imperfection shape in shell buckling abstract for the evaluation of the imperfection sensitivity of elastic and elastic plastic shells a fully nonlinear finite element method has been developed that directly gives the worst imperfection shape connected to the ultimate limit load the approach uses no approximations such as asymptotical theories or computations in the deep postcritical range the key point of the method is the description of imperfections as nodal degrees of freedom at the element level these unknown quantities are implemented by isoparametric shape functions in a finite shell element including finite rotations and thickness stretch the ultimate buckling load and the corresponding worst imperfection shape is defined by two different criteria and numerically determined by an extended system of nonlinear equations in the computation of the structurally stable collapse the deflections the imperfection shape the eigenvector and the lowest possible load level are obtained the method is illustrated by several numerical examples

how to recognize the order of infinitesimal mechanisms a numerical approach structures presenting kinematical inderterminacy are usually called mechanisms this paper is entirely concerned with assemblies which reveal themselves to be mechanisms at a null value of the load among them a first distinction is made between infinitesimal and finite ones the former being characterized by one or several directions of lower but not zero stiffness whereas the latter show at least one finite admissible displacement for which none of the bars undergoes any elongation moreover there exists the possibility to make a further distinction among the infinitesimal mechanisms according to which is the order of the stiffness along the direction considered above the way of evaluating this order is to perform a local analysis of the strain energy of the assembly once the displacement field is parametrized in terms of a suitable parameter by means of a finite element technique this analysis can be easily performed through the numerical approach presented in this report

on nonlinear beam models from the point of view of computational post buckling analysis abstract the buckling and post buckling analysis of elastic planar frames is considered and the use of geometrically exact beam models is thereby advocated it is shown that usual technical beam models fail to predict correctly the curvature of the post buckling curve at bifurcation even for standard problems of elastic stability theory it is also argued that versatile and efficient computational procedures for bifurcation analysis of general planar frames are to be based on unconstrained beam models some remarks on finite element representation of nonlinear beam models are passed in conclusion

mode jumping and attractive paths in multimode elastic buckling this paper summarizes a part of the first author s ph d thesis completely devoted to multimode elastic buckling within an fem strategy the theoretical arguments unfold among critical points on radial paths the unique post critical paths variationally defined algebraic characterizations proposition demonstrations and so on by aiming to prove that the complexity of the phenomenon of multimode buckling secondary bifurcations post critical attractive paths can be theoretically explained 1997 by john wiley sons ltd

path following analysis of thin walled structures and comparison with asymptotic post critical solutions a path following non linear elastic analysis for structures composed of assemblages of flat slender elastic panels is presented the proposed path following method employs fem technology and a kinematical model to analyse these structures using a koiter asymptotic approach as a result it is possible to verify the accuracy achieved by the asymptotic method the proposed mixed path following formulation is both efficient and robust with regards to the locking extrapolation phenomenon that strongly affects compatible formulations the use of an hc finite element makes it possible to avoid the problem of the finite rotations in the space maintaining a high degree of continuity and making the numeric formulation simple and efficient copyright 2002 john wiley sons ltd

the calculation of probabilities in rejecting bioequivalence methods are given for deriving the lower and upper bounds of the probabilities for rejecting bioequivalence except when two formulations are nearly equal the lower and upper bounds become very close and thus give an exact probability the methods can be used in two or higher way crossover or parallel groups designs one can also determine the sample size from the equations the results are compared with the probabilities obtained by simulation