certificateless threshold ring signature we propose a t out of n certificateless threshold ring signature cl trs scheme and prove its security under a new and stronger set of security models the models capture a new adversarial capability called user partial key replacement attack which has been considered practical and realistic but has never been formalized before the new scheme requires only a constant number of bilinear pairing operations for signature verification it also has a compact signature size which is linear to the number of non signers i e n t rather than that of actual signers we also propose a 1 out of n cl trs i e a certificateless ring signature scheme which has the most efficient verification among all the certificateless ring signature schemes currently known

an algebraic equation for linear operators let t be a linear operator on a vector space v possibly of infinite dimension over a general field k we solve the functional equation p t f where p k x and f an algebraic operator on v are given for nilpotent f we give an explicit linear system which determines the solutions by their similarity classes the method is based on a canonical decomposition theorem

a coupled momentum method for modeling blood flow in three dimensional deformable arteries abstract blood velocity and pressure fields in large arteries are greatly influenced by the deformability of the vessel moreover wave propagation phenomena in the cardiovascular system can only be described considering wall deformability since blood is usually described as an incompressible fluid however computational methods for simulating blood flow in three dimensional models of arteries have either considered a rigid wall assumption for the vessel or significantly simplified or reduced geometries computing blood flow in deformable domains using standard techniques like the ale method remains a formidable problem for large realistic anatomic and physiologic models of the cardiovascular system we have developed a new method to simulate blood flow in three dimensional deformable models of arteries the method couples the equations of the deformation of the vessel wall at the variational level as a boundary condition for the fluid domain we consider a strong coupling of the degrees of freedom of the fluid and the solid domains and a linear membrane model enhanced with transverse shear for the vessel wall the effect of the vessel wall boundary is therefore added in a monolithic way to the fluid equations resulting in a remarkably robust scheme we present here the mathematical formulation of the method and discuss issues related to the fluid solid coupling membrane formulation time integration method and boundary and initial conditions implementation is discussed and results with simple geometries as well as large subject specific models are presented

fluid structure interaction and multi body contact application to aortic valves in this article we present a partitioned procedure for fluid structure interaction problems in which contacts among different deformable bodies can occur a typical situation is the movement of a thin valve e g the aortic valve immersed in an incompressible viscous fluid e g the blood in the proposed strategy the fluid and structure solvers are considered as independent black boxes that exchange forces and displacements the structure solvers are moreover not supposed to manage contact by themselves the hypothesis of non penetration among solid objects defines a non convex optimization problem to solve the latter we use an internal approximation algorithm that is able to directly handle the cases of thin structures and self contacts a numerical simulation on an idealized aortic valve is finally realized with the aim of illustrating the proposed scheme

attribute based signcryption scheme based on linear codes compared with traditional schemes in which encryption follows a signature the attribute based signcryption absc scheme not only costs less both in terms of both computation and communication but also provides message confidentiality ensures the authenticity of a message and attests to the attributes of the sender in this paper we first formalize a selective attribute security model of the attribute based signcryption based on linear codes then we construct a flexible and efficient absc scheme based on a secret sharing method called linear codes secret sharing scheme this absc scheme breaks the threshold limit and employs diverse attribute sets by constructing the access structures on linear codes in addition our scheme achieves confidentiality against chosen ciphertext attacks and unforgeability against chosen message attacks in the selective attribute model finally we compare the proposed scheme with existing schemes in terms of their properties and efficiency

an adaptive formally second order accurate version of the immersed boundary method like many problems in biofluid mechanics cardiac mechanics can be modeled as the dynamic interaction of a viscous incompressible fluid the blood and a visco elastic structure the muscular walls and the valves of the heart the immersed boundary method is a mathematical formulation and numerical approach to such problems that was originally introduced to study blood flow through heart valves and extensions of this work have yielded a three dimensional model of the heart and great vessels in the present work we introduce a new adaptive version of the immersed boundary method this adaptive scheme employs the same hierarchical structured grid approach but a different numerical scheme as the two dimensional adaptive immersed boundary method of roma et al a multilevel self adaptive version of the immersed boundary method ph d thesis courant institute of mathematical sciences new york university 1996 an adaptive version of the immersed boundary method j comput phys 153 2 1999 509 534 and is based on a formally second order accurate i e second order accurate for problems with sufficiently smooth solutions version of the immersed boundary method that we have recently described b e griffith c s peskin on the order of accuracy of the immersed boundary method higher order convergence rates for sufficiently smooth problems j comput phys 208 1 2005 75 105 actual second order convergence rates are obtained for both the uniform and adaptive methods by considering the interaction of a viscous incompressible flow and an anisotropic incompressible viscoelastic shell we also present initial results from the application of this methodology to the three dimensional simulation of blood flow in the heart and great vessels the results obtained by the adaptive method show good qualitative agreement with simulation results obtained by earlier non adaptive versions of the method but the flow in the vicinity of the model heart valves indicates that the new methodology provides enhanced boundary layer resolution differences are also observed in the flow about the mitral valve leaflets

contragredient equivalence a canonical form and some applications abstract let a and c be m by n complex matrices and let b and d be n by m complex matrices the pair a b is contragrediently equivalent to the pair c d if there are square nonsingular complex matrices x and y such that xay 1 c and ybx 1 d contragredient equivalence is a common generalization of four basic equivalence relations similarity consimilarity complex orthogonal equivalence and unitary equivalence we develop a complete set of invariants and an explicit canonical form for contragredient equivalence and show that a a t is contragrediently equivalent to c c t if and only if there are complex orthogonal matrices p and q such that c paq using this result we show that the following are equivalent for a given n by n complex matrix a 1 1 a qs for some complex orthogonal q and some complex symmetric s 2 2 a t a is similar to aa t 3 3 a a t is contragrediently equivalent to a t a 4 4 a q 1 a t q 2 for some complex orthogonal q 1 q 2 5 5 a pa t p for some complex orthogonal p we then consider a linear operator on n by n complex matrices that shares the following properties with transpose operators for every pair of n by n complex matrices a and b a preserves the spectrum of a b a a and c ab b a we show that a a is contragrediently similar to b b if and only if a x 1 bx 2 for some nonsingular x 1 x 2 that satisfy x 1 1 x 1 and x 1 2 x 2 we also consider a factorization of the form a xy where x 1 x and y y we use the canonical form for the contragredient equivalence relation to give a new proof of a theorem of flanders concerning the relative sizes of the nilpotent jordan blocks of ab and ba we present a sufficient condition for the existence of square roots of ab and ba and close with a canonical form for complex orthogonal equivalence

local equivalence of rank 2 quantum mixed states we investigate the equivalence of quantum mixed states under local unitary transformations for a class of rank 2 mixed states a sufficient and necessary condition of local equivalence is obtained by giving a complete set of invariants under local unitary transformations such that two states in this class are locally equivalent if and only if all these invariants have equal values for them

a new ring signature scheme with signer admission property in this paper we introduce an extended ring signature scheme in which the actual signer has the ability to admit to having signed a document at his will generally speaking this scheme can be considered as an extension and improvement of the ring signature suggested by rivest et al in 2001 the proposed scheme is called signer admission ring signature which combines the idea of the designated confirmer signatures proposed by chaum in 1994 and the designated verifier proofs proposed by jakobsson et al in 1996 this paper presents a scenario explaining why the signer admission property is valuable in real life applications an actual signer may possibly want to expose himself if in doing so he will acquire an enormous benefit here we propose a generic construction of the signer admission ring signature as well as a demonstration modified from rivest et al s scheme to achieve signer admission

practical fully distributed signatures provably secure in the standard model a distributed signature scheme allows participants in a qualified set to jointly generate a signature which cannot be forged even when any unqualified set of participants collude together in this paper we propose an efficient scheme that supports any monotone access structures and show its unforgeability and robustness under the computational diffie hellman cdh assumption in the standard model for 192 bit security its secret key shares and signature fragments are as short as 511 bits and 1022 bits which are shorter than existing schemes assuming random oracle we then propose two extensions the first one allows new participants to dynamically join the system without any help from the dealer the second one supports a type of multipartite access structures where the participant set is divided into multiple disjoint groups and each group is bounded so that a distributed signature cannot be generated unless a pre defined number of participants from multiple groups work together finally we present a fully distributed signature scheme such that the centralized trusted dealer can be removed from the system and the secret keys shares can be jointly computed by the involved participants we propose a cdh based distributed signature scheme in the standard model we provide two extensions of the basic distributed signature scheme we propose a distributed key generation protocol over bilinear group we provide a cdh based fully distributed signature scheme in the standard model

solutions of equivariance for a polynomial like iterative equation using fixed point theorems we discuss continuous solutions of equivariance for a polynomial like iterative equation on the real line where is a closed subgroup of the general linear group gl r our main results guarantee the existence of solutions with certain kinds of symmetry we show that under restrictive hypotheses similar results can be proved in a higher dimensional case where the symmetry group is a topologically finitely generated subgroup of the group generated by rotations and dilations in n dimensional euclidean space

a continuum based finite element formulation for the implicit solution of multibody large deformation frictional contact problems in this paper a formulation is presented for the finite element treatment of multibody large deformation frictional contact problems the term multibody is used to mean that when two bodies mechanically contact both may be deformable a novel aspect of the approach advocated is that the equations governing contact are developed in the continuum setting first before deriving the corresponding finite element equations this feature distinguishes the current work from many earlier treatments of contact problems and renders it considerably more general in particular the approach yields a characterization of the frictional constraint assuming a coulomb law suitable for arbitrary discretizations in either two or three dimensions a geometric framework is constructed within which both frictionless and frictional response are naturally described making subsequent finite element discretization a straightforward substitution of finite dimensional solution spaces for their continuum counterparts to our knowledge this general formulation and implementation of the frictional contact problem in a finite element setting has not been reported previously in the literature the development includes exact linearization of the statement of virtual work which enables optimal convergence properties for newton raphson solution strategies and which appears to be highly desirable if not essential for the general robustness of implicit finite element techniques since the theory and subsequent linearization require no limitations on the amount of deformation or relative sliding that can occur the resulting treatment of frictional contact is suitable for a wide range of examples displaying significant non linear behaviour this assertion is substantiated through presentation of a variety of examples in both two and three dimensions

notes on the security of certificateless aggregate signature schemes abstract secure aggregate signature schemes are very useful tools in special areas where the signatures on many different messages generated by many different users need to be compressed quite recently an efficient certificateless aggregate signature scheme was presented by xiong et al 2013 although they proved its security in the random oracle model under the standard computational diffie hellman assumption we find that their conclusion is wrong in this paper we give security analysis to their scheme by showing four kinds of concrete attacks the first two kinds of attacks come from an honest but curious kgc and a malicious but passive kgc respectively while the last two are from the collusion of inside signers or the collusion of an insider signer with a malicious but passive kgc our analysis indicates coalition attacks especially those from the collusion of an inside signer with a malicious kgc are practical and destructive and hence should be prevented in the design of clas schemes we also put forward a secure certificateless aggregate signature scheme our new aggregate signature scheme results in a short aggregate signature that is valid if and only if every individual signature involved in the aggregation is valid

fluid structure partitioned procedures based on robin transmission conditions in this article we design new partitioned procedures for fluid structure interaction problems based on robin type transmission conditions the choice of the coefficient in the robin conditions is justified via simplified models the strategy is effective whenever an incompressible fluid interacts with a relatively thin membrane as in hemodynamics applications we analyze theoretically the new iterative procedures on a model problem which represents a simplified blood vessel system in particular the robin neumann scheme exhibits enhanced convergence properties with respect to the existing partitioned procedures the theoretical results are checked using numerical experimentation

computer modeling of cardiovascular fluid structure interactions with the deforming spatial domain stabilized space time formulation hemodynamic factors such as the wall shear stress are believed to affect a number of cardiovascular diseases including atherosclerosis and aneurysm since resolving phenomena in a living human body is currently beyond the capabilities of in vivo measurement techniques computer modeling is expected to play an important role in gaining a better understanding of the relationship between the cardiovascular diseases and the hemodynamic factors we have developed a computer modeling technique for cardiovascular hemodynamic simulations with this modeling technique patient specific 3d geometry of an artery can be analyzed we take into account some of the important factors in human body for the purpose of demonstrating in vivo situations in a virtual world the interaction between the blood flow and the deformation of the arterial walls is a factor that we are specifically focusing on for such fluid structure interactions we have developed a computer modeling tool based on the deforming spatial domain stabilized space time dsd sst formulation this simulation tool is applied to a patient specific model under pulsatile blood flow conditions the simulations show that the flow behavior with compliant arterial walls is different from what we see with rigid arterial walls consequently the distribution of the wall shear stress on the compliant arterial walls is significantly different from that on the rigid arterial walls we deduce that the compliance of the arterial walls needs to be taken into account in cardiovascular hemodynamic simulations and the computer modeling tool we have developed can be effective in investigation of cardiovascular diseases

computation of canonical matrices for chains and cycles of linear mappings van dooren linear algebra appl 27 1979 103 constructed an algorithm for the computation of all irregular summands in kronecker s canonical form of a matrix pencil the algorithm is numerically stable since it uses only unitary transformations we construct a unitary algorithm for computation of the canonical form of the matrices of a chain of linear mappings v1 v2 vt andextend van dooren s algorithm to the matrices of a cycle of linear mappings whereall vi are complex vector spaces and each line denotes or

space time adaptive finite elements for nonlocal parabolic variational inequalities abstract this article considers the error analysis of finite element discretizations and adaptive mesh refinement procedures for nonlocal dynamic contact and friction both in the domain and on the boundary for a large class of parabolic variational inequalities associated to the fractional laplacian we obtain a priori and a posteriori error estimates and study the resulting space time adaptive mesh refinement procedures particular emphasis is placed on mixed formulations which include the contact forces as a lagrange multiplier corresponding results are presented for elliptic problems our numerical experiments for 2 dimensional model problems confirm the theoretical results they indicate the efficiency of the a posteriori error estimates and illustrate the convergence properties of space time adaptive as well as uniform and graded discretizations

the centralizer of an endomorphism over an arbitrary field abstract the centralizer of an endomorphism of a finite dimensional vector space is known when the endomorphism is nonderogatory or when its minimal polynomial splits over the field it is also known for the real jordan canonical form in this paper we characterize the centralizer of an endomorphism over an arbitrary field and compute its dimension the result is obtained via generalized jordan canonical forms for separable and nonseparable minimal polynomials in addition we also obtain the corresponding generalized weyr canonical forms and the structure of its centralizers which in turn allows us to compute the determinant of its elements

a fluid structure interaction method with solid rigid contact for heart valve dynamics a computational method is proposed for problems where fluid structure interaction is combined with solid rigid contact this combination is particularly important for the dynamics and impact of heart valves the navier stokes equation in an eulerian setting is coupled to a neo hookean solid model using a lagrangian description a fictitious domain method extended with a local mesh adaptation algorithm provides the required flexibility with respect to the motion and deformation of the valve in addition it ensures the solids ability of sustaining pressures present in the fluid making use of the fact that the fluid and solid mesh are not required to be connected conformingly it is shown that the model can be extended with a contact algorithm without introducing meshing complications near the contact surfaces

certificateless undeniable signature scheme in this paper we present the first certificateless undeniable signature scheme the scheme does not suffer from the key escrow problem which is inherent in identity based cryptosystems also it can avoid the onerous management of certificates particularly by using some cryptographic and mathematical techniques we guarantee that the scheme s two component protocols satisfy the properties of zero knowledge proofs to address the security issues we extend security notions of undeniable signatures to the complex certificateless setting and consider two different types of adversaries based on these formally defined security notions we prove that in the random oracle model the certificateless undeniable signature scheme is secure in the sense of existential unforgeability under the bilinear diffie hellman assumption and is secure in the sense of invisibility under the decisional bilinear diffie hellman assumption

a partitioned fluid structure algorithm for elastic thin valves with contact we present a numerical method to simulate the movements of a thin valve immersed in an incompressible viscous fluid the fluid and structure meshes are not matching the kinematic continuity is imposed using lagrange multipliers the method therefore belongs to the fictitious domain fd family this approach allows very large displacements we propose a partitioned fluid structure algorithm which keeps the fluid and structure solvers independent and which is able to manage contact without assuming that the structure solvers include contact capabilities various numerical tests are proposed in particular when the displacement is moderate we show that the results are in good agreement with arbitrary lagrangian eulerian ale simulations we then present results with contact on a rigid wall finally we show that the proposed approach can be mixed with ale when the wall is elastic

nitsche xfem for the coupling of an incompressible fluid with immersed thin walled structures abstract in this paper we introduce a nitsche xfem method for fluid structure interaction problems involving a thin walled elastic structure lagrangian formalism immersed in an incompressible viscous fluid eulerian formalism the fluid domain is discretized with an unstructured mesh not fitted to the solid mid surface mesh weak and strong discontinuities across the interface are allowed for the velocity and pressure respectively the fluid solid coupling is enforced consistently using a variant of nitsche s method with cut elements robustness with respect to arbitrary interface intersections is guaranteed through suitable stabilization several coupling schemes with different degrees of fluid solid time splitting implicit semi implicit and explicit are investigated a series of numerical test in 2d involving static and moving interfaces illustrates the performance of the different methods proposed

on ptak s derivation of the jordan normal form some readers of 1 might appreciate the following comments that make more explicit how ptak s beautiful insight there leads to a trivial proof of the basics of the jordan normal form the proof of theorem 1 of 1 can also be based on the observation that x being finite dimensional the sequence 0 ker a ker a2 must eventually be stationary i e ker a ker aq p for some q and all p 0 for such q let xr and xs be the range and the kernel respectively of a hence dim x dim xr dim xs further for any x xr xs x az for some z and so z ker a2q ker a hence x 0 therefore x is the direct sum of the two a invariant subspaces xs and xr and a is regular on xr since a is and nilpotent on xs in the setup and notation of theorem 2 of 1 there must be by duality some y0 in y for which x0aq 1 y0 0 hence the q order matrix x0aj 1 y0a q i i j 1 q is triangular with nonzero diagonal entries therefore invertible and this guarantees that x is the direct sum x0 x with x0 the linear span of x0aj 1 j 1 q and x the annihilator of y0a q i i 1 q both of which are ainvariant moreover it shows x0aj 1 j 1 q to be a basis for x0 and the matrix representation with respect to this basis of a restricted to x0 has the familiar form of a jordan block for the eigenvalue 0 now x being finite dimensional there are a invariant direct sum decompositions x x1 xm that are minimal in the sense that none of its summands is the direct sum of two nontrivial a invariant subspaces take any one such then the matrix representation for a with respect to any basis made up from bases for the summands xi is block diagonal with the ith block the matrix representation of the restriction ai of a to xi with respect to the chosen basis for xi assuming the underlying field to be algebraically closed the restriction ai of a to xi has some eigenvalue i and in view of the minimality of xi theorem 1 ensures

artificial added mass instabilities in sequential staggered coupling of nonlinear structures and incompressible viscous flows this note investigates the so called arti cial added mass e ect which is responsible for devastating instabilities within sequentially staggered fluid structure interaction fsi simulations where incompressible fluids are considered a discrete representation of the added mass operatorma is given and instability conditions are evaluated for different temporal discretisation schemes it is proven that for every sequentially staggered scheme and given spatial discretisation of a problem a mass ratio between fluid and structural mass density can be found at which the coupled system becomes unstable the analysis is quite general and does not depend upon the particular spatial discretisation schemes used however here special attention is put on stabilised finite elements employed on the fluid partition numerical investigations further highlight the results

certificateless threshold signature scheme from bilinear maps a t n threshold signature scheme allows t or more group members to generate signatures on behalf of a group with n members in contrast to the traditional public key cryptography based on public key infrastructure pki and identity based public key cryptography id pkc certificateless public key cryptography cl pkc offers useful properties as it does not require any certificates to ensure the authenticity of public keys and the key escrow problem is eliminated in this paper we investigate the notion of threshold signature schemes in cl pkc we start by pointing out the drawbacks in the two existing certificateless threshold signature schemes subsequently we present an elaborate description of a generic certificateless t n threshold signature scheme with a new security model the adversaries captured in the new model are more powerful than those considered in the existing schemes furthermore we establish the simulatability for certificateless threshold signature schemes and prove the relationship between the security of certificateless threshold signature schemes and that of the underlying non threshold certificateless signature schemes as an instantiation we present a concrete certificateless threshold signature scheme based on bilinear maps using the techniques of verifiable secret sharing and distributed key generation the proposed scheme is shown to be existentially unforgeable against adaptively chosen message attacks assuming the hardness of computational diffie hellman cdh problem

an unfitted formulation for the interaction of an incompressible fluid with a thick structure via an xfem dg approach a numerical procedure that combines an extended finite element formulation and a discontinuous galerkin technique is presented with the final aim of providing an effective tool for the simulation of three dimensional 3d fluid structure interaction problems in this work we consider a thick structure immersed in a fluid we describe the numerical models and discuss the specific implementation issues arising in three dimensions finally 3d numerical results are provided to show the effectiveness of the approach

a projection semi implicit scheme for the coupling of an elastic structure with an incompressible fluid we address the numerical simulation of fluid structure systems involving an incompressible viscous fluid this issue is particularly difficult to face when the fluid added mass acting on the structure is strong as it happens in hemodynamics for example indeed several works have shown that in such situations implicit coupling seems to be necessary in order to avoid numerical instabilities although significant improvements have been achieved during the last years solving implicit coupling often exhibits a prohibitive computational cost in this work we introduce a semi implicit coupling scheme which remains stable for a reasonable range of the discretization parameters the first idea consists in treating implicitly the added mass effect whereas the other contributions geometrical non linearities viscous and convective effects are treated explicitly the second idea relies on the fact that this kind of explicit implicit splitting can be naturally performed using a chorin temam projection scheme in the fluid we prove conditional stability of the scheme for a fully discrete formulation several numerical experiments point out the efficiency of the present scheme compared to several implicit approaches

a three dimensional computational analysis of fluid structure interaction in the aortic valve numerical analysis of the aortic valve has mainly been focused on the closing behaviour during the diastolic phase rather than the kinematic opening and closing behaviour during the systolic phase of the cardiac cycle moreover the fluid structure interaction in the aortic valve system is most frequently ignored in numerical modelling the effect of this interaction on the valve s behaviour during systolic functioning is investigated the large differences in material properties of fluid and structure and the finite motion of the leaflets complicate blood valve interaction modelling this has impeded numerical analyses of valves operating under physiological conditions a numerical method known as the lagrange multiplier based fictitious domain method is used to describe the large leaflet motion within the computational fluid domain this method is applied to a three dimensional finite element model of a stented aortic valve the model provides both the mechanical behaviour of the valve and the blood flow through it results show that during systole the leaflets of the stented valve appear to be moving with the fluid in an essentially kinematical process governed by the fluid motion

an efficient certificateless aggregate signature with constant pairing computations an aggregate signature scheme enables an algorithm to aggregate n signatures of n distinct messages from n users into a single short signature this primitive is useful in resource constrained environment since they allow bandwidth and computational savings recently in order to eliminate the use of certificates in certified public key cryptography and the key escrow problem in identity based cryptography the notion of certificateless public key cryptography was introduced in this paper we present an efficient certificateless aggregate signature scheme with constant pairing computations the security of the proposed scheme can be proved to be equivalent to the standard computational diffie hellman problem in the random oracle with a tight reduction furthermore our scheme does not require synchronization for aggregating randomness which makes it more suitable for ad hoc networks

applications of the duality method to generalizations of the jordan canonical form abstract the jordan normal form for a matrix over an arbitrary field and the canonical form for a pair of matrices under contragredient equivalence are derived using ptak s duality method

simulatability and security of certificateless threshold signatures we analyze the relationship between the notion of certificateless public key cryptography cl pkc and identity based schemes without a trusted private key generator pkg formally define the security of certificateless threshold signatures and propose a concrete implementation based on bilinear pairings to exhibit the security of our proposal we develop the theory of simulatability and relationship between the certificateless threshold signatures and the underlying non threshold id based signatures we show that the proposed scheme is robust and existentially unforgeable against adaptively chosen message attacks under cdh assumption in the random oracle model

certificateless threshold cryptosystem secure against chosen ciphertext attack this paper proposes the first certificateless threshold decryption scheme which avoids both the single point of failure in the distributed networks and the inherent key escrow problem in identity based cryptosystem the scheme is secure against threshold chosen ciphertext attack it tolerates the type i adversary that can replace public key and the type ii adversary that has access to the system s master key the formal proof of security is presented in the random oracle model assuming some underlying problems closely related to the bilinear diffie hellman problem are computationally hard