Showing papers by "Polytechnic University of Catalonia published in 1989"
TL;DR: In this article, a constitutive model based on an internal variable-formulation of plasticity theory for the non-linear analysis of concrete is presented, which uses a new yield criterion which matches experimental data quite well and it accounts for both elastic and plastic stiffness degradations effects.
3,080 citations
TL;DR: In this paper, a numerical scheme for crack modelling by means of continuous displacement fields is presented, where a crack is modelled as a limiting case of two singular lines (with continuous displacements, but discontinuous displacement gradients across them) which tend to coincide with each other.
Abstract: A numerical scheme for crack modelling by means of continuous displacement fields is presented. In two-dimensional problems a crack is modelled as a limiting case of two singular lines (with continuous displacements, but discontinuous displacement gradients across them) which tend to coincide with each other. An analysis of the energy dissipated inside the band bounded by both lines allows one to obtain an expression for the characteristic length as the ratio between the energy dissipated per unit surface area (fracture energy) and the energy dissipated per unit volume (specific energy) at a point. The application of these mathematical expressions to the finite element discretized medium allow one to obtain a general spatial and directional expression for the characteristic length which guarantees the objectivity of the results with respect to the size of the finite element mesh. The numerical results presented show the reliability of the proposed expressions.
449 citations
TL;DR: In this paper, an n -degrees of freedom Hamiltonian system near an elliptic equilibrium point is considered, and the system is put in normal form (up to an arbitrary order and with respect to some resonance module) and estimates are obtained for both the size of the remainder and for the domain of convergence of the transformation leading to normal form.
205 citations
TL;DR: A new parameter I = I(G) is introduced for a loopless digraph G, which can be thought of as a generalization of the girth of a graph, and maximally connected and superconnected iterated line digraphs and (undirected) graphs are characterized.
Abstract: This paper introduces a new parameter I = I(G) for a loopless digraph G, which can be thought of as a generalization of the girth of a graph. Let k, λ, δ, and D denote respectively the connectivity, arc-connectivity, minimum degree, and diameter of G. Then it is proved that λ = δ if D ⩽ 2I and κ k = δ if D ⩽ 2I - 1. Analogous results involving upper bounds for k and λ are given for the more general class of digraphs with loops. Sufficient conditions for a digraph to be super-λ and super-k are also given. As a corollary, maximally connected and superconnected iterated line digraphs and (undirected) graphs are characterized.
136 citations
TL;DR: In this paper, the analysis of frames is considered, in which a specially favorable structure of equations permits a solution of the equilibrium equations, since they are uncoupled from the remaining (strain-displacement and material) laws.
54 citations
TL;DR: The effect of temperature and concentration on the viscosity of clarified and depectinized pear juice was examined in this paper, and an expression for the combined effect was given.
41 citations
TL;DR: In this paper, the additive-log-ratio cokriging estimator is shown to be invariant under permutation of components of the untransformed regionalized composition.
Abstract: To avoid spurious spatial correlation when analyzing the spatial covariance structure of regionalized compositions, additive-log-ratio transformation can be used. Here, the additive-log-ratio cokriging estimator, derived in a natural way from this transformation, is shown to be invariant under permutation of components of the untransformed regionalized composition. It leads, as expected, to an exact interpolation. As original data, predicted values of the regionalized composition at unknown points add up to the same constant c and lie between 0 and c.
34 citations
TL;DR: Hamiltonian calculations are performed using a loop-labeled basis where the full set of identities for the SU(/ital N/) gauge models has been incorporated and the eigenvalue problem leads to a linear set of finite-difference equations easily amenable to numerical treatment.
Abstract: Hamiltonian calculations are performed using a loop-labeled basis where the full set of identities for the SU(/ital N/) gauge models has been incorporated. The loops are classified as clusterlike structures and the eigenvalue problem leads to a linear set of finite-difference equations easily amenable to numerical treatment. Encouraging results are reported for SU(2) at spatial dimension 2.
34 citations
11 Jul 1989
TL;DR: This paper focuses on three different aspects which can be considered to be recent trends within theory and applications of algebraic specification.
Abstract: In this paper we focus on three different aspects which can be considered to be recent trends within theory and applications of algebraic specification.
31 citations
TL;DR: In this paper, the initial Extended Octtree model is generalized in order to support general vertices with n faces and specific algorithms for the Boolean operations and Octtree visualization are presented.
28 citations
TL;DR: In this paper, a simple model of a classical particle in a heat bath under the influence of external noise is studied, where the heat bath is reduced to an internal colored noise (Ornstein-Uhlenbeck noise).
Abstract: A very simple model of a classical particle in a heat bath under the influence of external noise is studied. By means of a suitable hypothesis, the heat bath is reduced to an internal colored noise (Ornstein–Uhlenbeck noise). In a second step, an external noise is coupled to the bath. The steady state probability distributions are obtained.
TL;DR: Tubular all-solid-state iodide and bromide selective electrodes with channels drilled through the crystalline heterogeneous membranes have been prepared for use in flow-injection analysis (FIA) and show a Nernstian response over the range between 5 x 10(-5) and O.
TL;DR: In this paper, it is shown that the temperature for forward transformation is always lower than standard ones in the domain of t ★ studied and that the cycle of hysteresis is always wider than the standard one.
TL;DR: In this paper, the effect of grain size on martensitic transformation in Zn and Al shape memory alloys subjected to two thermal treatments in order to retain β phase has been studied by means of calorimetry and acoustic emission.
TL;DR: In this article, a variational principle is used to deduce the Hamilton-Dirac equations for a constrained Hamiltonian system, and an algorithm is proposed to obtain the final constraint manifold and the dynamical vector field on it using vector fields on the phase space.
Abstract: Hamilton-Dirac equations for a constrained Hamiltonian system are deduced from a variational principle. In the local problem for such systems an algorithm is proposed to obtain the final constraint manifold and the dynamical vector field on it using vector fields on the phase space. The global problem is solved in terms of fiber bundles associated with the problem.
01 Jan 1989
TL;DR: In this paper, the authors studied the TE propagation in a realistic nonlinear non-Kerr type waveguide with a saturable intensity dependent refractive index medium bounded by linear materials.
21 Aug 1989
TL;DR: It is observed that language classes located between P and NP have complete problems, and characterizations of these classes are found using robust machines with bounded access to the oracle, and in terms of nondeterministic complexity classes with polylog running time.
Abstract: We study certain language classes located between P and NP that are defined by polynomial time machines with bounded amount of nondeterminism. We observe that these classes have complete problems, and find characterizations of the classes using robust machines with bounded access to the oracle, and in terms of nondeterministic complexity classes with polylog running time. We also study the relationship of these classes to P and NP.
TL;DR: In this article, a formulation for the general analysis of plane frames has been presented, which permits the consideration of the nonlinear and time-dependent behavior of materials at one-dimensional fiber level and the second order equilibrium effects.
01 Oct 1989
TL;DR: In this article, the authors study the development of (algebraic) specifications with incomplete specifications, i.e. specifications in which some objects (data sorts or operations) are not fully described.
Abstract: In this paper we study the development of (algebraic) specifications. The main issues are the following: 1) We are able to work with "incomplete" specifications, i.e. specifications in which some objects (data sorts or operations) are not fully described. Technically, this is handled by means of loose semantics with data constraints. Two basic kinds of refinements are used or the specification building: horizontal and vertical refinements. Horizontal refinements are defined as loose extensions, whether vertical refinements are defined by means of refinement morphisms. The combination of both kinds of refinements (horizontal composition) provides a form of parameter passing, in fact the results obtained here generalize the results of the standard approach. A notion of relative persistency is introduced allowing to obtain full compatibility between the model and the specification level semantics for the kind of specification building operations used here. Moreover, proof-theoretic sufficient conditions are given for checking this property.
TL;DR: In this paper, a formulation for high order directional differentiation of functions defined through integration is presented, which is used for sensitivity analysis in optimal shape design problems by the finite elements method.
TL;DR: In this paper, the dynamic behavior of the phase of the generated field in a Doppler-broadened optically-pumped far-infrared laser is theoretically investigated for the first time, which allows to establish the actual symmetry of the main attractor in the phase space, explaining the heteroclynic character of the chaotic behavior observed in experiments.
TL;DR: A morphologic and morphometric study of this organ fixed by arterial perfusion was performed in patients with hereditary spherocytosis, three with autoimmune haemolytic anaemia and six with Hodgkin's disease without splenic involvement.
Abstract: With the aim of contributing to a better understanding of the haemolytic function of the spleen, a morphologic and morphometric study of this organ fixed by arterial perfusion was performed in nine patients with hereditary spherocytosis (HS), three with autoimmune haemolytic anaemia (AHA) and six with Hodgkin's disease without splenic involvement (controls). The spleen weight in HS and AHA (621 +/- 429 g, mean +/- SD) was significantly increased with respect to controls (168 +/- 36 g) (P = 0.003). In HS the red cell retention in the cords of Billroth was significantly increased (203 +/- 68 per 10(4) microns 2) with respect to the cases with AHA (93 +/- 35 per 10(4) microns 2) and to the controls (57 +/- 28 per 10(4) microns 2) (P = 0.004). In HS and AHA the number of macrophages per 10(4) microns 2 of red pulp was significantly increased (5.41 +/- 1.10 and 7.52 +/- 2.91, respectively) with respect to the controls (3.25 +/- 0.58) (P less than 0.003). There was no statistically significant difference between the number of macrophages in HS and AHA. The transmission (TEM) and scanning electron microscopy (SEM) studies demonstrated predominantly red cell retention in the cords of HS spleens, red cell phagocytosis by cordal macrophages in AHA spleens and in a lesser intensity in HS spleens, and phagocytosis of haematic corpuscles by sinus endothelial cells (SEC) in the cases of HS. These quantitative studies allow a better understanding of splenic red cell destruction in haemolytic syndromes.
TL;DR: This paper examines here the existence of approximations in NC of P-complete problems and shows how the tools of log-space reductions can be used to make inferences about the best possible performance of approximation of problems that are hard to parallelize.
Abstract: We examine here the existence of approximations in NC of P-complete problems. We show that many P-complete problems (such as UNIT, PATH, circuit value etc.) cannot have an approximating solution in NC for any value of the absolute performance ratio R of the approximation, unless P=NC. On the other hand, we exhibit of a purely combinatorial problem (the High Connectivity subgraph problem) whose behaviour with respect to fast parallel approximations is of a threshold type. This dichotomy in the behaviour of approximations of P-complete problems is for the first time revealed and we show how the tools of log-space reductions can be used to make inferences about the best possible performance of approximations of problems that are hard to parallelize.
TL;DR: In this article, a very efficient strategy to determine the optimal retrofitting solution for a multiproduct batch/semicontinuous chemical plant has been developed, taking into account capital investments and other production costs.
TL;DR: In this article, the Peltier effect is used for heating and cooling in shape memory alloys, and temperature detection is by means of a Pt-100 resistance with a resolution of 0.001 ohm (0.003 K).
TL;DR: In this article, the authors consider a three-dimensional hyperelastic cylinder and study the asymptotic behavior of the deformations of the cross-sections in an equilibrium state.
Abstract: We consider a three-dimensional hyperelastic cylinder in Ω = D × [0, ∞]. We study the asymptotic behaviour of the deformations of the cross-sections in an equilibrium state. In this case we show that the solutions either have exponential decay or exponential growth. We give some initial conditions such that the latter case occurs.
TL;DR: In this article, the authors derived the equations of motion for vehicles with directionally sliding wheels by means of the virtual work method and determined the required driving torques from them by using the pseudo-inverse matrix.
TL;DR: In this article, the authors studied the kinetic behavior of the dye when integrated continuously in an isothermal solution over a period of 60 min and found that at low exhaustion the system followed an Arrhenius law, contrary to the behaviour at high exhaustion where the dye absorption was almost independent from temperature.
Abstract: Following on from previous papers by the authors concerning the integration dyeing method, this paper studies the kinetic behaviour of the dye when integrated continuously in an isothermal solution over a period of 60 min. The dyeing systems selected were acid dyes on wool and cationic dyes on Leacril 16 fibre. Curves of the kinetics of dye absorption by the fibres were similar to those of the addition of dye to the dyebath. At low exhaustion the systems followed an Arrhenius law, contrary to the behaviour at high exhaustion where the dye absorption was almost independent from temperature. A mathematical method is described to assess the total amount of the dye to be added in relation with the desired temperature and exhaustion.