Showing papers by "Polytechnic University of Catalonia published in 1990"
238 citations
TL;DR: In this article, the relationship between the DKT (Discrete Kirchhoff Theory) element and the Reissner-Mindlin assumptions has been discussed and the reasons for their success explained.
113 citations
TL;DR: In this paper, a plastic damage model for nonlinear finite element analysis of concrete is presented, which is based on standard plasticity theory for frictional materials and allows to include elastic and plastic stiffness degradation effects.
108 citations
06 May 1990
TL;DR: A theoretical analysis of the effect of three different kinds of imbalances between the parallel signal paths in a real LINC transmitter is presented, which include the power gain and delay delay between the two RF paths and the different nonlinear characteristics of both RF power amplifiers.
Abstract: The effects of RF signal processing impairments in a LINC transmitter are analyzed. A theoretical analysis of the effect of three different kinds of imbalances between the parallel signal paths in a real LINC transmitter is presented. These include the power gain and delay (or phase) imbalance between the two RF paths and the different nonlinear characteristics of both RF power amplifiers. In all cases analytical expressions have been obtained in order to evaluate the effect of the imbalances on the performance of the LINC transmitter. The gain and the phase imbalance between both power amplifiers appears as a serious constraint on performance. The system degradations are described in terms of the undesired response rejection at the system output. A classical two tones test has been used. >
92 citations
TL;DR: In this paper, rates and signatures for simple cases of vector-like fermions are discussed in some detail, and the authors discuss the probability that these fermion signatures exist at hadron colliders.
65 citations
TL;DR: Two quiescent current sensor circuits are proposed and discussed, oriented to different testing applications such as the external functional ATE environment, and the built-in self-testing (BIST) design for both on-line and off-line strategies.
Abstract: Many integrated circuit processing defects may cause changes in the value of the quiescent power supply current. Not all of these changes are detectable using classical functional testing techniques. Testing techniques based on the quiescent power supply current inspection have been reported to be efficient in the detection of a wide set of well known physical defects (including bridges and stuck-on). Two quiescent current sensor circuits are proposed and discussed. These circuits are oriented to different testing applications such as the external functional ATE environment, and the built-in self-testing (BIST) design for both on-line and off-line strategies. >
62 citations
TL;DR: It is observed that these classes have complete problems and a characterization of the classes using robust machines with bounded access to the oracle is found, obtaining some other results in this direction.
Abstract: We study certain language classes located betweenP andNP that are defined by polynomial-time machines with a bounded amount of nondeterminism. We observe that these classes have complete problems and find a characterization of the classes using robust machines with bounded access to the oracle, obtaining some other results in this direction. We also study questions related to the existence of complete tally sets in these classes and closure of the classes under different types of polynomial-time reducibilities.
60 citations
TL;DR: A general method for determining the coefficients of a differentiator that maximizes the error between actual and ideal low-pass differentiator filters when signal and noise spectra are known is presented.
Abstract: A general method for determining the coefficients of a differentiator that maximizes the error between actual and ideal low-pass differentiator (LPD) filters when signal and noise spectra are known is presented. Several examples of digital filters suitable for QRS complex and P-T wave processing in ECG are presented. The technique is applied to ECG signal processing for three common sampling rates. >
52 citations
01 Mar 1990
TL;DR: This work closes up substantially the gaps between the known lower and upper bounds for these succinct problems, in most cases matching optimally the lower and the upper bound.
Abstract: Highly regular graphs can be represented advantageously by some kind of description shorter than the full adjacency matrix; a natural succinct representation is by means of a boolean circuit computing the adjacency matrix as a boolean function The complexity of the decision problems for several graph-theoretic properties changes drastically when this succinct representation is used to present the input We close up substantially the gaps between the known lower and upper bounds for these succinct problems, in most cases matching optimally the lower and the upper bound
48 citations
TL;DR: The generators are characterized, the concept of dimension is introduced and algoriths in oder to calculate a minimal generating family in the finite case are developed.
40 citations
TL;DR: It is shown that a Moore-like bound on the order of such digraphs can be attained only when D ≤ 4, and an appropriate lower bound is derived and a construction is presented that provides bipartiteDigraphs of any (even) order whose diameter does not exceed this lower bound in more than one.
Abstract: For its implications in the design of interconnection networks, it is interesting to find
(a) (di)graphs with given maximum (out-)degree d and diameter D that have large order;
(b) (di)graphs of given order and maximum (out-)degree d that have small diameter.
(Di)graphs of either type are often called dense.
This paper considers the case of bipartite digraphs. For problem (a) it is shown that a Moore-like bound on the order of such digraphs can be (and in fact is) attained only when D ≤ 4. For D > 4 a construction is presented that yields a family of bipartite digraphs with order larger than (d4 — 1)/d4 times the above-mentioned bound. For problem (b) an appropriate lower bound is derived and a construction is presented that provides bipartite digraphs of any (even) order whose diameter does not exceed this lower bound in more than one.
TL;DR: A description of how a subset of planar rational Bezier curves can be used to define single-valued curves in polar coordinates is given and an angular parameter is derived from the recursive algorithm for evaluating a rational curve.
Abstract: A description of how a subset of planar rational Bezier curves can be used to define single-valued curves in polar coordinates is given. For this subset, an angular parameter is derived from the recursive algorithm for evaluating a rational curve. The resulting parametrization admits an expression in terms of sinusoidal basis functions. Curves of degree-two are conics with focus at the origin of coordinates.
TL;DR: The propagation characteristics of the leaky modes in planar anisotropic waveguides with a multilayer structure have been investigated by means of a compact rigorous formalism and particular attention has been devoted to the variation of the loss coefficient as a function of buffer thickness and buffer refractive index.
Abstract: The propagation characteristics of the leaky modes in planar anisotropic waveguides with a multilayer structure have been investigated by means of a compact rigorous formalism. The leakage losses and leaky transition angle have been studied for the fundamental and first hybrid modes. An inhomogeneous waveguide and buffered step index type structure have been discussed. Particular attention has been devoted to the variation of the loss coefficient of the leaky modes as a function of buffer thickness and buffer refractive index. A notably different behavior has been obtained for various configurations.
01 Jan 1990
TL;DR: In this paper, a global graph transformation is developed to obtain estimates for certain invariant manifolds of a class of area preserving diffeomorphisms with symmetries, and a lower bound of this angle is given for a large set of values of the parameters.
TL;DR: A comparison of two different approaches to the design of a ground-water-quality monitoring network indicates that a network designed by use of geostatistical techniques generally will require larger sample sizes than networks designed byUse of traditional techniques, but the geost atistical techniques can provide data adequate to describe both stochastic and spatial features of water-quality variables.
Abstract: Two different approaches to the design of a ground-water-quality monitoring network may be appropriate, depending on the type of information desired. First, where the objective is to determine what ground-water-quality characteristics are like in an area (statistical quantification of typical concentrations, as given by the mean or median, or percentage of wells exceeding various use standards), networks can be designed to provide estimates of known reliability using standard parametric and nonparametric statistical techniques. This approach can provide information adequate to perform general water-quality assessments where the intention of the monitoring network is to provide data about general suitability of the water for various uses. Second, where the objective is to maximize areal ground-water-quality information, networks also can be designed using geostatistical techniques, such as kriging. This second approach would be appropriate when information is needed on where particular problem areas may exist.
Both approaches were applied to 1965 chloride data from a deep confined aquifer in the Llobregat delta near Barcelona, Spain. Traditional statistical techniques are demonstrated to design a network that would provide an estimated median chloride concentration. A method is introduced that can be used to determine the sample size necessary to describe any selected quantile with known precision. On the basis of 120 observations in the 1965 data set, between 13 and 25 wells would be necessary to estimate the median chloride concentration within 40 percent of the true median with 95-percent confidence. Kriging, a geostatistical technique, was applied to the data set to determine the minimum number of wells necessary to include in the network to retain the essential spatial information of the original network. By use of this technique, the original network of 120 wells was reduced by 17.5 percent to 99 wells, while the standard error was increased by only 1 percent.
A comparison of these two approaches indicates that a network designed by use of geostatistical techniques generally will require larger sample sizes than networks designed by use of traditional techniques, but the geostatistical techniques can provide data adequate to describe both stochastic and spatial features of water-quality variables. Detailed description of spatial variability requires many sample points for extremely variable data. On the basis of results presented in this paper, prediction errors for chloride concentrations in ground water at selected points in the Llobregat delta were as much as 300 percent. Nevertheless, even the modified network of 99 wells would produce statistical estimates adequate for most general water-quality assessments, in addition to retaining the spatial information contained in the original 1965 data set.
TL;DR: In this article, an on-line extraction system with completely continuous flow analysis prior to the liquid chromatographic (LC) column was used for the determination of the organophosphorus pesticides tetrachlorvinphos and parathion-methyl and their degradation products 2,4,5-trichlorophenol and 4-nitrophenol, respectively, and the chlorinated phenoxy acids 2.4-D, 2, 4-5-T and silvex in water samples.
TL;DR: In this article, a model of surface recombination current and carrier concentration that takes into account the surface variables (surface states, surface voltage, etc) and the injection level in the bulk is developed.
Abstract: The surface recombination velocity is usually taken as a constant parameter to define a boundary condition for the continuity equation. In this paper, a model of surface recombination current and carrier concentration that takes into account the surface variables (surface states, surface voltage, …) and the injection level in the bulk is developed. The results obtained allow two main regimes of recombination to be distinguished: injection limited and surface limited recombination. We can assign a constant value to S only for surfaces working under certain conditions. Its value and its range of validity depend on the set of surface and bulk parameters and also on the injection level.
TL;DR: This work solves the lattice covering time problem exactly in one dimension both for reflecting and periodic boundary conditions.
TL;DR: In this article, les substituants electroattracteurs ou donneurs sur le potentiel d'oxydation des monomeres (3-4-diethyl, 3-acetyl-, 3-methoxy carbonyl-, 3 carboxy, 3methoxyl, 4-methyl-pyrrole) and la conductivite des polymeres correspondants obtenus par polymerisation electrolytique.
TL;DR: It is shown that a simple monolayer-liposome model can be used to simulate experimentally observed interactions between lipid vesicles and cell surfaces and a simple theoretical model is formulated to interpret the variation with time of surface pressure as a function of liposome concentration.
01 Jan 1990
TL;DR: The phase diagram of the plastic crystals Neopentylglycol (HPG) and Pentaglycerin (PG) has been established from 288 Κ until the liquid state as discussed by the authors.
Abstract: The phase diagram of the plastic crystals Neopentylglycol (HPG) and Pentaglycerin (PG) has been established from 288 Κ until the liquid state. The NPG/PG system exhibits a demixing region in the solid state as a consequence of the difference between the ordered low-temperature forms of the pure compounds; the solid solution boundaries have been determined (0.07 and 0.53 molar fraction of PG) at 288 K. The equilibrium domains between the two solid phases and the plastic phase show an eutectoid invariant, with eutectoid composition of 0.29 ± 0.02 molar fraction of PG and eutectoid temperature of 298.1 ± 1.1 K. In the plastic phase, total miscibility is observed and, from a crystallographic point of view, an ideal behaviour can be assumed for the alloys. The plastic-liquid equilibrium shows a Gibbs minimum corresponding to a concentration of 0.21 ±0.02 molar fraction of PG and a temperature of 379.6 ± 2.0 K.
TL;DR: In this paper, it was shown that aging at 475 °C produces the decomposition of the alloy in zones rich in chromium via spinodal decomposition, and that the high rate of embrittlement observed, compared with that which occurs in Fe-Cr binary alloys of similar chromium content, is related to a faster development of the spinodic decomposition in the steel studied.
Abstract: Superferritic stainless steels become embrittled when aged in a temperature interval around 475 °C, This phenomenon has been studied in the alloy Fe-28Cr-2Mo-4Ni-Nb by measuring the decrease in the energy absorbed in the impact test as a function of ageing time at 475 °C. The change which occurs in the microstructure has been studied by small-angle neutron scattering. It is shown that ageing at 475 °C produces the decomposition of the alloy in zones rich in chromium via spinodal decomposition. The high rate of embrittlement observed, compared with that which occurs in Fe-Cr binary alloys of similar chromium content, is related to a faster development of the spinodal decomposition in the steel studied.
TL;DR: In this paper, the suitability of the generalized Langevin equation (GLE) for a realistic description of the behavior of a system of interacting particles in solution is discussed and the required effective memory functions, which are dependent on the concentration of solute, are obtained by solving a generalized Volterra equation.
Abstract: The suitability of the generalized Langevin equation (GLE) for a realistic description of the behavior of a system of interacting particles in solution is discussed. This study is focused on the GLE for a system of non-Brownian particles, i.e., the masses and the sizes of the solute particles are similar to those of the bath particles. The random and frictional forces on the atoms of the solute due to their collisions with the solvent atoms are characterized from molecular dynamics simulations of simple dense liquid mixtures. The required effective memory functions, which are dependent on the concentration of solute, are obtained by solving a generalized Volterra equation. The validity of the usual assumptions on the statistical properties of the random forces is carefully analyzed, paying special attention to their Gaussianity. The reliability of stochastic simulations based on the GLE is also discussed.
TL;DR: In this article, the dynamics of a coherently pumped ring laser with a homogeneously broadened four-level medium is analyzed theoretically, considering linearly polarized pump and generated laser beams.
Abstract: The dynamic behavior of a coherently pumped ring laser with a homogeneously broadened four-level medium is analyzed theoretically, considering linearly polarized pump and generated laser beams. The laser is shown to be much more stable when these polarizations are parallel than when they are orthogonal. In the latter case the instability pump threshold can be as low as four times the first laser threshold, and the laser dynamics shows Lorenz-type features.
TL;DR: This paper describes the properties and related issues of such an interface, known as the back-end manager (BEM), and its relationship to the proposed KBFE architecture.
Abstract: Front Ends for Open and Closed User Systems (FOCUS) is an ESPRIT/2 (no. 2620) project aimed at designing tools and techniques for the construction of knowledge-based front ends (KBFEs) for open-user systems (reusable software components, libraries, etc) and closed-user systems (free-standing software, packages, etc). An important part of the project involves the establishment of an architecture for KBFEs and the specification of the KBFE/back-end interface. This paper describes the properties and related issues of such an interface, known as the back-end manager (BEM), and its relationship to the proposed KBFE architecture.
TL;DR: In this paper, the authors examined the nonlinear dynamics of a truncated system modelling low-Prandtl-number thermal convection, where the primary flow is not a straight roll and the dynamics is dominated by the production of axial flow along the axis of bent rolls or of swirl along ring vortices.
Abstract: The aim of the paper is to examine the nonlinear dynamics of a truncated system modelling low-Prandtl-number thermal convection. The model describes situations where the primary flow is not a straight roll and the dynamics is dominated by the production of axial flow along the axis of bent rolls or of swirl along ring vortices. The physical mechanism for these processes is a spontaneous growth (i.e. bifurcation) of a vertical vorticity mode, breaking the two-dimensional symmetry of the system. A description of the model can be found in Massaguer & Mercader (1988) where the physics and the numerical results have been checked against laboratory experiments. The nonlinear dynamics of that model will be discussed in the more academic case of free boundaries, as it has been shown that for sufficiently small Prandtl numbers straight rolls cannot be expected to be the primary flow near the onset of convection (Busse & Bolton 1984). Two clearly differentiated time-dependent regimes have been found and they correspond to small and intermediate Peclet numbers. In the former regime there exists a transition to chaos with the whole scenario being dependent on a symmetry invariance common to a large number of confined flows. The route to chaos is made up of a sequence of homoclinic explosions giving rise to a cascade of period doublings, with the whole scenario being different from that of a Feigenbaum's cascade.
05 Sep 1990
TL;DR: The authors present a method to implement systolic algorithms (SAs) using pipelined functional units (PFUs) and describe an efficient implementation of a non-time-homogeneous SA with data contraflow for QR decomposition.
Abstract: The authors present a method to implement systolic algorithms (SAs) using pipelined functional units (PFUs). This kind of unit makes it possible to improve the throughput of a processor because of the possibility of initiating a new operation before the previous one has been completed. The method permits transformation of a SA so that it can be efficiently executed using PFUs. The method is based on two temporal transformations (slowdown and retiming) and one spatial transformation (coalescing). The temporal transformations permit the modification of the SA in such a way that dependences established by the PFU are preserved. The spatial transformation improves the hardware utilization. The method was applied to 1-D SAs with data contraflow. To demonstrate the effectiveness of the method, the authors describe an efficient implementation of a non-time-homogeneous SA with data contraflow for QR decomposition. >
01 Jan 1990
TL;DR: In this article, the salinity of groundwater recharge in arid lands is high due to the concentration of rain-contributed and airborne salts by evapotranspiration in the upper layer of the ground.
Abstract: Groundwater recharge in arid lands is only a very small fraction of rainfall, its salinity is high due to the concentration of rain-contributed and airborne salts by evapotranspiration in the upper layer of the ground. This is enhanced in windy coastal areas and islands due to the important contribution of airborne marine salts. There brackish to salty groundwater is commonly found. Examples from the Canary Islands are presented and discussed, and possible explanations are outlined. Local solutions for water supply are briefly presented.