Showing papers by "Polytechnic University of Turin published in 1987"
TL;DR: Under suitable conditions, diffraction gives rise to an instability which leads to the emergence of a stationary spatial dissipative structure in the transverse profile of the transmitted beam.
Abstract: We consider a nonlinear, passive optical system contained in an appropriate cavity, and driven by a coherent, plane-wave, stationary beam. Under suitable conditions, diffraction gives rise to an instability which leads to the emergence of a stationary spatial dissipative structure in the transverse profile of the transmitted beam.
927 citations
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28 Aug 1987TL;DR: In this paper, the authors proposed a geometrical description of the shell structure of the nucleus with major closed shells at nucleon number 50, 82, 126, and 126.
Abstract: The spectroscopy of medium mass and heavy nuclei is characterized by the occurrence of low-lying collective states. However, the structure of these states, their arrangement into bands and their electromagnetic properties change from nucleus to nucleus. The changes are related to the shell structure of the nucleus with major closed shells at nucleon number 50, 82, 126. The traditional way to analyze collective spectra has been the geometrical description of Bohr and Mottelson1. In this description two limiting cases can be discussed easily, that of a harmonic vibrator with energy levels proportional to the angular momentum I and that of a rigid rotor with energy levels proportional to the square of the angular momentum I(I+1). The description of the intermediate situations is much more difficult, although several calculations have been done by Kumar and Baranger2 to which the interested reader is referred.
376 citations
TL;DR: In this article, anomalous effects occurring in actual realizations of coplanar waveguides for microwave integrated circuits on GaAs substrates, such as the influence of an upper shield, conductor backing, finite-extent ground planes, and line-to-line coupling, are discussed and evaluated.
Abstract: Parasitic effects occurring in actual realizations of coplanar waveguides (CPW) for microwave integrated circuits on GaAs substrates, such as the influence of an upper shield, conductor backing, finite-extent ground planes, and line-to-line coupling, are discussed and evaluated. CAD-oriented analytical expressions are obtained for the electrical quasi-TEM parameters of the relevant waveguiding structures by means of exact or approximate conformal mapping techniques. Differences in electrical behavior with respect to ideal CPW's are highlighted, and practical design criteria are obtained for keeping cover height, ground-plane width, and line-to-line spacing effects to a minimum.
365 citations
361 citations
TL;DR: In this article, the authors studied the operator given by Ω where K is a standard Calderon-Zygmund kernel, and P is a real polynomial on R n × R n.
241 citations
TL;DR: In this paper, the distribution of glass beads in suspension in a stirred tank was examined as a function of the stirrer type, and the size and concentration of the solid particles, and a dimensionless number was theoretically derived, and was able to correlate the variation in the quality of the suspension, for a given geometric system.
145 citations
TL;DR: In this paper, it was shown that the algebraic method for decoding three-errorcorrecting BCH codes is also applicable to complete decoding of the (23,12,7) Golay code.
Abstract: It is shown that the algebraic method for decoding three-error-correcting BCH codes is also applicable to complete decoding of the (23,12,7) Golay code.
132 citations
TL;DR: In this paper, the variation in hardness of the borided layer obtained on iron alloys was defined and related to an increase in chromium, nickel and carbon contents, and it was found that chromium increases the hardness both of the entire boride layer as a whole and of the components, even though these values are systematically lower than those measured on pure borides.
Abstract: The variation in hardness of the phases (Fe, M)B and (Fe, M)2B (M ≡ Cr or Ni), which are the predominant components of the borided layer obtained on iron alloys, was defined and related to increase in chromium, nickel and carbon contents. It was found that chromium increases the hardness both of the borided layer as a whole and of the boride components, even though these values are systematically lower than those measured on pure borides. Carbon, which is insoluble in this type of phase, accumulates at the boride-matrix interface and, because of its modification of the boron diffusion mechanism, it indirectly increases the hardness of the borided surface. Nickel reduces slightly but systematically the hardness of the borides, in particular of the (Fe, Ni)2B phase in which it has its highest concentration.
66 citations
TL;DR: In this article, a technique for the evaluation of static and dynamic potentials due to source distributions defined on domains with simple shape is presented, where the domains considered are polyhedral regions and, in two-dimensional problems, plane polygons, on which uniform or linearly varying source distributions are defined.
Abstract: A technique for the evaluation of static and dynamic potentials due to source distributions defined on domains with simple shape is presented. The domains considered are polyhedral regions and, in two-dimensional problems, plane polygons, on which uniform or linearly varying source distributions are defined. It is shown how three-dimensional (two-dimensional) potential integrals are always reducible to surface (line) integrals with nonsingular kernel, by use of a nonlinear transformation for the integration variables that permits analytic integration. In the static case the integration on the boundary is performed analytically and closed form results are given. In the dynamic case the expressions of the boundary integrals are given in a form suitable for numerical integration. The use of matrix notation allows for very compact expressions readily translatable into computer programs.
64 citations
TL;DR: In this paper, an analytical description of the profile of the indexes of refraction of birefringent Ti:LiNbO 3 channel waveguides was developed to compute the optical mode field distributions.
Abstract: Using an analytical description of the profile of the indexes of refraction of birefringent Ti:LiNbO 3 channel waveguides, a very fast method was developed to compute the optical mode field distributions. Using these results, field overlap integrals were evaluated to calculate the pump threshold power of integrated optical parametric oscillators with Ti:LiNbO 3 channel waveguides. A variation of the guide parameters enabled the determination of optimized profiles yielding minimum oscillation threshold. The pump threshold power of doubly and singly resonant structures was evaluated as a function of the resonator parameters, waveguide losses, mirror reflectivities, and device length. In the doubly resonant configuration, threshold powers lower than 10 mW can be expected.
53 citations
TL;DR: In this article, the authors considered interpolatory quadrature rules for the Jacobi polynomial Pn(α,β) and showed that R_n = O(n^k \log n) small in −1+e≦λ≦1−e.
Abstract: We consider interpolatory quadrature rules of the type
$$\begin{gathered} \frac{{d^k }}{{d\lambda ^k }}\int\limits_{ - 1}^1 {(1 - x)^\alpha (1 + x)^\beta } \frac{{f(x)}}{{x - \lambda }}dx = \sum\limits_{i = 1}^n {w_{ni}^{(k)} (\lambda )f(x_{ni} ) + R_n^{(k)} (f),} \hfill \\ k = 0,1,..., \alpha ,\beta > 0,--- \hfill \\ \end{gathered}$$
where the nodes {xni} are the zeros of the Jacobi polynomialPn(α,β)(x). In particular we prove that
$$\sum\limits_{i = 1}^n {\left| {w_{ni}^{(k)} (\lambda )} \right| = O(n^k \log n)}$$
uniformly in −1+e≦λ≦1−e. Furthermore we show that whenk=1,f(x) ∈Cp[−1, 1],p≧1, andf(p)(x)∈Hμ[−1, 1], 0<μ≦1, we have
$$R_n^{(1)} (f) = O(n^{ - p - \mu + 1 + \delta } ),$$
δ>0 small as we like, uniformly in −1+e≦λ≦1−e.
TL;DR: In this article, the problem of contact between two elastic bodies under the assumption of nonzero initial gap in the potential contact region is studied and the related variational inequality is stated and existence, uniqueness and local regularity results are proved for its solution.
Abstract: The problem of contact between two elastic bodies is studied under the assumption of nonzero initial gap in the potential contact region. The related variational inequality is stated and existence, uniqueness, and local regularity results are proved for its solution.
TL;DR: In this article, a general loss expression was obtained, which permits one to compute total power losses, just knowing two parameters, which can be easily derived from a d.c. and a 50 Hz loss measurements in GO 3% SiFe, or from the average grain size in NO 3%SiFe.
Abstract: By using a recently developed theoretical model, which takes into proper account on a statistical basis the contributions to energy dissipation deriving from microscopic magnetization processes, a general loss expression is obtained, which permits one to compute total power losses, just knowing two parameters. These can easily be derived from a d.c. and a 50 Hz loss measurements in GO 3% SiFe, or from a single d.c. loss value and from the average grain size in NO 3%SiFe. The equation is used to compute total losses between d.c. and 100 Hz for peak inductions variable between 0.1 and 1.7 T in GO and NO laminations. Calculated losses are found to be in excellent agreement with experimental measurements performed on the studied materials over the same wide ranges of frequencies and peak inductions.
TL;DR: In this paper, the problem of optimal sampling design for parameter estimation when data are generated by linear models is addressed, where the measurements are assumed to be corrupted by an unknown but bounded additive noise.
Abstract: The problem of optimal sampling design for parameter estimation when data are generated by linear models is addressed. The measurements are assumed to be corrupted by an unknown but bounded additive noise. The sampling design assumes that the number of samples is unconstrained and no replication is allowed. Two main results are shown: 1) for particular classes of linear models, the optimal number of measurements is equal to the number of parameters, as in the statistical context; 2) the uncertainty intervals of the parameter estimates are bounded from above by quantities that can be computer a priori, knowing only the model and the error structure.
TL;DR: Based on multilist traversal, fraternal event processing, list events, and levelizing, advances are presented here in simulation speed, accuracy, and generality of fault simulation of circuits described at multiple levels of abstraction.
Abstract: Fault simulation of circuits described at multiple levels of abstraction (RT, gate, switch) is a major problem in the area of CAD and testing. Although the concurrent paradigm is generally acknowledged as the most efficient, several techniques are crucial to successfully extend it to multilevel simulation of large circuits. In particular, based on multilist traversal, fraternal event processing, list events, and levelizing, advances are presented here in simulation speed, accuracy, and generality. For zero-delay elements, the simulation of irrelevant activity is avoided, but the accuracy of structural (interconnect) logic simulation is maintained. What is described here has been implemented in MOZART, and detailed experimental results are reported. Relative to the good machine, the average faulty machine is simulated 900 to 17 000 times faster. The approach presented is not restricted to fault simulation, and is thus applicable to the new area of concurrent case simulation.
01 Mar 1987
TL;DR: This work presents a graphical language, based on Prot nets, for building the specification of discrete event simulation models, and illustrates its application to the simulation of a manufacturing cell.
Abstract: Prot nets are an extension to Petri nets, since they can be given a sophisticated semantics by assigning formal inscriptions to the objects of the net. In several applications to CIM (computer integrated manufacturing) systems they proved to give suitable support to object oriented programming, operational specification and rapid prototyping. In this work we present a graphical language, based on Prot nets, for building the specification of discrete event simulation models, and we illustrate its application to the simulation of a manufacturing cell.
TL;DR: In this article, the Enskog-Boltzmann equation is considered with an analysis of the well-posedness of the initial-value problem in unbounded domains and some new global existence and uniqueness results for the solutions of the problem are provided under suitable assumptions about the size of the norm of the original data and about the rate of decay to zero at infinity in the phase space.
Abstract: The Enskog-Boltzmann equation, a partial differential integral equation of the hyperbolic type, is a model which generalizes the classical Boltzmann equation to high gas densities and is here considered with an analysis of the well-posedness of the initial-value problem in unbounded domains. Some new global existence and uniqueness results for the solutions of the initial-value problem and a discussion on the asymptotic stability are provided under suitable assumptions about the size of the norm of the initial data and about the rate of decay to zero at infinity in the phase space.
TL;DR: A new method based on recent results of the General Theory of Optimal Algorithm and a nonlinear modelling technique based on Group Method of Data Handling are considered to derive forecasts and show that the Optimal Error and GMDH predictors provide accurate one step ahead forecasts with respect to those obtained by some linear and nonlinear statistical models.
TL;DR: In this paper, the authors investigated the influence of the thickness in the range between 3 and 15 μm for MBBA and derived simultaneously from the experiments the surface anchoring energy and the sum of the flexoelectric coefficients; the found values are in good agreement with those derived by other groups with different techniques.
Abstract: The reorientation process of an HAN cell submitted to electric fields is studied both theoretically and experimentally. To isolate the flexoelectric effect from the dielectric one, the experiments are made under d.c. and a.c. excitations. Preliminary results on 6 μm thick MBBA have been reported. In this paper we investigate the influence of the thickness in the range between 3 and 15 μm for MBBA. The theoretical model includes into the free energy the flexoelectric term in the hypothesis that the true inner electric field is due to the effective conduction anisotropy. In such a way we derive simultaneously from the experiments the surface anchoring energy and the sum of the flexoelectric coefficients; the found values are in good agreement with those derived by other groups with different techniques.
TL;DR: A linearization scheme is proposed for the general Hamiltonian of an interacting fermion system, consisting of a mean-field approximation in which pairing and umklapp play dominant roles.
Abstract: A linearization scheme is proposed for the general Hamiltonian of an interacting fermion system, consisting of a mean-field approximation in which pairing and umklapp play dominant roles. A variety of models emerge, characterized by a hierarchy of spectrum-generating algebras and superalgebras, of which some are supersymmetric. The superconducting phase transition is shown to be related to supersymmetry breaking.
TL;DR: On peut exprimer la qualite de la distribution en fonction de la vitesse d'agitation et de la Vitesse de sedimentation.
01 May 1987
TL;DR: A high-level Petri net model of the software architecture of an experimental MIMD multiprocessor system for Artificial Intelligence applications is derived by direct translation of the code corresponding to the assumed workload.
Abstract: A high-level Petri net model of the software architecture of an experimental MIMD multiprocessor system for Artificial Intelligence applications is derived by direct translation of the code corresponding to the assumed workload. Hardware architectural constraints are then easily added, and formal reduction rules are used to simplify the model, which is then further approximated to obtain a performance model of the system based on generalized stochastic Petri nets. From the latter model it is possible to estimate the optimal multiprogramming level of each processor so as to achieve the maximum performance in terms of overall throughput (number of tasks completed per unit time).
TL;DR: Influence du systeme d'admission sur les turbulences a petite echelle dans un moteur diesel rapide is discussed in this article, where the authors propose a solution to solve this problem.
Abstract: Influence du systeme d'admission sur les turbulences a petite echelle dans un moteur diesel rapide
TL;DR: The centered distribution functions and their moments are constructed for the generalized multiphoton squeezed states recently defined, and it is shown that such states are non-Gaussian, and exhibit higher-order squeezing, depending on the choice of either the squeezing parameter or the generalized boson number.
Abstract: The centered distribution functions and their moments are constructed for the generalized multiphoton squeezed states recently defined by the authors. It is shown that such states are non-Gaussian, and exhibit higher-order squeezing, depending on the choice of either the squeezing parameter or the generalized boson number.
TL;DR: In this paper, a tracer injection technique was used and the dynamic responses were interpreted using three different models: the axial dispersion model (PD), the stagnant zones model (PE), and the AXIAL dispersion and stagnant zones models (PDE) to investigate the hydrodynamics of liquid phase.
TL;DR: In this paper, an absolute frequency standard for the submillimetre region was proposed for the metastable triplet of 24Mg with an accuracy of ± 3 × 10-11 with respect to a Cs standard.
Abstract: Advances towards the realization of an absolute frequency standard in the submillimetre region are reported. The 3P1 ↔ 3P0, Δmj = 0 fine-structure transition in the metastable triplet of 24Mg has been observed in an atomic beam with a Ramsey-type interrogation technique. Its frequency, measured with an accuracy of ± 3 × 10-11 with respect to a Cs standard, turned out to be ν0 = (601 277 157 860 ± 20) Hz.
TL;DR: In this article, the optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced by magnetron sputtering (SP) and glow discharge (GD) were studied as a function of the film thickness.
01 Mar 1987
TL;DR: Closed queueing network analysis is the technique used to solve the continuous problem and a rule based module has been established to heuristically solve the combinatorial problem.
Abstract: Production scheduling on a flexible manufacturing system is a mixed continuous combinatorial optimization problem. Closed queueing network analysis is the technique we used to solve the continuous problem. Around it a rule based module has been established to heuristically solve the combinatorial problem. Two schedulers have been implemented, considering shorter or longer intervals of time, both based on the new solution paradigm for production scheduling.
TL;DR: In this paper, the analysis of a class of nonlinear kinetic equations derived on the basis of the Enskog theory for dense gases is discussed, and the physical problem of the derivation of the equation and the mathematical problem of analysis of the existence and uniqueness of the solutions to the initial value problem are both reviewed and discussed in details.
Abstract: This review paper deals with the analysis of a class of nonlinear kinetic equations derived on the basis of the Enskog theory for dense gases. The physical problem of the derivation of the equation and the mathematical problem of the analysis of the existence and uniqueness of the solutions to the initial value problem are both reviewed and discussed in details. Some new results are also given.