scispace - formally typeset
Search or ask a question

Showing papers by "Polytechnic University of Turin published in 1986"


Book ChapterDOI
01 Jun 1986
TL;DR: In this paper, a class of Petri nets in which transitions can fire after either a deterministic or a random, exponentially distributed, firing delay is defined, and a solution technique is presented to obtain the steady-state probability distribution over markings, introducing restrictions on the use of deterministic firing delays.
Abstract: A class of Petri nets (DSPN) in which transitions can fire after either a deterministic or a random, exponentially distributed, firing delay is defined, and a solution technique is presented to obtain the steady-state probability distribution over markings, introducing restrictions on the use of deterministic firing delays. An example of application of this modeling technique is presented to demonstrate the impact that the use of a mix of deterministic and exponentially distributed firing delays (instead of all exponentially distributed firing delays) can have on performance and reliability estimates.

377 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the policy function which describes an optimal path can be of any type, for discount factors small enough, and that the stability of the accumulation paths depends on the discount parameter.

349 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the occurrence of periodic and chaotic phenomena in infinite horizon duopoly games where firms maximize their discounted sum of profits and use Markov-perfect equilibrium strategies.

147 citations


Journal ArticleDOI
TL;DR: The rule-based FMS production scheduling system described here is based on an Antonio Elia system and has a fellowship with Digital Equipearlier system developed with a traditional approach.
Abstract: lexible automation can enhance Thus, the FMS manager must be proproductivity dramatically-but it vided with adequate software support for F does so by increasing the complexity two tasks: of operations and the difficulty ofproduc*Production scheduling. This schedultion scheduling, which often means that ing takes a medium term horizon (two *_* * ahuman decisions fail quality and timing weeks) and determines the estimated startgoals. A flexible manufacturing system ing times of lots to allocate auxiliary a * e a * * * (FMS) can process many types of parts resources, such as manpower for arrangproduced in lots from the release times of ing pallets. The scheduling is subject to raw materials to the due dates of comseveral constraints, such as planned pleted parts. maintenance periods of machines and raw An FMS requires production schedulmaterial availability times. ing that can handle the changes flexibility * Real-time rescheduling. This activity demands. Production scheduling-deteris invoked when the planned schedule mining a schedule (a sequence) of part lots must be modified because unexpected to be machined in the EMS-must meet events occur, for example, when a mathe due dates of lots while taking into acchine breaks down or raw materials are count several related problems, such as (1) minimizing machine idle times, (2) queues at machines, and (3) work in progress. The rule-based FMS production sched___________________________________ uling system described here is based on an Antonio Elia now has a fellowship with Digital Equipearlier system developed with a traditional

115 citations


Journal ArticleDOI
TL;DR: In this paper, a Korn's inequality and miscellaneous results of duality, traces, density and orthogonality are established for the study of Norton-Hoff materials.
Abstract: Some specific functional spaces are required for the study of Norton-Hoff materials. For this purpose we establish here a Korn's inequality and miscellaneous results of duality, traces, density and orthogonality.

102 citations


Journal ArticleDOI
TL;DR: It is proved that least-squares algorithms enjoy strong optimality properties, and that these properties do not hold for other frequently used projection algorithms, such as least-absolute-values or minimax algorithms, corresponding to a description of the measurement error in h or l∞ norm, respectively.

96 citations


Journal ArticleDOI
TL;DR: Several related classes of operators on nilpotent Lie groups are considered, which involve oscillatory factors that are exponentials of imaginary polynomials and convolutions with singular kernels supported on lower-dimensional submanifolds and validity in the general context not requiring the existence of dilations that are automorphisms.
Abstract: Several related classes of operators on nilpotent Lie groups are considered. These operators involve the following features: (i) oscillatory factors that are exponentials of imaginary polynomials, (ii) convolutions with singular kernels supported on lower-dimensional submanifolds, (iii) validity in the general context not requiring the existence of dilations that are automorphisms.

45 citations


Journal ArticleDOI
TL;DR: A simple solution is given to a particular case of optimal information, called optimal sampling design, which is of great interest in system and identification theory.

44 citations


Journal ArticleDOI
TL;DR: It is shown that a carefully designed Ungerboeck code does not shape the spectrum and simple sufficient conditions are found for the spectrum of Unger boeck-coded signals to be equal to the Spectrum of uncoded signals.
Abstract: Simple sufficient conditions are found for the spectrum of Ungerboeck-coded signals to be equal to the spectrum of uncoded signals. It is shown that a carefully designed Ungerboeck code does not shape the spectrum.

43 citations



Journal ArticleDOI
TL;DR: In this paper, the authors consider the disturbance decoupling problem for distributed parameter systems, with special attention to the case of delay systems, and present several examples which illustrate the difficulties of the infinite dimensional theory for the general distributed parameter system and for delay systems.
Abstract: In this paper we consider the disturbance decoupling problem for distributed parameter systems, with special attention to the case of delay systems. We present several examples which illustrate the difficulties of the infinite dimensional theory for the case of general distributed parameter systems and for the case of delay systems. In this last case we single out a class of subspaces whose invariant properties are easily characterized and which seems to be interesting from the point of view of the applications.

Journal ArticleDOI
01 Jun 1986
TL;DR: An object-oriented approach for building distributed systems using ADA as the target language, exploiting its tasking and structuring mechanisms and the possibility of using a knowledge-based user interface promote rapid prototyping and reusability.
Abstract: This paper presents an object-oriented approach for building distributed systems. An example taken from the field of computer integrated manufacturing systems is taken as a guideline. According to this approach a system is built up through three steps: control and synchronization aspects for each class of objects are treated first using PROT nets, which are a high-level extension to Petri nets; then data are introduced specifying the internal states of the objects as well as the messages they send each other; finally the connections between the objects are introduced by means of a data flow diagram between classes. The implementation uses ADA as the target language, exploiting its tasking and structuring mechanisms. The flexibility of the approach and the possibility of using a knowledge-based user interface promote rapid prototyping and reusability.

Journal ArticleDOI
TL;DR: In this article, a contraction of S U (2) to the three-dimensional Heisenberg group is defined by considering the action of the two groups on appropriate manifolds in ℂ2.
Abstract: A contraction ofS U (2) to the three-dimensional Heisenberg group is defined by considering the action of the two groups on appropriate manifolds in ℂ2. The infinite-dimensional irreducible unitary representations of the Heisenberg group are then shown to be limits of (finite-dimensional) irreducible representations ofS U (2).

Journal ArticleDOI
TL;DR: In this article, a detailed study of the optical properties of sputtered hydrogenated amorphous silicon films with varying hydrogen concentration is presented, in detail, from a point of view of understanding the well known Tauc rule and the alternate relations being proposed in recent years.
Abstract: A detailed study of the optical properties of sputtered hydrogenated amorphous silicon films with varying hydrogen concentration is presented here. The energy dependence of the absorption coefficient is looked into, in detail, from a point of view of understanding the well known Tauc rule and the alternate relations being proposed in recent years. Spectroscopic and band‐structural models like Wemple–Didomenico and Penn are then utilized to analyze the optical parameters near the band‐gap region of the wavelength spectra. Extensive comparisons of our results are made with those of sputtered a‐Si:H films of other workers, glow discharge prepared a‐Si:H, chemically vapor deposited and evaporated a‐Si, and also crystalline silicon. The similarities in the variation of the optical properties of a‐Si:H with increasing hydrogen concentration (or decreasing measurement temperature) to that of crystalline silicon with decreasing measurement temperature lead us to interesting conclusions. Thus, it seems that decrea...

Journal ArticleDOI
TL;DR: Satisfactory agreement was obtained between simulated and experimental data indicating that this model continues to be useful for describing the metabolism of bile acids and may also be of value for describingThe metabolism of drugs whose metabolism is similar to that of biles acids.
Abstract: The metabolism and enterohepatic circulation of chenodeoxycholic acid (CDC), a major primary bile acid in man, has been stimulated using a multicompartmental physiological pharmacokinetic model which was previously reported and used to simulate the metabolism of cholic acid. The model features compartments and linear transfer coefficients. Compartments, which are defined as the pools of single chemical species in well defined anatomical volumes, are aggregated into nine 'spaces' based on anatomical and physiological considerations (liver, gall-bladder, bile ducts, duodeno-jejunum, ileum, colon, portal blood, sinusoidal blood, and general circulation). Each space contains several compartments which correspond to the compounds present in that space, for example, the compound in question and its biotransformation products. For CDC (as for cholic acid in the previous simulation) each space contains three compartments corresponding to the unconjugated bile acid, its glycine amidate, and its taurine amidate. Transfer coefficients, which denote the fractional amount of the compartment's contents exiting per unit time, are categorized according to function: flow, for example gall-bladder contraction (which involves transfer of all substances contained in the space at the same fractional rate); biotransformation (which transfers the substrate from one compartment to another within the same space); or transport (which denotes movements between contiguous compartments, belonging to different spaces across a diffusion membrane or a cellular barrier). The model is made time-dependent by incorporating meals which trigger gall-bladder emptying and modify intestinal flow. The transfer coefficients in the cholic acid model were modified for the CDC model since there is indirect evidence that CDC amidates (probably chenodeoxycholylglycine) are absorbed from the duodeno-jejunum and the first pass hepatic clearance of CDC species differs from that of cholyl species. The model was then used with all existing experimental data to simulate CDC metabolism in healthy humans over a 24-h period during which three meals were ingested. Satisfactory agreement was obtained between simulated and experimental data indicating that this model continues to be useful for describing the metabolism of bile acids and may also be of value for describing the metabolism of drugs whose metabolism is similar to that of bile acids.

Journal ArticleDOI
TL;DR: In this article, an axiomatic proof of the second theorem of Bertini is given and the extent to which it can be applied to weak normality is shown. But this proof is not applicable to weak normalization.

Journal ArticleDOI
TL;DR: A new multistage interconnection network is presented in this paper, able to handle the communications between the connected devices correctly, even in the presence of fault(s) in the network.
Abstract: A new multistage interconnection network is presented in this paper. It is able to handle the communications between the connected devices correctly, even in the presence of fault(s) in the network. This goal is achieved by using redundant paths with a fast procedure able to dynamically reroute the message. It is also shown that the rerouting properties are still valid when broadcasting transmission is used.

Journal ArticleDOI
01 Jun 1986-Networks
TL;DR: New decomposition methods for the determination of optimal paths without interference (independent decom position), of k node-disjoint paths with minimal total costs and of optimal Steiner trees are presented.
Abstract: In many practical situations, connection structures have to be laid out in an environment with a strong inner structure. This article presents a new general mathematical formulation of cor responding design problems in which the layout possibilities are represented by a network. Because in practice such networks are often very large and sparse, there is great interest in the utilization of decomposition techniques for the optimization of connection structures. New decomposition methods for the determination of optimal paths without interference (independent decom position), of k node-disjoint paths with minimal total costs and of optimal Steiner trees are presented. The new methods are compared with other techniques under different aspects of practical importance.

Journal ArticleDOI
TL;DR: In this article, generalized stochastic Petri net (GSPN) models are used to analyze the performance of a class of multiple-bus multiprocessor systems, exploiting the unusual simplicity of the state space of the Markov chains derived by firing the reachability graphs of GSPNs.

Book ChapterDOI
01 Jun 1986
TL;DR: A compact, analytically tractable model is developed and validated by comparing its results with those obtained from the detailed model by simulation, showing that the proposed compact model can be used to obtain accurate performance estimates in the considered case, which had previously been considered intractable.
Abstract: Petri net models in which transitions can be associated with either deterministic or exponentially distributed firing times are developed to investigate the performance of a local area network with a linear topology in which a single bus is accessed by a finite population of stations randomly located along the bus using the 1-persistent CSMA/CD protocol. A detailed model is first constructed, mainly for specification purposes. Indeed, from such a model results can be obtained only through simulation. A compact, analytically tractable model is then developed, and it is validated by comparing its results with those obtained from the detailed model by simulation. Some performance curves show that the proposed compact model can be used to obtain accurate performance estimates in the considered case, which had previously been considered intractable.

Journal ArticleDOI
TL;DR: In this article, the crystallographic characteristics and the equilibrium ratios for solid solutions containing 33 and 50 at% boron which belong to the Fe-Ni-B system are described.
Abstract: The crystallographic characteristics and the equilibrium ratios for solid solutions containing 33 and 50 at% boron which belong to the Fe-Ni-B system are described. The study was carried out on samples obtained by diffusion at 1073 K, of mixtures of the elements in powder form. It was possible to confirm the existence of a complete solid solution between the compounds Fe2B and Ni2B. On the other hand, there are two solid solutions containing 50 at% boron: one is derived from the compound FeB in which up to 70% of the iron atoms can be substituted by nickel, the other derives from the boride NiB and extends as far as the component (Ni0.85Fe0.15)B. Curves were obtained indicating the variation of lattice parameters and volume of the respective elementary cells with composition for these solid solutions. The different insertion of nickel in the borides was also quantified and the relative limit distribution coefficient was evaluated. Its value is consistent with those calculated on analogous borides of transition elements at the same temperature.

Journal ArticleDOI
TL;DR: In this article, a quantitative study was carried out on the differentiated distribution of chromium and nickel in the phases constituting the borided layer, where the chromium spreads from the matrix towards the bored layer where it is concentrated in the phase richest in boron (Fe, M)B. Nickel behaves in the opposite manner.
Abstract: Synthetic ferrous alloys containing chromium and/or nickel were prepared and borided at 1173 K with powders containing B4C, KBF4 and SiC for times varying from 20 to 60 h. The surface layers composed of borides of type (Fe, M)B and (Fe, M)2B were characterized by means of X-ray diffraction, microscopic observations, analysis with the microprobe and microhardness measurements. A quantitative study was carried out on the differentiated distribution of chromium and nickel in the phases constituting the borided layer. The chromium spreads from the matrix towards the borided layer, where it is concentrated in the phase richest in boron (Fe, M)B. Nickel behaves in the opposite manner. Alloys without carbon were used in order to avoid the formation of an area containing carbides and boron carbides, situated between the borided layer and the matrix, which could influence chromium distribution. The distribution phenomenon is in accordance with what was found in the study of Fe-M-B ternary systems (M=Cr, Ni). The influence of chromium and nickel on the thickness, the morphology and the microhardness of the borided layer are discussed.

Proceedings ArticleDOI
08 Jun 1986
TL;DR: In this paper, the authors present an analysis of the turbomachines of the Ecole polytechnique federale de Lausanne EPFL, n° 613 (1986).
Abstract: Keywords: Turbomachinery ; Unsteady Flows ; Numerical Analyses These Ecole polytechnique federale de Lausanne EPFL, n° 613 (1986)Laboratoire de thermique appliquee et de turbomachines Reference doi:10.5075/epfl-thesis-613Print copy in library catalog Record created on 2007-04-25, modified on 2016-08-08

Journal ArticleDOI
TL;DR: In this paper, a study of the high-pressure early-Alpine re-equilibration in the eclogites and metasedimentary cover of the Val d'Ala di Lanzo ophiolite has been made.
Abstract: A study has been made of the high-pressure early-Alpine re-equilibration in the eclogites and metasedimentary cover of the Val d'Ala di Lanzo ophiolite. All of the main high-pressure minerals have been analysed and their compositions used to determine re-equilibration temperatures. The minimum conditions proposed (P= 1.3 GPa, T= 450–460°C) are also indicated by the presence of a jadeite+quartz-bearing metagranite. The temperatures are compared with those reported for similar eclogites from the Voltri Group, the Aosta Valley and the Valais. Comparison of recalculated temperatures shows that the temperature (and probably the pressure) of the eclogitic re-equilibration increased in the Aosta Valley and the Valais, in keeping with what has been observed in the internal Penninic basement of the Gran Paradiso and Monte Rosa crystalline massifs.

Journal ArticleDOI
TL;DR: It turns out that Lyapunov functions correspond to a stronger type of asymptotic stability, which is specified via higher-order prolongational extensions of the reachable map of the system.
Abstract: This paper is concerned with the characterization of asymptotic stability of a dynamical polysystem in the vicinity of a compact set in terms of a properly defined Lyapunov function. It turns out that Lyapunov functions correspond to a stronger type of asymptotic stability, which is specified via higher-order prolongational extensions of the reachable map of the system.


Journal ArticleDOI
TL;DR: In this paper, the authors measured the twist rotation at the wall-nematic liquid crystal interface in MBBA and ZLI 1738 samples placed in a magnetic field giving a pure twist deformation.
Abstract: We measured the twist rotation at the wall-nematic liquid crystal interface in MBBA and ZLI 1738 samples placed in a magnetic field giving a pure twist deformation. Homogeneous boundary conditions were obtained by rubbing two silane coated glasses softly with teflon. In the samples examined, a rotation angle of the order of 10° was obtained with a magnetic field of 5 kOe. This corresponds to an extrapolation length and an anchoring constant of the order of 1 μm and 0.005 dyn/cm respectively. Measurements were made by analysing the light transmitted through the samples. It is shown that in such experiments the adiabatic theorem cannot be considered valid, since even very small deviations from adiabaticity play a leading role in determining the intensity and the polarization state of the transmitted beam Mesure de la rotation de torsion pres de l'interface entre un cristal liquide nematique et une paroi pour des echantillons de MBBA et ZLI 1738 places dans un champ magnetique qui induit une deformation de torsion pure. Les mesures sont realisees par analyse de la lumiere transmise

Journal ArticleDOI
TL;DR: In this article, a new approach is proposed for studying the optical properties of anisotropic stratified media that makes use of a suitable perturbative treatment of Berreman's 4 × 4 matrix, which describes light propagation in these structures.
Abstract: A new approach is proposed for studying the optical properties of anisotropic stratified media that makes use of a suitable perturbative treatment of Berreman’s 4 × 4 matrix, which describes light propagation in these structures. The method consists in finding a new basis for the 4 × 4 matrix in which a specific problem may be treated in a more convenient way. This allows one easily to obtain information about quantities of immediate physical meaning and to find simple approximate expressions for the optical properties having particular interest in experiments. The case of light propagation in cholesteric and chyral smectic liquid crystals at small incidence angles is studied in detail.

Journal ArticleDOI
TL;DR: The preparation details and chrystallographic characteristics of BaLaFeO4 are reported in this article, where tetragonal cell dimensions (ao=3921±0002; c o =13175±0005 A ), in contrast with those elsewhere reported, well agree both with those for CaLaEOO4 and SrLaEoO4 isomorphous compounds and the ionic radii of the three alkali-earth metals, and the Mossbauer spectrum at 90°K confirms both the oxidation number for iron and the deformation of oxygen octa