Showing papers by "Polytechnic University of Turin published in 1995"
18 Dec 1995
TL;DR: Model-checking algorithms for extensions of pCTL and p CTL* to systems in which the probabilistic behavior coexists with nondeterminism are presented, and it is shown that these algorithms have polynomial-time complexity in the size of the system.
Abstract: The temporal logics pCTL and pCTL* have been proposed as tools for the formal specification and verification of probabilistic systems: as they can express quantitative bounds on the probability of system evolutions, they can be used to specify system properties such as reliability and performance. In this paper, we present model-checking algorithms for extensions of pCTL and pCTL* to systems in which the probabilistic behavior coexists with nondeterminism, and show that these algorithms have polynomial-time complexity in the size of the system. This provides a practical tool for reasoning on the reliability and performance of parallel systems.
683 citations
TL;DR: Improvements obtained in dealing with job shop scheduling using a heuristic technique based on Genetic Algorithms are presented.
381 citations
TL;DR: In this paper, duality transformations in N = 2, d = 4 Yang-Mills theory coupled to n = 2 supergravity were considered, and the implications of duality symmetry on all N > 2 extended supergravities are briefly mentioned.
326 citations
TL;DR: In this paper, generic features of eleven dimensional supergravity compactified down to five dimensions on an arbitrary Calabi-Yau threefold were considered and the possible relation with the heterotic string compactified on K 3 × S 1 was discussed.
251 citations
TL;DR: In this paper, the authors show that the nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes, and that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of defects and heterogeneities being limited.
Abstract: The nominal tensile strength of concrete structures is constant for relatively large sizes, whereas it decreases with the size for relatively small sizes. When, as usually occurs, the experimental investigation does not exceed one order of magnitude in the scale range, a unique tangential slope in the bilogarithmic strength versus size diagram is found. On the other hand, when the scale range extends over more than one order of magnitude, a continuous transition from slope −1/2 to zero slope may appear. This means that for smaller scales a self-similar distribution of Griffith cracks is prevalent, whereas for larger scales the disorder is not visible, the size of the defects and heterogeneities being limited. In practice there may be a dimensional transition from disorder to order. The assumption of multifractality for the damaged material microstructure represents the basis for the so-called multifractal scaling law. This is a best-fit method that imposes the concavity of the bilogarithmic curve upwards, in contrast to the size effect law of Bažant. The relevant results in the literature for ranges in scale extending over more than one order of magnitude are analysed.
218 citations
TL;DR: A general expression for the magnetoresistance in granular magnetic systems is obtained, and shown to accurately fit all the experimental curves, indicating that this effect is basically determined by the ratios between two distinct correlation ranges for the magnetic-moment fluctuations and the electronic mean free path.
Abstract: Room-temperature measurements of magnetization and giant magnetoresistance were performed on rapidly solidified granular ${\mathrm{Cu}}_{100\ensuremath{-}x}{\mathrm{Co}}_{x}$ systems ($x=5, 10, 15$). The magnetoresistance of melt-spun ${\mathrm{Cu}}_{100\ensuremath{-}x}{\mathrm{Co}}_{x}$ ribbons was enhanced either by suitable furnace annealings or by exploiting the dc Joule-heating technique in the attempt of precipitating smaller magnetic particles. The particle-size distribution, the particle density, and mean distance are obtained for all compositions and heat treatments through a suitable analysis of the magnetic behavior of samples. The magnetoresistance is plotted as a function of the reduced magnetization, and a significant deviation from the quadratic behavior predicted by the independent-moment approach is observed at low fields. A simple theory taking explicitly into account the correlation existing among the magnetic particles is proposed. A general expression for the magnetoresistance in granular magnetic systems is obtained, and shown to accurately fit all the experimental curves, indicating that this effect is basically determined by the ratios between two distinct correlation ranges for the magnetic-moment fluctuations and the electronic mean free path.
185 citations
TL;DR: This correspondence addresses the problem of inferring the shape of the unknown object O from the reconstructed object R, and considers two cases: R is the closest approximation of O which can be obtained from its silhouettes, i.e., its visual hull; and R is a generic reconstructed object.
Abstract: Each 2D silhouette of a 3D unknown object O constrains O inside the volume obtained by back-projecting the silhouette from the corresponding viewpoint. A set of silhouettes specifies a boundary volume R obtained by intersecting the volumes due to each silhouette. R more or less closely approximates O, depending on the viewpoints and the object itself. This approach to the reconstruction of 3D objects is usually referred to as volume intersection. This correspondence addresses the problem of inferring the shape of the unknown object O from the reconstructed object R. For doing this, the author divides the points of the surface of R into hard points, which belong to the surface of any possible object originating R, and soft points, which may or may not belong to O. The author considers two cases: In the first case R is the closest approximation of O which can be obtained from its silhouettes, i.e., its visual hull; in the second case, R is a generic reconstructed object. In both cases the author supplies necessary and sufficient conditions for a point to be hard and gives rules for computing the hard surfaces. >
184 citations
TL;DR: In this paper, the eigenfunctions of the Dirac operator on spheres and real hyperbolic spaces of arbitrary dimension are computed by separating variables in geodesic polar coordinates.
Abstract: The eigenfunctions of the Dirac operator on spheres and real hyperbolic spaces of arbitrary dimension are computed by separating variables in geodesic polar coordinates. These eigenfunctions are used to derive the heat kernel of the iterated Dirac operator on these spaces. They are then studied as cross sections of homogeneous vector bundles, and a group-theoretic derivation of the spinor spherical functions and heat kernel is given based on Harish-Chandra's formula for the radial part of the Casimir operator.
183 citations
TL;DR: In this article, a new iterative approach to the solution of the Boltzmann equation is presented, and the convergence of the iteration procedure is checked in reference to an isotropic solid subjected to a thermal gradient.
Abstract: A new iterative approach to the solution of the Boltzmann equation is presented. The convergence of the iteration procedure is checked in reference to an isotropic solid subjected to a thermal gradient. The resulting thermal conductivity for an argon cyrstal at 80 K is consistent with the answer of a variational calculation previously performed in the frame of the same model. The extension of the method to any kind of transport problems, for any system of interacting particles, is suggested.
181 citations
TL;DR: In this article, a new technique of checking the machine quality of a Rapid Prototyping (RP) workpiece according to the ANSI-ISO standards is presented, and the surface of RP model were observed by SEM microscope.
181 citations
TL;DR: The paper introduces the detection techniques, reviews and compares the methods of spectral estimation based on FFT and autoregressive models, and discusses their applications and limitations in extracting information from the surface myoelectric signal with particular regard to myoeLECTric manifestations of localised muscle fatigue during sustained contractions.
Abstract: During sustained voluntary or electrically elicited muscle contractions the surface myoelectric signal is nonstationary and it undergoes progressive changes reflecting the modifications of the motor unit action potentials and their propagation velocity. In particular, during sustained electrical stimulation, the evoked signals show progressive amplitude, time scaling and shape modification. The quantitative evaluation of these changes is important for non-invasive muscle characterisation and may be performed in either the time or frequency domain using parametric and nonparametric spectral analysis as well as alternative methodologies. The paper introduces the detection techniques, reviews and compares the methods of spectral estimation based on FFT and autoregressive models, and discusses their applications and limitations in extracting information from the surface myoelectric signal with particular regard to myoelectric manifestations of localised muscle fatigue during sustained contractions.
TL;DR: In this paper, a method for the synthesis of optical filters consisting of a cascade of N-coupled rings is presented based on the definition of a polynomial whose roots are the zeros of the channel-dropping transmittance characteristic and provides directly the ring electrical lengths and the mutual coupling coefficients.
Abstract: A method for the synthesis of optical filters consisting of a cascade of N-coupled rings is presented. The procedure is based on the definition of a polynomial whose roots are the zeros of the channel-dropping transmittance characteristic and provides directly the ring electrical lengths and the mutual coupling coefficients. A design example of a Chebyshev-type 6-ring bandpass filter is presented.
TL;DR: In this paper, a post mortem on concrete fracture surfaces of specimens broken in direct tension has been carried out, yielding non-integer (fractal) dimensions of profiles, which are then related to the normalized fracture energy of the material.
Abstract: Experimental evidence of the fractality of fracture surfaces has been widely recognized in the case of concrete, ceramics and other disordered materials. An investigationpost mortem on concrete fracture surfaces of specimens broken in direct tension has been carried out, yielding non-integer (fractal) dimensions of profiles, which are then related to the ‘renormalized fracture energy’ of the material. No unique value for the fractal dimension can be defined: the assumption of multifractality for the damaged, material microstructure produces a dimensional increment of the dissipation space with respect to the number 2, and represents the basis for the so-called multifractal scaling law. A transition from extreme Brownian disorder (slope 1/2) to extreme order (zero slope) may be evidenced in the bilogarithmic diagram: the nominal fracture energyGF increases with specimen size by following a nonlinear trend. Two extreme scaling regimes can be identified, namely the fractal (disordered) regime, corresponding to the smallest sizes, and the homogeneous (ordered) regime, corresponding to the largest sizes, for which an asymptotic constant value ofGF is reached.
TL;DR: Receiver structures for the direct detection of binary and multilevel digital optical modulation schemes employing the modulation of the state of polarization of light, or polarization shift keying (POLSK), are proposed and accurately analyzed, and results make POLSK schemes look promising for very-long-haul transmission.
Abstract: Receiver structures for the direct detection of binary and multilevel digital optical modulation schemes employing the modulation of the state of polarization of light, or polarization shift keying (POLSK), are proposed and accurately analyzed, in the presence of optical amplifier ASE noise and electrical receiver noise. A comprehensive set of results shows that the performance of the binary system is approximately 3 dB better than IM/DD (on peak optical power), and stays so for a wide range of optical filter bandwidths. As a somewhat unexpected result, the multilevel schemes show a lower sensitivity to the use of a wide optical filter than the binary one. As a consequence, transmitting 3 b/symbol on a cubic constellation on the Poincare sphere brings about virtually no penalty, whereas transmitting 2 b/symbol has a better performance than binary transmission, for even relatively low values of the optical filter bandwidth. A clear explanation of this phenomenon has been found. These results suggest that narrow-bandwidth and therefore low-dispersion, multilevel, POLSK transmission could be performed with no penalty. Together with the low excitation of nonlinear effects in the fiber that polarization modulation seems to ensure, these results make POLSK schemes look promising for very-long-haul transmission. >
09 May 1995
TL;DR: A new search strategy particularly effective for very large vocabulary word recognition, performs a tree based, time synchronous, left-to-right beam search that develops time-dependent acoustic and phonetic hypotheses.
Abstract: The paper presents a fast segmental Viterbi algorithm. A new search strategy particularly effective for very large vocabulary word recognition. It performs a tree based, time synchronous, left-to-right beam search that develops time-dependent acoustic and phonetic hypotheses. At any given time, it makes active a sub-word unit associated to an arc of a lexical tree only if that time is likely to be the boundary between the current and the next unit. This new technique, tested with a vocabulary of 188892 directory entries, achieves the same results obtained with the Viterbi algorithm, with a 35% speedup. Results are also presented for a 718 word, speaker independent continuous speech recognition task.
TL;DR: This model reproduces all the peculiar features of the photoluminescence behavior of a-C:H films, such as the nonactivated dependence upon temperature.
Abstract: Amorphous hydrogenated carbon films show a characteristic photoluminescence behavior that is of great interest for the study of their electronic structure. In the present paper we develop a model of the photoluminescence process in a polymerlike hydrocarbon on the basis of a mixed ${\mathit{sp}}^{2\mathrm{\ensuremath{-}}}$${\mathit{sp}}^{3}$ hybridization of the carbon atoms in this material. The ${\mathit{sp}}^{2}$ phase is assumed to be confined in clusters embedded within a ${\mathit{sp}}^{3}$ matrix. We assume excitation and recombination to take place within a single cluster. Thus the overall photoluminescence signal consists of the contribution of all single clusters, having different energy-gap values ${\mathit{E}}_{\mathit{g}}$, due to their various sizes and/or shapes. Applying the model to experimental data, we deduce a material-characteristic function f(${\mathit{E}}_{\mathit{g}}$) that turns out to be representative of the distribution of the different energy-gap values ${\mathit{E}}_{\mathit{g}}$ of the ${\mathit{sp}}^{2}$ clusters in the film. The good agreement with experimental data suggests that the classical Tauc gap ${\mathit{E}}_{\mathrm{Tauc}}$ in a-C:H films is a value averaging over all single-cluster gap values ${\mathit{E}}_{\mathit{g}}$. Moreover, our model reproduces all the peculiar features of the photoluminescence behavior of a-C:H films, such as the nonactivated dependence upon temperature.
TL;DR: In this paper, a conceptual model to analyse innovations originating from the diffusion of Information Technologies in the banking sector is proposed, which emphasizes the crucial role played by demand-pull variables in stimulating innovative behavior under the smart automation regime.
08 Oct 1995
TL;DR: Three AC motors are compared for application in high-performance controlled drives: induction, brushless, and synchronous reluctance motors, optimized under common design assumptions, thus defining the most suitable solution for each field.
Abstract: Three AC motors are compared for application in high-performance controlled drives: induction, brushless, and synchronous reluctance motors. Their design is optimized under common design assumptions, Then, the given stall-torques are compared to each other. In addition, the quadrature reactances are compared, as affecting overload and flux-weakening performances. Finally, applicative considerations are given, thus defining the most suitable solution for each field.
01 Jan 1995
TL;DR: A software generation methodology that takes advantage of the very restricted class of specifications and allows for tight control over the implementation cost, and exploits several techniques from the domain of Boolean function optimization is proposed.
Abstract: Software components for embedded reactive real-time applications must satisfy tight code size and run-time constraints. Cooperating Finite State Machines provide a convenient intermediate format for embedded system co-synthesis, between high-level specification languages and software or hardware implementations. We propose a software generation methodology that takes advantage of the very restricted class of specifications and allows for tight control over the implementation cost. The methodology exploits several techniques from the domain of Boolean function optimization. We also describe how the simplified control/data-flow graph used as an intermediate representation can be used to accurately estimate the size and timing cost of the final executable code.
TL;DR: In this paper, the application of the Kirchhoff transformation to the thermal analysis of semiconductor devices with temperature-dependent and piecewise inhomogeneous thermal conductivity is discussed. But the authors do not consider the case where the ratio of thermal conductivities is temperature independent, unless the apparent temperature is continuous.
Abstract: The paper presents a discussion on the application of the Kirchhoff transformation to the thermal analysis of semiconductor devices with temperature-dependent and piecewise inhomogeneous thermal conductivity. The Kirchhoff transformation is shown to generally reduce the problem to the solution of the linear heat equation with nonlinear jump conditions on the apparent temperature across subdomains, unless the ratio of the thermal conductivities is temperature independent, in which case the apparent temperature is continuous. In many practical cases, the temperature dependence of the thermal conductivity can be approximated in all subdomains so as to enforce this condition; one and two-dimensional examples are discussed to show that in realistic configurations (devices with metal heat sinks, multilayered structures made of different semiconductors) the error thereby introduced is acceptably low.
25 Sep 1995
TL;DR: New methods for the compile-time analysis of the behavior of active rules are proposed, based on the distinction between mutual triggering and mutual activation of rules, to provide a systematic identification of reactive behaviors which can be guaranteed to terminate and reactive behaviorsWhich may lead to infinite rule processing.
Abstract: In this paper, we propose new methods for the compile-time analysis of the behavior of active rules, based on the distinction between mutual triggering and mutual activation of rules. This distinction motivates the introduction of two graphs defining rule interaction, called triggering and activation graphs respectively. Analysis techniques presented in this paper are focused on the problem of termination; results provide a systematic identification of reactive behaviors which can be guaranteed to terminate and reactive behaviors which may lead to infinite rule processing.
TL;DR: A solution approach for a joint process plan selection and job shop scheduling problem, taking both operations cost and makespan into account within a multi-objective framework is proposed.
Abstract: The job shop scheduling literature deals with problems characterized by a fixed linear process plan for each job: it is assumed that the process planning problem has been solved before scheduling, and no flexibility in the process plan is considered. Our aim here is to propose a solution approach for a joint process plan selection and job shop scheduling problem, taking both operations cost and makespan into account within a multi-objective framework. Due to the complexity of the problem, a two-phase hierarchical method is proposed. In the first phase, a relaxed version of the problem is solved, yielding an approximation of the set of efficient process plans with respect to cost and load balancing objectives. Each process plan is then considered and the corresponding scheduling problem is solved by tabu search; the process plan selection is improved by a two-level hierarchical tabu search algorithm.
TL;DR: The authors propose a solution to the parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable iterative decoding structure that outperforms all codes reported in the past for the same throughput.
Abstract: We propose a new solution to parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable iterative decoding structure. Examples are given for throughputs 2 bits/sec/Hz with 8PSK and 16QAM signal constellations.
TL;DR: An approach based on multiple-criteria decision aid (MCDA) methods has been introduced for the prioritization of technical/engineering design requirements during the quality function deployment (QFD) process as discussed by the authors.
Abstract: An approach based on multiple-criteria decision aid (MCDA) methods has been introduced for the prioritization of technical/engineering design requirements during the quality function deployment (QFD) process. The proposed method allows the avoidance of the rigid procedure under which the relationship matrix coefficients are turned from an ordinal into a cardinal scale. A comparison analysis is carried out between the “traditional” approach and the proposed one. A numerical example is also provided so as to highlight the main differences between the two methods.
TL;DR: The results are exact in the limit of a large number of hidden units, showing that MLN are a class of exactly solvable models with a simple interpretation of replica symmetry breaking.
Abstract: We analytically derive the geometrical structure of the weight space in multilayer neural networks (MLN), in terms of the volumes of couplings associated to the internal representations of the training set. Focusing on the parity and committee machines, we deduce their learning and generalization capabilities both reinterpreting some known properties and finding new exact results. The relationship between our approach and information theory as well as the Mitchison--Durbin calculation is established. Our results are exact in the limit of a large number of hidden units, showing that MLN are a class of exactly solvable models with a simple interpretation of replica symmetry breaking.
TL;DR: In this article, the authors analyzed the change in iron losses due to the switching frequency in soft magnetic materials supplied by PWM inverter and reported the values of iron losses vs switching frequency, for different values of the fundamental flux density and assigned modulation parameters.
Abstract: In the paper change in iron losses due to the switching frequency in soft magnetic materials supplied by PWM inverter, is analyzed. Experimental tests with several samples of material and switching frequency from 1 kHz up to about 20 kHz, are reported. Values of iron losses vs switching frequency, for different values of the fundamental flux density and assigned modulation parameters, are presented for the materials investigated.
08 Oct 1995
TL;DR: The authors deal with the effects of the inverter characteristics on the iron losses increment in induction motors fed by PWM controlled converters by considering the influence of modulation index; modulation waveform; and switching frequency.
Abstract: In this paper, the authors deal with the effects of inverter characteristics on iron losses in induction motors fed by pulsewidth modulation (PWM) controlled power converters. Laboratory tests based on no-load input power measurements were carried out and in order to avoid the influence of mechanical losses and rotor copper losses, which are difficult to be measured or computed, a special test bench with an unconventional test device was employed. In particular, the influence of the following inverter parameters are considered: modulation index; modulation waveform; and switching frequency. Complete experimental results are presented and discussed.
TL;DR: For the first time a set of series expansions is implemented allowing these special functions to be evaluated efficiently within a prescribed accuracy for real Fortran subroutines.
Abstract: Portable Fortran subroutines computing the Fermi-Dirac integral Fj(x) and the incomplete Fermi-Dirac integral Fj(x,b) are presented. For the first time a set of series expansions is implemented allowing these special functions to be evaluated efficiently within a prescribed accuracy for real jand x.
TL;DR: In this article, a finite element computer model for the transient thermohydraulics of compressible helium in a cable-in-conduit (CICC) with central cooling hole, as presently envisaged for superconducting magnets of the International Thermonuclear Experimental Reactor (ITER), is presented.
Abstract: We present here a finite element computer model (Mithrandir) for the transient thermohydraulics of compressible helium in a Cable-In-Conduit Conductor (CICC) with central cooling hole, as presently envisaged for superconducting magnets of the International Thermonuclear Experimental Reactor (ITER). In the model the He in the hole and that in the cable bundle are treated as separate fluids, each characterized by its own flow and thermodynamic properties, coupled by exchanges of mass, momentum and energy. Results for the simulation of a quench both with and without a wall delimiting the central cooling hole are discussed. Time and space convergence of the code are demonstrated numerically.