Showing papers by "Polytechnic University of Turin published in 1994"
TL;DR: This paper addresses the problem of finding which parts of a nonconvex object are relevant for silhouette-based image understanding and introduces the geometric concept of visual hull of a 3-D object, which is the maximal object silhouette-equivalent to S.
Abstract: Many algorithms for both identifying and reconstructing a 3-D object are based on the 2-D silhouettes of the object. In general, identifying a nonconvex object using a silhouette-based approach implies neglecting some features of its surface as identification clues. The same features cannot be reconstructed by volume intersection techniques using multiple silhouettes of the object. This paper addresses the problem of finding which parts of a nonconvex object are relevant for silhouette-based image understanding. For this purpose, the geometric concept of visual hull of a 3-D object is introduced. This is the closest approximation of object S that can be obtained with the volume intersection approach; it is the maximal object silhouette-equivalent to S, i.e., which can be substituted for S without affecting any silhouette. Only the parts of the surface of S that also lie on the surface of the visual hull can be reconstructed or identified using silhouette-based algorithms. The visual hull depends not only on the object but also on the region allowed to the viewpoint. Two main viewing regions result in the external and internal visual hull. In the former case the viewing region is related to the convex hull of S, in the latter it is bounded by S. The internal visual hull also admits an interpretation not related to silhouettes. Algorithms for computing visual hulls are presented and their complexity analyzed. In general, the visual hull of a 3-D planar face object turns out to be bounded by planar and curved patches. >
1,585 citations
TL;DR: In this article, it was shown that the sum of the dimensional decrement (for material ligament) and the dimensional increment (for fracture surface) must be lower than unity.
422 citations
TL;DR: In this paper, the problem of the size effects on tensile strength and fracture energy of brittle and disordered materials (concrete, rocks, ceramics, etc.) is reconsidered under a new and unifying light cast on by fractal geometry.
354 citations
TL;DR: A membrane is commonly regarded as a barrier capable of being selectively permeated by some components of a mixture or changing the composition of a fluid stream that flows through it due to a certain driving force (a pressure, concentration, or electric potential gradient) as mentioned in this paper.
Abstract: A membrane is commonly regarded as a barrier capable of being selectively permeated by some components of a mixture or, at least, of changing the composition of a fluid stream that flows through it due to a certain driving force (a pressure, concentration, or electric potential gradient) Permselectivity is thus considered as the most distinctive property of a membrane
247 citations
TL;DR: In this paper, the authors used three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus.
Abstract: Tests were carried out using three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus. The method enables a stress versus strain curve to be plotted with the descending (softening) branch up to the point where the cross-section of the tensile specimen breaks away. The principal purpose is to avoid any spurious effect that might provide a fallacious explanation of the recurring size effects on apparent tensile strength and fictitious fracture energy. Once the secondary effects have been excluded, only the disorder and fractality of the concrete microstructure remain to explain such fundamental trends. In the case of tensile strength, the dimensional decrement represents self-similar weakening of the material ligament, due to pores, voids, defects, cracks, aggregates, inclusions, etc. Analogously, in the case of fracture energy, the dimensional increment represents self-similar tortuosity of the fracture surface, as well as self-similar overlapping and distribution of microcracks in the direction orthogonal to that of the forming macrocrack.
194 citations
TL;DR: Boundary integral equations which employ integrals which exist only if defined in the Cauchy principal value sense or as the Hadamard finite part are currently used with success to solve many two-and three-dimensional problems of applied mechanics as mentioned in this paper.
178 citations
166 citations
TL;DR: The Hermite approach is found to be suitable for classification of spectral shapes and compression of spectral information of either voluntary or evoked signals, and very promising for neuromuscular diagnosis and assessment.
Abstract: Nonstationary signals with finite time support are frequently encountered in electrophysiology and other fields of biomedical research. It is often desirable to have a compact description of their shape and of their time evolution. For this purpose, Fourier analysis is not necessarily the best tool. The Hermite-Rodriguez and Associated Hermite basis functions are applied in this work. Both are based on the product of Hermite polynomials and Gaussian functions. Their general properties relevant to biomedical signal processing are reviewed. Preliminary applications are described concerning the analysis and description of: a) test signals such as a square pulse and a single cycle of a sinewave, b) electrically evoked myoelectric signals, and c) power spectra of either voluntary or evoked signals. It is shown that expansions with only five to ten terms provide an excellent description of the computer simulated and real signals. It is shown that these two families of Hermite functions are well suited for the analysis of nonstationary biological evoked potentials with compact time support. An application to the estimation of scaling factors of electrically evoked myoelectric signals is described. The Hermite functions show advantages with respect to the more traditional spectral analysis, especially in the case of signal truncation due to stimulation with interpulse intervals smaller than the duration of the evoked response. Finally, the Hermite approach is found to be suitable for classification of spectral shapes and compression of spectral information of either voluntary or evoked signals. The approach is very promising for neuromuscular diagnosis and assessment because of its capability for information compression and waveform classification. >
145 citations
05 Sep 1994
TL;DR: In this paper, the synchronous reluctance motor drive is illustrated as a new incoming technology solution and the obtainable performance in terms of torque per volume is compared to that of brushless and induction motors.
Abstract: The modern synchronous reluctance motor drive is illustrated as a new incoming technology solution. High anisotropy motor design is briefly summarized. The obtainable performance in terms of torque-per-volume is then compared to that of brushless and induction motors. With reference to traditional vector current control, the peculiarities of the synchronous reluctance motor drive are shown. Moreover, the effect of some second-order control aspects are evidenced, together with the possible advantages of adoption of flux-observer based schemes. Finally, both research and industrial trends in this field are summarized. >
144 citations
TL;DR: In this article, the stability of cellular neural networks (CNNs) and Delayed Cellular Neural Networks (DCNNs) is addressed by means of Lyapunov functions (functionals in the delayed case); new classes of nonpositive templates, describing CNN's and DCNN's, are shown to be stable and some conditions are found ensuring the complete stability of dominant template DCNNs and CNN's with nonmonotonic output functions.
Abstract: In this paper the problem of the stability of Cellular Neural Networks (CNN's) and Delayed Cellular Neural Networks (DCNN's) is addressed by means of Lyapunov functions (functionals in the delayed case); new classes of nonpositive templates, describing CNN's and DCNN's, are shown to be stable and some conditions are found ensuring the complete stability of dominant template DCNN's and CNN's with nonmonotonic output functions. >
136 citations
TL;DR: In this article, the authors focused on the major hurdles along the way of exploitation of these possibilities: high costs, low permeability, synthesis of defect-free permselective years, instability of membranes and catalysts, sealing of membranes into modules, etc.
TL;DR: A general theory is proposed based on the modelling of cellular interactions in a framework similar to the one of nonlinear statistical mechanics in order to validate the proposed theory of tumor progression despite an active immune defense system.
TL;DR: A new receiver structure, which solves the problem of the excess penalties incurred in the presence of channel dichroism, is proposed and analyzed and the optimum maximum likelihood receiver operating symbol by symbol is derived.
Abstract: Multilevel digital coherent optical modulation schemes based on the state of polarization of a fully polarized lightwave are proposed and analyzed. Based on the complete statistical characterization of the Stokes parameters, extracted through appropriate signal processing in the presence of shot and additive Gaussian noise, the optimum maximum likelihood receiver operating symbol by symbol is derived. The exact performance in terms of the average symbol error probability is found. Optimum constellations for the case of equipower 4, 8, 16 and 32 signals are found on the basis of the minimization of the error probability for a given average power. Their performance turns out to be promising as compared to other standard modulation techniques. The spectral analysis of polarization modulated signals is presented. A new receiver structure, which solves the problem of the excess penalties incurred in the presence of channel dichroism, is proposed and analyzed. >
01 Jun 1994
TL;DR: A description of the algorithms to evaluate the main parameters determining the performance of a trellis-coded modulation (TCM) scheme is presented and the algorithms are compared in terms of computational complexity and tested on a set of multidimensional PSK codes.
Abstract: A description of the algorithms to evaluate the main parameters determining the performance of a trellis-coded modulation (TCM) scheme is presented. TCM schemes are divided into classes that have an increasing degree of symmetry, so as to properly match the various algorithms to each class. The algorithms are compared in terms of computational complexity and tested on a set of multidimensional PSK codes. >
TL;DR: In this article, a geometrical interpretation of the Risks-Wempner method and a new algorithm to choose the appropriate root of a nonlinear constraint equation are presented.
02 Oct 1994
TL;DR: An approach based on Genetic Algorithms suitable for even the largest benchmark circuits, together with a prototype system named GATTO is described and its effectiveness (in terms of result quality and CPU time requirements) for circuits previously unmanageable is illustrated.
Abstract: This paper is concerned with the question of automated test pattern generation for large synchronous sequential circuits and describes an approach based on Genetic Algorithms suitable for even the largest benchmark circuits, together with a prototype system named GATTO. Its effectiveness (in terms of result quality and CPU time requirements) for circuits previously unmanageable is illustrated. The flexibility of the new approach enables users to easily trade off fault coverage and CPU time to suit their needs.
15 Oct 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The LUNA project as discussed by the authors is a pilot project focused initially on cross section measurements of the reaction within the thermal energy region of the sun, and the experimental sensitivity was improved by more than four orders of magnitude over that of previous work.
Abstract: A compact high-current 50 kV ion accelerator facility including a windowless gas target system, a beam calorimeter, and detector telescopes in close geometry has been built and tested. The data acquisition and analysis involved a multiparameter system and a Monte Carlo program. The LUNA facility, presently installed at the Gran Sasso underground laboratory, is a pilot project focused initially on cross section measurements of the ^3He(^3He, 2p)^4He reaction within the thermal energy region of the sun. To achieve this goal, the experimental sensitivity has been improved by more than four orders of magnitude over that of previous work.
TL;DR: Various numerical simulations of ultrasonic pulses propagating through solids carried out on a massively parallel computer, accompanied by visualizations of the resulting wavefield are illustrated.
Abstract: Parallel processing has changed the way much computational physics is done. Areas such as condensed matter physics, fluid dynamics, and other fields are making use of massively parallel computers to solve immense and important problems in new ways. Simulating wave propagation is another area that has benefited through the use of parallel processing. This is graphically illustrated in this article by various numerical simulations of ultrasonic pulses propagating through solids carried out on a massively parallel computer. These computations are accompanied by visualizations of the resulting wavefield. The calculations and visualizations, together, can be completed in only seconds to several minutes and compare well with experimental data. The computations and parallel processing techniques described should be important in related fields, such as geophysics, acoustics, and mechanics.
TL;DR: In this paper, the problem of tunnel face stability is studied and the analysis of the stabilizing effect achieved by pre-reinforcement of the core which has to be excavated is dealt with in Italy, the insertion of longitudinal fibreglass pipes in the ground has proved to be efficient in solving face instability problems.
Abstract: The problem of tunnel face stability is studied and the analysis of the stabilizing effect achieved by pre-reinforcement of the core which has to be excavated is dealt with In Italy, the insertion of longitudinal fibreglass pipes in the ground has proved to be efficient in solving face instability problems A thorough review of other applications of the technology has been carried out The results of a series of parametric, three-dimensional, elasto-plastic finite element analyses are presented The tunnel excavation with or without support and face reinforcement is simulated in the models The stresses, plastic zones and displacements in the ground, pipes and lining have been studied The support effect of the pipes is demonstrated by the results Face reinforcement significantly reduces the displacements of the face The stresses in the material at the face are also charged from tension to compression, thus enhancing face stability
TL;DR: In this article, the moduli space of vacua in N = 2 supersymmetric Yang-Mills theory was studied and the Picard-Fuchs type of differential equations expressing the existence of a flat holomorphic connection were shown to be second order equations.
TL;DR: In this article, a simple relation between the residues of μ(λ) at these poles and the (known) degeneracies of Δ on the N -sphere is obtained.
TL;DR: A division algorithm in which the quotient-digit selection is performed by rounding the shifted residual in carry-save form by finding several convenient values of the radix.
Abstract: A division algorithm in which the quotient-digit selection is performed by rounding the shifted residual in carry-save form is presented. To allow the use of this simple function, the divisor (and dividend) is prescaled to a range close to one. The implementation presented results in a fast iteration because of the use of carry-save forms and suitable recodings. The execution time is calculated and several convenient values of the radix are selected. Comparison with other dividers for radices 2/sup 9/ to 2/sup 18/ is performed using the same assumptions. >
TL;DR: The critical thickness of the cell for the transition from planar to periodic alignment as a function of the surface energy in the presence of a magnetic field is found.
Abstract: Recently we investigated the occurrence of static periodic stripes in a hybrid aligned nematic cell. Assuming that the tilt anchoring was stronger at the planar wall than at the homeotropic wall, we have found the critical thickness of the cell for the transition from planar to periodic alignment as a function of the surface energy in the presence of a magnetic field. Here we study, for the same kind of cell, the critical thickness between the periodic and the aperiodic deformed structure by means of an appropriate numerical technique. As expected, such a threshold was found to be greater than the asymptotic threshold between planar and aperiodic structures. We performed an experiment, which allowed us to give an estimate of the surfacelike elastic constant ${\mathit{K}}_{24}$.
TL;DR: In this paper, a standard spectral collocation scheme can be stabilized by adding extra trial/test functions with local support (bubbles), and applications are given to a scalar advection-diffusion problem and to the Stokes problem.
TL;DR: Volterra-series models of magnetic-saturation recording channels are used to derive readback structures that compensate for channel nonlinearities, and it was found that symbol-by-symbol preliminary detection performs adequately.
Abstract: Volterra-series models of magnetic-saturation recording channels are used to derive readback structures that compensate for channel nonlinearities. These structures are based on a canceler of linear and nonlinear channel distortions, and can achieve significant improvement in terms of mean-square error and error probability. Proper operation of the canceler requires reliable preliminary decisions to be taken on the information symbols. These decisions are obtained by passing the received signal through a linear equalizer, then processing the equalized signal through a symbol-by-symbol detector or a Viterbi detector. By using the data obtained in [4] for magneto-resistive heads, it was found that symbol-by-symbol preliminary detection performs adequately. A Volterra model was also obtained experimentally for the recording channel generated by magneto-inductive heads that exhibit higher-order nonlinear effects. In order to recover data from this highly distorted channel the preliminary detection scheme needs a 4-state Viterbi detector. >
TL;DR: A novel extension of LOTOS, one of the two formal specification languages that were standardized by ISO, is presented, specifically conceived to integrate performance analysis and formal verification.
Abstract: Performance analysis and formal correctness verification of computer communication protocols and distributed systems have traditionally been considered as two separate fields. However, their integration can be achieved by using formal description techniques as paradigms for the development of performance models. This paper presents a novel extension of LOTOS, one of the two formal specification languages that were standardized by ISO. The extension is specifically conceived to integrate performance analysis and formal verification. The extended language syntax and semantics are formally defined, along with a mapping from extended specifications to performance models, The mapping preserves the specified observable behavior. Two simple examples, a stop-and-wait protocol and a time-sharing system, are used to concretely demonstrate the new approach and to validate it. >
TL;DR: In this paper, the advantages of this rapid heating technique are highlighted, and the average grain size of Joule-heated samples is significantly lower than in the furnace-annealed alloy.
TL;DR: The ability of the scalar Preisach model (PM) to describe magnetic interactions and Henkel plots is discussed in this article, where it is shown that the random interactions described by the PM switching field distribution p(/spl alpha/,/spl beta/) always have a net demagnetizing-like effect on remanences.
Abstract: The ability of the scalar Preisach model (PM) to describe magnetic interactions and Henkel plots is discussed. It is shown that the random interactions described by the PM switching field distribution p(/spl alpha/,/spl beta/) always have a net demagnetizing-like effect on remanences. The connection between the properties of p(/spl alpha/,/spl beta/) and those of Henkel plots is investigated. In particular, it is shown that, when p(/spl alpha/,/spl beta/)=f(/spl alpha/)f(/spl minus//spl beta/), the remanence law i/sub d//i/sub /spl infin//=1/spl minus/2/spl radic/i/sub r//i/sub /spl infin//, completely independent of f(/spl alpha/), holds. The joint presence of random interactions and mean-field effects is dealt with through the moving PM (MPM), in which an additional field proportional to magnetization acts on each PM elementary loop. The classification of Henkel plots by MPM is discussed. In particular, it is shown that Henkel plots exhibiting both magnetizing-like and demagnetizing-like deviations are a certain indication of the joint presence of random interactions and magnetizing-like mean-field effects. Theoretical predictions are compared with recent Henkel plot measurements on magnetic recording media, superconductors, thin films, hard magnets, and soft magnetic materials. >
TL;DR: In this article, an improved procedure for calculating iron losses in electrical machine cores is presented, based on physical models and experiments on losses in magnetic laminations, under one-and two-dimensional fields, and exploits a finite element computation of the flux distribution in the core.
TL;DR: In this article, the feasibility of a process for ammonia removal and recovery from high temperature waste waters is assessed, where NH 3 is stripped away in a packed column by means of air which is continuously looped to a further absorption unit.