Showing papers by "Polytechnic University of Turin published in 1985"
TL;DR: In this article, the theory of optimal algorithms for problems which cannot be solved exactly is investigated, which allows for the derivation of new and interesting results in parameter estimation and in time series prediction in situations where no reliable statistical hypothesis can be made on the functions and modeling errors involved.
Abstract: This paper deals with the theory of optimal algorithms for problems which cannot be solved exactly. The theory developed allows for the derivation of new and interesting results in parameter estimation and in time series prediction in situations where no reliable statistical hypothesis can be made on the functions and modeling errors involved, but only a bound on them is known, in particular, the derivation of computationally simple optimal algorithms for these two problems is investigated. The practical effectiveness of the algorithms obtained is illustrated by several numerical examples.
252 citations
TL;DR: In this paper, a model is presented to describe flow in segments of collapsible tube mounted between two rigid tubes and surrounded by a pressurized container, and the model predicts self-excited oscillations whose amplitude is large enough to be observable only if the flow in the collapsible tubes becomes supercritical.
Abstract: A new model is presented to describe flow in segments of collapsible tube mounted between two rigid tubes and surrounded by a pressurized container. The new features of the model are the inclusion of (a) longitudinal wall tension and (b) energy loss in the separated flow downstream of the time-dependent constriction in a collapsing tube, in a manner which is consistent with the one-dimensional equations of motion. As well as accurately simulating steady-state collapse, the model predicts self-excited oscillations whose amplitude is large enough to be observable only if the flow in the collapsible tube becomes supercritical somewhere (fluid speed exceeding long-wave propagation speed). The dynamics of the oscillations is dominated by longitudinal movement of the point of flow separation, in response to the adverse pressure gradient associated with waves propagating backwards and forwards between the (moving) narrowest point of the constriction and the tube outlet.
184 citations
TL;DR: The effects of various plant extracts on the dissolution of mild steel in HCl solutions were studied in this article, where Papaia, Poinciana pulcherrima, Cassia occidentalis and Datura stramonium seeds were investigated.
125 citations
TL;DR: A comparison between the two approaches to parameter identification from measurements corrupted by unknown-but-bounded errors is outlined and a combined use of the positive aspects of both procedures is proposed.
83 citations
TL;DR: In this paper, a comparison of the Adomian decomposition method and regular perturbation techniques applied to the solution of nonlinear vector random differential equations is made. And the comparison shows that the decomposition is easier to compute and supplies quantitatively reliable results.
59 citations
TL;DR: A distributed rule-based system for automatic speech recognition is described and experiments on the automatic segmentation and recognition of phrases, made of connected letters and digits, are described and discussed.
Abstract: A distributed rule-based system for automatic speech recognition is described. Acoustic property extraction and feature hypothesization are performed by the application of sequences of operators. These sequences, called plans, are executed by cooperative expert programs. Experimental results on the automatic segmentation and recognition of phrases, made of connected letters and digits, are described and discussed.
47 citations
01 Jan 1985
TL;DR: It is shown how the choice of the architecture of a multiprocessor system can be guided by analytical performance predictions in conjunction with implementation issues, and the modeling tools that were developed for this purpose.
Abstract: This chapter describes a multiprocessor performance evaluation case study, and the modeling tools that were developed for this purpose. It is shown how the choice of the architecture of a multiprocessor system can be guided by analytical performance predictions in conjunction with implementation issues. The goal of the project of a multiprocessor system is the development of an efficient architecture which should not experience bottlenecks at the physical level due to contention for shared resources. A description is given of how the comparison among candidate architectures must be done using common assumptions and a similar workload model. Only after this preliminary work can an architecture be chosen and implemented as a good compromise between performance and implementation costs.
34 citations
TL;DR: In this paper, the expressions for the consistent mass and gyroscopic matrices for a constant section shaft element are obtained taking into account both shear deformation and transversal inertia.
Abstract: The expressions for the consistent mass and gyroscopic matrices for a constant section shaft element are obtained taking into account both shear deformation and transversal inertia. The results are compared with closed form solutions, which are available in simple cases. The results obtained show that the study of the dynamic behaviour of the rotor with a model which includes rotational inertia but not shear deformation is, at least in the case examined, misleading. Formulae for matrix condensation and for taking into account the effects of axial load and of a linear unbalance distribution are given. Damped systems can be studied using the same model, provided that damping can be assumed to be of either viscous or hysteretic type. Some formulations found in the literature are however not considered correct. An application of consistent matrices to a model which includes damping and uses matrix condensation is shown.
34 citations
TL;DR: The power spectrum of the surface myoelectric signal is known to undergo compression during sustained muscle contractions and isknown to be modified in most neuromuscular pathological situations.
Abstract: The power spectrum of the surface myoelectric signal is known to undergo compression during sustained muscle contractions and is known to be modified in most neuromuscular pathological situations.
33 citations
TL;DR: In this paper, a second-order probabilistic load flow technique is presented, which takes into account the effects of nonlinearities in the system equations and of different dispatching strategies.
32 citations
TL;DR: In this article, it is shown that the stable director configurations are described by functions with discontinuous derivatives at the boundaries, and that all the solutions given in literature, which are found by explicitly assuming the continuity of the derivatives, must be revised.
Abstract: The boundary energy terms dependent on the first derivative of the director are analysed theoretically. Although these terms necessarily arise from nonlocal interactions, they are generally written as purely surface terms. We show that, in this case, the stable director configurations are described by functions with discontinuous derivatives at the boundaries. All the solutions given in literature, which are found by explicitly assuming the continuity of the derivatives, must, therefore, be revised. In a more correct formulation of the problem, the ranges of the interaction forces should be taken into account and continuous solutions are then obtained, which are generally well approximated by the discontinuous ones. The approximation, instead, is not good in the case of the energy term proposed by Dubois-Violette and Parodi, where the discontinuity has the form of a Dirac function. In this case a physically meaningful solution can be found only on the basis of a more suitable expression of the boundary energy.
TL;DR: In this article, a spectral formulation of the scattering problem relative to planar passive arrays in a stratified medium is presented, and the solution is obtained in terms of generalized scattering matrix by means of the Galerkin version of the Moment Method technique.
Abstract: A spectral formulation of the scattering problem relative to planar passive arrays in a stratified medium is presented. The solution is obtained in terms of generalized scattering matrix by means of the Galerkin version of the Moment Method technique. Further, an original approach to solve the multiple grid problem which allows to treat efficiently also cases of closely spaced arrays is presented. Comparisons with experimental results relative to crossed dipole arrays are presented.
TL;DR: On classe les groupes de type Heisenberg sur lesquels des fonctions L 1 A(N) invariant commutent as mentioned in this paper are invariant.
Abstract: On classe les groupes de type Heisenberg sur lesquels des fonctions L 1 A(N) invariantes commutent
TL;DR: In this paper, the same authors considered a general case where the direction of the propagating waves and the orientation of the dielectric tensor make an arbitrary angle with respect to the rotation axis.
Abstract: An optical model is considered describing a wide class of optically anisotropic media such as chiral smectic liquid crystals and, in the limiting cases, cholesteric liquid crystals and anisotropic homogeneous media. It describes a structure having a periodicity along a given axis generated by a uniform rotation of the dielectric tensor. Maxwell's equations for this model, studied so far only in particular cases, are here solved for the general case where the direction of the propagating waves and the orientation of the dielectric tensor make an arbitrary angle with respect to the rotation axis. The resolving procedure involves the evaluation of the eigenmodes of the electromagnetic wave, i.e. the Bloch waves intrinsic to the specific periodic structure, which reduce to the ordinary and extraordinary waves in the limiting case of anisotropic homogeneous structures. The dispersion relation for the eigenmodes is deduced, allowing the study of the optical properties of this structure on a general basis. The Bragg reflection bands are found to be constitued alternatively by singlets and triplets. In general the even order bands are triplets whose lateral peaks correspond to the Bragg instabilities of each eigenmode, while the central peak is common to both eigenmodes and gives total reflection with a mode exchange. The odd order bands are singlets whose characteristics are very similar to the central peak of the triplets. The polarization properties of the eigenmodes are studied in the particular case of locally uniaxial media, where the Bloch waves show an abrupt polarization change for a particular value of the angle between the optical axis and the rotation axis Etude d'un modele optique pour decrire des cristaux liquides smectiques chiraux et, a la limite, des cristaux liquides cholesteriques et des milieux homogenes anisotropes/structures presentant une periodicite le long d'un axe donne, produite par une rotation uniforme du Tenseur dielectrique). Resolution des equations de Maxwell dans le cas general ou la propagation des ondes et l'orientation de l'axe de rotation du tenseur dielectrique forment un angle arbitraire: calcul des ondes de Bloch propres a la structure periodique, qui se reduisent aux ondes ordinaires et extraordinaires pour une structure homogene anisotrope. Deduction des proprietes optiques (bandes de reflexion de Bragg)
TL;DR: In this paper, it was shown that the Betti number of a projective variety is upper semicontinuous for any fixed n. The relation between Betti numbers and Hilbert functions is studied.
Abstract: This paper is dedicated to the study of Hilbert functions and Betti numbers of the projective varieties in a flat family. We prove that the Hilbert function H(X
y
,n),y ∈ Y-a parameter scheme-is lower semicontinuous for any fixed n. In case Y is integral and noetherian we obtain the well-known fact that the set V ⊂Y where H(X
y
,n)is maximal for all n's is open and nonempty. We show also that bi(X
y
)-the i- th Betti number of Xy—is upper semicontinuous for y ∈ V. The paper contains also a number of results concerning the relations among the various Betti numbers.
TL;DR: In this paper, a measurement method to detect the knock-resistance and especially the knock limited conditions of high-speed s.i.d. engines is described, and its operating principles, based on statistical criteria, are described and verified by means of experimental tests.
Abstract: A measurement method to detect the knock-resistance and, especially, the knock-limited conditions of high-speed s.i. engines is described. Two instruments are used in conjunction: the first instrument measures a knock intensity index I.D. related to knock-typical pressure oscillations in the combustion chamber; the second instrument detects the knock-limited conditions in real time, by means of I.D. This latter instrument, which can be properly used as a knock-limit detector in operating-parameter control systems for automotive engines, is analyzed in detail. Its operating principles, based on statistical criteria, are described and verified by means of experimental tests. The checking tests carried out at high speed, both on a mass-produced automotive engine and on a prototype, are described. The knock resistance of the prototype, in its whole working range, is then analyzed.
TL;DR: In this article, a fluxdifference splitting method has been proposed for the numerical solution of hyperbolic problems and successfully implemented for unsteady flows for two-dimensional or axisymmetric steady supersonic flows.
TL;DR: On considere les solutions propres des equations de Maxwell pour la propagation lumineuse dans un cristal liquide cholesterique parfait d'ondes de Bloch ayant, en principe, un nombre infini de composantes de Fourier.
Abstract: On considere les solutions propres des equations de Maxwell pour la propagation lumineuse dans un cristal liquide cholesterique parfait. Il s'agit d'ondes de Bloch ayant, en principe, un nombre infini de composantes de Fourier. On etudie les amplitudes relatives de ces composants en fonction de la frequence angulaire, ω, et de l'angle d'incidence, θi, dans le but de determiner les conditions dans lesquelles les solutions propres peuvent etre approchees par une superposition de quelques ondes planes. Determination de ces solutions approchees, qui sont en general plus simples et plus precises que celles donnees anterieurement pour des cas similaires
01 Jan 1985
TL;DR: A cubic phase was synthesized by solid reaction in the La-Li-Me-O system (Me ≡ Fe) which was isostructural with those already known in systems with Me ≡ Pt or Ti as mentioned in this paper.
Abstract: A cubic phase was synthesized by solid reaction in the La-Li-Me-O system (Me ≡ Fe) which was isostructural with those already known in systems with Me ≡ Pt or Ti. An X-ray analysis based on 379 unique diffractometer reflections at room temperature (Mo Kα radiation; λ = 0.71069 A ) established that the LaLi0.5Fe0.2O2.09 phase crystallizes in space group Im3m with a = 12.231(1) A , Z = 32, dobs = 5.47gcm−3, dcalc = 5.48g cm−3, F(000) = 2574 and μ = 1438.9. The solution was obtained by a direct method and the refinement was performed using the least-squares procedure; the final R value was 0.038. A detailed description of the structure is given.
TL;DR: In this article, it has been shown that it is necessary to restrict the applied bias voltage to the very minimum necessary to produce photocurrent saturation, otherwise non-reversible degradation of quantum efficiency may occur.
Abstract: Oxide-bias measurement techniques to determine front-surface recombination losses in the silicon photodiode self-calibration technique have been investigated. With the water-drop method it has been shown necessary to restrict the applied bias voltage to the very minimum necessary to produce photocurrent saturation, otherwise non-reversible degradation of quantum efficiency may occur. The corona technique has been found to give satisfactory results only on initial application, as a drastic increase in front-region recombination loss is produced.
TL;DR: In this paper, the chemical and crystallographic characteristics of a new phase in the La-Au-Li-O system, La2Au0.5Lio 0.5O4, have been studied.
Abstract: The chemical and crystallographic characteristics of a new phase in the La-Au-Li-O system, La2Au0.5Lio0.5O4, have been studied. This compound was obtained by heating a mechanical mixture of metallic Au, La2O3 and Li2O in air at 750 °C. The X-ray powder-diffraction patterns show, in addition to the typical reflections of a K2NiF4-type structure, other lines that can only be indexed with a pseudotetragonal supercell. Li and Au ordering in the perovskite layers implies a transition from the tetragonal space group I4/mmm to the orthorhombic space group Cmmm with the unit cell a = 0.5767(1), b = 1.2472(2), c = 0.5767(1) nm. The structure was refined to an R value of 0.081.
TL;DR: In this paper, a detailed model which takes into account such optical processes as transmission, absorption and reflection in the cell has been tried out, and it has shown that a device layout planned to optimize the use of incident light is needed to achieve good performances.
TL;DR: In this article, a 12-discrete velocity model of the Boltzmann equation was used to solve the shock-wave propagation problem for a binary gas mixture, and the solution was found in an approximated analytical form expressed by an expansion in Legendre polynomials.
Abstract: In the present paper the shock-wave propagation problem for a binary gas mixture is studied by means of a 12-discrete velocity model of the Boltzmann equation. From a mathematical standpoint the problem consists in solving a set of six ordinary nonlinear differential equations with limit conditions. The solution is found in an approximated analytical form expressed by an expansion in Legendre polynomials. Finally an application is proposed and comparisons with previous theoretical and experimental results are given.
TL;DR: In this paper, the τ-functions represent the totality of solutions for hierarchies of equations in soliton theory and are identified with the coherent states of the infinite dimensional Lie algebra gl(∞).
01 Aug 1985
TL;DR: This paper presents a rapid prototyping methodology for the carrying out of control systems in which high level Petri nets provide the common framework to integrate the main phases of software development: specification, validation, performance evaluation, implementation.
Abstract: This paper presents a rapid prototyping methodology for the carrying out of control systems in which high level Petri nets provide the common framework to integrate the main phases of software development: specification, validation, performance evaluation, implementation.Petri nets are shown to be translatable into Ada program structures concerning processes and their synchronizations.
TL;DR: The interpretation of results of a chemical reaction carried out in a trickle bed reactor is not immediate when the key reactants are volatile; in fact some authors state that the overall conversion rate increases at very low liquid flow rates, i.e., when the catalyst is unevenly wetted as discussed by the authors.
Abstract: The interpretation of results of a chemical reaction carried out in a trickle bed reactor is not immediate when the key reactants are volatile; in fact some authors state that the overall conversion rate increases at very low liquid flow rates, ie when the catalyst is unevenly wetted In these conditions, the reactants may penetrate inside the catalyst pellets directly through the “dry” zones; therefore the mass transfer resistance is diminished and the conversion rate can be increased
To investigate this phenomenon tests on the catalytic oxidation of ethyl alcohol dissolved in water were performed at different operating conditions in a trickle bed reactor An interpretation of the results was tried by using two different models based on partially wetted particles This approach considers both the cases in which “dry” zones are active or not for mass transfer and mass transfer rates are affected or not by the chemical reaction
L'interpretation des resultats d'une reaction chimique qui se produit dans un reacteur “trickle bed” n'est pas immediate lorsque les principaux reactifs sont valatils; en fait, certains autenurs affirment que la vitesse globale de conversion augmente lorsque le debit de liquide est tres faible c'est-a0dire lorsque le catalyseur n'est pas mouille de maniere uniforme, Dans ces conditions, les reactifs peuvent penetrer directement dans les pastilles du catalyuseur par les zones seches; it s'ensuit que la resistance au transfert de masse decroit et que la vitesse de conversion peut augmenter
Pour etudier l'effet de ce phenomene sur l'oxydation de l'alcool ethylique dissous dans l'eau, on a fait des essaid dans un reacteur “trickle bed” dans differentes conditions operatories On a essaye d'interpreter les resultats en employant deux modeles differents bases sur des paticules partiellement mouillees ON consideter les resultats en employant les cas ou les zones “seches” sont actives pour le transfer de matiere que ceux ou elles ne le sont pas, et les cas u les vitesses de transfert de matiere sont affectees ou non par la reaction chimique
TL;DR: In this paper, the authors investigated the effect of rounding of the cutting edge on the tool life and found that the greater the radius of the edge, the longer tool life until a limit value of the radius is reached.