Showing papers by "Polytechnic University of Turin published in 1988"
TL;DR: In this paper, the authors measured the loss per cycle (sinusoidal flux waveform) versus magnetizing frequency f/sub m/(0 > 0) for a single cycle.
Abstract: Measurements are reported of the loss per cycle (sinusoidal flux waveform) versus magnetizing frequency f/sub m/(0 >
1,587 citations
TL;DR: It is concluded that a surface myoelectric signal detected on the skin above a leg muscle and having a peak-to-peak amplitude of up to 16.6% of a signal detected above a neighboring muscle may be due to cross-talk rather than to activation of the muscle below the electrode.
328 citations
TL;DR: In this article, two different techniques for the calculation of optical modes of Ti: LiNbO/sub 3/ channel waveguides and finite element method are presented, and the effective indices and field distributions obtained by both techniques are compared for wavelengths of 0.6 and 1.2 mu m, for both quasi-TE and -TM polarization, considering Y-cut and Z-cut crystal orientation and both isotropic and anisotropic Ti/sup 4+/ diffusion.
Abstract: Two different techniques for the calculation of optical modes of Ti:LiNbO/sub 3/ channel waveguides are presented. The first one is an almost analytical technique based on the effective-refractive-index method. The second one is based on the well-known finite-element method. Both approaches use a rather realistic waveguide model considering crystal anisotropy, wavelength dispersion of the refractive index distributions, and also the nonlinear dependence of the ordinary refractive index on the Ti/sup 4+/ concentration. Effective indices and field distributions obtained by both techniques are compared for wavelengths of 0.6 and 1.2 mu m, for both quasi-TE and -TM polarization, considering Y-cut and Z-cut crystal orientation and both isotropic and anisotropic Ti/sup 4+/ diffusion. >
171 citations
TL;DR: On etudie des operateurs de convolution singuliers sur des groupes de Lie nilpotents generaux, and plus specifiquement des operators don les noyaux ont pour supports des varietes de faible dimension and peuvent aussi contenir des facteurs polynomiaux exponentiels oscillatoires as discussed by the authors.
141 citations
TL;DR: A discrete system with memory, inserted between the source and the modulator, is designed with the aim of providing an equivalent channel with a distortionless linear part and no nonlinearities up to a given order.
Abstract: The compensation of channel nonlinearities in digital radio communication systems is considered. A discrete system with memory, inserted between the source and the modulator, is designed with the aim of providing an equivalent channel with a distortionless linear part and no nonlinearities up to a given order. This design is based on a Volterra series model of the channel and on the theory of pth-order inverse systems. Since the compensator design is based on a mathematical model of the channel, the problem of model identification is considered. A modeling technique is described that uses computer simulation and orthogonal Volterra series. Several examples show the performance of this class of compensators. >
128 citations
TL;DR: Different approaches to hardware verification are first examined, and formal verification and automated synthesis are compared to show how they cooperate in producing zero-defect designs.
Abstract: Formal verification techniques are analyzed, focusing on two key points: suitable representation systems and mechanizable proofs. Different approaches to hardware verification are first examined, and formal verification and automated synthesis are compared to show how they cooperate in producing zero-defect designs. The different techniques are evaluated. Cross fertilization with software verification techniques is discussed. >
106 citations
TL;DR: In this paper, the equations of motion for the study of the fiexural dynamic behaviour of a general rotating system, based on the finite element method and on the use of complex co-ordinates, are described.
101 citations
TL;DR: In this paper, a degenerate parametric oscillator is considered and it is shown that the cavity can display bistable or self-pulsing behavior when the product of the two detuning parameters is positive (negative).
Abstract: We consider a degenerate parametric oscillator and show that, when the cavity is detuned both with respect to the pump and with respect to its subharmonic, the system can display bistable or self-pulsing behaviour. Bistability (self-pulsing) requires that the product of the two detuning parameters is positive (negative). In the self-pulsing regime, the system exhibits period doubling and chaos. We generalize our steady-state analysis to the case in which the cavity has a poor finesse for the pump mode.
99 citations
TL;DR: A phase belonging to the ternary system La2O3-Li2O-Me2O5 (Me=Nb, Ta) was prepared and characterized both chemically and structurally as mentioned in this paper.
93 citations
TL;DR: In this paper, the authors deal with global stabilizability at the origin of a homogeneous vector field by means of homogeneous feedbacks of the same degree and give a sufficient condition, which turns out to be also necessary in the linear case.
76 citations
TL;DR: The theoretical aspects of the encoding process are investigated, resulting in a precise definition of linear codes together with theorems that clarify how they can be obtained, and several new results in terms of error event and bit error probabilities are presented.
Abstract: The theoretical aspects of the encoding process are investigated, resulting in a precise definition of linear codes together with theorems that clarify how they can be obtained. A particular subset of linear codes, called superlinear codes, for which the performance analysis is highly simplified is identified. The most relevant performance measures for the analysis of this class of codes are discussed. The minimum Euclidean distance and the event and bit error probabilities are found analytically using the uniform error property (when applicable) or variations on it. This yields accurate upper and lower bounds to the error rate at the price of reasonable computational complexity. The theory is then applied to the search for 'good' codes and to their performance evaluation. The cases of 16- and 32-PSK codes, which are good candidates for use in digital satellite transmission, are considered. Several new results in terms of error event and bit error probabilities are presented, showing considerable gains in terms of SNR with respect to the uncoded case. >
TL;DR: The main claim is that transverse effects can be responsible for low threshold instabilities and is more plausible to explain the observed pulsations in many lasers than what is available in terms of the traditional plane-wave theories.
Abstract: We generalize the traditional Maxwell-Bloch theory of a ring laser and analyze the dynamical role of transverse effects. With the help of a suitable extension of the uniform-field limit we perform an essentially analytical study of the steady-state and linear-stability properties of a ring resonator containing a homogeneously broadened active medium. In this context we incorporate the effects of curved reflecting surfaces, the possible lack of transverse uniformity of the pump, and the detailed structure of the cavity modes. In the uniform-field limit we prove that the laser steady state is of the single-mode variety and that lack of stability can be induced in this field configuration even only a few percent above the threshold for laser action. Thus our main claim is that transverse effects can be responsible for low threshold instabilities. This explanation is more plausible to explain the observed pulsations in many lasers than what is available in terms of the traditional plane-wave theories.
TL;DR: On considere l'existence d'une integrale premiere lisse and l'existing mesure invariante equivalente a la mesure de Lebesgue for des systemes differentiels dans le plan as discussed by the authors.
TL;DR: This paper studies the following problem: Under what circumstances are maximum likelihood estimators optimal in the worst case?
01 Oct 1988
TL;DR: PRETOB is an object-oriented Computer Aided Software Engineering system based on high level Petri nets called PROT nets that addresses discrete event dynamic systems, such as process control systems and communication protocols.
Abstract: This paper presents PROTOB, an object-oriented Computer Aided Software Engineering system based on high level Petri nets called PROT nets. It consists of several tools supporting specification, modelling and prototyping activities within the framework of the operational software life cycle paradigm. As its major application area it addresses discrete event dynamic systems, such as process control systems and communication protocols.
TL;DR: Some extensions of the optimality results obtained in previous work on algorithms used in the field of system identification in the light of information-based complexity are presented.
TL;DR: In this paper, a class of multidimensional signals based on generalized group alphabets is introduced and its basic properties are derived, and two coding schemes are considered: G. Ungerboeck's scheme (1982) for combination with convolutional codes, and V.V. Ginzburg's (1984) scheme for combination of block codes.
Abstract: A class of multidimensional signals, based on generalized group alphabets, is introduced and its basic properties are derived. The combination of generalized group alphabets and coding is also examined: two coding schemes are considered-G. Ungerboeck's scheme (1982) for combination with convolutional codes, and V.V. Ginzburg's (1984) scheme for combination with block codes. It is concluded that the performance of these schemes makes them attractive for transmission over band-limited digital channels. >
TL;DR: In this article, sufficient conditions for the stability of families of characteristic polynomials of discrete-time systems are given. But these conditions cannot be extended in genera to obtain necessary conditions for families of continuous time systems.
Abstract: The theorem of Kharitonov on the Hurwitz property of interval families of polynomials cannot be extended, in genera, to obtain sufficient conditions for the stability of families of characteristic polynomials of discrete-time systems. Necessary and sufficient conditions for this stability problem are given. Such conditions naturally give rise to a computationally efficient stability test which requires the solution of a one-parameter optimization problem and which can be considered as a counterpart to the Kharitonov test for continuous-time systems. At the same time, the method used to derive the stability conditions provides a procedure for solving another stability robustness problem, i.e. the estimation of the largest domain of stability with a rectangular box shape around given nominal values of the polynomial coefficients. >
TL;DR: In this paper, the use of two-and three-dimensional parametric curved subdomains (elements) in the numerical solution of electromagnetic problems formulated in terms of volume integro-differential equations is considered, and a technique to evaluate the static and dynamic moment integrals on these domains is presented.
Abstract: The use of two- and three-dimensional parametric curved subdomains (elements) in the numerical solution of electromagnetic problems formulated in terms of volume integro-differential equations is considered, and a technique to evaluate the static and dynamic moment integrals on these domains is presented. In the source region, the evaluation of the moment integrals is performed by separating the integrands into a singular and a regular part. The regular integrals are numerically evaluated in a parameter space where the integration domain assumes a very simple form. The singular integrals are shown to be always reducible to nonsingular boundary integrals by use of a nonlinear transformation for the integration variables and an analytic integration on one variable. The reduced singular integrals are then evaluated numerically in a second parameter space, where the boundary of the original curved element is expressed in a simple form. Two simple two-dimensional scattering problems in the frequency domains are considered to compare the results obtained using quadratic isoparametric curved elements against the results given by linear expansion functions on triangular elements. The use of curved parametric elements permit a better geometrical description of the problem, a reduced number of unknowns, shorter computation times, and more accurate results with respect to the usually employed linear elements. >
TL;DR: In this article, the asymptotic expression for the radome Green's function that allows the characterization of radome by itself, independently of any specific antenna, is identified.
Abstract: Performance is evaluated by a method based on the reciprocity theorem. The asymptotic expression for the radome Green's function that allows the characterization of the radome by itself, independently of any specific antenna, is identified. The concept of the modified aperture distribution, which radiating in free space produces the same pattern as the radome-covered antenna, is introduced. It can be used for the design of the radome stratification and for the optimization of the antenna location. On the basis of the formulation of a computer code has been developed that analyzes the degradation induced by radomes with surfaces and dielectric stratifications that can be defined numerically. Theoretical predictions and experimental results are compared. >
TL;DR: In this article, the authors examined the barium rich region of the system BaOCuOO at temperatures between 800 and 900°C in presence of gaseous atmospheres with different partial pressures of oxygen (i.e. 1; 0.21; 1.10 −6 atm), and two new compounds corresponding to the formulae Ba 2 CuOO 3 and Ba 3 CuO 4 have been identified.
TL;DR: In this article, the authors discuss aspects of laser dynamics that are connected with transverse effects and show that a laser capable of operating simultaneously in more than one transverse mode can develop temporal instabilities and pulsations at gain values close to the lasing threshold and within experimental reach, and also approach steady state configurations in which several transverse resonances develop synchronized oscillation.
TL;DR: In this paper, the effects of impurities on the processes of hydrogen evolution and oxygen reduction on the negative plates of lead-acid batteries have been tested by measuring the gas pressure in sealed vessels containing cycled, wet, negative plates.
TL;DR: In this paper, a conical beam element for rotor dynamic analysis is proposed, with circular or annular cross-section, based on the Timoshenko beam theory, and the procedure for the computation of stiffness, mass, gyroscopic damping matrices and of the unbalance vector is fully described.
TL;DR: In this paper, the relation between the spectral theory for linear operators and the complex theory of interpolation for families of Banach spaces is studied, and an invertibility theorem is proven, and size estimates for the spectra of operators on the interpolation spaces are given.
11 Apr 1988
TL;DR: A field oriented control scheme is proposed, not requiring any shaft transducer, and its theoretical limits are outlined, confirming the practical feasibility for a wide field of applications.
Abstract: A field oriented control scheme is proposed, not requiring any shaft transducer. The flux-estimation problems in such conditions are considered. A suitable method is proposed and its theoretical limits are outlined. A prototype system has been implemented, on this basis, and the experimental results are given, confirming the practical feasibility for a wide field of applications. >
01 Mar 1988
TL;DR: In this paper, a general formalism was developed to describe the dynamical behavior of an ensemble of two-level systems in a Fabry-Perot cavity, and the main result is a set of space and time-dependent, integro-differential equations for the slowly varying radiation and atomic variables, which derive through a precise analysis of the slowly-varying amplitude approximation in the presence of counter-propagating fields.
Abstract: We develop a general formalism to describe the dynamical behavior of an ensemble of two-level systems in a Fabry-Perot cavity. Our main result is a set of space and time-dependent, integro-differential equations for the slowly varying radiation and atomic variables, which we derive through a precise analysis of the slowly-varying amplitude approximation in the presence of counter-propagating fields. With the help of new and properly chosen variables we recast these equations in a form that makes their boundary conditions formally identical to those of an ideal Fabry-Perot resonator, and introduce in a natural way a modal structure even for systems with arbitrary mirror reflectivity. We derive simplified forms of these equations in the uniform field limit and within the more general single-frequency approximation. Finally, we extend our formulation to include driven systems such as optically bistable devices and the laser with an injected signal.
TL;DR: In this paper, the reliability factor of the BaO-Y 2 O m3 -CkO-O system was investigated. And the results showed that the reliability of this system depends on both the observed and calcklated intensities of the CkO 6 octahedra.
TL;DR: In this article, surface layers having elevated hardness were produced by ion nitriding of titanium and α-β alloys of Ti-6wt.%Al-4wt.%.
Abstract: Surface layers having elevated hardness were produced by ion nitriding of titanium and α-β alloys of Ti-6wt.%Al-4wt.%V, Ti-4wt.%Al-2wt.%Sn4wt.%Mo and Ti-4wt.%Al-2wt.%Mn. The treatment was conducted at temperatures between 1073 and 1273 K for times of 4–32 h, using gaseous mixtures of nitrogen and hydrogen containing 20–80 vol.% nitrogen. X-ray diffraction, optical microscopy and microhardness were used to characterize the hardened surfaces. In most of the samples, this surface was composed of the phases δ (TiN type), ϵ (Ti 2 N type) and α (solid solution of nitrogen in titanium); in other cases only the δ and α phases were present. The operating parameters which influence the composition of the layer were identified and the particular crystalline texture of the ϵ phase is discussed.
TL;DR: Soit H 1 le groupe de Heisenberg a 3 dimensions constitue des matrices triangulaires inferieures g=(x,y,z) On etudie des operateurs maximaux sur H 1 associes a la famille a 2 parametres des dilatations Dδ, e(x, y,z)=(Sx, ey, δ∈Z) and en determinant leurs proprietes de L p -limitation
Abstract: Soit H 1 le groupe de Heisenberg a 3 dimensions constitue des matrices triangulaires inferieures g=(x,y,z) On etudie des operateurs maximaux sur H 1 associes a la famille a 2 parametres des dilatations Dδ , e(x,y,z)=(Sx, ey, δ∈Z) et en determinant leurs proprietes de L p -limitation