Showing papers by "Polytechnic University of Turin published in 1983"

Nonlinear Equalization of Digital Satellite Channels

Abstract: Conventional techniques attempting to compensate for the influence of linear and nonlinear distortion in digital satellite channels include optimization of channel filtering. With conventional linear filtering it has been experienced that there is still room for considerable improvement, so that it appears reasonable to investigate some forms of nonlinear filtering in an attempt to cope with those distortions. In this paper a nonlinear equalizer structure is proposed, and its performance is analyzed. It is shown, by some examples Of application to a 4-phase PSK satellite channel, that it can prove quite effective in terms of a tradeoff between performance improvement and hardware complexity.

Multichannel Local Area Network Protocols

Abstract: Multiple-access protocols suitable for packet switching local area networks that use several parallel broadcast channels are presented and analyzed by evaluating their throughput and delay characteristics. The local network architecture is first described, then the network performances are evaluated considering a variety of multiple-access schemes that are derived from CSMA and CSMA-CD protocols, by extending the original single channel schemes to a multiple channel system. It is shown that significant performance improvements are achievable with the multiple channel option. Further advantages obtained with the proposed network architecture are a higher reliability and fault tolerance, and a modular network design that allows a gradual system growth following users' demands.

A class of generalised stochastic petri nets for the performance evaluation of multiprocessor systems

Abstract: Graph models have been proposed by many authors as a useful tool for the analysis of peculiar features of computer systems such as concurrency, synchronization, communication, and cooperation among subsystems. Much of the work in this field is related to the original ideas developed by C. A. Petri. These graph models are today generally known as Petri Nets (PNs).

Parameters of coplanar waveguides with lower ground plane

Abstract: A new analytical expression for the impedance and the permittivity of coplanar waveguides with lower ground plane is presented. Although approximate in principle, this expression shows very good agreement with the upper or lower bounds of the parameters, computed via a spectral-domain variational approach.

Modeling Bus Contention and Memory Interference in a Multiprocessor System

Abstract: Stochastic models of contention for shared resources in an experimental multiprocessor prototype are presented and are validated with simulation and measurement results. Three modeling techniques are used (stochastic Petri nets, Markov chains, and queueing networks) that represent the system operations as Markovian stochastic processes. Each technique is best suited to a specific stage of the analysis. An integrated use of these techniques represents a very powerful tool for the performance analysis of multiprocessor systems and provides ways of investigating several extensions of the prototype architecture. Simulation results and measurements performed on the hardware prototype validate the analysis and show that the accuracy of the analytical results is excellent.

Dispersion relation for propagation of light in cholesteric liquid crystals

Abstract: A general theory of the light propagation in periodic structures characterized by a uniform rotation of the dielectric tensor about a given axis is presented. Starting from a fundamental approach of Dreher and Meier, which is mostly numerical, an analytical solution of the characteristic equation has been found which can be used to calculate the wave vectors as a function of $\ensuremath{\omega}$ and of the incidence angle ${\ensuremath{\theta}}_{i}$. The electromagnetic wave is described as a superposition of elementary modes having the form of Bloch waves. Each elementary mode is represented by a sum of plane waves elliptically polarized, whose wave vectors are the roots of the characteristic equation. The analysis of the solutions of such an equation allows us to draw a more complete map of the stability and instability regions for light propagation in helical structures than the ones currently available in the literature. The coexistence of two distinct modes, with different polarization states, determines the shape of the stability map. Each mode presents a series of Bragg instabilities. Between the two Bragg instabilities of the same order a further instability exists which is common to both modes and does not satisfy the Bragg conditions. All instability bands, with the exception of only one of the first order, vanish at normal incidence. This occurs for any value of the optical anisotropy and is a peculiarity of perfectly ordered helical structures. The bandwidth increases with ${\ensuremath{\theta}}_{i}$, and overlapping may occur. Typical plots of dispersion curves and attenuation constants are reported. Finally, we compute the intensity and the polarization state of the light reflected from a thin film, in order to clarify the controversial point about the structure\char22{}doublet or triplet\char22{}of the higher-order reflection bands.

Biomechanical design of the total ankle prosthesis.

Abstract: The load bearing joints of the human body and particularly the ankle are often seriously damaged because of different pathological events. During the last 10 years a lot of total ankle prostheses have been studied and implanted, in consequence of the inadequate results obtained by arthrodesis (i.e. the fusion of the joint).The aim of this paper is to analyze mechanical features (functional, kinematic, and strength) of the ankle joint in order to provide optimized design criteria of an arthroprosthesis substituting the disabled joint.

investigations of the La-Mn-O system

Abstract: Solid state equilibrium relations were studied in the region of the La-Mn-O system bounded by LaMnO3, MnO and La2O3. In the temperature range 900–1380°C the defective perovskite LaMnO3−λ coexists directly in equilibrium with lanthanum oxide and manganous oxide. Above 1380°C an intermediate phase with the formula La2MnO4.15 appears. This phase has a structure of the K2NiF4 type with cation vacancies. The number of anion vacancies in LaMnO3−λ increases with increasing temperature; at the limiting composition the value of λ changes from 0.015 at 900°C to 0.095 at 1450°C. The behaviour of the oxygen pressure of the LaMnO3−λ-La2O3-MnO equilibrium system agrees with this variation in the composition of the LaMnO3−λ phase.

Computer recognition of plosive sounds using contextual information

Abstract: The design of the plosive consonant recognition component of a speech understanding system is described. The recognition rules used incorporate information on coarticulatory and multiple cue effects. The rule combination and scoring system is a fuzzy model of the human speech perception and information integration mechanism. These rules can be also used in classical stochastic models or dynamic programming approaches to automatic speech recognition.

On the relationship between global and local controllability

Abstract: Given a pair(X0,D), whereX0 is a vector field andD is a family of vector fields on a manifoldM, we can define a system affine in the control, i.e., the new family of all the vector fields of the formX0 +uX, whereX ∈D andu is a real parameter. Such a system will be called globally controllable if each state is reachable from each other, whenever unbounded values foru are allowed. It is proved that a system affine in the control is globally controllable if and only if in any set of a suitable partition ofM there exist points locally controllable with bounded values foru. Further, it is proved that, under more restrictive assumptions, global controllability implies the existence of points locally controllable at a fixed time with bounded values foru. In the case of simply connected manifolds, a full equivalence among all the forms of controllability considered here is obtained.

Short term load forecasting in electric power systems: A comparison of ARMA models and extended wiener filtering

Abstract: On-line prediction of electric load in the buses of the EHV grid of a power generation and transmission system is basic information required by on-line procedures for centralized advanced dispatching of power generation. This paper presents two alternative approaches to on-line short term forecasting of the residual component of the load obtained after the removal of the base load from a time series of total load. The first approach involves the use of stochastic ARMA models with time-varying coefficients. The second consists in the use of an extension of Wiener filtering due to Zadeh and Ragazzini. Real data representing a load process measured in an area of Northern Italy and simulated data reproducing a non-stationary process with known characteristics constitute the basis of a numerical comparison allowing one to determine under which conditions each method is more appropriate.

Non-conservative forces, Lagrangians and quantisation

Abstract: Two examples of the motion of an object through a medium against friction are discussed, showing that the equations of motion can be derived from a lagrangian, which is no longer the difference between the kinetic and potential energy of the system. The transposition of the same problems into the quantum world is also performed using the canonical formalism and the related difficulties are discussed.

Optical Properties of Cholesteric Liquid Crystals at Oblique Incidence

Abstract: The optical properties of a periodic structure characterized by a uniform rotation of the dielectric tensor about a given axis are theoretically analyzed. The electromagnetic wave is described as a superposition of elementary modes having the form of Bloch waves. Each elementary mode is represented by a sum of plane waves elliptically polarized, whose wavevectors are the solutions of a characteristic equation. This equation, presented in a preceding paper, is furtherly analyzed, in order to obtain the wave vectors in terms of a power series of a small parameter δ, representing the anisotropy of the dielectric tensor. The coefficients of the series up to terms containing δ6 are explicitly given, and the corresponding truncation errors computed. The spectral composition and the polarization states of the Bloch waves are also analyzed and discussed for different values of the incidence angle in the frequency range containing the lower reflection bands. In particular it is shown that in the regions b...

A review of fault models for lsi/vlsi devices

Abstract: The review paper deals with problems concerning fault modelling for LSI/VLSI devices. Both random and regular logic are considered, and different fault classes are discussed for each, including stuck-at, bridging, functional and time-dependent faults. Specific fault models are then considered for microprocessors, RAMs and PLAs

Alternating electromagnetic field computation in laminated cores

Abstract: A finite element method is developed to compute alternating electromagnetic fields in laminated cores. The method is applied to a simplified model problem in order to evaluate power losses in mitered overlap joints. The influence of eddy currents on the magnetic field distribution in the neighborhood of the mitered joints is discussed. The power losses ate evaluated for cores with different overlap lengths.

Oxidation of ethyl alcohol in trickle-bed reactors: analysis of the conversion rate

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, i.e. 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.

Production of ethanol with Saccharomyces cerevisiae in a continuous reactor. Note I: kinetics of immobilized yeast

Abstract: Continuous production of ethanol by fermentation with immobilized yeasts gives a better yield and capacity and can be better controlled than conventional processes with batch reactors and a suspended biomass. This paper (the first of three) examines the operative conditions for immobilizing Saccharomyces Cerevisiae on beech wood cubes. After preliminary evaluation of the non-influence of mass transfer phenomena and the extent of alcoholic inhibition, an experimental investigation of the kinetics for a metabolic reaction in a continuous recycle reactor was carried out. The kinetic equation was found to be a Michaelis-Menten type with uncompetitive inhibition by substrate, and linear inhibition by product.

Thermal expansion and vacancy formation volume

Abstract: When the total Hamiltonian of a perfect lattice is expanded in terms of the displacements of the ions from the average positions, the effect of linear and cubic terms is shown to be equivalent to a system of Eshelby's expansion centres present in the lattice and responsible for thermal dilation. The pressure exerted by these expansion centres is added to the pressure deriving from the part of the Hamiltonian which is independent of the ion dynamical variables: the equation of state of the solid is simply obtained by equating the sum of the above two terms to the external pressure. In this paper the theory is confined to perfect crystals, in order to provide a general basis of interest for the next parts of the work, devoted to the problem of vacancy formation volume.

Thick coatings by thermo-chemical deposition in spouted beds

Abstract: Spouted beds are an established way of coating nuclear fuel microspheres with pyrolytic carbon or silicon carbide by high-temperature thermochemical reactions. In recent years, similar coatings have aroused particular interest as bio-compatible materials. This paper describes the differences between these two applications, and the changes that must be made to the coating process and furnace to control both the overall surface of the bed material and its increase in volume. It is shown that a satisfactory control can be achieved by continuous feeding of small particles, followed by the continuous withdrawal of variously coated particles. Experiments on two columns with internal diameter of 0.08 and 0.14 m, respectively, showed that segregation phenomena may occur, depending on the flow dynamics, and that the way in which a steady state is brought about will depend on the position of the discharge pipe in the bed. Les lits “spoutes” constituent un moyen courant pour recouvrir des microspheres de combustible nucleaire de carbone pyrolytique ou de carbure de silicum, en employant des reactions thermochimiques a temperature elevee. Durant les dernieres annees, les recouvrements du type precite ont suscite un interět particulier en raison de leur biocompatibilite.

A Quasi-Monolithic Approach to Microwave Ga-As Integrated Circuits

Abstract: A new class of microwave integrated circuits is presented, having definite advantages over both the hybrid and the fully monolithic solutions. A theoretical analysis correlating the S parameters of a flip-chip mounted FET device with those of a fully monolithic device is then reported, which permits to develop a straightforward and very efficient testing technique for monolithic ICs. Practical examples of the new circuits and of the testing technique are finally described.