Showing papers by "Polytechnic University of Milan published in 1989"

What you always wanted to know about Datalog (and never dared to ask)

Abstract: Datalog, a database query language based on the logic programming paradigm, is described. The syntax and semantics of Datalog and its use for querying a relational database are presented. Optimization methods for achieving efficient evaluations of Datalog queries are classified, and the most relevant methods are presented. Various improvements of Datalog currently under study are discussed, and what is still needed in order to extend Datalog's applicability to the solution of real-life problems is indicated. >

Double epitaxy improves single-photon avalanche diode performance

Abstract: A new single-proton avalanche diode (SPAD) with double-epitaxial silicon structure is presented. The device has a time response with short diffusion tail (270 ps time-constant), high resolution (45 ps FWHM, full-width at half maximum of the peak) and low noise, i.e. low-dark-count rate.

A failure-inducement model of research and development expenditure

Abstract: Empirical evidence for the Schumpeterian suggestion of a positive relationship between profitability and innovative effort is slim. In fact, the opposite is often suggested. An alternative ‘failure-inducement’ hypothesis, argues that firms make innovative efforts when performance falls below a minimum threshold, resulting in a negative relationship between profitability and R&D expenditures. Data on R&D expenditures in Italian industry in the early 1980s- a period of severe economic crisis - show that both hypotheses are relevant for firms whose profits are well above or well below average, respectively.

Risk capital financing and the separation of ownership and control in business groups

Abstract: This paper analyses business groups, composed of legally independent firms connected through a network of cross-shareholdings. A model which allows to calculate the value of the firms of a group and the integrated ownership shares held by an outside stockholder, is described. A taxonomy for the collection of risk capital generalizing the one which applies for a single firm is proposed; the connection between the process of raising risk capital and the separation of ownership from control in business groups is demonstrated and given a formal mathematical description. Empirical evidence relating to the amount of risk capital collected by Italian business groups in the '80s and to the extent of the divorce between ownership and control is also provided.

Conjugated Diene Polymerization

Abstract: The polymerization of conjugated dialkenes with transition metal catalysts began in 1954, soon after the first results on the polymerization of propylene had been obtained. The first stereoregular dialkene polymer obtained was a polyisoprene with a structure similar to that of natural rubber.1 An isoprene polymer with a structure identical to that of natural gutta percha was obtained soon after,2 along with stereoregular polymers of butadiene and pentadiene.2–4

An algebra for structured office documents

Abstract: We describe a data model for structured office information objects, which we generically call “documents,” and a practically useful algebraic language for the retrieval and manipulation of such objects. Documents are viewed as hierarchical structures; their layout (presentation) aspect is to be treated separately. The syntax and semantics of the language are defined precisely in terms of the formal model, an extended relational algebra.The proposed approach has several new features, some of which are particularly useful for the management of office information. The data model is based on nested sequences of tuples rather than nested relations. Therefore, sorting and sequence operations and the explicit handling of duplicates can be described by the model. Furthermore, this is the first model based on a many-sorted instead of a one-sorted algebra, which means that atomic data values as well as nested structures are objects of the algebra. As a consequence, arithmetic operations, aggregate functions, and so forth can be treated inside the model and need not be introduced as query language extensions to the model. Many-sorted algebra also allows arbitrary algebra expressions (with Boolean result) to be admitted as selection or join conditions and the results of arbitrary expressions to be embedded into tuples. In contrast to other formal models, this algebra can be used directly as a rich query language for office documents with precisely defined semantics.

Dynamic Interaction of Railway Systems with Large Bridges

Abstract: SUMMARY In this paper have been described - railway runability problems on large span bridges; - the state-of-art of the methodologies adopted for a systematic analysis of the dynamic behaviour of railway vehicles running on a deformable structure, with particular reference to large span suspension bridges; - some meaningful experimental and analytical results, related to railway runability of large span bridges.

24 h sequential spectral analysis of arterial blood pressure and pulse interval in free-moving subjects

Abstract: A procedure for the 24-h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects is discussed. It includes: (1) sampling of a 24-h intra-arterial BP recording and extraction of the systolic and diastolic BP and PI from each heart beat followed by storage into separate series: (2) high-pass filtering and a splitting of each series into consecutive records of 256 values; and (3) estimation of power spectral density via fast Fourier transform (FFT) in each stationary record and computation of the power of each target oscillation. Using this procedure data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique was analyzed. The results revealed different patterns for the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. A second spectral estimate based on autoregressive modeling was performed. The results validate the FFT approach. >

Synthetic aperture radar:a new application for wave equation techniques1

Abstract: The techniques of downward continuation and imaging invented for seismic waves can be applied to other types of waves. We show how they can be applied to electromagnetic surveys conducted with Synthetic Aperture Radar (SAR). The algorithms used closely follow those used for seismic waves. Differences are induced by alternate wavelengths, wave velocities, distances between sources and reflectors, etc. We analyse in detail a survey carried out using a satellite; difficulties arise from because the orbit of the satellite cannot be approximated by a simple straight line if the spatial resolution of the survey is high. We determine appropriate techniques for the correction of the distortion induced by the latter and we delimit the resolution of the observed data, as seen from a satellite. Finally we show examples of the application of the technique of seismic migration to satellite data that were irradiated to Earth during the short but productive life of Seasat.

Fast and efficient gradient projection algorithm for dynamic generation dispatching

Abstract: A gradient projection algorithm is presented for the dynamic dispatch of thermal generations, based upon an active set strategy and exploiting second order information in determining the descent directions. The algorithm is adapted to the model of the dynamic dispatch problem which consists of the minimisation of a nonlinear objective function subject to quadratic equality constraints and linear inequality constraints. The envisaged algorithm can be applied to the dispatching of thermal units during the steep load pick-up and drop-down periods over short time intervals, and can also be used in the day-before scheduling after the unit commitment has been performed. Efficiency is demonstrated by tests on large-scale networks representative of the Italian EHV system. The limited CPU time requirements also suggest a possible on-line application in determining the constrained participation factors to be used in the Automatic Generation Control function.

Measuring the economic effectiveness of flexible automation: a new approach

Abstract: SUMMARY This paper outlines a method for the evaluation of flexible manufacturing systems (FMS), which considers both economics and strategic aspects. The firm strategic position, in fact, is turned into a few performance indicators, each expressed numerically. The manufacturing system must perform within given values of these indicators, which act as constraints. Then connections between the cost of obtaining strategic performances and the flexibility of the manufacturing system are defined; this allows one to express net cash flows, used to compute profitability, as a function of the strategic position of the firm. The simplifying assumptions used in implementing the method on a VAX/VMS are specified. A case study, concerning the application of the model to a leading Italian firm in the automotive industry, is briefly discussed.

Steel-to-concrete Bond After Concrete Splitting ; Test results

Abstract: The definite trend towards the use of large-diameter rebars and the introduction of high-strength steels (f y=500 to 600 MPa) make it necessary to study the effects of longitudinal splitting on the steel-to-concrete bond. The study of splitting effects requires firstly basic tests to be performed in order to gather experimental information on bond and confinement stresses acting at the bar-to-concrete interface. For this purpose, three series of tests were recently carried out at the Politecnico di Milano. The results make it possible to ascertain a few basic properties of the bond after concrete splitting, and to formulate empirical constitutive laws regarding the stresses and the displacements (bar slip and opening of the splitting crack). All specimens consisted of a short deformed bar embedded in a concrete block, which had a preformed splitting crack in the plane passing through the bar axis: twelve specimens (Tests A and C) were fitted up with a round deformed bar having crescent-shaped lugs (Db=18 mm); seven specimens (Tests B) were fitted up with a specially machined deformed bar having a rectangular cross-section and straigth, lugs, so that concrete deterioration close to the bar could be investigated at the surface of the specimen, by means of the moire technique. The tests were carried out at constant slip rate, up to very large slip values ( $${{\delta _{t_{max} } } \mathord{\left/ {\vphantom {{\delta _{t_{max} } } {D_b = 0.25 to 0.30}}} \right. \kern- ulldelimiterspace} {D_b = 0.25 to 0.30}}$$ ); both the ascending and the descending branches of the stress-slip curves were measured, for four different values of the opening of the splitting crack. The agreement among the results of the three series is generally satisfactory and often very good: consequently, constitutive laws regarding the four main variables (crack opening and bar slip, shear and confinement stresses) can be worked out, as will be shown in a companion paper on constitutive relationships and on concrete deterioration at the bar-to-concrete interface.

The Impact of Just‐in‐time on Production System Performance: An Analytical Framework

Abstract: Part of a research programme being undertaken in Italy on the applicability of the just‐in‐time (JIT) approach. The programme includes both the development of methodological concepts to evaluate JIT applicability and an extensive survey of the value of JIT implementation as seen by Italian industry. Two levels of performances are identified: o First, the various performances at system level (critical manufacturing tasks) where the dimensions and measurement of productivity, service, quality and flexibility are defined; o Second, “operating conditions” being the variables describing the characteristics of single production factors and their interconnection (such as efficiencies, capability, process flexibility and lead times) The set of JIT techniques in the area of product, process, organisation, planning and control and supply are classified, the ways the techniques impact on operating conditions and, through them, on performance at production system level are analysed. A paradigm of JIT approach results...

Spiral silicon drift detectors

Abstract: An advanced large-area silicon photodiode and X-ray detector, called the spiral drift detector, was designed, produced, and tested. The detector has a very small capacitance of about 0.1 pF and a leakage current under 1 nA at room temperature. All electrons generated at the silicon-silicon oxide interface are collected on a guard rather than contributing to the detector leakage current. The decrease of the leakage current reduces the parallel noise of the detector. This decrease and the very small capacitance of the detector anode with a capacitively matched preamplifier may improve the energy resolution of spiral drift detectors operating at room temperature to about 50 electrons RMS. This resolution is in the range attainable at present only by cooled semiconductor detectors. >

On the rotational components of seismic motion

Abstract: The surface motion during an earthquake is different from point to point depending on the propagation properties of the seismic waves. Rocking and torsion are thus present in the free field, in proportion to the spatial derivatives of the surface motion with respect to a given direction. These derivatives are inversely proportional to the apparent wave velocity in that direction, so the smaller the wave apparent velocity, the more important its contribution to the rotations. In this respect, a marked contribution to surface rotations from surface waves is expected. A mathematical model is presented, based on a detailed representation of soil impedance, an approximate identification of surface waves and a deconvolution of body waves in P and SV contributions. Through this model the surface motion obtained from the records of strong-motion accelerometers can be expressed as a superposition of plane waves of known wavelengths. Rocking response spectra are computed and results are compared with previously published spectra. A sensitivity analysis is performed on some parameters of the model.

Kinetics of multimonomer emulsion polymerization. The pseudo-homopolymerization approach

Abstract: By generalizing the Smith–Ewart theory, a system of polymer particle population balances is developed for describing the kinetics of emulsion polymerization processes involving any number of monomer species. Each population is characterized by the number of active radicals of each type present inside each particle, and described through a size distribution function. An approximation procedure is proposed for reducing the original system to that typical of homopolymerization processes, thus characterizing each population-only through the overall number of radicals, without any significant loss of accuracy. The reliability of such “pseudo-homopolymerization approach” is tested by comparison with polymer composition vs. monomer conversion experimental data for the ternary system acrylonitrile–styrene–methyl methacrylate.

Convex analysis and global optimization of joint actuator location and control problems

Abstract: It is shown that the optimal value of the continuous-time linear-quadratic problem regarded as a function of the system model and index parameters exhibits properties (convexity, concavity, and monoticity) specially suitable for optimization purposes. Based on this fact, a procedure for the global solution determination of eventually nonconvex problems, involving the above-mentioned function, is proposed. Such problems embody some known designs, such as filtering under noise uncertainty or precision constraints and optimal actuator/sensor location. The last problem is deeply analyzed, and two practical applications, namely satellite attitude control and large flexible system control, are included. >

Reconfiguration of VLSI arrays by covering

Abstract: In VLSI arrays, redundant cells are added as spares. The proposed approach is applicable as an offline technique at either production time and/or run time. Reconfiguration is implemented by index mapping using a sequence of two operators. A reconfiguration algorithm which utilizes index mapping is proposed. This algorithm uses a new approach to the assignment problem. It is shown that reconfiguration of fault-free cells is equivalent to a covering of faulty cells by spare cells. It is also established that in a two-dimensional array the optimal spare assignment is given by a maximum matching. This translates to a maximum flow. It is shown that a variation of the matching preserves the optimality of the assignment, while reducing the time complexity of the reconfiguration algorithm Characterization theorems for index mapping and simulation results to substantiate the practicality of the approach are presented. >

Some uses of Green's theorem in solving the Navier-Stokes equations

Abstract: This paper gives a review of methods where Green's theorem may be employed in solving numerically the Navier–Stokes equations for incompressible fluid motion. They are based on the concept of using the theorem to transform local boundary conditions given on the boundary of a closed region in the solution domain into global, or integral, conditions taken over it. Two formulations of the Navier–Stokes equations are considered: that in terms of the streamfunction and vorticity for two-dimensional motion and that in terms of the primitive variables of the velocity components and the pressure. In the first formulation overspecification of conditions for the streamfunction is utilized to obtain conditions of integral type for the vorticity and in the second formulation integral conditions for the pressure are found. Some illustrations of the principle of the method are given in one space dimension, including some derived from two-dimensional flows using the series truncation method. In particular, an illustration is given of the calculation of surface vorticity for two-dimensional flow normal to a flat plate. An account is also given of the implementation of these methods for general two-dimensional flows in both of the mentioned formulations and a numerical illustration is given.

On the convergence of solutions of the enskog equation to solutions of the boltzmann equation

Abstract: For the Enskog equation with a symmetrized kernel in a box an existence theorem is proved for initial data with finite mass, energy and entropy. Then by letting the diameter of the molecules go to zero we prove the weak convergence of solutions of the Enskog equation to solutions of the Boltzmann equation.

Absorbed solution theory models for multicomponent adsorption equilibria

Abstract: A new approach is developed for applying ideal and real adsorbed solution theory models to the description of multicomponent adsorption equilibria at fixed pressure. This allows ignoring single-component behavior in the Henry's law region, P → O, but introduces new parameters that must be evaluated from binary equilibrium data. Comparisons with various sets of experimental data show that the new approach gives results as good as the classical one, but without requiring knowledge of the single component behavior in the Henry's law region; more over, it removes the sensitivity to the type of model adopted in fitting single-component equilibrium data.

On serial-input multipliers for two's complement numbers

Abstract: The author shows that a multiplier already proposed by T. Rhyne and N.R. Strader (see ibid., vol.C-35, p.896-901 (1986)) for unsigned numbers can be used for two's complement numbers as well, provided only that the content of the input registers is held constant, after the introduction of the operand's sign bits, for a number of clock periods equal to the operand's length. The result is derived by the properties of sign-extended two's complement numbers. The known multiplier includes a linear array of (5, 3) parallel counters and a set of three static registers for the internal carriers. It is shown that a logically equivalent multiplier can be built using two linear arrays of full adders and two carry registers. In a faster circuit, an additional carry register is required. >

On the reaction of catenapoly(diphenoxy‐λ5‐phosphazene) with sulfur trioxide

Abstract: The reaction of catenapoly(diphenoxy-λ5-phosphazene) (1) with SO3 in 1,2-dichloroethane at 15°C, applying a mole ratio m = [SO3]/[-–P(OC6H5)2N—] ≤ 1,0 and subsequent quenching with water, leads to catenapoly(diphenoxy-λ5-phosphazene-co-diphenoxy-λ5-phosphazenium hydrogen sulfate) (2) containing up to 57% protonated nitrogen. At m > 1,0 C-sulfonation occurs, resulting in the formation of water-soluble catenapoly[diphenoxy-λ5-phosphazene-co-diphenoxy-λ5-phosphazenium hydrogen sulfate-co-bis(sulfophenoxy)-λ5-phosphazenium hydrogen sulfate] (3). The latter can be converted into catenapoly[diphenoxy-λ5-phosphazene-co-bis(sulfophenoxy)-λ5-phosphazene] (4b) by treatment with alkali and subsequent percolating through a cation exchange resin. Analytical results show that C-sulfonation is preceded by the formation of a polymer-SO3 donor-acceptor complex.