Showing papers by "Polytechnic University of Milan published in 1972"
TL;DR: In this article, a formal deduction of the Boltzmann equation from the Liouville equation is presented for the case of rigid spheres, and the main result is that, under the assumptions of a sufficiently smooth N-particle distribution function for a smooth limit to exist and of an initial datum which satisfies (at least for N → ∞) the chaos assumption.
Abstract: A formal deduction of the Boltzmann equation from the Liouville equation is presented for the case of rigid spheres. The main result is that, in the Boltzmann limit (number of molecules tending to infinity, diameter tending to zero, finite mean free path), the Boltzmann equation follows under the assumptions of a sufficiently smooth N-particle distribution function for a smooth limit to exist and of an initial datum which satisfies (at least for N → ∞) the chaos assumption. Possible extensions to molecules interacting with central forces and to dense gases are briefly discussed.
94 citations
TL;DR: In this article, the inelastic flexural behavior of reinforced concrete beams is described by a trilinear (or, in general, multi-inear) moment-rotation relationship.
Abstract: The inelastic flexural behaviour of reinforced concrete beams is described, as usual, by a trilinear (or, in general, multilinear) moment–rotation relationship. The analysis of beams and frames subject to given external actions is formulated as a ‘linear complementary problem’ and, in two dual ways, as a ‘quadratic programming problem’. These problems are solved by means of classical and recent algorithms in use in operations research. By the procedures pointed out it is also possible to calculate the distribution of plastic deformations along the beams. Two methods are proposed for the evaluation of the safety factor against local failure due to limited rotation capacity: the solution technique of the direct one essentially consists of an application of the simplex method for linear programming. Finally, a procedure is established for determining, allowing for the irreversibility of plastic rotations, the structural response to non-proportional loading histories which consist of individually proportional stages. Illustrative examples are given.
69 citations
TL;DR: In leaves of Chinese cabbage infected with cauliflower mosaic virus, inclusion bodies, made of amorphous material and virus particles, were found in the cytoplasm of most parenchyma cells of the mesophyll and veins, and also in epidermal cells.
56 citations
56 citations
TL;DR: The critical energy for stochasticity observed in classical systems, for physical values of the parameters in the problem, is of the order of magnitude of the quantum zero-point energy.
45 citations
TL;DR: The video-signal bandwidth reduction obtained by interframe differential transmission is hindered by rapid movements of the objects and the camera, so a simple movement compensation procedure can be obtained by dividing the image into zones and transmitting for each zone a displacement vector relating to a zone in the previous flame that is maximally correlated with it.
Abstract: The video-signal bandwidth reduction obtained by interframe differential transmission is hindered by rapid movements of the objects and the camera A simple movement compensation procedure can be obtained by dividing the image into zones and then transmitting for each zone a displacement vector relating the zone to a zone in the previous flame that is maximally correlated with it The effectiveness of such a procedure is studied on a model of the random video process, obtained as a derivation of a three-dimensional telegraph signal In particular, it is shown that for this model, the optimal procedure for finding the most correlated zone in the previous frame is the one matching the intersections of the contour lines The optimal size of the zone for which a single displacement vector has to be transmitted is also determined
40 citations
TL;DR: A family of four procedures to compute the inverse 1/X of a given binary number X normalized between 0.5 and 1 is described, which can be implemented by combinatorial networks.
Abstract: A family of four procedures to compute the inverse 1/X of a given binary number X normalized between 0.5 and 1 is described. The quotient is obtained in redundant binary form, i.e., in a base 2 code in which digits can assume any positive or negative integer value. All methods here described can be implemented by combinatorial networks; the dividers realized in this way are very fast because all carry propagations take place at the same time.
37 citations
TL;DR: In this paper, simple expressions useful for the optimal choice of the filter have been derived and compared with experimental results and some problems connected with the irradiation in filtered beams are also pointed out and discussed.
33 citations
TL;DR: In this paper, a body having ideally elastoplastic constitutive laws with associated flow laws is considered and a finite elements description is assumed, where the flow laws are described by finite elements.
Abstract: Bodies having ideally elastoplastic constitutive laws with associated flow laws are considered. Finite elements description is assumed.
31 citations
TL;DR: In this article, experimental results for the transition energies and for the radiative lifetimes of M and R centers in alkali halides are given for a simple hydrogen-like model.
Abstract: New experimental results are given for the transition energies and for the radiative lifetimes of M and R centers in alkali halides. The experimental values of the absorption energies and of the radiative lifetime are then compared to theoretical values, calculated on the basis of a simple hydrogen-like model.
Neue experimentelle Ergebnisse uber die Ubergangsenergien und die Strahlungslebensdauern von M- und R- Zentren in Alkalihalogeniden werden mitgeteilt. Die experimentellen Werte fur die Absorptionsenergien und fur die Strahlungslebensdauern werden mit theoretischen Werten verglichen, die unter der Annahme eines einfachen wasserstoffahnlichen Models berechnet wurden.
29 citations
TL;DR: In this paper, a flat plate, placed in a uniform free molecular flow, is investigated by means of a non trivial gas-surface interaction model proposed by the authors Drag and lift coefficients and lift to drag ratio are calculated for a large number of values of some meaningful parameters, such as the speed ratio, the gas-wall temperature ratio, and two coefficients contained in the reemission model.
Abstract: Aerodynamic forces acting on a flat plate, placed in a uniform free molecular flow, are investigated by means of a non trivial gas-surface interaction model proposed by the authors Drag and lift coefficients and lift to drag ratio are calculated for a large number of values of some meaningful parameters, such as the speed ratio, the gas-wall temperature ratio, the attack angle and two coefficients contained in the reemission model Simple analytical expressions, different from the classical ones, are obtained for very high or very low speed ratio values
TL;DR: In this paper, the existence and uniqueness theorems for the bounded and almost periodic solution of some non-linear equations and inequalities of evolution were studied, and some existence et.
Abstract: We show some existence et uniqueness theorems for the bounded and almost periodic solution of some non linear equations and inequalities of evolution.
TL;DR: In this article, two unfolding methods, SAND II and SPECTRA, are compared with nine threshold detectors irradiated in the center of the core of the L54 reactor, and the relative merits of the two methods are presented and discussed.
TL;DR: The reaction of α-chlorooximes or the isomeric nitrosochlorides with keto-stabilized dimethylsulphonium or triphenylarsonium ylides affords trans-5-acyl-Δ2-isoxazolines (VIIa-m) in good yields as mentioned in this paper.
TL;DR: In this article, the authors interpreted the observed ferromagnetism in solids of some rare-earth compounds (EuO, EuS, GdN) at very low temperatures on the basis of a mechanism involving indirect exchange between f-electrons on different cations via their outer closed shells.
TL;DR: In this article, a comprehensive analysis of geometrically non-linear structural problems by the finite element method is presented, based on a variational principle stating the incremental equilibrium through the stationarity of a functional that could be defined as the incremental total potential energy.
Abstract: The paper shows a comprehensive analysis of geometrically non linear structural problems by the finite element method. The theoretical approach is based on a variational principle stating the incremental equilibrium through the stationarity of a functional that could be defined as the incremental total potential energy. The analysis is carried out in two distinct phases: first a prediction of the behaviour of the structure subjected to an increment of load then a correction by means of Newton Raphson method of the results obtained in the previous incremental step. The approach makes it possible to determine the complete load deflection curve either in the prebuckling region or in the postbuckling one and to find out the critical load taking into account the deflection prior to buckling (non linearized buckling analysis).
TL;DR: In this article, structural properties of sensitivity systems, i.e., systems generating the state sensitivity coefficients of a linear time-invariant system (basic system), are presented.
Abstract: Structural properties of “sensitivity systems”, i.e. systems generating the state sensitivity coefficients of a linear time-invariant system (“basic system”) are presented. A formula for the eigenvalues sensitivity coefficients is first derived and the multiplicity of eigenvalues, in the minimal polynomial of the Sensitivity System is discussed. Then, a necessary and sufficient condition for the cyclicity of the Sensitivity System is given and uncontrollability of the Sensitivity System is proved whenever the number of parameters is sufficiently large. All the results enable conclusions about structural properties of the Sensitivity System in terms of the structure of the basic system.
TL;DR: An optimal (suboptimal) periodic control for a single-input single-output time-invariant linear system is shown to be easily obtainable via a describing function approach.
Abstract: This paper deals with a periodic optimization problem. Specifically, an optimal (suboptimal) periodic control for a single-input single-output time-invariant linear system is shown to be easily obtainable via a describing function approach. This also allows pointing out some interesting features of the problem and the significant role played by the concept of resonance frequency.
TL;DR: In this paper, the existence of resonant excitons in the lowest band of free electron-hole pairs is investigated on the basis of a $T$-matrix approach for both CdTe and ZnTe.
Abstract: The existence of resonant excitons in the lowest band of free electron-hole pairs is investigated on the basis of a $T$-matrix approach for both CdTe and ZnTe. The numerical calculations are performed following Hermanson's method. It is shown that such resonances exist and are related to interacting electron-hole pairs lying in a sizable volume of $k$ space along the $\ensuremath{\Lambda}$ line. It turns out that the line shape of the resonant absorption structure is quite sensitive to the energy-band behavior in the above-mentioned region of $k$ space. A comparison is made between the energy band, as deduced from the present analysis, and band-structure calculations, as available in the literature.
TL;DR: In this paper, a baseline restorer has been developed in which both the restorer time constant and the positive and negative voltage thresholds can be varied independently, thus reaching higher resolving power in nuclear spectroscopy.
TL;DR: In this article, it was shown that superexchange interactions between unpaired electron spins of two paramagnetic cations in a solid via a diamagnetic anion (X) already occur in first order of exchange perturbation theory, i.e., without considering excited (charge-transfer) states of the system MXM.
TL;DR: In this article, the authors observed new stimulated lines which appear in the wing of the Rayleigh line in CS 2 under picosecond excitation, which are due to intermolecular scattering.
TL;DR: The results of lifetime measurements of the relaxed excited triplet state of the M centre, 3M*, in KCl are given in this article, and the conclusion may be drawn that a conversion 3M* 1M* occurs with high probability.
Abstract: The results of lifetime measurements of the relaxed excited triplet state of the M centre, 3M*, in KCl are given. The emission has the same decay time constant when exciting in the 1M and in the 3M bands: τ = τ(1M*). The conclusion may be drawn that a conversion 3M* 1M* occurs with high probability.
Die Ergebnisse von Lebensdauermessungen des angeregten Triplettzustandes 3M* in KCl werden mitgeteilt. Die Emission hat bei Anregung in der 1M-Bande und 3M-Bande die gleiche Zeitkonstante: τ = τ(1M*). Man kann daraus schliesen, das eine Konversion 3M* 1M* mit hoher Wahrscheinlichkeit stattfindet.
TL;DR: In this article, the authors characterized a particular but relevant aspect of the dynamic behavior of binary distillation systems by means of an "asymmetric function" defined as the ratio of the settling times of the leaving and back transients.
TL;DR: Stimulated low-frequency Raman lines have been observed in liquid benzene under picosecond laser excitation as discussed by the authors, and their frequencies agree with those observed in spontaneous scattering in crystalline benzene at low temperatures.
TL;DR: In this article, a numerical solution for a fluid motion in a circular pipe orifice is compared with experimental results, and good agreement between the piezometric heads and head losses computed and those obtained in experiments is found.
Abstract: A numerical solution for a fluid motion in a circular pipe orifice is compared with experimental results. Knowledge of the velocity field allows us to find the pressure field. There is good agreement between the piezometric heads and head losses computed and those obtained in experiments.
TL;DR: In this article, a necessary and sufficient condition for state terminal insensitivity in time-invariant linear systems is given for the particular case of a single input and a single parameter.
Abstract: A necessary and sufficient condition for state terminal insensitivity in time-invariant linear systems is given for the particular case of a single input and a single parameter. It leads to a sufficient condition for the construction of an algebraic state feedback which allows the system to be terminal insensitive.