Showing papers by "Polytechnic University of Milan published in 1971"
TL;DR: In this article, the problem of a mathematical description of the relation between the distribution functions of impinging and emerging molecules at a solid wall is considered, and the acceptable models are set forth.
Abstract: The problem of a mathematical description of the relation between the distribution functions of impinging and emerging molecules at a solid wall is considered. Under suitable assumptions, of a rather general nature, certain properties of the acceptable models are set forth. These properties are then used to prove certain basic inequalities (including the one necessary to prove the H-theorem in presence of physical walls) as. well as constructing a specific model containing two disposable parameters. Preliminary comparisons of this model with experiment seem satisfactory.
429 citations
TL;DR: It is proved that several algorithms which perform a thinning transformation when applied to the picture in parallel do not change the connectivity properties of the picture.
Abstract: If a picture contains elongated objects of different thicknesses, one can make measurements on it which are thickness-invariant by first transforming it so that each object is thinned down to a \"medial line\" of constant thickness. Several algorithms are described which perform such a thinning transformation when applied to the picture in parallel. It is proved that these algorithms do not change the connectivity properties of the picture.
278 citations
TL;DR: In this paper, a proof of the extended Ramo's theorem is given, in order to clarify the matter, the simple case of a unidimensional problem relevant to semiconductor detectors is fully discussed.
148 citations
TL;DR: In this paper, the structural response to rates of loads and dislocations (e.g. thermal strains) is studied and the following results are obtained; 1) six extremum properties of the solutions, which reduce the incremental problem to a quadratic programming problem; two of these properties are valid without restrictions; 2.
145 citations
TL;DR: In this paper, the measuring apparatus used for experimental wind tunnel studies is described together with the test procedure and salient results, and a mechanical model is developed to explain the nature of the phenomenon.
Abstract: The measuring apparatus used for experimental wind tunnel studies is described together with the test procedure and salient results. After an analysis of the results, a mechanical model is developed to explain the nature of the phenomenon.
80 citations
TL;DR: In this paper, a monometallic mechanism of monomer complexation and addition to the growing chain for the isotactic polymerization of an α-olefin in the presence of α-, γ- or δ-TiCl3 is proposed, which avoids the back-jump of the Ti-R bond required by the COSSEE-ARLMAN mechanism.
Abstract: A monometallic mechanism of monomer complexation and addition to the growing chain for the isotactic polymerization of an α-olefin in the presence of α-, γ- or δ-TiCl3 is proposed, which avoids the back-jump of the Ti-R bond required by the COSSEE-ARLMAN mechanism. The overall activation energy for propagation involved in the latter mechanism should be higher than that allowed by the mechanism proposed here, which may be more easily reconciled with the figure found for polypropylene (∼ 5 kcal/mole). The steric requirement for a Ti atom on the side surface of a crystal to be catalytically active is that monomer complexation must be possible on both the Ti valencies pointing outside: this requires the active site to be slightly protruding above the two neighbouring layers. Each active site is intrinsically chiral; the cis-opening of the double bond is in agreement with the mechanism.
57 citations
29 citations
TL;DR: In this article, the reaction between bromolithiummethane and carbonyl compounds has been studied and the influence of the solvent on the reaction course is also discussed.
27 citations
TL;DR: The results support the hypothesis that the lowering of the polysomal shoulder and the formation of monosomes are not the effect of ribonuclease action, but the consequence of an interference with recycling of ribosomes on mRNA.
24 citations
Proceedings Article•
01 Sep 197122 citations
TL;DR: In this article, the response of bundles of several cables subjected to harmonic exciting forces is analyzed and it is shown how spacer characteristics expressed by the spacer elastic matrix will impose particular types of natural modes and how excessive spacer stiffness will cause severe bending strains to occur on the cable close to spacer clamps.
Abstract: This paper deals with the response of bundles of several cables subjected to harmonic exciting forces. It shows how the spacer characteristics expressed by the spacer elastic matrix will impose particular types of natural modes and how excessive spacer stiffness will cause severe bending strains to occur on the cable close to the spacer clamps.
TL;DR: In this article, the authors reported new stimulated inelastic scattering phenomena which occur in liquids under picosecond laser excitation, which can be interpreted as due to: (i) scattering in the far wing of the Rayleigh line; (ii) librations of molecules in molecular complexes; (iii) intermolecular vibrations in quasi-crystalline structures.
TL;DR: In this article, a simple asymptotic formula for the high-order complex eigenvalues has been obtained for the rectilinear rod model of neutrons and a complete series expansion of the outgoing density has been given.
Abstract: The rectilinear or rod model of neutron transport consists of a segment which is assumed to be capable of transporting particles. Such particles (neutrons) can move only to the right or to the left on the segment at a constant speed, and suffer scattering, capture and fission. We have shown that the time-eigenvalue spectrum of this model is made of a finite, non-void set of real eigenvalues, plus infinitely many complex eigenvalues, distributed in pairs of complex conjugates. A simple asymptotic formula for the high-order complex eigenvalues has been obtained. As an application, we have considered the following initial value problem: find the outgoing density of neutrons, at one end of the rod, at any time after the injection of a neutron pulse at the same end. A complete series expansion of the outgoing density has been given. The successive time-derivatives of this expansion show certain characteristic discontinuities which are due to the motion, from one end of the rod to the other, of discont...
01 Jan 1971
TL;DR: In this article, an elasto plastic beam and frame theory allowing for unstable bending characteristics is presented, and the notion of falling-moment plastic hinge is assumed, i.e. plastic deformations are supposed to consist of relative rotations ρ in some sections.
Abstract: Strainsoftening (unstable) flexural behavior (Fig.1a) has been observed in triangulated steel frames, reinforced concrete and composite beams and joints in precast concrete constructions; its strong implications in the overall structural response have been emphasized, and a systematic study often advocated but so far only begun (cf. [1–7]). The aim of this presentation is to supply a basis for an elasto plastic beam and frame theory allowing for unstable bending characteristics. Nonflexural deformations, interactions and geometrical second order effects are negleted. The notion of “falling-moment plastic hinge” is assumed, i.e. plastic deformations are supposed to consist of relative rotations ϑin some sections. Some prevois results [6,8,9] are specialized or extended; the new ones admit generalizations not pursued here. Important related topics, such as dynamics after the onset of instability and combined presence of physical (softening) and gemetrical unstabilizing effects, will be discussed elsewhere.
TL;DR: In this article, the spectral properties of filaments of light in C$S 2$ under high spatial resolution and with picosecond excitation were analyzed and it was shown that a steady-state pulse with constant diameter develops in the filaments.
Abstract: An analysis of the spectral properties of filaments of light in C${\mathrm{S}}_{2}$ under high spatial resolution and with picosecond excitation is presented. It is shown that a steady-state pulse with constant diameter develops in the filaments. This and other results indicate that self-trapped filaments rather than tracks of moving foci have been observed.
TL;DR: The spectra of Δ3- and Δ4-pyrrolin-2-one were analyzed and the sign of all the coupling constants determined by tickling and triple resonance experiments as discussed by the authors.
Abstract: The spectra of Δ3- and Δ4-pyrrolin-2-one were analysed and the sign of all the coupling constants determined by tickling and triple resonance experiments. A positive allylic interaction (Jxz in 2) is reported and four-bond couplings are discussed in particular. Deuterium exchange affords evidence for the tautomeric equilibrium between 1 and 2.
TL;DR: In this article, the elastic modulus of isotactic polypropylene, polyacrylic acid and polyac acrylic acid were measured vs. temperature in three different amounts (12·3, 41 and 57 percent).
TL;DR: In this article, a general theory of the elimination process (vertex elimination on a graph) is developed and connections of this theory with the secondary optimization problem of Nonserial Dynamic Programming and with the numerical solution of systems of linear equations by Gaussian elimination are pointed out.
TL;DR: A survey of various methods of solution of the linearized Boltzmann equation for rarefied gas dynamics is given in this paper, including spectral problems, analytical methods, variational and numerical techniques as well as existence and uniqueness theory.
Abstract: A survey is made of various methods of solution of the linearized Boltzmann equation for rarefied gas dynamics. Included are spectral problems, analytical methods, variational and numerical techniques as well as existence and uniqueness theory.
Journal Article•
TL;DR: In this article, the potential performance of carbon dioxide as working fluid is recognized to be similar to that of steam, which justifies thorough thermodynamic analysis of possible cycles, including simple cycles and more complex cycle arrangements.
Abstract: The potential performance of carbon dioxide as working fluid is recognized to be similar to that of steam, which justifies thorough thermodynamic analysis of possible cycles.The substantially better results achievable with CO2 with respect to other gases are due to the real gas behaviour in the vicinity of the Andrews curve. Simple cycles benefit from the reduced compression work, but their efficiency is compromised by significant losses caused by irreversible heat transfer. Their economy, however, is appreciably better than that of perfect gas cycles. More complex cycle arrangements, six of which are proposed and analyzed in detail, reduce heat transfer losses while maintaining the advantage of low compression work and raise cycle efficiency to values attained only by the best steam practice.Some of the cycles presented were conceived to give a good efficiency at moderate pressure which is of particular value in direct-cycle nuclear applications.The favourable influence on heat transfer coefficients of the combined variation with pressure of mechanical, thermal and transport properties, due to real gas effects, is illustrated. Technical aspects as turbo-machines dimensions and heat transfer surfaces needed for regeneration are also considered.Cooling water requirements are found to be not much more stringent than in steam stations.Copyright © 1969 by ASME
TL;DR: In this paper, the reaction between carbonyl/stabilized sulphonium ylides and primary α-halocarbonyl compounds (1) affords cyclopropanes (III) arising from two ylidic units and one unit from the helo compound in good yields.
TL;DR: In this article, the authors calculate the corresponding time behavior of the nonlinear refractive index of light filaments in CS 2 under picosecond excitation, and their results seem to be in rough agreement with the moving focus picture.
TL;DR: In this paper, the frequency sweep and sub-picosecond structure of mode-locked lasers are discussed and it is shown that these results can be easily explained by a previously published theory of mode locking.
TL;DR: In this paper, the authors considered a generic structure made up of elements with rigid perfectly plastic standard material and random plasticity constant, however distributed around the average value, and showed that the limit load of structures having elements of average plasticity constants is greater than or equal to the average values of the limit loads of all the feasible structures.
Abstract: A generic structure is considered, made up of elements with rigid perfectly plastic standard material and random plasticity constant, however distributed around the average value. The limit load of structures having elements of average plasticity constant is shown to be greater than or equal to the average value of the limit loads of all the feasible structures, thus generalising a theorem [1] formulated for framed structures.
01 Jan 1971
TL;DR: CADEP, a problem-oriented language for positioning geometric patterns in a two-dimensional space, is presented and shown to be a good starting point for future research.
Abstract: In this paper CADEP, a problem-oriented language for positioning geometric patterns in a two-dimensional space, is presented.
TL;DR: In this paper, a procedimento per verifica dell'isomorfismo di two grafi semplici non orientati is presented, i.e.
Abstract: Viene presentato un procedimento per la verifica dell'isomorfismo di due grafi semplici non orientati.
TL;DR: In this paper, the authors considered the possibility of transferring a time-invariant linear system from each initial state to any terminal state in a finite time and in such a way that the terminal condition is insensitive to small parameter variations.
Abstract: Discussed in this short paper is a controllability question pertaining to a class of sensitivity problems. More specifically, the possibility is considered of transferring a time-invariant linear system from each initial state to any terminal state in a finite time and in such a way that the terminal condition is insensitive to small parameter variations. Partial controllability, suitably defined, leads to a necessary and sufficient condition for the existence of the solution to such a problem. Terminal output insensitivity is also discussed and a similar result is proved when the output transformation is not affected by some parameter variations.
TL;DR: Signal insensitivity, suitably defined in terms of Frechet derivative, is proved to be equivalent to signal invariance in linear time-invariant systems as discussed by the authors, and relations between signal-insensitivity and controllability-observability properties of the system are briefly reviewed.
Abstract: Signal insensitivity, suitably defined in terms of Frechet derivative, is proved to be equivalent to signal invariance in linear time-invariant systems. Then, relations between signal-insensitivity and controllability-observability properties of the system are briefly reviewed.