Showing papers by "Polytechnic University of Milan published in 1968"
TL;DR: The problem of obtaining the skeleton of a digitized figure is reduced to an optimal policy problem and a hierarchy of methods of defining the skeleton is proposed; in the more complicated ones, thekeleton is relatively invariant under rotation.
Abstract: The problem of obtaining the skeleton of a digitized figure is reduced to an optimal policy problem. A hierarchy of methods of defining the skeleton is proposed; in the more complicated ones, the skeleton is relatively invariant under rotation. Two algorithms for computing the skeleton are defined, and the corresponding computer programs are compared. A criterion is proposed for determining the most significant skeleton points.
282 citations
TL;DR: In this paper, the problem of the deviation from the linear elastic, of the response of a nonlinear discrete structure to given loads, is formulated for various classes of cases, and all the problems considered are shown to be reducible to a single mathematical model: the quadratic program with sign constraints only.
Abstract: The search for the deviation from the linear elastic, of the response of a nonlinear discrete structure to given loads, is formulated for various classes of cases. All the problems considered are shown to be reducible to a single mathematical model: the quadratic program with sign constraints only. The Kubn-Tucker theorem for quadratic programming directly supplies the appropriate extremum principles, for which some physical interpretations are proposed. Other results of quadratic programming theory prove to be useful in the discussion of the structural problems considered.
126 citations
TL;DR: In this article, it was shown that the analysis problem in terms of finite (not incremental) stresses, is amenable to the Kuhn-Tucker conditions of a quadratic program.
Abstract: For elastic perfectly plastic discretized structures acted upon by given loads and dislocations, it is shown, under holonomic constitutive laws or no local unloading hypothesis, that the formulation of the analysis problem in terms of finite (not incremental) stresses, is amenable to the Kuhn-Tucker conditions of a quadratic program. Then it is readily derived a generalized form of the principle of Haar and Karman, together with an extremum theorem for displacements and plastic strains, which is the dual of the preceding one. As special cases of this theorems known variational principles follow, which thus turn out to be related in pairs by the duality notion as understood in programming theory. Also the statical and kinematical theorems of limit analysis are proved by means of the unitary conceptual framework supplied by quadratic programming.
105 citations
100 citations
TL;DR: In this article, a hermitian dynamical matrix in terms of Cartesian displacement coordinates is derived starting from a harmonic force constant matrix expressed using the Wilson's internal displacement coordinates.
88 citations
TL;DR: In this article, from fresh bulbs of many varieties of daffodils, two compounds have been extracted, which show no basic properties since the nitrogen is amidic in character.
77 citations
TL;DR: In this article, a mechanism of formation of catalytic complexes and a polymerization mechanism is also proposed that can justify both the type of stereoregularity of the polymer and the variation of steric regularity on varying the polymerization conditions.
Abstract: Polymerizations of propylene to syndiotactic polymer have been carried out in the presence of the catalyst system VCl4-Al(C2H5)2Cl-anisole. The data obtained have been related to those previously reported concerning the catalyst system, VCl4-Al(C2H5)2Cl. It was thus possible to propose a mechanism of formation of the catalytic complexes and to put forward or confirm some hypotheses on their constitution.
A polymerization mechanism is also proposed that can justify both the type of stereoregularity of the polymer and the variation of steric regularity on varying the polymerization conditions.
Propylen wurde mit dem Katalysatorsystem VCL4-Al(C2H5)2Cl-Anisol zu syndiotaktischem Polypropylen polymerisiert. Die Ergebnisse werden mit fruheren Versuehen verglichen, bei denen das binare System VCl4-Al(C2H5)2Cl verwendet wurde. Aus den erhaltenen Daten konnten ein Bildungsmechanismus und die mutmasliche Struktur des katalytisch wirksamen Komplexes abgeleitet werden. Ferner wird ein Polymerisationsmechanismus mus vorgeschlagen, der sowohl den Typ der Stereoregularitat als auch deren Anderung mit wechselnden Polymerisationsbedingungen erkart.
66 citations
TL;DR: By the study of differently deuterated homopolymers and copolymers of propylene, it was demonstrated that the double bond addition is cis in the syndiotactic polymerization of polyethylene as mentioned in this paper.
Abstract: By the study of differently deuterated homopolymers and copolymers of propylene it is demonstrated that the double bond addition is cis in the syndiotactic polymerization of propylene. Furthermore it is confirmed that the addition to the double bond is cis also in the isotactic polymerization.
Durch das Studium von unterschiedlich deuterierten Homopolymeren und Copolymeren des Propylens wird nachgewiesen, das bei der. syndiotaktischen Polymerisation des Propylens cis-Addition erfolgt; weiter wird bestatigt, das auch bei der isotaktischen Polymerisation cis-Addition eintritt.
57 citations
49 citations
TL;DR: In this article, two new diterpenes, sideridiol C 20 H 32 O 2 and siderol C 22 H 34 O 3, were extracted from the corols of Sideritis sicula Ucria (Fam. Labiatae).
47 citations
TL;DR: In this paper, the equilibrium melting temperature of isotactic polypropylene and of a number of its mixtures with hexadecane, α-chloronaphthalene, decalin and naphthalenes is determined by extrapolation of several experimental melting temperature data obtained by rapid melting of each sample isothermally crystallized at different temperatures.
TL;DR: In this paper, the authors show that the copolymers show a tendency to an alternating sequence distribution if prepared by syndiospecific catalysts, whereas they show a random distribution when prepared by non-stereospecific or by isospecial catalysts.
Abstract: Binary copolymerizations of ethylene, propylene and butene-1 were studied. The copolymers show a tendency to an alternating sequence distribution if prepared by syndiospecific catalysts, whereas they show a random distribution when prepared by non-stereospecific or by isospecific catalysts.
These facts indicate that syndiotacticity is due to steric interactions between monomer and last unit of the growing chain end and that isotacticity is due to steric interactions between monomer and counter-ion. The propylene-butene-1 copolymerization shows that the side-chain rotations of the last added unit are hindered in the presence of syndiospecific catalysts.
Binare Copolymerisationen von Athylen, Propylen und Buten-1 wurden durchgefuhrt. Werden bei der Polymerisation syndiospezifische Katalysatoren angewendet, dann ist die Sequenzverteilung im Copolymeren nicht mehr statistisch, sondern mehr alternierend, wahrend statistische Copolymere mit nicht-stereospezifischen und isospezifischen Katalysatoren entstanden.
Diese Befunde weisen darauf hin, das Syndiotaktizitat auf sterischer Wechselwirkung zwischen dem Monomeren und der letzten Einheit der wachsenden Kette beruht; Isotaktizitat hingegen entsteht durch sterische Wechselwirkung zwischen Monomerem und Gegen-Ion. Die Propylen-Buten-Copolymerisationen zeigten, das die Seitenkettenbeweglichkeit der letzten eingebauten Einheit in Gegenwart syndiospezifischer Katalysatoren herabgesetzt ist.
TL;DR: In this article, a simple method is described which provides a system of coordinates which factor the same matrices to the maximum extent allowed by the symmetry of the molecule, which may be obtained equally well for molecules or polymers.
TL;DR: In this paper, the laser-Raman spectra of hexagonal polyoxymethylene, deuteropolyoxymylene (deutero paraformaldehyde) and orthorhombic polyoxide (OPE) have been analyzed.
TL;DR: In this article, an ideal time variant system has been synthetized for the analysis of a sequence of random pulses and its performance has been evaluated under the hypothesis of gaussian noise and taking as criterion for the evaluation of amplitude resolution the rms deviation.
TL;DR: In this article, the collapse theorems for materials which do not exhibit normality of the strain rate vector to the yield surface in the superposed stress and strain rate spaces are considered.
Abstract: The paper discusses the collapse theorems for materials which do not exhibit normality of the strain rate vector to the yield surface in the superposed stress and strain rate spaces. The consequences of the lack of normality on the designs for minimum weight are considered.
TL;DR: The concentration of active macroradicals in the grafting reaction is measured with the of a slinplified kinetic scheme as discussed by the authors, and the influence of the concentration of both monomer and initiator, and of the type of solvent used on the percentage of grafting was studied.
Abstract: The polymerization of methyl acrylate in an atactic polypropylene solution in the presence of radical initiators (benzoylperoxide, tert-butylperpivalte, α.α′-azoisobutyronitrile, Iauroylperoxide) yields a mixture of grafted polymethylacrylate/polypropylene copolymer and a methyl acrylate homopolymer.
The crude polymers are fractionated and the influence of the concentration of both monomer and initiator, and of the type ofsolvent used on the percentage of grafting was studied.
The concentration of active macroradicals in the grafting reaction is measured with the of a slinplified kinetic scheme.
Die Polymerisation von Acrylaauremethylester in enter Losun von ataktischem Poly- propylen mit radikalbildenden Initiatoren (Benzoylperoxid, Perpivalinaure-tert-butylester, Azoispbuttersauredinitril, Lauroylperoxid) ergibt eine Mischung von Acrylsauremethyl- ester/Polypropylen-Pfropcopolymeren und von homopolymerem Acryauremethylester.
Die rohen Polymeren wurden fraktioniert, und der Elnflus der beigen Monomoren, des Initiators und der Vri des Losungsmittels auf das Ausmas der Pfrop- fungsreaktion wurde untersuelit.
Die konzentration der aktiven Makroradikale bei der Pfropfungsreation wird an Hand cines vereinfachten kinetischeti Schemas adgeschatzt.
TL;DR: The crystal structure of 1, 2 isotactic poly-4-methyl pentadiene crystallized in modification II has been studied by X-ray diffraction spectra of stretched fibres as discussed by the authors.
TL;DR: In this article, it was shown that for a class of linear time invariant open-loop systems, it is not possible to achieve the terminal sensitivity of terminal conditions when the number of plant-parameters is not smaller than the control variables.
Abstract: This correspondence deals with terminal sensitivity of linear dynamical systems. Specifically, it is shown here that, for a class of linear time invariant open-loop systems, it is not possible to achieve the insensitivity of terminal conditions when the number of plant-parameters is not smaller than the number of control variables.
TL;DR: In this paper, the problem of achieving the highest resolution in the amplitude measurement of pulses randomly spaced in time is considered, taking into account both noise and pile-up fluctuations due to slow signal tails.
TL;DR: In this paper, the effect of vanishing viscous damping on the stability of non-conservative linear elastic systems is studied, with special reference to systems that lose stability statically through the emergence of new equilibrium configurations close to the principal one, i.e. by divergence.
Abstract: A study of the effect of vanishing viscous damping on the stability of nonconservative linear elastic systems, with special reference to systems that lose stability statically through the emergence of new equilibrium configurations close to the principal one, i. e. by divergence. It is shown that in this case slight damping presents a wide range of effects on the stability of the system.
TL;DR: In this article, the limit analysis of three-dimensional rigid-perfectly plastic continua with associated flow-law (standard materials) is discussed and some approximate procedures which follow from Mura-Lee variational method and from upper and lower bound theorems are presented.
Abstract: The paper discusses the limit-analysis of three-dimensional rigid-perfectly plastic continua with associated flow-law (standard materials) It presents some approximate procedures which follow from Mura-Lee variational method and from upper and lower bound theorems
TL;DR: In this article, an elastoplastic beam-column model with one degree of freedom subjected statically to an on-center or off-center axial compressive force is considered, resulting from a transverse periodic acting force in resonance with the structure in the elastic range.
Abstract: An elastoplastic beam-column model with one degree of freedom subjected statically to an on-center or off-center axial compressive force is considered. Its dynamic behavior in the elastoplastic range, resulting from a transverse periodic acting force in resonance with the structure in the elastic range, is examined. The principal features are highlighted by a phase plane study.
TL;DR: In this article, a study of the response of a continuum to given loads is carried out assuming a piecewise linear yield locus, normality, noninteracting yield planes and linear strain bardening, and minimum properties for the plastic strain rates in the incremental case and for plastic strains satisfying holonomic and nonholonomic stress-strain laws.
Abstract: A study of the response of a continuum to given loads is carried out assuming a piecewise linear yield locus, normality, non-interacting yield planes and linear strain bardening. Minimum properties are determined for the plastic strain rates in the incremental case and for plastic strains satisfying holonomic and non-holonomic stress-strain laws, thus extending to continua the minimum properties determined elsewhere for discrete structural linear hardening systems.
TL;DR: Coriolis coupling coefficients for degenerate vibrations, cartesian and internal mean amplitudes for trimethylamine-H 9 and D 9 have been calculated from a valence force field, discussed previously, and derived from an overlay calculation on aliphatic amines as discussed by the authors.
TL;DR: The planar isomer of perhydrotriphenylene (PHTP) is a new host molecule for the inclusion polymerization of butadiene as discussed by the authors, which is obtained by γ-irradiation of the PHTP-monomer adduct.
Abstract: The planar isomer of perhydrotriphenylene (PHTP) is a new host molecule for the inclusion polymerization of butadiene. By γ-irradiation of the PHTP-monomer adduct an inclusion compound between PHTP and the polymer is obtained, as revealed by its melting point. The recovered polymer has a highly regular trans-1.4-structure. The effect of different variables (dose, dose-rate, PHTP/monomer ratio) has also been studied.
TL;DR: In this paper, a discrete Eulerian model is described through which a set of centered finite difference equations for spherical media can be derived on the basis of clear physical principles, namely, the explicit conservation of mass, momentum, and energy.
TL;DR: In this article, a passive Q-switched ruby laser utilizing a special rooftop prism cavity was used to obtain a single transverse and longitudinal mode self-locked beam with a 40 cm long resonator.
Abstract: Results are reported on a passive Q -switched ruby laser utilizing a special rooftop prism cavity. With a 40 cm long resonator, a single transverse and longitudinal mode has been obtained. With a 3 meter long resonator, a single transverse mode self-locked beam has been obtained.