Showing papers by "Polytechnic University of Milan published in 1974"

Bounds on Error in Signal Parameter Estimation

Abstract: In this correspondence, the problem of lower bounds on mean-square error in parameter estimation is considered. Lower bounds on mean-square error can be used, for instance, to bound the performances, namely the attainable output signal-to-noise ratio, of pulse modulation transmission systems, such as pulse-position modulation (PPM) or pulse-frequency modulation (PFM). The tightest lower bounds to mean-square error previously known are the Ziv-Zakai bounds; the analysis carried out in this paper, which is based on an inequality first obtained by Kotel'nikov, leads to lower bounds tighter than previously known bounds.

I Self-Focusing, Self-Trapping, and Self-Phase Modulation of Laser Beams

Abstract: Publisher Summary This chapter discusses the self-action effects of a powerful and quasi-monochromatic light wave, which propagates in a nonlinear isotropic medium. Among these self-action effects, the chapter gives emphasis on the processes of self-focusing, self-trapping, and self-phase-modulation. The experimental and theoretical material presented in the chapter offers evidence that much progress is made in this field in the past few years. The main physical effects have been predicted and observed experimentally, and a mathematical framework has been developed that makes it possible to trace, at least qualitatively, the main features of these self-action effects. The importance and impact of self-action effects in the field of quantum electronics should be stressed. The propagation of a powerful light wave in a nonlinear medium is by itself a very interesting case of nonlinear diffraction. Moreover, the study of self-action effects has led to a considerably greater understanding of the physical mechanisms of nonlinear polarization, which is of the nonlinear dynamic behavior of matter.

Dynamic non-shakedown theorem for elastic perfectly-plastic continua

Abstract: Sufficient and necessary conditions of a kinematic nature are established for alternating plasticity or incremental collapse (i.e. inadaptation or non-shakedown) of elastic perfectly-plastic media subjected to given histories of loads and thermal strains, in the presence of significant inertia and viscous damping forces. The classical second shakedown theorem, due to W.T. Koiter, is thus extended to the dynamic range.

Advances in Homolytic Substitution of Heteroaromatic Compounds

Abstract: Publisher Summary The most interesting development in the field of homolytic aromatic substitution is the realization that polar effects in several reactions play a role important based on the transiton state. The extent of these effects is determined by both the nature of the free radicals and the reacting substrates so that strong polar effects were observed not only with strongly polar radicals, but also with moderately polar radicals, such as carbon-free radicals, if the reacting substrate has a marked polar nature. Homolytic animation is of great interest in the homocyclic aromatic series with a selectivity and versatility comparable to that of electrophilic substitution. Homolytic substitutions with nucleophilic radicals are of great importance for protonated heteroaromatic bases but of lesser interest using nonprotonated heteroaromatic bases and homocyclic aromatic substrates. Among these nucleophilic radicals the use of alkyl, acyl, carbamoyl, α-oxyalkyl, and α- N -alkyl radicals has proved to be very successful. The aryl radicals were used in obtaining a deeper understanding of the homolytic arylation of heteroaromatics, but the sensitivity to polar effects is too low to give significant selectivity from the synthetic point of view.

Digital microspectrofluorometry by multichannel scaling and single photon detection

Abstract: A careful analysis of the requirements for microspectrofluorometric measurements has been made. General problems encountered in the measurement of light intensity and spectral distributions are considered, together with some special factors arising when measuring the fluorescence emitted by single cells. Criteria for evaluating microspectrofluorometric apparatus are given, and the relative merits of analog and digital methods are compared.

Liquid phase epoxidation of cyclohexene by tert-butyl hydroperoxide on a Mo-based catalyst

Abstract: A kinetic and spectroscopic study has been carried out on the epoxidation of cyclohexene by tert-butyl-hydroperoxide in the presence of MoO2(oxine)2. This catalyst gives quantitative yields of cyclohexene oxide at 80 °C, and is quite stable in t-BuO2H itself. The kinetic investigation of the reaction leads to the following rate law rate = k[t-BuO2H] [cyclohexene] [MoO2(oxine)2]. On the basis of a spectroscopic study, the presence of a catalyst—hydroperoxide reversible complex as the active species in the epoxidation is advanced. The spectroscopic study also indicates that the formation of this active species comes from the opening of a Mo—chelate bond. An oxidative degradation product of the catalyst, which was less soluble and less active than MoO2(oxine)2 and had been obtained by prolonged heating, was isolated and tested as an epoxidation catalyst. The presence of molybdenum—peroxy groups in this compound is indicated by permanganate titration and its infrared spectrum. The influence of the nature of the ligand on activity and selectivity were also investigated. Very strong ligands lead to inactive catalysts, while very labile ligands lead to catalysts with low selectivity.

Oxidation of 1-butene to maleic anhydride and carbon oxides on molybdate-based catalysts

Abstract: The catalytic activity of MnMoO4, β-FeMoO4, a-CoMoO4 and CdMoO4 in the oxidation of butenes has been investigated in a wide range of experimental conditions both in a stirred-tank gradientless reactor and in a pulse microreactor. Some of the catalysts investigated showed good selectivity to maleic anhydride; the other products were mainly CO and CO2. The oxidation runs carried out in a pulse microreactor showed that the catalytic behaviour of the catalysts investigated strongly depended on whether oxygen was or was not present in the gas phase. At a low oxygen percentage, butadiene is the main product for all the catalysts. Therefore the partial pressure of oxygen is a key to modify the selectivity. In the absence of oxygen, CdMoO4 was not active, whereas CO and CO2 were the main products. It was therefore proposed that gaseous oxygen must take a direct part in the formation of oxidised products. As the second metal (Mn(II), Fe(II), Co(II), Cd(II)) of the catalysts investigated is unable to oxidise the reduced form of molybdenum, a direct interaction of reduced molybdenum with oxygen must be hypothesised. In addition, the tetrahedral coordination of Mo (a common structural feature of all the catalysts investigated) can play an important role in giving a reactive form of adsorbed molecular oxygen which is responsible for the formation of maleic anhydride, CO and CO2. Bismuth molybdates, which present an octahedral coordination of molybdenum and a second metal (Bi(III)) that can oxidise Mo(V), show a catalytic behaviour quite different from that of the investigated catalysts.

Study of the interaction between CoMoO4 and 341-1341-1341-1-Al2O3 by Raman spectroscopy

Abstract: Raman spectroscopy has been used to study the solid state reaction of MoO3 and CoMoO4 with γ-Al2O3 and the compounds formed upon the adsorption of Co(II) an Mo (VI) on γ-Al2O3. Results show that γ-Al2O3 endows CoMoO4 and MoO3 with a high reactivity, giving Raman-inactive compounds.

Upper bounds on dynamic deformations of elastoplastic continua

Abstract: Suitable measures of plastic and of total deflections developed over a time interval by an elastic-perfectly plastic continuous structure in the presence of significant inertia and viscous forces, is shown to be bounded from above by a quantity which can be evaluated merely on the basis of a linear-elastic dynamic analysis. The results achieved are extended to elastic-workhardening bodies under the assumption of piecewiselinear yield surfaces. The practical use of the present results is checked comparatively by a simple example.

A modified geoelectrical procedure using polardipole arrays—an example of application to deep exploration

Abstract: Dipole soundings are more sensitive to noise caused by lateral and superficial inhomogeneities than Schlumberger soundings. However, the former are preferable for deep explorations in view of the relatively short cables required. The simple solution of carrying out the field work by means of dipole spreads, and to transform the dipole resistivity diagrams into Schlumberger ones by means of proper formulae would be valid only for smooth and regular curves; but often, owing to the presence of lateral noises, the dipole data show a considerable scatter. For such cases a “continuous dipole sounding” method is proposed for which all successive dipoles are contiguous, so that all parts of the profiles are covered and interpolation is not necessary. Obviously the moving dipoles have lengths proportional to their distances, so that they appear equal in the usual bilogarithmic scale. It follows that only polar-dipole arrays may be used. The transition from a dipole to the corresponding Schlumberger apparent resistivity diagram requires an integration constant which is not unequivocally determined. Therefore, the solution is not unique, but all possible derived Schlumberger diagrams have a common part. Similarly, they have some common interpretative results, which may be referred to the original dipole diagram obtained in the field. A special measurement technique is required since the dipole-dipole voltages to be determined are noticeably smaller than the Schlumberger ones. This is true also because dipole soundings are used for great depths and for long distances between the two dipoles.

Catalytic behaviour of Mo-based catalysts in liquid phase epoxidation of propylene by hydroperoxides

Abstract: The activity of different Mo-based catalysts in propylene epoxidation by t-BuO2H was investigated. MoO2(C13H10O2N)2 and MoO2 (oxine)2 gave quantitative yields in propylene oxide; other compounds were inactive and MoO2 (acac)2 was less active and selective.

An indirect method for minimal essential sets

Abstract: Further results on minimal essential sets in directed graphs are presented and an indirect algorithm based on the analysis of the complementary graph is derived.

Contribution to the knowledge of the relationship between the electrochemical and corrosion behaviour and the structure of metallic materials subjected to cold plastic deformation

Abstract: Within the framework of a systematic study of the effect of cold plastic deformation on the electrochemical behaviour (anodic and cathodic characteristics) and the corrosion behaviour (corrosion rates in the active region, evaluated by the method of Stem and Geary and by loss in weight) of metallic materials, the results relating to the case of austenitic stainless steels AISI 304, 304 L and 316, ARMCO iron and nickel deformed by tension and immersed in de-aerated sulphuric acid solution are presented and discussed with the aim of interpreting these aspects of their behaviour on the basis of the “structure” of the deformed materials. Beitrag zur Kenntnis der Beziehungen zwk schen dem elektrochemischen und dem Korrosionsverhalten sowie dem Gefuge von metallischen Werkstoffen nach plastischer Verformung Im Rahmen einer systematischen Untersuchung uber die Wirkung einer plastischen Kaltverformung auf das elektrochemische (anodische und kathodische) Verhalten und das Korrosionsverhalten (Korrosionsgeschwindigkeit im Aktivbereich, ermittelt nach Sterm und Geary durch Bestimmen des Gewichtsverlustes) von metallischen Werkstoffen werden die Ergebnisse mitgeteilt, die mit den nichtrostenden austenitischen Stahlen AISI 304, 304 L und 316, Armco-eisen und wurden durch Zugbeanspruchung verformt und dann in entlufteter Schwefelsaure gepruft. Die Ergebnisse werden erortert, mit dem Ziel, das Verhalten der Werstoffe in Abhangigkeit von ihrer Struktur darzustellen.

After‐stack multichannel filters without mixing effects *

Abstract: Several types of multichannel filters have been introduced in the past with the purpose of rejecting, in a seismic section, coherent noise having a slope different from that of the signal. These filters, generally, tend to introduce a certain amount of mixing and therefore the output trace shows increased horizontal coherence. This is due to the model on which these filters are based, since the hypothesis is posed that the reflectors are continuous. This may be dangerous since it could lead to mistaken interpretations, for example when small faults or breaks are made to disappear in the output section. Other problems that could arise in the application of multichannel filters after-stack are space-aliasing and high-pass filtering. The former occurs when coherent noise is rejected with apparent Velocity V and frequency fa=V/X, where X is the distance between traces. In this case, the signal also is distorted since it is rejected in the same frequency range. The high pass filtering effect occurs when the multichannel filter is designed to remove low coherent noise with high apparent velocity. In the paper a family of multichannel filters is presented based on a model of the seismic section such that minimum mixing effects appear. The filters are designed to give good results even in the case of low frequency and high velocity coherent noise. Some practical examples are shown.

Finite element techniques in plane limit problems

Abstract: Limit analysis of plane structures is formulated by applying a finite element linear programming technique that was previously proposed by the same author.

Validity of the three‐center, four‐electron model for stability of rare gas halides on the basis of exchange perturbation theory

Abstract: In a previous publication [1] we analyzed the stability of rare gas halides on the basis of exchange perturbation theory of the Rayleigh-Schrodinger type, using a three-center, four-electron model. In this paper, the analysis is extended to a (n + 1)-center, (n + 2)-electron model for rare gas halides of composition RXn, where R is the rare gas atom and X the halogen atom, in order to investigate the validity of the three-center, four-electron model. The compounds analyzed are XeFn, XeCln, KrFn and KrCln with n = 3 and 4, in different geometric configurations and for different states of total spin S. As before, we use exchange perturbation theory in first and second orders. The results are in good agreement with those obtained in the previous analysis and with experiments. Specifically, it is found that chlorides of rare gas atoms are not stable, that XeF4 has the square-planar configuration and that trifluorides cannot exist. The possible existence of KrF4 is discussed.

Grafted polypropylene membranes for purification of water containing sodium alkylbenzenesulfonate

Abstract: The possibility of eliminating sodium alkylbenzenesulfonate (ABS) from water by reverse osmosis was examined by operating with polypropylene membranes grafted with poly(acrylic acid). Flux through the membranes decreases with increasing thickness. For 23μ thickness and 0.5 1./hr-m2 flux, the rejection is 100% (operating pressure, 50 atm: concentration, 1 g ABS/l.). For 5μ thickness the rejection is lower and is related to ABS concentration: rejection increases with increasing concentration and reaches 60% for concentrations higher than 5 g ABS/l. (flux, 51./hr-m2; operating pressure, 50 atm). This is ascribed to the prevailing ultrafiltration as regards the reverse osmosis. ABS, at higher concentrations than the critical value, gives micelles whose dimensions might be compared to pores. The membrane behavior is influenced by previous treatments; when the membrane has been conditioned in NaCl solution, it is more selective and more permeable; the rejection reaches 90% with fluxes of 6.8 l./hr-m2 for concentrations of 5 g ABS/1. (operating pressure, 50 atm). In order to relate the properties to the structure of membranes, we have examined them by electron microscope. The ion exchange which takes place between membrane and NaCl and between membrane and ABS has also been studied.

A study of the behaviour of titanium in acidic solutions part II – Behaviour of the macrocouple titanium in aerated acidic solution‐titanium in deareated acidic solution

Abstract: The electrochemical behaviour of the macrocouple [titanium (shielded and unshielded) in deaerated acidic solution]/(titanium in aerated acidic solution) has been investigated in order to establish the reasons for the anomalous behaviour of titanium in the presence of shielded areas that has been reported in the literature and is sometimes observed in process equipment, and then to determine the conditions that favour the crevice corrosion of titanium in the same solutions On the basis of the experimental results, it has been possible to establish the criticality of stabilization of the macrocouple in 0.5 M H2SO4 at temperatures close to room temperature (in the sense that the macrocouple always tends towards conditions of complete passivity) and to interpret this behaviour on the basis of the theory of mixed potentials. Untersuchung des Verhaltens von Titan in sauren Losungen. 2. Verhalten des Makroelements (Titan in belufteter saurer Losung) (Titan in entlufteter saurer Losung) Das elektrochemische Verhalten des Makroelements (Ti – mit und ohne Abschirmung – in entlufteter saurer Losung) wurde untersucht mit dem Ziel, Anomalien im Verhalten des Titans in Gegenwart abgeschirmter Flachen zu klaren, das nach Literaturberichten gelegentlich an chemischen Apparaten auftritt. Auf der Grundlage der so erhaltenen Ergebnisse bestimmen die Verf. die Bedingungen, welche die Verf. die Bedingungen, welche die Spaltkorrosion begunstigen, wenn Titan der Einwirkung derartiger Losungen ausgesetzt wird. Aufgrund der experimentellen Ergebnisse konnten die kritischen Bedingungen bezuglich der Stabilisierung des Makroelements in 0,5 m Schwefelsaure in der Nahe der Umgebungstemperatur ermittelt werden, wo das Makroelement nach vollkommener Passivierung strebt; dieses Verhalten konnte aufgrund der Mischpotentialbildung interpretiert werden.