Sulla interazione ionosferica delle onde elettromagnetiche

Sunto. Si stabilisce il legame non lineare, di tipo ereditario, fra densità di corrente e campo elettrico (quest’ultimo variabile col tempo con legge qualsiasi), che, nella ionosfera, è alla base di vari fenomeni d’interazione fra onde elettromagnetiche interessanti le radio-comunicazioni (cross-modulation, self-modulation, ecc.). In tal modo si colmano certe lacune della teoria ? ereditaria ? dei detti fenomeni e si ricollegano quantitativamente i risultati di questa con le acquisizioni della teoria ? elementare ?. Lavoro eseguito nell’ambito dell’attività dei Gruppi di ricerca matematica del Consiglio Nazionale delle Ricerche.     

Su un metodo di approssimazione nella teoria dell’interazione fra onde elettromagnetiche

Riassunto Si dimostra la convergenza uniforme delle approssimazioni successive ottenute risolvendo un problema concernente l'interazione delle onde elettromagnetiche in un plasma ionosferico.

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Résumé On démontre la convergence uniforme des approximations successives obtenues en résolvant un problème concernant l'interaction des ondes électromagnétiques dans un plasma ionosphérique.

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Lavoro eseguito nell'ambito dell'attività dei Gruppi di ricerca matematica del Consiglio Nazionale delle Ricerche.     

Sur alcuni problemi dell'elettrodinamica stazionaria dei superconduttori ciclici

Riassunto Si studia il problema matematico dell'esistenza delle correnti persistenti in un superconduttore molteplicemente connesso.

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Résumé On étudie le problème mathématique de l'existence des courants persistants dans un supra-conducteur multiplement connexe.

     

Sulla influenza della polarizzazione delle radio-onde nei fenomeni di interazione ionosferica

Riassunto Si studia l'influenza della polarizzazione delle radio-onde su alcuni fenomeni non lineari nella ionosfera tramite una nuova e più completa relazione funzionale fra i vettori densità di corrente e campo elettrico. Tale studio riguarda la comparsa di onde di banda laterale e la loro dipendenza dalle direzioni di polarizzazione delle onde interagenti.

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Summary The influence of radio wave polarization on some nonlinear phenomena in the inosphere is studied through a new and more complete functional relation between current density and electric field vectors. This study is concerned with the occurrence of ?sideband? waves and their dependence on the polarization directions of interacting waves.

     

Su una questione di dinamica non lineare

Riassunto Si analizza il comportamento asintotico dei moti di ampiezza qualsiasi di un pendolo con smorzamento viscoso funzione del tempo.

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Résumé On analyse le comportement asymptotique des mouvements d'amplitude quelconque d'un pendule avec amortissement visqueux fonction du temps.

     

Effetti di risonanza nell'interazione fra radio-onde in un plasma magnetoattivo

Riassunto Si studiano alcuni effetti di risonanza che si presentano nell'interazione non lineare fra una radio-onda ?potente? di pulsazione ω₁ e una ?più debole? di pulsazione ω₂ in un magnetoplasma (ionosfera). Più precisamente, si mostra che, oltre ai ben noti fenomeni di cross e self-modulation, in condizioni particolari, si ha un notevole aumento dell'intensità delle onde di banda laterale associate a quelle interagenti e delle armoniche di pulsazione 3ω₁ dell'onda ?potente?.

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Summary Some resonance effects are studied occurring in nonlinear interaction of a ?strong? radio wave of cyclic frequency ω₁ with another ?weaker? radio wave of cyclic frequency ω₂ in magnetoplasma (ionosphere). More precisely, it is shown that, besides the well-known phenomena of cross and self-modulation, in particular conditions, there is a large increase in the strength of the ?sideband? waves associated with the interacting waves and of ?strong? wave harmonics of cyclic frequency 3ω₁.

     

A variable kinematic Ritz formulation for vibration study of quadrilateral plates with arbitrary thickness

A new variable kinematic Ritz method applied to free vibration analysis of arbitrary quadrilateral thin and thick isotropic plates is presented. Carrera's unified formulation and the versatile pb-2 Ritz method are properly combined to build a powerful yet simple modeling and solution framework. The proposed technique allows to generate arbitrarily accurate Ritz solutions from a large variety of refined two-dimensional plate theories by expanding so-called Ritz fundamental nuclei of the plate mass and stiffness matrices. Theoretical development of the present methodology is described in detail. Convergence and accuracy of the method are examined through several examples on thin, moderately thick, and very thick plates of rectangular, skew, trapezoidal and general quadrilateral shapes, with an arbitrary combination of clamped, free and simply supported edges. Present results are compared with existing three-dimensional solutions from open literature. Maximum and average differences of various higher-order plate theories and three-dimensional results are also presented with the aim of providing useful guidelines on the choice of appropriate plate theory to get a desired accuracy on frequency parameters.     

Catalyzed Beckmann rearrangement of cyclohexanone oxime in heterogeneous liquid/solid system: Part 2: Influence of acid catalysts and organic promoters

The influence of some transition metal oxide promoters in the catalyzed Beckmann rearrangement of cyclohexanone oxime was studied by preparing several heterogeneous H₂SO₄/M/SiO₂ catalysts using SiO₂ as support and H₂SO₄ as acid source. A definite effect of each metal has been observed and the best results have been obtained with Cr-, Zr- and Zn-oxides based promoter, which have shown an improved selectivity towards -caprolactam formation if compared to the H₂SO₄/SiO₂ catalytic system. Moreover, the influence of some organic promoters on the reaction pathway was investigated. Acetic and trifluoroacetic anhydrides gave the best results, even if only the latter allowed the rearrangement even without solid acid catalysts. The transacetylation of the cyclohexanone oxime by using the acetyl caprolactam, which is the product of rearrangement of the acetyl cyclohexanone oxime, was studied for developing a step wise catalytic cycle. Finally, some preliminary results on a homogeneous organic catalyzed process are reported.     

Free vibration analysis of ribbed plates by a combined analytical–numerical method

An easy to code and computationally efficient analytical–numerical method for quick prediction of the modal characteristics of rectangular ribbed plates is presented. The approach is suitable for low-frequency free vibration analysis of thin rectangular plates reinforced by a small number of light stiffeners. The assumed-modes method is used to formulate the equations of motion of the plate and the rib separately. The motion of the built-up structure is then obtained by enforcing appropriate continuity conditions between the two. The resulting sparse generalized eigenvalue problem can be profitably solved by reliable methods to calculate only a small set of selected eigenmodes. An alternative formulation is also proposed for the single-ribbed case which leads to a compact analytical form of the frequency equation whose solution can be easily determined either graphically or numerically. The present method demonstrates good agreement with published results and standard finite element analysis.