On the Collapse of Masonry Arches

In this paper a constitutive equation for masonry arches is defined and its main properties are proven; in this equation to each pair of generalized strains (, ), with the extensional strain and the curvature change of the centre line, is assigned the pair of generalized internal forces (N,M), where N is the normal force and M the bending moment. Subsequently, the collapse of masonry arches is characterized and the static and kinematic theorems proven. Finally, a method for determining the collapse load in the case of circular arches subjected to their own weight and a vertical point load applied at a point of the extrados is presented. The results obtained, of interest in some applications, are summarized in a series of graphs.     

On the Balance Equation for Stresses Concentrated on Curves

Conditions of equilibrium of forces are formulated for a force system in a continuous body which consists of a bulk stress and a stress concentrated on a curve. The system of forces is interpreted as a tensor valued measure and the equilibrium of forces is interpreted in a weak sense. The divergence theorem is proved for bulk stress fields with the corresponding singularity. Examples of such stress fields are given.      

Graphs with independent perfect matchings

A graph with at least two vertices is matching covered if it is connected and each edge lies in some perfect matching. A matching covered graph G is extremal if the number of perfect matchings of G is equal to the dimension of the lattice spanned by the set of incidence vectors of perfect matchings of G. We first establish several basic properties of extremal matching covered graphs. In particular, we show that every extremal brick may be obtained by splicing graphs whose underlying simple graphs are odd wheels. Then, using the main theorem proved in 2 and 3 , we find all the extremal cubic matching covered graphs. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 19–50, 2005     

Power spectra of ionization irregularities in the equatorial ionosphere, evaluated by means of the analysis of phase scintillation of transionospheric signals at 40 MHz

Summary The analysis of the phase of signals at 40 MHz received at the equatorial station San Marco during summer 1975 shows power spectra of the phase scintillation following an inverse power law dependence on the frequency. A deduction is derived on the wave number dependence of the spatial power spectra of the electron density irregularities in the ionospheric regions traversed by the signals.

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Riassunto L'analisi della fase di segnali a 40 MHz ricevuti da una stazione posta presso la base San Marco nell'estate 1975 mostra spettri di potenza della scintillazione di fase con una dipendenza dalla frequenza del tipo inverso di potenza. Questo è messo in relazione con la dipendenza dal numero d'onda dello spettro spaziale delle irregolarità di ionizzazione nelle regioni ionosferiche traversate dai segnali.

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Резюме Анализ фазы сигналов при 40 МГц, полученных на экваториальной станции Сан Марко, в течение лета 1975 г., обнаруживает степенные спектры для сцинтилляции фазы, причем зависимость от частоты описывается обратным степенным законом. Это есть следствие зависимости от волнового числа простран-ственных степенных спектров иррегулярностей злектронной плотности в ионосферных областях, через которые проходят сигналы.

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To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Explicit solutions for complex tension-torsion tests in plasticity

For an elastic-plastic material obeying the clasical kinematic hardening rule of Melan, a deformation process reproducing the combined tension-torsion test of a thin tube is considered and the accompanying stress field analytically determined. This allows us to study the effect of the kinematic hardening modulus on the delay with which the stress follows the deformation path.

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Sommario In questo studio viene determinata l'espressione dello sforzo in un materiale elasto-plastico che segue la classica regola di incrudimento cinematico di Melan ed è soggetto a un processo di deformazione analogo a quello che ha luogo in un tubo sottile nel caso di una prova di tensione-torsione combinate. Cio' consente di studiare l'effetto del modulo di incrudimento cinematico sul ritardo con cui lo sforzo segue la traiettoria della deformazione.

     

The Johari-Goldstein β-relaxation of glass-forming binary mixtures

The present paper shows, by means of broadband dielectric measurements, that the primary α- and the secondary Johari-Goldstein (JG) β-processes in binary mixtures are strongly correlated. This occurs for different polar rigid probes dissolved in apolar glass-forming solvents, over a wide temperature and pressure range.We found that the coupling parameter n = 1 − β_KWW and the ratio between α- and β-relaxation time reduce on increasing the size of the solute solved within the same apolar matrix. Moreover, such a ratio is invariant when calculated at different combinations of P and T maintaining either the primary or the JG relaxation times constant. Dielectric spectra measured at different T-P combinations but with an invariant α-relaxation time are well superposed in both the α- and β-frequency ranges. Experimental results can be rationalized by Coupling Model equation.     

3‐Flows and Combs

Tutte's 3‐Flow Conjecture states that every 2‐edge‐connected graph with no 3‐cuts admits a 3‐flow. The 3‐Flow Conjecture is equivalent to the following: let G be a 2‐edge‐connected graph, let S be a set of at most three vertices of G; if every 3‐cut of G separates S then G has a 3‐flow. We show that minimum counterexamples to the latter statement are 3‐connected, cyclically 4‐connected, and cyclically 7‐edge‐connected.     

THE HADAMARD INEQUALITY FOR CONVEX FUNCTION VIA FRACTIONAL INTEGRALS

In this paper, we establish several inequalities for some differantiable mappings that are connected with the Riemann-Liouville fractional integrals. The analysis used in the proofs is fairly elementar...     

On the role of the definition of potential models in Gibbs ensemble phase equilibria simulations of the H2S-pentane mixture

The effect of treating explicitly the coulombic and polarization interactions is investigated through the calculation of the coexistence curve of the pentane-H₂S binary mixture. In this work, potential models have been developed for hydrogen sulphide and pentane, which include electrostatic sites—estimated from ab initio calculations—and polarizable sites—estimated from experimental data—in addition to Lennard-Jones sites. Compared to existing models, these new models have the same number of fitting parameters to experimental thermodynamic data. They are shown to correctly describe the coexistence curve of the pure compounds. When applied to the case of mixtures, together with Lorentz-Berthelot combining rules, they allow one to obtain a more accurate prediction of the coexisting compositions of the mixture. Furthermore, it is shown that the interaction energy in this kind of mixture cannot be properly described by using effective potential models usually considered for pure compounds.