Activated bond-breaking processes preempt the observation of a sharp glass-glass transition in dense short-ranged attractive colloids

We study-using molecular dynamics simulations-the temperature dependence of the dynamics in a dense short-ranged attractive colloidal glass to find evidence of the kinetic glass-glass transition predicted by the ideal mode coupling theory. According to the theory, the two distinct glasses are stabilized, one by excluded volume and the other by short-ranged attractive interactions. By studying the density autocorrelation functions, we discover that the short-ranged attractive glass is unstable. Indeed, activated bond-breaking processes slowly convert the attractive glass into the hard-sphere one, preempting the observation of a sharp glass-glass transition.     

Circular Dichroism of Some Isomeric Alkyl Pyridines

The UV. and CD. spectra of the optically active 2-, 3- and 4-(l-methylpropyl)-pyridines ( 1a , b , c ) and of the corresponding (2-methylbutyl)pyridines ( 2a , b , c ) have been investigated in hexane at RT. and at ?85°, in hexane/TFA and in aqueous HCl-solution. In 1c and 2c both the n → π* and the π → π* transitions are optically active, an n → π* transition being located above 265 nm. The position and the sign of the CD. bands are greatly influenced by the position and the nature of the alkyl substituent.     

Conditions of stability for thermoelastic continua

Meccanica - The paper studies the restrictions on the mechanical and thermal constitutive equations of an elastic isotropic material, in order to ensure the local stability under suitable...     

A Liquid-Crystal Study of Heptalene

The chiral structure of heptalene is characterised, for a given configuration, by helicities, which are opposite in the direction (x) of the central C(5a)-C(10a) bond and in the direction (y) of a line perpendicular to it, passing through the C(3)-and C(8)-atoms. These two helicities can be experimentally established and differentiated by the handedness of the cholesteric mesophases induced in a biphenyl-type liquid crystal (LC) by chiral heptalenes with substituents favouring the x or y orientation along the nematic director of the LC.     

The pillar of best efficiency

Let us imagine having to design an elastic vertical pillar that must transmit an axial compressive load. We know the extents of the upper and of the lower cross-sections of the pillar and its longitudinal length, but the profile of the lateral surface is arbitrary. We want to find the shape of this lateral surface in order that the distibution of the normal stresses at the bottom is as uniform as possible. A partial answer to the problem is given in two-dimensional elastostatics.     

Sugli insiemi di grandezze meccaniche derivate

Riassunto Si dà innanzi tutto un cenno del procedimento mediante il quale un insieme di grandezze meccaniche dotate di misura positiva può essere derivato da altri insiemi dello stesso tipo, per mezzo di una funzione generatrice che dipende dalle misure delle grandezze. Si stabilisce quindi la condizione necessaria e sufficiente che deve essere soddisfatta dalla funzione generatrice affinchè essa dia luogo ad insiemi indipendenti dalla scelta delle unità per le grandezze da cui sono derivati. Le soluzioni di un'equazione funzionale forniscono l'espressione di tutte le funzioni generatrici che soddisfano la precedente condizione di invarianza, insieme ad una condizione necessaria riguardante la osservabilità delle grandezze derivate. La trattazione è infine estesa alle grandezze dotate di misura algebrica.

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Summary An outline is first given of the process which is followed to derive a set of mechanical quantities with positive measure from other sets of the same type, by means of a generating function depending upon the measures. The necessary and sufficient condition is then found which must be satisfied by the generating function, to give rise to sets independent from the units chosen for the quantities from which they are derived. The solutions of a functional equation give the expression of all the generating functions which satisfy the above invariance condition, together with a necessary condition concerning the observable character of the derived quantities. The theory is finally extended to quantities with algebraic measures.

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A Dario Graffi nel suo 70^o compleanno

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Entrata in Redazione il 28 giugno 1975.     

Carbon 13 NMR spectra of pyridylbenz-X-azoles

The ¹³C nmr spectra of a series of pyridylbenzimidazoles and benzoxazoles and of their quaternary salts have been determined. The mutual effects of the two heterocyclic systems and the effect of the quaternization have been discussed. The results evidence the existence of some interactions between benzimidazole and pyridine moieties.