Physicochemical processes occurring during the formation of cellulose diacetate membranes—research of criteria for optimizing membrane performance—III. Evaporation Rate And Equilibrium Phase Separation

The kinetics of acetone evaporation from films obtained by casting solutions of cellulose diacetate-acetone-water-inorganic additive have been analysed. Three successive regimes of evaporation have been identified. The first two are exponential and end, respectively, at critical times t₁ and t₂. Casting solution compositions have been determined both at the instant of phase separation (cloud point) and upon complete gelation. Also, the period of evaporation required to produce total film opacification has been measured for certain systems. These measurements have shown that time t₁ corresponds to polymer precipitation at the film surface, and that time t₂ corresponds to complete gelation of the medium. The results illustrate the effects of film thickness, casting temperature and “swelling” or “gelling” characteristics of the inorganic additive on times t₁ and t₂.     

Domestic crude oil resource appraisal

This paper endeavours to estimate the cummulative level of discovery and production of crude oil in the United States where the importance of price and technological change is considered. Two separate functional specifications for the cumulative level are hypothesized and estimated. The results suggest that between 170 and 180 billion barrels will be ultimately recoverable of which 117 billion barrels have been produced through the end of 1989.     

The rotational and vibrational spectra of 1,3-dithiole- 2-one

Microwave spectra of 1,3-dithiole-2-one show that the molecule has a planar equilibrium conformation. IR and Raman spectra are analysed to give the normal modes of vibration.     

Enthalpies of sublimation and fusion for N-acetyl substituted glycine,L-alanine,and D-leucine amides

Enthalpies and entropies of sublimation for N-acetylglycine amide (NAGA), N-acetyl-L-alanine amide (L-NAAA), and N-acetyl-D-leucine amide (D-NALA) were determined from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method. Enthalpies and temperatures of fusion were measured by differential scanning calorimetry (DSC) and entropies of fusion were derived. No solid-to-solid transitions were detected from r.t. to fusion. Enthalpies of sublimation and fusion were combined to evaluate enthalpies of vaporization of the melts. The experimental results decreased inversely to the molecular mass. An interpretation of this trend in terms of the crystalline structure of these compounds is proposed.     

Sul minimo di funzionali definiti sullo spazio delle funzioni di variazione limitata inn dimensioni

Summary Given a proper normal integrand we define a functional on the space of functions of bounded variations inR ⁿ; sufficient conditions which assure the existence of the minimum of this functional are given.

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Entrata in Redazione il 27 aprile 1977.

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Lavoro eseguito nell'ambito dell'attività del Laboratorio per la Matematica Applicata.