Optimal performance of endoreversible quantum refrigerators

The derivation of general performance benchmarks is important in the design of highly optimized heat engines and refrigerators. To obtain them, one may model phenomenologically the leading sources of irreversibility ending up with results that are model independent, but limited in scope. Alternatively, one can take a simple physical system realizing a thermodynamic cycle and assess its optimal operation from a complete microscopic description. We follow this approach in order to derive the coefficient of performance at maximum cooling rate for any endoreversible quantum refrigerator. At striking variance with the universality of the optimal efficiency of heat engines, we find that the cooling performance at maximum power is crucially determined by the details of the specific system-bath interaction mechanism. A closed analytical benchmark is found for endoreversible refrigerators weakly coupled to unstructured bosonic heat baths: an ubiquitous case study in quantum thermodynamics

Gas Permeability and the Microstructure of Polymers

Abstract 1. The permeability to gas of high molecular-weight polymers is closely connected with the character of the interaction between separate links of adjacent macromolecules, which is governed by the form of the chain and the energy of the intermolecular bonds. 2. The magnitude of permeability increases with increases in the curvature of the principal-valence chains and in the dimensions of the side groups, decreases with increase in the energy of the intermolecular bonds, and is independent of the length of the main valence chains. 3. A comparison of the values of the activation energies and gas permeabilities of a series of polymers makes reasonable the assumption that the principal paths for the penetration of hydrogen molecules lie along the interface between the nonpolar groups of the macromolecular chains.</jats:p

The Solubility of N-Phenyl-2-Naphthylamine in Elastomers

Abstract The determination of the solubility of N-phenyl-2-naphthylamine in elastomers is of great importance in determining the correct percentage of this substance to add to an elastomer to protect it from oxidation. Kuzminskii˘ and Lezhnev have shown that the duration of the induction of the oxidation of rubber depends on the concentration of N-phenyl-2-naphthylamine inhibitor in the rubber.</jats:p

On some remarkable phenomena in Geissler tubes

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Diffusion of Antioxidants in Rubber

Abstract The study of the diffusion of polymers in order to determine the size and shape of the macromolecules in solutions has been the subject of numerous recent works. Considerably fewer studies have been devoted to the problem of the diffusion of low-molecular substances dissolved in polymers, and the existing works in this field refer principally to gas-polymer systems. It is also known that the rate of diffusion in polymers of solid and liquid low-molecular compounds governs in a number of cases the kinetics of processes of great practical importance. In particular, the kinetics of a process as important to the rubber industry as the oxidation of rubber is, to a large degree, related to the rate of diffusion of antioxidants and other soluble ingredients in the rubber. Rubber as a diffusion medium is distinguished from liquids and solid crystalline substances by certain properties which are governed by the characteristic heat movement of the macromolecules. Thus, Brün showed that Einstein's equation cannot be applied in the case of diffusion in rubber, and Barrer developed a theory of diffusion of gases in rubber, according to which the presence of an activation zone is necessary for the initial process of diffusion. The present study concerns the diffusion of certain solid antioxidants dissolved in rubber (phenyl-2-naphthylamine, dinaphthylamine, and dinaphthyl-phenylenediamine).</jats:p