Effect of p-toluensulfonic acid on oxidation of polyethylene and polyethylene-poly-p-methylstyrene blends

p-Toluensulfonic acid retards oxidation of polyethylene and, to a greater extent, of polyethylene-poly-p-methylstyrene blends. The real antioxidant is p-cresol, formed by p-toluensulfonic acid transformation in oxidizing polyethylene and, in blends, through peroxidation and subsequent acid-catalyzed decomposition of hydroperoxides of poly-p-methylstyrene.     

Anderson localization of expanding Bose-Einstein condensates in random potentials

We show that the expansion of an initially confined interacting 1D Bose-Einstein condensate can exhibit Anderson localization in a weak random potential with correlation length sigma(R). For speckle potentials the Fourier transform of the correlation function vanishes for momenta k>2/sigma(R) so that the Lyapunov exponent vanishes in the Born approximation for k>1/sigma(R). Then, for the initial healing length of the condensate xi(in)>sigma(R) the localization is exponential, and for xi(in)相似文献   

Variation of the parameters of inhibited oxidation of polyethylene in the region of phase transition

Parameters of oxidation of polyethylene with molecular oxygen in the presence of a phenolic antioxidant, 2,2-methylenebis(4-methyl-6-methylcyclohexylphenol), at 80–210°C were studied. The possible mechanism of interaction of the polymer with the antioxidant near the melting point was considered theoretically. The suggested theoretical relationships are consistent with experimental data.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1378–1381.Original Russian Text Copyright © 2004 by Shlyapnikov, Kolesnikova.     

Bose-einstein condensation in trapped dipolar gases

We discuss Bose-Einstein condensation in a trapped gas of bosonic particles interacting dominantly via dipole-dipole forces. We find that in this case the mean-field interparticle interaction and, hence, the stability diagram are governed by the trapping geometry. Possible physical realizations include ultracold heteronuclear molecules, or atoms with laser induced electric dipole moments.     

Antioxidant action in polymers: The role of ‘inert’ compounds in inhibited oxidation

Low-molecular-weight compounds which take no part in polymer oxidation can change the reactivities of other compounds dissolved in the polymer, including antioxidants, by redistributing the antioxidant molecules among the elements of the polymer structure. The effects may be comparable with chemical synergism between antioxidants of different types.     

Reaction of alkyl halide salts of nitrogen-containing heterocycles with sulfur dioxide in aqueous solutions

Complexes of quaternary salts with SO₂ are formed on saturation of aqueous solutions of alkyl halide salts of nitrogen-containing heterocycles with sulfur dioxide. The SO₂ concentration necessary for the precipitation of the complexes increases in the order I < Br < Cl and decreases as the alkyl group attached to the nitrogen becomes larger. The sulfur dioxide in the complexes is bonded through the halide ion by a charge-transfer coordinate bond, and their separation into an independent phase is due to a change in the degree of hydration during complexing. Several crystalline adducts are described, and the autooxidation of the SO₂ complex of pyridine methiodide is investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 966–969, July, 1972.     

The problem of “thermal explosion” in spin-polarized atomic hydrogen gas

The exponential character of the depolarization-rate temperature dependence in spin-polarized atomic hydrogen gas results in a “thermal explosion” phenomenon with increasing density. The inhomogeneous heating is stimulated by the three-body recombination, which in allowance for dipole-dipole interaction takes place at arbitrary spin states of colliding particles. The critical gas density is found to be in the range of 10¹⁸–10¹⁹ cm^?3 for the real parameters of the system.     

Phase fluctuations in Bose–Einstein condensates

We demonstrate the existence of phase fluctuations in elongated Bose–Einstein condensates (BECs) and study the dependence of these fluctuations on the system parameters. A strong dependence on temperature, atom number, and trapping geometry is observed. Phase fluctuations directly affect the coherence properties of BECs. In particular, we observe instances where the phase-coherence length is significantly smaller than the condensate size. Our method of detecting phase fluctuations is based on their transformation into density modulations after ballistic expansion. An analytic theory describing this transformation is developed. Received: 13 July 2001 / Revised version: 28 September 2001 / Published online: 23 November 2001