Random fields and quantum effects in proton glasses

The effects of quantum fluctuations on the proton glass phase in mixed hydrogen-bonded ferro-antiferroelectric systems are considered. The system is described in terms of the infinite-ranged Ising pseudospin glass model in a transverse tunneling field in the presence of random parallel fields. The stability limit of the high-temperature proton glass phase is determined within the thermofield dynamic approach, and the behavior or linear and nonlinear susceptibility is evaluated.     

Twist-grain boundary phase induced by Au nanoparticles in a chiral liquid crystal host

We report on the stabilisation of the liquid-crystalline, twist-grain boundary A (TGB_A) phase in mixtures of a chiral liquid crystal and surface-functionalised spherical Au nanoparticles (NPs) of 10 nm diameter. The results, obtained by calorimetric, optical, small-angle X-ray and plasmon resonance measurements, demonstrate that a TGB_A phase, which is metastable for the pure liquid crystal host, can be effectively stabilised for a 3 K range in the presence of NPs. Moreover, the role of NPs size on the TGB_A stabilisation is briefly discussed.     

Stability of the C *-Algebra Associated with Twisted CCR

The universal enveloping C ^*-algebra A of twisted canonical commutation relations is considered. It is shown that, for any (–1,1), the C ^*-algebra A is isomorphic to the C ^*-algebra A ₀ generated by partial isometries t _i ,t _i ^*,i=1,¨,d satisfying the relations t _i ^* t _j = _ij (1– _k<i t _k t _k ^*), t _j t _i =0, ij and it is proved that the Fock representation of A is faithful.     

On matrix types of prime varieties of associative algebras

Some answer is obtained to the problem by A. R. Kemer: We show that for a given number k and all sufficiently large p every prime variety of associative algebras of matrix type k over a field of characteristic p > 0 is regular.     

Phonon scattering by paraelastic defects

The relaxation timeτ(ω) for the scattering of the lattice waves of frequencyω by the paraelastic defects has been calculated by using the Feynman graph method, applied to a previous theoretical model [8]. A simple expression for the resonance component ofτ(ω)⁻¹ has been derived.

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Zusammenfassung Die Relaxationszeitτ(ω) für die Streuung der Gitterwellen der Frequenzω an den paraelastischen Defekten wurde nach der Methode der Feynmanschen Graphen berechnet, wobei ein früheres theoretisches Modell [8] angewendet wurde. Ein einfacher Ausdruck für den Resonanzteil vonτ(ω)⁻¹ wurde hergeleitet.

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Résumé Nous avons calculé le temps de relaxationτ(ω) des ondes du réseau de fréquenceω, qui sont diffusées par des défauts para-élastiques, en appliquant la méthode des graphes de Feynman à un modèle théorique antérieur [8]. Une simple expression pour la partie résonante deτ(ω)⁻¹ a été dérivée.

     

Temperature dependence and anisotropy of the hole drift mobility in monoclinic tetracyanoethylene

The tensor of the hole drift mobility is determined in monoclinic tetracyanoethylene by the transient photoconductivity technique. The principal tensor components amount to μ₁ = 0.21, μ₂ = 0.10 and μ₃ = 0.15 cm²/V s at room temperature. Above 250 K the mobility is a decreasing function of temperature and follows an exp(E/kT) dependence (E = 0.08 eV) which is inconsistent with both band and hopping models. Below 250 K the mobility is controlled by a hole trapping level of 0.28 eV deep. The photogeneration efficiency is found to be independent of temperature and proportional to the light intensity.     

Tricritical point in classical spin systems with random transverse fields

The existence of a tricritical point is demonstrated for a classical n-vector model with annealed random transverse fields, and the corresponding tricritical temperature T_t and distribution width σ_t are evaluated within Landau theory for continuous spin dimensionality -2 < n < 10.     

Invariants of the crystallographic system <Emphasis Type="Italic">E</Emphasis><Subscript>8</Subscript>, algebraic polytopes,and 3D ordered structures

It is shown that constructions of algebraic geometry select peculiar subsystems of vectors of the first coordination sphere of the 8D crystallographic lattice E ₈. A correspondence between such subsystems and pairs of 4D systems of vectors specifying vertices of “algebraic” polytopes on a 3D sphere is established. A 136-vertex algebraic polytope, whose symmetry determines the structure of a number of ordered diamond-like structures, is considered as an example.