In quasicrystals, there are not only conventional, but also phason displacement fields and associated Burgers vectors. We have calculated approximate solutions for the elastic fields induced by two-, three-and fivefold straight screw-and edge-dislocations in infinite icosahedral quasicrystals by means of a generalized perturbation method. Starting from the solution for elastic isotropy in phonon and phason spaces, corrections of higher order reflect the two-, three-and fivefold symmetry of the elastic fields surrounding screw dislocations. The fields of special edge dislocations display characteristic symmetries also, which can be seen from the contributions of all orders.

We derive a microscopic equation of motion for the dynamical orientational correlators of molecular crystals. Our approach is based upon mode coupling theory. Compared to liquids we find four main differences: (i) the memory kernel contains Umklapp processes if the total momentum of two orientational modes is outside the first Brillouin zone, (ii) besides the static two-molecule orientational correlators one also needs the static one-molecule orientational density as an input, where the latter is nontrivial due to the crystal's anisotropy, (iii) the static orientational current density correlator does contribute an anisotropic, inertia-independent part to the memory kernel, (iv) if the molecules are assumed to be fixed on a rigid lattice, the tensorial orientational correlators and the memory kernel have vanishing l, l ′ = 0 components, due to the absence of translational motion. The resulting mode coupling equations are solved for hard ellipsoids of revolution on a rigid sc-lattice. Using the static orientational correlators from Percus-Yevick theory we find an ideal glass transition generated due to precursors of orientational order which depend on X0 and ϕ, the aspect ratio and packing fraction of the ellipsoids. The glass formation of oblate ellipsoids is enhanced compared to that for prolate ones. For oblate ellipsoids with X0 0.7 and prolate ellipsoids with X0 4, the critical diagonal nonergodicity parameters in reciprocal space exhibit more or less sharp maxima at the zone center with very small values elsewhere, while for prolate ellipsoids with 2 X0 2.5 we have maxima at the zone edge. The off-diagonal nonergodicity parameters are not restricted to positive values and show similar behavior. For 0.7 X0 2, no glass transition is found because of too small static orientational correlators. In the glass phase, the nonergodicity parameters show a much more pronounced q-dependence.

We derive the Ornstein-Zernike equation for molecular crystals of axially symmetric particles and apply the Percus-Yevick approximation. The one-particle orientational distribution function rho((1)) (Omega) has a nontrivial dependence on the orientation Omega, in contrast to a liquid, and is needed as an input. Despite some differences, the Ornstein-Zernike equation for molecular crystals has a similar structure as for liquids. We solve both equations numerically for hard ellipsoids of revolution on a simple cubic lattice. Compared to molecular liquids, the orientational correlators in direct and reciprocal space exhibit less structure. However, depending on the lengths a and b of the rotation axis and the perpendicular axes of the ellipsoids, respectively, different behavior is found. For oblate and prolate ellipsoids with b greater, similar 0.35 (in units of the lattice constant), damped oscillations in distinct directions of direct space occur for some of the orientational correlators. They manifest themselves in some of the correlators in reciprocal space as a maximum at the Brillouin zone edge, accompanied by a maximum at the zone center for other correlators. The oscillations indicate alternating orientational fluctuations, while the maxima at the zone center originate from ferrorotational fluctuations. For a less, similar 2.5 and b less, similar 0.35, the oscillations are weaker, leading to no marked maxima at the Brillouin zone edge. For a greater, similar 3.0 and b less, similar 0.35, no oscillations occur any longer. For many of the orientational correlators in reciprocal space, an increase of a at fixed b or vice versa leads to a divergence at the zone center q=0, consistent with the formation of ferrorotational long-range fluctuations, and for some oblate and prolate systems with b less, similar 1.0 a simultaneous tendency to divergence of few other correlators at the zone edge is observed. Comparison of the orientational correlators with those from Monte Carlo simulations shows satisfactory agreement. From these simulations we also obtain a phase boundary in the a-b plane for order-disorder transitions.

51 pairs of clients and counselors at a Southwestern university counseling and research training clinic were assessed for ethnic similarities in relation to the therapeutic alliance and counseling outcomes in 6 sessions of counseling. Analysis showed after 6 sessions symptom distress was reduced. Also, counselors and clients who had similar ethnicity had significantly more positive counseling outcomes than ethnically dissimilar pairings, but ethnic similarity was not related to the nature of the therapeutic alliance and therapeutic alliance was not a correlate of counseling outcomes.

We have investigated the glassy behavior of a molecular crystal built up with chloroadamantane molecules. For a simple model of this molecule and a rigid fcc lattice a MD-simulation was performed from which we obtained the dynamical orientational correlators S kk 0 ðq; tÞ and the 'self' correlators S ðsÞ kk 0 ðtÞ, with k = (', m), k 0 = (' 0 , m 0 ). Our investigations are for the diagonal correlators k = k 0 . Since the lattice constant decreases with decreasing temperature which leads to an increase of the steric hindrance of the molecules, we find a strong slowing down of the relaxation. It has a high sensitivity on k, k 0 . For most (', m), there is a two-step relaxation process, but practically not for (', m) = (2, 1), (3, 2), (4, 1) and (4, 3). Our results are consistent with the a-relaxation scaling laws predicted by mode coupling theory from which we deduce the glass transition temperature T MD c ffi 217 K. From a first-principle solution of the mode coupling equations we find T MCT c ffi 267 K. Furthermore mode coupling theory reproduces the absence of a two-step relaxation process for (', m) = (2, 1), (3, 2), (4, 1) and (4, 3), but underestimates the critical nonergodicity parameters by about 50 per cent for all other (', m). It is suggested that this underestimation originates from the anisotropic crystal field which is not accounted for by mode coupling theory. Our results also imply that phonons have no essential influence on the long time relaxation.