The orientational glass instability and localization in (KCN) x (KBr)1−x and (KCN) x (NaCN)1−x

Substitutional disorder in mixed crystals with orientational and translational degrees of freedom leads to the appearance of random strain fields. The strains act as static scattering centers for dynamic modes. Near a ferroelastic phase transition where the crystal is very soft, internal friction processes dominate the dynamic restoring forces. The resulting nonergodic instability marks the onset of the orientational glass state, which is characterized by a freezing-in of orientational and translational modes without long range order. The method is based on the study of dynamic equations of mode-coupling type and was originally developed by Götze for the Anderson localization.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Reorientations and random fields in plastic crystals

A simple Ising-like model is presented to describe the phase diagram of plastic crystals. In addition to a bilinear coupling between translations and rotations a reorientation-translation coupling is introduced via random fields which couple solely to rotational degrees of freedom. The physical basis of the reorientation-translation coupling is discussed using the rotational state hypothesis. The present approach is found to be consistent with some recent neutron experiments.     

The coupling of valence shell and particle-hole degrees of freedom in a partial random phase approximation

It is well known that the random phase approximation breaks down in the absence of a substantial energy gap between occupied and unoccupied single-particle states. Particle-hole excitations are then inevitably accompanied by substantial rearrangements of the particles in the neighbourhood of the Fermi surface. To accommodate this situation, a partial RPA is introduced which corresponds to replacing only the particle-hole degrees of freedom by bosons but leaving the valence space degrees of freedom intact. The PRPA is therefore a mapping of the many-fermion dynamics into the dynamics of a coupled boson-valence space. In application of the PRPA, algebraic methods, of either a fermionic or Lie algebra type, can be introduced, if desired, to facilitate the treatment of the valence space degrees of freedom. Results of applications are presented in which the valence space particles are treated in the rotational and SU(3) models, and are coupled strongly to giant dipole and quadrupole resonances.     

Cavity cooling of translational and ro-vibrational motion of molecules: ab initio-based simulations for OH and NO

We present detailed calculations on the basis of our recent proposal for simultaneous cooling of the rotational, vibrational and external molecular degrees of freedom [1]. In this method, the molecular ro-vibronic states are coupled by an intense laser and an optical cavity via coherent Raman processes enhanced by the strong coupling with the cavity modes. For a prototype system, OH, we showed that the translational motion is cooled to a few μK and the molecule is brought to the internal ground state in about a second. Here, we investigate numerically the dependence of the cooling scheme on the molecular polarizability, selecting NO as a second example. Furthermore, we demonstrate the general applicability of the proposed cooling scheme to initially vibrationally and rotationally hot molecular systems. PACS 33.80.Ps; 32.80.Lg; 42.50.Pq     

Cumulative author index of Volumes 351 to 360

The dynamic evolution of granular gases is fundamentally different from molecular gases due to the energy loss during collisions. Nevertheless techniques of kinetic theory are useful in a regime, when the granular particles are moving rapidly and the gas is sufficiently dilute. In these lecture notes we analyse in detail the collision of two rough particles which is inelastic due to incomplete normal and tangential restitution as well as Coulomb friction. Based on the Walton model a time evolution operator for the many particle system is introduced, a formalism which is well suited for simple approximations. We discuss free cooling of granular particles with particular emphasis on the exchange of energy between rotational and translational degrees of freedom.     

Rigid rotators and diatomic molecules via Tsallis statistics

We obtain an analytic expression for the specific heat of a system of N rigid rotators exactly in the high temperature limit, and via a perturbative approach in the low temperature limit. We then evaluate the specific heat of a diatomic gas with both translational and rotational degrees of freedom, and conclude that there is a mixing between the translational and rotational degrees of freedom in nonextensive statistics.     

Rovibrational excitation within the infinite conical well: Desorption of diatomic molecules

An analytic model for the hindered rotational states of a diatomic molecule adsorbed upright on a solid surface is discussed. Various model dynamics situations, within the sudden approximation, designed to simulate desorption are presented and rotational state distributions are calculated including both rotational and translational degrees of freedom. Criteria are established for observing rotationally cool desorbed molecules.     

Effects of the Quenched Random Crystal Field on the Dynamic Spin-1 Blume-Capel Model

In this study, we have analyzed the dynamical phase transitions of spin-1 Blume-Capel model with quenched random crystal field under the effect of a time dependent oscillating magnetic field. We have obtained the magnetic field, temperature (h,T) cross sections of the global phase diagram for constant values of the concentration and the amplitude of the single-ion anisotropy within mean field approximation. There are regions of the phase space where both ordered and disordered phases coexist. In addition, the dynamic phase transition from one regime to the other can be a first- or a second-order depending on the region in the phase diagram. Hence, the system exhibits a number of interesting phenomena and a rich variety of phase diagrams with type being according to the concentration p of active local crystal fields.     

Calculation of the thermodynamic potentials of changes in translational, rotational, and vibrational degrees of freedom in the dimerization of aromatic molecules

The work presents a method for calculating the thermodynamic potentials (free Gibbs energy, enthalpy, and entropy) and an analysis of the contributions of changes in translational, rotational, and vibrational degrees of freedom to the energy characteristics of the dimerization of aromatic compounds. On the whole, changes in the Gibbs energy caused by these contributions were shown to exceed the experimental energies of dimerization in solution in magnitude, which was evidence of the necessity of taking them into account for the aggregation of molecules. We determined changes in the Gibbs energy and entropy of translational, rotational, and vibrational (mechanical) degrees of freedom and the enthalpy of vibrations, which can be used to analyze the energy characteristics of dimerization reactions. These dimerization energy components should be calculated separately for each compound.     

Temporal and structural characteristics of a two-dimensional gas of hard needles

We have simulated the dynamics of a 2D gas of hard needles by event-oriented molecular dynamics. Various quantities namely translational and rotational diffusion constants and intermediate self-scattering function have been explored and their dependence on density is obtained. Despite absence of positional ordering, the rotational degree of freedom behaves nontrivially. Slowing down is observed in the angular part of the motion. It is shown that above a certain density the rotational mean-square displacement exhibits a three-stage regime including a plateau.     

Cavity cooling of internal molecular motion

We predict that it is possible to cool rotational, vibrational, and translational degrees of freedom of molecules by coupling a molecular dipole transition to an optical cavity. The dynamics is numerically simulated for a realistic set of experimental parameters using OH molecules. The results show that the translational motion is cooled to a few muK and the internal state is prepared in one of the two ground states of the two decoupled rotational ladders in a few seconds. Shorter cooling times are expected for molecules with larger polarizability.     

A spectral finite element for analysis of wave propagation in uniform composite tubes

A spectral finite element model (SFEM) for analysis of coupled broadband wave propagation in composite tubular structure is presented. Wave motions in terms of three translational and three rotational degrees of freedom at tube cross-section are considered based on first order shear flexible cylindrical bending, torsion and secondary warping. Solutions are obtained in wavenumber space by solving the coupled wave equation in 3-D. An efficient and fully automated computational strategy is developed to obtain the wavenumbers of coupled wave modes, spectral element shape function, strain-displacement matrix and the exact dynamic stiffness matrix. The formulation emphasizes on a compact matrix methodology to handle large-scale computational model of built-up network of such cylindrical waveguides. Thickness and frequency limits for application of the element is discussed. Performance of the element is compared with analytical solution based on membrane shell kinematics. A map of the distribution of vibrational modes in wavelength and time scales is presented. Effect of fiber angle on natural frequencies, phase and group dispersions are also discussed. Numerical simulations show the ease with which dynamic responses can be obtained efficiently. Parametric studies on a clamped-free graphite-epoxy composite tube under short-impulse load are carried out to obtain the effect of various composite configurations and tube geometries on the response.     

Entanglement dynamics of a strongly driven trapped atom

We study the entanglement between the internal electronic and the external vibrational degrees of freedom of a trapped atom which is driven by two lasers into electromagnetically induced transparency. It is shown that basic features of the intricate entanglement dynamics can be traced to Landau-Zener splittings (avoided crossings) in the spectrum of the atom-laser field Hamiltonian. We further construct an effective Hamiltonian that describes the behavior of entanglement under dissipation induced by spontaneous emission processes. The proposed approach is applicable to a broad range of scenarios for the control of entanglement between electronic and translational degrees of freedom of trapped atoms through suitable laser fields.     

Theory of phonon linewidth in orientationally disordered crystals

The dynamics of coupled translational (T) and rotational (R) modes is studied with special reference to the experimental situation in the alkali cyanides. The dynamic equations are extended and, in addition to the bilinear T-R coupling, anharmonic interactions of the form T-T-R are considered. These interactions lead to additional friction coefficients for translational and rotational motion. Transport coefficients are evaluated with mode-mode coupling theory. The validity of orientational relaxation models coupled to lattice vibration is confirmed as a particular case of the present theory at low frequencies. An extension to the high frequency regime is proposed.Dedicated to Prof. Dr. H.E. Müser ob the occasion of his 60th birthday     

Rotational effect in two-dimensional cooperative directed transport

In this review we investigate the rotation effect in the motion of coupled dimer in a two-dimensional asymmetric periodic potential. Free rotation does not generate directed transport in translational direction, while we find it plays an critical role in the motors motility when the dimer moves under the effect of asymmetry ratchet potential. In the presence of external force, we study the relation between the average current and the force numerically and theoretically. The numerical results show that only appropriate driving force could produce nonzero current and there are current transitions when the force is large enough. An analysis of stability analysis of limit cycles is applied to explain the occurrence of these transitions. Moreover, we numerically simulate the transport of this coupled dimer driven by the random fluctuations in the rotational direction. The existence of noise smooths the current transitions induced by the driving force and the resonance-like peaks which depend on the rod length emerge in small noise strength. Thanks to the noise in the rotational direction, autonomous motion emerges without the external force and large noise could make the current reversal happen. Eventually, the new mechanism to generate directed transport by the rotation is studied.     

Quasiregular concentric waves in heterogeneous lattices of coupled oscillators

We study the pattern formation in a lattice of locally coupled phase oscillators with quenched disorder. In the synchronized regime quasiregular concentric waves can arise which are induced by the disorder of the system. Maximal regularity is found at the edge of the synchronization regime. The emergence of the concentric waves is related to the symmetry breaking of the interaction function. An explanation of the numerically observed phenomena is given in a one-dimensional chain of coupled phase oscillators. Scaling properties, describing the target patterns are obtained.