Optimal Energy Dissipation in Sliding Friction Simulations

Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the removal of the frictionally generated Joule heat. Building upon general pre-existing formulation, we implement a fully microscopic dissipation approach which, based on a parameter-free, non-Markovian, stochastic dynamics, absorbs Joule heat equivalently to a semi-infinite solid and harmonic substrate. As a test case, we investigate the stick-slip friction of a slider over a two-dimensional Lennard-Jones solid, comparing our virtually exact frictional results with approximate ones from commonly adopted dissipation schemes. Remarkably, the exact results can be closely reproduced by a standard Langevin dissipation scheme, once its parameters are determined according to a general and self-standing variational procedure

Creation and manipulation of entanglement in spin chains far from equilibrium

We investigate creation, manipulation, and steering of entanglement in spin chains from the viewpoint of quantum communication between distant parties. We demonstrate how global parametric driving of the spin-spin coupling and/or local time-dependent Zeeman fields produce a large amount of entanglement between the first and the last spin of the chain. This occurs whenever the driving frequency meets a resonance condition, identified as "entanglement resonance". Our approach marks a promising step towards an efficient quantum state transfer or teleportation in solid state system. Following the reasoning of Zueco et al. [1], we propose generation and routing of multipartite entangled states by use of symmetric tree-like structures of spin chains. Furthermore, we study the effect of decoherence on the resulting spin entanglement between the corresponding terminal spins.Comment: 10 pages, 8 figure

Tensor field of weakly inhomogeneous orientational ordering in the theory of liquid crystals

[No abstract available

Statistical thermodynamics of multicomponent systems (mixtures) in the quasilattice coordination approximation

Based on the well-known concepts of statistics of nearest neighbors in a lattice and on the BethePeierls-Guggenheim quasichemical approximation, combination rules are obtained allowing us to express the thermodynamic functions of multicomponent systems (mixtures) with given chemical and coordination composition in terms of thermodynamic functions of the pure subsystems. © 1977 Plenum Publishing Corporation

Statistical thermodynamics of multicomponent systems of nonspherical molecules taking account of the short-range order in a quasichemical approximation

It is shown that short-range order can be taken into account effectively for a liquid multicomponent system (mixture) of molecules with internal (particularly orientation) degrees of freedom within the framework of a quasichemical approximation (in the Guggenheim formulation) by using a vector in the space of internal states of the molecule (correlation vector) which is introduced together with the ordinary set (vector) of occupation numbers describing the longrange order. A closed system of equations is obtained in the correlation vector representation for the thermodynamic functions and occupation numbers of chemically distinct components in the space of internal states of the molecule, and its variational formulation is given. The possibilities for using the results obtained in the theory of the liquid-crystal state are discussed. © 1978 Plenum Publishing Corporation

Integral equation for the angular distribution function of an anisotropic fluid taking account of short-range order in a quasichemical approximation

An integral equation for the one-particle angular distribution function of nonspherical molecules is formulated on the basis of the thermodynamically closed system of equations obtained earlier for the occupation numbers of a multicomponent mixture of molecules with internal degrees of freedom. It is shown that this equation goes over into a known equation of Vlasov-Onsager type for large coordination numbers (for strongly elongated molecules), and yields a known rigorous result which does not contain a phase transition into the anisotropic state in the one-dimensional case. The criterion for such a transition is formulated in the form of an eigenvalue problem for the kernel of the equation obtained. In the case of single-axis molecules, an explicit expression is given for its kernel which takes account of the anisotropy in both the attraction and repulsion as well as the finite compressibility of the substance. For a binary liquid-crystal mixture, an equation is obtained in explicit analytic form within the framework of the XYZ-model for the transition line of an isotropic fluid (IF) into a nematic liquid crystal (NLC), which agrees with experiment for individual NLC. Formulas are hence obtained for a computation of the parameters of the interaction anisotropy in terms of the IF-NLC transition line parameters, and also specific results for para-azoxyanisole (PAA). © 1978 Plenum Publishing Corporation