Quantum effects in spin dynamics of one dimensional systems

We present a review of recent results concerning dynamical spin correlation functions of quantum spin chains with nearest neighbor exchange interactions. Zero and finite temperature results, as well as the influence of a magnetic field are discussed for s = 1/2, with special emphasis on quantum effects which can be observed experimentally. We also investigate the dependence on spin quantum number between extreme quantum (s = 1/2) and classical (s = ∞) systems

Personality, motives and learning environment as predictors of self-determined learning motivation

This study investigates how well can personality, motives for studying and the perceived learning environment predict self-determined learning motivation in higher education. Previous research has predominantly focused on the interrelation between learning environment and self-determined motivation or on the outcomes of self-determined learning motivation. The question whether relatively stable personality dispositions preform self-determined learning motivation has been largely neglected. The theoretical basis of this study is the differential psychology model, the “Big Five” model (Goldberg, 1999; McCrae et al., 2000), as well as Deci and Ryan’s (2002a) self-determination theory. The data of 730 students were analyzed by the means of regression analyses, with personality traits (Big Five), study motives and the perception of the teaching-learning environment as independent variables and self-determined learning motivation as a dependent variable. The results of hierarchical regression analyses show that the personality dimensions of conscientiousness, neuroticism and openness predict a large part of the variance of learning motivation and that additional predictors are motives to study and the perception of the learning environments

Anisotropic Quantum Spin Chains

We have studied two models for anisotropic quantum spin chains. (i) XY‐chain with a field in the plane: The magnetization of the ferromagnet behaves as h1/3 for small fields, in agreement with scaling laws. The antiferromagnet shows a critical field at which the ground state is a simple Néel state and which separates power law from exponential decay of spatial correlations. (ii) Anisotropic XY‐chain: The dynamic z‐component spin correlation function can be decomposed into a spin wave and a soliton contribution. The nature of quantum soliton excitations is studied and their form compared to soliton solutions of classical equations of motion

Quantum Spin Chains

Serious scientific interest in one-dimensional (1-D) physics arose in the early 1960’s. This interest was stimulated by exact as well as accurate numerical solutions to a variety of quantum spin chain problems [1]. The potential relevance of such solutions to real experimental systems was first demonstrated by Griffiths [2] in conjunction with workers at the Kamerlingh Onnes Laboratorium, Leiden. Theory and experiment were shown to be in excellent agreement for a naturally quasi-1-D Heisenberg spin 1/2 antiferromagnet, copper tetrammine sulphate [Cu(NH3)4SO4·H2O]. Further stimulus to the new field of quasi-1-D magnetism was provided by an annotated collection of reprinted papers on a variety of 1-D model systems, including lattice gases, dynamical disordered crystal lattices, many-fermion gases (electron gases) as well as magnets. The collection appeared in book form, and remains today an important introduction to 1-D theory [3]

Volatile anaesthetics reduce neutrophil inflammatory response by interfering with CXC receptor-2 signalling

Background Growing evidence suggests a protective effect of volatile anaesthetics in ischaemia-reperfusion (I/R)-injury, and the accumulation of neutrophils is a crucial event. Pro-inflammatory cytokines carrying the C-X-C-motif including interleukin-8 (IL-8) and CXC-ligand 1 (CXCL1) activate CXC receptor-1 (CXCR1; stimulated by IL-8), CXC receptor-2 (CXCR2; stimulated by IL-8 and CXCL1), or both to induce CD11b-dependent neutrophil transmigration. Inhibition of CXCR1, CXCR2, or both reduces I/R-injury by preventing neutrophil accumulation. We hypothesized that interference with CXCR1/CXCR2 signalling contributes to the well-established beneficial effect of volatile anaesthetics in I/R-injury. Methods Isolated human neutrophils were stimulated with IL-8 or CXCL1 and exposed to volatile anaesthetics (sevoflurane/desflurane). Neutrophil migration was assessed using an adapted Boyden chamber. Expression of CD11b, CXCR1, and CXCR2 was measured by flow cytometry. Blocking antibodies against CXCR1/CXCR2/CD11b and phorbol myristate acetate were used to investigate specific pathways. Results Volatile anaesthetics reduced CD11b-dependent neutrophil transmigration induced by IL-8 by >30% and CD11b expression by 18 and 27% with sevoflurane/desflurane, respectively. This effect was independent of CXCR1/CXCR2 expression and CXCR1/CXCR2 endocytosis. Inhibition of CXCR1 signalling did not affect downregulation of CD11b with volatile anaesthetics. Blocking of CXCR2-signalling neutralized effects by volatile anaesthetics on CD11b expression. Specific stimulation of CXCR2 with CXCL1 was sufficient to induce upregulation of CD11b, which was impaired with volatile anaesthetics. No effect of volatile anaesthetics was observed with direct stimulation of protein kinase C located downstream of CXCR1/CXCR2. Conclusion Volatile anaesthetics attenuate neutrophil inflammatory responses elicited by CXC cytokines through interference with CXCR2 signalling. This might contribute to the beneficial effect of volatile anaesthetics in I/R-injur

How to quantify deterministic and random influences on the statistics of the foreign exchange market

It is shown that prize changes of the US dollar - German Mark exchange rates upon different delay times can be regarded as a stochastic Marcovian process. Furthermore we show that from the empirical data the Kramers-Moyal coefficients can be estimated. Finally, we present an explicite Fokker-Planck equation which models very precisely the empirical probabilitiy distributions.Comment: 3 figure

Charge and spin dynamics in the one-dimensional t−Jzt-J_z and t−Jt-J models

The impact of the spin-flip terms on the (static and dynamic) charge and spin correlations in the Luttinger-liquid ground state of the 1D $t-J$ model is assessed by comparison with the same quantities in the 1D $t-J_z$ model, where spin-flip terms are absent. We employ the recursion method combined with a weak-coupling or a strong-coupling continued-fraction analysis. At $J_z/t=0^+$ we use the Pfaffian representation of dynamic spin correlations. The changing nature of the dynamically relevant charge and spin excitations on approach of the transition to phase separation is investigated in detail. The $t-J_z$ charge excitations (but not the spin excitations) at the transition have a single-mode nature, whereas charge and spin excitations have a complicated structure in the $t-J$ model. In the $t-J_z$ model, phase separation is accompanied by N\'eel long-range order, caused by the condensation of electron clusters with an already existing alternating up-down spin configuration (topological long-range order). In the $t-J$ model, by contrast, the spin-flip processes in the exchange coupling are responsible for continued strong spin fluctuations (dominated by 2-spinon excitations) in the phase-separated state.Comment: 11 pages (RevTex). 14 Figures available from author