A microscopic approach to spin dynamics: about the meaning of spin relaxation times

We present an approach to spin dynamics by extending the optical Bloch equations for the driven two-level system to derive microscopic expressions for the transverse and longitudinal spin relaxation times. This is done for the 6-level system of electron and hole subband states in a semiconductor or a semiconductor quantum structure to account for the degrees-of-freedom of the carrier spin and the polarization of the exciting light and includes the scattering between carriers and lattice vibrations on a microscopic level. For the subsystem of the spin-split electron subbands we treat the electron-phonon interaction in second order and derive a set of equations of motion for the 2x2 spin-density matrix which describes the electron spin dynamics and contains microscopic expressions for the longitudinal (T_1) and the transverse (T_2) spin relaxation times. Their meaning will be discussed in relation to experimental investigations of these quantities.Comment: 9 pages, 3 figures, Replacement of cond-mat/0407358 due to substantial revisio

On the existence of self-similar spherically symmetric wave maps coupled to gravity

We present a detailed analytical study of spherically symmetric self-similar solutions in the SU(2) sigma model coupled to gravity. Using a shooting argument we prove that there is a countable family of solutions which are analytic inside the past self-similarity horizon. In addition, we show that for sufficiently small values of the coupling constant these solutions possess a regular future self-similarity horizon and thus are examples of naked singularities. One of the solutions constructed here has been recently found as the critical solution at the threshold of black hole formation.Comment: 15 pages, LaTe

EIT ground-state cooling of long ion strings

Electromagnetically-induced-transparency (EIT) cooling is a ground-state cooling technique for trapped particles. EIT offers a broader cooling range in frequency space compared to more established methods. In this work, we experimentally investigate EIT cooling in strings of trapped atomic ions. In strings of up to 18 ions, we demonstrate simultaneous ground state cooling of all radial modes in under 1 ms. This is a particularly important capability in view of emerging quantum simulation experiments with large numbers of trapped ions. Our analysis of the EIT cooling dynamics is based on a novel technique enabling single-shot measurements of phonon numbers, by rapid adiabatic passage on a vibrational sideband of a narrow transition

An operator expansion for integrable quantum field theories

A large class of quantum field theories on 1+1 dimensional Minkowski space, namely, certain integrable models, has recently been constructed rigorously by Lechner. However, the construction is very abstract and the concrete form of local observables in these models remains largely unknown. Aiming for more insight into their structure, we establish a series expansion for observables, similar but not identical to the well-known form factor expansion. This expansion will be the basis for a characterization and explicit construction of local observables, to be discussed elsewhere. Here, we establish the expansion independent of the localization aspect, and analyze its behavior under space-time symmetries. We also clarify relations with deformation methods in quantum field theory, specifically, with the warped convolution in the sense of Buchholz and Summers.Comment: minor corrections and clarifications, as published in J. Phys A; 24 page

Deformations of Fermionic Quantum Field Theories and Integrable Models

Considering the model of a scalar massive Fermion, it is shown that by means of deformation techniques it is possible to obtain all integrable quantum field theoretic models on two-dimensional Minkowski space which have factorizing S-matrices corresponding to two-particle scattering functions S_2 satisfying S_2(0) = -1. Among these models there is for example the Sinh-Gordon model. Our analysis provides a complement to recent developments regarding deformations of quantum field theories. The deformed model is investigated also in higher dimensions. In particular, locality and covariance properties are analyzed.Comment: 20 page

Direct determination of vibrational density of states change on ligand binding to a protein

The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium

Teaching periodontal pocket charting to dental students: a comparison of computer assisted learning and traditional tutorials

AIM: The aim of this study was to compare the effectiveness of a computer assisted learning (CAL) programme with that of traditional small group tutorials in teaching theoretical and practical aspects of periodontal pocket charting. METHOD: Sixty-one third year undergraduate dental students were randomized to either receive a tutorial or to work through the CAL programme. Students using the CAL programme completed questionnaires relating to previous computer experience and the ease of use of the programme. All students were assessed immediately after the intervention by means of a confidence log, a practical exercise and a further confidence log. They were assessed again three weeks later by means of a confidence log and a multiple-choice written test. RESULTS: There were very few significant differences between groups for any of the assessments used. However, subjective comments indicated that students occasionally felt disadvantaged if they had not received a tutorial. CONCLUSION: CAL and traditional teaching methods are equally effective in teaching periodontal pocket charting to undergraduate dental students