A relativistic coupled-channel formalism for the pion form factor

The electromagnetic form factor of a confined quark-antiquark pair is calculated within the framework of point-form relativistic quantum mechanics. The dynamics of theexchanged photon is explicitly taken into account by treating theelectromagnetic scattering of an electron by a meson as a relativistic two-channel problem for a Bakamjian-Thomas type mass operator. This approach guarantees Poincare invariance. Using a Feshbach reduction the coupled-channel problem can be converted into a one-channel problem for the elastic electron-meson channel. By comparing the one-photon-exchange optical potential at the constituent and hadronic levels, we are able to unambiguously identify the electromagnetic meson form factor. Violations of cluster-separability properties, which are inherent in the Bakamjian-Thomas approach, become negligible for sufficiently large invariant mass of the electron-meson system. In the limit of an infinitely large invariant mass, an equivalence with form-factor calculations done in front-form relativistic quantum mechanics is established analytically.Comment: 3 pages, 1 figure, submitted to EPJ Web of Conference

Point-form quantum field theory and meson form factors

We shortly review point-form quantum field theory, i.e. the canonical quantization of a relativistic field theory on a Lorentz-invariant surface of the form $x_\mu x^\mu = \tau^2$. As an example of how point-form quantum field theory may enter the framework of relativistic quantum mechanics we discuss the calculation of the electromagnetic form factor of a confined quark-antiquark pair (e.g. the pion).Comment: 3 pages, 2 figures. Based on a talk presented by W. Schweiger at the 20th European Conference on Few-Body Problems in Physics, September 10-14 2007, Pisa, Ital

Dropping cold quantum gases on Earth over long times and large distances

We describe the non-relativistic time evolution of an ultra-cold degenerate quantum gas (bosons/fermions) falling in Earth's gravity during long times (10 sec) and over large distances (100 m). This models a drop tower experiment that is currently performed by the QUANTUS collaboration at ZARM (Bremen, Germany). Starting from the classical mechanics of the drop capsule and a single particle trapped within, we develop the quantum field theoretical description for this experimental situation in an inertial frame, the corotating frame of the Earth, as well as the comoving frame of the drop capsule. Suitable transformations eliminate non-inertial forces, provided all external potentials (trap, gravity) can be approximated with a second order Taylor expansion around the instantaneous trap center. This is an excellent assumption and the harmonic potential theorem applies. As an application, we study the quantum dynamics of a cigar-shaped Bose-Einstein condensate in the Gross-Pitaevskii mean-field approximation. Due to the instantaneous transformation to the rest-frame of the superfluid wave packet, the long-distance drop (100m) can be studied easily on a numerical grid.Comment: 18 pages latex, 5 eps figures, submitte

Can we enhance the ability to return to work among workers with stress-related disorders?

<p>Abstract</p> <p>Background</p> <p>Stress-related disorders are widespread and responsible for high societal costs e.g. sick leave payment and reduced productivity. The aim of this study was to evaluate the effect of an intervention program on return to work or labour market.</p> <p>Methods</p> <p>In a controlled interventional study design we compared 72 emotionally distressed patients, who received support during 2006, with 89 control individuals who had also been sick listed for emotional distress. Intervention was provided by trained psychologists and social workers who were in continuous dialog with the patients, providing counselling e.g. on decisions concerning resumption of work, support to families, participation in meetings with the workplace. Basically, the controls and the intervention group share the same access to welfare benefits. The main outcome was time to return to labour market (TTR).</p> <p>Results</p> <p>The baseline characteristics were similar in the two groups. There were no differences in the rate of resuming work between the two groups. About 80% in both groups had returned to the labour market after one year.</p> <p>Conclusion</p> <p>An intervention program with psychological stress management and case management did not improve work capability compared to usual care. Work resumption as a single outcome probably is an insensitive parameter of intervention management quality, and should be supplemented by other data on different aspects of treatment.</p

Development and evaluation of a strength-based method to promote employment of work-disability benefit recipients with multiple problems:A feasibility study

Background For people with disabilities, chances to find or keep work are negatively affected by multiple problems like lower education, poverty and poor health. Furthermore, although active labour market policies proved to be effective for unemployed in general, success rates are poor for persons who are unemployed due to multiple problems. The present study aims to describe the development of a method as well as professional training to teach its application, and to assess the feasibility of method and training. The Strength-based method (CARm) aims to promote employment of work-disability benefit recipients with multiple problems. Methods The main principles of the Strength model were redesigned for better applicability in a population of work-disability beneficiaries, resulting in the CARm method. As part of the CARm method, a training module for Labour Experts (LEs) was developed. To assess the new designed method and training, a one-group, pre-post design was used. Data were collected from eight participating LEs, five female and 3 male, aged between 41and 55 years and having 2–17 years working experience. We used self-report questionnaires and a semi-structured discussion meeting after the training sessions with the LEs. Results Eight labour experts (LEs) from the Dutch Social Security Institute participated in the study. Most LEs felt an improvement in their ability to ascertain developmental needs, opportunities and threats in the client’s situation. Three months after the training, LEs almost unanimously agreed on the statements ‘I expect to use the CARm method more frequently in the future’ and ‘I use the CARm method in daily practice whenever possible’. The overall rating for the training on a scale from 1 to 10 was 7.6 (range 7–9). The overall satisfaction with the trainers was good. Conclusions The CARm method and training was found to be a feasible approach to facilitate LEs working at the UWV reintegration service to support clients with multiple problems. Sufficient managerial support for participating LEs is a key factor for successful implementation of CARm. Results show that CARm is worth testing for efficacy in a future trial