Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei

Spin relaxation in quantum Hall ferromagnet regimes is studied. As the initial non-equilibrium state, a coherent deviation of the spin system from the ${\vec B}$ direction is considered and the breakdown of this Goldstone-mode state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring non-exponentially with time is studied in terms of annihilation processes in the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate is calculated analytically even if the initial deviation is not small. This relaxation channel competes with the relaxation mechanisms due to spin-orbit coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page

Key signal contributions in photothermal deflection spectroscopy

We report on key signal contributions in photothermal deflection spectroscopy (PDS) of semiconductors at photon energies below the bandgap energy and show how to extract the actual absorption properties from the measurement data. To this end, we establish a rigorous computation scheme for the deflection signal including semi-analytic raytracing to analyze the underlying physical effects. The computation takes into account linear and nonlinear absorption processes affecting the refractive index and thus leading to a deflection of the probe beam. We find that beside the linear mirage effect, nonlinear absorption mechanisms make a substantial contribution to the signal for strongly focussed pump beams and sample materials with high two-photon absorption coefficients. For example, the measured quadratic absorption contribution exceeds 5% at a pump beam intensity of about ${1.3}\times{10^{5}}\;{W}/{cm^{2}}$ in Si and at ${5}\times{10^{4}}\;{W}/{cm^{2}}$ in GaAs. In addition, our method also includes thermal expansion effects as well as spatial gradients of the attenuation properties. We demonstrate that these effects result in an additional deflection contribution which substantially depends on the distance of the photodetector from the readout point. This distance dependent contribution enhances the surface related PDS signal up to two orders of magnitude and may be misinterpreted as surface absorption if not corrected in the analysis of the measurement data. We verify these findings by PDS measurements on crystalline silicon at a wavelength of 1550 nm and provide guidelines how to extract the actual attenuation coefficient from the PDS signal.Comment: 10 pages, 16 figures, submitted to Journal of Applied Physiv

Sensor Concept for Controlled Laser Cleaning via Photodiode

Abstract. In the field of laser cleaning of artworks the effect of “over-cleaning” is a commonly well known problem. The detection of laser induced plasma is one possibility in order to identify the kind of material just being irradiated by the laser beam. LIBS is a powerful method for the extraction of spectral information. Instead the detection of the plasma intensity contains much less information. However, this can be realised by using a fast photodiode. It has turned out that for several applications in laser cleaning of artworks a reliable identification of layers during the cleaning process is possible. In cooperation with restorers we proved that this low-cost method may be used for online monitoring as well as automated closed loop cleaning.

Bound States in a Quantized Hall Ferromagnet

We report on a study of the quasielectron-quasihole and skyrmion-antiskyrmion bound states in the $\nu=1$ quantum Hall regime. The short range attraction potential is assumed to be determined by a point magnetic impurity. The calculations are performed within the strong field approximation when the binding energy and the characteristic electron-electron interaction energy are smaller than the Landau level spacing. The Excitonic Representation technique is used in that case.Comment: 8 page

Comment on "Spin relaxation in quantum Hall systems"

W. Apel and Yu.A. Bychkov have recently considered the spin relaxation in a 2D quantum Hall system for the filling factor close to unity [PRL v.82, 3324 (1999)]. The authors considered only one spin flip mechanism (direct spin-phonon coupling) among several possible spin-orbit related ones and came to the conclusion that the spin relaxation time due to this mechanism is quite short: around $10^{-10}$ s at B=10 T (for GaAs). This time is much shorter than the typical time ($10^{-5}$ s) obtained earlier by D. Frenkel while considering the spin relaxation of 2D electrons in a quantizing magnetic field without the Coulomb interaction and for the same spin-phonon coupling. I show that the authors' conclusion about the value of the spin-flip time is wrong and have deduced the correct time which is by several orders of magnitude longer. I also discuss the admixture mechanism of the spin-orbit interaction.Comment: 1 pag

Re-thinking risk communication: information needs of patients, health professionals and the public regarding MRSA – the communicative behaviour of a public health network in Germany responding to the demand for information

Objectives: Multidrug resistant organisms (MDRO), including Meticillin-resistant Staphylococcus aureus (MRSA), and health care associated infections (HCAIs) are pressing issues for health care systems across the world. Information and communication are considered key tools for the prevention and management of infectious diseases. Public Health Authorities (PHA) are in a unique position to communicate with health care professionals, patients and the public regarding the health risks. Study design: We used PHA helpdesk interaction data to first ascertain the information requirements of those getting in contact with the service, and secondly to examine the communicative behaviour of the PHA, with a view to improving the quality of communication strategies. Methods: Data on helpdesk interactions between 2010 and 2012 were obtained from a MDRO network of nine German PHAs. 501 recordings were coded and descriptive statistics generated for further qualitative thematic analysis. Results: Our analysis revealed a similar pattern of questions among different groups. Key areas of need for information were around eradication, cleaning and isolation measures. Reported problems were a lack of expert knowledge and continuity of treatment. The helpdesk response was mainly a conversation offering scientific advice, but also included other communication services that went beyond the provision of scientific facts, such as follow-up calls, referral suggestions and consultations on behalf of the caller. These social communication activities seem to have an important impact on the acceptability of public health recommendations and use of the helpdesk

EMC studies on systems with hybrid filter circuits for modern aircraft applications

In this contribution, a new approach for EMC-filter design is presented. Due to the increasing electrification of modern aircraft, as a result of the More Electric Aircraft concept, new strategies and approaches are required to fulfill the strict EMC aircraft standards (DO-160/ED-14 – Sec. 20). Consequently the weight and volume of the used filter components can be reduced. A promising approach could be a combination of passive and active filters. For the same attenuation effect, so-called hybrid filters achieve either savings in weight and volume, or can obtain an additional filtering effect with minimal weight increase of an existing system. In this paper, the underlying theory is explained in detail, carried out in a simulation tool and the gained insight is demonstrated with a sample measurement

Re-thinking risk communication: information needs of patients, health professionals and the public regarding MRSA – the communicative behaviour of a public health network in Germany responding to the demand for information

Objectives: Multidrug resistant organisms (MDRO), including Meticillin-resistant Staphylococcus aureus (MRSA), and health care associated infections (HCAIs) are pressing issues for health care systems across the world. Information and communication are considered key tools for the prevention and management of infectious diseases. Public Health Authorities (PHA) are in a unique position to communicate with health care professionals, patients and the public regarding the health risks. Study design: We used PHA helpdesk interaction data to first ascertain the information requirements of those getting in contact with the service, and secondly to examine the communicative behaviour of the PHA, with a view to improving the quality of communication strategies. Methods: Data on helpdesk interactions between 2010 and 2012 were obtained from a MDRO network of nine German PHAs. 501 recordings were coded and descriptive statistics generated for further qualitative thematic analysis. Results: Our analysis revealed a similar pattern of questions among different groups. Key areas of need for information were around eradication, cleaning and isolation measures. Reported problems were a lack of expert knowledge and continuity of treatment. The helpdesk response was mainly a conversation offering scientific advice, but also included other communication services that went beyond the provision of scientific facts, such as follow-up calls, referral suggestions and consultations on behalf of the caller. These social communication activities seem to have an important impact on the acceptability of public health recommendations and use of the helpdesk