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

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

Development of an information platform for new grid users in the biomedical field

Bringing new users into grids is a top priority for all grid initiatives and one of the most challenging tasks. Especially in life sciences it is essential to have a certain amount of users to establish a critical mass for a sustainable grid and give feedback back to the technological middleware layer. Based on the presumable lack of grid IT knowledge it is notably more arduous to satisfy user demands although here the requirements are especially demanding. Therefore, the development of an information- and learning platform could support the efforts of grid experts to guide new users. By providing a platform about grid technology and their feasibilities for users of the community of biomedicine potential, users could be supported using the high potential of their discipline

Development of an information platform for new grid users in the biomedical field

Bringing new users into grids is a top priority for all grid initiatives and one of the most challenging tasks. Especially in life sciences it is essential to have a certain amount of users to establish a critical mass for a sustainable grid and give feedback back to the technological middleware layer. Based on the presumable lack of grid IT knowledge it is notably more arduous to satisfy user demands although here the requirements are especially demanding. Therefore, the development of an information- and learning platform could support the efforts of grid experts to guide new users. By providing a platform about grid technology and their feasibilities for users of the community of biomedicine potential, users could be supported using the high potential of their discipline

Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer Quantized-Hall Regime

The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs heterostructure is studied (in the clean limit) where the 2D electron-gas (2DEG), being in an odd-integer quantum-Hall state, is in fact a spin dielectric. Of the two channels of phonon absorption associated with excitation of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons, involves a change of the spin state of the system and the other does not. We show that the phonon-absorption rate corresponding to the former channel (in the paper designated as the second absorption channel) is finite at zero temperature ($T$), whereas that corresponding to the latter (designated as the first channel) vanishes for $T\to 0$. The long-wavelength limit, being the special case of the first absorption channel, corresponds to sound (bulk and surface) attenuation by the 2DEG. At the same time, the ballistic phonon propagation and heat absorption are determined by both channels. The 2DEG overheat and the attendant spin-state change are found under the conditions of permanent nonequilibrium phonon pumping.Comment: 26 pages, 2 figure

Antiphased Cyclotron-Magnetoplasma Mode in a Quantum Hall System

An antiphased magnetoplasma (MP) mode in a two-dimensional electron gas (2DEG) has been studied by means of inelastic light scattering (ILS) spectroscopy. Unlike the cophased MP mode it is purely quantum excitation which has no classic plasma analogue. It is found that zero momentum degeneracy for the antiphased and cophased modes predicted by the first-order perturbation approach in terms of the {\it e-e} interaction is lifted. The zero momentum energy gap is determined by a negative correlation shift of the antiphased mode. This shift, observed experimentally and calculated theoretically within the second-order perturbation approach, is proportional to the effective Rydberg constant in a semiconductor material.Comment: Submitted to Phys. Rev.

Valency of rare earths in RIn3 and RSn3: Ab initio analysis of electric-field gradients

In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a 111Cd impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of the system.Comment: 10 page

Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)