Die Bestimmungsgründe der räumlichen Verteilung des ökologischen Landbaus in Deutschland

Die Bestimmungsgründe der räumlichen Verteilung des ökologischen Landbaus sind nicht eindeutig geklärt. Daher werden verschiedene Faktoren hinsichtlich ihres Einflusses auf den Flächenanteil und die regionale Verteilung des ökologischen Landbaus in Deutschland untersucht. In diesem Beitrag werden erste und in einigen Punkten noch vorläufige Ergebnisse eines laufenden Forschungsprojektes dargestellt

Observation of extremely slow hole spin relaxation in self-assembled quantum dots

We report the measurement of extremely slow hole spin relaxation dynamics in small ensembles of self-assembled InGaAs quantum dots. Individual spin orientated holes are optically created in the lowest orbital state of each dot and read out after a defined storage time using spin memory devices. The resulting luminescence signal exhibits a pronounced polarization memory effect that vanishes for long storage times. The hole spin relaxation dynamics are measured as a function of external magnetic field and lattice temperature. We show that hole spin relaxation can occur over remarkably long timescales in strongly confined quantum dots (up to ~270 us), as predicted by recent theory. Our findings are supported by calculations that reproduce both the observed magnetic field and temperature dependencies. The results suggest that hole spin relaxation in strongly confined quantum dots is due to spin orbit mediated phonon scattering between Zeeman levels, in marked contrast to higher dimensional nanostructures where it is limited by valence band mixing.Comment: Published by Physical Review

Verarbeitung und Vermarktung von ökologischem Schweinefleisch in Baden-Württemberg

Die Zielsetzung dieser Arbeit ist, Qualitätsansprüche an ökologisch erzeugtes Schweinefleisch und dessen Verarbeitungsprodukte aufzuzeigen. Dabei sollen einerseits die Qualitätsansprüche und mögliche Probleme auf der Verbraucherebene erfasst und andererseits auf der Verarbeiterebene auftretende Probleme hinsichtlich des Bezugs, der Verarbeitung und Vermarktung von Ökoschweinefleisch und Ökoschweinefleischerzeugnissen aufgezeigt werden. Um Informationen zur Thematik zu erhalten, wurden Verbraucher und Verarbeiter unabhängig voneinander befragt. Die Befragungen der Verbraucher und Verarbeiter erfolgte im Großraum Stuttgart

On the Convergence of Learning Algorithms in Bayesian Auction Games

Equilibrium problems in Bayesian auction games can be described as systems of differential equations. Depending on the model assumptions, these equations might be such that we do not have a rigorous mathematical solution theory. The lack of analytical or numerical techniques with guaranteed convergence for the equilibrium problem has plagued the field and limited equilibrium analysis to rather simple auction models such as single-object auctions. Recent advances in equilibrium learning led to algorithms that find equilibrium under a wide variety of model assumptions. We analyze first- and second-price auctions where simple learning algorithms converge to an equilibrium. The equilibrium problem in auctions is equivalent to solving an infinite-dimensional variational inequality (VI). Monotonicity and the Minty condition are the central sufficient conditions for learning algorithms to converge to an equilibrium in such VIs. We show that neither monotonicity nor pseudo- or quasi-monotonicity holds for the respective VIs. The second-price auction's equilibrium is a Minty-type solution, but the first-price auction is not. However, the Bayes--Nash equilibrium is the unique solution to the VI within the class of uniformly increasing bid functions, which ensures that gradient-based algorithms attain the {equilibrium} in case of convergence, as also observed in numerical experiments

Nerve Terminal Degeneration Is Independent of Muscle Fiber Genotype in SOD1G93A Mice

Background: Motor neuron degeneration in SOD1 G93A transgenic mice begins at the nerve terminal. Here we examine whether this degeneration depends on expression of mutant SOD1 in muscle fibers. Methodology/Principal Findings: Hindlimb muscles were transplanted between wild-type and SOD1 G93A transgenic mice and the innervation status of neuromuscular junctions (NMJs) was examined after 2 months. The results showed that muscles from SOD1 G93A mice did not induce motor terminal degeneration in wildtype mice and that muscles from wildtype mice did not prevent degeneration in SOD1 G93A transgenic mice. Control studies demonstrated that muscles transplanted from SOD1 G93A mice continued to express mutant SOD1 protein. Experiments on wildtype mice established that the host supplied terminal Schwann cells (TSCs) at the NMJs of transplanted muscles. Conclusions/Significance: These results indicate that expression of the mutant protein in muscle is not needed to cause motor terminal degeneration in SOD1 G93A transgenic mice and that a combination of motor terminals, motor axons and Schwann cells, all of which express mutant protein may be sufficient

Analysis of the temperature-dependent quantum point contact conductance in view of the metal-insulator transition in two dimensions

The temperature dependence of the conductance of a quantum point contact has been measured. The conductance as a function of the Fermi energy shows temperature-independent fixed points, located at roughly multiple integers of $e^{2}/h$. Around the first fixed point at e$^{2}$/h, the experimental data for different temperatures can been scaled onto a single curve. For pure thermal smearing of the conductance steps, a scaling parameter of one is expected. The measured scaling parameter, however, is significantly larger than 1. The deviations are interpreted as a signature of the potential landscape of the quantum point contact, and of the source-drain bias voltage. We relate our results phenomenologically to the metal-insulator transition in two dimensions.Comment: 5 pages, 3 figure

Spatial modulation of dark versus bright stimulus responses in the mouse visual system

A fundamental task of the visual system is to respond to both increases and decreases of luminance with action potentials (ON and OFF responses1–4). OFF responses are stronger, faster, and more salient than ON responses in primary visual cortex (V1) of both cats5,6 and primates,7,8 but in ferrets9 and mice,10 ON responses can be stronger, weaker,11 or balanced12 in comparison to OFF responses. These discrepancies could arise from differences in species, experimental techniques, or stimulus properties, particularly retinotopic location in the visual field, as has been speculated;9 however, the role of retinotopy for ON/OFF dominance has not been systematically tested across multiple scales of neural activity within species. Here, we measured OFF versus ON responses across large portions of visual space with silicon probe and whole-cell patch-clamp recordings in mouse V1 and lateral geniculate nucleus (LGN). We found that OFF responses dominated in the central visual field, whereas ON and OFF responses were more balanced in the periphery. These findings were consistent across local field potential (LFP), spikes, and subthreshold membrane potential in V1, and were aligned with spatial biases in ON and OFF responses in LGN. Our findings reveal that retinotopy may provide a common organizing principle for spatial modulation of OFF versus ON processing in mammalian visual systems