Probing the Shape of Quantum Dots with Magnetic Fields

A tool for the identification of the shape of quantum dots is developed. By preparing a two-electron quantum dot, the response of the low-lying excited states to a homogeneous magnetic field, i.e. their spin and parity oscillations, is studied for a large variety of dot shapes. For any geometric configuration of the confinement we encounter characteristic spin singlet - triplet crossovers. The magnetization is shown to be a complementary tool for probing the shape of the dot.Comment: 11 pages, 4 figure

Zusammenfassende Dokumentation des Laborautomatisierungssystems Radar für die Analytik einer Kernbrennstoff Wiederaufarbeitungsanlage

This report represents the condensed documentation of the computer-based laboratory automation system RADRAR (Remote Analytical Data Acquisition and Reduction) for the analytical laboratory of a reprocessing facility for high temperature reactor fuel elements. The essential tasks of the system are on-line open-loop process control based on in-line measurements and automation of the offline analytical laboratory. The in-line measurements (at 55 tanks of the chemical process area) provide density-, liquid-, level-, and temperature values. The concentration value of a single component may easily be determined, if the solution consists of no more than two phases. The automation of the off-line analytical laboratory contains laboratory organization including sample management and data organization and computer-aided sample transportation control, data acquisition and data processing at chemical and nuclear analytical devices. The computer system consists of two computer-subsystems: a front end system for sample central registration and in-line process control and a central size system for the off-line analytical tasks. The organization of the application oriented system uses a centralized data base. Similar data processing functions concerning different analytical management tasks are structured into the following subsystem: man machine interface, interrupt- and data acquisition system, data base, protocol service and data processing. The procedures for the laboratory managernent (organization and experiment sequences) are defined by application data bases. Following the project phases, engineering requirements-, design-, assembly-, start up- and test run phase are described. In additionfigures on expenditure and experiences are given and the system concept is discussed

Farmer Participatory Early-Generation Yield Testing of Sorghum in West Africa: Possibilities to Optimize Genetic Gains for Yield in Farmers’ Fields

The effectiveness of on-farm and/or on-station early generation yield testing was examined to maximize the genetic gains for sorghum yield under smallholder famer production conditions in West Africa. On-farm first-stage yield trials (augmented design, 150 genotypes with subsets of 50 genotypes tested per farmer) and second-stage yield trials (replicated α-lattice design, 21 test genotypes) were conducted, as well as on-station α-lattice first- and second-stage trials under contrasting phosphorous conditions. On-farm testing was effective, with yield showing significant genetic variance and acceptable heritabilities (0.56 in first- and 0.61 to 0.83 in second-stage trials). Predicted genetic gains from on-station yield trials were always less than from direct testing on-farm, although on-station trials under low-phosphorus and combined over multiple environments improved selection efficiencies. Modeling alternative designs for on-farm yield testing (augmented, farmer-as-incomplete-block, multiple lattice, and augmented p-rep) indicated that acceptable heritabilities (0.57 to 0.65) could be obtained with all designs for testing 150 progenies in 20 trials and 75 plots per farmer. Ease of implementation and risk of errors would thus be key criteria for choice of design. Integrating results from on-station and on-farm yield testing appeared beneficial as progenies selected both by on-farm and on-station first-stage trials showed higher on-farm yields in second-stage testing

Induction of Apoptosis and T Helper 2 (Th2) Responses Correlates with Peptide Affinity for the Major Histocompatibility Complex in Self-reactive T Cell Receptor Transgenic Mice

Multiple sclerosis is an autoimmune disease thought to be mediated by CD4+ T helper cells (Th). Experimental autoimmune encephalomyelitis is a rodent model of multiple sclerosis and has been used extensively to explore a variety of immunotherapies using soluble protein or peptide antigens. The underlying mechanisms of such therapy have been attributed to induction of T cell anergy, a switch in Th1 to Th2 responses, or peripheral deletion of autoreactive T cells. In this study, we have developed transgenic mice expressing a T cell receptor (TCR) specific for the NH2-terminal peptide Ac1-11 of the autoantigen myelin basic protein to explore the mechanism of soluble peptide therapy. T cells from these mice are highly skewed toward the CD4 population and have an abnormal thymic architecture, a phenomenon found in other TCR transgenic mice that exhibit a highly skewed CD4/CD8 ratio. Soluble Ac1-11 or the analogues Ac1-11[4A] or Ac1-11[4Y] (which bind to the major histocompatibility complex [MHC] class II molecule I-Au with increasing affinities) given intravenously activates T cells, rendering cells hyperresponsive in vitro for at least two days after injection. Concomitantly, T cells apoptose in the periphery, the degree of which correlates with the affinity of the peptide for the MHC. In addition, a shift in the T helper phenotype of the surviving T cells occurs such that the low affinity peptide, Ac1-11, induces primarily a Th1 response, whereas the highest affinity peptide, Ac1-11[4Y], induces primarily a Th2 type response. These data show that both the nature and the presumed number of the peptide–MHC complexes formed during specific peptide therapy affect both the degree of peripheral programmed cell death as well as the outcome of the T helper subset response in vivo, leading to amelioration of disease