Jens Dietrich

Stochastic Processes during Mouse Blastocyst Patterning

Mammalian preimplantation development serves to form a blastocyst, a structure that is able to implant into the mother’s uterus to support further development of the embryo proper. In the developing conceptus, the first differentiation events separate the epithelial trophectoderm from the inner cell mass, which is comprised of the primitive endoderm and embryo-generating epiblast. Although the process of blastocyst formation may appear simple, its morphogenesis and the mechanism(s) of lineage specification are not yet fully understood. Here we discuss findings that suggest the involvement of stochastic processes and the influence of external cues in the patterning process during mouse preimplantation development.

Origins of electrostatic potential wells at dislocations in polycrystalline Cu(In,Ga)Se2 thin films

Thin-film solar cells based on Cu(In,Ga)Se2 (CIGSe) reach high power-conversion efficiencies in spite of large dislocation densities of up to 1010–1011 cm−2. The present work gives insight into the structural and compositional properties of dislocations in CIGSe thin films, which are embedded in a complete solar cell stack. These properties are related to the average electrical potential distributions obtained by means of inline electron holography. At a part of the dislocations studied, the average electrostatic potential shows local minima, all with depths of about −1.4 V. The measured average electrostatic potential distributions were modeled in order to reveal possible influences from strain fields, excess charge, and also compositional changes at the dislocation core. Cu depletion around the dislocation core, as evidenced by atom-probe tomography, explains best the measured potential wells. Their influences of the strain field around the dislocation core and of excess charge at the dislocation core are small. A structural model of dislocations in CIGSe thin films is provided which includes a Cu-depleted region around the dislocation core and gives a possible explanation for why decent photovoltaic performances are possible in the presence of rather large dislocation densities.

Strategies for two-dimensional crystallization of proteins using lipid monolayers

Strategies for Two-Dimensional Crystallization of Proteins Using Lipid Monolayers presents an overview of different methods that lead to structure determination by electron microscopy. These methods have proven to be extremely successful, especially for elucidating the structure of membrane proteins. Electron crystallography has become an important tool for structure determination of such proteins. This book covers the different practical approaches to two-dimensional crystallization of soluble as well as membrane proteins. From there it takes the reader to equally important issues, such as sample transfer and sample preparation for electron microscopy. In addition, the text provides an introduction to membrane protein structural biology and cryo-electron crystallography, as well as an in-depth discussion on two-dimensional crystallization and surface crystallization.

Compositional Gradients in Cu(In,Ga)Se

Cu(In,Ga)Se

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Thin Films for Solar Cells and Their Effects on Structural Defects

(CIGSe) absorber layers used in thin-film solar cells exhibit, when grown in a multistage process, compositional gradients of Ga and In. In this study, the correlations between the Ga gradient and the microstructure are studied by means of transmission electron microscopy (TEM) imaging combined with energy-dispersive X-ray spectroscopy (EDX), allowing the determination of structural defects and elemental distributions at identical sample positions. The occurrence of linear defects (dislocations) and planar defects (stacking faults and microtwins) of CIGSe layers was studied by means of TEM images. The Ga distributions obtained from EDX elemental distribution maps and structural parameters from the literature were used to calculate the lattice parameters c and a and the gradient dc/ dx perpendicular to the substrate. We found a correlation between the magnitude of dc/dx and the occurrence of dislocations within individual large grains. From the presented results, a threshold value of the Ga gradient of 12–13at.%/μm can be estimated for the formation of misfit dislocations.

Purification and two-dimensional crystallization of highly active cytochrome b 6 f complex from spinach

The purification and two‐dimensional crystallization of highly active cytochrome b 6 f complex from spinach is described. The preparation shows all spectroscopic characteristics of the pure complex. The electron transfer activity of 450±60 electrons per s is the highest in vitro activity reported to date. Using dimethyl sulfoxide (DMSO) as a solvent for the electron donor enhanced the performance and reproducibility of the assay. The high yield and the high activity of the protein make it an ideal candidate for biophysical and structural studies. Preliminary two‐dimensional crystallization experiments yielded several different forms of two‐dimensional and thin three‐dimensional crystals, exhibiting varying degrees of order.

Transformation einer industriell geprägten Unternehmensstruktur zu einer service- und wissensbasierten Organisation

Unternehmungen sind heute wie fruher den vielschichtigen Veranderungen ihrer Umfelder ausgesetzt. Als aktuelle Herausforderungen hervorgehoben seien hier die Globalisierung, Technisierung und Okologisierung1 verbunden mit einer wachsenden Dynamik und Komplexitat.2 Die daraus folgende Notwendigkeit schneller und zugleich fundierter Entscheidungen verknupft mit dem kontinuierlich steigenden Druck zu Produkt- und Prozessinnovationen stellt damit hohe Anforderungen an die Reagibilitat der eigenen Fuhrungs-, Leistungs- und Unterstutzungsprozesse und ist ein akutes Managementproblem (Abbildung 1).

Effect of compositional gradients on structural defects in Cu(In, Ga)Se 2 thin films for solar cells

The objective of this work is to study the influence of compositional gradients on the microstructure of Cu(In, Ga)Se2 (CIGSe) absorber layers for thin-film solar cells. The deposition of CIGSe films in a multi-stage coevaporation process leads to compositional gradients of gallium and indium, in dependence on process parameters such as the integral gallium content. Transmission electron microscopy (TEM) imaging combined with energy-dispersive X-ray spectroscopy (EDX) enables the determination of structural defects and elemental distributions at identical sample positions. The occurrence of linear (dislocations) and planar defects (stacking faults, microtwins) is studied by means of TEM images along the length of the CIGSe layers. The spatial distribution of the grains is given by electron-backscatter diffraction (EBSD) pattern-quality maps. Elemental distribution maps obtained by EDX exhibit strong Ga/In gradients inside a single large grain along the absorber depth. However, the CIGSe film shows no lateral variations within our measurement accuracy parallel to the substrate inside the grains or in the vicinity of the grain boundaries.