Electrical characterization of zirconium silicate films obtained from novel MOCVD precursors

In the present work, the potential of zirconium silicate (ZrSi_xO_y) films as an alternative gate dielectric to SiO₂ for future technology generations is demonstrated. Novel single-source precursors for MOCVD of zirconium silicate were synthesized and ZrSi_xO_y layers were deposited. I–V and C–V measurement data are presented and detected charge trapping phenomena are discussed.     

Epigenetic reprogramming in embryonic and foetal development upon somatic cell nuclear transfer cloning

The birth of 'Dolly', the first mammal cloned from an adult donor cell, has sparked a flurry of research activities to improve cloning technology and to understand the underlying mechanism of epigenetic reprogramming of the transferred somatic cell nucleus. Especially in ruminants, somatic cell nuclear transfer (SCNT) is frequently associated with pathological changes in the foetal and placental phenotype and has significant consequences for development both before and after birth. The most critical factor is epigenetic reprogramming of the transferred somatic cell nucleus from its differentiated status into the totipotent state of the early embryo. This involves an erasure of the gene expression program of the respective donor cell and the establishment of the well-orchestrated sequence of expression of an estimated number of 10 000-12 000 genes regulating embryonic and foetal development. The following article reviews the present knowledge on the epigenetic reprogramming of the transferred somatic cell nucleus, with emphasis on DNA methylation, imprinting, X-chromosome inactivation and telomere length restoration in bovine development. Additionally, we briefly discuss other approaches towards epigenetic nuclear reprogramming, including the fusion of somatic and embryonic stem cells and the overexpression of genes crucial in the formation and maintenance of the pluripotent status. Improvements in our understanding of this dramatic epigenetic reprogramming event will be instrumental in realising the great potential of SCNT for basic biological research and for various agricultural and biomedical applications.     

Membranen in der medizinischen Verfahrenstechnik

Membranes in medical process engineering . Synthetic membranes not only represent the essential components of an artificial kidney or an artificial lung but are also used as wound dressing and in systems for controlled release of drugs in certain long-term therapeutic measures or as part of an artificial pancreas. By far the greatest present economic significance of membranes is their use in the so-called artificial kidney. Considerable cost saving would result if patients could undertake ?home dialysis”?. This requires the development of new, simpler artificial kidneys and thus higher-performance membranes. The latest trend in ?artificial kidneys”?, the so-called method of ?hemodiafiltration”? warants special mention. The separation process is no longer effected only by diffusion but also by convection, i.e. the driving force is the pressure difference between the two sides of the membrane. This paper addresses problems encountered in the development and use of membranes in medicine, recent applications such as the controlled release of active components, or plasma separation, and demonstrates the potential of membranes in medicine.     

Nanoscale Thermometry with a Quantum Dot

A two-terminal quantum dot bridging a temperature difference can operate as a thermometer by probing the Fermi-Dirac distributions of the electron gas on both sides of the quantum dot. This thermometry requires that the dot’s energy levels are spaced in energy by many kT and that the intrinsic energetic width of the energy resonances are either much larger or much smaller than kT. We compare these two regimes of operation and discuss the intermediate regime which separates them. Quantum-dot thermometry can assist in mesoscopic thermal experiments where short-distance temperature gradients elude most thermometry techniques.     

Recovery of groundwater N2O at the soil surface and its contribution to total N2O emissions

Production and accumulation of the major greenhouse gas nitrous oxide (N₂O) in surface groundwater might contribute to N₂O emissions to the atmosphere. We report on a ¹⁵N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K¹⁵NO₃ tracer solution (60 atom%) was applied to the surface groundwater on an 8 m² measuring plot using 45 injection points in order to stimulate production of ¹⁵N₂O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N₂O fluxes at the soil surface were low and in a range between ?7.6 and 29.1 μg N₂O-N m^?2 h^?1. ¹⁵N enrichment of N₂O decreased considerably upwards in the profile. In the surface groundwater, we found a ¹⁵N enrichment of N₂O between 13 and 42 atom%. In contrast, ¹⁵N enrichment of N₂O in flux chambers at the soil surface was very low, but a detectable ¹⁵N enrichment was found at all sampling events. Fluxes of groundwater-derived ¹⁵N-N₂O were very low and ranged between 0.0002 and 0.0018 kg N₂O-N ha^?1 year^?1, indicating that indirect N₂O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N₂O dynamics at the soil–atmosphere interface is predominantly governed by topsoil parameters. However, highest ¹⁵N enrichments of N₂O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table. We assume that such fluctuations may enhance diffusive N₂O fluxes from the surface groundwater to the atmosphere for a short time.     

Diffusion-weighted MRI in sporadic Creutzfeldt-Jakob disease

Diffusion-weighted MRI (DWI) was used in three patients with autopsy-proven sporadic Creutzfeldt-Jakob disease (CJD) to provide a rapid noninvasive way to make this sometimes confusing diagnosis. DWI prompted the diagnosis of CJD at an early stage and appears to be particularly useful for monitoring the progression of the disease. We suggest that patients with suspected CJD and no abnormalities on T2- and proton density-weighted images may have cortical involvement on DWI.     

The role of collagen in bone apatite formation in the presence of hydroxyapatite nucleation inhibitors

Bone is a composite material in which collagen fibrils form a scaffold for a highly organized arrangement of uniaxially oriented apatite crystals. In the periodic 67 nm cross-striated pattern of the collagen fibril, the less dense 40-nm-long gap zone has been implicated as the place where apatite crystals nucleate from an amorphous phase, and subsequently grow. This process is believed to be directed by highly acidic non-collagenous proteins; however, the role of the collagen matrix during bone apatite mineralization remains unknown. Here, combining nanometre-scale resolution cryogenic transmission electron microscopy and cryogenic electron tomography with molecular modelling, we show that collagen functions in synergy with inhibitors of hydroxyapatite nucleation to actively control mineralization. The positive net charge close to the C-terminal end of the collagen molecules promotes the infiltration of the fibrils with amorphous calcium phosphate (ACP). Furthermore, the clusters of charged amino acids, both in gap and overlap regions, form nucleation sites controlling the conversion of ACP into a parallel array of oriented apatite crystals. We developed a model describing the mechanisms through which the structure, supramolecular assembly and charge distribution of collagen can control mineralization in the presence of inhibitors of hydroxyapatite nucleation.