Monolayers of graphite rotated by a defined angle: hexagonal superstructures by STM

Received: 27 March 1998     

1-Ethoxycarbonyl-3-ferrocenyl-propan-1,3-dion und Ferrocen-1,1'bis(2,4-dioxobutansäureethylester) als Liganden für Übergangsmetallionen. Kristallstruktur von Bis(1-ethoxycarbonyl-3-ferrocenyl-propan-1,3dionato)kupfer(II)

1-Ethoxycarbonyl-3-ferrocenyl-propane-1,3-dion and Ferrocene-1,1′bis(2,4-dioxobutanoic acid ethylester) as Ligands for Transition Metal Ions. Crystal Structure of Bis(1-ethoxycarbonyl-3-ferrocenyl-propane-1,3dionato)copper(II) The ligands 1-ethoxycarbonyl-3-ferrocenyl-propane-1,3-dion and ferrocene-1,1′-bis(2,4-dioxo-butanoic acid ethylester) have been prepared by reaction of acetylferrocene or 1,1′-diacetylferrocene and diethyl oxalate. They yield neutral chelates with Cu^II, Ni^II, Zn^II, Co^II, and Mn^II. The acid dissociation constants of the ligands and the stability constants of their metal complexes including Fe^II complexes are reported. The structure of bis(1-ethoxycarbonyl-3-ferrocenyl-propane-1,3-dionato)copper(II) was determined by X-ray structure analysis. A cis arrangement with a nearly square planar coordination sphere at the Cu atom is found.     

Deep levels in low‐energy electron‐irradiated 4H‐SiC

Deep levels introduced by low‐energy (200 keV) electron irradiation in n‐type 4H‐SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo‐EPR). After irradiation, several DLTS levels, EH1, EH3, Z_1/2, EH5 and EH6/7, often reported in irradiated 4H‐SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, V_C⁺ and V_C^‐, respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo‐EPR, we suggest that the EH6/7 (at ～E_C – 1.6 eV) and EH5 (at ～E_C – 1.0 eV) electron traps may be related to the single donor (+ | 0) and the double acceptor (1– | 2–) level of V_C, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Samuel compactification for quasi-uniform biframes

The paircover approach is used to explore the links between quasi-uniform and proximal biframes. The Samuel compactification for quasi-uniform biframes is constructed and its universal property discussed.     

The effect of the diphosphine basicity on the excited-state properties of trans-(N2)2W(R2PCH2CH2PR2)2: identification of near-degenerate, luminescent 3MLCT and 3LF terms

Absorption spectra (77 and 298 K), luminescence spectra (5-80 K), and luminescence lifetimes (5-80 K) for the title complexes have been correlated to increasing diphosphine basicity (R = 4-CF(3)-Ph < 4-H-Ph < 4-CH(3)O-Ph < Et). As a consequence, spectral peaks have been assigned to (1,3)MLCT (B(1u), W --> phosphorus) and (1,3)LF (B(2g)) terms. As the ligand basicity increases, the (3)MLCT bands observed in absorption blue-shift nearly 8000 cm(-1) and the vibrationally structured (3)LF bands observed in emission red-shift approximately 1300 cm(-1). (3)LF terms lie lowest in energy in the 4-H-Ph, 4-CH(3)O-Ph, and Et compounds, and temperature-dependent lifetime data suggest emission from each be assigned to the equilibrated, spin-orbit split levels of the (3)LF term. The (3)LF and (3)MLCT excited-state terms lie close in energy in the 4-CF(3)-Ph compound, resulting in an emission band shape that is temperature-dependent. At 77 K, the emission band is broad and structureless and is assigned to arise primarily from the (3)MLCT term. As the temperature is lowered toward 5 K, the (3)MLCT emission diminishes in intensity accompanied by the development of a vibrational structure that is characteristic of emission from the (3)LF term. These excited-state terms satisfy the requirements (different orbital origins, near-degeneracy) for separation by a Franck-Condon energy barrier, resulting in simultaneous emission from both terms between 5 and 77 K.     

Technical aspects and evaluation methodology for the application of two automated brain MRI tumor segmentation methods in radiation therapy planning

The purpose of this study was to design the steps necessary to create a tumor volume outline from the results of two automated multispectral magnetic resonance imaging segmentation methods and integrate these contours into radiation therapy treatment planning. Algorithms were developed to create a closed, smooth contour that encompassed the tumor pixels resulting from two automated segmentation methods: k-nearest neighbors and knowledge guided. These included an automatic three-dimensional (3D) expansion of the results to compensate for their undersegmentation and match the extended contouring technique used in practice by radiation oncologists. Each resulting radiation treatment plan generated from the automated segmentation and from the outlining by two radiation oncologists for 11 brain tumor patients was compared against the volume and treatment plan from an expert radiation oncologist who served as the control. As part of this analysis, a quantitative and qualitative evaluation mechanism was developed to aid in this comparison. It was found that the expert physician reference volume was irradiated within the same level of conformity when using the plans generated from the contours of the segmentation methods. In addition, any uncertainty in the identification of the actual gross tumor volume by the segmentation methods, as identified by previous research into this area, had small effects when used to generate 3D radiation therapy treatment planning due to the averaging process in the generation of margins used in defining a planning target volume.     

Impurities in thin-film silicon: Influence on material properties and solar cell performance

The influence of oxygen and nitrogen impurities on the material properties of a-Si:H and μc-Si:H films and on the corresponding solar cell performances was studied. For intentional contamination of the i-layer the impurities were inserted by two contamination sources: (i) directly into the plasma through a leak at the chamber wall or (ii) into the gas supply line. The critical oxygen and nitrogen concentrations for silicon solar cells were determined as the lowest concentration of these impurities in the i-layer causing a deterioration of the cell performance. Similar critical concentrations for a-Si:H and μc-Si:H cells in the range of 4–6 × 10¹⁸ cm^? 3 for nitrogen and 1–5 × 10¹⁹ cm^? 3 for oxygen by applying a chamber leak are observed. Similar increase of conductivity with increasing impurity concentration in the a-Si:H and μc-Si:H films is found. A more detailed study shows that the critical oxygen concentration depends on the contamination source and the deposition parameters. For a-Si:H cells, the application of the gas pipe leak leads to an increased critical oxygen concentration to 2 × 10²⁰ cm^? 3. Such an effect was not observed for nitrogen. For μc-Si:H, a new deposition regime with reduced discharge power was found where the application of the gas pipe leak can also result in an increase of the oxygen concentration to 1 × 10²⁰ cm^? 3.     

Substantial improvements in large-scale redocking and screening using the novel HYDE scoring function

The HYDE scoring function consistently describes hydrogen bonding, the hydrophobic effect and desolvation. It relies on HYdration and DEsolvation terms which are calibrated using octanol/water partition coefficients of small molecules. We do not use affinity data for calibration, therefore HYDE is generally applicable to all protein targets. HYDE reflects the Gibbs free energy of binding while only considering the essential interactions of protein-ligand complexes. The greatest benefit of HYDE is that it yields a very intuitive atom-based score, which can be mapped onto the ligand and protein atoms. This allows the direct visualization of the score and consequently facilitates analysis of protein-ligand complexes during the lead optimization process. In this study, we validated our new scoring function by applying it in large-scale docking experiments. We could successfully predict the correct binding mode in 93% of complexes in redocking calculations on the Astex diverse set, while our performance in virtual screening experiments using the DUD dataset showed significant enrichment values with a mean AUC of 0.77 across all protein targets with little or no structural defects. As part of these studies, we also carried out a very detailed analysis of the data that revealed interesting pitfalls, which we highlight here and which should be addressed in future benchmark datasets.