Influence of Microstructure and Surface Activation of Dual‐Phase Membrane Ce0.8Gd0.2O2−δ–FeCo2O4 on Oxygen Permeation

Dual‐phase oxygen transport membranes are fast‐growing research interest for application in oxyfuel combustion process. One such potential candidate is CGO‐FCO (60 wt% Ce_0.8Gd_0.2O_2?δ–40 wt% FeCo₂O₄) identified to provide good oxygen permeation flux with substantial stability in harsh atmosphere. Dense CGO‐FCO membranes of 1 mm thickness were fabricated by sintering dry pellets pressed from powders synthesized by one‐pot method (modified Pechini process) at 1200°C for 10 h. Microstructure analysis indicates presence of a third orthorhombic perovskite phase in the sintered composite. It was also identified that the spinel phase tends to form an oxygen deficient phase at the grain boundary of spinel and CGO phases. Surface exchange limitation of the membranes was overcome by La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) porous layer coating over the composite. The oxygen permeation flux of the CGO‐FCO screen printed with a porous layer of 10 μm thick LSCF is 0.11 mL/cm² per minute at 850°C with argon as sweep and air as feed gas at the rates of 50 and 250 mL/min.     

Compression connectors for Stranded Aluminum power conductors

Twelve different commercial compression connectors for 240 mm/sup 2/ stranded aluminum cable conductors have been examined in order to identify and clarify the correlations between the quality of a connector and its design characteristics, assembly procedures, and other relevant parameters. The quality of the connectors is assessed with basis in resistance measurements during short-circuit tests and thermal cycling as specified by the IEC 61238-1 standard. Visual inspections of cross-sectioned connections, hardness measurements, and other examinations revealed that large mechanical deformations in connector-conductor interfaces significantly improve the quality. Connecting soft (annealed) conductors is considerably more difficult than hard-drawn conductors, but excellent results can be obtained if the work hardening during compression increases the conductor hardness to a level approaching that of hard conductors. The sequence in which the compression indents is made can be decisive for the quality of a connector. Unless the connector barrel or sleeve contains excessive amounts of contacting compound, it is advantageous to set the first indents at the ends of the barrel and the last ones in the middle.     

A Servo-Controlled, Whole Body, Blood Perfusion System as a Pressure/Flow Clamp

To study the peripheral vascular system of anesthetized dogs, a whole body, blood perfusion system was developed to provide 1) a nonpulsatile output of 2) constant pressure (0-300 mm Hg), or 3) constant flow (0-3 liters/minute), or 4) any output characteristic between these extremes, and 5) the output controllable from a voltage command signal. Output is determined by pneumatic pressure, adjusted by a servo valve from the error signal, which drives the blood from a reservoir into the animal's aorta. The error signal is derived from the difference between either a flowmeter or pressure-gage signal and an adjustable set-point voltage, or any combination of these signals. Response time is less than 1 sec. Heat and gas exchange are provided by a double-walled disk oxygenator. Plasma hemoglobin accumulation is typically 0.2 mg/ml hour.     

A hydrogen bond surrogate approach for stabilization of short peptide sequences in alpha-helical conformation

Alpha-helices constitute the largest class of protein secondary structures and play a major role in mediating protein-protein interactions. Development of stable mimics of short alpha-helices would be invaluable for inhibition of protein-protein interactions. This Account describes our efforts in developing a general approach for constraining short peptides in alpha-helical conformations by a main-chain hydrogen bond surrogate (HBS) strategy. The HBS alpha-helices feature a carbon-carbon bond derived from a ring-closing metathesis reaction in place of an N-terminal intramolecular hydrogen bond between the peptide i and i + 4 residues. Our approach is centered on the helix-coil transition theory in peptides, which suggests that the energetically demanding organization of three consecutive amino acids into the helical orientation inherently limits the stability of short alpha-helices. The HBS method affords preorganized alpha-turns to overcome this intrinsic nucleation barrier and initiate helix formation. The HBS approach is an attractive strategy for generation of ligands for protein receptors because placement of the cross-link on the inside of the helix does not block solvent-exposed molecular recognition surfaces of the molecule. Our metathesis-based synthetic strategy utilizes standard Fmoc solid phase peptide synthesis methodology, resins, and reagents and provides HBS helices in sufficient amounts for subsequent biophysical and biological analyses. Extensive conformational analysis of HBS alpha-helices with 2D NMR, circular dichroism spectroscopies and X-ray crystallography confirms the alpha-helical structure in these compounds. The crystal structure indicates that all i and i + 4 C=O and NH hydrogen-bonding partners fall within distances and angles expected for a fully hydrogen-bonded alpha-helix. The backbone conformation of HBS alpha-helix in the crystal structure superimposes with an rms difference of 0.75 A onto the backbone conformation of a model alpha-helix. Significantly, the backbone torsion angles for the HBS helix residues fall within the range expected for a canonical alpha-helix. Thermal and chemical denaturation studies suggest that the HBS approach provides exceptionally stable alpha-helices from a variety of short sequences, which retain their helical conformation in aqueous buffers at exceptionally high temperatures. The high degree of thermal stability observed for HBS helices is consistent with the theoretical predictions for a nucleated helix. The HBS approach was devised to afford internally constrained helices so that the molecular recognition surface of the helix and its protein binding properties are not compromised by the constraining moiety. Notably, our preliminary studies illustrate that HBS helices can target their expected protein receptors with high affinity.     

Visuelle Textanalyse Interaktive Exploration von semantischen Inhalten

Methoden und Techniken zur automatischen Verarbeitung und inhaltlichen Erfassung gro?er Mengen an Textdokumenten haben in den vergangenen Jahren enorm an Bedeutung gewonnen. W?hrend einerseits die Verfügbarkeit und der Zugang zu digitalisierten Textdokumenten bis dato in ungeahntem Ma?e gestiegen sind, erweist sich die Erfassung des semantischen Inhalts solcher Dokumentsammlungen als problematisch. Dem expandierenden Forschungsfeld der visuellen Textanalyse und Textvisualisierung kommt dabei eine Schlüsselrolle bei der L?sung von Problemstellungen aus der Praxis zu. Anhand aktueller Anwendungsbeispiele und einem überblick über den Stand der Forschung erl?utert dieser Artikel die vielf?ltigen M?glichkeiten, die sich durch visuelle Textanalyse ergeben.