Asphalt

Ohne Zusammenfassung     

Optical properties of sol-gel fiber optic applicators for laser interstitial therapy

A new type of applicator for interstitial laser coagulation is proposed in this paper. The new fiber optic applicator is made by removing the original fiber cladding and replacing it with a sol-gel coating. The sol-gel coating was prepared from the silicate precursor TEOS (tetraethylorthosilicate), mixed with ethanol in acid, which catalyzes hydrolysis. The material is produced with the factor R = 20, where R denotes the number of solvent moles to the number of TEOS moles. In these studies, optical fibers were used from Laser Components (core diameter 400 μm, HCS, low OH). The external jacket was mechanically removed, leaving a remaining 2-cm length of bare fiber. The modified dip-coating method was used to cover the bare fibers with sol-gel material. Two types of applicators were produced: pure sol-gel coated devices and applicators with sol-gel coating doped with photosensitive dyes. The photodynamic activity of chlorophyll-based Photolon and Protoporphyrin IX (PPIX) incorporated within the sol-gels was studied spectrophotometrically. It was demonstrated that sol-gel applicators are capable of performing laser interstitial coagulation using a semiconductor cw laser at 980 nm. It was also demonstrated that the incorporated photosensibilizers retain their photochemical activity. Original Text ? Astro, Ltd., 2006.     

Ueber Zuckerbestimmung

Ohne Zusammenfassung     

Characterization of the enhanced peroxidatic activity of amyloid β peptide–hemin complexes towards neurotransmitters

Binding of heme to the amyloid peptides Aβ40/42 is thought to be an initial step in the development of symptoms in the early stages of Alzheimer’s disease by enhancing the intrinsic peroxidatic activity of heme. We found considerably higher acceleration of the reaction for the physiologically relevant neurotransmitters dopamine and serotonin than reported earlier for the artificial substrate 3,3′,5,5′-tetramethylbenzidine (TMB). Thus, the binding of hemin to Aβ peptides might play an even more crucial role in the early stages of Alzheimer’s disease than deduced from these earlier results. To mimic complex formation, a new surface architecture has been developed: The interaction between the truncated amyloid peptide Aβ1-16 and hemin immobilized on an aminohexanethiol spacer on a gold electrode has been analyzed by cyclic voltammetry. The resulting complex has a redox pair with a 25 mV more cathodic formal potential than hemin alone.     

Quinoprotein glucose dehydrogenase modified thick-film electrodes for the amperometric detection of phenolic compounds in flow injection analysis

The use of thick-film electrodes as basic transducers for highly sensitive amperometric biosensors using PQQ (pyrroloquinoline quinone) dependent glucose dehydrogenase (GDH) with short response times is described. The enzyme is embedded in a polyurethane matrix on top of a platinum based thick film electrode and its ability to reduce oxidized phenolic compounds is exploited. The electrochemical amplification is based on the oxidation of the analyte on the surface of the electrode followed by its enzymatic reduction. Different parameters of the glucose dehydrogenase electrode system using dopamine as a model analyte were optimized, e.g., membrane thickness, pH value, buffer system, flow rate and storage conditions. Using optimized parameters the sensitivity and detection limits for various phenolic compounds were evaluated. The comparison of electrodes from the identical as well as from different batches shows the ability to produce a number of well reproducible sensors showing remarkably small differences with respect to parameters as sensitivity, response times, and measuring range. Received: 15 August 2000 / Revised: 17 October 2000 / Accepted: 24 October 2000     

Palladium(II) and Platinum(II) Complexes with Bisphosphanes, [S2C=C(CN)2]2– and [Se2C=C(CN)2]2– as Chelating Ligands

The palladium(II) and platin(II) 1, 1‐dicyanoethylene‐2, 2‐dithiolates [(L–L)M{S₂C=C(CN)₂}] (M = Pd: L–L = dppm, dppe, dcpe, dpmb; M = Pt: dppe, dcpe, dpmb) were prepared either from[(L–L)MCl₂] and K₂[S₂C=C(CN)₂] or from [(PPh₃)₂M{S₂C=C(CN)₂}] and the bisphosphane. Moreover, [(dppe)Pt{S₂C=C(CN)₂}]was obtained from [(1, 5‐C₈H₁₂)Pt{S₂C=C(CN)₂}] and dppeby ligand exchange. The 1, 1‐dicyanoethylene‐2, 2‐diselenolates[(dppe)M{Se₂C=C(CN)₂}] (M = Pd, Pt) were prepared from[(dppe)MCl₂] and K₂[Se₂C=C(CN)₂]. The oxidation potentials of the square‐planar palladium and platinum complexes were determined by cyclic voltammetry. The reaction of [(dcpe)Pd(S₂C=O)] with TCNE led to a ligand fragment exchange and gave the 1, 1‐dicyanoethylene‐2, 2‐dithiolate [(dcpe)Pd{S₂C=C(CN)₂}] in good yield.     

Laser welding with filler wire

New applications such as welding of material combinations and the ability to fill opening gaps between the workpieces offer new prospects for laser beam welding processes with filler wire. To guarantee good quality, vertical distance variations between wire tip and weld pool are, above all, not permissible as this causes globular metal transfer and would accordingly result in strongly rippled, unclean welds. A process-internal signal, recorded by a sensor, helps to solve this problem. The automatic tracking of the vertical wire position is possible on-line via a controller. In this way, the running process can be optimized and a consistently good weld quality can be achieved.