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  • Author: P. K. Thomas x
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Official Journal of the German Society of Clinical Chemistry and Laboratory Medicine

It is generally believed that metal nanoparticles strongly quench the singlet-excited states of chromophores when attached to nanoparticle surfaces, through an energy-transfer mechanism, which limits their application in optoelectronic devices and photonic materials. Recent studies of fluorophore-linked metal nanoparticles reveal that there is a dramatic suppression in the quenching of the singlet-excited state of these molecules and they possess unusual photophysical properties. A summary of our work on the photophysical and excited-state properties of chromophore-functionalized gold nanoparticles is presented in this article. Pyrene-capped gold nanoparticles showed normal fluorescence in nonpolar solvents and an intermolecular excimer formation at higher loadings. The quenching of the emission, observed in pyrene-labeled gold nanoparticles in polar solvents, is attributed to the formation of pyrene radical cation through a photoinduced electron-transfer process. We have also functionalized gold nanoparticles using a thiol derivative of fullerene. The quenching of fluorescence and decreased yields of triplet-excited state, observed in these systems, are attributed to an energy-transfer process.

Abstract

Nickel-Iron based superalloy (43Ni-14Cr, wt%) is used as high temperature material in space based transportation systems. It retains its high strength (>100 MPa) upto 800°C alongwith good cryogenic properties, hot corrosion resistance and phase stability at elevated temperatures. The alloy was melted in vacuum induction melting furnace and was refined through vacuum arc refining process. Hot working and heat treatment of the alloy was carried out and the material was characterized for its mechanical properties at different temperatures. Microstructural analysis was conducted at different stages of processing in order to optimize the processing parameters. This paper brings out the work carried out on the process development for this alloy.

Abstract

Different shrinkage types may cause serious durability dilemma on restrained concrete parts due to crack formation and propagation. Several classes of fibres are used by concrete industry in order to reduce crack size and crack number. In previous studies, most of these fibre types were found to be effective in reducing the number and sizes of the cracks, but not in shrinkage strain reduction. This study deals with the influence of a newly introduced type of polyethylene fibre on drying shrinkage reduction. The novel fibre is a polyethylene microfibre in a new geometry, which is proved to reduce the amount of total shrinkage in mortars. This special hydrophobic polyethylene microfibre also reduces moisture loss of mortar samples. The experimental results on short and long-term drying shrinkage as well as on several other properties are reported. The hydrophobic polyethylene microfibre showed promising improvement in shrinkage reduction even at very low concentrations (0.1% of cement weight).

Abstract

Neural prostheses partially restore body functions by technical nerve excitation after trauma or neurological diseases. External devices and implants have been developed since the early 1960s for many applications. Several systems have reached nowadays clinical practice: Cochlea implants help the deaf to hear, micturition is induced by bladder stimulators in paralyzed persons and deep brain stimulation helps patients with Parkinson's disease to participate in daily life again. So far, clinical neural prostheses are fabricated with means of precision mechanics. Since microsystem technology opens the opportunity to design and develop complex systems with a high number of electrodes to interface with the nervous systems, the opportunity for selective stimulation and complex implant scenarios seems to be feasible in the near future. The potentials and limitations with regard to biomedical microdevices are introduced and discussed in this paper. Target specifications are derived from existing implants and are discussed on selected applications that has been investigated in experimental research: a micromachined implant to interface a nerve stump with a sieve electrode, cuff electrodes with integrated electronics, and an epiretinal vision prosthesis.

 

Neuroprothesen können Funktionen des Körpers nach traumatischer Verletzung oder neurologischer Erkrankung teilweise durch technische Nervenerregung wiederherstellen. Seit den frühen sechziger Jahren des letzten Jahrhunderts wurden externe Hilfsmittel und Implantate für viele Anwendungen entwickelt. Einige Systeme sind im heutigen klinischen Alltag angekommen: Cochlea Implantate helfen Ertaubten zu hören, Querschnittgelähmte benutzen Blasenstimulatoren zur Miktion, und Tiefenhirnstimulation erlaubt Patienten mit Morbus Parkinson wieder am täglichen Leben teilzunehmen. Bislang sind die Neuroprothesen im klinischen Einsatz feinwerktechnisch hergestellt. Seit die Mikrosystemtechnik die Möglichkeit eröffnet, komplexe Systeme mit einer groβen Anzahl von Elektroden als Schnittstelle zum Nervensystem zu entwerfen und herzustellen, scheint die Umsetzung von selektiver Stimulation und komplexen Szenarien für Implantate in nahe Zukunft gerückt zu sein. In diesem Artikel sollen Chancen und Grenzen biomedizinischer Mikrosysteme gezeigt werden. Gewünschte Spezifikationen werden von vorhandenen Anwendungen abgeleitet und an ausgewählten Beispielen aus der experimentellen Forschung diskutiert: ein Mikroimplantat in Siebform als Schnittstelle zu einem Nervenstumpf, Manschettenelektroden mit integrierter Elektronik und eine epiretinale Sehprothese.