Thermodynamische Stabilität makromolekularer Kristalle

The density of free energy of a chain crystal contains two terms of opposed sign dependent on the numberN of chain elements in the straight section of the macromolecules between the surfaces of the crystal perpendicular to thec-axis. The surface energy contributes a positive term decreasing withN. The amplitude Φ of the periodic lattice field opposing the chain translation in thec-axis yields the negative term. Due to the incoherent longitudinal thermal vibration of the four first-order neighbours of any chain the fieldΦ is smeared out. Its amplitude decreases the more the higherN and hence yields an increase in free energy density with increasingN. As a consequence of the opposite sign of surface energy and lattice field changes withN the free energy density shows a minimum at finiteN corresponding to the thermodynamically stable crystal thickness. With increasing temperature and lower interaction between adjacent chainsN increases in perfect qualitative agreement with experimental data.     

Untersuchungen zur Stabilität 131J-markierten Inulins in vivo

Nach Entwicklung eines ¹³¹J-markierten J-J-Propylinulins von ausreichender Reinheit und Lagerungsstabilität wurde die Stabilität des Präparates in vivo geprüft. Bei 14 untersuchten Patienten fand sich mit einer statischen Sicherheit von 90% eine Abspaltung von freiem ¹³¹J aus der Verbindung bereits 2 h p.i., so daβ die Anwendung des Präparates für Clearance-und Inulinraumbestimmungen derziet nicht empfehlenswert erscheint.     

Untersuchung der Oberflächeninhomogenität von Metallen mit der Radioindikationsmethode

Eine neue Methode zur Untersuchung der Oberβächeninhomogenitāt mit Hilfe der Festkörper-Spurdetektoren wurde entwickelt. Die Vertcilung der Spuren gibt einc gute Möglichkeit, den kathodischen bzw. anodischen Flächenteil von Metalloberflāchen zu bestimmen. Die beschriebene Methode ist relativ einfach. Sie erlaubt eine Prognostizierung der Anfllösungsstellen bzw. der Stellen, wo Rosterscheinungen zu erwarten sind.     

Kontrastreiche und von Aufladungsstörungen freie Abbildung hochisolierender Oberflächen mittels Sekundärelektronen

The apparent secondary electron yield from metal surfaces (Au, W, Al, Zn, Ag, Ni and Cu) with a polymeride layer of varying thickness was measured. It was found that even with a layer thickness of as much as 40 Å and a primary energy of 25 kev there were clearly noticeable differences in emission from the various substances. This effect can be used for the electron emission microscopy of specimens consisting of insulating materials. In some cases, satisfactory images of such specimens could not be obtained in a reproducible way if other methods, e.g. Cevales' partial evaporation method were applied. If a carbon layer 30 Å in thickness was evaporated onto the insulating specimen surface byBradley's procedure, well contrasted images free from disturbances by surface charges could be obtained from specimens such as glass, thermally etched A1₂O₃ and other minerals. In these images, a resolution limit of 800 Å was attained.     

Zur Herstellung von aufgedampften Bleiselenidschichten hoher mechanischer und elektrischer Stabilität

A method is described how PbSe-layers may be prepared in vacuum by co-evaporation of single crystal leadselenide and elementary selenium. The influence of additionally evaporated selenium on layer conductance during the preparation provides information concerning the process of condensation and film formation. The evaporation and deposition parameters thus gained lead to a technique of preparing films which show well reproducible properties and high photosensitivity.