Bestimmung der Abtragungsraten von Zirconium,Tantal und der Legierung Tantal-40Niob in fluoridhaltiger azeotroper Salpetersäure mit Hilfe der Radiotracer-Methode

The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10^?6 to 5 · 10^?4 mm/y, for tantalum: 10^?8 to 4 · 10^?6 mm/y, and for the Ta-40Nb alloy: 2 · 10^?7 to 8 · 10^?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F^? and at a temperature of 108°C, corrosion rates between 5.3 · 10^?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10^?3 mm/y at 50°C/280 ppm F^? and 1.4 · 10^?2 mm/y at 110°C/320 ppm F^?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.     

Doubly resonant Ti:sapphire laser

A CW Ti:sapphire laser that operates simultaneously at two frequencies is described. This mode of operation was obtained with an intracavity dispersive prism and two separate feedback paths. An alternative means of achieving dual frequency operation was demonstrated using a birefringent filter. Repetitive Q-switching produced an increase in the range of wavelengths over which dual frequency operation was obtained     

Studies on elemental tellurium under high pressure

A non-linear behaviour in the resistance of tellurium as a function of pressure has been observed. At each pressure the resistance shows a time variation. At lower pressures, the normalized resistance increases with time, and at higher pressures, the normalized resistance decreases exponentially as a function of time. This change in behaviour with respect to time occurs in the region of the steepest descent in the resistance versus pressure plot. However, the magnitude of the change in the resistance with time is small compared to a change in the resistance with pressure. The origin of this behaviour is suggested to be linked with the generation and annealing of localized charged defects. This revised version was published online in November 2006 with corrections to the Cover Date.     

Bioceramics

Ceramics, glasses, and glass-ceramics are increasingly being tested for use in the human body. These materials often have excellent chemical properties for biomedical use, but they are brittle and show fatigue. Careful analysis of their mechanical properties is needed to determine appropriate applications. Hydroxylapatite is emerging as the most promising bioceramic because it shows no foreign body reactions and bonds strongly to bone; if properly made without pores or second phases it has excellent fatigue resistance. Glass-ceramics containing hydroxylapatite crystals also show good promise for many applications. Different forms of these materials, such as dense, granular, mixed granular with plaster of Paris, and coatings on metals are being tested and have very good potential as bioceramics.     

Substrate uptake by Gordonia amarae in activated sludge foams by FISH-MAR.

Gordonia amarae is a right-angled branching filament belonging to the mycolic acid-containing Actinobacteria which is commonly found in many foaming activated sludge wastewater treatment plants. Although studies on different substrates as sole carbon sources by pure cultures of G. amarae have been carried out, none have examined substrate uptake by this organism in situ. Uptake of several hydrophilic and hydrophobic substrates by G. amarae was evaluated in situ using a combination of fluorescence in situ hybridization and microautoradiography. G. amarae could assimilate a range of both hydrophilic and hydrophobic substrates. From the data, G. amarae appears to be physiologically active under aerobic, anaerobic and anoxic condition (NO2 and NO3) for some substrates. This might explain why attempts to control foaming caused by G. amarae using anoxic and anaerobic selectors have been unsuccessful. This study emphasizes that bacteria can behave differently in situ to pure cultures and that it is important to evaluate the in situ physiology of these bacteria if we are to better understand their role in the wastewater treatment process.     

The Future of Mixing Research

This paper is the result of a plenary discussion session held at the 11^th European Conference on Mixing. Three perspectives on mixing research are explored: that of the industrialist, the equipment manufacturer, and the academic researcher. There was strong agreement that, while the one dimensional problems are reasonably well understood and many engineers thus perceive that mixing is simple, current practice actually requires us to address complex, multi‐dimensional problems with interactions between mixing, reaction, multi‐phase physics, surface phenomena, and transport phenomena. Understanding these multi‐scale, multi‐mechanism problems requires models which include interactions between the phenomena, and allow the effects of these interactions to emerge. Developing these models will require us to shift our perspective on mixing from one of equipment design to one of the mixing field as a fundamental physical mechanism.     

Synchronization properties of two coupled multisection semiconductor lasers emitting chaotic light

We present numerical simulations describing the dynamics of two multisection semiconductor lasers emitting in a chaotic regime coupled in a master-slave configuration. By changing the current of the passive section of the master laser, we observe a change in the maximum correlation between the outputs of the two systems. These devices are promising candidates for on-off phase-shift keying encryption.