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.     

A new general equivalence transformation for mixed lumped and nonuniform distributed networks with synthesis applications

Contents A new general equivalence transformation for cascades of lossless nonuniform transmission lines (NTL's) and lumped reactance two-ports (LRT's) is presented. Based on this transformation a new synthesis method for NTL's and NTL-LRT cascades is established, by means of which microwave filters and matching sections can be constructed on the basis of a rational function of the complex frequency. Thus, given specifications can practically be met arbitrarily well. In contrast to others the new method is at the same time exact and easy to handle. A synthesis example is given at the end.

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Eine neue allgemeine Äquivalenztransformation für gemischt-kon-zentriert-ungleichförmig-verteilte Netzwerke mit Syntheseanwendungen

Übersicht Es wird eine neue allgemeine Äquivalenztrans-formation für Kettenschaltungen aus (verlustlosen inhomogenen) Leitungen und (konzentrierten) Reaktanzzweitoren vorgestellt. Auf der Grundlage dieser Transformation wird ein neues Syntheseverfahren für Leitungen und Leitungs-Reaktanzzweitor-Kettenschaltungen begründet, mit Hilfe dessen Mikrowellenfilter und-anpassungsglieder auf der Grundlage einer rationalen Funktion der komplexen Frequenz konstruiert werden können. Somit können vorgegebene Spezifikationen praktisch beliebig genau realisiert werden. Im Gegensatz zu anderen ist das neue Verfahren gleichzeitig exakt und leicht zu handhaben. Am Schluß ist ein Synthesebeispiel angegeben.

     

Lyapunov-based control for switched power converters

Beginning with fundamental properties such as passivity or incremental passivity of the network elements comprised by a switched power converter, the nominal open-loop operation of a broad class of such converters is shown to be stable in the large via a Lyapunov argument. The obtained Lyapunov function is then shown to be useful for designing globally stabilizing controls that include adaptive schemes for handling uncertain nominal parameters. Numerical simulations illustrate the application of this control approach in DC-DC converters