How can teachers’ beliefs affect their professional development?

This paper describes a qualitative study that examines in more detail the question of how teachers’ beliefs may influence the intention to implement change as suggested by a professional development initiative. Several teachers in Germany took part in a professional development initiative for modelling. The course comprised five workshops spread over 2008. A part of our evaluation of the course involved interviewing six teachers after they had taken part. Teachers were interviewed about the impact the course had had on them, the opportunities and any related impediments they saw for modelling, and the way in which they typically taught. The interviews were evaluated using codes. Although the sample is very small, the cases allow for interesting insights, and for the hypotheses that teachers’ beliefs about effective teaching seem to have a major impact on whether or not they intend to change their classroom practice, as suggested by the professional development initiative, and on whether or not teachers perceive the context in which they are teaching (school head, parents, students, etc.) as supportive.     

Network forming properties of various proteins adsorbed at the air/water interface in relation to foam stability

A series of proteins was studied with respect to their ability to form a network at the air/water interface and their suitability as foaming agents and foam stabilizers. Proteins were chosen with a range of structures from flexible to rigid/globular: beta-casein, beta-lactoglobulin, ovalbumin, and (soy) glycinin. Experiments were performed at neutral pH except for glycinin, which was studied at both pH 3 and pH 6.7. The adsorption process was followed with an automated drop tensiometer (ADT). Network forming properties were assessed in terms of surface dilational modulus (determined with the ADT), the critical falling film length (L(still)) and flow rate (Q(still)) below which a stagnant film exists (as measured with the overflowing cylinder technique), and the fracture stress and fracture strain measured in surface shear. It was found that glycinin (pH 3) can form an interfacial gel in a very short time, whereas beta-casein has very poor network-forming properties. Hardly any foam could be produced at the chosen conditions with glycinin (pH 6.7) and with ovalbumin, whereas beta-casein, beta-lactoglobulin, and glycinin (pH 3) were good foaming agents. It seems that adsorption and unfolding rate are most important for foam formation. Once the foam is formed, a rigid network might favor stabilizing the foam.     

Carbon nanotubes as schottky barrier transistors

We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.     

Laser-induced fluorescence thermometry and concentration measurements on NOA–X (0-0) transitions in the exhaust gas of high pressure CH4/air flames

Laser-Induced Fluorescence (LIF) excitation spectra in the NOA–X (0-0) band were used for temperature measurements in the postflame region of high-pressure CH₄/air flames. To improve the quality of the measured spectra and to perform reliable line-shape measurements, the initial mixture was doped with approximately 400 ppm NO. At pressures up to 18 bar, excellent agreement was obtained between NO LIF temperatures and NARS/rotational Raman temperatures. Effective broadening coefficients were also determined in these flames. Problems with quantitative concentration measurements of NO and single-pulse temperature measurements at high pressures are discussed.     

Thermal grating and broadband degenerate four-wave mixing spectroscopy of OH in high-pressure flames

2 ∑–X²Π(0,0) band of OH has been studied in premixed methane/air flames using a cw Ar⁺ laser probe. Measurements of flame temperature and pressure were derived from fits of theoretical simulations to the observed time variation of signals over a pressure range of 10 to 40 bar and for different stoichiometry that were in agreement with independent measurements using N₂ CARS and predictions of a one-dimensional flame calculation. Broadband DFWM spectra in the same band of OH were observed up to a pressure of 9 bar, above which signals were obtained only from scattering from thermal gratings. Received: 10 November 1997/Revised version: 28 May 1998     

Planar nets of Ti atoms comprising squares and rhombs in the new binary antimonide Ti2Sb

The new binary antimonide Ti(2)Sb was found to crystallize in a distorted variant of the La(2)Sb type, which contains a square planar La net with short La-La bonds. In the Ti(2)Sb structure, the corresponding Ti net is deformed to squares and rhombs in order to enhance Ti-Ti bonding, as proven by single-crystal X-ray investigation in combination with the real-space pair distribution function technique utilizing both X-ray and neutron powder diffraction data. Electronic structure calculations revealed a lowering of the total energy caused by the disorder, the major driving force being strengthened Ti-Ti interactions along the diagonal of the Ti(4) rhombs.     

Four-color fluorescence correlation spectroscopy realized in a grating-based detection platform

We have developed a filterless multicolor detection unit for fluorescence correlation spectroscopy (FCS). This grating-based setup is continuously tunable for multicolor separation and is thus a powerful alternative to the classical cascade of dichroic mirrors and filters. Our tailored platform allows for accommodation of up to 15 detection channels covering the entire visible spectral range. As a proof of principle, we successfully demonstrate simultaneous FCS of four distinct fluorescent quantum dot species being mixed in aqueous solution. Grating-based detection allows for spectral high-resolution FCS in a stable and compact setup and is a feasible tool for quantitative investigation of complexbiomolecular dynamics on a single molecule level.