Kinetics of crystal nucleation and growth in Pd77.5Cu6Si16.5 glass

Samples of Pd_77.5Cu₆Si_16.5glass, both produced in a drop tube by cooling the melt at 1700 K/s and by directional solidification with a cooling rate of 221 K/s were heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy of partially devitrified samples shows that the crystallization proceeds similarly in the both samples by growth of spherical regions in the interior. A modified Kissinger analysis is used to obtain the activation energy for crystal growth (411 KJ/mol). An expression for the steady state homogeneous nucleation frequency was calculated and its applicability was verified by annealing. Constant differences (5 · 10¹² and 4 · 10¹¹ nuclei/m³ for the drop tube produced spheres and the ds samples respectively) was observed to prevail between the calculated homogeneous density of nuclei and that estimated from micrographs, suggesting heterogeneous nucleation.     

In situ uv visible reflectance spectroscopic investigation of the nickel electrode-alkaline solution interface

An in situ uv visible reflectance spectroscopic technique is used to investigate the nickel electrode-alkaline solution interface. It is shown that by recording the change in relative reflectivity of the surface vs the potential applied to the electrode, at various fixed wavelengths, it is possible to get the spectra of superficial layers.Reflection-absorption spectra were thus obtained respectively for the hydroxide αNi(OH)₂ (two maxima at 360 and 500 nm) and the oxyhydroxide NiOOH (broad band with a maximum at 500–550 nm), providing new insights concerning the reversibility of some of the electrochemical processes which occur on the electrode surface when varying the potential.     

A new cutting-stock heuristic for scheduling production

This study interprets a scheduling problem in the woven fiberglass industry as an example of the cutting-stock problem; where wasted production capacity rather than wasted material is to be controlled. The solution is complicated due to the need to consider setup costs, so a heuristic is developed and tested. Comparison to one company's a historical production decisions indicates that both wasted capacity and setup Costs can be substantially reduced through application of the heuristic.     

Designing a powerful learning environment to promote durable conceptual change

The purpose of this study was to investigate the long-term effectiveness of a three-dimensional (3D) computer modeling supported predict–observe–explain (POE) strategy on pre-service science teachers' understanding of lunar concepts. Thirty-three preservice teachers participated in the study. A questionnaire was used to assess participants' understanding of the phases of the Moon and eclipses before, after, and 22 months after the instruction. Semi-structured interviews were conducted with six participants before and after the instruction. The results demonstrated that few participants had a scientific understanding about the targeted lunar concepts before the instruction. However, the majority of the participants had a scientific understanding after the instruction indicating that the instructional intervention was quite effective in facilitating conceptual change. The results also demonstrated that twenty-two months after the instruction most participants maintained their scientific conceptual understanding suggesting that the powerful learning environment designed for this study was effective in promoting a durable conceptual change.     

Some applications of multiwire chambers to the detection of electromagnetic radiations

New structures and new gas fillings have extended the domains of applications of multiwire chambers. They can be used for the detection and imaging of UV light, X-rays, γ-rays in the energy range useful for nuclear medicine.     

A wide dynamic range experiment to measure high energy γ-showers in air by detecting Cherenkov light in the middle ultraviolet

An experiment to study high energy γ rays from localized cosmic sources is described. A number of Al mirrors reflects the Cherenkov light emitted by the showers into photosensitive gas chambers on the mirror focal plane. The use of gas chambers with large active areas allows a sensitivity superior to existing experiments to be reached. Pad readout gives the required angular accuracy. The chamber is sensitive to the middle ultraviolet Cherenkov light produced by the showers in the atmosphere. Since the ozone in the upper atmosphere absorbs the direct ultraviolet light from any outer source, the lower level atmosphere provides a large dark volume in which the Cherenkov radiation from the showers can be isolated.     

Measurement of the beam-beam parameter by exciting coherent betatron oscillation

Four coherent betatron oscillation modes induced by the beam-beam interaction we observed in the TRISTAN Main Ring (MR) during two e⁺ and two e⁻ bunches colliding operation. These modes are extracted using a phase mixing technique and used for measuring beam-beam parameters. The luminosity, the coupling coefficient and the emittance are estimated from the observation. The emittance agrees with the expected value to within 15% accuracy.