Closing the feedback loop: physics undergraduates’ use of feedback comments on laboratory coursework

The laboratory notebooks of physics undergraduates taking two second-year practical courses were audited to discover whether they had used feedback comments in their subsequent coursework. Ninety-five per cent of the 37 students on the first course and 100% of the 14 students on the second course whose work was audited had used feedback. The marker’s comments were classified into two groups based on whether they addressed simple (mastery) or complex (developmental) learning outcomes. Mastery comments were more likely to be acted on than developmental comments which aimed to extend students’ skills and understanding to higher levels. This has implications for the use of feedback audit as a quality control process, since the feedback which is most commonly applied by students is not the most valuable for the development of higher order skills. Following reflection on the results for the first course, students taking the second course were given responsibility for checking their peers’ notebooks against preset criteria. Peer checking improved students’ marks but did not eliminate the need for mastery feedback. It is argued that a direct audit of students’ use of feedback is particularly valuable when undertaken by the teacher who provides the feedback

Self-consistent solutions to the intersubband rate equations in quantum cascade lasers: Analysis of a GaAs/AlxGa1-xAs device

The carrier transition rates and subband populations for a GaAs/AlGaAs quantum cascade laser operating in the mid-infrared frequency range are calculated by solving the rate equations describing the electron densities in each subband self-consistently. These calculations are repeated for a range of temperatures from 20 to 300 K. The lifetime of the upper laser level found by this self-consistent method is then used to calculate the gain for this range of temperatures. At a temperature of 77 K, the gain of the laser is found to be 34 cm(-1)/(kA/cm(-2)), when only electron–longitudinal-optical phonon transitions are considered in the calculation. The calculated gain decreases to 19.6 cm(-1)/(kA/cm(-2)) when electron–electron transition rates are included, thus showing their importance in physical models of these devices. Further analysis shows that thermionic emission could be occurring in real devices. © 2001 American Institute of Physics

Artificial gravity spin deployment system Patent

Development of method for producing artificial gravity in manned spacecraf

Drying apparatus for photographic sheet material

An elongated drying chamber is provided with transport means for carrying photographic sheet material edgewise with the sheets in end-to-end relationship past a plurality of tubes that issue drying air streams. The tubes are slotted a distance equal to substantially the full width of the sheet material for complete, gentle drying by sheets of air. A common plenum supplies the tubes with heated air; the air is directed from the tube slots at a pronounced angle to the sheet surface to provide for arraying the tubes close to the surface for maximum drying effect while minimizing the danger of mechanical interference between the edges of the sheets and the slots in the tubes. The driver for the transport is housed in an enclosure between the plenum and the drying chamber; an air return duct is provided along another side to complete insulation of the drying chamber from ambient conditions

Low-temperture electrostatic silicon-to-silicon seals using sputtered borosilicate glass

Silicon members are hermetically sealed to each other. Process produces no measurable deformation of silicon surfaces and is compatible with package designs of tight tolerance. Seals have been made with glass coatings in 10-mm to 20-mm thickness range without any prior annealing of coated silicon substrates

Stark ladders as tunable far-infrared emitters

A superlattice of GaAs/Ga(1 – x)Al(x)As quantum wells forms a Stark ladder under the influence of a perpendicular electric field. A two level incoherent emitter system, formed by radiative intersubband transitions between adjacent wells, is investigated as a tunable far-infrared radiation source. Intersubband transition rates are calculated at 4, 77, and 300 K for applied fields from 0 to 40 kV cm(–1). It is shown that the quantum efficiency of the radiative emission reaches a maximum at low temperatures for a field of 32 kV cm(–1). Under these conditions the emission wavelength is 38 µm with an estimated power output of 1.1 mW. © 1998 American Institute of Physics

The development of radiation resistant insulating layers for planar silicon technology, 29 May 1968 - 28 June 1969

Ion implantation method for improving radiation resistance of thermal oxides on silico