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Teacher education programs have a critical role in supporting prospective teachers’ connections between theory and practice. In this study, we examined three prospective secondary mathematics teachers’ discourses regarding collective argumentation during and after a unit of instruction addressing collective argumentation and ways they recontextualized their on-campus coursework (theory) into their student teaching (practice) as demonstrated by their support for students’ mathematical arguments during student teaching. Through a recursive process of coding data from interviews, reflections, and classroom discussions, we constructed descriptions of participants’ discourses about argumentation based in their coursework and identified three themes about collective argumentation in the prospective teachers’ discourses: the purposes of argumentation, the role of the teacher in argumentation, and characteristics of effective mathematical arguments. Analysis using extended Toulmin diagrams of classroom data from participants’ student teaching showed that these three interrelated themes were visible in the participants’ enactment of moves supporting collective argumentation. Our study opens spaces for future investigations into how teachers recontextualize their learning from coursework (theory) into their practice.

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.

PPS filter media is one of the best available filter media for dust collection in the coal-fired power plant, but the performance of PPS filter media is influenced by SO2 in the flue gas. In this paper, effect of SO2 on PPS filter media was studied. Through the analysis of mechanical performance, microscopic characteristics and chemical structure of PPS filter media, it is considered that PPS filter media has good corrosion resistance to SO2, at the same time, SO2 also has definite corrosive effect on the PPS filter media, and corrosion increases with the increase of SO2 concentration and aging time. The temperature has accelerating effect on the corrosion.

Design for high efficiency, high power traveling wave electroabsorption modulator using Intra-Step-Barrier Quantum Well (IQW) and Peripheral Coupled waveguide (PCW) designs are presented. Both of these designs have separately yielded EAMs with high optical power handling and low Vp properties, in an analog fiber link configuration. The IQW EAM has low Vp (~0.73 V) and high power handling (100 mW). The lumped element IQW EAM has achieved a link gain of -16 dB, a multi-octave SFDR of 110 dB-Hz2/3 and a single-octave SFDR of 121dB-Hz4/5 at the 1543 nm wavelength. The PCW MQW EAM with lumped element configuration can achieve a low link low, a high multi-octave SFDR at the same wavelength. The traveling wave properties of these EAMs are under investigation.

We review the design and fabrication of the traveling wave (TW) electrode for the EAM for high speed and high power operation. In one approach, EAMs with improved saturation properties have been demonstrated via the lowering of the hole barrier by applying appropriate strain at the well/barrier interface. An alternate approach to enhance the saturation power of the quantum well modulator is via the use of a barrier step inside the well to suppress the onset of the red shift in the quantum-confined Stark effect to a higher electric field. In these approaches, however, the saturation power is optimized without incorporating the modulation frequency considerations.

The objective of this program was to advance the performance of a semiconductor waveguide modulator in external modulated RF fiber-optic links for space-based and airborne platforms such as true time delay beam formation and beam steering subsystems in phased array antennas. Device and material approaches were investigated to improve the modulator based on semiconductor structures for achieving high spur free dynamic range (SFDR) and high frequency operation. In these approaches, the semiconductor optical modulators were specifically designed to achieve high slope efficiency and high center frequency, while with minimal generation of spurious signals. The fiber-optic links using these modulators are expected to satisfy the low noise figure, high center frequencies, low drive power requirements. The following were the main goals in this program: (1) to design and test electroabsorption waveguide modulator for high multi-octave SFDR and high slope efficiency and high saturation optical power operation, and (2) to collaborate with technical personnel at Air Force Research Laboratory at Rome on the overall link design and provide prototype electroabsorption waveguide modulator for link evaluation.

A new approach for linearizing electroabsorption modulators (EAM) is presented here. It will be very useful for broadband, analog, radio frequency fiber-optic links. In this approach, two or more EAM will be fabricated in series on the same waveguide. Theoretical analysis shows that cancellation of both the second order and third order harmonic distortions can be obtained simultaneously by using proper electrode length and by biasing appropriately the electrodes, leading to an enhancement of the multi-octave spurious free dynamic range (SFDR). Simulation shows that the SFDR of the optical link for the two-electrode case is 10 dB larger than that for a single electrode case. Experimental confirmation of the theoretical prediction on distortion reduction is also presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.