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When half-cycle wide mid-grey test elements are superimposed on a black and white square wave induction grating, their apparent lightness is a linear function of their phase relationship with the induction grating; being judged lightest when in phase with the black bars of the grating, and darkest when in phase with the white bars. This finding justifies(More)
We present the results of oxygen isotope and electron-microprobe analyses of sphaerosiderites obtained from Cretaceous paleosols in Iowa. The sphaerosiderite ␦ 18 O values record Creta-ceous meteoric groundwater chemistry and an overall waning of brackish groundwater inundation during alluvial-plain aggrada-tion and soil genesis. We focus on horizons that(More)
Reflecting on analyses of data from our respective design-based research studies of mathematical cognition and learning, we propose the utility of the instrumental genesis model (Vérillon & Rabadel, 1995) for examining students' engagement with designed learning artifacts. The model has helped each of us to account for gaps between intended and enacted(More)
Uniform SnO(2) nanorod arrays were deposited on a 4 inch SiO(2)/Si wafer by plasma-enhanced chemical vapor deposition (PEVCD) at low deposition temperature of around 300 degrees C. The SnO(2) nanorods were connected at the roots, thus the nanorod sensors could be fabricated by a feasible way compatible with microelectronic processes. The surface of the(More)
This paper reports on a design-based research project in which we are developing collaborative activities for classroom networks. Research in generative design has explored classroom activities that analogize the many participants in a classroom with an often-infinite family of mathematical objects. By contrast, our project focuses on classroom activity(More)