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91.
Generalization and proof are defining activities within mathematics, yet the focus of "school" proof has often been on form
over meaning, on established results rather than exploration and discovery. Computer-based microworlds offer opportunities
for students to notice and describe patterns, formulate generalizations, and generate and test mathematics conjectures. This
paper examines the work of a group of middle and high school students who used a microworld for transformation geometry to
investigate the composition of reflections. The students‘conjectures are described in terms of a learning paths chart for
the task, as well as through a detailed analysis of the work of one pair of students. A general scheme for describing informal
exploration and reasoning prior to formal proof is offered, and the role of social support in the learning of proof is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
George B. Kauffman Laurie M. Kauffman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1997,109(19):2222-2223
93.
This obituary-tribute for Fred Basolo (1920–2007), the Charles E. and Emma H. Morrison Professor of Chemistry Emeritus at Northwestern University and 1983 President of the American Chemical Society, who died of congestive heart failure on February 27, 2007, discusses his life and work in chemical education, coordination chemistry, inorganic reaction kinetics and mechanisms, and service to science and society. 相似文献
94.
Hong Piao Laurie Le Tarte William A. Hennessy N. Fairley 《Surface and interface analysis : SIA》2007,39(6):493-500
The recent development of XPS instrumentation with near‐micron spatial resolution has advanced the capability of elemental and chemical‐state imaging accompanied by small‐area analysis (down to 15 µm). In this paper, the combined use of X‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) at enhanced spatial resolution is shown to have significantly improved the understanding of interfacial delamination and related problems encountered in the production of electronic devices in the field of microelectronics. An example of the application of surface analysis for ITO/Mo adhesion problems will be presented. The mathematical procedure using principal component analysis (PCA) in the reduction of noise in XPS images will also be described. The dramatic improvements in the image contrast and chemical component determination from multispectral image data sets will be presented. This study is intended to explore the contributions given by advanced surface analysis tools to solve real‐world problems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
95.
The behaviour of metal ions during titration with triethylenetetraminehexaacetic acid (TTHA) in several supporting electrolytes was investigated by d.c. and square-wave polarography. The composition of the complexes (M2L or ML) formed during titration is reported as well as the [M] : [L] ratio corresponding to the end-point of amperometric titration. The optimal conditions (by d.c. and s.w. detection) are given for titrations of Cu(II), Ni(II), Cd(II), Pb(II) and Zn(II) based on the reduction current of metal ions, as well as for titrations of Cu(II), Cd(II), Pb(II), Zn(II), Al(III), Ca(II) and Mg(II) based on the anodic current of TTHA. Application of the anodic current of TTHA permits determinations of polarographically inactive metals and is valuable in analysis of mixtures. 相似文献
96.
Isolation and concentration of mercury by reduction of mercury(II) with acidic tin(II) chloride solution and absorption of mercury vapour in acidic permanganate solution is combined with potentiometric titration with dithiooxamide. The simple procedure is applicable to 5–100 ppb mercury in 1-dm3 samples. Recoveries from organomercurials are discussed. 相似文献
97.
98.
Deposition of calcium carbonate films by a polymer-induced liquid-precursor (PILP) process 总被引:7,自引:0,他引:7
A polypeptide additive has been used to transform the solution crystallization of calcium carbonate to a solidification process of a liquid-phase mineral precursor. In situ observations reveal that polyaspartate induces liquid–liquid phase separation of droplets of a mineral precursor. The droplets deposit on the substrate and coalesce to form a coating, which then solidifies into calcitic tablets and films. Transition bars form during the amorphous to crystalline transition, leading to sectorization of calcite tablets, and the defect textures and crystal morphologies are atypical of solution grown crystals. The formation of nonequilibrium crystal morphologies using an acidic polypeptide may have implications in the field of biomineralization, and the environmentally friendly aspects of this polymer-induced liquid-precursor (PILP) process may offer new techniques for aqueous-based processing of ceramic films, coatings, and particulates. 相似文献
99.
100.
McCunn LR Bennett DI Butler LJ Fan H Aguirre F Pratt ST 《The journal of physical chemistry. A》2006,110(3):843-850
The photodissociation of propargyl chloride (C3H3Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C3H3 radicals were performed, along with measurements of the Cl + C3H3 and HCl + C3H2 recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl (2P3/2) and Cl (2P1/2) (hereafter Cl) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 +/- 0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl+ mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin-orbit state Cl atoms. The maximum internal energy of the radicals produced in the low-recoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C3+ ions in the mass spectrometer. 相似文献