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121.
This paper reports on a study that introduces and applies the K5Connected Cognition Diagram as a lens to explore video data showing teachers’ interactions related to the partitioning of regions by axes in a three-dimensional geometric space. The study considers “semiotic bundles” ( Arzarello, 2006), introduces “semiotic connections,” and discusses the fundamental role each plays in developing individual understanding and communication with peers. While all teachers solved the problem posed, many failed to make or verbalize connections between the types of semiotic resources introduced during their discussions. 相似文献
122.
We report on the deformation of an air-water surface with a totally reflected low-power laser beam, inducing a convex mirror effect on the beam propagation. This bending is stronger close to the critical angle and depends on the polarization of the laser light. A model, leading to a simple dependence between the Goos-H?nchen shift and the radius of curvature of the interface, supports these observations. Bendings with radius of curvature as low as 0.10 m are demonstrated. 相似文献
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125.
Colloidal crystallization takes advantage of the strong interfacial forces and tunable interactions that organize particles into regular structures at small scales. Thus, colloidal crystallization and patterning provide a powerful and simple method to functionalize planar surfaces with applications to optical, catalytic, sensing, and cleansing materials. Nevertheless, the ability to pattern topologically more complex surfaces such as curved, confined, or soft substrates can open new avenues for novel, "intelligent", and responsive materials. We present one step in this direction by characterizing colloidal crystallization inside circular capillaries: a nearly periodic banding is observed, and the colloidal packing is dictated by confinement produced by the wedge-like region formed by a capillary confined meniscus. The packing consists of a succession of hexagonally close-packed regions, which are separated by narrow regions of "buckled phase crystals". 相似文献
126.
1,4-Dioxen-2-yl lithium reacts with ketones or aldehydes to give alcohols which lead after an allylic rearrangement under mild conditions, followed by reduction and hydrolysis to α-hydroxymethyl ketones in fair yields. 相似文献
127.
The usefulness of carboxamidomethyl esters (CAM esters) as a carboxyl protecting group for peptide synthesis was demonstrated. The synthesis of the chemotactic peptide For-Met-Leu-Phe-OH as well as the synthesis of Met-enkephalin using CAM ester as carboxyl terminal protection were performed. These esters showed good stability during acidolytic removal of BOC N-protecting group, during hydrogenolysis of Z N-protecting group and during removal of FMOC N-protecting group. CAM esters were selectively and rapidly cleaved by NaOH 0.5 N or by Na2CO3. However, we did not succeed in removing selectively the CAM ester when β-benzyl ester of aspartic acid was present in the sequence. 相似文献
128.
Etrillard J Axelos MA Cantat I Artzner F Renault A Weiss T Delannay R Boué F 《Langmuir : the ACS journal of surfaces and colloids》2005,21(6):2229-2234
We report on small-angle neutron scattering (SANS) and X-ray scattering (SAXS) investigations of foam films stabilized by sodium dodecyl sulfate. Previous measurements on dry foams (Axelos, M. A. V.; Boue, B. Langmuir 2003, 19, 6598) have shown the presence of spikes in the two-dimensional scattering data which suggest that the incident beam is reflected on some film surfaces. The latter interpretation is confirmed by new neutron studies performed on ordered ("bamboo") foams which allow selection of single films. In the first case, we show that the spikes of the scattered intensity can be obtained by reflection on two parts of the foam, namely, the films and the Plateau borders. With synchrotron radiation, first observations of distinct interference fringes have allowed an accurate determination of the film thickness. A comparison with X-ray and neutron data is made, opening a general discussion about the capabilities of small-angle scattering techniques for studying the microscopic properties of foam films. 相似文献
129.
An in terlaboratory study of the determination of cadmium, copper and lead in seawater by electrothermal atomic absorption spectrometry.The reproducibility of a selective extraction method on Chelex-100 resin in the Ca2+ form, described previously, was tested on seawater with and without addition of Cd, Cu and Pb. The metals extracted were determined by electrothermal atomic absorption spectrometry (a.a.s.). The results obtained by the three laboratories participating in these tests prove the validity of the method for the determination of cadmium and copper. The largest dispersion of results, observed for lead, is related to the poorest precision of electrothermal a.a.s. for this element. 相似文献
130.
[reaction: see text] A one-pot tandem cross-metathesis/hydrogenation/cyclization procedure was achieved at room temperature, under 1 atm of hydrogen, in the presence of a ruthenium catalyst and PtO(2) showing the compatibility of the two catalysts. This tandem reaction allows the synthesis of substituted lactones and lactols from acrylic acid and acrolein, respectively, in the presence of unsaturated alcohols. 相似文献