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41.
Recognizing and responding to students' thinking is essential in teaching mathematics, especially when students provide incorrect solutions. This study examined, through a teaching scenario task, elementary preservice teachers' interpretations of and responses to a student's work on a task involving reflective symmetry. Findings revealed that a majority of preservice teachers identified the student's errors from conceptual aspects of reflection rather than from procedural aspects. However, when they responded to the student's errors, preservice teachers tried to cope with them by invoking procedural knowledge. This study also revealed the three types of responses and two different forms of address by preservice teachers to student errors; these categories might provide insight into the difficulties arising in communication between students and teachers. 相似文献
42.
Catalytic one-pot synthesis of fenestrane derivatives from dienediynes was developed: fenestranes were synthesized in high yields by a dicobalt octacarbonyl-catalyzed tandem cycloaddition of dienediynes. 相似文献
43.
N-Phenyl alkyl amides were synthesized by the cobalt on charcoal-catalyzed one-pot reaction of alkene and aniline under carbon monoxide; this is the first heterogeneous catalytic formation of N-phenyl alkyl amides. 相似文献
44.
We point out that, in analogy with spin waves in antiferromagnets, all parameters describing the real-time propagation of soft pions at temperatures below the QCD chiral phase transition can be expressed in terms of static correlators. This allows, in principle, the determination of the soft pion dispersion relation on the lattice. Using scaling and universality arguments, we determine the critical behavior of the parameters of pion propagation. We predict that, when the critical temperature is approached from below, the pole mass of the pion drops despite the growth of the pion screening mass. This fact is attributed to the decrease of the pion velocity near the phase transition. 相似文献
45.
46.
Electromagnetically induced transparency is an effect observed in atomic systems, originating from quantum interference, in which electromagnetic transitions to and from a certain quantum state become suppressed. This dark state is also characterized by a quantum phase, relative to other states, which theoretically should stop evolving, but remain phase coherent, during transparency. We test this theoretical prediction using techniques developed for liquid-state nuclear magnetic resonance quantum computation, applied to a spin-7/2 nuclear spin system. A sequence of quantum operations is applied to create the dark state, and during transparency its phase evolution is measured relative to a reference state using Ramsey interferometry. Experimental measurements of the fringe visibility are in excellent agreement with theoretical expectations, taking into account measured decoherence rates. 相似文献
47.
We consider a system of N nonrelativistic bosons in two dimensions, interacting weakly via a short-range attractive potential. We show that for N large, but below some critical value, the properties of the N-boson bound state are universal. In particular, the ratio of the binding energies of (N+1)- and N-boson systems, B(N+1)/B(N), approaches a finite limit, approximately 8.567, at large N. We also confirm previous results that the three-body system has exactly two bound states. We find for the ground state B(0)(3)=16.522 688(1)B2 and for the excited state B(1)(3)=1.270 409 1(1)B2. 相似文献
48.
This study was carried out to develop a cost-, labor- and efficiency-effective elimination method of pesticide residues in ginseng extract. A two-phase partition method between soybean oil and distilled water or aqueous ginseng extract was employed for the elimination of pesticide residues. Content of the pesticides was determined by gas chromatography with electron capture or nitrogen phosphorus detector. A total of 15 pesticides representing four categories (organochlorine, organophosphorus, carbamate, pyrethroid) were spiked (ca. 2 ppm) to 2 ml soybean oil in a test tube and the oil was mixed with 6 ml distilled water or 10% aqueous ginseng extract. The test tubes were then vortexed (2 min) and centrifuged at 3000 rpm for 15 min to separate the oil and aqueous layers. Each layer was harvested and subjected to quantitative analysis of pesticides. The average distribution ratio of the pesticides to the oil layer was 94.4 +/- 6.7% in the mixture of the oil and distilled water, and 105.5 +/- 6.6% in the mixture of the oil and ginseng extract. No significant qualitative and quantitative change of ginsenosides, the active ingredients of Panax ginseng, was observed in the ginseng extract before and after the oil treatment. These results suggest that two-phase partition chromatography between soybean oil and the aqueous phase is a cost-, labor- and efficiency-effective reliable method for the elimination of pesticide residues in ginseng extract. 相似文献
49.
To prove feasibility of proton chemical shift imaging ((1)H CSI) during stereotactic procedure, authors performed (1)H CSI in combination with a stereotactic headframe and selected targets according to local metabolic information, evaluated the pathologic results. The (1)H CSI directed stereotactic biopsy was performed in four patients. (1)H CSI and conventional Gd-enhancement stereotactic MRI were performed simultaneously after the fitting of a stereotactic headframe. Focal areas of increased phosphocholine(Cho)/phosphocreatine(Cr) and Lactate/Cr ratios were selected as target sites in the stereotactic MR images. (1)H CSI is possible with the stereotactic headframe in place. Pathologic samples taken from areas of increased Cho/Cr ratios and decreased NAA/Cr ratios provided information upon increased cellularity, mitoses and cellular atypism, and facilitated diagnosis. Pathologic samples taken from areas of increased Lac/Cr ratio showed predominant feature of necrosis. (1)H CSI was feasible with the stereotactic headframe in place. The final pathologic results obtained were concordant with the local metabolic information from (1)H CSI. We believe that (1)H CSI-directed stereotactic biopsy has the potential to significantly improve the accuracy of stereotactic biopsy targeting. 相似文献
50.
Heterobimetallic Ru/Co nanoparticles, immobilized on charcoal, were synthesized and used as catalysts in the Pauson-Khand-type reaction in the presence of pyridylmethyl formate instead of carbon monoxide; the catalysts were effective for intra- and intermolecular reactions and easily reused without loss of catalytic activity. 相似文献