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21.
The intention of the research reported here was to seek explanations for low achievement in school mathematics, as conventionally assessed, that derive from broad understandings of mathematics as social. Such a broad social perspective can provide explanations for low achievement, which could lead to different understandings and hence to different teaching approaches. This study centered on 5- to 8-year-old children from a White working-class area in England. Data were collected during visits to the children in school, in their homes, and in the broader community over a 3-year period. Parents, teachers, and other professionals in the broad school context were interviewed, and data were also collected from school documents and policy statements. Interpretations of these data in terms of ways of understanding children's achievements in school mathematics are put forward. The potential effects of these factors on low schooled numeracy attainment are discussed, together with some possible strategic implications for practice and policy. 相似文献
22.
Roberto D. Galvão Luis Gonzalo Acosta Espejo Brian Boffey 《Annals of Operations Research》2006,143(1):31-44
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better
distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical
issues and difficulties encountered.
A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with
some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing
countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons
for this outcome are analysed. 相似文献
23.
24.
The thermolysis of dicarbonylcyclopentadienyliron dimer in a sealed tube at 300°C has been reported to produce ferrocene, carbon monoxide, carbon dioxide, cyclopentadiene and elemental iron. We observe in addition to these products the production of biferrocene and elemental carbon. Thermolysis of carbonylcyclopentadienyliron tetramer (produced from the dimer by thermolysis in refluxing xylene) produces ferrocene, iron and carbon monoxidre; no biferrocene, carbon dioxide or elemental carbon are produced. A scheme is proposed to account for these products. 相似文献
25.
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27.
Brian Dipert 《电子设计技术》2003,10(8):52-62
DRAM供应商希望有朝一日一种产品大小规格能适应所有的应用要求,但各种各样的设备要求则与之相差甚远.DRAM用户也许更喜欢定制的芯片,但价格会格外昂贵.双方会在保持原则的同时作出足够的让步以达成顺利的交易么? 相似文献
28.
Manju Rajeswaran Thomas N. Blanton David R. Whitcomb Nicholas Zumbulyadis Brian J. Antalek Scott T. Misture 《Journal of solid state chemistry》2006,179(4):1053-1059
In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of such a silver complex with poor solubility. The usual routes to preparing single crystals using recrystallization from a cooperating solvent resulted in polycrystalline powder samples. We propose a crystal structure for AgBZT, solved from synchrotron X-ray powder diffraction data, using a direct-space Monte Carlo simulated annealing approach. AgBZT crystals are monoclinic, (P21/c), with unit cell dimensions, a=14.8052(3) Å, b=3.7498(4) Å, c=12.3495(12) Å, and β=114.200(6)°. The AgBZT complex is constructed from all three of the Benzotriazole (BZT) nitrogens bonding to a separate silver atom. As a consequence of this bonding mode, the structure is a highly cross-linked, coordination polymer. 相似文献
29.
Brian H. Davison Nhuan P. Nghiem Gerald L. Richardson 《Applied biochemistry and biotechnology》2004,114(1-3):653-669
More than 25 sorbents were tested for uptake of succinic acid from aqueous solutions. The best resins were then tested for
successive loading and regeneration using hotwater. The key desired properties for an ideal sorbent are high capacity, complete
stable regenerability, and specificity for the product. The best resins have a stable capacity of about 0.06 g of succinic
acid/g of resin at moderate concentrations (1–5 g/L) of succinic acid. Several sorbents were tested more exhaustively for
uptake of succinic acid and for successive loading and regeneration using hot water. One resin, XUS 40285, has a good stable
isotherm capacity, prefers succinate over glucose, and has good capacities at both acidic and neutral pH. Succinic acid was
removed from simulated media containing salts, succinic acid, acetic acid, and sugar using a packed column of sorbent resin,
XUS 40285. The fermentation byproduct, acetate, was completely separated from succinate. A simple hot water regeneration successfully
concentrated succinate from 10 g/L (inlet) to 40–110 g/L in the effluent. If successful, this would lower separation costs
by reducing the need for chemicals for the initial purification step. Despie promising initial results of good capacity (0.06
g of succinic/g of sorbent), 70% recovery using hot water, and a recovered concentration of >100 g/L, this regeneration was
not stable over 10 cycles in the column. Alternative regeneration schemes using acid and base were examined. Two (XUS 40285
and XFS-40422) showed both good stable capacities for succinic acid over 10 cycles and >95% recovery in a batch operation
using a modified extraction procedure combining acid and hot water washes. These resins showed comparable results with actual
broth. 相似文献
30.
Brian Dipert 《电子设计技术》2006,13(6):56-58,60,62,64,66-67
蓝色激光(Blu-ray,简称蓝光,以下同)光盘和HD DVD均开始进入量产,但格式大战的赢家还不明朗。红色激光:简称红光,以下同)格式仍是某些应用的可靠替代方案,但用户版权限制和显示器与视觉的限制使格式的未来令人疑惑。 相似文献