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1.
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
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3.
S. N. Liddick P. F. Mantica R. V.F. Janssens B. A. Brown M. P. Carpenter A. D. Davies M. Honma M. Horoi T. Mizusaki A. C. Morton W. F. Mueller T. Otsuka J. Pavan H. Schatz A. Stolz S. L. Tabor B. E. Tomlin M. Wiedeking 《The European physical journal. Special topics》2007,150(1):135-136
We have utilized the selective process of β decay to
populate low-energy excited states in the neutron-rich 22Ti,
23V, 24Cr, and 25Mn nuclei. The goal was to systematically
track the monopole shift of the νf5/2 single-particle
level with increased occupancy of the πf7/2 orbital.
The β-decay properties of the parent nuclides, along
with the low-energy structure of the daughters, are
presented and compared with the results of shell model calculations
employing the GXPF1 interaction. 相似文献
4.
This paper describes studies on the feasibility of an asymmetric Favorskii rearrangement of a meso-dihaloketone substrate. In the racemic series, metal amide bases in the presence of amines give poor to reasonable yields of ring-contracted unsaturated cyclopentyl amides, whilst amines in aqueous solvent mixtures afford cyclopentyl amides in good to excellent yields. A range of chiral non-racemic amines are screened, a tiny diastereo-bias is observed and a tentative mechanistic rationale for the diastereoselective process is proposed. 相似文献
5.
Philip E. Gill Walter Murray Michael A. Saunders John A. Tomlin Margaret H. Wright 《Discrete Optimization》2008,5(2):151-158
We pay homage to George B. Dantzig by describing a less well-known part of his legacy–his early and dedicated championship of the importance of systems optimization in solving complex real-world problems. 相似文献
6.
Cantoni A. Walker J. Tomlin T.-D. 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(5):1032-1040
We characterize a proposed metastability measurement system in which asynchronous data input and sampling clock frequencies trigger metastability. We develop an equation describing the time interval between data and clock inputs for practical frequencies and show that it takes on discrete values in the absence of jitter and that the presence of jitter perturbs these values. Finally, we present experimental results supporting our characterization 相似文献
7.
J. A. Tomlin 《Mathematical Programming》1988,42(1-3):69-84
Special Ordered Sets provide a powerful means of modeling nonconvex functions and discrete requirements, though there has been a tendency to think of them only in terms of multiple-choice zero-one programming. This paper emphasizes the origins and generality of the special ordered set concept, and describes an application in which type 2 sets are used in several forms to model both logical conditions and nonlinear functions.Now at IBM Almaden Research Center, San Jose, CA 95120. 相似文献
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The elastic tunnel current versus bias over the range ± 1 V in junctions of the type A1-I(X)-M where M = Pb, Ag, Cu or Au and X is 2- 3- or 4-pyridinecarboxaldehyde has been used to determine parameters which describe the barrier in each. Little variation attributable to the different dopants is observed but there are substantial effects attributable to the top metal M in both clean and doped junctions. It is suggested that electron densities of states are responsible. The potential step between dopant and metal M decreases in the sequence Au:Pb:Ag. Evidence is collated from a number of sources to suggest that hydroxyl dipole layers influence the metal-organic interface potential step both in aqueous-solution-doped tunnel junctions and in SERS systems. 相似文献
10.
Hughes KJ Griffiths JF Fairweather M Tomlin AS 《Physical chemistry chemical physics : PCCP》2006,8(27):3197-3210
The purpose of this paper is to show the application of global uncertainty analysis to comprehensive and reduced kinetic models as a tool to identify important thermochemical and reaction rate parameters as determinants of the conditions leading to autoignition. Propane oxidation is taken as the test case. The simulation of experimental investigations of the cool flames and two-stage ignitions, via the pressure-temperature ignition diagram, show that existing kinetic models for the low temperature combustion of propane at sub-atmospheric pressures reflect a greater reactivity than seems to be appropriate. That is, the models lead to a prediction of two-stage ignition at pressures somewhat lower and with ignition delays shorter than is found experimentally. The inconsistency between experiment and numerical simulation seems not to be an inherent problem of the qualitative structure of the models, but may derive from uncertainties in the parameters within the mechanism. By use of "brute force", Morris-one-at-a-time and Monte-Carlo simulations, we show that uncertainties in only a small number of parameters, and falling well within the errors that may reasonably be assigned, can shift the response appropriately. Moreover, it appears that in the low temperature combustion regime, thermochemistry is at least as, if not more, important than the reaction rates, yet usually receives less attention within sensitivity studies. In the present case, the main factors controlling the temperature reached in the first stage of two-stage ignition and the time to ignition appear to be connected with the thermochemistry of three specific hydroperoxyalkyl radicals and their derivatives. Other factors, such as heat and mass transport are also addressed, and their effects are mitigated to some extent by evaluation of initial and revised models against experimental data for ignition delay obtained under microgravity. The results highlight more general issues that pertain to the numerical simulation of the combustion of higher hydrocarbons and contribute to the development of the protocol necessary for testing kinetic models before they are ready for use in a predictive capacity. 相似文献