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1.
Tine Wedege 《ZDM》2007,39(3):251-260
A framework is presented for analyzing gender perspectives in mathematics education (structural, symbolic, personal and interactional gender), and the Danish and Norwegian researchers’/teachers’ work within the field of gender and mathematics is presented with reference to these four perspectives. Furthermore, the gender issue in TIMSS and PISA is briefly discussed. The main thread through the article is the researchers’ willingness and intentions of investigating the gender perspectives in mathematics education. However, so far, these research intentions have not been realized in Denmark and Norway. 相似文献
2.
Histamine is an important compound from a physiological point of view, but it is toxic since the absorption of low amounts of histamine can cause abdominal pains accompanied with vomiting. Why we have developed a new method for histamine analysis in order to improve Lerke and Bell method. From the absorption spectra, we showed that the stoichiometry of the complex histamine-orthophthalaldehyde (OPA) is 1:1. From the emission spectra, it was observed that the complex fluorescence is inhibited in acidic medium. In alkaline medium, an exaltation of fluorescence was observed, but the complex histamine-OPA was unstable. Nevertheless, kinetic study showed that good linear correlations between the fluorescence maxima of the formed complex and the histamine concentration could be obtained in this alkaline medium. 相似文献
3.
Boehmite xerogels are prepared by hydrolysis of Al(OC4H9)3 followed by peptization with HNO3 (H+/Al = 0, 0.07, 0.2). XRD and TEM show that these gels are made of nanosized crystals (5-9 nm in width and 3 nm thick). According to the amount of acid, no significant differences are found in size and shape, but only in the spatial arrangement of the crystallites. Nitrogen adsorption-desorption isotherms of nonpeptized gels are of type IV, whereas isotherms of peptized gels are of type I. These isotherms are analyzed by the t-plot method. The majority of pore volume results from intercrystalline mesopores, but the peptized gels also contain intercrystalline micropores. The particle packing is very dense for the gel peptized with H+/Al = 0.2 (porosity = 0.26), but it is less dense in non-peptized gel (porosity = 0.44). Heating these gels under vacuum creates, from 250 degrees C onwards, an intracrystalline microporosity resulting from the conversion of boehmite into transition alumina. But heating also causes intercrystalline micropores collapsing. The specific surface area increases up to a limit temperature (300 degrees C for nonpeptized gels and 400 degrees C for peptized) beyond which sintering of the particles begins and the surface decreases. The PSD are calculated assuming a cylindrical pore geometry and using the corrected Kelvin equation proposed by Kruk et al. Peptized xerogels give a monomodal distribution with a maximum near 2 nm and no pores are larger than 6 nm. Nonpeptized gels have a bimodal distribution with a narrow peak near to 2 nm and a broad unsymmetrical peak with a maximum at 4 nm. Heating in air above 400 degrees C has a strong effect on the porosity. As the temperature increases, there is a broadening of the distribution and a marked decrease of small pores (below 3 nm). However, even after treatment at 800 degrees C, micropores are still present. 相似文献
4.
Drouet C Alphonse P Fierro JL Rousset A 《Journal of colloid and interface science》2000,225(2):440-446
The equilibrium and kinetics of adsorption of NO and CO on nonstoichiometric nickel-copper manganites have been investigated through volumetric measurements. The adsorption isotherms were satisfactorily fitted to the Freundlich equation. The equilibrium coverages at 298 K were found to depend closely on the chemical composition of the oxide; thus, a decrease in the coverage beyond a maximum copper extent was observed. The adsorption isotherms of NO at various temperatures in the range from 298 to 473 K showed that the equilibrium coverage decreases with increasing temperature. This behavior enabled us to follow the logarithmic decrease of the heat of adsorption of NO on such surfaces. The adsorptions of NO and CO on surfaces preadsorbed with CO and NO, respectively, were also studied. These experiments showed the ability of NO to displace CO preadsorbed molecules whereas the contrary did not hold, suggesting the existence of common adsorption sites as well as some specific CO adsorption sites. Finally, some kinetic data are reported showing that the experimental adsorption results fit the Elovich equation (with t(0) approximately 0), although two distinct rate processes could be identified. Copyright 2000 Academic Press. 相似文献
5.
This work investigates the influence of temperature on the binding capacity of bovine serum albumin (BSA), soybean trypsin inhibitor and L-glutamic acid to a CIM (DEAE) weak anion-exchange disk monolithic column. The binding capacity was determined experimentally under dynamic conditions using frontal analysis. The effect on the dynamic binding capacity of dimers present in the BSA solution has been evaluated and a closed-loop frontal analysis was used to determine the equilibrium binding capacities. The binding capacity for both BSA and soybean trypsin inhibitor increased with increasing temperature. In the case of L-glutamic acid, an increase in the binding capacity was observed with temperature up to 20 degrees C. A further increase in temperature caused a decrease of the dynamic binding capacity. 相似文献
6.
A series of 1,6-dienes is cyclized to cyclopentene derivatives under neutral conditions with palladium chloride in ethanol or with in situ generated LPd2+ in acetonitrile. 相似文献
7.
A Hybrid Finite Volume Method for Advection Equations and Its Applications in Population Dynamics 下载免费PDF全文
Chang Yang Léon Matar Tine 《Numerical Methods for Partial Differential Equations》2017,33(4):1114-1142
We present in this article a very adapted finite volume numerical scheme for transport type‐equation. The scheme is an hybrid one combining an anti‐dissipative method with down‐winding approach for the flux (Després and Lagoutière, C R Acad Sci Paris Sér I Math 328(10) (1999), 939–944; Goudon, Lagoutière, and Tine, Math Method Appl Sci 23(7) (2013), 1177–1215) and an high accurate method as the WENO5 one (Jiang and Shu, J Comput Phys 126 (1996), 202–228). The main goal is to construct a scheme able to capture in exact way the numerical solution of transport type‐equation without artifact like numerical diffusion or without “stairs” like oscillations and this for any regular or discontinuous initial distribution. This kind of numerical hybrid scheme is very suitable when properties on the long term asymptotic behavior of the solution are of central importance in the modeling what is often the case in context of population dynamics where the final distribution of the considered population and its mass preservation relation are required for prediction. © 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1114–1142, 2017 相似文献
8.
Synthesis process of nanowired Al/CuO thermite 总被引:1,自引:0,他引:1
M. Petrantoni C. Rossi V. Conédéra D. Bourrier P. Alphonse 《Journal of Physics and Chemistry of Solids》2010,71(2):80-85
Al/CuO nanothermites were fabricated by thermal oxidation of copper layer at 450 °C for 5 h and by aluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2 μm in size. The copper has been deposited by electroplating or thermal evaporation depending on the required thickness. The obtained diameter of Al/CuO nanowires is 150-250 nm. Al/CuO nanowires composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermic reactions occurred at 515 and 667 °C and total energy release of this thermite is 10 kJ/cm3. 相似文献
9.
We describe the functions needed in the determination of the rate of convergence of best $L^\infty $ rational approximation to $\exp ( - x)$ on [0,∞) when the degree n of the approximation tends to ∞ (“1/9” problem). 相似文献
10.
Fluorimetric Determination of Histamine in Fish Using Micellar Media and Fluorescamine as Labelling Reagent 总被引:1,自引:0,他引:1
Adamou R Coly A Douabalé SE Saleck ML Gaye-Seye MD Tine A 《Journal of fluorescence》2005,15(5):679-688
An analytical method based on the use of fluorescamine to produce a fluorescent derivative with histamine and combined with
micellar-enhanced fluorescence detection of the formed complex is developed for the sensitive and rapid determination of histamine
in fishes. The fluorescence properties of the obtained complex in water and micellar solutions of sodium dodecyl sulfate (SDS),
cetyltrimethylammonium chloride (CTAC) and brij-700 are reported. Physicochemical variables influencing the sensitivity of
the method (pH, micellar, fluorescamine and NaCl relative concentrations) have been optimized. The stability of the formed
complex, as shown by kinetic study, depends on the pH of the solution. Linear calibration curves allowing an effective histamine
determination were established with large linear dynamic range (LDR), and low limits of detection (LOD) between 0.5 and 33
ng mL−1, according to the solvent. Application to the analysis of fish samples (sardines) yielded satisfactory results. The method
seems to be suitable for environmental fish quality control.
Presented in part, at the 39th IUPAC Congress and the 86th Conference of the Canadian Society for Chemistry, August, 10–15,
2003, Ottawa (Canada). 相似文献