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361.
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363.
Kin Keung Poon Kwan Lam Wong 《International Journal of Mathematical Education in Science & Technology》2017,48(5):735-755
The use of dynamic geometry software (DGS) is becoming increasingly familiar among teachers, but letting students conduct inquiries using computers is still not a welcome idea. In addition to logistics and discipline concerns, many teachers believe that mathematics at the lower secondary level can be learned efficiently through practice alone. Thus, the application of DGS remains limited to demonstration and explanation. This article discusses how a set of pre-constructed dynamic geometry (DG) materials was designed to teach the ‘similar triangles’ concept. The reactions and behaviour of students with relatively low levels of mathematic achievement are also analysed. Finally, the potential value of pre-constructed DG materials, with lab sheets and teacher intervention, in inquiry activities for junior-level students is discussed. 相似文献
364.
Kin Hong Liew Wan Zurina Samad Norazzizi Nordin Poh Lee Loh Joon Ching Juan Mohd Ambar Yarmo Badrul Hisham Yahay Rahimi M.Yusop 《催化学报》2015,(5):771-777
A new heterogeneous catalyst composed of Pd nanoparticles immobilized within a HypoG el resin has been prepared in the absence of any ligands using an extensive cross-linking method.This newly developed nanocatalyst was characterized by N_2 adsorption-desorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX),Fourier transform infrared spectroscopy and inductively coupled plasma-mass spectrometer(ICP-MS)techniques.TEM and XRD results revealed that the Pd nanoparticles were well dispersed with diameters in the range of 4–12 nm,and an average size of about 8 nm.The cross-linked Pd catalyst demonstrated excellent catalytic activity towards the synthesis of a series of biaryl compounds by the reaction of various aryl halides(e.g.,bromides andiodides)with phenylboronic acid in the presence of tetrabutylammonium bromide.ICP-MS analysis indicated that there was only 0.25%weight loss of Pd(0.55±0.02 ppm)from the supported catalyst after the first cycle reaction.Furthermore,the catalyst showed excellent reusability(up to five uses)with consistently high levels of catalytic activity following its recovery by filtration. 相似文献
365.
The specificity in chemical perturbation of crystal structure is examined by investigating the efffect of the position of particular substituent group on the crystal structure. 1,2,3,5-tetra-halobenzenes are chosen for this study. A comparative study of Raman phonon spectra of 1,2,3,5-tetrachlorobenzene; 1,2,3-trichloro-5-bromobenzene; and 1,3,5-trichloro-2-bromo-benzene crystals reveals that former two have the same crystal structure, while the latter has a different crystal structure. It is inferred that a bromine group substitution in 2-position of 1,2,3,5-tetrachlorbenzene creates a lattice instability which gives rise to a different crystal structure for 1,3,5-trichloro-2-bromobenzene. The nature of this instability is discussed. Mixed crystals of 1,2,3,5-tetrachlorobenzene and 1,2,3-trichloro-5-bromobenzene are studied to establish phonon correlation and deloalization. 相似文献
366.
Zenken Kin Yutaka Ohmori Mitsuo Komatsu Manabu Tsumura 《Journal of Physics and Chemistry of Solids》2006,67(11):2326-2330
The optical and electroluminescent properties of 3,4,6-triphenyl-α-pyrone (α-pyrone), a new blue fluoresce dye, are investigated using films prepared by wet and dry process and organic light-emitting diodes (OLEDs) fabricated with an α-pyrone-emitting layer. The optical properties of α-pyrone are found to be affected by its crystallinity. In the fabrication of OLEDs, wet processing (spin coating) is shown to be more suitable for preparation of the α-pyrone layer than dry processing (thermal evaporation). The best device performance is obtained for a device prepared using poly (n-vinylcarbazole) as the dye host, and a bathocuproine/tris-(8-hydroxyquinoline)aluminum bilayer as a hole-blocking and carrier-injection layer. The maximum luminance of this device is 3000 cd/m2 at a current density of 0.2 A/cm2, with a current efficiency of 1.8 cd/A at 0.02 A/cm2. 相似文献
367.
Guoqing Gu Kin Wah Yu 《中国颗粒学报》2005,(2)
A general theory on charges relaxation process in particle-fluid systems is introduced in this article. The method to derive analytical solutions for the charge relaxation equation is illustrated, and some respects for this theory are discussed in detail. 相似文献
368.
We report on the spectroscopic optical coherence tomography of highly scattering media using a parallel detection scheme incorporated
with an ultrabroadband femtosecond Ti:sapphire laser in the range of 700--880 nm. A plurality of spectrally-resolved reflectance
profiles are simultaneously measured in a single longitudinal scan, from which information on the spectral content of the
sample is derived. Differential absorption measurements of scattering media with known characteristics are performed to demonstrate
the potential use in quantitative analysis. 相似文献
369.
Nonlinear hydrodynamic and thermoacoustic oscillations of a bluff-body stabilised turbulent premixed flame 总被引:1,自引:0,他引:1
Chin Yik Lee Larry Kin Bong Li Matthew P. Juniper Robert Stewart Cant 《Combustion Theory and Modelling》2016,20(1):131-153
Turbulent premixed flames often experience thermoacoustic instabilities when the combustion heat release rate is in phase with acoustic pressure fluctuations. Linear methods often assume a priori that oscillations are periodic and occur at a dominant frequency with a fixed amplitude. Such assumptions are not made when using nonlinear analysis. When an oscillation is fully saturated, nonlinear analysis can serve as a useful avenue to reveal flame behaviour far more elaborate than period-one limit cycles, including quasi-periodicity and chaos in hydrodynamically or thermoacoustically self-excited system. In this paper, the behaviour of a bluff-body stabilised turbulent premixed propane/air flame in a model jet-engine afterburner configuration is investigated using computational fluid dynamics. For the frequencies of interest in this investigation, an unsteady Reynolds-averaged Navier–Stokes approach is found to be appropriate. Combustion is represented using a modified laminar flamelet approach with an algebraic closure for the flame surface density. The results are validated by comparison with existing experimental data and with large eddy simulation, and the observed self-excited oscillations in pressure and heat release are studied using methods derived from dynamical systems theory. A systematic analysis is carried out by increasing the equivalence ratio of the reactant stream supplied to the premixed flame. A strong variation in the global flame structure is observed. The flame exhibits a self-excited hydrodynamic oscillation at low equivalence ratios, becomes steady as the equivalence ratio is increased to intermediate values, and again exhibits a self-excited thermoacoustic oscillation at higher equivalence ratios. Rich nonlinear behaviour is observed and the investigation demonstrates that turbulent premixed flames can exhibit complex dynamical behaviour including quasiperiodicity, limit cycles and period-two limit cycles due to the interactions of various physical mechanisms. This has implications in selecting the operating conditions for such flames and for devising proper control strategies for the avoidance of thermoacoustic instability. 相似文献
370.
A novel synthetic strategy was developed for the preparation of magnetic core-shell (MCS) particles consisting of hydrophobic poly(methyl methacrylate) cores with hydrophilic chitosan shells and gamma-Fe2O3 nanoparticles inside the cores via copolymerization of methyl methacrylate from chitosan in the presence of vinyl-coated gamma-Fe2O3 nanoparticles. The magnetic core-shell particles were characterized with transmission electron microscopy, field-emission scanning electron microscopy, particle size and zeta-potential measurements, vibrating sample magnetometry, and atomic force microscopy, respectively. The MCS particles were less than 200 nm in diameter with a narrow size distribution (polydispersity = 1.09) and had a good colloidal stability (critical coagulation concentration = 1.2 M NaCl at pH 6.0). Magnetization study of the particles indicated that they exhibited superparamagnetism at room temperature and had a saturation magnetization of 2.7 A m2/kg. The MCS particles were able to form a continuous film on a glass substrate, where magnetic nanoparticles could evenly disperse throughout the film. Thus, these new materials should be extremely useful in various applications. 相似文献