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411.
Mostak Ahmed Mubarak A. Khan Md. Rezwan Miah Syed Abdul Monim M. Anwar H. Khan 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):927-936
Polyethyleneterephthalate (PET) based proton exchange membrane for using in fuel cells was successfully prepared by gamma radiation-induced graft copolymerization of styrene monomer onto PET film and the consequent selective sulfonation of the grafting chain in the film state using chlorosulfonic acid (ClSO3H). The effects of grafting conditions (e.g., monomer concentration, irradiation dose) on the degree of grafting and sulfonation condition (e.g., optimum concentration of ClSO3H) on the degree of sulfonation were studied. The degree of grafting, the degree of sulfonation and the physico-chemical properties (such as, water uptake, mechanical strength, thermal durability, hydrolytic stability, oxidative stability) of the gamma radiation-induced grafted membrane were found to be better when compared to those of the UV-radiation grafted membrane. The membrane shows higher ion exchange capacity (0.9 mmol g?1) and higher proton conductivity (0.075 S cm?1), similar to those of Nafion membrane. 相似文献
412.
The electronic and optical properties of tetragonal barium titanate (BaTiO3) have been investigated by use of first-principles density functional theory on a plane wave basis, by use of norm-conserving pseudopotentials in the localized density approximation. For accuracy, experimental lattice parameters reported in the literature were used. The band structure, total and partial density of states (DOS), and Born effective charges of tetragonal BaTiO3 were obtained from first-principles calculations. The partial DOS and Born effective charges indicate that the Ti–O bonds are partially covalent and the Ba–O bonds are partially ionic. The complex dielectric functions for ordinary and extraordinary optical polarization were calculated, and were in reasonable agreement with those from previous first-principles calculations. The refractive index, extinction coefficient, reflectivity, and energy-loss spectrum for both types pf polarization were calculated from the complex dielectric function; the results obtained were an improvement on other published results. 相似文献
413.
Anwar Al-Yatama 《Photonic Network Communications》2014,27(1):34-46
One of the most important performance measurements in wavelength-division multiplexing (WDM) networks is the call blocking probability. In this paper, we present an approximate analytical method to evaluate the blocking probabilities in survivable WDM networks with dynamically arriving connection requests. Our approach utilizes the wavelength independence whereby WDM network can be regarded as an aggregation of disjoint single wavelength sub-networks with a common physical topology. In each single wavelength sub-network, we derive the calculation of the blocking probability from an exact analysis. We assume dedicated protection with fixed routing and either first-fit or random wavelength assignment. Simulation results demonstrate the accuracy of the proposed method. 相似文献
414.
Steroidal ketone thiosemicarbazones (4–6), obtained from the corresponding ketones(1–3), on oxidative cyclization with H2O2 at 0°C provide title compounds (7–9), respectively. The structures of these compounds have been established on the basis of their elemental analytical and spectral data. 相似文献
415.
416.
M. S. Rafique M. Khaleeq-ur-Rahman T. Firdos K. Aslam M. Shahbaz Anwar M. Imran H. Latif 《Laser Physics》2007,17(9):1138-1145
A pulsed Nd:YAG laser (10 mJ, 12 ns, 1064 nm) was employed to study the IR irradiation effects on metallic samples of cadmium. The laser was irradiated for 100, 200, and 300 shots under a vacuum ~10?3 Torr. The results were investigated using a Hi Tech S3000H Scanning Electron Microscope (SEM) and X’pert Pro PANalytical X-ray Diffractometer (XRD). The micrographs obtained from SEM reveal that the surface morphological changes have occurred in the form of a crater. The forward expansion of plasma into an ambient gas coupled with the recondensation of the target surface results in the formation of debris. Large temperature gradients produce variations in the thermal resistance that leads to the distributed shape of the heat-affected zone. The hydrodynamic effects are apparent with a liquid flow to form the recast material around the periphery of the laser focal area. The turbulent resolidified material is formed when surface asperities are accelerated away from the liquid surface during each laser pulse due to melting followed by the thermal expansion of the liquid. The positive feed back of the repeated pulses resulted in the form of ripples. Grains appear on the surface as evidence of heterogeneous nucleation. The confirmation of the formation of these structures has been done by X-ray Diffractometer (XRD). 相似文献
417.
Anwar Usman Ibrahim Abdul Razak Hoong-Kun Fun Suchada Chantrapromma Yan Zhang Jian-Hua Xu 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1438-1440
In the title compound, C25H19NO4, the indole moiety is not completely planar, the heterocyclic ring being distorted very slightly towards a half-chair conformation. The benzoyl and 4-methoxyphenyl substituents are individually almost planar and are in a bisecting and nearly perpendicular configuration, respectively, with respect to the plane of the indole moiety. The molecular and packing structures in the crystal are stabilized by intramolecular and intermolecular C—H⋯O interactions. 相似文献
418.
Thierry Woignier Juan Primera Anwar Hashmy 《Journal of Sol-Gel Science and Technology》2006,40(2-3):201-207
Volcanic soil comprises weathering products such as allophane, originating from a leaching process of volcanic ashes and glasses.
These soils are interesting in terms of mitigation of the greenhouse effect (C sequestration), because they are known for
accumulating more C than non-volcanic soils. Allophanes are natural amorphous silicates and have physical features very close
to those of synthetic gels. Knowledge of the allophanic soil structure is required to understand the sequestration mechanism.
In this paper, nitrogen adsorption-desorption experiments, measured on allophanic soil samples, show that the hydraulic diameter
(Dh) is shifted towards smaller size while the pore volume (Vp) and specific surface area (S) increase, when the allophane content of the soil increases. We introduce a numerical model
to simulate the structure of this “natural gel”. The algorithm is based on Diffusion-Limited Cluster-Cluster Aggregation in
which larger particles hinder the DLCA. As a function of the relative content of allophane (gel) and larger particles, the
textural properties (Vp, S, Dh) of the different simulated structure are calculated using a simple triangulation method.
Numerical results are in good agreement with experimental data and from the simulated data, we can derive the permeability
evolution as a function of the allophane content. We show that at the scale of the allophanic aggregates the calculated permeability
is low and could be an important parameter to explain the larger C content of allophanic soils. Because of the low allophanic
aggregate permeability, the fluid exchanges and chemical reactions are slow. This gel-allophane analogy and DLCA model allow
proposing a different approach to describe the properties of these peculiar soils. 相似文献
419.
420.