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1.
Kasem K. Kasem Franklin A. Schultz 《Journal of Inorganic and Organometallic Polymers》1994,4(4):377-390
Multiply charged electroactive anions [IrCl
6
2–
, Fe(CN)
6
3–
, and W(CN)
8
4–
] are electrostatically incorporated in polymeric films of tris(4-vinyl-4-methyl-2,2-bipyridine) ruthenium(II) [poly-Ru(vbpy)
3
2+
] from aqueous trifluoroacetate solution. Values of apparent diffusion coefficients (D
ct) and heterogenous electron transfer rates (k
et) are measured for these anions as a function of their relative concentration (
M/
Ru) in the film.D
ct andk
et decrease systematically as
M/
Ru increases in a manner that is independent of charge and chemical identity of the ion. This result suggests that a nonchemical process, presumably electrostatic cross-linking, limits diffusional motion and is responsible for the decrease inD
ct andk
et with increasing anion content. Protonated polyvinyl-pyridine films exhibit similar ranges and variations inD
ct andk
et, which suggest similar structures and mechanisms of charge transport for these films and poly-Ru(vbpy)
3
2+
. 相似文献
2.
Pisith Sam Pruettha Nanakorn Kasem Theerakittayakorn Pana Suttakul 《International Journal of Mechanics and Materials in Design》2017,13(3):363-383
In this study, the effective elastic constants of several 2D and 3D frame-like periodic cellular solids with different unit-cell topologies are analytically derived using the homogenization method based on equivalent strain energy. The analytical expressions of strain energy of a unit cell under different strain modes are determined using a generic symbolic object-oriented finite element (FE) program written in MATLAB. The obtained analytical expressions of the strain energy are then used to symbolically compute the effective elastic constants that include Young’s moduli, Poisson’s ratios, and shear moduli. The obtained analytical effective elastic constants are numerically verified using results from an ordinary numerical FE program. The obtained closed-form effective elastic constants are also compared with some existing solutions from the literature. This study demonstrates that symbolic computation platforms can be properly used to provide efficient methodologies for finding useful analytical solutions of mechanical problems. Without the symbolic object-oriented FE program in this study, elaborate and tedious analytical analysis has to be manually performed for each different unit cell. The symbolic object-oriented FE program provides analytical analysis of unit cells that is accurate and fast. The object-oriented programming technique allows the symbolic FE program in this study to be efficiently implemented. 相似文献
3.
K.K. Kasem 《Journal of Applied Electrochemistry》2001,31(10):1125-1129
Novel solid films of a mixed polynuclear hexacyano iron(III) and decavanadates have been electrochemically prepared. The colour of these solid thin films ranged from yellow to blue depending on the thickness. The cyclic voltammograms (CVs) of these solid films indicate the involvement of both vanadium and iron redox centres in performing the electrochemical activities. Evidence of the catalytic activities of these films towards the reduction of some small oxoanions has been reported. 相似文献
4.
On the Use of Calcium Fluoride as an Infrared-Transparent First Body for In Situ Temperature Measurements in Sliding Contact 总被引:1,自引:0,他引:1
This article presents an investigation of the temperature changes in dry sliding contact for braking applications. An original
metrology method was developed using a special pad with a calcium fluoride ‘window’ in its centre. As calcium fluoride is
transparent to infrared radiation (up to 92% in 1–5 μm spectra), it allows access to the disc surface during friction for
estimating its temperature using a two-colour pyrometer. Using this set-up, the surface temperature of the disc was successfully
determined during friction. In addition, the temperature in the contact area was compared to that measured immediately outside
the contact area; the difference between them proved to be very minimal (<5%). The effect of introducing a calcium fluoride
‘window’ on friction was also studied, and the results show that its use does not affect the friction coefficient. Finally,
the wear mechanisms of the calcium fluoride were studied through the characterisation of the worn surfaces using several techniques. 相似文献
5.
6.
M. A. Abdelkareem E. T. Kasem N. Nakagawa E. A. M. Abdelghani A. A. Elzatahry K. A. Khalil N. A. M. Barakat 《Fuel Cells》2014,14(4):607-613
Mass transfer is a key parameter affecting the performance of the passive direct methanol fuel cells (DMFCs), which work under natural convection. In this study, effect of carbon nanofibers (CNFs) addition to the cathode microporous layer (MPL) on the performance of the passive DMFCs was investigated. The results indicated that CNFs content has a significant influence on both of the mass transport and the electrochemical surface area (ECSA). Interestingly, addition of the CNFs (20 wt.%) leads to increase the power density of the passive DMFC to 160% compared to pristine carbon black MPL. At low current density, the CNFs content has no influence on the performance, while at high current density the maximum performance can be obtained at 20 wt.% CNFs then the performance decreases with further increase in the CNFs content. Although the highest catalyst utilization is observed at 40 wt.% CNFs, a maximum power density of 36 mW cm–2 can be obtained at 20 wt.% CNFs and this is related to the significant effect of the mass transfer resistance under the passive operation conditions. Overall, addition of CNFs to the MPL can be considered an effective strategy to modify the passive DMFCs performance. 相似文献
7.
Fathalla M. El-Amin Mohamed A. Kasem 《International journal for numerical methods in engineering》1978,12(1):159-167
The flexural stiffness for a horizontally curved beam element is developed for nodal parameters wi, (?w/?s)i, βi, (?β/?s)i, (?2β/?s2)i, (?3β/?s3)i by assuming a cubic displacement function for vertical deflection w, and a seventh order polynomical function for the angle of twist β, along the length of the curved beam. The element gives good accuracy with even coarse mesh for the analysis of horizontally-curved steel beam with open thin-walled bisymmetrical cross-section. Warping restraint is considered in the derivation of the stiffness matrix, which has considerable influence on the behavior and design of steel bridges curved in-plan. The results obtained from such a new element are compared with those given by a lower order finite element, developed previously by the first author, and with theoretical solutions for the particular problem. 相似文献
8.
An improved fault ride-through strategy for doubly fed induction generator-based wind turbines 总被引:1,自引:0,他引:1
Kasem A.H. El-Saadany E.F. El-Tamaly H.H. Wahab M.A.A. 《Renewable Power Generation, IET》2008,2(4):201-214
Keeping the generators operating during transient grid faults becomes an obligation for the bulk wind generation units connected to the transmission network and it is highly desired for distribution wind generators. A proposed scheme is implemented to keep the wind-power DFIG operating during transient grid faults. Challenges imposed on the generator configuration and the control during the fault and recovering periods are presented. A comprehensive time domain model for the DFIG with the decoupled dq controller is implemented using Matlab/Simulink software. Intensive simulation results are discussed to ensure the validity and feasibility of the proposed fault ride through technique. The scheme protects the DFIG components, fulfills the grid code requirements and optimises the hardware added to the generator. 相似文献
9.
Kasem K. Kasem Franklin A. Schultz 《Journal of Inorganic and Organometallic Polymers and Materials》1994,4(4):377-390
Multiply charged electroactive anions [IrCl 6 2? , Fe(CN) 6 3? , and W(CN) 8 4? ] are electrostatically incorporated in polymeric films of tris(4-vinyl-4′-methyl-2,2′-bipyridine) ruthenium(II) [poly-Ru(vbpy) 3 2+ ] from aqueous trifluoroacetate solution. Values of apparent diffusion coefficients (D ct) and heterogenous electron transfer rates (k et) are measured for these anions as a function of their relative concentration (Γ M/Γ Ru) in the film.D ct andk et decrease systematically asΓ M/Γ Ru increases in a manner that is independent of charge and chemical identity of the ion. This result suggests that a nonchemical process, presumably electrostatic cross-linking, limits diffusional motion and is responsible for the decrease inD ct andk et with increasing anion content. Protonated polyvinyl-pyridine films exhibit similar ranges and variations inD ct andk et, which suggest similar structures and mechanisms of charge transport for these films and poly-Ru(vbpy) 3 2+ . 相似文献
10.
In this study, the effect of the substrate roughness on adhesion of mushroom-shaped microstructure was experimentally investigated. To do so, 12 substrates having different isotropic roughness were prepared from the same material by replicating topography of different surfaces. The pull-off forces generated by mushroom-shaped microstructure in contact with the tested substrates were measured and compared with the pull-off forces generated by a smooth reference. It was found that classical roughness parameters, such as average roughness (Ra) and others, cannot be used to explain topography-related variation in pull-off force. This has led us to the development of an integrated roughness parameter capable of explaining results of pull-off measurements. Using this parameter, we have also found that there is a critical roughness, above which neither smooth nor microstructured surface could generate any attachment force, which may have important implications on design of both adhesive and anti-adhesive surfaces. 相似文献