摘要 :
The static response of beams constructed of graphite--epoxy and piezoelectric laminate (hybrid laminate) subjected to electric field and thermal (i.e. self-strained) loading is considered. Two theoretical formulations are consider...
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The static response of beams constructed of graphite--epoxy and piezoelectric laminate (hybrid laminate) subjected to electric field and thermal (i.e. self-strained) loading is considered. Two theoretical formulations are considered: uncoupled which ignores the 'direct piezo- electric effect' (induced electric field due to variation in stress), and 'coupled' which includes the direct piezoelectric effect. A hierarchical finite element approximation of the governing equations using reduced material stiffness coefficients is developed. The electromagnetic potential is assumed to vary piecewise linearly through each piezoelectric lamina and the lamina surface that is in contact with a structural lamina is assumed to be grounded. Beam displacement theory is based on Reissner--Mindlin shear deformation theory. Sample problems are presented demonstrating the accuracy of the developed finite element model, and the response of hybrid laminates to self-strained loading.
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The square-like WCH nanosheets were synthesized by hydrothermal treatment of irregular WO_3 nanosheets prepared through acidification of Na_2WO_4•2H_2O. The obtained square-like and irregular WO_3 nanosheets were characterized wi...
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The square-like WCH nanosheets were synthesized by hydrothermal treatment of irregular WO_3 nanosheets prepared through acidification of Na_2WO_4•2H_2O. The obtained square-like and irregular WO_3 nanosheets were characterized with field emission scanning electron microscopy, X-ray powder diffraction and transmission electron microscopy. The gas sensing properties of sensors based on as-prepared samples were investigated. The results indicated that both samples exhibited high response to NO_2. The sensor based on square-like WO_3 nanosheets exhibited remarkably enhanced response and faster response/recovery time for NO_2 compared with that based on irregular nanosheets. Especially, the sensor based on square-like WO_3 nanosheets could detect NO_2 down to 40ppb, which covered environmental standard. A possible reason for the influence of unique structure on the sensing properties of sensors based on square-like WO_3 was proposed.
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Nitrogen-doped TiO_2 materials have been shown to exhibit visible-light photoactivity, but the operative mechanism(s) are not well understood. Here we use structurally and compositionally well-defined epitaxial films of TiO_(2-x)N...
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Nitrogen-doped TiO_2 materials have been shown to exhibit visible-light photoactivity, but the operative mechanism(s) are not well understood. Here we use structurally and compositionally well-defined epitaxial films of TiO_(2-x)N_x anatase (001) and rutile (110) (x≤ ～0.02) to show a qualitative difference between the visible-light activities for the two polymorphs. Holes generated by visible light at N sites in anatase (001) readily diffuse to the surface and oxidize adsorbed trimethyl acetate while the same in rutile (110) remain trapped in the bulk. In light of the low doping densities that can be achieved in phase-pure material, conventional wisdom suggests that holes should be trapped at N sites in both polymorphs. Although the detailed mechanism is not yet understood, these results suggest that the hole hopping probability is much higher along the [001] direction in N-doped anatase than along the [110] direction in N-doped rutile.
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It has been acknowledged that infill drilling can improve the recovery of hydrocarbons by accelerating production as most reservoirs in the world are not homogeneous. With the increasing demand for energy and higher oil and gas pr...
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It has been acknowledged that infill drilling can improve the recovery of hydrocarbons by accelerating production as most reservoirs in the world are not homogeneous. With the increasing demand for energy and higher oil and gas prices, more and more fields all over the world are undergoing infill drilling.
This paper discusses two recently developed techniques to determine the infill drilling potential in large tight gas reservoirs and it summarizes what petroleum engineers have learnt about the application of those two techniques. Field examples are also included in this paper to demonstrate the usefulness, as well as the limitations, of these techniques to help independent operators develop operation and design strategies for current and future infill drilling projects in large tight gas basins.
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This paper reports an innovative, scientific and yet practicable approach developed in assisting a large-scale high-rise residential building developer in Hong Kong for monitoring the competitiveness in the switchboard supply to h...
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This paper reports an innovative, scientific and yet practicable approach developed in assisting a large-scale high-rise residential building developer in Hong Kong for monitoring the competitiveness in the switchboard supply to her development projects. In this study, a pricing indicator was developed for monitoring whether the pricing levels charged to developer had attained a competitive level. Our results revealed that the pricing level charged to the developed was far from competitive, and the high cost was contributed by inadequate competitiveness in the switchboard supply as a result of the practice of including only a limited number of suppliers on the pre-qualification list. By relaxing the prc-qualification requirements, the pricing level dropped to a very competitive level after two additional suppliers being included on the list.
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摘要 :
Networks deploying hierarchical routing are recursively partitioned into sub-networks that do not reveal full details of their internal structure outside their domains. Instead, na aggregated view of certain parameters that are as...
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Networks deploying hierarchical routing are recursively partitioned into sub-networks that do not reveal full details of their internal structure outside their domains. Instead, na aggregated view of certain parameters that are associated with traversal within such sub-networks between their border nodes is advertised. The ATM PNNI standard and the Intenet Nimrod architecture both adopt this approach for routing. This paper studies the effectiveness of ATM hierarchical routing protocols on networks with different hierarchical structures by simulation. Our study shows that, in general, the hierarchical source routing performs well, compared to the global routing strategy which imposes no hierarchy, while utilizing less storage and communication overheads. For certain networks and topologies, the hierarchical routing performs better than the global routing. Different hierarchies imposed on the same topologies have significantly different performance on the throughput and routing delay. This suggests the necessity of studying the hierarchy design for communication networks using hierarchical routing.
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We report on the study of a single-photon-emitting diode at 77 K. The device is composed of InAs/GaAs quantum dots embedded in the i-region of a p-i-n diode structure. The high signal to noise ratio of the electroluminescence, as ...
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We report on the study of a single-photon-emitting diode at 77 K. The device is composed of InAs/GaAs quantum dots embedded in the i-region of a p-i-n diode structure. The high signal to noise ratio of the electroluminescence, as well as the small second order correlation function at zero-delay g~((2))(0), implies that the device has a low multiphoton emission probability. By comparing the device performances under different excitation conditions, we have, in detail, discussed the basic parameters, such as signal to noise ratio and g~((2))(0), and provided some useful information for the future application.
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We report the observation of two distinct modes of rate-dependent behavior during contact cycling tests. One is a higher pull-off force at low cycling rates and the other is a higher pull-off force at high cycling rates. Subsequen...
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We report the observation of two distinct modes of rate-dependent behavior during contact cycling tests. One is a higher pull-off force at low cycling rates and the other is a higher pull-off force at high cycling rates. Subsequent investigation of these contacts using scanning electron microscopy (SEM) demonstrates that these two rate-dependent modes can be related to brittle and ductile separation modes. The former behavior is indicative of brittle separation, whereas the latter accompanies ductile separation. Thus by monitoring the rate dependence of the pull-off force, the type of separation mode can be identified during cycling without interrupting the test to perform SEM.
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