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911.
A model is presented for kinetic growth processes in flames, based on neutron, X-ray, and light-scattering data on commercial fumed silica powders. The model and data are consistent with the existence of fractally rough primary particles aggregated into highly ramified clusters. By mapping onto kinetic models, four processes are identified that determine the structure of the powders: kinetic nucleation, ballistic polymerization, sintering, and diffusion-limited aggregation. 相似文献
912.
913.
Alok Gupta Leigh L. Linden Dale O. Stahl Andrew B. Whinston 《Information Technology and Management》2001,2(2):175-191
There has been a sustained argument in Internet community regarding the utility, feasibility, and sustainability of the usage-based Internet traffic pricing versus the attractiveness of non-usage-based pricing from consumer perspective. Using a simulated network of well defined services we investigate the benefits: (i) received by the system as a whole, and (ii) received by individuals and groups of customers, when part of the network has no-usage based pricing whereas the other part employs an economic usage based pricing. Our simulation results indicate that not only are the systemwide benefits enhanced by usage-based pricing, but also the users who lose out are precisely the people who should be denied access during the peak periods. 相似文献
914.
The purpose of this study was to determine the effect of leads (or hypertext node previews) on cognitive load and learning. Leads provided a brief summary of information in the linked node, which helped orient the reader to the linked information. Dependent variables included measures of cognitive load: self-report of mental effort, reading time, and event-related desynchronization percentage of alpha, beta and theta brain wave rhythms; and learning performance: a recall task, and tests of domain and structural knowledge. Results indicated that use of leads reduced brain wave activity that may reflect split attention and extraneous cognitive load, and improved domain and structural knowledge acquisition. Further, findings provide insights into differentiating the types of cognitive load apparent in hypertext-assisted learning environments. Use of EEG measures allowed examination of instantaneous cognitive load, which showed that leads may be influencing germane load—reducing mental burden associated with creating coherence between two linked node. The self-report of mental effort measure appears more closely associated with overall and intrinsic load. 相似文献
915.
Kyriakos C. Labropoulos Sriram Rangarajan Dale E. Niesz Stephen C. Danforth 《Journal of the American Ceramic Society》2001,84(6):1217-1224
Dynamic rheology was used to study the gelation behavior of agar gel based aqueous binders (1–3 wt%) for powder injection molding. Typical gelation temperatures, T gel , and liquefaction temperatures, T liq , were 36° and 78°C, respectively. The thermal history of the gels was found to influence T gel and the asymptotic storage modulus, G '. A higher degree of undercooling (Δ T = T gel − T hold ) enhanced the driving force for gelation. G ' master curves were created and revealed a relatively weak frequency dependence. G ' increased significantly with agar content. The shape of the gel's relaxation spectrum was found to be independent of agar content, indicating that the nature of the relaxation processes does not change significantly. 相似文献
916.
André Müller Sara E. C. Dale Miles A. Engbarth Simon J. Bending Laurence M. Peter Andreas Knittel Hans Fangohr 《Advanced functional materials》2011,21(10):1874-1880
Three dimensional ferromagnet–superconductor core–shell structures are realized by electrocrystallisation and their magnetic properties investigated. We observe fully re‐entrant core superconductivity in increasing fields that survives well above the bulk critical field due to compensation effects. The net measured magnetization of optimized structures could be switched from absolute para(ferro‐)magnetic to diamagnetic by tuning the external magnetic field. Micromagnetic simulations of the structures are in good qualitative agreement with our results. 相似文献
917.
Igor De la Varga Javier Castro Dale Bentz Jason Weiss 《Cement and Concrete Composites》2012,34(9):1001-1008
This paper focuses on testing performed on mixtures that would be consistent with the mortar portion of a concrete bridge deck mixture for many state departments of transportation. In this work a relatively large percentage of cement (40%, 60%, or 80% by volume) is replaced with Class C fly ash. To overcome concerns associated with slow set and early-age strength development that are often expressed with the high volume fly ash mixtures (HVFA), the water-to-cementitious materials ratio (w/cm) by mass has been reduced from a conventional value of 0.42 to 0.30. To overcome potential complications that the low w/cm may cause in terms of self-desiccation, internal curing (IC) with prewetted lightweight aggregate was used to reduce shrinkage and increase hydration. By adopting this approach (lowering the w/c and using IC) IC HVFA mixtures show additional benefits that should permit their broader application. 相似文献
918.
Konstantinos Kyritsis Christopher Hall Dale P. Bentz Nicola Meller Moira A. Wilson 《Journal of the American Ceramic Society》2009,92(3):694-701
Cement-based materials used to seal geothermal or deep oil wells are exposed to severe conditions. Optimizing engineering properties such as strength and permeability is therefore very important. We have synthesized hydroceramic materials for such applications based on the CaO−Al2 O3 −SiO2 −H2 O (CASH) system and cured them over a range of temperatures (200°–350°C). Depending on initial composition and curing temperature, hydroceramics of complex and diverse mineralogy and microstructure are formed. The minerals found include portlandite, jaffeite, xonotlite, gyrolite, 11 Å tobermorite, truscottite, hydrogarnet, and calcium aluminum silicate hydrate. These cement-based hydroceramic materials develop complicated pore structures, which strongly affect bulk properties. We report the compressive strength and permeability of these materials and show how these bulk engineering properties are related to microstructure. The compressive strength was found to be in the range 2–52 MPa and the intrinsic permeability in the range 0.5 × 10−17 to 3300 × 10−17 m2 . Scanning electron microscopy (SEM) was used for imaging the hydroceramic microstructures. Further, we have computed the intrinsic permeability from 2-D SEM images by using the Stokes equation solver, Permsolver, applied to reconstructed 3-D images and the results are shown to be in good agreement with experimentally determined values. 相似文献
919.
Dale Cigoy 《数字社区&智能家居》2009,(6):42-44
无线通信产业的巨大成长意味着对于无线设备的元器件和组件的测试迎来了大爆发.包括对组成通信系统的各种RFIC和微波单片集成电路的测试。这些测试通常需要很高的频率. 相似文献
920.
Dale D. McClure Julien Deligny John M. Kavanagh David F. Fletcher Geoffrey W. Barton 《化学工程与技术》2014,37(4):652-658
The impact of surfactant addition on the overall holdup, drag coefficient, and bubble size distribution (BSD) in a bubble column operating at industrially relevant superficial velocities was analyzed. A range of surfactants was examined, including alcohols, sugars, and antifoaming agents. It was ascertained that the effect of a surfactant on the holdup and BSD could be related to the chemical structure of the compound, specifically its hydrophilic/hydrophobic nature as characterized by the octanol/water partition coefficient. Addition of 2‐propanol to an air/water system induces a behavior similar to the fermentation media used in aerobic bioprocesses, meaning that such a system can be applied as a meaningful physical analogue in pilot‐scale experimentation. 相似文献