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51.
Y. Xu A. Goyal K.J. Leonard E.D. Specht D. Shi M. Paranthaman 《Journal of the American Ceramic Society》2006,89(3):914-920
YBa2 Cu3 O7− δ (YBCO or Y123) films on rolling-assisted biaxially textured substrates (RABiTS) were prepared via a fluorine-free metallorganic deposition (MOD) through spin coating, burnout, and high temperature anneal. The effects of substrate texture and surface energy of the CeO2 cap layer were investigated. Except for the commonly accepted key factors, such as the textures of substrate and buffer layers, we found some other factors, for example, the deposition temperature of the cap layer, are also critical to the epitaxial growth of Y123 phase. With the CeO2 cap layer deposited at relative high temperature of 700°C, a critical current density, J c , over 1 MA/cm2 has been demonstrated for the first time on Ni-RABiTS by a fluorine-free MOD method. Whereas for samples with CeO2 cap layers deposited at a lower temperature of 600°C, even though XRD data showed a better texture on these buffer layers, texture degradations of YBCO grains under the optimized processing conditions were observed and a lower oxygen partial pressure around 40 ppm was necessary for the epitaxial growth of Y123 phase. As a result, J c fell to 0.45 MA/cm2 at 77 K. The observed phenomena points to the change of surface energy and reactivity of the CeO2 cap layer with respect to the CeO2 deposition temperature. In this paper, the YBCO phase diagram was also summarized. 相似文献
52.
Plant fibers are rich in cellulose and they are a cheap, easily renewable source of fibers with the potential for polymer reinforcement. The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of polymeric materials. Hemp, sisal, jute, and kapok fibers were subjected to alkalization by using sodium hydroxide. The thermal characteristics, crystallinity index, reactivity, and surface morphology of untreated and chemically modified fibers have been studied using differential scanning calorimetry (DSC), X‐ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. Following alkalization the DSC showed a rapid degradation of the cellulose between 0.8 and 8% NaOH, beyond which degradation was found to be marginal. There was a marginal drop in the crystallinity index of hemp fiber while sisal, jute, and kapok fibers showed a slight increase in crystallinity at caustic soda concentration of 0.8–30%. FTIR showed that kapok fiber was found to be the most reactive followed by jute, sisal, and then hemp fiber. SEM showed a relatively smooth surface for all the untreated fibers; however, after alkalization, all the fibers showed uneven surfaces. These results show that alkalization modifies plant fibers promoting the development of fiber–resin adhesion, which then will result in increased interfacial energy and, hence, improvement in the mechanical and thermal stability of the composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2222–2234, 2002 相似文献
53.
Haiqing?Liu S.?Kay?ObendorfEmail author Michael?J.?Leonard Timothy?J.?Young Michael?J.?Incorvia 《Journal of surfactants and detergents》2005,8(4):311-317
The adsorption of aroma chemicals on cotton fabric was studied relative to the surfactant concentration, surfactant type,
water solubility, and fiber morphology. The adsorption increased with increasing surfactant concentration to a maximum near
the critical micelle concentration, then decreased with further increases in surfactant concentration. The adsorption also
was found to be highly dependent on the fiber surface area and pore structure; dramatic differences were observed between
untreated and mercerized cotton fabric and are believed to be due to morphological differences. Cationic and anionic surfactants
increased the aroma chemical adsorption, which varied with surfactant type, with cetyltrimethylammonium chloride (CTAC)>sodium
dodecyl sulfate (SDS)>H2O. Water solubility also influenced adsorption; in most cases, adsorption increased with water solubility. In addition, adsorption
was also influenced by chemical structure and hydrophobic interactions. The adsorption of aroma chemicals on cotton fabric
can be attributed to the aqueous solution being physically held in capillaries and pore structures within the fibular structure
of cotton fiber and also to molecular interactions among the aroma chemical molecules, surfactants, and cotton substrate. 相似文献
54.
Joe Kelly Mark Leonard Chutima Tantigate Ahmad Safari 《Journal of the American Ceramic Society》1997,80(4):957-964
Ceramic lead magnesium niobate–lead titanate ((1-x)PMN-x PT) of different compositions has been prepared by the columbite precursor method. This study discusses compositions ranging from 0.94PMN–0.06PT to 0.60PM–N0.40PT, focusing on two areas of the (1-x)PMNx PT system: compositions that exhibit electrostrictive behavior, and those that show piezoelectric behavior. In electrostrictive compositions where x is in the range of 0.06–0.20, the dielectric constant and electromechanical coupling factor dependencies on the bias field are evaluated. The optimal electromechanical properties are obtained with the composition 0.82PMN–0.18PT, measured at temperature T = Tm (the temperature of maximum dielectric constant) = 80°C and with a dc bias of 5 kV/cm. X–ray diffractometry is used to show that the (1-x)PMN-x PT system has a compositionally wide two–phase region and that 0.655PMN–0.345PT is the morphotropic phase boundary (MPB) composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (piezoelectric charge coefficient ( d33 ) value of 720 pC/N, dielectric constant ( K ) value of 5400, and electromechanical planar and thickness coupling coefficient ( kp and kt , respectively) values of 62% and 46%, respectively) are obtained at the MPB composition. 相似文献
55.
Cationic bulk polymerization of 1,3-dioxolan has been carried out in sealed ampoules using a high vacuum technique. The polymerization is initiated with triethyl oxonium hexafluorophosphate and the equilibrium between monomer and active polymer is attained within a few hours. Specific volumes of pure monomer and polymer in solution of its own monomer have been measured. Equilibrium measurements have been performed in the 40° to 141·4°C temperature range and the ceiling temperature is estimated to be 144° ± 2°C. The effect of short polymer chains on the equilibrium is discussed briefly. Values of ΔGlc, the free energy of polymerization of one mole of pure liquid monomer to one base-mole of amorphous polymer, are computed making allowance for the non-ideal mixing. Respective values of ?17.5 ± 0.8 kJ/mol and ?47.9 ± 2.2JK?1mol?1 are deduced for the corresponding ΔHlc and ΔSlc. ΔGlc is also computed from published data on equilibrium polymerization of 1,3-dioxolan in various solvents and the combined results for both types of polymerization yield ΔHlc = ?16.7 ± 0.5kJ/mol and ΔSlc = ?45.8 ± 1.5JK?1mol?1 for the 20° to 140°C range. 相似文献
56.
Geetanjali Yadav Leonard A. Fabiano Lindsay Soh Julie Zimmerman Ramkrishna Sen Warren D. Seider 《American Institute of Chemical Engineers》2021,67(1):e16992
Algae-to-biodiesel processes are hindered by high costs and low energy return on investment.1,2. Herein, three foci in research improve algae-to-biodiesel processes by: (1) reducing high installation and energy costs in the CO2 sequestration, cultivation, and harvesting stages; (2) improving oil extraction and biodiesel generation; and (3) increasing utilization of the proteins in lipid-extracted biomass (e.g., for animal feed), as well as the omega-3 fatty acids for nutraceuticals and food supplements. A process is introduced that uses carbon dioxide to aid in all three of these foci. CO2 is used first in the form of microbubbles to lyse algae cell walls, releasing triglyceride oils. CO2 also aids with transesterification of these triglycerides using methanol. At low temperatures (353.15–368.15 K) and intermediate pressures (5–10 MMPa), carbon dioxide causes methanol to dissolve partially in the triglyceride phase and triglyceride to dissolve partially in the methanol phase, increasing the transesterification reaction rate. Due to the nondestructive nature of these processes, other metabolites can also be harvested providing improvements in both mass and economic efficiency with an overall sharp reduction in the modeled price of biodiesel. 相似文献
57.
Factor Graph Modeling of Rigid‐body Dynamics for Localization,Mapping, and Parameter Estimation of a Spinning Object in Space
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This paper presents a new approach for solving the simultaneous localization and mapping problem for inspecting an unknown and uncooperative object that is spinning about an arbitrary axis in space. This approach probabilistically models the six degree‐of‐freedom rigid‐body dynamics in a factor graph formulation. Using the incremental smoothing and mapping system, this method estimates a feature‐based map of the target object, as well as this object's position, orientation, linear velocity, angular velocity, center of mass, principal axes, and ratios of inertia. This solves an important problem for spacecraft proximity operations. Additionally, it provides a generic framework for incorporating rigid‐body dynamics that may be applied to a number of other terrestrial‐based applications. To evaluate this approach, the Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) were used as a testbed within the microgravity environment of the International Space Station. The SPHERES satellites, using body‐mounted stereo cameras, captured a dataset of a target object that was spinning at ten rotations per minute about its unstable, intermediate axis. This dataset was used to experimentally evaluate the approach described in this paper, and it showed that it was able to estimate a geometric map and the position, orientation, linear and angular velocities, center of mass, and ratios of inertia of the target object. 相似文献
58.
Douglas L. Gardner Leonard S. Mark Marvin J. Dainoff Wei Xu 《International journal of human-computer interaction》2013,29(2):153-165
Modern ergonomic chairs typically have several dimensions that can be adjusted independently of one another. Finding a desirable setting for any one dimension can depend on how other dimensions are set, thereby confronting users with a significant control problem. One design strategy for dealing with this problem has been to link changes in seatpan and backrest angles in some ratio, such that a one‐degree change in seatpan angle is associated with a two‐ or three‐degree change in backrest angle. However, there is no evidence to justify the choice of a particular ratio. This article presents data that addresses this issue. Subjects, performing either an entry or verification task, could adjust the chair to any position. Backrest and seatpan angles were plotted over time and analyzed using both graphical and statistical methods. The resulting scatter plots do not support the industry standard, 1:2 or 1:3 ratio, of changes in seatpan to backrest angles. The possibility of a variable linkage is discussed; however, problems associated with such a solution raise the possibility that control issues might be best addressed through training and exploration. 相似文献
59.
保证所有管道中石油从一端流向另一端不泄漏要比它的探测更加困难。比较图中的3个系统,可以看到这项技术在40多年来是如何逐步发展的。 相似文献
60.
Derek A. Paley Naomi Ehrich Leonard Rodolphe Sepulchre 《Systems & Control Letters》2008,57(3):209-215
We provide a cooperative control algorithm to stabilize symmetric formations to motion around closed curves suitable for mobile sensor networks. This work extends previous results for stabilization of symmetric circular formations. We study a planar particle model with decentralized steering control subject to limited communication. Because of their unique spectral properties, the Laplacian matrices of circulant graphs play a key role. We illustrate the result for a skewed superellipse, which is a type of curve that includes circles, ellipses, and rounded parallelograms. 相似文献