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31.
The characterization of carbon surface activity in the absence of gasification was attempted using oxygen isotope exchange in CO2 over spectroscopically pure natural graphite, the surface activity being characterized by the rate of approach to isotopic equilibrium. The probable mechanism of exchange is via the first step in the carbon-CO2 reaction, the dissociation of CO2 over a carbon free site: . Assuming this mechanism to hold for isotopic exchange, the theoretical rate equation was derived. The rate constants i1, and j1, were obtained from previous studies. Theoretical calculations show that the exchange rate is negligible over natural graphite at temperatures much below gasification conditions. Experimental verification of the theoretical analysis was not possible due to the activity of the quartz boat, holding the graphite, for catalyzing the exchange reaction. The exchange reaction was successfully followed over the Pt and CaO supported on a graphitized carbon black, in which case the activity was much, much greater than that ovgr the empty quartz boat. 相似文献
32.
Lesa Lorenzen Huber Kalpana Shankar Kelly Caine Kay Connelly L. Jean Camp Beth Ann Walker 《International journal of human-computer interaction》2013,29(7):441-455
In-home technologies can support older adults' activities of daily living, provide physical safety and security, and connect elders to family and friends. They facilitate aging in place while reducing caregiver burden. One of older adults' primary concerns about in-home technologies is their potential to reduce human contact, particularly from cherished caregivers. In this exploratory in situ study, we provided an ecosystem of networked monitoring technologies to six older adults and their caregivers. We analyzed the amount and content of communication between them. The amount of noncomputer-mediated communication did not decrease through the 6-week study. The content of communication coalesced into four themes: communication about the technologies, communication facilitated by technologies, intrusiveness of technologies, and fun and playfulness with the technologies. Results suggest that in-home technologies, designed with sensitivity to older adults' primary motivations, have the potential to shape and tailor important relationships in later life. 相似文献
33.
James Alfred Walker Katharina Völk Stephen L. Smith Julian Francis Miller 《Genetic Programming and Evolvable Machines》2009,10(4):417-445
Parallel and distributed methods for evolutionary algorithms have concentrated on maintaining multiple populations of genotypes,
where each genotype in a population encodes a potential solution to the problem. In this paper, we investigate the parallelisation
of the genotype itself into a collection of independent chromosomes which can be evaluated in parallel. We call this multi-chromosomal evolution
(MCE). We test this approach using Cartesian Genetic Programming and apply MCE to a series of digital circuit design problems
to compare the efficacy of MCE with a conventional single chromosome approach (SCE). MCE can be readily used for many digital
circuits because they have multiple outputs. In MCE, an independent chromosome is assigned to each output. When we compare
MCE with SCE we find that MCE allows us to evolve solutions much faster. In addition, in some cases we were able to evolve
solutions with MCE that we unable to with SCE. In a case-study, we investigate how MCE can be applied to to a single objective
problem in the domain of image classification, namely, the classification of breast X-rays for cancer. To apply MCE to this
problem, we identify regions of interest (RoI) from the mammograms, divide the RoI into a collection of sub-images and use
a chromosome to classify each sub-image. This problem allows us to evaluate various evolutionary mutation operators which
can pairwise swap chromosomes either randomly or topographically or reuse chromosomes in place of other chromosomes. 相似文献
34.
35.
Moritz Tebbe Elizabeth Galati Gilbert C. Walker Eugenia Kumacheva 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(37)
Future progress in nanoscience and nanotechnology necessitates further development of versatile, labor‐, and cost‐efficient surface patterning strategies. A new approach to nanopatterning is reported, which utilizes surface segregation of a smooth layer of an end‐grafted homopolymer in a poor solvent. The variation in polymer grafting density yields a range of surface nanostructures, including randomly organized pinned spherical micelles, worm‐like structures, networks, and porous films. The capability to use the polymer patterns for site‐specific deposition of small molecules, polymers, or nanoparticles is shown. This versatile strategy enables patterning of curved surfaces with direct access to the substrate and no need in changing polymer composition to realize different surface patterns. 相似文献
36.
We describe a type of multilayer dielectric coating designed to enhance the intensity of evanescent waves. The coating consists of a stack of alternating high- and low-index quarter-wave layers followed by a final low-index layer whose thickness is chosen to optimize the evanescent-wave intensity. Indirect measurements of the film properties are in good agreement with theory. 相似文献
37.
A. Erb J. -Y. Genoud F. Marti M. Däumling E. Walker R. Flükiger 《Journal of Low Temperature Physics》1996,105(3-4):1023-1028
We report on the absence of the so-called fishtail or peak effect in the magnetisation curves of properly oxygenated high purity (5N) single crystals of YBa2Cu3O7–. As we recently reported [1] high pressure oxygenation procedures are suitable to produce a monotonous dependence of the critical current density with the magnetic field. In this article we report furthermore how to reversibly produce or remove this effect on the same crystal by proper oxygenation methods. Along with the high purity of the samples, — due to crystal growth in non reactive BaZrO3 crucibles —, this proves that at least in pure samples the fishtail effect is due to different oxygenation states and/or oxygen distributions. In less pure samples, however, other sources for this anomaly like metallic impurities can act as an additional source for the fishtail anomaly. 相似文献
38.
Barrett CP Blair P Buller GS Neilson DT Robertson B Smith EC Taghizadeh MR Walker AC 《Applied optics》1996,35(35):6934-6944
We describe an optical system developed to form the basis of a 64 × 64 free-space optical matrix-matrix crossbar switch. The design and performance of each of the main optical components is discussed: lenses, diffractive optical elements, and polarizing beamsplitters, together with the optomechanical hardware design. For these components, throughput levels of -6.9 dB have been achieved, which is compatible with full system operation at 10(-12) bit error rates at ≥270 Mbits s(-1). 相似文献
39.
I. Maggio-Aprile Ch. Renner A. Erb E. Walker Ø. Fischer 《Journal of Low Temperature Physics》1996,105(5-6):1129-1134
Scanning Tunneling Spectroscopy (STS) measurements have been carried out on the high Tc superconductor (HTS) YBa2Cu3O7– (YBCO). Using very high quality single crystals as well as hard tips, we obtained differential conductance spectra which showed various conductance features in agreement with other spectroscopic techniques. The reproducibility of our spectra allowed us to map for the first time the vortex lattice on a HTS using a STS technique1. The vortices are arranged in a short range order oblique lattice, while the cores of the flux lines show an anisotropic shape. These observations can be related to the in-plane anisotropy of YBCO. 相似文献
40.
SM Riordan CJ McIver BM Walker VM Duncombe TD Bolin MC Thomas 《Canadian Metallurgical Quarterly》1996,91(9):1795-1803
OBJECTIVES: To i) document the sensitivity and specificity of a combined scintigraphic/lactulose breath hydrogen test for small intestinal bacterial overgrowth and ii) investigate the validity of currently accepted definitions of an abnormal lactulose breath hydrogen test based on "double peaks" in breath hydrogen concentrations. METHODS: Twenty-eight subjects were investigated with culture of proximal small intestinal aspirate and a 10-g lactulose breath hydrogen test combined with scintigraphy. Gastroduodenal pH, the presence or absence of gastric bacterial overgrowth, and the in vitro capability of overgrowth flora to ferment lactulose were determined. RESULTS: Sensitivity (16.7%) and specificity (70.0%) of the lactulose breath hydrogen test alone for small intestinal bacterial overgrowth were poor. Combination with scintigraphy resulted in 100% specificity, because double peaks in serial breath hydrogen concentrations may occur as a result of lactulose fermentation by cecal bacteria. Sensitivity increased to 38.9% with scintigraphy, because a single rise in breath hydrogen concentrations, commencing before the test meal reaches the cecum, may occur in this disorder. Sensitivity remained suboptimal irrespective of the definition of small intestinal bacterial overgrowth used, the nature of the overgrowth flora, favorable luminal pH, the presence of concurrent gastric bacterial overgrowth, or the in vitro ability of the overgrowth flora to ferment lactulose. CONCLUSIONS: Definitions of an abnormal lactulose breath hydrogen test based on the occurrence of double peaks in breath hydrogen concentrations are inappropriate. Not even the addition of scintigraphy renders this test a clinically useful alternative to culture of aspirate for diagnosing small intestinal bacterial overgrowth. 相似文献