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91.
Philip L. Walker Shiro Matsumoto Tamotsu Hanzawa Takatoshi Muira Ismail M.K. Ismail 《Fuel》1983,62(2):140-149
Calcium is the most important in-situ catalyst for gasification of US coal chars in O2, CO2 and H2O. It is a poor catalyst for gasification of chars by H2. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O2, CO2 and H2O. Carbon monoxide inhibits catalysis of the CH2O reaction by calcium, potassium and sodium; H2 inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH2O reaction. Iron is not an important catalyst for the gasification of chars in O2, CO2 and H2O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H2 + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H2O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron. 相似文献
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95.
Ashwin Kumar Vutha Benyamin Davaji Chung Hoon Lee Glenn M. Walker 《Microfluidics and nanofluidics》2014,17(5):871-878
We demonstrate the use of heat to count microscopic particles. A thermal particle detector (TPD) was fabricated by combining a 500-nm-thick silicon nitride membrane containing a thin-film resistive temperature detector with a silicone elastomer microchannel. Particles with diameters of 90 and 200 μm created relative temperature changes of 0.11 and ?0.44 K, respectively, as they flowed by the sensor. A first-order lumped thermal model was developed to predict the temperature changes. Multiple particles were counted in series to demonstrate the utility of the TPD as a particle counter. 相似文献
96.
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
97.
Microporous carbon of high purity was produced by the carbonization of Saran at 900° followed by activation in either CO2 at 900°, O2 at 300°, or air at 425°. The activated carbons were characterized using N2 adsorption at ?195° CO2 adsorption at 25°, and mercury and helium displacements. Hydrogen sulfide oxidation (at H2S pressures between 0.4–3.8 Torr) by O2 (in excess of stoichiometric amount) was studied between 100–160° using a microbalance, that is by weighing the build-up of sulfur on the carbon. The predominant reaction, was first order in H2S concentration and independent of O2 concentration. The rate was only slightly reduced by sulfur build-up to at least 36%, by weight, on the carbon. The oxidation rate was significantly higher over the O2-activated carbon than over the CO2-activated carbon. Throughout the studies, oxidation rates could be correlated with area active to O2 chemisorption. It is concluded that H2S oxidation proceeds via rapid dissociative chemisorption of oxygen on carbon sites followed by reaction with H2S. Rates of H2S oxidation were also studies over commercial, granular activated carbons of significant ash contents. 相似文献
98.
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
99.
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
100.
CM Otto MC Mickel JW Kennedy EL Alderman TM Bashore PC Block JA Brinker D Diver J Ferguson DR Holmes 《Canadian Metallurgical Quarterly》1994,89(2):642-650
BACKGROUND: To identify predictors of long-term outcome after balloon aortic valvuloplasty, we analyzed data on 674 adults (mean age, 78 +/- 9 years; 56% were women) undergoing this procedure at 24 clinical centers who had a mean initial increase in aortic valve area of 0.3 cm2. METHODS AND RESULTS: Baseline data included clinical, echocardiographic, and catheterization variables. Follow-up data included mortality, cause of death, rehospitalization, 6-month echocardiography, and functional status. Kaplan-Meier curves and log-rank tests were used to evaluate survival in subgroups. Multivariate Cox regression models were used to identify independent predictors of survival. Overall survival was 55% at 1 year, 35% at 2 years, and 23% at 3 years, with the majority of deaths (70%) classified as cardiac by an independent review committee. Rehospitalization was common (64%), although 61% of survivors at 2 years reported improved symptoms. Echocardiography at 6 months (n = 115) showed restenosis from the postprocedural valve area of 0.78 +/- 0.31 cm2 to 0.65 +/- 0.25 cm2 (P < .0001). With stepwise multivariate analysis, sequentially adding clinical, echocardiographic, and catheterization variables, the overall model identified independent predictors of survival as baseline functional status, baseline cardiac output, renal function, cachexia, female gender, left ventricular systolic function, and mitral regurgitation. Baseline and postprocedural variables were examined to identify which subgroup of patients has the best outcome after aortic valvuloplasty. A "lower-risk" subgroup (28% of the study population), defined by normal left ventricular systolic function and mild clinical functional limitation, had a 3-year survival of 36% compared with 17% in the remainder of the study group. CONCLUSIONS: Long-term survival after balloon aortic valvuloplasty is poor with 1- and 3-year survival rates of 55% and 23%, respectively. Although survivors report fewer symptoms, early restenosis and recurrent hospitalization are common. 相似文献