Mathematics, Statistics, and Physicshttp://hdl.handle.net/10057/1192018-04-23T03:31:47Z2018-04-23T03:31:47ZEffect of support pretreatment temperature on the performance of an iron Fischer-Tropsch catalyst supported on silica-stabilized aluminaKeyvanloo, KamyarHuang, BaiyuOkeson, TrentHamdeh, Hussein H.Hecker, William C.http://hdl.handle.net/10057/149482018-04-22T20:31:18Z2018-02-12T00:00:00ZEffect of support pretreatment temperature on the performance of an iron Fischer-Tropsch catalyst supported on silica-stabilized alumina
Keyvanloo, Kamyar; Huang, Baiyu; Okeson, Trent; Hamdeh, Hussein H.; Hecker, William C.
The effect of support material pretreatment temperature, prior to adding the active phase and promoters, on Fischer-Tropsch activity and selectivity was explored. Four iron catalysts were prepared on silica-stabilized alumina (AlSi) supports pretreated at 700 degrees C, 900 degrees C, 1100 degrees C or 1200 degrees C. Addition of 5% silica to alumina made the AlSi material hydrothermally stable, which enabled the unusually high support pretreatment temperatures (>900 degrees C) to be studied. High-temperature dehydroxylation of the AlSi before impregnation greatly reduces FeO center dot Al2O3 surface spinel formation by removing most of the support-surface hydroxyl groups leading to more effectively carbided catalyst. The activity increases more than four-fold for the support calcined at elevated temperatures (1100-1200 degrees C) compared with traditional support calcination temperatures of <900 degrees C. This unique pretreatment also facilitates the formation of epsilon'-Fe2.2C rather than chi-Fe2.5C on the AlSi support, which shows an excellent correlation with catalyst productivity.
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2018-02-12T00:00:00ZIncreasing stability in the inverse source problem with attenuation and many frequenciesIsakov, Victor, 1947-Lu, Shuaihttp://hdl.handle.net/10057/147792018-04-01T00:25:33Z2018-01-01T00:00:00ZIncreasing stability in the inverse source problem with attenuation and many frequencies
Isakov, Victor, 1947-; Lu, Shuai
We study the interior inverse source problem for the Helmholtz equation from boundary Cauchy data of multiple wave numbers. The main goal of this paper is to understand the dependence of increasing stability on the attenuation, both analytically and numerically. To implement it we use the Fourier transform with respect to the wave numbers, explicit bounds for analytic continuation, and observability bounds for the wave equation. In particular, by using Carleman estimates for the wave equation we trace the dependence of exact observability bounds on the constant damping. Numerical examples in 3 spatial dimension support the theoretical results.
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2018-01-01T00:00:00ZIsotropic random fields with infinitely divisible marginal distributionsWang, FangfangLeonenko, NikolaiMa, Chunshenghttp://hdl.handle.net/10057/145552018-02-08T17:36:57Z2018-01-01T00:00:00ZIsotropic random fields with infinitely divisible marginal distributions
Wang, Fangfang; Leonenko, Nikolai; Ma, Chunsheng
A simple but efficient approach is proposed in this paper to construct the isotropic random field in (d 2), whose univariate marginal distributions may be taken as any infinitely divisible distribution with finite variance. The three building blocks in our building tool box are a second-order Levy process on the real line, a d-variate random vector uniformly distributed on the unit sphere, and a positive random variable that generates a Polya-type function. The approach extends readily to the multivariate case and results in a vector random field in with isotropic direct covariance functions and with any specified infinitely divisible marginal distributions. A characterization of the turning bands simulation feature is also derived for the covariance matrix function of a Gaussian or elliptically contoured random field that is isotropic and mean square continuous in R-d.
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2018-01-01T00:00:00ZA generalization of ''Existence and behavior of the radial limits of a bounded capillary surface at a corner''Crenshaw, Julie N.Echart, Alexandra K.Lancaster, Kirk E.http://hdl.handle.net/10057/145542018-02-08T17:36:35Z2018-02-01T00:00:00ZA generalization of ''Existence and behavior of the radial limits of a bounded capillary surface at a corner''
Crenshaw, Julie N.; Echart, Alexandra K.; Lancaster, Kirk E.
The principal existence theorem (i.e., Theorem 1) of "Existence and behavior of the radial limits of a bounded capillary surface at a corner" (Pacific J. Math. 176:1 (1996), 165-194) is extended to the case of a contact angle gamma which is not bounded away from 0 and pi (and depends on position in a bounded domain Omega is an element of R-2 with a convex corner at O = (0, 0)). The lower bound on the size of "side fans"(i.e., Theorem 2 in the above paper) is extended to the case of such contact angles for convex and nonconvex corners.
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2018-02-01T00:00:00Z