177,282 research outputs found
Zirconia/Titania Catalysts for Carbon Dioxide Utilisation
No full textReaction and conversion of CO2 to chemicals is a challenging area of research. The objective of this work is to study and investigate the use of mixed metal oxide Zr/Ti oxide and related catalysts for the conversion and utilisation of CO2. The first reaction studied was propane dehydrogenation using CO2 to produce propene. Then, the study extended to investigate the direct reaction of CO2 as whole molecule with methane, ethane, acetylene, ethylene and propane to synthesis carboxylic acids.
The catalysts were prepared in several ways. Four methods were based on coprecipitation of the mixed catalyst from solutions of zirconium (IV) oxynitrate hydrate and titanium (IV) chloride. Other methods involved impregnation, based on titanium (IV) oxide. Catalysts were characterised by nitrogen adsorption, by powder X-ray diffraction, by ammonia temperature programmed desorption and, ultimately, in terms of catalytic activities.
The powder X-ray diffraction patterns of the impregnated titania-rich Zr/Ti oxide catalysts showed that ZrO2 dissolved in the solid anatase phase of titania. At higher concentrations, the ZrO2 appeared as a separate tetragonal phase. Low zirconia content Zr/Ti oxide catalysts showed significantly increased surface areas and higher acidities than the individual oxides. A range of other metal oxides were added as third metal
oxides in these mixtures, but none had significant impacts on surface areas or on surface acidities.
Propane dehydrogenation is thermodynamically limited. The only possible route is a radical mechanism for H2 removal via a surface process. The catalytic activities at low CO2:propane ratio showed that Zr/Ti oxide exhibited the higher activity than single oxides, but activities were all too low to be of economic significance.
In contrast, using higher CO2:propane ratio improved the propene yield and selectivity to values comparable to those achieved with the industrial chromium based catalyst. The catalyst showed selectivity to C-H bond breaking to form propene over C-C bond breaking to make ethene. The study demonstrated that CO2 was utilised mainly for the reverse water gas shift reaction (RWGS) to remove hydrogen from the catalyst surface.
The study showed that the Zr/Ti oxide catalysts exhibited higher stability compared to the industrial catalysts at slightly higher gas space velocity. Thermogravimetric analysis showed that Zr/Ti oxide catalyst assists coke gasification in the presence of CO2 at 600 oC.
The other mixed oxide catalysts generally showed lower surface acidities and higher selectivities to C-C bond breaking products over the desired propene product.
The second study was the direct reaction of CO2 with CH4 to produce acetic acid. Again, this reaction is thermodynamically unfavourable and the only possible route must involve a radical species by which reactants are concentrated on the catalyst surface. Evidence of methyl surface species formation in the presence of methane was indeed found over the Zr/Ti oxide catalyst. With CO2 methane reacted with CO2 to form acetic acid over Zr/Ti oxide catalysts. The C-C insertion mechanism is proposed by which methyl surface species formed on the catalyst and reacted with CO2. This was followed by hydrogenation to form acetic acid.
Reactions of CO2 with ethane, ethylene, acetylene and propene were also studied, in the hope of observing direct insertion to produce the corresponding carboxylic acid. In fact, lower acids were formed in all cases, suggesting a radical mechanism involving C-C bond breaking over Zr/Ti oxide catalyst.
Interestingly, acetic acid was formed with all these precursor hydrocarbons, and it appears that it occurs via C≡C, C=C, C-C and C-H bond breaking
Planar Multibranch Open-Loop Robotic Manipulators Subjected to Ground Collision
No full textIn this article, a recursive approach is used to dynamically model a tree-type robotic system with floating base. Two solution procedures are developed to obtain the time responses of the mentioned system. A set of highly nonlinear differential equations is employed to obtain the dynamic behavior of the system when it has no contact with the ground or any object in its environment (flying phase); and a set of algebraic equations is exploited when this tree-type robotic system collides with the ground (impact phase). The Gibbs–Appell (G–A) formulation in recursive form and the Newton’s impact law are applied to derive the governing equations of the aforementioned robotic system for the flying and impact phases, respectively. The main goal of this article is a systematic algorithm that is used to divide any tree-type robotic system into a specific number of open kinematic chains and derive the forward dynamic equations of each chain, including its inertia matrix and right-hand side vector. Then, the inertia matrices and the right-hand side vectors of all these chains are automatically integrated to construct the global inertia matrix and the global right-hand side vector of the whole system. In fact, this work is an extension of Shafei and Shafei (2016, “A Systematic Method for the Hybrid Dynamic Modeling of Open Kinematic Chains Confined in a Closed Environment,” Multibody Syst. Dyn., 38(1), pp. 21–42.), which was restricted to a single open kinematic chain. So, to show the effectiveness of the suggested algorithm in deriving the motion equations of multichain robotic systems, a ten-link tree-type robotic system with floating base is simulated.</jats:p
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
Get PDFBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
ÇUBUKÇU, E., ZEYBEK, R., SHAFEI, N. (2010). Farklı Konut Bölgelerinde Yaşayanların Fiziksel Aktivite Alışkanlıklarının Karşılaştırılması. , 5(2).
No full textLetter from R. R. Zellick, Assistant Trust Officer, Anglo California National Bank of San Francisco, to Joseph R. Goodman, October 2, 1942
No full textLetter from R. R. Zellick, Assistant Trust Officer at The Anglo California National Bank of San Francisco, to Joseph R. Goodman, regarding property owned by Dave Tatsuno. Zellick mentions a dispute between current tenants and Tatsuno, and that Tatsuno has asked Goodman to help locate trustworthy tenants.Personal correspondence, organizational records, government documents, publications, and other papers created or collected by Joseph R. Goodman documenting the forced removal and incarceration of Japanese Americans during World War II, as well as organized resistance to incarceration. Included in the collection are records of the Japanese Young Men's Christian Association and the Japanese American Citizens' League in San Francisco, including papers of the Japanese YMCA's executive secretary Lincoln Kanai; Sakai family papers; Goodman's correspondence to and from Japanese American incarcerees, organizations opposing forced removal and incarceration of Japanese Americans, the War Relocation Authority, and others; publications, photographs, and ephemera from the Topaz Relocation Center, where Goodman taught high school; War Relocation Authority records and publications; and newspaper clippings, pamphlets, and reports about forced removal and incarceration created by various government, religious, and civic organizations, in California and nationwide
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Liftings for noncomplete probability spaces
No full textThe current state of knowledge concerning liftings for noncomplete probability spaces is discussed. This is a somewhat expanded version of the author's talk given at the 1991 Summer Conference on General Topology and Applications in Honor of Mary Ellen Rudin and Her Work.PT: S; CR: BURKE MR, IN PRESS P AM MATH S BURKE MR, 1991, ISRAEL J MATH, V73, P33 BURKE MR, 1992, ISRAEL J MATH, V79, P289 CARLSON T, THEOREM LIFTING CHRISTENSEN JPR, 1974, TOPOLOGY BOREL STRUC FREMLIN DH, 1989, HDB BOOLEAN ALGEBRAS, P877 INOESCUTULCEA A, 1966, 5TH P BERK S MATH ST, V2 IONESCUTULCEA A, 1967, CONTRIBUTIONS PROB 1, P63 IONESCUTULCEA A, 1969, TOPICS THEORY LIFTIN JECH TJ, 1978, SET THEORY JOHNSON RA, 1980, P AM MATH SOC, V80, P234 JUST W, IN PRESS T AM MATH S KUPKA J, 1983, INDIANA U MATH J, V32, P717 LOSERT V, 1983, LNM, V1080, P95 MAHARAM D, 1958, P AM MATH SOC, V9, P987 SHELAH S, 1983, ISRAEL J MATH, V45, P90 TALAGRAND M, 1982, P AM MATH SOC, V84, P379 VONNEUMANN J, 1931, CRELLES J MATH, V165, P109; NR: 18; TC: 0; J9: ANN N Y ACAD SCI; PG: 4; GA: BZ86BSource type: Electronic(1
Hansen, Lee (Lee R.). Union, non-union, and managerial pay plan state employees, 2008-2019
No full text1 online resource (2 pages)"July 1, 2021."Provides the number of union and non-union state employees in each of the last 14 years. Also provides the number of state employees paid under the state's managerial pay plan during each of those years. Updates OLR research report 2019-R-011
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