197,327 research outputs found
Superstructure of moraesite: a synchrotron study
No full textMoraesite (Lindberg et al., 1953) is a hydrated berillophosphate with ideal chemical formula Be2(PO4)(OH)·4H2O. Its structure has been known since 1992 (Merlino & Pasero, 1992) and refined in the space group C2/c, a = 8.553(6) Å, b = 12.319(6) Å, c = 7.155(8) Å, β = 97.93(9)°. The main structural feature of moraesite is the presence of large structural cavities occupied by water molecules. The latter are implicated in a complex system of hydrogen bonds where two possible hydrogen bond schemes are equally possible. Few very weak superstructure reflections were observed (Merlino & Pasero, 1992), indicating that the true unit cell of moraesite was probably three times larger, with a b parameter of 36.96 Å and space group symmetry Cc. It was suggested by the authors that the ordering of the hydrogen bond system, concerted with minor adjustments of the structure, could be responsible for the triplication of the b axis. X-ray diffraction data, more recently obtained through synchrotron radiation, confirmed the occurrence of superstructure reflections which were indexed on the basis of an unit cell with tripled b axis. The superstructure of moraesite (a = 8.572(3) Å, b = 36.971(8) Å = 3 x bsub, c = 7.153(2) Å, β = 97.72(1)°, space group Cc) was refined up to R = 0.081 for 1789 unique reflections with Fo > 4sigma(Fo) and 0.0906 for all 2088 data. The structural refinement confirmed that the triplication of the parameter b is due to the ordering of the two possible hydrogen bonding schemes.
1) Lindberg M.L., Pecora W.T. & Barbosa A.L.M. (1953) - Moraesite, a new hydrous beryllium phosphate from Minas Gerais, Brazil. American Mineralogist, 38, 1126-1133.
2) Merlino S. & Pasero M. (1992) - Crystal chemistry of beryllophosphates: The crystal structure of moraesite, Be2(PO4)(OH)·4H2O, Zeitschrift für Kristallographie, 201, 253-262
MOSANDRITE: STRUCTURAL AND CRYSTAL-CHEMICAL RELATIONSHIPS WITH RINKITE
No full textemical (EPM data), TG–DSC studies and structural investigations indicate that mosandrite presents a particular chemical
composition (low Ca, Na and F contents, high amount of H2O), unit-cell parameters (a 7.398, b 5.595, c 18.662 Å, b 101.37°,
V 757.29 Å3; space-group symmetry P21/c; Z = 2), and a rinkite-type structure characterized by a low occupancy of the M(2) and M(3) sites
Intern experience at CH���M Hill, Inc.: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical referencesA review of the author's internship experience with CH���M HILL, Inc.
during the period September 1975 through May 1976 is presented. During this nine month
internship the author worked as an Engineer II in the Industrial Processes discipline of this
large consulting engineering firm... The author's prime responsibility was as one of three
lead design engineers on the design of a large wastewater treatment facility for a pulp mill
in Hoquiam, Washington owned by ITT Rayonier Inc. The work generally consisted of the design
of individual treatment units and associated piping and pumping. The purpose of the project
was to provide wastewater treatment capabilities that would satisfy the effluent limitations
(standards) imposed upon the mill by the State of Washington Department of Ecology and the
U.S. Environmental Protection Agency. The author's assignment also entailed necessary
interaction with the project manager and other CH���M HILL design engineers and support staff
members, the client's representatives, and representatives of two other consulting engineering
firms working on the project. Thus, the internship position at CH���M HILL provided considerable
experience coordinating the author's work with the work of other engineers, guiding the design
and administrative efforts of a support staff, and interacting regularly with the client and
other consulting firms. This broad exposure to a variety of engineering and organizational
problems provided a valuable educational experience
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
Minerals and materials: building principles and applications - A special issue in honour of Giovanni Ferraris and Stefano Merlino. Preface
No full textDistinct domains in guarinite from Monte Somma, Italy: crystal structures and crystal chemistry.
No full texttract“Guarinite” is a typical accessory mineral of the Monte Somma syenite; it belongs to the cuspidine group and displays a domain structure. “Guarinite” contains up to three distinct domains, corresponding to three different ways to connect disilicate groups and walls of octahedra; these may all be simultaneously present in the same crystal. The domains present in the crystals of “guarinite” have cell type I, II and IV, according to the classification scheme proposed for cuspidine-group minerals. Domain IV is the most common, and domain I is the rarest; domain II may occur as the only domain, whereas domain I occurs only in association with domain IV, which invariably predominates. So far, the actual structure of the various domains had not been defined. EPMA and single-crystal structural studies indicate that domain I of “guarinite” displays space group P1, with a 10.973(2), b 10.306(1), c 7.367(3) Å, a 90.03(3), b 109.63(3), g 90.11(2)°, with a crystal-chemical formula Ca3(Ca0.72
Zr0.28)S1.00(Zr0.86M0.14)S1.00(Ca0.59Mn0.25Fe0.16)S1.00(Na1.20Ca0.76)S1.96(Si1.98O7)2(F2.88O1.12)S4.00, where M represents Nb, Ti, Al, Sr, and REE. Domain I is isostructural with hiortdahlite II, and its crystal structure was refined to a final R of 0.072. Domain II of “guarinite” displays space group P1211, with a 10.836(1), b 10.270(1), c 7.296(1) Å, b 109.13(3)°, with a crystal-chemical formula Ca3Zr(Nb0.56Fe0.15Mn0.10Ti0.10Zr0.09)S1.00(Ca0.72Mn0.18M0.10)S1.00(Na0.77Ca0.23)S1.00(Na0.80Ca0.22)S1.02(Si2O7)2(O2.17
F1.83)S4.00, where M represents Al, Mg, Sr and Y. Domain II is isostructural with wöhlerite, and its crystal structure was refined to a final R of 0.045. Domain IV of “guarinite” adopts space group P1, with a 10.970(2), b 10.943(2), c 7.365(1) Å, a 109.63(2), b 109.65(2), g 83.39(1)°, with a crystal-chemical formula Ca4Zr(Ca0.31Mn0.25Fe0.16Zr0.14M0.14)S1.00(Na1.20
Ca0.76)S1.96(Si1.98O7)2(F2.88O1.12)S4.00, where M represents Nb, Ti, Al, Sr and REE. Domain IV is isostructural with hiortdahlite I, and its crystal structure was refined to a final R of 0.067. One should note that the refinements of domain I and domain IV (both twinned) have been carried out on the same crystal. EMPA and SEM studies show the presence of chemically homogeneous crystals as well as crystals with distinct chemical zoning due to a wide variation of the major elements Nb, Ca, Na, F, and pointing to the possible coupled substitution Nb5+ + 2Na+ + O2– →← 3Ca2+ + F– as one of the main mechanisms of chemical variation
The Tobermorite-Like Layer in Non-Tobermorite Minerals
No full textThe tobermorite-like layer (TLL) is a characteristic feature in all the structures of the natural and synthetic compounds of the tobermorite group /1/. In those structures eptahedra of calcium cations, characterized by ‘a pyramidal part on one side and a dome part on the other side joining the equatorial oxygen atoms’, form columns through edge sharing; the columns are connected each other, once again through edge sharing, and adjacent columns present the pyramidal apical ligands on opposite sides of the resulting infinite layers. These layers, decorated with wollastonite chains on both sides, build up the ‘complex layers’ which are the basic structural module in all the phases of the tobermorite group (Fig. 1). TLL is a recurrent feature in several natural phases belonging to distinct mineral groups. In the structures of the compounds of the rinkite group the TLL is decorated on both sides by disilicate groups and is accompanied by an infinite ‘octahedral’ layer in building up the structural arrangement. Dovyrenite /2/ and roumaite /3/ are closely related to the minerals of the rinkite group and differ only in the way of decoration of the TLL by the disilicate groups. Fukalite /4/ too presents the TLL, decorated on both sides by four-repeat silicate chains and carbonate groups; tilleyite-type polyhedral layers are also present as distinct modules in building up the structural arrangement. The ubiquitous occurrence of TLL is related to its chemical and structural flexibility: the chemical and geometrical variations of the TLL in the different structures are described and discussed. Key-words: layered silicates, crystal structures, mineralogical crystallography. References /1/ Merlino S., Bonaccorsi E., Armbruster T. (1999): American Mineralogist, 84, 1613–1621. /2/ Kadiyski M., Armbruster T., Galuskin E.V., Pertsev N.N., Zadov A.E., Galuskina I.O., Wrzalik R., Dzierżanowski P., Kislov E.V. (2008): American Mineralogist, 93, 456-462. /3/ Biagioni C., Bonaccorsi E., Merlino S., Parodi G.C., Perchiazzi N., Chevrier V. (2008): Plinius, 34, 211. /4/ Merlino S., Bonaccorsi E., Grabezhev A.I., Zadov A.E., Pertsev N.N., Chukanov N.V. (2009): American Mineralogist, 94, 323–333
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
X-ray and HRTEM study of sursassite: crystal structure, stacking disorder and sursassite - pumpellyite intergrowth
No full textSursassite is monoclinic, space Group P21/m, a = 8.70, b = 5.79, c = 9.78 A, beta = 108.9°. The crystal structure was determined with X-rays and refined to R = 0.065, obtaining Mn2Al3[(OH)3(SiO4)(Si2O7)] as ideal crystal chemical formula. Sursassite, isostructural with macfallite Ca2Mn3[(OH)3(SiO4)(Si2O7)], is closely related to pumpellyite Ca2Al3[(OH)3(SiO4)(Si2O7)]. In fact both sursassite and pumpellyite, apart from the different chemical composition, are built up by common structural layers, which are repeated by different stacking vectors. As a result, faulted stacking sequences are energetically possible. Examination by high resolution transmission electron microscopy (HRTEM) shows that frequent (001) pumpellyite-like lamellae are intergrown with thicker sursassite-like lamellae. Usually, the guest lamellae are a few unit cell thick along [001] and continuous along the (001) plane, although also rare interrupted lamellae are found
M-regularity and the fourier-mukai transform
No full textThis is a survey of M-regularity and its applications, expanding on lectures given by the second author at the Seattle conference, in August 2005, and at the Luminy workshop "Geometrie Algebrique Complexe", in October 2005
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