1,721,113 research outputs found
Phase transition study of thermal energy storage materials AMPL-NPG solid solution
No full textThesis Number: 2864.Online access for this thesis was created in part with support from the Institute of Museum and Library Services (IMLS) administered by the Nevada State Library, Archives and Public Records through the Library Services and Technology Act (LSTA). To obtain a high quality image or document please contact the DeLaMare Library at https://unr.libanswers.com/ or call: 775-784-6945.The thermal and structural behavior of binary AMPL (2-amino-2-methyl-1,3-propanediol) - NPG (2,2-dimathyl-1,3-propanediol) system was studied
Phase transitions in pentaerythritol and 2-amino-2-methyl-1,3-propanediol binaries
Full text linkThesis Number: 3607.Online access for this thesis was created in part with support from the Institute of Museum and Library Services (IMLS) administered by the Nevada State Library, Archives and Public Records through the Library Services and Technology Act (LSTA). To obtain a high quality image or document please contact the DeLaMare Library at https://unr.libanswers.com/ or call: 775-784-6945.Organic molecular plastic crystals such as polyalcohols and amines reversibly absorb large amounts of heat during solid state phase transitions. These materials have potential applications in thermal energy storage for solar buildings. A binary phase diagram for two such energetic plastic crystals, pentaerythritol (PE) and 2-amino-2-methyl-1. 3- propanediol (AM PL) is proposed. This diagram was determined by high temperature Guinier x-ray diffraction and differential scanning calorimetric methods. The phase diagram in this study is rather complex with two eutectoids at 34 C and 147 C and a peritectic at 184 C. The low temperature phases of PE and AMPL are in equilibrium between 20 C and 84 C in the composition range of 12 to 98 mol % AMPL The solubility of AMPL in PE is very high, up to 45 mol % AMPL in PE at 147 C. The solubility of PE in AMPL is very low. Only up to 10 mol % PE in AMPL at 84 C. The details of detem1inati on of phase equilibria by calorimetry and x-ray diffraction methods are presented
Solid State Studies of [ReH9]-2 Complexes from Ambient to Extreme Conditions: High Volumetric Capacity Hydrogen Storage
Full text linkThe implementation of new alternative energy concepts is essential considering the increased pollution and exploitation of fossil energy resources. As the simplest and most abundant element, hydrogen has the potential to energy system. Solid state transition metal hydrides based on Re and transition metals are very attractive materials for hydrogen and energy storage due to their large volumetric capacity, providing a safe and efficient way of storing hydrogen. The [ReH9]-2 ion continues to captivate researchers because of its stability, unusually high oxidation state of rhenium metal (VII), D3h symmetry (tricapped trigonal prism); with 9 hydrogen atoms coordinating to Re atom. In this study, the effect of pressure on the metal-hydrogen bonding and the consequence on the hydrogen absorption and desorption are investigated for M[ReH9]-2, where M= Na, K, and Ba. Understanding the chemical and physical properties of metal hydrides at ambient as well as elevated pressure and temperature conditions will in sequence assist in the design of suitable storage materials with optimum thermodynamic parameters.The BaReH9 complex was synthesized and evaluated under ambient to extreme environments. For this compound, we report bulk moduli for lower and higher pressures obtained by fitting of pressure and volume data using obtained using 3rd order Birch-Murnaghan equation of state. The results exhibited a possible orientation disorder in the crystal without any phase transformation in the studied pressure, which is a divergence from computational studies. Grüneisen parameters were also calculated and reported here. High pressure studies of Na2ReH9 and K2ReH9 were also performed, report the assignment of vibrational spectroscopy at ambient condition. The structural behavior of Na2ReH9 and K2ReH9 performed at high pressure, using in-situ Raman spectroscopic and high resolution synchrotron x-ray diffraction, studies revealed new phase transformations above 9 GPa and 16 GPa for both Na2ReH9 and K2ReH9 due to compression. We deduced that the phase transformations occur to relieve this repulsion due to H-H interaction of two [ReH9]-2 ions as volume of the unit cell reduces due to pressure increases.Two new deuterated transition metal hydrides (Na2ReD9 and BaReD9) were successfully synthesized by reaction via metathesis reaction in deuterated ethanol. Raman and IR spectroscopy showed isotopic shift with (H/D) of ~1.4. The crystal structure of BaReD9 has been determined by synchrotron powder diffraction and the results were consistent with the P63/mmc (#194) space group, with lattice parameters a = 5.2924 (±0.0006) Å and c = 9.3286 (±0.0014) Å. In summary, the effect of pressure on the metal-hydrogen bonding of BaReH9, Na2ReH9, and K2ReH9 were investigated using synchrotron x-ray, Raman and IR spectroscopy. BaReH9 is stable up to the studied pressure while Na2ReH9 and K2ReH9 exhibit phase transformation at higher pressures. Two new deuterated transition metal hydrides (Na2ReD9 and BaReD9) were successfully synthesized and characterized
Temperature dependence of the elastic modulus of (Ni<inf>0.6</inf>Nb<inf>0.4</inf>)<inf>1-x</inf>Zr<inf>x</inf> membranes: Effects of thermal treatments and hydrogenation
No full textAmorphous (Ni0.6Nb0.4)1−xZrx membranes were investigated by means of X-ray diffraction, thermogravimetry, differential thermal analysis and tensile modulus measurements. Crystallization occurs only above 673 K, and even after hydrogenation the membranes retain their mainly amorphous nature. However, after exposure to gaseous hydrogen, the temperature dependence of the tensile modulus, M, displays large variations. The modulus of the hydrogen reacted membrane is higher with respect to the pristine samples in the temperature range between 298 K and 423 K. Moreover, a sharp drop in M is observed upon heating to approximately 473 K, well below the glass transition temperature of these glasses. We propose that the changes in the moduli as a function of temperature on the hydrogenated samples are due to the formation of nanocrystalline phases of Zr hydrides in (Ni0.6Nb0.4)1−xZrx-H membanes
New Studies of the Physical Properties of Metallic Amorphous Membranes for Hydrogen Purification
Full text linkAmorphous metallic membranes display promising properties for hydrogen purification up
to an ultrapure grade (purity > 99.999%). The hydrogen permeability through amorphous membranes
has been widely studied in the literature. In this work we focus on two additional properties, which
should be considered before possible application of such materials: the propensity to crystallize
at high temperatures should be avoided, as the crystallized membranes can become brittle; the
hydrogen solubility should be high, as solubility and permeability are proportional. We investigate
the crystallization process and the hydrogen solubility of some membranes based on Ni, Nb, and
Zr metals, as a function of Zr content, and with the addition of Ta or B. The boron doping does
not significantly affect the crystallization temperature and the thermal stability of the membrane.
However, the hydrogen solubility for p ~7 bar is as high as H/M ~0.31 at T = 440 °C and H/M ~0.27
at T = 485 °C. Moreover, the membrane does not pulverize even after repeated thermal cycles and
hydrogenation processes up to 485 C and 7 bar, and it retains its initial shape
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Igneous Geology of the Keystone Window, Simpson Park Mountains, Eureka County, Nevada: Age, Distribution, Composition, and Relationship to Carlin-style Gold Mineralization
No full textKeystone is an early-stage gold exploration project operated by U.S. Gold Corp. located in the northern Simpson Park Mountains, in the Battle Mountain-Eureka mineral belt of north-central Nevada. Dating of ore-stage minerals and cross-cutting relationships between mineralization and dikes elsewhere in Nevada shows that most Carlin-type gold deposits (CTDs) formed over a short interval in the Eocene (~42-35 Ma), coeval with a distinct pulse of arc magmatism that supplied heat and permissively, metals for CTDs. The on-trend location of Keystone, 25 km south of the giant Cortez Hills and Goldrush CTDs, together with widespread alteration of a domed lower plate structural window in the Roberts Mountains allochthon (RMA) that is cored by an Eocene intermediate pluton, make it ideal for the study of proximal to distal styles of Eocene mineralization, including CTDs. U-Pb zircon and 40Ar/39Ar dating in conjunction with mapping of igneous rocks and alteration provide constraints on the timing and style of magmatism and mineralization.A major normal fault along Keystone’s west flank tilted units moderately east, exposing a 2 km thick crustal section that includes Eocene volcanic rocks, the RMA, lower plate carbonates, and abundant intrusions. Eocene igneous rocks comprise the 4.1 km2 intermediate composite Walti pluton, which domed surrounding wall rocks, and abundant porphyritic, intermediate to silicic stocks, dikes, lavas, and tuffs. All Eocene rocks are shoshonitic to high-K calc-alkaline, metaluminous to weakly peraluminous, and were emplaced from ~36-34.5 Ma. A ~25 km2 magnetic anomaly coincides with the Walti pluton and indicates much larger intrusions at depth. The anomaly is of similar size to the magnetic anomaly associated with the Eocene Bullion intrusion (22 km2) in the southern Carlin trend and the Copper Canyon stock (11 km2), which is associated with the Phoenix-Fortitude gold skarns. Trace-element geochemistry, petrography, crosscutting relations, and isotopic dating of Eocene igneous rocks at Keystone support a complex magmatic evolution with likely varied sources. Older andesite of McClusky Creek, Mud Springs diorite and Gund diorite are interpreted as a separate magmatic system from the later Walti granodiorite to diorite intrusion and its related rocks.The composition and timing of igneous rocks at Keystone are consistent with the last stages of mid-Cenozoic, dominantly intermediate composition magmatism in northeast Nevada, which was active from ~44 to 34 Ma and migrated rapidly southwestward. This Eocene magmatism was characterized by shallow intrusion and mostly effusive volcanism. After ~34 Ma and generally at or immediately south of Keystone, magmatism became dominantly silicic and pyroclastic, part of the Oligocene ignimbrite flare-up of central Nevada (e.g. the nearby ~34 Ma Caetano and Hall Creek calderas). The change in style and composition of mid-Cenozoic magmatism at this latitude coincides with a change in the distribution of Eocene Carlin-type gold deposits from major deposits (+5 Moz contained Au) to the north, to relatively smaller deposits to the south. Whether the change in the magnitude of Carlin-type gold mineralization is directly or indirectly related to changes in mid-Cenozoic magmatism is uncertain and an area of future research.40Ar/39Ar dating of biotite from an alkaline basalt in the Valmy Formation yielded a plateau age of 466.1±0.7 Ma, which is Middle Ordovician. This age is consistent with biostratigraphic ages from conodonts and radiolaria at Keystone. Alkaline mafic rocks at Keystone solely occur in the Ordovician Valmy and Cambrian-Ordovician Comus formations as sills, volcanogenic debris flows, and pillows, typically intercalated with limestone. These rocks, in addition to unusual mineralogy, have distinctive and unusually high concentrations of both compatible and incompatible trace elements consistent with ocean island basalts (OIB) and unlike depleted mid-ocean ridge basalts (MORB) or arc-related basalts. OIBs likely reflect intraplate or hotspot-related magmatism that developed as a series of seamounts during deposition of rocks of the Valmy and Comus formations and which were later tectonically transported eastward to the Keystone area during Late Devonian/Early Mississippian Antler thrusting. The age, lithologic, and geochemical similarities of these rocks to the Comus Formation in the Osgood Mountains is permissive for their correlation and is particularly important, since the Comus is the principal host unit in the Getchell trend Carlin-type gold deposits.U-Pb zircon dating of conglomerate resting on Paleozoic rocks of the RMA yielded a maximum depositional age of 35.62±0.32 Ma. Conglomeratic rocks elsewhere are commonly correlated with the Paleozoic Antler overlap sequence based on the abundance of RMA-derived chert and quartzite clasts. The recognition of this Eocene conglomerate is important not only for regional mapping but also for understanding the development of Eocene basins, some of which are hydrocarbon-bearing, and for characterizing the switch from late Cretaceous Sevier contraction to an early Cenozoic extensional regime. The basal Eocene conglomerate is the oldest exposed Cenozoic unit at Keystone and is used to constrain the Eocene paleosurface and estimate the depth that Eocene intrusions were emplaced and that mineralization occurred. Hydrothermal activity at Keystone was constrained by field relations and 40Ar/39Ar of illite in altered igneous rocks. The Walti pluton is associated with proximal Pb-Zn-Cu skarn, at the site of the historic Keystone mine. Distal epithermal and Carlin-style mineralization occurs outboard of hornfels halos in overlying and adjacent strata. Drilling by U.S. Gold Corp. commonly intercepted mineralized breccia and jasperoid at the Paleozoic upper- to lower-plate transition, and argillized dikes adjacent to decarbonatized Paleozoic lower-plate carbonate rocks, both of which contain strongly anomalous gold and high concentrations of As, Sb, Hg, Bi, W, Se, and/or Tl. Illite from two samples of altered andesite dikes of McClusky Creek did not yield 40Ar/39Ar plateaus but nonetheless produced geologically reasonable weighted mean ages of 35.71±0.12 Ma and 35.54±0.06 Ma, which are slightly younger than the ~35.99 to 35.85 Ma 40Ar/39Ar igneous hornblende ages. Thus, the illite ages from the altered andesite dikes are considered the best approximate for the age of Carlin-type gold mineralization in the northeastern area of Keystone. A rhyolite porphyry intrusion exhibited the most sericitic and argillic alteration after the altered dikes, and 40Ar/39Ar dating of sanidine from the unaltered core of the rhyolite yielded an age of 35.43±0.06 Ma. This rhyolite porphyry is possibly the youngest intrusion at Keystone, and is preferentially altered over adjacent intrusions. This suggests the rhyolite intruded an extensional structure that also controlled hydrothermal fluids. Abundant quartz porphyry rhyolite dikes at the nearby Cortez Hills CTD have been interpreted as syn-mineralization because they are altered and locally mineralized; these pre-Caetano caldera dikes are of similar age and composition to the rhyolite porphyry at Keystone
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
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