900 resultados para gold bloc


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The purpose of my dissertation was to examine the competition between the U.S.-led Western bloc and the Soviet bloc in the less developed world during Détente. I assessed whether or not the Soviet bloc pushed for strategic gains in the less developed world in the middle-to-late 1970's and whether this contributed to the U.S. decision to abandon Détente in 1979. I made the attempt to test the international relations theory of balance of threat realism (Walt, 1992). I accomplished the test in two ways. First, I measured the foreign aid allocations (military and economic) made by each respective bloc towards the Third World by using a quantitative approach. Second, I examined U.S. archives using the process-tracing/historical method. The U.S. archives gave me the ability to evaluate how U.S. decision-makers and U.S. intelligence agencies interpreted the actions of the Soviet bloc. They also gave me the chance to examine the U.S. response as we evaluated the policies that were pushed by key U.S. decision-makers and intelligence agencies. On the question of whether or not the Soviet bloc was aggressive, the quantitative evidence suggested that it was not. Instead, the evidence found the Western-bloc to have been more aggressive in the less developed world. The U.S. archives also showed Soviet actions to have been defensive. Key U.S. decision-makers and intelligence agencies attested to this. Finally, the archives show that U.S. officials pushed for aggressive actions against the Third World during the final years of Détente. Thus, balance of threat realism produced an incorrect assessment that U.S. aggression in the late 1970's was a response to Soviet aggression during Détente. The evidence suggests structural Marxism and domestic politics can better explain U.S./Western actions. The aggressive foreign aid allocations of the West, coupled with evidence of U.S. decision-makers/agencies vehemently concerned about the long-term prospects of the West, strengthened structural Marxism. Domestic politics can also claim to explain the actions of U.S. decision-makers. I found extensive archival evidence of bureaucratic inter-agency conflict between the State Department and other intelligence agencies in areas of strategic concern to the U.S.

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One of the many promising applications of metal/ceramic joining is in biomedical implantable devices. This work is focused on vacuum brazing of C.P titanium to 96% alumina ceramic using pure gold as the filler metal. A novel method of brazing is developed where resistance heating of C.P titanium is done inside a thermal evaporator using a Ta heating electrode. The design of electrode is optimized using Ansys resistive heating simulations. The materials chosen in this study are biocompatible and have prior history in implantable devices approved by FDA. This research is part of Boston Retinal implant project to make a biocompatible implantable device (www.bostonretina.org). ^ Pure gold braze has been used in the construction of single terminal feedthrough in low density hermetic packages utilizing a single platinum pin brazed to an alumina or sapphire ceramic donut (brazed to a titanium case or ferrule for many years in implantable pacemakers. Pure gold (99.99%) brazing of 96% alumina ceramic with CP titanium has been performed and evaluated in this dissertation. Brazing has been done by using electrical resistance heating. The 96% alumina ceramic disk was manufactured by high temperature cofired ceramic (HTCC) processing while the Ti ferrule and gold performs were purchased from outside. Hermetic joints having leak rate of the order of 1.6 × 10-8 atm-cc/ sec on a helium leak detector were measured. ^ Alumina ceramics made by HTCC processing were centreless grounded utilizing 800 grit diamond wheel to provide a smooth surface for sputtering of a thin film of Nb. Since pure alumina demonstrates no adhesion or wetting to gold, an adhesion layer must be used on the alumina surface. Niobium (Nb), Tantalum (Ta) and Tungsten (W) were chosen for evaluation since all are refractory (less dissolution into molten gold), all form stable oxides (necessary for adhesion to alumina) and all are readily thin film deposited as metals. Wetting studies are also performed to determine the wetting angle of pure gold to Ti, Ta, Nb and W substrates. Nano tribological scratch testing of thin film of Nb (which demonstrated the best wetting properties towards gold) on polished 96% alumina ceramic is performed to determine the adhesion strength of thin film to the substrate. The wetting studies also determined the thickness of the intermetallic compounds layers formed between Ti and gold, reaction microstructure and the dissolution of the metal into the molten gold.^

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The diagnosis of Von Willebrand's disease (VWD) may sometimes be difficult because of the variability of the results obtained over time in individuals. Moreover, blood group, age, pregnancy and inflammatory stimuli influence the level of Von Willebrand Factor (VWF). The purpose of this thesis was to screen and characterize antibodies to Von Willebrand factor and to evaluate the most promising ones in a gold- Sol assay for VWF on the CA-6000 analyzer. Seven different lots of Anti-VWF antibodies, 3 polyclonal and 4 monoclonal Ab's were screened and evaluated. Two of these antibodies (Sunol R01358 and MAVWF-AP) were selected for preparation of a Gold coated antibody solution. The preliminary testing of these gold coated antibodies on CA-6000 Analyzer showed no immunoreactivity toward VWF for both individual and pooled plasma (from normal healthy donors). Although measurement of VWF for normal plasma with this technique was not demonstrated, these data will be valuable for future work on the design of sensitive and accurate automated sol Gold Immunoassays for the diagnosis of VWD.

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The objective of this research was to find Young's elastic modulus for thin gold films at room and cryogenic temperatures based on the flexional model which has not been previously attempted. Electrical Sonnet simulations and numerical methods using Abacus for the mechanical responses were employed for this purpose. A RF MEM shunt switch was designed and a fabrication process developed in house. The switch is composed of a superconducting YBa2Cu3O7 coplanar waveguide structure with an Au bridge membrane suspended above an area of the center conductor covered with BaTiO3 dielectric. The Au membrane is actuated by the electrostatic attractive force acting between the transmission line and the membrane when voltage is applied. The value of the actuation force will greatly depend on the switch pull-down voltage and on the geometry and mechanical properties of the bridge material. Results show that the elastic modulus for Au thin film can be 484 times higher at cryogenic temperature than it is at room temperature.

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We acknowledge the contribution of Dr. N. Perret to this work. EPSRC support for free access to the TEM/SEM facility at the University of St. Andrews and financial support to Dr. X. Wang and Y. Hao through the Overseas Research Students Award Scheme (ORSAS) are also acknowledged.

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General note: Title and date provided by Bettye Lane.

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General note: Title and date provided by Bettye Lane.

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It has been observed that Viking Age gold finds in Scandinavia and Britain are frequently associated with watery environments and may represent ritual or votive depositions. There is also evidence, literary and archaeological, for the ritual deposition of some silver hoards in the Viking world. This paper considers the evidence of those Viking Age gold and silver hoards and single finds from Ireland that derive from watery locations, including crannogs and their environs. It is noted that all recorded gold hoards, with one exception, have an apparent association with water or watery places and thus conform to the patterns noted elsewhere. Most of the crannog finds, which are invariably of silver, are from the midland region, and it is noted that a high proportion of them contain ingots and hack-silver and are thus most probably economic rather than ritual in function. It is suggested that these types of hoards evidence a close economic relationship between the Hiberno-Scandinavians of Dublin and the Southern Uí Néill rulers of this area. Some of the remaining silver hoards—from bogs, rivers, lakes, small islands and shorelines—which vary in terms of their contents, with both complete ornaments and hack-silver being represented, may have been ritually deposited, but this is difficult to establish with any degree of certainty. A general discussion of ritual hoarding is presented, and it is concluded that this practice may have been more commonplace than has generally been accepted to date and that some, at least, of the ‘watery’ finds from Ireland were indeed deposited in a ritual context.

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Template-directed synthesis is a promising route to realize vanadate-based 1-D nanostructures, an example of which is the formation of vanadium pentoxide nanotubes and associated nanostructures. In this work, we report the interchange of long-chained alkyl amines with alkyl thiols. This reaction was followed using gold nanoparticles prepared by the Chemical Liquid Deposition (CLD) method with an average diameter of ∼0.9 nm and a stability of ∼85 days. V2 O5 nanotubes (VOx-NTs) with lengths of ∼2 μm and internal hollow diameters of 20-100 nm were synthesized and functionalized in a Au-acetone colloid with a nominal concentration of ∼ 4 × 1 0- 3 mol dm-3. The interchange reaction with dodecylamine is found only to occur in polar solvents and incorporation of the gold nanoparticles is not observed in the presence of n-decane.

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We report the results of a study into the factors controlling the quality of nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent postetch pattern definition, and minimum feature size all depend on the quality of the Au substrate used in material mask atomic nanolithographic experiments. We find that sputtered Au substrates yield much smoother surfaces and a higher density of {111}-oriented grains than evaporated Au surfaces. Phase imaging with an atomic force microscope shows that the quality and percentage coverage of SAM adsorption are much greater for sputtered Au surfaces. Exposure of the self-assembled monolayer to an optically cooled atomic Cs beam traversing a two-dimensional array of submicron material masks mounted a few microns above the self-assembled monolayer surface allowed determination of the minimum average Cs dose (2 Cs atoms per self-assembled monolayer molecule) to write the monolayer. Suitable wet etching, with etch rates of 2.2 nm min-1, results in optimized pattern definition. Utilizing these optimizations, material mask features as small as 230 nm in diameter with a fractional depth gradient of 0.820 nm were realized.

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A detailed study of the self-assembly and coverage by 1-nonanethiol of sputtered Au surfaces using molecular resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au surface composed predominantly of {111} oriented grains. The domains of the alkanethiol monolayer are observed with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. STM imaging shows that the (4 × 2) superlattice structure is observed as a (3 × 2√3) structure when imaged under noncontact AFM conditions. The 1-nonanethiol molecules reside in the threefold hollow sites of the Au{111} lattice and aligned along its lattice vectors. The self-assembled monolayer (SAM) contains many nonuniformities such as pinholes, domain boundaries, and monatomic depressions which are present in the Au surface prior to SAM adsorption. The detailed observations demonstrate limitations to the application of 1-nonanethiol as a resist in atomic nanolithography experiments to feature sizes of ∼20 nm.

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Gold nanoparticles (Au NPs) with diameters ranging between 5-60 nm have been synthesised in water, and further stabilized with polyethylene glycol-based thiol polymers (mPEG-SH). Successful PEGylation of the Au NPs was confirmed by Dynamic Light scattering (DLS) and Zeta potential measurements. PEG coating of the Au NPs is the key of their colloidal stabilty, and its successful applications. Catalytic efficiency testing of the PEG-AuNPs were carried out on homocoupling of boronic acid. PEG-Au NPs with AuNps diameter < 30 nm were useful as catalyst in water. Finally, the PEG-Au NPs were also shown to be stable in biological fluid and not cytotoxic on B16.F10 cell line, making them attractive for further studies.

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In the last two decades, the field of homogeneous gold catalysis has been

extremely active, growing at a rapid pace. Another rapidly-growing field—that of

computational chemistry—has often been applied to the investigation of various gold-

catalyzed reaction mechanisms. Unfortunately, a number of recent mechanistic studies

have utilized computational methods that have been shown to be inappropriate and

inaccurate in their description of gold chemistry. This work presents an overview of

available computational methods with a focus on the approximations and limitations

inherent in each, and offers a review of experimentally-characterized gold(I) complexes

and proposed mechanisms as compared with their computationally-modeled

counterparts. No aim is made to identify a “recommended” computational method for

investigations of gold catalysis; rather, discrepancies between experimentally and

computationally obtained values are highlighted, and the systematic errors between

different computational methods are discussed.

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Gold nanoparticles (Au NPs) with diameters ranging between 15 and 150 nm have been synthesised in water. 15 and 30 nm Au NPs were obtained by the Turkevich and Frens method using sodium citrate as both a reducing and stabilising agent at high temperature (Au NPs-citrate), while 60, 90 and 150 nm Au NPs were formed using hydroxylamine-o-sulfonic acid (HOS) as a reducing agent for HAuCl4 at room temperature. This new method using HOS is an extension of the approaches previously reported for producing Au NPs with mean diameters above 40 nm by direct reduction. Functionalised polyethylene glycol-based thiol polymers were used to stabilise the pre-synthesised Au NPs. The nanoparticles obtained were characterised using uv-visible spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Further bioconjugation on 15, 30 and 90 nm PEGylated Au NPs were performed by grafting Bovine Serum Albumin, Transferrin and Apolipoprotein E (ApoE).