Program for development of strain tolerant thermal barrier coating system

The results of thermal conductivity, thermal expansion and high cycle fatigue tests conducted on coating systems are presented. These results show that the thermal conductivity of coating system 8 at approximately 982 C (1800 F) is substantially higher than system 3 while no significant differences were observed in the thermal expansion measurements up to approximately 1316 C (2400 F). High cycle fatigue (HCF) testing, which was conducted at room temperature and several stress levels, showed both coatings to be extremely resistant to spallation in HCF

CO adsorption on (111) and (100) surfaces of the Pt sub 3 Ti alloy. Evidence for parallel binding and strong activation of CO

The CO adsorption on a 40 atom cluster model of the (111) surface and a 36 atom cluster model of the (100) surface of the Pt3Ti alloy was studied. Parallel binding to high coordinate sites associated with Ti and low CO bond scission barriers are predicted for both surfaces. The binding of CO to Pt sites occurs in an upright orientation. These orientations are a consequence of the nature of the CO pi donation interactions with the surface. On the Ti sites the orbitals donate to the nearly empty Ti 3d band and the antibonding counterpart orbitals are empty. On the Pt sites, however, they are in the filled Pt 5d region of the alloy band, which causes CO to bond in a vertical orientation by 5 delta donation from the carbon end

Development of strain tolerant thermal barrier coating systems, tasks 1 - 3

Insulating ceramic thermal barrier coatings can reduce gas turbine airfoil metal temperatures as much as 170 C (about 300 F), providing fuel efficiency improvements greater than one percent and durability improvements of 2 to 3X. The objective was to increase the spalling resistance of zirconia based ceramic turbine coatings. To accomplish this, two baseline and 30 candidate duplex (layered MCrAlY/zirconia based ceramic) coatings were iteratively evaluated microstructurally and in four series of laboratory burner rig tests. This led to the selection of two candidate optimized 0.25 mm (0.010 inch) thick plasma sprayed partially stabilized zirconia ceramics containing six weight percent yttria and applied with two different sets of process parameters over a 0.13 mm (0.005 inch) thick low pressure chamber sprayed MCrAlY bond coat. Both of these coatings demonstrated at least 3X laboratory cyclic spalling life improvement over the baseline systems, as well as cyclic oxidation life equivalent to 15,000 commercial engine flight hours

A method of billing third generation computer users

A method is presented for charging users for the processing of their applications on third generation digital computer systems is presented. For background purposes, problems and goals in billing on third generation systems are discussed. Detailed formulas are derived based on expected utilization and computer component cost. These formulas are then applied to a specific computer system (UNIVAC 1108). The method, although possessing some weaknesses, is presented as a definite improvement over use of second generation billing methods

Spontaneous superconductivity and optical properties of high-Tc cuprates

We suggest that the high temperature superconductivity in cuprate compounds may emerge due to interaction between copper-oxygen layers mediated by in-plane plasmons. The strength of the interaction is determined by the c-axis geometry and by the ab-plane optical properties. Without making reference to any particular in-plane mechanism of superconductivity, we show that the interlayer interaction favors spontaneous appearance of the superconductivity in the layers. At a qualitative level the model describes correctly the dependence of the transition temperature on the interlayer distance, and on the number of adjacent layers in multilayered homologous compounds. Moreover, the model has a potential to explain (i) a mismatch between the optimal doping levels for critical temperature and superconducting density and (ii) a universal scaling relation between the dc-conductivity, the superfluid density, and the superconducting transition temperature.Comment: 4.4 pages, 2 figures; v2 matches the published version (clarifying remarks and references are added

Size Gap for Zero Temperature Black Holes in Semiclassical Gravity

We show that a gap exists in the allowed sizes of all zero temperature static spherically symmetric black holes in semiclassical gravity when only conformally invariant fields are present. The result holds for both charged and uncharged black holes. By size we mean the proper area of the event horizon. The range of sizes that do not occur depends on the numbers and types of quantized fields that are present. We also derive some general properties that both zero and nonzero temperature black holes have in all classical and semiclassical metric theories of gravity.Comment: 4 pages, ReVTeX, no figure

Electronic structure of strongly correlated d-wave superconductors

We study the electronic structure of a strongly correlated d-wave superconducting state. Combining a renormalized mean field theory with direct calculation of matrix elements, we obtain explicit analytical results for the nodal Fermi velocity, v_F, the Fermi wave vector, k_F, and the momentum distribution, n_k, as a function of hole doping in a Gutzwiller projected d-wave superconductor. We calculate the energy dispersion, E_k, and spectral weight of the Gutzwiller-Bogoliubov quasiparticles, and find that the spectral weight associated with the quasiparticle excitation at the antinodal point shows a non monotonic behavior as a function of doping. Results are compared to angle resolved photoemission spectroscopy (ARPES) of the high temperature superconductors.Comment: final version, comparison to experiments added, 4+ pages, 4 figure

Numerical study of fractionalization in an Easy-axis Kagome antiferromagnet

Based on exact numerical calculations, we show that the generalized Kagome spin model in the easy axis limit exhibits a spin liquid, topologically degenerate ground state over a broad range of phase space. We present an (to our knowledge the first) explicit calculation of the gap (and dispersion) of ``vison'' excitations, and exponentially decaying spin and vison 2-point correlators, hallmarks of deconfined, fractionalized and gapped spinons. The region of the spin liquid phase includes a point at which the model is equivalent to a Heisenberg model with purely two-spin interactions. Beyond this range, a negative ``potential'' term tunes a first order transition to a magnetic ordered state. The nature of the phase transition is also discussed in light of the low energy spectrum. These results greatly expand the results and range of a previous study of this model in the vicinity of an exactly soluble point.Comment: 4 pages, 5 figure

THE ADOPTION AND DIFFUSION OF LEVEL FIELDS AND BASINS

Strategic investments in agriculture often are lumpy and irreversible, with significant impacts on operating and fixed costs. Leveling cotton fields to zero slope in central Arizona is a strategic decision made by relatively younger farmers who are farming fine-textured soils in irrigation districts with higher expected water costs. The diffusion of the technology across the region between 1968-89 appears to be both a function of institutional changes (e.g., the Groundwater Management Act of 1980, the Central Arizona Project) and the long-run expected price changes induced by these new policies.Crop Production/Industries,

Numerical Renormalization Group Study of Pseudo-Fermion and Slave-Boson Spectral Functions in the Single Impurity Anderson Model

We use the numerical renormalization group to calculate the auxiliary spectral functions of the $U=\infty$ Anderson impurity model. The slave--boson and pseudo--fermion spectral functions diverge at the threshold with exponents $\alpha_{b}$ and $\alpha_{f}$ given in terms of the conduction electron phase shifts by the X--ray photoemission and the X--ray absorption exponents respectively. The exact exponents obtained here depend on the impurity occupation number, in contrast to the NCA results. Vertex corrections in the convolution formulae for physical Green's functions are singular at the threshold and may not be neglected in the Fermi liquid regime.Comment: 12 pages, RevTeX 3.0, 2 PS figures appende