34,407 research outputs found
Thermal-barrier coatings for utility gas turbines
The potential of thermal barrier coatings for use in utility gas turbines was assessed. Pressurized passage and ambient pressure doped fuel burner rig tests revealed that thermal barrier coatings are not resistant to dirty combustion environments. However, present thermal barrier coatings, such as duplex partially stabilized zirconia and duplex Ca2SiO4 have ample resistance to the thermo-mechanical stress and temperature levels anticipated for heavy duty gas turbines firing clean fuel as revealed by clean fuel pressurized passage and ambient pressure burner rig tests. Thus, it is appropriate to evaluate such coatings on blades, vanes and combustors in the field. However, such field tests should be backed up with adequate effort in the areas of coating application technology and design analysis so that the field tests yield unequivocal results
Diffusive Boundary Layers in the Free-Surface Excitable Medium Spiral
Spiral waves are a ubiquitous feature of the nonequilibrium dynamics of a
great variety of excitable systems. In the limit of a large separation in
timescale between fast excitation and slow recovery, one can reduce the spiral
problem to one involving the motion of a free surface separating the excited
and quiescent phases. In this work, we study the free surface problem in the
limit of small diffusivity for the slow field variable. Specifically, we show
that a previously found spiral solution in the diffusionless limit can be
extended to finite diffusivity, without significant alteration. This extension
involves the creation of a variety of boundary layers which cure all the
undesirable singularities of the aforementioned solution. The implications of
our results for the study of spiral stability are briefly discussed.Comment: 6 pages, submitted to PRE Rapid Com
Overlay metallic-cermet alloy coating systems
A substrate, such as a turbine blade, vane, or the like, which is subjected to high temperature use is coated with a base coating of an oxide dispersed, metallic alloy (cermet). A top coating of an oxidation, hot corrosion, erosion resistant alloy of nickel, cobalt, or iron is then deposited on the base coating. A heat treatment is used to improve the bonding. The base coating serves as an inhibitor to interdiffusion between the protective top coating and the substrate. Otherwise, the protective top coating would rapidly interact detrimentally with the substrate and degrade by spalling of the protective oxides formed on the outer surface at elevated temperatures
Development of tunable high pressure CO2 laser for lidar measurements of pollutants and wind velocities
The problem of laser energy extraction at a tunable monochromatic frequency from an energetic high pressure CO2 pulsed laser plasma, for application to remote sensing of atmospheric pollutants by Differential Absorption Lidar (DIAL) and of wind velocities by Doppler Lidar, was investigated. The energy extraction principle analyzed is based on transient injection locking (TIL) at a tunable frequency. Several critical experiments for high gain power amplification by TIL are presented
Corrosion resistant thermal barrier coating
A thermal barrier coating system for protecting metal surfaces at high temperature in normally corrosive environments is described. The thermal barrier coating system includes a metal alloy bond coating, the alloy containing nickel, cobalt, iron, or a combination of these metals. The system further includes a corrosion resistant thermal barrier oxide coating containing at least one alkaline earth silicate. The preferred oxides are calcium silicate, barium silicate, magnesium silicate, or combinations of these silicates
Coating with overlay metallic-cermet alloy systems
A base layer of an oxide dispersed, metallic alloy (cermet) is arc plasma sprayed onto a substrate, such as a turbine blade, vane, or the like, which is subjected to high temperature use. A top layer of an oxidation, hot corrosion, erosion resistant alloy of nickel, cobalt, or iron is then arc plasma sprayed onto the base layer. A heat treatment is used to improve the bonding. The base layer serves as an inhibitor to interdiffusion between the protective top layer and the substrate. Otherwise, the 10 protective top layer would rapidly interact detrimentally with the substrate and degrade by spalling of the protective oxides formed on the outer surface at elevated temperatures
Rate statistics for radio noise from lightning
Radio frequency noise from lightning was measured at several frequencies in the HF - VHF range at the Kennedy Space Center, Florida. The data were examined to determine flashing rate statistics during periods of strong activity from nearby storms. It was found that the time between flashes is modeled reasonably well by a random variable with a lognormal distribution
Mechanisms underlying sequence-independent beta-sheet formation
We investigate the formation of beta-sheet structures in proteins without
taking into account specific sequence-dependent hydrophobic interactions. To
accomplish this, we introduce a model which explicitly incorporates both
solvation effects and the angular dependence (on the protein backbone) of
hydrogen bond formation. The thermodynamics of this model is studied by
comparing the restricted partition functions obtained by "unfreezing"
successively larger segments of the native beta-sheet structure. Our results
suggest that solvation dynamics together with the aforementioned angular
dependence gives rise to a generic cooperativity in this class of systems; this
result explains why pathological aggregates involving beta-sheet cores can form
from many different proteins. Our work provides the foundation for the
construction of phenomenological models to investigate the competition between
native folding and non-specific aggregation.Comment: 20 pages, 5 figures, Revtex4, simulation mpeg movie available at
http://www-physics.ucsd.edu/~guochin/Images/sheet1.mp
Finite element analysis of structures in the plastic range
Finite element analysis of structures in plastic rang
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