13,296 research outputs found
Durability of zirconia thermal-barrier ceramic coatings on air-cooled turbine blades in cyclic jet engine operation
Thermal barrier ceramic coatings of stabilized zirconia over a bond coat of Ni Cr Al Y were tested for durability on air cooled turbine rotor blades in a research turbojet engine. Zirconia stabilized with either yttria, magnesia, or calcia was investigated. On the basis of durability and processing cost, the yttria stabilized zirconia was considered the best of the three coatings investigated
Micrasema kluane, a probable stepping stone to the Arctic (Trichoptera, Brachycentridae)
The arctic fauna has tactily been considered as a collection of offshoots arising from elements of the boreal deciduous forest, its neighboring biome to the south. Two circumstances make this conjecture plausible. First, the Arctic has a relatively small fauna compared to biomes south of it, and second, the animal species found in the Arctic usually show phylogenetic affinities to groups found in more southern regions. In order to test the validity of the boreal-to-arctic evolutionary pathway, it is necessary to discover circumstances in which the arctic species are derived entities that evolved from more ancestral southern relatives
The structure of trailing vortices generated by model rotor blades
Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described
Uniqueness of a Negative Mode About a Bounce Solution
We consider the uniqueness problem of a negative eigenvalue in the spectrum
of small fluctuations about a bounce solution in a multidimensional case. Our
approach is based on the concept of conjugate points from Morse theory and is a
natural generalization of the nodal theorem approach usually used in one
dimensional case. We show that bounce solution has exactly one conjugate point
at with multiplicity one.Comment: 4 pages,LaTe
Ceraclea enodis, A New Species of Sponge-Feeding Caddisfly (Trichoptera:Leptoceridae) Previously Misidentified
A new species of Trichoptera, Ceraclea (C.) enodis, of the Ceraclea (C.) senilis Group, was discovered in freshwater sponge in the Little River in Montgomery County, North Carolina. Illustrations and descriptions of the male, female, larva, pupa, and larval case are given. Adults resemble those C. cancellata (Betten), the mature larva looks like that of C. maculata (Banks), the younger larva may be confused with C. transverasa (Hagen), and the pupa has anal rods rather like those of C. spngillovorax (Resh); but all life history forms can be distinguished reliably from these species by consistent morphological characters and the sponge habitat of late instar larvae. Although few or no larvae and pupae were found in streams near the type locality, adults are reported from Ontario to Georgia to Illinois and Michigan, suggesting that the species may be widespread buy local in abundance. Ceraclea enodis was found in fairly clean, 1st to 4th order streams containing the freshwater sponge Anheteromeyenia ryderi Potts (Porifera:Spongillidae) and loose, flat rocks
Renormalized One-loop Theory of Correlations in Disordered Diblock Copolymers
A renormalized one-loop theory (ROL) is used to calculate corrections to the
random phase approximation (RPA) for the structure factor \Sc(q) in
disordered diblock copolymer melts. Predictions are given for the peak
intensity , peak position , and single-chain
statistics for symmetric and asymmetric copolymers as functions of ,
where is the Flory-Huggins interaction parameter and is the degree
of polymerization. The ROL and Fredrickson-Helfand (FH) theories are found to
yield asymptotically equivalent results for the dependence of the peak
intensity upon for symmetric diblock copolymers in the
limit of strong scattering, or large , but yield qualitatively
different predictions for symmetric copolymers far from the ODT and for
asymmetric copolymers. The ROL theory predicts a suppression of
and a decrease of for large values of , relative to the RPA
predictions, but an enhancement of and an increase in
for small (). By separating intra- and
inter-molecular contributions to , we show that the decrease in
near the ODT is caused by the dependence of the intermolecular
direct correlation function, and is unrelated to any change in single-chain
statistics, but that the increase in at small values of is
a result of non-Gaussian single-chain statistics.Comment: 16 pages, 13 figures, submitted to J. Chem. Phy
Wave localization in binary isotopically disordered one-dimensional harmonic chains with impurities having arbitrary cross section and concentration
The localization length for isotopically disordered harmonic one-dimensional
chains is calculated for arbitrary impurity concentration and scattering cross
section. The localization length depends on the scattering cross section of a
single scatterer, which is calculated for a discrete chain having a wavelength
dependent pulse propagation speed. For binary isotopically disordered systems
composed of many scatterers, the localization length decreases with increasing
impurity concentration, reaching a mimimum before diverging toward infinity as
the impurity concentration approaches a value of one. The concentration
dependence of the localization length over the entire impurity concentration
range is approximated accurately by the sum of the behavior at each limiting
concentration. Simultaneous measurements of Lyapunov exponent statistics
indicate practical limits for the minimum system length and the number of
scatterers to achieve representative ensemble averages. Results are discussed
in the context of future investigations of the time-dependent behavior of
disordered anharmonic chains.Comment: 8 pages, 10 figures, submitted to PR
The development of thirty self-administering and self-scoring elaborative thinking exercises
Thesis (Ed.M.)--Boston Universit
Elastodynamics of radially inhomogeneous spherically anisotropic elastic materials in the Stroh formalism
A method is presented for solving elastodynamic problems in radially
inhomogeneous elastic materials with spherical anisotropy, i.e.\ materials such
that in a spherical coordinate system
. The time harmonic displacement field is expanded in a separation of variables form with dependence on
described by vector spherical harmonics with -dependent
amplitudes. It is proved that such separation of variables solution is
generally possible only if the spherical anisotropy is restricted to transverse
isotropy with the principal axis in the radial direction, in which case the
amplitudes are determined by a first-order ordinary differential system.
Restricted forms of the displacement field, such as ,
admit this type of separation of variables solutions for certain lower material
symmetries. These results extend the Stroh formalism of elastodynamics in
rectangular and cylindrical systems to spherical coordinates.Comment: 15 page
- …