28,256 research outputs found
Internally coated air-cooled gas turbine blading
Ten candidate modified nickel-aluminide coatings were developed using the slip pack process. These coatings contain additives such as silicon, chromium and columbium in a nickel-aluminum coating matrix with directionally solidified MAR-M200 + Hf as the substrate alloy. Following a series of screening tests which included strain tolerance, dynamic oxidation and hot corrosion testing, the Ni-19A1-1Cb (nominal composition) coating was selected for application to the internal passages of four first-stage turbine blades. Process development results indicate that a dry pack process is suitable for internal coating application resulting in 18 percent or less reduction in air flow. Coating uniformity, based on coated air-cooled blades, was within + or - 20 percent. Test results show that the presence of additives (silicon, chromium or columbium) appeared to improve significantly the ductility of the NiA1 matrix. However, the environmental resistance of these modified nickel-aluminides were generally inferior to the simple aluminides
Ionized dopant concentrations at the heavily doped surface of a silicon solar cell
Data are combined with concentrations obtained by a bulk measurement method using successive layer removal with measurements of Hall effect and resistivity. From the MOS (metal-oxide-semiconductor) measurements it is found that the ionized dopant concentration N has the value (1.4 + or - 0.1) x 10 to the 20th power/cu cm at distances between 100 and 220 nm from the n(+) surface. The bulk measurement technique yields average values of N over layers whose thickness is 2000 nm. Results show that, at the higher concentrations encountered at the n(+) surface, the MOS C-V technique, when combined with a bulk measurement method, can be used to evaluate the effects of materials preparation methodologies on the surface and near surface concentrations of silicon cells
Efficient, designable, and broad-bandwidth optical extinction via aspect-ratio-tailored silver nanodisks
Subwavelength resonators, ranging from single atoms to metallic
nanoparticles, typically exhibit a narrow-bandwidth response to optical
excitations. We computationally design and experimentally synthesize tailored
distributions of silver nanodisks to extinguish light over broad and varied
frequency windows. We show that metallic nanodisks are two-to-ten-times more
efficient in absorbing and scattering light than common structures, and can
approach fundamental limits to broadband scattering for subwavelength
particles. We measure broadband extinction per volume that closely approaches
theoretical predictions over three representative visible-range wavelength
windows, confirming the high efficiency of nanodisks and demonstrating the
collective power of computational design and experimental precision for
developing new photonics technologies
Solutions for real dispersionless Veselov-Novikov hierarchy
We investigate the dispersionless Veselov-Novikov (dVN) equation based on the
framework of dispersionless two-component BKP hierarchy. Symmetry constraints
for real dVN system are considered. It is shown that under symmetry reductions,
the conserved densities are therefore related to the associated Faber
polynomials and can be solved recursively. Moreover, the method of hodograph
transformation as well as the expressions of Faber polynomials are used to find
exact real solutions of the dVN hierarchy.Comment: 14 page
Finite element analysis of stress distribution and the effects of geometry in a laser-generated single-stage ceramic tile grout seal using ANSYS
Optimisation of the geometry (curvature of the vitrified enamel layer) of a laser-generated single-stage ceramic tile grout seal has carried out with a finite element (FE) model. The overall load bearing capacities and load-displacement plots of three selected geometries were determined experimentally by the indentation technique. Simultaneously, a FE model was developed utilising the commercial ANSYS package to simulate the indentation. Although the load-displacement plots generated by the FE model consistently displayed stiffer identities than the experimentally obtained results, there was reasonably close agreement between the two sets of results. Stress distribution profiles of the three FE models at failure loads were analysed and correlated so as to draw an implication on the prediction of a catastrophic failure through an analysis of FE-generated stress distribution profiles. It was observed that although increased curvatures of the vitrified enamel layer do enhance the overall load-bearing capacity of the single-stage ceramic tile grout seal and bring about a lower nominal stress, there is a higher build up in stress concentration at the apex that would inevitably reduce the load-bearing capacity of the enamel glaze. Consequently, the optimum geometry of the vitrified enamel layer was determined to be flat
Severe discrepancies between experiment and theory in the superconducting proximity effect
The superconducting proximity effect is investigated for SN double layers in
a regime where the resulting transition temperature T_{c} does not depend on
the mean free paths of the films and, within limits, not on the transparency of
the interface. This regime includes the thin film limit and the normalized
initial slope S_{sn}= (d_{s}/T_{s})|dT_{c}/dd_{n}|. The experimental results
for T_{c} are compared with a numerical simulation which was recently developed
in our group. The results for the SN double layers can be devided into three
groups: (i) When N = Cu, Ag, Au, Mg a disagreement between experiment and
theory by a factor of the order of three is observed, (ii) When N = Cd, Zn, Al
the disagreement between experiment and theory is reduced to a factor of about
1.5, (iii) When N = In, Sn a reasonably good agreement between experiment and
theory is observed
Comment on "Quantum Decoherence in Disordered Mesoscopic Systems"
In a recent paper, Phys. Rev. Lett. 81, 1074 (1998), Golubev and Zaikin (GZ)
found that ``zero-point fluctuations of electrons'' contribute to the dephasing
rate extracted from the magnetoresistance. As a result, the dephasing rate
remains finite at zero temperature. GZ claimed that their results ``agree well
with the experimental data''. We point out that the GZ results are incompatible
with (i) conventional perturbation theory of the effects of interaction on weak
localization (WL), and (ii) with the available experimental data. More detailed
criticism of GZ findings can be found in cond-mat/9808053.Comment: 1 page, no figure
Quantitative Simulation of the Superconducting Proximity Effect
A numerical method is developed to calculate the transition temperature of
double or multi-layers consisting of films of super- and normal conductors. The
approach is based on a dynamic interpretation of Gorkov's linear gap equation
and is very flexible. The mean free path of the different metals, transmission
through the interface, ratio of specular reflection to diffusive scattering at
the surfaces, and fraction of diffusive scattering at the interface can be
included. Furthermore it is possible to vary the mean free path and the BCS
interaction NV in the vicinity of the interface. The numerical results show
that the normalized initial slope of an SN double layer is independent of
almost all film parameters except the ratio of the density of states. There are
only very few experimental investigations of this initial slope and they
consist of Pb/Nn double layers (Nn stands for a normal metal). Surprisingly the
coefficient of the initial slope in these experiments is of the order or less
than 2 while the (weak coupling) theory predicts a value of about 4.5. This
discrepancy has not been recognized in the past. The autor suggests that it is
due to strong coupling behavior of Pb in the double layers. The strong coupling
gap equation is evaluated in the thin film limit and yields the value of 1.6
for the coefficient. This agrees much better with the few experimental results
that are available.
PACS: 74.45.+r, 74.62.-c, 74.20.F
Interaction induced ferro-electricity in the rotational states of polar molecules
We show that a ferro-electric quantum phase transition can be driven by the
dipolar interaction of polar molecules in the presence a micro-wave field. The
obtained ferro-electricity crucially depends on the harmonic confinement
potential, and the resulting dipole moment persists even when the external
field is turned off adiabatically. The transition is shown to be second order
for fermions and for bosons of a smaller permanent dipole moment, but is first
order for bosons of a larger moment. Our results suggest the possibility of
manipulating the microscopic rotational state of polar molecules by tuning the
trap's aspect ratio (and other mesoscopic parameters), even though the later's
energy scale is smaller than the former's by six orders of magnitude.Comment: 4 pages and 4 figure
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