110,991 research outputs found
Structure-property characterization of rheocast and VADER processed IN-100 superalloy
Two recent solidification processes have been applied in the production of IN-100 nickel-base superalloy: rheocasting and vacuum arc double electrode remelting (VADER). A detailed microstructural examination has been made of the products of these two processes; associated tensile strength and fatigue crack propagation (FCP) rate at an elevated temperature were evaluated. In rheocasting, processing variables that have been evaluated include stirring speed, isothermal stirring time and volume fraction solid during isothermal stirring. VADER processed IN-100 was purchased from Special Metals Corp., New Hartford, NY. As-cast ingots were subjected to hot isostatic pressing (HIP) and heat treatment. Both rheocasting and VADER processed materials yield fine and equiaxed spherical structures, with reduced macrosegregation in comparison to ingot materials. The rheocast structures are discussed on the basis of the Vogel-Doherty-Cantor model of dendrite arm fragmentation. The rheocast ingots evaluated were superior in yield strength to both VADER and commercially cast IN-100 alloy. Rheocast and VADER ingots may have higher crack propagation resistance than P/M processed material
Irreducible Characters of General Linear Superalgebra and Super Duality
We develop a new method to solve the irreducible character problem for a wide
class of modules over the general linear superalgebra, including all the
finite-dimensional modules, by directly relating the problem to the classical
Kazhdan-Lusztig theory. We further verify a parabolic version of a conjecture
of Brundan on the irreducible characters in the BGG category \mc{O} of the
general linear superalgebra. We also prove the super duality conjecture
A simple mean field equation for condensates in the BEC-BCS crossover regime
We present a mean field approach based on pairs of fermionic atoms to
describe condensates in the BEC-BCS crossover regime. By introducing an
effective potential, the mean field equation allows us to calculate the
chemical potential, the equation of states and the atomic correlation function.
The results agree surprisingly well with recent quantum Monte Carlo
calculations. We show that the smooth crossover from the bosonic mean field
repulsion between molecules to the Fermi pressure among atoms is associated
with the evolution of the atomic correlation function
Controlling the accuracy of unconditionally stable algorithms in Cahn-Hilliard Equation
Given an unconditionally stable algorithm for solving the Cahn-Hilliard
equation, we present a general calculation for an analytic time step \d \tau
in terms of an algorithmic time step \dt. By studying the accumulative
multi-step error in Fourier space and controlling the error with arbitrary
accuracy, we determine an improved driving scheme \dt=At^{2/3} and confirm
the numerical results observed in a previous study \cite{Cheng1}.Comment: 4 pages, late
Haar expectations of ratios of random characteristic polynomials
We compute Haar ensemble averages of ratios of random characteristic
polynomials for the classical Lie groups K = O(N), SO(N), and USp(N). To that
end, we start from the Clifford-Weyl algebera in its canonical realization on
the complex of holomorphic differential forms for a C-vector space V. From it
we construct the Fock representation of an orthosymplectic Lie superalgebra osp
associated to V. Particular attention is paid to defining Howe's oscillator
semigroup and the representation that partially exponentiates the Lie algebra
representation of sp in osp. In the process, by pushing the semigroup
representation to its boundary and arguing by continuity, we provide a
construction of the Shale-Weil-Segal representation of the metaplectic group.
To deal with a product of n ratios of characteristic polynomials, we let V =
C^n \otimes C^N where C^N is equipped with its standard K-representation, and
focus on the subspace of K-equivariant forms. By Howe duality, this is a
highest-weight irreducible representation of the centralizer g of Lie(K) in
osp. We identify the K-Haar expectation of n ratios with the character of this
g-representation, which we show to be uniquely determined by analyticity, Weyl
group invariance, certain weight constraints and a system of differential
equations coming from the Laplace-Casimir invariants of g. We find an explicit
solution to the problem posed by all these conditions. In this way we prove
that the said Haar expectations are expressed by a Weyl-type character formula
for all integers N \ge 1. This completes earlier work by Conrey, Farmer, and
Zirnbauer for the case of U(N).Comment: LaTeX, 70 pages, Complex Analysis and its Synergies (2016) 2:
Long-Distance Contributions to D^0-D^0bar Mixing Parameters
Long-distance contributions to the - mixing parameters and
are evaluated using latest data on hadronic decays. In particular, we
take on two-body and decays to evaluate the contributions of
two-body intermediate states because they account for of hadronic
decays. Use of the diagrammatic approach has been made to estimate
yet-observed decay modes. We find that is of order a few
and of order from hadronic and modes. These are in good
agreement with the latest direct measurement of - mixing
parameters using the and decays by
BaBar. We estimate the contribution to from the modes using the
factorization model and comment on the single-particle resonance effects and
contributions from other two-body modes involving even-parity states.Comment: 18 pages and 1 figure; footnotes and references added; to appear in
Phys. Rev.
Modelling Epsilon Aurigae without solid particles
Three components can be expected to contribute to the emission of epsilon Aurigae. There is a primary F star. There is an opaque disk which occults it, and there is a gas stream which is observed to produce absorption lines. Evidence that the disk is not responsible for the gas stream lines comes both from the radial velocities, which are too small, and from the IR energy distribution out of eclipse, which shows free-free emission that would produce inadequate optical depth in electron scattering. The color temperature of the IR excess can give misleading indications of low temperature material. Free-free emission at 10,000 K between 10 and 20 microns has a color temperature of 350 K. Attempts to mold the system are discussed
A BGG-type resolution for tensor modules over general linear superalgebra
We construct a Bernstein-Gelfand-Gelfand type resolution in terms of direct
sums of Kac modules for the finite-dimensional irreducible tensor
representations of the general linear superalgebra. As a consequence it follows
that the unique maximal submodule of a corresponding reducible Kac module is
generated by its proper singular vector.Comment: 11pages, LaTeX forma
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SLS Processing Studies of Nylon 11 Nanocomposites
Selective Laser Sintering (SLS) is widely used for rapid prototyping/manufacturing of
nylon 11 and nylon 12 parts. This processing technique has not been explored for
nylon nanocomposites. This study investigates the technicalities of processing nylon
11-clay and nylon-carbon nanofiber nanocomposites with SLS. Microstructural
analyses of the SLS powders and parts were conducted under SEM. Results suggest
that SLS processing is possible with the new nylon 11 nanocomposites. Yet the SLS
parts built have inferior properties relative to those of injection molding, suggesting
that more fine tuning for the processing is required.Mechanical Engineerin
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