10,082 research outputs found
Scalar--Flat Lorentzian Einstein--Weyl Spaces
We find all three-dimensional Einstein--Weyl spaces with the vanishing scalar
curvatureComment: 4 page
Design rules for dislocation filters
The efficacy of strained layer threading dislocation filter structures in
single crystal epitaxial layers is evaluated using numerical modeling for (001)
face-centred cubic materials, such as GaAs or Si(1-x)Ge(x), and (0001)
hexagonal materials such as GaN. We find that threading dislocation densities
decay exponentially as a function of the strain relieved, irrespective of the
fraction of threading dislocations that are mobile. Reactions between threading
dislocations tend to produce a population that is a balanced mixture of mobile
and sessile in (001) cubic materials. In contrast, mobile threading
dislocations tend to be lost very rapidly in (0001) GaN, often with little or
no reduction in the immobile dislocation density. The capture radius for
threading dislocation interactions is estimated to be approx. 40nm using cross
section transmission electron microscopy of dislocation filtering structures in
GaAs monolithically grown on Si. We find that the minimum threading dislocation
density that can be obtained in any given structure is likely to be limited by
kinetic effects to approx. 1.0e+04 to 1.0e+05 per square cm.Comment: 18 pages, 9 figure
A pathway to accurate potential energy curves on NISQ devices
We present a practical workflow to compute the potential energy curve of the
hydrogen molecule on near intermediate-scale quantum (NISQ) devices. The
proposed approach uses an extrapolation scheme to deliver, with only few
qubits, full configuration interaction results close to the basis-set limit. We
show that despite the limitations imposed by the noisy nature of simulated
quantum hardware, it is possible to recover realistic electronic correlation
values, if we also estimate expectation values of the Hartree-Fock ground state
energy. Using two models of noisy quantum experiments, we evaluate the
performance of a scheme that requires at most a double-zeta basis set (3-21G,
in this case) and compare with the most accurate Born-Oppenheimer potential
energy curves available in the literature. Our flexible approach is implemented
using simple variational ansatzes combined with straightforward mitigation
techniques and thus we expect it to be also suitable for other energy
estimation quantum schemes
A Survey for Outer Satellites of Mars: Limits to Completeness
We surveyed the Hill sphere of Mars for irregular satellites. Our search
covered nearly the entire Hill Sphere, but scattered light from Mars excluded
the inner few arcminutes where the satellites Phobos and Deimos reside. No new
satellites were found to an apparent limiting red magnitude of 23.5, which
corresponds to radii of about 0.09 km using an albedo of 0.07.Comment: 5 figures (1 color), 2 Tables, to appear in AJ Nov. 200
Increasing Needs and Solutions for Non-Baseload Operation of Nuclear Power Plants
Operation at steady full power, i.e. baseload operation, of nuclear power plants (NPPs) is
usually considered to be the most efficient use of capital investment. Therefore, design and
operation of most existing nuclear power plants (NPPs) are optimised to operate in baseload mode.
Recently, there is an increasing need to operate NPPs in non-baseload mode, specifically
performing frequency control and load following. These needs are typically due to a large nuclear
generating capacity, increasing share of renewable generation, deregulation or evolution of the
electricity supply systems and markets. Re-optimization of NPP design and operation for nonbaseload
(flexible) mode of operation necessitates operational, economic and financial
rearrangements to maintain the capital investment, in addition the adaptation of technical and
regulatory changes. This paper discusses the aspects of design or operation of NPPs in flexible
mode based on the existing knowledge and experience and it is primarily based on the recent study
that was prepared by the International Atomic Energy Agency (IAEA)
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