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)