933 research outputs found
Effect of distributed energy systems on the electricity grid
A feasibility study is being carried out at Ecotricity into a distributed
energy storage system comprising Energy stores (batteries) placed at
consumer level (in customer’s homes). The aim is to flatten consumer
demand and make better use of home-based generation. The Study
Group considered the mechanism of connecting batteries to the local
distribution system, the ability to meet engineering requirements for the
standard of the connection, and the potential impact of large numbers of
such connections on stability of the local distribution network. Network
and (DC-AC) invertor models were used to examine network connection
transients. A statistical model was proposed to estimate the distribution
of key electrical parameters to determine the likelihood of engineering
standards being exceeded. The Study Group also considered stochastic
methods of modelling wind speed, to better understand the requirements
for battery energy storage as a complement to wind power
Short and slim nacelle design for ultra-high BPR engines
An optimisation method consisting of the non-dominated sorting genetic algorithm (NSGA-II) and computational fluid dynamics of aero-engine nacelles is outlined. The method is applied to three nacelle lengths to determine the relative performance of different ultra-high bypass ratio engine nacelles. The optimal designs at each nacelle length are optimised for three objective functions: cruise drag, drag rise Mach number and change in spillage drag from mid to end of cruise. The Pareto sets generated from these optimisation computations demonstrate that the design space for short nacelles is much narrower in terms of these performace metrics and there are significant penalties in the off design conditions compared to the longer nacelle. Specifically the minimum spillage drag coefficient attainable, for a nacelle with a drag rise Mach number above 0.87, was 0.0040 for the shortest nacelle compared to 0.0005 for a nacelle which was 23% longer
An optimization method for nacelle design
A multi-objective optimiZation method is demonstrated using an evolutionary genetic algorithm. The applicability of this method to preliminary nacelle design is demonstrated by coupling it with a response surface model of a wide range of nacelle designs. These designs were modelled using computational fluid dynamics and a Kriging interpolation was carried out on the results. The NSGA-II algorithm was tested and verified on established multi-dimensional problems. Optimisation on the nacelle model provided 3-dimensional Pareto surfaces of optimal designs at both cruise and off-design conditions. In setting up this methodology several adaptations to the basic NSGA-II algorithm were tested including constraint handling, weighted objective functions and initial sample size. The influence of these operators is demonstrated in terms of the hyper volume of the determined Pareto set
Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions
0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2.
While Tc remained largely unchanged, Jc was strongly enhanced. The best sample
(only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5
A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and
equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions
of nano-scale precipitates of DyB4 and MgO were observed within the grains. The
room temperature resistivity decreased with Dy2O3 indicative of improved grain
connectivity.Comment: 13 pages, 4 figures and 1 tabl
Understanding Heisenberg's 'Magical' Paper of July 1925: a New Look at the Calculational Details
In July 1925 Heisenberg published a paper [Z. Phys. 33, 879-893 (1925)] which
ended the period of `the Old Quantum Theory' and ushered in the new era of
Quantum Mechanics. This epoch-making paper is generally regarded as being
difficult to follow, perhaps partly because Heisenberg provided few clues as to
how he arrived at the results which he reported. Here we give details of
calculations of the type which, we suggest, Heisenberg may have performed. We
take as a specific example one of the anharmonic oscillator problems considered
by Heisenberg, and use our reconstruction of his approach to solve it up to
second order in perturbation theory. We emphasize that the results are
precisely those obtained in standard quantum mechanics, and suggest that some
discussion of the approach - based on the direct computation of transition
amplitudes - could usefully be included in undergraduate courses in quantum
mechanics.Comment: 24 pages, no figures, Latex, submitted to Am. J. Phy
Singular measures and the key of G
We construct a sequence ofdoubling measures, whose doubling constants tend to 1, all for which kill a G[delta] set of full Lebesgue measure
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Introducing creativity techniques and software apps to the care of people with dementia
This poster reports research to introduce creative problem solving techniques and software to the care for people with dementia in residential homes
Improved Current Densities in MgB2 By Liquid-Assisted Sintering
Polycrystalline MgB2 samples with GaN additions were prepared by reaction of
Mg, B, and GaN powders. The presence of Ga leads to a low melting eutectic
phase which allowed liquid phase sintering and produces plate-like grains. For
low-level GaN additions (5% at. % or less), the critical transition
temperature, Tc, remained unchanged and in 1T magnetic field, the critical
current density, Jc was enhanced by a factor of 2 and 10, for temperatures of
\~5K and 20K, respectively. The values obtained are approaching those of hot
isostatically pressed samples.Comment: 12 pages, 1 table, 4 figures, accepted in Applied Physics Letter
Thin-Film Trilayer Manganate Junctions
Spin-dependent conductance across a manganate-barrier-manganate junction has
recently been demonstrated. The junction is a LaSrMnO%
-SrTiO-La SrMnO trilayer device supporting
current-perpendicular transport. Large magnetoresistance of up to a factor of
five change was observed in these junctions at 4.2K in a relatively low field
of the order of 100 Oe. Temperature and bias dependent studies revealed a
complex junction interface structure whose materials physics has yet to be
understood.Comment: 20 pages, 14 figures. To appear in Phil. Trans. R. Soc. Lond. A
vol.356 (1998
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