31,220 research outputs found
LETS get real: constraints on the development of Local Exchange Trading Schemes
Local Exchange Trading Schemes (LETS) are widely promoted as a new tool for local economic development, but until recently the focus has been on their alleged ‘potential’ rather than the realities of their operation. This paper assesses the practical economic role of LETS by examining the amount of trading conducted, and demonstrates that both the volume of trading and the value of the trades are very low. Drawing on an intensive case study of the first UK LETS created explicitly as part of a local authority’s anti-poverty strategy, explanations for the low levels of participation are suggested, and significant structural constraints on the development of LETS are identified
Ground penetrating radar migration with uncertain parameters
The focusing principle of Kirchoff migration is described. This allows the introduction of optical focusing techniques that can be used to focus migration. Three focus measures are described that are useful for optimising migration. Simple optimisation routines are implemented that model uncertainties in the migration parameters. The focus measures are then used as cast functions to be maximised. Results show that these measures are useful in optimising migration when there are uncertainties in the parameter
The calibratrion of dopplergrams and magnetograms at BBSO
The calibration procedure for the Big Bear Solar Observatory (BBSO) videomagnetograph in which the radial velocity of the sidereal rotation of the Sun is used as a calibrator is described. One of the key points of the procedure is to eliminate the effects of the Earth's motion relative to the Sun and the temperature instability of the birefringent filter by tuning the bandpass of the birefringent filter. The other is to make the light level of the direct image of the videomagnetograph the same both in Doppler and in Zeeman modes in order to reduce the errors introduced by imperfect linearity of the transfer curve of the camera tube. Some practical problems of calibration are discussed for further improvement
Superhumps in V348 Pup
The eclipsing novalike cataclysmic variable star V348 Pup exhibits a
persistent luminosity modulation with a period 6 per cent longer than its 2.44
hour orbital-period (Porb). This has been interpreted as a `positive superhump'
resulting from a slowly precessing non-axisymmetric accretion disc
gravitationally interacting with the secondary. We find a clear modulation of
mid-eclipse times on the superhump period, which agrees well with the
predictions of a simple precessing eccentric disc model. Our modelling shows
that the disc light centre is on the far side of the disc from the donor star
when the superhump reaches maximum light. This phasing suggests a link between
superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the
full lightcurve and maximum entropy eclipse mapping both show that the disc
emission is concentrated closer to the white dwarf at superhump maximum than at
superhump minimum. We detect additional signals consistent with the beat
periods between the implied disc precession period and both (1/2)Porb and
(1/3)Porb.Comment: 13 pages, 13 figures, accepted for publication in MNRA
A new measurement of the cosmic ray energy spectrum between 3 x 10 to the 15th power eV and 3 x 10 to the 16th power eV
A new Cerenkov photon density spectrum measurement is reported. The derivation of the primary cosmic ray energy spectrum for energies from 3x10 to the 15th power eV to 3x10 to the 16th power eV are presented
Chemical Analysis of Surfaces Using Alpha Particles
Chemical analysis of surfaces using alpha particle interactions in instruments incorporating curium 242 alpha sources and semiconductor silicon detector
The chemical analysis experiment for the Surveyor lunar mission
Alpha particle detector experiment for chemical analysis of lunar surface by Surveyor spacecraf
Circuit quantum acoustodynamics with surface acoustic waves
The experimental investigation of quantum devices incorporating mechanical
resonators has opened up new frontiers in the study of quantum mechanics at a
macroscopic level. Superconducting microwave circuits have proven to be
a powerful platform for the realisation of such quantum devices, both in cavity
optomechanics, and circuit quantum electro-dynamics (QED).
While most experiments to date have involved localised nanomechanical
resonators, it has recently been shown that propagating surface acoustic waves
(SAWs) can be piezoelectrically coupled to superconducting qubits, and
confined in high-quality Fabry-Perot cavities up to microwave frequencies in
the quantum regime, indicating the possibility of realising coherent
exchange of quantum information between the two systems. Here we present
measurements of a device in which a superconducting qubit is embedded in, and
interacts with, the acoustic field of a Fabry-Perot SAW cavity on quartz,
realising a surface acoustic version of cavity quantum electrodynamics. This
quantum acoustodynamics (QAD) architecture may be used to develop new quantum
acoustic devices in which quantum information is stored in trapped on-chip
surface acoustic wavepackets, and manipulated in ways that are impossible with
purely electromagnetic signals, due to the times slower speed of
travel of the mechanical waves.Comment: 12 pages, 9 figures, 1 tabl
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