25,912 research outputs found
A new method for treating optimal trajectories with restricted segments
New method for treating optimal trajectorie
The heavy ion composition in 3HE-rich solar flares
The 3He-rich flares show a tendency to be enriched in heavy ions, and that this enrichment covers the charge range through Fe. The discovery of this association was responsible, in part, for the discarding of 3He enrichment models which involved spallation or thermonuclear reactions, since such models were unable to produce heavy nuclei enhancement. Results of a survey of heavy nucleus abundances observed in 66 3He-rich flares which occurred over the period October 1978 to June 1982 are presented
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Remote sensing of intertidal morphological change in Morecambe Bay, U.K., between 1991 and 2007
Tidal Flats are important examples of extensive areas of natural environment that remain relatively unaffected by man. Monitoring of tidal flats is required for a variety of purposes. Remote sensing has become an established technique for the measurement of topography over tidal flats. A further requirement is to measure topographic changes in order to measure sediment budgets. To date there have been few attempts to make quantitative estimates of morphological change over tidal flat areas. This paper illustrates the use of remote sensing to measure quantitative and qualitative changes in the tidal flats of Morecambe Bay during the relatively long period 1991–2007. An understanding of the patterns of sediment transport within the Bay is of considerable interest for coastal management and defence purposes. Tidal asymmetry is considered to be the dominant cause of morphological change in the Bay, with the higher currents associated with the flood tide being the main agency moulding the channel system. Quantitative changes were measured by comparing a Digital Elevation Model (DEM) of the intertidal zone formed using the waterline technique applied to satellite Synthetic Aperture Radar (SAR) images from 1991–1994, to a second DEM constructed from airborne laser altimetry data acquired in 2005. Qualitative changes were studied using additional SAR images acquired since 2003. A significant movement of sediment from below Mean Sea Level (MSL) to above MSL was detected by comparing the two Digital Elevation Models, though the proportion of this change that could be ascribed to seasonal effects was not clear. Between 1991 and 2004 there was a migration of the Ulverston channel of the river Leven north-east by about 5 km, followed by the development of a straighter channel to the west, leaving the previous channel decoupled from the river. This is thought to be due to independent tidal and fluvial forcing mechanisms acting on the channel. The results demonstrate the effectiveness of remote sensing for measurement of long-term morphological change in tidal flat areas. An alternative use of waterlines as partial bathymetry for assimilation into a morphodynamic model of the coastal zone is also discussed
The heavy ion compositional signature in 3He-rich solar particle events
A survey of the approx. 1 MeV/nucleon heavy ion abundances in 66 He3-rich solar particle events was performed using the Max-Planck-Institut/University of Maryland and Goddard Space Flight Center instruments on the ISEE-3 spacecraft. The observations were carried out in interplanetary space over the period 1978 October through 1982 June. Earlier observations were confirmed which show an enrichment of heavy ions in HE3-rich events, relative to the average solar energetic particle composition in large particle events. For the survey near 1.5 MeV/nucleon the enrichments compared to large solar particle events are approximately He4:C:O:Ne:Mg:Si:Fe = 0.44:0.66:1.:3.4:3.5:4.1:9.6. Surprising new results emerging from the present broad survey are that the heavy ion enrichment pattern is the same within a factor of approx. 2 for almost all cases, and the degree of heavy ion enrichment is uncorrelated with the He3 enrichment. Overall, the features established appear to be best explained by an acceleration mechanism in which the He3 enrichment process is not responsible for the heavy ion enrichment, but rather the heavy ion enrichment is a measure of the ambient coronal composition at the sites where the He3-rich events occur
A Study of Female Circumcision in Eastern Nigeria: Its Medical Significance
Abstract Not Provided
Evolving UK policy on diversity in the armed services: multiculturalism and its discontents
Reflecting a generally multiculturalist rhetoric, UK policy in this area has hitherto focussed on enhancing the degree to which the armed services represent or reflect the ethnic makeup of the UK population. Ambitious targets have been set and some progress made in moving towards them. However, the dynamics of population change, together with the diverse preferences of ethno-religious minorities, have meant that the goal of representativeness has remained out of reach. At the same time, the armed services have continued to struggle with an ongoing recruitment problem while the volume of operational commitments has shown little sign of reducing
High-precision determination of the light-quark masses from realistic lattice QCD
Three-flavor lattice QCD simulations and two-loop perturbation theory are
used to make the most precise determination to date of the strange-, up-, and
down-quark masses, , , and , respectively. Perturbative matching
is required in order to connect the lattice-regularized bare- quark masses to
the masses as defined in the \msbar scheme, and this is done here for the first
time at next-to-next-to leading (or two-loop) order. The bare-quark masses
required as input come from simulations by the MILC collaboration of a
highly-efficient formalism (using so-called ``staggered'' quarks), with three
flavors of light quarks in the Dirac sea; these simulations were previously
analyzed in a joint study by the HPQCD and MILC collaborations, using
degenerate and quarks, with masses as low as , and two values of
the lattice spacing, with chiral extrapolation/interpolation to the physical
masses. With the new perturbation theory presented here, the resulting \msbar\
masses are m^\msbar_s(2 {GeV}) = 87(0)(4)(4)(0) MeV, and \hat m^\msbar(2
{GeV}) = 3.2(0)(2)(2)(0) MeV, where \hat m = \sfrac12 (m_u + m_d) is the
average of the and masses. The respective uncertainties are from
statistics, simulation systematics, perturbation theory, and
electromagnetic/isospin effects. The perturbative errors are about a factor of
two smaller than in an earlier study using only one-loop perturbation theory.
Using a recent determination of the ratio due to
the MILC collaboration, these results also imply m^\msbar_u(2 {GeV}) =
1.9(0)(1)(1)(2) MeV and m^\msbar_d(2 {GeV}) = 4.4(0)(2)(2)(2) MeV. A
technique for estimating the next order in the perturbative expansion is also
presented, which uses input from simulations at more than one lattice spacing
One- and two-particle microrheology
We study the dynamics of rigid spheres embedded in viscoelastic media and
address two questions of importance to microrheology. First we calculate the
complete response to an external force of a single bead in a homogeneous
elastic network viscously coupled to an incompressible fluid. From this
response function we find the frequency range where the standard assumptions of
microrheology are valid. Second we study fluctuations when embedded spheres
perturb the media around them and show that mutual fluctuations of two
separated spheres provide a more accurate determination of the complex shear
modulus than do the fluctuations of a single sphere.Comment: 4 pages, 1 figur
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Improving River Flood Extent Delineation From Synthetic Aperture Radar Using Airborne Laser Altimetry
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Using airborne laser altimetry to improve river flood extents delineated from SAR data
Flood extent maps derived from SAR images are a useful source of data for validating hydraulic models of river flood flow. The accuracy of such maps is reduced by a number of factors, including changes in returns from the water surface caused by different meteorological conditions and the presence of emergent vegetation. The paper describes how improved accuracy can be achieved by modifying an existing flood extent delineation algorithm to use airborne laser altimetry (LiDAR) as well as SAR data. The LiDAR data provide an additional constraint that waterline (land-water boundary) heights should vary smoothly along the flooded reach. The method was tested on a SAR image of a flood for which contemporaneous aerial photography existed, together with LiDAR data of the un-flooded reach. Waterline heights of the SAR flood extent conditioned on both SAR and LiDAR data matched the corresponding heights from the aerial photo waterline significantly more closely than those from the SAR flood extent conditioned only on SAR data
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