529 research outputs found
Relativistic Mean Field calculations of nuclear properties in early stages of stellar collapse
We use the Relativistic Mean Field (RMF) method to calculate properties of
neutron rich, usually deformed nuclei, important for equation of state
calculations and which have significant abundance in the early stages of
stellar collapse. We compare the results of our microscopic calculations with
existing cold nuclear equations of state based on macroscopic liquid drop model
and the FRLDM model.Comment: 4 pages , Latex, 4 figures, uses espcrc1.sty. To appear in Nucl.
Phys. A, proceedings of "Nuclei in the Cosmos 1996" 4th International
Symposium on Nuclear Astrophysics. e-mail contact: [email protected]
Experimentation and modelling of near field explosions
Repeatable experimental results and numerical work has shown that using the Jones-Wilkins-Lee (JWL) equation of
state (EOS) will give very accurate results of peak pressures and impulse delivered to a rigid target at large scaled
distances. However, recent experiments/numerical modelling at small scaled distances show that the JWL will overpredict
peak pressures and impulse due to the assumption of (near) instantaneous energy release from detonation.
The results of this experimental/numerical study are presented herein. In the experimental work PE4 spheres at two
different scaled distances have been tested using an array of Hopkinson Pressure Bars (HPB) at specific points on a
rigid target to measure the local pressure-time histories. From the HPB measurements, it appears that below certain
scaled distances there are chemical-physical mechanisms that do not have sufficient time to contribute to the energy
driving the loading mechanisms, explaining the over-prediction of the JWL. Importantly though, the experimental
results show that at very small scaled distances (0.172 m/kg1/3) the test to test percentage variation is very low
(5.1%); whilst at larger scaled distances (0.819 m/kg1/3) it is much higher (23.1%). This paper presents a model
which describes the process by which experimental results move from repeatable to variable to repeatable as scaled
distance increases from the extreme near field to far field
The impact of deep-sea fisheries and implementation of the UNGA Resolutions 61/105 and 64/72. Report of an international scientific workshop
The scientific workshop to review fisheries management, held in Lisbon in May 2011, brought together 22 scientists and fisheries experts from around the world to consider the United Nations General Assembly (UNGA) resolutions on high seas bottom fisheries: what progress has been made and what the outstanding issues are. This report summarises the workshop conclusions, identifying examples of good practice and making recommendations in areas where it was agreed that the current management measures fall short of their target
Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe
Finite element simulation of plates under non-uniform blast loads using a point-load method: Buried explosives
There are two primary challenges associated with assessing the adequacy of a protective structure to resist explosive events: firstly the spatial variation of load acting on a target must be predicted to a sufficient level of accuracy; secondly, the response of the target to this load must also be quantified. When a high explosive is shallowly buried in soil, the added confinement given by the geotechnical material results in a blast which is predominantly directed vertically. This imparts an extremely high magnitude, spatially non-uniform load on the target structure. A recently commissioned experimental rig designed by the authors has enabled direct measurements of the blast load resulting from buried explosive events. These direct measurements have been processed using an in-house interpolation routine which evaluates the load acting over a regular grid of points. These loads can then be applied as the nodal-point loads in a finite element model. This paper presents results from a series of experiments where a free-flying plate was suspended above a shallow buried explosive. Dynamic and residual deformations are compared with finite element simulations of plates using the experimentally recorded, and interpolated, nodal point-loads. The results show very good agreement and highlight the use of this method for evaluating the efficacy of targets subjected to non-uniform blast loads
Ground and excited states Gamow-Teller strength distributions of iron isotopes and associated capture rates for core-collapse simulations
This paper reports on the microscopic calculation of ground and excited
states Gamow-Teller (GT) strength distributions, both in the electron capture
and electron decay direction, for Fe. The associated electron and
positron capture rates for these isotopes of iron are also calculated in
stellar matter. These calculations were recently introduced and this paper is a
follow-up which discusses in detail the GT strength distributions and stellar
capture rates of key iron isotopes. The calculations are performed within the
framework of the proton-neutron quasiparticle random phase approximation
(pn-QRPA) theory. The pn-QRPA theory allows a microscopic
\textit{state-by-state} calculation of GT strength functions and stellar
capture rates which greatly increases the reliability of the results. For the
first time experimental deformation of nuclei are taken into account. In the
core of massive stars isotopes of iron, Fe, are considered to be
key players in decreasing the electron-to-baryon ratio () mainly via
electron capture on these nuclide. The structure of the presupernova star is
altered both by the changes in and the entropy of the core material.
Results are encouraging and are compared against measurements (where possible)
and other calculations. The calculated electron capture rates are in overall
good agreement with the shell model results. During the presupernova evolution
of massive stars, from oxygen shell burning stages till around end of
convective core silicon burning, the calculated electron capture rates on
Fe are around three times bigger than the corresponding shell model
rates. The calculated positron capture rates, however, are suppressed by two to
five orders of magnitude.Comment: 18 pages, 12 figures, 10 table
UK monitoring and deposition of tephra from the May 2011 eruption of Grímsvötn, Iceland
Mapping the transport and deposition of tephra is important for the assessment of an eruption’s impact on health, transport, vegetation and infrastructure, but it is challenging at large distances from a volcano (> 1000 km), where it may not be visible to the naked eye. Here we describe a range of methods used to quantify tephra deposition and impact on air quality during the 21–28 May 2011 explosive basaltic eruption of Grímsvötn volcano, Iceland. Tephra was detected in the UK with tape-on-paper samples, rainwater samples, rainwater chemistry analysis, pollen slides and air quality measurements. Combined results show that deposition was mainly in Scotland, on 23–25 May. Deposition was patchy, with adjacent locations recording different results. Tape-on-paper samples, collected by volunteer citizen scientists, and giving excellent coverage across the UK, showed deposition at latitudes >55°N, mainly on 24 May. Rainwater samples contained ash grains mostly 20–30 μm long (maximum recorded grainsize 80 μm) with loadings of up to 116 grainscm-2. Analysis of rainwater chemistry showed high concentrations of dissolved Fe and Al in samples from N Scotland on 24–27 May. Pollen slides recorded small glass shards (3–4 μm long) deposited during rainfall on 24–25 May and again on 27 May. Air quality monitoring detected increased particulate matter concentrations in many parts of the country. An hourly concentration of particles 53°N) on 24 May but no negative effects on health were reported. Although the eruption column reached altitudes of 20 km above sea level, air mass trajectories suggest that only tephra from the lowest 4 km above sea level of the eruption plume was transported to the UK. This demonstrates that even low plumes could deliver tephra to the UK and suggests that the relative lack of basaltic tephra in the tephrochronological record is not due to transport processes
Neutrino capture by r-process waiting-point nuclei
We use the Quasiparticle Random Phase Approximation to include the effects of
low-lying Gamow-Teller and first forbidden strength in neutrino capture by very
neutron-rich nuclei with N = 50, 82, or 126. For electron neutrinos in what is
currently considered the most likely r-process site the capture cross sections
are two or more times previous estimates. We briefly discuss the reliability of
our calculations and their implications for nucleosynthesis.Comment: 9 pages, 4 figure
Life path analysis: scaling indicates priming effects of social and habitat factors on dispersal distances
1. Movements of many animals along a life-path can be separated into repetitive ones within home ranges and transitions between home ranges. We sought relationships of social and environmental factors with initiation and distance of transition movements in 114 buzzards Buteo buteo that were marked as nestlings with long-life radio tags.
2. Ex-natal dispersal movements of 51 buzzards in autumn were longer than for 30 later in their first year and than 35 extra-natal movements between home ranges after leaving nest areas. In the second and third springs, distances moved from winter focal points by birds that paired were the same or less than for unpaired birds. No post-nuptial movement exceeded 2 km.
3. Initiation of early ex-natal dispersal was enhanced by presence of many sibs, but also by lack of worm-rich loam soils. Distances travelled were greatest for birds from small broods and with relatively little short grass-feeding habitat near the nest. Later movements were generally enhanced by the absence of loam soils and short grassland, especially with abundance of other buzzards and probable poor feeding habitats (heathland, long grass).
4. Buzzards tended to persist in their first autumn where arable land was abundant, but subsequently showed a strong tendency to move from this habitat.
5. Factors that acted most strongly in ½-km buffers round nests, or round subsequent focal points, usually promoted movement compared with factors acting at a larger scale. Strong relationships between movement distances and environmental characteristics in ½-km buffers, especially during early ex-natal dispersal, suggested that buzzards became primed by these factors to travel far.
6. Movements were also farthest for buzzards that had already moved far from their natal nests, perhaps reflecting genetic predisposition, long-term priming or poor habitat beyond the study area
Affleck-Dine baryogenesis in the local domain
For Affleck-Dine baryogenesis to proceed, there must have been two types of
phase transitions. One is the destabilized-stabilized phase transition of the
flat direction, which is in general induced by the Hubble parameter. The other
is the phase transition related to the A-term, which induces the misalignment
of the relative phase of the flat direction. In the conventional Affleck-Dine
baryogenesis they are supposed to start almost simultaneously. Of course these
phase transitions can take place separately, but the latter must not be later
than the former because the phase transition of the A-term can not produce any
baryon number when there is no condensate of the relative charge.
In this paper we try to construct models where the original idea of
Affleck-Dine baryogenesis is realized in a different way. We show examples in
which the local domain of the false vacuum with the required condensate is
formed after inflation and collapses in a safe way so that the domain wall
problem is avoided. We also show examples where the phase transition of the
A-term starts before the decay of the condensate. As in the conventional
Affleck-Dine mechanism, the phase transition of the A-term produces baryon
number in the local domain of the condensate. We construct scenarios where our
mechanism produces sufficient baryon asymmetry of the Universe.Comment: 18pages, latex2e, to appear in PR
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