19,018 research outputs found
Higgs fields, bundle gerbes and string structures
We use bundle gerbes and their connections and curvings to obtain an explicit
formula for a de Rham representative of the string class of a loop group
bundle. This is related to earlier work on calorons.Comment: 15 page
Low-Energy Heavy-Ion Reactions and the Skyrme Effective Interaction
The Skyrme effective interaction, with its multitude of parameterisations,
along with its implemen- tation using the static and time-dependent density
functional (TDHF) formalism have allowed for a range of microscopic
calculations of low-energy heavy-ion collisions. These calculations allow
variation of the effective interaction along with an interpretation of the
results of this variation informed by a comparison to experimental data.
Initial progress in implementing TDHF for heavy-ion collisions necessarily used
many approximations in the geometry or the interaction. Over the last decade or
so, the implementations have overcome all restrictions, and studies have begun
to be made where details of the effective interaction are being probed. This
review surveys these studies in low energy heavy-ion reactions, finding
significant effects on observables from the form of the spin-orbit interaction,
the use of the tensor force, and the inclusion of time-odd terms in the density
functional.Comment: submitted to Prog. Part. Nucl. Phy
Mass distributions in a variational model
The time-dependent Hartree-Fock approach may be derived from a variational
principle and a Slater Determinant wavefunction Ansatz. It gives a good
description of nuclear processes in which one-body collisions dominate and has
been applied with success to giant resonances and collisions around the
barrier. It is inherently unable to give a good description of two-body
observables. A variational principle, due to Balian and Veneroni has been
proposed which can be geared to good reproduction of two-body observables.
Keeping the Slater Determinant Ansatz, and restricting the two-body observables
to be the squares of one-body observables, the procedure can be implemented as
a modification of the time-dependent Hartree-Fock procedure. Applications,
using the Skyrme effective interaction, are presented for the mass
distributions of fragments following de-excitation of the giant dipole
resonance in S-32. An illustration of the method's use in collisions is given.Comment: 5 pages, proceedings of XXXII Symposium on Nuclear Physics, Cocoyoc,
Mexic
Cause of the charge radius isotope shift at the \emph{N}=126 shell gap
We discuss the mechanism causing the `kink' in the charge radius isotope
shift at the N=126 shell closure. The occupation of the 1 neutron
orbital is the decisive factor for reproducing the experimentally observed
kink. We investigate whether this orbital is occupied or not by different
Skyrme effective interactions as neutrons are added above the shell closure.
Our results demonstrate that several factors can cause an appreciable
occupation of the 1 neutron orbital, including the magnitude of the
spin-orbit field, and the isoscalar effective mass of the Skyrme interaction.
The symmetry energy of the effective interaction has little influence upon its
ability to reproduce the kink.Comment: 4 pages, 4 figures, to be submitted to proceedings of INPC 201
Shapes and Dynamics from the Time-Dependent Mean Field
Explaining observed properties in terms of underlying shape degrees of
freedom is a well--established prism with which to understand atomic nuclei.
Self--consistent mean--field models provide one tool to understand nuclear
shapes, and their link to other nuclear properties and observables. We present
examples of how the time--dependent extension of the mean--field approach can
be used in particular to shed light on nuclear shape properties, particularly
looking at the giant resonances built on deformed nuclear ground states, and at
dynamics in highly-deformed fission isomers. Example calculations are shown of
Si in the first case, and Pu in the latter case.Comment: 9 pages, 5 figures, to appear in proceedings of International
Workshop "Shapes and Dynamics of Atomic Nuclei: Contemporary Aspects"
(SDANCA-15), 8-10 October 2015, Sofia, Bulgari
Influence of convective transport on tropospheric ozone and its precursors in a chemistry-climate model
The impact of convection on tropospheric O<sub>3</sub> and its precursors has been examined in a coupled chemistry-climate model. There are two ways that convection affects O<sub>3</sub>. First, convection affects O<sub>3</sub> by vertical mixing of O<sub>3</sub> itself. Convection lifts lower tropospheric air to regions where the O<sub>3</sub> lifetime is longer, whilst mass-balance subsidence mixes O<sub>3</sub>-rich upper tropospheric (UT) air downwards to regions where the O<sub>3</sub> lifetime is shorter. This tends to decrease UT O<sub>3</sub> and the overall tropospheric column of O<sub>3</sub>. Secondly, convection affects O<sub>3</sub> by vertical mixing of O<sub>3</sub> precursors. This affects O<sub>3</sub> chemical production and destruction. Convection transports isoprene and its degradation products to the UT where they interact with lightning NO<sub>x</sub> to produce PAN, at the expense of NO<sub>x</sub>. In our model, we find that convection reduces UT NO<sub>x</sub> through this mechanism; convective down-mixing also flattens our imposed profile of lightning emissions, further reducing UT NO<sub>x</sub>. Over tropical land, which has large lightning NO<sub>x</sub> emissions in the UT, we find convective lofting of NO<sub>x</sub> from surface sources appears relatively unimportant. Despite UT NO<sub>x</sub> decreases, UT O<sub>3</sub> production increases as a result of UT HO<sub>x</sub> increases driven by isoprene oxidation chemistry. However, UT O<sub>3</sub> tends to decrease, as the effect of convective overturning of O<sub>3</sub> itself dominates over changes in O<sub>3</sub> chemistry. Convective transport also reduces UT O<sub>3</sub> in the mid-latitudes resulting in a 13% decrease in the global tropospheric O<sub>3</sub> burden. These results contrast with an earlier study that uses a model of similar chemical complexity. Differences in convection schemes as well as chemistry schemes – in particular isoprene-driven changes are the most likely causes of such discrepancies. Further modelling studies are needed to constrain this uncertainty range
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