12,978 research outputs found
Prediction and analysis of long-term variability of temperature and salinity in the Irish Sea
The variability of temperature and salinity in the Irish Sea over the 40 year period 1960 - 1999 is investigated using a free-running fine-resolution local area model. The skill of the model to represent observed temperature and salinity variability is assessed using conductivity-temperature-depth survey data ( 3397 profiles) and a long time series of measurements from Cypris station (southwest of Isle of Man). This clearly demonstrates that the model can reproduce the observed seasonal and longer-term cycles in temperature, with mean and RMS errors of - 0.01 degrees C and 0.78 degrees C. Particularly apparent is the long-term warming trend at Cypris station and throughout the model domain. Model estimates of salinity are less accurate and are generally too saline (mean and RMS errors are 0.79 and 0.98 practical salinity units). Inaccuracies are likely to arise from boundary conditions and forcing (riverine and surface). However, while absolute values are not particularly well represented, the model reproduces many of the trends in the salinity variability observed at Cypris station, suggesting that the dominant physical processes in the Irish Sea, with timescales up to similar to 3 years, are well represented. The model is also used to investigate the variability in temperature stratification. While stratification is confined to approximately the same geographical area in each year of the simulation, there is significant variability in the timing of the onset and breakdown of stratification and in the peak surface to bed temperature difference. Together, these results suggest that a local area model with limited boundary conditions may be sufficiently accurate for climatic investigation of some (locally forced) parameter
Neutrinoless double-beta decay matrix elements in large shell-model spaces with the generator-coordinate method
We use the generator-coordinate method with realistic shell-model
interactions to closely approximate full shell-model calculations of the matrix
elements for the neutrinoless double-beta decay of Ca, Ge, and
Se. We work in one major shell for the first isotope, in the
space for the second and third, and finally in two major
shells for all three. Our coordinates include not only the usual axial
deformation parameter , but also the triaxiality angle and
neutron-proton pairing amplitudes. In the smaller model spaces our matrix
elements agree well with those of full shell-model diagonalization, suggesting
that our Hamiltonian-based GCM captures most of the important valence-space
correlations. In two major shells, where exact diagonalization is not currently
possible, our matrix elements are only slightly different from those in a
single shell.Comment: 8 pages, 7 figure
The helical instability of the positive column in crossed fields and in annular plasma configurations Interim report
Helical instability of positive column in crossed fields and in annular plasma configuration
An x-band waveguide cell for study of microwave propagation through magnetoplasma technical report no. 16
Metal X-band waveguide cell for study of microwave propagation through magnetoplasm
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Reduced regulator dependence of neutron-matter predictions with chiral interactions
We calculate the energy per particle in infinite neutron matter
perturbatively using chiral N3LO two-body potentials plus N2LO three-body
forces. The cutoff dependence of the predictions is investigated by employing
chiral interactions with different regulators. We find that the inclusion of
three-nucleon forces, which are consistent with the applied two-nucleon
interaction, leads to a strongly reduced regulator dependence of the results.Comment: 7 pages, 8 figures, 1 table, to be published in Physical Review
Three-nucleon interactions: A frontier in nuclear structure
Three-nucleon interactions are a frontier in understanding and predicting the
structure of strongly-interacting matter in laboratory nuclei and in the
cosmos. We present results and discuss the status of first calculations with
microscopic three-nucleon interactions beyond light nuclei. This coherent
effort is possible due to advances based on effective field theory and
renormalization group methods in nuclear physics.Comment: 7 pages, 11 figures, talk at International Symposium on New Facet of
Three-Nucleon Force (FM50), Tokyo, October, 200
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