343 research outputs found
Adaptive Eigenvalue Computation - Complexity Estimates
This paper is concerned with the design and analysis of a fully adaptive
eigenvalue solver for linear symmetric operators. After transforming the
original problem into an equivalent one formulated on , the space of
square summable sequences, the problem becomes sufficiently well conditioned so
that a gradient type iteration can be shown to reduce the error by some fixed
factor per step. It then remains to realize these (ideal) iterations within
suitable dynamically updated error tolerances. It is shown under which
circumstances the adaptive scheme exhibits in some sense asymptotically optimal
complexity.Comment: submitted to Math. Com
Domain decomposition and locality optimization for large-scale lattice Boltzmann simulations
We present a simple, parallel and distributed algorithm for setting up and
partitioning a sparse representation of a regular discretized simulation
domain. This method is scalable for a large number of processes even for
complex geometries and ensures load balance between the domains, reasonable
communication interfaces, and good data locality within the domain. Applying
this scheme to a list-based lattice Boltzmann flow solver can achieve similar
or even higher flow solver performance than widely used standard graph
partition based tools such as METIS and PT-SCOTCH
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
Statistical -decay from highly excited states is determined by the
nuclear level density (NLD) and the -ray strength function
(SF). These average quantities have been measured for several nuclei
using the Oslo method. For the first time, we exploit the NLD and SF to
evaluate the -width in the energy region below the neutron binding
energy, often called the quasi-continuum region. The lifetimes of states in the
quasi-continuum are important benchmarks for a theoretical description of
nuclear structure and dynamics at high temperature. The lifetimes may also have
impact on reaction rates for the rapid neutron-capture process, now
demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure
Statistical properties of Pu, and Pu(n,) cross section calculation
The level density and gamma-ray strength function (gammaSF) of 243Pu have
been measured in the quasi-continuum using the Oslo method. Excited states in
243Pu were populated using the 242Pu(d,p) reaction. The level density closely
follows the constant-temperature level density formula for excitation energies
above the pairing gap. The gammaSF displays a double-humped resonance at low
energy as also seen in previous investigations of actinide isotopes. The
structure is interpreted as the scissors resonance and has a centroid of
omega_{SR}=2.42(5)MeV and a total strength of B_{SR}=10.1(15)mu_N^2, which is
in excellent agreement with sum-rule estimates. The measured level density and
gammaSF were used to calculate the 242Pu(n,gamma) cross section in a neutron
energy range for which there were previously no measured data.Comment: 9 pages, 8 figure
Statistical properties of the well deformed Sm nuclei and the scissors resonance
The Nuclear Level Densities (NLDs) and the -ray Strength Functions
(SFs) of Sm have been extracted from (d,p)
coincidences using the Oslo method. The experimental NLD of Sm is
higher than the NLD of Sm, in accordance with microscopic calculations.
The SFs of Sm are in fair agreement with QRPA calculations
based on the D1M Gogny interaction. An enhancement is observed in the
SF for both Sm nuclei around 3 MeV in excitation energy and
is attributed to the M1 Scissors Resonance (SR). Their integrated strengths
were found to be in the range 1.3 - 2.1 and 4.4 - 6.4 for
Sm and Sm, respectively. The strength of the SR for Sm
is comparable to those for deformed even-even Sm isotopes from nuclear
resonance fluorescence measurements, while that of Sm is lower than
expected
Nuclear Level Density and -ray Strength Function of and the impact on the i-process
Proton- coincidences from reactions between
a beam and a deuterated polyethylene target have been
analyzed with the inverse Oslo method to find the nuclear level density (NLD)
and -ray strength function (SF) of . The
capture cross section has been calculated
using the Hauser-Feshbach model in TALYS using the measured NLD and SF
as constraints. We confirm that acts as a
bottleneck when relying on one-zone nucleosynthesis calculations. However, we
find that the impact of this reaction is strongly damped in multi-zone
low-metallicity AGB stellar models experiencing i-process nucleosynthesis.Comment: Submitted to Phys. Rev.
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