79 research outputs found
Strichartz estimates on Schwarzschild black hole backgrounds
We study dispersive properties for the wave equation in the Schwarzschild
space-time. The first result we obtain is a local energy estimate. This is then
used, following the spirit of earlier work of Metcalfe-Tataru, in order to
establish global-in-time Strichartz estimates. A considerable part of the paper
is devoted to a precise analysis of solutions near the trapping region, namely
the photon sphere.Comment: 44 pages; typos fixed, minor modifications in several place
Free Versus Constrained Evolution of the 2+1 Equivariant Wave Map
We compare the numerical solutions of the 2+1 equivariant Wave Map problem
computed with the symplectic, constraint respecting Rattle algorithm and the
well known fourth order Runge-Kutta method. We show the advantages of the
Rattle algorithm for constrained system compared to the free evolution with the
Runge-Kutta method. We also present an expression, which represents the energy
loss due to constraint violation. Taking this expression into account we can
achieve energy conservation for the Runge-Kutta scheme, which is better than
with the Rattle method. Using the symplectic scheme with constraint enforcement
we can reproduce previous calculations of the equivariant case without imposing
the symmetry explicitly, thereby confirming that the critical behaviour is
stable.Comment: 16 pages, 8 figures. Formula for the scaling function on p. 13
corrected and two typos eliminated; otherwise agrees with the published pape
On the relation between mathematical and numerical relativity
The large scale binary black hole effort in numerical relativity has led to
an increasing distinction between numerical and mathematical relativity. This
note discusses this situation and gives some examples of succesful interactions
between numerical and mathematical methods is general relativity.Comment: 12 page
Total prompt γ
The total prompt γ-ray energy distributions for the neutron-induced fission of 235U, 239,241Pu at incident neutron energy of 0.025 eV ‒ 100 keV, and the spontaneous fission of 252Cf were measured using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments by a parallel-plate avalanche counter. DANCE is a highly segmented, highly efficient 4π γ-ray calorimeter. Corrections were made to the measured distribution by unfolding the two-dimension spectrum of total γ-ray energy vs multiplicity using a simulated DANCE response matrix. The mean values of the total prompt γ-ray energy, determined from the unfolded distributions, are ~ 20% higher than those derived from measurements using single γ-ray detector for all the fissile nuclei studied. This raises serious concern on the validity of the mean total prompt γ-ray energy obtained from the product of mean values for both prompt γ-ray energy and multiplicity
The Mini-CAPTAIN Liquid Argon Time Projection Chamber
This manuscript describes the commissioning of the Mini-CAPTAIN liquid argon
detector in a neutron beam at the Los Alamos Neutron Science Center (LANSCE),
which led to a first measurement of high-energy neutron interactions in argon.
The Mini-CAPTAIN detector consists of a Time Projection Chamber (TPC) with an
accompanying photomultiplier tube (PMT) array sealed inside a
liquid-argon-filled cryostat. The liquid argon is constantly purified and
recirculated in a closed-loop cycle during operation. The specifications and
assembly of the detector subsystems and an overview of their performance in a
neutron beam are reported.Comment: 21 pages, 27 figure
Measurement of the Neutron Cross Section on Argon Between 95 and 720 MeV
We report an extended measurement of the neutron cross section on argon in
the energy range of 95-720 MeV. The measurement was obtained with a 4.3-hour
exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. Compared
to an earlier analysis of the same data, this extended analysis includes a
reassessment of systematic uncertainties, in particular related to unused wires
in the upstream part of the detector. Using this information we doubled the
fiducial volume in the experiment and increased the statistics by a factor of
2.4. We also shifted the analysis from energy bins to time-of-flight bins. This
change reduced the overall considered energy range, but improved the
understanding of the energy spectrum of incoming neutrons in each bin. Overall,
the new measurements are extracted from a fit to the attenuation of the neutron
flux in five time-of-flight regions: 140 ns - 180 ns, 120 ns - 140 ns, 112 ns -
120 ns, 104 ns - 112 ns, 96 ns - 104 ns. The final cross sections are given for
the flux-averaged energy in each time-of-flight bin:
(syst) b,
(syst) b,
(syst) b,
(syst) b,
(syst) b.Comment: 15 pages, 7 tables, 11 figures. Prepared for submission to PR
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