502 research outputs found
A domain-specific analysis system for examining nuclear reactor simulation data for light-water and sodium-cooled fast reactors
Building a new generation of fission reactors in the United States presents
many technical and regulatory challenges. One important challenge is the need
to share and present results from new high-fidelity, high-performance
simulations in an easily usable way. Since modern multiscale, multi-physics
simulations can generate petabytes of data, they will require the development
of new techniques and methods to reduce the data to familiar quantities of
interest (e.g., pin powers, temperatures) with a more reasonable resolution and
size. Furthermore, some of the results from these simulations may be new
quantities for which visualization and analysis techniques are not immediately
available in the community and need to be developed.
This paper describes a new system for managing high-performance simulation
results in a domain-specific way that naturally exposes quantities of interest
for light water and sodium-cooled fast reactors. It describes requirements to
build such a system and the technical challenges faced in its development at
all levels (simulation, user interface, etc.). An example comparing results
from two different simulation suites for a single assembly in a light-water
reactor is presented, along with a detailed discussion of the system's
requirements and design.Comment: Article on NiCE's Reactor Analyzer. 23 pages. Keywords: modeling,
simulation, analysis, visualization, input-outpu
Optical spin pumping of modulation doped electrons probed by a two-color Kerr rotation technique
We report on optical spin pumping of modulation electrons in CdTe-based
quantum wells with low intrinsic electron density (by 10^10 cm^{-2}). Under
continuous wave excitation, we reach a steady state accumulated spin density of
about 10^8 cm^{-2}. Using a two-color Hanle-MOKE technique, we find a spin
relaxation time of 34 ns for the localized electrons in the nearly unperturbed
electron gas. Independent variation of the pump and probe energies demonstrates
the presence of additional non-localized electrons in the quantum well, whose
spin relaxation time is substantially shorter
Isotropic, Nematic and Smectic A Phase Behaviour in a Fictitious Field
Phase behaviours of liquid crystals under external fields, conjugate to the
nematic order and smectic order, are studied within the framework of mean field
approximation developed by McMillan. It is found that phase diagrams, of
temperature vs interaction parameter of smectic A order, show several
topologically different types caused by the external fields. The influences of
the field conjugate to the smectic A phase, which is fictitious field, are
precisely discussed.Comment: To be published in J. Phys. Soc. Jpn. vol.73 No.
Zero- and one-dimensional magnetic traps for quasi-particles
We investigate the possibility of trapping quasi-particles possessing spin
degree of freedom in hybrid structures. The hybrid system we are considering
here is composed of a semi-magnetic quantum well placed a few nanometers below
a ferromagnetic micromagnet. We are interested in two different micromagnet
shapes: cylindrical (micro-disk) and rectangular geometry. We show that in the
case of a micro-disk, the spin object is localized in all three directions and
therefore zero-dimensional states are created, and in the case of an elongated
rectangular micromagnet, the quasi-particles can move freely in one direction,
hence one-dimensional states are formed. After calculating profiles of the
magnetic field produced by the micromagnets, we analyze in detail the possible
light absorption spectrum for different micromagnet thicknesses, and different
distances between the micromagnet and the semimagnetic quantum well. We find
that the discrete spectrum of the localized states can be detected via
spatially-resolved low temperature optical measurement.Comment: 15 pages, 9 figure
Spin and orbital frustration in MnSc_2S_4 and FeSc_2S_4
Crystal structure, magnetic susceptibility, and specific heat were measured
in the normal cubic spinel compounds MnSc_2S_4 and FeSc_2S_4. Down to the
lowest temperatures, both compounds remain cubic and reveal strong magnetic
frustration. Specifically the Fe compound is characterized by a Curie-Weiss
temperature \Theta_{CW}= -45 K and does not show any indications of order down
to 50 mK. In addition, the Jahn-Teller ion Fe^{2+} is orbitally frustrated.
Hence, FeSc_2S_4 belongs to the rare class of spin-orbital liquids. MnSc_2S_4
is a spin liquid for temperatures T > T_N \approx 2 K.Comment: 4 pages, to be published in Physical Review Letter
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