579 research outputs found
The Multifragmentation Freeze--Out Volume in Heavy Ion Collisions
The reduced velocity correlation function for fragments from the reaction Fe
+ Au at 100 A~MeV bombarding energy is investigated using the
dynamical--statistical approach QMD+SMM and compared to experimental data to
extract the Freeze--Out volume assuming simultaneous multifragmentation.Comment: 8 pages; 3 uuencoded figures available with figures command, LateX,
UCRL-J-1157
Assessment of ion kinetic effects in shock-driven inertial confinement fusion implosions using fusion burn imaging
The significance and nature of ion kinetic effects in D3He-filled, shock-driven inertial confinement
fusion implosions are assessed through measurements of fusion burn profiles. Over this series of
experiments, the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number,
NK) was varied from 0.3 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma
conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match
measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured
the observed yield trends [Rosenberg et al., Phys. Rev. Lett. 112, 185001 (2014)]. Here, spatially
resolved measurements of the fusion burn are used to examine kinetic ion transport effects in
greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional
integrated quantities to one-dimensional profiles. In agreement with the previous findings, a comparison
of measured and simulated burn profiles shows that models including ion transport effects
are able to better match the experimental results. In implosions characterized by large Knudsen
numbers (NK3), the fusion burn profiles predicted by hydrodynamics simulations that exclude
ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally
observed profiles, which are centrally peaked. In contrast, a hydrodynamics simulation that
includes a model of ion diffusion is able to qualitatively match the measured profile shapes.
Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the
observed trends, though further refinement of the models is needed for a more complete and
quantitative understanding of ion kinetic effects
First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions
The deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes [D. T. Casey et al., Phys. Rev. Lett. 108, 075002 (2012)], are not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions
quasiharmonic equations of state for dynamically-stabilized soft-mode materials
We introduce a method for treating soft modes within the analytical framework
of the quasiharmonic equation of state. The corresponding double-well
energy-displacement relation is fitted to a functional form that is harmonic in
both the low- and high-energy limits. Using density-functional calculations and
statistical physics, we apply the quasiharmonic methodology to solid periclase.
We predict the existence of a B1--B2 phase transition at high pressures and
temperatures
Accounting students' IT applicaton skills over a 10-year period
This paper reports on the changing nature of a range of information technology (IT) application skills that students declare on entering an accounting degree over the period from 1996 to 2006. Accounting educators need to be aware of the IT skills students bring with them to university because of the implications this has for learning and teaching within the discipline and the importance of both general and specific IT skills within the practice and craft of accounting. Additionally, IT skills constitute a significant element within the portfolio of employability skills that are increasingly demanded by employers and emphasized within the overall Higher Education (HE) agenda. The analysis of students' reported IT application skills on entry to university, across a range of the most relevant areas of IT use in accounting, suggest that their skills have continued to improve over time. However, there are significant differential patterns of change through the years and within cohorts. The paper addresses the generalizability of these findings and discusses the implications of these factors for accounting educators, including the importance of recognising the differences that are potentially masked by the general increase in skills; the need for further research into the changing nature, and implications, of the gender gap in entrants' IT application skills; and the low levels of entrants' spreadsheet and database skills that are a cause for concern
Landau Analog Levels for Dipoles in the Noncommutative Space and Phase Space
In the present contribution we investigate the Landau analog energy
quantization for neutral particles, that possesses a nonzero permanent magnetic
and electric dipole moments, in the presence of an homogeneous electric and
magnetic external fields in the context of the noncommutative quantum
mechanics. Also, we analyze the Landau--Aharonov--Casher and
Landau--He--McKellar--Wilkens quantization due to noncommutative quantum
dynamics of magnetic and electric dipoles in the presence of an external
electric and magnetic fields and the energy spectrum and the eigenfunctions are
obtained. Furthermore, we have analyzed Landau quantization analogs in the
noncommutative phase space, and we obtain also the energy spectrum and the
eigenfunctions in this context.Comment: 20 pages, references adde
Measurement of the electron electric dipole moment using YbF molecules
The most sensitive measurements of the electron electric dipole moment d_e
have previously been made using heavy atoms. Heavy polar molecules offer a
greater sensitivity to d_e because the interaction energy to be measured is
typically 10^3 times larger than in a heavy atom. We report the first
measurement of this kind, for which we have used the molecule YbF. Together,
the large interaction energy and the strong tensor polarizability of the
molecule make our experiment essentially free of the systematic errors that
currently limit d_e measurements in atoms. Our first result d_e = (- 0.2 \pm
3.2) x 10^-26 e.cm is less sensitive than the best atom measurement, but is
limited only by counting statistics and demonstrates the power of the method.Comment: 4 pages, 4 figures. v2. Minor corrections and clarifications made in
response to referee comment
Core conditions for alpha heating attained in direct-drive inertial confinement fusion
It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)10.1103/PhysRevLett.117.025001] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.United States. Department of Energy (DE-FC02-04ER54789)United States. National Nuclear Security Administration (DE-NA0001944
Maxwell Duality, Lorentz Invariance, and Topological Phase
We discuss the Maxwell electromagnetic duality relations between the
Aharonov-Bohm, Aharonov-Casher, and He-McKellar-Wilkens topological phases,
which allows a unified description of all three phenomena. We also elucidate
Lorentz transformations that allow these effects to be understood in an
intuitive fashion in the rest frame of the moving quantum particle. Finally, we
propose two experimental schemes for measuring the He-McKellar-Wilkens phase.Comment: 10 pages, 2 figure
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