91 research outputs found
Static and Dynamic Chain Structures in the Mean-Field Theory
We give a brief overview of recent work examining the presence of
-clusters in light nuclei within the Skyrme-force Hartree-Fock model.
Of special significance are investigations into -chain structures in
carbon isotopes and O. Their stability and possible role in fusion
reactions are examined in static and time-dependent Hartree-Fock calculations.
We find a new type of shape transition in collisions and a centrifugal
stabilization of the chain state in a limited range of angular
momenta. No stabilization is found for the chain.Comment: Fusionn 11 Conference, St. Malo, France, 201
Single-particle dissipation in TDHF studied from a phase-space perspective
We study dissipation and relaxation processes within the time-dependent
Hartree-Fock approach using the Wigner distribution function. On the technical
side we present a geometrically unrestricted framework which allows us to
calculate the full six-dimensional Wigner distribution function. With the
removal of geometrical constraints, we are now able to extend our previous
phase-space analysis of heavy-ion collisions in the reaction plane to
unrestricted mean-field simulations of nuclear matter on a three-dimensional
Cartesian lattice. From the physical point of view we provide a quantitative
analysis on the stopping power in TDHF. This is linked to the effect of
transparency. For the medium-heavy Ca+Ca system we examine the
impact of different parametrizations of the Skyrme force, energy-dependence,
and the significance of extra time-odd terms in the Skyrme functional.Comment: 7 pages, 4 figures, 2 videos. arXiv admin note: substantial text
overlap with arXiv:1201.526
Equilibration in the time-dependent Hartree-Fock approach probed with the Wigner distribution function
Calculating the Wigner distribution function in the reaction plane, we are
able to probe the phase-space behavior in time-dependent Hartree-Fock during a
heavy-ion collision. We compare the Wigner distribution function with the
smoothed Husimi distribution function. Observables are defined to give a
quantitative measure for local and global equilibration. We present different
reaction scenarios by analyzing central and non-central and
collisions. It is shown that the initial phase-space
volumes of the fragments barely merge. The mean values of the observables are
conserved in fusion reactions and indicate a "memory effect" in time-dependent
Hartree-Fock. We observe strong dissipation but no evidence for complete
equilibration.Comment: 12 pages, 10 figure
Transportation energy conservation data book edition i 5
This document contains statistical information on the major transportation modes, their respective energy consumption patterns, and other pertinent factors influencing performance in the transportation sector. Data relating to past, present, and projected energy use and conservation in the transportation sector are presented under seven chapter headings. These focus on (1) modal transportation characteristics, (2) energy characteristics of the transportation sector, (3) energy conservation alternatives involving the transportation sector, (4) government impacts on the transportation sector, (5) the supply of energy to the transportation sector, (6) characteristics of transportation demand, and (7) miscellaneous reference materials such as energy conversion factors and geographical maps. References are included for each set of data presented, and a more general bibliography is included at the end of the book. In addition, a glossary of key terms and a subject index is provided for the user. A second edition of this document is scheduled for publication in September 1977.
Document type: Repor
Optically driving the radiative Auger transition
In a radiative Auger process, optical decay is accompanied by simultaneous
excitation of other carriers. The radiative Auger process gives rise to weak
red-shifted satellite peaks in the optical emission spectrum. These satellite
peaks have been observed over a large spectral range: in the X-ray emission of
atoms; close to visible frequencies on donors in semiconductors and quantum
emitters; and at infrared frequencies as shake-up lines in two-dimensional
systems. So far, all the work on the radiative Auger process has focussed on
detecting the spontaneous emission. However, the fact that the radiative Auger
process leads to photon emission suggests that the transition can also be
optically excited. In such an inverted radiative Auger process, excitation
would correspond to simultaneous photon absorption and electronic
de-excitation. Here, we demonstrate optical driving of the radiative Auger
transition on a trion in a semiconductor quantum dot. The radiative Auger and
the fundamental transition together form a -system. On driving both
transitions of this -system simultaneously, we observe a reduction of
the fluorescence signal by up to . Our results demonstrate a type of
optically addressable transition connecting few-body Coulomb interactions to
quantum optics. The results open up the possibility of carrying out THz
spectroscopy on single quantum emitters with all the benefits of optics:
coherent laser sources, efficient and fast single-photon detectors. In analogy
to optical control of an electron spin, the -system between the
radiative Auger and the fundamental transitions allows optical control of the
emitters' orbital degree of freedom.Comment: 8 pages, 6 figure
Anomalous Dynamics of Forced Translocation
We consider the passage of long polymers of length N through a hole in a
membrane. If the process is slow, it is in principle possible to focus on the
dynamics of the number of monomers s on one side of the membrane, assuming that
the two segments are in equilibrium. The dynamics of s(t) in such a limit would
be diffusive, with a mean translocation time scaling as N^2 in the absence of a
force, and proportional to N when a force is applied. We demonstrate that the
assumption of equilibrium must break down for sufficiently long polymers (more
easily when forced), and provide lower bounds for the translocation time by
comparison to unimpeded motion of the polymer. These lower bounds exceed the
time scales calculated on the basis of equilibrium, and point to anomalous
(sub-diffusive) character of translocation dynamics. This is explicitly
verified by numerical simulations of the unforced translocation of a
self-avoiding polymer. Forced translocation times are shown to strongly depend
on the method by which the force is applied. In particular, pulling the polymer
by the end leads to much longer times than when a chemical potential difference
is applied across the membrane. The bounds in these cases grow as N^2 and
N^{1+\nu}, respectively, where \nu is the exponent that relates the scaling of
the radius of gyration to N. Our simulations demonstrate that the actual
translocation times scale in the same manner as the bounds, although influenced
by strong finite size effects which persist even for the longest polymers that
we considered (N=512).Comment: 13 pages, RevTeX4, 16 eps figure
The monomer-dimer problem and moment Lyapunov exponents of homogeneous Gaussian random fields
We consider an "elastic" version of the statistical mechanical monomer-dimer
problem on the n-dimensional integer lattice. Our setting includes the
classical "rigid" formulation as a special case and extends it by allowing each
dimer to consist of particles at arbitrarily distant sites of the lattice, with
the energy of interaction between the particles in a dimer depending on their
relative position. We reduce the free energy of the elastic dimer-monomer (EDM)
system per lattice site in the thermodynamic limit to the moment Lyapunov
exponent (MLE) of a homogeneous Gaussian random field (GRF) whose mean value
and covariance function are the Boltzmann factors associated with the monomer
energy and dimer potential. In particular, the classical monomer-dimer problem
becomes related to the MLE of a moving average GRF. We outline an approach to
recursive computation of the partition function for "Manhattan" EDM systems
where the dimer potential is a weighted l1-distance and the auxiliary GRF is a
Markov random field of Pickard type which behaves in space like autoregressive
processes do in time. For one-dimensional Manhattan EDM systems, we compute the
MLE of the resulting Gaussian Markov chain as the largest eigenvalue of a
compact transfer operator on a Hilbert space which is related to the
annihilation and creation operators of the quantum harmonic oscillator and also
recast it as the eigenvalue problem for a pantograph functional-differential
equation.Comment: 24 pages, 4 figures, submitted on 14 October 2011 to a special issue
of DCDS-
Smart garment for trunk posture monitoring: A preliminary study
© 2008 Wong and Wong; licensee BioMed Central Ltd
Diversity Strategies for Nuclear Power Plant Instrumentation and Control Systems
This report presents the technical basis for establishing acceptable mitigating strategies that resolve diversity and defense-in-depth (D3) assessment findings and conform to U.S. Nuclear Regulatory Commission (NRC) requirements. The research approach employed to establish appropriate diversity strategies involves investigation of available documentation on D3 methods and experience from nuclear power and nonnuclear industries, capture of expert knowledge and lessons learned, determination of best practices, and assessment of the nature of common-cause failures (CCFs) and compensating diversity attributes. The research described in this report does not provide guidance on how to determine the need for diversity in a safety system to mitigate the consequences of potential CCFs. Rather, the scope of this report provides guidance to the staff and nuclear industry after a licensee or applicant has performed a D3 assessment per NUREG/CR-6303 and determined that diversity in a safety system is needed for mitigating the consequences of potential CCFs identified in the evaluation of the safety system design features. Succinctly, the purpose of the research described in this report was to answer the question, 'If diversity is required in a safety system to mitigate the consequences of potential CCFs, how much diversity is enough?' The principal results of this research effort have identified and developed diversity strategies, which consist of combinations of diversity attributes and their associated criteria. Technology, which corresponds to design diversity, is chosen as the principal system characteristic by which diversity criteria are grouped to form strategies. The rationale for this classification framework involves consideration of the profound impact that technology-focused design diversity provides. Consequently, the diversity usage classification scheme involves three families of strategies: (1) different technologies, (2) different approaches within the same technology, and (3) different architectures within the same technology. Using this convention, the first diversity usage family, designated Strategy A, is characterized by fundamentally diverse technologies. Strategy A at the system or platform level is illustrated by the example of analog and digital implementations. The second diversity usage family, designated Strategy B, is achieved through the use of distinctly different technologies. Strategy B can be described in terms of different digital technologies, such as the distinct approaches represented by general-purpose microprocessors and field-programmable gate arrays. The third diversity usage family, designated Strategy C, involves the use of variations within a technology. An example of Strategy C involves different digital architectures within the same technology, such as that provided by different microprocessors (e.g., Pentium and Power PC). The grouping of diversity criteria combinations according to Strategies A, B, and C establishes baseline diversity usage and facilitates a systematic organization of strategic approaches for coping with CCF vulnerabilities. Effectively, these baseline sets of diversity criteria constitute appropriate CCF mitigating strategies for digital safety systems. The strategies represent guidance on acceptable diversity usage and can be applied directly to ensure that CCF vulnerabilities identified through a D3 assessment have been adequately resolved. Additionally, a framework has been generated for capturing practices regarding diversity usage and a tool has been developed for the systematic assessment of the comparative effect of proposed diversity strategies (see Appendix A)
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