11,839 research outputs found
A new Fermi smearing approach for scattering of multi-GeV electrons by nuclei
The cross section for electron scattering by nuclei at high momentum
transfers is calculated within the Fermi smearing approximation (FSA), where
binding effects on the struck nucleon are introduced via the relativistic
Hartree approximation (RHA). The model naturally preserves current
conservation, since the response tensor for an off-shell nucleon conserves the
same form that for a free one but with an effective mass. Different
parameterizations for the inelastic nucleon structure function, are analyzed.
The smearing at the Fermi surface is introduced through a momentum distribution
obtained from a perturbative nuclear matter calculation. Recent CEBAF data on
inclusive scattering of 4.05 GeV electrons on Fe are well reproduced for
all measured geometries for the first time, as is evident from the comparison
with previous calculations.Comment: 8 pages in Revtex4 style, 6 eps figures, to appear in Physical Review
On the Analytic Structure of the Quark Self-Energy in Nambu-Jona- Lasinio Models
The self-energy of quarks is investigated for various models which are
inspired by the Nambu--Jona-Lasinio (NJL) model. Including, beyond the
Hartree-Fock approximation, terms up to second-order in the quark interaction,
the real and imaginary parts of scalar and vector components of the self-energy
are discussed. The second-order contributions depend on the energy and momentum
of the quark under consideration. This leads to solutions of the Dirac equation
which are significantly different from those of a free quark or a quark with
constant effective mass, as obtained in the Hartree-Fock approximation.Comment: 15 pages LaTeX, 6 figures can be obtained from author
An automatic visual analysis system for tennis
This article presents a novel video analysis system for coaching tennis players of all levels, which uses computer vision algorithms to automatically edit and index tennis videos into meaningful annotations.
Existing tennis coaching software lacks the ability to automatically index a tennis match into key events, and therefore, a coach who uses existing software is burdened with time-consuming manual video editing. This work aims to explore the effectiveness of a system to automatically detect tennis events. A secondary aim of this work is to explore the bene- fits coaches experience in using an event retrieval system to retrieve the automatically indexed events. It was found that automatic event detection can significantly improve the experience of using video feedback as part of an instructional coaching session. In addition to the automatic detection of key tennis events, player and ball movements are automati- cally tracked throughout an entire match and this wealth of data allows users to find interesting patterns in play. Player and ball movement information are integrated with the automatically detected tennis events, and coaches can query the data to retrieve relevant key points during a match or analyse player patterns that need attention. This coaching software system allows coaches to build advanced queries, which cannot be facilitated with existing video coaching solutions, without tedious manual indexing. This article proves that the event detection algorithms in this work can detect the main events in tennis with an average precision and recall of 0.84 and 0.86, respectively, and can typically eliminate man- ual indexing of key tennis events
Non-Markovian finite-temperature two-time correlation functions of system operators of a pure-dephasing model
We evaluate the non-Markovian finite-temperature two-time correlation
functions (CF's) of system operators of a pure-dephasing spin-boson model in
two different ways, one by the direct exact operator technique and the other by
the recently derived evolution equations, valid to second order in the
system-environment interaction Hamiltonian. This pure-dephasing spin-boson
model that is exactly solvable has been extensively studied as a simple
decoherence model. However, its exact non-Markovian finite-temperature two-time
system operator CF's, to our knowledge, have not been presented in the
literature. This may be mainly due to the fact, illustrated in this article,
that in contrast to the Markovian case, the time evolution of the reduced
density matrix of the system (or the reduced quantum master equation) alone is
not sufficient to calculate the two-time system operator CF's of non-Markovian
open systems. The two-time CF's obtained using the recently derived evolution
equations in the weak system-environment coupling case for this non-Markovian
pure-dephasing model happen to be the same as those obtained from the exact
evaluation. However, these results significantly differ from the non-Markovian
two-time CF's obtained by wrongly directly applying the quantum regression
theorem (QRT), a useful procedure to calculate the two-time CF's for
weak-coupling Markovian open systems. This demonstrates clearly that the
recently derived evolution equations generalize correctly the QRT to
non-Markovian finite-temperature cases. It is believed that these evolution
equations will have applications in many different branches of physics.Comment: To appear in Phys. Rev.
Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL_(61)
The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) à 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration
Representation of the pulsed output from a mode-locked laser using quantum field theory and an application in multiphoton ionisation
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