23,437 research outputs found
Stability of optically-active charged excitons in quasi-two dimensional systems
A negatively charged quasi-two dimensional exciton () is solved exactly
numerically in the presence of a uniform perpendicular B-field. Various
quasi-two dimensional geometries are studied. The charge distribution of the
parallel to the B-field is found to be crucial in determining the
stability of the optically-active and hence its photoluminescence (PL)
signature. The theory provides a quantitative explanation of recent
experimental results obtained for a GaAs quantum well. Effects are found which
cannot be described within a lowest Landau level approximation.
PACS: 78.20.Ls 78.66.-w 73.20.DxComment: Minor revisions, mainly removal of the term trion in favour of the
term charged-exciton to comply with Physical Review B. To be published as a
Rapid Communication in Physical Review
Hybrid Search: Effectively Combining Keywords and Semantic Searches
This paper describes hybrid search, a search method supporting both document and knowledge retrieval via the flexible combination of ontologybased search and keyword-based matching. Hybrid search smoothly copes with
lack of semantic coverage of document content, which is one of the main limitations of current semantic search methods. In this paper we define hybrid search formally, discuss its compatibility with the current semantic trends and present a reference implementation: K-Search. We then show how the method outperforms both keyword-based search and pure semantic search in terms of precision and recall in a set of experiments performed on a collection of about 18.000 technical documents. Experiments carried out with professional users show that users understand the paradigm and consider it very powerful and reliable. K-Search has been ported to two applications released at Rolls-Royce
plc for searching technical documentation about jet engines
Report of the Terrestrial Bodies Science Working Group. Volume 8: The comets
The determination of the nuclear and atmospheric properties of comets, and the interaction of the solar wind with the comet tail are scientific objectives for a mission to one or more comets in the next decade. Recommended priorities for direct cometary exploration are listed
Retransmission of water resources data using the ERTS-1 data collection system
There are no author-identified significant results in this report
Observations of cosmic ray induced phosphenes
Phosphene observations by astronauts on flights near and far from earth atmosphere are discussed. It was concluded that phosphenes could be observed by the naked eye. Further investigation is proposed to determine realistic human tolerance levels for extended missions and to evaluate the need to provide special spacecraft shielding
Realistic Expanding Source Model for Invariant One-Particle Multiplicity Distributions and Two-Particle Correlations in Relativistic Heavy-Ion Collisions
We present a realistic expanding source model with nine parameters that are
necessary and sufficient to describe the main physics occuring during
hydrodynamical freezeout of the excited hadronic matter produced in
relativistic heavy-ion collisions. As a first test of the model, we compare it
to data from central Si + Au collisions at p_lab/A = 14.6 GeV/c measured in
experiment E-802 at the AGS. An overall chi-square per degree of freedom of
1.055 is achieved for a fit to 1416 data points involving invariant pi^+, pi^-,
K^+, and K^- one-particle multiplicity distributions and pi^+ and K^+
two-particle correlations. The 99-percent-confidence region of parameter space
is identified, leading to one-dimensional error estimates on the nine fitted
parameters and other calculated physical quantities. Three of the most
important results are the freezeout temperature, longitudinal proper time, and
baryon density along the symmetry axis. For these we find values of 92.9 +/-
4.4 MeV, 8.2 +/- 2.2 fm/c, and 0.0222 + 0.0096 / - 0.0069 fm^-3, respectively.Comment: 37 pages and 12 figures. RevTeX 3.0. Submitted to Physical Review C.
Complete preprint, including device-independent (dvi), PostScript, and LaTeX
versions of the text, plus PostScript files of all figures, are available at
http://t2.lanl.gov/publications/publications.html or at
ftp://t2.lanl.gov/publications/res
An investigation for the development of an integrated optical data preprocessor
A laboratory model of a 16 channel integrated optical data preprocessor was fabricated and tested in response to a need for a device to evaluate the outputs of a set of remote sensors. It does this by accepting the outputs of these sensors, in parallel, as the components of a multidimensional vector descriptive of the data and comparing this vector to one or more reference vectors which are used to classify the data set. The comparison is performed by taking the difference between the signal and reference vectors. The preprocessor is wholly integrated upon the surface of a LiNbO3 single crystal with the exceptions of the source and the detector. He-Ne laser light is coupled in and out of the waveguide by prism couplers. The integrated optical circuit consists of a titanium infused waveguide pattern, electrode structures and grating beam splitters. The waveguide and electrode patterns, by virtue of their complexity, make the vector subtraction device the most complex integrated optical structure fabricated to date
On the molecules of numerical semigroups, Puiseux monoids, and Puiseux algebras
A molecule is a nonzero non-unit element of an integral domain (resp.,
commutative cancellative monoid) having a unique factorization into
irreducibles (resp., atoms). Here we study the molecules of Puiseux monoids as
well as the molecules of their corresponding semigroup algebras, which we call
Puiseux algebras. We begin by presenting, in the context of numerical
semigroups, some results on the possible cardinalities of the sets of molecules
and the sets of reducible molecules (i.e., molecules that are not
irreducibles/atoms). Then we study the molecules in the more general context of
Puiseux monoids. We construct infinitely many non-isomorphic atomic Puiseux
monoids all whose molecules are atoms. In addition, we characterize the
molecules of Puiseux monoids generated by rationals with prime denominators.
Finally, we turn to investigate the molecules of Puiseux algebras. We provide a
characterization of the molecules of the Puiseux algebras corresponding to
root-closed Puiseux monoids. Then we use such a characterization to find an
infinite class of Puiseux algebras with infinitely many non-associated
reducible molecules.Comment: 21 pages, 2 figure
The vortex dynamics of a Ginzburg-Landau system under pinning effect
It is proved that the vortices are attracted by impurities or inhomogeities
in the superconducting materials. The strong H^1-convergence for the
corresponding Ginzburg-Landau system is also proved.Comment: 23page
Photoionization and Photoelectric Loading of Barium Ion Traps
Simple and effective techniques for loading barium ions into linear Paul
traps are demonstrated. Two-step photoionization of neutral barium is achieved
using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by
excitation above the ionization threshold using a nitrogen gas laser (337 nm).
Isotopic selectivity is achieved by using a near Doppler-free geometry for
excitation of the triplet 6s6p 3P1 state. Additionally, we report a
particularly simple and efficient trap loading technique that employs an
in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3
caption -added reference [15
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