5,434 research outputs found
Narrowband spectroscopy by all-optical correlation of broadband pulses
High peak power ultrafast lasers are widely used in nonlinear spectroscopy
but often limit its spectral resolution because of the broad frequency
bandwidth of ultrashort laser pulses. Improving the resolution by achieving
spectrally narrow excitation of, or emission from, the resonant medium by means
of multi-photon interferences has been the focus of many recent developments in
ultrafast spectroscopy. We demonstrate an alternative approach, in which high
resolution is exercised by detecting narrow spectral correlations between
broadband excitation and emission optical fields. All-optical correlation
analysis, easily incorporated into the traditional spectroscopic setup, enables
direct, robust and simultaneous detection of multiple narrow resonances with a
single femtosecond pulse.Comment: 5 pages, 4 figures, submitted to PR
Longitudinal and Transverse Response Functions in ^(56)Fe(e,e') at Momentum Transfer near 1 GeV/c
Inclusive electron-scattering cross sections have been measured for ^(56)Fe in the quasielastic region at electron energies between 0.9 and 4.3 GeV, at scattering angles of 15° and 85°. Longitudinal and transverse response functions at a q of 1.14 GeV/c have been extracted using a Rosenbluth separation. The experimental Coulomb sum has been obtained with aid of an extrapolation. The longitudinal response function, after correction for Coulomb distortion, is lower than quasifree-scattering-model predictions at the quasielastic peak and on the high-ω side
Linguistics
Contains reports on four research projects.National Institutes of Health (Grant MH-13390-01U. S. Air Force (Electronic Systems Division) under Contract AF 19(628)-248
The OLYMPUS Internal Hydrogen Target
An internal hydrogen target system was developed for the OLYMPUS experiment
at DESY, in Hamburg, Germany. The target consisted of a long, thin-walled,
tubular cell within an aluminum scattering chamber. Hydrogen entered at the
center of the cell and exited through the ends, where it was removed from the
beamline by a multistage pumping system. A cryogenic coldhead cooled the target
cell to counteract heating from the beam and increase the density of hydrogen
in the target. A fixed collimator protected the cell from synchrotron radiation
and the beam halo. A series of wakefield suppressors reduced heating from beam
wakefields. The target system was installed within the DORIS storage ring and
was successfully operated during the course of the OLYMPUS experiment in 2012.
Information on the design, fabrication, and performance of the target system is
reported.Comment: 9 pages, 13 figure
Deriving Bisimulation Congruences: 2-categories vs precategories
G-relative pushouts (GRPOs) have recently been proposed by the authors as a new foundation for Leifer and Milner’s approach to deriving labelled bisimulation congruences from reduction systems. This paper develops the theory of GRPOs further, arguing that they provide a simple and powerful basis towards a comprehensive solution. As an example, we construct GRPOs in a category of ‘bunches and wirings.’ We then examine the approach based on Milner’s precategories and Leifer’s functorial reactive systems, and show that it can be recast in a much simpler way into the 2-categorical theory of GRPOs
Expressiveness modulo Bisimilarity of Regular Expressions with Parallel Composition (Extended Abstract)
The languages accepted by finite automata are precisely the languages denoted
by regular expressions. In contrast, finite automata may exhibit behaviours
that cannot be described by regular expressions up to bisimilarity. In this
paper, we consider extensions of the theory of regular expressions with various
forms of parallel composition and study the effect on expressiveness. First we
prove that adding pure interleaving to the theory of regular expressions
strictly increases its expressiveness up to bisimilarity. Then, we prove that
replacing the operation for pure interleaving by ACP-style parallel composition
gives a further increase in expressiveness. Finally, we prove that the theory
of regular expressions with ACP-style parallel composition and encapsulation is
expressive enough to express all finite automata up to bisimilarity. Our
results extend the expressiveness results obtained by Bergstra, Bethke and
Ponse for process algebras with (the binary variant of) Kleene's star
operation.Comment: In Proceedings EXPRESS'10, arXiv:1011.601
One- and two-particle microrheology
We study the dynamics of rigid spheres embedded in viscoelastic media and
address two questions of importance to microrheology. First we calculate the
complete response to an external force of a single bead in a homogeneous
elastic network viscously coupled to an incompressible fluid. From this
response function we find the frequency range where the standard assumptions of
microrheology are valid. Second we study fluctuations when embedded spheres
perturb the media around them and show that mutual fluctuations of two
separated spheres provide a more accurate determination of the complex shear
modulus than do the fluctuations of a single sphere.Comment: 4 pages, 1 figur
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