2,237 research outputs found
Competition between the Modulation Instability and Stimulated Brillouin Scattering in a Broadband Slow Light Device
We observe competition between the modulation instability (MI) and stimulated
Brillouin scattering (SBS) in a 9.2-GHz broadband SBS slow light device, in
which a standard 20-km-long single-mode LEAF fibre is used as the SBS medium.
We find that MI is dominant and depletes most of the pump power when we use an
intense pump beam at ~1.55 {\mu}m, where the LEAF fibre is anomalously
dispersive. The dominance of the MI in the LEAF-fibre-based system suppresses
the SBS gain, degrading the SBS slow light delay and limiting the SBS
gain-bandwidth to 126 dB \cdot GHz. In a dispersion-shifted highly nonlinear
fibre, the SBS slow light delay is improved due to the suppression of the MI,
resulting in a gain-bandwidth product of 344 dB \cdot GHz, limited by our
available pump power of 0.82 W
Casimir micro-sphere diclusters and three-body effects in fluids
Our previous article [Phys. Rev. Lett. 104, 060401 (2010)] predicted that
Casimir forces induced by the material-dispersion properties of certain
dielectrics can give rise to stable configurations of objects. This phenomenon
was illustrated via a dicluster configuration of non-touching objects
consisting of two spheres immersed in a fluid and suspended against gravity
above a plate. Here, we examine these predictions from the perspective of a
practical experiment and consider the influence of non-additive, three-body,
and nonzero-temperature effects on the stability of the two spheres. We
conclude that the presence of Brownian motion reduces the set of experimentally
realizable silicon/teflon spherical diclusters to those consisting of layered
micro-spheres, such as the hollow- core (spherical shells) considered here.Comment: 11 pages, 9 figure
Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing
We demonstrate that weak parametric interaction of a fundamental beam with
its third harmonic field in Kerr media gives rise to a rich variety of families
of non-fundamental (multi-humped) solitary waves. Making a comprehensive
comparison between bifurcation phenomena for these families in bulk media and
planar waveguides, we discover two novel types of soliton bifurcations and
other interesting findings. The later includes (i) multi-humped solitary waves
without even or odd symmetry and (ii) multi-humped solitary waves with large
separation between their humps which, however, may not be viewed as bound
states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.
Newly Developed and Validated Eosinophilic Esophagitis Histology Scoring System and Evidence that it Outperforms Peak Eosinophil Count for Disease Diagnosis and Monitoring
Eosinophilic esophagitis is diagnosed by symptoms, and at least 15 intraepithelial eosinophils per high power field in an esophageal biopsy. Other pathologic features have not been emphasized. We developed a histology scoring system for esophageal biopsies that evaluates eight features: eosinophil density, basal zone hyperplasia, eosinophil abscesses, eosinophil surface layering, dilated intercellular spaces, surface epithelial alteration, dyskeratotic epithelial cells and lamina propria fibrosis. Severity (grade) and extent (stage) of abnormalities were scored using a 4 point scale (0 normal; 3 maximum change). Reliability was demonstrated by strong to moderate agreement among 3 pathologists who scored biopsies independently (p≤0.008). Several features were often abnormal in 201 biopsies (101 distal, 100 proximal) from 104 subjects (34 untreated, 167 treated). Median grade and stage scores were significantly higher in untreated compared to treated subjects (p≤0.0062). Grade scores for features independent of eosinophil counts were significantly higher in biopsies from untreated compared to treated subjects (basal zone hyperplasia p≤0.024 and dilated intercellular spaces p≤0.005), and were strongly correlated (r-square\u3e0.67). Principal components analysis identified 3 principal components that explained 78.2% of the variation in the features. In logistic regression models, 2 principal components more closely associated with treatment status than log distal peak eosinophil count (r-square 17, area under the curve 77.8 vs r-square 9, area under the curve 69.8). In summary, the eosinophilic esophagitis histology scoring system provides a method to objectively assess histologic changes in the esophagus beyond eosinophil number. Importantly, it discriminates treated from untreated patients, uses features commonly found in such biopsies, and is utilizable by pathologists after minimal training. These data provide rationales and a method to evaluate esophageal biopsies for features in addition to peak eosinophil count
Dispersive Approach to Semileptonic Form-Factors in Heavy-to-Light Meson Decays
We study the semileptonic decays of heavy mesons into light pseudoscalars by
making use of dispersion relations. Constraints from heavy quark symmetry,
chiral symmetry and perturbative QCD are implemented into a dispersive model
for the form-factors. Large deviations from -pole dominance are observed
in . We discuss the model prediction for this mode and its
possible impact on the extraction of .Comment: 30 pages, including 5 Postcript figure
Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties
New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in
presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene
catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which
are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote
an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within
the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic
process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting
endotherm. These results indicate that polyethylene macrochains can grow up during polymerization
either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements.
Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the
crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the
nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is
raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the
final processing temperature
Aerosol meteorology of Maritime Continent for the 2012 7SEAS southwest monsoon intensive study - Part 2: Philippine receptor observations of fine-scale aerosol behavior
Abstract. The largest 7 Southeast Asian Studies (7SEAS) operations period within the Maritime Continent (MC) occurred in the August–September 2012 biomass burning season. Data included were observations aboard the M/Y Vasco, dispatched to the Palawan Archipelago and Sulu Sea of the Philippines for September 2012. At these locations, the Vasco observed MC smoke and pollution entering the southwest monsoon (SWM) monsoonal trough. Here we describe the research cruise findings and the finer-scale aerosol meteorology of this convectively active region. This 2012 cruise complemented a 2-week cruise in 2011 and was generally consistent with previous findings in terms of how smoke emission and transport related to monsoonal flows, tropical cyclones (TC), and the covariance between smoke transport events and the atmosphere's thermodynamic structure. Biomass burning plumes were usually mixed with significant amounts of anthropogenic pollution. Also key to aerosol behavior were squall lines and cold pools propagating across the South China Sea (SCS) and scavenging aerosol particles in their path. However, the 2012 cruise showed much higher modulation in aerosol frequency than its 2011 counterpart. Whereas in 2011 large synoptic-scale aerosol events transported high concentrations of smoke into the Philippines over days, in 2012 measured aerosol events exhibited a much shorter-term variation, sometimes only 3–12 h. Strong monsoonal flow reversals were also experienced in 2012. Nucleation events in cleaner and polluted conditions, as well as in urban plumes, were observed. Perhaps most interestingly, several cases of squall lines preceding major aerosol events were observed, as opposed to 2011 observations where these lines largely scavenged aerosol particles from the marine boundary layer. Combined, these observations indicate pockets of high and low particle counts that are not uncommon in the region. These perturbations are difficult to observe by satellite and very difficult to model. Indeed, the Navy Aerosol Analysis and Prediction System (NAAPS) simulations captured longer period aerosol events quite well but largely failed to capture the timing of high-frequency phenomena. Ultimately, the research findings of these cruises demonstrate the real world challenges of satellite-based missions, significant aerosol life cycle questions such as those the future Aerosol/Clouds/Ecosystems (ACE) will investigate, and the importance of small-scale phenomena such as sea breezes, squall lines, and nucleation events embedded within SWM patterns in dominating aerosol life cycle and potential relationships to clouds
Microphysical Approach to Nonequilibrium Dynamics of Quantum Fields
We examine the nonequilibrium dynamics of a self-interacting
scalar field theory. Using a real time formulation of finite temperature field
theory we derive, up to two loops and , the effective equation of
motion describing the approach to equilibrium. We present a detailed analysis
of the approximations used in order to obtain a Langevin-like equation of
motion, in which the noise and dissipation terms associated with quantum
fluctuations obey a fluctuation-dissipation relation. We show that, in general,
the noise is colored (time-dependent) and multiplicative (couples nonlinearly
to the field), even though it is still Gaussian distributed. The noise becomes
white in the infinite temperature limit. We also address the effect of
couplings to other fields, which we assume play the r\^ole of the thermal bath,
in the effective equation of motion for . In particular, we obtain the
fluctuation and noise terms due to a quadratic coupling to another scalar
field.Comment: 30 pages, LaTex (uses RevTex 3.0), DART-HEP-93/0
Learning From Early Attempts to Generalize Darwinian Principles to Social Evolution
Copyright University of Hertfordshire & author.Evolutionary psychology places the human psyche in the context of evolution, and addresses the Darwinian processes involved, particularly at the level of genetic evolution. A logically separate and potentially complementary argument is to consider the application of Darwinian principles not only to genes but also to social entities and processes. This idea of extending Darwinian principles was suggested by Darwin himself. Attempts to do this appeared as early as the 1870s and proliferated until the early twentieth century. But such ideas remained dormant in the social sciences from the 1920s until after the Second World War. Some lessons can be learned from this earlier period, particularly concerning the problem of specifying the social units of selection or replication
Predictions on , and from QCD Light-Cone Sum Rules
The form factors of the , and transitions
are calculated from QCD light-cone sum rules (LCSR) and used to predict the
widths and differential distributions of the exclusive semileptonic decays
, and ,
where . The current theoretical uncertainties are estimated. The LCSR
results are found to agree with the results of lattice QCD calculations and
with experimental data on exclusive semileptonic D decays. Comparison of the
LCSR prediction on with the CLEO measurement yields a
value of |V_{ub}| in agreement with other determinations.Comment: 24 pages, 12 figures, Latex, epsfig, some additional remarks on the
two-pole parameterization, prediction on the form factor added,
version to appear in Phys. Rev.
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