1,557 research outputs found
Radiation induced force between two planar waveguides
We study the electromagnetic force exerted on a pair of parallel slab
waveguides by the light propagating through them. We have calculated the
dependence of the force on the slab separation by means of the Maxwell--Stress
tensor formalism and we have discussed its main features for the different
propagation modes: spatially symmetric (antisymmetric) modes give rise to an
attractive (repulsive) interaction. We have derived the asymptotic behaviors of
the force at small and large separation and we have quantitatively estimated
the mechanical deflection induced on a realistic air-bridge structure.Comment: 10 pages, 6 figure
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Tropospheric reactive odd nitrogen over the South Pacific in austral springtime
The distribution of reactive nitrogen species over the South Pacific during austral springtime appears to be dominated by biomass burning emissions and possibly lightning and stratospheric inputs. The absence of robust correlations of reactive nitrogen species with source-specific tracers (e.g., C2H2 [combustion], CH3Cl [biomass burning], C2Cl4 [industrial],210Pb [continental], and 7Be [stratospheric]) suggests significant aging and processing of the sampled air parcels due to losses by surface deposition, OH attack, and dilution processes. Classification of the air parcels based on CO enhancements indicates that the greatest influence was found in plumes at 3–8 km altitude in the distributions of HNO3 and peroxyacetyl nitrate (PAN). Here mixing ratios of these species reached 600 parts per trillion by volume (pptv), values surprisingly large for a location several thousand kilometers removed from the nearest continental areas. The mixing ratio of total reactive nitrogen (the NOy sum), operationally defined in this paper as measured (NO + HNO3 + PAN + CH3ONO2 + C2H5ONO2) + modeled (NO2), had a median value of 285 pptv within these plumes compared with 120 pptv in nonplume air parcels. Particle NO−3 was not included in this analysis of the NOy sum due to its 10- to 15-min sampling time resolution, but, in general, it was \u3c10% of the NOy sum. Comparison of the two air parcel classifications for NOy and alkyl nitrate distributions showed no perceivable plume influence, but recycling of reactive nitrogen may have masked this direct effect. In the marine boundary layer, the NOy sum averaged 50 pptv in both air parcel classifications, being somewhat isolated from the polluted conditions above it by the trade wind inversion. In this region, however, alkyl nitrates appear to have an important marine source where they comprise 20–80% of the NOy sum in equatorial and high-latitude regions over the South Pacific
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Troposheric Reactive Odd Nitrogen Over the South Pacific in Austral Springtime
Expansion of pinched hypersurfaces of the Euclidean and hyperbolic space by high powers of curvature
We prove convergence results for expanding curvature flows in the Euclidean
and hyperbolic space. The flow speeds have the form , where and
is a positive, strictly monotone and 1-homogeneous curvature function. In
particular this class includes the mean curvature . We prove that a
certain initial pinching condition is preserved and the properly rescaled
hypersurfaces converge smoothly to the unit sphere. We show that an example due
to Andrews-McCoy-Zheng can be used to construct strictly convex initial
hypersurfaces, for which the inverse mean curvature flow to the power
loses convexity, justifying the necessity to impose a certain pinching
condition on the initial hypersurface.Comment: 18 pages. We included an example for the loss of convexity and
pinching. In the third version we dropped the concavity assumption on F.
Comments are welcom
The Sagnac effect in Coupled-Resonator Slow-Light Waveguide Structures
We study the effect of rotation on the propagation of electromagnetic waves
in slow-light waveguide structures consisting of coupled micro-ring resonators.
We show that such configurations exhibit new a type of the Sagnac effect which
can be used for the realization of highly-compact integrated rotation sensors
and gyroscopes
Fast and slow light in zig-zag microring resonator chains
We analyze fast and slow light transmission in a zig-zag microring resonator
chain. This novel device permits the operation in both regimes. In the
superluminal case, a new ubiquitous light transmission effect is found whereby
the input optical pulse is reproduced in an almost simultaneous manner at the
various system outputs. When the input carrier is tuned to a different
frequency, the system permits to slow down the propagating optical signal.
Between these two extreme cases, the relative delay can be tuned within a broad
range
Statistical Estimation Procedures for the ''burn-in'' Process
Statistical estimation procedures for identifying and eliminating poor quality or defective item
A Fluctuation Analysis of the Bolocam 1.1mm Lockman Hole Survey
We perform a fluctuation analysis of the 1.1mm Bolocam Lockman Hole Survey,
which covers 324 square arcmin to a very uniform point source-filtered RMS
noise level of 1.4 mJy/beam. The fluctuation analysis has the significant
advantage of utilizing all of the available data. We constrain the number
counts in the 1-10 mJy range, and derive significantly tighter constraints than
in previous work: the power-law index is 2.7 (+0.18, -0.15), while the
amplitude is equal to 1595 (+85,-238) sources per mJy per square degree, or
N(>1 mJy) = 940 (+50,-140) sources/square degree (95% confidence). Our results
agree extremely well with those derived from the extracted source number counts
by Laurent et al (2005). Our derived normalization is about 2.5 times smaller
than determined by MAMBO at 1.2mm by Greve et al (2004). However, the
uncertainty in the normalization for both data sets is dominated by the
systematic (i.e., absolute flux calibration) rather than statistical errors;
within these uncertainties, our results are in agreement. We estimate that
about 7% of the 1.1mm background has been resolved at 1 mJy.Comment: To appear in the Astrophysical Journal; 22 pages, 9 figure
Radio Continuum Jet in NGC 7479
The barred galaxy NGC 7479 hosts a remarkable jet-like radio continuum
feature: bright, 12-kpc long in projection, and hosting an aligned magnetic
field. The degree of polarization is 6%-8% along the jet, and remarkably
constant, which is consistent with helical field models. The radio brightness
of the jet suggests strong interaction with the ISM and hence a location near
the disk plane. We observed NGC 7479 at four wavelengths with the VLA and
Effelsberg radio telescopes. The equipartition strength is 35-40 micro-G for
the total and >10 micro-G for the ordered magnetic field in the jet. The jet
acts as a bright, polarized background. Faraday rotation between 3.5 and 6 cm
and depolarization between 6 and 22 cm can be explained by magneto-ionic gas in
front of the jet, with thermal electron densities of ~0.06 cm**(-3) in the bar
and ~0.03 cm**(-3) outside the bar. The regular magnetic field along the bar
points toward the nucleus on both sides. The regular field in the disk reveals
multiple reversals, probably consisting of field loops stretched by a shearing
gas flow in the bar. The projection of the jet bending in the sky plane is in
the sense opposite to that of the underlying stellar and gaseous spiral
structure. The bending in 3-D is most easily explained as a precessing jet,
with an age less than 10**6 years. Our observations are consistent with very
recent triggering, possibly by a minor merger. NGC 7479 provides a unique
opportunity to study interaction-triggered 15-kpc scale radio jets within a
spiral galaxy.Comment: 18 pages, 21 figures, accepted for publication in the Astrophysical
Journa
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