32,722 research outputs found
Exact States in Waveguides With Periodically Modulated Nonlinearity
We introduce a one-dimensional model based on the nonlinear
Schrodinger/Gross-Pitaevskii equation where the local nonlinearity is subject
to spatially periodic modulation in terms of the Jacobi dn function, with three
free parameters including the period, amplitude, and internal form-factor. An
exact periodic solution is found for each set of parameters and, which is more
important for physical realizations, we solve the inverse problem and predict
the period and amplitude of the modulation that yields a particular exact
spatially periodic state. Numerical stability analysis demonstrates that the
periodic states become modulationally unstable for large periods, and regain
stability in the limit of an infinite period, which corresponds to a bright
soliton pinned to a localized nonlinearity-modulation pattern. Exact
dark-bright soliton complex in a coupled system with a localized modulation
structure is also briefly considered . The system can be realized in planar
optical waveguides and cigar-shaped atomic Bose-Einstein condensates.Comment: EPL, in pres
The effect of 3He impurities on the nonclassical response to oscillation of solid 4He
We have investigated the influence of impurities on the possible supersolid
transition by systematically enriching isotopically-pure 4He (< 1 ppb of 3He)
with 3He. The onset of nonclassical rotational inertia is broadened and shifts
monotonically to higher temperature with increasing 3He concentration,
suggesting that the phenomenon is correlated to the condensation of 3He atoms
onto the dislocation network in solid 4He.Comment: 4 page
Influence of aerosol acidity on the chemical composition of secondary organic aerosol from β-caryophyllene
The secondary organic aerosol (SOA) yield of β-caryophyllene photooxidation is enhanced by aerosol acidity. In the present study, the influence of aerosol acidity on the chemical composition of β-caryophyllene SOA is investigated using ultra performance liquid chromatography/electrospray ionization-time-of-flight mass spectrometry (UPLC/ESI-TOFMS). A number of first-, second- and higher-generation gas-phase products having carbonyl and carboxylic acid functional groups are detected in the particle phase. Particle-phase reaction products formed via hydration and organosulfate formation processes are also detected. Increased acidity leads to different effects on the abundance of individual products; significantly, abundances of organosulfates are correlated with aerosol acidity. To our knowledge, this is the first detection of organosulfates and nitrated organosulfates derived from a sesquiterpene. The increase of certain particle-phase reaction products with increased acidity provides chemical evidence to support the acid-enhanced SOA yields. Based on the agreement between the chromatographic retention times and accurate mass measurements of chamber and field samples, three β-caryophyllene products (i.e., β-nocaryophyllon aldehyde, β-hydroxynocaryophyllon aldehyde, and β-dihydroxynocaryophyllon aldehyde) are suggested as chemical tracers for β-caryophyllene SOA. These compounds are detected in both day and night ambient samples collected in downtown Atlanta, GA and rural Yorkville, GA during the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS)
Dispersive force between dissimilar materials: geometrical effects
We calculate the Casimir force or dispersive van der Waals force between a
spherical nanoparticle and a planar substrate, both with arbitrary dielectric
properties. We show that the force between a sphere and a plane can be
calculated through the interacting surface plasmons of the bodies. Using a
Spectral Representation formalism, we show that the force of a sphere made of a
material A and a plane made of a material B, differ from the case when the
sphere is made of B, and the plane is made of A. We found that the difference
depends on the plasma frequency of the materials, the geometry, and the
distance of separation between sphere and plane. The differences show the
importance of the geometry, and make evident the necessity of realistic
descriptions of the sphere-plane system beyond the Derjaguin Approximation or
Proximity Theorem Approximation
Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs)
Current atmospheric models do not include secondary
organic aerosol (SOA) production from gas-phase reactions
of polycyclic aromatic hydrocarbons (PAHs). Recent
studies have shown that primary emissions undergo oxidation
in the gas phase, leading to SOA formation. This
opens the possibility that low-volatility gas-phase precursors
are a potentially large source of SOA. In this work,
SOA formation from gas-phase photooxidation of naphthalene,
1-methylnaphthalene (1-MN), 2-methylnaphthalene (2-
MN), and 1,2-dimethylnaphthalene (1,2-DMN) is studied in
the Caltech dual 28-m^3 chambers. Under high-NO_x conditions
and aerosol mass loadings between 10 and 40μgm^(−3),
the SOA yields (mass of SOA per mass of hydrocarbon reacted)
ranged from 0.19 to 0.30 for naphthalene, 0.19 to 0.39
for 1-MN, 0.26 to 0.45 for 2-MN, and constant at 0.31 for
1,2-DMN. Under low-NO_x conditions, the SOA yields were
measured to be 0.73, 0.68, and 0.58, for naphthalene, 1-
MN, and 2-MN, respectively. The SOA was observed to be
semivolatile under high-NO_x conditions and essentially nonvolatile
under low-NO_x conditions, owing to the higher fraction
of ring-retaining products formed under low-NO_x conditions.
When applying these measured yields to estimate
SOA formation from primary emissions of diesel engines
and wood burning, PAHs are estimated to yield 3–5 times
more SOA than light aromatic compounds over photooxidation
timescales of less than 12 h. PAHs can also account for
up to 54% of the total SOA from oxidation of diesel emissions,
representing a potentially large source of urban SOA
Critical Casimir force in He films: confirmation of finite-size scaling
We present new capacitance measurements of critical Casimir force-induced
thinning of He films near the superfluid/normal transition, focused on the
region below where the effect is the greatest. He films of
238, 285, and 340 \AA thickness are adsorbed on N-doped silicon substrates with
roughness . The Casimir force scaling function ,
deduced from the thinning of these three films, collapses onto a single
universal curve, attaining a minimum at
. The collapse confirms the finite-size
scaling origin of the dip in the film thickness. Separately, we also confirm
the presence down to of the Goldstone/surface fluctuation force, which
makes the superfluid film thinner than the normal film.Comment: 4 pages, 3 figures, submitted to PR
Supersolid Helium at High Pressure
We have measured the pressure dependence of the supersolid fraction by a
torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9
bar. The supersolid fraction in the low temperature limit increases from 0.6 %
at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar
before showing a monotonic decrease with pressure extrapolating to zero near
170 bar.Comment: 4 pages, 4 figure
Gas adsorption/desorption in silica aerogels: a theoretical study of scattering properties
We present a numerical study of the structural correlations associated to gas
adsorption/desorption in silica aerogels in order to provide a theoretical
interpretation of scattering experiments. Following our earlier work, we use a
coarse-grained lattice-gas description and determine the nonequilibrium
behavior of the adsorbed gas within a local mean-field analysis.
We focus on the differences between the adsorption and desorption mechanisms
and their signature in the fluid-fluid and gel-fluid structure factors as a
function of temperature. At low temperature, but still in the regime where the
isotherms are continuous, we find that the adsorbed fluid density, during both
filling and draining, is correlated over distances that may be much larger than
the gel correlation length. In particular, extended fractal correlations may
occur during desorption, indicating the existence of a ramified cluster of
vapor filled cavities. This also induces an important increase of the
scattering intensity at small wave vectors. The similarity and differences with
the scattering of fluids in other porous solids such as Vycor are discussed.Comment: 16 pages, 15 figure
Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene
The current work focuses on the detailed evolution of the chemical composition of both the gas- and aerosol-phase constituents produced from the OH-initiated photooxidation of naphthalene under low- and high-NO_x conditions. Under high-NO_x conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO_2 + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NO_x chemistry, ring-retaining compounds appear to dominate the low-NO_x gas-phase products owing to the RO_2 + HO_2 pathway. We are able to chemically characterize 53−68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios measured in bulk samples by high-resolution electrospray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as the ratios observed with online high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting that the chemical compositions and oxidation levels found in the chemically-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO_3), and other high-molecular-weight (MW) products are not observed in either the low- or high-NO_x SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO_3), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high- and low-NO_x conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high- and low-NO_x SOA. We propose that the major gas- and aerosol-phase products observed are generated through the formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chemical similarity between the laboratory SOA and ambient aerosol collected from Birmingham, Alabama (AL) and Pasadena, California (CA) confirm the importance of PAH oxidation in the formation of aerosol within the urban atmosphere
Halo Sampling, Local Bias and Loop Corrections
We develop a new test of local bias, by constructing a locally biased halo
density field from sampling the dark matter-halo distribution. Our test differs
from conventional tests in that it preserves the full scatter in the bias
relation and it does not rely on perturbation theory. We put forward that bias
parameters obtained using a smoothing scale R can only be applied to computing
the halo power spectrum at scales k ~ 1/R. Our calculations can automatically
include the running of bias parameters and give vanishingly small loop
corrections at low-k. Our proposal results in much better agreement of the
sampling and perturbation theory results with simulations. In particular,
unlike the standard interpretation of local bias in the literature, our
treatment of local bias does not generate a constant power in the low-k limit.
We search for extra noise in the Poisson corrected halo power spectrum at
wavenumbers below its turn-over and find no evidence of significant positive
noise (as predicted by the standard interpretation) while we find evidence of
negative noise coming from halo exclusion for very massive halos. Using
perturbation theory and our non-perturbative sampling technique we also
demonstrate that nonlocal bias effects discovered recently in simulations
impact the power spectrum only at the few percent level in the weakly nonlinear
regime.Comment: 25 pages, 14 figures; V2: significant revision including more details
about halo exclusion and low-k noise. Conclusions unchange
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