544 research outputs found
Biomass burning and pollution aerosol over North America: Organic components and their influence on spectral optical properties and humidification response
Thermal analysis of aerosol size distributions provided size resolved volatility up to temperatures of 400°C during extensive flights over North America (NA) for the INTEX/ICARTT experiment in summer 2004. Biomass burning and pollution plumes identified from trace gas measurements were evaluated for their aerosol physiochemical and optical signatures. Measurements of soluble ionic mass and refractory black carbon (BC) mass, inferred from light absorption, were combined with volatility to identify organic carbon at 400°C (VolatileOC) and the residual or refractory organic carbon, RefractoryOC. This approach characterized distinct constituent mass fractions present in biomass burning and pollution plumes every 5–10 min. Biomass burning, pollution and dust aerosol could be stratified by their combined spectral scattering and absorption properties. The “nonplume” regional aerosol exhibited properties dominated by pollution characteristics near the surface and biomass burning aloft. VolatileOC included most water-soluble organic carbon. RefractoryOC dominated enhanced shortwave absorption in plumes from Alaskan and Canadian forest fires. The mass absorption efficiency of this RefractoryOC was about 0.63 m2 g−1 at 470 nm and 0.09 m2 g−1 at 530 nm. Concurrent measurements of the humidity dependence of scattering, γ, revealed the OC component to be only weakly hygroscopic resulting in a general decrease in γ with increasing OC mass fractions. Under ambient humidity conditions, the systematic relations between physiochemical properties and γ lead to a well-constrained dependency on the absorption per unit dry mass for these plume types that may be used to challenge remotely sensed and modeled optical properties
Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers
We present experimental results on a model system for studying wave
propagation in a complex medium exhibiting low frequency resonances. These
experiments enable us to investigate a fundamental question that is relevant
for many materials, such as metamaterials, where low-frequency scattering
resonances strongly influence the effective medium properties. This question
concerns the effect of correlations in the positions of the scatterers on the
coupling between their resonances, and hence on wave transport through the
medium. To examine this question experimentally, we measure the effective
medium wave number of acoustic waves in a sample made of bubbles embedded in an
elastic matrix over a frequency range that includes the resonance frequency of
the bubbles. The effective medium is highly dispersive, showing peaks in the
attenuation and the phase velocity as functions of the frequency, which cannot
be accurately described using the Independent Scattering Approximation (ISA).
This discrepancy may be explained by the effects of the positional correlations
of the scatterers, which we show to be dependent on the size of the scatterers.
We propose a self-consistent approach for taking this "polydisperse
correlation" into account and show that our model better describes the
experimental results than the ISA
Anomalous transparency of water-air interface for low-frequency sound
Sound transmission through water-air interface is normally weak because of a
strong mass density contrast. Here we show that the transparency of the
interface increases dramatically at low frequencies. Rather counterintuitively,
almost all acoustic energy emitted by a sufficiently shallow monopole source
under water is predicted to be radiated into atmosphere. Physically, increased
transparency at lower frequencies is due to the increasing role of
inhomogeneous waves and a destructive interference of direct and
surface-reflected waves under water. The phenomenon of anomalous transparency
has significant implications for acoustic communication across the water-air
interface, generation of ambient noise, and detection of underwater explosions.Comment: 29 pages, including 4 figure
Surface plasmon resonance study of the actin-myosin sarcomeric complex and tubulin dimers
Biosensors based on the principle of surface plasmon resonance (SPR)
detection were used to measure biomolecular interactions in sarcomeres and
changes of the dielectric constant of tubulin samples with varying
concentration. At SPR, photons of laser light efficiently excite surface
plasmons propagating along a metal (gold) film. This resonance manifests itself
as a sharp minimum in the reflection of the incident laser light and occurs at
a characteristic angle. The dependence of the SPR angle on the dielectric
permittivity of the sample medium adjacent to the gold film allows the
monitoring of molecular interactions at the surface. We present results of
measurements of cross-bridge attachment/detachment within intact mouse heart
muscle sarcomeres and measurements on bovine tubulin molecules pertinent to
cytoskeletal signal transduction models.Comment: Submitted to Journal of Modern Optics *Corresponding author: Andreas
Mershin ([email protected]
Combining airborne gas and aerosol measurements with HYSPLIT: a visualization tool for simultaneous evaluation of air mass history and back trajectory consistency
The history of air masses is often investigated using backward trajectories
to gain knowledge about processes along the air parcel path as well as
possible source regions. Here, we describe a refined approach that
incorporates airborne gas, aerosol, and environmental data into back
trajectories and show how this technique allows for simultaneous evaluation
of air mass history and back trajectory reliability without the need to
calculate trajectory errors.
<br><br>
We use the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT)
model and add a simple semi-automated computing routine to facilitate
high-frequency coverage of back trajectories initiated along free
tropospheric (FT) flight tracks and profiles every 10 s. We integrate our in
situ physiochemical data by color-coding each of these trajectories with its
corresponding in situ tracer values measured at the back trajectory start
points along the flight path. The unique color for each trajectory aids
assessment of trajectory reliability through the visual clustering of air
mass pathways of similar coloration.
Moreover, marked changes in trajectories associated with marked changes evident
in measured physiochemical or thermodynamic properties of an air mass add credence
to trajectories. This is particularly true when these air mass properties are
linked to trajectory features characteristic of recognized sources or processes.
This visual clustering of air mass pathways is of particular value for large-scale 3-D flight tracks
common to aircraft experiments where air mass features of interest are often
spatially distributed and temporally separated.
<br><br>
The cluster-visualization tool used here reveals that most FT back
trajectories with pollution signatures measured in the central equatorial
Pacific reach back to sources on the South American continent over
10 000 km away and 12 days back in time, e.g., the Amazonian basin. We also
demonstrate the distinctions in air mass properties between these and
trajectories that penetrate deep convection in the Inter-Tropical Convergence
Zone. Additionally, for the first time we show consistency of modeled
precipitation along back trajectories with scavenging signatures in the
aerosol measured for these trajectories
Modelling Quantum Mechanics by the Quantumlike Description of the Electric Signal Propagation in Transmission Lines
It is shown that the transmission line technology can be suitably used for
simulating quantum mechanics. Using manageable and at the same time
non-expensive technology, several quantum mechanical problems can be simulated
for significant tutorial purposes. The electric signal envelope propagation
through the line is governed by a Schrodinger-like equation for a complex
function, representing the low-frequency component of the signal, In this
preliminary analysis, we consider two classical examples, i.e. the Frank-Condon
principle and the Ramsauer effect
Ray-based description of normal mode amplitudes in a range-dependent waveguide
An analogue of the geometrical optics for description of the modal structure
of a wave field in a range-dependent waveguide is considered. In the scope of
this approach the mode amplitude is expressed through solutions of the ray
equations. This analytical description accounts for mode coupling and remains
valid in a nonadiabatic environment. It has been used to investigate the
applicability condition of the adiabatic approximation. An applicability
criterion is formulated as a restriction on variations of the action variable
of the ray.Comment: 11 pages, 5 figure
A complex ray-tracing tool for high-frequency mean-field flow interaction effects in jets
This paper presents a complex ray-tracing tool for the calculation of high-frequency Green’s functions in 3D mean field jet flows. For a generic problem, the ray solution suffers from three main deficiencies: multiplicity of solutions, singularities at caustics, and the determining of complex solutions. The purpose of this paper is to generalize, combine and apply existing stationary media methods to moving media scenarios. Multiplicities are dealt with using an equivalent two-point boundary-value problem, whilst non-uniformities at caustics are corrected using diffraction catastrophes. Complex rays are found using a combination of imaginary perturbations, an assumption of caustic stability, and analytic continuation of the receiver curve. To demonstrate this method, the ray tool is compared against a high-frequency modal solution of Lilley’s equation for an off-axis point source. This solution is representative of high-frequency source positions in real jets and is rich in caustic structures. A full utilization of the ray tool is shown to provide excellent results<br/
Explicit asymptotic modelling of transient Love waves propagated along a thin coating
The official published version can be obtained from the link below.An explicit asymptotic model for transient Love waves is derived from the exact equations of anti-plane elasticity. The perturbation procedure relies upon the slow decay of low-frequency Love waves to approximate the displacement field in the substrate by a power series in the depth coordinate. When appropriate decay conditions are imposed on the series, one obtains a model equation governing the displacement at the interface between the coating and the substrate. Unusually, the model equation contains a term with a pseudo-differential operator. This result is confirmed and interpreted by analysing the exact solution obtained by integral transforms. The performance of the derived model is illustrated by numerical examples.This work is sponsored by the grant from Higher Education of Pakistan and by the Brunel University’s “BRIEF” research award
- …