56,675 research outputs found
Wildfire Smoke Particle Properties and Evolution, from Space-Based Multi-Angle Imaging
Emitted smoke composition is determined by properties of the biomass burning source and ambient ecosystem. However, conditions that mediate the partitioning of black carbon (BC) and brown carbon (BrC) formation, as well as the spatial and temporal factors that drive particle evolution, are not understood adequately for many climate and air-quality related modeling applications. In situ observations provide considerable detail about aerosol microphysical and chemical properties, although sampling is extremely limited. Satellites offer the frequent global coverage that would allow for statistical characterization of emitted and evolved smoke, but generally lack microphysical detail. However, once properly validated, data from the National Aeronautics and Space Administration (NASA) Earth Observing Systems Multi-Angle Imaging Spectroradiometer (MISR) instrument can create at least a partial picture of smoke particle properties and plume evolution. We use in situ data from the Department of Energys Biomass Burning Observation Project (BBOP) field campaign to assess the strengths and limitations of smoke particle retrieval results from the MISR Research Aerosol (RA) retrieval algorithm. We then use MISR to characterize wildfire smoke particle properties and to identify the relevant aging factors in several cases, to the extent possible. The RA successfully maps qualitative changes in effective particle size, light absorption, and its spectral dependence, when compared to in situ observations. By observing the entire plume uniformly, the satellite data can be interpreted in terms of smoke plume evolution, including size-selective deposition, new-particle formation, and locations within the plume where BC or BrC dominates
Search for Free Fractional Electric Charge Elementary Particles
We have carried out a direct search in bulk matter for free fractional
electric charge elementary particles using the largest mass single sample ever
studied - about 17.4 mg of silicone oil. The search used an improved and highly
automated Millikan oil drop technique. No evidence for fractional charge
particles was found. The concentration of particles with fractional charge more
than 0.16e (e being the magnitude of the electron charge) from the nearest
integer charge is less than particles per nucleon with 95%
confidence.Comment: 10 pages,LaTeX, 4 PS figures, submitted to PR
Interferometric scattering enables fluorescence-free electrokinetic trapping of single nanoparticles in free solution
Anti-Brownian traps confine single particles in free solution by closed-loop
feedback forces that directly counteract Brownian motion. The extended-duration
measurement of trapped objects allows detailed characterization of
photophysical and transport properties, as well as observation of infrequent or
rare dynamics. However, this approach has been generally limited to particles
that can be tracked by fluorescent emission. Here we present the
Interferometric Scattering Anti-Brownian ELectrokinetic trap (ISABEL trap),
which uses interferometric scattering rather than fluorescence to monitor
particle position. By decoupling the ability to track (and therefore trap) a
particle from collection of its spectroscopic data, the ISABEL trap enables
confinement and extended study of single particles that do not fluoresce, that
only weakly fluoresce, or which exhibit intermittent fluorescence or
photobleaching. This new technique significantly expands the range of nanoscale
objects that may be investigated at the single-particle level in free solution.Comment: Manuscript and SI; videos available upon reques
Fractional quantum Hall states of atoms in optical Lattices
We describe a method to create fractional quantum Hall states of atoms
confined in optical lattices. We show that the dynamics of the atoms in the
lattice is analogous to the motion of a charged particle in a magnetic field if
an oscillating quadrupole potential is applied together with a periodic
modulation of the tunneling between lattice sites. We demonstrate that in a
suitable parameter regime the ground state in the lattice is of the fractional
quantum Hall type and we show how these states can be reached by melting a Mott
insulator state in a super lattice potential. Finally we discuss techniques to
observe these strongly correlated states.Comment: 4+epsilon pages including 3 figures. V2: Changes in the presentatio
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