63 research outputs found
Cancellation of atmospheric turbulence effects in entangled two-photon beams
Turbulent airflow in the atmosphere and the resulting random fluctuations in
its refractive index have long been known as a major cause of image
deterioration in astronomical imaging and figures among the obstacles for
reliable optical communication when information is encoded in the spatial
profile of a laser beam. Here we show that using correlation imaging and a
suitably prepared source of photon pairs, the most severe of the disturbances
inflicted on the beam by turbulence can be cancelled out. Other than a
two-photon light source, only linear passive optical elements are needed and,
as opposed to adaptive optics techniques, our scheme does not rely on active
wavefront correction.Comment: 5 pages, 3 figure
Self-Averaging Scaling Limits of Two-Frequency Wigner Distribution for Random Paraxial Waves
Two-frequency Wigner distribution is introduced to capture the asymptotic
behavior of the space-frequency correlation of paraxial waves in the radiative
transfer limits. The scaling limits give rises to deterministic transport-like
equations. Depending on the ratio of the wavelength to the correlation length
the limiting equation is either a Boltzmann-like integral equation or a
Fokker-Planck-like differential equation in the phase space. The solutions to
these equations have a probabilistic representation which can be simulated by
Monte Carlo method. When the medium fluctuates more rapidly in the longitudinal
direction, the corresponding Fokker-Planck-like equation can be solved exactly.Comment: typos correcte
Effects of in vitro Brevetoxin Exposure on Apoptosis and Cellular Metabolism in a Leukemic T Cell Line (Jurkat)
Harmful algal blooms (HABs) of the toxic dinoflagellate, Karenia brevis, produce red tide toxins, or brevetoxins. Significant health effects associated with red tide toxin exposure have been reported in sea life and in humans, with brevetoxins documented within immune cells from many species. The objective of this research was to investigate potential immunotoxic effects of brevetoxins using a leukemic T cell line (Jurkat) as an in vitro model system. Viability, cell proliferation, and apoptosis assays were conducted using brevetoxin congeners PbTx-2, PbTx-3, and PbTx-6. The effects of in vitro brevetoxin exposure on cell viability and cellular metabolism or proliferation were determined using trypan blue and MTT (1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan), respectively. Using MTT, cellular metabolic activity was decreased in Jurkat cells exposed to 5 – 10 μg/ml PbTx-2 or PbTx-6. After 3 h, no significant effects on cell viability were observed with any toxin congener in concentrations up to 10 μg/ml. Viability decreased dramatically after 24 h in cells treated with PbTx-2 or -6. Apoptosis, as measured by caspase-3 activity, was significantly increased in cells exposed to PbTx-2 or PbTx-6. In summary, brevetoxin congeners varied in effects on Jurkat cells, with PbTx-2 and PbTx-6 eliciting greater cellular effects compared to PbTx-3
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MP3 - A meteorology and physical properties package to explore air-sea interaction on Titan
The exchange of mass, heat and momentum at the air:sea interface are profound influences on the terrestrial environment, affecting the intensity of hurricanes, the size of waves and lake-effect precipitation. Titan presents us with an opportunity to study these processes in a novel physical context, with a different sea, atmosphere and gravity. The MP3 instrument, under development for the proposed Discovery mission TiME (Titan Mare Explorer [1,2]) is an integrated suite of small, simple sensors that combines the function of traditional meteorology packages with liquid physical properties and depth-sounding : these latter functions follow the concept of - and indeed use spare elements from - the Huygens Surface Science Package (SSP,[3]). However, unlike Huygens’ brief and dynamic 3 hours of measurement, in TiME’s 6-Titan-day (96 Earth day) nominal mission enabled by radioisotope power, MP3 will have an unprecedented long-term measurement opportunity in one of the most evocative environments in the solar system, Titan’s sea Ligeia Mare
On time reversal mirrors
The concept of time reversal (TR) of scalar wave is reexamined from basic
principles. Five different time reversal mirrors (TRM) are introduced and their
relations are analyzed. For the boundary behavior, it is shown that for
paraxial wave only the monopole TR scheme satisfies the exact boundary
condition while for spherical wave only one of the mixed mode TR scheme, after
multiplication by two, satisfies the exact boundary condition. The asymptotic
analysis of the near-field focusing property is presented. It is shown that to
have a subwavelength focal spot the TRM should involve dipole fields. The
monopole TR is extremely ineffective to focus below wavelength as the focal
spot size decreases logarithmically with the distance between the source and
TRM. Contrary to the matched field processing and the phase processor, both of
which resemble TR, TR in a weak- or non-scattering medium is usually biased in
the longitudinal direction, especially when TR is carried out on a {\em single}
plane with a {finite} aperture. This is true for all five TR schemes. On the
other hand, the TR focal spot has been shown repeatedly in the literature, both
theoretically and experimentally, to be centered at the source point when the
medium is multiply scattering. A reconciliation of the two seemingly
conflicting results is found in the random fluctuations in the intensity of the
Green function for a multiply scattering medium and the notion of
scattering-enlarged effective aperture
Determination of early summer pasture conditions to optimize forage and calf productivity and profitability
Forages can be valuable elements in a sustainable production system. The date when animals are first allowed to graze on pastures can impact the quality and amount of forages available. This study explored various factors that influence successful grazing
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