1,684 research outputs found
Femtolensing and Picolensing by Axion Miniclusters
Non-linear effects in the evolution of the axion field in the early Universe
may lead to the formation of gravitationally bound clumps of axions, known as
``miniclusters.'' Minicluster masses and radii should be in the range and cm, and in plausible
early-Universe scenarios a significant fraction of the mass density of the
Universe may be in the form of axion miniclusters. If such axion miniclusters
exist, they would have the physical properties required to be detected by
``femtolensing.''Comment: 7 pages plus 2 figures (Fig.1 avalible upon request), LaTe
Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward delta Orionis by the Interstellar Medium Absorption Profile Spectrograph
Studies of the abundances of deuterium in different astrophysical sites are
of fundamental importance to answering the question about how much deuterium
was produced during big bang nucleosynthesis and what fraction of it was
destroyed later. With this in mind, we used the Interstellar Medium Absorption
Profile Spectrograph (IMAPS) on the ORFEUS-SPAS II mission to observe at a
wavelength resolution of 4 km/s (FWHM) the L-delta and L-epsilon absorption
features produced by interstellar atomic deuterium in the spectrum of delta Ori
A. A chi-square analysis indicated that 0.96 < N(D I)< 1.45e15 cm^{-2} at a 90%
level of confidence, and the gas is at a temperature of about 6000K. To obtain
an accurate value of N(H I) needed for a determination of the atomic ratio of D
to H, we measured the L-alpha absorption features in 57 spectra of delta Ori in
the IUE archive. From our measurement of N(H I)= 1.56e20 cm^{-2}, we found that
N(D I)/N(H I)= 7.4(+1.9,-1.3)e-6 (90% confidence). Our result for D/H contrasts
with the more general finding along other lines of sight that D/H is
approximately 1.5e-5. The underabundance of D toward delta Ori A is not
accompanied by an overabundance of N or O relative to H, as one might expect if
the gas were subjected to more stellar processing than usual.Comment: 37 pages, 6 figures. Submitted to the Astrophysical Journa
Submesoscale dispersion in the vicinity of the Deepwater Horizon spill
Reliable forecasts for the dispersion of oceanic contamination are important
for coastal ecosystems, society and the economy as evidenced by the Deepwater
Horizon oil spill in the Gulf of Mexico in 2010 and the Fukushima nuclear plant
incident in the Pacific Ocean in 2011. Accurate prediction of pollutant
pathways and concentrations at the ocean surface requires understanding ocean
dynamics over a broad range of spatial scales. Fundamental questions concerning
the structure of the velocity field at the submesoscales (100 meters to tens of
kilometers, hours to days) remain unresolved due to a lack of synoptic
measurements at these scales. \textcolor{black} {Using high-frequency position
data provided by the near-simultaneous release of hundreds of accurately
tracked surface drifters, we study the structure of submesoscale surface
velocity fluctuations in the Northern Gulf Mexico. Observed two-point
statistics confirm the accuracy of classic turbulence scaling laws at
200m50km scales and clearly indicate that dispersion at the submesoscales is
\textit{local}, driven predominantly by energetic submesoscale fluctuations.}
The results demonstrate the feasibility and utility of deploying large clusters
of drifting instruments to provide synoptic observations of spatial variability
of the ocean surface velocity field. Our findings allow quantification of the
submesoscale-driven dispersion missing in current operational circulation
models and satellite altimeter-derived velocity fields.Comment: 9 pages, 6 figure
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