5,549 research outputs found
Long-term record of aerosol optical properties and chemical composition from a high-altitude site (Manora Peak) in Central Himalaya
A long-term study, conducted from February 2005 to July 2008, involving chemical composition and optical properties of ambient aerosols from a high-altitude site (Manora Peak: 29.4°N, 79.5°E, ~1950ma.s.l.) in the central Himalaya is reported here. The total suspended particulate (TSP) mass concentration varied from 13 to 272 µgm.3 over a span of 42 months. Aerosol optical depth (AOD) and TSP increase significantly during the summer (April-June) due to increase in the concentration of mineral dust associated with the long-range transport from desert regions (from the middle-East and Thar Desert in western India). The seasonal variability in the carbonaceous species (EC, OC) is also significantly pronounced, with lower concentrations during the summer and monsoon (July-August) and relatively high during the post-monsoon (September-November) and winter (December-March). On average, total carbonaceous aerosols (TCA) and water-soluble inorganic species (WSIS) contribute nearly 25 and 10% of the TSP mass, respectively. The WSOC/OC ratios range from 0.36 to 0.83 (average: 0.55±0.15), compared to lower ratios in the Indo-Gangetic Plain (range: 0.35-0.40), and provide evidence for the enhanced contribution from secondary organic aerosols. The mass fraction of absorbing EC ranged from less than a percent (during the summer) to as high as 7.6% (during the winter) and absorption coefficient (babs, at 678 nm) varied between 0.9 to 33.9Mm-1 (1Mm-1=10-6 m-1). A significant linear relationship between babs and EC (µgCm-3) yields a slope of 12.2 (±2.3) m2 g-1, which is used as a measure of the mass absorption efficiency (σabs) of EC
Toward a unified theory of sparse dimensionality reduction in Euclidean space
Let be a sparse Johnson-Lindenstrauss
transform [KN14] with non-zeroes per column. For a subset of the unit
sphere, given, we study settings for required to
ensure i.e. so that preserves the norm of every
simultaneously and multiplicatively up to . We
introduce a new complexity parameter, which depends on the geometry of , and
show that it suffices to choose and such that this parameter is small.
Our result is a sparse analog of Gordon's theorem, which was concerned with a
dense having i.i.d. Gaussian entries. We qualitatively unify several
results related to the Johnson-Lindenstrauss lemma, subspace embeddings, and
Fourier-based restricted isometries. Our work also implies new results in using
the sparse Johnson-Lindenstrauss transform in numerical linear algebra,
classical and model-based compressed sensing, manifold learning, and
constrained least squares problems such as the Lasso
Night sky at the Indian Astronomical Observatory during 2000-2008
We present an analysis of the optical night sky brightness and extinction
coefficient measurements in UBVRI at the Indian Astronomical Observatory (IAO),
Hanle, during the period 2003-2008. They are obtained from an analysis of CCD
images acquired at the 2 m Himalayan Chandra Telescope at IAO. Night sky
brightness was estimated using 210 HFOSC images obtained on 47 nights and
covering the declining phase of solar activity cycle-23. The zenith corrected
values of the moonless night sky brightness in mag/square arcsecs are 22.14(U),
22.42(B), 21.28(V), 20.54(R) and 18.86(I) band. This shows that IAO is a dark
site for optical observations. No clear dependency of sky brightness with solar
activity is found. Extinction values at IAO are derived from an analysis of
1325 images over 58 nights. They are found to be 0.36 in U-band, 0.21 in
B-band, 0.12 in V-band, 0.09 in R-band and 0.05 in I-band. On average,
extinction during the summer months is slightly larger than that during the
winter months. No clear evidence for a correlation between extinction in all
bands and the average night time wind speed is found. Also presented here is
the low resolution moonless optical night sky spectrum for IAO covering the
wavelength range 3000-9300 \AA. Hanle region thus has the required
characteristics of a good astronomical site in terms of night sky brightness
and extinction, and could be a natural candidate site for any future large
aperture Indian optical-infrared telescope(s).Comment: 18 pages, 7 figures, uses basi.cls, accepted for publication in
Bulletin of the Astronomical Society of Indi
Free convective combustion on vertical surfaces-variable property analysis and experiments
This paper treats the problem of free convective combustion of near vertical fuel surfaces in quiescent oxidant atmosphere, both theoretically and experimentally. The theory improves on existing theories in terms of taking into account variable thermodynamic and transport properties. The locally similar solutions obtained numerically are compared with earlier predictions as well as experiments on mass burn rate, flame stand off and other features. While comparison in the case of some fuels seems bettered by the use of variable properties, the not-too good a comparision in other cases is traced to experimental inaccuracies more particularly related to the non-achievement of steady combustion. To remedy this, an experimental apparatus was carefully designed and the results of these experiments show good comparison with theoretical predictions in all cases considered
The finite temperature QCD using 2+1 flavors of domain wall fermions at N_t = 8
We study the region of the QCD phase transition using 2+1 flavors of domain
wall fermions (DWF) and a lattice volume with a fifth dimension
of . The disconnected light quark chiral susceptibility, quark number
susceptibility and the Polyakov loop suggest a chiral and deconfining crossover
transition lying between 155 and 185 MeV for our choice of quark mass and
lattice spacing. In this region the lattice scale deduced from the Sommer
parameter is GeV, the pion mass is MeV
and the kaon mass is approximately physical. The peak in the chiral
susceptibility implies a pseudo critical temperature MeV
where the first error is associated with determining the peak location and the
second with our unphysical light quark mass and non-zero lattice spacing. The
effects of residual chiral symmetry breaking on the chiral condensate and
disconnected chiral susceptibility are studied using several values of the
valence .Comment: 41 pages, 10 tables, 13 figure
Conserved Charge Fluctuations from Lattice QCD and the Beam Energy Scan
We discuss the next-to-leading order Taylor expansion of ratios of cumulants
of net-baryon number fluctuations. We focus on the relation between the
skewness ratio, , and the kurtosis ratio,
. We show that differences in these two
cumulant ratios are small for small values of the baryon chemical potential.
The next-to-leading order correction to however is
approximately three times larger than that for . The former thus
drops much more rapidly with increasing beam energy, . We argue
that these generic patterns are consistent with current data on cumulants of
net-proton number fluctuations measured by the STAR Collaboration at
~GeV.Comment: 4 pages, 4 figures, contribution to the Quark Matter 2015 proceeding
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