110 research outputs found
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Refined forest land use classification with implications for United States national carbon accounting
The United States provides annual estimates of carbon sources and sinks as part of its National Green-house Gas Inventory (NGHGI). Within this effort, carbon stocks and fluxes are reported for six land use categories that are relevant to economic sectors and land use policy. The goal of this study is to develop methodologies that will allow the US to align with an internationally agreed upon forest land use definition which requires forest to be able to reach 5 m in height at maturity. Models to assess height potential are available for a majority of US forests except for woodland ecosystems. We develop a set of models to assess height potential in these systems. Our results suggest that ∼13.5 million ha of forests are unlikely to meet the international definition of forests due to environmental limitations to maximum attainable height. The incorporation of this height criteria in the NGHGI results in a carbon stock transfer of ∼848 Tg from the forest land use to woodland land use (a sub-category of grasslands) with minimal effect on sequestration rates. The development of a forest land use definition sensitive to climatic factors in this study enables a land use classification system that can be responsive to climate change effects on land uses themselves while being more consistent across a host of international and domestic carbon reporting efforts
The Galactic Chemical Evolution of phosphorus observed with IGRINS
Phosphorus (P) is considered to be one of the key elements for life, making
it an important element to look for in the abundance analysis of spectra of
stellar systems. Yet, there exists only a handful of spectroscopic studies to
estimate the P abundances and investigate its trend across a range of
metallicities. We have observed full HK band spectra at a spectral resolving
power of R=45,000 with IGRINS instrument. Abundances are determined using SME
in combination with 1D MARCS stellar atmosphere models. The investigated sample
of stars have reliable stellar parameters estimated using optical FIES spectra
(GILD; J\"onsson et al. in prep.). In order to determine the P abundances from
the 16482.92 Angstrom P line, we take special care of the CO() blend.
We determine the C, N, O abundances from atomic carbon and a range of
non-blended molecular lines (CO, CN, OH) which are aplenty in the H band region
of K giant stars, assuring an appropriate modelling of the blending
CO() line. We present [P/Fe] vs [Fe/H] trend for 38 K giant stars in
the metallicity range of -1.2 dex [Fe/H] 0.4 dex. We find that our
trend matches well with the compiled literature sample of prominently dwarf
stars and limited number of giant stars. Our trend is found to be higher by
0.05 - 0.1 dex compared to the theoretical chemical evolution trend in
Cescutti et al. 2012 resulting from core collapse supernova (type II) of
massive stars with the P yields from Kobayashi et al. (2006) arbitrarily
increased by a factor of 2.75. Thus the enhancement factor might need to be
0.05 - 0.1 dex higher to match our trend. We also find an empirically
determined primary behaviour for phosphorus. Furthermore, the phosphorus
abundance is found to be elevated by 0.6 - 0.9 dex in two metal poor
s-enriched stars compared to the theoretical chemical evolution trend.Comment: 13 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at 2.76 TeV
We report on the first measurement of the triangular , quadrangular
, and pentagonal charged particle flow in Pb-Pb collisions at 2.76
TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show
that the triangular flow can be described in terms of the initial spatial
anisotropy and its fluctuations, which provides strong constraints on its
origin. In the most central events, where the elliptic flow and
have similar magnitude, a double peaked structure in the two-particle azimuthal
correlations is observed, which is often interpreted as a Mach cone response to
fast partons. We show that this structure can be naturally explained from the
measured anisotropic flow Fourier coefficients.Comment: 10 pages, 4 figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/387
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