1,725 research outputs found
Sources of variations in total column carbon dioxide
Observations of gradients in the total CO_2 column,
(CO2), are expected to provide improved constraints
on surface fluxes of CO_2. Here we use a general circulation
model with a variety of prescribed carbon fluxes to investigate how variations in (CO_2) arise. On diurnal scales, variations are small and are forced by both local fluxes and advection. On seasonal scales, gradients are set by the north-south flux distribution. On synoptic scales, variations arise due to large-scale eddy-driven disturbances of the meridional gradient. In this case, because variations in (CO_2) are tied to synoptic
activity, significant correlations exist between (CO_2)
and dynamical tracers. We illustrate how such correlations
can be used to describe the north-south gradients of (CO_2)
and the underlying fluxes on continental scales. These simulations suggest a novel analysis framework for using column observations in carbon cycle science
Nuclear corrections in neutrino-nucleus DIS and their compatibility with global NPDF analyses
We perform a global chi^2-analysis of nuclear parton distribution functions
using data from charged current neutrino-nucleus deep-inelastic scattering
(DIS), charged-lepton-nucleus DIS, and the Drell-Yan (DY) process. We show that
the nuclear corrections in nu-A DIS are not compatible with the predictions
derived from l^+A DIS and DY data. We quantify this result using a
hypothesis-testing criterion based on the chi^2 distribution which we apply to
the total chi^2 as well as to the chi^2 of the individual data sets. We find
that it is not possible to accommodate the data from nu-A and l^+A DIS by an
acceptable combined fit. Our result has strong implications for the extraction
of both nuclear and proton parton distribution functions using combined
neutrino and charged-lepton data sets.Comment: 5 page
Floristic Composition and Natural History Characteristics of Dry Forests in the Pacific
We compare the floristic composition of tropical dry forests at the stand level using Gentry's transect method (0.1 ha) in some of the largest and highest-quality remaining fragments in the Pacific (Hawai'i, 15 sites; Fiji, 9; the Marianas, 3; the Marquesas, 6; New Caledonia, 7) and compare results with neotropical dry forests. A total of 299 species or morphospecies =2.5 cm diameter at breast height were identified from all 40 sites in the Pacific. Rubiaceae (28 spp.), Euphorbiaceae (25 spp.), Fabaceae (23 spp.), Sapindaceae (18 spp.), and Myrtaceae (17 spp.) were the most speciose families in Pacific dry forest; however, no family dominated across regions in the Pacific. The most common species by frequency and density in each region were native with the exception of Hawai'i, which contains a high number of nonnative species. Observed and estimated (Chao 2) levels of native species richness show that New Caledonia and Fiji contain the highest species richness followed by Hawai'i, the Marianas, and the Marquesas. There is very little overlap at the native species level among regions, with Hawaiian dry forests the most dissimilar at the native species, genus, and family level and New Caledonia and Fiji the most similar. Unlike mainland neotropical dry forest, dry forests in the Pacific contain very few deciduous species and a low proportion of wind-dispersed species.There is a high proportion of dioecious species in Hawai'i, which is similar to the neotropics; however, other Pacific regions have fewer dioecious species
nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework
We present the new nCTEQ15 set of nuclear parton distribution functions with
uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear
dependence using data on nuclei all the way up to 208^Pb. The uncertainties are
determined using the Hessian method with an optimal rescaling of the
eigenvectors to accurately represent the uncertainties for the chosen tolerance
criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY)
processes, we also include inclusive pion production data from RHIC to help
constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of
the data sets with specific nPDF flavor components, and asses the impact of
individual experiments. We also provide comparisons of the nCTEQ15 set with
recent fits from other groups.Comment: 35 page
Perturbative QCD Analysis of Local Duality in a fixed W^2 Framework
We study the global Q^2 dependence of large x, F_2 nucleon structure function
data, with the aim of providing a perturbative-QCD based, quantitative analysis
of parton-hadron duality. As opposed to previous analyses at fixed x, we use a
framework in fixed W^2. We uncover a breakdown of the twist-4 approximation
with a renormalon type improvement at O(1/Q^4) which, by affecting the initial
evolution of parton distributions, will have consequences for pQCD analyses
also at large x and very large Q^2.Comment: RevTex4, 8 pages, 3 figure
Post-Newtonian Approximation in Maxwell-Like Form
The equations of the linearized first post-Newtonian approximation to general
relativity are often written in "gravitoelectromagnetic" Maxwell-like form,
since that facilitates physical intuition. Damour, Soffel and Xu (DSX) (as a
side issue in their complex but elegant papers on relativistic celestial
mechanics) have expressed the first post-Newtonian approximation, including all
nonlinearities, in Maxwell-like form. This paper summarizes that DSX
Maxwell-like formalism (which is not easily extracted from their celestial
mechanics papers), and then extends it to include the post-Newtonian
(Landau-Lifshitz-based) gravitational momentum density, momentum flux (i.e.
gravitational stress tensor) and law of momentum conservation in Maxwell-like
form. The authors and their colleagues have found these Maxwell-like momentum
tools useful for developing physical intuition into numerical-relativity
simulations of compact binaries with spin.Comment: v4: Revised for resubmission to Phys Rev D, 6 pages. v3: Reformulated
in terms of DSX papers. Submitted to Phys Rev D, 6 pages. v2: Added
references. Changed definitions & convention
Total column CO_2 measurements at Darwin, Australia â site description and calibration against in situ aircraft profiles
An automated Fourier Transform Spectroscopic (FTS) solar observatory was established in Darwin, Australia in August 2005. The laboratory is part of the Total Carbon Column Observing Network, and measures atmospheric column abundances of CO_2 and O_2 and other gases. Measured CO_2 columns were calibrated against integrated aircraft profiles obtained during the TWP-ICE campaign in JanuaryâFebruary 2006, and show good agreement with calibrations for a similar instrument in Park Falls, Wisconsin. A clear-sky low airmass relative precision of 0.1% is demonstrated in the CO2 and O2 retrieved column-averaged volume mixing ratios. The 1% negative bias in the FTS X_(CO_2) relative to the World Meteorological Organization (WMO) calibrated in situ scale is within the uncertainties of the NIR spectroscopy and analysis
Toward accurate CO_2 and CH_4 observations from GOSAT
The column-average dry air mole fractions of atmospheric carbon dioxide and methane (X_(CO_2) and X_(CH_4)) are inferred from observations of backscattered sunlight conducted by the Greenhouse gases Observing SATellite (GOSAT). Comparing the first year of GOSAT retrievals over land with colocated ground-based observations of the Total Carbon Column Observing Network (TCCON), we find an average difference (bias) of â0.05% and â0.30% for X_(CO_2) and X_(CH_4) with a station-to-station variability (standard deviation of the bias) of 0.37% and 0.26% among the 6 considered TCCON sites. The root-mean square deviation of the bias-corrected satellite retrievals from colocated TCCON observations amounts to 2.8 ppm for X_(CO_2) and 0.015 ppm for X_(CH_4). Without any data averaging, the GOSAT records reproduce general source/sink patterns such as the seasonal cycle of X_(CO_2) suggesting the use of the satellite retrievals for constraining surface fluxes
Compatibility of global NPDF analyses of neutrino DIS and charged-lepton DIS data
The neutrino deep inelastic scattering (DIS) data is very interesting for
global analyses of proton and nuclear parton distribution functions (PDFs)
since they provide crucial information on the strange quark distribution in the
proton and allow for a better flavor decompositon of the PDFs. In order to use
neutrino DIS data in a global analysis of proton PDFs nuclear effects need to
be understood. We study these effects with the help of nuclear PDFs extracted
from global analyses of charged-lepton DIS, Drell-Yan and neutrino DIS data at
next-to-leading order in QCD.Comment: Contribution to the XXIst International Europhysics Conference on
High Energy Physics, 21-27 July 2011, Grenoble, Franc
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