183 research outputs found
A probabilistic approach to emission-line galaxy classification
We invoke a Gaussian mixture model (GMM) to jointly analyse two traditional
emission-line classification schemes of galaxy ionization sources: the
Baldwin-Phillips-Terlevich (BPT) and vs. [NII]/H
(WHAN) diagrams, using spectroscopic data from the Sloan Digital Sky Survey
Data Release 7 and SEAGal/STARLIGHT datasets. We apply a GMM to empirically
define classes of galaxies in a three-dimensional space spanned by the
[OIII]/H, [NII]/H, and EW(H), optical
parameters. The best-fit GMM based on several statistical criteria suggests a
solution around four Gaussian components (GCs), which are capable to explain up
to 97 per cent of the data variance. Using elements of information theory, we
compare each GC to their respective astronomical counterpart. GC1 and GC4 are
associated with star-forming galaxies, suggesting the need to define a new
starburst subgroup. GC2 is associated with BPT's Active Galaxy Nuclei (AGN)
class and WHAN's weak AGN class. GC3 is associated with BPT's composite class
and WHAN's strong AGN class. Conversely, there is no statistical evidence --
based on four GCs -- for the existence of a Seyfert/LINER dichotomy in our
sample. Notwithstanding, the inclusion of an additional GC5 unravels it. The
GC5 appears associated to the LINER and Passive galaxies on the BPT and WHAN
diagrams respectively. Subtleties aside, we demonstrate the potential of our
methodology to recover/unravel different objects inside the wilderness of
astronomical datasets, without lacking the ability to convey physically
interpretable results. The probabilistic classifications from the GMM analysis
are publicly available within the COINtoolbox
(https://cointoolbox.github.io/GMM\_Catalogue/).Comment: Accepted for publication in MNRA
Distribution, localization, and phylogeny of abundant populations of Crenarchaeota in anaerobic granular sludge
Eight anaerobic granular sludges were surveyed for Crenarchaeota using rRNA gene cloning. Microbial arrangement and substrate uptake patterns were elucidated by fluorescent in situ hybridization and beta imaging. Group 1.3 Crenarchaeota represented up to 50% of Archaea and 25% of the total microbiota in five sludges. Crenarchaeota were localized in close association with methanogenic Archaea
Multi-Parton Interactions at the LHC
We review the recent progress in the theoretical description and experimental
observation of multiple parton interactions. Subjects covered include
experimental measurements of minimum bias interactions and of the underlying
event, models of soft physics implemented in Monte Carlo generators,
developments in the theoretical description of multiple parton interactions and
phenomenological studies of double parton scattering. This article stems from
contributions presented at the Helmholtz Alliance workshop on "Multi-Parton
Interactions at the LHC", DESY Hamburg, 13-15 September 2010.Comment: 68 page
PRIMAP-crf: UNFCCC CRF data in IPCC 2006 categories
All Annex I Parties to the United Nations Framework Convention on Climate
Change (UNFCCC) are required to report domestic emissions on an annual basis
in a Common Reporting Format (CRF). In 2015, the CRF data reporting was
updated to follow the more recent 2006 guidelines from the IPCC and the
structure of the reporting tables was modified accordingly. However, the
hierarchical categorisation of data in the IPCC 2006 guidelines is not
readily extracted from the reporting tables. In this paper, we present the
PRIMAP-crf data as a re-constructed hierarchical dataset according to the
IPCC 2006 guidelines. Furthermore, the data are organised in a series of tables containing all available
countries and years for each individual gas and category reported. It is
therefore readily usable for climate policy assessment, such as the
quantification of emissions reduction targets.In addition to single gases, the Kyoto basket of greenhouse gases
(CO2, N2O, CH4, HFCs, PFCs, SF6, and
NF3) is provided according to multiple global warming potentials. The
dataset was produced using the PRIMAP emissions module. Key processing steps
include extracting data from submitted CRF Excel spreadsheets, mapping CRF
categories to IPCC 2006 categories, constructing missing categories from
available data, and aggregating single gases to gas baskets. Finally, we
describe key aspects of the data with relevance for climate policy: the
contribution of NF3 to national totals, changes in data reported over
subsequent years, and issues or difficulties encountered when processing
currently available data. The processed data are available under an Open Data
CC BY 4.0 license, and are available at
https://doi.org/10.5880/pik.2018.001.</p
Coherent Parton Showers with Local Recoils
We outline a new formalism for dipole-type parton showers which maintain
exact energy-momentum conservation at each step of the evolution. Particular
emphasis is put on the coherence properties, the level at which recoil effects
do enter and the role of transverse momentum generation from initial state
radiation. The formulated algorithm is shown to correctly incorporate coherence
for soft gluon radiation. Furthermore, it is well suited for easing matching to
next-to-leading order calculations.Comment: 24 pages, 3 figure
A Poincare-Covariant Parton Cascade Model for Ultrarelativistic Heavy-Ion Reactions
We present a new cascade-type microscopic simulation of nucleus-nucleus
collisions at RHIC energies. The basic elements are partons (quarks and gluons)
moving in 8N-dimensional phase space according to Poincare-covariant dynamics.
The parton-parton scattering cross sections used in the model are computed
within perturbative QCD in the tree-level approximation. The Q^2 dependence of
the structure functions is included by an implementation of the DGLAP mechanism
suitable for a cascade, so that the number of partons is not static, but varies
in space and time as the collision of two nuclei evolves. The resulting parton
distributions are presented, and meaningful comparisons with experimental data
are discussed.Comment: 30 pages. 11 figures. Submitted to Phys.Rev.
Hard Interactions of Quarks and Gluons: a Primer for LHC Physics
In this review article, we develop the perturbative framework for the
calculation of hard scattering processes. We undertake to provide both a
reasonably rigorous development of the formalism of hard scattering of quarks
and gluons as well as an intuitive understanding of the physics behind the
scattering. We emphasize the importance of logarithmic corrections as well as
power counting of the strong coupling constant in order to understand the
behavior of hard scattering processes. We include "rules of thumb" as well as
"official recommendations", and where possible seek to dispel some myths.
Experiences that have been gained at the Fermilab Tevatron are recounted and,
where appropriate, extrapolated to the LHC.Comment: 118 pages, 107 figures; to be published in Reports on Progress in
Physic
Theoretical Uncertainties in Electroweak Boson Production Cross Sections at 7, 10, and 14 TeV at the LHC
We present an updated study of the systematic errors in the measurements of
the electroweak boson cross-sections at the LHC for various experimental cuts
for a center of mass energy of 7, 10 and 14 TeV. The size of both electroweak
and NNLO QCD contributions are estimated, together with the systematic error
from the parton distributions. The effects of new versions of the MSTW, CTEQ,
and NNPDF PDFs are considered.Comment: PDFLatex with JHEP3.cls. 22 pages, 43 figures. Version 2 adds the
CT10W PDF set to analysis and updates the final systematic error table and
conclusions, plus several citations and minor wording changes. Version 3 adds
some references on electroweak and mixed QED/QCD corrections. Version 4 adds
more references and acknowledgement
Les Houches 2013: Physics at TeV Colliders: Standard Model Working Group Report
This Report summarizes the proceedings of the 2013 Les Houches workshop on
Physics at TeV Colliders. Session 1 dealt primarily with (1) the techniques for
calculating standard model multi-leg NLO and NNLO QCD and NLO EW cross sections
and (2) the comparison of those cross sections with LHC data from Run 1, and
projections for future measurements in Run 2.Comment: Proceedings of the Standard Model Working Group of the 2013 Les
Houches Workshop, Physics at TeV Colliders, Les houches 3-21 June 2013. 200
page
- …