5,016 research outputs found
Inclusive Jet Production, Parton Distributions, and the Search for New Physics
Jet production at the Tevatron probes some of the smallest distance scales
currently accessible. A gluon distribution that is enhanced at large x compared
to previous determinations provides a better description of the Run 1b jet data
from both CDF and D0. However, considerable uncertainty still remains regarding
the gluon distribution at high x. In this paper, we examine the effects of this
uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet
cross section comparisons to Run 1b data. We also calculate the range of
contributions still possible from any new physics. Predictions are also made
for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron
and for the LHC.Comment: 50 pages, 31 figures, RevTe
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
Economic Assessment of South African Urban Green Spaces Using the Proximity Principle: Municipal Valuation vs. Market Value
<p>Urban green spaces (UGSs) deliver ecosystem services and potential economic benefits like increases in proximate residential property prices. The proximity principle (PP) premises that property prices increase as distance to UGS decreases. The PP has generally been confirmed by studies using municipal valuations and market values internationally. Conversely, South African studies have mostly employed municipal valuations and results have rejected the PP. There is an accepted interrelationship, but also often discrepancies, between municipal valuations and market values, presenting scope for this article to explore whether negative results are confirmed when market values replace municipal valuations in PP studies in the South African context. Accordingly, a statistical analysis of market values is completed in the Potchefstroom case study, where five test sites are replicated from studies that employed municipal valuations for longitudinal comparison. Results verify generally higher market values than municipal valuations and confirm the PP in two, but reject the PP in three, of five test sites. Previous studies employing municipal valuations in the case study confirmed the PP in one instance, thus presenting certain, but limited, inconsistencies between findings based on municipal valuation vs. market value. Results suggest that the marketâs willingness to pay for UGS proximity is sensitive to the ecosystem services and disservices rendered by specific UGS, but not significantly more than reflected in municipal valuations. Overall, findings underscore the need to protect and curate features that encourage willingness to pay for UGS proximity to increase municipal valuations and property taxes to help finance urban greening.</p></jats:p
Les Houches Guidebook to Monte Carlo Generators for Hadron Collider Physics
Recently the collider physics community has seen significant advances in the
formalisms and implementations of event generators. This review is a primer of
the methods commonly used for the simulation of high energy physics events at
particle colliders. We provide brief descriptions, references, and links to the
specific computer codes which implement the methods. The aim is to provide an
overview of the available tools, allowing the reader to ascertain which tool is
best for a particular application, but also making clear the limitations of
each tool.Comment: 49 pages Latex. Compiled by the Working Group on Quantum
ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV
Colliders'', Les Houches, France, May 2003. To appear in the proceeding
Effects of Higher-Order Threshold Corrections in High-E_T Jet Production
Results for higher-order threshold enhancements in high-E_T jet production in
hadron-hadron collisions are presented. Expressions are given for the
next-to-next-to-leading order (NNLO) threshold corrections to the single-jet
inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The
corrections are found to be small for the specific choice of E_T/2 for the
factorization and renormalization scales, and the corrected cross section shows
a substantial reduction of the scale dependence. A comparison to experimental
results from the Tevatron is presented.Comment: 24 pages LaTeX, 5 figure
Inflationary perturbation theory is geometrical optics in phase space
A pressing problem in comparing inflationary models with observation is the
accurate calculation of correlation functions. One approach is to evolve them
using ordinary differential equations ("transport equations"), analogous to the
Schwinger-Dyson hierarchy of in-out quantum field theory. We extend this
approach to the complete set of momentum space correlation functions. A formal
solution can be obtained using raytracing techniques adapted from geometrical
optics. We reformulate inflationary perturbation theory in this language, and
show that raytracing reproduces the familiar "delta N" Taylor expansion. Our
method produces ordinary differential equations which allow the Taylor
coefficients to be computed efficiently. We use raytracing methods to express
the gauge transformation between field fluctuations and the curvature
perturbation, zeta, in geometrical terms. Using these results we give a compact
expression for the nonlinear gauge-transform part of fNL in terms of the
principal curvatures of uniform energy-density hypersurfaces in field space.Comment: 22 pages, plus bibliography and appendix. v2: minor changes, matches
version published in JCA
Structure and Metal Binding Properties of Chlamydia trachomatis YtgA
Copyright © 2019 American Society for Microbiology. All Rights Reserved. The obligate intracellular pathogen Chlamydia trachomatis is a globally significant cause of sexually transmitted bacterial infections and the leading etiological agent of preventable blindness. The first-row transition metal iron (Fe) plays critical roles in chlamydial cell biology, and acquisition of this nutrient is essential for the survival and virulence of the pathogen. Nevertheless, how C. trachomatis acquires Fe from host cells is not well understood, since it lacks genes encoding known siderophore biosynthetic pathways, receptors for host Fe storage proteins, and the Fe acquisition machinery common to many bacteria. Recent studies have suggested that C. trachomatis directly acquires host Fe via the ATP-binding cassette permease YtgABCD. Here, we characterized YtgA, the periplasmic solute binding protein component of the transport pathway, which has been implicated in scavenging Fe(III) ions. The structure of Fe(III)-bound YtgA was determined at 2.0-Ă
resolution with the bound ion coordinated via a novel geometry (3 Ns, 2 Os [3N2O]). This unusual coordination suggested a highly plastic metal binding site in YtgA capable of interacting with other cations. Biochemical analyses showed that the metal binding site of YtgA was not restricted to interaction with only Fe(III) ions but could bind all transition metal ions examined. However, only Mn(II), Fe(II), and Ni(II) ions bound reversibly to YtgA, with Fe being the most abundant cellular transition metal in C. trachomatis. Collectively, these findings show that YtgA is the metal-recruiting component of the YtgABCD permease and is most likely involved in the acquisition of Fe(II) and Mn(II) from host cells. Importance: Chlamydia trachomatis is the most common bacterial sexually transmitted infection in developed countries, with an estimated global prevalence of 4.2% in the 15- to 49-year age group. Although infection is asymptomatic in more than 80% of infected women, about 10% of cases result in serious disease. Infection by C. trachomatis is dependent on the ability to acquire essential nutrients, such as the transition metal iron, from host cells. In this study, we show that iron is the most abundant transition metal in C. trachomatis and report the structural and biochemical properties of the iron-recruiting protein YtgA. Knowledge of the highresolution structure of YtgA will provide a platform for future structure-based antimicrobial design approaches
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