1,267 research outputs found
Determination of polarized parton distribution functions with recent data on polarization asymmetries
Global analysis has been performed within the next-to-leading order in
Quantum Chromodynamics (QCD) to determine polarized parton distributions with
new experimental data in spin asymmetries. The new data set includes JLab,
HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and
deuteron in lepton scattering. Our new analysis also utilizes the double-spin
asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0},
measured by the PHENIX collaboration. Because of these new data, uncertainties
of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS
measurements are valuable for determining Delta d_v(x) at large x and Delta
qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of
Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at
large x by using the HERMES data on g_1^d in comparison with the COMPASS ones
at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres
What did HERA teach us about the structure of the proton?
Starting in 2008 the H1 and ZEUS experiments have been combining their data
in order to provide the most complete and accurate set of deep-inelastic data
as the legacy of HERA. The present review presents these combinations, both
published and preliminary, and explores how they have been used to give
information on the structure of the proton. The HERAPDF parton distribution
functions (PDFs) are presented and compared with other current PDFs and with
data from the Tevatron and LHC colliders.Comment: 49 pages, 49 figures, to be published in J.Phys.
On track to achieve No Net Loss of forest at Madagascarâs biggest mine
Meeting the Sustainable Development Goals requires reconciling development with biodiversity conservation. Governments and lenders increasingly call for major industrial developments to offset unavoidable biodiversity loss, but there are few robust evaluations of whether offset interventions ensure No Net Loss (NNL) of biodiversity. We focus on the biodiversity offsets associated with the high-profile Ambatovy mine in Madagascar and evaluate their effectiveness at delivering NNL of forest. As part of their efforts to mitigate biodiversity loss, Ambatovy compensate for forest clearance at the mine site by slowing deforestation driven by small-scale agriculture elsewhere. Using a range of methods, including extensive robustness checks exploring 116 alternative model specifications, we show that the offsets are on track to avert as much deforestation as was caused by the mine. This encouraging result shows that biodiversity offsetting can contribute towards mitigating environmental damage from a major industrial development, even within a weak state, but there remain important caveats with broad application. Our approach could serve as a template to facilitate other evaluations and so build a stronger evidence-base of the effectiveness of No Net Loss interventions
Clustering aspects in nuclear structure functions
For understanding an anomalous nuclear effect experimentally observed for the
beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility
(JLab), clustering aspects are studied in structure functions of deep inelastic
lepton-nucleus scattering by using momentum distributions calculated in
antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple
shell model for comparison. According to the AMD, the Be-9 nucleus consists of
two alpha-like clusters with a surrounding neutron. The clustering produces
high-momentum components in nuclear wave functions, which affects nuclear
modifications of the structure functions. We investigated whether clustering
features could appear in the structure function F_2 of Be-9 along with studies
for other light nuclei. We found that nuclear modifications of F_2 are similar
in both AMD and shell models within our simple convolution description although
there are slight differences in Be-9. It indicates that the anomalous Be-9
result should be explained by a different mechanism from the nuclear binding
and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by
the maximum local densities, the Be-9 anomaly can be explained by the AMD
picture, namely by the clustering structure, whereas it certainly cannot be
described in the simple shell model. This fact suggests that the large nuclear
modification in Be-9 should be explained by large densities in the clusters.
For example, internal nucleon structure could be modified in the high-density
clusters. The clustering aspect of nuclear structure functions is an unexplored
topic which is interesting for future investigations.Comment: 11 pages, LaTeX, 10 eps files, Physical Review C in pres
Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model
Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to .Comment: 23 pages, LaTe
Lagrangian statistics of particle pairs in homogeneous isotropic turbulence
We present a detailed investigation of the particle pair separation process
in homogeneous isotropic turbulence. We use data from direct numerical
simulations up to Taylor's Reynolds number 280 following the evolution of about
two million passive tracers advected by the flow over a time span of about
three decades. We present data for both the separation distance and the
relative velocity statistics. Statistics are measured along the particle pair
trajectories both as a function of time and as a function of their separation,
i.e. at fixed scales. We compare and contrast both sets of statistics in order
to gain an insight into the mechanisms governing the separation process. We
find very high levels of intermittency in the early stages, that is, for travel
times up to order ten Kolmogorov time scales. The fixed scale statistics allow
us to quantify anomalous corrections to Richardson diffusion in the inertial
range of scales for those pairs that separate rapidly. It also allows a
quantitative analysis of intermittency corrections for the relative velocity
statistics.Comment: 16 pages, 16 figure
Patterns in island endemic forest-dependent bird research: the Caribbean as a case-study
From Springer Nature via Jisc Publications RouterHistory: received 2018-10-25, rev-recd 2019-03-19, registration 2019-04-26, accepted 2019-04-26, online 2019-05-04, epub 2019-05-04, ppub 2019-06Publication status: PublishedAbstract: Unequal patterns in research effort can result in inaccurate assessments of species extinction risk or ineffective management. A group of notable conservation concern are tropical island endemic birds, many of which are also forest-dependent, which increases their vulnerability to extinction. Yet, island bird species have received limited research attention compared to their continental congeners, despite this taxon being globally regarded as well-studied. We used the insular Caribbean, a globally important endemism hotspot with high rates of deforestation, to explore research bias of island and regional endemic forest-dependent birds. A review of the published literature (n = 992) found no significant increase in the number of studies over the search period. Research effort was significantly higher among species with threatened status, long generation time, wide habitat breadth and low to intermediate elevational distributions. Among family groups, the Psittacidae received the highest research effort, while the Cuculidae were the most underrepresented family (30-fold higher and six-fold less than expected, respectively). We found geographic biases in effort, with Jamaica having six-fold less and Puerto Rico eight times more research than expected for their level of endemism. These patterns likely reflect individual interests and limited capacity and funding, typical of Small Island Developing States. With over 50% of species in this review having declining population trends, we recommend prioritizing research that emphasises conservation- and management-relevant data across underrepresented families and islands, by fostering greater collaboration between researchers, practitioners and the existing local amateur ornithological community
Demonstrating frequency-dependent transmission of sarcoptic mange in red foxes
Understanding the relationship between disease transmission and host density is essential for predicting disease spread and control. Using long-term data on sarcoptic mange in a red fox Vulpes vulpes population, we tested long-held assumptions of density- and frequency-dependent direct disease transmission. We also assessed the role of indirect transmission. Contrary to assumptions typical of epidemiological models, mange dynamics are better explained by frequency-dependent disease transmission than by density-dependent transmission in this canid. We found no support for indirect transmission. We present the first estimates of R0 and age-specific transmission coefficients for mange in foxes. These parameters are important for managing this poorly understood but highly contagious and economically damaging disease
Contrasting responses of native ant communities to invasion by an ant invader, Linepithema humile
Invasive alien species pose a serious threat to the integrity and function of natural ecosystems. Understanding how these invaders alter natural communities is therefore an important aspect in predicting the likely future outcomes of biological invasions. Many studies have documented the consequences of invasive alien species on native community structure, through the displacement and local extinction of native species. However, sampling methods and intensities are rarely standardised across such studies, meaning that it is not clear whether differences in response among native communities to the same invader species are due to biological differences between the invaded regions, or differences in the methodologies used. Here we use a matched sampling methodology to compare the effects of the Argentine ant (Linepithema humile Mayr) on native ant community assemblages in two distinct biogeographical regions that share similar ecologies: Girona (Spain) and Jonkershoek Nature Reserve (South Africa). We found a strong negative association between L. humile presence and native ant species richness within both geographic regions. However, the effects differed between the two study regions: in Girona, a single native ant species (Plagiolepis pygmaea) persisted in invaded sites; by contrast, substantially more native ant species persisted at invaded sites in Jonkershoek Nature Reserve. In addition, in Jonkershoek Nature Reserve, the abundance of certain native species appeared to increase in the presence of L. humile. This study therefore demonstrates the potential variable effects of an invasive species in contrasting locations within different biogeographical regions. Future work should explore the causes of this differential resistance among communities and expand standardised sampling approaches to more invaded zones to further explore how local biotic or abiotic conditions of a region determine the nature and extent of impact of L. humile invasion on native ant communities
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