1,293 research outputs found
The Structure of the Proton in the LHC Precision Era
We review recent progress in the determination of the parton distribution
functions (PDFs) of the proton, with emphasis on the applications for precision
phenomenology at the Large Hadron Collider (LHC). First of all, we introduce
the general theoretical framework underlying the global QCD analysis of the
quark and gluon internal structure of protons. We then present a detailed
overview of the hard-scattering measurements, and the corresponding theory
predictions, that are used in state-of-the-art PDF fits. We emphasize here the
role that higher-order QCD and electroweak corrections play in the description
of recent high-precision collider data. We present the methodology used to
extract PDFs in global analyses, including the PDF parametrization strategy and
the definition and propagation of PDF uncertainties. Then we review and compare
the most recent releases from the various PDF fitting collaborations,
highlighting their differences and similarities. We discuss the role that QED
corrections and photon-initiated contributions play in modern PDF analysis. We
provide representative examples of the implications of PDF fits for
high-precision LHC phenomenological applications, such as Higgs coupling
measurements and searches for high-mass New Physics resonances. We conclude
this report by discussing some selected topics relevant for the future of PDF
determinations, including the treatment of theoretical uncertainties, the
connection with lattice QCD calculations, and the role of PDFs at future
high-energy colliders beyond the LHC.Comment: 170 pages, 85 figures, version to be published in Physics Report
Towards Ultimate Parton Distributions at the High-Luminosity LHC
Since its start of data taking, the LHC has provided an impressive wealth of
information on the quark and gluon structure of the proton. Indeed, modern
global analyses of parton distribution functions (PDFs) include a wide range of
LHC measurements of processes such as the production of jets, electroweak gauge
bosons, and top quark pairs. In this work, we assess the ultimate constraining
power of LHC data on the PDFs that can be expected from the complete dataset,
in particular after the High-Luminosity (HL) phase, starting in around 2025.
The huge statistics of the HL-LHC, delivering ab to
ATLAS and CMS and ab to LHCb, will lead to an
extension of the kinematic coverage of PDF-sensitive measurements as well as to
an improvement in their statistical and systematic uncertainties. Here we
generate HL-LHC pseudo-data for different projections of the experimental
uncertainties, and then quantify the resulting constraints on the PDF4LHC15 set
by means of the Hessian profiling method. We find that HL-LHC measurements can
reduce PDF uncertainties by up to a factor of 2 to 4 in comparison to
state-of-the-art fits, leading to few-percent uncertainties for important
observables such as the Higgs boson transverse momentum distribution via
gluon-fusion. Our results illustrate the significant improvement in the
precision of PDF fits achievable from hadron collider data alone, and motivate
the continuation of the ongoing successful program of PDF-sensitive
measurements by the LHC collaborations.Comment: 30 pages, 20 figure
Analyzing the Spread of Chagas Disease with Mobile Phone Data
We use mobile phone records for the analysis of mobility patterns and the
detection of possible risk zones of Chagas disease in two Latin American
countries. We show that geolocalized call records are rich in social and
individual information, which can be used to infer whether an individual has
lived in an endemic area. We present two case studies, in Argentina and in
Mexico, using data provided by mobile phone companies from each country. The
risk maps that we generate can be used by health campaign managers to target
specific areas and allocate resources more effectively.Comment: 6 pages, 6 figure
Conflict-free strides for vectors in matched memories
Address transformation schemes, such as skewing and linear transformations, have been proposed to achieve conflict-free access to one family of strides in vector processors with matched memories. The paper extends these schemes to achieve this conflict-free access for several families. The basic idea is to perform an out-of-order access to vectors of fixed length, equal to that of the vector registers of the processor. The hardware required is similar to that for the access in order.Peer ReviewedPostprint (author's final draft
Detaching from the negative by reappraisal: the role of right superior frontal gyrus (BA9/32)
The ability to reappraise the emotional impact of events is related to long-term mental health. Self-focused reappraisal (REAPPself), i.e., reducing the personal relevance of the negative events, has been previously associated with neural activity in regions near right medial prefrontal cortex, but rarely investigated among brain-damaged individuals. Thus, we aimed to examine the REAPPself ability of brain-damaged patients and healthy controls considering structural atrophies and gray matter intensities, respectively. Twenty patients with well-defined cortex lesions due to an acquired circumscribed tumor or cyst and 23 healthy controls performed a REAPPself task, in which they had to either observe negative stimuli or decrease emotional responding by REAPPself. Next, they rated the impact of negative arousal and valence. REAPPself ability scores were calculated by subtracting the negative picture ratings after applying REAPPself from the ratings of the observing condition. The scores of the patients were included in a voxel-based lesion-symptom mapping (VLSM) analysis to identify deficit related areas (ROI). Then, a ROI group-wise comparison was performed. Additionally, a whole-brain voxel-based-morphometry (VBM) analysis was run, in which healthy participant's REAPPself ability scores were correlated with gray matter intensities. Results showed that (1) regions in the right superior frontal gyrus (SFG), comprising the right dorsolateral prefrontal cortex (BA9) and the right dorsal anterior cingulate cortex (BA32), were associated with patient's impaired down-regulation of arousal, (2) a lesion in the depicted ROI occasioned significant REAPPself impairments, (3) REAPPself ability of controls was linked with increased gray matter intensities in the ROI regions. Our findings show for the first time that the neural integrity and the structural volume of right SFG regions (BA9/32) might be indispensable for REAPPself. Implications for neurofeedback research are discussed.Fil: Falquez, Rosalux. University of Heidelberg; AlemaniaFil: Couto, Juan Blas Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Neurociencia Cognitiva. Fundación Favaloro. Instituto de Neurociencia Cognitiva; ArgentinaFil: Ibáñez Barassi, Agustín Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Neurociencia Cognitiva. Fundación Favaloro. Instituto de Neurociencia Cognitiva; ArgentinaFil: Freitag, Martin T.. German Cancer Research Center; AlemaniaFil: Berger, Moritz. German Cancer Research Center; AlemaniaFil: Arens, Elisabeth A.. University of Heidelberg; AlemaniaFil: Lang, Simone. University of Heidelberg; AlemaniaFil: Barnow, Sven. University of Heidelberg; Alemani
Modeling and frequency domain analysis of nonlinear compliant joints for a passive dynamic swimmer
In this paper we present the study of the mathematical model of a real life
joint used in an underwater robotic fish. Fluid-structure interaction is
utterly simplified and the motion of the joint is approximated by D\"uffing's
equation. We compare the quality of analytical harmonic solutions previously
reported, with the input-output relation obtained via truncated Volterra series
expansion. Comparisons show a trade-off between accuracy and flexibility of the
methods. The methods are discussed in detail in order to facilitate
reproduction of our results. The approach presented herein can be used to
verify results in nonlinear resonance applications and in the design of
bio-inspired compliant robots that exploit passive properties of their
dynamics. We focus on the potential use of this type of joint for energy
extraction from environmental sources, in this case a K\'arm\'an vortex street
shed by an obstacle in a flow. Open challenges and questions are mentioned
throughout the document.Comment: 12 p, 5 fig, work in progress, collaborative wor
Three-dimensional submerged wall jets and their transition to density flows: Morphodynamics and implications for the depositional record
Jets that expand from an orifice into an ambient water body represent a basic flow model for depositional environments related to expanding flows. Momentum-dominated jets evolve into gravity-dominated density flows. To understand this transition and its sedimentological relevance, three-dimensional tank experiments with submerged wall jets were conducted, systematically varying parameters such as the initial density difference, bed slope, grain size and sediment supply. Bedform successions could be subdivided into those related to the jet and those related to the density flow. Jet deposits included early-stage bedforms, scours and mouth bars. Early-stage bedforms are asymmetrical dunes that spread concentrically from the orifice. Sediment entrainment by eddies from the expanding jets led to the formation of scours and mouth bars. Flows with lesser initial density difference produced more elongate scours. Conversely, scours became deeper for denser incoming flows. Coarser-grained sediment caused the formation of higher and steeper mouth bars and vice versa. The transition from momentum-dominated jets to gravity-dominated density flows occurred approximately at the mouth-bar crest. Hydraulic jumps were absent in the expanding jet regions and at the transitions to density flows. Instead, complex flow patterns and circulations were inferred from the velocity measurements within the scour and at the mouth-bar crests. Bedform trains related to the density flow were controlled by the grain size and sediment supply. Coarse-grained sediment and high supply rates caused strong mouth-bar aggradation and flow splitting, leading to the formation of bedform trains laterally adjacent to the mouth bar. Fine-grained sediment and low supply rates caused the formation of bedform trains downflow of the mouth bar. The symmetrical bedforms deposited by the density flows always displayed an in-phase relationship with the flow, indicating that they were antidunes. The experimental jet deposits resemble successions known from subaqueous ice-contact fans and deep water channel-lobe transition zones
Re-examining models of shallow-water deltas: Insights from tank experiments and field examples
Shallow-water deltas remain enigmatic in terms of placing the observed facies within a coherent process-based depositional model. Here we report tank experiments on mouth-bar formation from shallow water pure and stratified jets that, combined with recent flume experiments on bedforms, suggest new interpretations of field observations from shallow-water delta outcrops. Our experiments imply that the height, geometry and bedforms of the mouth bars depend on the jet properties and grain size of the supplied sediment. Pure jets with very coarse-grained sediment formed a high and steep mouth bar that is characterised by steep angle-of-repose cross bedding with related avalanche processes (grain flows) on the lee side. The experiments with stratified jets imply that mouth-bar deposition and growth are dominated by supercritical density flows that evolve from the initial jets on the lee side of the growing mouth bar. In stratified jets with very coarse-grained sediment, deposition on the mouth-bar lee side was both from grain-flow avalanches and density flows. While deposition on the upper lee slope was dominated by grain flows, a concentric field of low relief, asymmetric, downflow-migrating bedforms evolved on the lower slope and beyond the mouth bar. In the stratified jet with medium-grained sediment a very low relief mouth bar formed within a concentric field of low, asymmetric, downflow-migrating bedforms covering the entire lee slope and the area beyond. Many previous field studies show that mouth bars deposited from dense stratified jets (hyperpycnal flows) are characterised by a distinct facies assemblage of coarse-grained cross-stratified or low-angle cross-stratified sandstone passing downslope into finer-grained plane-parallel, or “quasi-parallel” laminated sand and into climbing-ripple cross-laminated sandstone. Comparison to flume and tank experiments suggests that the proximal coarse-grained planar and trough cross-stratified sandstones could represent deposition by supercritical dunes that pass downslope into antidunes, characterised by sinusoidal stratification and/or low-angle cross stratification. The repeated vertical transition between antidune deposits and climbing-ripple cross-laminated sandstone may indicate the superposition of ripples onto antidunes in finer-grained sediments, indicating ripple formation under supercritical flow conditions. Similar bedforms/sedimentary structures have previously been interpreted as hummocky cross-stratification or swaley cross-stratification and attributed to combined flows in storm-dominated settings, which probably in some cases must be revised
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