The Eastern Canadian Arctic at ca. 6 ka BP: A Time of Transition

The middle Holocene was a time of definite environmental transition in the Eastern Canadian Arctic. Based on several proxy indicators (pollen, diatoms, foraminifera, molluscs and nearshore sedimentation rates), it appears that a thermal maximum occurred around middle Holocene (6-4 ka), several thousand years after the insolation maximum — a lag caused by the thermal inertia of the earlier massive ice sheet. Terrestrial records indicate that a warming began around 6 ka, both in the subarctic (Labrador - Ungava) and on Baffin Island. Marine records, on the other hand, suggested major water structure changes around 6 ka both in the Northeastern Canadian Arctic and also along the East Greenland coast with evidence of a marine surface water temperature maximum at 8 ka. We hypothesize that the marine circulation changes, both along the Baffin Island and along the East Greenland coasts, were primarily driven by glacio-isostatic uplift of the Arctic Channels. With the cessation of water flow of Atlantic (warmer) origin, and decrease in water volume from the deeper parts of the Arctic Ocean through the Arctic Channels, the export through the Fram and Denmark straits increased and the water column changed. Changes in the concentration and duration of sea ice along the eastern Canadian coast would have had important repercussions on the biota of the coastal marine and terrestrial ecosystems.L'Holocène moyen a été une période de transition bien déterminée dans l'est de l'Arctique canadien. Selon de nombreux indicateurs (pollen, diatomées, foraminifères, mollusques et taux de sédimentation côtiers), il semble qu'un maximum thermique ait été atteint vers le milieu de l'Holocène (6-4 ka), plusieurs milliers d'années après le maximum d'insolation — un retard dû à l'inertie thermique causée par la présence de l'immense inlandsis. Les données terrestres démontrent qu'un réchauffement s'est amorcé vers 6 ka, à la fois dans le subarctique (Labrador, Ungava) et dans l'île de Baffin. Les données marines, d'autre part, indiquent qu'il y a eu des changements de structure de l'eau vers 6 ka à la fois dans le nord-est de l'Arctique canadien et le long de la côte du Groenland avec des indices de températures maximales marines de surface à 8 ka. Nous posons l'hypothèse selon laquelle les changements de circulation marine, à la fois le long de l'île de Baffin et le long de la côte est du Groenland ont été provoqués par le relèvement isostatique des chenaux arctiques. Avec l'arrêt de l'écoulement (plus chaud) en provenance de l'Atlantique et la diminution du cubage d'eau provenant des grandes profondeurs de l'océan Arctique dans les chenaux arctiques, l'évacuation par les détroits de Fram et du Danemark s'est accrue et la colonne d'eau s'est modifiée. Les changements de concentration et de durée de la glace marine le long de la côte est du Canada auraient eu d'importantes répercussions sur les écosystèmes marins côtiers et terrestres.Das mittlere Holozân war eine eindeutige Umwelt-Ùbergangszeit in der ostkanadischen Arktis. Gestùtzt auf zahlreiche Indikatoren (Pollen, Kieselalgen, Foraminiferen, Mollusken und die Sedimentationsrate am Ufer) scheint es, dap ein thermales Maximum um die Mitte des Holozàns erreicht wurde (6-4 ka), mehrere tausend Jahre nach dem Sonneneinstrahlungsmaximum - eine Verzôgerung, welche durch die thermale Trâgheit der frùheren massiven Eisdecke bewirkt wurde. Belege zu Land zeigen, daB eine Erwârmung um 6 ka begann, sowohl in der Subarktis (Labrador-Ungava) wie auch auf der Baffin-lnsel. Meeresbelege andererseits weisen auf bedeutende Wasserstruktur-Ànderungen um 6 ka, sowohl in der nordôstlichen kanadischen Arktis wie auch entlang der Kùste von Ost-Grônland, mit Anhaltspunkten fur maximale Wassertemperaturen an der Meeresober-flâche um 8 ka. Wir stellen die Hypothèse auf, daB die Wechsel der marinen Zirkulation, sowohl entlang der Baffin-lnsel wie auch der Kùsten von Ost-Grônland, in erster Linie durch die glazial-isostatische Anhebung der arktischen Kanâle hervorgerufen wurden. Mit der Beendigung des (wàrmeren) Wasserflusses vom Atlantik und der Abnahme des Wasservolumes von den tieferen Teilen des arktischen Ozeans durch die arktischen Kanâle nahm die Ausfuhr durch die Meeregen von Fram und Danemark zu, und die Wassersàule ânderte sich. Die Wechsel in der Konzentration und Dauer des Meereises entlang der ostkanadischen Kùste sollen bedeutende Auswirkungen auf Ôkosysteme an der Meereskùste und zu Land gehabt haben

Presence of procoagulant peripheral blood mononuclear cells in severe COVID-19 patients relate to ventilation perfusion mismatch and precede pulmonary embolism

PURPOSE: Pulmonary emboli (PE) contribute substantially to coronavirus disease 2019 (COVID-19) related mortality and morbidity. Immune cell-mediated hyperinflammation drives the procoagulant state in COVID-19 patients, resulting in immunothrombosis. To study the role of peripheral blood mononuclear cells (PBMC) in the procoagulant state of COVID-19 patients, we performed a functional bioassay and related outcomes to the occurrence of PE. Secondary aims were to relate this functional assay to plasma D-dimer levels, ventilation perfusion mismatch and TF expression on monocyte subsets. METHODS: PBMC from an ICU biobank were obtained from 20 patients with a computed tomography angiograph (CTA) proven PE and compared to 15 COVID-19 controls without a proven PE. Functional procoagulant properties of PBMC were measured using a modified fibrin generation time (MC-FGT) assay. Tissue factor (TF) expression on monocyte subsets were measured by flow cytometry. Additional clinical data were obtained from patient records including end-tidal to arterial carbon dioxide gradient. RESULTS: MC-FGT levels were highest in the samples taken closest to the PE detection, similar to the end-tidal to arterial carbon dioxide gradient (ETCO2 - PaCO2), a measurement to quantify ventilation-perfusion mismatch. In patients without proven PE, peak MC-FGT relates to an increase in end-tidal to arterial carbon dioxide gradient. We identified non-classical, CD16 positive monocytes as the subset with increased TF expression. CONCLUSION: We show that the procoagulant state of PBMC could aid in early detection of PE in COVID-19 ICU patients. Combined with end-tidal to ETCO2 - PaCO2 gradient, these tests could improve early detection of PE on the ICU.</p

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Operation and performance of the ATLAS semiconductor tracker

The semiconductor tracker is a silicon microstrip detector forming part of the inner tracking system of the ATLAS experiment at the LHC. The operation and performance of the semiconductor tracker during the first years of LHC running are described. More than 99% of the detector modules were operational during this period, with an average intrinsic hit efficiency of (99.74±0.04)%. The evolution of the noise occupancy is discussed, and measurements of the Lorentz angle, δ-ray production and energy loss presented. The alignment of the detector is found to be stable at the few-micron level over long periods of time. Radiation damage measurements, which include the evolution of detector leakage currents, are found to be consistent with predictions and are used in the verification of radiation background simulations

Measurement of event-shape observables in Z→ℓ+ℓ− events in pp collisions at √ s=7 TeV with the ATLAS detector at the LHC

Event-shape observables measured using charged particles in inclusive $Z$-boson events are presented, using the electron and muon decay modes of the $Z$ bosons. The measurements are based on an integrated luminosity of $1.1 {\rm fb}^{-1}$ of proton--proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy $\sqrt{s}=7$ TeV. Charged-particle distributions, excluding the lepton--antilepton pair from the $Z$-boson decay, are measured in different ranges of transverse momentum of the $Z$ boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and $\mathcal{F}$-parameter, which are in particular sensitive to properties of the underlying event at small values of the $Z$-boson transverse momentum. The Sherpa event generator shows larger deviations from the measured observables than Pythia8 and Herwig7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high $Z$-boson transverse momenta than at low $Z$-boson transverse momenta and for the observables that are less sensitive to the number of charged particles in the event.Comment: 36 pages plus author list + cover page (54 pages total), 14 figures, 4 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2014-0

Search for H→γγ produced in association with top quarks and constraints on the Yukawa coupling between the top quark and the Higgs boson using data taken at 7 TeV and 8 TeV with the ATLAS detector

A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 4.5 fb−14.5 fb−1 of proton–proton collisions at a center-of-mass energy of 7 TeV and 20.3 fb−1 at 8 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the tt¯H production cross section. The observed exclusion upper limit at 95% confidence level is 6.7 times the predicted Standard Model cross section value. In addition, limits are set on the strength of the Yukawa coupling between the top quark and the Higgs boson, taking into account the dependence of the tt¯H and tH cross sections as well as the H→γγ branching fraction on the Yukawa coupling. Lower and upper limits at 95% confidence level are set at −1.3 and +8.0 times the Yukawa coupling strength in the Standard Model