Proglacial icings as indicators of glacier thermal regime : ice thickness changes and icing occurrence in Svalbard

Proglacial icings (also known as naled or aufeis) are frequently observed in the forefields of polar glaciers. Their formation has been ascribed to the refreezing of upwelling groundwater that has originated from subglacial melt, and thus the presence of icings has been used as evidence of polythermal glacier regime. We provide an updated analysis of icing occurrence in Svalbard and test the utility of icings as an indicator of thermal regime by comparing icing presence with: (1) mean glacier thickness, as a proxy for present thermal regime; and (2) evidence of past surge activity, which is an indicator of past thermal regime. A total of 279 icings were identified from TopoSvalbard imagery covering the period 2008-2012, of which 143 corresponded to icings identified by Bukowska-Jania and Szafraniec (2005) from aerial photographs from 1990. Only 46% of icings observed in 2008-2012 were found to occur at glaciers with thicknesses consistent with a polythermal regime, meaning a large proportion were associated with glaciers predicted to be of a cold or transitional thermal regime. As a result, icing presence alone may be an unsuitable indicator of glacier regime. We further found that, of the 279 glaciers with icings, 63% of cold-based glaciers and 64% of transitional glaciers were associated with evidence of surge activity. We therefore suggest that proglacial icing formation in Svalbard may reflect historical (rather than present) thermal regime, and that icings possibly originate from groundwater effusion from subglacial taliks that persist for decades following glacier thinning and associated regime change

Morphology, flow dynamics and evolution of englacial conduits in cold ice

Meltwater routing through ice masses exerts a fundamental control over glacier dynamics and mass balance, and proglacial hydrology. However, despite recent advances in mapping drainage systems in cold, Arctic glaciers, direct observations of englacial channels and their flow conditions remain sparse. Here, using Terrestrial Laser Scanning (TLS) surveys of the main englacial channel of cold-based Austre Brøggerbreen (Svalbard), we map and compare an entrance moulin reach (122 m long) and exit portal reach (273 m long). Analysis of channel planforms, longitudinal profiles, cross-sections and morphological features reveals evidence of spatial variations in water flow conditions and channel incision mechanisms, and the presence of vadose, epiphreatic and phreatic conditions. The entrance reach, located at the base of a perennial moulin, was characterised by vadose, uniform, channel lowering at annual timescales, evidenced by longitudinal grooves, whereas the exit portal reach showed both epiphreatic and vadose conditions, along with upstream knickpoint migration at intra-annual timescales. Fine-scale features, including grooves and scallops, were readily quantified from the TLS point cloud, highlighting the capacity of the technique to inform palaeoflow conditions, and reveal how pulses of meltwater from rainfall events may adjust englacial conduit behaviour. With forecasts of increasing Arctic precipitation in the coming decades, and a progressively greater proportion of glaciers comprising cold ice, augmenting the current knowledge of englacial channel morphology is essential to constrain future glacier hydrological system change

Turning universal O into rare Bombay type blood

Red blood cell antigens play critical roles in blood transfusion since donor incompatibilities can be lethal. Recipients with the rare total deficiency in H antigen, the Oh Bombay phenotype, can only be transfused with group Oh blood to avoid serious transfusion reactions. We discover FucOB from the mucin-degrading bacteria Akkermansia muciniphila as an -1,2-fucosidase able to hydrolyze Type I, Type II, Type III and Type V H antigens to obtain the afucosylated Bombay phenotype in vitro. X-ray crystal structures of FucOB show a three-domain architecture, including a GH95 glycoside hydrolase. The structural data together with site-directed mutagenesis, enzymatic activity and computational methods provide molecular insights into substrate specificity and catalysis. Furthermore, using agglutination tests and flow cytometry-based techniques, we demonstrate the ability of FucOB to convert universal O type into rare Bombay type blood, providing exciting possibilities to facilitate transfusion in recipients/patients with Bombay phenotype

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

Azimuthal anisotropy of charged particles at high transverse momenta in PbPb collisions at sqrt(s[NN]) = 2.76 TeV

The azimuthal anisotropy of charged particles in PbPb collisions at nucleon-nucleon center-of-mass energy of 2.76 TeV is measured with the CMS detector at the LHC over an extended transverse momentum (pt) range up to approximately 60 GeV. The data cover both the low-pt region associated with hydrodynamic flow phenomena and the high-pt region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v2) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0-60% most-central events, the observed v2 values are found to first increase with pt, reaching a maximum around pt = 3 GeV, and then to gradually decrease to almost zero, with the decline persisting up to at least pt = 40 GeV over the full centrality range measured.Comment: Replaced with published version. Added journal reference and DO

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

Search for new physics with same-sign isolated dilepton events with jets and missing transverse energy

A search for new physics is performed in events with two same-sign isolated leptons, hadronic jets, and missing transverse energy in the final state. The analysis is based on a data sample corresponding to an integrated luminosity of 4.98 inverse femtobarns produced in pp collisions at a center-of-mass energy of 7 TeV collected by the CMS experiment at the LHC. This constitutes a factor of 140 increase in integrated luminosity over previously published results. The observed yields agree with the standard model predictions and thus no evidence for new physics is found. The observations are used to set upper limits on possible new physics contributions and to constrain supersymmetric models. To facilitate the interpretation of the data in a broader range of new physics scenarios, information on the event selection, detector response, and efficiencies is provided.Comment: Published in Physical Review Letter

Compressed representation of a partially defined integer function over multiple arguments

In OLAP (OnLine Analitical Processing) data are analysed in an n-dimensional cube. The cube may be represented as a partially defined function over n arguments. Considering that often the function is not defined everywhere, we ask: is there a known way of representing the function or the points in which it is defined, in a more compact manner than the trivial one

Measurement of the Z/gamma* + b-jet cross section in pp collisions at 7 TeV

The production of b jets in association with a Z/gamma* boson is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV and recorded by the CMS detector. The inclusive cross section for Z/gamma* + b-jet production is measured in a sample corresponding to an integrated luminosity of 2.2 inverse femtobarns. The Z/gamma* + b-jet cross section with Z/gamma* to ll (where ll = ee or mu mu) for events with the invariant mass 60 < M(ll) < 120 GeV, at least one b jet at the hadron level with pT > 25 GeV and abs(eta) < 2.1, and a separation between the leptons and the jets of Delta R > 0.5 is found to be 5.84 +/- 0.08 (stat.) +/- 0.72 (syst.) +(0.25)/-(0.55) (theory) pb. The kinematic properties of the events are also studied and found to be in agreement with the predictions made by the MadGraph event generator with the parton shower and the hadronisation performed by PYTHIA.Comment: Submitted to the Journal of High Energy Physic