1,287 research outputs found
Long-profile evolution of transport-limited gravel-bed rivers
Alluvial and transport-limited bedrock rivers constitute the majority of
fluvial systems on Earth. Their long profiles hold clues to their present
state and past evolution. We currently possess first-principles-based
governing equations for flow, sediment transport, and channel morphodynamics
in these systems, which we lack for detachment-limited bedrock rivers. Here
we formally couple these equations for transport-limited gravel-bed river
long-profile evolution. The result is a new predictive relationship whose
functional form and parameters are grounded in theory and defined through
experimental data. From this, we produce a power-law analytical solution and
a finite-difference numerical solution to long-profile evolution.
Steady-state channel concavity and steepness are diagnostic of external
drivers: concavity decreases with increasing uplift rate, and steepness increases
with an increasing sediment-to-water supply ratio. Constraining free
parameters explains common observations of river form: to match observed
channel concavities, gravel-sized sediments must weather and fine –
typically rapidly – and valleys typically should widen gradually. To match the empirical
square-root width–discharge scaling in equilibrium-width gravel-bed rivers,
downstream fining must occur. The ability to assign a cause to such
observations is the direct result of a deductive approach to developing
equations for landscape evolution.</p
Short communication: <i>age2exhume</i> – a MATLAB/Python script to calculate steady-state vertical exhumation rates from thermochronometric ages and application to the Himalaya
Interpreting cooling ages from multiple thermochronometric systems and/or
from steep elevation transects with the help of a thermal model can provide
unique insights into the spatial and temporal patterns of rock exhumation.
Although several well-established thermal models allow for a detailed
exploration of how cooling or exhumation rates evolved in a limited area or
along a transect, integrating large, regional datasets in such models
remains challenging. Here, we present age2exhume, a thermal model in the
form of a MATLAB or Python script, which can be used to rapidly obtain a
synoptic overview of exhumation rates from large, regional
thermochronometric datasets. The model incorporates surface temperature
based on a defined lapse rate and a local relief correction that is
dependent on the thermochronometric system of interest. Other inputs include
sample cooling age, uncertainty, and an initial (unperturbed) geothermal
gradient. The model is simplified in that it assumes steady, vertical
rock uplift and unchanging topography when calculating exhumation rates. For
this reason, it does not replace more powerful and versatile
thermal–kinematic models, but it has the advantage of simple implementation
and rapidly calculated results. We also provide plots of predicted
exhumation rates as a function of thermochronometric age and the local
relief correction, which can be used to simply look up a first-order
estimate of exhumation rate. In our example dataset, we show exhumation
rates calculated from 1785 cooling ages from the Himalaya associated with
five different thermochronometric systems. Despite the synoptic nature of
the results, they reflect known segmentation patterns and changing
exhumation rates in areas that have undergone structural reorganization.
Moreover, the rapid calculations enable an exploration of the sensitivity of
the results to various input parameters and an illustration of the
importance of explicit modeling of thermal fields when calculating
exhumation rates from thermochronometric data.</p
Detection of Head-to-Tail DNA Sequences of Human Bocavirus in Clinical Samples
Parvoviruses are single stranded DNA viruses that replicate in a so called “rolling-hairpin” mechanism, a variant of the rolling circle replication known for bacteriophages like ϕX174. The replication intermediates of parvoviruses thus are concatemers of head-to-head or tail-to-tail structure. Surprisingly, in case of the novel human bocavirus, neither head-to-head nor tail-to-tail DNA sequences were detected in clinical isolates; in contrast head-to-tail DNA sequences were identified by PCR and sequencing. Thereby, the head-to-tail sequences were linked by a novel sequence of 54 bp of which 20 bp also occur as conserved structures of the palindromic ends of parvovirus MVC which in turn is a close relative to human bocavirus
Tectonic denudation and topographic development in the Spanish Sierra Nevada
The denudation history of the rapidly uplifting western part of the Spanish Sierra Nevada was assessed using apatite fission track (AFT) ages and 10Be analyses of bedrock and fluvial sediments. Major contrasts in the denudation history are recorded within the 27 km2 Río Torrente catchment. Upland areas are characterized by low-relief, low slope angles, and locally the preservation of shallow marine sediments, which have experienced <200 m of erosion in the last 9 Myr. However, AFT age determinations from samples collected close to the marine sediments imply >2 km of denudation since circa 4 Ma. The minimum denudation rates of 0.4 mm yr−1 derived from AFT also contrast with the slow medium-term (104 years) erosion rates (0.044 ± 0.015 mm yr−1) estimated from 10Be measurements at high elevations. The local medium-long-term contrasts in denudation rates within the high Sierra Nevada indicate that much of the unroofing occurs by tectonic denudation on flat-lying detachments. In lower elevation parts of the catchment, rapid river incision coupled to rock uplift has produced ∼1.6 km of relief, implying that the rivers and adjacent hillslopes close to the edge of the orogen are sensitive to normal-fault-driven changes in base level. However, these changes are not transmitted into the low-relief slowly eroding upland areas. Thus the core of the mountain range continues to increase in elevation until the limits of crustal strength are reached and denudation is initiated along planes of structural weakness. We propose that this form of tectonic denudation provides an effective limit to relief in young orogens
Combinations of β-lactam or aminoglycoside antibiotics with plectasin are synergistic against methicillin-sensitive and methicillin-resistant Staphylococcus aureus.
Bacterial infections remain the leading killer worldwide which is worsened by the continuous emergence of antibiotic resistance. In particular, methicillin-sensitive (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) are prevalent and the latter can be difficult to treat. The traditional strategy of novel therapeutic drug development inevitably leads to emergence of resistant strains, rendering the new drugs ineffective. Therefore, rejuvenating the therapeutic potentials of existing antibiotics offers an attractive novel strategy. Plectasin, a defensin antimicrobial peptide, potentiates the activities of other antibiotics such as β-lactams, aminoglycosides and glycopeptides against MSSA and MRSA. We performed in vitro and in vivo investigations to test against genetically diverse clinical isolates of MSSA (n = 101) and MRSA (n = 115). Minimum inhibitory concentrations (MIC) were determined by the broth microdilution method. The effects of combining plectasin with β-lactams, aminoglycosides and glycopeptides were examined using the chequerboard method and time kill curves. A murine neutropenic thigh model and a murine peritoneal infection model were used to test the effect of combination in vivo. Determined by factional inhibitory concentration index (FICI), plectasin in combination with aminoglycosides (gentamicin, neomycin or amikacin) displayed synergistic effects in 76-78% of MSSA and MRSA. A similar synergistic response was observed when plectasin was combined with β-lactams (penicillin, amoxicillin or flucloxacillin) in 87-89% of MSSA and MRSA. Interestingly, no such interaction was observed when plectasin was paired with vancomycin. Time kill analysis also demonstrated significant synergistic activities when plectasin was combined with amoxicillin, gentamicin or neomycin. In the murine models, plectasin at doses as low as 8 mg/kg augmented the activities of amoxicillin and gentamicin in successful treatment of MSSA and MRSA infections. We demonstrated that plectasin strongly rejuvenates the therapeutic potencies of existing antibiotics in vitro and in vivo. This is a novel strategy that can have major clinical implications in our fight against bacterial infections
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
Palaeozoic-Recent geological development and uplift of the Amanos Mountains (S Turkey) in the critically located northwesternmost corner of the Arabian continent
<p>We have carried out a several-year-long study of the Amanos Mountains, on the basis of which we present new sedimentary and structural evidence, which we combine with existing data, to produce the first comprehensive synthesis in the regional geological setting. The ca. N-S-trending Amanos Mountains are located at the northwesternmost edge of the Arabian plate, near the intersection of the African and Eurasian plates. Mixed siliciclastic-carbonate sediments accumulated on the north-Gondwana margin during the Palaeozoic. Triassic rift-related sedimentation was followed by platform carbonate deposition during Jurassic-Cretaceous. Late Cretaceous was characterised by platform collapse and southward emplacement of melanges and a supra-subduction zone ophiolite. Latest Cretaceous transgressive shallow-water carbonates gave way to deeper-water deposits during Palaeocene-Eocene. Eocene southward compression, reflecting initial collision, resulted in open folding, reverse faulting and duplexing. Fluvial, lagoonal and shallow-marine carbonates accumulated during Late Oligocene(?)-Early Miocene, associated with basaltic magmatism. Intensifying collision during Mid-Miocene initiated a foreland basin that then infilled with deep-water siliciclastic gravity flows. Late Miocene-Early Pliocene compression created mountain-sized folds and thrusts, verging E in the north but SE in the south. The resulting surface uplift triggered deposition of huge alluvial outwash fans in the west. Smaller alluvial fans formed along both mountain flanks during the Pleistocene after major surface uplift ended. Pliocene-Pleistocene alluvium was tilted towards the mountain front in the west. Strike-slip/transtension along the East Anatolian Transform Fault and localised sub-horizontal Quaternary basaltic volcanism in the region reflect regional transtension during Late Pliocene-Pleistocene (<4 Ma).</p
Human bocavirus (HBoV) in children with respiratory tract infection by enzyme linked immunosorbent assay (ELISA) and qualitative polymerase chain reaction (PCR)
<p>Abstract</p> <p>Background</p> <p>Human bocavirus (HBoV) is a recently discovered parvovirus associated with mild to severe lower respiratory tract infections in children, the aim of the work was determination of human bocavirus in nasopharyngeal aspirate (NPA) of infants by qualitative PCR and determination of acute human bocavirus infection by estimation of immunoglobulin M (IgM) antibodies in serum by enzyme linked immunosorbent assay.</p> <p>Results</p> <p>Twenty two (22%) out of the 100 NPA specimens of the patients with respiratory manifestations were positive for HBoV by qualitative PCR, while ELISA revealed positive HBoV IgM antibodies in 18 (18%) patients who were also positive by PCR. Non of the controls were positive by both techniques. The correlation study between ELISA and PCR revealed high significant association, (p < 0.001, X<sup>2 </sup>= 36 and agreement = 96%). Also PCR detected 4 (18.1%) NPA samples as HBoV positive cases among the patients that were not identified by ELISA. This could be due to high sensitivity and efficacy of PCR. ELISA being less sensitive than RT-PCR, sensitivity was (81.8% vs 100%), the efficacy was 97.7% in ELISA versus 99.7% for RT-PCR.</p> <p>Conclusion</p> <p>HBoV infections could be diagnosed in NPA of children by conventional PCR as a rapid and sensitive technique. While ELISA was a reliable serologic analysis for diagnosis of acute HBoV infection by estimation IgM antibodies in serum.</p
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente
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