1,439 research outputs found
Coherent Parton Showers with Local Recoils
We outline a new formalism for dipole-type parton showers which maintain
exact energy-momentum conservation at each step of the evolution. Particular
emphasis is put on the coherence properties, the level at which recoil effects
do enter and the role of transverse momentum generation from initial state
radiation. The formulated algorithm is shown to correctly incorporate coherence
for soft gluon radiation. Furthermore, it is well suited for easing matching to
next-to-leading order calculations.Comment: 24 pages, 3 figure
Next-to-leading order QCD predictions for W+W+jj production at the LHC
Because the LHC is a proton-proton collider, sizable production of two
positively charged W-bosons in association with two jets is possible. This
process leads to a distinct signature of same sign high-pt leptons, missing
energy and jets. We compute the NLO QCD corrections to the QCD-mediated part of
pp -> W+W+jj. These corrections reduce the dependence of the production
cross-section on the renormalization and factorization scale to about +- 10
percent. We find that a large number of W+W+jj events contain a relatively hard
third jet. The presence of this jet should help to either pick up the W+W+jj
signal or to reject it as an unwanted background.Comment: 15 pages, 5 (lovely) figures, v3 accepted for publication in JHEP,
corrects tables in appendi
Inhibition of Phosphodiesterase 3A by Cilostazol Dampens Proinflammatory Platelet Functions
Objective: platelets possess not only haemostatic but also inflammatory properties, which combined are thought to play a detrimental role in thromboinflammatory diseases such as acute coronary syndromes and stroke. Phosphodiesterase (PDE) 3 and -5 inhibitors have demonstrated efficacy in secondary prevention of arterial thrombosis, partially mediated by their antiplatelet action. Yet it is unclear whether such inhibitors also affect platelets’ inflammatory functions. Here, we aimed to examine the effect of the PDE3A inhibitor cilostazol and the PDE5 inhibitor tadalafil on platelet function in various aspects of thromboinflammation. Approach and results: cilostazol, but not tadalafil, delayed ex vivo platelet-dependent fibrin formation under whole blood flow over type I collagen at 1000 s−1. Similar results were obtained with blood from Pde3a deficient mice, indicating that cilostazol effects are mediated via PDE3A. Interestingly, cilostazol specifically reduced the release of phosphatidylserine-positive extracellular vesicles (EVs) from human platelets while not affecting total EV release. Both cilostazol and tadalafil reduced the interaction of human platelets with inflamed endothelium under arterial flow and the release of the chemokines CCL5 and CXCL4 from platelets. Moreover, cilostazol, but not tadalafil, reduced monocyte recruitment and platelet-monocyte interaction in vitro. Conclusions: this study demonstrated yet unrecognised roles for platelet PDE3A and platelet PDE5 in platelet procoagulant and proinflammatory responses
Single-inclusive production of large-pT charged particles in hadronic collisions at TeV energies and perturbative QCD predictions
The single inclusive spectrum of charged particles with transverse momenta
pT=3-150 GeV/c measured at midrapidity by the CDF experiment in
proton-antiproton (p-pbar) collisions at sqrt(s)=1.96 TeV is compared to
next-to-leading order (NLO) perturbative QCD calculations using the most recent
parametrizations of the parton distributions and parton-to-hadron fragmentation
functions. Above pT~20 GeV/c, there is a very sizeable disagreement of the
Tevatron data compared to the NLO predictions and to xT-scaling expectations,
suggesting a problem in the experimental data. We also present the predictions
for the pT-differential charged hadron spectra and the associated theoretical
uncertainties for proton-proton (p-p) collisions at LHC energies
(sqrt(s)=0.9-14 TeV). Two procedures to estimate the charged hadron spectra at
LHC heavy-ion collision energies (sqrt(s)=2.76,5.5 TeV) from p-p measurements
are suggested.Comment: 23 pages, 9 figures. A few text additions. Accepted for publication
in JHE
Improving NLO-parton shower matched simulations with higher order matrix elements
In recent times the algorithms for the simulation of hadronic collisions have
been subject to two substantial improvements: the inclusion, within parton
showering, of exact higher order tree level matrix elements (MEPS) and,
separately, next-to-leading order corrections (NLOPS). In this work we examine
the key criteria to be met in merging the two approaches in such a way that the
accuracy of both is preserved, in the framework of the POWHEG approach to
NLOPS. We then ask to what extent these requirements may be fulfilled using
existing simulations, without modifications. The result of this study is a
pragmatic proposal for merging MEPS and NLOPS events to yield much improved
MENLOPS event samples. We apply this method to W boson and top quark pair
production. In both cases results for distributions within the remit of the NLO
calculations exhibit no discernible changes with respect to the pure NLOPS
prediction; conversely, those sensitive to the distribution of multiple hard
jets assume, exactly, the form of the corresponding MEPS results.Comment: 38 pages, 17 figures. v2: added citations and brief discussion of
related works, MENLOPS prescription localized in a subsection. v3: cited 4
more MEPS works in introduction
PDF dependence of Higgs cross sections at the Tevatron and LHC: response to recent criticism
We respond to some criticism questioning the validity of the current Standard
Model Higgs exclusion limits at the Tevatron, due to the significant dependence
of the dominant production cross section from gluon-gluon fusion on the choice
of parton distribution functions (PDFs) and the strong coupling (alpha_S). We
demonstrate the ability of the Tevatron jet data to discriminate between
different high-x gluon distributions, performing a detailed quantitative
comparison to show that fits not explicitly including these data fail to give a
good description. In this context we emphasise the importance of the consistent
treatment of luminosity uncertainties. We comment on the values of alpha_S
obtained from fitting deep-inelastic scattering data, particularly the
fixed-target NMC data, and we show that jet data are needed for stability. We
conclude that the Higgs cross-section uncertainties due to PDFs and alpha_S
currently used by the Tevatron and LHC experiments are not significantly
underestimated, contrary to some recent claims.Comment: 44 pages, 19 figures. v2: version published in JHEP (paragraph added
at bottom of p.15
The Thermal Design, Characterization, and Performance of the SPIDER Long-Duration Balloon Cryostat
We describe the SPIDER flight cryostat, which is designed to cool six
millimeter-wavelength telescopes during an Antarctic long-duration balloon
flight. The cryostat, one of the largest to have flown on a stratospheric
payload, uses liquid helium-4 to deliver cooling power to stages at 4.2 and 1.6
K. Stainless steel capillaries facilitate a high flow impedance connection
between the main liquid helium tank and a smaller superfluid tank, allowing the
latter to operate at 1.6 K as long as there is liquid in the 4.2 K main tank.
Each telescope houses a closed cycle helium-3 adsorption refrigerator that
further cools the focal planes down to 300 mK. Liquid helium vapor from the
main tank is routed through heat exchangers that cool radiation shields,
providing negative thermal feedback. The system performed successfully during a
17 day flight in the 2014-2015 Antarctic summer. The cryostat had a total hold
time of 16.8 days, with 15.9 days occurring during flight.Comment: 15 pgs, 17 fig
Photon Radiation with MadDipole
We present the automation of a subtraction method for photon radiation using
the dipole formalism within the MadGraph framework. The subtraction terms are
implemented both in dimensional regularization and mass regularization for
massless and massive cases and non-collinear-safe observables are accounted
for.Comment: 23 pages, 2 figures, minor additions, references added, version
published in JHE
Effects of gestational age at birth on cognitive performance : a function of cognitive workload demands
Objective: Cognitive deficits have been inconsistently described for late or moderately preterm children but are consistently found in very preterm children. This study investigates the association between cognitive workload demands of tasks and cognitive performance in relation to gestational age at birth.
Methods: Data were collected as part of a prospective geographically defined whole-population study of neonatal at-risk children in Southern Bavaria. At 8;5 years, n = 1326 children (gestation range: 23–41 weeks) were assessed with the K-ABC and a Mathematics Test.
Results: Cognitive scores of preterm children decreased as cognitive workload demands of tasks increased. The relationship between gestation and task workload was curvilinear and more pronounced the higher the cognitive workload: GA2 (quadratic term) on low cognitive workload: R2 = .02, p<0.001; moderate cognitive workload: R2 = .09, p<0.001; and high cognitive workload tasks: R2 = .14, p<0.001. Specifically, disproportionally lower scores were found for very (<32 weeks gestation) and moderately (32–33 weeks gestation) preterm children the higher the cognitive workload of the tasks. Early biological factors such as gestation and neonatal complications explained more of the variance in high (12.5%) compared with moderate (8.1%) and low cognitive workload tasks (1.7%).
Conclusions: The cognitive workload model may help to explain variations of findings on the relationship of gestational age with cognitive performance in the literature. The findings have implications for routine cognitive follow-up, educational intervention, and basic research into neuro-plasticity and brain reorganization after preterm birth
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