157 research outputs found
Current Conservation in the Covariant Quark-Diquark Model of the Nucleon
The description of baryons as fully relativistic bound states of quark and
glue reduces to an effective Bethe-Salpeter equation with quark-exchange
interaction when irreducible 3-quark interactions are neglected and separable
2-quark (diquark) correlations are assumed. This covariant quark-diquark model
of baryons is studied with the inclusion of the quark substructure of the
diquark correlations. In order to maintain electromagnetic current conservation
it is then necessary to go beyond the impulse approximation. A conserved
current is obtained by including the coupling of the photon to the exchanged
quark and direct ``seagull'' couplings to the diquark structure. Adopting a
simple dynamical model of constituent quarks and exploring various
parametrisations of scalar diquark correlations, the nucleon Bethe-Salpeter
equation is solved and the proton and neutron electromagnetic form factors are
calculated numerically. The resulting magnetic moments are still about 50% too
small, the improvements necessary to remedy this are discussed. The results
obtained in this framework provide an excellent description of the electric
form factors (and charge radii) of the proton, up to a photon momentum transfer
of 3.5GeV^2, and the neutron.Comment: 30 Pages, LaTeX2e, revised version, minor modifiactions to the text,
some phrases eliminated, some remarks adde
AIOps for a Cloud Object Storage Service
With the growing reliance on the ubiquitous availability of IT systems and
services, these systems become more global, scaled, and complex to operate. To
maintain business viability, IT service providers must put in place reliable
and cost efficient operations support. Artificial Intelligence for IT
Operations (AIOps) is a promising technology for alleviating operational
complexity of IT systems and services. AIOps platforms utilize big data,
machine learning and other advanced analytics technologies to enhance IT
operations with proactive actionable dynamic insight.
In this paper we share our experience applying the AIOps approach to a
production cloud object storage service to get actionable insights into
system's behavior and health. We describe a real-life production cloud scale
service and its operational data, present the AIOps platform we have created,
and show how it has helped us resolving operational pain points.Comment: 5 page
Competing exciton localization effects due to disorder and shallow defects in semiconductor alloys
We demonstrate that excitons in semiconductor alloys are subject
to competing localization effects due to disorder (random potential fluctuations)
and shallow point defects (impurities). The relative importance of these effects
varies with alloy chemical composition, impurity activation energy as well as
temperature. We evaluate this effect quantitatively for MgxZn1−xO : Al (0 6
x 6 0.058) and find that exciton localization at low (2 K) and high (300 K)
temperatures is dominated by shallow donor impurities and alloy disorder,
respectively
MHD simulations of formation, sustainment and loss of Quiescent H-mode in the all-tungsten ASDEX Upgrade
Periodic edge localized modes (ELMs) are the non-linear consequences of
pressure-gradient-driven ballooning modes and current-driven peeling modes
becoming unstable in the pedestal region of high confinement fusion plasmas. In
future tokamaks like ITER, large ELMs are foreseen to severely affect the
lifetime of wall components as they transiently deposit large amounts of heat
onto a narrow region at the divertor targets. Several strategies exist for
avoidance, suppression, or mitigation of these instabilities, such as the
naturally ELM-free quiescent H-mode (QH-mode). In the present article, an ASDEX
Upgrade equilibrium that features a QH-mode is investigated through non-linear
extended MHD simulations covering the dynamics over tens of milliseconds. The
equilibrium is close to the ideal peeling limit and non-linearly develops
saturated modes at the edge of the plasma. A dominant toroidal mode number of
is found, for which the characteristic features of the edge harmonic
oscillation are recovered. The saturated modes contribute to heat and particle
transport preventing pedestal build-up to the ELM triggering threshold. The
non-linear dynamics of the mode, in particular its interaction with the
evolution of the edge safety factor is studied, which suggest a possible new
saturation mechanism for the QH-mode. The simulations show good qualitative and
quantitative agreement to experiments in AUG. In particular, the processes
leading to the termination of QH-mode above a density threshold is studied,
which results in the transition into an ELM regime. In the vicinity of this
threshold, limit cycle oscillations are observed.Comment: Revised version with modifications from review process include
Spatio-temporal evolution of global surface temperature distributions
Climate is known for being characterised by strong non-linearity and chaotic
behaviour. Nevertheless, few studies in climate science adopt statistical
methods specifically designed for non-stationary or non-linear systems. Here we
show how the use of statistical methods from Information Theory can describe
the non-stationary behaviour of climate fields, unveiling spatial and temporal
patterns that may otherwise be difficult to recognize. We study the maximum
temperature at two meters above ground using the NCEP CDAS1 daily reanalysis
data, with a spatial resolution of 2.5 by 2.5 degree and covering the time
period from 1 January 1948 to 30 November 2018. The spatial and temporal
evolution of the temperature time series are retrieved using the Fisher
Information Measure, which quantifies the information in a signal, and the
Shannon Entropy Power, which is a measure of its uncertainty -- or
unpredictability. The results describe the temporal behaviour of the analysed
variable. Our findings suggest that tropical and temperate zones are now
characterized by higher levels of entropy. Finally, Fisher-Shannon Complexity
is introduced and applied to study the evolution of the daily maximum surface
temperature distributions.Comment: 7 pages, 4 figure
Forests for the New Millennium - MAKING FORESTS WORK FOR PEOPLE AND NATURE
THE WAYS IN WHICH FORESTS ARE PERCEIVED AND USED HAVE CHANGED DRAMATICALLY OVER RECENT YEARS. FORESTS ARE NO LONGER SEEN SIMPLY AS A SOURCE OF TIMBER, BUT AS COMPLEX ECOSYSTEMS WHICH SUSTAIN LIVELIHOODS AND PROVIDE A RANGE OF PRODUCTS AND ENVIRONMENTAL SERVICES. IT IS NOW WIDELY RECOGNISED THAT FORESTS CAN CONTRIBUTE TO RURAL DEVELOPMENT AND POVERTY ALLEVIATION.Forest, economics, livelihoods
The combination of autofluorescence endoscopy and molecular biomarkers is a novel diagnostic tool for dysplasia in Barrett's oesophagus.
OBJECTIVE: Endoscopic surveillance for Barrett's oesophagus (BO) is limited by sampling error and the subjectivity of diagnosing dysplasia. We aimed to compare a biomarker panel on minimal biopsies directed by autofluorescence imaging (AFI) with the standard surveillance protocol to derive an objective tool for dysplasia assessment. DESIGN: We performed a cross-sectional prospective study in three tertiary referral centres. Patients with BO underwent high-resolution endoscopy followed by AFI-targeted biopsies. 157 patients completed the biopsy protocol. Aneuploidy/tetraploidy; 9p and 17p loss of heterozygosity; RUNX3, HPP1 and p16 methylation; p53 and cyclin A immunohistochemistry were assessed. Bootstrap resampling was used to select the best diagnostic biomarker panel for high-grade dysplasia (HGD) and early cancer (EC). This panel was validated in an independent cohort of 46 patients. RESULTS: Aneuploidy, p53 immunohistochemistry and cyclin A had the strongest association with dysplasia in the per-biopsy analysis and, as a panel, had an area under the receiver operating characteristic curve of 0.97 (95% CI 0.95 to 0.99) for diagnosing HGD/EC. The diagnostic accuracy for HGD/EC of the three-biomarker panel from AFI+ areas was superior to AFI- areas (p<0.001). Compared with the standard protocol, this panel had equal sensitivity for HGD/EC, with a 4.5-fold reduction in the number of biopsies. In an independent cohort of patients, the panel had a sensitivity and specificity for HGD/EC of 100% and 85%, respectively. CONCLUSIONS: A three-biomarker panel on a small number of AFI-targeted biopsies provides an accurate and objective diagnosis of dysplasia in BO. The clinical implications have to be studied further
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