893 research outputs found
On one master integral for three-loop on-shell HQET propagator diagrams with mass
An exact expression for the master integral I_2 arising in three-loop
on-shell HQET propagator diagrams with mass is derived and its analytical
expansion in the dimensional regularization parameter epsilon is given.Comment: 6 pages, 1 figure; v3: completely re-written, 2 new authors, many new
results, additional reference
Pressure dependence and mechanism of Mn promotion of silica-supported Co catalyst in the Fischer-Tropsch reaction
The mechanism of Mn promotion of a silica-supported Co catalyst in the Fischer-Tropsch reaction has been studied at varying pressures up to 20 bar. IR spectroscopy in combination with DFT calculations suggest adsorbed CO is activated by reaction with an oxygen vacancy in the MnO, which covers the Co surface. This leads to a higher activity, higher CHx coverage and thus higher C5+ and lower CH4 selectivity. Increasing the pressure magnifies the selectivity differences. However, above around 4 bar, the effect of Mn on the selectivities is reversed and the C5+ selectivity is decreased by Mn addition. This is tentatively attributed to Mn promoting the C-O bond dissociation but not the chain growth. Formed monomers have to migrate to stepped sites for chain growth on the Co surface. Whilst this is migration is not impeded by co-adsorbates at low pressure, migration could be hindered by especially the high CO coverage at high pressure
Expanded Access as a source of real-world data: An overview of FDA and EMA approvals
Aims: To identify, characterize and compare all Food and Drug Administration (FDA) and European Medicines Agency (EMA) approvals that included real-world data on efficacy from expanded access (EA) programmes. Methods: Cross-sectional study of FDA (1955–2018) and EMA (1995–2018) regulatory approval documentation. We automated searching for terms related to EA in 22,506 documents using machine learning techniques. We included all approvals where EA terms appeared in the regulatory documentation. Our main outcome was the inclusion of EA data as evidence of clinical efficacy. Characterization was based on approval date, disease area, orphan designation and whether the evidence was supportive or pivotal. Results: EA terms appeared in 693 out of 22,506 (3.1%) documents, which referenced 187 approvals. For 39 approvals, data from EA programmes were used to inform on clinical efficacy. The yearly number of approvals with EA data increased from 1.25 for 1993–2013 to 4.6 from 2014–2018. In 13 cases, these programmes formed the main evidence for approval. Of these, patients in EA programmes formed over half (median 71%, interquartile range: 34–100) of the total patient population available for efficacy evaluation. Almost all (12/13) approvals were granted orphan designation. In 8/13, there were differences between regulators in approval status and valuation of evidence. Strikingly, 4 treatments were granted approval based solely on efficacy from EA. Conclusion: Sponsors and regulators increasingly include real-world data from EA programmes in the efficacy profile of a treatment. The indications of the approved treatments are characterized by orphan designation and high unmet medical need
Modulation formats for multi-core fiber transmission
©2014 Optical Society of America We investigate high dimensional modulation formats for multi-core fibers (MCFs) and spatial superchannels. We show that the low skew variations between MCF cores maybe exploited to generate 'multi-core' formats that offer significant advantages over independently transmitting conventional 4-dimensional formats in each core. We describe how pulse position modulation formats may be transposed to the spatial domain and then investigate a family of modulation formats referred to as core-coding, one of which has the same power and spectral efficiency as polarization switched quaternary phase shift keying but with half of the optical power, potentially improving non-linear tolerance for long distance transmission, albeit at the cost of implementation challenges. Finally, we investigate the application of set-partitioning to multi-core formats using a single-parity check bit transmitted in one quadrature of one polarization in one of the cores and polarization-division multiplexing quadrature phase shift keying data in all remaining cores. We observe that for high core counts, an advantage of almost 3 dB in asymptotic power efficiency may be obtained with negligible impact on spectral efficiency, which translates into experimentally measured reduction in the required optical signal-to-noise ratio of up to 1.8 dB at a bit-error-rate of 10-5 and the same data-rate, and additional transmission reach of up to 20%
Primordial non-Gaussianity in the Bispectrum of the Halo Density Field
The bispectrum vanishes for linear Gaussian fields and is thus a sensitive
probe of non-linearities and non-Gaussianities in the cosmic density field.
Hence, a detection of the bispectrum in the halo density field would enable
tight constraints on non-Gaussian processes in the early Universe and allow
inference of the dynamics driving inflation. We present a tree level derivation
of the halo bispectrum arising from non-linear clustering, non-linear biasing
and primordial non-Gaussianity. A diagrammatic description is developed to
provide an intuitive understanding of the contributing terms and their
dependence on scale, shape and the non-Gaussianity parameter fNL. We compute
the terms based on a multivariate bias expansion and the peak-background split
method and show that non-Gaussian modifications to the bias parameters lead to
amplifications of the tree level bispectrum that were ignored in previous
studies. Our results are in a good agreement with published simulation
measurements of the halo bispectrum. Finally, we estimate the expected signal
to noise on fNL and show that the constraint obtainable from the bispectrum
analysis significantly exceeds the one obtainable from the power spectrum
analysis.Comment: 34 pages, 15 figures, (v3): matches JCAP published versio
Virtual O(\a_s) corrections to the inclusive decay
We present in detail the calculation of the O(\a_s) virtual corrections to
the matrix element for b \to s \g. Besides the one-loop virtual corrections
of the electromagnetic and color dipole operators and , we include
the important two-loop contribution of the four-Fermi operator . By
applying the Mellin-Barnes representation to certain internal propagators, the
result of the two-loop diagrams is obtained analytically as an expansion in
. These results are then combined with existing O(\a_s)
Bremsstrahlung corrections in order to obtain the inclusive rate for B \to X_s
\g. The new contributions drastically reduce the large renormalization scale
dependence of the leading logarithmic result. Thus a very precise Standard
Model prediction for this inclusive process will become possible once also the
corrections to the Wilson coefficients are available.Comment: 29 pages, uses epsfig.sty, 12 postscript figures include
Impact of machine-learning CT-derived fractional flow reserve for the diagnosis and management of coronary artery disease in the randomized CRESCENT trials
Objective: To determine the potential impact of on-site CT-derived fractional flow reserve (CT-FFR) on the diagnostic efficiency and effectiveness of coronary CT angiography (CCTA) in patients with obstructive coronary artery disease (CAD) on CCTA. Methods: This observational cohort study included patients with suspected CAD who had been randomized to cardiac CT in the CRESCENT I and II trials. On-site CT-FFR was blindly performed in all patients with at least one ≥ 50% stenosis on CCTA and no exclusion criteria for CT-FFR. We retrospectively assessed the effect of adding CT-FFR to the CT protocol in patients with a stenosis ≥ 50% on CCTA in terms of diagnostic effectiveness, i.e., the number of additional tests required to determine the final diagnosis, reclassification of the initial management strategy, and invasive coronary angiography (ICA) efficiency, i.e., ICA rate without ≥ 50% CAD. Results: Fifty-three patients out of the 372 patients (14%) had at least one ≥ 50% stenosis on CCTA of whom 42/53 patients (79%) had no exclusion criteria for CT-FFR. CT-FFR showed a hemodynamically significant stenosis (≤ 0.80) in 27/53 patients (51%). The availability of CT-FFR would have reduced the number of patients requiring additional testing by 57%-points compared with CCTA alone (37/53 vs. 7/53, p < 0.001). The initial management strategy would have changed for 30 patients (57%, p < 0.001). Reserving ICA for patients with a CT-FFR ≤ 0.80 would have reduced the number of ICA following CCTA by 13%-points (p = 0.016). Conclusion: Implementation of on-site CT-FFR may change management and improve diagnostic efficiency and effectiveness in patients with obstructive CAD on CCTA. Key Points: • The availability of on-site CT-FFR in the diagnostic evaluation of patients with obstructive CAD on CCTA would have significantly reduced the number of patients requiring additional testing compared with CCTA alone. • The implementation of on-site CT-FFR would have changed the initial management strategy significantly in the patients with obstructive CAD on CCTA. • Restricting ICA to patients with a positive CT-FFR would have significantly reduced the ICA rate in patients with obstructive CAD on CCTA
Linear square-mass trajectories of radially and orbitally excited hadrons in holographic QCD
We consider a new approach towards constructing approximate holographic duals
of QCD from experimental hadron properties. This framework allows us to derive
a gravity dual which reproduces the empirically found linear square-mass
trajectories of universal slope for radially and orbitally excited hadrons.
Conformal symmetry breaking in the bulk is exclusively due to infrared
deformations of the anti-de Sitter metric and governed by one free mass scale
proportional to Lambda_QCD. The resulting background geometry exhibits dual
signatures of confinement and provides the first examples of holographically
generated linear trajectories in the baryon sector. The predictions for the
light hadron spectrum include new relations between trajectory slopes and
ground state masses and are in good overall agreement with experiment.Comment: 33 pages, 5 figures, updated to the extended version published in
JHEP, vector meson bulk potential and metric corrected, comments and
references added, phenomenology and conclusions unchange
The Magnetic Sun: Reversals and Long-Term Variations
A didactic introduction to current thinking on some aspects of the solar
dynamo is given for geophysicists and planetary scientists.Comment: 17 pages, 9 figures; Space Science Rev., in pres
Constraints on the Nucleon Strange Form Factors at Q^2 ~ 0.1 GeV^2
We report the most precise measurement to date of a parity-violating
asymmetry in elastic electron-proton scattering. The measurement was carried
out with a beam energy of 3.03 GeV and a scattering angle =6
degrees, with the result A_PV = -1.14 +/- 0.24 (stat) +/- 0.06 (syst) parts per
million. From this we extract, at Q^2 = 0.099 GeV^2, the strange form factor
combination G_E^s + 0.080 G_M^s = 0.030 +/- 0.025 (stat) +/- 0.006 (syst) +/-
0.012 (FF) where the first two errors are experimental and the last error is
due to the uncertainty in the neutron electromagnetic form factor. This result
significantly improves current knowledge of G_E^s and G_M^s at Q^2 ~0.1 GeV^2.
A consistent picture emerges when several measurements at about the same Q^2
value are combined: G_E^s is consistent with zero while G_M^s prefers positive
values though G_E^s=G_M^s=0 is compatible with the data at 95% C.L.Comment: minor wording changes for clarity, updated references, dropped one
figure to improve focu
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