4,921 research outputs found
A systematic review of the role of non-magnified endoscopy for the assessment of H. pylori infection.
Background There is growing interest in the endoscopic recognition of H. pylori infection, and application to routine practice. We present a systematic review of the current literature regarding diagnosis of H. pylori during standard (non-magnified) endoscopy, including adjuncts such as image enhancement and computer-aided diagnosis. Method The Medline and Cochrane databases were searched for studies investigating the performance of non-magnified optical diagnosis for H. pylori, or those which characterised mucosal features associated with H. pylori infection. Studies were preferred with a validated reference test as the comparator, although were included if at least one validated reference test was used. Results 20 suitable studies were identified and included for analysis. In total, 4,703 patients underwent investigation including white light endoscopy, narrow band imaging, i-scan, blue-laser imaging, and computer-aided diagnostic techniques. The endoscopic features of H. pylori infection observed using each modality are discussed and diagnostic accuracies reported. The Regular Arrangement of Collecting Venules (RAC) is an important predictor of the H. pylori naïve stomach. ‘Mosaic’ and ‘Mottled’ patterns have a positive association with H. pylori infection. The ‘Cracked’ pattern may be a predictor of an H. pylori negative stomach following eradication. Conclusions This review summarises the current progress made in endoscopic diagnosis of H. pylori infection. At present there is no single diagnostic approach that provides validated diagnostic accuracy. Further prospective studies are required, as is the development of a validated classification system. Early studies in Computer-Aided Diagnosis suggest potential for a high level of accuracy but real-time results are awaited
Contribution of Scalar Loops to the Three-Photon Decay of the Z
I corrected 3 mistakes from the first version: that were an omitted Feynman
integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in
eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed
drastically. Doing an expansion in the Higgs mass I show that the matrix
element is identically 0 in the order (MZ/MH)^2, which is due to gauge
invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is
that the scalar contribution to this decay rate is several orders of magnitude
smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail,
OCIP/C-93-5, UQAM-PHE-93/0
Four jet event shapes in electron-positron annihilation
We report next-to-leading order perturbative QCD predictions of 4 jet event
shape variables for the process e+e- \to 4 jets obtained using the general
purpose Monte Carlo EERAD2. This program is based on the known `squared' one
loop matrix elements for the virtual \gamma^* \to 4 parton contribution and
squared matrix elements for 5 parton production. To combine the two distinct
final states numerically we present a hybrid of the commonly used subtraction
and slicing schemes based on the colour antenna structure of the final state
which can be readily applied to other processes. We have checked that the
numerical results obtained with EERAD2 are consistent with next-to-leading
order estimates of the distributions of previously determined four jet-like
event variables. We also report the next-to-leading order scale independent
coefficients for some previously uncalculated observables; the light hemisphere
mass, narrow jet broadening, Aplanarity and the 4 jet transition variables with
respect to the JADE and Geneva jet finding algorithms. For each of these
observables, the next-to-leading order corrections calculated at the physical
scale significantly increase the rate compared to leading order (the K factor
is approximately 1.5 -- 2). With the exception of the 4 jet transition
variables, the published DELPHI data lies well above the O(\alpha_s^3)
predictions. The renormalisation scale uncertainty is still large and in most
cases the data prefers a scale significantly smaller than the physical scale.
This situation is reminiscent of that for three jet shape variables, and should
be improved by the inclusion of power corrections and resummation of large
infrared logarithms.Comment: 41 pages, LaTeX, 16 figures, discussion of Aplanarity adde
Antenna subtraction for jet production observables in full colour at NNLO
We describe the details of the calculation of the full colour NNLO QCD corrections to jet production observables at the LHC with antenna subtraction. All relevant matrix elements for the process pp → jj at NNLO in full colour are colour-decomposed and given in a N and n expansion, making identification of leading and subleading colour contributions transparent. The colour-ordered antenna subtraction method has previously successfully been used to construct the NNLO subtraction terms for processes with up to five partons or in the leading colour approximation. However, it is challenged by the more involved subleading colour structure of the squared matrix elements in processes with six or more partons. Here, we describe the methods needed to successfully construct the NNLO subtraction terms for the subleading colour contributions to dijet production within the antenna subtraction formalism
Antenna subtraction for jet production observables in full colour at NNLO
We describe the details of the calculation of the full colour NNLO QCD corrections to jet production observables at the LHC with antenna subtraction. All relevant matrix elements for the process pp → jj at NNLO in full colour are colour-decomposed and given in a N and n expansion, making identification of leading and subleading colour contributions transparent. The colour-ordered antenna subtraction method has previously successfully been used to construct the NNLO subtraction terms for processes with up to five partons or in the leading colour approximation. However, it is challenged by the more involved subleading colour structure of the squared matrix elements in processes with six or more partons. Here, we describe the methods needed to successfully construct the NNLO subtraction terms for the subleading colour contributions to dijet production within the antenna subtraction formalism
Antenna subtraction for jet production observables in full colour at NNLO
We describe the details of the calculation of the full colour NNLO QCD corrections to jet production observables at the LHC with antenna subtraction. All relevant matrix elements for the process pp → jj at NNLO in full colour are colour-decomposed and given in a N and n expansion, making identification of leading and subleading colour contributions transparent. The colour-ordered antenna subtraction method has previously successfully been used to construct the NNLO subtraction terms for processes with up to five partons or in the leading colour approximation. However, it is challenged by the more involved subleading colour structure of the squared matrix elements in processes with six or more partons. Here, we describe the methods needed to successfully construct the NNLO subtraction terms for the subleading colour contributions to dijet production within the antenna subtraction formalism
The Boson Loop Background to H -> ZZ at Photon-photon Colliders
We have performed a complete one-loop calculation of in the Standard Model, including both gauge bosons and fermions
in the loop. We confirm the large irreducible continuum background from the
-boson loop found by Jikia. We have included the photon-photon luminosity,
and find that the continuum background of transverse boson pairs prohibits
finding a heavy Higgs with mass \gtap 350 GeV in this decay mode.Comment: 16 pages + 4 PS figures included (uuencoded), MAD/PH/77
Intramolecular vibronic dynamics in molecular solids: C60
Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.
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