114 research outputs found
Electromagnetic form factors of the baryon octet in the perturbative chiral quark model
We apply the perturbative chiral quark model at one loop to analyze the
electromagnetic form factors of the baryon octet. The analytic expressions for
baryon form factors, which are given in terms of fundamental parameters of
low-energy pion-nucleon physics (weak pion decay constant, axial nucleon
coupling, strong pion-nucleon form factor), and the numerical results for
baryon magnetic moments, charge and magnetic radii are presented. Our results
are in good agreement with experimental data.Comment: 15 pages, 6 figures, to be published in Eur. Phys. J.
Near-threshold production of omega mesons in the pn -> d omega reaction
The first measurement of the p n -> d omega total cross section has been
achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium
cluster-jet target. The momentum of the fast deuteron was measured in the ANKE
spectrometer at COSY-Juelich and that of the slow "spectator" proton p(sp) from
the p d -> p(sp) d omega reaction in a silicon telescope placed close to the
target. The cross sections lie above those measured for p p -> p p omega but
seem to be below theoretical predictions.Comment: 7 pages, 8 figures; second approach to describe the background has
been added; results changed insignificantly, EPJ in pres
Triangulations and Severi varieties
We consider the problem of constructing triangulations of projective planes
over Hurwitz algebras with minimal numbers of vertices. We observe that the
numbers of faces of each dimension must be equal to the dimensions of certain
representations of the automorphism groups of the corresponding Severi
varieties. We construct a complex involving these representations, which should
be considered as a geometric version of the (putative) triangulations
Assessment and topographic characterization of locoregional recurrences in head and neck tumours
Purpose:
To evaluate the differences between three methods of classification of recurrences in patients with head
and neck tumours treated with Radiation Therapy (RT).
Materials and methods:
367 patients with head and neck tumours were included in the study. Tumour
recurrences were delineated in the CT images taken during patient follow-up and deformable registration was used
to transfer this volume into the planning CT. The methods used to classify recurrences were:
methodCTV
quantified
the intersection volume between the recurrence and the Clinical Target Volume (CTV);
methodTV
quantified the
intersection between the Treated Volume and the recurrence (for method CTV and TV, recurrences were classified
in-field if more than 95% of their volume were inside the volume of interest, marginal if the intersection was
between 20-95% and outfield otherwise); and
methodCOM
was based on the position of the Centre Of Mass of the
recurrence. A dose assessment in the recurrence volume was also made.
Results:
The 2-year Kaplan-Meier locoregional recurrence incidence was 10%. Tumour recurrences occurred in 22
patients in a mean time of 16.5 ± 9.4 months resulting in 28 recurrence volumes. The percentage of in-field recurrences
for methods CTV, TV and COM was 7%, 43% and 50%, respectively. Agreement between the three methods in
characterizing individually in-field and marginal recurrences was found only in six cases. Methods CTV and COM agreed
in 14. The percentage of outfield recurrences was 29% using all methods. For local recurrences (in-field or marginal to
gross disease) the average difference between the prescribed dose and
D
98%
in the recurrence volume was -5.2 ± 3.5%
(range: -10.1%-0.9%).
Conclusions:
The classification of in-field and marginal recurrences is very dependent on the method used to
characterize recurrences. Using methods TV and COM the largest percentage of tumour recurrences occurred in-field in
tissues irradiated with high doses.
Keywords:
Head and neck tumours, Radiation therapy, Characterization of tumour recurrences, Geometric methods,
Dosimetric assessmen
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at 2.76 TeV
We report on the first measurement of the triangular , quadrangular
, and pentagonal charged particle flow in Pb-Pb collisions at 2.76
TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show
that the triangular flow can be described in terms of the initial spatial
anisotropy and its fluctuations, which provides strong constraints on its
origin. In the most central events, where the elliptic flow and
have similar magnitude, a double peaked structure in the two-particle azimuthal
correlations is observed, which is often interpreted as a Mach cone response to
fast partons. We show that this structure can be naturally explained from the
measured anisotropic flow Fourier coefficients.Comment: 10 pages, 4 figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/387
Planck intermediate results I : Further validation of new Planck clusters with XMM-Newton
Peer reviewe
Planck Intermediate Results II: Comparison of SunyaevâZeldovich measurements from Planck and from the Arcminute Microkelvin Imager for 11 galaxy clusters
A comparison is presented of SunyaevâZeldovich measurements for 11 galaxy clusters as obtained by Planck and by the ground-based interferom- eter, the Arcminute Microkelvin Imager. Assuming a universal spherically-symmetric Generalised Navarro, Frenk & White (GNFW) model for the cluster gas pressure profile, we jointly constrain the integrated Compton-Y parameter (Y500) and the scale radius (Ξ500) of each cluster. Our resulting constraints in the Y500 â Ξ500 2D parameter space derived from the two instruments overlap significantly for eight of the clusters, although, overall, there is a tendency for AMI to find the SunyaevâZeldovich signal to be smaller in angular size and fainter than Planck. Significant discrepancies exist for the three remaining clusters in the sample, namely A1413, A1914, and the newly-discovered Planck cluster PLCKESZ G139.59+24.18. The robustness of the analysis of both the Planck and AMI data is demonstrated through the use of detailed simulations, which also discount confusion from residual point (radio) sources and from diffuse astrophysical foregrounds as possible explanations for the discrepancies found. For a subset of our cluster sample, we have investigated the dependence of our results on the assumed pressure profile by repeating the analysis adopting the best-fitting GNFW profile shape which best matches X-ray observations. Adopting the best-fitting profile shape from the X-ray data does not, in general, resolve the discrepancies found in this subset of five clusters. Though based on a small sample, our results suggest that the adopted GNFW model may not be sufficiently flexible to describe clusters universally
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