429 research outputs found
A Brief Introduction to Chiral Perturbation Theory
A brief introduction to the subject of chiral perturbation theory (pt)
is presented, including a discussion of effective field theory and applications
of pt in the arena of purely mesonic interactions as well as in the sector.Comment: 15 pages, talk given at TAPS detector workshop, Rez, Czech Republic,
Sept. 1999, to be published in Czech. J. Phy
Comment on ``Evidence for Narrow Baryon Resonances in Inelastic pp Scattering''
Compton scattering data are sensitive to the existence of low-mass resonances
reported by Tatischeff et al. We show that such states, with their reported
properties, are excluded by previous Compton scattering experiments.Comment: One page, submitted to PR
Endoscopic Resection of Sinonasal Malignancy: A Systematic Review and Meta-analysis
OBJECTIVES: The use of endoscopic approaches for sinonasal malignancy resection has increased, but survival data are limited secondary to disease rarity and new surgical technique. Here we present a systematic review and meta-analysis of endoscopic endonasal resection of sinonasal malignancy.
DATA SOURCES: MEDLINE, PubMed Central, NCBI Bookshelf, Cochrane Library, clinicaltrials.gov, National Guideline Clearinghouse.
REVIEW METHODS: PRISMA/MOOSE guidelines were followed. MeSH terms were "endoscopic" AND ("esthesioneuroblastoma" OR "sinonasal adenocarcinoma" OR "squamous cell carcinoma" OR "sinonasal undifferentiated carcinoma"). For studies in which individual-level data were available, results were obtained by direct pooling. For studies in which only summary Kaplan-Meier curves were available, numerical data were extracted, traced, and aggregated by fitting a Weibull model.
RESULTS: Of 320 studies identified, 35 case series were included (n = 952 patients), with 15 studies analyzed via aggregate modeling and 20 studies analyzed via direct pooling. Two- and 5-year survival rates for patients in aggregate modeling were 87.5% and 72.3%, respectively (mean follow-up: 32.9 months). Two- and 5-year survival for patients in direct pooling were 85.8% and 83.5%, respectively (mean follow-up: 43.0 ± 19.5 months). Significant overall survival difference was found between low- and high-grade cancers (P = .015) but not between low- and high-stage cancers (P = .79).
CONCLUSION: Overall 2- and 5-year survival rates are comparable and sometimes greater than those from open craniofacial resection. Survival rates significantly differ by cancer grade but not stage. Journals and investigators should be encouraged to publish retrospective and prospective case series with staged survival updates based on established guidelines
Cepheid Calibration of the Peak Brightness of SNe Ia -- IX. SN 1989B in NGC 3627
(Abridged) Repeated imaging observations have been made of NGC 3627 with the
HST in 1997/98, over an interval of 58 days. Images were obtained on 12 epochs
in the F555W band and on five epochs in the F814W band. The galaxy hosted the
prototypical, `Branch normal', type Ia supernova SN 1989B. A total of 83
variables have been found, of which 68 are definite Cepheid variables with
periods ranging from 75 days to 3.85 days. The de-reddened distance modulus is
determined to be (m-M)_0= 30.22+/-0.12 (internal uncertainty) using a subset of
the Cepheid data whose reddening and error parameters are secure.
The photometric data of Wells et al. (1994), combined with the Cepheid data
for NGC 3627 give M_B(max)= -19.36+/-0.18 and M_V(max)= -19.34+/-0.16 for SN
1989B. Combined with the previous six calibrations in this program, plus two
additional calibrations determined by others gives the mean absolute magnitudes
at maximum of = -19.48+/-0.07 and = -19.48 +/-0.07 for `Branch
normal' SNe Ia at this interim stage in the calibration program.
The second parameter correlations of M(max) of blue SNe Ia with decay rate,
color at maximum, and Hubble type are re-investigated. The dependence of
on decay rate is non-linear, showing a minimum for decay rates between
1.0< Delta m_15 <1.6. Magnitudes corrected for decay rate show no dependence on
Hubble type, but a dependence on color remains. Correcting both the fiducial
sample of 34 SNe Ia with decay-rate data and the current 8 calibrating SNe Ia
for the correlation with decay rate as well as color gives H_0= 60+/-2
(internal) km/s/Mpc, in both B and V. The same value to within 4% is obtained
if only the SNe Ia in spirals (without second parameter corrections) are
considered.Comment: 32 pages (with 7 tables and 14 figures) LaTeX, uses emulateapj.sty; a
full-resolution version with complete figs. 4 and 5 is available at
http://www.astro.unibas.ch/cosmology/papers.html ; accepted for publication
in Ap
Chiral Perturbation Theory and Nucleon Polarizabilities
Compton scattering offers in principle an intriguing new window on nucleon
structure. Existing experiments and future programs are discussed and the state
of theoretical understanding of such measurements is explored.Comment: 15 page standard Latex file---invited talk at Chiral Dynamics
Workshop, Mainz, Germany---typos correcte
Heating, Ventilating, and Air-Conditioning: Recent Advances in Diagnostics and Controls to Improve Air-Handling System Performance
Measurement of the Electric and Magnetic Polarizabilities of the Proton
The Compton scattering cross section on the proton has been measured at
laboratory angles of 90 and 135 using tagged photons in the
energy range 70--100 MeV and simultaneously using untagged photons in the range
100--148~MeV. With the aid of dispersion relations, these cross sections were
used to extract the electric and magnetic polarizabilities, and
respectively, of the proton. We find
in agreement with a model-independent dispersion sum rule, and
where the errors shown are statistical, systematic, and model-dependent,
respectively. A comparison with previous experiments is given and global values
for the polarizabilities are extracted.Comment: 35 pages, 11 PostScript figures, uses RevTex 3.
Virtual Compton Scattering off the Nucleon in Chiral Perturbation Theory
We investigate the spin-independent part of the virtual Compton scattering
(VCS) amplitude off the nucleon within the framework of chiral perturbation
theory. We perform a consistent calculation to third order in external momenta
according to Weinberg's power counting. With this calculation we can determine
the second- and fourth-order structure-dependent coefficients of the general
low-energy expansion of the spin-averaged VCS amplitude based on gauge
invariance, crossing symmetry and the discrete symmetries. We discuss the
kinematical regime to which our calculation can be applied and compare our
expansion with the multipole expansion by Guichon, Liu and Thomas. We establish
the connection of our calculation with the generalized polarizabilities of the
nucleon where it is possible.Comment: 26 pages, 2 Postscript figures, RevTex using epsfi
Cluster Transformation Coefficients for Structure and Dynamics Calculations in n-Particle Systems: Atoms, Nuclei, and Quarks
The structure and dynamics of an n-particle system are described with coupled
nonlinear Heisenberg's commutator equations where the nonlinear terms are
generated by the two-body interaction that excites the reference vacuum via
particle-particle and particle-hole excitations. Nonperturbative solutions of
the system are obtained with the use of dynamic linearization approximation and
cluster transformation coefficients. The dynamic linearization approximation
converts the commutator chain into an eigenvalue problem. The cluster
coefficients factorize the matrix elements of the (n)-particles or
particle-hole systems in terms of the matrix elements of the (n-1)-systems
coupled to a particle-particle, particle-hole, and hole-hole boson. Group
properties of the particle-particle, particle-hole, and hole-hole permutation
groups simplify the calculation of these coefficients. The particle-particle
vacuum-excitations generate superconductive diagrams in the dynamics of
3-quarks systems. Applications of the model to fermionic and bosonic systems
are discussed.Comment: 13 pages, 5 figures, Wigner Proceedings for Conference Wigner
Centenial Pecs, July 8-12, 200
Dirac-Foldy term and the electromagnetic polarizability of the neutron
We reconsider the Dirac-Foldy contribution to the neutron electric
polarizability. Using a Dirac equation approach to neutron-nucleus scattering,
we review the definitions of Compton continuum (), classical
static (), and Schr\"{o}dinger () polarizabilities
and discuss in some detail their relationship. The latter is the
value of the neutron electric polarizability as obtained from an analysis using
the Schr\"{o}dinger equation. We find in particular , where is the magnitude of the magnetic moment
of a neutron of mass . However, we argue that the static polarizability
is correctly defined in the rest frame of the particle, leading to
the conclusion that twice the Dirac-Foldy contribution should be added to
to obtain the static polarizability .Comment: 11 pages, RevTeX, to appear in Physical Review
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