1,266 research outputs found
Fringe field simulations of a non-scaling FFAG accelerator
Fixed-field Alternating Gradient (FFAG) accelerators offer the potential of
high-quality, moderate energy ion beams at low cost. Modeling of these
structures is challenging with conventional beam tracking codes because of the
large radial excursions of the beam and the significance of fringe field
effects. Numerous tune resonances are crossed during the acceleration, which
would lead to beam instability and loss in a storage ring. In a non-scaling
FFAG, the hope is that these resonances can be crossed sufficiently rapidly to
prevent beam loss. Simulations are required to see if this is indeed the case.
Here we simulate a non-scaling FFAG which accelerates protons from 31 to 250
MeV. We assume only that the bending magnets have mid-plane symmetry, with
specified vertical bending field in the mid-plane (y=0). The magnetic field can
be obtained everywhere using a power series expansion, and we develop
mathematical tools for calculating this expansion to arbitrary order when the
longitudinal field profile is given by an Enge function. We compare the use of
a conventional hard-edge fringe with a more accurate, soft-edge fringe field
model. The tune 1/3 resonance is the strongest, and crossing it in the
hard-edge fringe model results in a 21% loss of the beam. Using the soft-edge
fringe model the beam loss is less than 6%.Comment: 12 pages; 12 figure
Surface superconducting states in a polycrystalline MgB sample
We report results of dc magnetic and ac linear low-frequency study of a
polycrystalline MgB sample. AC susceptibility measurements at low
frequencies, performed under dc fields parallel to the sample surface, provide
a clear evidence for surface superconducting states in MgB.Comment: 4 pages and 5 figure
Small-sample corrections for score tests in Birnbaum-Saunders regressions
In this paper we deal with the issue of performing accurate small-sample
inference in the Birnbaum-Saunders regression model, which can be useful for
modeling lifetime or reliability data. We derive a Bartlett-type correction for
the score test and numerically compare the corrected test with the usual score
test, the likelihood ratio test and its Bartlett-corrected version. Our
simulation results suggest that the corrected test we propose is more reliable
than the other tests.Comment: To appear in the Communications in Statistics - Theory and Methods,
http://www.informaworld.com/smpp/title~content=t71359723
Luminous superclusters: remnants from inflation
We derive the luminosity and multiplicity functions of superclusters compiled
for the 2dF Galaxy Redshift Survey, the Sloan Digital Sky Survey (Data Release
4), and for three samples of simulated superclusters. We find for all
supercluster samples Density Field (DF) clusters, which represent high-density
peaks of the class of Abell clusters, and use median luminosities/masses of
richness class 1 DF-clusters to calculate relative luminosity/mass functions.
We show that the fraction of very luminous (massive) superclusters in real
samples is more than tenfolds greater than in simulated samples. Superclusters
are generated by large-scale density perturbations which evolve very slowly.
The absence of very luminous superclusters in simulations can be explained
either by non-proper treatment of large-scale perturbations, or by some yet
unknown processes in the very early Universe.Comment: 6 pages, 3 Figures, submitted for Astronomy and Astrophysic
Marketing live broilers in New York City, Bulletin, no. 234
The Bulletin is a publication of the New Hampshire Agricultural Experiment Station, College of Life Sciences and Agriculture, University of New Hampshire, Durham, New Hampshire
Book Reviews
Book reviews by Felix Morley, Aaron I. Abell, Thomas M. Scanlon, Anton-Hermann Chroust, and Richard O\u27Sullivan
Superclusters of galaxies from the 2dF redshift survey. I. The catalogue
We use the 2dF Galaxy Redshift Survey data to compile catalogues of
superclusters for the Northern and Southern regions of the 2dFGRS, altogether
543 superclusters at redshifts 0.009 < z < 0.2. We analyse methods of compiling
supercluster catalogues and use results of the Millennium Simulation to
investigate possible selection effects and errors. We find that the most
effective method is the density field method using smoothing with an
Epanechnikov kernel of radius 8 Mpc/h. We derive positions of the highest
luminosity density peaks and find the most luminous cluster in the vicinity of
the peak, this cluster is considered as the main cluster and its brightest
galaxy the main galaxy of the supercluster. In catalogues we give equatorial
coordinates and distances of superclusters as determined by positions of their
main clusters. We also calculate the expected total luminosities of the
superclusters.Comment: 16 pages, 11 figures, submitted for Astronomy and Astrophysics.
High-resolution pdf file and supplementary data can be found at
http://www.aai.ee/~maret/2dfscl.htm
Book Reviews
Book reviews by Edward F. Barrett, Alfred L. Scanlan, Robert T. Molloy, Aaron I. Abell, and Robert E. Sullivan
Book Reviews
Book reviews by Aaron I. Abell, John W. Curran, Louis Charles Kaplan, Robert T. Molloy, R. W. Mulligan, Alfred Long Scanlan, John H. Sheehan, and Robert E. Sullivan
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