3,332 research outputs found
Relations between some invariants of algebraic varieties in positive characteristic
We discuss relations between certain invariants of varieties in positive
characteristic, like the a-number and the height of the Artin-Mazur formal
group. We calculate the a-number for Fermat surfacesComment: 13 page
Modelling storm response on gravel beaches using XBeach-G
EPRSC New Understanding and Prediction of Storm Impacts on Gravel beaches (NUPSIG; EP/H040056/1) and Adaptation and Resilience of Coastal Energy Supply (ARCEoS; EP/IO35390/1). The full text is under embargo until 01.12.15. Published by ICE Publishin
A New Limit on the Antiproton Lifetime
Measurements of the cosmic ray pbar/p ratio are compared to predictions from
an inhomogeneous disk-diffusion model of pbar production and propagation within
the Galaxy, combined with a calculation of the modulation of the interstellar
cosmic ray spectra as the particles propagate through the heliosphere to the
Earth. The predictions agree with the observed pbar/p spectrum. Adding a finite
pbar lifetime to the model, we obtain the limit tau_pbar > 0.8 Myr (90 % C.L.).Comment: 13 pages, 3 encapsulated Postscript figures, uses AASTeX; accepted by
Astrophysical Journal; minor change
Fragmentation cross sections of 158 A GeV Pb ions in various targets measured with CR39 nuclear track detectors
We report the measurement of the fragmentation cross sections in high-energy
nucleus-nucleus collisions using the 158 A GeV Pb beam from the CERN-SPS. The
fragments have charges changed from that of the incident projectile nucleus by
, with 8 <\Delta Z <75. The targets range from
polyethylene to lead. Charge identification is made with CR39 nuclear track
detectors, measured with an automatic image analyzer system. The measured
fragmentation cross sections are parameterized with an empirical relation in
terms of the atomic mass of the target, and of the charge of the final
fragment.Comment: 16 pages, 5 figure
Neutrino Physics, Superbeams, and the Neutrino Factory
We summarize what has been learned about the neutrino mass spectrum and
neutrino mixing, identify interesting open questions that can be answered by
accelerator neutrino facilities of the future, and discuss the importance and
physics of answering them.Comment: To appear in the Proceedings of the 4th International Workshop on
Neutrino Factories (Nu Fact 02). LaTeX, 10 pages, 1 eps figur
An ultrashort pulse ultra-violet radiation undulator source driven by a laser plasma wakefield accelerator
Narrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 106 per shot for a 100 period undulator, with a mean peak brilliance of 1 × 1018 photons/s/mrad2/mm2/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs
The Kr2Det project: Search for mass-3 state contribution |U_{e3}|^2 to the electron neutrino using a one reactor - two detector oscillation experiment at Krasnoyarsk underground site
The main physical goal of the project is to search with reactor antineutrinos
for small mixing angle oscillations in the atmospheric mass parameter region
around {\Delta}m^{2}_{atm} ~ 2.5 10^{-3} eV^2 in order to find the element
U_{e3} of the neutrino mixing matrix or to set a new more stringent constraint
(U_{e3} is the contribution of mass-3 state to the electron neutrino flavor
state). To achieve this we propose a "one reactor - two detector" experiment:
two identical antineutrino spectrometers with 50 ton liquid scintillator
targets located at ~100 m and ~1000 m from the Krasnoyarsk underground reactor
(~600 mwe). In no-oscillation case ratio of measured positron spectra of the
\bar{{\nu}_e} + p \to e^{+} + n reaction is energy independent. Deviation from
a constant value of this ratio is the oscillation signature. In this scheme
results do not depend on the exact knowledge of the reactor power, nu_e
spectra, burn up effects, target volumes and, which is important, the
backgrounds can periodically be measured during reactor OFF periods. In this
letter we present the Krasnoyarsk reactor site, give a schematic description of
the detectors, calculate the neutrino detection rates and estimate the
backgrounds. We also outline the detector monitoring and calibration
procedures, which are of a key importance. We hope that systematic
uncertainties will not accede 0.5% and the sensitivity U^{2}_{e3} ~4 10^{-3}
(at {\Delta}m^{2} = 2.5 10^{-3} eV^2) can be achieved.Comment: Latex 2e, 9 pages and 5 ps figure
Moment inversion problem for piecewise D-finite functions
We consider the problem of exact reconstruction of univariate functions with
jump discontinuities at unknown positions from their moments. These functions
are assumed to satisfy an a priori unknown linear homogeneous differential
equation with polynomial coefficients on each continuity interval. Therefore,
they may be specified by a finite amount of information. This reconstruction
problem has practical importance in Signal Processing and other applications.
It is somewhat of a ``folklore'' that the sequence of the moments of such
``piecewise D-finite''functions satisfies a linear recurrence relation of
bounded order and degree. We derive this recurrence relation explicitly. It
turns out that the coefficients of the differential operator which annihilates
every piece of the function, as well as the locations of the discontinuities,
appear in this recurrence in a precisely controlled manner. This leads to the
formulation of a generic algorithm for reconstructing a piecewise D-finite
function from its moments. We investigate the conditions for solvability of the
resulting linear systems in the general case, as well as analyze a few
particular examples. We provide results of numerical simulations for several
types of signals, which test the sensitivity of the proposed algorithm to
noise
Field-Dependent Tilt and Birefringence of Electroclinic Liquid Crystals: Theory and Experiment
An unresolved issue in the theory of liquid crystals is the molecular basis
of the electroclinic effect in the smectic-A phase. Recent x-ray scattering
experiments suggest that, in a class of siloxane-containing liquid crystals, an
electric field changes a state of disordered molecular tilt in random
directions into a state of ordered tilt in one direction. To investigate this
issue, we measure the optical tilt and birefringence of these liquid crystals
as functions of field and temperature, and we develop a theory for the
distribution of molecular orientations under a field. Comparison of theory and
experiment confirms that these materials have a disordered distribution of
molecular tilt directions that is aligned by an electric field, giving a large
electroclinic effect. It also shows that the net dipole moment of a correlated
volume of molecules, a key parameter in the theory, scales as a power law near
the smectic-A--smectic-C transition.Comment: 18 pages, including 9 postscript figures, uses REVTeX 3.0 and
epsf.st
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