10,560 research outputs found
On the spectrum of the magnetohydrodynamic mean-field alpha^2-dynamo operator
The existence of magnetohydrodynamic mean-field alpha^2-dynamos with
spherically symmetric, isotropic helical turbulence function alpha is related
to a non-self-adjoint spectral problem for a coupled system of two singular
second order ordinary differential equations. We establish global estimates for
the eigenvalues of this system in terms of the turbulence function alpha and
its derivative alpha'. They allow us to formulate an anti-dynamo theorem and a
non-oscillation theorem. The conditions of these theorems, which again involve
alpha and alpha', must be violated in order to reach supercritical or
oscillatory regimes.Comment: 35 pages, 4 figures, to be published in SIAM J. Math. Anal
Radial flow afterburner for event generators and the baryon puzzle
A simple afterburner including radial flow to the randomized transverse
momentum obtained from event generators, Pythia and Hijing, has been
implemented to calculate the ratios and compare them with available
data. A coherent trend of qualitative agreement has been obtained in
collisions and in for various centralities. Those results indicate that
the radial flow does play an important role in the so called baryon puzzle
anomaly.Comment: 11 pages, 5 figures. To appear in Journal of Physics
Parametric Feedback Resonance in Chaotic Systems
If one changes the control parameter of a chaotic system proportionally to the distance between an arbitrary point on the strange attractor and the actual trajectory, the lifetime τ of the most stable unstable periodic orbit in the vicinity of this point starts to diverge with a power law. The volume in parameter space where τ becomes infinite is finite and from its nonfractal boundaries one can determine directly the local Liapunov exponents. The experimental applicability of the method is demonstrated for two coupled diode resonators
Reducing the Probability of False Positive Research Findings by Pre-Publication Validation - Experience with a Large Multiple Sclerosis Database
*Objective*
We have assessed the utility of a pre-publication validation policy in reducing the probability of publishing false positive research findings. 
*Study design and setting*
The large database of the Sylvia Lawry Centre for Multiple Sclerosis Research was split in two parts: one for hypothesis generation and a validation part for confirmation of selected results. We present case studies from 5 finalized projects that have used the validation policy and results from a simulation study.
*Results*
In one project, the "relapse and disability" project as described in section II (example 3), findings could not be confirmed in the validation part of the database. The simulation study showed that the percentage of false positive findings can exceed 20% depending on variable selection. 
*Conclusion*
We conclude that the validation policy has prevented the publication of at least one research finding that could not be validated in an independent data set (and probably would have been a "true" false-positive finding) over the past three years, and has led to improved data analysis, statistical programming, and selection of hypotheses. The advantages outweigh the lost statistical power inherent in the process
Hydrodynamic emission of strange and non-strange particles at RHIC and LHC
The hydrodynamic model is used to describe the single-particle spectra and
elliptic flow of hadrons at RHIC and to predict the emission angle dependence
of HBT correlations at RHIC and LHC energies.Comment: 6 pages LaTeX, 3 postscript figures. Proceedings for the conference
"Strange Quark Matter 2003", Atlantic Beach, NC, March 12-17, 2003, to appear
in J. Phys.
Final state interactions in two-particle interferometry
We reconsider the influence of two-particle final state interactions (FSI) on
two-particle Bose-Einstein interferometry. We concentrate in particular on the
problem of particle emission at different times. Assuming chaoticity of the
source, we derive a new general expression for the symmetrized two-particle
cross section. We discuss the approximations needed to derive from the general
result the Koonin-Pratt formula. Introducing a less stringent version of the
so-called smoothness approximation we also derive a more accurate formula. It
can be implemented into classical event generators and allows to calculate FSI
corrected two-particle correlation functions via modified Bose-Einstein
"weights".Comment: 12 pages RevTeX, 2 ps-figures included, submitted to Phys. Rev.
Quasifission and fusion-fission in massive nuclei reactions. Comparison of reactions leading to the Z=120 element
The yields of evaporation residues, fusion-fission and quasifission fragments
in the Ca+Sm and O+W reactions are analyzed
in the framework of the combined theoretical method based on the dinuclear
system concept and advanced statistical model. The measured yields of
evaporation residues for the Ca+Sm reaction can be well
reproduced. The measured yields of fission fragments are decomposed into
contributions coming from fusion-fission, quasifission, and fast-fission. The
decrease in the measured yield of quasifission fragments in
Ca+Sm at the large collision energies and the lack of
quasifission fragments in the Ca+Sm reaction are explained by
the overlap in mass-angle distributions of the quasifission and fusion-fission
fragments. The investigation of the optimal conditions for the synthesis of the
new element =120 (=302) show that the Cr+Cm reaction is
preferable in comparison with the Fe+Pu and Ni+U
reactions because the excitation function of the evaporation residues of the
former reaction is some orders of magnitude larger than that for the last two
reactions.Comment: 27 pages, 12 figures, submitted to Phys. Rev.
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