229,371 research outputs found
Do we know how to count powers in pionless and pionful effective field theory?
In this article I summarize recent progress in the effective field theory
approach to low energy nuclear systems, with a focus on the power counting
issue. In the pionless sector, where the power counting is quite well
understood at the nucleon-nucleon (NN) level, I discuss some recent
developments toward few- and many-body calculations. In the pionful sector, I
focus on the actively debated issue of power counting in the NN sector and some
recent developments toward a model-independent NN interaction. Finally, the
scenario that the power counting might depend on the number of particles is
discussed.Comment: 19 pages, 1 figure. Contributions to the EPJA topical issue: The
tower of effective (field) theories and the emergence of nuclear phenomena.
Published versio
Direct Transient Analysis of a Fuze Assembly by Axisymmetric Solid Elements
A fuze assembly, which consists of three major parts, nose, collar and sleeve, was designed to survive severe transverse impact giving a maximum base acceleration of 20.000 G. It is shown that hoop failure occurred in the collar after the impact. They also showed that by bonding the collar to the nose, the collar was able to survive the same impact. To find out the effectiveness of the bonding quantitatively, axisymmetric solid elements TRAPAX and TRIAAX were used in modelling the fuze and direct transient analysis was performed. The dynamic stresses in selected elements on the bonded and unbonded collars were compared. The peak hoop stresses in the unbonded collar were found to be up to three times higher than those in the bonded collar. The NASTRAN results explained the observed hoop failure in the unbonded collar. In addition, static and eigenvalue runs were performed as checks on the models prior to the transient runs. The use of the MPCAX cards and the existence and contributors of the calculated first several nearly identical natural frequencies are addressed
Recent progress towards a chiral effective field theory for the NN system
Since Weinberg's proposal two decades ago, chiral effective field theory in
the NN sector has been developed and applied up to order . In
principle it could provide a model-independent description of nuclear force
from QCD. However, in spite of its huge success, some open issues such as the
renormalization group invariance and power counting, still remain to be solved.
In this talk we refine the chiral effective field theory approach to the NN
system based on a renormalization group analysis. Our results show that a truly
model-independent description of NN system can be obtained by a new power
counting which treats the subleading order corrections perturbatively.Comment: Contribution to the proceedings of the Seventh International
Symposium on Chiral Symmetry in Hadrons and Nuclei, Beijing, October 2013. 4
pages, 1 figur
Fragmentation or Recombination at High p_T?
All hadronization processes, including fragmentation, are shown to proceed
through recombination. The shower partons in a jet turn out to play an
important role in describing the p_T spectra of hadrons produced in heavy-ion
collisions. Due to the recombination of the shower partons with the soft
thermal partons, the structure of jets produced in AA collisions is not the
same as that of jets produced in pp collisions.Comment: Talk given at Quark Matter 200
Remote Sensing of Giant Reed with QuickBird Satellite Imagery
QuickBird high resolution (2.8 m) satellite imagery was
evaluated for distinguishing giant reed (
Arundo donax
L.) infestations
along the Rio Grande in southwest Texas. (PDF has 5 pages.
Power-law Behavior of High Energy String Scatterings in Compact Spaces
We calculate high energy massive scattering amplitudes of closed bosonic
string compactified on the torus. We obtain infinite linear relations among
high energy scattering amplitudes. For some kinematic regimes, we discover that
some linear relations break down and, simultaneously, the amplitudes enhance to
power-law behavior due to the space-time T-duality symmetry in the compact
direction. This result is consistent with the coexistence of the linear
relations and the softer exponential fall-off behavior of high energy string
scattering amplitudes as we pointed out prevously. It is also reminiscent of
hard (power-law) string scatterings in warped spacetime proposed by Polchinski
and Strassler.Comment: 6 pages, no figure. Talk presented by Jen-Chi Lee at Europhysics
Conference (EPS2007), Manchester, England, July 19-25, 2007. To be published
by Journal of Physics: Conference Series
A mathematical model of the effect of a predator on species diversity
Mathematical model determines reaction between new predator and microbe competitor when the competitor is the predator's sole nutrient resource. The model utilizes differential equations to describe the interactions with the specific growth rates, and analyzes these growth rates as they are affected by population density and nutrient concentration
Recursive Integral Method with Cayley Transformation
Recently, a non-classical eigenvalue solver, called RIM, was proposed to
compute (all) eigenvalues in a region on the complex plane. Without solving any
eigenvalue problem, it tests if a region contains eigenvalues using an
approximate spectral projection. Regions that contain eigenvalues are
subdivided and tested recursively until eigenvalues are isolated with a
specified precision. This makes RIM an eigensolver distinct from all existing
methods. Furthermore, it requires no a priori spectral information. In this
paper, we propose an improved version of {\bf RIM} for non-Hermitian eigenvalue
problems. Using Cayley transformation and Arnoldi's method, the computation
cost is reduced significantly. Effectiveness and efficiency of the new method
are demonstrated by numerical examples and compared with 'eigs' in Matlab
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