57,185 research outputs found
Relativistic Spin-Flavor States in Light Front Dynamics
Orthonormal spin-flavor wave functions of Lorentz covariant quark models of
the Bakamjian-Thomas type are constructed for nucleon resonances. Three
different bases are presented. The manifestly Lorentz covariant Dirac-Melosh
basis is related to the Pauli-Melosh basis and the symmetrized Bargmann-Wigner
basis that are manifestly orthogonal.Comment: 30 pages, 8 tables, no figs; submitted to Ann.Phys.(NY
Present-day Mars' seismicity predicted from 3-D thermal evolution models of interior dynamics
©2018. American Geophysical UnionThe Interior Exploration using Seismic Investigations, Geodesy and Heat Transport mission, to be launched in 2018, will perform a comprehensive geophysical investigation of Mars in situ. The Seismic Experiment for Interior Structure package aims to detect global and regional seismic events and in turn offer constraints on core size, crustal thickness, and core, mantle, and crustal composition. In this study, we estimate the present‐day amount and distribution of seismicity using 3‐D numerical thermal evolution models of Mars, taking into account contributions from convective stresses as well as from stresses associated with cooling and planetary contraction. Defining the seismogenic lithosphere by an isotherm and assuming two end‐member cases of 573 K and the 1073 K, we determine the seismogenic lithosphere thickness. Assuming a seismic efficiency between 0.025 and 1, this thickness is used to estimate the total annual seismic moment budget, and our models show values between 5.7 × 1016 and 3.9 × 1019 Nm
Association of ultracold double-species bosonic molecules
We report on the creation of heterospecies bosonic molecules, associated from
an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated
magnetic field close to two Feshbach resonances. We measure the binding energy
of the weakly bound molecular states versus the Feshbach field and compare our
results to theoretical predictions. We observe the broadening and asymmetry of
the association spectrum due to thermal distribution of the atoms, and a
frequency shift occurring when the binding energy depends nonlinearly on the
Feshbach field. A simple model is developed to quantitatively describe the
association process. Our work marks an important step forward in the
experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure
Gel Electrophoresis of DNA Knots in Weak and Strong Electric Fields
Gel electrophoresis allows to separate knotted DNA (nicked circular) of equal
length according to the knot type. At low electric fields, complex knots being
more compact, drift faster than simpler knots. Recent experiments have shown
that the drift velocity dependence on the knot type is inverted when changing
from low to high electric fields. We present a computer simulation on a lattice
of a closed, knotted, charged DNA chain drifting in an external electric field
in a topologically restricted medium. Using a simple Monte Carlo algorithm, the
dependence of the electrophoretic migration of the DNA molecules on the type of
knot and on the electric field intensity was investigated. The results are in
qualitative agreement with electrophoretic experiments done under conditions of
low and high electric fields: especially the inversion of the behavior from low
to high electric field could be reproduced. The knot topology imposes on the
problem the constrain of self-avoidance, which is the final cause of the
observed behavior in strong electric field.Comment: 17 pages, 5 figure
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