5,599 research outputs found
Generalized Hamilton-Jacobi equations for nonholonomic dynamics
Employing a suitable nonlinear Lagrange functional, we derive generalized
Hamilton-Jacobi equations for dynamical systems subject to linear velocity
constraints. As long as a solution of the generalized Hamilton-Jacobi equation
exists, the action is actually minimized (not just extremized)
Interaction of Conical Membrane Inclusions: Effect of Lateral Tension
Considering two rigid conical inclusions embedded in a membrane subject to
lateral tension, we study the membrane-mediated interaction between these
inclusions that originates from the hat-shaped membrane deformations associated
with the cones. At non-vanishing lateral tensions, the interaction is found to
depend on the orientation of the cones with respect to the membrane plane. The
interaction of inclusions of equal orientation is repulsive at all distances
between them, while the inclusions of opposite orientation repel each other at
small separations, but attract each other at larger ones. Both the repulsive
and attractive forces become stronger with increasing lateral tension. This is
different from what has been predicted on the basis of the same static model
for the case of vanishing lateral tension. Without tension, the inclusions
repel each other at all distances independently of their relative orientation.
We conclude that lateral tension may induce the aggregation of conical membrane
inclusions.Comment: 10 pages (revtech), 5 figures (postscript
Calculation of isotope shifts and relativistic shifts in CI, CII, CIII and CIV
We present an accurate ab initio method of calculating isotope shifts and
relativistic shifts in atomic spectra. We test the method on neutral carbon and
three carbon ions. The relativistic shift of carbon lines may allow them to be
included in analyses of quasar absorption spectra that seek to measure possible
variations in the fine structure constant, alpha, over the lifetime of the
Universe. Carbon isotope shifts can be used to measure isotope abundances in
gas clouds: isotope abundances are potentially an important source of
systematic error in the alpha-variation studies. These abundances are also
needed to study nuclear reactions in stars and supernovae, and test models of
chemical evolution of the Universe
Precision calculation of energy levels for four-valent Si I
We report results of the calculation of the low-lying levels of neutral Si
using a combination of the configuration interaction and many-body perturbation
theory (CI+MBPT method). We treat Si I as an atom with four valence electrons
and use two different starting approximations, namely and .
We conclude that both approximations provide comparable accuracy, on the level
of 1%
Enhancement of the electric dipole moment of the electron in PbO
The a(1) state of PbO can be used to measure the electric dipole moment of
the electron d_e. We discuss a semiempirical model for this state, which yields
an estimate of the effective electric field on the valence electrons in PbO.
Our final result is an upper limit on the measurable energy shift, which is
significantly larger than was anticipated earlier: .Comment: 4 pages, revtex4, no figures, submitted to PR
Hyperfine quenching of the metastable states in divalent atoms
Hyperfine quenching rates of the lowest-energy metastable and
states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried
out using ab initio relativistic many-body methods. The computed lifetimes may
be useful for designing novel ultra-precise optical clocks and trapping
experiments with the fermionic isotopes. The resulting natural widths of
the clock transition are 0.44 mHz for Mg, 2.2 mHz for
Ca, 7.6 mHz for Sr, 43.5 mHz for Yb, and 38.5 mHz for
Yb. Compared to the bosonic isotopes, the lifetime of the states
in fermionic isotopes is noticeably shortened by the hyperfine quenching but
still remains long enough for trapping experiments.Comment: 10 pages, 1 figure, submitted to Phys. Rev.
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