3,096 research outputs found
Structure and stability of chiral beta-tapes: a computational coarse-grained approach
We present two coarse-grained models of different levels of detail for the
description of beta-sheet tapes obtained from equilibrium self-assembly of
short rationally designed oligopeptides in solution. Here we only consider the
case of the homopolymer oligopeptides with the identical sidegroups attached,
in which the tapes have a helicoid surface with two equivalent sides. The
influence of the chirality parameter on the geometrical characteristics, namely
the diameter, inter-strand distance and pitch, of the tapes have been
investigated. The two models are found to produceequivalent results suggesting
a considerable degree of universality in conformations of the tapes.Comment: 24 pages, 5 PS figures. Accepted to J. Chem. Phy
Two-color interference stabilization of atoms
The effect of interference stabilization is shown to exist in a system of two
atomic levels coupled by a strong two-color laser field, the two frequencies of
which are close to a two-photon Raman-type resonance between the chosen levels,
with open channels of one-photon ionization from both of them. We suggest an
experiment, in which a rather significant (up to 90%) suppression of ionization
can take place and which demonstrates explicitly the interference origin of
stabilization. Specific calculations are made for H and He atoms and optimal
parameters of a two-color field are found. The physics of the effect and its
relation with such well-known phenomena as LICS and population trapping in a
three-level system are discussed.Comment: the paper includes 1 TeX file and 16 picture
Extended symmetrical classical electrodynamics
In the present article, we discuss a modification of classical
electrodynamics in which ``ordinary'' point charges are absent. The modified
equations contain additional terms describing the induced charges and currents.
The densities of the induced charges and currents depend on the vector k and
the vectors of the electromagnetic field E and B. It is shown that the vectors
E and B can be defined in terms of two 4-potentials and the components of k are
the components of the 4-tensor of the third rank. The Lagrangian of modified
electrodynamics is defined. The conditions are derived at which only one
4-potential determines the behavior of the electromagnetic field. It is also
shown that static modified electrodynamics can describe the electromagnetic
field in the inner region of the electric monopole. In the outer region of the
electric monopole the electric field is governed by the Maxwell equations. It
follows from boundary conditions at the interface between the inner and outer
regions of the monopole that the vector k has a discrete spectrum. The electric
and magnetic fields, energy and angular momentum of the monopole are found for
different eigenvalues of k
Three-body properties of low-lying Be resonances
We compute the three-body structure of the lowest resonances of Be
considered as two neutrons around an inert Be core. This is an extension
of the bound state calculations of Be into the continuum spectrum. We
investigate the lowest resonances of angular momenta and parities, ,
and . Surprisingly enough, they all are naturally occurring in
the three-body model. We calculate bulk structure dominated by small distance
properties as well as decays determined by the asymptotic large-distance
structure. Both and have two-body Be-neutron d-wave
structure, while has an even mixture of and d-waves. The
corresponding relative neutron-neutron partial waves are distributed among ,
, and d-waves. The branching ratios show different mixtures of one-neutron
emission, three-body direct, and sequential decays. We argue for spin and
parities, , and , to the resonances at 0.89, 2.03, 5.13,
respectively. The computed structures are in agreement with existing reaction
measurements.Comment: To be published in Physical Review
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