27,163 research outputs found
Interaction induced dimerization in zigzag single wall carbon nanotubes
We derive a low-energy effective model of metallic zigzag carbon nanotubes at
half filling. We show that there are three important features characterizing
the low-energy properties of these systems: the long-range Coulomb interaction,
umklapp scattering and an explicit dimerization generated by interactions. The
ratio of the dimerization induced gap and the Mott gap induced by the umklapp
interactions is dependent on the radius of the nanotube and can drive the
system through a quantum phase transition with SU(2)_1 quantum symmetry. We
consider the physical properties of the phases on either side of this
transition which should be relevant for realistic nanotubes.Comment: 8 pages, 5 figure
Spectral properties of molecular oligomers. A non-Markovian quantum state diffusion approach
Absorption spectra of small molecular aggregates (oligomers) are considered.
The dipole-dipole interaction between the monomers leads to shifts of the
oligomer spectra with respect to the monomer absorption. The line-shapes of
monomer as well as oligomer absorption depend strongly on the coupling to
vibrational modes. Using a recently developed approach [Roden et. al, PRL 103,
058301] we investigate the length dependence of spectra of one-dimensional
aggregates for various values of the interaction strength between the monomers.
It is demonstrated, that the present approach is well suited to describe the
occurrence of the J- and H-bands
Effective electric field: quantifying the sensitivity of searches for new P,T-odd physics with EuCl6HO
Laboratory-scale precision experiments are a promising approach to searching
for physics beyond the standard model. Non-centrosymmetric solids offer
favorable statistical sensitivity for efforts that search for new fields, whose
interactions violate the discrete parity and time-reversal symmetries. One
example is the electric Cosmic Axion Spin Precession Experiment (CASPEr-e),
which is sensitive to the defining interaction of the QCD axion dark matter
with gluons in atomic nuclei. The effective electric field is the parameter
that quantifies the sensitivity of such experiments to new physics. We describe
the theoretical approach to calculating the effective electric field for
non-centrosymmetric sites in ionic insulating solids. We consider the specific
example of the EuCl6HO crystal, which is a particularly promising
material. The optimistic estimate of the effective electric field for the
Eu isotope in this crystal is 10 MV/cm. The calculation uncertainty is
estimated to be two orders of magnitude, dominated by the evaluation of the
Europium nuclear Schiff moment
Archimedes' law and its corrections for an active particle in a granular sea
We study the origin of buoyancy forces acting on a larger particle moving in
a granular medium subject to horizontal shaking and its corrections before
fluidization. In the fluid limit Archimedes' law is verified; before the limit
memory effects counteract buoyancy, as also found experimentally. The origin of
the friction is an excluded volume effect between active particles, which we
study more exactly for a random walker in a random environment. The same
excluded volume effect is also responsible for the mutual attraction between
bodies moving in the granular medium. Our theoretical modeling proceeds via an
asymmetric exclusion process, i.e., via a dissipative lattice gas dynamics
simulating the position degrees of freedom of a low density granular sea.Comment: 22 pages,5 figure
On Nonlinear Dynamics of the Pendulum with Periodically Varying Length
Dynamic behavior of a weightless rod with a point mass sliding along the rod
axis according to periodic law is studied. This is the pendulum with
periodically varying length which is also treated as a simple model of child's
swing. Asymptotic expressions for boundaries of instability domains near
resonance frequencies are derived. Domains for oscillation, rotation, and
oscillation-rotation motions in parameter space are found analytically and
compared with numerical study. Two types of transitions to chaos of the
pendulum depending on problem parameters are investigated numerically.Comment: 8 pages, 8 figure
Untersuchungen über die Wirkung von Pflanzenextrakten (Echinacea Complex) bei akuter Strahlenkrankheit von Mäusen
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