269 research outputs found
On the theory of light scattering in molecular liquids
The theory of light scattering for a system of linear molecules with
anisotropic polarizabilities is considered. As a starting point for our theory,
we express the result of a scattering experiment in VV and VH symmetry as
dynamic correlation functions of tensorial densities with
and . , denote indices of spherical harmonics. To account for all
observed hydrodynamic singularities, a generalization of the theory of
Schilling and Scheidsteger \cite{schilling97} for these correlation functions
is presented, which is capable to describe the light scattering experiments
from the liquid regime to the glassy state. As a microscopic theory it fulfills
all sum rules contrary to previous {\em phenomenological} theories. We
emphasize the importance of the helicity index for the microscopic theory
by showing, that only the existence of components lead to the well known
Rytov dip in liquids and to the appearance of transversal sound waves in VH
symmetry in the deeply supercooled liquid and the glass. Exact expressions for
the phenomenological frequency dependent rotation translation coupling
coefficients of previous theories are derived.Comment: 30 pages including 15 figures, submitted to EPJ B, revised version a
detailed discussion on the depolarization ratio is added and the discussion
on the hydrodynamic analysis is enlarge
Microscopic Dynamics of Hard Ellipsoids in their Liquid and Glassy Phase
To investigate the influence of orientational degrees of freedom onto the
dynamics of molecular systems in its supercooled and glassy regime we have
solved numerically the mode-coupling equations for hard ellipsoids of
revolution. For a wide range of volume fractions and aspect ratios
we find an orientational peak in the center of mass spectra
and about one decade
below a high frequency peak. This orientational peak is the counterpart of a
peak appearing in the quadrupolar spectra and
. The latter peak is almost insensitive on
for close to one, i.e. for weak steric hindrance, and broadens strongly
with increasing . Deep in the glass we find an additional peak between
the orientational and the high frequency peak. We have evidence that this
intermediate peak is the result of a coupling between modes with and
, due to the nondiagonality of the static correlators.Comment: 6 figures, 12 page
A Tableaux Calculus for Reducing Proof Size
A tableau calculus is proposed, based on a compressed representation of
clauses, where literals sharing a similar shape may be merged. The inferences
applied on these literals are fused when possible, which reduces the size of
the proof. It is shown that the obtained proof procedure is sound,
refutationally complete and allows to reduce the size of the tableau by an
exponential factor. The approach is compatible with all usual refinements of
tableaux.Comment: Technical Repor
Dynamical precursor of nematic order in a dense fluid of hard ellipsoids of revolution
We investigate hard ellipsoids of revolution in a parameter regime where no
long range nematic order is present but already finite size domains are formed
which show orientational order. Domain formation leads to a substantial slowing
down of a collective rotational mode which separates well from the usual
microscopic frequency regime. A dynamic coupling of this particular mode into
all other modes provides a general mechanism which explains an excess peak in
spectra of molecular fluids. Using molecular dynamics simulation on up to 4096
particles and on solving the molecular mode coupling equation we investigate
dynamic properties of the peak and prove its orientational origin.Comment: RevTeX4 style, 7 figure
Pseudogap and photoemission spectra in the attractive Hubbard model
Angle-resolved photoemission spectra are calculated microscopically for the
two-dimensional attractive Hubbard model. A system of self-consistent T-matrix
equations are solved numerically in the real-time domain. The single-particle
spectral function has a two-peak structure resulting from the presense of bound
states. The spectral function is suppressed at the chemical potential, leading
to a pseudogap-like behavior. At high temperatures and densities the pseudogap
diminishes and finally disappears; these findings are similar to experimental
observations for the cuprates.Comment: 5 pages, 4 figures, published versio
Diffusion and localization in quantum random resistor networks
The theoretical description of transport in a wide class of novel materials
is based upon quantum percolation and related random resistor network (RRN)
models. We examine the localization properties of electronic states of diverse
two-dimensional quantum percolation models using exact diagonalization in
combination with kernel polynomial expansion techniques. Employing the local
distribution approach we determine the arithmetically and geometrically
averaged densities of states in order to distinguish extended, current carrying
states from localized ones. To get further insight into the nature of
eigenstates of RRN models we analyze the probability distribution of the local
density of states in the whole parameter and energy range. For a recently
proposed RRN representation of graphene sheets we discuss leakage effects.Comment: 6 pages, 4 figure
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