4,425 research outputs found
Tests of mode-coupling theory in two dimensions
We analyze the glassy dynamics of a binary mixtures of hard disks in two
dimensions. Predictions of the Mode-Coupling theory(MCT) are tested with
extensive Brownian dynamics simulations. Measuring the collective particle
density correlation functions in the vicinity of the glass transition we verify
four predicted mixing effects. For instance, for large size disparities, adding
a small amount of small particles at fixed packing fraction leads to a speed up
in the long time dynamics, while at small size disparity it leads to a slowing
down. Qualitative features of the non-ergodicity parameters and the
-relaxation which both depend in a non-trivial way on the mixing ratio
are found in the simulated correlators. Studying one system in detail we are
able to determine its ideal MCT glass transition point as and
test MCT predictions quantitatively.Comment: 12 pages, 18 figure
A twist in the geometry of rotating black holes: seeking the cause of acausality
We investigate Kerr-Newman black holes in which a rotating charged
ring-shaped singularity induces a region which contains closed timelike curves
(CTCs). Contrary to popular belief, it turns out that the time orientation of
the CTC is opposite to the direction in which the singularity or the ergosphere
rotates. In this sense, CTCs "counter-rotate" against the rotating black hole.
We have similar results for all spacetimes sufficiently familiar to us in which
rotation induces CTCs. This motivates our conjecture that perhaps this
counter-rotation is not an accidental oddity particular to Kerr-Newman
spacetimes, but instead there may be a general and intuitively comprehensible
reason for this.Comment: 21 pages, 5 figures; replaced to match published version forthcoming
in General Relativity and Gravitatio
Optical M0bius Strips in Three Dimensional Ellipse Fields: Lines of Linear Polarization
The minor axes of, and the normals to, the polarization ellipses that
surround singular lines of linear polarization in three dimensional optical
ellipse fields are shown to be organized into Mobius strips and into structures
we call rippled rings (r-rings). The Mobius strips have two full twists, and
can be either right- or left-handed. The major axes of the surrounding ellipses
generate cone-like structures. Three orthogonal projections that give rise to
15 indices are used to characterize the different structures. These indices, if
independent, could generate 839,808 geometrically and topologically distinct
lines; selection rules are presented that reduce the number of lines to 8,248,
some 5,562 of which have been observed in a computer simulation. Statistical
probabilities are presented for the most important index combinations in random
fields. It is argued that it is presently feasible to perform experimental
measurements of the Mobius strips, r-rings, and cones described here
theoretically
Glass transition of binary mixtures of dipolar particles in two dimensions
We study the glass transition of binary mixtures of dipolar particles in two
dimensions within the framework of mode-coupling theory, focusing in particular
on the influence of composition changes. In a first step, we demonstrate that
the experimental system of K\"onig et al. [Eur. Phys. J. E 18, 287 (2005)] is
well described by point dipoles through a comparison between the experimental
partial structure factors and those from our Monte Carlo simulation. For such a
mixture of point particles we show that there is always a plasticization
effect, i.e. a stabilization of the liquid state due to mixing, in contrast to
binary hard disks. We demonstrate that the predicted plasticization effect is
in qualitative agreement with experimental results. Furthermore, also some
general properties of the glass transition lines are discussed.Comment: 12 pages, 8 figures, J. Non-Cryst. Solids (in print
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