2,200 research outputs found
Simultaneous Ejection of Six Electrons at a Constant Potential by Hexakis(4-ferrocenylphenyl)benzene
A simple synthesis of a dendritic hexaferrocenyl electron donor (5) is described in which six ferrocene moieties are connected at the vertices of the propeller of the hexaphenylbenzene core. The molecular structure of 5 is confirmed by X-ray crystallography. An electrochemical analysis along with redox titrations (which are tantamount to coulometry) confirmed that it ejects six electrons at a single potential
Green-Kubo formula for heat conduction in open systems
We obtain an exact Green-Kubo type linear response result for the heat
current in an open system. The result is derived for classical Hamiltonian
systems coupled to heat baths. Both lattice models and fluid systems are
studied and several commonly used implementations of heat baths, stochastic as
well as deterministic, are considered. The results are valid in arbitrary
dimensions and for any system sizes. Our results are useful for obtaining the
linear response transport properties of mesoscopic systems. Also we point out
that for systems with anomalous heat transport, as is the case in
low-dimensional systems, the use of the standard Green-Kubo formula is
problematic and the open system formula should be used.Comment: 4 page
Tailoring symmetry groups using external alternate fields
Macroscopic systems with continuous symmetries subjected to oscillatory
fields have phases and transitions that are qualitatively different from their
equilibrium ones. Depending on the amplitude and frequency of the fields
applied, Heisenberg ferromagnets can become XY or Ising-like -or, conversely,
anisotropies can be compensated -thus changing the nature of the ordered phase
and the topology of defects. The phenomena can be viewed as a dynamic form of
"order by disorder".Comment: 4 pages, 2 figures finite dimension and selection mechanism clarifie
Distribution of sizes of erased loops of loop-erased random walks in two and three dimensions
We show that in the loop-erased random walk problem, the exponent
characterizing probability distribution of areas of erased loops is
superuniversal. In d-dimensions, the probability that the erased loop has an
area A varies as A^{-2} for large A, independent of d, for 2 <= d <= 4. We
estimate the exponents characterizing the distribution of perimeters and areas
of erased loops in d = 2 and 3 by large-scale Monte Carlo simulations. Our
estimate of the fractal dimension z in two-dimensions is consistent with the
known exact value 5/4. In three-dimensions, we get z = 1.6183 +- 0.0004. The
exponent for the distribution of durations of avalanche in the
three-dimensional abelian sandpile model is determined from this by using
scaling relations.Comment: 25 pages, 1 table, 8 figure
From Gravitons to Giants
We discuss exact quantization of gravitational fluctuations in the half-BPS
sector around AdSS background, using the dual super Yang-Mills
theory. For this purpose we employ the recently developed techniques for exact
bosonization of a finite number of fermions in terms of bosonic
oscillators. An exact computation of the three-point correlation function of
gravitons for finite shows that they become strongly coupled at
sufficiently high energies, with an interaction that grows exponentially in
. We show that even at such high energies a description of the bulk physics
in terms of weakly interacting particles can be constructed. The single
particle states providing such a description are created by our bosonic
oscillators or equivalently these are the multi-graviton states corresponding
to the so-called Schur polynomials. Both represent single giant graviton states
in the bulk. Multi-particle states corresponding to multi-giant gravitons are,
however, different, since interactions among our bosons vanish identically,
while the Schur polynomials are weakly interacting at high enough energies.Comment: v2-references added, minor changes and typos corrected; 24 pages,
latex, 3 epsf figure
Word Processors with Line-Wrap: Cascading, Self-Organized Criticality, Random Walks, Diffusion, Predictability
We examine the line-wrap feature of text processors and show that adding
characters to previously formatted lines leads to the cascading of words to
subsequent lines and forms a state of self-organized criticality. We show the
connection to one-dimensional random walks and diffusion problems, and we
examine the predictability of catastrophic cascades.Comment: 6 pages, LaTeX with RevTeX package, 4 postscript figures appende
Velocity Correlations, Diffusion and Stochasticity in a One-Dimensional System
We consider the motion of a test particle in a one-dimensional system of
equal-mass point particles. The test particle plays the role of a microscopic
"piston" that separates two hard-point gases with different concentrations and
arbitrary initial velocity distributions. In the homogeneous case when the
gases on either side of the piston are in the same macroscopic state, we
compute and analyze the stationary velocity autocorrelation function C(t).
Explicit expressions are obtained for certain typical velocity distributions,
serving to elucidate in particular the asymptotic behavior of C(t). It is shown
that the occurrence of a non-vanishing probability mass at zero velocity is
necessary for the occurrence of a long-time tail in C(t). The conditions under
which this is a tail are determined. Turning to the inhomogeneous
system with different macroscopic states on either side of the piston, we
determine its effective diffusion coefficient from the asymptotic behavior of
the variance of its position, as well as the leading behavior of the other
moments about the mean. Finally, we present an interpretation of the effective
noise arising from the dynamics of the two gases, and thence that of the
stochastic process to which the position of any particle in the system reduces
in the thermodynamic limit.Comment: 22 files, 2 eps figures. Submitted to PR
Dimensional structural constants from chiral and conformal bosonization of QCD
We derive the dimensional non-perturbative part of the QCD effective action
for scalar and pseudoscalar meson fields by means of chiral and conformal
bosonization. The related structural coupling constants L_5 and L_8 of the
chiral lagrangian are estimated using general relations which are valid in a
variety of chiral bosonization models without explicit reference to model
parameters. The asymptotics for large scalar fields in QCD is elaborated, and
model-independent constraints on dimensional coupling constants of the
effective meson lagrangian are evaluated. We determine also the interaction
between scalar quarkonium and the gluon density and obtain the scalar
glueball-quarkonium potential.Comment: 21 pages, LaTe
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