54 research outputs found
Equi-intensity Distribution of Optical Reflectance in a Fibrous Turbid Medium
doi:10.1364/AO.49.000838Light propagation in a fibrous anisotropic scattering medium is quite different from that in an isotropic medium. Both the anisotropic diffuse equation (ADE) and the continuous time random walk (CTRW) theory predict that the equi-intensity profiles of the surface reflectance have an elliptical shape in a fibrous turbid medium. In this study, we simulated the spatially resolved surface reflectance in a fibrous sample using a Monte Carlo model. A parametric equation was used to quantitatively characterize the geometric profiles of the reflectance patterns. The results indicated that the equi-intensity profiles of surface reflectance had elliptical shapes only when evaluated at distances far away from the incident point. The length ratio of the two orthogonal axes of the ellipse was not affected by the sample optical properties when the ratio of reduced scattering coefficients along the two axes is the same. But the relationship between the aforementioned two ratios was different from the predication of ADE theory. Only for fibers of small sizes did the fitted axes ratios approach the values predicted from the ADE
theory.This project was supported in part by National
Science Foundation (NSF) grant CBET0643190
Resolution of simple singularities yielding particle symmetries in a space-time
A finite subgroup of the conformal group SL(2,C) can be related to invariant
polynomials on a hypersurface in C^3. The latter then carries a simple
singularity, which resolves by a finite iteration of basic cycles of
deprojections. The homological intersection graph of this cycles is the Dynkin
graph of an ADE Lie group. The deformation of the simple singularity
corresponds to ADE symmetry breaking. A 3+1-dimensional topological model of
observation is constructed, transforming consistently under SL(2,C), as an
evolving 3-dimensional system of world tubes, which connect ``possible points
of observation". The existence of an initial singularity for the 4-dimensional
space-time is related to its global topological structure. Associating the
geometry of ADE singularities to the vertex structure of the topological model
puts forward the conjecture on a likewise relation of inner symmetries of
elementary particles to local space-time structure.Comment: 16 pages, LaTe
Rectification by charging -- the physics of contact-induced current asymmetry in molecular conductors
We outline the qualitatively different physics behind charging-induced
current asymmetries in molecular conductors operating in the weakly interacting
self-consistent field (SCF) and the strongly interacting Coulomb Blockade (CB)
regimes. A conductance asymmetry arises in SCF because of the unequal
mean-field potentials that shift a closed-shell conducting level differently
for positive and negative bias. A very different current asymmetry arises for
CB due to the unequal number of open-shell excitation channels at opposite bias
voltages. The CB regime, dominated by single charge effects, typically requires
a computationally demanding many-electron or Fock space description. However,
our analysis of molecular Coulomb Blockade measurements reveals that many novel
signatures can be explained using a {{simpler}} orthodox model that involves an
incoherent sum of Fock space excitations and {\it{hence treats the molecule as
a metallic dot or an island}}. This also reduces the complexity of the Fock
space description by just including various charge configurations only, thus
partially underscoring the importance of electronic structure, while retaining
the essence of the single charge nature of the transport process. We finally
point out, however, that the inclusion of electronic structure and hence
well-resolved Fock space excitations is crucial in some notable examples.Comment: 12 pages, 10 figure
On Structure Constants of Theories
Structure constants of minimal conformal theories are reconsidered. It is
shown that {\it ratios} of structure constants of spin zero fields of a
non-diagonal theory over the same evaluated in the diagonal theory are given by
a simple expression in terms of the components of the eigenvectors of the
adjacency matrix of the corresponding Dynkin diagram. This is proved by
inspection, which leads us to carefully determine the {\it signs} of the
structure constants that had not all appeared in the former works on the
subject. We also present a proof relying on the consideration of lattice
correlation functions and speculate on the extension of these identities to
more complicated theories.Comment: 32 page
Full Counting Statistics of Charge Transfer in Coulomb Blockade Systems
Full counting statistics (FCS) of charge transfer in mesoscopic systems has
recently become a subject of significant interest, since it proves to reveal an
important information about the system which can be hardly assessed by other
means. While the previous research mostly addressed the FCS of non- interacting
systems, the present paper deals with the FCS in the limit of strong
interaction. In this Coulomb blockade limit the electron dynamics is known to
be governed by a master equation. We develop a general scheme to evaluate the
FCS in such case, this being the main result of the work presented. We
illustrate the scheme, by applying it to concrete systems. For generic case of
a single resonant level we establish the equivalence of scattering and master
equation approach to FCS. Further we study a single Coulomb blockade island
with two and three leads attached and compare the FCS in this case with our
recent results concerning an open dot either with two and three terminals. We
demonstrate that Coulomb interaction suppresses the relative probabilities of
large current fluctuations.Comment: 17 pages, 16 figure
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