695 research outputs found
Irreversibility in response to forces acting on graphene sheets
The amount of rippling in graphene sheets is related to the interactions with
the substrate or with the suspending structure. Here, we report on an
irreversibility in the response to forces that act on suspended graphene
sheets. This may explain why one always observes a ripple structure on
suspended graphene. We show that a compression-relaxation mechanism produces
static ripples on graphene sheets and determine a peculiar temperature ,
such that for the free-energy of the rippled graphene is smaller than
that of roughened graphene. We also show that depends on the structural
parameters and increases with increasing sample size.Comment: 4 pages, 4 Figure
Exact Two-Point Correlation Functions of Turbulence Without Pressure in Three-Dimensions
We investigate exact results of isotropic turbulence in three-dimensions when
the pressure gradient is negligible. We derive exact two-point correlation
functions of density in three-dimensions and show that the density-density
correlator behaves as , where . It is shown that, in three-dimensions, the energy
spectrum in the inertial range scales with exponent . We also discuss the time scale for which our
exact results are valid for strong 3D--turbulence in the presence of the
pressure. We confirm our predictions by using the recent results of numerical
calculations and experiment.Comment: 9 pages, latex, no figures, we have corrected the our basic
equations. We predict the inertial-range exponent for the energy spectrum for
3D-turbulence without pressure. We will present the detail of calculation and
the results for 2D-turbulence elsewhere. Also some references are adde
Extended multiplet structure in Logarithmic Conformal Field Theories
We use the process of quantum hamiltonian reduction of SU(2)_k, at rational
level k, to study explicitly the correlators of the h_{1,s} fields in the
c_{p,q} models. We find from direct calculation of the correlators that we have
the possibility of extra, chiral and non-chiral, multiplet structure in the
h_{1,s} operators beyond the `minimal' sector. At the level of the vacuum null
vector h_{1,2p-1}=(p-1)(q-1) we find that there can be two extra non-chiral
fermionic fields. The extra indicial structure present here permeates
throughout the entire theory. In particular we find we have a chiral triplet of
fields at h_{1,4p-1}=(2p-1)(2q-1). We conjecture that this triplet algebra may
produce a rational extended c_{p,q} model. We also find a doublet of fields at
h_{1,3p-1}=(\f{3p}{2}-1)(\f{3q}{2}-1). These are chiral fermionic operators if
p and q are not both odd and otherwise parafermionic.Comment: 24 pages LATEX. Minor corrections and extra reference
Extended chiral algebras in the SU(2)_0 WZNW model
We investigate the W-algebras generated by the integer dimension chiral
primary operators of the SU(2)_0 WZNW model. These have a form almost identical
to that found in the c=-2 model but have, in addition, an extended Kac-Moody
structure. Moreover on Hamiltonian reduction these SU(2)_0 W-algebras exactly
reduce to those found in c=-2. We explicitly find the free field
representations for the chiral j=2 and j=3 operators which have respectively a
fermionic doublet and bosonic triplet nature. The correlation functions of
these operators accounts for the rational solutions of the
Knizhnik-Zamolodchikov equation that we find. We explicitly compute the full
algebra of the j=2 operators and find that the associativity of the algebra is
only guaranteed if certain null vectors decouple from the theory. We conjecture
that these algebras may produce a quasi-rational conformal field theory.Comment: 18 pages LATEX. Minor corrections. Full j=2 algebra adde
Uncertainty in the Fluctuations of the Price of Stocks
We report on a study of the Tehran Price Index (TEPIX) from 2001 to 2006 as
an emerging market that has been affected by several political crises during
the recent years, and analyze the non-Gaussian probability density function
(PDF) of the log returns of the stocks' prices. We show that while the average
of the index did not fall very much over the time period of the study, its
day-to-day fluctuations strongly increased due to the crises. Using an approach
based on multiplicative processes with a detrending procedure, we study the
scale-dependence of the non-Gaussian PDFs, and show that the temporal
dependence of their tails indicates a gradual and systematic increase in the
probability of the appearance of large increments in the returns on approaching
distinct critical time scales over which the TEPIX has exhibited maximum
uncertainty.Comment: 5 pages, 5 figures. Accepted to appear in IJMP
Logarithmic conformal field theory with boundary
This lecture note covers topics on boundary conformal field theory, modular
transformations and the Verlinde formula, and boundary logarithmic CFT. An
introductory review on CFT with boundary and a discussion of its applications
to logarithmic cases are given. LCFT at is mainly discussed.Comment: 38 pages, 4 figures, LaTeX. Notes of lectures at the International
Summer School on Logarithmic Conformal Field Theory and its Applications,
Sept. 2001, IPM, Tehran. Typos fixe
Controlling surface statistical properties using bias voltage: Atomic force microscopy and stochastic analysis
The effect of bias voltages on the statistical properties of rough surfaces
has been studied using atomic force microscopy technique and its stochastic
analysis. We have characterized the complexity of the height fluctuation of a
rough surface by the stochastic parameters such as roughness exponent, level
crossing, and drift and diffusion coefficients as a function of the applied
bias voltage. It is shown that these statistical as well as microstructural
parameters can also explain the macroscopic property of a surface. Furthermore,
the tip convolution effect on the stochastic parameters has been examined.Comment: 8 pages, 11 figures
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