1,022 research outputs found
Branched Polymers on the Given-Mandelbrot family of fractals
We study the average number A_n per site of the number of different
configurations of a branched polymer of n bonds on the Given-Mandelbrot family
of fractals using exact real-space renormalization. Different members of the
family are characterized by an integer parameter b, b > 1. The fractal
dimension varies from to 2 as b is varied from 2 to infinity. We
find that for all b > 2, A_n varies as , where
and are some constants, and . We determine the
exponent , and the size exponent (average diameter of polymer
varies as ), exactly for all b > 2. This generalizes the earlier results
of Knezevic and Vannimenus for b = 3 [Phys. Rev {\bf B 35} (1987) 4988].Comment: 24 pages, 8 figure
A Model for Quantum Stochastic Absorption in Absorbing Disordered Media
Wave propagation in coherently absorbing disordered media is generally
modeled by adding a complex part to the real part of the potential. In such a
case, it is already understood that the complex potential plays a duel role; it
acts as an absorber as well as a reflector due to the mismatch of the phase of
the real and complex parts of the potential. Although this model gives expected
results for weakly absorbing disordered media, it gives unphysical results for
the strong absorption regime where it causes the system to behave like a
perfect reflector. To overcome this issue, we develop a model here using
stochastic absorption for the modeling of absorption by "fake", or "side",
channels obviating the need for a complex potential. This model of stochastic
absorption eliminates the reflection that is coupled with the absorption in the
complex potential model and absorption is proportional to the magnitude of the
absorbing parameter. Solving the statistics of the reflection coefficient and
its phase for both the models, we argue that stochastic absorption is a
potentially better way of modeling absorbing disordered media.Comment: 5 pages, 4 figure
Hofstadter butterflies of bilayer graphene
We calculate the electronic spectrum of bilayer graphene in perpendicular
magnetic fields nonperturbatively. To accommodate arbitrary displacements
between the two layers, we apply a periodic gauge based on singular flux
vortices of phase . The resulting Hofstadter-like butterfly plots show a
reduced symmetry, depending on the relative position of the two layers against
each other. The split of the zero-energy relativistic Landau level differs by
one order of magnitude between Bernal and non-Bernal stacking.Comment: updated to refereed and edited versio
Synthesis of phased cylindrical ARC antennas arrays
5 p.International audienceThis paper describes a new approach to synthesize cylindrical antenna arrays controlled by the phase excitation, to synthesize directive lobe and multilobe patterns with steered zero. The proposed method is based on iterative minimization of a function that incorporates constraints imposed in each direction. An 8-element cylindrical antenna has been simulated and tested for various types of beam configurations
Electric Machines: Tool in MATLAB
This chapter presents an educational modeling and parametric study of specific types of transformers, generators, and motors used in power system. Equivalent circuit models are presented and basic equations are developed. Through tests and operating conditions, essential parameters for each presented machine are extracted. Graphical user interface (GUI) on MATLAB software is used to study and analyze each element. GUI allows better comprehension and clearer vision to analyze the performance of each electric machine, thus, a complementary educational tool. In addition, GUI permits optimal collaborative learning situations when linked with the theoretical expansion and, thus, is a teaching process that forges the connection between traditional subjects and science education
BIOSORPTION OF METHYLENE BLUE FROM WASTE WATER USING LEBANESE CYMBOPOGON CITRATUS (CITRONNELLE)
The objective of this study was to investigate the possibility of using Lebanese Cymbopogon citratus stem as an alternative adsorbent for the removal of methylene blue from aqueous solutions. Different parameters such as the effect of initial concentration, pH, adsorbent dose, contact time and temperature were studied. Maximum adsorption capacity (61%) of MB was obtained at PH=6 an initial concentration 200 mg/L after 24h and at 25 ˚C. The adsorption isotherm was better described by a Freundlich model rather than a Langmiur model. Based on these results, it can be concluded that the stems of Cymbopogon citratus is effective as an alternative adsorbent for MB remediation in waste water
Random-phase reservoir and a quantum resistor: The Lloyd model
We introduce phase disorder in a 1D quantum resistor through the formal
device of `fake channels' distributed uniformly over its length such that the
out-coupled wave amplitude is re-injected back into the system, but with a
phase which is random. The associated scattering problem is treated via
invariant imbedding in the continuum limit, and the resulting transport
equation is found to correspond exactly to the Lloyd model. The latter has been
a subject of much interest in recent years. This conversion of the random phase
into the random Cauchy potential is a notable feature of our work. It is
further argued that our phase-randomizing reservoir, as distinct from the well
known phase-breaking reservoirs, induces no decoherence, but essentially
destroys all interference effects other than the coherent back scattering.Comment: 4 pages,5 figure
Decohering d-dimensional quantum resistance
The Landauer scattering approach to 4-probe resistance is revisited for the
case of a d-dimensional disordered resistor in the presence of decoherence. Our
treatment is based on an invariant-embedding equation for the evolution of the
coherent reflection amplitude coefficient in the length of a 1-dimensional
disordered conductor, where decoherence is introduced at par with the disorder
through an outcoupling, or stochastic absorption, of the wave amplitude into
side (transverse) channels, and its subsequent incoherent re-injection into the
conductor. This is essentially in the spirit of B{\"u}ttiker's
reservoir-induced decoherence. The resulting evolution equation for the
probability density of the 4-probe resistance in the presence of decoherence is
then generalised from the 1-dimensional to the d-dimensional case following an
anisotropic Migdal-Kadanoff-type procedure and analysed. The anisotropy, namely
that the disorder evolves in one arbitrarily chosen direction only, is the main
approximation here that makes the analytical treatment possible. A
qualitatively new result is that arbitrarily small decoherence reduces the
localisation-delocalisation transition to a crossover making resistance moments
of all orders finite.Comment: 14 pages, 1 figure, revised version, to appear in Phys. Rev.
BIOSORPTION OF METHYLENE BLUE FROM WASTE WATER USING LEBANESE CYMBOPOGON CITRATUS (CITRONNELLE)
The objective of this study was to investigate the possibility of using Lebanese Cymbopogon citratus stem as an alternative adsorbent for the removal of methylene blue from aqueous solutions. Different parameters such as the effect of initial concentration, pH, adsorbent dose, contact time and temperature were studied. Maximum adsorption capacity (61%) of MB was obtained at PH=6 an initial concentration 200 mg/L after 24h and at 25 ˚C. The adsorption isotherm was better described by a Freundlich model rather than a Langmiur model. Based on these results, it can be concluded that the stems of Cymbopogon citratus is effective as an alternative adsorbent for MB remediation in waste water
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