2,439 research outputs found
Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects
Investigations of the magnetic properties of graphenes prepared by different
methods reveal that dominant ferromagnetic interactions coexist along with
antiferromagnetic interactions in all the samples. Thus, all the graphene
samples exhibit room-temperature magnetic hysteresis. The magnetic properties
depend on the number of layers and the sample area, small values of both
favoring larger magnetization. Molecular charge-transfer affects the magnetic
properties of graphene, interaction with a donor molecule such as
tetrathiafulvalene having greater effect than an electron-withdrawing molecule
such as tetracyanoethyleneComment: 16 pges, 5 figure
The conditional tunneling time for reflection using the WKB wave-function
We derive an expression for the conditional time for the reflection of a wave
from an arbitrary potential barrier using the WKB wavefunction in the barrier
region. Our result indicates that the conditional times for transmission and
reflection are equal for a symmetric barrier within the validity of the WKB
approach.Comment: 4 pages RevTeX, 1 eps figure include
Time for pulse traversal through slabs of dispersive and negative (, ) materials
The traversal times for an electromagnetic pulse traversing a slab of
dispersive and dissipative material with negative dielectric permittivity
() and magnetic permeability () have been calculated by using
the average flow of electromagnetic energy in the medium. The effects of
bandwidth of the pulse and dissipation in the medium have been investigated.
While both large bandwidth and large dissipation have similar effects in
smoothening out the resonant features that appear due to Fabry-P\'{e}rot
resonances, large dissipation can result in very small or even negative
traversal times near the resonant frequencies. We have also investigated the
traversal times and Wigner delay times for obliquely incident pulses and
evanescent pulses. The coupling to slab plasmon polariton modes in frequency
ranges with negative or is shown to result in large traversal
times at the resonant conditions. We also find that the group velocity mainly
contributes to the delay times for pulse propagating across a slab with n=-1.
We have checked that the traversal times are positive and subluminal for pulses
with sufficiently large bandwidths.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Complete controllability of quantum systems
Sufficient conditions for complete controllability of -level quantum
systems subject to a single control pulse that addresses multiple allowed
transitions concurrently are established. The results are applied in particular
to Morse and harmonic-oscillator systems, as well as some systems with
degenerate energy levels. Morse and harmonic oscillators serve as models for
molecular bonds, and the standard control approach of using a sequence of
frequency-selective pulses to address a single transition at a time is either
not applicable or only of limited utility for such systems.Comment: 8 pages, expanded and revised versio
Quenching of fluorescence of aromatic molecules by graphene due to electron transfer
Investigations on the fluorescence quenching of graphene have been carried
out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester
(PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II).
Absorption and photoluminescence spectra of I and II recorded in mixture with
increasing the concentrations of graphene showed no change in the former, but
remarkable quenching of fluorescence. The property of graphene to quench
fluorescence of these aromatic molecules is shown to be associated with
photo-induced electron transfer, on the basis of fluorescence decay and
time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure
Estimation and Testing in Type I Generalized Half Logistic Distribution
A generalization of the half logistic distribution is developed through exponentiation of its cumulative distribution function and termed the Type I Generalized Half Logistic Distribution (GHLD). GHLD’s distributional characteristics and parameter estimation using maximum likelihood and modified maximum likelihood methods are presented with comparisons. Comparison of Type I GHLD and the exponential distribution is conducted via likelihood ratio criterion
Study of Mach reflection in inviscid flows
In this paper, we study the Mach reflection phenomenon in inviscid flows
using a higher order discontinuous Galerkin method and overset grids. We use
the shock capturing procedure proposed in Siva Prasad Kochi et al. using
overset grids to capture the discontinuities occurring in the supersonic flow
over a wedge accurately. In this procedure, we obtain a coarse grid solution
first and using the troubled cell data, we construct an overset grid which is
approximately aligned to all the discontinuities. We rerun the solver with the
coarse grid solution as the initial condition while using the troubled cell
indicator and the limiter only on the overset grid. This allows us to capture
the discontinuities accurately. Using this procedure, we have obtained the
solution for Mach and flow over a wedge for various wedge angles
and determined the detachment criterion and the Von Neumann condition
accurately. We have also determined the Mach stem height for various wedge
angles for these Mach numbers. We have also demonstrated the hysteresis that
occurs in the transition from regular reflection to Mach reflection.Comment: 11 pages, 8 Figures, 2 Table
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