1,118 research outputs found
Lag synchronization and scaling of chaotic attractor in coupled system
We report a design of delay coupling for lag synchronization in two
unidirectionally coupled chaotic oscillators. A delay term is introduced in the
definition of the coupling to target any desired lag between the driver and the
response. The stability of the lag synchronization is ensured by using the
Hurwitz matrix stability. We are able to scale up or down the size of a driver
attractor at a response system in presence of a lag. This allows compensating
the attenuation of the amplitude of a signal during transmission through a
delay line. The delay coupling is illustrated with numerical examples of 3D
systems, the Hindmarsh-Rose neuron model, the R\"ossler system and a Sprott
system and, a 4D system. We implemented the coupling in electronic circuit to
realize any desired lag synchronization in chaotic oscillators and scaling of
attractors.Comment: 10 pages, 7 figure
Sensory organ like response determines the magnetism of zigzag-edged honeycomb nanoribbons
We present an analytical theory for the magnetic phase diagram for zigzag
edge terminated honeycomb nanoribbons described by a Hubbard model with an
interaction parameter U . We show that the edge magnetic moment varies as ln U
and uncover its dependence on the width W of the ribbon. The physics of this
owes its origin to the sensory organ like response of the nanoribbons,
demonstrating that considerations beyond the usual Stoner-Landau theory are
necessary to understand the magnetism of these systems. A first order magnetic
transition from an anti-parallel orientation of the moments on opposite edges
to a parallel orientation occurs upon doping with holes or electrons. The
critical doping for this transition is shown to depend inversely on the width
of the ribbon. Using variational Monte-Carlo calculations, we show that
magnetism is robust to fluctuations. Additionally, we show that the magnetic
phase diagram is generic to zigzag edge terminated nanostructures such as
nanodots. Furthermore, we perform first principles modeling to show how such
magnetic transitions can be realized in substituted graphene nanoribbons.Comment: 5 pages, 5 figure
Symmetry-dependent phonon renormalization in monolayer MoS2 transistor
Strong electron-phonon interaction which limits electronic mobility of
semiconductors can also have significant effects on phonon frequencies. The
latter is the key to the use of Raman spectroscopy for nondestructive
characterization of doping in graphene-based devices. Using in-situ Raman
scattering from single layer MoS electrochemically top-gated field effect
transistor (FET), we show softening and broadening of A phonon with
electron doping whereas the other Raman active E mode remains
essentially inert. Confirming these results with first-principles density
functional theory based calculations, we use group theoretical arguments to
explain why A mode specifically exhibits a strong sensitivity to
electron doping. Our work opens up the use of Raman spectroscopy in probing the
level of doping in single layer MoS-based FETs, which have a high on-off
ratio and are of enormous technological significance.Comment: 5 pages, 3 figure
Effect of twist level and twist direction of core (double) yarn on dref-3 spun yarn
In this study, an attempt has been made to understand the behaviour of friction spun yarn by introducing doubled yarns as core with diversity in twist level and direction. ‘Z’ twisted 15tex (40s Ne) parent yarn has been used for doubling purposes. To examine the effect of doubling, three twist levels are chosen, viz. 50, 60 and 70 % of the parent yarn twist for both the directions viz. S and Z. Thus, six samples of doubled yarns are prepared. These samples are tested for the count, twist, breaking force and elongation. These yarns are introduced as core into DREF-3 friction spinning system; keeping the sheath fibre constant viz. combed cotton sliver of 0.15 hank for all the samples. The twist direction of the doubled yarn used as core is found to be the influential factor for the breaking force and elongation of the friction spun yar
Spin-induced asymmetry reaction - The formation of asymmetric carbon by electropolymerization
We describe the spin polarization–induced chirogenic electropolymerization of achiral 2-vinylpyridine, which forms a layer of enantioenhanced isotactic polymer on the electrode. The product formed is enantioenriched in asymmetric carbon polymer. To confirm the chirality of the polymer film formed on the electrode, we also measured its electron spin polarization properties as a function of its thickness. Two methods were used: First, spin polarization was measured by applying magnetic contact atomic force microscopy, and second, magnetoresistance was assessed in a sandwich-like four-point contact structure. We observed high spin-selective electron transmission, even for a layer thickness of 120 nm. A correlation exists between the change in the circular dichroism signal and the change in the spin polarization, as a function of thickness. The spin-filtering efficiency increases with temperature
Localized States at Zigzag Edges of Multilayer Graphene and Graphite Steps
We report the existence of zero energy surface states localized at zigzag
edges of -layer graphene. Working within the tight-binding approximation,
and using the simplest nearest-neighbor model, we derive the analytic solution
for the wavefunctions of these peculiar surface states. It is shown that zero
energy edge states in multilayer graphene can be divided into three families:
(i) states living only on a single plane, equivalent to surface states in
monolayer graphene; (ii) states with finite amplitude over the two last, or the
two first layers of the stack, equivalent to surface states in bilayer
graphene; (iii) states with finite amplitude over three consecutive layers.
Multilayer graphene edge states are shown to be robust to the inclusion of the
next nearest-neighbor interlayer hopping. We generalize the edge state solution
to the case of graphite steps with zigzag edges, and show that edge states
measured through scanning tunneling microscopy and spectroscopy of graphite
steps belong to family (i) or (ii) mentioned above, depending on the way the
top layer is cut.Comment: 6 pages, 4 figure
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