2,853 research outputs found
Visualizing Strain-induced Pseudo magnetic Fields in Graphene through an hBN Magnifying Glass
The remarkable properties of graphene are inherent to its 2D honeycomb
lattice structure. Its low dimensionality, which makes it possible to rearrange
the atoms by applying an external force, offers the intriguing prospect of
mechanically controlling the electronic properties. In the presence of strain,
graphene develops a pseudo-magnetic field (PMF) which reconstructs the band
structure into pseudo Landau levels (PLLs). However, a feasible route to
realizing, characterizing and controlling PMFs is still lacking. Here we report
on a method to generate and characterize PMFs in a graphene membrane supported
on nano-pillars. A direct measure of the local strain is achieved by using the
magnifying effect of the Moir\'e pattern formed against a hexagonal Boron
Nitride (hBN) substrate under scanning tunneling microscopy (STM). We quantify
the strain induced PMF through the PLLs spectra observed in scanning tunneling
spectroscopy (STS). This work provides a pathway to strain induced engineering
and electro-mechanical graphene based devices.Comment: 23 pages, 10 figure
Uniform approximations for non-generic bifurcation scenatios including bifurcations of ghost orbits
Gutzwiller's trace formula allows interpreting the density of states of a
classically chaotic quantum system in terms of classical periodic orbits. It
diverges when periodic orbits undergo bifurcations, and must be replaced with a
uniform approximation in the vicinity of the bifurcations. As a characteristic
feature, these approximations require the inclusion of complex ``ghost
orbits''. By studying an example taken from the Diamagnetic Kepler Problem,
viz. the period-quadrupling of the balloon-orbit, we demonstrate that these
ghost orbits themselves can undergo bifurcations, giving rise to non-generic
complicated bifurcation scenarios. We extend classical normal form theory so as
to yield analytic descriptions of both bifurcations of real orbits and ghost
orbit bifurcations. We then show how the normal form serves to obtain a uniform
approximation taking the ghost orbit bifurcation into account. We find that the
ghost bifurcation produces signatures in the semiclassical spectrum in much the
same way as a bifurcation of real orbits does.Comment: 56 pages, 21 figure, LaTeX2e using amsmath, amssymb, epsfig, and
rotating packages. To be published in Annals of Physic
New sufficient conditions of existence, moment estimations and non confluence for SDEs with non-Lipschitzian coefficients
The objective of the present paper is to find new sufficient conditions for the existence of unique strong solutions to a class of (time-inhomogeneous) stochastic differential equations with random, non-Lipschitzian coefficients. We give an example to show that our conditions are indeed weaker than those relevant conditions existing in the literature. We also derive moment estimations for the maximum process of the solution. Finally, we present a sufficient condition to ensure the non confluence property of the solution of time-homogeneous SDE which, in one dimension, is nothing but stochastic monotone property of the solution
Tuning a Circular p-n Junction in Graphene from Quantum Confinement to Optical Guiding
The motion of massless Dirac-electrons in graphene mimics the propagation of
photons. This makes it possible to control the charge-carriers with components
based on geometrical-optics and has led to proposals for an all-graphene
electron-optics platform. An open question arising from the possibility of
reducing the component-size to the nanometer-scale is how to access and
understand the transition from optical-transport to quantum-confinement. Here
we report on the realization of a circular p-n junction that can be
continuously tuned from the nanometer-scale, where quantum effects are
dominant, to the micrometer scale where optical-guiding takes over. We find
that in the nanometer-scale junction electrons are trapped in states that
resemble atomic-collapse at a supercritical charge. As the junction-size
increases, the transition to optical-guiding is signaled by the emergence of
whispering-gallery modes and Fabry-Perot interference. The creation of tunable
junctions that straddle the crossover between quantum-confinement and
optical-guiding, paves the way to novel design-architectures for controlling
electronic transport.Comment: 16 pages, 4 figure
Effect of Salivation by Facial Somatosensory Stimuli of Facial Massage and Vibrotactile Apparatus
We studied the effects of salivary promotion of fluid secretion after hand massage, and the apparatus of vibrotactile stimulation (89 Hz frequency, 15 min) in normal humans. Personal massage cannot be performed on handicap and stroke patients, and then giving hand massage to them for 5 min massage gives a tired feeling. So, we focused 3 min stranger massage. Salivary glands can discharge the accumulated saliva by extrusion from the acinus glands’ massages as described in the recent Japanese textbook. We think that this method may not produce realistic recovery. Our aim ideas are to relieve stress and increase temperature with lightly touch massage of the skin and for a 1 cycle of 1 s. We recorded RR interval of ECG, total salivation, facial skin temperature, OxyHb of fNIRS on the frontal cortex, and amylase activity for the autonomic changes. In increased 2°C of the facial skin temperature, the hand massage had a need for 3 min and the vibrotactile stimulation for 15 min. Increase from 700 to 1000 ms of RR intervals had a need for 3 min in the hand massage and had 15 min in the vibrotactile stimulation. Although vibrotactile stimulation needs long time of 4–7 years as effective recovery, hand massage may have more effect with a repetition of day after day
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