187 research outputs found
Optically and Electrically Tunable Dirac Points and Zitterbewegung in Graphene-Based Photonic Superlattices
We demonstrate that graphene-based photonic superlattices provide a versatile
platform for electrical and all-optical control of photonic beams with
deep-subwavelength accuracy. Specifically, by inserting graphene sheets into
periodic metallo-dielectric structures one can design optical superlattices
that posses photonic Dirac points (DPs) at frequencies at which the spatial
average of the permittivity of the superlattice, ,
vanishes. Similar to the well-known zero- bandgaps, we show that these
zero- DPs are highly robust against structural disorder. We
also show that, by tuning the graphene permittivity via the optical Kerr effect
or electrical doping, one can induce a spectral variation of the DP exceeding
\SI{30}{\nano\meter}, at mid-IR and THz frequencies. The implications of this
wide tunability for the photonic Zitterbewegung effect in a vicinity of the DP
are explored too.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B as a Rapid
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Comparisons between heat pipe, thermoelectric system, and vapour compression refrigeration system for electronics cooling
Passive systems such as air for electronics cooling have now effectively reached their limits. This paper evaluated three comparable systems for electronics cooling, including heat pipe (HP, passive system), thermoelectric (TE) and vapour compression refrigeration (VCR) systems (active systems). Mathematical model has been built for the heat pipe and the thermoelectric system respectively. Measurements have been conducted to validate the model and to compare the performance among a HP, a single stage TE system and a two-stage TE system, a combination of the HP and the TE system, and a VCR system using an oil-free linear compressor. Close agreements between the modelling and measurements have been achieved in terms of electric power input and cooling capacity at various temperatures. The HP improved the cooling capacity and the coefficient of performance (COP) of the TE system by 53% and 42% respectively at a cold end temperature of 10 °C. Heat pipe is more attractive for cooling large devices at higher temperatures. Two-stage TE system can be used for cooling devices at lower temperatures. VCR system is capable of dissipating much higher heat flux (200 W/cm2 ) at lower temperature than all other technologies
Surface modes in plasmonic Bragg fibers with negative average permittivity
We investigate surface modes in plasmonic Bragg fibers composed of
nanostructured coaxial cylindrical metal-dielectric multilayers. We demonstrate
that the existence of surface modes is determined by the sign of the spatially
averaged permittivity of the plasmonic Bragg fiber, \bar{% \varepsilon}.
Specifically, localized surface modes occur at the interface between the
cylindrical core with and the outermost uniform
dielectric medium, which is similar to the topologically protected plasmonic
surface modes at the interface between two different one-dimensional planar
metal-dielectric lattices with opposite signs of the averaged permittivity.
Moreover, when increasing the number of dielectric-metal rings, the propagation
constant of surface modes with different azimuthal mode numbers is approaching
that of surface plasmon polaritons formed at the corresponding planar
metal/dielectric interface. Robustness of such surface modes of plasmonic Bragg
fibers is demonstrated too.Comment: 10 pages, 5 figures, Optics Express, to be publishe
Atrial fibrillation and electrophysiology in transgenic mice with cardiac-restricted overexpression of FKBP12
Cardiomyocyte-restricted overexpression of FK506-binding protein 12 transgenic (αMyHC-FKBP12) mice develop spontaneous atrial fibrillation (AF). The aim of the present study is to explore the mechanisms underlying the occurrence of AF in αMyHC-FKBP12 mice. Spontaneous AF was documented by telemetry in vivo and Langendorff-perfused hearts of αMyHC-FKBP12 and littermate control mice in vitro. Atrial conduction velocity was evaluated by optical mapping. The patch-clamp technique was applied to determine the potentially altered electrophysiology in atrial myocytes. Channel protein expression levels were evaluated by Western blot analyses. Spontaneous AF was recorded in four of seven αMyHC-FKBP12 mice but in none of eight nontransgenic (NTG) controls. Atrial conduction velocity was significantly reduced in αMyHC-FKBP12 hearts compared with NTG hearts. Interestingly, the mean action potential duration at 50% but not 90% was significantly prolonged in αMyHC-FKBP12 atrial myocytes compared with their NTG counterparts. Consistent with decreased conduction velocity, average peak Na+ current ( INa) density was dramatically reduced and the INa inactivation curve was shifted by approximately +7 mV in αMyHC-FKBP12 atrial myocytes, whereas the activation and recovery curves were unaltered. The Nav1.5 expression level was significantly reduced in αMyHC-FKBP12 atria. Furthermore, we found increases in atrial Cav1.2 protein levels and peak L-type Ca2+ current density and increased levels of fibrosis in αMyHC-FKBP12 atria. In summary, cardiomyocyte-restricted overexpression of FKBP12 reduces the atrial Nav1.5 expression level and mean peak INa, which is associated with increased peak L-type Ca2+ current and interstitial fibrosis in atria. The combined electrophysiological and structural changes facilitated the development of local conduction block and altered action potential duration and spontaneous AF. NEW & NOTEWORTHY This study addresses a long-standing riddle regarding the role of FK506-binding protein 12 in cardiac physiology. The work provides further evidence that FK506-binding protein 12 is a critical component for regulating voltage-gated sodium current and in so doing has an important role in arrhythmogenic physiology, such as atrial fibrillation
Transport Anisotropy in One-dimensional Graphene Superlattice in the High Kronig-Penney Potential Limit
One-dimensional graphene superlattice subjected to strong Kronig-Penney (KP)
potential is promising for achieving electron lensing effect, while previous
studies utilizing the modulated dielectric gates can only yield a moderate,
spatially dispersed potential profile. Here, we realize high KP potential
modulation of graphene via nanoscale ferroelectric domain gating. Graphene
transistors are fabricated on PbZrTiO back-gates
patterned with periodic, 100-200 nm wide stripe domains. Due to band
reconstruction, the h-BN top-gating induces satellite Dirac points in samples
with current along the superlattice vector , a feature absent in
samples with current perpendicular to . The satellite Dirac point
position scales with the superlattice period () as , with
. These results can be well explained by the high KP
potential scenario, with the Fermi velocity perpendicular to quenched
to about 1% of that for pristine graphene. Our study presents a promising
material platform for realizing electron supercollimation and investigating
flat band phenomena.Comment: 12 pages, 5 figures, and Supplemental Materia
Remote surface optical phonon scattering in ferroelectric Ba\u3csub\u3e0.6\u3c/sub\u3eSr\u3csub\u3e0.4\u3c/sub\u3eTiO\u3csub\u3e3\u3c/sub\u3e gated graphene
We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba0.6Sr0.4TiO3 films, with field effect mobility up to 23,000 cm2 V−1 s−1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba0.6Sr0.4TiO3, from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for by considering the scattering from the intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter dominated by the mode at 35.8 meV. Our study reveals the room temperature mobility limit of ferroelectric-gated graphene transistors imposed by RSO phonon scattering
Remote Surface Optical Phonon Scattering in Ferroelectric BaSrTiO Gated Graphene
We report the effect of remote surface optical (RSO) phonon scattering on
carrier mobility in monolayer graphene gated by ferroelectric oxide. We
fabricate monolayer graphene transistors back-gated by epitaxial (001)
BaSrTiO films, with field effect mobility up to 23,000
cmVs achieved. Switching the ferroelectric polarization
induces nonvolatile modulation of resistance and quantum Hall effect in
graphene at low temperatures. Ellipsometry spectroscopy studies reveal four
pairs of optical phonon modes in BaSrTiO, from which we
extract the RSO phonon frequencies. The temperature dependence of resistivity
in graphene can be well accounted for by considering the scattering from the
intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter
dominated by the mode at 35.8 meV. Our study reveals the room temperature
mobility limit of ferroelectric-gated graphene transistors imposed by RSO
phonon scattering.Comment: 15 pages, 6 figure
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