10,482 research outputs found
Manipulation of heat current by the interface between graphene and white graphene
We investigate the heat current flowing across the interface between graphene
and hexagonal boron nitride (so-called white graphene) using both molecular
dynamics simulation and nonequilibrium Green's function approaches. These two
distinct methods discover the same phenomena that the heat current is reduced
linearly with increasing interface length, and the zigzag interface causes
stronger reduction of heat current than the armchair interface. These phenomena
are interpreted by both the lattice dynamics analysis and the transmission
function explanation, which both reveal that the localized phonon modes at
interfaces are responsible for the heat management. The room temperature
interface thermal resistance is about mK/W in zigzag
interface and mK/W in armchair interface, which
directly results in stronger heat reduction in zigzag interface. Our
theoretical results provide a specific route for experimentalists to control
the heat transport in the graphene and hexagonal boron nitride compound through
shaping the interface between these two materials.Comment: accepted by EP
Raman spectroscopy of epitaxial graphene on a SiC substrate
The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has
attracted a lot of interest as it may speed up the application of graphene for
future electronic devices. The interaction of EG and the SiC substrate is
critical to its electronic and physical properties. In this work, Raman
spectroscopy was used to study the structure of EG and its interaction with SiC
substrate. All the Raman bands of EG blue shift from that of bulk graphite and
graphene made by micromechanical cleavage, which was attributed to the
compressive strain induced by the substrate. A model containing 13 x 13
honeycomb lattice cells of graphene on carbon nanomesh was constructed to
explain the origin of strain. The lattice mismatch between graphene layer and
substrate causes the compressive stress of 2.27 GPa on graphene. We also
demonstrate that the electronic structures of EG grown on Si and C terminated
SiC substrates are quite different. Our experimental results shed light on the
interaction between graphene and SiC substrate that are critical to the future
applications of EG.Comment: 20 pages, 5 figure
Guiding optical flows by photonic crystal slabs made of dielectric cylinders
We investigate the electromagnetic propagation in two-dimensional photonic
crystals, formed by parallel dielectric cylinders embedded a uniform medium.
The frequency band structure is computed using the standard plane-wave
expansion method, while the propagation and scattering of the electromagnetic
waves are calculated by the multiple scattering theory. It is shown that within
partial bandgaps, the waves tend to bend away from the forbidden directions.
Such a property may render novel applications in manipulating optical flows. In
addition, the relevance with the imaging by flat photonic crystal slabs will
also be discussed.Comment: 5 pages, 5 figure
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The Clinical Utility of a Precision Medicine Blood Test Incorporating Age, Sex, and Gene Expression for Evaluating Women with Stable Symptoms Suggestive of Obstructive Coronary Artery Disease: Analysis from the PRESET Registry.
Background: Evaluating women with symptoms suggestive of coronary artery disease (CAD) remains challenging. A blood-based precision medicine test yielding an age/sex/gene expression score (ASGES) has shown clinical validity in the diagnosis of obstructive CAD. We assessed the effect of the ASGES on the management of women with suspected obstructive CAD in a community-based registry. Materials and Methods: The prospective PRESET (A Registry to Evaluate Patterns of Care Associated with the Use of Corus® CAD in Real World Clinical Care Settings) Registry (NCT01677156) enrolled 566 patients presenting with symptoms suggestive of stable obstructive CAD from 21 United States primary care practices from 2012 to 2014. Demographics, clinical characteristics, and referrals to cardiology or further functional and/or anatomical cardiac studies after ASGES testing were collected for this subgroup analysis of women from the PRESET Registry. Patients were followed for 1-year post-ASGES testing. Results: This study cohort included 288 women with a median age 57 years. The median body mass index was 29.2, with hyperlipidemia and hypertension present in 48% and 43% of patients, respectively. Median ASGES was 8.5 (range 1-40), with 218 (76%) patients having low (≤15) ASGES. Clinicians referred 9% (20/218) low ASGES versus 44% (31/70) elevated ASGES women for further cardiac evaluation (odds ratio 0.14, p < 0.0001, adjusted for patient demographics and clinical covariates). Across the score range, higher ASGES were associated with a higher likelihood of posttest cardiac referral. At 1-year follow-up, low ASGES women experienced fewer major adverse cardiac events than elevated ASGES women (1.3% vs. 4.2% respectively, p = 0.16). Conclusions: Incorporation of ASGES into the diagnostic workup demonstrated clinical utility by helping clinicians identify women less likely to benefit from further cardiac evaluation
Can the Lepton Flavor Mixing Matrix Be Symmetric?
Current neutrino oscillation data indicate that the 3x3 lepton flavor mixing
matrix V is likely to be symmetric about its V_{e3}-V_{\mu 2}-V_{\tau 1} axis.
This off-diagonal symmetry corresponds to three pairs of {\it congruent}
unitarity triangles in the complex plane. Terrestrial matter effects can
substantially modify the genuine CP-violating parameter and off-diagonal
asymmetries of V in realistic long-baseline experiments of neutrino
oscillations.Comment: RexTex 14 pages (4 PS figures). More discussions adde
Coupled valence and spin state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3
The coupled valence and spin state transition (VSST) taking place in
(Pr0.7Sm0.3)0.7Ca0.3CoO3 was investigated by soft x-ray absorption spectroscopy
(XAS) experiments carried out at the Pr-M4,5, Co-L2,3, and O-1s edges. This
VSST is found to be composed of a sharp Pr/Co valence and Co spin state
transition centered at T*=89.3 K, followed by a smoother Co spin-state
evolution at higher temperatures. At T < T*, we found that the praseodymium
displays a mixed valence Pr3+/Pr4+ with about 0.13 Pr4+/f.u., while all the
Co3+ is in the low-spin (LS) state. At T around T*, the sharp valence
transition converts all the Pr4+ to Pr3+ with a corresponding Co3+ to Co4+
compensation. This is accompanied by an equally sharp spin state transition of
the Co3+ from the low to an incoherent mixture of low and high spin (HS)
states. An involvement of the intermediate spin (IS) state can be discarded for
the Co3+. While above T* and at high temperatures the system shares rather
similar properties as Sr-doped LaCoO3, at low temperatures it behaves much more
like EuCoO3 with its highly stable LS configuration for the Co3+. Apparently,
the mechanism responsible for the formation of Pr4+ at low temperatures also
helps to stabilize the Co3+ in the LS configuration despite the presence of
Co4+ ions. We also found out that that the Co4+ is in an IS state over the
entire temperature range investigated in this study (10-290 K). The presence of
Co3+ HS and Co4+ IS at elevated temperatures facilitates the conductivity of
the material.Comment: 19 pages, 7 figures, Accepted in PR
Demonstration of acoustic waveguiding and tight bending in phononic crystals
Citation: Baboly, M. G., Raza, A., Brady, J., Reinke, C. M., Leseman, Z. C., & El-Kady, I. (2016). Demonstration of acoustic waveguiding and tight bending in phononic crystals. Applied Physics Letters, 109(18), 4. doi:10.1063/1.4966463The systematic design, fabrication, and characterization of an isolated, single-mode, 90 degrees bend phononic crystal (PnC) waveguide are presented. A PnC consisting of a 2D square array of circular air holes in an aluminum substrate is used, and waveguides are created by introducing a line defect in the PnC lattice. A high transmission coefficient is observed (-1 dB) for the straight sections of the waveguide, and an overall 2.3 dB transmission loss is observed (a transmission coefficient of 76%) for the 90 degrees bend. Further optimization of the structure may yield higher transmission efficiencies. This manuscript shows the complete design process for an engineered 90 degrees bend PnC waveguide from inception to experimental demonstration. Published by AIP Publishing
Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides
We performed resonant soft X-ray diffraction on known charge density wave
(CDW) compounds, rare earth tri-tellurides. Near the (3d - 4f) absorption
edge of rare earth ions, an intense diffraction peak is detected at a
wavevector identical to that of CDW state hosted on Te planes, indicating a
CDW-induced modulation on the rare earth ions. Surprisingly, the temperature
dependence of the diffraction peak intensity demonstrates an exponential
increase at low temperatures, vastly different than that of the CDW order
parameter. Assuming 4f multiplet splitting due to the CDW states,we present a
model to calculate X-ray absorption spectrum and resonant profile of the
diffraction peak, agreeing well with experimental observations. Our results
demonstrate a situation where the temperature dependence of resonant X-ray
diffraction peak intensity is not directly related to the intrinsic behavior of
the order parameter associated with the electronic order, but is dominated by
the thermal occupancy of the valence states.Comment: 7 pages, 5 figure
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