67,937 research outputs found
Room-temperature ballistic transport in narrow graphene strips
We investigate electron-phonon couplings, scattering rates, and mean free
paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our
calculations for these graphene nanostrips show both the expected similarity
with single-wall carbon nanotubes (SWNTs) and the suppression of the
electron-phonon scattering due to a Dirichlet boundary condition that prohibits
one major backscattering channel present in SWNTs. Low-energy acoustic phonon
scattering is exponentially small at room temperature due to the large phonon
wave vector required for backscattering. We find within our model that the
electron-phonon mean free path is proportional to the width of the nanostrip
and is approximately 70 m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure
Linear Optical CNOT Gate in the Coincidence Basis
We describe the operation and tolerances of a non-deterministic, coincidence
basis, quantum CNOT gate for photonic qubits. It is constructed solely from
linear optical elements and requires only a two-photon source for its
demonstration.Comment: Submitted to Physical Review
Anisotropic constitutive relationships in energetic materials: PETN and HMX
This paper presents results of first-principles density functional calculations of the equation of state (EOS) of PETN-I and beta-HMX. The isotropic EOS for hydrostatic compression has been extended to include uniaxial compressions in the [100], [010], [001], [110], [101], [011], and [111] directions up to compression ratio V/V0 = 0.70. Equilibrium properties, including lattice parameters and elastic constants, as well as hydrostatic EOS are in good agreement with available experimental data. The shear stresses of uniaxially compressed PETN-I and beta-HMX have been evaluated and their behavior as a function of compression ratio has been used to make predictions of shock sensitivity of these EMs. A comparison of predicted sensitivities with available experimental data has also been performed
Systematic study of d-wave superconductivity in the 2D repulsive Hubbard model
The cluster size dependence of superconductivity in the conventional
two-dimensional Hubbard model, commonly believed to describe high-temperature
superconductors, is systematically studied using the Dynamical Cluster
Approximation and Quantum Monte Carlo simulations as cluster solver. Due to the
non-locality of the d-wave superconducting order parameter, the results on
small clusters show large size and geometry effects. In large enough clusters,
the results are independent of the cluster size and display a finite
temperature instability to d-wave superconductivity.Comment: 4 pages, 3 figures; updated with version published in PRL; added
values of Tc obtained from fit
High-Fidelity Z-Measurement Error Correction of Optical Qubits
We demonstrate a quantum error correction scheme that protects against
accidental measurement, using an encoding where the logical state of a single
qubit is encoded into two physical qubits using a non-deterministic photonic
CNOT gate. For the single qubit input states |0>, |1>, |0>+|1>, |0>-|1>,
|0>+i|1>, and |0>-i|1> our encoder produces the appropriate 2-qubit encoded
state with an average fidelity of 0.88(3) and the single qubit decoded states
have an average fidelity of 0.93(5) with the original state. We are able to
decode the 2-qubit state (up to a bit flip) by performing a measurement on one
of the qubits in the logical basis; we find that the 64 1-qubit decoded states
arising from 16 real and imaginary single qubit superposition inputs have an
average fidelity of 0.96(3).Comment: 4 pages, 4 figures, comments welcom
Efficient slow-light coupling in a photonic crystal waveguide without transition region
We consider the coupling into a slow mode that appears near an inflection point in the band structure of a photonic crystal waveguide. Remarkably, the coupling into this slow mode, which has a group index n(g) > 1000, can be essentially perfect without any transition region. We show that this efficient coupling occurs thanks to an evanescent mode in the slow medium, which has appreciable amplitude and helps satisfy the boundary conditions but does not transport any energy. (C) 2008 Optical Society of AmericaPublisher PDFPeer reviewe
Normalizing the Temperature Function of Clusters of Galaxies
We re-examine the constraints which can be robustly obtained from the
observed temperature function of X-ray cluster of galaxies. The cluster mass
function has been thoroughly studied in simulations and analytically, but a
direct simulation of the temperature function is presented here for the first
time. Adaptive hydrodynamic simulations using the cosmological Moving Mesh
Hydro code of Pen (1997a) are used to calibrate the temperature function for
different popular cosmologies. Applying the new normalizations to the
present-day cluster abundances, we find for a hyperbolic universe, and for a spatially flat universe with a cosmological constant.
The simulations followed the gravitational shock heating of the gas and dark
matter, and used a crude model for potential energy injection by supernova
heating. The error bars are dominated by uncertainties in the heating/cooling
models. We present fitting formulae for the mass-temperature conversions and
cluster abundances based on these simulations.Comment: 20 pages incl 5 figures, final version for ApJ, corrected open
universe \gamma relation, results unchange
Phase Diagram of a 2D Vertex Model
Phase diagram of a symmetric vertex model which allows 7 vertex
configurations is obtained by use of the corner transfer matrix renormalization
group (CTMRG), which is a variant of the density matrix renormalization group
(DMRG). The critical indices of this model are identified as and
.Comment: 2 pages, 5 figures, short not
First-principles anisotropic constitutive relationships in β-cyclotetramethylene tetranitramine (β-HMX)
First-principles density functional theory calculations have been performed to obtain constitutive relationships in the crystalline energetic material β-cyclotetramethylene tetranitramine (β-HMX). In addition to hydrostatic loading, uniaxial compressions in the directions normal to the {100}, {010}, {001}, {110}, {101}, {011}, and {111} planes have been performed to investigate the anisotropic equation of state (EOS). The calculated lattice parameters and hydrostatic EOS are in reasonable agreement with the available experimental data. The uniaxial compression data show a significant anisotropy in the principal stresses, change in energy, band gap, and shear stresses, which might lead to the anisotropy of the elastic-plastic shock transition and shock sensitivity of β-HMX
- …