199,675 research outputs found
Potential barrier of Graphene edges
We calculated row resolved density of states, charge distribution and work
function of graphene's zigzag and armchair edge (either clean or terminated
alternatively with H, O or OH group). The zigzag edge saturated via OH group
has the lowest work function of 3.76 eV, while the zigzag edge terminated via O
has the highest work function of 7.74 eV. The angle-dependent potential barrier
on the edge is fitted to a multi-pole model and is explained by the charge
distribution.Comment: 16 pages, 8 figures. Copyright (2011) American Institute of Physics.
This article may be downloaded for personal use only. Any other use requires
prior permission of the author and the American Institute of Physics. This
article appeared in (J. Appl. Phys. 109 (2011) 114308) and may be found at
(http://link.aip.org/link/?JAP/109/114308
Effect of charged impurities on graphene thermoelectric power near the Dirac point
In graphene devices with a varying degree of disorders as characterized by
their carrier mobility and minimum conductivity, we have studied the
thermoelectric power along with the electrical conductivity over a wide range
of temperatures. We have found that the Mott relation fails in the vicinity of
the Dirac point in high-mobility graphene. By properly taking account of the
high temperature effects, we have obtained good agreement between the Boltzmann
transport theory and our experimental data. In low-mobility graphene where the
charged impurities induce relatively high residual carrier density, the Mott
relation holds at all gate voltages
Unconstrained video monitoring of breathing behavior and application to diagnosis of sleep apnea
This paper presents a new real-time automated infrared video monitoring technique for detection of breathing anomalies, and its application in the diagnosis of obstructive sleep apnea. We introduce a novel motion model to detect subtle, cyclical breathing signals from video, a new 3-D unsupervised self-adaptive breathing template to learn individuals' normal breathing patterns online, and a robust action classification method to recognize abnormal breathing activities and limb movements. This technique avoids imposing positional constraints on the patient, allowing patients to sleep on their back or side, with or without facing the camera, fully or partially occluded by the bed clothes. Moreover, shallow and abdominal breathing patterns do not adversely affect the performance of the method, and it is insensitive to environmental settings such as infrared lighting levels and camera view angles. The experimental results show that the technique achieves high accuracy (94% for the clinical data) in recognizing apnea episodes and body movements and is robust to various occlusion levels, body poses, body movements (i.e., minor head movement, limb movement, body rotation, and slight torso movement), and breathing behavior (e.g., shallow versus heavy breathing, mouth breathing, chest breathing, and abdominal breathing). © 2013 IEEE
BCS-BEC crossover in bilayers of cold fermionic polar molecules
We investigate the quantum and thermal phase diagram of fermionic polar molecules loaded in a bilayer trapping potential with perpendicular dipole moment. We use both a BCS-theory approach that is most reliable at weak coupling and a strong-coupling approach that considers the two-body bound dimer states with one molecule in each layer as the relevant degree of freedom. The system ground state is a Bose-Einstein condensate (BEC) of dimer bound states in the low-density limit and a paired superfluid (BCS) state in the high-density limit. At zero temperature, the intralayer repulsion is found to broaden the regime of BCS-BEC crossover and can potentially induce system collapse through the softening of roton excitations. The BCS theory and the strongly coupled dimer picture yield similar predictions for the parameters of the crossover regime. The Berezinskii-Kosterlitz-Thouless transition temperature of the dimer superfluid is also calculated. The crossover can be driven by many-body effects and is strongly affected by the intralayer interaction which was ignored in previous studies
Structure and decays of nuclear three-body systems: the Gamow coupled-channel method in Jacobi coordinates
Weakly bound and unbound nuclear states appearing around
particle thresholds are prototypical open quantum systems. Theories of such
states must take into account configuration mixing effects in the presence of
strong coupling to the particle continuum space.
To describe structure and decays of three-body systems, we
developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by
employing the complex-momentum formalism. We benchmarked the new framework
against the complex-energy Gamow Shell Model (GSM).
The GCC formalism is expressed in Jacobi coordinates, so
that the center-of-mass motion is automatically eliminated. To solve the
coupled-channel equations, we use hyperspherical harmonics to describe the
angular wave functions while the radial wave functions are expanded in the
Berggren ensemble, which includes bound, scattering and Gamow states.
We show that the GCC method is both accurate and robust. Its
results for energies, decay widths, and nucleon-nucleon angular correlations
are in good agreement with the GSM results.
We have demonstrated that a three-body GSM formalism
explicitly constructed in cluster-orbital shell model coordinates provides
similar results to a GCC framework expressed in Jacobi coordinates, provided
that a large configuration space is employed. Our calculations for
systems and O show that nucleon-nucleon angular correlations are
sensitive to the valence-neutron interaction. The new GCC technique has many
attractive features when applied to bound and unbound states of three-body
systems: it is precise, efficient, and can be extended by introducing a
microscopic model of the core.Comment: 10 pages, 8 figure
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