145,617 research outputs found
Effect of disorder with long-range correlation on transport in graphene nanoribbon
Transport in disordered armchair graphene nanoribbons (AGR) with long-range
correlation between quantum wire contact is investigated by transfer matrix
combined with Landauer's formula. Metal-insulator transition is induced by
disorder in neutral AGR. Thereinto, the conductance is one conductance quantum
for metallic phase and exponentially decays otherwise when the length of AGR is
infinity and far longer than its width. Similar to the case of long-range
disorder, the conductance of neutral AGR first increases and then decreases
while the conductance of doped AGR monotonically decreases, as the disorder
strength increases. In the presence of strong disorder, the conductivity
depends monotonically and non-monotonically on the aspect ratio for heavily
doped and slightly doped AGR respectively.Comment: 6 pages, 8 figures; J. Phys: Condensed Matter (May 2012
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Effects of biomass burning, lightning, and convection on O-3, CO, and NOy over the tropical Pacific and Australia in August-October 1998 and 1999
The Numerical Solution of Scalar Field for Nariai Case in 5D Ricci-flat SdS Black String Space with Polynomial Approximation
As one exact candidate of the higher dimensional black hole, the 5D
Ricci-flat Schwarzschild-de Sitter black string space presents something
interesting. In this paper, we give a numerical solution to the real scalar
field around the Nariai black hole by the polynomial approximation. Unlike the
previous tangent approximation, this fitting function makes a perfect match in
the leading intermediate region and gives a good description near both the
event and the cosmological horizons. We can read from our results that the wave
is close to a harmonic one with the tortoise coordinate. Furthermore, with the
actual radial coordinate the waves pile up almost equally near the both
horizons.Comment: 8 pages, 4 figure
Voltage controlled nuclear polarization switching in a single InGaAs quantum dot
Sharp threshold-like transitions between two stable nuclear spin
polarizations are observed in optically pumped individual InGaAs self-assembled
quantum dots embedded in a Schottky diode when the bias applied to the diode is
tuned. The abrupt transitions lead to the switching of the Overhauser field in
the dot by up to 3 Tesla. The bias-dependent photoluminescence measurements
reveal the importance of the electron-tunneling-assisted nuclear spin pumping.
We also find evidence for the resonant LO-phonon-mediated electron
co-tunneling, the effect controlled by the applied bias and leading to the
reduction of the nuclear spin pumping rate.Comment: 5 pages, 2 figures, submitted to Phys Rev
Possible observation of phase separation near a quantum phase transition in doubly connected ultrathin superconducting cylinders of aluminum
The kinetic energy of superconducting electrons in an ultrathin, doubly
connected superconducting cylinder, determined by the applied flux, increases
as the cylinder diameter decreases, leading to a destructive regime around
half-flux quanta and a superconductor to normal metal quantum phase transition
(QPT). Regular step-like features in resistance vs. temperature curves taken at
fixed flux values were observed near the QPT in ultrathin Al cylinders. It is
proposed that these features are most likely resulted from a phase separation
near the QPT in which normal regions nucleate in a homogeneous superconducting
cylinder.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
The disk-outflow system in the S255IR area of high mass star formation
We report the results of our observations of the S255IR area with the SMA at
1.3 mm in the very extended configuration and at 0.8 mm in the compact
configuration as well as with the IRAM-30m at 0.8 mm. The best achieved angular
resolution is about 0.4 arcsec. The dust continuum emission and several tens of
molecular spectral lines are observed. The majority of the lines is detected
only towards the S255IR-SMA1 clump, which represents a rotating structure
(probably disk) around the young massive star. The achieved angular resolution
is still insufficient for conclusions about Keplerian or non-Keplerian
character of the rotation. The temperature of the molecular gas reaches 130-180
K. The size of the clump is about 500 AU. The clump is strongly fragmented as
follows from the low beam filling factor. The mass of the hot gas is
significantly lower than the mass of the central star. A strong DCN emission
near the center of the hot core most probably indicates a presence of a
relatively cold ( K) and rather massive clump there. High velocity
emission is observed in the CO line as well as in lines of high density tracers
HCN, HCO+, CS and other molecules. The outflow morphology obtained from
combination of the SMA and IRAM-30m data is significantly different from that
derived from the SMA data alone. The CO emission detected with the SMA traces
only one boundary of the outflow. The outflow is most probably driven by jet
bow shocks created by episodic ejections from the center. We detected a dense
high velocity clump associated apparently with one of the bow shocks. The
outflow strongly affects the chemical composition of the surrounding medium.Comment: 19 pages, 23 figures, accepted by The Astrophysical Journa
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