8,547 research outputs found
T-Shape Molecular Heat Pump
We report on the first molecular device of heat pump modeled by a T-shape
Frenkel-Kontorova lattice. The system is a three-terminal device with the
important feature that the heat can be pumped from the low-temperature region
to the high-temperature region through the third terminal. The pumping action
is achieved by applying a stochastic external force that periodically modulates
the atomic temperature. The temperature, the frequency and the system size
dependence of heat pump are briefly discussed.Comment: 6 figure
Entanglement distribution maximization over one-side Gaussian noisy channel
The optimization of entanglement evolution for two-mode Gaussian pure states
under one-side Gaussian map is studied. Even there isn't complete information
about the one-side Gaussian noisy channel, one can still maximize the
entanglement distribution by testing the channel with only two specific states
Can Electric Field Induced Energy Gaps In Metallic Carbon Nanotubes?
The low-energy electronic structure of metallic single-walled carbon nanotube
(SWNT) in an external electric field perpendicular to the tube axis is
investigated. Based on tight-binding approximation, a field-induced energy gap
is found in all (n, n) SWNTs, and the gap shows strong dependence on the
electric field and the size of the tubes. We numerically find a universal
scaling that the gap is a function of the electric field and the radius of
SWNTs, and the results are testified by the second-order perturbation theory in
weak field limit. Our calculation shows the field required to induce a 0.1
gap in metallic SWNTs can be easily reached under the current
experimental conditions. It indicates a kind of possibility to apply nanotubes
to electric signal-controlled nanoscale switching devices
Spheres and Prolate and Oblate Ellipsoids from an Analytical Solution of Spontaneous Curvature Fluid Membrane Model
An analytic solution for Helfrich spontaneous curvature membrane model (H.
Naito, M.Okuda and Ou-Yang Zhong-Can, Phys. Rev. E {\bf 48}, 2304 (1993); {\bf
54}, 2816 (1996)), which has a conspicuous feature of representing the circular
biconcave shape, is studied. Results show that the solution in fact describes a
family of shapes, which can be classified as: i) the flat plane (trivial case),
ii) the sphere, iii) the prolate ellipsoid, iv) the capped cylinder, v) the
oblate ellipsoid, vi) the circular biconcave shape, vii) the self-intersecting
inverted circular biconcave shape, and viii) the self-intersecting nodoidlike
cylinder. Among the closed shapes (ii)-(vii), a circular biconcave shape is the
one with the minimum of local curvature energy.Comment: 11 pages, 11 figures. Phys. Rev. E (to appear in Sept. 1999
A large sample of low surface brightness disk galaxies from the SDSS. I: The sample and the stellar populations
We present the properties of a large sample (12,282) of nearly face-on low
surface brightness (LSB) disk galaxies selected from the main galaxy sample of
SDSS-DR4. These properties include B-band central surface brightness mu_0(B),
scale lengths h, integrated magnitudes, colors, and distances D. This sample
has mu_0(B) values from 22 to 24.5 mag arcsec^{-2} with a median value of 22.42
mag arcsec^{-2}, and disk scale lengths ranging from 2 to 19 kpc. They are
quite bright with M_B taking values from -18 to -23 mag with a median value of
-20.08 mag. There exist clear correlations between logh and M_B, logh and logD,
logD and M_B. However, no obvious correlations are found between mu_0(B) and
logh, colors etc. The correlation between colors and logh is weak even though
it exists. Both the optical-optical and optical-NIR color-color diagrams
indicate that most of them have a mixture of young and old stellar populations.
They also satisfy color-magnitude relations, which indicate that brighter
galaxies tend generally to be redder. The comparison between the LSBGs and a
control sample of nearly face-on disk galaxies with higher surface brightness
(HSB) with mu_0(B) from 18.5 to 22 mag arcsec^{-2} show that, at a given
luminosity or distance, the observed LSB galaxies tend to have larger scale
lengths. These trends could be seen gradually by dividing both the LSBGs and
HSBGs into two sub-groups according to surface brightness. A volume-limited
sub-sample was extracted to check the incompleteness of surface brightness. The
only one of the property relations having an obvious change is the relation of
logh versus mu_0(B), which shows a correlation in this sub-sample.Comment: 14 pages, 18 figures, accepted for publication in MNRA
Adaptive obstacle detection for mobile robots in urban environments using downward-looking 2D LiDAR
Environment perception is important for collision-free motion planning of outdoor mobile robots. This paper presents an adaptive obstacle detection method for outdoor mobile robots using a single downward-looking LiDAR sensor. The method begins by extracting line segments from the raw sensor data, and then estimates the height and the vector of the scanned road surface at each moment. Subsequently, the segments are divided into either road ground or obstacles based on the average height of each line segment and the deviation between the line segment and the road vector estimated from the previous measurements. A series of experiments have been conducted in several scenarios, including normal scenes and complex scenes. The experimental results show that the proposed approach can accurately detect obstacles on roads and could effectively deal with the different heights of obstacles in urban road environments
Square patterns in Rayleigh-Benard convection with rotation about a vertical axis
We present experimental results for Rayleigh-Benard convection with rotation
about a vertical axis at dimensionless rotation rates in the range 0 to 250 and
upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with
predictions of linear stability analysis. For rotation rates greater than 70
and close to onset, the patterns are cellular with local four-fold coordination
and differ from the theoretically expected Kuppers-Lortz unstable state. Stable
as well as intermittent defect-free square lattices exist over certain
parameter ranges. Over other ranges defects dynamically disrupt the lattice but
cellular flow and local four-fold coordination is maintained.Comment: ReVTeX, 4 pages, 7 eps figures include
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