5,533 research outputs found
Giant Colloidal Diffusivity on Corrugated Optical Vortices
A single colloidal sphere circulating around a periodically modulated optical
vortex trap can enter a dynamical state in which it intermittently alternates
between freely running around the ring-like optical vortex and becoming trapped
in local potential energy minima. Velocity fluctuations in this randomly
switching state still are characterized by a linear Einstein-like diffusion
law, but with an effective diffusion coefficient that is enhanced by more than
two orders of magnitude.Comment: 4 pages, 4 figure
Isobar of an ideal Bose gas within the grand canonical ensemble
We investigate the isobar of an ideal Bose gas confined in a cubic box within
the grand canonical ensemble, for a large yet finite number of particles, N.
After solving the equation of the spinodal curve, we derive precise formulae
for the supercooling and the superheating temperatures which reveal an N^{-1/3}
or N^{-1/4} power correction to the known Bose-Einstein condensation
temperature in the thermodynamic limit. Numerical computations confirm the
accuracy of our analytical approximation, and further show that the isobar
zigzags on the temperature-volume plane if N is greater than or equal to 14393.
In particular, for the Avogadro's number of particles, the volume expands
discretely about 10^5 times. Our results quantitatively agree with a previous
study on the canonical ensemble within 0.1% error.Comment: 6 pages, 2 figures; Reference added. Accepted for publication in
Phys. Rev.
Development of Transgenic Tall Fescue Plants with Enhanced Tolerance to Multiple Abiotic Stresses
Spontaneous phase oscillation induced by inertia and time delay
We consider a system of coupled oscillators with finite inertia and
time-delayed interaction, and investigate the interplay between inertia and
delay both analytically and numerically. The phase velocity of the system is
examined; revealed in numerical simulations is emergence of spontaneous phase
oscillation without external driving, which turns out to be in good agreement
with analytical results derived in the strong-coupling limit. Such
self-oscillation is found to suppress synchronization and its frequency is
observed to decrease with inertia and delay. We obtain the phase diagram, which
displays oscillatory and stationary phases in the appropriate regions of the
parameters.Comment: 5 pages, 6 figures, to pe published in PR
Path Tracking Controller of Quadruped Robot for Obstacle Avoidance Using Potential Functions Method
This paper proposes a tracking controller for obstacle avoidance of a quadruped robot using potential functions method. The followings are done for this task. At first, a ceiling-mounted camera system is installed for image processing. The goal point and obstacles are separated and recognized by a color recognition method. Second, a path planning algorithm using potential functions method is proposed to generate the path to avoid obstacles and to plan a path for the quadruped robot to reach from start point to goal point. Third, a quadruped robot is chosen as the mobile platform for this study and the kinematic model for the robot is presented. Fourth, a tracking controller is designed for the quadruped robot to track the trajectory based on the backstepping method using Lyapunov function. Finally, the simulation results are presented to show the effectiveness of the proposed trajectory planning algorithm and the tracking controller. [Keywords— Path tracking; back stepping; obstacles avoidance; potential functions; quadruped robot]
Collinear Factorization for Single Transverse-Spin Asymmetry in Drell-Yan Processes
We study the scattering of a single parton state with a multi-parton state to
derive the complete results of perturbative coefficient functions at leading
order, which appear in the collinear factorization for Single transverse-Spin
Asymmetry(SSA) in Drell-Yan processes with a transversely polarized hadron in
the initial state. We find that the factorization formula of SSA contains
hard-pole-, soft-quark-pole- and soft-gluon-pole contributions. It is
interesting to note that the leading order perturbative coefficient functions
of soft-quark-pole- and soft-gluon-pole contributions are extracted from parton
scattering amplitudes at one-loop, while the functions of hard-pole
contributions are extracted from the tree level amplitudes at tree-level. Our
method to derive the factorization of SSA is different than the existing one in
literature. A comparison of our results with those obtained by other method is
made.Comment: 27 pages, 14 figures, text improved, to appear in Phys. Rev.
EM Decay of X(3872) as the charmonium
The recently BaBar results raise the possibility that X(3872) has negative
parity. This makes people reconsider assigning X(3872) to the state. In this paper we give a general form of the wave function of
mesons. By solving the instantaneous Bethe-Salpeter equation, we get
the mass spectrum and corresponding wave functions. We calculate
electromagnetic decay widths of the first state which we assume to be
the X(3872) particle. The results are keV, eV and keV. The ratio of branch fractions
of the second and first channel is about 0.002, which is inconsistent with the
experimental value . So X(3872) is unlikely to be a
charmonium state. In addition, we obtain a relatively large decay width for
channel which is keV.Comment: Revised versio
Ordered Phases of Itinerant Dzyaloshinsky-Moriya Magnets and Their Electronic Properties
A field theory appropriate for magnets that display helical order due to the
Dzyaloshinsky-Moriya mechanism, a class that includes MnSi and FeGe, is used to
derive the phase diagram in a mean-field approximation. The helical phase, the
conical phase in an external magnetic field, and recent proposals for the
structure of the A-phase and the non-Fermi-liquid region in the paramagnetic
phase are discussed. It is shown that the orientation of the helical pitch
vector along an external magnetic field within the conical phase occurs via two
distinct phase transitions. The Goldstone modes that result from the long-range
order in the various phases are determined, and their consequences for
electronic properties, in particular the specific heat, the single-particle
relaxation time, and the electrical and thermal conductivities, are derived.
Various aspects of the ferromagnetic limit, and qualitative differences between
the transport properties of helimagnets and ferromagnets, are also discussed.Comment: 22pp, 8 eps fig
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