117,627 research outputs found
Channel Parameters Estimation Algorithm Based on The Characteristic Function under Impulse Noise Environment
Under communication environments, such as wireless sensor networks, the noise observed usually exhibits impulsive as well as Gaussian characteristics. In the initialization of channel iterative decoder, such as low density parity check codes, it is required in advance to estimate the channel parameters to obtain the prior information from the received signals. In this paper, a blind channel parameters estimator under impulsive noise environment is proposed, which is based on the empirical characteristic function in MPSK/MQAM higher-order modulation system. Simulation results show that for various MPSK/MQAM modulations, the estimator can obtain a more accurate unbiased estimation even though we do not know which kind of higher-order modulation is used
Experimental study of contact transition control incorporating joint acceleration feedback
Joint acceleration and velocity feedbacks are incorporated into a classical internal force control of a robot in contact with the environment. This is intended to achieve a robust contact transition and force tracking performance for varying unknown environments, without any need of adjusting the controller parameters, A unified control structure is proposed for free motion, contact transition, and constrained motion in view of the consumption of the initial kinetic energy generated by a nonzero impact velocity. The influence of the velocity and acceleration feedbacks, which are introduced especially for suppressing the transition oscillation, on the postcontact tracking performance is discussed. Extensive experiments are conducted on the third joint of a three-link direct-drive robot to verify the proposed scheme for environments of various stiffnesses, including elastic (sponge), less elastic (cardboard), and hard (steel plate) surfaces. Results are compared with those obtained by the transition control scheme without the acceleration feedback. The ability of the proposed control scheme in resisting the force disturbance during the postcontact period is also experimentally investigated
Finding The Sign Of A Function Value By Binary Cellular Automaton
Given a continuous function , suppose that the sign of only has
finitely many discontinuous points in the interval . We show how to use
a sequence of one dimensional deterministic binary cellular automata to
determine the sign of where is the (number) density of 1s in
an arbitrarily given bit string of finite length provided that satisfies
certain technical conditions.Comment: Revtex, uses amsfonts, 10 page
PSR B1828-11: a precession pulsar torqued by a quark planet?
The pulsar PSR B1828-11 has long-term, highly periodic and correlated
variations in both pulse shape and the rate of slow-down. This phenomenon may
provide evidence for precession of the pulsar as suggested previously within
the framework of free precession as well as forced one. On a presumption of
forced precession, we propose a quark planet model to this precession henomenon
instead, in which the pulsar is torqued by a quark planet. We construct this
model by constraining mass of the pulsar (), mass of the planet
() and orbital radius of the planet (). Five aspects
are considered: derived relation between and ,
movement of the pulsar around the center of mass, ratio of and
, gravitational wave radiation timescale of the planetary system,
and death-line criterion. We also calculate the range of precession period
derivative and gravitational wave strength (at earth) permitted by the model.
Under reasonable parameters, the observed phenomenon can be understood by a
pulsar () with a quark planet
() orbiting it. According to the calculations
presented, the pulsar would be a quark star because of its low mass, which
might eject a lump of quark matter (to become a planet around) during its
birth.Comment: 6 pages, 3 figures, accepted by MNRAS (Letters
Quantum Phase Transitions beyond the Landau's Paradigm in Sp(4) Spin System
We propose quantum phase transitions beyond the Landau's paradigm of Sp(4)
spin Heisenberg models on the triangular and square lattices, motivated by the
exact Sp(4) SO(5) symmetry of spin-3/2 fermionic cold atomic system
with only wave scattering. On the triangular lattice, we study a phase
transition between the spin ordered phase and a
spin liquid phase, this phase transition is described by an O(8) sigma model in
terms of fractionalized spinon fields, with significant anomalous scaling
dimensions of spin order parameters. On the square lattice, we propose a
deconfined critical point between the Neel order and the VBS order, which is
described by the CP(3) model, and the monopole effect of the compact U(1) gauge
field is expected to be suppressed at the critical point.Comment: 6 pages, 3 figure
Point trajectory planning of flexible redundant robot manipulators using genetic algorithms
The paper focuses on the problem of point-to-point trajectory planning for flexible redundant robot manipulators (FRM) in joint space. Compared with irredundant flexible manipulators, a FRM possesses additional possibilities during point-to-point trajectory planning due to its kinematics redundancy. A trajectory planning method to minimize vibration and/or executing time of a point-to-point motion is presented for FRMs based on Genetic Algorithms (GAs). Kinematics redundancy is integrated into the presented method as planning variables. Quadrinomial and quintic polynomial are used to describe the segments that connect the initial, intermediate, and final points in joint space. The trajectory planning of FRM is formulated as a problem of optimization with constraints. A planar FRM with three flexible links is used in simulation. Case studies show that the method is applicable
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