82,394 research outputs found
Criticality and Continuity of Explosive Site Percolation in Random Networks
This Letter studies the critical point as well as the discontinuity of a
class of explosive site percolation in Erd\"{o}s and R\'{e}nyi (ER) random
network. The class of the percolation is implemented by introducing a best-of-m
rule. Two major results are found: i). For any specific , the critical
percolation point scales with the average degree of the network while its
exponent associated with is bounded by -1 and . ii).
Discontinuous percolation could occur on sparse networks if and only if
approaches infinite. These results not only generalize some conclusions of
ordinary percolation but also provide new insights to the network robustness.Comment: 5 pages, 5 figure
Nuclear Spin Relaxation Rate of Disordered -wave Superconductors
Based on an effective Hamiltonian with the binary alloy disorder model
defined in the triangular lattice, the impurity scattering effects on the
density of states and especially on the spin-lattice relaxation rate of
-wave superconductors are studied by solving numerically the
Bogoliubov-de Gennes equations. In the clean limit, the coherence peak of
is observed as expected. More intriguingly, for strong scattering
potential, the temperature dependence of exhibits the two different
power law behaviors near and at low temperatures, respectively,
which is in good agreement with the nuclear quadrupolar resonance measurement.Comment: 4 pages, 3 figure
Dynamics of compressible edge and bosonization
We work out the dynamics of the compressible edge of the quantum Hall system
based on the electrostatic model of Chklovskii et al.. We introduce a
generalized version of Wen's hydrodynamic quantization approach to the dynamics
of sharp edge and rederive Aleiner and Glazman's earlier result of multiple
density modes. Bosonic operators of density excitations are used to construct
fermions at the interface of the compressible and incompressible region. We
also analyze the dynamics starting with the second-quantized Hamiltonian in the
lowest Landau level and work out the time development of density operators.
Contrary to the hydrodynamic results, the density modes are strongly coupled.
We argue that the coupling suppresses the propagation of all acoustic modes,
and that the excitations with large wavevectors are subject to decay due to
coupling to the dissipative acoustic modes.A possible correction to the
tunneling density of states is discussed.Comment: 7 pages, Revtex, 1 figur
Iwasawa Effects in Multi-layer Optics
There are many two-by-two matrices in layer optics. It is shown that they can
be formulated in terms of a three-parameter group whose algebraic property is
the same as the group of Lorentz transformations in a space with two space-like
and one time-like dimensions, or the group which is a standard
theoretical tool in optics. Among the interesting mathematical properties of
this group, the Iwasawa decomposition drastically simplifies the matrix algebra
under certain conditions, and leads to a concise expression for the S-matrix
for transmitted and reflected rays. It is shown that the Iwasawa effect can be
observed in multi-layer optics, and a sample calculation of the S-matrix is
given.Comment: RevTex 10 pages including 1 psfi
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
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