29,699 research outputs found
Observation of backscattering-immune chiral electromagnetic modes without time reversal breaking
A strategy is proposed to realize robust transport in time reversal invariant
photonic system. Using numerical simulation and microwave experiment, we
demonstrate that a chiral guided mode in the channel of a three-dimensional
dielectric woodpile photonic crystal is immune to the scattering of a square
patch of metal or dielectric inserted to block the channel. The chirality based
robust transport can be realized in nonmagnetic dielectric materials without
any external field.Comment: 16 pages, 5 figure
Spinon Fermi surface in a cluster Mott insulator model on a triangular lattice and possible application to 1T-TaS
1T-TaS is a cluster Mott insulator on the triangular lattice with 13 Ta
atoms forming a star of David cluster as the unit cell. We derive a two
dimensional XXZ spin-1/2 model with four-spin ring exchange term to describe
the effective low energy physics of a monolayer 1T-TaS, where the effective
spin-1/2 degrees of freedom arises from the Kramers degenerate spin-orbital
states on each star of David. A large scale density matrix renormalization
group simulation is further performed on this effective model and we find a
gapless spin liquid phase with spinon Fermi surface at moderate to large
strength region of four-spin ring exchange term. All peaks in the static spin
structure factor are found to be located on the "" surface of half-filled
spinon on the triangular lattice. Experiments to detect the spinon Fermi
surface phase in 1T-TaS are discussed.Comment: 5+11 pages, 4+13 figure
Exact Algorithms for Maximum Independent Set
We show that the maximum independent set problem (MIS) on an -vertex graph
can be solved in time and polynomial space, which even is
faster than Robson's -time exponential-space algorithm
published in 1986. We also obtain improved algorithms for MIS in graphs with
maximum degree 6 and 7, which run in time of and
, respectively. Our algorithms are obtained by using fast
algorithms for MIS in low-degree graphs in a hierarchical way and making a
careful analyses on the structure of bounded-degree graphs
Illusion optics: The optical transformation of an object into another object
We propose to use transformation optics to generate a general illusion such
that an arbitrary object appears to be like some other object of our choice.
This is achieved by using a remote device that transforms the scattered light
outside a virtual boundary into that of the object chosen for the illusion,
regardless of the profile of the incident wave. This type of illusion device
also enables people to see through walls. Our work extends the concept of
cloaking as a special form of illusion to the wider realm of illusion optics.Comment: Including a paper and its auxiliary materia
Vision-aided nonlinear control framework for shake table tests
The structural response under the earthquake excitations can be simulated by
scaled-down model shake table tests or full-scale model shake table tests. In
this paper, adaptive control theory is used as a nonlinear shake table control
algorithm which considers the inherent nonlinearity of the shake table system
and the Control-Structural Interaction (CSI) effect that the linear controller
cannot consider, such as the Proportional-Integral-Derivative (PID) controller.
The mass of the specimen can be assumed as an unknown variation and the unknown
parameter will be replaced by an estimated value in the proposed control
framework. The signal generated by the control law of the adaptive control
method will be implemented by a loop-shaping controller. To verify the
stability and feasibility of the proposed control framework, a simulation of a
bare shake table and experiments with a bare shake table with a two-story frame
were carried out. This study randomly selects Earthquake recordings from the
Pacific Earthquake Engineering Research Center (PEER) database. The simulation
and experimental results show that the proposed control framework can be
effectively used in shake table control.Comment: 10 pages, 7 figures, accepted in the Canadian Conference - Pacific
Conference on Earthquake Engineering 2023, Vancouver, British Columbi
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