6,673 research outputs found
Theory and optimization of transformation-based quadratic spherical cloaks
Based on the concept of the cloak generating function, we propose a numerical
method to compute the invisibility performance of various quadratic spherical
cloaks and obtain optimal invisibility results. A non-ideal discrete model is
used to calculate and optimize the total scattering cross-sections of different
profiles of the generating function. A bell-shaped quadratic spherical cloak is
found to be the best candidate, which is further optimized by controlling
design parameters involved. Such improved invisibility is steady even when the
model is highly discretized.Comment: 18 pages, 9 figure
An inverse method of designing cylindrical cloaks without knowing coordinate transformation
An inverse way to define the parameters of ideal cylindrical cloaks is
developed, in which the interconnection between the parameters is revealed for
the first time without knowing a specific coordinate transformation. The
required parameters are derived in terms of the integral form of cloaking
generators, which is very general and allows us to examine the significance of
the parametric profiles. The validity of such inverse way and the invisibility
characteristics are presented in full-wave numerical simulation of plane wave
scattering by cloaked cylinders.Comment: 6 pages, 1 figur
Analytical spectral-domain scattering theory of a general gyrotropic sphere
We propose an analytical scattering theory in spectral domain to model the
electromagnetic (EM) fields of a gyrotropic sphere in terms of the
eigen-functions and their associated spectral eigenvalues/coefficients in a
recursive integral form. Applying the continuous boundary conditions of
electromagnetic fields on the surface between the free space and gyrotropic
sphere, the spectral coefficients of transmitted fields inside the gyrotropic
sphere and the scattered fields in the isotropic host medium can be obtained
exactly by expanding spherical vector wave eigenfunctions. Numerical results
are provided for some representative cases, which are compared to the results
from adaptive integral method (AIM). Good agreement demonstrates the validity
of the proposed analytical scattering theory for gyrotropic spheres in spectral
domain using Fourier transform.Comment: 18 pages, 4 figure
Estimating the Probability of Wind Ramping Events: A Data-driven Approach
This letter proposes a data-driven method for estimating the probability of
wind ramping events without exploiting the exact probability distribution
function (PDF) of wind power. Actual wind data validates the proposed method
Creation of Tunable Homogeneous Thermal Cloak with Constant Conductivity
Invisible cloak has long captivated the popular conjecture and attracted
intensive research in various communities of wave dynamics, e.g., optics,
electromagnetics, acoustics, etc. However, their inhomogeneous and extreme
parameters imposed by transformation-optic method will usually require
challenging realization with metamaterials, resulting in narrow bandwidth,
loss, polarization-dependence, etc. On the contrary, we demonstrate that
tunable thermodynamic cloak can be achieved with homogeneous and finite
conductivity only employing naturally available materials. The controlled
localization of thermal distribution inside the coating layer has been
presented, and it shows that an incomplete cloak can function perfectly.
Practical realization of such homogeneous thermal cloak has been suggested by
using two naturally occurring conductive materials, which provides an
unprecedentedly plausible way to flexibly realize flexible thermal cloak and
manipulate thermal flow.Comment: 12 pages, 4 figure
Twisted Acoustics
We use metasurfaces to enable acoustic orbital angular momentum (a-OAM) based
multiplexing in real-time, postprocess-free and sensor-scanning-free fashions
to improve the bandwidth of acoustic communication, with intrinsic
compatibility and expandability to cooperate with other multiplexing
technologies. The mechanism relied on encoding information onto twisted beams
is numerically and experimentally demonstrated by realizing the real-time
picture transfer, which differs from existing static data transfer by encoding
data onto OAM states. Our study can boost the capacity of acoustic
communication links and offer potential to revolutionize relevant fields
Robust Unit Commitment Considering Strategic Wind Generation Curtailment
Wind generation is traditionally treated as a non-dispatchable resource and
is fully absorbed unless there are security issues. To tackle the operational
reliability issues caused by the volatile and non-dispatchable wind generation,
many dispatch frameworks have been proposed, including robust unit commitment
(RUC) considering wind variation. One of the drawbacks that commonly exist in
those dispatch frameworks is increased demand on flexibility resources and
associated costs. To improve wind dispatchability and reduce flexibility
resource costs, in this paper, we propose a novel RUC model considering
strategic wind generation curtailment (WGC). Strategic WGC can reduce wind
uncertainty and variability and increase the visibility of wind generation
capacity. As a result, the ramping requirement for wind generation will be
reduced and ramp-up capability of wind generation can be increased, leading to
reduced day-ahead operational cost with guaranteed operational reliability
requirement of power systems. The economic benefits also include profits gained
by wind farm by providing ramping-up capacities other auxiliary services. We
also propose a solution algorithm based on the column and constraint generation
(C&CG). Simulations on the IEEE 39-bus system and two larger test systems
demonstrate the effectiveness of the proposed RUC model and efficiency of the
proposed computational methodology.Comment: arXiv admin note: substantial text overlap with arXiv:1510.0331
Cloaking the magnons
We propose two approaches to cloak the spin waves (magnons) by investigating
magnetization dynamics. One approach is based on a spatially inhomogeneous
anisotropic magnetic moment tensor. The other mechanism is using a spatially
inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous
external magnetic field. For both approaches, the damping tensor is also
inhomogeneous and anisotropic. The magnetic characteristic functions of the
magnetic materials have been theoretically derived for both mechanisms. A
non-magnetic core, which prevents magnons from entering and consequently
distorts the spin wave propagation, can be cloaked by a structured magnetic
shell to redirect the spin wave around the core using the above design
mechanisms. We discuss the feasibility of the proposed mechanisms in an
ensemble of quantum dot molecules and magnetic semiconductors. The proposed
approaches shed light on transformation magnonics, and can be utilized for
future spin-wave lenses, concentrators, low back-scattering waveguides, and
ultimately quantum computing.Comment: Accepted for publication in Phys. Rev.
IncepText: A New Inception-Text Module with Deformable PSROI Pooling for Multi-Oriented Scene Text Detection
Incidental scene text detection, especially for multi-oriented text regions,
is one of the most challenging tasks in many computer vision applications.
Different from the common object detection task, scene text often suffers from
a large variance of aspect ratio, scale, and orientation. To solve this
problem, we propose a novel end-to-end scene text detector IncepText from an
instance-aware segmentation perspective. We design a novel Inception-Text
module and introduce deformable PSROI pooling to deal with multi-oriented text
detection. Extensive experiments on ICDAR2015, RCTW-17, and MSRA-TD500 datasets
demonstrate our method's superiority in terms of both effectiveness and
efficiency. Our proposed method achieves 1st place result on ICDAR2015
challenge and the state-of-the-art performance on other datasets. Moreover, we
have released our implementation as an OCR product which is available for
public access.Comment: Accepted by IJCAI 201
Can scaling analysis be used to interpret the anti-parity-time symmetry in heat transfer?
In a previous work (Li et al. Science 364, 170) [1], we proposed a heat
transfer system that preserves the anti-parity-time (APT) symmetry, and observe
the rest-to-motion phase transition during the symmetry breaking. Recently, it
was suggested (Zhao et al. arXiv:1906.08431) [2] that the behaviours of the
system can be understood using scaling analysis based on the P\'eclet and
Nusselt numbers (Pe and Nu). It was further proposed that there exists a third
regime in the phase diagram in addition to the symmetric and symmetry broken
phases. Although we appreciate the proposal to characterize the contributions
of coupling, diffusion, and advection with dimensionless numbers, here we show
that they do not help to predict or interpret the behaviours of the APT system.
The dimensionless numbers do not provide enough details about the system to
conclude that there is a motionless phase, a phase transition, to find the
critical point, or to give the correct phase diagram with only two regimes
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