33,517 research outputs found
Finite-Difference Time-Domain Study of Guided Modes in Nano-plasmonic Waveguides
A conformal dispersive finite-difference time-domain (FDTD) method is
developed for the study of one-dimensional (1-D) plasmonic waveguides formed by
an array of periodic infinite-long silver cylinders at optical frequencies. The
curved surfaces of circular and elliptical inclusions are modelled in
orthogonal FDTD grid using effective permittivities (EPs) and the material
frequency dispersion is taken into account using an auxiliary differential
equation (ADE) method. The proposed FDTD method does not introduce numerical
instability but it requires a fourth-order discretisation procedure. To the
authors' knowledge, it is the first time that the modelling of curved
structures using a conformal scheme is combined with the dispersive FDTD
method. The dispersion diagrams obtained using EPs and staircase approximations
are compared with those from the frequency domain embedding method. It is shown
that the dispersion diagram can be modified by adding additional elements or
changing geometry of inclusions. Numerical simulations of plasmonic waveguides
formed by seven elements show that row(s) of silver nanoscale cylinders can
guide the propagation of light due to the coupling of surface plasmons.Comment: 6 pages, 10 figures, accepted for publication, IEEE Trans. Antennas
Propaga
A Radial-Dependent Dispersive Finite-Difference Time-Domain Method for the Evaluation of Electromagnetic Cloaks
A radial-dependent dispersive finite-difference time-domain (FDTD) method is
proposed to simulate electromagnetic cloaking devices. The Drude dispersion
model is applied to model the electromagnetic characteristics of the cloaking
medium. Both lossless and lossy cloaking materials are examined and their
operating bandwidth is also investigated. It is demonstrated that the perfect
"invisibility" from electromagnetic cloaks is only available for lossless
metamaterials and within an extremely narrow frequency band.Comment: 18 pages, 10 figure
Fast k-means based on KNN Graph
In the era of big data, k-means clustering has been widely adopted as a basic
processing tool in various contexts. However, its computational cost could be
prohibitively high as the data size and the cluster number are large. It is
well known that the processing bottleneck of k-means lies in the operation of
seeking closest centroid in each iteration. In this paper, a novel solution
towards the scalability issue of k-means is presented. In the proposal, k-means
is supported by an approximate k-nearest neighbors graph. In the k-means
iteration, each data sample is only compared to clusters that its nearest
neighbors reside. Since the number of nearest neighbors we consider is much
less than k, the processing cost in this step becomes minor and irrelevant to
k. The processing bottleneck is therefore overcome. The most interesting thing
is that k-nearest neighbor graph is constructed by iteratively calling the fast
-means itself. Comparing with existing fast k-means variants, the proposed
algorithm achieves hundreds to thousands times speed-up while maintaining high
clustering quality. As it is tested on 10 million 512-dimensional data, it
takes only 5.2 hours to produce 1 million clusters. In contrast, to fulfill the
same scale of clustering, it would take 3 years for traditional k-means
Energy-storage properties and electrocaloric effects of Pb(1-3x/2)LaxZr0.85Ti0.15O3 antiferroelectric thick films
1-µm-Pb(1-3x/2)LaxZr0.85Ti0.15O3 (PLZT) antiferroelectric (AFE) thick films with x = 0.08,
0.10, 0.12, and 0.14 were deposited on LaNiO3/Si (100) substrates by a sol-gel method. The
dielectric properties, energy-storage performance, electrocaloric effect, and leakage current behavior
were investigated in detail. With increasing La content, dielectric constant and saturated polarizations
of the thick films were gradually decreased. A maximum recoverable energy-storage density of 38
J/cm3 and efficiency of 71% were achieved in the thick films with x = 0.12 at room temperature.
Moreover, a large reversible adiabatic temperature change ∆T = 25.0
o
C was presented in the thick
films with x = 0.08 at 127
o
C at 990 kV/cm. All the samples had a lower leakage current density
below 10-
6
A/cm2 at room temperature. These results indicated that the PLZT AFE thick films could
be a potential candidate for applications in high energy-storage density capacitors and cooling
devices
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