220 research outputs found
Estimation of the complex frequency of a harmonic signal based on a linear least squares method
AbstractIn this study, we propose a simple linear least squares estimation method (LLS) based on a Fourier transform to estimate the complex frequency of a harmonic signal. We first use a synthetically-generated noisy time series to validate the accuracy and effectiveness of LLS by comparing it with the commonly used linear autoregressive method (AR). For an input frequency of 0.5 mHz, the calculated deviations from the theoretical value were 0.004‰ and 0.008‰ for the LLS and AR methods respectively; and for an input 5 × 10−6 attenuation, the calculated deviations for the LLS and AR methods were 2.4% and 1.6%. Though the theory of the AR method is more complex than that of LLS, the results show LLS is a useful alternative method. Finally, we use LLS to estimate the complex frequencies of the five singlets of the 0S2 mode of the Earth's free oscillation. Not only are the results consistent with previous studies, the method has high estimation precisions, which may prove helpful in determining constraints on the Earth's interior structures
Estimating Photometric Redshifts of Quasars via K-nearest Neighbor Approach Based on Large Survey Databases
We apply one of lazy learning methods named k-nearest neighbor algorithm
(kNN) to estimate the photometric redshifts of quasars, based on various
datasets from the Sloan Digital Sky Survey (SDSS), UKIRT Infrared Deep Sky
Survey (UKIDSS) and Wide-field Infrared Survey Explorer (WISE) (the SDSS
sample, the SDSS-UKIDSS sample, the SDSS-WISE sample and the SDSS-UKIDSS-WISE
sample). The influence of the k value and different input patterns on the
performance of kNN is discussed. kNN arrives at the best performance when k is
different with a special input pattern for a special dataset. The best result
belongs to the SDSS-UKIDSS-WISE sample. The experimental results show that
generally the more information from more bands, the better performance of
photometric redshift estimation with kNN. The results also demonstrate that kNN
using multiband data can effectively solve the catastrophic failure of
photometric redshift estimation, which is met by many machine learning methods.
By comparing the performance of various methods for photometric redshift
estimation of quasars, kNN based on KD-Tree shows its superiority with the best
accuracy for our case.Comment: 28 pages, 4 figures, 3 tables, accepted for publication in A
Enhancing extraordinary transmission of light through a metallic nano slit with a nano cavity antenna
The extraordinary transmission of light through a nano slit in a metal film
is enhanced by introducing a nano cavity antenna formed by a nearby metallic
nano-strip over the slit opening. For a fixed wavelength, the width of the
metallic nano-strip should be chosen to make the horizontal
metal-insulator-metal waveguide of finite length resonant as a Fabry-Perot
cavity. When such a cavity antenna is used to enhance the transmission through
a non-resonant nano slit, the slit should be opened at a position with maximal
magnetic field in the horizontal resonant cavity. It is shown that an optimized
cavity antenna can enhance greatly the transmission of light through a
non-resonant nano slit (by about 20 times) or a resonant nano slit (by 124%).
The transmission spectrum of the nano slit can also be tuned by adjusting the
width of the metallic nano-strip. Such a transmission enhancement with a nano
cavity antenna is studied for the first time and the physical mechanism is
explained.Comment: 4 pages, 5 figure
Ultra-broadband Microwave Metamaterial Absorber
A microwave ultra-broadband polarization-independent metamaterial absorber is
demonstrated. It is composed of a periodic array of metal-dielectric
multilayered quadrangular frustum pyramids. These pyramids possess resonant
absorption modes at multi-frequencies, of which the overlapping leads to the
total absorption of the incident wave over an ultra-wide spectral band. The
experimental absorption at normal incidence is above 90% in the frequency range
of 7.8-14.7GHz, and the absorption is kept large when the incident angle is
smaller than 60 degrees. The experimental results agree well with the numerical
simulation.Comment: 10 pages, 5 figures,submitted to AP
Optical Curtain Effect: Extraordinary Optical Transmission Enhanced by Antireflection
In this paper, we employ an antireflective coating which comprises inverted π-shaped metallic grooves to manipulate the behaviour of a transverse-magnetic (TM)-polarised plane wave transmitted through a periodic nanoslit array. At normal incidence, such scheme cannot only retain the optical curtain effect in the output region but also generate the extraordinary transmission of light through the nanoslits with the total transmission efficiency as high as 90 %. Besides, we show that the spatially invariant field distribution in the output region as well as the field distribution of resonant modes around the inverted π-shaped grooves can be reproduced immaculately when the system is excited by an array of point sources beneath the inverted π-shaped grooves. Furthermore, we investigate the influence of centre groove and side-corners of the inverted π-shaped grooves on suppressing the reflection of light, respectively. Based on our work, it shows promising potential in applications of enhancing the extraction efficiency as well as controlling the beaming pattern of light emitting diodes.National Natural Science Foundation (China) (Grants 11204205, 60976018, 61274056 and 60990320)Natural Foundation of Shanxi (Grant 2012011020-4)Taiyuan University of Technology (Special Foundation and Starting Research Fund
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