Two-dimensional low-frequency K4LiH3(SO4)4 crystal lattice vibrations

Speckles are inherent to SAR. They hide and undermine several relevant information contained in the SAR images. In this paper, a despeckling algorithm using the shrinkage of two-dimensional discrete orthonormal S-transform (2D-DOST) coefficients in the transform domain along with shock filter is proposed. Also, an attempt has been made as a post-processing step to preserve the edges and other details while removing the speckle. The proposed strategy involves decomposing the SAR image into low and high-frequency components and processing them separately. A shock filter is used to smooth out the small variations in low-frequency components, and the high-frequency components are treated with a shrinkage of 2D-DOST coefficients. The edges, for enhancement, are detected using a ratio-based edge detection algorithm. The proposed method is tested, verified, and compared with some well-known models on C-band and X-band SAR images. A detailed experimental analysis is illustrated.

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Tunable characteristics of low-frequency bandgaps in two-dimensional multivibrator phononic crystal plates under prestrain

Scientific Reports ◽

10.1038/s41598-021-87904-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Hai-Fei Zhu ◽

Xiao-Wei Sun ◽

Ting Song ◽

Xiao-Dong Wen ◽

Xi-Xuan Liu ◽

...

Keyword(s):

Phononic Crystal ◽

Real Life ◽

Low Frequency ◽

Acoustic Vibration ◽

Crystal Plate ◽

Frequency Noise ◽

Two Dimensional ◽

The Matrix ◽

Noise Frequency ◽

Realtime Control

AbstractIn view of the influence of variability of low-frequency noise frequency on noise prevention in real life, we present a novel two-dimensional tunable phononic crystal plate which is consisted of lead columns deposited in a silicone rubber plate with periodic holes and calculate its bandgap characteristics by finite element method. The low-frequency bandgap mechanism of the designed model is discussed simultaneously. Accordingly, the influence of geometric parameters of the phononic crystal plate on the bandgap characteristics is analyzed and the bandgap adjustability under prestretch strain is further studied. Results show that the new designed phononic crystal plate has lower bandgap starting frequency and wider bandwidth than the traditional single-sided structure, which is due to the coupling between the resonance mode of the scatterer and the long traveling wave in the matrix with the introduction of periodic holes. Applying prestretch strain to the matrix can realize active realtime control of low-frequency bandgap under slight deformation and broaden the low-frequency bandgap, which can be explained as the multiple bands tend to be flattened due to the localization degree of unit cell vibration increases with the rise of prestrain. The presented structure improves the realtime adjustability of sound isolation and vibration reduction frequency for phononic crystal in complex acoustic vibration environments.

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Tunable low-frequency bandgaps of a new two-dimensional multi-component phononic crystal under different pressures, geometric parameters and pre-compression strains

Mechanics of Advanced Materials and Structures ◽

10.1080/15376494.2021.1916139 ◽

2021 ◽

pp. 1-16

Author(s):

Xiao-Wei Sun ◽

Hai-Fei Zhu ◽

Xing-Lin Gao ◽

Ting Song ◽

Zi-Jiang Liu

Keyword(s):

Phononic Crystal ◽

Low Frequency ◽

Geometric Parameters ◽

Two Dimensional

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Effective real-space correlations of crystal lattice vibrations

Journal of Physics and Chemistry of Solids ◽

10.1016/j.jpcs.2020.109773 ◽

2020 ◽

pp. 109773

Author(s):

Roman Tomaschitz

Keyword(s):

Crystal Lattice ◽

Real Space ◽

Lattice Vibrations

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Two-dimensional mobile breather scattering in a hexagonal crystal lattice

Physical Review E ◽

10.1103/physreve.103.022212 ◽

2021 ◽

Vol 103 (2) ◽

Author(s):

Jānis Bajārs ◽

J. Chris Eilbeck ◽

Benedict Leimkuhler

Keyword(s):

Crystal Lattice ◽

Two Dimensional ◽

Hexagonal Crystal

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Glaciation and deglaciation mechanisms in a coupled two-dimensional climate—ice-sheet model

Journal of Glaciology ◽

10.1017/s0022143000015707 ◽

1993 ◽

Vol 39 (131) ◽

pp. 45-49 ◽

Cited By ~ 19

Author(s):

André Berger ◽

Hubert Gallée ◽

Christian Tricot

Keyword(s):

Ice Core ◽

Ice Sheets ◽

Low Frequency ◽

Two Dimensional ◽

Atmospheric Concentration ◽

Last Glacial ◽

Simulated Climate ◽

Milankovitch Theory ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract A two-dimensional model which links the atmosphere, the mixed layer of the ocean, the sea ice, the continents, the ice sheets and their underlying bedrock has been used to test the Milankovitch theory over the last glacial—interglacial cycle. It was found that the orbital variations alone can induce, in such a system, feed-backs sufficient to generate the low-frequency part of the climatic variations over the last 122 kyear. These simulated variations at the astronomical time-scale are broadly in agreement with ice volume and sea-level reconstructions independently obtained from geological data. Imperfections in the simulated climate were the insufficient southward extent of the ice sheets and the too small hemispheric cooling during the last glacial maximum. These deficiencies were partly remedied in a further experiment (Gallée and others, in press) by using the time-dependent CO2 atmospheric concentration given by the Vostok ice core in addition to the astronomical forcing. For this second experiment, the main mechanisms and feedbacks responsible for the glaciation and the deglaciation in the model are discussed here.

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Far Infrared Group Frequencies. V. Oximes and Aldoximes

Applied Spectroscopy ◽

10.1366/000370273774333939 ◽

1973 ◽

Vol 27 (1) ◽

pp. 22-26 ◽

Cited By ~ 5

Author(s):

S. M. Craven ◽

F. F. Bentley ◽

D. F. Pensenstadler

Keyword(s):

Hydrogen Bond ◽

Infrared Spectra ◽

Low Frequency ◽

Far Infrared ◽

Torsional Vibrations ◽

Lattice Vibrations ◽

Dilute Solutions ◽

Solid Samples ◽

Bending Modes ◽

Bond Stretch

The low frequency infrared spectra from 450 to 75 cm−1 of seven oximes and five aldoximes have been recorded for pure samples and for dilute solutions in cyclohexane. An intense characteristic band is present in the solution spectra at 367 ± 10 cm−1. This characteristic band shifts to 275 ± 10 cm−1 in the spectra of the OD compounds. The 367 ± 10 cm−1 and 275 ± 10 cm−1 bands are assigned to OH and OD torsional vibrations. A comparison of the solution spectra with spectra of the solid samples indicated that the OH … N hydrogen bond stretch of oximes and aldoximes occurs in 300 to 200 cm−1 region. Strong bands also are present in 140 to 100 cm−1 region which are due to OH … N bending modes or perhaps lattice vibrations.

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