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Identifying boundary between near field and far field in ground vibration caused by surface loading

Journal of Central South University 2014年第8期21卷 3284-3294页

作者：高广运宋健杨峻 Department of Geotechnical Engineering Tongji University Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education (Tongji University) Department of Civil Engineering The University of Hong Kong

The boundary between the near and far fields is generally defined as the distance from the vibration source beyond which ground vibrations are mainly dominated by Rayleigh waves. It is closely related to the type of vibration source and the soil properties. Based on the solutions of the Lamb＇s problem, the boundary at the surface between the near and far fields of ground vibration was investigated for a harmonic vertical concentrated load and an infinite line load at the surface of a visco-elastic half-space. Particularly, the variation of the boundary with the material damping was investigated for both cases. The results indicate that the material damping slightly contributes to the attenuation of vibrations in the near-source region, but significantly reduces the vibrations in the region that is at some distance away from the source. When taking the material damping into consideration, the boundary between the near and far fields tends to move towards the vibration source. Compared with the vibrations caused by a concentrated load, the vibrations induced by an infinite line load can affect a larger range of the surrounding environment, and they attenuate more slowly. This means the boundary between the near field and far field should move fitrther away from the source. Finally, the boundaries are defined in terms of R-wave length （2R） and Poisson ratio of the ground （o）. For the case of a point load, the boundary is located at the distance of （5.0-6.0）2R for v≤0.30 and at the distance of （2.0--3.0）2R for v≥0.35. For the case of an infinite line load, the boundary is located at the distance （5.5-6.5）2rt for v≤0.30 and at the distance （2.5--3.5）2R for v≥0.35.

关键词： boundary near field far field active isolation passive isolation visco-elastic half-space concentrated load line distributed load

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Microsphere femtosecond laser sub-50 nm structuring in far field via non-linear absorption

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Opto-Electronic Advances 2023年第6期6卷 8-17页

作者： Zhenyuan Lin Kuan Liu Tun Cao Minghui Hong Pen-Tung Sah Institute of Micro-Nano Science and Technology Xiamen UniversityXiamen 361102China School of Optoelectronic Engineering and Instrumentation Science Dalian University of TechnologyDalian 116024China Department of Electrical and Computer Engineering National University of Singapore4 Engineering Drive 3117576Singapore

Creation of arbitrary features with high resolution is critically important in the fabrication of nano-optoelectronic ***,sub-50 nm surface structuring is achieved directly on Sb2S3 thin films via microsphere femtosecond laser irradi-ation in far *** varying laser fluence and scanning speed,nano-feature sizes can be flexibly *** small patterns are attributed to the co-effect of microsphere focusing,two-photons absorption,top threshold effect,and high-repetition-rate femtosecond laser-induced incubation *** minimum feature size can be reduced down to~30 nm(λ/26)by manipulating film *** fitting analysis between the ablation width and depth predicts that the feature size can be down to~15 nm at the film thickness of~10 nm.A nano-grating is fabricated,which demonstrates desirable beam diffraction *** nano-scale resolution would be highly attractive for next-generation laser nano-lithography in far field and in ambient air.

关键词： non-linear effect microsphere femtosecond laser far field

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Zernike-coefficient extraction via helical beam reconstruction for optimization(ZEHBRO) in the far field

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High Power Laser Science and Engineering 2023年第6期11卷 213-222页

作者： J.B.Ohland D.Posor U.Eisenbarth V.Iancu R.Ungureanu D.Ursescu V.Bagnoud GSI Helmholtzzentrum für Schwerionenforschung DarmstadtGermany Institut für angewandte Physik Technische Universität DarmstadtDarmstadtGermany Helmholtz-Institut Jena JenaGermany ELI-NP Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering(IFIN-HH)M agureleIlfovRomania Faculty of Physics University of BucharestM agureleIlfovRomania Center for Advanced Laser Technologies(CETAL) National Institute for LaserPlasma and Radiation Physics(INFLPR)M agureleIlfovRomania

The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations,such as astigmatism,coma and *** poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an *** developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field.A fast,iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval *** output of our algorithm can be used to optimize the focal ring,as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure-Nuclear Physics facility.

关键词： beam quality far field orbital angular momentum ring intensity phase retrieval wavefront

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Critical distance of far field for basic radiation element

Critical distance of far field for basic radiation element

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2007 4th International Symposium on Electromagnetic Compatibility(EMC’2007)

The paper provides a new method to determine the critical distance of the far-field （FF） of a basic radiation element by calculating the relative error between approximate and exact FF values in three respects:field value in maximum radiation direction;the pattern of FF and wave *** result is obtained and recommended as critical distance of the basic radiation element,which is approached engineering requirement and calculation process is reduced *** can be widely used in antenna analysis and EMC prediction.

关键词： Computation Electromagnetics EMC far field critical distance

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Spectral anomalies and spectral switches of partially coherent and polychromatic light diffracted at an aperture

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Science China(Physics,Mechanics & Astronomy) 2004年第1期47卷 24-35页

作者： Lü Baida1, 3 & PAN Liuzhan1, 2 1. Institute of Laser Physics and Chemistry, Sichuan University, Chengdu 610064, China 2. Department of Physics, Luoyang Normal College, Luoyang 471022, China 3. State Key Laboratory of Laser Technology, Huazhong University of Science and Technology, Wuhan 430074, China Correspondence should be addressed to L Baida (email: badalu@***) Received July 10, 2003 1. Institute of Laser Physics and Chemistry Sichuan University 610064 Chengdu China 2. State Key Laboratory of Laser Technology Huazhong University of Science and Technology 430074 Wuhan China 3. Department of Physics Luoyang Normal College 471022 Luoyang China

Based on the propagation theory of partially coherent light in the space-frequency domain, the anomalous spectral behavior and spectral switches in the far field of partially coherent and polychromatic light diffracted at an aperture are studied. It is shown that, as compared with spatially fully coherent and polychromatic light whose spectral anomalies are induced only by aperture diffraction, the spectral anomalies and spectral switches of partially coherent and polychromatic light depend on the aperture diffraction, spatial correlationβ and bandwidth of the original spectrum. Detailed numerical calculations are made to illustrate the behavior of spectral switches of partially coherent and polychromatic light, and the results for spatially fully coherent and polychromatic light are treated as a special case ofβ=1 and included in our theory.

关键词： spectral anomaly spectral switch partially coherent and polychromatic light far field aperture diffraction

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PERTURBATION ANALYSIS FOR WAVE EQUATION OF NONLINEAR ELASTIC ROD

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Applied Mathematics and Mechanics(English Edition) 2006年第9期27卷 1233-1238页

作者：吕克璞郭鹏张磊易金桥段文山 College of Physics and Electronic Engineering Northwest Normal University Lanzhou 730070 P. R. China

The longitudinal oscillation of a nonlinear elastic rod with lateral inertia was studied. Based on the far field and simple wave theory, a nonlinear SchrSdinger （NLS） equation was established under the assumption of small amplitude and long wavelength. It is found that there are NLS envelop solitons in this system. Finally the soliton solution of the NLS equation was presented.

关键词： nonlinear elastic rod far field NLS equation

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Four-core fiber-based bending sensor

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Frontiers of Optoelectronics 2008年第Z2期1卷 231-236页

作者： Shigang ZHAO Xue WANG Libo YUAN National University Science Park Harbin Engineering University Harbin 150001 China Department of Physics Harbin Engineering University

A novel four-core fiber-based bending sensor has been proposed. The four-core fiber is used as the sensing element, the four cores of the fiber act as a four-beam interferometer, and the far-field interferogram grids with periodical distributions are formed on the fiber output end. Since the phase difference is a function of the radius of curvature, the change of the radius of curvature shifts the far-field interferometric grid pattern. A low-coherence laser diode with wavelength of 650 nm is adopted to illuminate the fiber, and the interferogram pattern in the farfield is recorded by a CCD camera. The relationship between the far-field grid pattern intensity distribution and the radius of curvature is established theoretically and confirmed experimentally.

关键词： fiber optics four-core fiber bending sensor far field grid pattern

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Evaluation of ground motion parameters and seismic response of reinforced concrete buildings from the Mw 6.9,2011 Sikkim earthquake

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Geohazard Mechanics 2023年第2期1卷 162-178页

作者： Faisal Mehraj Wani Jayaprakash Vemuri Rajaram Chenna Ecole Centrale College of Engineering Mahindra UniversityHyderabadIndia Rajeev Gandhi Memorial College of Engineering and Technology NandyalIndia

The continuous collision of the Eurasian plate and the Indian plate has resulted in several earthquakes in the Himalayan *** 6.9 Mw 2011 Sikkim earthquake,which caused immense damage to the built environment in Sikkim,was triggered by an intraplate source on the overriding Eurasian *** ground motions from the earthquake were recorded at stations established by IIT Roorkee as part of the PESMOS *** this paper,near-field and far-field ground motions from this earthquake were analyzed to evaluate their key characteristics and examine their time-frequency features by employing Fast Fourier Transforms(FFTs)and Continuous Wavelet Transforms(CWTs).A comparison between the ground motion parameters of near-field and far-field seismic waves highlights the distinct characteristics of near-field ground ***,the impact of near-field and far-field ground motions on the seismic response of a code-compliant RC building is *** results from the non-linear time history analyses indicate that the roof displacements,drift ratio and strain induced in the frame elements are less than the code-prescribed maximum ***,the demand and capacity levels for the RC frame elements were evaluated to compute the performance *** results indicate that the extensive damage to reinforced concrete buildings in the 2011 Sikkim quake was primarily due to the nonengineered nature of the structures and also due to the non-compliance of the built structures to the seismic design code provisions.

关键词： Fast fourier transform Continuous wavelet transform Near field far field Ground motion parameters 2011 Sikkim Earthquake Reinforced Concrete Structures

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Power Estimation of Acoustic Sources by Sensor Array Processing

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Open Journal of Acoustics 2013年第2期3卷 1-7页

作者： Joseph Lardies Hua Ma Marc Berthillier Department of Applied Mechanics Institute Franche-Comte Electronique Mecanique Thermique et Optique-Sciences et TechnologiesUniversity of Franche-ComteBesanconFrance

A constant problem is to localize a number of acoustic sources, to separate their individual signals and to estimate their strengths in a propagation medium. An acoustic receiving array with signal processing algorithms is then used. The most widely used algorithm is the conventional beamforming algorithm but it has a very low resolution and high sidelobes that may cause a signal leakage problem. Several new signal processors for arrays of sensors are derived to evaluate the strengths of acoustic signals arriving at an array of sensors. In particular, we present the covariance vector estimator and the pseudoinverse of the array manifold matrix estimator. The covariance vector estimator uses only the correlations between sensors and the pseudoinverse of the array manifold matrix estimator operates with the minimum eigenvalues of the covariance matrix. Numerical and experimental results are presented.

关键词： Array Signal Processing Acoustic Array Acoustic Power Estimation Beamforming far field

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