1982 ◽  
Vol 13 (5) ◽  
pp. 289-292 ◽  
Author(s):  
P Bouchaud ◽  
N G Gaggioli

2013 ◽  
Vol 27 (18) ◽  
pp. 1350135 ◽  
Author(s):  
F. HERRERÍAS-AZCUÉ ◽  
A. GONZÁLEZ-VEGA ◽  
J. TORRES-ARENAS ◽  
G. GUTIÉRREZ-JUÁREZ

A photoacoustic model with one degree of freedom in the spatial coordinates for a plane sample is studied. The model proposed considers a sample with Beer's law absorption immersed in a fluid with different acoustical impedance. An analytical solution for this problem is given. It is shown that the generated PA wave is composed of a pressure peak followed by a reflected and inverted pulse with diminished magnitude. It is also remarked that the form described for the pulse has a periodicity related to the sample's width and attenuated by the reflection coefficient. It is noted that, due to this attenuation, information about the sample's width is more easily detected at the irradiation side. Border cases are taken for equal impedances and infinite sample width.


2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yang Qian ◽  
Dalin Zhao ◽  
Haowei Zeng

Direct position determination (DPD) of noncircular (NC) sources with multiple nested arrays (NA) is investigated in this paper. Noncircular sources are used to expand the dimension of the received signal matrix, so the number of identifiable information sources and the accuracy of direct position determination are improved. Furthermore, nested array increases spatial degree of freedom. In this paper, the high-dimensional search problem of noncircular sources is investigated. Therefore, we propose algorithm dimension reduction subspace data fusion (RD-SDF) to reduce complexity and increase positioning accuracy. Simulation results show that the proposed RD-SDF algorithm for multiple nested arrays with noncircular sources has improved positioning accuracy with higher spatial degree of freedom than SDF, Capon, and two-step algorithms with uniform linear array and circular sources (CS).


2013 ◽  
Vol 308 ◽  
pp. 304-308 ◽  
Author(s):  
Li Dong ◽  
Xiao-Ming Xiu ◽  
Hong-Zhi Shen ◽  
Ya-Jun Gao ◽  
X.X. Yi

2008 ◽  
Vol 21 (1) ◽  
pp. 134-148 ◽  
Author(s):  
Zhengyu Liu ◽  
Na Wen ◽  
Yun Liu

Abstract A statistical method is developed to assess the full climate feedback of nonlocal climate feedbacks. The method is a multivariate generalization of the univariate equilibrium feedback assessment (EFA) method of Frankignoul et al. As a pilot study here, the generalized EFA (GEFA) is applied to the assessment of the feedback response of sea surface temperature (SST) on surface heat flux in a simple ocean–atmosphere model that includes atmospheric advection. It is shown that GEFA can capture major features of nonlocal climate feedback and sheds light on the dynamics of the atmospheric response, as long as the spatial resolution (or spatial degree of freedom) is not very high. Given a sample size, sampling error tends to increase significantly with the spatial resolution of the data. As a result, useful estimates of the feedback can only be obtained at sufficiently low resolution. The sampling error is also found to increase significantly with the spatial scale of the atmospheric forcing and, in turn, the SST variability. This implies the potential difficulty in distinguishing the nonlocal feedbacks arising from small-scale SST variability. These deficiencies call for further improvements on the assessment methods for nonlocal climate feedbacks.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Long Zhu ◽  
Andong Wang ◽  
Mingliang Deng ◽  
Bing Lu ◽  
Xiaojin Guo

AbstractVortex beams carrying orbital angular momentum (OAM), which featuring helical phase front, have been regarded as an alternative spatial degree of freedom for optical mode coding and multiplexing. For most reported OAM-based mode coding schemes, data information is only encoded by different OAM mode states. In this paper, we introduce a novel design technique to construct vortex array phase grating (VAPGs) for the flexible generation of vortex arrays, and employ the proposed VAPGs to realize multi-dimensional space/mode/amplitude coding/decoding. By designing VAPGs with different parameters and loading them on to a single spatial light modulator (SLM), we successfully generate vortex array with different mode states and relative power in the experiments. Moreover, a 10-bit multi-dimensional space/mode/amplitude data coding/decoding scheme for image transfer in free-space link with a zero bit-error-rate is experimentally demonstrated, which confirm the feasibility of our proposed VAPG-based coding/decoding scheme.


2021 ◽  
Author(s):  
Long Zhu ◽  
Andong Wang ◽  
Mingliang Deng ◽  
Bing Lu ◽  
Xiaojin Guo

Abstract Vortex beams carrying orbital angular momentum (OAM), which featuring helical phase front, have been regarded as an alternative spatial degree of freedom for optical mode coding and multiplexing. For most reported OAM-based mode coding schemes, data information is only encoded by different OAM mode states. In this paper, we introduce a novel design technique to construct vortex array phase grating (VAPGs) for the flexible generation of vortex arrays, and employ the proposed VAPGs to realize multi-dimensional space/mode/amplitude coding/decoding. By designing VAPGs with different parameters and loading them on to a single spatial light modulator (SLM), we successfully generate vortex array with different mode states and relative power in the experiments. Moreover, a 10-bit multi-dimensional space/mode/amplitude data coding/decoding scheme for image transfer in free-space link with a zero bit-error-rate is experimentally demonstrated, which confirm the feasibility of our proposed VAPG-based coding/decoding scheme.


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