With the assistance of mechanosensory lateral line system, fish can perceive minute water motions in complex underwater environments. Inspired by the constriction within canal nearby canal neuromast in fish lateral line system, we proposed a novel canal artificial lateral line (CALL) device with constriction in canal nearby the sensing element. The designed CALL device consisted of a poly(vinylidene fluoride-trifluoroethylene)/polyimide cantilever as the sensing element and a polydimethylsiloxane (PDMS) microfluid canal. Two types of CALL devices, i.e., CALL with straight canal (S-CALL) and CALL with constriction canal (C-CALL), were developed and characterized employing a dipole source. Experimental results showed that the proposed C-CALL device achieved a pressure gradient detection limit of 0.64 Pa m −1 , which was much lower than the S-CALL device. It indicates that the constriction in the canal nearby the sensing element could enhance the hydrodynamic pressure sensing performance of the CALL device. In addition, the constriction could modify the frequency response of the CALL device, and the C-CALL device achieved higher voltage output than S-CALL in high-frequency domain.
For the study of propagation characteristics in underwater acoustic channels, a geometrybased model is introduced to represent the multipath scattering environments between a transmitter (Tx) and a mobile receiver (MR). To consider the impact of the scattering environments on the propagation characteristics with low complexity, we adopt a rectangle to describe the communication environments of the vertical cross section of the ocean, where the scatterers are assumed to be randomly distributed on the surface and bottom of the sea. In the model, we first derive the closed-form expressions for the probability density functions (PDFs) of the angle of departure (AoD) and angle of arrival (AoA) statistics. Then, we investigate the spatial and frequency correlation functions of two different propagation paths. The numerical simulation results fit the conventional results very well, which demonstrate that the proposed model has the ability to describe the underwater acoustic communication environments. INDEX TERMS Underwater acoustic channels, geometry-based channel model, angle of departure AoD and angle of arrival AoA statistics, spatial and frequency correlation functions. I. INTRODUCTION A. MOTIVATION Underwater wireless networks, which have the advantages of scientific exploration, tactical surveillance, and offshore exploration, have been widely researched in wireless communication systems [1]. To make these applications feasible, it is important to design and analyse wireless underwater acoustic communication systems. In light of this, statistical propagation characteristics of underwater communication channel are necessary to assess system performance to improve the quality of a communication system [2]. B. RELATED WORKS The existing literatures have done a variety of studies on the simulation of underwater acoustic wireless channels, which are usually based on the experimental data obtained in some The associate editor coordinating the review of this manuscript and approving it for publication was Guan Gui.
The development of more effective environmental policies is a common concern among scholars, government and the public. This paper attempts to investigate whether the environmental policy mix can really work. Taking the “Five Water Co-Treatment” policy of Zhejiang Province as an example, we applied the synthetic control method to examine the impact of multi-objective environmental policies on industrial sewage discharge and urban sewage discharge in Zhejiang. Further, we analyzed the effect of industrial value added and the length of water pipelines on sewage discharge and examined the potential environmental Kuznets curve (EKC) relationships. Our results of synthetic control imply that the “Five Water Co-Treatment” policy has increased the industrial and urban sewage discharge. However, the results of the extended analysis show that this is a process of standardizing sewage discharge and an embodiment of enhanced sewage treatment capacity. Therefore, we believe that the “Five Water Co-Treatment” policy is effective and should continue to advance.
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