基于Fournier Forand体积散射函数的水中激光脉冲后向散射特性分析模型

基于Fournier Forand体积散射函数,建立了一种水中激光脉冲后向散射仿真模型.运用该模型可用Monte Carlo方法模拟光子在水中的传播过程,并得到光波后向散射的冲击响应.将初始激光脉冲与冲击响应进行卷积并求其傅里叶谱,即可得到激光脉冲后向散射信号的时域和频域特征.利用该模型分析了入射为高斯型激光脉冲时,水...     

Experimental assessment of a multicarrier underwater acoustic communication system

This paper presents a multicarrier communication system which transmits information on independent subcarriers to achieve an increased data rate. For this system, a passive-phase conjugation (PPC) based receiver structure is assessed by processing data collected in sea trials. Based on temporal diversity (pulse compression) exploited by PPC processing, an adaptive multichannel decision feedback equalizer is used to remove intersymbol interference, where spatial diversity is exploited by adaptive multichannel combination. The digital phase-locked loop (DPLL) technique is implemented for carrier-phase tracking. In the scenario of low input signal-to-noise ratios (SNRs), the receiver structure achieved superior performance using a common DPLL. In a depth-fluctuated environment, two sea experiments were conducted over ranges of 2 km and 4 km, respectively, and this communication system was assessed with a data rate of 4 kbps. In terms of mean square error, output SNR and bit error rate, this receiver structure has demonstrated its performance for the multicarrier communication system.     

Coherent underwater communication using passive time reversal over multipath channels

Passive time reversal exploits underwater acoustic channels’ spatial and temporal diversity. It can refocus multipath propagated signal at the receiver and can be realized simply by the passive phase conjugation (PPC) method. By the temporal focusing, time delay spread caused by multipath propagation is mitigated for spectral efficient coherent communications. However, the PPC method is unable to eliminate multipath and is limited by channel variations. An adaptive equalizer is therefore needed to compensate residual multipath after refocusing and to track channel temporal variations. Spatial diversity is obtained by using a vertical receiving array. In this paper we used 4-hydrophone array and demonstrated that the adaptive decision feedback equalization in conjunction with PPC significantly decreased the bit error rate.     

现场侦检装备在应对化学威胁中的应用与发展

近年来,国内外不断发生的化学恐怖袭击和化学事故仍然是当今人类生存、国家安全所面临的重大威胁。化学侦检是防化应急处置与救援的眼睛,熟练掌握和正确使用侦检装备是应对化学威胁、降低损失和伤亡的关键因素。基于化学传感等技术的侦检装备具有响应快速、智能便携的特点,并且在远程监测和实时值守等方面具有优势。该文针对涵盖电化学传感器、质量敏感型传感器、红外传感器、拉曼传感器、离子迁移谱仪、火焰光度检测器、光致电离检测器、远程遥测传感装备等在内的现场侦检装备,从原理、性能、优势和不足等方面进行了概述,重点阐述了侦检装备在应对化学威胁方面的最新进展,并对其发展趋势、应用前景进行了展望,以期为化学侦检装备在应对化学威胁中的深入研究与应用提供参考。     

Pandemic-Driven Development of a Medical-Grade,Economic and Decentralized Applicable Polyolefin Filament for Additive Fused Filament Fabrication

A polyolefin with certified biocompatibility according to USP class VI was used by our group as feedstock for filament-based 3D printing to meet the highest medical standards in order to print personal protective equipment for our university hospital during the ongoing pandemic. Besides the chemical resistance and durability, as well as the ability to withstand steam sterilization, this polypropylene (PP) copolymer is characterized by its high purity, as achieved by highly efficient and selective catalytic polymerization. As the PP copolymer is suited to be printed with all common printers in fused filament fabrication (FFF), it offers an eco-friendly cost–benefit ratio, even for large-scale production. In addition, a digital workflow was established focusing on common desktop FFF printers in the medical sector. It comprises the simulation-based optimization of personalized print objects, considering the inherent material properties such as warping tendency, through to validation of the process chain by 3D scanning, sterilization, and biocompatibility analysis of the printed part. This combination of digital data processing and 3D printing with a sustainable and medically certified material showed great promise in establishing decentralized additive manufacturing in everyday hospital life to meet peaks in demand, supply bottlenecks, and enhanced personalized patient treatment.     

直升机声测设备探测距离估计方法

直升机声测设备用于探测低空飞行的直升机,探测距离是其关键性能。为了精确测定探测距离,可以运用探测结果与机载数据综合分析的方法。此种方法需要较多人员和其它设备,包括机载设备,在设备研制的初期较繁琐。本文提出了一种简便的直升机声测设备探测距离估计方法,此方法不需要使用机载设备,对直升机飞行基本无约束,通过对大量实测数据处理,针对某直升机声测设备该方法的平均误差在7%以内。     

对FD-GLB-Ⅱ型新型焦利氏秤的改进

对FD-GLB-Ⅱ型新型焦利氏秤做了改进,改进后的振子质量可变,很好的满足了实验教学中对弹簧阵子简谐振动关系式的验证要求.     

低温装置中温度测量的热沉问题

文中讨论了低温装置中的热沉问题。为减少因电引线导热对温度计的热负荷 ,提高温度测量的精度 ,在温度计的引线中加入热沉将是非常必要而且有效的手段。文中解决了不同边界条件下所需的热沉长度的求解问题 ,并讨论了其实际应用     

The development of recent high-power ultrasonic transducers for Near-well ultrasonic processing technology

With the reduction of crude oil throughout the world, enhance oil recovery technology has become a major oil research topics, which can greatly increase the recovery ratio of the crude oil before the dawning of renewable energy era. Near-well ultrasonic processing technology, as one new method, has attracted more attention for Enhanced Oil Recovery due to its low cost, good applicability and no environmental pollution in recent rears. There are two important relevant aspects about Near-well ultrasonic processing technology: (a) how to enhance the oil flow through the rocks into the pumping pool and (b) how to reduce the oil viscosity so that it can be easier to pump. Therefore, how to design a high-power ultrasonic equipment with excellent performance is crucial for Near-well ultrasonic processing technology. In this paper, recent new high-power ultrasonic transducers for Near-well ultrasonic processing technology are summarized. Each field application of them are also given. The purpose of this paper is to provide reference for the further development of Near-well ultrasonic processing technology.With the reduction of crude oil throughout the world, enhance oil recovery technology has become a major oil research topics, which can greatly increase the recovery ratio of the crude oil before the dawning of renewable energy era. Near-well ultrasonic processing technology, as one new method, has attracted more attention for Enhanced Oil Recovery due to its low cost, good applicability and no environmental pollution in recent rears. There are two important relevant aspects about Near-well ultrasonic processing technology: (a) how to enhance the oil flow through the rocks into the pumping pool and (b) how to reduce the oil viscosity so that it can be easier to pump. Therefore, how to design a high-power ultrasonic equipment with excellent performance is crucial for Near-well ultrasonic processing technology. In this paper, recent new high-power ultrasonic transducers for Near-well ultrasonic processing technology are summarized. Each field application of them are also given. The purpose of this paper is to provide reference for the further development of Near-well ultrasonic processing technology     

Processing and properties of engineering plastics recycled from waste electrical and electronic equipment (WEEE)

The characteristics of engineering plastics used in the preparation of electrical and electronic equipment were studied. More specifically, their thermal response was recorded by DSC experiments, the rheological properties were investigated via MFI tests and the mechanical properties were evaluated with tensile tests. The aim was to establish a procedure for recycling the same engineering plastics deriving from waste of electrical and electronic equipment (WEEE), which offers the additional advantage of using the as-received waste stream as a recyclable mixture, i.e. without sorting and classification of its components.The experimental results showed that blends of PC with ABS or ABS/HIPS can be prepared by direct mixing and this, would allow easy handling of the engineering plastics coming from WEEE, i.e. blending without the need of sorting. These mixtures can be easily processed and display acceptable mechanical properties with reasonable cost. Therefore, the processing characteristics and properties of the systems studied in this work could be the key for the design of an interesting approach for handling solid plastic waste from electrical and electronic devices.