Two Monte Carlo-based simulators for imaging-system modeling and projection simulation of flat-panel X-ray source

The advantages of a flat-panel X-ray source(FPXS)make it a promising candidate for imaging applications.Accurate imaging-system modeling and projection simulation are critical for analyzing imaging performance and resolving overlapping projection issues in FPXS.The conventional analytical ray-tracing approach is limited by the number of patterns and is not applicable to FPXS-projection calculations.However,the computation time of Monte Carlo(MC)simulation is independent of the size of the patterned arrays in FPXS.This study proposes two high-efficiency MC projection simulators for FPXS:a graphics processing unit(GPU)-based phase-space sampling MC(gPSMC)simulator and GPU-based fluence sampling MC(gFSMC)simulator.The two simulators comprise three components:imaging-system modeling,photon initialization,and physical-interaction simulations in the phantom.Imaging-system modeling was performed by modeling the FPXS,imaging geometry,and detector.The gPSMC simulator samples the initial photons from the phase space,whereas the gFSMC simulator performs photon initialization from the calculated energy spectrum and fluence map.The entire process of photon interaction with the geometry and arrival at the detector was simulated in parallel using multiple GPU kernels,and projections based on the two simulators were calculated.The accuracies of the two simulators were evaluated by comparing them with the conventional analytical ray-tracing approach and acquired projections,and the efficiencies were evaluated by comparing the computation time.The results of simulated and realistic experiments illustrate the accuracy and efficiency of the proposed gPSMC and gFSMC simulators in the projection calculation of various phantoms.

Giant Magnetostrictive Material Loudspeaker System Acoustic Radiation Simulation

An infinite panel model of giant magnetostrictive material loudspeaker system （GMMLS） is proposed by making use of finite element method（FEM）. Bending wave eigenfunction is introduced to describe the acoustic radiation condition of the panel. Far-field response in different conditions is calculated by changing the mass surface density. Conclusion is obtained by analyzing the curves simulated, that panel which has larger mass surface density can hardly generate far-field acoustic radiation for lower frequency, while the panel has smaller mass surface density generates far-field acoustic radiation for lower frequency evenly and stronger.

The Management Platform for Online Rate of Meteorological Early-warning Loudspeakers

The meteorological early-warning loudspeaker is a specific initiative for the meteorological departments to address the issues concerning issues concerning agriculture,countryside and farmers.Its significance is that it can promptly deliver the early-warning information concerning some meteorological disasters(such as torrential rains,typhoons,cold wave,hail)to the areas affected,so as to provide reference and protection for agricultural production and effectively reduce the loss of agricultural producers.Up to now,the meteorological early-warning loudspeakers in Benxi have covered the villages.However,due to irregular occurrence of meteorological disasters,the listeners will turn off the information receivers of meteorological early-warning loudspeakers when they fail to receive meteorological information for a long time,so that the users can not promptly know the early-warning information regarding some sudden meteorological disasters.In view of this,the meteorological departments have introduced a series of management measures,such as the daily use of loudspeakers to publish weather forecast information,aimed at improving the online rate and usage rate of meteorological loudspeakers.And the management platform for online rate of meteorological early-warning loudspeakers is an important part of the management system.

The Model Identification and Parameter Forecast of Electrophonic Loudspeaker

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Giant Magnetostrictive Material Exciter for Panel Loudspeaker

The exciter component in a panel loudspeaker has a profound effect on the overall performance of the system. The equivalent circuit analysis of the combination of giant magnetostrictive material exciter and distributed mode panel is introduced and how exciter parameters influence panel lo＇udspeaker＇ s performance is discussed. Numerical predictions are given in order to show how these influences are manifested.

Potential and Limits of a High-Density Hemispherical Array of Loudspeakers for Spatial Hearing and Auralization Research

A hemispherical array of 196 independent loudspeakers has been constructed for laboratory research on spatial hearing, auralization, sound-field quality and spatial audio signal processing. The array of small loudspeakers is supported by a geodesic frame with a radius is 2.4 m. With this relatively high spatial density of sound sources, spatially quantized rendering of sound fields should be viable for a variety of applications, and this paper considers the potential and limits of this approach in relation to human spatial hearing capacities. The paper also considers the combined use of multiple loudspeakers for the rendering low-frequency components of sound sources in order to extend the low-frequency response of the system.

Audiobeam loudspeaker system based on TMS320VC5509A

An audiobeam loudspeaker system based on the fixed-point digital signal processor(DSP)TMS320VC5509A(VC5509A for short)is developed to emit audible sound with high directivity along a selected path.This system is composed of preamplifier,anti-aliasing filter,ADC(analog to digital converter),VC5509A basic system,DAC(digital to analog converter),smoothing filter,ultrasonic power amplifier and ultrasonic transducer array.VC5509A is used to implement the key signal preprocessing algorithms,such as signal preprocessing,amplitude modulation,carrier signal generator,etc.The experiments show that this system has the advantages of high accuracy and good stability.

Influence of the Number of Loudspeakers on the Timbre in Horizontal and Mixed-Order Ambisoncis Reproduction

Ambisonics is a series of flexible spatial sound reproduction systems based on spatial harmonics decomposition of sound field.Traditional horizontal and spatial Ambisonics reconstruct horizontal and spatial sound field with certain order of spatial harmonics,respectively.Both the Shannon-Nyquist spatial sampling frequency limit for accurately reconstructing sound field and the complexity of system increase with the increasing order of Ambisonics.Based on the fact that the horizontal localization resolution of human hearing is higher than vertical resolution,mixed-order Ambisonics(MOA)reconstructs horizontal sound field with higher order spatial harmonics,while reconstructs vertical sound field with lower order spatial harmonics,and thereby reaches a compromise between the perceptual performance and the complexity of system.For a given order horizontal Ambisoncis or MOA reproduction,the number of horizontal loudspeakers is flexible,providing that it exceeds some low limit.By using Moore’s revised loudness model,the present work analyzes the influence of the number of horizontal loudspeakers on timbre both in horizontal Ambisonics and MOA reproduction.The binaural loudness level spectra(BLLS)of Ambisoncis reproduction are calculated and then compared with those of target sound field.The results indicate that below the Shannon-Nyquist limit of spatial sampling,increasing the number of horizontal loudspeakers influence little on BLLS then timbre.Above the limit,however,the BLLS for Ambisoncis reproduction deviate from those of target sound field.The extent of deviation depends on both the direction of target sound field and the number of loudspeakers.Increasing the number of horizontal loudspeakers may increase the change of BLLS then timbre in some cases,but reduce the change in some other cases.For MOA,the influence of the number of horizontal loudspeakers on BLLS and timbre reduces when virtual source departs from horizontal plane to the high or low elevation.The subjective evaluation experiment also validates the analysis.

Vibrations of revolution shells in turning-point range and applications in loudspeakers

An overview of the research conducted in the area of linear and nonlinear vibrations of loudspeakers and revolution shells was given in the turning-point frequency range in Chapter 1. It shows that some problems concerning vibrations of shells in the turning-point range have to be further studied. The linear vibrations of truncated revolution shells with the first-order turningpoint were systematically investigated in the turningpoint range from Chapter 2 to Chapter 6, including the general solutions for the free vibration, the eigenvalues under various boundary conditions, the forced vibrations driven by an edge force or an edge displacement and some related special effects, and the applications in loudspeaker vibrations. The nonlinear autoparametric vibration was examined in Chapter 7. Main results are listed as follows.

The Life Course of a Long-Lasting Affection Medium:A Fieldwork Based on the Communication Practice of the Rural Loudspeakers in North China

The loudspeakers played a crucial role in rural community during the COVID-19 pandemic,and had returned to the public with the help of short video platforms.However,with the continued popularity of digital media,is the revival of the loudspeakers which belong to traditional media just a flash in the pan?What the historic process of return has the loudspeakers undergone?Based on these questions,the paper applies Bourdieu’s sense of practice theory,focuses on“habit”throughout,adopts the research methods of online ethnography and fieldwork,and conducts participant observation and targeted in-depth interviews in a village in North China for about nine months.The study found that:(1)There is the lag of habit in the state’s handling of social relations in villages.Based on rational habit,village cadres used the loudspeakers to manifest their physical presence and restructure their authority;the villagers,operating under perceptual habit,rationalized the presence of the loudspeakers through using the key words such as elders,nostalgia,and homesickness;(2)the loudspeakers was maintained under the habit of village cadres and ordinary villagers,and the outbreak of the epidemic made the loudspeakers as an habit truly“appearing”;(3)the young village cadres,on the other hand,acquired this habit through imitation,transposed the loudspeakers into the short video platform,and carried out different forms of experimentation and innovation,thus surpassing the previous forms of loudspeakers practice.The return of the loudspeakers is the result of the game of different habits.As a long-lasting affection medium,the loudspeakers,on the one hand,has become an important media scene and memory field indispensable to rural community,and on the other hand,the people living on this land have a deep attachment to the loudspeakers,which is indirectly transformed into the bearer of homesickness.This brings new inspiration for us to rethink the relationship between the traditional media and the new media,the iteration of cadres and the change of rural community.

Graphene Electrostatic Loudspeaker as an Alternative to Current Loudspeaker Designs

As a new nanomaterial graphene has broad application prospects.Its mechanical strength,low mass and other aspects of the superior features,enable the production of lighter,better quality loudspeakers.This paper will briefly describe the physical and structural properties of graphene,analyze the structure and advantages of graphene loudspeakers and then compare it with other loudspeakers.

Unidirectional Sound Signage for Speech Frequency Range Using Multiple-Loudspeaker Reproduction System

Human safety is the most important issue in disaster management. Speech is a sound signal containing information that is easily and quickly understood by humans. Using speech as sound signage in emergency systems can effectively increase human safety in low or poor visibility conditions such as in smoke-filled situations. However, reflections of sound through walls, floor surfaces, and ceilings will affect clarity of speech. Unfortunately, because of the characteristics of sound reproduction systems, a single loudspeaker propagates sound waves omni-directionally at low frequencies. This paper proposes a simple multiple-loudspeaker system for reproducing sound with uni-directional characteristics. The proposed system consists mainly of a primary loudspeaker for introducing sound in the desired beam, a secondary loudspeaker for reducing gain in the undesired direction, and digital filters. An adaptive finite-impulse-response (FIR) filter is used to produce the controlling sound by implementing a filtered-x least-mean-square algorithm, and a delay filter for adjusting the time alignment of sound propagation between primary and secondary sources at the control point. Several operational conditions for illustrating real situations and reflections were considered in an anechoic chamber. Experimental results show the directivity patterns of the proposed multiple-loudspeaker system for the required conditions. In a low frequency range, the system is able to control unidirectional propagation;there is a sound beam in the desired direction and, conversely, reduction of gain in the undesired direction around the control point.

考虑扬声器指向性补偿的声场再现方法研究

在实验室环境下精准再现基于测试或仿真的声环境,对降噪优化设计与声品质评价研究具有重要意义。常用的基于扬声器阵列的声场再现方法能在特定的空间区域内再现原始声场分布,提供更为真实的临场感和沉浸感,但扬声器的指向性特性较差会降低声场再现的精度。本文提出一种考虑扬声器指向性补偿的声场再现方法用于提高声场再现的精度。该方法基于扬声器指向性的声压表达模型,利用坐标变换的方法将空间观测点转换到以扬声器为中心的局部坐标系下,并采用插值的方法实现空间观测点的指向性补偿;最后采用声压匹配的方法求解扬声器驱动权重,实现声场的精准再现。开展基于仿真指向性补偿和实测指向性补偿的声场再现试验,结果表明考虑指向性补偿比不考虑补偿的声场再现精度平均提高了约22.37%,验证了所提声场再现方法的有效性。

基于GA-BP神经网络模型的石墨烯发声器研究

为了解决传统石墨烯发声器物理模型计算量大、精度不高的问题,提出了一种基于GA遗传算法的BP神经网络模型,该算法模型具有更高的精度和适应性。首先,介绍了石墨烯热声发声原理以及实验设计,建立了GA-BP神经网络模型。其次,对模型的参数进行了调节,并对比了基于dropout、基于正则化、基于正则化和GA遗传算法的三种神经网络模型。随后在模型中输入石墨烯发声器的正弦激励幅值、频率以及测量距离,使用GA遗传算法对隐藏层的权值和偏置进行全局寻优,将寻优结果代入BP神经网络,最终预测出给定条件下的声压级。结果表明,在均使用正则化的条件下,BP神经网络预测准确度为98.05%,均方差为0.23;GA-BP神经网络预测准确度达到98.62%,均方差仅为0.14。优化后精准度提高了0.57%,均方差降低了41.36%,展现出更加优异的准确性和适应性。该研究为预测多类特征传感器的非线性输出结果提供了一种高精准度、高适应性的方案。

基于模态应变能的扬声器盆架优化

针对扬声器轻量化及结构刚度、强度较高要求的设计目标,通过有限元方法进行模态及谐响应分析,对扬声器盆架低频模态应变能集中位置进行优化。优化后,一阶频率由547.3 Hz提高至995 Hz。网格迭代后,一阶频率提升至1031.6 Hz,且模态应变能趋于均匀分布。对应变能较小且非集中的区域进行轻量化优化,通过最小柔度方法对开窗区域进行拓扑优化,在中间部分质量减小40%的情况下,使一阶频率由1300.5 Hz提高至1386.6 Hz,同时使刚性提高。对0.6 mm、0.8 mm、1 mm厚度的扬声器盆架进行对比,从刚度、加速度两个维度进行验证。在有限元分析的基础上,对试验后产生严重变形的扬声器盆架进行基于模态应变能的实际优化,优化后一阶频率由1290.8 Hz提高至1755.9 Hz,同时刚性增大,应变能分布更均匀,变形得到改善。

乡村振兴下村干部的媒介治理:现状、困境与出路

媒介技术在乡村社会的发展进程中发挥了重要作用,了解村干部利用媒介参与乡村治理的现状、困境,对于促进乡村治理、组织振兴具有重要的现实意义。研究村干部在现实语境中进行乡村治理时主要使用的乡村大喇叭和村级微信群后发现,二者的张力共治促进了村干部治理逻辑的转变、完成了村干部的上传下达并构成了乡村振兴的媒介平台,但也面临着传播器物年久失修、治理缺乏联动、村干部媒介素养较低等现实问题,需从传播器物、传播主体、外部力量三方面共同发力,进一步推进村干部的媒介治理实践及组织振兴。

基于NSGA-Ⅱ算法的阵元间距多目标优化

针对定向扬声器换能器阵列设计的复杂性与不确定性问题,提出了一种基于NSGA-Ⅱ算法的矩形换能器阵元间距多目标优化方法。基于矩形换能器主要结构参数与阵元间距之间的动态性能分析,建立了以方向锐度角、主瓣波束宽度以及旁瓣级为协同优化目标的阵元间距解析函数和约束条件;在此基础上,采用NSGA-Ⅱ算法对所构建的多目标模型进行优化,由此获取矩形换能器阵元间距的最优可选集。仿真结果表明:在满足各项目标协同优化以及约束条件的情况下,所提出的矩形换能器阵元间距设计方法可实现换能器阵列旁瓣级较小且阵列指向性较好的定向扬声器。

扩音对讲系统在LNG接收站的应用及发展综述

分析适用于LNG接收站的扩音对讲系统设计方法。从系统结构、工作原理、传输方式、功能特点等方面详细论述了无主机型扩音对讲系统、有主机型扩音对讲系统、全数字IP型扩音对讲系统和5G型扩音对讲系统这四种扩音对讲系统的功能特点和差异性。通过对四种扩音对讲系统在LNG接收站中应用的优缺点和发展局限性分析对比,提出了在我国现阶段LNG接收站中应用最为广泛的扩音对讲系统设计方案为全数字IP型扩音对讲系统。通过介绍扩音对讲系统的功能和全数字IP型扩音对讲系统在LNG接收站应用案例,详细介绍了数字IP型扩音对讲系统在LNG接收站中的设计方法。阐述了基于5G网络技术的5G型扩音对讲系统在LNG接收站应用的局限性并对其发展进行了展望。

车载扬声器网罩开孔率对其频响及音质的影响

车载扬声器大多布置在车内门板、A柱等位置,为了车内美观需求,一般会使用网罩将其遮挡。然而,网罩的遮挡将会导致扬声器的辐射特性产生变化,对车内电声重放效果产生不利的影响。文章研究不同开孔率网罩对于扬声器频响及其音质的影响,首先从理论分析了网罩对于扬声器辐射特性的阻碍作用,然后客观测量了安装不同开孔率网罩扬声器的频率响应特性,最后通过主观实验验证了不同开孔率网罩对扬声器重放信号音质的影响。研究结果表明,网罩对于扬声器频响的影响主要体现在高频区域,同时网罩的开孔率越小,对扬声器辐射特性的阻碍越大,文章为车内扬声器网罩的开孔率设计提供了重要的参考依据。