Multiple attenuation using λ–f domain high-resolution Radon transform

The parabolic Radon transform has been widely used in multiple attenuation. To further improve the accuracy and efficiency of the Radon transform, we developed the 2- fdomain high-resolution Radon transform based on the fast and modified parabolic Radon transform presented by Abbad. The introduction of a new variable 2 makes the transform operator frequency-independent. Thus, we need to calculate the transform operator and its inverse operator only once, which greatly improves the computational efficiency. Besides, because the primaries and multiples are distributed on straight lines with different slopes in the 2-fdomain, we can easily choose the filtering operator to suppress the multiples. At the same time, the proposed method offers the advantage of high-resolution Radon transform, which can greatly improve the precision of attenuating the multiples. Numerical experiments suggest that the multiples are well suppressed and the amplitude versus offset characteristics of the primaries are well maintained. Real data processing results further verify the effectiveness and feasibility of the method.

High attenuation mucoid impaction in allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis(ABPA) is a complex hypersensitivity syndrome triggered against antigens of Aspergillus fumigatus,a fungus that most commonly colonizes the airways of patients with bronchial asthma and cystic fibrosis.It presents clinically with refractory asthma,hemoptysis and systemic manifestations including fever,malaise and weight loss.Radiologically,it presents with central bronchiectasis and recurrent episodes of mucus plugging.The mucus plugs in ABPA are generally hypodense but in up to 20% of patients the mucus can be hyperdense on computed tomography.This paper reviews the literature on the clinical significance of hyperattenuated mucus in patients with ABPA.

Design and Verification of High Attenuation Vibration Isolation Damper in Remote Sensing Satellite Transport

To solve the safe horizontal transportation by rail&road of remote sensing satellite problem in the process of unpredictable dynamic load,a high attenuation vibration isolation damper(hereinafter referred to as vibration isolation damper)was developed.By simulation analysis and transportation test using satellite structural model and engineering prototype,validity and reliability of the vibration isolation damper was verified,which can meet the requirements of vibration and shock from various transportation conditions.

Theoretical analysis on ground vibration attenuation using sub-track asphalt layer in high-speed rails

Using a finite element method （FEM） program, a Portland cement concrete slab trackbed （So）, and a sub- track asphalt roadbed （RAC-S） were modeled under high- speed train loads to analyze their responses to ground vibration attenuation, by considering 10, 15, 20, 25, and 30 thick sub-track asphalt layer replaced on the top of the upper subgrade. FEM results show that the vibration amplitude of RAC-S is at least three times lower than the vibration for So. The maximum vibration amplitude of RAC-S is linearly increased with train speed. The vertical acceleration is found to be reduced by more than 10 % when the asphalt layer thickness is increased from 10 to 20 cm. However, the reduction in vertical acceleration is only about 1% when the thickness of the asphalt layer changes from 20 to 30 cm. The vibration level is slightly lower if the asphalt layer has higher resilient modulus in the seasons of autumn or winter. This theoretical analysis indicates that a railway substructure that consists of a 10-20 cm thick high modulus asphalt layer located at the top of trackbed shows a good performance in ground vibration control for high-speed rails.

The Application of China's High Speed Railway Earthquake Early Warning System in Jakarta-Bandung HSR

Earthquake has a significant impact on operation safety of the high speed railway,and for Jakarta-Bandung High Speed Railway(HSR)in Indonesia where it is earthquake-prone,it is necessary to establish an earthquake early warning system to strengthen its earthquake resistance.Based on the principle and technical characteristics of China's high speed railway earthquake early warning system and combining the actual situations of Jakarta-Bandung HSR in Indonesia,this paper describes how to implement China's high speed railway earthquake early warning system in Jakarta-Bandung HSR.It focuses on optimizations in environmental adaptation design and seismic network interface design,earthquake attenuation model parameter adjustment and terminal software interface adjustment,so as to make the system better suit the local situations,and meet operation requirements and guarantee safe operation of Jakarta-Bandung HSR.

Tomography for Q of the Eastern Section of the Tianshan Area from High-frequency Attenuation of S-wave

Based on the waveform data of 5,076 local earthquakes recorded at 25 stations in Xinjiang during the period from 2009 to 2014 and the observation reports provided by the Xinjiang Digital Seismic Network,a data set of 19,140 attenuation factors t*is obtained by fitting the high-frequency attenuation of S-wave spectra with a genetic algorithm. The spatial distribution of Q_S is determined by inverting the t*data with seismic tomography. The results show that the average Q0 in eastern Tianshan is 520,and there is a significant correlation between the Q_S value distribution or attenuation characteristics it disclosed and the surface structure of the study area. The Q_S value is lower in the intersection area of the mountain basin which is located on the north and south sides of the Tianshan Mountains,and the high Q_S distribution is more concentrated inside the Tianshan orogenic belt. The M≥6. 0 earthquakes have been basically located in the Low-Q_S region since 1900. 24 high heat flow points in eastern Tianshan are located at the north and south of Tianshan Mountains where low Q_S exists,indicating a negative correlation. In addition,there is a positive correlation between the velocity structure and the attenuation structure in the study area,which reflects the consistency of the 2-D attenuation structure with the velocity structure and the two-dimensional density structure.

Attenuation coefficients of gamma and X-rays passing through six materials

The aim of this study was to determine the attenuation of gamma and X-rays with different energies caused by passage through different materials.To this end,different materials with a range of atomic numbers were chosen to measure gamma and X-ray attenuation coefficients and to explore the mechanisms of interaction of gamma and X-rays with matter of various kinds.It is shown that the attenuation coefficients first decrease and then increase with increase in the radiation(photon)energy.The attenuation of gamma and X-rays passing through materials with high atomic number is greater than that in materials with low atomic number.The attenuation minimum is related to the atomic number of the irradiated materials.The larger the atomic number is,the lower the energy corresponding to attenuation minimum is.Photoelectric and Compton effects are the main processes when gamma rays pass through individual materials with high and low atomic numbers,respectively.Therefore,for radiotherapy and radiation protection,different methods should be considered and selected for the use of gamma and X-rays of different energies for use in different materials.

基于高阶累积量ESPRIT算法的指数衰减正弦信号参数估计

工程应用中环境噪声多表现为高斯有色噪声,而针对高斯白噪声进行处理的算法失效问题,提出了一种高斯色噪声环境中用于多分量衰减正弦信号频率和衰减因子估计的四阶累积量ESPRIT算法。首先,推导出四阶累积量与观测样本中的自相关矩阵和互相关矩阵之间的关系,求出其四阶累积量矩阵。其次,通过对四阶累积量进行广义特征值分解,根据广义特征值即可得到信号衰减因子和频率的估计值。最后对所提算法进行了仿真实验验证,在混合信噪比为0 dB时,所提算法针对多分量衰减正弦信号角频率和衰减因子的平均估计误差分别为0.002 0πrad和0.002 0。在高斯白噪声和高斯色噪声背景下与ESPRIT算法和Prony算法相比具有更强的噪声抑制能力和更高的估计精度。

高静压下长杆中轴向应力波衰减研究

针对用于非常规页岩油开发的可控冲击波设备负载推送杆,该文提出了一种可用于高静压环境的内置吸收杆应力波衰减结构,基于LSDYAN软件与简化Johnson-Cook本构模型,开展了推送杆中应力波衰减规律的数值模拟研究。首先,基于试验数据对材料模型参数及数值算法的可靠性进行验证,在此基础上计算了不同外部环境、不同载荷参数及不同吸收杆参数对应力波衰减效果的影响。研究结果表明:外部是否存在静压对吸收杆的应力波吸收效果无显著影响,但静压会在空腔区造成部分应力集中,在50 MPa外压力下内壁等效集中应力峰值可达100 MPa;吸收杆对应力波能量的吸收效果取决于其脱离壁面前注入其中的能量;在载荷参数适配的条件下,通过串接多个吸收杆结构可以增加对应力波的衰减效果。研究结果可为水下高静压环境下的结构抗冲击防护设计提供指导与参考。

基于谐波分解恢复弱势信号的高分辨率处理技术

地震资料高分辨率处理是预测薄储集层的有效手段,高分辨率处理的主要目的是有效恢复地震高、低频信息和拓宽频带,同时保持资料的信噪比和保真度。基于谐波分解恢复弱势信号的高分辨率处理技术,以压缩小波变换为基础,根据信号谐波分量对地震高、低频弱势信号进行恢复。首先,基于有效频带内的地震信号,采用压缩小波变换将其分解为各基频信号,然后计算各基频信号的高次谐波与低次谐波,将计算出的高次谐波与低次谐波加入小波变换系数中,最后进行小波逆变换,即可恢复高、低频弱势信号。在实现过程中,仅仅在有效频带内估算基频信号,能较好地保持信号的信噪比。地震信号的小波变换系数与地层反射系数具有一致性,因此该技术具有较高的保真度,可以较好保持相对振幅关系。实际应用表明,在保持资料信噪比的同时,该技术能大幅拓宽地震资料的频带,处理后的地震剖面断点更清楚,分辨能力改善明显,能较好地识别6 000 m以深约40 m的薄储集层。

高分辨太赫兹衰减全反射频域光谱系统

由于水对太赫兹(THz)波具有强烈的吸收,含水样本的太赫兹光谱检测面临重大挑战。为解决太赫兹光谱对含水样本的高灵敏检测问题,本文提出并实验验证了一种太赫兹衰减全反射(ATR)的高分辨频域光谱系统。该系统采用创新式光混频相干检测技术,获得了出色的动态范围和分辨力性能,在0.3~1.2 THz范围内,峰值动态范围超过100 dB,频率分辨力高达100 MHz。创新式的ATR架构有效提升了灵敏度,在对不同浓度α-乳糖水溶液的实验测量中,实现了对水溶液样本的直接、精确定量检测。

高铁开通对城市能源利用效率的影响机制及空间溢出效应研究

将高铁开通视为一项准自然实验,基于2006—2019年城市面板数据,运用多期双重差分法实证检验高铁开通对城市能源利用效率的影响,并进一步分析其影响机制及空间溢出效应。研究发现:(1)高铁开通对城市的能源利用效率具有显著的提升作用。(2)高铁开通通过提高铁路货运效率、替代公路客运、优化产业结构及促进技术创新,提升了城市的能源利用效率。(3)高铁开通对邻近城市的能源利用效率存在正向空间溢出效应,并存在800公里的空间距离衰减边界。(4)高铁开通对城市能源利用效率的提升作用在不同区域、等级、规模、资源禀赋的城市存在显著的异质性,其中对中西部城市、小城市、普通城市、资源型城市的能源利用效率提升作用更为显著;此外,高铁开通对衰退型的资源型城市能源利用效率的促进效果最大,对成熟型的资源型城市的影响次之,但对成长型和可再生型的资源型城市不存在显著性影响。研究结论为理解高铁在能源利用效率方面的作用提供了新视角和新证据,也为实现“节能减排”和“交通强国”提供了政策启示。

基于GaAs E/D PHEMT工艺的Ku波段双通道幅相控制多功能芯片

基于GaAs增强/耗尽型赝配高电子迁移率晶体管(E/D PHEMT)工艺设计了一款14~18 GHz的双通道多功能芯片。芯片集成了单刀双掷(SPDT)开关、6 bit数控移相器、4 bit数控衰减器和增益补偿放大器。采用正压控制开关以减小控制位数;优化移相、衰减和放大等电路拓扑结构,以获得良好的幅相特性;采用紧凑布局、双通道对称的版图设计,以实现小尺寸和高性能。测试结果表明,+5 V电压下,接收通道增益大于3 dB,1 dB压缩点输出功率大于8 dBm;发射通道增益大于1 dB,1 dB压缩点输出功率大于2 dBm;64态移相均方根误差小于2.5°,16态衰减均方根误差小于0.3 dB,芯片尺寸为3.90 mm×2.25 mm。该多功能芯片可实现对射频信号幅度和相位的高精度控制,可广泛应用于微波收发模块。

基于超声多尺度衰减的螺栓轴向应力评价

针对超声波传统衰减法测量高强度短螺栓应-力时,难以达到预期精度,提出了一种基于超声散射衰减理论和小波多尺度分解的测量螺栓应力的方法。基于立方晶系材料的瑞利散射,推导了超声衰减系数与应力关系的理论模型。利用小波变换得到各个尺度的衰减系数并定义加权超声多尺度衰减系数,结合粒子群优化算法和灰色关联分析确定衰减系数最优尺度组合及其归一化权重系数,建立轴向应力的超声多尺度衰减测量模型。利用搭建的螺栓轴向应力超声波测量系统,对普通螺栓进行轴向应力测量,证明了该方法的可行性。对比了多尺度衰减法与渡越时间和传统衰减法对高强度短螺栓轴向应力的测量结果,验证了多尺度超声衰减法更适合高强度短螺栓的轴向应力测量。

2021年5月21日漾濞M_(S)6.4地震极震区地形效应对地震动特性的影响

基于对2021年5月21日漾濞M_(S)6.4地震微观震中秀岭村进行的震害调查,利用流动观测地形台阵观测资料,分析了地形效应对地震动特性的影响。结果表明,若地震波垂直山脉走向入射,陡坡会放大地震波的高频部分,且不同高程处,山脉垂向低频差异较大,山脉走向低频差异较小。利用谱衰减法计算高频衰减参数的场地影响项κ_(0),分析了水平和竖向分量的κ_(0)与场地软弱程度和卓越频率的相关性,其结果表明,在小尺度范围内,水平分量和竖向分量的κ_(0)均具有较强的空间不均匀性。

一种基于2 bit阶梯波时间调制的高精度幅度调控方法

本文介绍了一种基于2 bit阶梯波时间调制(step-wave time-modulation,SWTM)的高精度幅度调控方法。首先建立了2 bit SWTM理论模型,分析了阶梯波形对射频信号时间调制的幅度调控精度影响;然后设计了2 bit SWTM电路,进行了高精度幅度调控实验。测试结果表明,在40 MHz信号带宽下,该2 bit SWTM电路实现了0~31.75 dB衰减动态范围的7 bit幅度调控,误差范围小于±(0.1+0.8%AS)dB,均方根误差为0.07 dB。

高速铁路站桥一体高架车站无砟轨道减振研究

为进行站桥一体高速铁路车站振动控制,以减振CRTSⅢ型板式无砟轨道为研究对象,采用落轴试验、现场行车测试和有限元动力仿真相结合的方法,分析轨道减振效果并预测车站最大振动。结果表明:高速铁路车站区段铺设减振轨道不会影响行车安全,隔振垫刚度为0.03 N/mm^(3)时可实现轨道动力响应和减振效果的均衡;减振轨道振动控制效果显著,落轴试验最大分频插入损失为32.9 dB,车站行车测试总插入损失可达11.4 dB;铺设减振轨道后站台及候车厅振动均满足鼓励值要求,高架候车厅比地面候车厅振动约增大4 dB;建议在高速铁路车站区段,尤其是在列车不停站通过情况下,铺设减振CRTSⅢ型板式无砟轨道。

高应力状态下两河口堆石料蠕变特性试验研究

堆石料是土石坝的主要填筑材料,其蠕变特性直接决定着土石坝工后变形的大小。对两河口水电站砾石土心墙堆石坝的两种筑坝堆石料,开展室内大型三轴蠕变试验,结果表明:①在低应力水平下,试验侧向应变为正;在高应力水平下,试验侧向应变为负;②采用幂函数外推30 a对应的试验值,将其作为堆石料蠕变试验的极限应变,所得剩余蠕变与时间呈良好的幂函数关系;③最终剪切蠕变与剪应力呈倍数关系,轴向蠕变衰减幂指数与剪切蠕变衰减幂指数基本相等,最终轴向蠕变是最终剪切蠕变的1.5倍。最后,提出了更简洁的两参数幂函数蠕变模型,模型参数物理含义明确,便于在工程中使用。研究可为土石坝工后变形的初步估算提供参考。

高功率激光器光束质量测量的衰减缩束仿真研究

光束质量因子M^(2)是表征高功率激光器横模特性的主要参数,针对目前光束质量分析仪只能用于小口径、低功率激光器光束质量评估的问题,开展了高功率激光器光束质量测量的衰减缩束技术原理与仿真研究。建立了衰减缩束组件的仿真模型,利用有限元的方法对光学元件在高功率激光下的热致像差进行研究,得出热致像差的峰谷(PV)值小于82 nm时,对光束质量因子的影响小于5%。当光束通过衰减组件时,如果发生退偏,光束质量因子将偏小。基于泽尼克多项式和光束质量因子计算模型,研究分析了缩束组件波前畸变对测量的影响,并通过Zemax仿真分析看出,在装调时入射光与缩束组件中心光轴夹角视场小于7°时,对光束质量因子测量的影响小于5%。

高速标准破片速度衰减规律试验研究

为研究符合北约STANAG 4496标准的高速破片在空气中运动的规律,设计了一种使用30 mm弹道炮发射的破片弹,并用多组区截测速装置获得标准破片在1400~2200 m/s速度范围内的运动数据。在此基础上,采用数值仿真和理论分析2种方式对破片在空气中运动的速度衰减规律进行了研究,利用CFX软件模拟破片在空气中运动的受力情况来推导破片运动速度,仿真与实测速度的最大误差为2.71%;结合破片运动方程建立了速度衰减模型,推导出破片运动过程中迎风面积的极值,结果表明:破片衰减系数k为0.008899;破片空气阻力系数cx取值范围为[0.99304,1.61721],并通过试验验证了速度衰减模型。