A new model for film bulk acoustic wave resonators

Based on cavity resonance and sandwich composite plate （3D） theoretical model for frequency dispersion characterization theory, this paper presents a universal three-dimensional and displacement profile shapes of the film bulk acoustic resonator （FBARs）. This model provides results of FBAR excited thickness-extensional and flexure modes, and the result of frequency dispersion is proposed in which the thicknesses and impedance of the electrodes and the piezoelectric material are taken into consideration; its further simplification shows good agreement with the modified Butterworth-Van-Dyke （MBVD） model. The displacement profile reflects the vibration stress distribution of electrode shapes and the lateral resonance effect, which depends on the axis ratio of the electrode shapes a/b. The results are consistent with the 3D finite element method modeling and laser interferometry measurement in general.

Effects of the slot width and angular position on the mode splitting in slotted optical microdisk resonator

A novel slotted optical microdisk resonator, which significantly enhances light–matter interaction and provides a promising approach for increasing the sensitivity of sensors, is theoretically and numerically investigated. In this slotted resonator, the mode splitting is generated due to reflection of the slot. Remarkably, effects of the slot width and angular position on the mode splitting are mainly studied. The results reveal that the mode splitting is a second function of the slot width, and the maximum mode splitting induced by the slot deformation is achieved with 2.7853 × 10~9Hz∕nm. Therefore, the slotted resonator is an excellent candidate for pressure and force sensing. Besides, the influence of the slot angular position on the mode splitting is a cosine curve with the highest sensitivity of 1.23 × 10^(11)Hz∕deg; thus, the optical characteristic demonstrates that the slotted resonator can be used for inertial measurements.

Effects of core position of locally resonant scatterers on low-frequency acoustic absorption in viscoelastic panel

Locally resonant sonic materials, due to their ability to control the propagation of low-frequency elastic waves, have become a promising option for underwater sound absorption materials. In this paper, the finite element method is used to investigate the absorption characteristics of a viscoelastic panel periodically embedded with a type of infinite-long noncoaxially cylindrical locally resonant scatterers(LRSs). The effect of the core position in the coating layer of the LRS on the low-frequency(500 Hz–3000 Hz) sound absorption property is investigated. With increasing the longitudinal core eccentricity e, there occur few changes in the absorptance at the frequencies below 1500 Hz, however, the absorptance above 1500 Hz becomes gradually better and the valid absorption(with absorptance above 0.8) frequency band(VAFB)of the viscoelastic panel becomes accordingly broader. The absorption mechanism is revealed by using the displacement field maps of the viscoelastic panel and the steel slab. The results show two typical resonance modes. One is the overall resonance mode(ORM) caused by steel backing, and the other is the core resonance mode(CRM) caused by LRS. The absorptance of the viscoelastic panel by ORM is induced mainly by the vibration of the steel slab and affected little by core position. On the contrary, with increasing the core eccentricity, the CRM shifts toward high frequency band and decouples with the ORM, leading to two separate absorption peaks and the broadened VAFB of the panel.

Anterolateral rotatory instability in vivo correlates tunnel position after anterior cruciate ligament reconstruction using bone-patellar tendon-bone graft

AIM To quantitatively assess rotatory and anterior-posterior instability in vivo after anterior cruciate ligament(ACL) reconstruction using bone-patellar tendon-bone(BTB) autografts, and to clarify the influence of tunnel positions on the knee stability.METHODS Single-bundle ACL reconstruction with BTB autograft was performed on 50 patients with a mean age of 28 years using the trans-tibial(TT)(n = 20) and trans-portal(TP)(n = 30) techniques. Femoral and tibial tunnel positions were identified from the high-resolution 3 D-CT bone models two weeks after surgery. Anterolateral rotatory translation was examined using a Slocum anterolateral rotatory instability test in open magnetic resonance imaging(MRI) 1.0-1.5 years after surgery, by measuring anterior tibial translation at the medial and lateral compartments on its sagittal images. Anterior-posterior stability was evaluated with a Kneelax3 arthrometer.RESULTS A total of 40 patients(80%) were finally followed up. Femoral tunnel positions were shallower(P < 0.01) and higher(P < 0.001), and tibial tunnel positions were more posterior(P < 0.05) in the TT group compared with the TP group. Anterolateral rotatory translations in reconstructed knees were significantly correlated with the shallow femoral tunnel positions(R = 0.42, P < 0.01), and the rotatory translations were greater in the TT group(3.2 ± 1.6 mm) than in the TP group(2.0 ± 1.8 mm)(P < 0.05). Side-to-side differences of Kneelax3 arthrometer were 1.5 ± 1.3 mm in the TT, and 1.7 ± 1.6 mm in the TP group(N.S.). Lysholm scores, KOOS subscales and reinjury rate showed no difference between the two groups.CONCLUSION Anterolateral rotatory instability significantly correlated shallow femoral tunnel positions after ACL reconstruction using BTB autografts. Clinical outcomes, rotatory and anterior-posterior stability were overall satisfactory in both techniques, but the TT technique located femoral tunnels in shallower and higher positions, and tibial tunnels in more posterior positions than the TP technique, thus increased the anterolateral rotation. Anatomic ACL reconstruction with BTB autografts may restore knee function and stability.

Position and Velocity Time Delay for Suppression Vibrations of a Hybrid Rayleigh-Van der Pol-Duffing Oscillator

In this paper,we used time delay feedback to minimize the vibrations of a hybrid Rayleigh–van der Pol–Duffing oscillator.This system is a one-degree-offreedom containing the cubic and fifth nonlinear terms and an external force.We applied the multiple scales method to get the solution from first approximation.Graphically and numerically,we studied the system before and after adding time delay feedback at the primary resonance case(
ffi!).We used MATLAB program to simulate the efficacy of different parameters and the time delay on the main system.

Pore throat structure heterogeneity and its effect on gas-phase seepage capacity in tight sandstone reservoirs:A case study from the Triassic Yanchang Formation,Ordos Basin

The microscopic heterogeneity of pore-throat structures in tight sandstone is a crucial parameter for understanding the transport mechanism of fluid flow.In this work,we firstly developed the new procedure to characterize the pore size distribution(PSD)and throat size distribution(TSD)by combining the nuclear magnetic resonance(NMR),cast thin section(CTS),and constant-rate mercury injection(CRMI)tests,and used the permeability estimated model to verify the full-scale PSD and TSD.Then,we respectively analyzed the fractal feature of the pore and throat,and characterized the heterogeneity of pores and throats.Finally,we elaborated the effect of the pore and throat heterogeneity on the gas-phase seepage capacity base on the analysis of the simple capillary tube model and gas-flooding experiment.The results showed that(1)The PSD and TSD of the tight sandstone sample ranged from 0.01 to 10 mm and from 0.1 to 57 mm,respectively,mainly contributed by the micropores and mesopores.Meanwhile,the permeability estimated by the PSD and TSD was consistent with the experimental permeability,and relative error was lower than 8%.(2)The PSD and TSD exhibited multifractal characteristics,and singularity strength range,Δα,could be used as the indicator for characterizing the heterogeneity of pore and throat.Furthermore,the throat of the sample showed stronger heterogeneity than that the pore.(3)The throats played an important role for the fluid transport in the tight sandstone,and the effect of the throat heterogeneity on the gas-phase seepage capacity was different under the lower and higher injection pressure.The macropores and micropores maybe respectively become the preferential migration pathways at the lower and higher injection pressure.In the end,the identification plate was established in our paper,and could be described the relationship among the throat heterogeneity,injection pressure,permeability and flow path of the gas phase in the tight sandstone.

An artificial neural network for detecting weld position in arc welding process

A kind of self organizing artificial neural network used for weld detection is presented in this paper, and its concepts and issues are discussed. The network can transform the weld visual information into typical patterns and match with the weld data collected on line, and so realize the accurate detection of the weld position in arc welding process.

内腔式非稳腔DF激光光束质量研究

激光光束质量是衡量激光器应用性能的重要指标之一,面向远距离光电对抗应用场景,本文开展了非链式脉冲氟化氘(DF)激光器非稳腔设计和光束质量提升技术研究。设计了3组不同放大倍率的正分支虚共焦非稳腔,搭建了凸面腔镜横向和轴向两种支撑结构的非稳腔实验装置,其中横向支撑结构内置循环水冷却通道。以86.5%环围能量定义激光光斑大小,选用β因子评价激光光束质量,比较两种支撑方式下的输出能量和光束质量。研究发现:相同条件下,轴向支撑结构的非稳腔输出能量较横向支撑结构高6%,但远场发散角较横向支撑大9%;水冷横向支撑结构虽存在部分能量遮挡,但其较好的热稳定性显著提升了激光光束质量。在M=2.25的横向支撑内腔式非稳腔条件下获得了光束质量因子β=1.83、发散角θ_(0.865)=0.63 mrad的激光光束。该条件下的激光单脉冲能量为2.34 J,激光脉宽为88.2 ns,峰值功率达到26.5 MW。

致密砂岩储层可动流体分布特征及主控因素

针对鄂尔多斯盆地富县地区长8储层流体分布差异显著、孔隙结构复杂、渗流能力相对薄弱等问题,选取研究区5块典型岩样开展测试分析,利用铸体薄片、扫描电镜(SEM)、X衍射黏土矿物分析(XRD)、恒速压汞实验,对可动流体主控因素进行分析。研究表明:致密砂岩储层中可动流体饱和度为26.31%~50.61%,平均值为35.15%;可动流体孔喉半径为0.10~0.50μm;T_(2)截止值为6.69~49.90 ms,可动流体最小孔喉半径为0.16~0.36μm。储层渗透率较孔隙度对可动流体的控制更强;中值半径、最大孔喉半径、平均孔喉半径与可动流体均具有正相关性,中值半径影响较大;长石含量越高,越容易形成长石溶孔,可动流体饱和度越大;I类和Ⅱ类储层中高岭石含量较高,呈分散质点式填充孔隙,Ⅲ类储层中伊利石和伊蒙混层含量较高,呈搭桥式分割孔隙,是堵塞孔喉的主要原因。该研究成果可为提高致密油藏采收率提供参考和借鉴。

具有p-Laplacian算子的分数阶问题共振正解的存在性

本文研究了具有p-拉普拉斯算子的分数阶微分方程在两种边界条件下的共振正解存在的问题.利用Leggett-Williams范型定理的方法,获得了一些新的存在性结果,推广了该类问题已有的研究结果.

变弯度导叶铰接位置对风扇振动特性的影响

针对变弯度导叶尾迹激励引起的转子叶片共振,基于谐响应模态叠加法对风扇转子进行强迫振动分析,研究了不同铰接位置的变弯度导叶对风扇气动性能及其振动特性的影响。结果表明,随着铰接位置向尾缘移动,风扇转子流量、压比和效率增加,稳定裕度降低,主要影响下游转子叶根部位的进气角度。在气动激励方面,随着铰接位置后移,转子叶片表面的压力幅值增大,相位变化剧烈,通过将非定常气动力转换到模态空间中,可以看到叶片所受模态气动力在铰接位置为35%C (C为轴向弦长)的情况下达到最大值,后呈现先减小后增加的规律,这与振动响应的变化规律一致。铰接位置对所关注的高阶局部模态的气动阻尼影响较小,最大差异为0.046%。在振动响应方面,转子叶片的振动应力随铰接位置剧烈改变,且为非单调变化。在设计位置处叶片的振动应力最小,在35%C处振动应力达到设计位置的15倍。对于本文所研究的模型及工况,最优铰接位置为45%C,与仅考虑气动性能的25%C不同。因此在变弯度导叶设计时,需要考虑其对叶片振动特性的影响。

自适应图像接收线圈应用于仰卧位乳腺磁共振成像研究

目的:本文探讨了自适应图像接收(AIR)线圈在仰卧位乳腺磁共振成像的可行性。方法:纳入53例乳腺磁共振检查的患者作为研究对象,仰卧位检查时采用AIR线圈,与常规俯卧位乳腺线圈成像进行图像质量对比,包括图像信噪比(SNR)、对比噪声比(CNR)、对比度、图像伪影、清晰度和整体评分。同时,对不同体位图像病灶显示能力进行评估,对比不同体位图像病灶SNR、CNR、病灶边缘清晰度;并比较病灶的最大长径、病灶距乳头和胸骨中点的距离。结果:仰卧位T_(2)WI图像的对比度高于俯卧位(0.59±0.02 vs.0.54±0.01),DWI图像脂肪SNR高于俯卧位(12.08±2.95 vs.9.31±0.91,T_(2)WI图像病灶的SNR大于俯卧位(120.41±31.86 vs.34.25±4.60),且仰卧位病灶距离胸骨中点的距离大于俯卧位(113.99±2.03 vs.86.64±2.14),差异有统计学意义(P<0.05)。仰卧位图像在伪影、清晰度和整体评分与俯卧位无统计学差别。病灶边缘的显示两种体位无差别。结论:采用AIR线圈的仰卧位乳腺磁共振成像与常规俯卧位图像质量、病灶的评估效能大致相仿,值得推广。

基于模型熵处理的泥浆脉冲信号去噪方法研究

泥浆正脉冲传输技术在石油钻探中应用非常广泛,但泥浆正脉冲信号包含大量噪声,其中泵噪声为主要噪声来源,不仅时域上完全覆盖有用信号,而且频域上存在频谱混叠。在泵噪声特性的基础上,建立了一种泵噪声状态空间模型(线性时不变模型),引入最大相关熵准则去除泵噪声的野值,利用基于熵处理的标准卡尔曼滤波对泵噪声进行重构和滤波。此外,为实时处理信号的需求,采用随机共振原则滤除泵噪声后的剩余随机噪声。同时,模拟了稳态/非稳态泵噪声状态下几种不同信噪比的含噪泥浆正脉冲信号,分析评价方案的噪声抑制能力。结果表明,该方案能够抑制甚至去除原始信号中的稳态/非稳态泵噪声,可以将信号的信噪比提高约5~24 dB。

四川盆地中部须家河组致密砂岩储层孔喉结构分类评价

致密砂岩储层具有非均质性强、孔喉关系复杂和孔渗相关关系差等特点。以四川盆地中部须家河组致密砂岩储层为研究对象,采用高压压汞和核磁共振法表征全孔径分布,建立全尺度的毛细管压力曲线,明确不同孔喉结构特征参数与储层宏观物性的关系,进行致密砂岩储层孔喉结构分类评价。结果表明:高压压汞实验中大孔(孔径≥50 nm)标定的核磁孔径分布可准确表征全孔径分布;全孔径分布谱图计算的峰度参数与孔隙度相关关系好,可评价储层宏观储集能力;伪毛细管压力曲线计算的相关因数和分形维数参数与渗透率相关关系好,可评价储层宏观渗流能力;研究区致密砂岩储层孔喉结构分为3类,由Ⅰ类到Ⅲ类,储集空间类型由残余粒间孔占优势向粒内溶孔占优势变化,峰度逐渐变小,分形维数变大,储集能力和渗流能力下降。该结果为提高致密砂岩气藏勘探与开发效率提供依据。

神经反馈增强积极情绪在抑郁症治疗中的应用

积极情绪的增强对抑郁症患者的临床症状改善和社会功能恢复具有重要意义。近年来神经反馈技术的发展为调控抑郁症积极情绪提供了有效的手段。传统积极情绪干预方法主观性强、治疗效果局限、缺乏可量化的客观评价指标,基于客观生理和影像指标的神经反馈技术在增强抑郁症积极情绪中具有重要的应用价值。神经反馈通过可视化方式将实时的大脑活动反馈给被试,让其能够使用特定的策略针对性地调控情绪相关脑区,客观定量地评价积极情绪的改善。现有的研究在实验范式、参数设置和个体疗效上存在较大异质性。通过回顾和总结神经反馈增强积极情绪的实验设计、研究的影响因素和基于神经影像标记物的目标靶点,强调了神经反馈实验设计和结果报告标准的重要性,探索性地提出了基于奖赏环路的潜在干预靶点及优化方案。有望为临床抑郁症积极情绪恢复提供可操作性的参考方案,为未来神经反馈技术在抑郁症临床症状治愈和社会功能康复中的转化应用和普及奠定基础。

利用自相似性实现医学图像合成的生成对抗网络

基于深度卷积的跨模态医学图像合成网络具有从大规模数据资源中学习非线性映射关系以进行局部生成的优势,但现有方法忽略了医学图像具有特征自相似性的特点,仅通过卷积来提取像素级别的特征信息,导致深层特征提取能力不足和语义信息表达不充分.为此,提出了基于图注意力块(Graph Attention Block,GAB)和全局块注意力块(Global Patch Attention Block,GPAB)的生成对抗网络(Graph Attention Block and Global Patch Attention Block Generative Adversarial Networks,GGPA-GAN).其中,用图注意力块和全局块注意力块捕捉医学图像切片间以及切片内的自相似性,进行深层特征的提取.此外,在生成器中加入二维位置编码,利用图像的空间位置信息来增强语义信息的表达能力.在HCP_S1200数据集和ADNI数据集上的实验结果表明,提出的网络在3T-7T、T1-T2的脑部MRI图像合成任务中相较于其他网络取得了最优的结果.在3T-7T脑部MRI图像合成任务中,相比Pix2pix合成方法,该方法在峰值信噪比(Peak Signal-to-Noise Ratio)、结构相似性指数(Structural Similarity Index)和平均绝对误差(Mean Absolute Error)方面分别提升了0.55、0.007和6.55.在T1-T2脑部MRI图像合成任务中,相比Pix2pix合成方法,在PSNR、SSIM和MAE分别提升了0.68、0.006和8.77.这些结果充分证明了此方法的有效性,为临床诊断提供了有力的帮助.

双端腔Ⅱ类倍频产生四组份纠缠光场

量子纠缠是执行量子计算和构建量子通信网络的关键资源,制备与操控纠缠态光场是实现量子信息处理的基础要素.本文提出了利用双端光学腔倍频产生四组份纠缠态的理论模型,从耦合波方程出发得到Ⅱ类倍频过程的传输矩阵,通过腔内自再现方程和输入输出传输矩阵理论研究了输出的两束倍频光的噪声特性;对于两束倍频光和两束基频泵浦场,利用多组份纠缠光场的充分必要判据PPT方法(positivity under partial transposition criterion)分析了最小辛本征值与泵浦功率及分析频率之间的关系,研究结果表明基频泵浦光与倍频光之间存在四组份纠缠.

基于多频段的良性阵发性位置性眩晕患者fMRI百分比振幅改变

目的 探讨通过静息态功能磁共振成像(resting-state functional magnetic resonance imaging, rs-fMRI)技术中的百分率振幅(percent amplitude of fluctuation, PerAF),分析良性阵发性位置性眩晕(benign paroxysmal positional vertigo,BPPV)患者多频段(经典频段、slow-4频段和slow-5频段)的脑自发活动的改变。方法 选取并分析20例BPPV患者(BPPV组)以及14例健康对照者(HC组)的rs-fMRI。结果 PerAF在不同频段的组间差异结果:1)在经典频段,与HC组相比较,BPPV组在左侧背外侧额上回、左侧辅助运动区PerAF值降低;2)在slow-4频段,与HC组相比较,BPPV组在左侧脑岛、左侧楔前叶、左侧额中回及左侧辅助运动区PerAF值降低;3)在slow-5频段,与HC组相比较,BPPV组在左侧额中回、左侧内侧和旁扣带回及左侧辅助运动区PerAF值降低。结论 BPPV患者静息态下存在多个脑区的功能异常,提示患者存在中枢功能紊乱与重塑。BPPV患者异常脑区对各频段的敏感性不同,提示患者自发性脑活动存在频率依赖性。

动力位下早期脊髓型颈椎病患者脊髓致压特点的有限元分析

背景:脊髓型颈椎病是导致中老年人功能障碍的进行性加重疾病,早期诊断困难,近年来临床上有学者发现动态磁共振成像(dMRI)技术可更早期发现动力位下的脊髓受压,但其具体生物力学机制亟待阐明。目的:探讨早期脊髓型颈椎病患者在动力位(过伸过屈位)下脊髓的生物力学致压特点,验证颈椎dMRI对早期脊髓型颈椎病诊断的有效性。方法:回顾性分析2022年1-6月在广西中医药大学第一附属医院骨科就诊并拍摄过颈段dMRI患者的病历资料,共纳入16例,分为2组,病理组为8例以黄韧带肥厚为主要征象的早期脊髓型颈椎病患者,男5例,女3例;正常组为8例正常退变人群,男4例,女4例。所有患者均已拍摄颈椎CT平扫、MRI平扫、dMRI平扫。此次研究分为以下3个部分实验进行阐述:①采集两组受试者dMRI图像的DCOM数据,并采集其颈椎CT、中立位MRI图像DCOM数据了解两组受试者在中立位下的骨质及软组织情况;②基于MRI及CT平扫的图像DCOM数据,使用逆向工程软件分别建模正常退变人群、脊髓型颈椎病早期患者的下颈椎(C3-7)三维有限元模型,分析脊髓、硬膜后部的等效应力、等效弹性应变数值,观察应力、应变分布情况;③得出应力、应变数据后进行组间数据对比,分析出早期脊髓型颈椎病在动力位下脊髓致压的力学特点,验证dMRI对早期脊髓型颈椎病诊断的有效性。结果与结论:①两组受试者下颈椎(C3-7)模型在模拟后伸、前屈、中立位时,其脊髓后部的应力、应变数值从大到小依次为后伸位>前屈位>中立位(P<0.05),应变数值从大到小依次为后伸位>前屈位>中立位(P<0.05);②与正常退变人群模型比较,病理组模型在前屈、后伸2种自由度下,其脊髓的等效应力、应变均较正常组模型增大(P<0.05),且脊髓后部应力、应变分布区域不规则;③在中立位下,两组模型脊髓的应变数值无明显差异(P>0.05),应变分布区域均匀规则;④提示在颈椎后伸位状态下,以黄韧带肥厚为主要征象的早期脊髓型颈椎病患者硬膜囊和脊髓后部均受压变形,脊髓的受压形变程度明显大于前屈位和中立位;中立位状态下,早期脊髓型颈椎病患者硬膜受压变形,脊髓无明显形变征象;此次研究从生物力学的角度验证了dMRI对早期脊髓型颈椎病诊断的有效性。

半球谐振子超精密修调方法研究

目的研究因谐振子质量缺陷而引起的频率裂解机制,进而对刚性轴位置进行质量高分辨率可控去除,提高陀螺精度。方法首先基于多区域配合划分法建立半球谐振子高精度有限元仿真模型,分析质量大小与位置对谐振子频差的影响规律。其次搭建谐振子振动特性检测平台,利用拍频法实现其频差值和刚性轴位置的精确辨识。最后结合仿真与辨识结果以及离子束加工方法确定谐振子超精密修调方案。结果优化网格划分方法后,谐振子有限元模型频差值小于0.0001Hz,当修调定位误差相同时,在一个范围内的质量去除比单点质量去除的修调效率更高;谐振子质量缺陷四次谐波刚性轴位置辨识精度可达0.1°,与常见的幅值法相比,其精度提高了一个数量级;通过三次点线结合方式进行质量修调后,谐振子频差值小于0.001Hz,修调效率与精度得到了提升。结论提出的谐振子仿真模型、振动特性测试方法以及离子束修调工艺精度较高且可行性较强,对实现半球谐振子性能高精度检测以及高质量加工具有重要意义。