A study of damping factors in perfectly matched layers for the numerical simulation of seismic waves

When simulating seismic wave propagation in free space, it is essential to introduce absorbing boundary conditions to eliminate reflections from artificially trtmcated boundaries. In this paper, a damping factor referred to as the Gaussian dmping factor is proposed. The Gaussian damping factor is based on the idea of perfectly matched layers （PMLs）. This work presents a detailed analysis of the theoretical foundations and advantages of the Gaussian damping factor. Additionally, numerical experiments for the simulation of seismic waves are presented based on two numerical models： a homogeneous model and a multi-layer model. The results show that the proposed factor works better. The Gaussian damping factor achieves a higher Signal-to-Noise Ratio （SNR） than previously used factors when using same number of PMLs, and requires less PMLs than other methods to achieve an identical SNR.

A time domain induced polarization relaxation time spectrum inversion method based on a damping factor and residual correction

Relaxation time spectra （RTS） derived from time domain induced polarization data （TDIP） are helpful to assess oil reservoir pore structures. However, due to the sensitivity to the signal-to-noise ratio （SNR）, the inversion accuracy of the traditional singular value decomposition （SVD） inversion method reduces with a decrease of SNR. In order to enhance the inversion accuracy and improve robustness of the inversion method to the SNR, an improved inversion method, based on damping factor and spectrum component residual correction, is proposed in this study. The numerical inversion results show that the oscillation of the RTS derived from the SVD method increased with a decrease of SNR, which makes it impossible to get accurate inversion components. However, the SNR has little influence on inversion components of the improved method, and the RTS has high inversion accuracy and robustness. Moreover, RTS derived from core sample data is basically in accord with the pore-size distribution curve, and the RTS derived from the actual induced polarization logging data is smooth and continuous, which indicates that the improved method is practicable.

Broad-Band FMR Linewidth of Co_2MnSi Thin Films with Low Damping Factor:The Role of Two-Magnon Scattering

The low Gilbert damping factor, which is usually measured by ferromagnetic resonance, is crucial in spintronic applications. Two-magnon scattering occurs when the orthogonMity of the ferromagnetic resonance mode and other degenerate spin wave modes was broken by magnetic anisotropy, voids, second phase, surface defects, etc., which is important in analysis of ferromagnetic resonance linewidth. Direct fitting to linewidth with Gilbert damping is advisable only when the measured linewidth is a linear function of measuring frequency in a broad band measurement. We observe the nonlinear ferromagnetic resonance linewidth of Co2MnSi thin films with respect to measuring frequency in broad band measurement. Experimental data could be well fitted with the model including two-magnon scattering with no fixed parameters. The fitting results show that two-magnon scattering results in the nonlinear linewidth behavior, and the Gilbert damping factor is much smaller than reported ones, indicating that our Co2MnSi films are more suitable for the applications of spin transfer torque.

Damping Factor Estimation of a Flexible-Matrix-Composite Body Pump

Two very important factors which determine the effectiveness of a pump are its volumetric and power efficiencies. Yin and Ghoneim constructed a prototype of a Flexible-Matrix-Composite (FMC) body pump with a very high volumetric efficiency or pumping potential (the relative volume reduction due to a relative input stroke). The high volumetric efficiency is attributed to the geometry of the pump’s structure (hyperboloid) as well as the high negative effective Poisson’s ratio of the 3-layer [θ/β/θ] flexible-matrix-composite (carbon/polyurethane) laminate adopted for the body of the pump. However, the power efficiency of the pump was not evaluated. It is the objective of the current paper to obtain an estimate of the power efficiency of the pump. The viscoelastic properties of the 3-layer FMC (carbon/polyurethane) laminate are evaluated experimentally using the Dynamic Mechanical Analyzer (DMA) as well as analytically by applying the correspondence principle together with the micro-mechanics approach. In order to obtain an estimate of the power efficiency of the FMC body pump, the axial and shear loss factors of a laminated infinitely long cylindrical tube as functions of β and θ fiber orientation angles are determined employing the Adam and Bacon approach. The analysis engenders high loss factors (greater than 0.4), which suggests that the power efficiency of the proposed pump using the 3-layer carbon/polyurethane laminate may be low.

Micro arc oxidation and electrophoretic deposition effect on damping and sound transmission characteristics of AZ31B magnesium Alloy

Micro arc oxidation(MAO) and electrophoretic deposition(EPD) process are employed to fabricate a dense coating on magnesium alloy to protect it from corrosion in engineering application. The EPD film changes the damping characteristic of magnesium alloy, and both the MAO and EPD process change the bending stiffness of samples being treated. Damping loss factor(DLF) test and sound transmission experiments were carried out for AZ31 B magnesium alloy with coating fabricated by MAO and EPD processes. The results indicate that DLF is improved in frequency range from 0-850 Hz. Bending stiffness of the samples is improved with MAO and EPD treatment. As a result, the sound transmission loss(LST) is improved in the stiffness control stage of the sound transmission verse frequency curve. To the samples by electrophoresis process, the LST is improved in frequency range from 2500-3200 Hz, because the damping loss factor is improved with EPD process. The results are useful for the surface treatment to enhance the damping loss factor, LST and widespread application of magnesium alloy while improving the corrosion resistance.

Damping properties of fly ash/epoxy composites

An inexpensive fly ash （FA）, which is from a waste product, was employed to prepare fly ash/epoxy composites. The purpose of this study is to characterize the contributions of matrix viscoelasticity, hollow structure characteristic （porosity）, and filler/matrix interface friction to the high vibration damping capacity of such composites. The damping properties of the composites were investigated in the temperature range of-40 to 150℃ and in the frequency range of 10 to 800 Hz by using a tension-compression mode. The results indicate that the peak value of damping loss factor （tan3） for the fly ash/epoxy composites can reach 0.70-0.90 in test specification, and the attenuation of damping loss factor is inconspicuous with increasing frequency. In addition, scanning electron microscope （SEM） was used to observe the morphology of the fly ash as well as its distribution in the matrix, which will help to analyze the effect of fly ash on the damping properties of the fly ash/epoxy composites.

DEPENDENCE OF DAMPING CHARACTERISTICS OF A BEAM WITH DAMPING RUBBER MAGNETIC POWDER ON RUBBER PROPERTY

A cantilever beam with Damping Material Applying Rubber Magnetic Powder （DRM） has been investigated. Two methods are selected to hold DRM to a vibrating steel beam, one is to attach DRM by the magnetic attractive force （called DRM beam） and the other by adhesive bonding （called AB-DRM beam）. Different from the damping property of AB-DRM beam caused by shear deformation of damping material, the damping property of DRM beam is characterized by the sliding frictional loss together with the internal loss of damping material. The authors established a formulation to predict the damping characteristics of DRM beam, which was validated experimentally. It is found that rubber material loss factor β has a decisive influence on damping improvement of DRM beam versus AB-DRM beam. If β is smaller than the critical value around 0.8255, a valid range of vibratory amplitude always exists in which DRM beam can achieve better damping than AB-DRM beam; conversely, if β is bigger than the critical value, the valid range does not exist when slide occurs. Such results are used to determine the merits and limitations of DRM and develop design guidelines.

High frequency characteristics of (Ni_(75)Fe_2)_x(Zn O)_(1-x) granular thin films with tunable damping coefficient

The effect of the volume fraction of ferromagnetic metal （x） in （Ni75Fe25）x（ZnO）1-x nanogranular thin films on microstructural, soft-magnetic, and high-frequency properties was investigated. Good soft-magnetic properties were obtained in a broad x range, with 0.55 〈 x 〈 0.82. High resolution transmission electron microscopy （HRTEM） observations reveal that the grain size of the samples is lower than 14 nm, and that it decreases with decreasing x. Of special interest, our investigation of the permeability spectra indicates that these films exhibit an adjustable frequency linewidth of resonance peak, dependant upon changing x. Correspondingly, large and adjustable damping coefficients （aeff） from 0.023 to 0.043 were achieved by decreasing x from 0.82 to 0.55. Combined with the HRTEM results, the variation of αeff with x was analyzed in detail.

Rational design of thermoelastic damping in microresonators with phase-lagging heat conduction law

The design of thermoelastic damping(TED)affected by the phase-lagging non-Fourier heat conduction effects becomes significant but challenging for enlarging the quality factor of widely-used microresonators operating in extreme situations,including ultra-high excitation frequency and ultra-low working temperature.However,there does not exist a rational method for designing the TED in the framework of non-Fourier heat conduction law.This work,therefore,proposes a design framework to achieve low thermoelastic dissipation of microresonators governed by the phase-lagging heat conduction law.The equation of motion and the heat conduction equation for phase-lagging TED microresonators are derived first,and then the non-Fourier TED design problem is proposed.A topology optimization-based rational design method is used to resolve the design problem.What is more,a two-dimensional(2D)plain-strain-based finite element method(FEM)is developed as a solver for the topology optimization process.Based on the suggested rational design technique,numerical instances with various phase lags are investigated.The results show that the proposed design method can remarkably reduce the dissipation of microresonators by tailoring their substructures.

脑血管疾病风险人群湿证相关特征的流行病学调查

【目的】探究广东地区脑血管疾病风险人群与中医湿证相关的流行病学特征。【方法】采用横断面研究的方法,调查330例广东常住居民脑血管疾病风险相关的临床资料,进行中医湿证诊断、量化评分及脑卒中风险评级,总结湿证分布规律并分析其影响因素。【结果】(1)诊断为湿证的研究对象共306例(占92.73%),风险组诊断为湿证人群的占比为93.82%(258/275),略高于健康组的87.27%(48/55),但差异无统计学意义(χ2=2.91,P=0.112),而风险组的湿证量化得分高于健康组,差异有统计学意义(Z=-2.24,P=0.025)。(2)在具有脑血管疾病危险因素的研究对象中,评价时间(χ2=26.11,P=0.001)、脑卒中风险等级(χ2=8.85,P=0.031)、脑卒中或短暂性脑缺血发作(TIA)病史(χ2=9.28,P=0.015)是脑血管病风险人群湿证等级的影响因素。【结论】湿证是广东地区人群常见的中医证候;具有脑血管疾病危险因素,尤其是脑卒中高风险人群、脑卒中或TIA病史患者,其湿证程度明显增高;未来在广东开展脑卒中预防工作应考虑湿证的评估与干预。

Study of Bed Friction Factor for the Wu River Estuary

In this research the bed friction effect is estimated of a river estuary by use of hydrodynamic analysis. The on-site sampled data of the Wu River estuary is applied to the analysis. There are many dynamic factors that affect the flow characteristics in the estuary. The effect of tide on the generation of tidal current, bottom friction and geometry effect is the focus of this paper. The Wu River estuary is about 15 hn in length, with a small bottom slope and no physical obstruction; thus the incident wave at the estuary is considered a progressive wave with damping effect. The amplitude reduction and phase shift of the incident wave are analyzed. By the analysis of celerity reduction factor of the estuary, the estimated value of mean resistance coefficient M（μ ,κ）, damping modulus μ, and wave number κ for the sections at observation stations can be determined. Furthermore, data gathered from on-site observations are applied for validation. Finally, Manning＇ s coefficient for each section of the observation stations can be determined. It is found that the value of Manning＇ s coefficient is small downstream and increases towards upstream, and that the bed friction effect of an estuary varies largely. The estimated results of the paper are compared with the empirical formulas and the modified solution for practical application is discussed.

Simultaneous Structure-Coupled Joint Inversion of Gravity and Magnetic Data Based on a Damped Least-Squares Technique

The structure-coupled joint inversion method of gravity and magnetic data is a powerful tool for?developing improved physical property models with high resolution and compatible features;?however, the conventional procedure is inefficient due to the truncated singular values decomposition?(SVD) process at each iteration. To improve the algorithm, a technique using damped leastsquares?is adopted to calculate the structural term of model updates, instead of the truncated SVD. This?produces structural coupled density and magnetization images with high efficiency. A so-called?coupling factor is introduced to regulate the tuning of the desired final structural similarity level.?Synthetic examples show that the joint inversion results are internally consistent and achieve?higher?resolution than separated. The acceptable runtime performance of the damped least squares?technique used in joint inversion indicates that it is more suitable for practical use than the truncated SVD method.

THE AUTO-ADJUSTABLE DAMPING METHOD FORSOLVING NONLINEAR EQUATIONS

The general approach for solving the nonlinear equations is linearizing the equations and forming various iterative procedures, then executing the numerical simulation. For the strongly nonlinear problems, the solution obtained in the iterative process is always difficult, even divergent due to the numerical instability. It can not fulfill the engineering requirements. Newton's method and its variants can not settle this problem. As a result, the application of numerical simulation for the strongly nonlinear problems is limited. An auto-adjustable damping method has been presented in this paper. This is a further improvement of Newton's method with damping factor. A set of vector of damping factor is introduced. This set of vector can be adjusted continuously during the iterative process in accordance with the judgement and adjustment. An effective convergence coefficient and quichening coefficient are employed to relax the restricted requirements for the initial values and to shorten the iterative process. Then, the numerical stability will be ensured for the solution of complicated strongly nonlinear equations. Using this method, some complicated strongly nonlinear heat transfer problems in airplanes and aeroengines have been numerically simulated successfully. It can be used for the numerical simulation of strongly nonlinear problems in engineering such as nonlinear hydrodynamics and aerodynamics, heat transfer and structural dynamic response etc.

脑血管疾病风险人群湿证相关的肠道菌群特征及影响因素研究

【目的】研究脑血管疾病风险人群湿证相关肠道菌群的特征及其影响因素。【方法】基于2021年10月至2023年2月在广东开展的脑血管疾病风险人群湿证相关的流行病学调查,纳入60例研究对象(包括脑血管疾病风险组41例和健康对照组19例),进行湿证诊断与脑卒中风险评级,收集粪便样本,采用高通量16S rRNA测序技术及生物信息学方法分析菌群特征。【结果】(1)共53例诊断为湿证(88.33%),风险组与健康组间及低、中、高危3组间在湿证诊断量化得分的组间比较有统计学差异(P=0.016;P=0.041)。(2)湿证组与非湿证组的肠道菌群物种种类及丰度无显著性差异。(3)在已诊断为湿证的人群中,健康组与风险组的Alpha多样性无显著性差异,而Beta多样性分析有显著性差异;LEfSe分析发现梭杆菌和乳杆菌富集于风险组;相关性分析提示差异菌与糖尿病、血脂异常、肥胖3个危险因素以及颈动脉内-中膜厚度(IMT)相关。(4)在已诊断为湿证且有脑血管疾病危险因素的人群中,低、中、高危3组的Alpha多样性无显著性差异,而Beta多样性分析则提示有显著性差异;LEfSe分析发现,Acidaminococcaceae、Phascolarctobacterium、Butyricimonas明显富集于低危组,Veillonellaceae明显富集于中危组,Ruminococcus 2、Alloprevotella明显富集于高危组;相关性分析提示,差异菌与高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、白细胞计数(WBC)、中性粒细胞计数(NEUT)相关。【结论】以湿证为主的广东地区人群,湿证程度与脑卒中风险有关,且呈现与亚临床动脉粥样硬化、炎性反应、脂质代谢相关的特征菌群。

悬索桥竖弯涡振MTMD减振控制效果和参数优化研究

为研究多重调谐质量阻尼器(Multiple Tuned Mass Damper,MTMD)抑制桥梁单阶涡振的性能,建立桥梁结构-MTMD系统竖弯涡振广义单自由度动力方程,以某大跨度悬索桥为背景进行MTMD减振控制效果和参数优化分析。采用数值方法求解动力方程,获得系统在简谐涡激力下达到稳态谐振时结构的动力放大系数和MTMD对结构的附加模态阻尼比,并与单一频率调谐质量阻尼器(Single Tuned Mass Damper,STMD)的减振控制效果进行对比,然后以附加模态阻尼比为目标对MTMD进行参数优化。结果表明:MTMD比最优参数STMD拥有更宽的控制频带和更好的减振效果,经优化后的MTMD减振性能优于最优参数STMD。实际应用MTMD时,应选择较大广义质量、5~7种频率规格,并根据二者找到无量纲频率范围和各TMD阻尼比的惟一最优取值。

柏薏灌肠液联合丹白颗粒治疗盆腔炎性疾病后遗症(湿热瘀结证)的临床研究

目的:探讨柏薏灌肠液联合丹白颗粒治疗盆腔炎性疾病后遗症(湿热瘀结证)的临床疗效。方法:选取2021年3月至2023年3月该院收治的盆腔炎性疾病后遗症(湿热瘀结证)患者90例,采用随机数字表法分为中药灌肠组、中药颗粒组和联合组,每组30例。中药灌肠组患者采用常规治疗+柏薏灌肠液,中药颗粒组患者采用常规治疗+丹白颗粒,联合组患者采用常规治疗+柏薏灌肠液+丹白颗粒。治疗3个月经周期后,评估三组患者的临床疗效、中医证候积分、血流动力学、炎症因子和治疗安全性。结果:联合组患者的总有效率为93.33%(28/30),高于中药灌肠组、中药颗粒组的70.00%(21/30)、66.67%(20/30),差异均有统计学意义(P<0.05)。治疗后,联合组患者中医证候积分(包括腰骶胀痛、经行不畅、带下增多和舌红苔黄积分)低于中药灌肠组、中药颗粒组,差异均有统计学意义(P<0.05)。治疗后,联合组患者子宫动脉收缩期最大流速、舒张末期最大流速和搏动指数高于中药灌肠组、中药颗粒组,阻力指数低于中药灌肠组、中药颗粒组,差异均有统计学意义(P<0.05)。治疗后,联合组患者炎症因子[白细胞介素18、前列腺素E2和β淀粉样前体蛋白]水平低于中药灌肠组、中药颗粒组,差异均有统计学意义(P<0.05)。联合组、中药灌肠组和中药颗粒组患者的不良反应发生率分别为13.33%(4/30)、10.00%(3/30)和6.67%(2/30),组间差异无统计学意义(P>0.05)。结论:柏薏灌肠液联合丹白颗粒治疗盆腔炎性疾病后遗症(湿热瘀结证)的效果良好,可改善患者中医证候,提高盆腔子宫动脉血流动力学,抑制炎症因子水平,安全性良好。

芍药汤治疗湿热内蕴型溃疡性结肠炎疗效及对患者炎症因子和T淋巴细胞亚群的影响

目的:观察芍药汤治疗溃疡性结肠炎(UC)患者(湿热内蕴证)的临床疗效及对患者炎症因子和T淋巴细胞亚群的影响。方法:选择接受治疗的110例UC患者作为研究对象,掷硬币法分为两组,各55例。对照组采取美沙拉秦治疗,观察组在对照组基础上采取芍药汤治疗,两组均连续治疗3个月。治疗3个月时比较两组患者临床疗效;比较两组治疗前、治疗3个月时临床症状、Mayo、Geboes指数评分、炎症因子、T淋巴细胞亚群(CD4^(+)、CD8^(+)、CD4^(+)/CD8^(+))及肠道菌群水平;统计并比较两组治疗期间不良反应发生情况。结果:治疗后,观察组总有效率高于对照组(P<0.05);治疗后,两组主症、次症及总分低于治疗前,观察组低于对照组(P<0.05);治疗后,两组Mayo活动指数、Geboes指数评分低于治疗前,观察组低于对照组(P<0.05);治疗后,两组超敏C反应蛋白(hs-CRP)、肿瘤坏死因子-α(TNF-α)、白细胞介素-6(IL-6)水平低于治疗前,观察组低于对照组(P<0.05);治疗后,两组CD4^(+)、CD4^(+)/CD8^(+)高于治疗前,CD8^(+)低于治疗前,观察组CD4^(+)、CD4^(+)/CD8^(+)高于对照组,CD8^(+)低于对照组(P<0.05);治疗后,两组双歧杆菌、乳酸杆菌高于治疗前,大肠杆菌低于治疗前,观察组大肠杆菌低于对照组(P<0.05);观察组发生1例恶心,1例皮肤瘙痒,对照组未发生不良反应(P>0.05)。结论:芍药汤能够有效改善湿热内蕴证UC患者临床症状,促进肠黏膜愈合,降低机体炎症反应,提高免疫功能,恢复胃肠道菌群平衡,提升临床疗效。

清肠化湿方联合美沙拉嗪治疗溃疡性结肠炎(湿热内蕴证)的疗效及对IL-6、IL-1β、IL-22的影响

目的:探究清肠化湿方联合美沙拉嗪治疗溃疡性结肠炎(湿热内蕴证)的疗效及对白细胞介素-6(IL-6)、白细胞介素-22(IL-22)、白细胞介素-1β(IL-1β)的影响。方法:选取2019年9月~2022年5月我院就诊104例溃疡性结肠炎(湿热内蕴证)患者作为观察对象,使用区组随机化法分为观察组(51例)和对照组(53例)。对照组采用美沙拉嗪进行治疗,观察组在其基础上给予清肠化湿方。比较两组患者治疗前、治疗2个月后临床症状改善情况(DAL评分、组织病理学评分)、中医证候积分、炎症指标[IL-6、IL-1β、IL-22]、生活质量[炎性肠病生活质量表(IBDQ)]的变化。结果:治疗2个月后,两组DAL评分、组织病理学评分、中医证候积分、血清IL-6、IL-1β、IL-22水平均显著降低,且观察组低于对照组(P均<0.05);两组治疗2个月后IBDQ各项评分及总分均显著升高,且观察组高于对照组(P均<0.05)。结论:清肠化湿方联合美沙拉嗪治疗溃疡性结肠炎患者疗效显著,可有效改善患者临床症状,降低炎症介质产生,从而提高患者生活质量。

炭黑N330用量对天然橡胶阻尼性能的影响

研究炭黑N330用量对天然橡胶(NR)阻尼性能的影响。结果表明:随着炭黑用量的增大,NR混炼胶的FL,Fmax和Fmax-FL增大,t90缩短;NR硫化胶的邵尔A型硬度、100%定伸应力、300%定伸应力、拉伸强度和撕裂强度增大,拉断伸长率和回弹值减小;NR硫化胶低温下的损耗因子(tanδ)峰值减小,高温下的tanδ呈增大趋势。随着温度的升高,NR硫化胶的tanδ减小,且炭黑N330用量大的NR硫化胶的tanδ减小速率大于炭黑N330用量小的NR硫化胶,表明高温下炭黑N330用量大的NR硫化胶的阻尼性能对温度变化更敏感。随着炭黑N330用量的增大,NR硫化胶的静刚度和动/静刚度比都增大,表明炭黑N330用量增大对NR硫化胶的阻尼性能有提升作用。