Electromechanical cracking in ferroelectrics driven by large scale domain switching

Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven jointly by both the singular and non-singular terms of the crack-tip electric field. Combining a full field solution with an energy based switching criterion, we obtain the switching zone by the large scale model around the tip of a stationary impermeable crack. It is observed that the switching zone by the large scale model is significantly different from that by the small scale model. According to the large scale switching zone, the switch-induced stress intensity factor (SIF) and the transverse stress (T-stress) are evaluated numerically. Via the SIF and T-stress induced by the combined loading and corresponding criteria, we address the crack initiation and crack growth stability simultaneously. The two theoretical predictions roughly coincide with the experimental observations.

Modified slow-fast analysis method for slow-fast dynamical systems with two scales in frequency domain

A modified slow-fast analysis method is presented for the periodically excited non-autonomous dynamical system with an order gap between the exciting frequency and the natural frequency.By regarding the exciting term as a slow-varying parameter,a generalized autonomous fast subsystem can be defined,the equilibrium branches as well as the bifurcations of which can be employed to account for the mechanism of the bursting oscillations by combining the transformed phase portrait introduced.As an example,a typical periodically excited Hartley model is used to demonstrate the validness of the method,in which the exciting frequency is far less than the natural frequency.The equilibrium branches and their bifurcations of the fast subsystem with the variation of the slow-varying parameter are presented.Bursting oscillations for two typical cases are considered,which reveals that,fold bifurcation may cause the the trajectory to jump between different equilibrium branches,while Hopf bifurcation may cause the trajectory to oscillate around the stable limit cycle.

Positively Worded Subscale Score of the Perceived Stress Scale Is Associated with Cognitive Domain Function

Objectives: To examine the cross-sectional associations of the separate subscales of the Perceived Stress Scale (PSS) and tests measuring cognitive domains in older adults. Methods: 897 adults over the age of 70 free of amnestic mild cognitive impairment and dementia and enrolled in the Einstein Aging Study made up the study sample. The PSS-14 was used to measure stress. Three cognitive domains (language, episodic memory, and frontal-executive) had previously been found using principle component analysis. Linear regression analyses were used to determine the relationship between the PSS subscales and cognitive domain function. Results: The study sample had a mean age of 79.1 years and 62.8% were female. Bivariate correlations show that the PSS-14 positively worded subscale of the PSS (PSS-PW) was significantly associated with all three cognitive domains (language: r = -0.15, p < 0.001;episodic memory: r = -0.16, p < 0.001;frontal-executive: r = -0.21, p <0.001) while the negatively worded subscale of the PSS (PSS-NW) was not significantly associated with any cognitive domain. In linear regression analyses adjusted for age, white race, gender, years of education, and depressive symptoms, the PSS-PW remained significantly associated with each of the cognitive domains. The PSS-NW was not associated with any cognitive domains in any model. The PSS-14 was significantly associated with language and episodic memory, but not the frontal-executive domain. Conclusion: Worse PSS-PW scores are associated with reduced cognitive function in the executive, memory, and language domains in nondemented older adults. The PSS-PW subscale correlated better with cognitive function than the overall PSS-14. Future research should evaluate the temporality of the association and if stress reduction therapies improve cognitive performance.

Radio-frequency transistors from millimeter-scale graphene domains

Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors （RF-FETs）. Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum os- cillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.

Large-Scale Ontology Development and Agricultural Application Based on Knowledge Domain Framework

The key activity to build semantic web is to build ontologies. But today, the theory and methodology of ontology construction is still far from ready. This paper proposed a theoretical framework for massive knowledge management- the knowledge domain framework （KDF）, and introduces an integrated development environment （IDE） named large-scale ontology development environment （LODE）, which implements the proposed theoretical framework. We also compared LODE with other popular ontology development environments in this paper. The practice of using LODE on management and development of agriculture ontologies shows that knowledge domain framework can handle the development activities of large scale ontologies. Application studies based on the described briefly. principle of knowledge domain framework and LODE was

Bayesian seismic multi-scale inversion in complex Laplace mixed domains

Seismic inversion performed in the time or frequency domain cannot always recover the long-wavelength background of subsurface parameters due to the lack of low-frequency seismic records. Since the low-frequency response becomes much richer in the Laplace mixed domains, one novel Bayesian impedance inversion approach in the complex Laplace mixed domains is established in this study to solve the model dependency problem. The derivation of a Laplace mixed-domain formula of the Robinson convolution is the first step in our work. With this formula, the Laplace seismic spectrum, the wavelet spectrum and time-domain reflectivity are joined together. Next, to improve inversion stability, the object inversion function accompanied by the initial constraint of the linear increment model is launched under a Bayesian framework. The likelihood function and prior probability distribution can be combined together by Bayesian formula to calculate the posterior probability distribution of subsurface parameters. By achieving the optimal solution corresponding to maximum posterior probability distribution, the low-frequency background of subsurface parameters can be obtained successfully. Then, with the regularization constraint of estimated low frequency in the Laplace mixed domains, multi-scale Bayesian inversion inthe pure frequency domain is exploited to obtain the absolute model parameters. The effectiveness, anti-noise capability and lateral continuity of Laplace mixed-domain inversion are illustrated by synthetic tests. Furthermore,one field case in the east of China is discussed carefully with different input frequency components and different inversion algorithms. This provides adequate proof to illustrate the reliability improvement in low-frequency estimation and resolution enhancement of subsurface parameters, in comparison with conventional Bayesian inversion in the frequency domain.

Dynamic interaction numerical models in the time domain based on the high performance scaled boundary finite element method

Consideration of structure-foundation-soil dynamic interaction is a basic requirement in the evaluation of the seismic safety of nuclear power facilities. An efficient and accurate dynamic interaction numerical model in the time domain has become an important topic of current research. In this study, the scaled boundary finite element method （SBFEM） is improved for use as an effective numerical approach with good application prospects. This method has several advantages, including dimensionality reduction, accuracy of the radial analytical solution, and unlike other boundary element methods, it does not require a fundamental solution. This study focuses on establishing a high performance scaled boundary finite element interaction analysis model in the time domain based on the acceleration unit-impulse response matrix, in which several new solution techniques, such as a dimensionless method to solve the interaction force, are applied to improve the numerical stability of the actual soil parameters and reduce the amount of calculation. Finally, the feasibility of the time domain methods are illustrated by the response of the nuclear power structure and the accuracy of the algorithms are dynamically verified by comparison with the refinement of a large-scale viscoelastic soil model.

考虑多尺度纹理特征的红外传感图像频域增强

红外传感图像质量容易受探测器和传输距离影响,导致图像亮度和对比度较低、轮廓细节模糊等问题。为此,提出了考虑多尺度纹理特征的红外传感图像频域增强方法。引入残差学习策略,基于多尺度纹理特征搭建多尺度卷积神经网络模型,进行图像去噪。对去噪后图像进行傅里叶变换,获取红外传感图像的低频图像和高频图像。针对低频图像部分,调节图像灰度和对比度以增强低频分量。针对高频图像部分,利用Log算子和Laplace算子增强图像细节及边缘。加权融合两者处理结果,选取Gamma校正调节对比度,增强高频分量。融合两种增强后图像,实现红外传感图像频域增强。实验结果表明,该方法峰值信噪比高于43,信息熵大于8,边缘强度超过82,对比度熵大于8.1,平均梯度大于8。

多尺度域视频监控图像光照分量智能校正方法

针对视频监控图像中存在的清晰度不足和光照不均匀等问题,提出了多尺度域视频监控图像光照分量智能校正方法。应用背景差分法与差值图二值化法对视频监控图像进行预处理,以减少噪声干扰。通过融合TH变换和BH变换来加强图像多尺度细节特征;利用控制因子控制锐化强度,以凸显细节特征,避免出现图像伪影情况。对图像光照分量进行自适应调节,利用二维伽马函数计算画面亮度平均值,以防止出现过度校正的情况,从而实现智能校正。测试结果表明,采用该方法校正的图像更清晰,画面光照分量均匀,图像失真较少,视觉效果较好。

亚波长尺度裂缝地震散射分辨分析

裂缝储层地震特征的准确识别已成为当前地震勘探的难点之一,特别是深层礁滩或碳酸盐岩储层,其大部分裂缝都在亚波长尺度,按照传统地震反射四分之一波长几何分辨准则是不能完全分辨的.传统研究裂缝地震响应的方法主要基于各向异性等效介质理论,但由于亚波长尺度裂缝微小且其地震反射弱并存在噪声干扰等问题,故该传统方法逼近精度有限.然而,这类部分可分辨裂缝可在地震散射范畴来分析和预测,本文基于散射聚焦分辨分析理论,提出了表征裂缝系统空间分布和形态特征的波数域散射成像矩阵方法,据此计算了含裂缝与不含裂缝的波数域成像矩阵之间的振幅差异性和结构差异性,从散射能量及其各向异性的角度分析了亚波长尺度裂缝的地震可识别性.均匀和复杂背景介质下的算例表明,振幅差异性随裂缝厚度和密度的变化规律显著,结构差异性随裂缝角度变化规律更加明显.同时讨论了随机噪声和排列长度等因素对裂缝系统地震散射可识别性的影响.排列长度和噪声对于裂缝厚度响应影响较小,主要影响高角度裂缝的识别,同时要求排列长度大于三倍目标深度才可应用该方法进行裂缝参数识别.

融合多尺度和频域特征的目标身份识别技术

拍摄设备、角度和光线的差异以及相似目标的干扰,给跨设备目标身份识别任务带来了严峻挑战。针对识别过程存在的类内差异和类间相似问题,提出了一种融合多尺度和频域特征的识别模型,在主干网络中加入注意力机制提高模型对高辨识特征的关注度;在分支网络中,设计了一种基于注意力的多尺度扩张融合模块对不同深度特征进行多粒度采样融合,增强网络的空间映射能力;在后处理阶段构造自学习的频域卷积模块,实现多尺度和频域特征的融合,利用频域信息提高度量相似目标的准确率。经过实验,算法在Veri776和VehicleID数据集的平均均值精度(mAP)和首次命中精度(Rank-1)分别获得了81.60%、97.20%和90.50%、85.30%,结果优于近些年主流方法,能够满足跨设备的多目标身份识别要求。

基于改进Faster R-CNN的红外目标检测算法

为提升红外目标的检测精度,提出了一种引入频域注意力机制的Faster R-CNN红外目标检测算法。首先,针对红外图像边缘模糊和噪声问题,设计了一种并行的图像增强预处理结构;其次,在Faster R-CNN中引入频域注意力机制,设计了一种新型红外目标检测主干网络;最后,引入路径增强金字塔结构,融合多尺度特征进行预测,利用底层网络丰富的位置信息,提升检测精度。在红外飞机的数据集上进行实验,结果表明,改进后的Faster R-CNN目标检测框架比以ResNet50为主干的算法的AP提升了7.6%。此外,与目前主流算法对比,本文算法提高了红外目标的检测精度,验证了算法改进的有效性。

基于尺度分析的CMA-GFS全球能量评估

全球模式能量循环和能量转换规律可准确反映模式动力和物理过程相互作用的物理机制,是诊断大气环流特征的重要方法。基于混合时空域能量循环框架,采用尺度分析方法,利用2022年中国气象局全球数值预报系统(CMA Global Forecast System,CMA-GFS)全球预报产品及欧洲中期天气预报中心第5代再分析资料(ECMWF reanalysis version 5,ERA5),考察CMA-GFS不同尺度下的能量蓄能及转换特征,以此诊断模式的误差来源。结果表明:CMA-GFS可有效预报大气能量循环基本特征,但其对斜压性的高估导致平均环流有效位能偏强,且具有随预报时效逐渐增长的趋势。定常和瞬变涡动能量分别受行星尺度和天气及以下尺度分量主导。涡动有效位能误差由模式斜压性决定,其中CMA-GFS的定常涡动有效位能偏高而瞬变涡动有效位能偏低。定常和瞬变涡动动能均存在系统性低估,负误差主要集中在副热带急流和极夜急流中心附近,偏强的正压输送使更多能量向平均环流转换,涡动能量偏弱。CMA-GFS的4种涡动能量在冬季预报偏低,而在夏季偏高或略偏低,严重削弱了季节变化影响。

大模型在军事垂直领域的应用

大模型技术是人工智能技术的飞跃式发展,使得大众看到人工智能的切实应用,利用大模型技术开展垂直领域应用是目前的研究热点,针对军事垂直领域的行业特点,本文提出一种基于开源大模型训练军事垂域大模型的技术路线。

基于频率域峭度谱迭代阈值的多尺度形态学轴承故障诊断方法

在复杂恶劣的环境中,存在滚动轴承故障信息难以准确提取的问题。因此,引用多尺度数学形态学对滚动轴承故障诊断开展研究。由于小尺度形态学滤波能较好的保存信号的细节特征,大尺度形态学滤波能有效抑制噪声,因此为了能更好的兼顾噪声抑制和故障特征信息保存,采用迭代阈值的方法选取尺度范围,运用频率域峭度谱方法计算出阈值,然后通过迭代自适应获取最佳尺度区间。多尺度形态学信号重构加权方法引用加权多尺度形态梯度算法,该方法能保证小尺度具有较小的权重,大尺度具有大权重。通过仿真和实验表明:多尺度形态学有效检测出滚动轴承故障信号,深度挖掘滚动轴承故障特征信息。

A seismic free field input model for FE-SBFE coupling in time domain

A seismic free field input formulation of the coupling procedure of the finite elelnent(FE)and the scaled boundary finite-element(SBFE)is proposed to perform the unbounded soil-structure interaction analysis in time domain. Based on the substructure technique,seismic excitation of the soil-structure system is represented by the free-field motion of an elastic half-space.To reduce the computational effort,the acceleration unit-impulse response function of the unbounded soil is decomposed into two functions:linear and residual.The latter converges to zero and can be truncated as required. With the prescribed tolerance parameter,the balance between accuracy and effMency of the procedure can be controlled. The validity of the model is verified by the scattering analysis of a hemi-spherical canyon subjected to plane harmonic P,SV and SH wave incidence.Numerical results show that the new procedure is very efficient for seismic problems within a nor- real range of frequency.The coupling procedure presented herein can be applied to linear and nonlinear earthquake re- sponse analysis of practical structures which are built on unbounded soil.

基于多尺度梯度域引导滤波的弱光照图像增强技术

光照较弱会导致图像出现颜色失真以及部分图像细节消失等问题,提出了基于多尺度梯度域引导滤波的弱光照图像增强方法。对弱光照图像进行多尺度梯度域引导滤波图像增强和Gamma校正,将BIQME作为目标函数,将主观图像增强问题转换为最优解问题,采用改进鸡群算法对目标函数优化求解,获取图像增强所需要的最优多尺度梯度域引导滤波参数和色调平衡参数,最终达到弱光照图像增强的目的。实验测试结果表明,所提方法可以增强弱光照图像的同时,改善弱光照图像质量和提升图像处理速度,图像处理速度控制在0.85 s以内。

基于复域超多维标度的混合TOA/AOA定位算法

针对全球卫星导航系统信号完全拒止环境下的定位问题,使用超宽带(UWB)技术获取测量信息,基于多维标度变换算法(MDS)提出一种复域下的混合测距信息(TOA)和测角信息(AOA)的超多维标度定位算法(TASMDS),并进一步构建了复域内的核矩阵,提出复域下的超多维标度定位算法(TA-CDSMDS)。对比3种算法的定位结果,以及10°、15°、20°测角误差和不同测距误差下的定位误差,得TA-CDSMDS算法相较于TA-SMDS和MDS,有更小的定位误差,更贴近克拉美罗下界;分析不同节点下3种的计算时间,TA-CDSMDS算法在优化TA-SMDS的基础上减少28%~48%的时间,具有更好的定位性能。

Frequency-domain generelaized singular peruturbation method for relative error model order reduction

A new mixed method for relative error model order reduction is proposed. In the proposed method the frequency domain balanced stochastic truncation method is improved by applying the generalized singular perturbation method to the frequency domain balanced system in the reduction procedure. The frequency domain balanced stochastic truncation method, which was proposed in [15] and [17] by the author, is based on two recently developed methods, namely frequency domain balanced truncation within a desired frequency bound and inner-outer factorization techniques. The proposed method in ttiis paper is a carry over of the frequency-domain balanced stochastic truncation and is of interest for practical model order reduction because in this context it shows to keep the accuracy of the approximation as high as possible without sacrificing the computational efficiency and important system properties. It is shown that some important properties of the frequency domain stochastic balanced reduction technique are extended to the proposed reduction method by using the concept and properties of the reciprocal systems. Numerical results show the accuracy, simplicity and flexibility enhancement of the method.