Seasonal variability of the mixed layer depth determined using an improved maximum angle method in the Arctic basins

To investigate the spatiotemporal variations in the mixed layer depth(MLD)in the Arctic basins,a new criterion to determine the MLD,called the improved maximum angle method(IMAM),was developed.A total of 45123 potential density profiles collected using Ice-Tethered Profilers(ITPs)in the Arctic basins during 2005-2021 were used to demonstrate the method’s effectiveness.By comparing the results obtained by the fixed threshold method(FTM),percentage threshold method(PTM),and maximum gradient method(MGM)for profiles in the Canada Basin,Makarov Basin,and Eurasian Basin,we determined that the quality index(1.0 for perfect identification of the MLD)of the IMAM regarding the assessment of the MLD determination method reached 0.94,which is much greater than those of other criteria.Moreover,two types of the density profiles were identified based on the mixed layer development stage.The MLDs of the typical profiles determined using the IMAM were found to have better consistency with the original definition.By utilizing the new mixed layer criterion,the seasonal variations and regional differences in the MLD in the Arctic basins were analyzed.Spatially,the summer and winter MLDs in the Canada Basin were the shallowest(13.55 m in summer,26.76 m in winter)than those in the Makarov(29.51 m in summer,49.08 m in winter)and Eurasian(20.36 m in summer,46.81 m in winter)basins due to the stable stratification in the upper ocean and the subsequent small effects of dynamic and thermodynamic processes(wind-driven stirring and brine rejection)in the Canada Basin.Seasonally,in the three Arctic basins,the average MLD was shallowest(22.77 m)in summer;it deepened through autumn and reached a winter maximum(41.12 m).

Integrated design optimization of composite frames and materials for maximum fundamental frequency with continuous fiber winding angles

Fiber reinforced composite frame structure is an ideal lightweight and large-span structure in the fields of aerospace,satellite and wind turbine.Natural fundamental frequency is one of key indicators in the design requirement of the composite frame since structural resonance can be effectively avoided with the increase of the fundamental frequency.Inspired by the concept of integrated design optmization of composite frame structures and materials,the design optimization for the maximum structural fundamental frequency of fiber reinforced frame structures is proposed.An optimization model oriented at the maximum structural fundamental frequency under a composite material volume constraint is established.Two kinds of independent design variables are optimized,in which one is variables represented structural topology,the other is variables of continuous fiber winding angles.Sensitivity analysis of the frequency with respect to the two kinds of independent design variables is implemented with the semi-analytical sensitivity method.Some representative examples in the manuscript demonstrate that the integrated design optimization of composite structures can effectively explore coupled effects between structural configurations and material properties to increase the structural fundamental frequency.The proposed integrated optimization model has great potential to improve composite frames structural dynamic performance in aerospace industries.

Optimal Guidance Law to Maximize Terminal Velocity for Missiles with Impact Angle Constraint

In this paper,an optimal guidance law for missiles with impact angle and miss distance constraints is proposed to achieve the maximal terminal velocity. The normal acceleration command that includes the timevarying coefficients is introduced to satisfy the desired impact angle as well as zero miss distance according to the geometric relation and relative motion parameters between missile and target. The problem is formulated as an optimal control problem by defining the angle of velocity error and flight-path angle as state variables and maximizing a performance index of the terminal velocity. The analytical form of the proposed guidance law is obtained as the solution of the optimal control problem combining optimal control theory and numerical value computation method. Nonlinear simulations of various situations demonstrate the performance and feasibility of the proposed optimal guidance law.

Elevation estimation for low-angle target based on reffection paths suppression

In the signal processing for metrewave radar, the reflection paths of target echoes can cause severe error in the elevation estimation for the low-angle target tracking. The exact angles of the reflection paths are unknown beforehand, and therefore, the reflection paths can not be suppressed easily. Therefore, in this article, an improved reflection paths suppression approach is presented. A block matrix aggregate is constructed based on the possible angles of the reflection paths. Combined with the beamforming-like processing, a generalized maximum likelihood estimation is derived to optimize the estimation. Moreover, the noise reduction method based on the Toeplitz covariance matrix is used for better performance. This approach is applied to the real data collected by the low-angle tracking radar with 8-channel vertical array. The experiment results show that the reflection effects are reduced and the accuracy of the elevation estimate is improved.

The largest negative refractive angles in uniaxial bicrystals

Using the Maxwell＇s equations, we carry out theoretical analysis on the maximum incident and refractive angles at which negative refraction can be realized at the interfaces associated with conventional uniaxial media. In the numerical analysis, the largest incident and refractive angles at which refraction arises are obtained by optimizing directions of the optical axis of the uniaxial bicrystal. Meanwhile, the optical parameters of the ordinary uniaxial bicrystals （including homogeneity- junction and heterogeneity-junction） are given, and some representative laser wavelengths, the largest incident and refractive angles are obtained. The relation between the largest incident angles （or refractive angles） and refractive index is also discussed.

小倾角对Ω形弯曲热管传热特性的影响

为研究小倾角对Ω形槽道弯曲热管传热特性的影响,搭建了热管传热性能实验台,基于实验对不同小倾角下热管的温度分布、总热阻、当量导热系数和最大输入功率进行分析。结果表明:在相同输入功率下,倾角为0°和倾角为负的热管壁温均匀性优于倾角为正的热管;倾角为正的热管总热阻最大,倾角为0°和倾角为负的热管总热阻相近;热管倾角为0°时的最大输入功率最高。热管安装和应用中易出现重力倾角偏差,研究结果表明,较小倾角会对Ω形槽道弯曲热管的传热性能造成影响。

一般三棱镜最小偏向角的实验条件

基于数学分析中求极值方法和导数性质,研究推导得到了一般三棱镜最小偏向角的条件,清楚地说明了偏向角最小时对应的条件与入射角、折射率和棱镜顶角的关系.应用Matlab得到关系曲线,从曲线得到一次导数为0对应的入射角、最小偏向角和二次导数的大小,同时给出了最小入射角对应的偏向角,对应折射率的棱镜最大顶角.应用Visio精准绘出了给定条件下的光线轨迹,从轨迹图中得到偏向角与相关条件的关系.研究结果表明,偏向角最小时对应的入射角与棱镜顶角、折射率有关,为实验或研究中要得到文献定义的偏向角和最小偏向角选择棱镜顶角、折射率参数提供理论依据,解决了教学和学习过程对于最小偏向角条件的理论分析困惑.

心电向量图参数与儿童肺动脉压相关性及对肺动脉高压的预测效能研究

目的 探讨心电向量图参数与儿童肺动脉压相关性及对肺动脉高压(pulmonary hypertension, PH)的预测效能。方法 选取2020年2月-2024年2月收治的124例疑似PH患儿,根据临床最终诊断结果分为PH组60例和无PH组64例,入院后均行心电图检查,同步记录常规心电图、心电向量图,比较2组基线资料及平均肺动脉压(mPAP)及心电图向量参数(QRS最大向量振幅、心室复极梯度方位角、QRS最大向量仰角、心室复极梯度仰角、QRS最大向量方位角、心室复极梯度振幅、QRS-T比值、QRS-T夹角),分析心电图向量参数与mPAP相关性及对PH的影响,受试者工作特征(ROC)曲线分析心电图向量参数对PH的预测效能。结果 PH组窦性心律患儿占比低于无PH组,房性心动过速、右心室肥大、房室传导阻滞患儿占比及mPAP高于无PH组(P<0.01)。PH组心室复极梯度方位角、QRS最大向量仰角、心室复极梯度仰角、QRS最大向量方位角、QRS-T夹角高于无PH组,心室复极梯度振幅低于无PH组(P<0.01)。心室复极梯度方位角、QRS最大向量仰角、心室复极梯度仰角、QRS最大向量方位角、QRS-T夹角与mPAP呈正相关(r=0.697、0.766、0.836、0.623、0.793,P<0.001、<0.001、<0.001、<0.001、<0.001),心室复极梯度振幅与mPAP呈负相关(r=-0.828,P<0.001)。Logistic回归分析显示,心室复极梯度方位角、QRS最大向量仰角、心室复极梯度仰角、QRS最大向量方位角、心室复极梯度振幅、QRS-T夹角对PH有影响(P<0.01)。ROC曲线分析显示,心室复极梯度方位角、QRS最大向量仰角、心室复极梯度仰角、QRS最大向量方位角、心室复极梯度振幅、QRS-T夹角联合预测PH的AUC为0.924,敏感度为78.33%,特异度为92.19%。结论 心电向量图参数与肺动脉压力具有显著相关性,临床可通过心电向量图参数预测评估PH,以针对性制订干预方案,改善预后。

基于混合高斯模型的无相位线路阻抗参数估计方法

输电线路阻抗参数的准确估计是配电网可靠分析的基础。已有方法估计线路阻抗需要利用测量电压电流的相位信息,但当实测数据相位角缺失时,已有方法将失效。对此,提出了一种基于混合高斯模型的无相位线路阻抗参数估计方法,该方法仅需要线路两端的电压幅值、有功功率和无功功率的实测数据。首先由电力线路的潮流关系建立含误差的线路阻抗估计模型,然后考虑到测量环境存在噪声干扰,通过引入双隐变量,将含误差的线路阻抗估计模型转化为混合高斯模型,得到线路阻抗的概率分布,并利用最大后验估计得到线路阻抗参数估计值,最后通过仿真验证所提方法能有效估计线路阻抗的大小,为相位缺失场景下的线路阻抗估计提供一个新策略。

自导作用距离不确知下基于最大熵分布的有利提前角计算

针对鱼雷自导作用距离不确知情况下的有利提前角解算问题,首先分析自导作用距离对鱼雷射击的影响,指出当鱼雷的实际自导作用距离小于其装订值时,解算得到的有利提前角会偏小,并会导致鱼雷的发现概率明显降低。其次定义了鱼雷的加权平均发现概率,在此基础上提出了一种最大化加权平均发现概率的有利提前角解算方法。然后基于最大熵原理,给出了鱼雷实际自导作用距离的2种最大熵分布模型,得到了该分布模型下的有利提前角求解公式。最后通过仿真得到了鱼雷自导作用距离不确知情况下的有利提前角。

船桥撞击力的神经网络预测与经验公式研究

为了减少船舶与桥梁撞击对人身和财产安全造成的危害,研究船舶与桥梁撞击力的最大值及其与其他影响因素之间的关系具有十分重要的意义。该文首先利用ANSYS/LS-DYNA软件建立了船舶撞桥的有限元模型,计算了不同撞击速度和撞击角度下船桥撞击力的最大值,并将计算结果与各国规范进行比较;然后,利用反向传播(back propagation,BP)神经网络技术,结合仿真计算数据,在最大撞击力值、撞击速度和撞击角度这3个训练参数下,创建了船桥最大撞击力的预测模型;最后,通过分析撞击速度和角度的散点图,拟合了1个最大撞击力与撞击速度和角度关系的经验公式,并将经验公式、有限元仿真计算结果和神经网络预测结果进行比较,验证了经验公式的准确性。该研究为快速评估船桥撞击是否会导致灾难性后果提供了1种有效的方法。

装配式建筑转角飘窗结构性能分析

文中利用数值仿真软件对装配式建筑转角飘窗地震作用下层间位移角、最大位移以及损伤程度进行分析。结果表明,随着楼层数的增加,X向层间位移角先增加、再降低、最后保持稳定,当地震波加载的终止时间从25 s增至55 s,再增加至70 s时,X向最大的层间位移增加幅度基本为3.62%。随着楼层数的增加,Y向层间位移角呈现先增加后降低的变化规律,装配式建筑结构各层X和Y向最大位移同样呈现不断增加的趋势。装配式住宅楼转角窗位置处的楼板混凝土出现一定的受拉损伤,但并不严重,证明本工程转角窗具有良好的抗震效果。

基于整流侧最大触发角限制的直流输电连续换相失败抑制方法

直流输电首次换相失败一般难以避免,但是可以采取一定的措施抑制连续换相失败。根据直流控制系统和等值电路,提出了整流侧换流器最大触发角计算公式,在逆变侧交流系统故障后及时根据计算结果对整流侧换流器最大触发角进行限制,可抑制直流输电连续换相失败。在PSCAD/EMTDC中搭建CIGRE HVDC标准测试模型进行仿真测试,测试结果验证了所提方法有效性,且适当增大限制程度,抑制成功率将增加。

Maximum Force of Inclined Pullout of A Torpedo Anchor in Cohesive Beds

Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not only to the safety and stability of vessels and other marine facilities, but also for an economical design. It is necessary to develop reliable formula for fast predicting their maximum inclined force of a torpedo anchor in cohesive beds. In this study, the maximum inclined force of a torpedo anchor vertically embedded in cohesive beds was extensively investigated. 316 sets of inclined pullout laboratory tests were carried out for 9 differently shaped torpedo anchors which were vertically embedded in different cohesive beds. The loading curves were automatically acquisitioned and their characteristics were analyzed. The load angle relative to the horizontal varied from 20° to 90°. A new formula for fast calculating the maximum inclined force of the torpedo anchor vertically embedded in cohesive beds was obtained based on force analysis and a nonlinear regression on the data from the present and other studies. Effect aspects on the tests are discussed and further studies are highlighted.

A predictive equation for residual strength using a hybrid of subset selection of maximum dissimilarity method with Pareto optimal multi-gene genetic programming

More accurate and reliable estimation of residual strength friction angle(/r)of clay is crucial in many geotechnical engineering applications,including riverbank stability analysis,design,and assessment of earthen dam slope stabilities.However,a general predictive equation for/r,with applicability in a wide range of effective parameters,remains an important research gap.The goal of this study is to develop a more accurate equation for/r using the Pareto Optimal Multi-gene Genetic Programming(POMGGP)approach by evaluating a comprehensive dataset of 290 experiments compiled from published literature databases worldwide.A new framework for integrated equation derivation proposed that hybridizes the Subset Selection of Maximum Dissimilarity Method(SSMD)with Multi-gene Genetic Programming(MGP)and Pareto-optimality(PO)to find an accurate equation for/r with wide range applicability.The final predictive equation resulted from POMGGP modeling was assessed in comparison with some previously published machine learning-based equations using statistical error analysis criteria,Taylor diagram,revised discrepancy ratio(RDR),and scatter plots.Base on the results,the POMGGP has the lowest uncertainty with U95=2.25,when compared with Artificial Neural Network(ANN)(U95=2.3),Bayesian Regularization Neural Network(BRNN)(U95=2.94),Levenberg-Marquardt Neural Network(LMNN)(U95=3.3),and Differential Evolution Neural Network(DENN)(U95=2.37).The more reliable results in estimation of/r derived by POMGGP with reliability 59.3%,and resiliency 60%in comparison with ANN(reliability=30.23%,resiliency=28.33%),BRNN(reliability=10.47%,resiliency=10.39%),LMNN(reliability=19.77%,resiliency=20.29%)and DENN(reliability=27.91%,resiliency=24.19%).Besides the simplicity and ease of application of the new POMGGP equation to a broad range of conditions,using the uncertainty,reliability,and resilience analysis confirmed that the derived equation for/r significantly outperformed other existing machine learning methods,including the ANN,BRNN,LMNN,and DENN equations。

The Maximum Effective Moment Criterion (MEMC) and Its Implications in Structural Geology

The MohroCoulomb criterion has been widely used to explain formation of fractures. However, it fails to explain large strain deformation that widely occurs in nature. There is presently a new theory, the MEMC, which is mathematically expressed as Meff = （（σ1-σ3） L.sin 2α sin α）/2, where σ1-σ3 represents the yield strength of the related rock, L is a unit length and a is the angle between σ1 and deformation bands. This criterion demonstrates that the maximum value appears at angles of ±54.7° to σ1 and there is a slight difference in the moment in the range of 55°±10°. The range covers the whole observations available from nature and experiments. Its major implications include： （1） it can be used to determine the stress state when the related deformation features formed; （2） it provides a new approach to determine the Wk of the related ductile shear zone if only the ratio of the vorticity and strain rate remains fixed; （3） It can be used to explain （a） the obtuse angle in the contraction direction of conjugate kink-bands and extensional crenulation cleavages, （b） formation of low-angle normal faults and high-angle reverse faults, （c） lozenge ductile shear zones in basement terranes, （d） some crocodile structures in seismic profiles and （e） detachment folds in foreland basins.

基于量测数据时序谱分布特性的电力系统暂态功角稳定在线判别

基于响应信息的电力系统暂态稳定判别是实现“实时决策,实时控制”的基础。然而此类方法的准确性受限于场景匹配以及发电机分群等中间环节。为更有效地辨识系统的暂态稳定性,该文以随机矩阵理论为基础,提出一种基于量测数据时序谱分布特性的电力系统暂态功角稳定判别方法。首先根据电力系统的暂态响应特性构建数据模型,并在实时分离窗矩阵的基础上构建插入矩阵模型以降低冗余历史数据对谱分布特性的影响。然后结合谱分布理论和增广矩阵法获取表示数据相关性的最大特征值偏移度(maximum eigenvalue deviation,MED)差值轨迹,并以物理机理严格分析不同稳定模式下MED差值轨迹与暂态功角稳定间的映射关系,从数据相关性的角度制定暂态功角稳定判据,基于量测数据实现暂态响应特性分析和暂态功角稳定在线判别。

任意荷载作用下梁-柱的新型实用算法

采用渐进积分法研究了简支梁-柱分别在横向分布力、横向集中力和力偶作用下的弯曲问题.构造了各种荷载作用下梁-柱的四阶微分迭代方程和边界条件.首先选取简支梁只有横向荷载的挠曲线作为梁-柱的初函数,然后将初函数代入梁-柱的四阶微分迭代方程进行积分,得到下一次迭代挠度函数,依次进行迭代积分运算.编程计算出了用轴力放大系数表示的最大挠度、最大转角和最大弯矩的简单多项式解析函数.经过六次迭代,与精确解相比,当梁-柱所受的轴向力是欧拉临界力的1/2以内时,误差可以控制在1%以内,达到了令人满意的工程精度要求.

杂化轨道成键能力及夹角计算公式的简洁推导

杂化轨道理论是化学键理论的重要内容,杂化轨道成键能力和杂化轨道之间的夹角是杂化轨道理论教学的重点和难点,多数教材通常直接给出相关公式,忽略导出过程,不能满足部分学生进阶学习的需要。本文给出了相关公式的简易推导,以期解疑释惑,加深学生对杂化轨道理论的认识和理解。

基于丰度反演及光谱变换的书画霉斑虚拟修复

古书画在保存过程中容易滋生霉斑病害,霉斑不仅影响书画的外观,还会对纸质文物造成不可逆转的永久性破坏。为了给霉斑清洗提供直观参考,提出基于丰度反演及光谱变换的书画霉斑提取与虚拟修复方法。选取与霉斑区域光谱曲线存在明显差异的450~600 nm之间244个波段作为特征波段,通过连续最大角凸锥端元提取与灰度分割,提取霉斑区域。再对高光谱影像进行主成分变换,选取包含信息量最大的前三主成分合成影像,利用Criminisi算法对霉斑区域进行修复,再将修复后的影像进行主成分逆变换,完成高光谱影像的虚拟修复。以中国近现代画家倪田的《捕鱼图》为例进行了研究,发现修复后的霉斑区域与画体融入性较好,边界自然平滑,均方根误差值普遍变小。研究结果可为书画霉斑清洗提供直观的修复依据,具有较强的实用性。