An efficient numerical scheme for solving fractional infinite-horizon optimal control problems

This paper presents an efficient numerical method to solve fractional infinite-horizon optimal control problems, where the dynamic control system depends on Caputo fractional derivatives. First, by a suitable change of variable, we transform the fractional infinite-horizon optimal control problem to a finite-horizon one. Then, with the help of an approximation, we replace the Caputo derivative to integer order derivative. According to the Pontryagin minimum principle (PMP) for optimal control problems and by constructing an error function, we define an unconstrained minimization problem. In the optimization problem, we use trial solutions for state, costate and control functions where these trial solutions are constructed by using two-layered perceptron neural network. Some numerical results are introduced to explain our main results.     

靶面激光光斑尺寸原位测量的研究

提供了一种简便易行的靶面激光光斑尺寸原位测量的方法。从高斯光束的横向光强分布特性出发,建立了激光烧蚀斑半径与辐照激光能量、光斑尺寸、烧蚀阈值间的关系式,模拟分析发现辐照激光光斑尺寸对烧蚀斑半径随辐照能量变化曲线有较大影响。对于脉宽为2 ms,波长为1064 nm的激光,实验测量了不同能量激光辐照下相纸烧蚀斑半径,并用推导出的关系式拟合测量数据,获得了靶面处光斑尺寸和样品烧蚀阈值。同时,也测量了不同位置处的光斑尺寸和样品烧蚀阈值,对高斯光束束腰位置和样品烧蚀阈值的光斑尺寸效应进行了验证。研究结果表明该技术结果可靠,简单高效。该技术可以为高能激光与固体物质相互作用的基础研究和激光加工等应用领域中实现简单方便地测量靶面光斑尺寸提供帮助。     

超生雾化降尘研究及应用

为解决某矿破碎筛分车间粉尘污染问题，采用喷嘴雾化理论设计喷嘴雾化降尘实验，并根据实验结果在该矿破碎筛分车间应用了超声雾化降尘技术。实验及应用结果表明：超声雾化发生器的液体雾化装置，气体辅助雾化装置和雾束形成器的几何结构影响喷雾的雾化参数与流量特性，液体雾化器与气体辅助雾化装置影响液体初次破碎与雾化，雾束形成器影响雾滴的二次破碎与约束液束形态；超声雾化发生器的气液比与气液压力比存在幂函数关系，幂指数为-1.09；雾滴粒径越小，雾滴的降尘效率越高，当雾滴D50为23 μm时，雾滴的降尘效率在94%以上；在破碎筛分车间振动筛给料皮带和筛上皮带受料点布置超声雾化发生器，超声雾化发生器开启后，车间内粉尘浓度降低至586～10.54 mg/m3，降尘效率在71.38%以上。     

A compromise between piezoelectricity and transparency in KNN-based ceramics: The dual functions of Li2O addition

Transparent ceramics with good electrical performance have recently drawn broad interest as promising multifunctional materials. Here, we report that a superior transmittance (T = 75 % at 2000 nm) and good piezoelectricity (d₃₃ ∼ 150 pC/N) can be simultaneously realized in 0.93K_0.5Na_0.5NbO₃-0.07SrZrO₃ (KNN-SZ) ceramics by Li₂O regulation. The effect of Li₂O regulation has two parts: first, the presence of Li₂O facilitates the grain growth of KNN-SZ, considering that it melts at a relatively low temperature as a proper sintering aid; second, the introduced Li⁺ causes local lattice distortion, resulting in the coexistence of orthogonal and tetragonal (O–T) phases. The enlarged grains reduce the light scattering by grain boundaries for a higher optical transmittance; meanwhile, large grains stand as a prerequisite for the macroscopic domain structure favoured for decent piezoelectricity, which could also be partly caused by the coexistence of O–T phases. We believe that these findings might make KNN-based ceramics a preferable candidate for optoelectronic devices.     

Grain size effect on microwave dielectric properties of Na2WO4 ceramics prepared by cold sintering process

In this work, cold sintering was adopted to prepare Na₂WO₄ ceramics with different grain sizes ranging from 0.632 μm to 17.825 μm. Their microstructures, complex impedance, and microwave dielectric properties were studied in-depth. It was found that samples with relative densities higher than 92% can be successfully synthesized by cold sintering process at a low temperature of 240 °C. However, their electrical properties have strong dependence on the grain size. Specifically, the resistance of grain boundaries decreases dramatically with the increase of grain sizes, while the quality factor has a positive correlation with the grain sizes of Na₂WO₄ ceramics. Excellent microwave dielectric properties, including permittivity = 5.80, Q × f = 22,000 GHz, and TCF = −70 ppm/°C, are obtained for Na₂WO₄ ceramics with a grain size of 4.477 μm prepared by cold sintering process.     

6061铝合金均匀化过程中AlMnSi弥散颗粒的析出尺寸对再结晶行为的影响

利用力学性能测试、光学显微镜、扫描电镜、透射电镜和能谱分析技术等手段研究了均匀化过程中AlMnSi弥散颗粒的析出尺寸对6061铝合金再结晶行为的影响。结果表明:AlMnSi弥散颗粒在均匀化过程中沿着铝基体[001]晶带轴析出长大,晶体结构为体心立方结构。随着均匀化温度的升高,弥散颗粒的析出尺寸逐渐增大,当AlMnSi弥散颗粒平均尺寸由0.07 μm增长到0.42 μm,最大尺寸由0.21 μm增大到1.12 μm时,力学性能则是先升高后降低。6061铝合金T6态组织仍为变形组织;AlMnSi弥散颗粒尺寸增大到1.12 μm,6061合金T6态组织中出现粗大再结晶,力学性能急剧降低。     

温拌LDPE改性沥青混合料性能研究

选择Sasobit和Evotherm 3G两种温拌剂对温拌LDPE沥青混合料制备工艺和性能进行研究。首先,比较变温等体积法和等黏温度法两种方法,并确定两种温拌混合料的拌和及击实温度。在此基础上,分别采用车辙试验、低温弯曲试验、中点加载弯曲试验以及冻融劈裂试验评价70#、LDPE、Sasobit-LDPE以及3G-LDPE四种沥青混合料的高温性能、低温性能、疲劳性能和水稳定性。结果表明,两种温拌技术均是可行的,Sasobit和3G温拌技术可使施工温度降低20℃和15℃。与热拌LDPE沥青混合料相比,Sasobit温拌沥青混合料具有更好的高温性能和水稳定性,在高应力比条件下抗疲劳性能更好,低温性能虽变差,但是优于70#沥青混合料;3G温拌沥青混合料的高温性能,低温性能以及水稳定性则与热拌LDPE沥青混合料各项性能较为接近,抗疲劳性能变差,但是优于70#沥青混合料。     

An automated patient monitoring using discrete‐time wireless sensor networks

In recent years, Internet of Things (IoT) devices are used for remote health monitoring. For remotely monitoring a patient, only the health information at different time points are not sufficient; predicted values of biomarkers (for some future time points) are also important. In this article, we propose a powerful statistical model for an efficient dynamic patient monitoring using wireless sensor nodes through Bayesian Learning (BL). We consider the setting where a set of correlated biomarkers are measured from a patient through wireless sensors, but the sensors only report the ordinal outcomes (say, good, fair, high, or very high) to the sink based on some prefixed thresholds. The challenge is to use the ordinal outcomes for monitoring and predicting the health status of the patient under consideration. We propose a linear mixed model where interbiomarker correlations and intrabiomarker dependence are modeled simultaneously. The estimated and the predicted values of the biomarkers are transferred over the internet so that health care providers and the family members of the patient can remotely monitor the patient. Extensive simulation studies are performed to assess practical usefulness of our proposed joint model, and the performance of the proposed joint model is compared to that of some other traditional models used in the literature.     

Self-learning residual model for fast intra CU size decision in 3D-HEVC

As an extension of the High Efficiency Video Coding (HEVC) standard, 3D-HEVC requires to encode multiple texture views and depth maps, which inherits the same quad-tree coding structure as HEVC. Due to the distinct properties of texture views and depth maps, existing fast intra prediction approaches were presented for the coding of texture views and depth maps, respectively. To further reduce the coding complexity of 3D-HEVC, a self-learning residual model-based fast coding unit (CU) size decision approach is proposed for the intra coding of both texture views and depth maps. Residual signal, which is defined as the difference between the original luminance pixel and the optimal prediction luminance pixel, is firstly extracted from each CU. Since residue signal is strongly correlated with the optimal CU partition, it is used as the feature of each CU. Then, a self-learning residual model is established by intra feature learning, which iteratively learns the features of the previously encoded coding tree unit (CTU) generated by itself. Finally, a binary classifier is developed with the self-learning residual model to early terminate CU size decision of both texture views and depth maps. Experimental results show the proposed fast intra CU size decision approach achieves 33.3% and 49.3% encoding time reduction on average for texture views and depth maps with negligible loss of overall video quality, respectively.     

空气弹簧液压悬置动特性及隔振特性研究

研究了具有可变刚度阻尼的发动机空气弹簧液压悬置的动特性和隔振特性。针对影响发动机空气弹簧液压悬置动特性的关键参数上液室等效体积刚度,采用理论和试验方法研究了上液室等效体积刚度的等效值,基于该等效值建立了空气弹簧液压悬置的理论模型,对空气腔开闭两种工况进行了空气弹簧液压悬置动特性的仿真和试验研究。搭建了发动机空气弹簧液压悬置系统试验台架,研究了台架各种激励频率下的空气弹簧液压悬置的隔振特性。结果表明:本研究采用的上液室等效体积刚度进行空气弹簧进行建模是正确、可行的,提高了空气弹簧建模效率和准确性;空气弹簧液压悬置在空气腔开启和关闭两种状态下,峰值动刚度增大幅值达78.5%,峰值阻尼角增大幅值达250%。台架试验表明:当台架激励频率小于25Hz时,悬置采用大刚度大阻尼;当台架激励频率大于等于25 Hz时,悬置采用小刚度小阻尼;悬置隔振率提升明显,不同频率下提升幅值达10%～67%。