Improved YOLO Based Detection Algorithm for Floating Debris in Waterway

Various floating debris in the waterway can be used as one kind of visual index to measure the water quality. The traditional image processing method is difficult to meet the requirements of real-time monitoring of floating debris in the waterway due to the complexity of the environment, such as reflection of sunlight, obstacles of water plants, a large difference between the near and far target scale, and so on. To address these issues, an improved YOLOv5s (FMA-YOLOv5s) algorithm by adding a feature map attention (FMA) layer at the end of the backbone is proposed. The mosaic data augmentation is applied to enhance the detection effect of small targets in training. A data expansion method is introduced to expand the training dataset from 1920 to 4800, which fuses the labeled target objects extracted from the original training dataset and the background images of the clean river surface in the actual scene. The comparisons of accuracy and rapidity of six models of this algorithm are completed. The experiment proves that it meets the standards of real-time object detection.     

碎片云动量特性数值仿真研究

 铝合金球形弹丸高速撞击薄铝板时,会造成薄铝板穿孔并自身发生破碎,在铝板前后两侧产生碎片云,分别为反溅碎片云和穿透碎片云。反溅碎片云及穿透碎片云具有各自的动量特性,对其动量特性的研究有助于为碎片云理论建模提供依据。采用AUTODYN V6.0软件对直径为6.35 mm的Al 1100-O球形弹丸高速正撞击6种厚度的Al 6061-T6薄板进行了数值仿真计算,撞击速度为1.0～5.0 km/s。得到上述两种碎片云的动量,确定了动量值随撞击速度v及薄板厚度δ的变化规律。同时,利用仿真得到的动量数据,采用多元回归方法,分别建立了两种碎片云动量模型。最后,对美国国家航空航天局（NASA）报告给出的7种工况下的撞击实验进行了数值仿真计算,并将动量值与实验结果进行了比较,得到的比较结果可用以分析数值仿真的有效性。     

超高速弹丸撞击三维编织C/SiC复合材料双层板结构的实验研究

 目前在航天器防护结构设计中,采用的方案仍是双层（或多层）屏蔽结构 。双层板屏蔽结构由前板、后板和空隙组成。实验采用一种新型三维四向碳纤维织物结构增强SiC陶瓷基复合材料（简写为3DBC/SiC）做前板,其在超高速弹丸冲击作用下发生粉末化,和铝板做前板相比,所形成的碎片云团中有效碎片数目大大减少,减轻了对后板的破坏作用。结果表明：3DBC/SiC是航天器防护结构设计中一种比较理想的防护材料。     

弹丸超高速撞击防护屏碎片云数值模拟

 低地球轨道的各类航天器易受到微流星体及空间碎片的超高速撞击。这些撞击损伤航天器飞行的关键系统,进而导致航天器发生灾难性失效。为了保证航天员的安全及航天器的正常运行,微流星体及空间碎片防护结构设计是航天器设计的一个重要问题。采用AUTODYN软件进行了弹丸超高速正撞击及斜撞击防护屏所产生碎片云的SPH法数值模拟,给出了二维及三维模拟结果;研究了防护屏厚度、弹丸形状、撞击速度以及材料模型等对碎片云的影响。模拟结果同高质量实验研究的结果进行了比较,模拟的碎片云形状和碎片云特征点的速度同实验相吻合。验证了数值模拟方法的有效性。     

Propagation‐based phase‐contrast X‐ray microtomography of a cerebral protection device retrieved after carotid artery stenting

Phase‐contrast synchrotron X‐ray microtomography (pcSyncX) based on the highly coherent X‐ray beam has previously been used to visualize the microstructures of biologic specimens, but it has never been used to evaluate embolic debris adherent on a cerebral protection device (CPD). The purpose of this study was to demonstrate the feasibility of pcSyncX for evaluating embolic debris during carotid artery stenting (CAS). Five patients (four males, age range 67–77 years) with severe carotid artery stenosis underwent CAS. The retrieved CPD was exposed to synchrotron radiation and 1000 pcSyncX projection images were obtained by rotating the CPD through 180°. An X‐ray shadow of a CPD was converted into a visual image by the scintillator. After microtomographic reconstruction, the three‐dimensionally reconstructed images were further segmented into the embolic debris and CPD. The total volume of emboli was calculated by summing the volume at each scanning level. The number of membrane pores covered by emboli as seen from the outer surface was counted and the percentage of covered area was calculated. Embolic debris was clearly demonstrated not only on the inner surface and within pores but also on the outer surface of the CPD. The mean total volume of embolic debris was 0.538 × 10^–6 mm³ (range 0.225–0.965 × 10^–6 mm³). Most (61.5%) of the debris was located at the apical one‐third of the CPD and 20.8% of the pore area was covered by debris.     

“清除太空垃圾”是否存在商机呢?

对太空轨道碎片清理的商业运营模式和是否存在商机问题建模进行研究。首先,提出了太空轨道碎片清理公司的商业运营模式,即以清理公司、保险公司和卫星公司为主体的三位一体的系统运营模式;其次,给出私营清理公司商机的定义,通过对运营系统资金费用的分析,定量建立系统正常运营的保险公司最低保单价格和卫星公司最高保险价格求解的模型,并分析了模型的可计算性,给出了商机存在的条件以及商机大小的计算方法;最后,借助于清除效率,建立3种不同轨道碎片清除模式下清除成本的模型,给出了计算不同清除方式下保险公司最低保单价格和卫星公司最高保险价格的模型,验证了定义的商机是合理的并可计算的。     

基于支持向量机的磨粒识别

由于神经网络的局限性,上个世纪末,支持向量机被提出和发展,它在模式识别方面有广泛的应用发展前途,并由最初的二元分类发展到现在的多元分类.本文根据支持向量机的最新发展,把最小二乘支持向量机应用在磨粒识别上,并取得了好的结果.     

Fire debris analysis by Raman spectroscopy and chemometrics

A paper reporting the use of Raman spectroscopy in fire debris analysis is presented. Five polymer based samples, namely carpet (polypropylene), nylon stockings (nylon), foam packaging (polystyrene), CD cases (polystyrene) and DVD cases (polypropylene) were burnt with each one of the following ignitable liquids: petrol, diesel, kerosene and ethanol. Raman shifts were obtained and, in some cases, peaks were identified to correspond to pyrolysis products in the form of alkanes, aromatic or polyaromatic compounds. All pyrolysis peaks were used to produce a Principal Component Analysis (PCA) of the burned samples with the different ignitable liquids. The change in the Raman spectra made it possible to identify some of the pyrolysis products produced in the combustion and also to identify the different plastic materials in fire debris, even when different fuels have been used and the chemical and structural identity of the plastic has been altered in the fire.     

超高速碰撞碎片云特征的SPH方法数值分析

 采用光滑粒子流体动力学（SPH）方法对不同形状的弹丸超高速碰撞形成的碎片云特性作了模拟分析,给出了靶孔直径和碎片云宽度随碰撞速度的变化规律、同一速度下不同形状的弹丸累积碎片分布规律、同种弹丸不同速度下的累积碎片分布规律、弹丸初始半径范围内的碎片云无量纲向前总动量M_D/M₀随膨胀距离L_E的变化以及碎片云前端速度的变化规律等。通过数据拟合,进一步给出了累积碎片百分数与碰撞速度和碎片质量的近似函数关系,计算表明该函数关系与数值结果吻合的很好。     

弹丸超高速撞击铝靶成坑数值模拟

 低地球轨道的各类航天器易受到微流星体及空间碎片的超高速撞击,损伤航天器飞行关键系统,进而导致航天器发生灾难性的失效。微流星体及空间碎片防护结构设计,是航天器设计的一个重要问题。采用AUTODYN软件进行了弹丸超高速正撞击及斜撞击铝靶成坑的数值模拟,给出了二维及三维模拟结果。研究了弹丸密度、弹丸形状、板厚度、弹丸速度、弹丸直径和弹丸撞击入射角等对靶成坑的影响。模拟结果同实验结果进行了比较,模拟的成坑形状和特征尺寸同实验相吻合。验证了数值模拟方法的有效性。