Construction of Oriented Structure in Inner Surface of Small-Diameter Artificial Blood Vessels:A Review

There is an urgent need for small-diameter artificial blood vessels in clinic.Physical,chemical and biological factors should be integrated to avoid thrombosis and intimal hyperplasia after implantation and to promote successful fabrication of small-diameter artificial blood vessels.From a physical perspective,the internal oriented structures of natural blood vessels plays an important role in guiding the directional growth of cells,improving the blood flow environment,and promoting the regeneration of vascular tissue.In this review,the effects of the oriented structures on cells,including endothelial cells(ECs),smooth muscle cells(SMCs)and stem cells,as well as the effect of the oriented structures on hemodynamics and vascular tissue remodeling and regeneration are introduced.Various forms of oriented structures(fibers,grooves,channels,etc.)and their construction methods are also reviewed.Conclusions and future perspectives are given.It is expected to give some references to relevant researches.

Bioprinting of Small-Diameter Blood Vessels

There has been an increasing demand for bioengineered blood vessels for utilization in both regenerative medicine and drug screening.However,the availability of a true bioengineered vascular graft remains limited.Three-dimensional(3D)bioprinting presents a potential approach for fabricating blood vessels or vascularized tissue constructs of various architectures and sizes for transplantation and regeneration.In this review,we summarize the basic biology of different blood vessels,as well as 3D bioprinting approaches and bioink designs that have been applied to fabricate vascular and vascularized tissue constructs,with a focus on small-diameter blood vessels.

Effect of heating methods on drying quality of small-diameter birch lumbers

Following a normal low temperature drying schedule, the small-diameter Birch lumbers （ 1 000mm× 45mm ×30mm） were dried with consecution-heats or intermittent-heating, visual drying defects （bow, crook, twist, check along grain and end check） were measured, and then statistical analyses were performed. It was found that the drying quality of small-diameter Birch lumbers could be improved with intermittent-heating, but the intermittent time should be prolonged. Prolonging intermittent time helped to weaken or even avoid wood distortion and drying checks. It wash＇ t helpful in avoiding crook. The drying quality of small-diameter Birch lumbers with all kinds of drying methods reached the second class of the Chinese National Standard. The drying quality reached the first class of the Chinese National Standard with the intermittent-heating in the area of visual wood defects.

SMALL-DIAMETER KOREAN PINES AND THEIR ROLES INNATURAL KOREAN PINE FOREST

Korean pine population strueture in natural Korean pine forest was studied through massive field investigation and indoor analvsis. Small-diameter Korean pines origination, growth charaeter and their roles in stand were discussed from the view of population origination and tree growth. The results show that small-diameter Korean pines origination and growth havc close relations to the overstory canopy structure dynamics and play an important role in the maintenance and development of Korean pine forest. The process from small-diameter trees to dominant canopy is a selfmaintenance phase, with diffieulty, in Korean pine population. To complete this phase, it not only demands some morphological characters and physiological conditions, but severe forest strueture conditions as well. The time for complating this phase needs separation from overstory Korean pines and converge with overstory broad-leaf trees. In vertical space, it needs to fell overstory canopy or reduce the layers of overstory canopy, and in horizontal space it should be separated from Korean pines but accompanied by broad-leaf trees.

Hopping-Aware Cluster Header Capability for Sensor Relocation in Mobile IoT Networks

Mobile sensor nodes such as hopping sensors are of critical importance in data collection.However,the occurrence of sensing holes is unavoidable due to the energy limitation of the nodes.Thus,it is evident that the relocation of mobile sensors is the most desirable method to recover the sensing holes.The previous research conducted by the authors so far demonstrated the most realistic hopping sensor relocation scheme,which is suitable for the distributed environment.In previous studies,the cluster header plays an essential role in detecting the sensing hole and requesting the neighboring cluster to recover the sensing hole that occurred in the sensor node.However,the limitations of the cluster header in the previously proposed relocation protocol are not fully considered.Because the cluster header jumps more frequently than non-header nodes,its energy con-sumption is relatively high compared to other nodes.Therefore,it is most likely to lead to header node failure and can lead to data loss on the network.In this paper,the jumping ability and energy consumption of the cluster header are seriously considered.Additional ability to replace cluster headers in case of failure is also implemented.Simulation results show that the data collection time can be further increased,which demonstrates the validity of the proposed algorithms.

Impact of Portable Executable Header Features on Malware Detection Accuracy

One aspect of cybersecurity,incorporates the study of Portable Executables(PE)files maleficence.Artificial Intelligence(AI)can be employed in such studies,since AI has the ability to discriminate benign from malicious files.In this study,an exclusive set of 29 features was collected from trusted implementations,this set was used as a baseline to analyze the presented work in this research.A Decision Tree(DT)and Neural Network Multi-Layer Perceptron(NN-MLPC)algorithms were utilized during this work.Both algorithms were chosen after testing a few diverse procedures.This work implements a method of subgrouping features to answer questions such as,which feature has a positive impact on accuracy when added?Is it possible to determine a reliable feature set to distinguish a malicious PE file from a benign one?when combining features,would it have any effect on malware detection accuracy in a PE file?Results obtained using the proposed method were improved and carried few observations.Generally,the obtained results had practical and numerical parts,for the practical part,the number of features and which features included are the main factors impacting the calculated accuracy,also,the combination of features is as crucial in these calculations.Numerical results included,finding accuracies with enhanced values,for example,NN_MLPC attained 0.979 and 0.98;for DT an accuracy of 0.9825 and 0.986 was attained.

Secure Web Application Technologies Implementation through Hardening Security Headers Using Automated Threat Modelling Techniques

This paper investigates whether security headers are enforced to mitigate cyber-attacks in web-based systems in cyberspace. The security headers examined include X-Content-Type-Options, X-Frame-Options, Strict-Transport-Security, Referrer-Policy, Content-Security-Policy, and Permissions-Policy. The study employed a controlled experiment using a security header analysis tool. The web-based applications (websites) were analyzed to determine whether security headers have been correctly implemented. The experiment was iterated for 100 universities in Africa which are ranked high. The purposive sampling technique was employed to understand the status quo of the security headers implementations. The results revealed that 70% of the web-based applications in Africa have not enforced security headers in web-based applications. The study proposes a secure system architecture design for addressing web-based applications’ misconfiguration and insecure design. It presents security techniques for securing web-based applications through hardening security headers using automated threat modelling techniques. Furthermore, it recommends adopting the security headers in web-based applications using the proposed secure system architecture design.

钠冷快堆小栅板联箱压降对组件流量分配影响研究

钠冷快堆堆芯采用大栅板联箱、小栅板联箱和组件的三级流量分配方式,小栅板联箱的压降影响组件的流量分配,进而影响堆芯的安全,因此进行钠冷快堆小栅板联箱压降对组件流量分配影响研究有重要意义。根据小栅板联箱压降造成组件流量分配偏差的机理,提出了理论计算模型和堆芯组件优化设计的方法,并针对中国实验快堆(CEFR)堆芯进行了组件压降的优化设计,通过优化设计降低了CEFR燃料组件流量分配负偏差。结果表明,在进行钠冷快堆堆芯热工水力设计时,需要结合实际堆芯布置分析组件压降设计值的优化方向,并进行敏感性分析,以确定组件的最优设计压降,将小栅板联箱压降对组件流量分配影响降低到最低程度。本文结果可为钠冷快堆堆芯热工水力设计提供参考。

机械-液压组合式大豆割台仿形装置设计与仿真

针对传统大豆割台仿形范围有限导致割台损失大、粮箱内含杂量高等问题,设计了一种机械-液压组合式大豆割台仿形装置,通过分段仿形提高了大豆割台的仿形范围。基于大豆割台几何关系,构建了割台液压油缸伸缩量和割台离地高度变化量之间的函数关系,为割台高度自适应调控提供了理论支撑。为了实现割台高度的自动化调控,设计了一种割台离地高度检测装置,并针对其工作过程中出现的仿形板下陷、跳动等问题,利用RecurDyn进行了动力学仿真,确定了复位扭簧的最佳扭矩为16N·m。通过田间试验验证了大豆割台仿形装置的仿形效果,为大豆收获机械设计提供了理论参考。

基于二阶欠阻尼阶跃响应的收获机割台液压缸选型分析

割台是谷物收获机的重要组成部分,割台性能的好坏决定着收获机在收获作业时的作业质量。割台液压缸选型确定方面,传统方式大多采用对割台质量及液压系统工作负载进行分析,利用经典力学的方式进行割台油缸的选型。随着自动控制理论的发展,割台高度闭环控制技术也越来越多地开始出现在国外领先收获机机型上,仅考虑力学负载分析的方法已经无法满足割台高度自动控制系统的需要。针对控制系统稳态分析的要求,割台油缸在满足工作负载的前提下,还需考虑系统的超调量、反应时间及过调震荡时间等因素。为此,进行割台升降运动过程建模分析,论证出割台控制模型为二阶欠阻尼模型系统,发现固有频率ωn与阻尼比ζ决定着系统动态指标。通过对液压缸内部分析,求出了割台液压缸系统的传递函数,确定出当其他机械参数不变时,割台油缸的管径影响着割台液压缸系统的固有频率ωn与阻尼比ζ。综合采用上升时间tr、峰值时间tp、超调量σ%和调节时间ts等4种系统稳态指标确定了最佳割台油缸参数,并进行了Amesim仿真试验。研究结果为后续无人驾驶谷物联合收获机的研发设计提供了割台装置控制策略的理论依据。

谷子联合收获机割台机架的振动分析与结构优化

为了降低谷子联合收获机在田间工作时的振动、减少割台损失率,利用SolidWorks对谷子割台机架进行三维建模,利用ANSYS软件对谷子割台机架优化前和优化后分别进行有限元分析,并用东华DH5902动态测试分析仪对计算机模态分析结果进行了验证。结果表明:优化前的第4阶模态为11.04Hz,其频率落在外部激振频率范围内;优化后的谷子割台机架各个阶次频率均避开了联合收获机各外部激振频率范围,有效避免了割台震动的产生。通过田间试验验证了改进前后的割台损失率,改进后的割台损失率降低了14.5%。研究成果可为降低谷子联合收获机振动及为谷子割台的减震设计提供了理论指导。

大豆收获机割台关键技术及损失研究现状分析

割台作为大豆收获机的核心部件,其技术性能直接关系到大豆的收获质量和收获损失率。针对割台仿形设计、割台高度控制技术、影响割台损失率的关键技术展开研究和分析。首先,综述割台仿形机构与割台高度控制的结构、工作原理及关键技术,对比分析国内外的研究差距。其次,针对大豆炸荚、割台关键技术与割台损失的相关性进行深入分析,探讨割台损失产生的主要原因和影响因素,提出关键技术的改进建议。最后,展望我国大豆收获机割台在多元化、智能化与自动化方向的发展趋势,大豆炸荚生物特性及大豆收获机收获损失研究方面的发展趋势。研究发现,我国现有大豆收获机存在割台仿形性能差、割台自适应控制技术滞后、割台损失率偏高等问题。同时有效揭示国内大豆收机割台仿形机构、割台升降装置、割台的自适应性及割刀等关键技术存在的问题,割台振动、割台位置与仿形及撞击力导致割台损失率高的原因,为我国大豆收获机割台关键技术的突破创新及降低收获损失的进一步研究提供重要参考。

甘薯茎叶收获仿垄型割台的设计与试验研究

为解决甘薯茎叶相互交错缠绕、难以分离导致收获困难的问题,设计了一种甘薯秧蔓收获机拨禾割台,并对锯齿形圆盘刀、拨禾轮式仿垄型割刀切割甘薯茎秆的过程进行力学和运动学分析,得到其作业参数范围。利用ANSYS和SolidWorks分别建立甘薯茎秆的柔性体和拨禾轮式仿垄型割台模型,将建立好的模型在ADAMS仿真软件中进行植株与割台之间的刚-柔耦合模型分析,得到割刀切割茎秆时所产生的切割力大小。以机组前进速度、割台转速、切割角度作为田间试验因素,甘薯秧蔓回收率为验证指标进行田间试验,并利用Design-Expert 13.0软件中Box-Behnken试验设计方法,研究各试验因素交互作用对甘薯秧蔓回收率的影响,建立回归模型,得到最优工作参数组合。结果表明,当机组前进速度为0.801m/s、割台转速为50.037r/min,切割角度为123.309°时,甘薯秧蔓的回收率达到91.524%。根据最优工作参数组合为作业参数进行田间试验验证,结果表明:甘薯秧蔓回收率的平均值为92.83%,相对误差小于5%,最优参数合理。

适于新疆单膜收获的大豆割台设计及拨禾过程分析

针对新疆大豆覆膜滴灌栽培技术,设计一款带有地形起伏检测装置的大豆割台。通过田间生长特性测量,确定适于新疆单膜大豆收获的拨禾轮主轴长度为2 000 mm、直径为650 mm。依此设计一种前置轮式地形检测装置,该装置安装于大豆割台两侧,确定检测装置角度转动量与割刀离地高度之间的关系式为:H=80-Δh=80-320(sinθ-sinθ′)。对所设计的大豆割台进行地面起伏检测试验,试验中实际距离与检测距离之间的相对误差均值为0.037~0.039。对拨禾轮工作原理进行分析,研究其产生拨禾作用时的拨禾速比范围。将拨禾轮三维模型导入Adams软件中,分析不同拨禾速比下弹齿的运动轨迹,发现当拨禾速比λ≤1.0时拨禾轮无拨禾作用,当λ>1.0时拨禾轮具有拨禾作用,但拨禾速比过大后,相邻弹齿间会产生作用重叠区域。设计的割台利于新疆大豆单膜收获,地形检测装置可为割台高度的实时调节提供依据。

4KHZ-330型食葵联合收获机设计与试验

针对食葵机械化收获水平低、损失大、含杂率高及籽粒破损严重等现状,该研究根据成熟期食葵生物特性,在传统联合收获机结构基础上设计一种4KHZ-330型食葵联合收获机,在割台上增设脱粒装置实现葵盘在割台上脱分,可有效缩短葵盘输送路径,提高清选质量。首先阐述食葵联合收获机的总体设计方案及动力传动模式,并对割脱一体式割台、割台升降机构、清选装置及气力输送装置等关键部件进行设计,确定相关参数。机具配套动力113 kW,工作幅宽为3300 mm,可一次完成食葵切割、脱粒、输送、清选、集籽、集草及卸载等工序。田间试验表明,收获机在低、中、高3种工作档位下,总损失率均低于4.0%,籽粒含杂率均低于5.0%,籽粒破损率均低于2.0%,生产率为0.40~0.85 hm^(2)/h,作业性能指标满足食葵机械化收获标准。作业过程中收获机各关键部件之间运动协调关系平稳,食葵喂入顺畅,工作效率高,可以作为食葵联合收获机使用。

悬臂式掘进机参数变型与交互式虚拟展示

针对现有掘进机设计中总体布局参数阶段效率低、易出错的问题,提出一种基于掘进机技术指标确定总体布局参数的方法。以EBZ200型矿用悬臂式掘进机为对象,首先对其进行功能模块的划分,随后分析得出各功能模块布局参数对掘进机总体性能指标的影响。通过Cinema 4D对掘进机模型进行绑定蒙皮处理,使用MATLAB计算性能逆算参数,采用MySQL构建相应的数据库,最后基于Unity3D引擎和C#脚本开发系统,根据掘进面的尺寸检索出合适的掘进机截割部参数组合,实现掘进机布局参数的可视化调整,同时实时显示布局参数变更对性能指标的影响,有效提升了掘进机的设计效率。

基于PID调控的割台仿形高度控制系统的设计

为降低谷物联合收获机收获作业时因割台高度不当造成的粮食损失,减少割茬高度过高对后续播种环节的影响,利用传感器监测地面起伏变化,设计了一种基于PID调控的割台高度自适应控制系统;设计了基于角度传感器的地面仿形监测机构与割台高度反馈机构,标定并拟合出割台高度与传感器电压信号的线性关系;加装集成式电磁比例阀替换原有割台控制电控换向阀,并进行PWM控制试验。同时,分析了整套自适应控制系统的结构与电液控制原理,并进行了多组田间对照试验,结果表明:设计的基于地面仿形的割台高度自适应控制系统具有稳定的响应速度和理想的控制效果,在平原地区作业时相较于传统人工控制割台的方式有明显的优势,能适应平原地形环境下5~11km/h收获作业速度的要求。研究结果为后续无人驾驶谷物联合收获机的研发设计提供了割台装置控制策略的理论依据。

VDES上行ID20信号帧头检测算法研究

为了提高VDES上行ID20信号在低信噪比和大多普勒频偏情况下的信号检测概率,提出了一种基于频率信道化的分段相关帧头检测算法。利用频率信道化将频偏范围缩小,在每个子信道内结合本地序列分段相关、非相干积累和与恒虚警门限比较等过程对信号帧头进行检测。介绍了ID20信号模型,描述了基于频率信道化的分段相关帧头检测算法原理,理论推导了虚警率与门限因子的关系,并对算法的性能进行仿真。仿真结果表明,该算法可以抵抗4 000 Hz大频偏,并且信噪比得到了明显改善,当检测概率为0.9时,相比于VDES中常用的差分帧头检测算法的检测性能,信噪比可以提高6.3 dB。

3D printed grafts with gradient structures for organized vascular regeneration

Synthetic vascular grafts suitable for small-diameter arteries(<6 mm) are in great need.However,there are still no commercially available small-diameter vascular grafts(SDVGs) in clinical practice due to thrombosis and stenosis after in vivo implantation.When designing SDVGs,many studies emphasized reendothelization but ignored the importance of reconstruction of the smooth muscle layer(SML).To facilitate rapid SML regeneration,a high-resolution 3D printing method was used to create a novel bilayer SDVG with structures and mechanical properties mimicking natural arteries.Bioinspired by the collagen alignment of SML,the inner layer of the grafts had larger pore sizes and high porosity to accelerate the infiltration of cells and their circumferential alignment,which could facilitate SML reconstruction for compliance restoration and spontaneous endothelialization.The outer layer was designed to induce fibroblast recruitment by low porosity and minor pore size and provide SDVG with sufficient mechanical strength.One month after implantation,the arteries regenerated by 3D-printed grafts exhibited better pulsatility than electrospun grafts,with a compliance(8.9%) approaching that of natural arteries(11.36%) and significantly higher than that of electrospun ones(1.9%).The 3D-printed vascular demonstrated a three-layer structure more closely resembling natural arteries while electrospun grafts showed incomplete endothelium and immature SML.Our study shows the importance of SML reconstruction during vascular graft regeneration and provides an effective strategy to reconstruct blood vessels through 3D-printed structures rapidly.

基于数据包头序列的物联网恶意流量检测

现有的基于机器学习(ML)的恶意流量检测方法,通常以高维的流量特征作为输入,并采用复杂模型,在实践中产生高误报率且资源占用较高。更重要的是,加密协议的广泛使用,使得数据包有效载荷特征很难被访问。幸运的是,物联网(IoT)设备的网络行为通常是有规律和周期性的,该特征反映在通信数据包序列上,每个数据包一定程度上描述了一次网络事件。基于此,本文提出了基于数据包头序列的恶意流量检测方法。它将流量序列转换为网络事件序列,并计算一组特征(即序列性、频率性、周期性和爆发性)来描述网络行为。实验环境包含一组真实的物联网设备,并将提出的方法部署在树莓派模拟的网关上。实验结果表明,与最新的检测方法相比,本文提出的方法能够在复杂网络环境下保持高准确性和低误报率,并提升了处理速率。