Enhancement of thermal rectification by asymmetry engineering of thermal conductivity and geometric structure for multi-segment thermal rectifier

Thermal rectification is an exotic thermal transport phenomenon,an analog to electrical rectification,in which heat flux along one direction is larger than that in the other direction and is of significant interest in electronic device applications.However,achieving high thermal rectification efficiency or rectification ratio is still a scientific challenge.In this work,we performed a systematic simulation of thermal rectification by considering both efforts of thermal conductivity asymmetry and geometrical asymmetry in a multi-segment thermal rectifier.It is found that the high asymmetry of thermal conductivity and the asymmetry of the geometric structure of multi-segment thermal rectifiers can significantly enhance the thermal rectification,and the combination of both thermal conductivity asymmetry and geometrical asymmetry can further improve thermal rectification efficiency.This work suggests a possible way for improving thermal rectification devices by asymmetry engineering.

A two-parameter multiple shooting method and its application to the natural vibrations of non-prismatic multi-segment beams

This paper presents an enhanced version of the standard shooting method that enables problems with two unknown parameters to be solved.A novel approach is applied to the analysis of the natural vibrations of Euler-Bernoulli beams.The proposed algorithm,named as two-parameter multiple shooting method,is a new powerful numerical tool for calculating the natural frequencies and modes of multi-segment prismatic and non-prismatic beams with different boundary conditions.The impact of the axial force and additional point masses is also taken into account.Due to the fact that the method is based directly on the fourth-order ordinary differential equation,the structures do not have to be divided into many small elements to obtain an accurate enough solution,even though the geometry is very complex.To verify the proposed method,three different examples are considered,i.e.,a three-segment non-prismatic beam,a prismatic column subject to non-uniformly distributed compressive loads,and a two-segment beam with an additional point mass.Numerical analyses are carried out with the software MATHEMATICA.The results are compared with the solutions computed by the commercial finite element program SOFiSTiK.Good agreement is achieved,which confirms the correctness and high effectiveness of the formulated algorithm.

Multi-segmented nanowires for vortex magnetic domain wall racetrack memory

A vortex domain wall's(VW) magnetic racetrack memory's high performance depends on VW structural stability,high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. Thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. This junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction(l) and vertically(d) in the y-direction. The VW structure became stable by manipulating magnetic properties, such as magnetic saturation(M_(4)) and magnetic anisotropy energy(K_(u)). In this case, increasing the values of M_(4) ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires,which contributes to maintenance of the storage memory's lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. Moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions(l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW(J_(d)) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the M_(4) and K_(u),can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires(multisegmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density(J_(d)) for moving the VW from one state to another was highly influenced by the offset area geometry(l and d) and the material's magnetic properties, such as the M_(4) and K_(u).

Multi-segment and Multi-ply Overlapping Process of Multi Coupled Activities Based on Valid Information Evolution

Complex product development will inevitably face the design planning of the multi-coupled activities, and overlapping these activities could potentially reduce product development time, but there is a risk of the additional cost. Although the downstream task information dependence to the upstream task is already considered in the current researches, but the design process overall iteration caused by the information interdependence between activities is hardly discussed; especially the impact on the design process＇ overall iteration from the valid information accumulation process. Secondly, most studies only focus on the single overlapping process of two activities, rarely take multi-segment and multi-ply overlapping process of multi coupled activities into account; especially the inherent link between product development time and cost which originates from the overlapping process of multi coupled activities. For the purpose of solving the above problems, as to the insufficiency of the accumulated valid information in overlapping process, the function of the valid information evolution （VIE） degree is constructed. Stochastic process theory is used to describe the design information exchange and the valid information accumulation in the overlapping segment, and then the planning models of the single overlapping segment are built. On these bases, by analyzing overlapping processes and overlapping features of multi-coupling activities, multi-segment and multi-ply overlapping planning models are built; by sorting overlapping processes and analyzing the construction of these planning models, two conclusions are obtained： （1） As to multi-segment and multi-ply overlapping of multi coupled activities, the total decrement of the task set development time is the sum of the time decrement caused by basic overlapping segments, and minus the sum of the time increment caused by multiple overlapping segments; （2） the total increment of development cost is the sum of the cost increment caused by all overlapping process. And then, based on overlapping degree analysis of these planning models, by the V1E degree function, the four lemmas theory proofs are represented, and two propositions are finally proved： （1） The multi-ply overlapping of the multi coupled activities will weaken the basic overlapping effect on the development cycle time reduction （2） Overlapping the multi coupled activities will decrease product development cycle, but increase product development cost. And there is trade-off between development time and cost. And so, two methods are given to slacken and eliminate multi-ply overlapping effects. At last, an example about a vehicle upper subsystem design illustrates the application of the proposed models; compared with a sequential execution pattern, the decreasing of development cycle （22%） and the increasing of development cost （3%） show the validity of the method in the example The proposed research not only lays a theoretical foundation for correctly planning complex product development process, but also provides specific and effective operation methods for overlapping multi coupled activities.

DDoS Defense Algorithm Based on Multi-Segment Timeout Technology

Through the analysis to the DDoS（distributed denial of service） attack, it will conclude that at different time segments, the arrive rate of normal SYN （Synchronization） package are similar, while the abnormal packages are different with the normal ones. Toward this situation a DDoS defense algorithm based on multi-segment timeout technology is presented, more than one timeout segment are set to control the net flow. Experiment results show that in the case of little flow, multi-segment timeout has the ability dynamic defense, so the system performance is improved and the system has high response rate.

High-power and high optical conversion efficiency diode-end-pumped laser with multi-segmented Nd：YAG/Nd：YVO-4

A novel flat-flat resonator consisting of two crystals（Nd：YAG ＋ Nd：YVO4） is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented（Nd：YAG ＋ Nd：YVO4） and conventional composite（Nd：YAG ＋ Nd：YAG） crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with Mx2= 4.82, My2= 5.48, and a pumping power of 136 W in the multi-segmented crystals（Nd：YAG ＋ Nd：YVO4）. Compared to conventional composite crystals（Nd：YAG ＋ Nd：YAG）, the optical-optical conversion efficiency of multi-segmented crystals（Nd：YAG ＋ Nd：YVO4） from 808 nm to 1064 nm is enhanced from 30% to 58.8%,while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%.

Double tractors swing microendoscopic discectomy technique for multi-segmental lumbar disc herniation

Objective To evaluate the effect of double tractors swing microendoscopic discectomy technique in multisegmental lumbar disc herniation.Methods From December 2006 to November 2009,153 patients with multisegmental lumbar disc herniation

Three-dimensional numerical analysis on combustion performance and flow of hybrid rocket motor with multi-segmented grain

This paper presents the combustion characteristics in hybrid rocket motors with multisegmented grain through three-dimensional numerical simulations.Multi-segmented grain is composed of several thin grains with two or more ports.The numerical model consists of Navier-Stokes equations with turbulence,solid fuel pyrolysis,chemical reactions,a fluid–solid coupling model and a regression rate model.The simulations adopt 90%Hydrogen Peroxide(HP)and PolyEthylene(PE)as the propellant combination.The effects of the rotation,port number,fuel grain segment number and mid-chamber length on the flow field and combustion performances are analyzed.The results indicate that the multi-segmented grain configuration can strengthen the flow field,and the regression rate and combustion efficiency are enhanced.Take the cases with two grain segments and three ports for example,the regression rate is increased by 32.4%-45.1%and the combustion efficiency increases by 6%-8.6%in different rotation angles.

Optimizing the cleanliness in multi-segment disk amplifiers based on vector flow schemes

The objective of maintaining the cleanliness of the multi-segment disk amplifier in Shenguang-II(SG-II) is to reduce laser-induced damage for optics. The flow field of clean gas, which is used for the transportation of contaminant particles,is a key factor affecting the cleanliness level in the multi-segment disk amplifier. We developed a gas–solid coupling and three-dimensional flow numerical simulation model. The three-dimensional and two-phase flow model is verified by the flow-field smog experiment and the particle concentration measurement experiment with the 130-disk amplifier in SG-II. By optimizing the boundary conditions with the same flow rate, the multi-inlet vector flow scheme can not only effectively reduce the purging time, but also prevent the reverse diffusion of contaminant particles in the multi-segment disk amplifier and the deposition of contaminant particles on the surface of the Nd:glass.

Multi-segment linear gradient optimization strategy based on resolution map in HPLC

Based on the mechanism of chromatographic retention (the relationship between the retention of solute and the mobile phase conditions) and method of resolution map, several methods of optimizing multi-segment linear gradient elution conditions were proposed according to the different separation requirements of various samples. These methods were verified using literature data. Moreover, the advantages and disadvantages of these methods were compared. It was proved that the third method is a fast optimization method which is capable of separating all the components with relatively high resolution.

A 14-bit wide temperature range differential SAR ADC with an on-chip multi-segment BGR

A 14-bit low power self-timed differential successive approximation（SAR） ADC with an on-chip multisegment bandgap reference（BGR） is described.An on-chip multi-segment BGR,which has a temperature coefficient of 1.3 ppm/℃and a thermal drift of about 100μV over the temperature range of -40 to 120℃is implemented to provide a high precision reference voltage for the SAR ADC.The Gray code form is utilized instead of binary form mode control to reduce substrate noise and enhance the linearity of the whole system.Self-timed bit-cycling is adopted to enhance the time efficiency.The 14-bit ADC was fabricated in a TSMC 0.13μm CMOS process. With the on-chip BGR,the SAR ADC achieves an SNDR of 81.2 dB（13.2 ENOB） and an SFDR of 85.2 dB with a conversion rate of 2 MS/s at room temperature and can keep an ENOB of more than 12 bits at a conversion rate of 2 MS/s over the temperature range from -40 to 120℃.

一种多段机翼水面起降地效无人机气动特性

为改善水面起降性能和气动性能,基于船身式机身、多段机翼和T尾融合设计思路,提出并设计了一种新型仿生式多段机翼地效无人机方案,采用N-S方程和K-Ω-SST湍流模型,详细研究了该型无人机在不同状态下的压力云图、压力系数及升阻特性。仿真结果表明,地效作用随离水高度的增加而减小,离水高度与平均几何弦长之比(高度弦长比H/c)接近1时,地效作用较为显著,无人机在离水高度0.2 m时,升力系数、升阻比分别提升21.91%和40.37%,阻力系数降低15.22%;对提出的多段机翼布局,地效飞行主要影响下表面压力系数和压力云图,下表面压力系数展向上由内向外正压增幅逐渐减小,弦向上前后缘附近压力系数较小,结合压力云图分析,地效对升力增幅的影响主要集中在中段和内段机翼下方区域;地效飞行可明显提高升力线斜率(H/c为1时提高了8.89%),迎角增加时升力系数增幅和阻力系数降幅均逐渐变大,升阻比增幅(H/c为1)在迎角2°后均达到26%以上;通过验证机的多轮水面起降和有、无地效飞行试验,证明设计方案具有优秀的气动性能和飞行性能,可为水质检测、水面地效运输、搜救侦察等提供应用平台。

MCFNet:融合上下文信息的多尺度视网膜动静脉分类网络

针对由于血管类间具有强相似性造成的动静脉错误分类问题,提出了一种新的融合上下文信息的多尺度视网膜动静脉分类网络(multi-scale retinal artery and vein classification network,MCFNet),该网络使用多尺度特征(multi-scale feature,MSF)提取模块及高效的全局上下文信息融合(efficient global contextual information aggregation,EGCA)模块结合U型分割网络进行动静脉分类,抑制了倾向于背景的特征并增强了血管的边缘、交点和末端特征,解决了段内动静脉错误分类问题。此外,在U型网络的解码器部分加入3层深度监督,使浅层信息得到充分训练,避免梯度消失,优化训练过程。在2个公开的眼底图像数据集(DRIVE-AV,LES-AV)上,与3种现有网络进行方法对比,该模型的F1评分分别提高了2.86、1.92、0.81个百分点,灵敏度分别提高了4.27、2.43、1.21个百分点,结果表明所提出的模型能够很好地解决动静脉分类错误的问题。

底部填芯多节段预制拼装空心桥墩抗震性能试验研究

为提高预应力连接预制节段拼装桥墩的抗震性能及施工便捷性,设计了一种底部填芯多节段预制拼装空心桥墩并进行了抗震试验研究。提出了该新型预制节段拼装桥墩填芯高度设计方法,设计了底部填芯预制节段拼装桥墩缩尺模型并开展了拟静力试验测试。基于试验结果分析了该新型桥墩在水平循环往复作用下的裂缝发展过程、失效模式、滞回性能、延性性能、耗能能力及桥墩接缝的开口大小等抗震性能。研究结果表明:所发展的底部填芯多节段预制拼装空心桥墩的失效模式为底部节段混凝土局部压溃,但范围较小,所提填芯高度的设计方法可行,可以使桥墩实现预期失效模式。该新型桥墩具有较小的残余位移、优异的耗能能力与延性性能,这表明此桥墩具有优异的抗震性能。

基于CNN和Transformer并行编码的腹部多器官图像分割

针对现有方法在腹部中小器官图像分割性能方面存在的不足,提出一种基于局部和全局并行编码的网络模型用于腹部多器官图像分割.首先,设计一种提取多尺度特征信息的局部编码分支;其次,全局特征编码分支采用分块Transformer,通过块内Transformer和块间Transformer的组合,既捕获了全局的长距离依赖信息又降低了计算量;再次,设计特征融合模块,以融合来自两条编码分支的上下文信息;最后,设计解码模块,实现全局信息与局部上下文信息的交互,更好地补偿解码阶段的信息损失.在Synapse多器官CT数据集上进行实验,与目前9种先进方法相比,在平均Dice相似系数(DSC)和Hausdorff距离(HD)指标上都达到了最佳性能,分别为83.10%和17.80 mm.

用于实时语义分割的丰富语义提取器网络

目的由于推理速度限制,网络深度较浅,实时语义分割网络提取的语义特征信息不足。此外,较浅的网络深度也限制了特征提取网络的能力,降低了其鲁棒性和适应能力。为此,方法提出一种用于实时语义分割的丰富语义提取器网络。首先针对语义特征信息提取不足的问题,引入丰富语义提取器,丰富语义提取器包括多尺度全局语义提取模块和语义融合模块。其次,利用多尺度全局语义提取模块可以提取丰富的多尺度全局语义,扩大网络的有效感受野,同时语义融合模块将多尺度局部语义与多尺度全局语义高效融合,使网络拥有更全面更丰富的语义信息。最后针对细节分支和语义分支的特点设计空间重构聚合模块,建模细节特征的上下文信息,增强特征表示,使2个分支高效聚合。结果在Cityscapes和ADE20K数据集上进行全面实验,所提出的RSENet分别以76帧/s和67帧/s的推理速度达到了75.6%和35.7%的MIoU。结论实验结果表明,在复杂场景语义信息的提取方面,本文所提出的网络能够深入挖掘并准确捕捉图像中语义信息。同时,在精度与速度的平衡方面也展现出了卓越的性能,不仅能够实现高精度的语义分割,而且推理速度非常快。这种高效的图像分割能力使得网络在实际应用场景中具有极高的实用性和可操作性。

基于激光雷达点云的动态驾驶场景多任务分割网络

在自动驾驶场景理解任务中进行准确的可行驶区域以及动静态物体分割对于后续的局部运动规划和运动控制至关重要。然而当前基于激光雷达点云的通用语义分割方法并不能在车端边缘计算设备上实现实时且鲁棒的预测,且不能预测当前时刻的物体运动状态。为解决该问题本文提出一种可行驶区域及动静态物体多任务分割网络MultiSegNet。该网络利用激光雷达输出的深度图及处理后得到的残差图像作为编码空间特征和运动特征的表征输入到网络用于特征学习,从而避免直接处理无序高密度点云。针对深度图在不同方向视角内目标分布数量差异较大的特点,本文提出了变分辨率分组输入策略。该方法能在降低网络计算量的同时提高网络的分割精度。为适配不同尺度目标所需要的卷积感受野尺寸本文提出了深度值引导的分层空洞卷积模块。同时本文为有效关联并融合不同时域下物体的空间位置和姿态信息提出了时空运动特征增强网络。为验证所提出MultiSegNet的有效性,本文在大规模点云驾驶场景数据集SemanticKITTI及nuScenes上进行验证。结果表明:可行驶区域、静态物体和动态物体的分割IoU分别达到98%、97%和70%,性能优于主流网络,且在边缘计算设备上实现实时推理。

融合多尺度特征和注意力机制的超声甲状腺结节分割

针对目前超声影像下甲状腺结节分割不够精准的问题,提出一种融合多尺度特征和注意力机制的超声甲状腺结节分割方法。该模型编码设计了多感受野通道选择模块,通过核心选择注意力对多个不同感受野的特征进行自适应加权组合,使包含目标的感受野通道占据主导。同时,设计自适应全局上下文模块自适应地提取瓶颈层多个尺度的全局上下文特征,以实现对瓶颈层高级语义的有效编码。此外,设计双注意力引导模块增强编解码器对等层之间的特征融合,以减少上采样过程中的信息损失。在公开的超声甲状腺结节数据集上进行实验,结果表明,文中所提方法优于其他对比网络,能更加精准地分割出甲状腺结节,有效提升了甲状腺结节的分割性能。

基于改进DeepLabv3的自然图像语义分割算法

针对DeepLabv3模型对自然图像语义分割时存在的图像局部细节信息丢失导致的误分割和物体边缘分割不完整的问题,提出了一种改进DeepLabv3模型的自然图像语义分割网络,能够以更高的准确率实现自然图像的语义分割.首先,使用ResNet101作为骨干网络进行特征提取,把ResNet101网络最后两层提取到的特征图输入到设计的ACMix多重融合模块(ACMix Multiple Fusion Module,AMFM)中,有效获取不同尺度的空间特征信息,将融合之后的结果作为空洞空间金字塔池化模块(Atrous Spatial Pyramid Pooling,ASPP)的输入.其次,添加辅助分支模块(Auxiliary Branch Module,ABM),将ResNet101网络第三层提取到的特征图输入到ABM中,有效提取更丰富的边缘特征信息.最后,将主分支和辅助分支的结果融合作为输出,融合后的输出不仅追踪到了不同尺度的空间特征信息,而且提取到了完整的边缘特征信息,从而使模型更有效地提高分割精度.PASCAL VOC 2012数据集的结果表明,改进后的模型相比于原模型分割精度提升了3.21%,与其它网络模型相比,也具有较好的分割精度.

融合编码器多尺度特征的RGB-D图像语义分割

针对语义分割任务中,室内场景中目标物体尺寸变化较大的问题,在ACFNet的基础上,提出融合编码器多尺度特征的RGB-D语义分割网络。首先,为有效利用网络提取的多尺度特征,提出结合池化操作的多尺度特征融合模块(PMFM),选择编码器不同阶段RGB和深度特征的融合特征作为该模块的输入;其次,设计改进的跳跃连接模块(ISCM),使用下一层级包含更多语义信息的特征图辅助修正当前层级的特征图,再经跳跃连接以拼接的方式传输到解码器对应阶段。将提出的网络模型应用到NYUD V2和SUN RGB-D数据集上,平均交并比分别达到了52.6%和48.8%。通过这两项改进,实验结果表明,上述方法达到了较高的分割准确率,优于对比的语义分割方法。