Impact Performance Research of Re-Entrant Octagonal Negative Poisson’s Ratio Honeycomb with Gradient Design

Based on the traditional re-entrant honeycomb,a novel re-entrant octagon honeycomb(ROH)is proposed.The deformation mode of the honeycomb under quasi-static compression is analyzed by numerical simulation,and the results are in good agreement with the experimental ones.The deformation modes,mechanical properties,and energy absorption characteristics of ROH along the impact and perpendicular directions gradient design are investigated under different velocities.The results indicated that the deformation mode of ROH is affected by gradient design along the direction of impact and impact speed.In addition,gradient design along the direction of impact can increase the initial peak stress of ROH and accelerate its densification phase.Gradient design perpendicular to the impact direction can enhance the energy absorption performance of ROH,especially for ROH,with wall thickness increasing from the inside outwards.Compared to ROH with uniform wall thickness at the same relative density,ROH with a gradient design can increase the plateau stress by over half.With the elevation of impact velocity,the plateau stress and specific energy absorption exhibit an upward trend,aligning with the dynamic performance pattern observed in conventional honeycombs.The results can be used as a reference for the design and application of honeycomb and provide a new idea for developing more efficient and reliable energy-absorbing materials.

带有无限到达源的Re-entrant Line的稳定性(英文)

用Foster判别准则,Weiss[13]给出了带有无限到达源的两站三步re-entrant line的稳定性的充分条件．本文用两种不同的方法得到了其稳定性的充分必要条件,即: 二维随机游动方法和Foster判别准则．同时,我们又用流体模型方法得到了系统稳定的充分条件,大大地简化了Weiss[13]的证明．

In-Plane Impact Dynamics Analysis of Re-Entrant Honeycomb with Variable Cross-Section

Due to the unique deformation characteristics of auxetic materials(Poisson’s ratioμ<0),they have better shock resistance and energy absorption properties than traditional materials.Inspired by the concept of variable crosssection design,a new auxetic re-entrant honeycomb structure is designed in this study.The detailed design method of re-entrant honeycomb with variable cross-section(VCRH)is provided,and five VCRH structures with the same relative density and different cross-section change rates are proposed.The in-plane impact resistance and energy absorption abilities of VCRH under constant velocity are investigated by ABAQUS/EXPLICIT.The results show that the introduction of variable cross-section design can effectively improve the impact resistance and energy absorption abilities of auxetic re-entrant honeycombs.The VCRH structure has better Young’s modulus,plateau stress,and specific energy absorption(SEA)than traditional re-entrant honeycomb(RH).The influence of microstructure parameters(such as cross-section change rateα)on the dynamic impact performance of VCRH is also studied.Results show that,with the increase in impact velocity andα,the plateau stress and SEA of VCRH increase.A positive correlation is also found between the energy absorption efficiency,impact load uniformity andαunder both medium and high impact speeds.These results can provide a reference for designing improved auxetic re-entrant honeycomb structures.

Design of a re-entrant double-staggered ladder circuit for V-band coupled-cavity traveling-wave tubes

The re-entrant double-staggered ladder slow-wave structure is employed in a high-power V-band coupled-cavity traveling-wave tube. This structure has a wide bandwidth, a moderate interaction impedance, and excellent thermal dissipation properties, as well as easy fabrication. A well-matched waveguide coupler is proposed for the structure. Combining the design of attenuators, a full-scale three-dimensional circuit model for the V-band coupled-cavity traveling- wave tube is constructed. The electromagnetic characteristics and the beam wave interaction of this structure are investigated. The beam current is set to be 100 mA, and the cathode voltage is tuned from 16.8 kV to 15.8 kV. The calculation results show that this tube can produce a saturated average output power over 100 W with an instantaneous bandwidth greater than 1.25 GHz in the frequency ranging from 58 GHz to 62 GHz. The corresponding gain and electronic efficiency can reach over 32 dB and 6.5%, respectively.

Visual Passive Ranging Method Based on Re-entrant Coaxial Optical Path and Experimental Verification

To overcome the shortcomings of the traditional passive ranging technology based on image, such as poor ranging accuracy, low reliability and complex system, a new visual passive ranging method based on re-entrant coaxial optical path is presented. The target image is obtained using double cameras with coaxial optical path. Since there is imaging optical path difference between the cameras, the images are different. In comparison of the image differences, the target range could be reversed. The principle of the ranging method and the ranging model are described. The relationship among parameters in the ranging process is analyzed quantitatively. Meanwhile,the system composition and technical realization scheme are also presented. Also, the principle of the method is verified by the equivalent experiment. The experimental results show that the design scheme is correct and feasible with good robustness. Generally, the ranging error is less than 10% with good convergence. The optical path is designed in a re-entrant mode to reduce the volume and weight of the system. Through the coaxial design,the visual passive range of the targets with any posture can be obtained in real time. The system can be widely used in electro-optical countermeasure and concealed photoelectric detection.

Design of S-band re-entrant cavity BPM

An S-band cavity BPM is designed for a new injector for HLS (Hefei Light Source). It consists of two cavities that work on 2448 MHz: a re-entrant position cavity tuned to TM110 mode and a reference cavity tuned to TM010 mode. Cut-through waveguides are used as pickups to suppress the monopole signal. Simulations with different assumption of dimension change are performed to evaluate errors caused by mechanical error and give general tolerance. Design of electronics is given. Theoretical resolution of this design is 31 nm.

非强占FBFS服务规则下Re-entrantLine排队网络的扩散逼近

本文研究了一个非强占静态优先权first-buffer-first-served(FBFS)服务规则下的re-entrantline排队网络.文章首先建立了一个极限定理,后通过分析队长和斜反射映射的关系,建立了队长过程和闲期过程的扩散逼近.

Effects of Cell Microtopology on the In-plane Dynamic Crushing Analysis of Re-entrant Square Cellular Material

With the development of three-dimensional printing technologies, so-called cellular materials have achieved increasingattention due to outstanding properties. Unlike pure solid structures, properties of cellular materials are influenced by bothutilized material and cell microtopology. The present paper proposes a novel type of re-entrant square cellular material.To explore the relationship between microtopology and macrodynamic responses systematically, an explicit dynamic finiteelement simulation method is used. This work starts by constructing theoretical models of relative density employing atwo-dimensional unit cell. Then, the effects of geometric features and configurations on dynamic properties are explored,and simulations indicate that variations of geometric parameters strongly affect properties and that the staggered re-entrantsquares are more stable than the regular re-entrant squares. Subsequently, the effects of the impact velocity on dynamiccrushing behaviors are elaborated. On this basis, the relationship of unit mass energy absorption and geometric features isobtained by employing the response surface method. Furthermore, with targets of maximum unit mass energy absorption andminimum relative density, the optimal structural parameters are achieved by using non-dominated sorting genetic algorithm.The study provides a detailed introduction to dynamic behaviors of cellular materials and guidance to design new structureswith superior characteristics of energy absorption.

Crashworthiness Optimization Design of Thin-Walled Tube Filled with Re-entrant Triangles Honeycombs

A novel re-entrant triangles-filled tube(RTT)is proposed through decoupling structural stiffness and energy absorption.Inner re-entrant triangles are employed to satisfy energy absorption,and outer thin wall is used to acquire high stiffness.This paper starts from establishment of theoretical models between geometric parameters of re-entrant triangles and relative density,equivalent elastic modulus and energy absorption characteristics,which are validated by experiments.On this basis,the optimal geometric parameters of unit cell are sought to maximize unit volume energy absorption and minimize relative density by adopting NSGA-II method.Subsequently,the cross-section of tube with optimal stiffness is obtained with targets for maximizing axial stiffness and lateral stiffness by employing static topology optimization method.To verify the proposed optimization method,RTT is analyzed and compared with positive Poisson’s ratio foam-filled tube(PFT),non-filled traditionally optimized tube(NTT)and pre-optimized square tube(PST).The results show that the novel RTT can improve stiffness and energy absorption performance simultaneously.Compared with the positive Poisson’s ratio material,re-entrant triangles honeycomb shows superior advantages in energy absorption.In comparison with the PFT,energy absorption of the RTT increases by 17.23%,and the peak crush force reduces by 5.04%.Therefore,the proposed decoupling design method demonstrates superiority in satisfying various performance requirements simultaneously.

Energy Absorption Characteristics of a Novel Asymmetric and Rotatable Re-entrant Honeycomb Structure

Based on the symmetric re-entrant honeycomb(S-RH)structure with negative Poisson’s ratios,a novel asymmetric and rotatable re-entrant honeycomb(AR-RH)structure was proposed.Both the S-RH structure and AR-RH structure were produced by the 3D printing technology.Through experimental test and finite element simulation,the deformation mechanism and energy absorption characteristics of the AR-RH structure and the S-RH structure with negative Poisson’s ratios at different impact velocities were compared.The experimental test and finite element simulation results show that the novel AR-RH structure with negative Poisson’s ratios has stronger energy absorption capacity than the S-RH structure,and it has been verified that the rotatability of AR-RH can indeed absorb energy.Furthermore,the degree of asymmetry of the AR-RH structure was discussed.

Laser Ablation and Chemical Oxidation Synergistically Induced Micro/Nano Re-entrant Structures for Super-Oleophobic Surface with Cassie State

Generally,re-entrant structures are a key part of fabricating superoleophobic surfaces,and this structure appears in almost all kinds of published research articles regarding superoleophobicity.However,the application of related fabrication methods is usually too complex and costly in real practice.In this paper,we present a simple method to generate micro-cauliflower structures,which work as re-entrant structures in microcone arrays,to promote the formation of superoleophobic surfaces.The heating process after alkali-assisted surface oxidation is the main reason for the appearance of a micro-ball structure,and the oxidation time can influence the size of the micro-ball.To the best of our knowledge,the influence of the heating process after alkali-assisted surface oxidation on the birth of the micro-ball structure is seldom researched.A low-surface-energy treatment was also analyzed in influencing the size of the re-entrant structure and its relative wettability.Droplets of 5μl of n-decane show contact angles of 155±1°on the as-prepared superoleophobic surface,and air pockets can be clearly seen underneath,indicating a stable Cassie contacting state and a promising application value in the near future.

Diffusion Approximation of a Multitype Re-entrant Line under Smaller-buffer-first-served Policy

This paper studies a multitype re-entrant line under smaller-buffer-first-served policy, which is an extension of first-buffer-first-served re-entrant line. We prove a heavy traffic limit theorem. The key to the proof is to prove the uniform convergence of the corresponding critical fluid model.

STABILITY OF HLPPS AND MODIFIED HLPPS POLICIES FOR THE RE-ENTRANT LINE

For a re-entrant line operating under the HLPPS service policy, the stability was proved by Bramson in 1996. A simple proof for the stability of the fluid model is given here. Also, the HLPPS service policy is modified according to the proportion of potential jobs and the stability of the fluid model under the modified one is proved.

Novel Hollow Re-entrant Structures Improving Hydrophobicity of Metal Surfaces

Re-entrant structures have drawn increasing attention because of their hydrophobicity.However,it is very difficult to manufacture re-entrant structures at the micron scale on metal surfaces.In this study,we designed and manufactured novel hollow re-entrant structures employing laser ablation and electrodeposition technology.This designed hollow re-entrant structure on metal surfaces has been fabricated successfully,which has high processing efficiency and good repeatability.The morphology and size of the hollow re-entrant structures were characterized.We found that the hydrophobic performance of hollow re-entrant structures was improved after being in the atmosphere for 3 days.After electrodeposition,the static contact angle was 133°.However,after being placed in the atmosphere for 3 days,the static contact angle was 140.4°,which is 5.2%higher than that after electrochemical deposition.We explained the cause of this phenomenon.The change of element content on the surface of hollow re-entrant structures was used to indicate the formation of metal oxide.After being in the atmosphere for 3 days,oxygen content increased by 0.4%.The metal surfaces with hollow re-entrant structures have a broader application prospect.

Evaluation of AVNRT & AVRT by Different Criteria: Old & New

The two most frequent causes of paroxysmal SVT are atrioventricular tachycardia (AVRT) and atrioventricular nodal re-entrant tachycardia (AVNRT). The purpose of this study was to assess the diagnostic efficacy of traditional and newly proposed ECG criteria in the identification of Avnrt and Avrt. Aim of the Study: The aim of this study was to evaluate Atrioventricular Nodal Reentrant Tachycardia (AVNRT) and Atrioventricular Re-entrant Tachycardia (AVRT) using both traditional and novel criteria. Methods: This prospective observational study was conducted at the Electrophysiology Unit, Department of Cardiology, National Institute of Cardiovascular Diseases (NICVD) in Dhaka, from February 2019 to January 2020. A total of 62 patients with Supraventricular Tachycardia (SVT) undergoing electrophysiology study (EPS) were included. Standard ECG criteria were applied for the differential diagnosis, and electrophysiological diagnoses were made using established criteria. Statistical analysis, including descriptive statistics and appropriate tests, was performed using SPSS 23.0. Result: In our study of 62 patients with Supraventricular Tachycardia (SVT), we found that 66.1% had AVNRT and 33.9% had AVRT. The mean age in AVNRT was higher than AVRT (41.3 ± 9.7 vs. 38.5 ± 14.3, p = 0.36) with statistically no significant difference, with similar gender distribution between AVNRT and AVRT groups. Classical AVNRT criteria were present in 30.6% of patients, and 45.2% showed a Pseudo R' wave in aVR. Additionally, 30.6% had an RP interval ≥100ms, more prevalent in AVRT patients (66.7%). Conclusion: Integrating traditional and novel criteria, including lead aVR analysis, enhances the electrocardiographic diagnosis of AVNRT and AVRT, offering a pathway to refined patient care.

Numerical Investigation of the Angle of Attack Effect on Cloud Cavitation Flow around a Clark-Y Hydrofoil

Cavitation is a prevalent phenomenon within the domain of ship and ocean engineering,predominantly occurring in the tail flow fields of high-speed rotating propellers and on the surfaces of high-speed underwater vehicles.The re-entrant jet and compression wave resulting from the collapse of cavity vapour are pivotal factors contributing to cavity instability.Concurrently,these phenomena significantly modulate the evolution of cavitation flow.In this paper,numerical investigations into cloud cavitation over a Clark-Y hydrofoil were conducted,utilizing the Large Eddy Simulation(LES)turbulence model and the Volume of Fluid(VOF)method within the OpenFOAM framework.Comparative analysis of results obtained at different angles of attack is undertaken.A discernible augmentation in cavity thickness is observed concomitant with the escalation in attack angle,alongside a progressive intensification in pressure at the leading edge of the hydrofoil,contributing to the suction force.These results can serve as a fundamental point of reference for gaining a deeper comprehension of cloud cavitation dynamics.

室上性心动过速机制的智能分类模型:基于十二导联穿戴式心电设备

目的基于十二导联穿戴式心电设备,探索室上性心动过速(SVT)机制鉴别的智能分类模型。方法选取356份SVT的穿戴式心电图,通过五折交叉验证的方式随机分为训练集、验证集建立智能分类模型,选取2021年10月~2023年3月诊断为SVT并行电生理检查及射频消融术的患者共101例作为测试集。对比心动过速诱发前后的心电图参数改变,基于多尺度深度神经网络,并加入窦性心律对比图增强训练,建立SVT机制分类的智能分类模型并验证诊断效能。进一步提取II,III,V1三导联心电信号建立分类模型,并对比其与十二导联智能分类模型的效能。结果101例测试集中68例为房室结折返性心动过速,33例为房室折返性心动过速。预训练模型在验证集中识别房室结折返性心动过速的最高精确率-召回率曲线下面积达到0.9492,F1评分为0.8195。最终II导联,III导联,V1导联,三导联与十二导联智能分类模型于测试集中的总F1评分分别为0.5597,0.6061,0.3419,0.6003与0.6136。对比十二导联,III导联的净重新分类指数与综合判别改善指数分别为-0.029(P=0.714)与-0.005(P=0.817)。结论基于多尺度深度神经网络,初步建立了穿戴式心电图对SVT机制分类的智能分类模型,并具有一定的准确性。

基于大涡模拟方法的可压缩空化流流场数值模拟分析

针对可压缩空化流流场细节特征,对空化的回射流机制与凝结激波机制下的空化云演化过程进行大涡模拟。通过对比文献实验数据验证了可压缩空化流数值模拟方法的可靠性,并分析了空化数σ、CN空化数、St数和压力损失系数K等无量纲参数,发现数值模拟对空化流压力-速度耦合计算的准确性方面还有待进一步提升。两种空化机制情况下,涡环生长是空化云脱落后耗散过程,涡环溃灭成游离涡是耗散结果;通过大涡模拟实现两种机制下的空化模拟,对比发现回射流机制的空化的无量纲参数偏差较少,凝结激波具有一定偏差;凝结激波的功率谱密度分析发现满足-7/3标度律,回射流满足-5/3标度律。

内凹蜂窝圆柱壳结构的轴向变形分析

基于平面内凹蜂窝理论建立了曲面内凹蜂窝圆柱壳模型,研究了曲面内凹蜂窝单元在轴向受力下的变形。利用能量法得到了单元在轴向受力下的变形表达式,根据变形表达式得到单元弹性模量。考虑了内凹蜂窝单元的轴向高度、径向宽度以及单元杆件的高宽比对弹性模量的影响。对以上参数进行了理论计算与有限元仿真,将所得结果进行对比与分析,可以得到以下结论:内凹蜂窝圆柱壳在轴向受力下弹性模量随单元轴向高度和杆件高宽比的增大而增大,随单元径向宽度增大而减小。

基于改进的多元宇宙算法的晶圆生产调度算法

针对以最小化最大完工时间为目标的晶圆生产制造系统的调度问题,提出了改进的多元宇宙算法。根据晶圆生产制造系统的特征,构建了一个整数规划模型。针对原始多元宇宙算法的局限性,分别从使用启发式规则生成初始种群、重新定义向最优宇宙移动策略和宇宙更新策略三个方面对算法进行改进。将原始多元宇宙算法、遗传算法、NEH启发式算法、迭代贪婪算法以及通过不同策略改进的多元宇宙算法进行对比实验,结果表明,所提方法可以高效地解决晶圆制造过程中的复杂现象。