Fabrication and Dealloying Behavior of Monolithic Nanoporous Copper Ribbons with Bimodal Channel Size Distributions

Monolithic nanoporous copper （NPC） ribbons with bimodal channel size distributions can be fabricated through chemical dealloying of Mg-32 Cu alloy in an acidic solution at room temperature. The microstructure of the as- dealloyed samples was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. These NPC ribbons are composed of interconnected large-sized channels （hundreds of nm） with highly porous channel walls （tens of nm）. Both large- and small-sized channels are open, bicontinuous, and interpenetrating. Additionally, it is the first time to find that the evolution process of porous structure along the thickness direction of samples during the dealloying is from the interior to exterior, which is just contrary to the coarsening process along the thickness direction during the post-dealloying. Meanwhile, the corresponding mechanism is discussed in detail.

Effects of finite-size neutrally buoyant particles on the turbulent channel flow at a Reynolds number of 395

A direct-forcing fictitious domain(DFFD) method is used to perform fully resolved numerical simulations of turbulent channel flows laden with large neutrally buoyant particles. The effects of the particles on the turbulence(including the mean velocity,the root mean square(RMS) of the velocity fluctuation, the probability density function(PDF) of the velocity, and the vortex structures) at a friction Reynolds number of 395 are investigated. The results show that the drag-reduction effect caused by finite-size spherical particles at low particle volumes is negligibly small. The particle effects on the RMS velocities at Re_τ = 395 are significantly smaller than those at Re_τ = 180, despite qualitatively the same effects, i.e., the presence of particles decreases the maximum streamwise RMS velocity near the wall via weakening the large-scale streamwise vortices,and increases the transverse and spanwise RMS velocities in the vicinity of the wall by inducing smaller-scale vortices. The effects of the particles on the PDFs of the fluid fluctuating velocities normalized with the RMS velocities are small, regardless of the particle size, the particle volume fraction, and the Reynolds number.

Grain size dependence of flow stress in ECAPed Ti with constant texture

The effect of grain size on the flow stress in an ECAPed Ti with a constant texture was investigated,assuming that 2,4,5 and 6 passes microstructures have a similar texture.The average size of recrystallized grains decreased to 0.5 μm,0.4 μm,and 0.3 μm with respect to the ECAP pass number of 2,4,and 6,respectively.The ultimate tensile strength (UTS) and yield strength (YS) increase with an increase in the number of pressing.The UTS and YS of the 6 passes ECAPed sample were found to be 740.2 MPa and 580.3 MPa,respectively.An equation for the flow stress of an ECAPed Ti with a constant texture as a function of the strain and grain size was derived for the ECAPed metal.The following equation was finally obtained:σ(ε)=103.9+1825ε-9.6ε1/2·d-1/2+8.3d-1/2.

Microstructure and tensile properties of ultrafine grained copper processed by equal-channel angular pressing

Equal-channel angular pressing （ECAP） process was applied to a 12 mm ×12 mm ×80 mm billet of pure copper （99.98 wt.%） at room temperature. The shear deformation characteristics, microstructure evolution, and tensile properties were investigated. A combination of high strength （-420 MPa） and high elongation to failure （-25%） was achieved after eight ECAP passes at room temperature. The mixing of ultrafme grains （-0.2 μm） with nanocrystalline grains （-80 nm） resulted in high tensile strength and ductility.

Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

In this study, annealed pure copper was extruded using equal channel angular extrusion （ECAE） for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life con-tinued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses （or high-cycle fatigue）, a maximum increase in fatigue resistance of approximately 500%was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000%was obtained for high-applied stresses （or low-cycle fatigue）. Optical microscopic examinations revealed grain refinements in the range of 32 to 4 μm. A maximum increase in impact energy absorption of 100%was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the ex-truded material during fatigue tests.

Solid Particles Injection in Gas Turbulent Channel Flow

This paper represents a review of the recent researches that investigate the behavior of the gas turbulent flow laden with solid particles. The significant parameters that influence the interactions between the both phases, such as particle size, loading ratio and the gas velocity, have been extensively reviewed. Those parameters are presented in dimensionless numbers in which the applicability of studying its effect in terms of all circumstances of the gas turbulent channel flow at different condition is possible. The represented results show that the turbulence degree is proportional to the particle size. It was found that at the most flow conditions even at low mass ratio, the particle shape, density and size significantly alter the turbulence characteristics. However, the results demonstrate that the particle Reynolds number is a vital sign: the turbulence field becomes weaker if particle Reynolds number is lower than the critical limit and vies verse. The gas velocity has a strong effect on the particles settling along the channel flow and as a result, the pressure drop will be affected.

Effect of equal channel angular extrusion on Al-6063 bending fatigue characteristics

The purpose of this investigation was to refine the grains of annealed 6063 aluminum alloy and to improve its yield stress and ul- timate strength. This was accomplished via the equal channel angular extrusion （ECAE） process at a temperature of 200℃ using route A, with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels for as many as 6 passes. The experiments were conducted on an Avery universal testing machine. The results showed that the grain diameter decreased from 45 μm to 2.8 μm after 6 extru- sion passes. The results also indicated that the major improvement in fatigue resistance occurred after the first pass. The subsequent passes improved the fatigue life but at a considerably lower rate. A maximum increase of 1100% in the case of low applied stresses and an ap- proximately 2200% increase in fatigue resistance in the case of high applied stresses were observed after 5 passes. The improvement of fa- tigue resistance is presumed to be due to （1） a reduction in the size and the number of Si crystals with increasing number of ECAE passes, （2） the aggregation of Cu during the ECAE process, （3） the formation and growth of CuA12 grains, and （4） grain refinement of the A1--6063 alloy during the ECAE process.

脉冲噪声下AUV水声通信盲均衡算法模拟仿真

针对存在琢稳定分布噪声的水声信道中传统常数模盲均衡算法(constant modulus algorithm,CMA)无法稳定收敛的问题,提出一种基于模拟退火粒子群算法优化的变步长分数低阶盲均衡算法(SAPSO-VSS-FLOSCMA),该算法将FLOSCMA的代价函数作为SAPSO算法的适应度函数,利用SAPSO算法搜索全局最优解代替盲均衡器的初始权向量,降低了FLOSCMA算法的稳态误差,并采用双曲正切函数调节FLOSCMA算法的步长因子加快算法的收敛速度。水声信道仿真结果表明,与CMA和FLOSCMA算法相比,SAPSO-VSS-FLOSCMA算法在收敛速度和稳态误差方面均得到提高,且误码率更低。

基于SWMM的车库顶板虹吸排水收集系统排水性能模拟

为探究车库顶板虹吸排水收集系统的排水性能,以重庆市某住宅小区车库顶板虹吸排水项目为例,提出了一种基于暴雨洪水管理模型(SWMM)的车库顶板虹吸排水模拟方法,结合径流系数法和现场实测数据对模型的可靠性和准确性进行了验证,并模拟分析了研究区的虹吸排水收集系统在不同设计重现期下的下渗与排水过程。结果表明,模型可较好地反映研究区虹吸系统的水力特性与排水能力,且在5年一遇设计重现期下虹吸排水管可较好地实现虹吸状态的启动,并有效排除车库顶板排水层内的滞水而未产生明显积水现象。但其排水槽尺寸设计存在充满度过低的问题,而采用逐渐增大排水槽尺寸的优化设计可显著增加充满度,提升排水利用率。

销售端回收的包装尺寸与产品线决策研究

本文通过构建逆向供应链中制造商主导零售商跟随的Stackelberg博弈模型,研究了零售商回收包装废弃物模式下,制造商如何决定产品包装尺寸和产品线选择的问题。首先,制造商做出产品包装尺寸、批发价格以及产品线的决策;其次,零售商从制造商购买产品后决定产品的零售价格和产品包装的回收率;最后,零售商回收的产品包装废弃物回到制造商。研究结果表明:当包装回收难度系数较低时,制造商应同时提供大小包装的产品;当包装回收难度系数不低时,仅提供小包装的产品是最优决策。当包装回收难度系数处于中间水平时,制造商会选择推出小包装的产品,小包装产品的回收率反而小于大包装产品的回收率,同时提供大小两种包装的产品时的回收率最低。有意思的是,单位回收价格的增加会导致零售商和制造商利润都增加,补贴价格的增加则导致两者的利润降低。

疏松砂岩油藏长期水驱高渗透通道形成机理研究

A油田疏松砂岩油藏由于长期水驱而呈现出高渗透通道发育的特征,而孔喉的大小和结构影响着堵剂的选择,因此,了解这些通道发育的特征对油田控水稳油具有重要意义。本文利用A油田提供的天然砂岩岩心设计了长期水驱实验,研究了在流体剪切应力长期作用下储层物性和孔喉微观结构的变化。结果表明,在长期水驱过程中,黏土矿物很容易发生运移,使得较小的孔喉逐渐消失,较大的孔喉进一步扩大,孔喉体积比变小,储层润湿性更多转变为水湿,进而导致油藏微观非均质性增强,储层物性改变,最终,注入水低效循环日趋严重,形成了高渗透通道。

基于变步长匹配追踪的G3-PLC系统信道估计算法

为合理利用电力线信道的稀疏特性,提高G3-PLC系统通信的可靠性,基于压缩感知(compressed sensing,CS)理论,提出一种稀疏度自适应的变步长前向后向匹配追踪(sparsity adaptive variable step size forward-backward pursuit,SA-VSSFBP)算法。该算法在前向后向匹配追踪算法(forward-backward pursuit,FBP)的基础上引入变步长自适应的思想,于迭代初期选择大步长以减小迭代次数,迭代后期使用小步长获得精确估计。同时利用原子匹配度测试进行稀疏度预估计,确保逼近真实稀疏度的前提下,加快迭代速度,减少算法运行的时间。仿真实验结果表明,对比传统的信道估计方式,压缩感知信道估计方式具有更优越的性能,且相较于正交匹配追踪算法(orthogonal matching pursuit,OMP)与FBP的压缩感知信道估计算法,文章提出的算法能够在保证精度与步长为1的FBP相当的情况下算法效率分别能够提升24.14%和47.2%。

物联网通信中的Polar信道编码技术优化研究

文章针对物联网通信中的Polar码研究了一种可变步长的编码方法,并探讨了固定码长与可变码长两种不同编码方法的性能比较。通过对比两种方法在不同信噪比条件下的误码率表现,结果显示可变码长Polar码在各个信噪比条件下均优于固定码长Polar码。这一研究为极化码在通信系统中的应用提供了重要参考,对于提高通信系统的可靠性和性能具有一定的指导意义。

基于机载细分光谱遥感影像的中小河道水体提取

卫星遥感影像被广泛应用于水质监测领域,在提取大型湖泊河流的水体边界、水体面积方面具有快速准确等优势,受分辨率影响,影像中存在混合像元等现象,在提取细小河流时容易出现误判情况。本文以太浦河支流部分河段为研究对象,分别使用NDWI、NDVI两种指数模型从高分辨率的细分光谱成像设备的高光谱影像中提取中小河道水体信息,分析同一影像两种指数提取结果的不同和同种水体指数不同阈值提取效果的差异性,并通过总体精度、识别水体面积等精度评价指标进行精度分析。结果表明,对于高分辨率的细分光谱遥感影像,阈值0.0008的NDWI水体指数模型的提取效果最好,总体精度达95.6932%,整体效果优于NDVI植被指数。

PEM燃料电池凸台流道性能三维仿真分析及结构参数优化

在氢能技术快速发展的背景下,作为关键应用之一的质子交换膜燃料电池(PEMFC)的流道设计受到重点研究。该研究通过构建基于实际尺寸的PEMFC全尺寸单流道模型,并在模型中嵌入不同形状的凸台结构,使用Comsol仿真分析探究凸台几何参数对电池性能的影响。结果表明:凸台结构能显著提升功率输出,电流密度增幅达到10%至31.25%,功率提高3%至9.2%;气体流速与功率输出与凸台高度呈正相关,0.2 mm高的矩形凸台性能最佳,显示适宜的凸台高度能有效提升PEMFC效率;通过增强传质效果、优化工质在燃料电池内部的分布,尤其改善流道后半段的水淹,凸台的设置可进一步增强电池功率。与凸台长度相比,凸台高度是主要的优化方向。该研究为全尺寸的PEMFC流道优化提供了理论上的支持,对提高氢能源效率具有指导意义。

大数据时代中小企业数字化营销渠道研究

在大数据时代,有效采集、存储与挖掘数据信息,对中小企业至关重要。中小企业开展数字化营销,需全面掌握市场信息,提升产品和服务精准度。该文分析了大数据营销关键技术原理,阐述了中小企业数字化营销必要性,并提出了应用策略,以期为其营销渠道建设提供思路。

数字时代中小微外贸企业品牌的渠道创新策略研究——基于服务主导逻辑视角

近几年,中小微外贸企业进出口规模占比愈加增大,民营企业主力作用逐渐增强。但中小微外贸企业传统的品牌体系建设观点和建设思路已难以适应数字时代消费者新型的生产生活方式及消费行为习惯,因此亟需对中小微外贸企业开展符合新时期数字时代特色的品牌创新渠道探索。本研究先从品牌建设的需求侧和供给侧出发,刻画数字时代消费者对品牌的需求和中小微外贸企业品牌的渠道现状,以作为本研究铺垫逻辑起点;再引入案例结合服务主导逻辑理论分析渠道创新经验,最后为发展中小微企业品牌创新渠道提出建议,以供参考。本研究将助力中小微企业精准利用渠道,以低成本实现品牌个性化推广,定向触达目标客户,增强品牌认知与信任,扩大品牌影响力与竞争力。

中小服装纺织企业市场营销渠道的优化策略探索

面对激烈的市场竞争,途径选择和营销战略的更新换代是中小服装纺织企业提高竞争力的重要手段。中小服装纺织企业面临的问题在于如何摆脱过往营销策略的束缚,制定富有弹性的市场应对机制,以此吸引目标消费群体,增加市场份额。传统的营销模式依赖于固定的销售网络和单一的宣传方式,已难以适应当前市场的多变性。在信息化时代背景下,消费者的个性化和多样化需求日益增加,致使中小服装纺织企业亟须对现有营销模式进行优化。优化战略的核心在于通过市场细分,明确目标消费者,对产品进行差异化设计,从而提供贴合市场需求的服装纺织产品。文章研究了中小服装纺织企业市场营销渠道的优化策略,旨在为相关人员提供参考。

雷达功率组件的金刚石微通道热沉激光加工工艺

为研究雷达功率组件金刚石微通道热沉的加工难题,开展了飞秒激光加工多晶金刚石微流道的工艺研究,仿真模拟了飞秒激光作用于金刚石表面的温度场分布,以及诱导去除过程,理论与实验研究了金刚石的烧蚀阈值,系统研究了激光能量、扫描速度、扫描次数、焦点位置等参量及其优化工艺参数对金刚石微槽尺寸的影响规律。结果表明:当飞秒激光功率大于0.3 W时,激光作用于金刚石的最高温度超过材料去除的气化温度,温度最高位置处于光斑中心,功率不会改变温度场的分布情形;飞秒激光加工金刚石的烧蚀阈值为1.80 J/cm2,金刚石微槽深度与激光功率、扫描次数正相关,与扫描速度负相关,与正负离焦量基本成对称分布关系,而金刚石微槽表面宽度则变化不明显;在激光功率为5 W,扫描速度为100 mm/s,扫描次数为30,离焦量为-0.5 mm的优化参数下,加工出的金刚石微槽结构形状规则,截面侧壁锥度控制在3°以内,表面无残渣、裂纹、崩边等缺陷,且内部也无裂纹等缺陷,加工一致性较高,实现了微通道的“冷”加工,可满足雷达功率组件金刚石热沉对微通道的高质量加工要求。