Porous layered La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3)perovskite with enhanced catalytic activities for oxygen reduction

Low-cost catalysts with high activity are in immediate demand for energy storage and conversion devices.In this study,polyvinyl pyrrolidone was used as a complexing agent to synthesize La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3)(LSCF)perovskite oxide.The obtained porous layered LSCF has a large specific surface area of 23.74 m^(2)/g,four times higher than that prepared by the traditional sol-gel method(5.08 m^(2)/g).The oxygen reduction reaction activity of the oxide in 0.1 mol/L KOH solution was studied using a rotating ring-disk electrode.In the tests,the initial potential of 0.88 V(vs.reversible hydrogen electrode)and the limiting diffusion current density of 5.02 mA/cm^(2)were obtained at 1600 r/min.Therefore,higher catalytic activity and stability were demonstrated,compared with the preparation of LSCF perovskite oxide by the traditional method.

Pore structure characteristics of the relative water-resisting layer on the top of the Ordovician in Longgu Coal Mine

In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture and pore structure features of the strata, and identified the main channels which govern the permeability and water-resisting ability of the strata. The permeability of the upper, central and lower strata shows as 2.0504 × 10^-3-2.782762× 10^-3, 4.1092 × 10^-3 -7.3387 × 10^-3 and 2.0891 ×10^-3-3.2705 × 10-3 μm^2, respectively, and porosity of that is 0.6786-0.9197%, 0.3109-0.3951% and 0.9829-1.8655%, respectively. The results indicate that： （I） the main channels of the relative water-resisting layer are the pore throats with a diameter more than 6 μm; （2） the major proportion of pore throats in the vertical flow channel and the permeability first increases and then sharply decreases; （3） the fractures occurring from the top to 20 m in depth of the strata were filled and there occurred almost no fracture under the depth of 40 m; and （4） the ratio of turning point of the main flow channel in the strata on top of Ordovician can be used to confirm the thickness of filled water-resisting lavers.

Coherent Spanwise Structures in Turbulent Boundary Layer over Drag-Reducing Riblets

The time series of velocity vector fields and their statistics in the turbulent boundary layer(TBL)over riblets and smooth plate were measured by utilizing a time-resolved particle image velocimetry(TR-PIV)system. The mean velocity profiles of the TBL were compared in the case of 0.13 m/s(the riblets with dimensionless peakto-peak spacing being approximately s?≈21)and 0.19 m/s( s?≈28)for these two kinds of plates, respectively. Two kinds of drag-reducing velocity profiles were illustrated and analyzed. Then the spatial topologies of the physical vorticity for the coherent spanwise structures were detected and extracted at the fourth scale by utilizing an improved quadrant splitting method(IQSM). Results revealed that nearly 6.17%, and 10.73%, of a drag reduction was separately achieved over the riblets surface. Besides, it was visualized that the drag-reduction was acquired by the riblets influencing the bursting ejection(Q2)and sweep(Q4)events of the coherent spanwise vortex structures, the Q4 events in particular. Based on such two drag-reducing cases of the riblets, lastly, a simplified KelvinHelmholtz-like linear instability model proposed initially by García-Mayoral and Jiménez(2011)has been discussed. It is still difficult to establish with certainty whether the observed phenomena, the appearance of coherent spanwise structures found at around or below y?≈20 in both cases of s?≈21 and s?≈28 and their topological changes, were consequences or causes of the breakdown of the viscous regime. We prefer to suggest that the interactions between those structures and the riblets, which contain the coherent spanwise structures extending toward the wall and penetrating into the riblet grooves, are the root causes.

Advances in efficient electrocatalysts based on layered double hydroxides and their derivatives

The explore and development of electrocatalysts have gained significant attention due to their indispensable status in energy storage and conversion systems, such as fuel cells, metal–air batteries and solar water splitting cells. Layered double hydroxides（LDHs） and their derivatives（e.g., transition metal alloys, oxides, sulfides, nitrides and phosphides） have been adopted as catalysts for various electrochemical reactions, such as oxygen reduction, oxygen evolution, hydrogen evolution, and COreduction, which show excellent activity and remarkable durability in electrocatalytic process. In this review, the synthesis strategies, structural characters and electrochemical performances for the LDHs and their derivatives are described. In addition, we also discussed the effect of electronic and geometry structures to their electrocatalytic activity. The further development of high-performance electrocatalysts based on LDHs and their derivatives is covered by both a short summary and future outlook from the viewpoint of the material design and practical application.

面向双模态红外图像差异的拟态融合方法

针对传统融合方法无法根据双模态红外图像差异特征的不同选择有效的融合策略的问题,提出了一种面向红外光强与偏振图像差异的拟态融合方法。首先计算图像特征差异度对差异特征进行粗筛,制定主差异特征类型的选取规则来确定图像组的主差异特征;然后构造特征融合度,以建立差异特征与拟态变元集中各层变元的映射,确定变元分层结构;最后在变元分层结构选择主差异特征类型的各层变元,比较不同拟态结构变元组合时差异特征的特征融合度,确定其最大值占比最高的拟态结构,形成变体。实验结果表明,经主观分析本文方法结果的视觉效果比对比方法结果的效果更优;经客观评价本文方法结果均为有效融合,因此本文方法实现了对融合策略的自适应选择并提高了图像的融合质量。

Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa\-2Cu\-3O\-7, LaBaCu\-2O\-5, La\-4BaCu\-5O 12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H\-2_TPR. It was found that their structures were layered ABO\-3 perovskite structure and they were the active catalysts for the NO reduction by CO. The existance of Cu 3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

水下高压抗润湿V型槽分级铜纳米线簇超疏水表面的减阻研究

针对水下减阻超疏水表面气层稳定性差的问题,提出了在金属铜基底上使用两步电化学沉积法,制备了一种具有V型槽结构、区室化簇状结构和微纳分级结构的铜纳米线超疏水表面,进行了水下高压气层稳定性测试和减阻测试。结果表明,该表面最高可在0.45 MPa水压下维持76%的未润湿区域。同时,该表面在平板流变仪层流减阻测试中可取得高达56%的减阻率,具有优异的减阻性能。V型槽分级铜纳米线簇超疏水表面兼具水下高压气层稳定性和减阻效果,可应用到实际船舶航行领域,为解决超疏水表面减阻应用的瓶颈问题提供方案。

消防员灭火防护服减层结构及其热防护性能评价

介绍了消防员灭火防护服减层结构的实现方式,运用国内外不同的热防护性能评价方法,对标准4层组合面料及3层、2层减层结构组合面料进行评价,并采用热人仪测试不同组合面料制成的灭火防护服的防护效果。结果表明,3层和2层减层结构组合面料能达到标准4层组合面料的性能,满足消防员灭火防护服要求,符合轻质化发展趋势。

六线钢箱叠合拱桥减振降噪方案研究

北京铁路枢纽丰台站改建工程高架层采用平层六线钢箱叠拱桥跨越北京西四环路。桥梁位于北京都市区,采用全钢结构,且桥上运行六线铁路,列车通过频繁,须开展结构降噪研究。基于统计能量分析法进行结构噪声的预测,得到桥梁附近不同位置的A计权声压级,本桥在列车通过时,声压级为62.0~78.9 dB(A),结构辐射噪声突出,随着距线路中心线的距离增加,结构辐射噪声衰减明显。桥梁各部分辐射的声压级大小规律为纵梁腹板>桥面板>纵梁下翼缘板。同时提出了采用约束阻尼层降低结构噪声的方案,桥梁敷设约束阻尼层后,场点噪声最多可降低4.3 dB(A),结构噪声降低了一半以上的能量,降噪效果明显。

On the drag reduction mechanism of hypersonic turbulent boundary layers subject to heated wall blowing

Turbulence drag reduction is of great significance for the range increase of hypersonic flight vehicles.The proposed velocity-temperature coupling control method(Liu et al,Phys Rev Fluids 6:044603,2021)is further extended to the hypersonic turbulent boundary layer.Direct numerical simulation results of four comparative cases show that the heated wall blowing achieves a drag reduction rate of 10.58%,which is about the sum of wall blowing(5.27%)and wall heating(6.35%).By evaluating the control efficiency,however,it is found that heated wall blowing is not as good as wall blowing and cannot obtain net energy saving rate.The modified FIK decompositions of skin friction coefficient indicate that the cliffy decrease of the mean convection term is the primary contribution for the drag reduction.Effects of the proposed control measure on turbu-lence statistics and coherent structures are also analyzed.Streamwise vortex is found to be away from the wall,thus leading to a lower friction drag.

Tomographic PIV investigation on coherent vortex structures over shark-skin-inspired drag-reducing riblets

Nature has shown us that the microstructure of the skin of fast-swimming sharks in the ocean can reduce the skin friction drag due to the well-known shark-skin effect.In the present study,the effect of shark-skin-inspired riblets on coherent vortex structures in a turbulent boundary layer（TBL） is investigated.This is done by means of tomographic particle image velocimetry（TPIV） measurements in channel fl ws over an acrylic plate of drag-reducing riblets at a friction Reynolds number of 190.The turbulent fl ws over drag-reducing riblets are verifie by a planar time-resolved particle image velocimetry（TRPIV） system initially,and then the TPIV measurements are performed.Two-dimensional（2D） experimental results with a dragreduction rate of around 4.81% are clearly visible over triangle riblets with a peak-to-peak spacing s＋of 14,indicating from the drag-reducing performance that the buffer layer within the TBL has thickened;the logarithmic law region has shifted upward and the Reynolds shear stress decreased.A comparison of the spatial topological distributions of the spanwise vorticity of coherent vortex structures extracted at different wall-normal heights through the improved quadrant splitting method shows that riblets weaken the amplitudesof the spanwise vorticity when ejection（Q2） and sweep（Q4） events occur at the near wall,having the greatest effect on Q4 events in particular.The so-called quadrupole statistical model for coherent structures in the whole TBL is verified Meanwhile,their spatial conditional-averaged topological shapes and the spatial scales of quadrupole coherent vortex structures as a whole in the overlying turbulent fl w over riblets are changed,suggesting that the riblets dampen the momentum and energy exchange between the regions of near-wall and outer portion of the TBL by depressing the bursting events（Q2 and Q4）,thereby reducing the skin friction drag.

Coordinating optimization-based sliding mode variable structure control for electro-hydraulic servo system

A sliding mode variable structure control （SMVSC） based on a coordinating optimization algorithm has been developed. Steady state error and control switching frequency are used to constitute the system performance indexes in the coordinating optimization, while the tuning rate of boundary layer width （BLW） is employed as the optimization parameter. Based on the mathematical relationship between the BLW and steady-state error, an optimized BLW tuning rate is added to the nonlinear control term of SMVSC. Simulation experiment results applied to the positioning control of an electro-hydraulic servo system show the comprehensive superiority in dynamical and static state performance by using the proposed controller is better than that by using SMVSC without optimized BLW tuning rate. This succeeds in coordinately considering both chattering reduction and high-precision control realization in SMVSC.

船式拖拉机气层减阻结构设计研究

针对船式拖拉机水田泥浆环境行驶阻力问题,展开船底气层减阻方法研究,设计了三角形、矩形和弧形3种不同肋条结构的船底,并通过仿真方法对其减阻效果和气层稳定性进行了深入分析。研究结果表明:气层减阻方法能有效降低船式拖拉机在泥浆环境中的行驶阻力,肋条结构船底能有效保持船底气层覆盖稳定性。其中,三角形肋条结构船底减阻效果较好,绝对减阻率为23.4%,且船底气层稳定性较好;在横倾角为3°时,气层覆盖率值可达到92%,绝对减阻率为14.7%。

含周期声学黑洞梁的板架结构振动特性

声学黑洞结构通过使结构厚度按幂率渐变,改变结构阻抗从而调控弯曲波在结构中的波长和波速,可实现能量在黑洞区域的聚集和耗散。目前关于声学黑洞结构的研究主要是针对嵌入式声学黑洞,基于周期声学黑洞结构在部分频带良好的减振特性,将带阻尼层的周期声学黑洞梁贴敷在薄板上,提升薄板的减振效果并起到加强板刚度的作用。采用有限元法研究带周期声学黑洞梁的板架结构的减振效果,并将其基于敷设阻尼层和黑洞梁材料进行对比分析。结果表明,含声学黑洞梁能明显削弱振动速度传递响应,较好抑制板的振动;敷设阻尼层能增强对板减振效果,且适当增加黑洞梁数量能提升结构抑振性能;钢质梁较铝质梁刚度更大,能进一步增加板架结构的抑制带宽和增强抑制效果。

光学天线支撑结构自由阻尼层减振技术研究

为了提高光学天线在微振动环境下的动力学特性,优化光学系统的成像质量,可以将自由阻尼层喷涂在次镜支撑薄梁的表面来达到减振降噪的目的。首先通过Zemax以及Minitab确定微振时次镜离焦对成像质量的影响,在此基础上分析了自由阻尼层减振的原理并在时域上对次镜的离焦量进行了数学建模。其次,通过Ansys进行瞬态动力学分析,提取时域上次镜的离焦量后用Matlab进行曲线拟合并与所得数学模型的曲线进行对比。分析结果表明,在0.2 g量级的正弦扰动下,铝合金制光学天线支撑结构表面喷涂0.5 mm厚的NiCrAlY自由阻尼层材料时,光学天线最大离焦量降低了21.9%,有效地提高了光学系统的抗振特性和成像质量。

竹单层顺纹拉伸性能测试与分析

竹材中纤维束密度从竹黄到竹青沿径向逐层增加,为了获得竹材任意单层的顺纹拉伸性能,基于竹材的层合特性,提出从竹青、竹黄两面逼近的削减法。从竹青、竹黄两侧按一定厚度依次削减至竹片中心层以获得不同厚度的测试试件,并测得其顺纹拉伸性能。研究建立竹单层与削减后试件的拉伸力学关系模型,获得相应竹单层的顺纹弹性模量及拉伸强度。通过对毛竹顺纹拉伸试验及计算分析,获得了沿径向弹性模量、拉伸强度的数学表达式;各单层的弹性模量与拉伸强度的计算式分别为E=5.86+34.02/[1+(x/1.34)^(2.21)]和σ=86.21+505.2/[1+(x/1.34)^(2.19)]。结果表明:毛竹的各层力学性能从竹青层至竹黄层逐渐递减;单层计算式误差随分层数增加而减小,当取单层厚度为0.5 mm(16等分)时,其竹材弹性模量与拉伸强度计算值与试验值的误差分别为2.41%,4.26%。本研究获得了毛竹顺纹弹性模量及拉伸强度沿径向的变化规律,对竹单层计算精度高,为竹材力学性能分析及利用提供了一种有效的方法。

含主动约束阻尼悬臂梁两种减振机理的模拟

以部分贴敷主动约束阻尼(active constrained layer damping,简称ACLD)悬臂梁为对象,研究了其所包含的两种减振机理的模拟方法。首先,通过分析ACLD结构的受力及变形,描述了ACLD减振中所包含的黏弹性层剪切耗能和压电层反相阻滞作用两种减振机理;其次,将黏弹性剪切变形体现在形函数中,再结合压电方程与力学公式推导出压电阻滞力,创建了包含两种减振机理的ACLD处理复合梁的动力学模型;最后,通过组建的ACLD悬臂梁减振实验系统对仿真分析结果进行了验证,同时对比分析了仅包含被动约束阻尼或压电反相阻滞单一减振机制以及ACLD处理时复合梁的时域响应。结果表明:仿真计算与实验值的最大偏差为18.6%,证明了所创建的包含两种减振机理分析模型的合理性;ACLD由于同时包含两种减振机理,其减振效果要优于单一的振动控制方法。

大别造山带地壳泊松比结构与超高压变质带——来自宽角反射与近垂直反射剖面的启示

综合宽角反射、近垂直反射的探测结果和有关地质资料,对大别造山带地壳结构和超高压变质带研究显示:大别造山带地壳具有层块结构特征。沿安义—庄墓剖面,上地壳有7个弹性块体,中地壳有5个,下地壳有4个。扬子与华北地块的主缝合带是超高压变质带,扬子地块与大别造山带的现今分界线是与郯庐断裂相交的太湖—马庙断裂,磨子潭—晓天断裂是大别造山带的北界,北淮阳构造带呈楔状向下插入,它与华北地块的分界是肥中断裂。郯庐断裂在中、上地壳近于直立,下地壳向西倾斜。超高压变质带的厚度为5～7km,产状向北插入到北大别块体之下,折返过程是构造就位,不是大别山的均匀抬升,折返的主运动面是水吼—五河高温剪切带。

沟槽面湍流边界层减阻的TRPIV测量

采用高时间分辨率粒子图像测速技术对沟槽壁面平板湍流边界层速度矢量场的时间序列及其统计量进行了实验测量,讨论了在同一来流速度下沟槽壁面对平均速度剖面﹑雷诺切应力及湍流强度的影响.用流向速度分量的多尺度空间局部平均结构函数辨识壁湍流多尺度相干结构,用条件采样和相位平均技术提取壁湍流多尺度相干结构喷射和扫掠事件的脉动速度、展向涡量的二维空间拓扑形态.结果表明,与同材料光滑壁面对比,沟槽壁面实现了10.73%的摩阻减小量;沟槽壁面湍流边界层湍流强度及雷诺切应力皆比光滑平板湍流边界层对应统计量小,说明沟槽壁面有效降低了湍流边界层内流体的脉动.通过比较壁湍流相干结构猝发事件各脉动速度分量与展向涡量的空间分布特征,肯定了沟槽壁面的减阻效果,发现沟槽壁面通过抑制相干结构猝发事件实现减阻.

低幅度构造油藏富集主控因素及成藏模式——以红河油田延安组油藏为例

为明确红河油田延安组低幅度构造油藏富集主控因素及成藏模式,在对油气藏类型及分布规律研究的基础上,采用油气分布与成藏条件叠合分析方法,对延安组成藏、主控因素及模式进行了研究。结果表明,红河油田延安组油气主要分布在差异压实作用形成的低幅度构造中。其成藏及主控因素为:有效烃源岩是油气富集的基础;分流河道砂体为油气聚集优质储层;油源断层组成优势输导通道;低幅度构造是油气富集的必要条件;有油源断层沟通发育的圈闭组成富集部位。最终根据断层沟通的圈闭类型建立了2种成藏模式:断层断开有效背斜圈闭,直接沟通储层及有效圈闭,富集成藏,或断层沟通储层边部,油气在浮力作用下向高处运移成藏;断层断开鼻隆圈闭,断层断开位置不在有效圈闭内,断层沟通储层边部,油气在浮力作用下向高处运移成藏。