Evidence for electronic and ionic limitations at the origin of the second voltage plateau in nickel electrodes,as deduced from impedance spectroscopy measurements

The second plateau occurring during the reduction of the nickel oxyhydroxide electrode (NOE) was studied by impedance spectroscopy on a cell with a pasted electrode prepared from commercial undoped β-Ni(OH)₂. Measurements were performed at diverse states of reduction and a large variation of impedance upon the transition from the first to the second plateau was observed. This variation mainly takes place at low frequencies and is hence related to ionic diffusion. We observed that the impedance becomes more capacitive on the second plateau meaning that the proton diffusion is limited. These results would be consistent with the gradual formation of an insulating layer of nickel hydroxide at the interface between the NOE and the electrolyte upon reduction. Once this layer becomes compact the ionic diffusion would be hindered and forced to occur through this layer, which could explain the voltage drop observed.     

室温下20钢高周次单轴棘轮行为的实验研究

通过对20钢的单轴应变控制循环和应力控制循环实验研究, 揭示了20钢在室温下的循环变形特性, 讨论了材料的循环软/硬化特性和材料的屈服平台以及平均应力、应力幅值和应力比对材料高周次棘轮行为的影响. 研究表明: 20钢表现出弱的、与应变幅值相关的循环硬化特性; 其棘轮行为依赖于平均应力、应力幅值和应力比的大小, 在高应力水平时的高周次循环后期, 棘轮变形会出现<再次增长的现象; 材料的屈服平台对棘轮行为有明显的影响, 在对20钢的棘轮行为进行本构描述时需要加以合理考虑.     

Mean out-of-plane dynamic plateau stresses of hexagonal honeycomb cores under impact loadings

Double-walled hexagonal honeycomb cores (DHHCs) are important cushioning materials and their out-of-plane impact properties depend upon their configuration parameters and impact velocities. In this paper, the reliable finite element (FE) model by using ANSYS/LS-DYNA was designed to investigate the relations between configuration parameters of DHHCs and their out-of-plane dynamic plateau stresses at the impact velocities from 3 to 350 m/s. FE simulations demonstrate, when all configuration parameters are kept constant, mean out-of-plane dynamic plateau stresses are related to impact velocities by conic curves. For a given impact velocity, mean out-of-plane dynamic plateau stresses are related to the ratios between cell wall thickness and edge length and to edge length ratios by power laws. There are complicated relations between mean out-of-plane dynamic plateau stresses and expanding angels, which are discussed in detail. Many empirical expressions on mean out-of-plane dynamic plateau stresses of DHHCs are suggested.     

黄土高原水土流失地区粮食生产潜力与发展主要途径

农业是国民经济的基础,粮食是基础的基础。黄土高原地区是中华民族文化的发祥地,也是我国历史上早期农牧业生产区和政治中心。粮食是谝我人民赖以生存的最基本产业。探索其发展规律,分析其障碍因素,寻求其发展潜力,采取“一靠政策,二靠科技,三靠投入,四靠保护,五靠工作”的战略措施,对同类地区的粮食发展具有重要意义。     

On the initial stage of plastic deformation of metal alloys

Plastic deformation has been studied for a range of metal alloys using speckle interferometry. It has been found that, in the initial stage, the process of plastic flow occurs by the propagation of a deformation front, which divides the deforming material into two regions differing with respect to the material’s state. The flow exhibits regular features that can be described in terms of a self-excited wave process manifesting itself in an active medium under external mechanical action.     

MH-Ni电池1.2 V放电电压平台的电化学研究

MH-Ni电池放电电压平台是一个十分复杂的问题,涉及电极材料、制作工艺及添加剂等多种因素.由于MH-Ni电池工作机理是基于电化学反应过程,因此这些因素的影响最终会通过电化学反应反映到电池的放电性能上.从电化学角度利用暂态测试技术--电流阶跃法对MH-Ni电池放电过程中影响电压变化的因素进行了研究,初步弄清了造成MH-Ni电池1.2 V电压平台衰减的电化学原因.结果表明,MH-Ni电池的重要电化学参数--欧姆内阻与放电电压平台有着重要关系.不同欧姆内阻的MH-Ni电池,其1.2 V放电电压平台衰减规律不尽相同.对于欧姆内阻较小的电池,1.2 V放电电压平台主要由非欧姆极化控制;欧姆内阻较大的电池,1.2 V放电电压平台主要由欧姆极化控制;欧姆内阻介于二者之间时,1.2 V放电电压平台由欧姆极化和非欧姆极化联合控制.研究中还发现,放电进入末期时,MH-Ni电池的非欧姆极化急剧上升导致电池电压迅速下降到放电截止电压,使电池终止放电.     

青藏羌塘地区隐伏裂陷槽的识别及油气远景

介绍了青藏高原羌塘盆地和措勤盆地的深部磁场特征,用隐伏裂陷槽的观点分析了这些特征。结合ＭＴ电性层深度图和中生界沉降带的厚度,将南北向正磁异常带(东经89°－90°)解释成晚古生代隐伏裂陷槽。该裂陷槽对北羌塘坳陷中生代的构造单元、沉积以及油气组合有很重要的控制作用。     

冲击压缩载荷作用下杨木的力学性能研究

通过SHPB动态压缩实验,对杨木在高应变率条件下的力学特性进行了研究。基于一维应力波理论的分析表明,尽管杨木相比于金属压杆具有较低的波阻抗,其SHPB动态压缩实验中试样两端的应力均匀性条件仍可以得到满足,而不需要进行入射波整形。通过在透射杆上使用半导体应变片,可以获得具有较高信噪比的透射波信号。结合杨木的准静态实验结果发现,其应力-应变曲线具有多孔材料的典型特征。轴向试样具有Ⅱ型吸能结构特征,失效应力和平台应力都具有应变率敏感性,其平台应力的敏感性稍弱;弦向试样具有Ⅰ型吸能结构特征,没有明显的失效强度,其平台应力具有应变率敏感性,与通常的Ⅰ型吸能结构相比存在一定差异。通过对实验数据的拟合,发现应变率对杨木失效强度的影响符合对数率。     

基于适应高原环境的武器装备防护包装设计方法探讨

针对典型高原环境特点及其对武器装备的影响,从设计技术要求确定、总体方案选用、功能特性设计和试验设计验证等方面探讨了如何设计适用、可靠的多功能综合防护包装,以提高武器装备的高原环境适应性。     

高原地区碳酸利多卡因在剖宫产术中的临床应用

目的:比较在高原地区不同麻醉方法用于剖宫产手术的麻醉效果及安全性。方法:选择60例行剖宫产手术患者,ASA I～II级, 随机分为2%盐酸利多卡因组(I组, 选择L1～2间隙行硬膜外穿刺向上置管3～4cm), 1.73%碳酸利多卡因组(II组, 麻醉穿刺方法同I组)和0.5%布比卡因重比重溶液组(III组, 选择L3～4间隙穿刺行腰硬联合阻滞)三组。比较三组间麻醉起效时间、麻醉完善时间、麻醉最高平面, 胎儿娩出时间, 记录麻醉对患者血压、心率的影响及患者的不良反应。结果:II组与I组比较麻醉起效快, 麻醉完善时间短, 胎儿娩出时间短;与III组比较对患者心率、血压影响小, 患者不良反应少, 差异有统计学意义。结论:高原地区低氧环境下在剖宫产手术中用碳酸利多卡因行硬膜外麻醉具有麻醉起效快、麻醉完善时间短、效果确切的特点, 而且对患者血流动力学影响小, 不良反应少, 提高了母婴术中安全性,是一种更为安全、可靠的麻醉方法。