Dislocation avalanches, strain bursts, and the problem of plastic forming at the micrometer scale

Under stress, many crystalline materials exhibit irreversible plastic deformation caused by the motion of lattice dislocations. In plastically deformed microcrystals, internal dislocation avalanches lead to jumps in the stress-strain curves (strain bursts), whereas in macroscopic samples plasticity appears as a smooth process. By combining three-dimensional simulations of the dynamics of interacting dislocations with statistical analysis of the corresponding deformation behavior, we determined the distribution of strain changes during dislocation avalanches and established its dependence on microcrystal size. Our results suggest that for sample dimensions on the micrometer and submicrometer scale, large strain fluctuations may make it difficult to control the resulting shape in a plastic-forming process.     

Dislocation mean free paths and strain hardening of crystals

Predicting the strain hardening properties of crystals constitutes a long-standing challenge for dislocation theory. The main difficulty resides in the integration of dislocation processes through a wide range of time and length scales, up to macroscopic dimensions. In the present multiscale approach, dislocation dynamics simulations are used to establish a dislocation-based continuum model incorporating discrete and intermittent aspects of plastic flow. This is performed through the modeling of a key quantity, the mean free path of dislocations. The model is then integrated at the scale of bulk crystals, which allows for the detailed reproduction of the complex deformation curves of face-centered cubic crystals. Because of its predictive ability, the proposed framework has a large potential for further applications.     

土地规模化流转的意愿、实践与逻辑分析——基于河南省H县的调查

不同的话语体系说明土地规模化流转的可能以及预期的后果,但是规模化流转的话语体系是否适合当前的农村现实?笔者以河南省H县村庄土地流转的情况为经验材料,考察了规模化土地流转能够达成的条件,分析出土地流转后形成的相关后果,认为土地大规模流转的制约性因素较大,尤其是乡村治权弱化甚至丧失后土地流转的利益分配失衡,土地规模化流转需...     

基于农机农艺融合的三七机械化 精密播种系统研究

以野标准化、规模化、工程化冶的现代农业发展思路,探索三七现代化种植模式。引入系统思想,将三七机 械化精密播种系统分为三七工厂化育苗农艺、机械化播种流程及标准、精密播种技术3 个子系统,从农机农艺融合 的视角,通过分析各系统的方法及技术集成,研究3 个子系统的统筹协调和相互适应性;对包衣三七种子的物理机 械特性（三轴尺寸、千粒重、孔隙率、休止角、滑动摩擦角）进行测定,得到包衣种子的3 轴尺寸平均值分别为6.20, 5.82,5.46 mm,千粒重165.86 g孔隙率32%,休止角平均值23.2毅,在不锈钢板、铁皮板、塑料板上的滑动摩擦角平均 值分别为21.6,27.65,29.5。     

贵州冬闲田马铃薯覆黑膜栽培模式研究

以早熟马铃薯品种费乌瑞它为材料,研究起垄黑膜覆盖栽培模式对冬马铃薯物候期、株高、叶面积及产量的影响效果。结果表明:与未覆膜对照相比,黑膜覆盖栽培模式可以提早出苗时间、现蕾期和成熟期,但对生育期影响不明显;对现蕾期株高、叶面积影响显著,叶面积可增加25.34%;对冬马铃薯的总产量及大薯产量影响极显著,总产量增产33.34%,大薯产量增产20.15%。该栽培模式是一种值得在西南地区冬闲田马铃薯生产中进行较大面积的示范推广的模式。     

泡塑富集ICP-MS测定土壤中痕量金(英文)

The aim of this study is to determine the trace amount of gold in soil sample using plastic foam enrichment-ICP-MS method.The national standard reference materials including GAu-2,GAu-10,GAu-11 and GAu-13 were used for parallel determination by ICPMS.The results showed that the method performed well in detection limit,precision and accuracy,indicating that the plastic foam enrichment-ICP-MS method could be used to determine the trace amounts of gold in soil sample.     

Determination of Trace Amounts of Gold in Soil Sample Using Plastic Foam Enrichment-ICP-MS Method

The aim of this study is to determine the trace amount of gold in soil sample using plastic foam enrichment-ICP-MS method.The national standard reference materials including GAu-2,GAu-10,GAu-11 and GAu-13 were used for parallel determination by ICPMS.The results showed that the method performed well in detection limit,precision and accuracy,indicating that the plastic foam enrichment-ICP-MS method could be used to determine the trace amounts of gold in soil sample.     

泡塑富集ICP-MS测定土壤中痕量金(英文)

The aim of this study is to determine the trace amount of gold in soil sample using plastic foam enrichment-ICP-MS method.The national standard reference materials including GAu-2,GAu-10,GAu-11 and GAu-13 were used for parallel determination by ICPMS.The results showed that the method performed well in detection limit,precision and accuracy,indicating that the plastic foam enrichment-ICP-MS method could be used to determine the trace amounts of gold in soil sample.     

方钢管混凝土柱-钢梁外隔板节点三维非线性有限元研究

采用通用有限元软件Ansys8.0,对一种新型方钢管混凝土节点进行三维非线性有限元数值模拟和不同强度等级的填充混凝土对节点受力性能影响分析,并与大尺度模型实验结果进行对比.分析结果表明:填充混凝土强度对节点的水平承载力有较大影响,随着混凝土强度的提高,节点的水平承载力增加;节点区域应力分布均匀.考察了不同钢管混凝土柱轴压比对节点力学性能地影响.结果表明:梁端先出现塑性铰,柱的刚度远大于两梁的刚度;节点区域混凝土应力分布均匀,没有出现压溃现象.有限元分析结果与模型试验结果拟合较好,证明了新型节点的可行性和合理性,有一定的工程应用价值.     

纳米单晶与多晶铜薄膜力学行为的数值模拟研究

通过对不同温度下单晶薄膜的拉伸性能的分子动力学模拟,从微观角度揭示了温度效应对材料性能的影响. 结果表明温度效应对材料的变形机理影响很大.0K温度下由于缺乏热激活软化的影响, 粒子运动所受到的阻碍较大, 薄膜的强度较高, 塑性变形主要来自于粒子的短程滑移.温度升高,粒子的热运动加剧,屈服强度降低, 塑性变形将主要来自于大范围的位错长程扩展.多晶薄膜的模拟结果表明, 虽然其晶粒形状较为特殊, 但是它仍然遵循反Hall-Petch关系.在模拟过程中,侧向应力最大值比拉伸方向应力的最大值滞后出现.位错只会从晶界产生并向晶粒内部传播,晶粒间界滑移是多晶薄膜塑性变形的主要来源.     

野生淡黄花百合鳞片的扦插繁殖技术研究

为了建立务川野生淡黄花百合鳞片的扦插繁殖技术体系,以野生淡黄花百合球茎鳞片为材料,探讨不同层次鳞片、不同湿度和不同NAA浓度对淡黄花百合鳞片扦插繁殖成活率、腐烂率、繁殖系数、平均根数及平均根长的影响。结果表明:采用淡黄花百合中层鳞片,将花盆口用塑料薄膜密封进行保湿扦插繁殖的效果最好,成活率达86.66%,增殖系数为1.85;仔球形成后揭开塑料薄膜降低湿度,以利小鳞茎生根,也可在扦插前用50mg/L浓度的NAA处理鳞片12h以促进壮苗和提高种球质量。     

林用钢拱架塑料大棚的结构设计研究

根据林区育苗生产的需要,本文对塑料大棚棚型的选择,材料及结构尺寸的确定进行了设计计算。并对试制生产的棚体结构进行了野外生产考验。认为该设计方案是合理的,其强度、刚度及稳定性均满足要求。     

大庆棚室产业发展现状与建议

为促进大庆棚室经济健康有序发展,由大庆市专家委员会牵头,相关涉农院所和部门组成联合调研组,采取走访、问卷、座谈、听取汇报等形式,对大庆棚室产业发展现状进行调研。结果表明:经过3a的快速发展,大庆在棚室建设、生产经营和技术服务等方面取得一定成绩,冬淡季果蔬自给率明显提高,市场营销体系初步形成。与此同时,存在着因棚室规模发展过快造成的空置、有效利用率低,棚室经济高效性尚未显现,中介服务作用相对较弱,品牌不足,产后服务欠缺等方面的问题。大庆市棚室经济发展还处于起步阶段,要把棚室经济作为强势产业加以培育,实现生产科技化、管理系统化和经营规模化,以保证棚室经济健康可持续发展。     

华北山石区落叶松混交林空间结构研究

为指导落叶松混交林抚育经营,对华北山石区落叶松混交林林分组成和空间分布格局进行研究。结果表明:样地A的总密度和总断面积均最小,为1 007株·hm~(-2)和24.446 4 m2·hm~(-2),样地C最大,为1 525株·hm~(-2)和47.280 2m2·hm~(-2),样地B居中;华北落叶松在样地A中胸径最大为18.6cm,样地B最小为18.1cm,而树高则相反。样地A的平均角尺度为0.358 8,均匀分布,林分处于较为稳定的状态,林分中落叶松为均匀分布状态;样地B平均角尺度为0.523 8,为团状分布,林分中落叶松为均匀分布;样地C的角尺度为0.508 5,为随机分布,林分中落叶松为均匀分布,云杉处于团状分布状态,五角枫和花楸处于随机分布状态。样地A直径大小比数的平均值为0.333 1,林分中落叶松和白桦的大小比数相差不大,表明林分空间分化程度比较小,两种树种的优势度相差无几;样地B的大小比数为0.487 2,林分中落叶松处于优势,而蒙古栎、山杨、五角枫和花楸处于劣势,其它树种处于中庸状态,而且各树种的大小比数有一定的差别;样地C的大小比数为0.484 5,云杉和华北落叶松处于绝对优势;样地A混交度为0.47,属于重度混交;样地B混交度为0.37,混交程度比较低下;而样地C混交度为0.83,说明杉落针阔混交林树种组成较多样化,结构更加稳定,在空间利用上也更加充分。     

居民旅游扶贫效应感知、参与能力及参与意愿测量量表的编制

在梳理相关学者对旅游扶贫效应感知的研究成果的基础上,通过深度访谈、专家意见和实证调研,运用探索性因子分析和验证性因子分析,构建了居民旅游扶贫效应感知、参与能力及参与意愿的测量量表。该量表包括7个维度共计33个题项。结果表明该量表具有较高的可靠性,可用于对居民旅游扶贫效应感知及参与行为的评估和测度。     

Functional box-counting and multiple elliptical dimensions in rain

Many physical systems that have interacting structures that span wide ranges in size involve substantial scale invariant (or scaling) subranges. In these regimes, the large and small scales are related by an operation that involves only the scale ratio. The system has no intrinsic characteristic size. In the atmosphere gravity causes differential stratification, so that the scale change involves new elliptical dimensions (d(el)). Fields that are extremely variable, such as rain, involve multiple scaling and dimensions that characterize the increasingly intense regions. Elliptical dimensional sampling and functional box-counting have been used to analyze radar rain data to obtain both the multiple dimensions of the rain field and the estimate d(el) = 2.22 +/- 0.07.     

吉林林区泥炭质土物理力学性质测定

对吉林区泥炭质土的物理力学性质进行试验测定，测定了泥炭质土的三相比例指标，并根据三个指标导出了几个其它物理性质指标。测定了样土的液塑限，计算出了出了液塑性指数，通过压缩试验测定了样土沉降量，计算出了压缩系数和压缩模量。通过样土抗剪试验确定了样土抗剪强度参数，计算出了样土最大承载力，这些基本参数的测定，为吉林林区运材道路路基设计的施工提供了依据。     

Deformation of (Mg,Fe)SiO3 post-perovskite and D' anisotropy

Polycrystalline (Mg(0.9),Fe(0.1))SiO3 post-perovskite was plastically deformed in the diamond anvil cell between 145 and 157 gigapascals. The lattice-preferred orientations obtained in the sample suggest that slip on planes near (100) and (110) dominate plastic deformation under these conditions. Assuming similar behavior at lower mantle conditions, we simulated plastic strains and the contribution of post-perovskite to anisotropy in the D' region at the Earth core-mantle boundary using numerical convection and viscoplastic polycrystal plasticity models. We find a significant depth dependence of the anisotropy that only develops near and beyond the turning point of a downwelling slab. Our calculated anisotropies are strongly dependent on the choice of elastic moduli and remain hard to reconcile with seismic observations.     

载体对26℃条件下牛粪厌氧处理性能的影响

在26℃低温条件下,采用两步发酵法观察玻璃纤维、尼龙纤维和岩棉对牛粪厌氧处理沼气产量、pH值、总COD去除率的影响。结果表明,添加载体对流动发酵期间的pH值没有显著影响;岩棉载体由于脱落导致较低的沼气产量,玻璃纤维和尼龙纤维载体对沼气产量的影响主要出现在发酵的16～30d,其沼气产量分别比对照提高13.30%和12.75%(P<0.05),在发酵的24～30d,添加玻璃纤维和尼龙纤维使总COD去除率分别提高10.86%和8.83%(P<0.05)。在低温条件下,采用两步的流动发酵可以在一定程度上提高反应器的沼气产量。     

云冷杉林和针阔叶混交林a-多样性的尺度效应与分形特征

具有环境梯度或小尺度生境异质性的群落,a 多样性在不同尺度及不同空间位置上的测定结果将存在差异。基于甘肃省莲花山国家级自然保护区 2条长 420 m、宽 10 m样带的群落调查数据,采用分形理论和方法研究了云冷杉林和针阔叶混交林群落 a 多样性测度随空间尺度变化的效应,以及 a 多样性测度与取样尺度之间的分形关系。结果表明:1)随着取样尺度逐步扩大,云冷杉林和针阔叶混交林群落物种丰富度指数和Shannon 指数值先急剧增长后趋于平稳,表现出一定范围内尺度对样带 a 多样性测度具有强烈影响。综合物种丰富度指数和Shannon 指数尺度变化曲线的估计,云冷杉林样带 a 多样性研究比较适宜的取样尺度为 60 m,而针阔叶混交林样带为 90 m,即云冷杉林样带上比较适宜的取样尺度明显小于针阔叶混交林样带;2)针阔叶混交林样带上 a 多样性与取样尺度之间的分形关系比云冷杉林样带更趋于多变,表明针阔叶混交林物种组成的空间异质性高于云冷杉林。