非粘性均匀沙群体沉降运动沉速公式的研究

从相对运动的观点出发,将非粘性均匀泥沙群体沉降运动概化为上升水流在悬浮颗粒层内的运动,通过量纲分析和动平衡状态受力分析,建立了泥沙群体沉降运动中阻力系数和雷诺数的表达式,并分别建立了层流区和紊流区均匀沙群体沉速的理论公式,其结构形式与目前常用的经验公式较为一致。应用实测资料对公式进行验证的结果表明,应用该理论公式的计算值与实测值吻合程度较好。同时通过分析讨论,提出了非均匀沙群体沉降速度问题的解决途径。     

小型联合收割机风筛式清选装置的理论研究

对采用离心风扇与单层鱼鳞筛的清选装置进行研究,分析了风筛配合作用下清选物料的受力情况,建立了物料运动的特征界限值公式和运动方程,为设计、使用小型谷物联合收割机上的简易清选装置提供了参考依据．     

Two-fraction model of initial sediment motion in gravel-Bed rivers

The prediction of sediment transport in gravel-bed rivers is essential to the management of land, water, and ecological resources in mountain regions. Dividing the bed sediment into two populations-sand and gravel-permits realistic and useful predictions of the onset of sediment transport. The critical flow initiating grain motion decreases rapidly with sand content over the transition from a gravel-framework bed to a sand-matrix bed. The two-fraction model provides a simple means of forecasting the movement of excess fine sediment supply. The model also helps to explain the development of the abrupt gravel-sand transition commonly observed in natural rivers.     

The onset of turbulence in pipe flow

Shear flows undergo a sudden transition from laminar to turbulent motion as the velocity increases, and the onset of turbulence radically changes transport efficiency and mixing properties. Even for the well-studied case of pipe flow, it has not been possible to determine at what Reynolds number the motion will be either persistently turbulent or ultimately laminar. We show that in pipes, turbulence that is transient at low Reynolds numbers becomes sustained at a distinct critical point. Through extensive experiments and computer simulations, we were able to identify and characterize the processes ultimately responsible for sustaining turbulence. In contrast to the classical Landau-Ruelle-Takens view that turbulence arises from an increase in the temporal complexity of fluid motion, here, spatial proliferation of chaotic domains is the decisive process and intrinsic to the nature of fluid turbulence.     

Coherent sensing of a mechanical resonator with a single-spin qubit

Mechanical systems can be influenced by a wide variety of small forces, ranging from gravitational to optical, electrical, and magnetic. When mechanical resonators are scaled down to nanometer-scale dimensions, these forces can be harnessed to enable coupling to individual quantum systems. We demonstrate that the coherent evolution of a single electronic spin associated with a nitrogen vacancy center in diamond can be coupled to the motion of a magnetized mechanical resonator. Coherent manipulation of the spin is used to sense driven and Brownian motion of the resonator under ambient conditions with a precision below 6 picometers. With future improvements, this technique could be used to detect mechanical zero-point fluctuations, realize strong spin-phonon coupling at a single quantum level, and implement quantum spin transducers.     

螺旋弹簧输送装置技术参数的分析研究

分析了螺旋弹簧输送装置的工作原理、物料在输送过程中的受力状态和运动状态 ,详细研究了各参数对临界转速和物料垂直向上分速度的影响。得出了螺旋弹簧输送装置的临界转速和垂直向上输送速度的理论计算公式 ,以供进一步试验研究     

上海无居民海岛潮间带沉积物粒径特性研究

利用激光粒度仪对上海无居民岛30个表层沉积物样品进行粒度特征分析,研究区域的6个无居民岛的沉积物类型共有5类,其分布为粉砂在九段沙、东风西沙、黄瓜沙和青草沙;砂在青草沙和顾园沙;粉砂质砂在扁担沙和青草沙;砂质粉砂在青草沙;粘土质粉砂在黄瓜沙。其中粉砂类沉积物分布最广。沉积物呈现分选系数差,偏态均为正偏,窄峰型的特征。由于研究区域处于长江口,丰富的流域来沙,特别是大量的细颗粒泥沙为潮滩的建造提供了充裕的物质来源;而复杂的径流、潮流和风浪的作用,则成为了塑造潮滩的重要动力条件。通过绘制Pejurp三角图式显示,无居民岛样品均处于在Ⅲ、Ⅳ动力区,水动力条件总体上较强,粒径较粗。除顾园沙外由海向岸(由低潮滩到高潮滩),水动力逐渐减弱,沉积物颗粒逐渐变细,砂的含量逐渐减少,粘土和粉砂的含量逐渐增多。研究亮点:对上海无居民岛潮间带沉积物进行了粒径特性的分析,结果显示沉积物分布以粉砂为主,分选性差,正偏,呈窄峰型,通过绘制Pejurp三角图式,表明研究区域总体水动力较强,并根据各无居民岛的环境特征分析其不同的沉积动力环境。     

广东湛江高桥红树林湿地沉积柱粒度特征

红树林是一种特殊的生物海岸类型,具有多种生态系统服务功能。以广东湛江高桥红树林湿地为研究区,在英罗湾的湾内和湾口的两片红树林集中分布区,沿水动力梯度,垂直于海岸布设两条样线进行柱状取样,并采用矩值法计算平均粒径、分选系数、偏度和峰度等粒度参数,分析了沉积物在水平和垂直方向上的粒度特征,旨在了解研究区红树林湿地生境演变过程。结果表明:1)沉积物以粉粒和砂粒组分为主,随着红树林发育成熟度和沉积过程,红树林内带和表层样点均呈细化趋势。2)粒度分布曲线可以看出,红树林外带更多受水动力条件的影响,样点沉积过程相似,内带的沉积因水动力条件和生物过程的影响而复杂,但白骨壤纯林的沉积环境相对稳定。3)粒度参数受水动力条件和生物地貌过程影响,空间异质性显著。水平方向上,湾内样线自内带向外表现为平均粒径变小(质地粗化)趋势,湾外样线平均粒径变化趋势性不明显,但有红海榄群落分布的中间带样点的粒度更细;沉积物分选性属于较差到差,频率曲线呈负偏到很正偏,峰度呈平坦到尖锐的分布。垂直方向上,自表层向下平均粒径减小、分选性变差、偏态值增加、峰态增加,反映出林下环境的沉积过程。4)相关性分析表明,粒度参数与不同粒级体积含量相关,平均粒径和峰度参数与黏粒、粉粒含量正相关而与砂粒含量负相关,分选系数和偏度与细颗粒物含量显著负相关。粒度参数之间的相关性表现为平均粒径与峰度正相关,而与分选系数和偏度负相关,分选系数与峰度负相关,偏度与峰度负相关。研究区沉积物的形成过程有多种作用共同参与,红树林的存在改变了海岸的水动力条件而影响沉积过程,研究结果对于了解百年尺度上红树林湿地的生物地貌形成过程具有一定意义。      

平面COUETTE流动的湍流斑研究

湍流斑是近壁剪切流动中的重要现象,它们的生成和发展与流动转捩和湍流的形成密切相关.采用Navier-Stokes方程直接数值模拟和壁面脉冲模型研究平面Cou-ette流动中湍流斑的生成和演化.高精度高分辨率的三维耦合紧致差分格式被用于数值计算.探讨了平面Couette流动中湍流斑的重要特征,包括高频脉动的形成、雷诺应力的产生、扰动的急剧增长和湍流斑形状的变化,特别是流向涡的复杂演化过程.结果表明层流流动中的湍流斑具有湍流流动中一些基本特征.     

Grain boundary-mediated plasticity in nanocrystalline nickel

The plastic behavior of crystalline materials is mainly controlled by the nucleation and motion of lattice dislocations. We report in situ dynamic transmission electron microscope observations of nanocrystalline nickel films with an average grain size of about 10 nanometers, which show that grain boundary-mediated processes have become a prominent deformation mode. Additionally, trapped lattice dislocations are observed in individual grains following deformation. This change in the deformation mode arises from the grain size-dependent competition between the deformation controlled by nucleation and motion of dislocations and the deformation controlled by diffusion-assisted grain boundary processes.     

花后干旱胁迫对大麦子粒碳、氮化合物积累的影响

以防雨池栽的方式研究了干旱胁迫对大麦花后子粒碳、氮化合物积累的影响,结果表明,淀粉和蛋白质沉积生理机制的明显差异是导致干旱胁迫下子粒淀粉沉积降低、蛋白质积累增加的内在因素;子粒形成后期的碳氮代谢互作在竞争和能量方面的差异也对淀粉沉积减少、蛋白质含量增加起一定的作用.     

Replication of apparent nonlinear seismic response with linear wave propagation models

It is necessary to understand ground-motion amplification by sediment, defined as the ratio of ground motions at sediment sites to those at rock sites, to predict seismic loadings for earthquake engineering. At sediment sites, observed weak-motion amplifications from magnitude 3 to 4 aftershocks of the 1994 Northridge earthquake were twice as large as magnitude 6.7 mainshock amplifications. Amplitude-dependent (nonlinear) amplification by sediment is one explanation. However, earthquake simulations with empirical impulse responses and elastic finite-difference calculations with weakly heterogeneous, random three-dimensional (3D) crustal velocity variations show that linear wave propagation can explain observed (apparently nonlinear) sediment responses. Random 3D velocity variations also reproduce the observed log-normal dispersion of peak ground motions. Deterministic wave propagation models are not adequate to quantify the scaling and dispersion of near-source ground motions.     

论粮农的经济利益与生产积极性

本文在分析了当前粮农生产积极性下降的表现及其原因的基础上,对提高粮农生产积极性的对策进行了探讨,提出了以提高粮农经济利益为核心,运用系统论的观点实施综合治理,以稳定和发展粮食生产的观点。     

排沙漏斗应用于自来水供水工程的试验研究

介绍了排沙漏斗在自来水供水工程中的试验研究,特别介绍和分析了排沙漏斗在处理高含沙水流时的截沙率和耗水率,对粒径大于0.075,0.050,0.025,0.010 mm和0.005 mm泥沙的平均截沙率分别达到90.41%,91.78%,90.84%,61.65%和59.64%,而平均排沙耗水量为12.31%.这充分说明了排沙漏斗可以处理极细粒泥沙.     

基于VAR模型的粮食价格指数统计分析

基于VAR模型,对2001～2010年我国粮食价格指数进行实证分析。通过建立VAR模型对粮食价格序列与CPI指数之间动态变化规律及影响机制进行定量分析,并结合脉冲响应函数对短期的未来粮食价格走势进行预测。结果表明：国内未来的粮食价格会有逐步回落的趋势,但仍将维持10%左右的涨幅。     

漏斗式全沙排沙技术在陕西东雷抽黄灌区泥沙治理的成功实践

介绍了黄河第一座排沙漏斗工程的成功运行经验，并对其其原型观测结果进行了分析：对粒径大于0．1，0．05，0．025mm泥沙的平均截沙率分别达到96．58％，81．37％和78．71％，而平均排沙耗水量为7．23％。这一结果充分说明排沙漏斗的截沙率和排沙耗水量等重要指标都远优于过去黄河上普遍采用的条渠或者复合型厢形沉沙池等排沙设施。同时也说明排沙漏斗能有效地排除推移质泥沙，对悬移质泥沙的排除亦非常有效，尤其是为黄河泥沙的治理开辟了一条新途径。     

黄土丘陵第Ⅲ副区典型流域水沙演变过程及其驱动因素分析

流域水沙演变过程是构建区域水土流失模型及评价水土保持措施效益的基础。为探讨气候与下垫面变化对流域水沙变化的影响,以黄土丘陵沟壑区第Ⅲ副区罗玉沟流域为例,采用水文要素累积距平、Mann-Kendall趋势性检验和双累积曲线等方法,分析了1986—2010年间流域水沙关系演变过程及驱动因素,并定量分析了驱动因素的影响。结果表明:1)流域径流量在1993年发生突变,其中1994—2010年(后期)较1986—1993年(前期)不同降水水平年的径流量和输沙量减少率大多超过50%;2)土地利用结构优化可改变流域水沙过程和水沙量,而沟道淤地坝工程的运行改变了水沙搭配关系,使流域单位径流输沙量显著降低;3)降水和土地利用变化对流域径流减少贡献率分别为18.48%和81.52%;降水和土地利用变化对泥沙减少贡献率则分别为27.15%和72.85%。      

Precession of the Earth as the Cause of Geomagnetism: Experiments lend support to the proposal that precessional torques drive the earth's dynamo

I have proposed that the precessional torques acting on the earth can sustain a turbulent hydromagnetic flow in the molten core. A gross balance of the Coriolis force, the Lorentz force, and the precessional force in the core fluid provided estimates of the fluid velocity and the interior magnetic field characteristic of such flow. Then these numbers and a balance of the processes responsible for the decay and regeneration of the magnetic field provided an estimate of the magnetic field external to the core. This external field is in keeping with the observations, but its value is dependent upon the speculative value for the electrical conductivity of core material. The proposal that turbulent flow due to precession can occur in the core was tested in a study of nonmagnetic laboratory flows induced by the steady precession of fluid-filled rotating spheroids. It was found that these flows exhibit both small wavelike instabilities and violent finite-amplitude instability to turbulent motion above critical values of the precession rate. The observed critical parameters indicate that a laminar flow in the core, due to the earth's precession, would have weak hydrodynamic instabilities at most, but that finite-amplitude hydromagnetic instability could lead to fully turbulent flow.     

耐低磷水稻基因型筛选评价指标

以14个不同基因型水稻为供试材料，对低磷和正常供磷两个处理下水稻分蘖期相对生物性状、相对磷吸收和利用效率以及成熟期相对产量进行研究。结果表明，相对地上部干质量可以作为分蘖期筛选水稻耐低磷能力的首选形态指标，其次是相对干物质量。筛选耐低磷水稻基因型时，在早期筛选的基础上，还要考虑成熟期的籽粒产量。     

水库底泥中镉释放影响因素及释放规律试验研究

[目的]研究水库底泥中镉的释放影响因素和规律。[方法]通过模拟试验,研究水动力等物理因素及水环境化学条件对珠江某水库底泥中Cd释放量的影响,探讨底泥中Cd的释放规律。[结果]在相同水深处,底泥中Cd释放量随Cd污染浓度的增大而逐渐增加。随着水深的增加,不同Cd污染浓度底泥中Cd释放量增大。随着流速的增大,底泥中Cd释放量增加,且释放量较大。0.115 m/s流速下的Cd释放量几乎是0.105 m/s流速下的1倍。随着泥沙粒径的增大,底泥中Cd释放量增加。Elovich方程等6个方程可较好地描述该水库底泥中镉释放的动力学规律,且二级反应动力学方程的拟合效果最好。[结论]水库底泥中Cd释放量随Cd污染程度和流速的增大而增加。