共查询到19条相似文献，搜索用时 234 毫秒
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研究了外在的离心力场对氯酸钠溶液结晶的影响,使用偏光显微镜考察了离心机的不同转速下,氯酸钠结晶过程中手性对称性破缺的统计结果.实验表明,作为一个物理因素,外在的离心力场能明显诱导氯酸钠溶液结晶的手性分布.当离心机转速较大时(如6000r/min),饱和溶液的结晶趋向于仅有一种构型——L型或D型,即能导致氯酸钠结晶的完全手性对称性破缺,且顺时针离心力场中D型晶体数量明显大于L型,而在逆时针离心力场中L型晶体数量却明显大于D型,并均随外力增大而效应增大.这些结果表明,外在离心力场可方向性地对氯酸钠溶液的不对称结晶过程产生重要影响. 相似文献
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观测表明暗物质粒子绕星系质心近似呈球对称运动,它们之间不存在相互碰撞或碰撞很弱,因此可以假设暗物质在宏观上与无粘滞流体类似,不必考虑暗物质晕中的切向应力而只需考虑法向应力.根据这一模型研究了暗物质在重力、离心力、法向力作用下的稳定运动,得出了暗物质的密度分布公式.该公式与现有的观测曲线符合的很好,从而证明了无粘滞流体模型是合理的,这对于研究暗物质很有意义. 相似文献
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《科技成果管理与研究》2011,(11):107-107
一种新发明的刻度密码转盘门锁（实用新型专利。专利号：200920237044．0）,在该锁的背面增加了一个与前面刻度数码相等、数码排列方向相反的转盘。在锁里面前两个开口转盘中各增加了一个辅助部件协助工作,这样,开解锁时无论从锁的前面或背面从顺时针或逆时针旋转解锁都是同一的三个数码组。 相似文献
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离心力场具有强化煤泥浮选作用,离心力场为主要分选设备-浮选旋流器和圆形浮选机。以及离,从理论上研究分析了离心力场浮选技术的先进性和缺陷,希望对离心力场浮选选设备有借鉴作用。 相似文献
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主要研究了硫、碲叶立德环丙烷化和环氧化反应的立体化学控制。通过添加剂、手性辅基、手性试剂等 3种策略,分别控制反应的非对映选择性和对映选择性。对烯丙基硫叶立德的不对称环氧化反应也进行了初步研究 相似文献
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《大科技．科学之谜》2008,(11):5
9月10日上午,随着终端计算机屏幕上最终亮起两个白点,国际物理学界一片欢腾。这标志着位于瑞士日内瓦的欧洲强子对撞机顺利完成了第一项重要测试。测试过程中,科学家将质子导入27公里的隧道,并让其按顺时针方向运行整条隧道长度。在顺时针测试获得成功后,欧洲核子中心计划进行逆时针测试。 相似文献
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通过测试向列液晶在不同的预倾角,初始角以及在不同力场作用下偏振光强度的变化,确定液晶分子发生扭曲变形的特性参数:扭曲角、变形的旋转时间和弛豫时间。测试结果表明:在相同力场作用下,液晶在取向层的预倾角愈大,液晶分子的扭曲变形程度也愈大;向列液晶在不同力场作用下产生形变的旋转时间和弛豫时间受液晶弹性常数和粘滞系数的影响,形变的旋转时间小于其弛豫时间;此外,向列液晶在取向层的初始角会影响液晶在力场作用下发生扭曲变形的程度,不同的力场强度下存在一对应于最大扭曲变形的初始角。 相似文献
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In this study, a viscometer, which can measure the viscosity of low-volume liquids (25 μl) within 30 s, was developed on a centrifugal platform. The centrifugal viscometer consists of a disk platform and a motor. Under disk rotation, centrifugal, Coriolis, and viscosity-induced drag forces result in deflection of liquid flow. The viscosity of the liquid sample is determined by the deflection angle of the liquid, which can be examined through image analysis or visual inspection. The viscosities of a series of Newtonian model fluids were tested by the centrifugal viscometer and the results showed good agreement with the ones tested by a conventional rotational viscometer. Since the centrifugal viscometer only requires a motor to function, the microfluidic disk can be produced in large quantities at a low cost through injection molding, and the deflection angle can be detected through visual inspection, it provides an inexpensive, easy to operate, and portable approach to measure low-volume liquid viscosity. 相似文献
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A new microchannel with a series of symmetric sharp corner structures is reported for passive size-dependent particle separation. Micro particles of different sizes can be completely separated based on the combination of the inertial lift force and the centrifugal force induced by the sharp corner structures in the microchannel. At appropriate flow rate and Reynolds number, the centrifugal force effect on large particles, induced by the sharp corner structures, is stronger than that on small particles; hence after passing a series of symmetric sharp corner structures, large particles are focused to the center of the microchannel, while small particles are focused at two particle streams near the two side walls of the microchannel. Particles of different sizes can then be completely separated. Particle separation with this device was demonstrated using 7.32 μm and 15.5 μm micro particles. Experiments show that in comparison with the prior multi-orifice flow fractionation microchannel and multistage-multiorifice flow fractionation microchannel, this device can completely separate two-size particles with narrower particle stream band and larger separation distance between particle streams. In addition, it requires no sheath flow and complex multi-stage separation structures, avoiding the dilution of analyte sample and complex operations. The device has potentials to be used for continuous, complete particle separation in a variety of lab-on-a-chip and biomedical applications. 相似文献
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运用螺旋理论推断秋水仙碱的构型 总被引：1，自引：0，他引：1
秋水仙碱是医治癌症的重要药物 ,其结构中不仅存在手性碳原子的构型问题 ,也存在类似于联苯衍生物的构型和构象问题 .确定了手性碳原子的构型 ,还必须确定两个芳环间的构型和构象 .运用笔者提出的螺旋理论 ,通过其旋光方向和旋光度可以方便地确定秋水仙碱两个芳环间的构型和构象 . 相似文献
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Biomolecular separation is crucial for downstream analysis. Separation technique mainly relies on centrifugal sedimentation. However, minuscule sample volume separation and extraction is difficult with conventional centrifuge. Furthermore, conventional centrifuge requires density gradient centrifugation which is laborious and time-consuming. To overcome this challenge, we present a novel size-selective bioparticles separation microfluidic chip on a swinging bucket minifuge. Size separation is achieved using passive pressure driven centrifugal fluid flows coupled with centrifugal force acting on the particles within the microfluidic chip. By adopting centrifugal microfluidics on a swinging bucket rotor, we achieved over 95% efficiency in separating mixed 20 μm and 2 μm colloidal dispersions from its liquid medium. Furthermore, by manipulating the hydrodynamic resistance, we performed size separation of mixed microbeads, achieving size efficiency of up to 90%. To further validate our device utility, we loaded spiked whole blood with MCF-7 cells into our microfluidic device and subjected it to centrifugal force for a mere duration of 10 s, thereby achieving a separation efficiency of over 75%. Overall, our centrifugal microfluidic device enables extremely rapid and label-free enrichment of different sized cells and particles with high efficiency. 相似文献
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面向知识经济的企业管理创新出现了新的趋势、新的特点、新的观念和新的方法,知识管理是企业管理的新重心。阐述了面向知识经济的企业管理,对知识经济时代的企业管理创新的力场进行了分析,提出了推进企业管理创新的力场的作用力与反作用力均衡作用的策略,使企业管理创新的推动力和阻碍力交互作用,推动企业创新。 相似文献
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集群中企业的成长不仅受到自身能力和相关企业及公共组织的影响,还与产业集群的属性有关,产业集群对企业成长的影响具有＂场效应＂的作用。将＂场思维＂引入到集群企业成长机制研究中,提出了影响集群企业成长的三种场力：基于组织间关系的场力、基于集成效应的场力和基于集成风险的场力;构建了基于成长场的集群企业成长模型,定量化解析了三种场力的构成和集群企业的成长机制。通过研究发现,三种场力的大小和集群企业的成长过程均与＂成长场＂场强、集成风险、组织质量、组织距离和组织嵌入度等要素有关,集群企业需要协调好各要素之间的关系,尽量增大企业在发展中所受到的正向场力作用,减小负向场力作用,从而实现企业的持续快速成长。 相似文献
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人们常常习惯于以地球为参照系,把物体的下落运动看作是只在重力作用下的初速度为零的匀加速直线运动。但实事上地球自转,存在自转角速度,是一个非惯性系,物体下落要考虑科里奥利力效应,下落就会向东偏离,如果再考虑到下落过程中所受的空气阻力作用,这种向东偏离就会增大。 相似文献
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Roger A. Grey Author Vitae 《Journal of The Franklin Institute》2006,343(3):214-222
The scientific theme for the 2005 Bower Award was Chemistry, specifically the field of Catalysis. The Franklin Institute, Philadelphia, Pennsylvania, awarded the 2005 Bower Award and Prize for achievement in Science to Henri B. Kagan for his seminal discovery of fundamental chemical principles that explain the impact of catalyst shape on its effectiveness in controlling chemical reactions, thus greatly simplifying the manufacture of pharmaceutically important compounds. Henri Kagan is widely recognized as a pioneer in the field of asymmetric catalysis. Starting in the early 1970s, his reports of the synthesis of the chiral bidentate diphosphine ligand and the demonstration of its use with soluble rhodium compounds to catalyze the efficient production of large enantiomeric excesses of chiral molecules in asymmetric hydrogenations has had far reaching effects on research in the field asymmetric catalysis. The concept of using chiral bidentate ligands of C2 symmetry has led the way for numerous developments in asymmetric catalysis. Later in 1986 his introduction of the concept and investigations into “nonlinear effects in asymmetric synthesis” using catalysts with chiral ligands that were not optically pure challenged the widely accepted assumption that the enantiomeric excess which is possible correlates linearly with the optical purity of the chiral ligands. He reported the first example in asymmetric catalysis where the optical purity of the product significantly exceeded the optical purity of the chiral ligand. 相似文献