共查询到20条相似文献，搜索用时 31 毫秒
1.
Optofluidic tweezer on a chip 总被引：1，自引：0，他引：1
A novel method to realize an optical tweezer involving optofluidic operation in a microchannel is proposed. To manipulate the optical tweezer, light from an optical fiber is passed through both PDMS (polydimethylsiloxane)-air surface lenses and an optofluidic region, which is located in a control channel. Two liquids with different refractive indices (RIs) are introduced into the control channel to form two different flow patterns (i.e., laminar and segmented flows), depending on the liquid compositions, the channel geometry, and the flow rates. By altering the shapes of the interface of the two liquids in the optofluidic region, we can continuously or intermittently control the optical paths of the light. To demonstrate the functionality of the proposed method, optical tweezer operations on a chip are performed. Changing the flow pattern of two liquids with different RIs in the optofluidic region results in successful trapping of a 25 μm diameter microsphere and its displacement by 15 μm. 相似文献
2.
A statistical analysis is presented for steady creep bending in a beam, where the material parameters are random processes along the neutral axis arising from random fluctuations in temperature and imperfection density. Analytical and numerical results are presented for the statistical properties of the normal stress and lateral velocity. It is found that whereas the normal stress shows very little random fluctuation the lateral velocity is highly random. The statistics of the lateral velocity generally show a significant dependence on the nominal value of the creep power and on the position along the neutral axis. 相似文献
3.
We present a new approach to enhance mixing in T-type micromixers by introducing a constriction in the microchannel under periodic electro-osmotic flow. Two sinusoidal ac electric fields with 180° phase difference and similar dc bias are applied at the two inlets. The out of phase ac electric field induces oscillation of fluid interface at the junction of the two inlet channels and the constriction. Due to the constriction introduced at the junction, fluids from these two inlets form alternative plugs at the constricted channel. These plugs of fluids radiate downstream from the constriction into the large channel and form alternate thin crescent-shaped layers of fluids. These crescent-shaped layers of fluids increase tremendously the contact surface area between the two streams of fluid and thus enhance significantly the mixing efficiency. Experimental results and mixing mechanism analysis show that amplitude and frequency of the ac electric field and the length of the constriction govern the mixing efficiency. 相似文献
4.
《Journal of The Franklin Institute》1986,322(1):49-72
This paper deals with the evaluation of the stress field in a plate with two unequal and collinear anti-plane shear cracks and a circular inclusion. The solution for the stress state is obtained in a series-form solution. A concrete example is given of a plate with two equal cracks and a circular inclusion subjected to anti-plane shear at infinity. The problem may describe the state of stress on an equatorial section of unidirectional fiber composite when cracks appear in meridional x sections between fibers. 相似文献
5.
This paper investigates the steady laminar flow in a porous medium of an incompressible viscous fluid impinging on a permeable stretching surface with heat generation. The resulting system of coupled non-linear ordinary differential equations is solved analytically via homotopy analysis method (HAM). Analytical results are presented for the wall shear stress and the wall heat transfer coefficient as well as the velocity and temperature profiles for some values of governing parameters such as Prandtl number, stretching parameter, porosity parameter and the heat generation/absorption parameter. Appropriate auxiliary parameter, ?, is determined by minimizing Euclidean norm of residual. The convergence of the obtained series solutions is explicitly studied. 相似文献
6.
To present three-directional forces at ten human fingertips, we previously developed a bimanual multi-fingered haptic interface consisting of two five-fingered haptic hands and two interface arms. However, there is a risk that the component parts of the haptic interface will collide while an operator is manipulating the interface. A collision could be hazardous for the operator, and thus collision avoidance is essential. To solve this problem, we propose a collision avoidance controller for the bimanual multi-fingered haptic interface. The proposed controller prevents collisions while reducing the collision-induced effects on the haptic display. We carried out several experiments, the results of which show the validity of the proposed collision avoidance controller for the bimanual multi-fingered haptic interface. 相似文献
7.
Manipulating flexible objects stirs a great deal of interest due to the potential applications in industry. Most previous research work with multiple manipulators, however, focused on developing control strategies for the manipulation of rigid bodies. This paper seeks to develop simple yet practical and efficient control scheme that enables cooperating arms to handle a flexible beam. Specifically the problem studied herein is that of two arms rigidly grasping a flexible beam and capable of generating forces/moments in such a way as to move a flexible beam along a predefined trajectory. The paper develops a sliding mode control law that provides robustness against model imperfection and uncertainty. It also provides an implicit stability proof. Given the bounds of uncertainty in the model of the flexible beam and choosing a switching surface that enforces trajectory tracking, a control algorithm is designed to push the states to remain on the switching surface. Simulation results for two three joint arms moving a flexible beam are presented to validate the theoretical results. 相似文献
8.
基于GIS和信息量法的甘肃南部白龙江流域泥石流灾害危险性评价 总被引：4，自引：0，他引：4
信息量法是泥石流危险性评价的重要方法之一,本文以甘肃南部白龙江流域为研究区,根据地形、地貌、地质、环境等条件,选取高程、坡度、岩性、土地利用类型、滑坡点密度、地质构造缓冲区及归一化植被指数(NDVI)等7个评价因子,进行泥石流灾害危险性评价.文章基于GIS技术的空间分析功能及信息量法的定量分析功能,对各类因子进行分级计算与信息量赋值,生成各评价因子的信息量图层,并进行叠加分析,最终得到甘肃南部白龙江流域泥石流危险性分区图.结果表明,中度危险区以上的区域包含88.91％的泥石流.随着危险等级的增加,泥石流沟面积占危险等级面积比也随之增大.在中度危险区、高度危险区和极高度危险区内发生的泥石流面积分别占到各危险等级面积的21.21％、34.09％和46.00％,分析结果与实际灾害分布特征吻合较好.由此可见,信息量法与GIS技术结合对泥石流灾害进行危险性评价具有较高的准确性. 相似文献
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10.
《Journal of The Franklin Institute》2007,344(5):520-534
The paper describes a method and a computer application for the computation of the velocity of acoustic waves excited in complicated multi-layered structures consisting of anisotropic piezoelectric and isotropic layers. The structure assumes to be unbounded in the lateral directions. The top and bottom layers are either semi-infinite in the vertical direction or they contact with media such as fluids, gases or vacuum. A special homogenization technique enables to account for bristle-like layers contacting with a fluid. The program is supplied with a user friendly graphical interface and can be useful for researchers working on acoustic sensors. 相似文献
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12.
We present the conformal coating of non-spherical magnetic particles in a co-laminar flow
microfluidic system. Whereas in the previous reports spherical particles had been coated with thin
films that formed spheres around the particles; in this article, we show the coating of
non-spherical particles with coating layers that are approximately uniform in thickness. The novelty
of our work is that while liquid-liquid interfacial tension tends to minimize the surface area of
interfaces—for example, to form spherical droplets that encapsulate spherical particles—in our
experiments, the thin film that coats non-spherical particles has a non-minimal interfacial area. We
first make bullet-shaped magnetic microparticles using a stop-flow lithography method that was
previously demonstrated. We then suspend the bullet-shaped microparticles in an aqueous solution and
flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from
a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the
particles reach the interface between the immiscible fluids. We observe that upon crossing the
oil-water interface, the microparticles become coated by a thin film of the aqueous fluid. When we
increase the two-fluid interfacial tension by reducing surfactant concentration, we observe that the
particles become trapped at the interface, and we use this observation to extract an approximate
magnetic susceptibility of the manufactured non-spherical microparticles. Finally, using
fluorescence imaging, we confirm the uniformity of the thin film coating along the entire curved
surface of the bullet-shaped particles. To the best of our knowledge, this is the first
demonstration of conformal coating of non-spherical particles using microfluidics. 相似文献
13.
《中国科学院院刊(英文版)》2008,22(2):88-89
The regulatory mechanism for neuronal migration in the developing cortex is a major unsolved problem in developmental neurobiology. It is generally accepted that the migration of newborn pyramidal neurons from the ventrieular zone toward upper cortical layers is guided by radial glial fibers in the developing cortex, and that the laminar structure of the cortex isformed through regulated attachment and detachment of migrating neurons with radial glial fibers. However, whether the radial migration of cortical neurons can be guided by a gradient of diffusible factors is unknown, a potential guidance mechanism that has long been overlooked. 相似文献
14.
本文从技术层面浅要阐述了在我国航天对地观测技术蓬勃发展中显现出来的几个主要方面的不足,这些不足点或问题是紧密关联而非孤立的,是不能回避的。为加速我国航天对地观测技术的发展,国家需从整体和全局上科学统筹改进。 相似文献
15.
《Information processing & management》2020,57(3):102211
Aspect-based sentiment analysis allows one to compute the sentiment for an aspect in a certain context. One problem in this analysis is that words possibly carry different sentiments for different aspects. Moreover, an aspect’s sentiment might be highly influenced by the domain-specific knowledge. In order to tackle these issues, in this paper, we propose a hybrid solution for sentence-level aspect-based sentiment analysis using A Lexicalized Domain Ontology and a Regularized Neural Attention model (ALDONAr). The bidirectional context attention mechanism is introduced to measure the influence of each word in a given sentence on an aspect’s sentiment value. The classification module is designed to handle the complex structure of a sentence. The manually created lexicalized domain ontology is integrated to utilize the field-specific knowledge. Compared to the existing ALDONA model, ALDONAr uses BERT word embeddings, regularization, the Adam optimizer, and different model initialization. Moreover, its classification module is enhanced with two 1D CNN layers providing superior results on standard datasets. 相似文献
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Clinical analysis of acute viral infection in blood requires the separation of viral particles from blood cells, since the cytoplasmic enzyme inhibits the subsequent viral detection. To facilitate this procedure in settings without access to a centrifuge, we present a microfluidic device to continuously purify bionanoparticles from cells based on their different intrinsic movements on the microscale. In this device, a biological sample is layered on top of a physiological buffer, and both fluids are transported horizontally at the same flow rate in a straight channel under laminar flow. While the micron sized particles such as cells sediment to the bottom layer with a predictable terminal velocity, the nanoparticles move vertically by diffusion. As their vertical travel distances have a different dependence on time, the micro- and nanoparticles can preferentially reside in the bottom and top layers respectively after certain residence time, yielding purified viruses. We first performed numerical analysis to predicate the particle separation and then tested the theory using suspensions of synthetic particles and biological samples. The experimental results using dilute synthetic particles closely matched the numerical analysis of a two layer flow system containing different sized particles. Similar purification was achieved using diluted blood spiked with human immunodeficiency virus. However, viral purification in whole blood is compromised due to extensive bioparticle collisions. With the parallelization and automation potential offered by microfluidics, this device has the potential to function as an upstream sample preparation module to continuously provide cell depleted bio-nanoparticles for downstream analysis. 相似文献
18.
根据杂交应力理性模式，基于一种修正的Hellinger－Reissuer原理，建立了具有一个无外力斜边的杂交应力元，其应力场由无边界面力在非协调位移上所作虚功之和为零的约束条件导出，将这种特殊元与具有一个无外力圆弧边的杂交应力元联合，可有效地分析具有倒圆角V型槽孔板的应力集中，并可提供远较一般假定位移及一般假定应力元准确的孔边应力分布。 相似文献
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20.
Wei-Chao Zheng Rui Xie Li-Qun He Yue-Heng Xi Ying-Mei Liu Zhi-Jun Meng Wei Wang Xiao-Jie Ju Gang Chen Liang-Yin Chu 《Biomicrofluidics》2015,9(4)
A novel microfluidic device for highly efficient and robust dialysis without membrane is highly desired for the development of portable or wearable microdialyzer. Here we report an enhanced H-filter with pillar array based on Fåhræus-Lindqvist effect (F-L effect) for highly efficient and robust membraneless dialysis of simplified blood for the first time. The H-filter employs two fluids laminarly flowing in the microchannel for continuously membraneless dialysis. With pillar array in the microchannel, the two laminar flows, with one containing blood cells and small molecules and another containing dialyzate solution, can form a cell-free layer at the interface as selective zones for separation. This provides enhanced mixing yet extremely low shear for extraction of small molecules from the blood-cell-containing flow into the dialyzate flow, resulting in robust separation with reduced cell loss and improved efficiency. We demonstrate this by first using Chlorella pyrenoidosa as model cells to quantitatively study the separation performances, and then using simplified human blood for dialysis. The advanced H-filter, with highly efficient and robust performance for membraneless dialysis, shows great potential as promising candidate for rapid blood analysis/separation, and as fundamental structure for portable dialyzer. 相似文献