共查询到20条相似文献，搜索用时 31 毫秒
1.
Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row ("dripping"), to multiple rows ("alternating"), to densely packed bubbles ("bamboo" and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate stable nitrogen bubbles in aqueous surfactant solution and stable droplets in oil containing dissolved surfactant. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters. 相似文献
2.
Kuo-yuan Chung Narayan Chandra Mishra Chen-chi Wang Feng-hui Lin Keng-hui Lin 《Biomicrofluidics》2009,3(2)
In this paper, we demonstrate for the first time the technique to using microfluidics to fabricate tissue engineering scaffolds with uniform pore sizes. We investigate both the bubble generation of the microfluidic device and the application of foam as a tissue engineering scaffold. Our microfluidic device consists of two concentric tapered channels, which are made by micropipettes. Nitrogen gas and aqueous alginate solution with Pluronic® F127 surfactant are pumped through the inner and the outer channels, respectively. We observe rich dynamic patterns of bubbles encapsulated in the liquid droplets. The size of the bubble depends linearly on the gas pressure and inversely on the liquid flow rate. In addition, monodisperse bubbles self-assemble into crystalline structures. The liquid crystalline foams are further processed into open-cell solid foams. The novel foam gel was used as a scaffold to culture chondrocytes. 相似文献
3.
技术创新网络在演化中表现出的高度不稳定严重削弱网络的创新输出,探索其演化动力有助于网络重构、提升网络绩效。文章区分网络关系形成和关系解散过程,综合外生节点属性和内生结构依赖,基于TERGMs（时序指数随机图模型）构建技术创新网络演化动力模型,并从生命周期视角下,对OLED（有机发光二极管显示技术）技术创新网络进行实证研究。实证结果表明：企业的技术创新能力在孕育期和成长期对合作关系形成具有显著积极作用,边共享伙伴在成长期显著积极影响关系形成,度扩展和度共享伙伴则在成熟期和再生期显著负向影响关系建立和关系解散过程。最后借助收敛性诊断和拟合优度检验验证了该模型的有效性。 相似文献
4.
运城盆地漏斗区水文地球化学演化规律 研究 总被引：3，自引：0，他引：3
该文通过对运城盆地漏斗区浅层水文地球化学系统的分析,利用反向地球化学反应路径模型NETPATH模拟盆地漏斗区浅层水文地球化学演化规律.从模拟结果可以看出,在整个模拟的水流路径上,石膏和石盐的溶解在多数情况下占据主导地位,萤石和云母接近平衡状态.这种水文地球化学演化规律说明,从漏斗区边缘到漏斗中心,地下水沿途溶蚀含水层中的石膏、石盐等含盐矿物,地下水中氯化物、硫酸根和钠离子含量沿水流路径逐渐升高,地下水水质逐步恶化.受人类活动的影响,在较短的时间尺度内盆地漏斗区的水文地球化学演化规律有明显的变化,地下水对方解石有从溶解状态向沉淀方向演化的趋势,整个水流路径上,方解石总交换量由1990年的 14.565变为2000年的-10.145. 相似文献
5.
Kang Kug Lee Toru Matsu-ura Andrew E. Rosselot Taylor R. Broda James M. Wells Christian I. Hong 《Biomicrofluidics》2021,15(1)
Perfused three-dimensional (3D) cultures enable long-term in situ growth and monitoring of 3D organoids making them well-suited for investigating organoid development, growth, and function. One of the limitations of this long-term on-chip perfused 3D culture is unintended and disruptive air bubbles. To overcome this obstacle, we invented an imaging platform that integrates an innovative microfluidic bubble pocket for long-term perfused 3D culture of gastrointestinal (GI) organoids. We successfully applied 3D printing technology to create polymer molds that cast polydimethylsiloxane (PDMS) culture chambers in addition to bubble pockets. Our developed platform traps unintended, or induced, air bubbles in an integrated PDMS pocket chamber, where the bubbles diffuse out across the gas permeable PDMS or an outlet tube. We demonstrated that our robust platform integrated with the novel bubble pocket effectively circumvents the development of bubbles into human and mouse GI organoid cultures during long-term perfused time-course imaging. Our platform with the innovative integrated bubble pocket is ideally suited for studies requiring long-term perfusion monitoring of organ growth and morphogenesis as well as function. 相似文献
6.
David Fernandez Rivas Bram Verhaagen James R. T. Seddon Aaldert G. Zijlstra Lei-Meng Jiang Luc W. M. van der Sluis Michel Versluis Detlef Lohse Han J. G. E. Gardeniers 《Biomicrofluidics》2012,6(3)
We present an ultrasonic device with the ability to locally remove deposited layers from a glass slide in a controlled and rapid manner. The cleaning takes place as the result of cavitating bubbles near the deposited layers and not due to acoustic streaming. The bubbles are ejected from air-filled cavities micromachined in a silicon surface, which, when vibrated ultrasonically at a frequency of 200 kHz, generate a stream of bubbles that travel to the layer deposited on an opposing glass slide. Depending on the pressure amplitude, the bubble clouds ejected from the micropits attain different shapes as a result of complex bubble interaction forces, leading to distinct shapes of the cleaned areas. We have determined the removal rates for several inorganic and organic materials and obtained an improved efficiency in cleaning when compared to conventional cleaning equipment. We also provide values of the force the bubbles are able to exert on an atomic force microscope tip. 相似文献
7.
化学示踪剂是研究干旱区地下水化学演化和补给来源追踪的有效手段之一。本文以Cl-为示踪剂,通过其他离子与Cl-的相互关系对石羊河流域地下水演化特征及影响因子进行分析:Br-/Cl-、Na+/Cl-、S042-/Cl-、HCO3-/Cl-、Ca2+/Cl-、Mg2+/Cl-相互关系指示了流域中游地区地下水与地表水补给关系密切,水质较好,水化学作用以溶滤为主,蒸发也起到一定作用,下游盆地地下水矿化度较高,不完全是现代降水的补给,石膏、方解石溶解和阳离子交换作用使得地下水富镁。总体而言,石羊河流域地下水演化在多种地球化学作用下进行,在以蒸发为主导动力的条件下,水岩相互作用和阳离子交换过程促使地下水演化为现代特征。 相似文献
8.
Flows in complex geometries, such as porous media or biological networks, often contain plugs of liquid flowing within air bubbles. These flows can be modeled in microfluidic devices in which the geometric complexity is well defined and controlled. We study the flow of wetting liquid plugs in a bifurcating network of micro-channels. In particular, we focus on the process by which the plugs divide as they pass each bifurcation. The key events are identified, corresponding to large modifications of the interface curvature, the formation of new interfaces, or the division of a single interface into two new ones. The timing of the different events and the amplitude of the curvature variations are analyzed in view of the design of an event-driven model of flow in branching micro-networks. They are found to collapse onto a master curve dictated by the network geometry. 相似文献
9.
Guillaume Mottet Karla Perez-Toralla Ezgi Tulukcuoglu Francois-Clement Bidard Jean-Yves Pierga Irena Draskovic Arturo Londono-Vallejo Stephanie Descroix Laurent Malaquin Jean Louis Viovy 《Biomicrofluidics》2014,8(2)
We present a low cost microfluidic chip integrating 3D micro-chambers for the capture and the
analysis of cells. This device has a simple design and a small footprint. It allows the
implementation of standard biological protocols in a chip format with low volume consumption. The
manufacturing process relies on hot-embossing of cyclo olefin copolymer, allowing the development of
a low cost and robust device. A 3D design of microchannels was used to induce high flow velocity
contrasts in the device and provide a selective immobilization. In narrow distribution channels, the
liquid velocity induces a shear stress that overcomes adhesion forces and prevents cell
immobilization or clogging. In large 3D chambers, the liquid velocity drops down below the threshold
for cell attachment. The devices can be operated in a large range of input pressures and can even be
handled manually using simple syringe or micropipette. Even at high flow injection rates, the 3D
structures protect the captured cell from shear stress. To validate the performances of our device,
we implemented immuno-fluorescence labeling and Fluorescence in Situ Hybridization
(FISH) analysis on cancer cell lines and on a patient pleural effusion sample. FISH is a Food and
Drug Administration approved cancer diagnostic technique that provides quantitative information
about gene and chromosome aberration at the single cell level. It is usually considered as a long
and fastidious test in medical diagnosis. This process can be easily implanted in our platform, and
high resolution fluorescence imaging can be performed with reduced time and computer intensiveness.
These results demonstrate the potential of this chip as a low cost, robust, and versatile tool
adapted to complex and demanding protocols for medical diagnosis. 相似文献
10.
为了确定重油催化裂化沉降器中液相组分的数量及其对结焦的贡献，以工业重油催化裂化装置的沉降器为研究对象，按照正构烷烃模型分子法确定基团组成的方法，利用已编写的气化率计算程序，求取了沉降器内反应油气的重组分——油浆馏分的气化率，确定反应油气的气、液相比例。计算结果表明，在实际工业操作条件下，重油催化裂化沉降器内的油浆馏分以气、液两相状态存在，其露点温度为488.8℃，露点温度直接取决于油浆终馏分的沸程，而且油浆分压对其泡点和露点温度也有较大影响。 相似文献
11.
风险投资网络演化与网络形成和网络解散密切相关。本研究利用CVSource数据库构建风险投资网络,从机构属性、二元关系、网络结构等多维度提出影响风险投资网络形成和网络解散的假设变量,采用分离时间指数随机图模型（STERGM）,探索我国风险投资网络的演化动力。研究发现,网络形成和网络解散的基础和演化驱动因子存在差异,网络形成是基于发现潜在伙伴的价值和匹配属性,而网络解散是基于对关系质量和未来价值的预期。具体而言,声誉、地理邻近性、结构嵌入和位置嵌入有利于网络关系的形成,且声誉和结构嵌入有利于网络关系持续;认知临近性和位置嵌入对网络关系解散有显著影响。研究结论有助于揭示风险投资网络演化的动力学机制。 相似文献
12.
An estimate of water levels due to the interaction of tide and surge associated with a storm including air bubble effects is made along the coastal region of Bangladesh. For this purpose, a vertically integrated shallow water model in Cartesian coordinate system is developed introducing air bubbles and is solved using nested finite difference schemes. A fine grid model covering the region between 21°15′N to 23°N and 89°E to 92° E has been nested into a coarse grid model covering the region between 15°N to 23°N and 85°E to 95°E in the Bay of Bengal to incorporate all the major islands and coastal bending accurately. By applying tidal forcing through the southern open boundary of the coarse grid model appropriate tidal conditions are generated in the problem domain. Numerical experiments are performed with the help of the model to simulate water levels due to tide and surge interaction including air bubble effects associated with the tropical storm of April 1991. The model results are found to be reasonable and the model can be found to simulate higher water levels in the presence of air bubbles. 相似文献
13.
[目的/意义]提取突发事件网络舆情中事件的因果和顺承关系,构建事理图谱揭示事理发展脉络和演化规律。[方法/过程]以微博相关评论为研究对象,分别通过因果关系标识、事件影响因子和时间因子等维度识别事件间的关系,提取因果和顺承事件对;采用层次聚类将相似度较高的事件泛化为一类,构建新冠肺炎网络舆情事理图谱,并对生成的舆情演化路径进行分析。[结果/结论]研究表明,因果关系演化路径具有事件少、演化路径短等规律性特点,且同时包含顺承关系事件和伪结果事件;顺承关系演化路径具有事件数量多、演化路径较长、交叠变化等规律性特点,且能够揭示舆情演化的关键节点。通过构建事理图谱可以快速区分突发事件舆情的噪音和关键信息,充分体现其在监测、预测和管理中的价值性。 相似文献
14.
在对知识流动相关文献进行梳理的基础上,对流体力学中的液体流动进行隐喻分析,研究知识流动与液体流动的对应关系。提出构建沿程损失模型的前提假设,应用流体力学圆管流动理论,构建基于流体力学的知识流动过程中的知识损失分析模型,对模型进行推导和求解。在此基础上,通过编程对知识流动沿程损失模型进行仿真模拟,绘制知识流动损失的变化趋势图像。通过研究发现知识流动过程中可以通过提高知识接收方自身知识接收上限及提高知识输出方的输出意愿、依靠科学决策方法等途径有效避免知识流动过程中产生不必要的损失,为提高知识传输效率提供了有益的借鉴。 相似文献
15.
日益高涨的房地产价格引发了人们对泡沫的激烈争论。本文运用功效系数法计算了综合预警系数,建立了基于BP神经网络的房地产泡预警系统,引入了敏感性分析甄别各指标在预警系统中的重要程度,并且利用北京房地产市场数据对其泡沫进行实证分析,指出该系统对于防范房地产泡沫,评价房地产市场是否处于健康和谐运行状态具有重要意义。 相似文献
16.
We present an optofluidic microvalve utilizing an embedded, surface plasmon-enhanced fiber optic microheater. The fiber optic microheater is formed by depositing a titanium thin film on the roughened end-face of a silica optical fiber that serves as a waveguide to deliver laser light to the titanium film. The nanoscale roughness at the titanium-silica interface enables strong light absorption enhancement in the titanium film through excitation of localized surface plasmons as well as facilitates bubble nucleation. Our experimental results show that due to the unique design of the fiber optic heater, the threshold laser power required to generate a bubble is greatly reduced and the bubble growth rate is significantly increased. By using the microvalve, stable vapor bubble generation in the microchannel is demonstrated, which does not require complex optical focusing and alignment. The generated vapor bubble is shown to successfully block a liquid flow channel with a size of 125 μm × 125 μm and a flow rate of ∼10 μl/min at ∼120 mW laser power. 相似文献
17.
The effects of gradients of bioactive molecules on the cell microenvironment are crucial in several biological processes, such as chemotaxis, angiogenesis, and tumor progression. The elucidation of the basic mechanisms regulating cell responses to gradients requires a tight control of the spatio-temporal features of such gradients. Microfluidics integrating 3D gels are useful tools to fulfill this requirement. However, even tiny flaws in the design or in the fabrication process may severely impair microenvironmental control, thus leading to inconsistent results. Here, we report a sequence of actions aimed at the design and fabrication of a reliable and robust microfluidic device integrated with collagen gel for cell culturing in 3D, subjected to a predetermined gradient of biomolecular signals. In particular, we developed a simple and effective solution to the frequently occurring technical problems of gas bubble formation and 3D matrix collapsing or detaching from the walls. The device here proposed, in Polydimethylsiloxane, was designed to improve the stability of the cell-laden hydrogel, where bubble deprived conditioning media flow laterally to the gel. We report the correct procedure to fill the device with the cell populated gel avoiding the entrapment of gas bubbles, yet maintaining cell viability. Numerical simulations and experiments with fluorescent probes demonstrated the establishment and stability of a concentration gradient across the gel. Finally, chemotaxis experiments of human Mesenchymal Stem Cells under the effects of Bone Morphogenetic Protein-2 gradients were performed in order to demonstrate the efficacy of the system in controlling cell microenvironment. The proposed procedure is sufficiently versatile and simple to be used also for different device geometries or experimental setups. 相似文献
18.
Droplet-based microfluidics has gained extensive research interest as it overcomes several challenges confronted by conventional single-phase microfluidics. The mixing performance inside droplets/slugs is critical in many applications such as advanced material syntheses and in situ kinetic measurements. In order to understand the effects of operating conditions on the mixing performance inside liquid slugs generated by a microfluidic T-junction, we have adopted the volume of fluid method coupled with the species transport model to study and quantify the mixing efficiencies inside slugs. Our simulation results demonstrate that an efficient mixing process is achieved by the intimate collaboration of the twirling effect and the recirculating flow. Only if the reagents are distributed transversely by the twirling effect, the recirculating flow can bring in convection mechanism thus facilitating mixing. By comparing the mixing performance inside slugs at various operating conditions, we find that slug size plays the key role in influencing the mixing performance as it determines the amount of fluid to be distributed by the twirling effect. For the cases where short slugs are generated, the mixing process is governed by the fast convection mechanism because the twirling effect can distribute the fluid to the flow path of the recirculating flow effectively. For cases with long slugs, the mixing process is dominated by the slow diffusion mechanism since the twirling effect is insufficient to distribute the large amount of fluid. In addition, our results show that increasing the operating velocity has limited effects on improving the mixing performance. This study provides the insight of the mixing process and may benefit the design and operations of droplet-based microfluidics. 相似文献
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20.
以波传播的观点 ,将流动工况视为连续波与动力波相互作用在特定流动条件下的非线性解 ,尝试提出了两相流分析的一种新思路 .从一维气液两相流守恒方程出发 ,应用气液两相流漂移流模型 ,推导了空泡率双曲型守恒方程 ,用特征线法数值求解气液两相流空泡率分布的传播过程 ,对传播稳定性和流型转变进行讨论 .数值分析表明 ,低空泡率时发生流型转变的位置相对于两相流平均速度将向下游蔓延 ;而高空泡率时则相对地向上游蔓延 ;空泡率很高时空泡率分布传播过程中将不会出现流型转变 .计算表明 :流型转变起始点的空泡率为 0 2 7,空泡率达到 0 5 8时流型转变终止 ;这与文献报告的气液两相流实验结果符合较好 相似文献