Emulsification in a microfluidic flow-focusing device: effect of the viscosities of the liquids

We report the results of a comparative study of microfluidic emulsification of liquids with different viscosities. Depending on the properties of the fluids and their rates of flow, emulsification occurred in the dripping and jetting regimes. We studied the characteristic features and typical dependence of the size and of the size distribution of droplets in each regime. For each liquid, we identified a range of hydrodynamic conditions promoting generation of highly monodisperse droplets. Viscosity played an important role in emulsification: highly viscous liquids were emulsified into larger droplets with lower polydispersity. Although it was not possible to provide a unified scaling for the volumes of the droplets, our results suggest that the break-up dynamics of the lower viscosity fluids resembles the rate-of-flow-controlled break-up, as reported earlier for the formation of bubbles in flow-focusing geometries [Garstecki P, Stone HA, Whitesides GM (2005) Phys Rev Lett 94:164501]. The results of this study can be helpful for a rationalized selection of liquids for the controlled formation of droplets with a predetermined size and with a narrow distribution of sizes.     

Pinch-off mechanism for Taylor bubble formation in a microfluidic flow-focusing device

The present work aims at studying the nonlinear breakup mechanism for Taylor bubble formation in a microfluidic flow-focusing device by using a high-speed digital camera. Experiments were carried out in a square microchannel with cross section of 600 × 600 μm. During the nonlinear collapse process, the variation of the minimum radius of bubble neck (r ₀) with the remaining time until pinch-off (τ) can be scaled by a power–law relationship: \(r_{0} \propto \tau^{\alpha } .\) Due to the interface rearrangement around the neck, the nonlinear collapse process can be divided into two distinct stages: liquid squeezing collapse stage and free pinch-off stage. In the liquid squeezing collapse stage, the neck collapses under the constriction of the liquid flow and the exponent α approaches to 0.33 with the increase in the liquid flow rate Q _l. In the free pinch-off stage, the value of α is close to the theoretical value of 0.50 derived from the Rayleigh–Plesset equation and is independent of Q _l.     

Anamorphic 3D geometry

An anamorphic image appears distorted from all but a few viewpoints. They have been studied by artists and architects since the early fifteenth century. Computer graphics opens the door to anamorphic 3D geometry. We are not bound by physical reality nor a static canvas. Here we describe a simple method for achieving anamorphoses of 3D objects by utilizing a variation of a simple projective map that is well-known in the computer graphics literature. The novelty of this work is the creation of anamorphic 3D digital models, resulting in a tool for artists and architects.     

Liquid flooded flow-focusing microfluidic device for in situ generation of monodisperse microbubbles

Current microbubble-based ultrasound contrast agents are administered intravenously resulting in large losses of contrast agent, systemic distribution, and strict requirements for microbubble longevity and diameter size. Instead we propose in situ production of microbubbles directly within the vasculature to avoid these limitations. Flow-focusing microfluidic devices (FFMDs) are a promising technology for enabling in situ production as they can produce microbubbles with precisely controlled diameters in real-time. While the microfluidic chips are small, the addition of inlets and interconnects to supply the gas and liquid phase greatly increases the footprint of these devices preventing the miniaturization of FFMDs to sizes compatible with medium and small vessels. To overcome this challenge, we introduce a new method for supplying the liquid (shell) phase to a FFMD that eliminates bulky interconnects. A pressurized liquid-filled chamber is coupled to the liquid inlets of an FFMD, which we term a flooded FFMD. The microbubble diameter and production rate of flooded FFMDs were measured optically over a range of gas pressures and liquid flow rates. The smallest FFMD manufactured measured 14.5 × 2.8 × 2.3 mm. A minimum microbubble diameter of 8.1 ± 0.3 μm was achieved at a production rate of 450,000 microbubbles/s (MB/s). This represents a significant improvement with respect to any previously reported result. The flooded design also simplifies parallelization and production rates of up to 670,000 MB/s were achieved using a parallelized version of the flooded FFMD. In addition, an intravascular ultrasound (IVUS) catheter was coupled to the flooded FFMD to produce an integrated ultrasound contrast imaging device. B-mode and IVUS images of microbubbles produced from a flooded FFMD in a gelatin phantom vessel were acquired to demonstrate the potential of in situ microbubble production and real-time imaging. Microbubble production rates of 222,000 MB/s from a flooded FFMD within the vessel lumen provided a 23 dB increase in B-mode contrast. Overall, the flooded design is a critical contribution towards the long-term goal of utilizing in situ produced microbubbles for contrast enhanced ultrasound imaging of, and drug delivery to, the vasculature.     

Novel swirl flow-focusing microfluidic device for the production of monodisperse microbubbles

A novel swirl flow-focusing microfluidic axisymmetric device for the generation of monodisperse microbubbles at high production rates to be used as in-line contrast agents for medical applications is presented. The swirl effect is induced upstream of the discharge orifice by a circular array of microblades which form a given angle with the radial direction. The induced vortical component on the focusing liquid stabilizes the gas meniscus by the vorticity amplification due to vortex stretching as the liquid is forced through the discharge orifice. The stabilized meniscus tapers into a steady gas ligament that breaks into monodisperse microbubbles. A reduction up to \(57\%\) in the microbubble diameter is accomplished when compared to conventional axisymmetric flow-focusing microdevices. An exhaustive experimental study is performed for various blade angles and numerous gas to liquid flow rate ratios, validating previous VoF numerical simulations. The microbubbles issued from the stabilized menisci verify prior scaling law of flow-focusing.     

Modeling 3D Euclidean geometry

This article compares five models of 3D Euclidean geometry-not theoretically, but by demonstrating how to implement a simple recursive ray tracer in each of them. It's meant as a tangible case study of the profitability of choosing an appropriate model, discussing the trade-offs between elegance and performance for this particular application. The models we compare are 3D linear algebra, 3D geometric algebra, 4D linear algebra, 4D geometric algebra, and 5D geometric algebra.     

Simulation of magnetic reconnection in 3D geometry

The mathematical model of magnetic reconnection in the vicinity of critical points is discussed in the frame of 3D magneto-hydrodynamics. A mixed problem for an initial magnetic configuration without external currents was formulated and solved numerically. The evolution of a magnetic field in the vicinity of the null point and null line for the case of the forced magnetic reconnection mode is considered. Results of computational experiments concerning the formation of complex self-organizing nonlinear structures are presented.     

Stereo geometry from 3D ego-motion streams

This paper addresses the problem of geometry determination of a stereo rig that undergoes general rigid motions. Neither known reference objects nor stereo correspondence are required. With almost no exception, all existing online solutions attempt to recover stereo geometry by first establishing stereo correspondences. We first describe a mathematical framework that allows us to solve for stereo geometry, i.e., the rotation and translation between the two cameras, using only motion correspondence that is far easier to acquire than stereo correspondence. Second, we show how to recover the rotation and present two linear methods, as well as a nonlinear one to solve for the translation. Third, we perform a stability study for the developed methods in the presence of image noise, camera parameter noise, and ego-motion noise. We also address accuracy issues. Experiments with real image data are presented. The work allows the concept of online calibration to be broadened, as it is no longer true that only single cameras can exploit structure-from-motion strategies; even the extrinsic parameters of a stereo rig of cameras can do so without solving stereo correspondence. The developed framework is applicable for estimating the relative three-dimensional (3D) geometry associated with a wide variety of mounted devices used in vision and robotics, by exploiting their scaled ego-motion streams.     

Application of a perspective cursor as a 3D locator device

The functionality of a 3D cursor is described. It can be used as a 3D locator device in such applications as interactive path planning (robotics), motion specification in 3D computer animation design, and wireframe modelling. With respect to the last of these applications, it is important that the cursor can be used either in constructive mode, as a set of three mutually orthogonal rulers, or in trace mode to copy a 2D perspective view of an object while reconstruction its 3D shape. As a special feature, the cursor may be equipped with a mirror of locations in scenes that are (partially) symmetric, but also allows 3D symmetric objects to be entered from 2D (perspective) views, while making use of symmetry as a clue for reconstructing z-coordinates.     

Affine-invariant geodesic geometry of deformable 3D shapes

Natural objects can be subject to various transformations yet still preserve properties that we refer to as invariants. Here, we use definitions of affine-invariant arclength for surfaces in R³ in order to extend the set of existing non-rigid shape analysis tools. We show that by re-defining the surface metric as its equi-affine version, the surface with its modified metric tensor can be treated as a canonical Euclidean object on which most classical Euclidean processing and analysis tools can be applied. The new definition of a metric is used to extend the fast marching method technique for computing geodesic distances on surfaces, where now, the distances are defined with respect to an affine-invariant arclength. Applications of the proposed framework demonstrate its invariance, efficiency, and accuracy in shape analysis.     

三维动态几何中直线消隐的实现

由于OpenGL图形系统没有提供现成的直线动态消隐的功能，因此在设计三维动态几何软件时，直线的动态消隐很困难。利用OpenGL图形系统，在研究现有的消隐技术——深度缓存算法的基础上，通过两条直线的叠加和视点移动角度的计算，实现了直线的动态消隐。而且，这种方法也适用于被曲面遮挡的直线的消隐，和被平面或者曲面遮挡的曲线的消隐。     

基于几何特征的3D模型隐写检测技术

针对3D模型自身独特结构, 筛选和提取其几何特征, 拟合验证其分布模型, 而后利用优化后的分类算法对三维模型有无隐秘信息隐写盲检测, 即针对空间域3D数据模型三角形网格几何特征隐写的信息隐藏检测分析。选取经典的空域隐写算法来构建数据库和训练分类器是实验前提。该算法不仅在低嵌入率、较小隐写容量条件下实现了有无隐写的正确检测, 而且形成了一套较完善的3D数据模型隐写分析实验流程框架。     

3D Motion recovery via affine Epipolar geometry

Algorithms to perform point-based motion estimation under orthographic and scaled orthographic projection abound in the literature. A key limitation of many existing algorithms is that they operate on the minimum amount of data required, often requiring the selection of a suitable minimal set from the available data to serve as a local coordinate frame. Such approaches are extremely sensitive to errors and noise in the minimal set, and forfeit the advantages of using the full data set. Furthermore, attention is seldom paid to the statistical performance of the algorithms.We present a new framework that allowsall available features to be used in the motion computations, without the need to select a frame explicitly. This theory is derived in the context of theaffine camera, which preserves parallelism and generalises the orthographic, scaled orthographic and para-perspective models. We define the affine epipolar geometry for two such cameras, giving the fundamental matrix in this case. The noise resistant computation of the epipolar geometry is discussed, and a statistical noise model constructed so that confidence in the results can be assessed.The rigid motion parameters are then determineddirectly from the epipolar geometry, using the novel rotation representation of Koenderink and van Doorn (1991). The two-view partial motion solution comprises the scale factor between views, the projection of the 3D axis of rotation and the cyclotorsion angle, while the addition of a third view allows the true 3D rotation axis to be computed (up to a Necker reversal). The computed uncertainties in these parameters permit optimal estimates to be obtained over time by means of a linear Kalman filter. Our theory extends work by Huang and Lee (1989), Harris (1990), and Koenderink and van Doorn (1991), and results are given on both simulated and real data.     

医学三维体数据中的几何测量方法研究

在应用医学图像诊断病情以及放射治疗计划制定中,器官及病变组织的几何测量具有重要的作用。文中基于医学三维体数据研究了空间中任意两点间的距离测量,基于面绘制的三角面片研究了组织器官表面积测量,基于体绘制研究了组织器官的体积测量,在实验中取得了较高的测量精度。     

Growth model for cholesterol accumulation in the wall of a simplified 3D geometry of the carotid bifurcation

Atherosclerosis is one of the leading causes of death in the first world countries nowadays. It is a vascular disease that affects medium and large size arteries, involving the formation of plaques within the artery wall. These plaques result from the accumulation of fat, cholesterol, cell debris, smooth muscle cells and other cells and substances, and may cause temporary or definitive lack of blood supply to an organ.This article proposes a model for cholesterol accumulation and plaque growth. The model is basically a mass balance of low density lipoproteins (LDL) in the intima. The inflow, outflow, oxidation, and consumption of LDL is modeled combining partial models and correlations available in the literature.The model was implemented into an open source finite volume code. Assuming steady blood flow, the code was used to predict lesion formation on a three-dimensional model of the carotid artery bifurcation, a location greatly studied for its role in supplying blood to some parts of the brain and for being related to strokes due to formation of atheromas. The simulation was carried out under physiologic conditions for blood pressure and LDL blood concentration.Results for LDL mass accumulation and intimal thickening over time, plaque shape, and location of thicker spots are reported, showing that the proposed model approximates reasonably well the intimal thickening obtained from post-mortem aortic fatty streaks and from B-mode ultrasonography of the carotid artery of healthy subjects reported by other authors.     

基于平面几何图形的立体浮雕建模技术

针对具有复杂曲面的艺术类浮雕建模问题,提出一种基于平面几何图形的解决方案。首先由二维区域和截面形状定义出浮雕曲面,浮雕则采用Z-MAP栅格在计算机内离散表示;然后把多个浮雕曲面通过六种可选方式融合成具有复杂外形的立体浮雕。为提高建模效率,给出一种针对二维区域内Z-MAP栅格点的快速遍历算法。最后通过多个应用实例,验证了上述技术方案。     

The 3D geometry modelling system (GEMO)

The Geometry Modelling System (GEMO), developed at Dresden University of Technology, covers the area of definition and manipulation of geometrical objects with regard to a further processing in a CAD/CAM system. The programming system GEMO has been designed modularly. The implemented algorithms are based on analytic and constructive geometrical methods. All modules have clearly defined interfaces, permitting a direct integration in CAD/CAM systems. Implementations for PCs and 32-bit computers are now available.     

Accurate reconstruction of 3D cardiac geometry from coarsely-sliced MRI

We present a comprehensive validation analysis to assess the geometric impact of using coarsely-sliced short-axis images to reconstruct patient-specific cardiac geometry. The methods utilize high-resolution diffusion tensor MRI (DTMRI) datasets as reference geometries from which synthesized coarsely-sliced datasets simulating in vivo MRI were produced. 3D models are reconstructed from the coarse data using variational implicit surfaces through a commonly used modeling tool, CardioViz3D. The resulting geometries were then compared to the reference DTMRI models from which they were derived to analyze how well the synthesized geometries approximate the reference anatomy. Averaged over seven hearts, 95% spatial overlap, less than 3% volume variability, and normal-to-surface distance of 0.32 mm was observed between the synthesized myocardial geometries reconstructed from 8 mm sliced images and the reference data. The results provide strong supportive evidence to validate the hypothesis that coarsely-sliced MRI may be used to accurately reconstruct geometric ventricular models. Furthermore, the use of DTMRI for validation of in vivo MRI presents a novel benchmark procedure for studies which aim to substantiate their modeling and simulation methods using coarsely-sliced cardiac data. In addition, the paper outlines a suggested original procedure for deriving image-based ventricular models using the CardioViz3D software.