物体渐变技术现状与发展

物体渐变技术在虚拟现实、工业模拟、科学计算可视化、动画生成等领域有着广泛的应用，具有十分重要的意义，近年来，有许多研究者提出了一些效果不错的算法，对这些算法进行了分析，并对物体渐变的基本原理、物体的表示方法与渐变技术间的紧密联系、二维物体渐变技术和三维物体渐变技术做了较全面的综述，探讨了现有物体渐变技术中需要改进的关键问题，并给出了渐变技术在未来的发展方向。     

增强现实中虚拟物体制作的研究*

增强现实是把计算机产生的虚拟物体合成到用户看到的真实世界中的一种技术。介绍了增强现实中虚拟物体所涉及的一些关键技术,包括虚拟物体的建模、摄像头标定、骨骼动画以及虚拟场景的优化,说明了如何将这些技术应用到实际系统中。     

Lindenmayer系统构建动态虚拟环境的研究

自然界中不仅包含规则的物体，而且还包含不规则的物体，正是这些使得现实世界丰富多彩。虚拟现实技术越来越受到人们的关注。该文介绍了L-系统的概念及其文法规则，并以它为理论基础，结合计算机图形学，以X3D为工具，生成虚拟的自然景物及不规则图形，如树木、叶子、花草等，并且通过引入动画机制来增强虚拟环境的真实感。     

用Authorware设计MCAI课件中的仿真动画

针对目前用Authorware动画图标设计二维动画的不足，巧妙运用Authorware提供的变量和函数来设计物体平抛运动的仿真动画，并给出了物体做平抛运动动画设计的原理、算法和流程。     

3DS MAX制作动画的实用技巧

本文是作者利用３ＤＳＭＡＸ为多媒体辅助教学软件制作动画的实践经验与体会,着重介绍了灯光的设置、动画背景图的调整、动画物体变色的实现、物体多个自用轴中心的实现、物体发生运动的防止、剖视物体张力的调整等方面的应用技巧。     

3DS MAX制作动画的实用技巧

本文是作者 利用３ＤＳ ＭＡＸ为多媒体辅助教学软件制作动画的实践经验与体会,着重介绍了灯光的设置,动画背景图的调整,动画物体变色的实现,物体多个自用轴中心的实现,物体发生运动的防止,剖视物体张力的调整等方面的应用技巧。     

3DS MAX中运用路径制作动画的技巧

在制作三维动画时,我们可能会遇到许多使物体沿路径运动的问题。沿路径运动,可分为运动、旋转、拉伸、变形等。本文将就这样一些问题,研究运用路径制作动画的技巧。 在3DS MAX中,可以通过两种方法来实现路径。一种方法是为物体的Position层级指定Path控制器,另一种是建立一个Path Deform物体,然后将物体链接到Path Deform物体上。下面让我们通过几个具体的实例来体验一下动画制作的乐趣吧！首先我们用     

三维动画实用技术（二）

二、变形效果的制作 1.节点数不等两物体之间的变形 在3DS中变形的起始物体和终止物体的节点数必须相等,否则就无法直接利用Key framer模块中的Object/Morph/Assign命令实现变形效果。其实节点数不同的物体之间也是完全可以实现变形效果的,只是需要一定的技巧,下面我们结合实例谈谈这种变形的实现过程。     

一种新的三维物体的渐变算法

本文研究了动画生成的物体渐变技术，基于图形的矢量表示法，提出了一种通过网格化一个三维物体来生成中间渐变物体的算法。给出了算法的形式化描述，并在Marlab上实现了该算法。计算结果表明，按这种算法产生的动画过渡平滑，节奏自然，画面流畅，且该算法具有稳定、高效、逼真和易控等优点。     

AFTER EFFECTS

创建物体动画最快速的方法是使用运动捕捉，这是一种以真实世界物体为动画而提供的运动。现在打开光盘After Effects Shortcut文件夹中的文件,依照我们循序渐进的技巧教程来学习如何使用这种方法。     

In situ colorimetric detection and mixing of glucose–enzyme droplets in an open-surface platform via Marangoni effect

Precise detection of glucose concentration in blood is critical in health monitoring and medical research. This paper describes a novel approach for enzymatic glucose sensing (glucose oxidase based) using thermal gradient in an open-surface platform. In order to obtain glucose concentration, droplets of enzyme and glucose with various concentrations are dispensed on a thin layer of fluorinert oil. By engineering the location of the droplet on the fluid surface and controlling the surface temperature drop of the fluid, surface deformation is created with fluid recirculating due to Marangoni convection. The surface deformation allows the microliter droplets to collide and mix at the hot spot. Image processing of the colorimetric reaction of the glucose and enzyme allows accurate determination of glucose concentration. The designed biosensor offers high repeatability, and concentration is measured within ±9.5 % of standard absorptiometry method. Contact-free manipulation of droplets, in situ measurement of glucose concentration, fast response time and high sensitivity are the key advantages of this device.     

Optical measurement of flow field and concentration field inside a moving nanoliter droplet

Droplets-based method has been employed to enhance mixing in microfluidic systems. This paper presents experimental studies of the recirculating flow field inside a moving droplet and the characterization of the mixing of two aqueous droplets. In the first part, the velocity field inside the moving water droplet was measured using the micro-particle image velocimetry (micro-PIV) technique. The PIV measurements showed that recirculation flow exists inside the droplet. However, the findings suggested that the outer layer of droplets move at a faster velocity than the central part. The result is different from what is reported by other researchers. In the second part, two water droplets, a de-ionized (DI) water droplet and another DI water droplet with fluorescent dye, were brought together by the carrier fluid to form a bigger droplet. The mixing between the two aqueous droplets was characterized by the fluorescent dye concentration distribution.     

Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation

We demonstrate controlled guiding of nanoliter emulsion droplets of polar liquids suspended in oil along shallow hydrophilic tracks fabricated at the base of microchannels located within microfluidic chips. The tracks for droplet guiding are generated by exposing the glass surface of polydimethylsiloxane (PDMS)-coated microscope slides via femtosecond laser ablation. The difference in wettability of glass and PDMS surfaces together with the shallow step-like transverse topographical profile of the ablated tracks allows polar droplets wetting preferentially the glass surface to follow the track. In this study, we investigate guiding of droplets of two different polar liquids (water/ethylene glycol) with and without surfactant suspended in an oil medium along surface tracks of different depths of 1, 1.5, and 2 \(\upmu\)m. The results of experiments are also verified with computational fluid dynamics simulations. Guiding of droplets along the tracks as a function of the droplet composition and size and the surface profile depth is evaluated by analyzing the trajectories of moving droplets with respect to the track central axis, and conditions for stable guiding are identified. The experiments and numerical simulations indicate that while the track topography plays a role in droplet guiding using 1.5- and 2-\(\upmu\)m deep tracks, for the case of the smallest track depth of 1 \(\upmu\)m, droplet guiding is mainly caused by surface energy modification along the track rather than the presence of a topographical step on the surface. Our results can be exploited to sort passively different microdroplets mixed in the same microfluidic chip, based on their inherent wetting properties, and they can also pave the way for guiding of droplets along reconfigurable tracks defined by surface energy modifications obtained using other external control mechanisms such as electric field or light.     

Nanoliter compound-droplet generation with composition variation

A new method for generation of nanoliter-volume, two-phase (compound) droplets with the ability to vary composition (i.e., encapsulant thickness) is presented. Thermocapillary-driven levitation of water droplets, a capability with potential for the improvement of lab-on-a-chip (LOC) processes, requires encapsulation by a secondary, less-volatile fluid that will also avoid the adverse effects of water-surface contamination on the driving surface motion. Key components of the closed system include the droplet generator actuated by a piezoelectric diaphragm, a pressure-control device, and a specialized nozzle for delivery of the encapsulating liquid. Experimental investigations demonstrate how system pressure variations allow composition changes, and voltage waveform input parameters regulate ejection dynamics, necessary for droplet capturing during the levitation process.     

Contact dynamics of nanodroplets in carbon nanotubes: effects of electric field,tube radius,and salt ions

We report contact dynamics of nanodroplets in carbon nanotubes using molecular dynamics simulations. The effects of electric field, nanotube radius, and salt ions included in the nanodroplets are explored in more detail. For the cases without applied electric field, the droplet fills the cross section of carbon nanotubes with small radius completely. When the tube radius becomes larger, the droplet retracts towards the surface of the nanotube to minimize the surface tension of the droplet and shows wider extension along the axial direction. When an electric field perpendicular to the axial direction of the carbon nanotubes is applied, the position and shape of the droplets are changed which is also related to the tube radius and whether the droplet contains salt ions. Unlike a planar surface, the nanotube limits spreading of the droplets along the radial direction. The variation of the center of mass of the droplets indicates a significant confinement to the position of the droplets in the electric field. For the salty water droplets, a strong electric field induces ejection of small water clusters from the droplet in a nanotube with large radius. As a consequence, the droplet and water clusters are separated and moved to two opposite sides of the nanotube by the electric field.     

Light fountain – a virtually enhanced stone sculpture

The article describes the making of an art piece combining stone sculpture and virtual water. The motivation for this art piece was to enrich the usual static format of a stone sculpture with a dynamic dimension. The dynamic dimension is attained with virtual water droplets running over the stone surface which behave as real water droplets. The 3-D surface of a specially carved stone sculpture is during an exhibition continuously captured by the Kinect sensor. Each water drop out of many thousands, which are introduced into the installation as evenly distributed rain drops, falling over the sculpture, are simulated individually to run over the stone surface following the largest slope. These simulated water drops are projected with a video projector as light points on the surface of the sculpture. An observer can enjoy simultaneously the haptic experience of touching the stone and observing a digitally generated but physically grounded animation.     

A deformable surface model for real-time water drop animation

A water drop behaves differently from a large water body because of its strong viscosity and surface tension under the small scale. Surface tension causes the motion of a water drop to be largely determined by its boundary surface. Meanwhile, viscosity makes the interior of a water drop less relevant to its motion, as the smooth velocity field can be well approximated by an interpolation of the velocity on the boundary. Consequently, we propose a fast deformable surface model to realistically animate water drops and their flowing behaviors on solid surfaces. Our system efficiently simulates water drop motions in a Lagrangian fashion, by reducing 3D fluid dynamics over the whole liquid volume to a deformable surface model. In each time step, the model uses an implicit mean curvature flow operator to produce surface tension effects, a contact angle operator to change droplet shapes on solid surfaces, and a set of mesh connectivity updates to handle topological changes and improve mesh quality over time. Our numerical experiments demonstrate a variety of physically plausible water drop phenomena at a real-time rate, including capillary waves when water drops collide, pinch-off of water jets, and droplets flowing over solid materials. The whole system performs orders-of-magnitude faster than existing simulation approaches that generate comparable water drop effects.     

基于GPU的屏幕空间镜头水滴实时渲染

为了实时模拟真实性高的镜头水滴,提出一种在可编程图形硬件中实现的镜头水滴渲染新方法。首先三维场景被渲染到一张场景纹理,然后在GPU着色器中为镜头水滴产生不规则边缘接触曲线,使用该曲线快速构建水滴的曲面,最后采用曲面的表面信息并根据水滴的光学属性渲染出水滴的折射效果。采用该方法,可以实时地在屏幕上渲染出镜头水滴效果。使用GPU着色器进行渲染,可以在渲染出效果逼真的水滴的情况下,获得实时的帧率。采用光线折射物理方法渲染出的水滴的效果比直接使用纹理贴图方式获得的水滴的效果更逼真。     

Contactless sensing of the conductivity of aqueous droplets in segmented flow

We present an electrode arrangement for the inline measurement of the conductivity of droplets in segmented flow by impedance spectroscopy. We use a thin-walled glass capillary with electrodes contacting the outer surface, so that the contactless measurement of conductivity of the liquid within the capillary is possible. The surface of the glass capillary is silanized resulting in a single hydrophobic surface across which droplets can freely move. We model the impedance of such insulated electrodes and use the model to optimize the electrode system. Measurement of solutions with various salt concentrations allows the performance of the electrode structure to be characterized. Subsequently, the measurement of the impedance response of the aqueous segments in two-phase flow was demonstrated. Measurements were firstly performed with an impedance analyzer and subsequently with a multi-sine measurement setup that is better suited to high-speed measurement of droplets. Previous electrical measurements of segmented flow sensed the difference in dielectric constant between the aqueous phase and the carrier fluid through measurement of capacitance. This work describes an electrical measurement of the conductivity of droplets in segmented flow, that is, the sensor senses a variable property of the droplet itself.     

Iridescent Water Droplets Beyond Mie Scattering

Looking at a cup of hot tea, an observer can see color patterns and granular textures both on the water surface and in the steam. Motivated by this example, we model the appearance of iridescent water droplets. Mie scattering describes the scattering of light waves by individual spherical particles and is the building block for both effects, but we show that other mechanisms must also be considered in order to faithfully reproduce the appearance. Iridescence on the water surface is caused by droplets levitating above the surface, and interference between light scattered by drops and reflected by the water surface, known as Quetelet scattering, is essential to producing the color. We propose a model, new to computer graphics, for rendering this phenomenon, which we validate against photographs. For iridescent steam, we show that variation in droplet size is essential to the characteristic color patterns. We build a droplet growth model and apply it as a post-processing step to an existing computer graphics fluid simulation to compute collections of particles for rendering. We significantly accelerate the rendering of sparse particles with motion blur by intersecting rays with particle trajectories, blending contributions along viewing rays. Our model reproduces the distinctive color patterns correlated with the steam flow. For both effects, we instantiate individual droplets and render them explicitly, since the granularity of droplets is readily observed in reality, and demonstrate that Mie scattering alone cannot reproduce the visual appearance.