Thermocapillary migrations of drops and bubbles

The transport phenomenon of drops or bubbles is a very important topic in fundamental hydrodynamics research and practical applications such as material processing and the chemical engineering. In microgravity environment, if drops or bubbles stay in a continuous phase with non-uniform temperature ¯eld, they will start to move as a result of the variance of the interface tension. This kind of movement is called the Marangoni migration. This review tries to sum up the main results in this ¯eld on theoretical analysis, numerical simulations and experiments. So far the theoretical analysis is still limited to the linear or weak nonlinear steady questions, while the current numerical simulations can already obtain the time- dependent process of the bubble/drop migration when the e®ect of heat convection is small. For strong heat convection problem, or when the Marangoni number is bigger than 100, no numerical result is in consistence with those of experiments so far. Some of the lastest numerical results are shown when heat convection is strong, and the main di®erence between strong and weak heat convection is analyzed. Finally, we also discuss the main unresolved problems in this ¯eld and some possible directions in the future.

Experimental Investigation of Pendant and Sessile Drops in Microgravity

The experiments regarding the contact angle behavior of pendant and sessile evaporating drops were carried out in microgravity environment. All the experiments were performed in the Drop Tower of Beijing, which could supply about 3.6 s of microgravity (free-fall) time. In the experiments, firstly, drops were injected to create before microgravity. The wettability at different surfaces, contact angles dependance on the surface temperature, contact angle variety in sessile and pendant drops were measured. Different influence of the surface temperature on the contact angle of the drops were found for different substrates. To verify the feasibility of drops creation in microgravity and obtain effective techniques for the forthcoming satellite experiments, we tried to inject liquid to create bigger drop as soon as the drop entering microgravity condition. The contact angle behaviors during injection in microgravity were also obtained.

Evaporation of Ethanol Drops on a Heated Substrate Under Microgravity Conditions

We present in this paper results obtained from a parabolic flight campaign regarding ethanol sessile drop evaporation under reduced gravity conditions. Drops are created using a syringe pump by means of injection through a PTFE (polytetrafluoroethylene) substrate. The drops are recorded using a video camera and an infrared camera to observe the thermal motion inside the drop and on the heating substrate. The experimental set-up presented in this paper enables the simultaneous visualization and access to the heat flux density that is transferred to the drop using a heat flux meter placed between the heating block and the PTFE substrate. We evidence original thermal spreading phenomena during the ethanol drop creation on a heated PTFE substrate. The drop exhibits specific behaviour which is discussed here. This work is performed in the frame of a French-Chinese collaboration (project IMPACHT) for future experiments in a Chinese scientific satellite.

Pressure drops of single and two-phase flows through T-type microchannel mixers

In this paper, preliminary experimental results are presented on pressure drop characteristics of single and two-phase flows through two T-type rectangular microchannel mixers with hydraulic diameters of 528 and 333 mum, respectively. It is shown that both N-2 and water single-phase laminar flows in microchannels, with consideration of experimental uncertainties, are consistent with classic theory, if additional effects, such as entrance effects that will interfere with the interpretation of experimental results, are eliminated by carefully designing the experiments. The obtained pressure drop data of N-2-water two-phase flow in micromixers are analyzed and compared with existing flow pattern-independent models. It is found that the Lockhart-Martinelli method generally underpredicts the frictional pressure drop. Thereafter, a modified correlation of C value in the Chisholm's equation based on linear regression of experimental data is proposed to provide a better prediction of the two-phase frictional pressure drop. Also among the homogeneous flow models investigated, the viscosity correlation of McAdams indicates the best performance in correlating the frictional pressure drop data (mean deviations within +/-20% for two micromixers both). Finally it is suggested that systematic studies are still required to accurately predict two-phase frictional performance in microchannels. (C) 2004 Elsevier B.V. All rights reserved.

Visual-Context Boosting for Eye Detection

Eye detection plays an important role in many practical applications. This paper presents a novel two-step scheme for eye detection. The first step models an eye by a newly defined visual-context pattern (VCP), and the second step applies semisupervised boosting for precise detection. VCP describes both the space and appearance relations between an eye region (region of eye) and a reference region (region of reference). The context feature of a VCP is extracted by using the integral image. Aiming to reduce the human labeling efforts, we apply semisupervised boosting, which integrates the context feature and the Haar-like features for precise eye detection. Experimental results on several standard face data sets demonstrate that the proposed approach is effective, robust, and efficient. We finally show that this approach is ready for practical applications.

G-quadruplex-based DNAzyme for sensitive mercury detection with the naked eye

Hg2+ is able to inhibit the peroxidase-like DNAzyme function of a T-containing G-quadruplex DNA via Hg2+-mediated T-T base pairs, which enables the visual detection of Hg2+ in the TMB-H2O2 reaction system with high selectivity and sensitivity.

Electrochemiluminescence of the Ru(bpy)(3)(2+)/S(2)O(8)(2-)system in purely aqueous solution at carbon paste electrode

The electrochemiluminescence (ECL) of the Ru(bgy)(3)(2-)/S2O82- system in purely aqueous solution at a carbon paste electrode can be clearly seen with the naked eye for Ru(bpy)(3)(2+) concentrations higher than 1 mmol L-1. The log-log plot of the emmitted light intensity vs. Ru(bpy)(3)(2+) concentration is linear over the region 10(-3)-10(-7) mol L-1 with a correlation coefficient of 0.997. The ECL intensity increases linearly with the S2O82- concentration from 10(-6) mol L-1 up to 0.3 mmol L-1 and drops off sharply at concentrations higher than 1 mmol L-1. In addition, a weak ECL signal was obtained when the potential was biased more negative than -0.6 V even in the absence of S2O82-.

THE COMPOUND EYE AS AN INDICATOR OF AGE AND SHRINKAGE IN ANTARCTIC KRILL

Laboratory studies have shown that Antarctic krill (Euphausia superba) shrink if maintained in conditions of low food availability. Recent studies have also demonstrated that E. superba individuals may be shrinking in the field during winter. If krill shrink during the winter, conclusions reached by length-frequency analysis may be unreliable because smaller animals may not necessarily be younger animals. In this study, the correlation between the body-length and the crystalline cone number of the compound eye was examined. Samples collected in the late summer show an apparent linear relationship between crystalline cone number and body-length. From a laboratory population, it appears that when krill shrink the crystalline cone number remains relatively unchanged. If crystalline cone number is little affected by shrinking, then the crystalline cone number may be a more reliable indicator of age than body-length alone. The ratio of crystalline cone number to body-length offers a method for detecting the effect of shrinking in natural populations of krill. On the basis of the crystalline cone number count, it appears from a field collection in early spring that E. superba do shrink during winter.

Automated cross-modal mapping in robotic eye/hand systems using plastic radial basis function networks

Q. Meng and M. H Lee, Automated cross-modal mapping in robotic eye/hand systems using plastic radial basis function networks, Connection Science, 19(1), pp 25-52, 2007.

Biologically inspired automatic construction of cross-modal mapping in robotic eye/hand systems

Q. Meng and M.H. Lee, 'Biologically inspired automatic construction of cross-modal mapping in robotic eye/hand systems', IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2006,) ,4742-49, Beijing, 2006.

Real Time Eye Tracking and Blink Detection with USB Cameras

A human-computer interface (HCI) system designed for use by people with severe disabilities is presented. People that are severely paralyzed or afflicted with diseases such as ALS (Lou Gehrig's disease) or multiple sclerosis are unable to move or control any parts of their bodies except for their eyes. The system presented here detects the user's eye blinks and analyzes the pattern and duration of the blinks, using them to provide input to the computer in the form of a mouse click. After the automatic initialization of the system occurs from the processing of the user's involuntary eye blinks in the first few seconds of use, the eye is tracked in real time using correlation with an online template. If the user's depth changes significantly or rapid head movement occurs, the system is automatically reinitialized. There are no lighting requirements nor offline templates needed for the proper functioning of the system. The system works with inexpensive USB cameras and runs at a frame rate of 30 frames per second. Extensive experiments were conducted to determine both the system's accuracy in classifying voluntary and involuntary blinks, as well as the system's fitness in varying environment conditions, such as alternative camera placements and different lighting conditions. These experiments on eight test subjects yielded an overall detection accuracy of 95.3%.

Modeling the Possible Influences of Eye Movements on the Refinement of Cortical Direction Selectivity

The second-order statistics of neural activity was examined in a model of the cat LGN and V1 during free-viewing of natural images. In the model, the specific patterns of thalamocortical activity required for a Bebbian maturation of direction-selective cells in VI were found during the periods of visual fixation, when small eye movements occurred, but not when natural images were examined in the absence of fixational eye movements. In addition, simulations of stroboscopic reming that replicated the abnormal pattern of eye movements observed in kittens chronically exposed to stroboscopic illumination produced results consistent with the reported loss of direction selectivity and preservation of orientation selectivity. These results suggest the involvement of the oculomotor activity of visual fixation in the maturation of cortical direction selectivity.

Neural Dynamics of Saccadic and Smooth Pursuit Eye Movement Coordination during Visual Tracking of Unpredictably Moving Targets

How does the brain use eye movements to track objects that move in unpredictable directions and speeds? Saccadic eye movements rapidly foveate peripheral visual or auditory targets and smooth pursuit eye movements keep the fovea pointed toward an attended moving target. Analyses of tracking data in monkeys and humans reveal systematic deviations from predictions of the simplest model of saccade-pursuit interactions, which would use no interactions other than common target selection and recruitment of shared motoneurons. Instead, saccadic and smooth pursuit movements cooperate to cancel errors of gaze position and velocity, and thus to maximize target visibility through time. How are these two systems coordinated to promote visual localization and identification of moving targets? How are saccades calibrated to correctly foveate a target despite its continued motion during the saccade? A neural model proposes answers to such questions. The modeled interactions encompass motion processing areas MT, MST, FPA, DLPN and NRTP; saccade planning and execution areas FEF and SC; the saccadic generator in the brain stem; and the cerebellum. Simulations illustrate the model’s ability to functionally explain and quantitatively simulate anatomical, neurophysiological and behavioral data about SAC-SPEM tracking.

Target Selection by Frontal Cortex During Coordinated Saccadic and Smooth Pursuit Eye Movement

Oculomotor tracking of moving objects is an important component of visually based cognition and planning. Such tracking is achieved by a combination of saccades and smooth pursuit eye movements. In particular, the saccadic and smooth pursuit systems interact to often choose the same target, and to maximize its visibility through time. How do multiple brain regions interact, including frontal cortical areas, to decide the choice of a target among several competing moving stimuli? How is target selection information that is created by a bias (e.g., electrical stimulation) transferred from one movement system to another? These saccade-pursuit interactions are clarified by a new computational neural model, which describes interactions among motion processing areas MT, MST, FPA, DLPN; saccade specification, selection, and planning areas LIP, FEF, SNr, SC; the saccadic generator in the brain stem; and the cerebellum. Model simulations explain a broad range of neuroanatomical and neurophysiological data. These results are in contrast with the simplest parallel model with no interactions between saccades and pursuit than common-target selection and recruitment of shared motoneurons. Actual tracking episodes in primates reveal multiple systematic deviations from predictions of the simplest parallel model, which are explained by the current model.

Miniature Eye Movements Enhance Fine Spatial Details

Our eyes are constantly in motion. Even during visual fixation, small eye movements continually jitter the location of gaze. It is known that visual percepts tend to fade when retinal image motion is eliminated in the laboratory. However, it has long been debated whether, during natural viewing, fixational eye movements have functions in addition to preventing the visual scene from fading. In this study, we analysed the influence in humans of fixational eye movements on the discrimination of gratings masked by noise that has a power spectrum similar to that of natural images. Using a new method of retinal image stabilization18, we selectively eliminated the motion of the retinal image that normally occurs during the intersaccadic intervals of visual fixation. Here we show that fixational eye movements improve discrimination of high spatial frequency stimuli, but not of low spatial frequency stimuli. This improvement originates from the temporal modulations introduced by fixational eye movements in the visual input to the retina, which emphasize the high spatial frequency harmonics of the stimulus. In a natural visual world dominated by low spatial frequencies, fixational eye movements appear to constitute an effective sampling strategy by which the visual system enhances the processing of spatial detail.