Transient response analysis and modeling of near wall flow conditions in a micro channel: evidence of slip flow

An experimental tool for determination of the near wall transport parameters in a micro channel, supported by flow simulation, is presented. The method is based on the transient flow response due to convective diffusion, in absence of specific adsorption. An approximately step-function type temporal solute concentration variation serves as the input signal. The associated response signal of a surface plasmon resonance sensor, acting as an integral part of a micro channel, has been taken as the output signal. It provides the flow-dependent change of the NaOH solute concentration in the channel within the optical detection and near wall distance interval 0 < d < 0.5 μm. The temporal signal evolution and response time, until an initially plain aqueous solution is replaced by the solute, varies inversely with solute concentration and flow rate. In the asymptotic limits, the near wall forced convective and diffusive channel transit times, along with the associated velocities, can be extracted and separated. A low convective near wall flow speed would account for 100% adsorption efficiency. The validity of the scaling relation for Fickian diffusive transport has been confirmed by experiments. Convective near wall flow reveals a distorted parabolic flow profile. This indicates relaxation of the no-slip condition, and presence of slip flow. Neither boundary layer formation, nor near wall micro turbulences have been observed. Eventually, a compact mathematical transient flow model, outlined in the Laplace domain for the electrical equivalent analogue circuit and applicable to the convective diffusion equation, has been developed for the flow transients.     

Effects of slip testing parameters on measured coefficient of friction

Slips and falls are a major cause of injuries in the workplace. Devices that measure coefficient of friction (COF) of the shoe–floor–contaminant interface are used to evaluate slip resistance in various environments. Testing conditions (e.g. loading rate, timing, normal force, speed, shoe angle) are believed to affect COF measurements; however, the nature of that relationship is not well understood. This study examines the effects of normal force (NF), speed, and shoe angle on COF within physiologically relevant ranges. A polyvinyl chloride shoe was tested using a modified industrial robot that could attain high vertical loads and relatively high speeds. Ground reaction forces were measured with a loadcell to compute COF. Experiment #1 measured COF over a range of NF (100–500 N) for two shoe angles (10° and 20°), four speeds (0.05, 0.20, 0.35, and 0.50 m/s), and two contaminants (diluted detergent and diluted glycerol). Experiment #2 further explored speed effect by testing seven speeds (0.01, 0.05, 0.20, 0.35, 0.50, 0.75, and 1.00 m/s) at a given NF (350 N) and shoe angle (20°) using the same two contaminants. Experiment #1 showed that faster speeds significantly decreased COF, and that a complex interaction existed between NF and shoe angle. Experiment #2 showed that increasing speed decreased COF asymptotically. The results imply that COF is dependent on film thickness separating the shoe and the heel, which is dependent on speed, shoe angle, and NF, consistent with tribological theory.     

The role of quantitative information about slip and grip force in prosthetic grasp stability

Prosthetic hands introduce an artificial sensorimotor interface between the prosthesis wearer and the environment that is prone to perturbations. We analyze theoretically and evaluate psychophysically the performance in stable grip control in conditions of physical grasps perturbation, such as object slip. Simulation results suggest that user-centered stable grasp control depends on two primal user parameters: reaction time to slip and grip force intensity. Experiments with human users indicate that a user’s response time can be controlled by relaying information about the speed of the slipping object, while minimal grip force intensity can be adjusted with information about grip force at the onset of the slip. Based on our theoretical and experimental findings, we propose a stable grasp control method for prosthetic hands.     

Available friction of ladder shoes and slip potential for climbing on a straight ladder

Straight ladder accidents are a major safety problem. As a leading cause of injuries involving straight ladders, slips at the ladder base occur when the required friction exceeds the available friction at the ladder shoe and floor interface. The objectives of this experiment were to measure the available friction at the base of a portable straight ladder in contact with a floor and to estimate the slip potential of the ladder. The results of friction measurements indicated that the measured friction coefficient on the oily surfaces differed among the six commercially available ladder shoes evaluated. A statistical model was used to compare the available friction results from the current study with the friction requirements under different climbing conditions from a previous study based on their stochastic distributions to estimate the slip potential at the base of the ladder. The results showed that different climbing conditions used in the previous study could be supported by available friction on dry surfaces. However, when the ladder was put onto oily surfaces, resulting in a significant reduction in the available friction due to contamination, slip potential was significantly increased.     

Effects of ad types, positions, animation lengths, and exposure times on the click-through rate of animated online advertisings

In this study, we focus on the click-through rate for the advertising effectiveness to examine the effects of design factors on animated online advertisings. A factorial experiment with repeated measuring was designed to collect a set of serially correlated click-through data. Ad types, positions, animation lengths, and exposure times were considered as the independent factors in this study. The generalized estimating equations (GEE) approach is introduced to the logistic regression models with correlated binary data. A goodness-of-fit statistic, quasi-likelihood information criterion (QIC) for data correlated models will be used for evaluating GEE-constructed models. The results showed a logistic regression model with order effect, two-factor interaction effect of ad types and ad positions, as well as ad positions and animation lengths are statistically significant. In addition, the GEE model with AR(1) correlation structures was well verified by the data.     

Stochastic optimization for the detection of changes in maternal heart rate kinetics during pregnancy

The stochastic optimization method ALOPEX IV has been successfully applied to the problem of detecting possible changes in the maternal heart rate kinetics during pregnancy. For this reason, maternal heart rate data were recorded before, during and after gestation, during sessions of exercises of constant mild intensity; ALOPEX IV stochastic optimization was used to calculate the parameter values that optimally fit a dynamical systems model to the experimental data. The results not only demonstrate the effectiveness of ALOPEX IV stochastic optimization, but also have important implications in the area of exercise physiology, as they reveal important changes in the maternal cardiovascular dynamics, as a result of pregnancy.     

Effects of anomalous characters and small stroke omissions on eye movements during the reading of Chinese sentences

We investigated the influence of typographical errors (typos) on eye movements and word recognition in Chinese reading. Participants' eye movements were tracked as they read sentences in which the target words were presented (1) normally, (2) with the initial stroke of the first characters removed (the omitted stroke condition) or (3) the first characters replaced by anomalous characters (the anomalous character condition). The results indicated that anomalous characters caused longer fixation durations and shorter outgoing forward saccade lengths than the correct words. This finding is consistent with the prediction of the theory of the processing-based strategy. Additionally, anomalous characters strongly disrupted lexical processing and whole sentence comprehension, but small stroke omissions did not. Implications of the effect of processing difficulty on forward saccade targeting for models of eye movement control during Chinese reading are discussed.     

Mechanisms of friction and assessment of slip resistance of new and used footwear soles on contaminated floors

Abstract

The great number of slipping accidents indicates that footwear providing good slip resistance must be rare. Slip resistance seems to be a purely physical phenomenon, however, more knowledge of the mechanisms of friction is needed to develop slip-resistant footwear and to ensure safer walking in slippery conditions. In the present study the influence of the normal wear of shoe heels and soles on their frictional properties was clarified. The slip resistance of three types of new and used safety shoes on four relatively slippery floor-contaminant combinations, was assessed with a prototype apparatus, which simulates the movements of a human foot and the forces applied to the underfoot surface during an actual slip. The used shoes were collected from 27 workers in a shipbuilding company and classified by sight into four wear classes: Good, satisfactory, poor, and worn-out. The assessed shoe heels and soles were in general more slippery when new compared to used heels and soles. However, footwear must be discarded before the tread pattern is worn-out. Used microcellular polyurethane (PU) heels and soles gave a considerably higher coefficient of kinetic friction (μ_k) on contaminated floors than used heels and soles made of compact nitrile (NR) and compact styrene rubber (SR). The heel-slide coefficient of kinetic friction (μ_kl) for used versus new shoes was on average 66% higher for PU (0·216 versus 0·130), 27% higher for SR (0·143 versus 0·113), and 7% lower for NR (0·098 versus 0·105). The fundamental mechanisms of friction between shoe soles and contaminated floors were also discussed, and experiments with seven slabs of sole materials were carried out to assess contact pressure effects from the viewpoint of slipping. Slip resistance particularly seemed to depend on the squeeze film and the contact pressure effects between the soling materials and the floor. An increasing contact pressure dramatically reduced the μ_k, thus indicating that the slip resistance varies considerably during the normal gait cycle. Hence, average friction readings are probably not at all decisive from the slip resistance point of view. An instantaneous coefficient of friction may be more relevant, because in walking the time available to achieve a sufficient coefficient of friction to avoid a slip is only a few tenths of a second.     

Effects of frame rate on vection and postural sway

The quality of stereoscopic 3D cinematic content is a major determinant for user experience in immersive cinema in both traditional theatres and cinematic virtual reality. One of the most important parameters is the frame rate of the content which has historically been 24 frames per second for movies, but higher frame rates are being considered for cinema and are standard for virtual reality. A typical behavioural response to immersive stereoscopic 3D content is vection, the visually-induced perception of self-motion elicited by moving scenes. In this work we investigated how participants’ vection varied with simulated virtual camera speed, frame rate, and motion blur produced by the virtual camera’s exposure, while viewing depictions of movement through a realistic virtual environment. We also investigated how their postural sway varied with these parameters and how sway covaried with levels of perceived self-motion. Results show that while average perceived vection significantly increased with 3D content frame rate and motion speed, motion blur had no significant effect on perceived vection. We also found that levels of postural sway induced by vection correlated positively with subjective ratings.     

Framework of grinding process modeling and simulation based on microscopic interaction analysis

This paper describes a framework of grinding process modeling to understand the grinding fundamentals and design grinding processes with predictive performance. The model regards grinding process as a time dependent process and an integration of microscopic interactions in the wheel-workpiece contact zone, including cutting, plowing, and sliding as well as other frictional interactions. The grinding process control and design are in fact to manage and balance all these interactions. The principles of microscopic interactions are analyzed and used to correlate the grinding process input parameters and performance output.     

Y型微管道中磁性纳米液体对混合率的影响

利用流动显示手段观测了Y型微管道内含纳米磁性颗粒的液体与去离子水的混合.研究了在Re=0.5～4,磁性颗粒体积分数0.38%-1.54%时,外加静磁场(场强40 Gs)对液体混合地影响.证实了磁场作用可以使完全混合长度大大缩短.同时初步分析了Re和体积分数Ψ对混合长度的影响.     

Effects of using different boundary conditions and computational domain dimensions on modeling and simulations of periodic metamaterial arrays in microwave frequencies

This article aims to demonstrate the effects of using different boundary conditions and different computational volume dimensions in numerical simulations of periodic metamaterial arrays. A double band metamaterial unit cell design will be utilized to show that use of different boundary conditions may result in simulation of dissimilar periodic array topologies with completely different electromagnetic responses. It will also be shown that dimensions of the computational volume may strongly affect the overall response of the metamaterial structure due to varying electromagnetic coupling between the array elements. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

铸坯定尺精确性的影响因素分析和改进

通过莱钢采用过各种定尺测量系统的优缺点,介绍了莱钢自主设计的测量辊定尺系统,分析了影响定尺精度的主要影响因素,并针对这些不利的因素采取相应的对策和改进措施,保证了较高的产品成材率。     

Effects of surface roughness and interface wettability on nanoscale flow in a nanochannel

Non-equilibrium molecular dynamics simulations have been carried out to investigate the effect of surface roughness and interface wettability on the nanorheology and slip boundary condition of simple fluids in a nanochannel of several atomic diameters width. The solid surfaces decorated with periodic nanostrips are considered as the rough surface in this study. The simulation results showed that the interface wettability and the surface roughness are important in determining the nanorheology of the nanochannel and fluid slip at solid–fluid interface. It is observed that the presence of surface roughness always suppresses the fluid slip for hydrophilic and hydrophobic surface nanochannels. For fluids over smooth and hydrophobic surfaces, the snapshots of fluid molecules show that an air gap or nanobubble exists at the fluid–solid interface, resulting in the apparent slip velocity. For a given surface with fixed interface wettability, the fluid velocities increase by increasing the driving force, while the driving force has no significant influence on the density structure of fluid molecules. The fluid slip and the flow rate are measured for hydrophilic and hydrophobic nanochannels. The flow rates in rough surface nanochannels are smaller than those of smooth surface walls due to the increase of drag resistance at the solid–fluid interface. The dependence between fluid slip and flow rate showed that the slip length increases approximately linearly with the flow rate for both the hydrophobic and hydrophilic surface nanochannels.     

Mesoscopic simulations of electroosmotic flow and electrophoresis in nanochannels

We review recent dissipative particle dynamics (DPD) simulations of electrolyte flow in nanochannels. A method is presented by which the slip length δB at the channel boundaries can be tuned systematically from negative to infinity by introducing suitably adjusted wall-fluid friction forces. Using this method, we study electroosmotic flow (EOF) in nanochannels for varying surface slip conditions and fluids of different ionic strength. Analytic expressions for the flow profiles are derived from the Stokes equation, which are in good agreement with the numerical results. Finally, we investigate the influence of EOF on the effective mobility of polyelectrolytes in nanochannels. The relevant quantity characterizing the effect of slippage is found to be the dimensionless quantity κδB, where 1/κ is an effective electrostatic screening length at the channel boundaries.     

Influence of shear deformation and rotary inertia on nonlinear free vibration of a beam with pinned ends

The method of multiple scales is used to analyze the nonlinear vibrations of a beam with pinned ends. The formulation incorporates the effects of the transverse shear deformation as well as the rotary inertia on the large amplitude vibration behaviour. A uniformly valid higher second-order perturbation solution is obtained. The predictions of nonlinear frequencies at different beam parameters are given. The influences of shear and rotary inertia are significant in the case of moderately thick and short beams undergoing large amplitude vibrations.     

Enlarging the domain of attraction and maximising convergence rate for delta operator systems with actuator saturation

In this paper, we present some new approaches to improve the feedback property of delta operator systems with actuator saturation. Both enlarging the domain of attraction and maximising the convergence rate are the desired feedback properties. The lifting technique is used to enlarge the domain of attraction for the delta operator systems subject to actuator saturation. The maximisation of convergence rate is realised by designing control gain inside a given ellipsoid. A necessary and sufficient condition is proposed for the contractive invariance of the given ellipsoid. Simulation results are provided to demonstrate the effectiveness of the developed techniques.     

基于平均变化率和空闲长度的丢包概率模型

针对RED队列丢包概率模型在计算丢包概率时精确性不足且未考虑网络流量的自相似性问题,提出了基于数据包入队速率平均变化率和队列空闲长度的队列丢包概率模型（DRED）,给出了相应的实现算法。DRED将网络流量状态引入到丢包概率的计算过程中,丢包概率随着网络流量状态的变化而变化,克服了RED队列丢包概率模型在平均队列长度大于队列最大阈值小于队列最大长度时直接将到达的数据包全部丢弃的弊端。实验结果表明,与RED相比,DRED丢包概率的计算更加精确,丢包率有所降低,吞吐量相对提高,端到端时延虽稍有增大,但时延抖动较小,网络的整体性能有一定提高。     

An apparatus and a method for determining the slip resistance of shoes and floors by simulation of human foot motions

An apparatus to measure the coefficient of kinetic friction (μ_k) between the shoe sole and the underfoot surface was constructed, and a method including criteria to evaluate the risk of slipping during walking was developed. The apparatus is a prototype stationary step simulator capable of simulating the movements of a human foot and the forces applied to the underfoot surface during an actual slip, and the drainage capability of the contact surface between the shoe sole and the flooring when different lubricants or contaminants are used.

The apparatus consists of a movable artificial foot controlled by a computer with the aid of three hydraulic cylinders. The frictional force (F_μ), the normal force (F_N) and their ratio (μ_k = F_μ/F_N) are measured with a two-way force platform when the foot slides along its surface. Two separate gait patterns, heel-slide (μ_k1) and sole-slide (μ_k2) gait pattern, are used for the evaluations. The method classifies studied shoe, lubricant and underfoot surface combinations into five slip resistance classes according to the measured μ_k1 The slip resistance assessments are specified with some complementary safety criteria, e.g., the ratio μ_k1/ μ_k2 The reliability of the developed measurement method was assessed in an international comparison test. According to available results discussed in this paper, our method seems to be valid and the slip resistance measurements seem to be repeatable.