Dynamics of fingertip contact during the onset of tangential slip

Through highly precise perceptual and sensorimotor activities, the human tactile system continuously acquires information about the environment. Mechanical interactions between the skin at the point of contact and a touched surface serve as the source of this tactile information. Using a dedicated custom robotic platform, we imaged skin deformation at the contact area between the finger and a flat surface during the onset of tangential sliding movements in four different directions (proximal, distal, radial and ulnar) and with varying normal force and tangential speeds. This simple tactile event evidenced complex mechanics. We observed a reduction of the contact area while increasing the tangential force and proposed to explain this phenomenon by nonlinear stiffening of the skin. The deformation''s shape and amplitude were highly dependent on stimulation direction. We conclude that the complex, but highly patterned and reproducible, deformations measured in this study are a potential source of information for the central nervous system and that further mechanical measurement are needed to better understand tactile perceptual and motor performances.     

Effect of skin hydration on the dynamics of fingertip gripping contact

The dynamics of fingertip contact manifest themselves in the complex skin movements observed during the transition from a stuck state to a fully developed slip. While investigating this transition, we found that it depended on skin hydration. To quantify this dependency, we asked subjects to slide their index fingertip on a glass surface while keeping the normal component of the interaction force constant with the help of visual feedback. Skin deformation inside the contact region was imaged with an optical apparatus that allowed us to quantify the relative sizes of the slipping and sticking regions. The ratio of the stuck skin area to the total contact area decreased linearly from 1 to 0 when the tangential force component increased from 0 to a maximum. The slope of this relationship was inversely correlated to the normal force component. The skin hydration level dramatically affected the dynamics of the contact encapsulated in the course of evolution from sticking to slipping. The specific effect was to reduce the tendency of a contact to slip, regardless of the variations of the coefficient of friction. Since grips were more unstable under dry skin conditions, our results suggest that the nervous system responds to dry skin by exaggerated grip forces that cannot be simply explained by a change in the coefficient of friction.     

Spatio-temporal skin strain distributions evoke low variability spike responses in cuneate neurons

A common method to explore the somatosensory function of the brain is to relate skin stimuli to neurophysiological recordings. However, interaction with the skin involves complex mechanical effects. Variability in mechanically induced spike responses is likely to be due in part to mechanical variability of the transformation of stimuli into spiking patterns in the primary sensors located in the skin. This source of variability greatly hampers detailed investigations of the response of the brain to different types of mechanical stimuli. A novel stimulation technique designed to minimize the uncertainty in the strain distributions induced in the skin was applied to evoke responses in single neurons in the cat. We show that exposure to specific spatio-temporal stimuli induced highly reproducible spike responses in the cells of the cuneate nucleus, which represents the first stage of integration of peripheral inputs to the brain. Using precisely controlled spatio-temporal stimuli, we also show that cuneate neurons, as a whole, were selectively sensitive to the spatial and to the temporal aspects of the stimuli. We conclude that the present skin stimulation technique based on localized differential tractions greatly reduces response variability that is exogenous to the information processing of the brain and hence paves the way for substantially more detailed investigations of the brain''s somatosensory system.     

Influence of physico-chemical,mechanical and morphological fingerpad properties on the frictional distinction of sticky/slippery surfaces

This study investigates how the fingerpad hydrolipid film, shape, roughness and rigidity influence the friction when it rubs surfaces situated in the slippery psychophysical dimension. The studied counterparts comprised two ‘real’ (physical) surfaces and two ‘virtual’ surfaces. The latter were simulated with a tactile stimulator named STIMTAC. Thirteen women and 13 men rubbed their right forefingers against the different surfaces as their arms were displaced by a DC motor providing constant velocity and sliding distance. Tangential and normal forces were measured with a specific tribometer. The fingerpad hydrolipid film was characterized by Fourier transform infrared spectroscopy. The shape and roughness of fingers were extrapolated from replicas. Indentation measurements were carried out to determine fingerpad effective elastic modulus. A clear difference was observed between women and men in terms of friction behaviour. The concept of tactile frictional contrast (TFC) which was introduced quantifies an individual''s propensity to distinguish two surfaces frictionally. The lipids/water ratio and water amount on the finger skin significantly influenced the TFC. A correlation was observed between the TFC and fingerpad roughness, i.e. the height of the fingerpad ridges. This is essentially owing to gender differences. A significant difference between men''s and women''s finger topography was also noted, because our results suggested that men have rougher fingers than women. The friction measurements did not correlate with the fingerpad curvature nor with the epidermal ridges'' spatial period.     

How to identify water from thickener aqueous solutions by touch

Water detection is one of the most crucial psychological processes for many animals. However, nobody knows the perception mechanism of water through our tactile sense. In the present study, we found that a characteristic frictional stimulus with large acceleration is one of the cues to differentiate water from water contaminated with thickener. When subjects applied small amounts of water to a glass plate, strong stick-slip phenomena with a friction force of 0.46 ± 0.30 N and a vertical force of 0.57 ± 0.36 N were observed at the skin surface, as shown in previous studies. Surprisingly, periodic shears with acceleration seven times greater than gravitational acceleration occurred during the application process. Finite-element analyses predicted that these strong stimuli could activate tactile receptors: Meissner''s corpuscle and Pacinians. When such stimuli were applied to the fingertips by an ultrasonic vibrator, a water-like tactile texture was perceived by some subjects, even though no liquid was present between the fingertip and the vibrator surface. These findings could potentially be applied in the following areas: materials science, information technology, medical treatment and entertainment.     

蒙皮约束下的动画角色模型分割方法

动画角色的数据重用可以提高游戏与动画的制作效率并丰富角色类型。针对模型数据重用的首要步骤——动画角色的三维网格分割问题,提出了一种蒙皮约束下的分割方法,利用蒙皮信息的运动相关性,产生依据该信息的部件预分割,在预分割结果上进行拓扑检查并调整,进而再对切口处进行优化处理,最终产生适合动画角色融合的网格部件。最后给出在用游戏公司提供的真实数据上对新方法进行的了测试,结果,证明了表明该新方法的简洁有效并说明了其适用范围。     

Surface tension measurements of metallic melts under microgravity

The surface tension of liquid metals and alloys was measured for the first time in microgravity using the oscillating drop technique. Data for pure gold, a congruently melting gold copper alloy, and an eutectic zirconium nickel alloy are presented. We find excellent agreement with available results obtained on Earth by the same technique, but only if the latter are corrected to account for gravity effects. This is not only shows the necessity for the correction of the surface tension data derived from Earth-bound oscillating drop experiments, but also proves its correctness.DeceasedPaper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

变体机翼大变形梯形蒙皮结构研究

首先介绍了变体机翼及蒙皮结构的发展研究现状,提出了大变形梯形蒙皮结构的构想.随后,建立了梯形蒙皮结构的力学分析数学模型,与有限元仿真分析结果进行了比较和分析,验证了所建立数学分析模型的正确性,为进一步开展制备和实验研究奠定了理论基础.     

Influence of epidermal hydration on the friction of human skin against textiles

Friction and shear forces, as well as moisture between the human skin and textiles are critical factors in the formation of skin injuries such as blisters, abrasions and decubitus. This study investigated how epidermal hydration affects the friction between skin and textiles.The friction between the inner forearm and a hospital fabric was measured in the natural skin condition and in different hydration states using a force plate. Eleven males and eleven females rubbed their forearm against the textile on the force plate using defined normal loads and friction movements. Skin hydration and viscoelasticity were assessed by corneometry and the suction chamber method, respectively.In each individual, a highly positive linear correlation was found between skin moisture and friction coefficient (COF). No correlation was observed between moisture and elasticity, as well as between elasticity and friction. Skin viscoelasticity was comparable for women and men. The friction of female skin showed significantly higher moisture sensitivity. COFs increased typically by 43% (women) and 26% (men) when skin hydration varied between very dry and normally moist skin. The COFs between skin and completely wet fabric were more than twofold higher than the values for natural skin rubbed on a dry textile surface.Increasing skin hydration seems to cause gender-specific changes in the mechanical properties and/or surface topography of human skin, leading to skin softening and increased real contact area and adhesion.     

Simulation of synthetic gecko arrays shearing on rough surfaces

To better understand the role of surface roughness and tip geometry in the adhesion of gecko synthetic adhesives, a model is developed that attempts to uncover the relationship between surface feature size and the adhesive terminal feature shape. This model is the first to predict the adhesive behaviour of a plurality of hairs acting in shear on simulated rough surfaces using analytically derived contact models. The models showed that the nanoscale geometry of the tip shape alters the macroscale adhesion of the array of fibres by nearly an order of magnitude, and that on sinusoidal surfaces with amplitudes much larger than the nanoscale features, spatula-shaped features can increase adhesive forces by 2.5 times on smooth surfaces and 10 times on rough surfaces. Interestingly, the summation of the fibres acting in concert shows behaviour much more complex that what could be predicted with the pull-off model of a single fibre. Both the Johnson–Kendall–Roberts and Kendall peel models can explain the experimentally observed frictional adhesion effect previously described in the literature. Similar to experimental results recently reported on the macroscale features of the gecko adhesive system, adhesion drops dramatically when surface roughness exceeds the size and spacing of the adhesive fibrillar features.     

In situ raman measurements of suspended individual single-walled carbon nanotubes under strain

We present a technique for in situ Raman measurements of suspended individual single-walled carbon nanotubes (SWNTs) under strain. We observe a strong change in the radial breathing mode intensity with increasing strain as the nanotube moves out of (or into) resonance, and for strain greater than approximately 2%, there is a clear irreversible upshift in the G-mode frequencies accompanied by an increase in intensity of a broad peak at a position associated with the D mode. For lower strain, the G-mode peaks (A1, E1, and E2) do not change significantly in position but change in relative intensity.     

A review of tissue-engineered skin bioconstructs available for skin reconstruction

Situations where normal autografts cannot be used to replace damaged skin often lead to a greater risk of mortality, prolonged hospital stay and increased expenditure for the National Health Service. There is a substantial need for tissue-engineered skin bioconstructs and research is active in this field. Significant progress has been made over the years in the development and clinical use of bioengineered components of the various skin layers. Off-the-shelf availability of such constructs, or production of sufficient quantities of biological materials to aid rapid wound closure, are often the only means to help patients with major skin loss. The aim of this review is to describe those materials already commercially available for clinical use as well as to give a short insight to those under development. It seeks to provide skin scientists/tissue engineers with the information required to not only develop in vitro models of skin, but to move closer to achieving the ultimate goal of an off-the-shelf, complete full-thickness skin replacement.     

肤色建模和肤色分割的人脸定位研究

为了实现彩色图像中人脸的精确定位,提出了一种基于肤色模型、肤色分割处理的人脸定位算法.通过建立肤色模型计算得到图像的相似度分布图,经自适应阈值的二值化处理后,再进行肤色分割,将非人脸区域去除:最终利用眼睛与嘴巴构成三角形特征结合人脸椭圆模板匹配定位人脸.实验结果表明,该算法对于复杂背景下的彩色图像中的人脸正面定位和人脸转动一定角度后定位都有较好效果.     

机器人主动式触觉的研究

报道了主动触觉实验系统的组成以及对目标的物理特性（刚性、回弹性、摩擦等）和表面形貌特征主动探测的结果，提出了重建表面特征三维触觉模型的方法。研制成作为系统核心部件的两种新型传感器─—指状六维力传感器和线阵式触觉传感器。前者样机性能指标：Ｆ＿ｘ，Ｆ＿ｙ：±３０Ｎ，Ｆ＿ｚ±５０Ｎ；Ｍ＿ｘ，Ｍ＿ｙ：±５０Ｎｃｍ，Ｍ＿ｚ：±６０Ｎｃｍ；精度：１％Ｆ．Ｓ．；耦合误差：２％Ｆ．Ｓ．；工作部尺寸Φ１０×３０ｍｍ。后者样机性能：一列１２个敏感元，间距１ｍｍ，灵敏度３Ｖ／ｍｍ。     

包装纸艺术的表达与发展

包装纸艺术是材料的艺术,从审美层次上来看,长期以来包装纸的材料独特性没有得到足够的重视.随着现代包装纸的日益丰富,包装纸的艺术表达越来越为人们所认同.通过包装纸艺术的表现基础.展开对包装纸艺术的再塑造处理分析,重点就是材料本身的特殊性和表现手段,以期达到对包装纸艺术价值的重视.     

Fracture energy of UHP-FRC under direct tensile loading applied at low strain rates

This research investigates the fracture energy of ultra-high performance fiber reinforced concretes (UHP-FRC) under direct tensile loading applied at relatively low strain rates. Nine UHP-FRC series incorporating three types of steel fibers (straight, end-hooked, and twisted fibers), each in three different fiber volume fractions, are tested under uniaxial tensile loading at four different strain rates, ranging from 0.0001 s⁻¹ to 0.1 s⁻¹. Particular attention is given to clearly distinguish between the dissipated energy during the strain hardening and softening portions of the loading regime. The test results show that: 1) the fracture energy is mainly influenced by a parameter, termed fiber factor, which is a function of the fiber volume fraction and slenderness, and 2) all three types of UHP-FRCs exhibit increases in fracture energy with increasing strain rates. The observed strain rate sensitivity of the fracture energy suggests it is likely associated with the strain sensitive micro-cracking that occurs during fiber pull-out.     

Wearable multifunctional organohydrogel-based electronic skin for sign language recognition under complex environments

Language barrier is the main cause of disagreement.Sign language,which is a common language in all the worldwide language families,is difficult to be entirely popularized due to the high cost of learning as well as the technical barrier in real-time translation.To solve these problems,here,we constructed a wearable organohydrogel-based electronic skin(e-skin)with fast self-healing,strong adhesion,extraor-dinary anti-freezing and moisturizing properties for sign language recognition under complex environ-ments.The e-skin was obtained by using an acrylic network as the main body,aluminum(Ⅲ)and bay-berry tannin as the crosslinking agent,water/ethylene glycol as the solvent system,and a polyvinyl al-cohol network to optimize the network performance.Using this e-skin,a smart glove was further built,which could carry out the large-scale data collection of common gestures and sign languages.With the help of the deep learning method,specific recognition and translation for various gestures and sign lan-guages could be achieved.The accuracy was 93.5％,showing the ultra-high classification accuracy of a sign language interpreter.In short,by integrating multiple characteristics and combining deep learning technology with hydrogel materials,the e-skin achieved an important breakthrough in human-computer interaction and artificial intelligence,and provided a feasible strategy for solving the dilemma of mutual exclusion between flexible electronic devices and human bodies.     

Evaluation of crack tip stress and strain fields under nonproportional loading in a viscoelastic material

The crack tip strain and stress fields in a viscoelastic material under nonproportional loading conditions are evaluated. In order to evaluate the strain field, the crack tip displacement field is measured by using the digital image correlation (DIC) technique. This displacement field is then approximated by using the theoretically obtained crack tip displacement field in viscoelastic materials. The result shows that the approximation method can smoothly reconstruct the experimentally obtained displacement field. From the approximated displacement field, the crack tip strain field can be precisely obtained by using the differential form of the theoretical displacement. On the other hand, the crack tip stress field is analyzed by using the stress function. This suggests that the strain and stress fields can be independently evaluated. In addition, different time dependencies between stress and strain fields near the crack tip are observed. Based on this experiment, we can discuss the several criteria for the crack propagation directions in viscoelastic materials.     

Relative Slip on Contact Surface under Partial Slip Fretting Fatigue Condition

Abstract:  A combined experimental–numerical approach was utilized to characterize the relative slip along the contact surface and its features under the partial slip fretting fatigue condition. Relative displacements at two locations on the substrate (specimen) and fretting pad were measured in fretting fatigue tests. These measurements were then utilized to validate finite element analysis. Effects of the coefficient of friction on the relative slip and contact condition were investigated. The stress state along the contact surface was also investigated. Two contact geometries were analysed: cylinder-on-flat and flat-on-flat. There was no change in relative displacement between locations away from the contact surface because of the change in the coefficient of friction, while relative slip on the contact surface was affected by coefficient of friction. In addition, stick/slip sizes were affected by the change in coefficient of friction. Comparison between present and previous finite element models showed that stress state, as well as a critical plane-based crack-initiation parameter, was not much different between these approaches, while relative slip on the contact surface changed considerably.