Brush Model Research Articles

Structure and elasticity of bush and brush-like models of the endothelial glycocalyx

The endothelial glycocalyx (EG), a sugar-rich layer that lines the luminal surface of blood vessels, is an important constituent of the vascular system. Although the chemical composition of the EG is fairly well known, there is no consensus regarding its ultrastructure. While previous experiments probed the properties of the layer at the continuum level, they did not provide sufficient insight into its molecular organisation. In this work, we investigate the EG mechanics using two simple brush and bush-like simulation models, and use these models to describe its molecular structure and elastic response to indentation. We analyse the relationship between the mechanical properties of the EG layer and several molecular parameters, including the filament bending rigidity, grafting density, and the type of ultrastructure . We show that variations in the glycan density determine the elasticity of the EG for small deformations, and that the normal stress may be effectively dampened by the EG layer, preventing the stress from being transferred to the cell membrane. Furthermore, our bush-like model allows us to evaluate the forces and energies required to overcome the mechanical resistance of the EG.

Adhesion state estimation based on improved tire brush model

On the basis of calculating the longitudinal force using the original brush model, we simplify the tire structure and consider the lateral force generated by the lateral elasticity of the tread. At the same time, the boundary conditions between the adhesion area and the slip zone in the contact area of the tire are fully discussed. By establishing an improved tire brush model, the error caused by neglecting the sideslip characteristics is avoided, and the adaptability of the tire model is improved. A double nonlinear compensation method based on the lateral acceleration deviation and the yaw rate deviation is employed to estimate the road adhesion coefficient, which is closer to the actual attachment situation than the standard calculation. Based on this model, the vehicle stability coefficient k is defined and calculated to describe the stability of the vehicle during the driving process. The modeling results show that the value of k is always in the stable range of [0, 1]. Therefore, the vehicle that utilizes the improved tire brush model is always within the controllable range in the driving process, which verifies the effectiveness of the model.

Haptic Decorating on the Surface of Virtual Clay Model

A novel haptic decorating method on the surface of virtual clay model is proposed. The relationship between brush deformation and endured force is researched for the first time by applying the spring-mass model to construct the 3D brush model. Then, the collision detection between virtual hairy brush and virtual clay model is researched based on collision algorithm of weighted average distance. When the hairy brush initially collides with 3D exterior, the tactility is simulated and the interactive virtual painting on the 3D exterior is carried out practically. The 3D brush stroke is formed by superimposing 3D brush footprints along the painting direction and controlling the stress of the brush. The ink quantity in the brush footprint is determined according to the proposed positive correlation between the exerted pressure on brush and outflow ink quantity of the brush. A painting storage method is also presented for storing and displaying 3D stroke painting results. The proposed method has been successfully applied in the 3D virtual painting system based on real-time force feedback technology. With this system, the 3D brush strokes with 3D half-dry and ink diffusion results can be painted with a Phantom Desktop haptic device, which effectively enhance reality to users.

AFM-based detection of glycocalyx degradation and endothelial stiffening in the db/db mouse model of diabetes

Degradation of the glycocalyx and stiffening of endothelium are important pathophysiological components of endothelial dysfunction. However, to our knowledge, these events have not been investigated in tandem in experimental diabetes. Here, the mechanical properties of the glycocalyx and endothelium in ex vivo mouse aorta were determined simultaneously in indentation experiments with an atomic force microscope (AFM) for diabetic db/db and control db/+ mice at ages of 11–19 weeks. To analyze highly heterogeneous aorta samples, we developed a tailored classification procedure of indentation data based on a bi-layer brush model supplemented with Hertz model for quantification of nanomechanics of endothelial regions with and without the glycocalyx surface. In db/db mice, marked endothelial stiffening and reduced glycocalyx coverage were present already in 11-week-old mice and persisted in older animals. In contrast, reduction of the effective glycocalyx length was progressive and was most pronounced in 19-week-old db/db mice. The reduction of the glycocalyx length correlated with an increasing level of glycated haemoglobin and decreased endothelial NO production. In conclusion, AFM nanoindentation analysis revealed that stiffening of endothelial cells and diminished glycocalyx coverage occurred in early diabetes and were followed by the reduction of the glycocalyx length that correlated with diabetes progression.

A virtual 3D interactive painting method for Chinese calligraphy and painting based on real-time force feedback technology

A novel 3D interactive painting method for Chinese calligraphy and painting based on force feedback technology is proposed. The relationship between the force exerted on the brush and the resulting brush deformation is analyzed and a spring-mass model is used to build a model of the 3D Chinese brush. The 2D brush footprint between the brush and the plane of the paper or object is calculated according to the deformation of the 3D brush when force is exerted on the 3D brush. Then the 3D brush footprint is obtained by projecting the 2D brush footprint onto the surface of the 3D object in real time, and a complete 3D brushstroke is obtained by superimposing 3D brush footprints along the painting direction. The proposed method has been successfully applied in a virtual 3D interactive drawing system based on force feedback technology. In this system, users can paint 3D brushstrokes in real time with a Phantom Desktop haptic device, which can effectively serve as a virtual reality interface to the simulated painting environment for users.

Dimerization and Long-Range Repulsion Established by Both Termini of the Microtubule-Associated Protein Tau.

Tau is a microtubule-associated protein found in neuronal axons that has several well-known functions, such as promoting microtubule polymerization, stabilizing microtubules against depolymerization, and spatially organizing microtubules in axons. Two contrasting models have been previously described to explain tau's ability to organize the spacing between microtubules: complementary dimerization of the projection domains of taus on adjacent microtubules or tau's projection domain acting as a polyelectrolyte brush. In this study, atomic force microscopy was used to interrogate intermolecular interactions between layers of tau protein immobilized on mica substrates and on silicon nitride atomic force microscope tips. On these surfaces, tau adopts an orientation comparable to that when bound to microtubules, with the basic microtubule binding domain immobilized and the acidic domains extending into solution. Force-distance curves collected via atomic force microscopy reveal that full length human tau, when assembled into dense surface-bound layers, can participate in attractive electrostatic interactions consistent with the previously reported dimerization model. However, modulating the ionic strength of the surrounding solution can change the structure of these layers to produce purely repulsive interactions consistent with a polyelectrolyte brush structure, thus providing biophysical evidence to support both the zipper and brush models. In addition, a pair of projection domain deletion mutants were examined to investigate whether the projection domain of the protein is essential for the dimerization and brush models. Force-distance curves collected on layers of these proteins demonstrate that the C-terminus can play a role analogous to that of the projection domain.

Interaction Forces between Pegylated Star-Shaped Polymers at Mica Surfaces.

We present a study focused on characterizing the interaction forces between mica surfaces across solutions containing star-shaped polymers with cationic ends. Using the surface forces apparatus, we show that the interaction forces in pure water between surfaces covered with the polymers can be adequately described by the dendronized brush model. In that framework, our experimental data suggest that the number of branches adsorbed at the surface decreases as the concentration of polymer in the adsorbing solution increases. The onset of interaction was also shown to increase with the concentration of polymer in solution up to distances much larger than the contour length of the polymer, suggesting that the nanostructure of the polymer film is significantly different from that of a monolayer. High compression of the polymer film adsorbed at low polymer concentration revealed the appearance of a highly structured hydration layer underneath the polymer layer. These results support that charged polymer chains do not necessarily come into close contact with the surface even if strong electrostatic interaction is present. Altogether, our results provide a comprehensive understanding of the interfacial behavior of star-shaped polymers and reveal the unexpected role of hydration water in the control of the polymer conformation.

Calligraphy-Stroke Learning Support System Using Projector and Motion Sensor

This paper presents a newly developed calligraphy-stroke learning support system. The system incorporates the following functions: a) Displaying brushwork, trajectory, and handwriting; b) recording and playback of an expert’s calligraphy-stroke; and c) teaching a learner a calligraphy-stroke. The following features of the system demonstrate the contributions of our study. (1) The system, which consists of a sensor and projector, is simple and compact, so as to be easily introduced to the usual educational fields and practical leaning situations. (2) Three-dimensional calligraphy-stroke is instructed by presenting two-dimensional visual information. (3) A trajectory region is generated in the form of continuous squares, calculated using a brush model based on the brush position information measured by a sensor. (4) Handwriting is expressed by mapping a handwriting texture image according to ink concentration and the brush handling state. The results of the trial experiment suggest the effectiveness of the learning support function in terms of letter form and calligraphy-stroke.

Calculating Membrane Area Compressibility from MD Simulations: a Novel Computational Framework

Like thin elastic sheets, lipid bilayers can bend and stretch, and are characterized by mechanical constants such as bending rigidity (Kc) and area compressibility (Ka), which define the free energy of bilayer deformation and thus have direct implications in quantifying the energetics of protein-membrane interactions. Limited experimental data for Kc and Ka of different lipid mixtures makes such calculations challenging. Existing computational methods for calculating Ka from MD simulations exhibit strong dependence on bilayer size, or require multiple simulations with constraints on the area, or tension. We present a novel computational framework that is independent of system size and requires analysis only of a single sufficiently converged simulation trajectory. The method is based on Helfrich's theory of elasticity by relating relative changes in area to relative changes in thickness. The distribution of local fluctuations in the thickness of each bilayer leaflet is used to construct a potential of mean force and recover the bilayer Ka from a quadratic fit. The rapid calculation utilizes freely available software packages. We present results for a variety of single and multicomponent bilayers of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin, utilizing simulation results at different temperatures and bilayer sizes. The calculated compressibility moduli range from 170 to 320 mN/m and agree for the majority of tested cases with values reported from experiments and other computational methods. We further validate our method in a comparison with an existing polymer brush model and confirm the linear relationship between thickness and (Kc/Ka) ˆ (1/2), all calculated from the simulation trajectories.

Analysis and optimisation of objective vehicle dynamics testing in winter conditions

ABSTRACTObjective testing of vehicle handling in winter conditions has not been implemented yet because of its low repeatability and its low signal-to-noise ratio. Enabling this testing, by identifying robust manoeuvres and metrics, was the aim of this study. This has been achieved by using both experimental data, gathered with steering-robot tests on ice, and simulation models of different complexities. Simple bicycle models with brush and MF-tyre models were built, both optimally parameterised against the experimental data. The brush model presented a better balance in complexity performance. This model was also implemented in a Kalman filter to reduce measurement noise; however, a simpler low-pass filter showed almost similar results at lower cost. A more advanced full vehicle model was built in VI-CarRealTime, based on kinematics and compliance data, damper measurements, and real tyre measurements in winter conditions. This model offered better results and was therefore chosen to optimise the initial manoeuvres through test design and simulations. A sensitivity analysis (ANOVA) of the experimental data allowed one to classify the robustness of the metrics. Finally, to validate the results, the proposed and the initial manoeuvres were tested back to back in a new winter campaign.

Cooperative Interactions between Different Classes of Disordered Proteins Play a Functional Role in the Nuclear Pore Complex of Baker's Yeast.

Nucleocytoplasmic transport is highly selective, efficient, and is regulated by a poorly understood mechanism involving hundreds of disordered FG nucleoporin proteins (FG nups) lining the inside wall of the nuclear pore complex (NPC). Previous research has concluded that FG nups in Baker’s yeast (S. cerevisiae) are present in a bimodal distribution, with the “Forest Model” classifying FG nups as either di-block polymer like “trees” or single-block polymer like “shrubs”. Using a combination of coarse-grained modeling and polymer brush modeling, the function of the di-block FG nups has previously been hypothesized in the Di-block Copolymer Brush Gate (DCBG) model to form a higher-order polymer brush architecture which can open and close to regulate transport across the NPC. In this manuscript we work to extend the original DCBG model by first performing coarse grained simulations of the single-block FG nups which confirm that they have a single block polymer structure rather than the di-block structure of tree nups. Our molecular simulations also demonstrate that these single-block FG nups are likely cohesive, compact, collapsed coil polymers, implying that these FG nups are generally localized to their grafting location within the NPC. We find that adding a layer of single-block FG nups to the DCBG model increases the range of cargo sizes which are able to translocate the pore through a cooperative effect involving single-block and di-block FG nups. This effect can explain the puzzling connection between single-block FG nup deletion mutants in S. cerevisiae and the resulting failure of certain large cargo transport through the NPC. Facilitation of large cargo transport via single-block and di-block FG nup cooperativity in the nuclear pore could provide a model mechanism for designing future biomimetic pores of greater applicability.

The influence of the contact features on the tyre wear in steady-state conditions

This paper focuses on invetigating the relationship between the contact features of the tyres and the tyre wear in a quantitative sense as a function of the tyre structure and the manoeuvre parameters by utilizing a modified theoretical tyre wear model. The modified tyre wear model was developed by combining a modified ring model for the tyres and a modified brush model and was validated. The model parameters were also identified by physical experiments. Moreover, the contact features were characterized as the contact length, the asymmetry factor and the rolling resistance shift in order to investigate the influence of the contact features on the tyre wear. The amount of wear versus the three key variables of the contact features with variations in the tyre parameters was plotted and analysed. The results show that the maximum normal contact pressure does not play the most important role in the tyre wear. An increase in the damping coefficient can lead to an increase in the tyre wear, whereas increases in the effective elastic constant, the effective bending density and the effective bending stiffness result in a decrease in wear. The three key variables of the contact features increase with increasing vertical load, increasing rolling velocity and increasing damping coefficient and with decreasing inflation pressure and decreasing effective bending stiffness. The tyre wear follows the same trend when the three key variables increase or decrease synchronously. This analysis provides a quantitative indication of the relationship between the contact features and the tyre wear in order to obtain guidelines for tyre manufacturers on how to achieve less tyre wear.

Pericellular Brush and Mechanics of Guinea Pig Fibroblast Cells Studied with AFM

The atomic force microscopy (AFM) indentation method combined with the brush model can be used to separate the mechanical response of the cell body from deformation of the pericellular layer surrounding biological cells. Although self-consistency of the brush model to derive the elastic modulus of the cell body has been demonstrated, the model ability to characterize the pericellular layer has not been explicitly verified. Here we demonstrate it by using enzymatic removal of hyaluronic content of the pericellular brush for guinea pig fibroblast cells. The effect of this removal is clearly seen in the AFM force-separation curves associated with the pericellular brush layer. We further extend the brush model for brushes larger than the height of the AFM probe, which seems to be the case for fibroblast cells. In addition, we demonstrate that an extension of the brush model (i.e., double-brush model) is capable of detecting the hierarchical structure of the pericellular brush, which, for example, may consist of the pericellular coat and the membrane corrugation (microridges and microvilli). It allows us to quantitatively segregate the large soft polysaccharide pericellular coat from a relatively rigid and dense membrane corrugation layer. This was verified by comparison of the parameters of the membrane corrugation layer derived from the force curves collected on untreated cells (when this corrugation membrane part is hidden inside the pericellular brush layer) and on treated cells after the enzymatic removal of the pericellular coat part (when the corrugations are exposed to the AFM probe). We conclude that the brush model is capable of not only measuring the mechanics of the cell body but also the parameters of the pericellular brush layer, including quantitative characterization of the pericellular layer structure.

Role of tau in the spatial organization of axonal microtubules: keeping parallel microtubules evenly distributed despite macromolecular crowding.

Opposing views have been proposed regarding the role of tau, the principal microtubule-associated protein in axons. On the one hand, tau forms cross-bridges at the interface between microtubules and induces microtubule bundling in neurons. On the other hand, tau is also considered a polymer brush which efficiently separates microtubules. In mature axons, microtubules are indeed arranged in parallel arrays and are well separated from each other. To reconcile these views, we developed a mechanistic model based on in vitro and cellular approaches combined to analytical and numerical analyses. The results indicate that tau forms long-range cross-bridges between microtubules under macromolecular crowding conditions. Tau cross-bridges prevent the redistribution of tau away from the interface between microtubules, which would have occurred in the polymer brush model. Consequently, the short-range attractive force between microtubules induced by macromolecular crowding is avoided and thus microtubules remain well separated from each other. Interestingly, in this unified model, tau diffusion on microtubules enables to keep microtubules evenly distributed in axonal sections at low tau levels.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-016-2216-z) contains supplementary material, which is available to authorized users.

Conceptual Search Engine using Non-Negative Matrix Factorizationand Brush Structure Model

Search for web pages of personwith given name constitutes notable fraction of queries to web search engines. Such a query would normally return Web Pages related to several namesakes. This list is counterproductive because the user finds it extremely difficult to scroll through many entries to find the desired information. So here we propose a new formulation of the conceptual problem where the goal is to explicitly output a collection of simple and meaningful conjunctions of attributes that defines the conceptual clusteringof brush structure model. This research work is mainly focused on affording a knowledge mining tool in the form of brush model that results in spite of web page URLS. The primary goal is to develop conceptual clustering web pagesusing Non-Negative Matrix Factorisation(NMF). The secondary goal to maintain that web pages using Brush structure model. In future, this Conceptual Clustering search engine using Brush structure model may be played as a powerful tool in the search engine.

Tyre induced vibrations of the car–trailer system

The lateral and yaw dynamics of the car–trailer combination are analysed by means of a single track model. The equations of motion are derived rigorously by means of the Appell–Gibbs equations for constant longitudinal velocity of the vehicle. The tyres are described with the help of the so-called delayed tyre model, which is based on a brush model with pure rolling contact. The lateral forces and aligning torques of the tyre/road interaction are calculated via the instantaneous lateral deformations in the contact patches. The linear stability analysis of the rectilinear motion is performed via the analytically determined characteristic function of the system. Stability charts are constructed with respect to the vehicle longitudinal velocity and the payload position on the trailer. Self-excited lateral vibrations are detected with different vibration modes at low and at high longitudinal speeds of the vehicle. The effects of the tyre parameters are also investigated.

Modeling aircraft braking performance on wet and snow/ice-contaminated runways

The paper deals with the modeling of friction between aircraft tires and contaminated runway surfaces. Wet, snow- and ice-covered surfaces are considered. A tire Brush model developed for aircraft braking on dry runways is adapted to take into account the effect of contaminants. Compared with a dry surface, contaminants are assumed to affect the static and dynamic friction coefficients, the tire stiffness, the tire slip ratio, and the length of the contact patch. Linear relationship is established between static and dynamic friction coefficients. The dynamic friction coefficient is reduced using an empirical model for wet surfaces and experimental fitting for snow- and ice-covered surfaces. The tire stiffness is modified considering the frequency and temperature dependence of the tire mechanical properties. Values on snow and ice are lower than those on wet and dry surfaces. A physical model is developed to calculate the length of the wet contact patch. Finally, it is assumed that the aircraft effective slip ratio is surface-dependent, and values are determined for each of the studied contaminants. Theoretical friction–slip curves are realistic in terms of shape and differentiation between surface conditions. The model is applied to a Falcon 20 aircraft and a runway monitoring device called IMAG (Instrument de Mesure Automatique de Glissance). Friction–slip and friction–speed curves are calculated and compared to experimental data. It was found that the model can be used to relate ground friction to aircraft braking performance with enough reliability.

Star Brushes Under Deformation: Structure and Thermodynamics

SummaryA planar polymer brush of arm‐grafted polymer stars subjected to external deformation is studied theoretically We propose a simple mean‐field model of the star brush that takes into account segregation of the brush‐forming stars in two populations: (i) those with weakly extended arms and (ii) those with a very strongly stretched grafting arm (stem) and all free arms extended towards brush periphery. The polymer density profile in the brush is assumed to have a “two‐step” shape. Stars in the extended population are assumed to be equally stretched, the position of extended stars' branching points sets the boundary between two parts of the brush. We show that the theory quantitatively accurately describes earlier numerical results obtained with Scheutjens‐Fleer numerical self‐consistent field (SF‐SCF) approach for free (non‐deformed) star brush. We study compression of a star brush by an impenetrable plane by using two complementary models, the SF‐ SCF approach and the developed mean‐field theory, and demonstrate a very good quantitative agreement between the two models. It is shown than depending on the grafting density of the stars, compression could affect the two‐population brush structure in opposite ways. In sparsely grafted brushes the fraction of stars in the stretched population increases while in densely grafted brushes it decreases with deformation.

The Simulation of the Brush Stroke Based on Force Feedback Technology

A novel simulation method of the brush stroke is proposed by applying force feedback technology to the virtual painting process. The relationship between force and the brush deformation is analyzed, and the spring-mass model is applied to construct the brush model, which can realistically simulate the brush morphological changes according to the force exerted on it. According to the deformation of the brush model at a sampling point, the brush footprint between the brush and the paper is calculated in real time. Then, the brush stroke is obtained by superimposing brush footprints along sampling points, and the dynamic painting of the brush stroke is implemented. The proposed method has been successfully applied to the virtual painting system based on the force feedback technology. In this system, users can implement the painting in real time with a Phantom Desktop haptic device, which can effectively enhance reality to users.

1A1-H10 制駆動トルク配分による四輪駆動車両のスリップ損失低減 : JC08モード電費の推定と効果評価

Electric vehicles are attracting considerable interests, but their shorter mileage per charge is a major drawback. In this study, we focus on the energy loss by slippage between tire and road surfaces, and the minimization of this loss by optimization of the traction/braking force distributions. The electric power consumptions under the running patterns of 10-15 mode and JC08 are theoretically estimated by taking account of the rolling resistance and air drag, utilizing the brush model. The drive-train configurations, such as rear-wheel drive or four-wheel drive will yield different mileage with the same vehicle and tire parameters. In our estimation, the four-wheel drive vehicle equipped with the optimum traction/braking force distribution improves the mileage on low μ road by 4.1% compared to rear-wheel drive vehicle.