Growing actin networks regulated by obstacle size and shape

Growing actin networks provide the driving force for the motility of cells and intracellular pathogens. Based on the molecular-level processes of actin polymerization, branching, capping, and depolymerization, we have developed a modeling framework to simulate the stochastic and cooperative behaviors of growing actin networks in propelling obstacles, with an emphasis on the size and shape effects on work capacity and filament orientation in the growing process. Our results show that the characteristic size of obstacles changes the protrusion power per unit length, without influencing the orientation distribution of actin filaments in growing networks. In contrast, the geometry of obstacles has a profound effect on filament patterning, which influences the orientation of filaments differently when the drag coefficient of environment is small, intermediate, or large. We also discuss the role of various parameters, such as the aspect ratio of obstacles, branching rate, and capping rate, in affecting the protrusion power of network growth.

Size and shape effects on Curie temperature of ferromagnetic nanoparticles

A simplified model was developed to describe the Curie temperature suppression of ferromagnetic nanoparticles. Based on a size and shape dependent model of cohesive energy, the critical temperature variations of ferromagnetic nanoparticles were deduced. It is predicted that the Curie temperature of nanoparticles depends on both size and shape conditions, among which the temperature suppression is strongly influenced by the particle size and the shape effect is comparably minor. The calculation values for freestanding nanoparticles are in good agreement with other theoretical model and the experimental results. The model is also potential for predictions for the nanoparticles embedded in different substrates.

Coupling effects of void size and void shape on the growth of prolate ellipsoidal microvoid

The combined effects of void size and void shape on the void growth are studied by using the classical spectrum method. An infinite solid containing an isolated prolate spheroidal void is considered to depict the void shape effect and the Fleck-Hutchinson phenomenological strain gradient plasticity theory is employed to capture the size effects. It is found that the combined effects of void size and void shape are mainly controlled by the remote stress triaxiality. Based on this, a new size-dependent void growth model similar to the Rice-Tracey model is proposed and an important conclusion about the size-dependent void growth is drawn： the growth rate of the void with radius smaller than a critical radius rc may be ignored. It is interesting that rc. is a material constant independent of the initial void shape and the remote stress triaxiality.

Modeling size-dependent thermo-mechanical behaviors of shape memory polymer Bernoulli-Euler microbeam

The objective of this paper is to model the size-dependent thermo-mechanical behaviors of a shape memory polymer (SMP) microbeam.Size-dependent constitutive equations,which can capture the size effect of the SMP,are proposed based on the modified couple stress theory (MCST).The deformation energy expression of the SMP microbeam is obtained by employing the proposed size-dependent constitutive equation and Bernoulli-Euler beam theory.An SMP microbeam model,which includes the formulations of deflection,strain,curvature,stress and couple stress,is developed by using the principle of minimum potential energy and the separation of variables together.The sizedependent thermo-mechanical and shape memory behaviors of the SMP microbeam and the influence of the Poisson ratio are numerically investigated according to the developed SMP microbeam model.Results show that the size effects of the SMP microbeam are significant when the dimensionless height is small enough.However,they are too slight to be necessarily considered when the dimensionless height is large enough.The bending flexibility and stress level of the SMP microbeam rise with the increasing dimensionless height,while the couple stress level declines with the increasing dimensionless height.The larger the dimensionless height is,the more obvious the viscous property and shape memory effect of the SMP microbeam are.The Poisson ratio has obvious influence on the size-dependent behaviors of the SMP microbeam.The paper provides a theoretical basis and a quantitatively analyzing tool for the design and analysis of SMP micro-structures in the field of biological medicine,microelectronic devices and micro-electro-mechanical system (MEMS) self-assembling.

A DESCRIPTION METHOD FOR ARBITRARILY SHAPED AND SIZED GRANULES IN 2D IMAGE

An alternative method is proposed in this letter for describing the arbitrary shape and size for granules in 2D image.After image binarization, the edge points on contour are detected, by which the centroid of the shape in question is sought using the moment calculation.Using Principal Component Analysis(PCA), the major and minor diameters are computed.Based on the signature curve-fitting, the first-order derivative is taken so as to seek all the characteristic vertices.By connecting the vertices found, the simplified polygon is formed and utilized for shape and size descriptive purposes.The developed algorithm is run on two given real particle images, and the execution results indicate that the computed parameters can technically well describe the shape and size for the original particles, being able to provide a ready-to-use database for machine vision system to perform related data processing tasks.

Size and Shape of Polymer Chain near a Flat Surface

The size and the shape of non-reversal random-walking polymer chains near an impenetrable, non-interacting flat surface are investigated by means of Monte Carlo simulation on the simple cubic lattice. It wasfound that both size and shape are dependent on the normal-to-surface distance z0 of the first segment of chain. Wefind that the size and shape of chains, characterized by mean square radius of gyration <S2> and mean asphericityparameter <A> respectively, show similar dependence on distance z0. Both <S2> and <A> reach the maximum atz0 = 0, then decrease with the increase of z0 and soon reach the minimum values, afterwards they go up continuouslyand approach to the limit values of free chain. The similar dependence of <S2> and <A> on z0 can be explained by apositive correlation between A and S2. However, the dependence of the correlation coefficient CA,S2 on z0 is verycomplicated and deserves further study. The overall density probability of segments is also investigated. Resultsshow that segments near the surface are relatively less, and the symmetrical distribution disappears when the chainlocates near the surface.

Conditions of Incipient Motion of Pebbles Based on Shape and the Equivalent Grain Size

Incipient motion of pebbles is an unsteady and random process,the main influence factors are pebble shape,non-uniformity,location in bed and flow condition.By virtue of the concept of the equivalent grain size,it is shown that d_ηfollows a normal distribution following a regression analysis of measured data.Consid- ering the influence of pebble shape and the relative exposure degree,formula of calculating the incipient veloc- ity for pebbles is deduced based on the equivalent grain size of pebble and the...

Real-Time Characterization of Crystal Shape and Size Distribution Based on Moving Window and 3D Imaging in a Stirred Tank

Crystal shape distribution, i.e. the multidimensional size distribution of crystals, is of great importance to their down-stream processing such as in filtration as well as to the end-use properties including the dissolution rate and bioavailability for crystalline pharmaceuticals. Engineering crystal shape and shape distribution requires knowledge about the growth behavior of different crystal facets under varied operational conditions e.g. supersaturations. Measurement of the facet growth rates and growth kinetics of static crystals in a crystallizer without stirring has been reported previously. Here attention is given to study on real-time characterization of the 3D facet growth behavior of crystals in a stirred tank where crystals are constantly moving and rotating. The measurement technique is stereo imaging and the crystal shape reconstruction is based on a stereo imaging camera model. By reference to a case study on potash alum crystallization, it is demonstrated that the crystal size and shape distributions (CSSD) of moving and rotating potash alum crystals in the solution can be reconstructed. The moving window approach was used to correlate 3D face growth kinetics with supersaturation (in the range 0.04 - 0.12) given by an ATR FTIR probe. It revealed that {100} is the fastest growing face, leading to a rapid reduction of its area, while the {111} face has the slowest growth rate, reflected in its area continuously getting larger.

New Method for Calculating Slit-Shaped Pore Size In Solids from Adsorption Isotherm

Assuming the pores in a porous solid to be slit-shaped,according to the principle of surface chemical thermody-namics,an equation for the calculation of pore size fromthe desorption branch of the isotherm of physical adsorp-tion of nitrogen on the porous solid at liquid nitrogentemperature is derived.The calculation results obtainedby different methods,namely,the classical method,BBmethod and the method of this paper,are compared.Comparison shows that the pore sizes d_T and d_H calculat-ed by the method of this paper and BB method respec-tively are larger than the pore size d_c calculated by theclassical method in the range 0【p/p_s【1;d_T】d_Hatp/p_s【0.71 and d_H】d_T at p/p_s】0.71;The results byBB method and the method of this paper tend to be thesame as that by the classical method while p/p_s ap-proaches 1.

An Experimental Study on the Effect of Foundation Depth, Size and Shape on Subgrade Reaction of Cohessionless Soil

The modulus of subgrade reaction ks depends on several factors such as the size and shape of the foundation as well as the embedment depth of the foundation. The present study is an experimental analysis using plate load test to determine the effect of foundation depth, size as well as the shape on the modulus of subgrade reaction (ks) of cohesionless soils. It was carried out by using nine rigid steel plates with different sizes and shapes (circular, square and retangular). The tests were carried out on cohessionless soil with different relative densities under different applied pressures. The settlement has been measured at the surface of the plate for different depths of footings. The ultimate bearing capacity [qu] has been determined from the stress-settlement relationships. The allowable bearing capacity (qa) was determined by dividing the ultimate bearing capacity (qu) by F.S. = 3.0, after which the corresponding settlement (Sa) has been obtained. However, ks was calculated based on dividing the allowable bearing capacity (qa) by the corresponding settlement (Sa). From the present study it is concluded that the subgrade reaction ks of cohessionless soil increases with increasing foundation depth as well as foundation size. In addition, subgrade reaction ks of cohessionless soil under rectangular footing is higher than that under square and that under circular one with same equivalent area. An empirical formula is presented to calculate the subgrade reaction ks of cohessionless soil under square foundation taking into consideration foundation depth. Fair agreement has been obtained between values of ks from the empirical formula at depth of footing = 0.00 B and Biot (1937) as well as Meyerhof and Baike (1965).

A New Simple Route to ZnS Quantized Particles with Tunable Size and Shape, and Size/Shape-Dependent Optical Properties

With the features of convenience and eco-friendly, the low-temperature solid-state reaction synthesis was successfully developed as a new approach to prepare quantum-sized ZnS nanocrystals. One major achievement is that the size and shape of ZnS nanocrystals can be tuned by adjusting the surfactant and its feed. The UV-Vis absorption spectra of quasispherical and one-dimensional quantum-sized ZnS nanocrystals all showed a blue-shift from the bulk counterpart, indicating large quantum confinement effects of ZnS nanocrystals. These ZnS nanocrystals all showed well-defined excitonic emission features. Contrastive studies on photoluminescence performances indicated that the bandedge emission experienced only the size-dependent quantum confinement effect, while the trap-state emission experienced the size- and shape-dependences. So we can design a purposeful synthesis route to ZnS nanocrystals with target luminescence emission performances.

基于图像识别的叶丝形态表征及其数值模拟

【背景和目的】研究一种叶丝颗粒的粒度和粒形表征方法,表征结果可用于其数值模拟的建模。【方法】采用图像分析技术,确定分散放置在二维平面上的每根叶丝的等面积圆当量径、最大弗雷特(Feret)径、圆形度和纵横比。【结果】(1)利用提出的叶丝颗粒图像采集和处理方法,通过对叶丝样品数据的统计分析,确定叶丝物料粒度和粒形的概率密度分布曲线,实现了长丝、中丝、短丝和碎丝4种长度叶丝物料的颗粒粒度和粒形表征,表征参数可定量的反映不同样品的颗粒尺寸和形状的差异。(2)离散单元法数值模拟结果表明叶丝的粒度和粒形性质对物料堆积高度有重要影响。本文基于实验测量得到的粒度和粒形概率分布曲线,生成了与实际形态分布一致的叶丝颗粒的数值模型,数值模拟结果与实验结果的偏差在1.3%以内。【结论】提出的方法从粒度和粒形对叶丝颗粒进行定量表征,表征结果一方面能反映不同物料的性质差异,另一方面可直接用于建立与实际情况接近的数值模型,从而准确预测不同长度叶丝颗粒的堆积高度。

基于机器视觉的E型卡簧尺寸检测方法

针对传统人工测量方式测量E型卡簧尺寸存在精度低、效率低等问题,提出一种基于机器视觉的E型卡簧尺寸检测方法。首先对灰度图像进行双边滤波,去除噪声;再利用形状匹配并结合先验知识快速准确定位测量区域,同时采用图像金字塔分层搜索策略提高匹配定位效率;然后在测量区域通过亚像素边缘检测方法进行亚像素级的边缘提取,获取出内、外径边缘和开口边缘;最后用迭代重加权最小二乘法拟合圆,用旋转法计算凸多边形之间的最小距离,实现尺寸的测量。试验结果表明,该检测方法测量精度高、测量效率高且稳定性好,满足工业自动化需求。

抛撒装药截面形状对爆炸抛撒过程的影响

针对抛撒装药能量输出方式决定爆炸驱动能力大小,传统的圆截面抛撒装药结构存在爆轰能量周向输出方式单一等问题,通过改变抛撒装药截面形状控制爆轰能量输出方式,研究了圆形、五角星形和花瓣形3种抛撒装药结构对被抛撒介质的爆炸驱动作用大小,抛撒装药结构的比药量均为2%,研究发现:装药爆炸驱动被抛撒介质的能力由其截面积大小决定,受抛撒装药截面形状的影响很小,分析原因主要是非圆截面抛撒装药爆炸产生的冲击波在传播过程中波阵面能量迅速匀化,无法对被抛撒介质产生定向加载效果;在壳体外壁有刻槽的情况下,主射流结构数量与刻槽数量相同,受抛撒装药结构截面形状影响不大。

粒径计算方法对细观混凝土数值建模的影响

采用最小包围盒(MBB)法确定骨料粒径,并与采用等体积球(EVS)法计算的骨料粒径进行比较,分析了这2种粒径计算方法对细观混凝土内部结构的影响.结果表明:采用MBB法计算的骨料粒径与室内试验采用筛分法确定的骨料粒径更为接近;与MBB法相比,EVS法低估了球状、片状和盘状骨料的粒径,且被低估的骨料占比由大到小依次为球状、片状和盘状,EVS法高估了棒状骨料的粒径;粒径计算方法对细观混凝土内部结构的影响因骨料形状类型不同而呈现一定差异性.

不同振荡热压烧结温度下90W-10Cu难熔合金组织及性能

用于高压电触头材料的90W-10Cu难熔合金由于具有高熔点和高比重差异,在高温长时间的粉末冶金过程中存在致密化困难和晶粒异常长大而影响其性能。在常规热压烧结基础上,振荡热压烧结(HOP)技术采用一定频率的循环振荡单轴压力代替静单轴压力,可快速促进陶瓷等材料的致密化。因此,为了研究振荡热压烧结对90W-10Cu难熔合金的低温烧结效果,本文将振荡热压烧结技术应用到90W-10Cu(质量分数)难熔合金的制备中,研究了烧结温度(1000~1300℃)对其微观组织、致密度、晶粒尺寸、硬度及电导率性能的影响。研究结果发现,振荡热压烧结90W-10Cu合金由W相基体和Cu相黏结相组成。随着烧结温度的升高,90W-10Cu难熔合金的致密度逐渐增大,在烧结温度最高为1300℃时,其致密度最高可达到99.35%,均高于同等温度下的热压烧结样品的致密度;而晶粒尺寸仅为4.97μm左右,没有异常长大,达到了细化晶粒的效果;同时,其W晶粒邻接度逐渐降低,合金的微观组织均匀性得到优化和改善;维氏硬度和电导率分别达到225.78 HV_(30)和27.88%国际退火铜标准(IACS),高于同等温度甚至高100℃时的热压烧结体,性能得到显著提升,达到了低温烧结效果。结果表明,振荡热压烧结能够有效地促进90W-10Cu难熔合金的致密化,降低烧结温度和抑制晶粒生长,显著优化其微观组织均匀性,有利于在较低温度下获得高致密度、晶粒细小、高硬度和高电导率的90W-10Cu难熔合金材料。

Effects of grain's shape-and size-polydispersities,orientation,and area fraction on tortuosity and permeability of 2D granular media

The microstructure of granular media, including grain's shape- and size-polydispersities, orientation, and area fraction can potentially affect its permeability. However, few studies consider the coupling effects of these features. This work employs geometrical probability and stereology to establish quantitative relationships between the above microstructural features and the geometric tortuosity of the two-dimensional granular media containing superellipse, superoval, and polygon grains. Then the lattice Boltzmann method (LBM) is used to determine the permeabilities of these granular media. By combining the tortuosity model and the LBM-derived permeabilities, modified K–C equations are formulated to predict the permeability and the shape factor, considering the grain's shape- and size-polydispersities, orientation, and area fraction. The reliability of these methods can be verified by comparing them with both our simulations and available experimental, theoretical, and numerical data reported in the literature. The findings implicate that the tortuosity and permeability of the granular media are strongly correlated with the grain's shape, orientation, and area fraction but unaffected by the size polydispersity and spatial arrangement of grains. Only circularity is not enough to derive a unified formula for considering the impact of grain shape on tortuosity and permeability, other shape parameters need to be explored in the future.

基于AI图像分析的铸造原砂粒度粒形检测法

铸造原砂的粒形和粒度分布是原砂生产和使用过程中的重要衡量指标。针对筛分法存在的测量效率和测量误差问题,本文提出一种基于人工智能(Artificial Intelligence:AI)图像分析的铸造原砂粒度粒形测试方法,即采用工业相机采集原砂图像,通过AI图像处理技术对图像进行实例分割,然后对图像进行特征提取,统计出原砂的粒度分布和粒形分布。研究结果表明:基于AI技术的BlendMask实例分割模型能有效地分离粘连砂粒;采用圆形度、形状因子和方形度三个特征参数对原砂粒形进行K-means聚类,能够准确分析砂粒的粒形特征;采用等效椭圆法、面积占比等效质量占比法,可准确测得烘焙砂、烘干砂和宝珠砂三种铸造原砂的粒度分布,满足行业精度要求。