A review of different pinch techniques

Individuals often pinch with preferred pinch techniques based on their experience and familiarity. However, researchers believe that pinch force exertions are not comparable across different pinch techniques. Hence, it is possible to pinch objects with incompatible pinch techniques during manual handling. This increases risks of developing musculoskeletal disorders. The preceding problem substantiates the need for a comprehensive understanding of definitions, categorisations and capacities of different pinch techniques. Nevertheless, the knowledge on pinch techniques appears to be highly dispersed and not compiled to a level systematic enough for further research. Thus, this review aims to develop a consolidated theoretical groundwork on pinch techniques. It presents an anthology of terminologies, previous findings and concepts underpinning different pinch techniques. While much research is still required, it is believed that an improved understanding on pinch techniques is now within sight, due to, in part, a structured review of their definitions, classifications and capacities.     

Development of particle size and shape measuring system for machine-made sand

Abstract

In recent years, the use of machine-made sand has gradually increased. Simultaneous monitoring of the particle size and shape of machine-made sand during its production is vital. Here, a machine-made sand size measuring methods were developed using vibration dispersion and high-speed video imaging and subsequently evaluated. Moreover, a software system for particle size and shape identification of machine-made sand was also developed using image processing algorithms. Experiment studies on this system were conducted, and the results show that the measurement results of particle size between the vibration screening method and imaging method are different. The measurement results of particle size obtained from the imaging method were affected by the degree of dispersion and particle shape of the machine-made sand. The particle shape parameter of the machine-made sand was modified to compensate for the measurement results of particle size. After compensation for measurement results of the sand size by the imaging method, the cumulative curve of the particle size distribution was in agreement with that obtained from the vibratory sieve method; the measurement error of sand size is less than 3%. Based on sphericity characterization of the particles, the particle shape measurement using the imaging method was accurate. Thus, the particle size and shape measuring system based on imaging method met the monitoring requirements for machine-made sand.     

纤维增强复合材料层合板缺口尺寸及形状效应数值模拟

通过考虑基体裂纹、纤维断裂、层内劈裂和层间脱层等破坏形式,建立三维有限元模型研究含中心圆孔和中心裂缝的准各向同性复合材料层合板([45/0/-45/90]_(2S))在拉伸载荷下的缺口尺寸效应及缺口形状效应。模拟结果显示:随着缺口尺寸的增大,层合板的破坏强度逐渐降低,然而,在本文研究范围内含中心裂缝的层合板破坏强度始终高于对应的含中心圆孔的层合板破坏强度。进一步分析有限元模拟结果表明,含中心裂缝的层合板亚临界损伤发生得更早,并且亚临界损伤范围更大,亚临界损伤会大大缓解缺口尖端的应力集中,从而使含中心裂缝层合板表现出更高的破坏强度。     

形状记忆聚氨酯

介绍了形状记忆聚氨酯的发展状况、记忆过程及原理、影响因素、合成制备以及应用 ,并指出了其目前性能上的不足及今后研究的重点。     

Particle shape effects on particle size measurement for crushed waste glass

Recently, narrow particle size distributions, as measured by sieve analysis, of crushed waste glass were used as a replacement for Portland cement in concrete. Their chemical reactivity was successfully studied as a function of this measure of particle size. Differences between sieve analysis and laser diffraction measures of particle size prompted this current re-analysis. Extremely careful sieving was used to divide the crushed waste glass particles into 0–25 μm, 25–38 μm, and 63–75 μm sieve size ranges, but laser diffraction did not agree with these particle size cutoffs. We use these same materials to try and understand the discrepancies between particle size as measured by laser diffraction and sieve analysis by using X-ray computed tomography followed by spherical harmonic analysis to measure the three-dimensional particle shape and size, as well as the length (L), width (W), and thickness (T) of each particle. We show how laser diffraction and X-ray CT results, along with sieve analyses, can be quantitatively related for these crushed waste glass particles in the approximate size ranges considered. In contrast to previous speculation, the particle width W does not have to correspond closely to the sieve opening – the correspondence depends on overall particle shape. In addition, we demonstrate how many particles are needed to analyze in order to achieve stable averages and distributions of the L/W, W/T, and L/T aspect ratios, which approximately define particle shape. These results have implications for how particle size is measured and interpreted in the cement and concrete and other industries.     

流线型回转体外形设计综述与线型拟合

综述了流线型回转体外形设计的主要方法：(1)具有精确数学表达式的几何组合外形曲线；(2)用源汇法设计回转体外形曲线；(3)用离散外形坐标型值表示的回转体线型。给出了流线型离散型值回转体线型的拟合解析表达式。这些外形设计方法与拟合解析表达式具有广泛的工程实用价值。     

表面活性剂在纳米材料形貌调控中的作用及机理研究进展

介绍了表面活性剂在纳米材料合成中的软模板作用和稳定分散作用,重点综述了利用表面活性剂在溶液中聚集形成的胶团、反胶团、微乳液、囊泡、液晶等各种有序聚集体辅助制备纳米材料的作用机理.展望了表面活性剂在纳米材料形貌调控中的应用前景.     

Quantitative evaluation of effects of shape and size of artificially introduced alumina particles on the fatigue strength of 1.5Ni---Cr---Mo (En24) steel

In order to investigate the effects of non-metallic inclusion on the fatigue strength of high-strength steels, in 1963 W.E. Duckworth and E. Ineson conducted fatigue tests using specimens that contained artificially added spherical and angular alumina particles of various controlled sizes. Although the fatigue tests were carried out under the same nominal stresses in rotating-bending and tension-compression tests the fatigue lives of specimens showed a large scatter. They reported in some detail typical complicated aspects of the effects of non-metallic inclusions on the fatigue strength.

In the present study the authors have reanalysed these complicated fatigue data using the prediction equation that was proposed by Murakami et al for the quantitative evaluation of the effects of small defects on fatigue strength. The geometrical parameter that controls the scatter of the fatigue strength is the square root of the projection area √ area and not the shape of the inclusions, whether they are spherical or angular. It is shown from the data from the failed specimens that the fatigue strength of materials containing inclusions larger than a critical size can be predicted by the Vickers hardness (Hv) of the matrix and √ area of the inclusion regardless of the shape.     

图像处理的珍珠形状大小检测系统研究

为了解决人工分选珍珠效率低、精度不高等问题,设计了一种基于图像处理的检测系统,采用单向底照明光源和穹顶光源结合的照明方案,采集珍珠图像,通过后续的图像处理后,转换到极坐标下,求出长短径,根据直径差可对珍珠形状大小进行有效地判别.实验结果表明,该系统测量值与千分尺测量值结果一致,误差在0.200mm以内,可满足珍珠厂家的检测要求.     

电脉冲肝育细化CuAlNi合金的宏观组织与铸态形状记忆效应

为细化晶粒和改善组织,用电脉冲孕育技术制备了CuAlNi记忆多晶合金,对未孕育和孕育处理合金的宏观组织进行了分析,测试了未孕育和孕育合金铸态形状记忆效应。结果表明：电脉冲处理使多晶CuAlNi合金铸锭的宏观组织得到明显改善,几乎由完全的等轴晶区构成,铸锭集中缩孔大大减小,合金的晶粒尺寸显著细化,脉冲孕育电压,频率,脉冲施加时间和铸模种类是影响孕育效果的因素,电脉冲孕育处理后材料铸态的形状记忆效应得到明显提高。     

A review of deformation and fatigue of metals at small size scales

Mechanical devices are being introduced whose size scale is well below that of conventional mechanical test specimens. The smallest devices have sizes in the nanometer range, though a good proportion of structural devices are of the micrometer scale. Development of these products raises the question of how their mechanical behaviour and reliability may be predicted. Conventional macroscopic test data can be used, but these are obtained using specimens whose size is much larger than the devices themselves. There is a risk that performance predictions will be inaccurate, due to the existence of size effects. This paper covers small size scale testing in metallic specimens and devices, concentrating on free‐standing specimens. To begin, some examples of micro‐scale devices are given. Fabrication methods for small metallic devices are then briefly described. This is followed by a review of experimental observations of mechanical properties in various metallic materials at the micro‐scale, highlighting the differences in results from different research groups and the gaps in our current knowledge. A section on computational and predictive modelling is included, in recognition of the role of modelling in device design and testing. Overall, the findings are that size effects are common, particularly in crystalline samples when the grain size is similar to one or more of the specimen dimensions. However, observations of size effects differ between studies and mechanical properties can vary widely, even for the same type of material. As a consequence, the relationships between specific device processing methods, specimen size and material properties must be adequately understood to ensure successful performance.     

Institutional considerations in watershed cumulative effects assessment and management

This paper examines the role of institutional arrangements as either facilitating or constraining the practice of watershed cumulative effects assessment and management (W-CEAM) within the context of the Grand River watershed (GRW), Canada. The research is based on document review, a focus group and 29 interviews conducted with academic experts, project proponents, government and watershed agencies representatives, non-governmental organization researchers, First Nations, and others with interest in the GRW. Information was gathered on existing policy and planning instruments, and relationships among the authorities and other partners that enable water resource management. Key facilitating factors for W-CEAM in the GRW include established institutions, a mature conservation authority and an ecological focus to resource management strategies, while constraining factors include obfuscation of leadership roles and lack of multi-scalar approaches to watershed science. We conclude that it is useful to conceptualize W-CEAM as characterized by both a managerial and a scientific ethos – the former facilitating the latter – and that institutional goodwill, political will and institutional capacity for innovation and creativity are additional institutional core requisites to W-CEAM.     

Image analysis algorithm and verification for on-line molecular sieve size and shape inspection

An online machine vision inspection method is proposed to implement feedback control of molecular sieve growth process in rotary drum granulation. An experimental platform, comprising of a high-resolution digital camera and an image analysis system, has been developed to confirm the validity of the method on particle size distribution (PSD) and sphericity measurements. Experiments were performed with non-uniform molecular sieve particles (1–3 mm diameter) obtained from production line. The particle images are first obtained through digital camera and are then processed by image analysis system. After separating the overlap particles and removing non-target particles of the images, the molecular sieve size and shape are computed in less than 0.9 s. The validity of the size measuring accuracy is confirmed through comparing with the results from micrometer. The experimental results show that the repetitive precision of the proposed inspection system is about ±1%, the diameter measurement error between image method and micrometer is about ±3%, single image inspection speed is around 0.9 s/frame. The proposed method is reliable to provide feedback information for control system in rotary drum granulation.     

Polydisperse powder mixtures: effect of particle size and shape on mixture stability

The effect of the shape and size of the components on the stability of mixtures was evaluated in binary mixtures of drug and carrier. Aspirin was used as model drug; spray-dried lactose and microcrystalline cellulose were used as carriers. The coefficient of variation (CV) of the drug in the mixture at various time intervals during mixing was used as a measure of homogeneity. The stability of mixtures was assessed under conditions that were conducive to segregation—in this case, prolonged mixing. The pattern of change in CV with time was analyzed in terms of convective, shear, and diffusive mixing stages. The variation resulting from a change in the shape of the carriers was smaller than that resulting from size differences. The segregation rate constant, calculated on the assumption of a first-order mixing process, was found to be larger in mixtures having components of different shape than in mixtures having components of similar shape. In mixtures of micronized drug and carrier, the pattern of change in the CV of drug with mixing time was attributed to the distribution of agglomerates of micronized drug during convective mixing, followed by shearing of agglomerates and, finally, the distribution of the primary particles during diffusive mixing. Mixtures of non-cohesive powders of similar size and shape behaved like random mixtures of non-interacting components.     

三维GIS中地层多比例尖灭自动建模技术

利用地质勘察数据导入到三维系统中,运用各种三维空间构模方法,自动进行地层推理与连接,生成三维地层模型。以多数据源自动生成模型,可以方便地使地学领域中的地质工作者从繁重的地质信息获取和地质解释手工劳动中解放出来,提高了三维地层建模的速度和构建质量。     

Manufacturing capabilities and performance: a critical analysis and review

In order to advance scientific knowledge, it is important to maintain consistency regarding the methodologies and units/levels of analysis employed to test a theory's main claims. Thus, this investigation provides a critical examination of the papers that have aimed to test the trade-off model and its competing concepts. The analysis focuses on the methodologies used to examine the validity of such models and theories, and also on the operationalisation of the variables that represent the level of analysis by which those theories are tested. To aid in the investigation, a framework to distinguish measures of performance with an internal and external reference and perspective is proposed. The results show that current methodologies, approaches and rationales used to determine the validity of the trade-off model or its rival concepts observe important limitations, as they do not address the trade-off model's core principles. Those limitations in turn make the results of those studies questionable. Consequently, it is proposed that in order to advance theory in our field, more consistent methods and approaches should be utilised.     

Creating novel granular mixtures as proppants: Insights to shape,size, and material considerations

Fragmentation of proppant particles in a pack subjected to compressive loading results in a loss of load bearing capacity. Addition of ductile particles to a brittle particle pack reduces particle fragmentation. Computational models simulating confined compression of a proppant pack with a mixture of brittle and ductile particles are developed. The effect of soft particle material, shape, and size on the fragmentation behavior of the brittle particle in a proppant pack is studied. The results showed that larger, nonuniform particles lead to higher incidence of particle fracture. More efficient pack compositions are proposed for further study and development.     

Ergonomics aspects of knob designs: a literature review

Hand-related apparatus designs that fail to accommodate appropriate hand postures can cause hand-related musculoskeletal disorders. While there have been studies on the handling and design of various hand-related apparatus, little has been written on the ergonomics aspects of knob designs. The aim of this paper is to review various knob designs and their ergonomics aspects. The literature review suggests that gearshift knobs, door knobs, gas valve knobs, butterfly nuts and screw knobs are common knobs used for daily living activities. Other knobs like the convex, knurled, spherical, cone-shaped and ridged knob are often used for industrial-related applications. The ergonomics considerations identified in knobs include aesthetic attraction, position, torque requirement and shape-coding. This literature review can be used as groundwork for the development of ergonomics theory and hand-related studies. Engineers can use this literature review to identify certain ergonomics aspects in knobs to improve equipment designs, operating efficiency and working comfort.     

Fe-Mn-Si-Cr-Ni-C系形状记忆合金时效效果的研究

通过SEM分析，研究了时效后不同成分Fe-Mn-Si-Cr-Ni-C系形状记忆合金形状记忆效应和微观组织，在1123K时效时，超低碳合金1的形状回复率随时效时间的增加一直呈直线上升的趋势，含碳0．18％合金2的形状回复率随时效时间的增加而增加，在300min达到最大值后将随时间的进一步增加而缓慢下降，SEM分析发现在合金2的晶界和晶内析出富铬，富锰和富硅的合金碳化物，而合金1仅在晶界有第二相析出，且第二相成分不同于合金2中的，合金2中第二相粒子的长大速度显著高于合金1中第二相粒子的长大速度，且数量也多得多，通过时效强化奥氏体基体，可显著提高合金的形状记忆效应。