Monitoring three-dimensional packings in microgravity

We present results from experiments with granular packings in three dimensions in microgravity as realized on parabolic flights. Two different techniques are employed to monitor the inside of the packings during compaction: (1) X-ray radiography is used to measure in transmission the integrated fluctuations of particle positions. (2) Stress-birefringence in three dimensions is applied to visualize the stresses inside the packing. The particle motions below the transition into an arrested packing are found to produce a well agitated state. At the transition, the particles lose their energy quite rapidly and form a stress network. With both methods, non-arrested particles (rattlers) can be identified. In particular, it is found that rattlers inside the arrested packing can be excited to appreciable dynamics by the rest-accelerations (g-jitter) during a parabolic flight without destroying the packings. At low rates of compaction, a regime of slow granular cooling is identified. The slow cooling extends over several seconds, is described well by a linear law, and terminates in a rapid final collapse of dynamics before complete arrest of the packing.     

包装造型设计艺术

包装造型设计是长期研讨的问题,造型设计是根据被包装产品的特征、环境因素和用户的要求等选择一定的材料,采用一定的技术方法,设计出内外结构合理的容器或制品,并根据使用材料的不同特点分软质和硬质包装容器两种。造型设计中的形、线、装饰、肌理是决定构成容器外形轮廓的元素之一,包装造型设计的最终目的促使消费者产生购买行为。     

瓦楞纸箱结构优化CAD系统

研究用计算机辅助优化设计瓦楞纸箱结构尺寸,使对于纸箱内每个单元内包装货物所花费的纸箱包装和流通运输整体费用最少。所开发的计算机软件,可以进行内包装件在瓦楞纸箱中的装箱方式和瓦楞纸箱货物在集装箱内的集装方式的最优选择,给出所需瓦楞纸板的配料图、瓦楞纸箱的制造尺寸图、瓦楞纸箱装箱排列图和集装箱集装排列图及有关数据。     

Characteristics of Reaction Propagation in TiN Combustion Synthesis Using Concentric Bilayered Cylindrical Compact

Based on combustion synthesis of titanium nitride with liquid nitrogen, the geometrical effects of the Ti compact has been investigated for the improvement of low conversion from Ti to TiN. Concentric bilayered cylindrical compacts with two kinds of packing densities, which consist of an inner column and an outer cylinder; normal cylindrical compacts were applied. It was clear that the propagation rate in the outer cylinder of the bilayered compact is almost the same as that of the normal compact under the same packing density condition, and that the propagation rate in the inner column of the bilayered compact is smaller than that in the outer cylinder. These facts imply that the propagation rate in the inner column could be drastically changed by outer packing density. By using the compact with smaller inner packing density than the outer one, advantageous conditions of using the inner column for nitridation could be realized: a greater quantity of liquid nitrogen is inside a sample (due to lower packing density) and smaller propagation rate (due to the above-mentioned geometrical effect). In spite of the condition that liquid nitrogen was used under 1 atm, products with higher conversion ratio could be obtained. In these experiments, the possibility of high nitridation using a concentric bilayered compact is indicated.     

基于虚拟仪器微压力真空包装气密性研究

目的利用虚拟仪器对真空包装气密性进行检测,判断食品包装是否存在泄漏。方法构建的真空包装检测系统由压力传感器测得信号,经过调理电路传至数据采集卡,并最终输送到计算机,通过Labview软件构建的虚拟仪器将变化的压力信号通过图形显示出来。结果通过实验,利用虚拟仪器对真空包装气密性密封进行检测,判断出了食品包装是否存在泄漏。加压结束后,容器内压力随时间增加会慢慢减小,则表明该包装有泄漏;加压结束后,容器内压力随时间基本保持不变,则表明包装的密封性良好。结论用虚拟仪器对真空包装气密性密封进行检测是以后重要的发展方向。     

基于模块化过冷解除的冰浆制取系统实验研究

过冷水法动态冰浆制取技术具有传热效率高、系统简单等优点,但过冷却器易发生冰堵是影响其稳定性的突出问题。本文提出一种基于模块化过冷解除装置的动态制冰系统,利用设置在过冷却器内的可灵活拆装式螺旋叶片对制冰溶液进行过冷解除,同时刮削换热壁面上粘附的冰晶。测试了不同工况下该制冰系统的性能,结果表明该制冰系统可稳定产出冰浆并有效改善冰堵问题,最高含冰率达9.1%,最大持续制冰时间可达521 s。冰浆含冰率与持续制冰时间成正比。NaCl添加剂质量分数为6%时对冰浆含冰率和持续制冰时间的改善效果显著。实验获得制冰系统最佳运行参数:制冰溶液体积流量为0.50 m^3/h、二次冷媒起始温度为-15℃、螺旋叶片转速为175~225 r/min。     

Prediction of ordered phases of encapsulated C60, C70, and C78 inside carbon nanotubes

We report the first detailed fully atomistic molecular dynamics study of the encapsulation of symmetric (C(60)) and asymmetric fullerenes (C(70) and C(78)) inside single-walled carbon nanotubes of different diameters. Different ordered phases have been found and shown to be tube diameter dependent. Rotational structural disorder significantly affecting the volume fraction of the packing was observed for the molecular arrangements of asymmetric fullerenes. Although these effects make more difficult the existence of ordered phases, our results showed that complex packing arrangements (very similar to the ones obtained for C(60)) are also possible for C(70) and C(78). Comparisons with results from continuum and hard-sphere models, ab initio electronic structure calculations, and simulations of the high-resolution transmission electron microscopy images of the obtained fullerene packing phases are also presented.     

Statics and dynamics of condensed DNA within phages and globules

Several controversial issues concerning the packing of linear DNA in bacteriophages and globules are discussed. Exact relations for the osmotic pressure, capsid pressure and loading force are derived in terms of the hole size inside phages under the assumption that the DNA globule has a uniform density. A new electrostatic model is introduced for computing the osmotic pressure of rod-like polyelectrolytes at very high concentrations. At intermediate packing, a reptation model is considered for DNA diffusing within a toroidal globule. Under tight-packing conditions a model of Coulomb sliding friction is proposed. A general discussion is given of our current understanding of the statics and dynamics of confined DNA in the context of the following experiments: characterization of the liquid crystalline phases, X-ray scattering by phages, osmotic-stress measurements, cyclization within globules and single-molecule determination of the loading forces.     

双侧面胶轮式拉膜机构的研究与设计

研究设计了一种全自动包装机的新型拉膜机构，该新型拉机构结构简单、轻巧、运行平稳，易于调节，拉膜力大、安装控制与运行成本低。     

Light-scattering efficiency of starch acetate pigments as a function of size and packing density

We study theoretically the light-scattering efficiency of paper coatings made of starch acetate pigments. For the light-scattering code we use a discrete dipole approximation method. The coating layer is assumed to consists of roughly equal-sized spherical pigments packed either at a packing density of 50% (large cylindrical slabs) or at 37% or 57% (large spheres). Because the scanning electron microscope images of starch acetate samples show either a particulate or a porous structure, we model the coatings in two complementary ways. The material can be either inside the constituent spheres (particulate case) or outside of those (cheeselike, porous medium). For the packing of our spheres we use either a simulated annealing or a dropping code. We can estimate, among other things, that the ideal sphere diameter is in the range 0.25-0.4 microm.     

Experimental study on improving operating conditions of wet cooling towers using various rib numbers of packing

There are different mass and heat transfer mechanisms between water and air flows inside wet cooling towers (WCTs) so that it is a very difficult task to manage or optimize their operations. In this experimental work, the WCT performance is parametrically investigated in order to understand effects of water flow rate, inlet water temperature, type and arrangement of packing, and mass flow rate of air. Three different types of PVC packings (7, 9 and 18 ribs) are studied in this article separately to investigate influences of rib numbers. Furthermore, operation of the WCT is investigated by changing the inlet water temperature, rib numbers of packing, and flow rate of air and water. Ultimately, a guideline is proposed to reach optimum operating conditions of WCTs by virtue of mathematical equations derived from regression analysis of the measured data.     

The nanometre-scale physiology of bone: steric modelling and scanning transmission electron microscopy of collagen�Cmineral structure

The nanometre-scale structure of collagen and bioapatite within bone establishes bone''s physical properties, including strength and toughness. However, the nanostructural organization within bone is not well known and is debated. Widely accepted models hypothesize that apatite mineral (‘bioapatite’) is present predominantly inside collagen fibrils: in ‘gap channels’ between abutting collagen molecules, and in ‘intermolecular spaces’ between adjacent collagen molecules. However, recent studies report evidence of substantial extrafibrillar bioapatite, challenging this hypothesis. We studied the nanostructure of bioapatite and collagen in mouse bones by scanning transmission electron microscopy (STEM) using electron energy loss spectroscopy and high-angle annular dark-field imaging. Additionally, we developed a steric model to estimate the packing density of bioapatite within gap channels. Our steric model and STEM results constrain the fraction of total bioapatite in bone that is distributed within fibrils at less than or equal to 0.42 inside gap channels and less than or equal to 0.28 inside intermolecular overlap regions. Therefore, a significant fraction of bone''s bioapatite (greater than or equal to 0.3) must be external to the fibrils. Furthermore, we observe extrafibrillar bioapatite between non-mineralized collagen fibrils, suggesting that initial bioapatite nucleation and growth are not confined to the gap channels as hypothesized in some models. These results have important implications for the mechanics of partially mineralized and developing tissues.     

Uniform diffusion of acetonitrile inside carbon nanotubes favors supercapacitor performance

An unusual behavior of liquid acetonitrile (AN) confined inside carbon nanotubes (CNTs) is predicted by molecular dynamics simulation. In contrast to water, which shows inhomogeneous variation of both translational and rotational diffusion with CNT diameter [ Nano Lett. 2003, 3, 589; 2004, 4, 619], the diffusion coefficient of AN changes uniformly and can be described by a simple analytic model. At the same time, the reorientation dynamics of AN vary irregularly in smaller CNTs because of specific packing structures. The uniform translational diffusion of the nonaqueous solvent is critical for stable performance of the new generation of supercapacitors [ Nat. Mater. 2006, 5, 987].     

Analysis of irregular three-dimensional packing problems in additive manufacturing: a new taxonomy and dataset

With most Additive Manufacturing (AM) technology variants, build processes take place inside an internal enclosed build container, referred to as a ‘build volume’. It has been demonstrated that the effectiveness with which this volume is filled with product geometries forms an important determinant of overall process efficiency in AM. For effective operations management, it is important to understand not only the problem faced, but also which methods have proved effective (or ineffective) for problems with these characteristics in the past. This research aims to facilitate this increased understanding. The build volume packing task can be formulated as a three-dimensional irregular packing (3DIP) problem, which is a combinatorial optimisation problem requiring the configuration of a set of arbitrary volumetric items. This paper reviews existing general cutting and packing taxonomies and provides a new specification which is more appropriate for classifying the problems encountered in AM. This comprises a clear-cut problem definition, a set of precise categorisation criteria for objectives and problem instances, and a simple notation. Furthermore, the paper establishes an improved terminology with terms that are familiar to, but not limited to, researchers and practitioners in the field of AM. Finally, this paper describes a new dataset to be used in the evaluation of existing and proposed computational solution methods for 3DIP problems encountered in AM and discusses the importance of this research for further underpinning work.     

Die Erweiterung des kombinierten Teilchen-/Rohr-Modells für den Druckabfall in gasdurchströmten Packungen mit dem Wegfaktor

In an introduction the development is demonstrated for the packing columns with a) dumped packing, b) fluidisable packing and c) structured packing. To calculate the pressure drop of any packing the theoretically developped particle- /pipe-model for sphere packing is extended with an adjusting parameter. For this the tortusoity factor μ is used. It is the quotient of the mean length of the streaming way and the shortest length of the streaming way, the height of the packing. For the dumped packing with the Raschig-ring the greatest tortuosity factor μ ≈ 2,0 was found; for the newer packing elements the tortuosity factor diminishes from μ ≈ 1,7 for the Pall-ring to μ=1,384 for the Super-ring. For the fluidisable packing with the hollow sphere according to the assumptions μ=1,0 is valid. The smallest tortuosity factor μ=0,933 was found for the structured packing Mellapak. The new model is demonstrated to be universally applicable.     

基于强化学习的机场行李装箱优化方法

目的针对因行李随旅客无序抵达而无法提前得知行李尺寸信息的机场行李装箱问题,以行李车的装箱空间利用率为优化目标,提出基于强化学习的行李在线装箱方法。方法首先,根据机场行李装箱的实际情况,建立行李装箱的数学模型;接着,针对行李在行李车内寻找合适装箱位置和姿态的问题,设计行李装箱位置选择方法和装箱姿态评价方法;最后,借助强化学习的"试错"学习模式,通过训练行李装箱模型获得行李在线装箱策略。结果在仿真实验中文中算法的行李车空间利用率能够达到82.9%,计算耗时0.39 s,这2项指标均优于机器学习算法。结论在求解机场行李在线装箱问题上具有较好的实用性。     

Bulk and interior packing densities of random close packing of hard spheres

The packing densities of random close packing of equal hard spheres (RCPHS) are studied. The RCPHS is generated by a rearrangement algorithm with an optimization subroutine. Traditionally defined packing density, bulk density, is found to be 0.635 ± 0.002 by extrapolation to infinite number of spheres. We propose that there exist a characteristic packing density without boundary effects. This interior packing density is calculated by two methods, resulting in values without statically significant difference. Interior packing density deduced from Voronoi diagram is 0.6690 ± 0.0006. Local packing density for each sphere is defined as ratio of its volume to volume of its corresponding Voronoi cell and is sensitive to sphere's local configuration and overlapping.     

An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity??C _u). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC.