High Packing Ratio Research Articles

Easy snap-folding of hexagonal ring origami by geometric modifications

Hexagonal ring origami is a type of foldable structure that has impressive packing abilities and can be tessellated into two-dimensional or three-dimensional surfaces without any gap or overlap. It can be folded under bending or twisting loads into a peach core-shaped configuration with only 10.6% of its initial area. However, in applications of large-scale foldable structures, folding by bending or twisting is usually technically difficult. Here, we propose strategies to facilitate easy snap-folding of the hexagonal ring by a simple point load or localized twist or squeeze. This is enabled by two geometric modifications made to the hexagonal ring: introducing residual strain and creating pre-twisted edges. By combining theoretical modeling, finite element simulations, and experiments, we systematically investigate the snap-folding behaviors of modified hexagonal rings with residual strain and pre-twisted edges. It is found that the geometric modifications promote easy snap-folding of the hexagonal ring by different mechanisms: introducing residual strain can significantly decrease the energy barrier and thus reduce the required moment to snap-fold the ring, while creating pre-twisted edges allows for easy out-of-plane deformation which is a necessary condition for a ring to fold. Combining the two methods further enables the snap-folding of the hexagonal ring by a point load or localized twist or squeeze. To demonstrate the easy folding of large assemblies of the modified rings, we construct various structures that can be snap-folded from their initial three-dimensional states to significantly lower-volume final states by a simple compression at the corners of the rings. We envision that the proposed geometric modification strategies can provide a new perspective on the rational design of easy-to-fold ring origami-based foldable functional structures with extremely high packing ratios.

Buckling behavior and damage mechanism analysis of fiber-reinforced shape memory polymer composites

Shape memory polymer composites (SMPCs) are emerging as an attractive material for space deployable structures due to their variable stiffness, programmable deformation, high packing ratio, and controllable deployment. However, the research on the deformation behaviors and damage mechanisms of SMPC was scarce. The buckling behaviors and damage mechanisms of out-of-plane buckling and in-plane buckling of fiber-reinforced SMPC were investigated in this study. The expression and evolution law of strain energy and key parameters of fiber buckling were studied. The effects of material parameters and size parameters on damage mode and critical damage curvature were analyzed quantitatively. It was found that in-plane buckling was more likely to occur without external constraints. The damage modes of in-plane buckling are classified as delamination, matrix cracking and fiber tensile fracture. Out-of-plane buckling is more susceptible to damage and has one more fiber buckling fracture damage mode than in-plane buckling. When the fiber volume content is below a certain value, only fiber tensile fracture damage mode will appear, regardless of the thickness. Delamination is more likely to occur in cases of out-of-plane buckling, and matrix cracking is more frequent in cases of in-plane buckling. Subsequently, the correctness of the theoretical analysis was verified by the bending test. The theoretical analysis in this study provides a theoretical foundation for SMPCs-based structural design.

Phase diagram and mechanics of snap-folding of ring origami by twisting

Ring origami is a new strategy to design bistable foldable/deployable structures by assembling multiple rings with the same geometry. The successful folding of ring origami assembly leverages the snap-folding capability of single rings. It is thus important to model the snap-folding of ring-shaped structures for the rational design of ring origami with good foldability, stability and high areal packing ratio. This paper studies the folding mechanics of differently shaped rings (circular, elliptical, rounded rectangular and rounded triangular rings) under twisting loads by developing theoretical and three-dimensional finite element analysis (FEA) models. The rod model is re-formulated for different ring geometries as two-point boundary value problem systems, which are then solved through numerical continuation, allowing one to capture complex equilibrium paths with multiple fold points. The rod model, verified by FEA simulations and experiments, can accurately, quantitatively capture the snap-folding behaviors for rings of different geometries. Using the rod model, we analyze the folding modes in terms of foldability, stability and snapping type. Phase diagrams of folding modes are then constructed with respect to geometric parameters for the ring profile and cross-section for differently shaped rings. Diagrams of areal packing ratios are obtained using the reduced planar rod model. This work provides comprehensive mechanics insights into the ring folding through twisting and can guide future ring origami design.

Finite element analysis for prediction of thermal conductivity of composites with high packing ratios of particles using representative volume element models

Polymer composites with high thermal conductivity offer new possibilities for thermal management in electric systems. The objective this paper is to develop the prediction method of the thermal conductivity of polymer composites with high packing ratios of fillers. Fillers were spherical alumina and boron nitride with platelet shape. Measurements of thermal conductivity of polymer composites using steady state method and finite element analysis for thermal conductivity using representative volume element (RVE) models of polymer composites were carried out. The analytical thermal conductivity of multi-scale RVE models increased with increasing homogenization numbers and volume fraction alumina. When contacts between fillers were considered in RVE models, the finite element analysis results and experimental results were in good agreement.

A fast and scalable mesh generation method of densely packed hollow fibers for membrane separations: Application to direct contact membrane distillation

Modeling research on membrane distillation requires simulations of coupled momentum, mass, and heat transfer phenomena. Hollow fiber modules are preferred in industrial applications due to their high packing ratio, resulting in the number of fibers on the order of O(102−103) packed in a vessel. In hollow fiber membrane distillation processes, computational fluid dynamics (CFD) simulations of multi-physics require high-quality meshes for accurate calculations. Mesh interfaces between two different phase regions should conform to satisfy continuity conditions of coupled momentum, heat, and mass transfer. Due to the distinct geometric characteristics of HF packing structures, a scalable meshing method is of great necessity but has not been actively researched. This work developed a numerical method to generate hexagonally packed structures of many fibers by forming a hexagonal unit-cell, consisting of the lumen, membrane, and shell regions. Individual cells are made by duplicating a seed cell and packed to create a self-similar, hexagonal packing of hollow fiber membranes for multi-physics CFD simulations. A new theoretical approach was developed to represent the effusion-like convective mass transfer as conductive heat transfer, and our CFD results were in good agreement with experimental observations. Theoretical methods and numerical algorithms developed in this study can contribute to the improved scalability of CFD simulations from lab-scale modules to pilot-scale systems.

Towards customizable thin-panel low-Z detector arrays: electrode design for increased spatial resolution ion chamber arrays

The purpose of the present development is to employ 3D printing to prototype an ion chamber array with a scalable design potentially allowing increased spatial resolution and a larger active area. An additional goal is to design and fabricate a custom size thin-panel detector array with low-Z components. As a proof of principle demonstration, a medium size detector array with 30 × 30 air-vented ion chambers was 3D-printed using PLA as frame for the electrodes. The active-area is 122 mm × 120 mm with 4 × 4 mm2 spatial resolution. External electrodes are cylindrical and made from conductive PLA. Internal electrodes are made from microwire. The array is symmetric with respect to the central plane and its thickness is 10 mm including build-up/-down plates of 2.5 mm thickness. Data acquisition is realized by biasing only selected chamber rows and reading only 30 chambers at a time. To test the device for potential clinical applications, 1D dose profiles and 2D dose maps with various square and irregular fields were measured. The overall agreement with the reference doses (film and treatment planning system) was satisfactory, but the measured dose differs in the penumbra region and in the field size dependence. Both of these features are related to the thin walls between neighboring ion chambers and different lateral phantom scatter in the detector panel vs homogeneous material. We demonstrated feasibility of radiation detector arrays with minimal number of readout channels and low-cost electronics. The acquisition scheme based on selected row or column ‘activation’ by bias voltage is not practical for 2D dosimetry but it allows for rapid turn-around when testing of custom arrays with the aid of multiple 1D dose profiles. Future progress in this area includes overcoming the limitations due high chamber packing ratio, which leads to the lateral scattering effects.

Prediction of thermal conductivity of polymer composites with high packing ratios of fillers by using representative volume element models

Prediction of thermal conductivity of polymer composites with high packing ratios of fillers by using representative volume element models

Thermal conductivity enhancement of erythritol phase change material with percolated aluminum filler

Abstract This paper describes a high thermal conductive phase change composite (PCC) of erythritol and Al filler with percolating network. The PCCs with various Al amounts were prepared by both melt-dispersion method and hot-press (HP) method. The effective thermal conductivity of PCCs was measured, and the distribution status of the erythritol and Al filler was observed. The percolated filler network in the PCCs can be easily formed by HP method, which is important for enhancing the thermal conductivity of PCCs. The PCM particles with nonuniform particle size and high packing ratio is essential for the formation of filler percolating network. A high thermal conductivity of 30 W m−1 K−1 can be obtained at a filler fraction of 42.2 vol%.

Effects of SPS pressure on the mechanical properties of high packing ratio bulk MgB2 superconductor

In order to investigate the effects of SPS pressure on the mechanical properties of MgB2 bulk, MgB2 bulk samples were processed by SPS under different pressures. Mechanical properties of these bulk samples were evaluated at room temperature through the bending tests for specimens cut from the bulk samples. Stress-strain behaviours of these bulk samples were almost linear until the fracture. No significant difference was observed for the Young’s modulus values among the bulk samples. The average bending strength values of these bulk samples were also similar to each other. However, the bending strength data of the samples processed under higher pressure scattered widely in comparison with those of the sample processed under lower pressure. The bending strength values were related with the pore sizes observed on the tensile side fracture surfaces.

Mechanical Properties of Bulk MgB2 Superconductors Processed by Spark Plasma Sintering at Various Temperatures

In order to improve the mechanical properties of bulk MgB2 superconductor, high packing ratio bulk samples were processed by spark plasma sintering (SPS) at various temperatures. Effects of the SPS temperature on the mechanical properties of the bulk MgB2 superconductor are investigated through bending tests of specimens cut from the bulk samples. Both Young's modulus and bending strength were improved by the increase in the SPS temperature. The improvements of the mechanical properties are mainly due to the improvement in the packing ratio. The relationships between the bending strength and packing ratio of the spark plasma sintered bulk samples are similar to those of other bulk MgB2 pieces processed by capsule method and hot isostatic pressing.

Моделирование отверждаемых цилиндрических элементов надувной антенны наноспутника

The usage of inflatable antennas for nanosatellites made of prepreg is considered in this paper. Antennas must have a high packing ratio and a simple reliable way of deployment. It is believed that bringing the antenna into working condition includes the process of hardening in a near-earth orbit. In this case the nanosatellite should perform a maneuver associated with a change in its orientation to the Sun. It is important for construction to exclude the unstability, which can lead to a violation of the technological regime. Folds should not appear in the unhardened construction in the process of maneuvering. Computational experiments for an inflatable antenna of the pin type in conditions when the nanosatellite makes a turn are performed. The results of the calculations showed that the lack of the folds in the inflatable antenna of the pin type can be achieved at an internal pressure respective with the value of one thousandth atmosphere. Undoubtedly the result depends on the geometric dimensions of the antenna and on the speed of maneuvering. For practical use it is possible to recommend a certainly higher pressure equal to one hundredth of the atmosphere.

Large electrorheological phenomena in graphene nano-gels

Large-scale electrorheology (ER) response has been reported for dilute graphene nanoflake-based ER fluids that have been engineered as novel, readily synthesizable polymeric gels. Polyethylene glycol (PEG 400) based graphene gels have been synthesized and a very high ER response (∼125 000% enhancement in viscosity under influence of an electric field) has been observed for low concentration systems (∼2 wt.%). The gels overcome several drawbacks innate to ER fluids. The gels exhibit long term stability, a high graphene packing ratio which ensures very high ER response, and the microstructure of the gels ensures that fibrillation of the graphene nanoflakes under an electric field is undisturbed by thermal fluctuations, further leading to mega ER. The gels exhibit a large yield stress handling caliber with a yield stress observed as high as ∼13 kPa at 2 wt.% for graphene. Detailed investigations on the effects of graphene concentration, electric field strength, imposed shear resistance, transients of electric field actuation on the ER response and ER hysteresis of the gels have been performed. In-depth analyses with explanations have been provided for the observations and effects, such as inter flake lubrication/slip induced augmented ER response. The present gels show great promise as potential ER gels for various smart applications.

Computational strategies to address chromatin structure problems

While the genetic information is contained in double helical DNA, gene expression is a complex multilevel process that involves various functional units, from nucleosomes to fully formed chromatin fibers accompanied by a host of various chromatin binding enzymes. The chromatin fiber is a polymer composed of histone protein complexes upon which DNA wraps, like yarn upon many spools. The nature of chromatin structure has been an open question since the beginning of modern molecular biology. Many experiments have shown that the chromatin fiber is a highly dynamic entity with pronounced structural diversity that includes properties of idealized zig-zag and solenoid models, as well as other motifs. This diversity can produce a high packing ratio and thus inhibit access to a majority of the wound DNA. Despite much research, chromatin’s dynamic structure has not yet been fully described. Long stretches of chromatin fibers exhibit puzzling dynamic behavior that requires interpretation in the light of gene expression patterns in various tissue and organisms. The properties of chromatin fiber can be investigated with experimental techniques, like in vitro biochemistry, in vivo imagining, and high-throughput chromosome capture technology. Those techniques provide useful insights into the fiber’s structure and dynamics, but they are limited in resolution and scope, especially regarding compact fibers and chromosomes in the cellular milieu. Complementary but specialized modeling techniques are needed to handle large floppy polymers such as the chromatin fiber. In this review, we discuss current approaches in the chromatin structure field with an emphasis on modeling, such as molecular dynamics and coarse-grained computational approaches. Combinations of these computational techniques complement experiments and address many relevant biological problems, as we will illustrate with special focus on epigenetic modulation of chromatin structure.

Low-Temperature Fracture Strength of MgB2Bulk Processed by Spark Plasma Sintering

Mechanical properties of a high packing ratio MgB 2 bulk sample processed by spark plasma sintering (SPS) were evaluated at 77 K through bending tests for specimens cut from the bulk sample. The effects of the packing ratio and temperature on the fracture strength of MgB 2 bulk are discussed. The fracture strength at 77 K of the MgB 2 bulk processed by SPS was higher than that at room temperature. The packing ratio of the MgB 2 bulk processed by SPS was higher than those of other MgB 2 bulks processed by sintering under the ambient pressure and hot isostatic pressing. The fracture strength was improved by increasing the packing ratio. The fracture strength at a very low temperature was estimated from the bending test results at 77 K and room temperature. The fracture strength at 20 K of the MgB 2 bulk processed by SPS was estimated to be around 425 MPa.

Rapid Generation of Particle Packs at High Packing Ratios for DEM Simulations of Granular Compacts

In this work we present a simple, fast technique for generating particle packs at high packing ratios aiming at the simulation of granular compacts via the discrete element method (DEM). We start from a random sequence addition particle generation algorithm to generate a layer of non-overlapping spherical particles that are let to evolve dynamically in time under the action of compacting or jamming pseudo forces. A layer-by-layer approach is then followed to generate multiple layers on top of each other. In the end, very dense packs with pre-defined bulk shapes and sizes (e.g. rectangles in two dimensions and prisms in three dimensions) are achieved. The influence of rolling motion (with particle rotation and spin) along with inter-particle friction on the density and ordering of the generated packs is assessed. Both congruent and inhomogeneous packs (with respect to particle sizes) are created and their packing properties evaluated. We believe that simple techniques for fast generation of particle packs at high packing ratios are essential tools for the DEM simulation of granular compacts.

Scale effects on the heat release rate, smoke production rate, and species yields for a vegetation bed

The burning of a vegetation bed was investigated employing the cone calorimeter and the furniture calorimeter for testing on a small and a large scale. Heat release rate, smoke production rate, and species yields were measured at both scales and with two different setups at the full scale. The results show a clear influence of the scale on: the peak of heat release rate, the smoke extinction area, the soot yield, and the rate of smoke release. The species yields appear to depend not only on the burning scale but also on the experimental setup. This study clearly shows that even for litter with high packing ratio, the results obtained at bench scale cannot be extended directly to the full scale.

High thermal conductivity phase change composite with percolating carbon fiber network

Abstract Latent heat storage (LHS) using phase change materials (PCM) is a promising technology for the effective use of solar and industrial exhaust heat. However, the heat transfer rate of an LHS system is severely limited by the low thermal conductivity of the PCM. Therefore, this paper describes the development of a high thermal conductivity phase change composite (PCC) with a percolating network of a high thermal conductivity filler. The relationship between the effective thermal conductivity of the PCC and the network structure of the filler was investigated. The PCC were prepared by the conventional melt-dispersion (MD) method and a novel hot-press (HP) method. Erythritol (melting point: 118 °C, thermal conductivity: 0.73 W m−1 K−1) was used as the PCM, and carbon fiber (thermal conductivity: 900 W m−1 K−1 in the fiber direction) was used as the high thermal conductivity filler. The effective thermal conductivity of the PCC was measured by the laser flash method and the network structures were observed by energy dispersive spectroscopy using a scanning electron microscope. As a result, we observed that the percolating filler network in the PCC could be easily formed by the HP method, presenting a higher thermal conductivity with less filler additive than the PCC fabricated by the MD method. Additionally, we found that PCM raw materials with a high packing ratio accelerated the formation of the percolating filler network.

Mechanical Properties of MgB2 Bulk Fabricated by Spark Plasma Sintering

A clear understanding of mechanical properties of superconducting bulk materials is required for their reliable integration together with other materials constituting the superconducting devices. In this study, evaluations of mechanical properties of a high packing ratio MgB2 bulk processed by Spark Plasma Sintering-SPS were carried out. Mechanical properties of the high packing ratio MgB2 bulk processed by SPS were improved than those of MgB2 bulks processed by conventional route. The improvement of the mechanical properties with increasing the packing ratio could be approximated by using exponential equations.

Modeling Studies of Chromatin Fiber Structure as a Function of DNA Linker Length

Chromatin fibers encountered in various species and tissues are characterized by different nucleosome repeat lengths (NRLs) of the linker DNA connecting the nucleosomes. While single cellular organisms and rapidly growing cells with high protein production have short NRL ranging from 160 to 189 bp, mature cells usually have longer NRLs ranging between 190 and 220 bp. Recently, various experimental studies have examined the effect of NRL on the internal organization of chromatin fiber. Here, we investigate by mesoscale modeling of oligonucleosomes the folding patterns for different NRL, with and without linker histone (LH), under typical monovalent salt conditions using both one-start solenoid and two-start zigzag starting configurations. We find that short to medium NRL chromatin fibers (173 to 209 bp) with LH condense into zigzag structures and that solenoid-like features are viable only for longer NRLs (226 bp). We suggest that medium NRLs are more advantageous for packing and various levels of chromatin compaction throughout the cell cycle than their shortest and longest brethren; the former (short NRLs) fold into narrow fibers, while the latter (long NRLs) arrays do not easily lead to high packing ratios due to possible linker DNA bending. Moreover, we show that the LH has a small effect on the condensation of short-NRL arrays but has an important condensation effect on medium-NRL arrays, which have linker lengths similar to the LH lengths. Finally, we suggest that the medium-NRL species, with densely packed fiber arrangements, may be advantageous for epigenetic control because their histone tail modifications can have a greater effect compared to other fibers due to their more extensive nucleosome interaction network.

Construction of recombinant adeno-associated virus vector coexpressing hVEGF 165 and hBMP 7 gene

Objective To construct recombinant adeno-associated virus co-expressing human vascular epithelial growth factor 165(hVEGF 165) and bone morphogenetic protein 7(hBMP 7), measure the virus titer and verify the recombination. Methods The AAV helper-free system was used as basis to generate recombinant AAV. The IRES sequence of plasmid pIRES was cut down and subcloned into ITR/ MCS containing vector pAAV-MCS to construct recombinant plasmid pAAV-MCSa-IRES-MCSb. The hVEGF 165 and hBMP 7 gene was amplified by PCR and inserted into upstream MCSa and downstream MCSb respectively. Then, recombinant plasmid pAAV-hVEGF 165-IRES-hBMP 7, pAAV-RC and pHelper were co-transfected into AAV-293 cells to complete rAAV-hVEGF 165-IRES-hBMP 7 packaging. The GFP labeled rAAV-IRES-GFP was simultaneously packaged by using the parallel plasmid pAAV-IRES-hrGFP. The efficiency of AAV packaging was monitored under fluorescent microscope and recombinant viral particles were harvested from infected AAV-293 cells. The virus titer was measured by infecting AAV-HT1080 cells, and the recombinant AAV-hVEGF 165-IRES-hBMP 7 was verified by PCR of the exogenous interest genes. Results Recombinant pAAV-hVEGF 165-IRES-hBMP 7 was verified by double digestion. GFP expression in AAV-293 could be observed under fluorescent microscope 72 h after transfection and the system provided a high packing ratio of 95%. The recombinant adeno-associated virus has a high titer of 5.5 × 10 11 vp/ml, and AAV-HT 1080 was infected at a ratio of 90%. The recombinant virus was confirmed by PCR of exogenous hBMP 7 and hVEGF 165 gene. Conclusion Recombinant rAAV-hVEGF 165-IRES-hBMP 7 was successfully constructed with a high virus titer, which may offer foundation for in vitro and in vivo experiments of hVEGF 165 and hBMP 7 co-expression and provide a new method for gene therapy of bone regeneration.