Designing Assemblies

This paper presents a theory to support the design of assemblies. It brings together prior work in a new synthesis, resulting in a top-down process for designing assemblies so that they deliver geometric Key Characteristics (KCs) that achieve top level customer requirements. The theory applies to assemblies that take the form of mechanisms (e.g. engines) or structures (e.g. aircraft fuselages), but has less relevance to assemblies that take the form of connective or distributive systems (e.g. hydraulic piping). The theory shows how kinematically constrained (statically determinate) assemblies can be unambiguously designed to satisfy geometrically-defined customer requirements. The top-down process presented here begins by creating a kinematic constraint structure and a systematic scheme by which parts are located in space relative to each other, followed by declaration of assembly features that join parts in such a way as to create the desired constraint relationships. This process captures design intent by creating a connective data model that contains information to support relevant analyses such as variation buildup, constraint analysis, and establishment of constraint-consistent assembly sequences. Adjustable assemblies, assemblies built using fixtures, and selective assemblies can also be described by this theory. Problems arising from multiple KCs and KC conflict can be identified. Issues unresolved by the theory are also noted.     

Characterization of heat-induced aggregates of concanavalin A using fluorescent probes

Proteins are prone to aggregate at high temperature. In order to investigate the heat-induced aggregation, Concanavalin A (Con A) was used as a model protein because disulfide formation doesn't occur throughout the aggregation process. With increasing temperature, fluorescence intensities of 8-anilino-1-naphthalenesulfonate (ANS) and thioflavin T (ThT) showed a maximum at around 45–50 °C. After the heating, the fluorescence intensities increased with decreasing temperatures. The enhancement of the fluorescence during cooling implies that the heat-induced aggregates of Con A possess porosity on this surface allowing the binding to fluorescent probes.     

Specific and unspecific binding of concanavalin A at monolayer surfaces

Fluorescence and electron microscopic studies with phospholipid monolayers containing concanavalin A and with or without a glycolipid as a specific ligand are presented. It is shown that the (unspecific) protein insertion in the absence of the glycolipid leads to protein patches that may exhibit uniform sizes and that may be due to the existence of long-range electrostatic forces resulting from a difference in the polarization of different protein and lipid areas.

By incorporating about 1 mol.% of the glycolipid, specific binding can be effected. This can dominate the unspecific process only in a narrow lateral pressure range between 5 and 15 mN m^-1. The data can be qualitatively understood, indicating that control of the interactions requires fine tuning of the head-group arrangement.     

Swelling behaviors of superabsorbent chitin/carboxymethylcellulose hydrogels

Novel superabsorbent chitin/carboxymethylcellulose (CMC) hydrogels were successfully prepared from mixture of CMC and chitin solution dissolved in 8 wt% NaOH/4 wt% urea aqueous system at low temperature by crosslinking with epichlorohydrin. The morphology and structure of the resultant composite hydrogels were investigated by scanning electron microscope, thermogravimetry, and Fourier transform infrared spectroscopy. The results indicated that the stiff chains of chitin are as a strong backbone in the hydrogel to support the pore wall, whereas the CMC contributed to water absorption. The maximum swelling ratio in water reached an exciting level of 1300 as the hydrogels still kept an intact appearance. Moreover, the hydrogels exhibited smart swelling and shrinking behaviors in NaCl and CaCl₂ aqueous solution, showing salt-responsive adsorption behaviors in different media. This work provided a “green” pathway to prepare chitin-based superabsorbent hydrogels, which would be potential for the application in the biodegradable water-absorbent material field.     

An amidated carboxymethylcellulose hydrogel for cartilage regeneration

An amidic derivative of carboxymethylcellulose was synthesized (CMCA). The new polysaccharide was obtained by converting a large percentage of carboxylic groups ( approximately 50%) of carboxymethylcellulose into amidic groups rendering the macromolecule quite similar to hyaluronan. Then, the polysaccharide (CMCA) was crosslinked. The behavior of CMCA hydrogel towards normal human articular chondrocytes (NHAC) was in vitro studied monitoring the cell proliferation and synthesis of extra cellular matrix (ECM) components and compared with a hyaluronan based hydrogel (Hyal). An extracellular matrix rich in cartilage-specific collagen and proteoglycans was secreted in the presence of hydrogels. The injectability of the new hydrogels was also analysed. An experimental in vivo model was realized to study the effect of CMCA and Hyal hydrogels in the treatment of surgically created partial thickness chondral defects in the rabbit knee. The preliminary results pointed out that CMCA hydrogel could be considered as a potential compound for cartilage regeneration.     

Supersolid Phases of Cold Atom Assemblies

We review recent theoretical results for soft-core Bose systems, and describe the low-temperature supersolid “droplet crystal” phase, predicted for a broad class of soft-core interactions. We identify the conditions on the inter-particle interaction that render such intriguing phase possible, and outline proposals for its observation. We argue this to be the prototypical supersolid, at least in the context of assemblies of ultracold atoms.     

Assemblies of biomaterials in mesoporous media

Assemblies of biomaterials onto mechanically stable inorganic structure are advantageous for the practical applications because of the potential to improve the stability and performance of biomaterials in the biocatalytic processes. Among many kinds of inorganic materials, mesoporous materials such as mesoporous silica and mesoporous carbon have attracted special attention owing to their well-defined structures and perfectly controlled pore geometries, which would lead to unique functions such as size selective adsorption of biomaterials. In the first part of this review, adsorption behaviors of proteins, enzymes, vitamins, and amino acids in aqueous solutions onto mesoporous media are systematically explained. Pore geometries (pore diameter and volume) of mesoporous materials are the crucial factors for the size selective adsorption of biomaterials, especially proteins, which often have a size comparable to pore dimension. The studies on the adsorption of biomaterials on the mesoporous carbon reveal that hydrophobic interaction between guest molecules and surface of the mesoporous materials is an important parameter which controls the amount of biomaterials adsorption. Enhanced adsorption of biomaterials was commonly observed at their isoelectric point, where electrostatic repulsion is minimized between the biomaterials. In addition, several functions such as biomolecular separation, reactor function, controlled drug release, and photochemical properties are discussed in the latter sections. Studies on assemblies of biomaterials in mesoporous media are still in initial stage, but the development of appropriately designed mesoporous materials would powerfully promote researches in these fascinating unexplored fields.     

Electromagnetic Shielding of Monolayer MXene Assemblies

Miniaturization of electronics demands electromagnetic interference (EMI) shielding of nanoscale dimension. The authors report a systematic exploration of EMI shielding behavior of 2D Ti₃C₂T_x MXene assembled films over a broad range of film thicknesses, monolayer by monolayer. Theoretical models are used to explain the shielding mechanism below skin depth, where multiple reflection becomes significant, along with the surface reflection and bulk absorption of electromagnetic radiation. While a monolayer assembled film offers ≈20% shielding of electromagnetic waves, a 24-layer film of ≈55 nm thickness demonstrates 99% shielding (20 dB), revealing an extraordinarily large absolute shielding effectiveness (3.89 × 10⁶ dB cm² g⁻¹). This remarkable performance of nanometer-thin solution processable MXene proposes a paradigm shift in shielding of lightweight, portable, and compact next-generation electronic devices.     

Failure Analysis of Fuel System Assemblies

Fuel system assemblies used on recreational watercraft failed after a short time in service in a seawater environment. Examination of the assemblies revealed significant degradation of the polyacetal connectors of the wire subassemblies. Optical and microscopic evaluations indicated the complete loss of connector material implying decomposition of the resin, along with mud-cracking and a rough surface morphology signifying chemical attack. An elemental analysis performed on both an intact connector and degraded connector suggested a potential chemical agent in the form of zinc chloride. At elevated temperatures, concentrated zinc chloride solutions are known to decompose polyacetal resins. The source of the zinc chloride was established as corrosion products that resulted during the dezincification of the internal brass connector through exposure to saltwater in the application.     

Nanoparticle Assemblies on Nanoinjection-Molded Polymer Templates

A mass-producible method for fabricating nanoparticle assemblies using nanoinjection-molded polymer templates with deposition and selective removal has been developed and characterized in this work. Results are demonstrated for assembly of multiple nanoparticle sizes and types in 1-D and 2-D formats over large areas. Template dimensions such as width and depth are used to control the assembled structures, including the quantity and type of nanoparticles in the assembly. This method offers a high-throughput, low-cost approach to nanoscale assembly for applications in optical, electronic, and biomedical devices.      

A Membrane-Associated Light-Harvesting Model is Enabled by Functionalized Assemblies of Gene-Doubled TMV Proteins

Photosynthetic light harvesting requires efficient energy transfer within dynamic networks of light-harvesting complexes embedded within phospholipid membranes. Artificial light-harvesting models are valuable tools for understanding the structural features underpinning energy absorption and transfer within chromophore arrays. Here, a method for attaching a protein-based light-harvesting model to a planar, fluid supported lipid bilayer (SLB) is developed.  The protein model consists of the tobacco mosaic viral capsid proteins that are gene-doubled to create a tandem dimer (dTMV). Assemblies of dTMV break the facial symmetry of the double disk to allow for differentiation between the disk faces. A single reactive lysine residue is incorporated into the dTMV assemblies for the site-selective attachment of chromophores for light absorption. On the opposing dTMV face, a cysteine residue is incorporated for the bioconjugation of a peptide containing a polyhistidine tag for association with SLBs. The dual-modified dTMV complexes show significant association with SLBs and exhibit mobility on the bilayer. The techniques used herein offer a new method for protein-surface attachment and provide a platform for evaluating excited state energy transfer events in a dynamic, fully synthetic artificial light-harvesting system.     

报废汽车拆解及"五大总成"回收再利用研究

分析我国报废汽车回收再利用现状及存在的问题,介绍主要拆解工艺并进行比较,提出了具体的适用场景.结合产业政策,重点介绍了发动机、方向机、变速器、前后桥、车架"五大总成"的回收再制造技术,以及新政策为报废汽车拆解行业带来的机遇.     

Biomimetic mineralization of calcium carbonate/carboxymethylcellulose microspheres for lysozyme immobilization

Porous calcium carbonate/carboxymethylcellulose (CaCO₃/CMC) microspheres were prepared by the biomimetic mineralization method for lysozyme immobilization via adsorption. The size and morphology of CaCO₃/CMC microspheres were characterized by transmitted electron microscopy (TEM) and zeta potential measurement. The lysozyme immobilization was verified by Fourier transform infrared (FTIR) spectroscopy. The effects of pHs and temperatures on lysozyme adsorption were investigated as well. It was revealed that CaCO₃/CMC microspheres could immobilize lysozyme efficiently via electrostatic interactions and a maximum adsorption capacity of 450 mg/g was achieved at pH 9.2 and 25 °C. Moreover, it was found that the adsorption process fitted well with the Langmuir isothermal model. In addition, UV, fluorescence, and circular dichroism (CD) spectroscopic studies showed that lysozyme maintained its original secondary structure during the adsorption/desorption process. Our study therefore demonstrated that CaCO₃/CMC microsphere can be used as a cost-effective and efficient support for lysozyme immobilization.     

羧甲基纤维素钠/壳聚糖复合海绵制备工艺研究

利用羧甲基纤维素钠、壳聚糖具有人体生物相容性好,促进伤口愈合和止血作用特点,所制备的复合海绵具有广阔的市场前景.本制备工艺采用浇铸/冷冻干燥技术,在单因素实验基础上再进行正交实验,得到最佳制备工艺条件为:羧甲基纤维素钠0.45g,壳聚糖0.14g,羧甲基纤维素钠溶液:壳聚糖溶液体积比为2:1,聚乙二醇0.4g,甘油0.2g,真空冷冻干燥时间26h,取得了较好结果.     

Ordered overgrowth of zeolite X onto crystals of zeolite A

The overgrowth between the zeolites X and A is described. The observations include A cubes with one or more X demi-octahedra grown onto the cube faces as well as cubes of zeolite A totally encapsulated by octahedral crystals of zeolite X. A molecular intergrowth model is suggested in which sodalite cages are strain-free bound to the A framework (through a double four-ring) as well as to the faujasite framework (through two double six-rings) with a T-atom binding efficiency of 67%. Also, the location of the overgrowth on the A surface is discussed.