Disassembly leveling and lot sizing for multiple product types: a basic model and its extension

We consider two interrelated problems that occurred in disassembly systems: disassembly leveling and lot sizing. Disassembly leveling, one of disassembly process planning decisions, is to determine disassembly structures that specify parts and/or subassemblies to be obtained from disassembling used/end-of-life products, and disassembly lot sizing is the problem of determining the amounts of disassembly operations required to satisfy the demands of their parts and/or subassemblies. Unlike the existing studies, this study considers the two problems at the same time for the objective of minimizing the sum of disassembly setup and operation costs. In particular, we consider a generalized version in which disassembly levels may be different even for products of the same type. Two types of the problem are considered in this study. The first one is the basic problem without parts commonality, i.e., products do not share their parts or subassemblies, for which a polynomial time optimal algorithm is suggested after developing a mathematical programming model. The second one is an extended problem with parts commonality. After developing another mathematical programming model for the extension, we prove that it is NP hard. Then, a heuristic algorithm is suggested together with its computational results.     

High-temperature thermo-mechanical behavior of functionally graded materials produced by plasma sprayed coating: Experimental and modeling results

Thermal barrier coatings are widely used in aerospace industries to protect exterior surfaces from harsh environments. In this study, functionally graded materials (FGMs) were investigated with the aim to optimize their high temperature resistance and strength characteristics. NiCrAlY bond coats were deposited on Inconel-617 superalloy substrate specimens by the low vacuum plasma spraying technique. Functionally graded Ni-yttria-stabilized zirconia (YSZ) coatings with gradually varying amounts of YSZ (20%-100%) were fabricated from composite powders by vacuum plasma spraying. Heat shield performance tests were conducted using a high- temperature plasma torch. The temperature distributions were measured using thermocouples at the interfaces of the FGM layers during the tests. A model for predicting the temperature at the bond coating–substrate interface was established. The temperature distributions simulated using the finite element method agreed well with the experimental results.     

Nanofiber‐Based Hydrocolloid from Colloid Electrospinning Toward Next Generation Wound Dressing

Nanofiber‐based hydrocolloid scaffold is prepared by colloid electrospinning of thermoplastic polyurethane (TPU)/sodium carboxymethyl cellulose (S.CMC) in tetrahydrofuran (THF)/dimethylformamide (DMF). The most suitable process of electrospinning for successful formation of fibers is investigated by controlling the concentration of polymeric solution and co‐solvent ratio. In order to accomplish high wettability, the amount of colloid (S.CMC) and the co‐solvent ratio (THF/DMF), which affects the morphology of fibers, are adjusted. Finally, the open wound healing effect is confirmed using nanofiber‐hydrocolloid from in vivo animal studies. A detailed study of the wound healing process is also demonstrated for the first time.

     

多级纳米孔分子筛在非均相催化中的应用现状及发展前景

传统分子筛因其单一的微孔孔道,在工业应用中表现为扩散阻力差、催化易失活,尤其在涉及大分子的反应过程中催化活性较差是阻碍其工业应用的现实难题,通过优化制备路线得到的多级纳米孔分子筛催化材料可有效解决传统分子筛存在的上述应用缺陷。多级纳米孔分子筛相比传统分子筛因其特殊的孔道结构和物化性能,在非均相催化方面具有丰富的催化活性位点、较短的扩散路径、较高的传递效率和较长的催化寿命,特别在涉及非均相催化反应的现代化学工业中展现出重要的潜在应用价值。综述多级纳米孔分子筛在烃类异构化反应、加氢裂化反应、烷基化与酰基化反应、烯烃氧化反应以及甲醇制烃类等反应中的诸多优势及潜在应用。     

1-(3-氨丙基)-2-甲基咪唑的催化合成、表征及应用

环氧树脂用的咪唑类固化剂多为固体和假性液体(低温下易析出的低熔点固体),工业应用不便。为了制得常温及低温下均呈液体的便于工业应用的咪唑固化剂,以1-氰乙基-2-甲基咪唑作为基本原料,骨架镍为催化剂,液氨为副反应抑制剂,乙醇作为溶剂,加压催化氢化合成液体咪唑固化剂1-(3-氨丙基)-2-甲基咪唑,考察氢气压力、液氨用量和催化剂循环使用次数对产率的影响,并通过元素分析、核磁共振氢谱和红外光谱对产物进行确证。结果表明,优化的反应条件为:反应温度100℃,氢气压力5 MPa,m(1-氰乙基-2-甲基咪唑)∶m[骨架镍(湿重)]∶m(液氨)∶m(乙醇)=139∶27.8∶42.5∶278,此条件下,产率可达96%。产物低至-35℃也不凝固,能良好地固化环氧树脂,表现出优异的工业适用性和固化性。     

Determination of tensile forces to enhance the supply stability of reinforced fiber

The manufacturing process of long fiber thermoplastic is initiated by supplying reinforced fiber wound in a spool dispenser. If problems such as tangling or kinking occur in the apparatus used for supplying the reinforced fiber in the long-fiber thermoplastic direct process, the productivity of the long-fiber thermoplastic decreases. Therefore, it is important to enhance the supply stability of reinforced fiber. In general, the increase in supply stability can be achieved by maintaining a steady balloon shape that is controlled by the unwinding velocity or tensile force of the reinforced fiber. In this research, the range of suitable tensile force was determined under the assumption that the unwinding velocity remained constant. The reinforced fiber was assumed to be inextensible, homogeneous, and isotropic and to have uniform density. The transient-state unwinding equation of motion to analyze the unwinding motion of reinforced fiber can be derived by using Hamilton’s principle for an open system in which mass can change within a control volume. In the process of solving the transient-state unwinding equation of motion, the exact two-point boundary conditions are adopted for each time step.     

Analysis of performance for centrifugal steam compressor

In this study, mean streamline and Computational fluid dynamics (CFD) analyses were performed to investigate the performance of a small centrifugal steam compressor using a latent heat recovery technology. The results from both analysis methods showed good agreement. The compression ratio and efficiency of steam were found to be related with those of air by comparing the compression performances of both gases. Thus, the compression performance of steam could be predicted by the compression performance of air using the developed dimensionless parameters.