Effects of different ultrahigh molecular weight polyethylene contents on the formation and evolution of hierarchical crystal structure of high-density polyethylene/ultrahigh molecular weight polyethylene blend fibers

In this paper, the blend fibers of ultrahigh molecular weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) were prepared by solution blending and gel spinning process. The uniformity of the blend fibers has been confirmed by rheological data and thermodynamic unimodal curve. They were further characterized by single fiber strength test, scanning electron microscopy, wide-angle X-ray diffraction, small-angle X-ray scattering, and so forth, to explore the structural evolution mechanism with the change of UHMWPE content. The results showed that when the molar content of UHMWPE was only 2.9 mol%, entanglement appeared in the structure of shish-kebab, and when the proportion reached 20 mol%, an interlocking structure could be observed. With the increase of UHMWPE content, kebab began to be networked, and when the content reached 33 mol%, kebab's orientation reached its peak. After that, the interlocking network structure gradually improved. When the content reached 50 mol%, the shish's orientation reached saturation, and the shish-kebab network became perfect. In addition, with the increase of UHMWPE content, stress-induced recrystallization occurred on the wafer, some kebab would be converted into shish crystals, and when the content exceeded 50 mol%, the microfibers began to merge, and the wafer became denser, but still had entanglements. Our work has proposed a quantitative explanation for the evolution of hierarchical crystal structure of HDPE/UHMWPE blend fibers.     

Self‐Forming Interlocking Interfaces on the Immiscible Polymer Bilayers via Gelation‐Mediated Phase Separation

Gelation‐mediated phase separation is applied to prepare immiscible polymer bilayer films with an interlocking interface structure. Polymer systems consisting of copolymer of urea and polydimethylsiloxane and epoxy are selected to demonstrate the feasibility. When the epoxy fraction exceeds 25 wt%, well‐defined bilayer structures self‐form by a one‐pot casting method in which the phase separation state is fixed by an evaporation‐induced gelation. Microscopy studies of the resulting bilayers clearly reveal that interlocking structures form during the bilayer films construct. The interlocking structures lead to an enhanced interfacial adhesion and higher fracture energy. The current strategy might offer a facile way to in situ create an interlocking interface between immiscible polymer systems.     

固相萃取-超高效液相色谱-串联质谱法测定人指甲中的三氯生和三氯卡班

建立了人指甲中三氯生和三氯卡班的固相萃取结合超高效液相色谱-串联质谱(UPLC-MS/MS)检测方法。指甲样品经氢氧化钠消化,C18柱富集净化后,通过Waters ACQUITY^TM UPLC HSS T3色谱柱(100 mm×2.1 mm, 1.8 μm) 分离,以甲醇和水为流动相进行梯度洗脱,采用三重四极杆串联质谱仪负离子模式进行检测,同位素内标法定量。三氯生和三氯卡班分别在0.5~500.0 μg/kg和0.1~100.0 μg/kg范围内线性关系良好,相关系数(r²)均为0.999,方法定量限分别为2.0 μg/kg和0.2 μg/kg。3个水平的平均加标回收率为95.9%~110.2%,相对标准偏差为0.6%~9.7%(n=6)。本方法具有良好的灵敏度、回收率和重复性,适合指甲中痕量目标污染物的测定。利用该方法分析了60份实际样品,目标物的检出率为100%,三氯生和三氯卡班的含量范围分别为     

Interface Between an Old Concrete and a Bonded Overlay: Debonding Mechanism

The ageing of concrete structures creates the need for their repair. The thin bonded overlay technique is widely used; it is particularly suitable for the repair of large concrete areas. It is appropriate for slabs on grade (mainly industrial floors), pavements, bridge decks, walls and tunnels. Toppings and linings are similar applications. The aim of the overlay may be to smooth a damaged surface, and/or to improve the mechanical capacity of a structure by increasing its thickness, or to provide additional cover for corrosion protection.The durability of such repairs or overlays depends on the durability of their bond with the base structure; it is usually the critical aspect. Work, carried out in Laboratoire Matériaux et Durabilité des Constructions (Laboratory for building Materials and Constructions Durability) in Toulouse, France, is part of a larger programme started in 1990. The programme objective is to achieve a thorough knowledge of the debonding mechanisms of an overlay. Design rules and practical recommendations eliminating or drastically reducing durability hazards are expected to be developed. The work reported here focuses on the debonding propagation along an interface, notably the major influence of the interlocking between the two faces of the debonding interface. The study relies on finite elements modelling and on the comparison with experiments.Having evidenced the major role of interlocking in the example of a crack propagation, the paper focuses on the actual case of an interface. Debonding propagates in mixed mode, mode I combined with mode II, bringing an extra degree of complexity. Beyond the problem of the mixed mode, an important issue is how interlocking changes while debonding propagates. Indeed, mode I debonding opening damages interlocking for both mode I and mode II. A mode II slip has the same coupled effect on interlocking. A very significant problem is taking into account the coupling of mode I and II displacements to evaluate the actual value of the interlocking at any step of the propagation.The involved parameters have been identified and a method is proposed to take into account the coupling. The comparison with experimental results is promising. This research opens a new approach on the mechanism of the propagation of a debonding along an interface. The next step will consider evolution of the interlocking in the case of fatigue loading.     

钢筋网水泥砂浆加固砖墙中关于拉结筋的试验研究

本文通过对拉结筋的试验研究，得到拉结筋的设置与否对于钢筋网水泥砂面层加固砖墙的承载力无影响的结论，因此，可采用扒钉或４寸钉子代替Ｓ形拉结筋以固定钢筋网于墙上，达到省工，省线的良好经济效果，在砖房加固工程中具有重要的实用意义。     

Theoretical analysis of flexible strain-gauge sensor with nanofibrillar mechanical interlocking

A flexible, and skin-attachable strain gauge sensor based on interconnected nanofibers was recently reported with discernible gauge factor for a flexible and highly sensitive pressure sensor. Here, we present a simple theory that can explain the observed electrical responses by employing the well-established friction law and electrical circuit analysis. The results are in good agreement with the experimental data obtained under physical loads.     

多基准站GPS定位靶场测试方法研究

CBTC(Communication Based Train Control,基于通信的列车控制)系统的联锁软件为SIL4级的高安全、高可靠软件,目前广泛使用的软件测试和仿真验证的结果严重依赖选取的测试向量,要保证高覆盖率的测试十分困难。EN50128中强烈推荐SIL4等级的软件使用形式化方法完成软件需求规格说明书和软件设计,因此,采用形式化的方法设计软件,是构造高可靠、高安全软件的一个重要途径。本文总结了现有的CBTC系统中联锁子系统集成方式及优缺点,并使用事件确定有限自动机ETDFA(Event deterministic finite automata)模型对适用性更优的升级型集成方式的联锁软件的联锁逻辑完成形式化定义,保证联锁逻辑的正确性,减少软件的不确定性描述。以办理进路为例生成联锁对象的ETDFA模型,验证该方法的有效性和可行性。该方法不仅为CBTC联锁软件的设计与开发提供新思路,而且有助于安全苛求软件的形式化验证与分析,提高联锁软件的安全性和正确性。     

从铁钉表面镀铜浅谈低年级学生科研思维培养

以铁钉表面镀铜为例,从Cu~(2+)直接氧化Fe实验中发现问题:铜镀层凸凹不平、易脱落。基于该问题,引导学生进行文献查阅,对问题进行分析,然后设计相关实验方案,进行实验操作,从而解决问题:获得表面均匀的铜镀层。通过问题发现、问题分析、文献资料查阅、实验方案设计、问题解决的思路培养低年级学生科研思维。     

Keratin-Based Composite Bioactive Films and Their Preservative Effects on Cherry Tomato

In this study, keratins were extracted from pig nail waste through the reduction method using L-cysteine as a reductant. Curcumin was successively incorporated in a mixed solution including keratin, gelatin, and glycerin to prepare different kinds of keratin/gelatin/glycerin/curcumin composite films. The morphology of the keratin/ gelatin/glycerin/curcumin composite films were examined using scanning electron microscopy. The structures and the molecular interactions between curcumin, keratin, and pectin were examined using Fourier transform infrared spectroscopy and X-ray diffraction, and the thermal properties were determined through thermogravimetric analysis. The tensile strengths of keratin/gelatin/glycerin/curcumin and keratin/gelatin/curcumin composite films are 13.73 and 12.45 MPa, respectively, and their respective elongations at break are 56.7% and 4.6%. In addition, compared with the control group (no film wrapped on the surface of tomato), the ratio of weight loss of the keratin (7.0%)/gelatin (10%)/glycerin (2.0%)/curcumin (1.0%) experimental groups is 8.76 ± 0.2%, and the hardness value of the tomatoes wrapped with composite films is 11.2 ± 0.39 kg/cm³. Finally, the composite films have a superior antibacterial effect against Staphylococcus aureus and Escherichia coli because of the addition of curcumin. As the concentration of curcumin reaches 1.0%, the antibacterial activity effect of the film is significantly improved. The diameter of the inhibition zone of E. coli is (12.16 ± 0.53) mm, and that of S. aureus is (14.532 ± 0.97) mm. The multifunctional keratin/gelatin/glycerin/curcumin bioactive films have great potential application in the food packaging industry.     

Small Worlds Among Interlocking Directors: Network Structure and Distance in Bipartite Graphs

We describe a methodology to examine bipartite relational data structures as exemplified in networks of corporate interlocking. These structures can be represented as bipartite graphs of directors and companies, but direct comparison of empirical datasets is often problematic because graphs have different numbers of nodes and different densities. We compare empirical bipartite graphs to simulated random graph distributions conditional on constraints implicit in the observed datasets. We examine bipartite graphs directly, rather than simply converting them to two 1-mode graphs, allowing investigation of bipartite statistics important to connection redundancy and bipartite connectivity. We introduce a new bipartite clustering coefficient that measures tendencies for localized bipartite cycles. This coefficient can be interpreted as an indicator of inter-company and inter-director closeness; but high levels of bipartite clustering have a cost for long range connectivity. We also investigate degree distributions, path lengths, and counts of localized subgraphs. Using this new approach, we compare global structural properties of US and Australian interlocking company directors. By comparing observed statistics against those from the simulations, we assess how the observed graphs are structured, and make comparisons between them relative to the simulated graph distributions. We conclude that the two networks share many similarities and some differences. Notably, both structures tend to be influenced by the clustering of directors on boards, more than by the accumulation of board seats by individual directors; that shared multiple board memberships (multiple interlocks) are an important feature of both infrastructures, detracting from global connectivity (but more so in the Australian case); and that company structural power may be relatively more diffuse in the US structure than in Australia.