超声后RADA16-I短肽纳米纤维支架重组装及成胶的研究

RADA16-I自组装短肽水溶液中形成纳米纤维并在盐离子作用下触发成水凝胶.RADA16-I纤维被大功率超声打断为小的原纤维片段.用AFM、CD和流变仪研究超声后纤维的重组装及其成胶性质.实验发现,超声未破坏纳米纤维二级结构,纤维仍保持β-sheet构型,超声4h后,小片段重组装为500nm的纤维,纤维虽未恢复到原长度,但仍未丧失其触发成胶的能力,只是在相同触发时间内达不到超声前的储能模量G′.还研究了超声对纳米纤维和成胶性能的影响,并提出相应的分子模型,这有助于短肽生物材料的应用,并对淀粉样蛋白病变的机理有一定的启示作用.     

基于溶剂置换的壳聚糖水凝胶的构建及力学性能研究

采用碱液置换丙二醇的方法制备物理交联壳聚糖水凝胶,研究了碱液浓度及三聚磷酸钠（TPP）离子交联预处理对凝胶结构和力学性能的影响。SEM观察结果表明水凝胶微观结构为富有纳米纤维的三维网络结构,且离子交联预处理在一定程度上会影响水凝胶内部结构的形成。无侧限压缩测试和动态力学分析（DMA）结果显示,未经离子交联的水凝胶在NaOH溶液浓度≤4mol/L时,力学性能随碱溶液浓度增大而增加,在NaOH溶液浓度为4mol/L时获得最优的力学性能;TPP交联后再经NaOH溶液处理的水凝胶其力学性能有所下降,当NaOH溶液浓度为2mol/L时可获得最优的力学性能。采用的2种物理交联方式在水凝胶形成过程中具有竞争关系。     

生物活性聚乙烯醇/羟基磷灰石复合水凝胶的结构与性能

本工作研究了聚乙烯醇和羟基磷灰石复合型生物活性水凝胶,探讨了工艺条件和配方对其拉伸强度,压缩强度,粘弹性、润滑性等生物力学性能的影响,观察和比较了复合水凝胶的微观形貌.研究表明聚乙烯醇和羟基磷灰石可形成接近纳米级的均匀分散结构,良好相容,使复合凝胶的力学强度和润滑性能提高,其应力松弛性能更接近天然软骨的粘弹性.     

羟基磷灰石纳米纤维增强甲基丙烯酸酐改性明胶复合水凝胶的制备及性能

采用溶剂热法制备了具有超高长径比的羟基磷灰石(HAP)纳米纤维,并将其与甲基丙烯酸酐改性明胶(GelMA)结合,利用紫外光交联制备了HAP纳米纤维/GelMA复合水凝胶。通过SEM、XRD、力学测试、溶胀测试、降解测试、细胞培养等对HAP纳米纤维/GelMA复合水凝胶进行结构表征和性能测试。SEM断面观察表明,HAP纳米纤维/GelMA水凝胶呈三维孔隙贯通的多孔结构。力学实验表明,HAP纳米纤维能有效增强水凝胶的弹性模量,且随着HAP纳米纤维添加量的增加,力学性能增强效果越明显。溶胀实验表明,当HAP纳米纤维质量分数为5.2wt%~14.2wt%时,HAP纳米纤维复合水凝胶的溶胀率变化不明显,当质量分数为18.2wt%时,溶胀率降低。降解实验表明,HAP纳米纤维的加入能有效保持水凝胶结构形态,使其更加稳定可控。细胞包裹培养实验表明,HAP纳米纤维/GelMA复合水凝胶能为细胞提供良好的三维生长环境,表现出优良的生物相容性。本实验制备的HAP纳米纤维/GelMA复合水凝胶在组织工程领域有着良好的应用前景。      

生物活性聚乙烯醇／羟基磷灰石复合水凝胶的结构与性能

本工作研究了聚乙烯醇和羟基磷灰石复合型生物活性水凝胶，探讨了工艺条件和配方对其拉伸强度，压缩强度，粘弹性、润滑性等生物力学性能的影响，观察和比较了复合水凝胶的微观形貌。研究表明聚乙烯醇和羟基磷灰石可形成接近纳米级的均匀分散结构，良好相容，使复合凝胶的力学强度和润滑性能提高，其应力松弛性能更接近天然软骨的粘弹性。     

2种羧基化纤维素衍生物对聚丙烯酰胺复合水凝胶力学性能的影响

为了深入理解羧基化纤维素衍生物聚集态结构和羧基含量对金属络合型复合水凝胶的增强增韧作用,文中分别在2种羧基化纤维素衍生物——聚阴离子纤维素(PAC)和TEMPO氧化纤维素纳米纤维(CNF)水体系中,进行了丙烯酰胺(AM)的自由基水溶液聚合,制备了PAM基复合水凝胶,进而经0.1 mol/L ZrOCl2水溶液处理,获得了力学性能更为优越的Zr(IV)络合型复合水凝胶.通过红外光谱、扫描电镜和压缩/拉伸力学对所得水凝胶进行了表征.结果表明,CNF或PAC的引入增强了PAM的氢键作用,赋予了水凝胶较高的力学性能,同等加量下纳米纤维状的CNF对PAM基水凝胶的增强效果高于PAC;引入Zr(IV)络合作用后,复合凝胶显著溶胀,但其内部网络结构却变得更加致密,PAC凝胶体系还出现了相互交织的纳米纤维结构;强烈的Zr(IV)-COO-络合作用使凝胶的力学性能大幅提高,同等加量下羧基含量较多的PAC增强效果更佳;羧基含量接近时,纳米结构的CNF增强效果更优.     

基于多巴胺改性纳米复合水凝胶的制备和性能

分别在酸性和碱性条件下用多巴胺修饰纳米羟基磷灰石制备纳米粒子改性的复合水凝胶并研究其性能,结果表明：多巴胺能在纳米羟基磷灰石表面生成氧化膜,且改性纳米粒子中的苯环与两性离子水凝胶高分子链形成共价键结合。同时,在酸性条件下多巴胺能提高纳米羟基磷灰石的分散性进而提高两性离子水凝胶的热稳定性(323℃才发生分解),也能提高水凝胶的网络结构强度(储能模量为2.7 MPa)和内耗能力(损耗因子为0.041)。而且,酸性纳米复合水凝胶的抗压能力达到11.66 MPa,比纯PSBMA两性离子水凝胶提高了32倍。这表明,酸性纳米复合水凝胶的结构特点和力学性能与天然软骨相似。     

LiOH/尿素溶剂体系制备高强度壳聚糖水凝胶膜

本文采用冷冻爆破法,将壳聚糖在LiOH/尿素溶液中溶胀,-60℃冷冻结冰,解冻搅拌后得到澄清壳聚糖溶液。壳聚糖碱溶液在硫酸/乙醇凝固浴中反相沉析,得到壳聚糖凝胶膜。此碱性溶剂体系法能避免壳聚糖降解,提高力学强度。力学测试结果表明,壳聚糖水凝胶膜拉伸强度为2.28MPa,最大拉伸应变(ε)达到226%。SEM观测到水凝胶微观结构类似蜂窝状,孔径均匀、致密,大小分布为50nm～5μm;XRD分析结果表明,碱溶液体系处理后壳聚糖晶型由α型转变成β型,结晶度降低。致密的结构和低结晶度是壳聚糖凝胶膜透明性和力学强度提高的重要原因。该性能优异的壳聚糖凝胶膜在关节软骨、创口敷料等方面有良好的应用前景。     

水解聚丙烯腈/大豆分离蛋白凝胶纤维的电刺激性能

采用水解聚丙烯腈(HPAN)和大豆分离蛋白(SPI)的共混水溶液复合得到纺丝原液,用自制纺丝设备挤到含一定量戊二醛和浓硫酸的饱和Na2SO4水溶液的凝固浴中,交联成型、拉伸干燥得到HPAN/SPI响应性水凝胶纤维,研究了电刺激性能.结果表明,在电解质溶液中非接触直流电场作用下,HPAN/SPI水凝胶纤维具有电流刺激响应性,表现为凝胶纤维弯曲现象.随着凝胶网络中-COOH含量的增加,纤维的弯曲度成阶段性增加,较高的聚丙烯腈含量使这种变化更为明显.HPAN/SPI水凝胶交联度、离子强度和pH的变化使得弯曲先增大后减少.在非直流电场的作用下,在wPAN=0.6,Na2SO4浓度为0.10 mol/L,pH=11水溶液中,电场强度为20 V时凝胶纤维的弯曲率达到极大值.该比例的HPAN/SPI凝胶纤维在Shiga凝胶弯曲理论中的Y取极大值.     

超快温度响应性纳米纤维水凝胶的制备及其用于药物的可控释放

先使用N-异丙基丙烯酰胺和N-羟甲基丙烯酰胺合成共聚物,以其为成纤聚合物用静电纺丝工艺制备纳米纤维,然后进行高速搅拌将纳米纤维切短并分散在叔丁醇中,最后进行冷冻干燥和热处理将切短的纳米纤维组装成具有多级多孔结构的纳米纤维水凝胶。这种纳米纤维水凝胶在水中具有良好的稳定性、压缩回弹性和显著的温度响应性。当水介质温度在20~55℃交替变化时它具有超快的温度响应性,达到消溶胀平衡的时间为34 s,达到溶胀平衡的时间为45 s。体外药物释放实验结果表明,当pH值为7.4的磷酸盐缓冲溶液的温度在15~47℃交替变化时,其中浸入的载模型药物葡聚糖的温度响应性纳米纤维水凝胶以“开/关”模式可控释放药物。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...