左旋聚乳酸/多壁碳纳米管/羟基磷灰石电纺丝纳米纤维的形态及生物降解性能

采用静电纺丝法制备了左旋聚乳酸/多壁碳纳米管/羟基磷灰石(PLLA/MW NT s/HA)杂化纳米纤维无纺毡,分析了MW NT s的加入对杂化纤维形态结构的影响,以及不同工艺条件下纤维的直径分布,并研究了纤维无纺毡在磷酸盐缓冲溶液(pH 7.4,37℃)中的体外降解过程。结果表明:MW NT s的加入使PLLA/HA纤维直径略有减小;PLLA/MW NT s/HA杂化纤维体系降解液的pH值下降到一定程度后,在降解后期呈缓慢上升趋势;碱性MW NT s/HA的加入抑制了PLLA降解过程中的自催化作用,减缓了PLLA的降解速度。     

电纺丝法制备纳米纤维薄膜的降解性能研究

电纺丝法制备了PLLA、PLGA、PLLA/PLA-PEG、PLLA/HA纳米纤维薄膜,用SEM表征了纳米纤维的形貌.在37℃,pH值为7.4的PBS溶液中对4种纳米纤维薄膜的降解性能进行研究,通过GPC测试降解过程中聚合物分子量的变化,SEM表征降解过程中纳米纤维形貌的变化.结果表明:PLGA薄膜降解速率较快,吸水率最高;PLLA/PLA-PEG次之;PLLA降解速率较慢,吸水率最低,HA的加入可调节PLLA的降解速率.     

激光熔融静电纺丝法制备PLLA及PLLA/nHA纤维支架及性能研究

利用激光熔融静电纺丝方法制备了PLLA和PLLA/nHA纤维支架,采用FTIR和DSC测试对支架材料的结构和热学性能进行表征,通过熔融电纺对PLLA和PLLA/nHA纤维支架进行体外降解实验,研究了失重率与降解时间的关系。同时对激光熔融和一般溶液电纺得到的PLLA和PLLA/nHA纤维支架进行细胞相容性实验,对两种方法所得支架的安全性进行评价。结果表明:nHA对PLLA的结构和晶型产生影响,并减缓PLLA的降解速度,激光熔融电纺支架更具安全性,其更适合组织工程应用。     

静电纺丝法制备高分子量聚左旋乳酸纳米纤维及其表征

利用静电纺丝法制备了高分子量聚左旋乳酸(PLLA)纳米纤维,研究了溶液浓度、纺丝距离和纺丝电压对纤维形貌的影响.用扫描电子显微镜(SEM)对纤维形貌进行了表征,结果表明,当PLLA溶液浓度为3%,纺丝距离为20.5cm,纺丝电压为13kV时得到的纤维形貌较好.再用差示扫描量热法(DSC)对纤维的热学性能进行了表征,用X...     

PAN/DMSO干湿法纺丝凝固工艺的研究

初步探讨了ＰＡＮ／ＤＭＳＯ溶液干湿法纺丝凝固工艺与纤维拉伸性能的关系。并对湿法纺丝与干湿法纺丝作了比较，结果表明，干湿法纺丝所得纤维的总牵伸倍数在一定范围内随纺丝凝固浴浓度的增大而增大；对于给定的ＰＡＮ／ＤＭＳＯ纺丝液体系，存在一较佳的凝固牵伸范围，空气干层的存在使得干湿纺纤维较湿纺纤维能承受更大的牵伸倍数，但空气层长度的确定存在一合适的范围，且空气干层的存在使得干湿纺纤维较湿纺纤维能随更大的牵伸倍数，但空气层长度的确定存在一合适的范围，且空气层长度对纤维总牵伸倍数的影响受到其它纺丝凝固工艺参数的影响。扫描电镜（ＳＥＭ）的研究结果表明，湿法纺丝所得的纤维存在各种表现缺陷，其中，表面沟槽是纺丝工艺本身所致，无法消除；干湿纺纤维的表面则光洁无沟槽，初步探讨了有关表面沟槽的形成机理。     

基于TPEE双组分扭曲螺旋电纺纤维的初探

首先利用静电纺丝法制备了热塑性聚酯弹性体(TPEE)纳米纤维.用扫描电镜(SEM)对纤维的形貌进行了表征,纤维的直径为300～600nm,讨论了纺丝液浓度和纺丝距离对纤维形貌产生的影响.然后在一定的负电压下制备了聚对苯二甲酸丁二醇酯(PBT)和聚左旋乳酸(PLLA)电纺纳米纤维,发现PBT和PLLA均具有良好的负极可纺...     

静电纺制备的PLLA/PCL复合支架性能及细胞相容性

利用静电纺丝技术制备了一系列不同比例的左旋聚乳酸/聚己内酯(PLLA/PCL)复合纳米纤维支架。通过扫描电镜、差热分析、宽角X射线衍射和接触角测试手段对支架结构与形态、结晶性能及亲水性进行了表征;采用在缓冲溶液中加酶的方式,研究了复合材料的降解性能;将体外培养的真皮成纤细胞接种至材料表面,用扫描电镜观察了成纤细胞在材料表面的生长情况。研究结果表明,电纺丝得到的复合支架纤维直径均一,且呈相互连通的多孔网状结构;脂肪酶的存在加速了支架材料的降解速度;成纤细胞在复合支架上具有良好的生长状态。     

左旋聚乳酸/右旋聚乳酸嵌段共聚物的共混物及其纤维的结构与性能

以右旋聚乳酸-聚乙二醇-右旋聚乳酸(PDLA-PEG-PDLA)三嵌段共聚物作为改性剂,通过熔融共混法及熔融纺丝-后牵伸两步法分别制备了左旋聚乳酸(PLLA)/PDLA-PEG-PDLA共混物及其共混纤维。采用差示扫描量热分析、热重分析、毛细管流变仪、扫描电镜、广角X射线衍射及力学性能测试等方法对共混物及其共混纤维的结晶行为、热性能、取向及力学性能等进行了研究。结果表明,熔融温度对PLLA及其共混物的结晶行为有较大的影响。当熔融温度为230℃时,共混物中PDLA-PEG-PDLA含量为10%时,α晶的结晶温度最高,为127℃;另外,共混物具有较好的纺丝性能,相同条件下制备的共混纤维的结晶度和取向度均高于纯PLLA纤维,当嵌段共聚物质量分数为2%时,共混纤维的结晶度及取向度最大,分别为27%和-0.39;嵌段共聚物的加入,对PLLA的热稳定性和力学性能的影响较小。     

激光熔融静电纺丝法制备PLLA/PCL/nHA复合纤维支架及细胞相容性评价

利用激光熔融静电纺丝技术制备了PLLA/PCL及PLLA/PCL/nHA复合纤维,热压后形成层压复合纤维支架。利用扫描电镜对纤维支架进行了表征,同时对其进行了亲水性的测试,最后通过倒置荧光显微镜和MTT实验对复合纤维支架的细胞相容性进行了评价。研究结果表明,层压复合纤维支架的直径和孔结构具有多样性,nHA能够提高PLLA/PCL层压纤维支架的亲水性,改善支架的细胞相容性,增加细胞的附着能力,提高细胞的存活率。     

荧光Lyocell纤维的制备和性能

通过共混方法将经预处理的荧光粉均匀分散在NMMO溶液中,采用Lyocell工艺通过干湿法纺丝成功制备了荧光Lyocell纤维,探讨了荧光粉用量对纺丝液流变性能及纤维的结构与性能的影响。结果表明,随着荧光粉用量的增加,Ly-ocell纺丝液的表观黏度先下降后上升,当荧光粉用量达到m(荧光粉)/m(纤维素)=3/100时,纺丝液的黏度呈最低值。此外,随着荧光粉用量的增加,纤维的荧光性能随之提高,但纤维内荧光颗粒的团聚现象逐渐加剧,导致纤维的力学强度和结晶度逐渐降低。     

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.……     

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.     

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...     

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.……     

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.     

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.     

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 ...