Microstructural changes in zein proteins during extrusion

Changes in proteins during extrusion may influence the texture of ready-to-eat (RTE) corn-based extruded foods. This study focused on microstructural changes and dispersal patterns of corn storage proteins, zeins, that occur during extrusion processing. Model systems were used that consisted of two types of corn protein: commercial zein and corn gluten meal (CGM), combined with corn starch. Commercial zein is not encased in protein bodies, whereas CGM is comprised of zeins encapsulated in protein bodies. Mixtures were extruded under conditions that resulted in different specific mechanical energy (SME). The microstructure of the resulting extrudates was analyzed using transmission electron microscopy (TEM) with immunogold labeling of the α-zein storage protein. The micrographs showed that the greatest zein dispersal occurred in CGM/starch extrudates, especially under high SME conditions. The micrographs also showed that, at both mild and harsh extrusion conditions, commercial zein/starch extrudates contained large protein aggregates. Under mild extrusion conditions, protein bodies in the CGM/starch extrudates partially retained their spherical shapes, but during harsher processing, protein bodies were disrupted and dispersed zein appeared to form fibrils. Such protein fibrils may influence texture and/or quality of extruded corn-based snacks and breakfast foods.     

Scanning probe microscopy studies of cereal seed storage protein structures

Scanning probe microscopes (SPMs) share a number of common features which give the techniques advantages over conventional light and electron microscopy. First, high resolution, up to the atomic level, is possible in certain cases, and second, they are nondestructive, requiring no staining or coating and the images can be obtained in the hydrated state or under water. Scanning probe microscopes, particularly scanning tunnelling microscopes (STM) and atomic force microscopes (AFM), have been used to study food-related systems, ranging from relatively large structures such as starch granules to the organisation of secondary structures in proteins and the interaction of proteins. The seed storage proteins (gluten) of wheat are responsible for the viscous and elastic properties of wheat doughs that allow them to be used for a wide range of different food products. Using AFM and STM, images of individual and groups of proteins have been obtained in both the dry and hydrated states. The ability to work in liquid environments allows the conformation of proteins to be determined under conditions approaching “native.” The AFM and STM have been used to image both gliadins and glutenins and to study their aggregative behaviour in relation to gluten and dough systems.     

Friction and wear properties of short carbon fiber reinforced aluminum matrix composites

The friction and wear properties of short carbon fibers (SCFs) reinforced aluminum matrix composite were studied. The influences of the fiber volume fraction, load applied, rotating speed, and wear mechanism were discussed. The results indicated that SCFs/Al composite had better tribological properties than Al alloy. The friction coefficient and wear mass loss decreased with the fiber volume fraction increased, but increased as the load and rotating speed increased, respectively. SCF reduced direct contact between the matrix and counterpart and improved the wear resistance of SCFs/Al composite greatly. The wear displayed a linear evolution in all the range of load. Surfaces before and after wear tests were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) spectroscopy.     

WC颗粒增强铁基表面复合材料的三体磨料磨损性能研究

设计、制备了一台三体磨料磨损实验机，对该实验机进行了重现性实验。以高铬铸铁为标样，利用该磨损实验机分别考察了WC颗粒体积分数、载荷与表面复合材料相对耐磨性能之间的关系。实验结果表明：本实验机的测试性能是可靠的；复合材料的三体磨料磨损性能与高铬铸铁标样相比有较明显的提高，在同一载荷下．复合材料的相对耐磨性能随着WC颗粒体积分数的增大呈先升高后降低的变化规律，WC颗粒体积分数为27％的复合材料相对耐磨性最高，达到高铬铸铁的5．12倍；而对于同一种复合材料，随着载荷的增大，其相对耐磨性呈增加趋势，其中WC颗粒体积分数为27％的复合材料增加最为明显；复合材料的三体磨料磨损机理为WC对周围组织的屏蔽作用，失效方式为WC颗粒因疲劳而片状剥落。     

静电纺丝制备多壁碳纳米管/聚酰亚胺复合纤维膜

采用电纺技术制备多壁碳纳米管(F-MWNTs)/聚酰亚胺(PI)复合纤维膜。酸化处理MWNTs,运用原位聚合法制备多壁碳纳米管(F-MWNTs)/聚酰胺酸(PAA)溶液,使用电纺技术制成F-MWNTs/PAA复合纤维膜,经热亚胺化为F-MWNTs/PI复合纤维膜。运用扫描电镜、透射电镜、X射线衍射、热重分析、电子拉力机、迅速热传导率计及体积电阻测量仪等对电纺复合纤维膜进行结构、组成及性能表征。结果表明,随着F-MWNTs含量增加,复合纤维膜热稳定性增强。含量为5wt%时,与纯PI纤维膜相比,复合纤维膜力学和导热性能显著提高,绝缘性能有所降低,但仍为绝缘材料。     

真空热压烧结SiC_p/Al复合材料的界面元素扩散及增强断裂机理

采用真空热压粉末冶金烧结工艺制备了含SiC颗粒体积分数分别为 5 %、15 %和 2 5 %的SiC颗粒增强铝基复合材料 ,结合其力学性能、扫描电镜和界面微区能谱分析结果 ,分析了SiC/Al复合材料的真空烧结过程中的界面现象 ,以及材料增强和断裂机理。结果表明 ,真空烧结过程中出现了界面反应 ,改善了界面结合强度 ,断裂破坏主要在基体上进行。随着SiC粒子体积分数的增加 ,SiCp/Al复合材料的抗拉强度增加 ,弹性模量显著增加 ,延伸率降低 ,材料脆性增加。     

LC-MS/MS分析结合优化提取工艺探究啤酒中麸质蛋白

大多数啤酒蛋白来自大麦和小麦,它们含有与乳糜泻疾病有关的富含脯氨酸的麸质蛋白成分.本研究选择0.1 mol/L醋酸铵甲醇和丙酮作为优化溶液,分别提取啤酒样品中醇不溶和醇溶的麸质蛋白组分,最大限度地获取麸质蛋白信息.采用优化的麸质蛋白提取工艺,结合液相色谱-质谱法(LC-MS/MS)分析8种市售啤酒的麸质蛋白.结果表明,...     

Fabrication and mechanical properties of PLLA and CPC composite scaffolds

The brittleness and insufficient strength of biomaterials such as calcium phosphate cement (CPC) limit their applications in physiologically non-load-bearing bone lesions. These limitations stimulated the research for developing degradable polymer-ceramic composite materials that can closely match the modulus of bones. In this study, poly (L-lactic acid)/calcium phosphate cement (PLLA/CPC) composite scaffolds were fabricated via a four-step process, namely, measurement, prototyping, compounding, and dissolving. The design and mechanical properties of the PLLA/CPC composite structures were theoretically and experimentally studied. The PLLA/CPC scaffold improved the mechanical properties of the CPC. The CPC??s compressive strength and strengthening percentage increase with higher PLLA volume. Such composites may have a clinical use for load-bearing bone fixation.     

阳极化处理对铝箔网与树脂基复合材料粘接性能的影响

采用磷酸阳极化工艺对铝箔网进行了表面处理,研究了阳极化工艺参数对其与树脂基复合材料粘接性能的影响,并对优化后工艺处理的铝箔网表面形貌及粘接性能进行了分析。结果表明:最佳工艺参数的去氧化时磷酸体积分数为16%,处理时间为6min,氧化时磷酸体积分数为16%,处理时间为23min;磷酸阳极化后,铝箔网表面生成一层疏松多孔的氧化膜,可以增大铝箔网表面与复合材料的粘接界面面积,并有良好的界面效应,有效地提高了粘接强度,与处理前的抗拉剪强度相比,提高了14.66%;同时铝箔网的耐蚀性也得到了较大提高。     

基于组合算法改进的谱库检索算法

本工作对Stein和Scott提出的SS组合算法（SS）进行改进,采用Kim等研究得到的权值因子优化该算法中对应的权值因子,并重新分配了加权点积相似度算法和峰比例算法的系数。采用改进的SS组合算法,在NIST 11标准参考谱库（212 961张质谱图）中检索了查询库中的30 932张质谱图,使用气相色谱-质谱联用仪分析了8种不同的化合物样品,并且在NIST 11参考库中检索对应的质谱图。为了评价该算法的性能,分别利用2种组合算法分析查询谱图或实验样品的准确度和相似度。结果表明：与之前的SS组合算法相比,使用本方法后,查询谱图在参考谱库中匹配的准确度平均提高了1.15%,并且查询库中94.45%谱图的相似度得到了提高;通过气相色谱-质谱联用仪得到的样品质谱图在参考谱库中有着更高的命中率,并且谱图的相似度平均提高了3.56%。改进的组合算法能够较好地提高待测谱图在参考库中的准确度和相似度,同时也可以利用这种方法改进以SS组合算法为理论基础的其他算法。     

喷射沉积SiC_p/Al-20Si复合材料高周疲劳行为研究

采用喷射沉积法制备15%(体积分数)4.5 m SiCp/Al-20Si复合材料及其基体合金,研究该组材料的微观组织、力学性能、高周疲劳性能以及疲劳断口形貌。结果表明:SiC颗粒的加入有利于提高材料的力学性能;复合材料及其基体的高调疲劳寿命随应力幅值的减小而增加,在相同应力幅值下,复合材料的疲劳寿命远远高于基体合金。疲劳裂纹从大颗粒的初晶Si的断裂以及Si相脱离处形核,并开始扩展。对于复合材料而言,SiC颗粒尺寸较小,不容易发生断裂,在形核过程中,当裂纹遇到SiC颗粒时,裂纹或者避开增强体,或者受阻于SiC颗粒,只能在基体合金中扩展,从而扩大了疲劳形核区的面积,提高了材料的疲劳寿命。Si颗粒的脱离、Si相的断裂以及SiC颗粒与基体界面的脱粘是复合材料疲劳断裂失效的主要机制。     

Prototype fabrication of a composite automobile body based on integrated structure

This paper describes the integrated fabrication and assembly approach used to replace a steel body cover in Samand Sarir automobile by composite one because composite could perform higher mechanical performance, i.e., strength, stiffness, and impact absorption energy at low velocity. Considering the integrated body as base design criteria, the steel cover is redesigned and fabricated by composite material. Tensile, flexural, and charpy impact tests were carried out to determine the properties of woven fabric laminated composite in [0/90°] and [±45°] fiber orientations. The selected composite laminate shows 2.9 times impact resistance; its desirability factors are improved 1.8 times for strength and 3.35 times for stiffness. Using finite element method, the impact of the composite body cover was simulated by ABAQUS for several thicknesses and fiber orientations. The FEM results indicate that finally laminated composite [0/90°]₇ can improve the crashworthiness of composite part in comparing to steel body cover. The integrated 3D preform of glass woven fabric was stitched like the shape of 3D model of body cover and placed in mold for prototype fabrication. It can be concluded that vacuum bagging as suggested fabrication method could be suitable for 3,000–5,000 annual production volume. Eventually, the fabricated composite body cover weighed 1.7 kg, which is 42% lighter than the steel body cover.     

添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响

考察了添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响。结果表明：添加少量纳米SiCp(体积分数为0．5％),轻微降低了铜基材料的导电率,显著提高了耐磨性,有效降低了铜／钢摩擦副之间的粘着作用和材料转移;130nm SiCp／Cu基复合材料的导电性和耐磨性都优于30nm SiCp／Cu基复合材料。     

Friction and wear behavior of electroless Ni-based CNT composite coatings

Ni-based carbon nanotube (CNT) composite coatings with different volume fraction (from 5 to 12 vol.%) of CNTs were deposited on medium carbon steel substrates by electroless plating. The friction and wear behavior of the composite coatings were investigated using a pin-on-disk wear tester under unlubricated condition. Friction and wear tests were conducted at a sliding speed of 0.0623 m s⁻¹ and at an applied load of 20 N. The experimental results indicated that the friction coefficient of the composite coatings decreased with increasing the volume fraction of CNTs due to self-lubrication and unique topological structure of CNTs. Within the range of volume fraction of CNTs from 0 to 11.2%, the wear rate of the composite coatings showed a steadily decreasing trend with increasing volume fraction of CNTs. Because of the conglomeration of CNTs in the matrix, however, the wear rate of the composite coatings increased with further increasing the volume fraction of CNTs.     

微米Wp/Cu基复合材料耐磨行为

以微米级的钨粉和铜粉为原料,采用冷压烧结方法制备出Wp/Cu基复合材料,并进行了热挤压加工,考察了该材料的耐磨行为。结果表明:该复合材料不仅具有良好的抗磨性能,而且适宜同40Cr钢组成在油润滑条件下工作的摩擦副;在油润滑条件下,其磨损体积损失仅是QSn6.5-0.4的11.6%,磨损表面呈Cu基体、凸出Wp和少量孔隙的耐磨组织,并且未发现来自40Cr钢的转移物。     

Sliding wear behavior of planar random zinc-alloy matrix composites

The friction and wear behavior of planar random zinc-alloy matrix composites reinforced by discontinuous carbon fibres under dry sliding and lubricated sliding conditions has been investigated using a block-on-ring apparatus. The effects of fibre volume fractions and loads on the sliding wear resistance of the zinc-alloy matrix composites were studied. Experiments were performed within a load range of 50–300 N at a constant sliding velocity of 0.8 m s⁻¹. The composites with different volume fractions of carbon fibres (0–30%) were used as the block specimens, and a medium-carbon steel used as the ring specimen. Increasing the carbon fibre volume fraction significantly decreased the coefficient of friction and wear rates of both the composites and the medium-carbon steel under dry sliding conditions. Under lubricated sliding conditions, however, increasing the carbon fibre volume fraction substantially increased the coefficient of friction, and slightly increased the wear of the medium-carbon steel, while reducing the wear of the composite.Under dry sliding conditions, an increasing load increased not only the wear rates of both the composite and the unreinforced zinc alloy, but also those of their corresponding steel rings. However, the rate of increase of wear with increasing load for both the composite and its corresponding steel ring was much smaller than for the unreinforced zinc alloy and its corresponding steel ring. The coefficient of friction under dry sliding conditions appeared to be constant as load increased within a load range of 50–150 N for both the composite and the unreinforced zinc alloy, but increased at the higher loads. Under any load the coefficient of friction of the composite was lower than half that of the unreinforced zinc alloy under dry sliding conditions.     

Effect of matrix/reinforcement particle size ratio (PSR) on the mechanical properties of extruded Al–SiC composites

This paper studied the combined effects of matrix-to-reinforcement particle size ratio (PSR) and SiC volume fraction on the mechanical properties of extruded Al–SiC composites. A powder metallurgy technique (PM) of cold pressing at 500 MPa followed by hot extrusion at 580 °C was adopted to produce Al/SiC composite. Aluminum powder of size 60 μm and silicon carbide with different sizes, i.e., 50, 20, and 8 μm, were used. Three different volume fractions of SiC were employed, i.e., 5, 10, and 15 %, for each investigated size using a constant extrusion ratio of 14.36. The effect of matrix-to-reinforcement PSR on the reinforcement spatial distribution, fabricability, and resulting mechanical properties of a PM-processed Al/SiC composite were investigated. It has been shown that small ratio between matrix to reinforcement particle size resulted in more uniform distribution of the SiC particles in the matrix. As the PSR increases, the agglomerations and voids increase and the reinforcement particulates seem to have nonuniform distribution. In addition, the agglomerations increased as the volume fraction of the SiC increased. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength, and elongation. Yield strength and ultimate tensile strength of the composite reinforced by PSR (1.2) are higher than those of composite reinforced by PSR (7.5), while the elongation shows opposite trend with yield strength and ultimate tensile strength.     

Application of the GTN model to predict the forming limit diagram of IF-Steel

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume fraction, and final void volume fraction. Furthermore, the experimental FLD of the specimen steel was considerably predicted using the obtained GTN model parameters.     

High-resolution cryo-scanning electron microscopy study of the macromolecular structure of fibronectin fibrils

High-resolution cryo-scanning electron microscopy was used to examine fibronectin fibrils formed in culture by human skin fibroblasts and in a cell-free system by denaturing soluble plasma fibronectin with guanidine. These studies indicate that the conformation of fibrils formed in culture and in a cell-free system appeared to be similar and that fibronectin fibrils have at least two distinct structural conformations. Fibronectin fibrils can be very straight structures with smooth surfaces or highly nodular structures. The average diameter of the nodules in these fibrils is 12 nm. Both conformations can be seen within an individual fibril indicating that they are not different types of fibronectin fibrils but rather different conformational states. Immunolabeling studies with a monoclonal antibody, IST-2, to the heparin II binding domain of fibronectin revealed that the epitope was buried in highly smooth fibrils, but it was readily exposed in nodular fibrils. We propose, therefore, that fibronectin fibrils are highly flexible structures and, depending on the conformation of the fibril, certain epitopes on the surface may be buried or exposed.     

基于ANSYS的三闭式SMA混杂复合材料箱型薄壁梁的模态分析

采用有限元分析软件ANSYS对SMA混杂复合材料箱型薄壁梁进行了模态分析。首先建立了SMA混杂复合材料箱型薄壁梁的有限元模型，运用ANSYS软件中的Material Designer模块建立SMA/石墨/环氧树脂复合材料模型并获得其材料参数，通过ANSYS复合材料ACP模块对复合材料箱型薄壁梁进行铺层，然后对SMA混杂复合材料箱型薄壁梁进行模态计算，讨论了配置方式、铺层角度、宽高比、单层SMA体积含量、SMA安装位置对固有频率的影响。