稻谷自然晾晒后显微结构分析研究

通过研究自然晾晒后稻谷内部的显微组织结构，可以分析稻谷应力裂纹的生成扩展机理。通过扫描电子显微镜观察，发现自然晾晒后的稻谷胚乳组织结构遭到轻微破坏，产生应力裂纹，籽实皮与胚乳之间的结合区域也有应力裂纹产生。应力裂纹首先生成在胚乳组织的中心部位，然后向四周扩展。产生应力裂纹时，只是裂纹两侧的胚乳组织遭到破坏，其它部位的胚乳组织状态良好。大多数应力裂纹扩展的路径都是穿越细胞壁，沿着淀粉颗粒的边缘进行扩展。分析研究稻谷自然晾晒后胚乳组织的形态结构以及应力裂纹的显微形态、生成位置和扩展方向，对稻谷应力裂纹检测技术的提高和干燥品质的评价都具有重要的价值。     

糙米机械破碎力学特性试验与分析

为了研究糙米机械破碎力学特性及其与籽粒结构特性的关系。采用物性测试仪对糙米的锥刺、三点弯曲、剪切、挤压4种机械破碎力学特性进行测试与分析,并对糙米和精米的破碎力学特性(三点弯曲)进行了比较。结果表明:糙米的断裂是由于内部胚乳组织不均匀,在外力作用下首先形成内部裂纹,裂纹尖端处的应力集中又进一步促进裂纹扩展,最终导致籽粒断裂;厚度为(1.0±0.5)mm的不同样品锥刺破碎力在10N左右,各样品籽粒内部的结合力相差较小,籽粒的断裂主要与厚度及胚乳特性有关,其中三点弯曲力更能反映籽粒的破碎特性,糙米的糠层对籽粒有一定的保护作用,糙米力学特性比精米好。该文为糙米储藏加工技术参数的确定提供依据。     

稻谷与钉齿碰撞损伤的有限元分析

建立了稻谷3层椭球体结构CAD模型,在前处理软件HyperMesh中划分网格,设置单元、材料属性和接触碰撞参数,生成了稻谷的有限元模型。利用LS-DYNA软件仿真分析了稻谷与钉齿碰撞过程,仿真结果表明：碰撞接触区为椭圆,受压应力作用,区域中心处应力值最大。籽实皮和胚乳的Von Mises等效应力值随碰撞速度的增加逐步增大。稻谷与钉齿碰撞时,胚乳达到临界Von Mises等效应力值31.68?MPa对应的临界速度为24.2?m/s,而籽实皮碰撞损伤的临界速度要大得多。稻谷与钉齿碰撞形成宏观应力裂纹是从胚乳中心或近中心扩展而成的。     

玉米应力裂纹的生成和扩展过程模拟

对玉米应力裂纹进行了分形分析,结果表明,玉米应力裂纹具有近似的自相似性,即分形特征,因此,可以用分形的理论进行研究。根据显微图像分析,认为分形形纹的扩展有4种机制,即沿晶扩展、穿晶扩展、沿晶和穿晶偶合扩展及分叉扩展。建立了各种应力裂纹扩展机制的分形模型,给出了生成元维数,模拟了整个剖面和局部显微状态下应力裂纹的扩展过程。     

基于Micro-CT图像处理的稻谷内部损伤定量表征与三维重构

在水稻脱粒、储运、加工过程中,外界机械作用力是造成稻谷损伤破损的主要方式,造成的内部裂纹肉眼无法观察但影响稻谷的存储、加工以及种子的发芽率等.该文利用质构仪对稻谷进行挤压力学特性试验,分析稻谷损伤破碎过程;对受不同载荷的稻谷进行CT扫描试验,结合数字图像处理方法对稻谷进行损伤表征分析与三维重构,旨在提出一种新的稻谷内部损伤定量评价方法.结果表明:伪彩色图像处理可以提高CT图像的视觉分辨率;灰度值以及灰度直方图分析可以识别稻谷的胚、胚乳以及裂纹大小,并定量分析;对分割后的二值图像进行像素点统计分析得到80,100,120,140,160N载荷下的损伤度分别为0,0.26%,0.39%,0.93%,1.79%;重构的三维模型可以看出裂纹一般沿着短轴方向扩展,随着载荷增大,原有裂纹逐渐变宽,并产生新的沿着长短轴的混合裂纹,直到糙米断裂.该研究可为谷物内部损伤定量表征分析提供新思路.     

玉米应力裂纹的生成和发展过程研究

观察了干燥、冷却和储存阶段玉米应力裂纹的生成和发展过程。结果显示，玉米应力裂纹生成在籽粒侧面的冠部，随时间的推移向脐部发展。单一裂纹的发展趋势是星状斑点－短裂纹－长裂纹。裂纹数量的发展趋势是单裂纹－双裂纹－龟裂纹。裂纹籽粒中，侧面有裂纹的占很大比例，正面和反面裂纹较少，出现正面及反面裂纹时裂纹已发展到龟裂阶段。总裂纹中大部分是冷后短暂的储存阶段生成和发展的裂纹     

稻米爆腰机理与碎米率

碾米过程中产生的碎米率与稻谷中的糙米的爆腰率有重要相关关系。米粒的主要成分是淀粉,淀粉以一定的晶体结构排列在米粒的胚乳细胞壁中,当淀粉在受热和受潮时,淀粉粒膨胀,使米粒产生热应力和水分应力差,当此拉应力大于米粒抗拉强度时,米粒内部就产生裂纹而形成爆腰米粒。稻谷在收获后期、收获后的干燥、贮藏中均会受到温度和水分变动而产生爆腰米粒,稻谷在加工过程中受到机械力的作用也会增加米粒的破碎。所以,降低碎米率应该从稻谷的收获后期就引起注意,防止温度和水分过大的波动,在稻谷加工中米粒应避免拉伸和弯曲的作用。     

基于瞬态流固耦合的混流式转轮叶片裂纹成因分析

某电站混流式水轮机转轮叶片历年出现不同程度的裂纹情况,为了分析该转轮叶片裂纹产生的原因,该文首先采用流体动力学技术,对该水轮机机组在额定水头下、不同负荷的4个工况进行了全三维的非定常湍流数值模拟,分析对比了各个工况下转轮内部流场的变化和压力脉动情况,计算结果表明:在低负荷情况下转轮内部出现叶道涡,叶道涡的存在使得转轮内部压力脉动变大,从而引起机组运行不稳定;其次采用结构有限元技术对转轮在上述4个工况下进行了动应力分析,模拟结果显示:应力最大发生在转轮上冠和叶片出口连接处,且在低负荷下动应力最大,最大值可达到164.3 MPa,长期在低负荷工况下运行容易引起叶片疲劳;最后对转轮单个叶片进行了模态分析,从模态分析结果可知叶片固有频率远离各个水力激振频率,因此不会发生水力共振。该文通过计算流体动力学(computational fluid dynamics)的方法全面分析了叶片产生裂纹的原因,并提出了相应的裂纹控制对策,为机组的稳定运行提供了参考。     

基于CT扫描与细观力学的植物侧根固土机理分析

为了探寻植物根系加固土体、防护边坡的作用机理,该文从细观角度对根系固土的力学特性进行了探讨,并利用长江科学院研制的CT三轴仪,分别对素土样和2种含根土样进行不固结不排水的CT实时三轴剪切试验。通过对试样3个断面在不同应变时刻所对应的CT扫描数据进行定量分析发现,3个扫描层中素土样的(CT数均值)ME-ε1关系曲线下降段和(CT数方差)SD-ε1关系曲线上升段的变化幅度均大于2种含根土样曲线相应阶段的变化幅度;这说明含根土体内部缺陷发育速度更慢,含根土样内部裂纹萌生和扩展得更加缓慢,根系具有阻裂作用。文中重点对3种土样在高度的7/16处的断面上的CT扫描图片进行了定性和定量分析。利用Matlab软件自编后处理程序,对CT扫描图片进行了二值化处理,并统计出断面上的裂隙率、根附近区域及其之外区域的总裂隙大小、最大裂隙区域的长度和宽度信息。通过对含根土样和素土样受压过程的CT演化图片和断面上统计的裂缝数据信息进行比较分析,来对比说明素土和含根土样中裂纹扩展以及试样破坏过程的差异,从而揭露了根系的阻裂作用和桥联作用。最后得出根系固土的细观力学机理主要表现为根系对土体的阻裂作用和桥联作用。     

敲击振动检测鸡蛋裂纹的初步研究

现代化的蛋品加工业中,传统的照蛋检测鸡蛋裂纹技术远不能满足生产的自动化要求,为了实现快速在线无损检测鸡蛋裂纹,试验通过在鸡蛋不同部位施加机械冲击,利用计算机处理产生的声音信号,分析壳裂鸡蛋和完好鸡蛋的响应频率差异。结果表明：敲击赤道不同的部位,完好鸡蛋各点的特征响应频率十分接近,而壳裂鸡蛋差别较大。根据赤道四点特征响应频率变异系数(CV),建立了初步分级算法,使得裂纹鸡蛋检出水平达到91%,对整批鸡蛋的分级准确率达到87%。     

A Rapid General Method for Appraising the Rheological Properties of the Starchy Endosperm of Cereal Grains

A rapid, simple method was developed to prepare small, parallelepipedal test samples of endosperm of wheat, corn, and rice grains. Compression tests performed on endosperm samples revealed the following mechanical properties: modulus of elasticity (E, GPa), breaking stress (σ_rup, MPa), and maximum breaking strain (∊_rup, %). All tests were performed on several endosperm test samples of each cereal species. The results displayed good repeatability and several significant differences in the mechanical behavior of different endosperm structures, especially among soft, hard, and durum wheats. Rice and corn endosperm displayed mechanical behavior similar to that of durum wheat endosperm. The method proposed appears to be sufficiently sensitive and repeatable for studying the incidence of hardness and vitreousness of cereal grain endosperm in relation to its suitability for milling.     

Effect of Broken Corn Levels on Water Absorption and Steepwater Characteristics

Broken corn created by grounding sound corn kernels was added back at levels of 0, 4, 8, 12, or 16%, by weight, to whole kernels of three corresponding hybrids: FR27 × FRMo17 (a soft endosperm corn), FR618 × FR600 (amedium‐hard endosperm corn), and FR618 × LH123 (a hard endosperm corn). The samples had been dried from 28% moisture content to 15% moisture content either by using ambient air at ≈25°C or at 110°C. Samples were steeped for 36 hr at 52°C in 0.15% sulfur dioxide and 0.5% lactic acid steeping solution. The steepwater characteristics, such as water absorption, solids and protein content in the steepwater, and steepwater pH, were measured by periodic sampling and analyzed. Broken corn level has a significant effect on the amount of solids released during steeping and steepwater protein content for all samples. Both steepwater solids and protein content increased linearly as broken corn content increased. Corn drying temperature, kernel hardness, and interactions between drying temperature and kernel hardness has a significant effect on steepwater solids and protein content and steepwater pH in both broken and unbroken corn. Corn dried at low temperature released more soluble solids and protein into the steepwater than corn dried at high temperature. Soft endosperm and medium‐hard endosperm corn released more soluble solids and protein into the steepwater than hard endosperm corn. Soft endosperm corn resulted in a higher steepwater pH than medium‐hard and hard endosperm corn. No significant effect of broken corn content on final moisture content of steeped corn and steepwater pH was observed.     

Effect of Stress Cracks on Corn Wet‐Milling Yields

U.S. No. 2 yellow dent corn was randomly probe‐sampled from rail cars being shipped to a wet‐milling plant from a Corn Belt local elevator. The probe samples were blended together and kernels were sorted into four levels of stress cracks (0, 1, 2, or multiple). Each level of stress cracking was then laboratory wet‐milled in triplicate. The only statistically observed differences were in total fiber and in protein content of the gluten meal fraction. The starch yield difference between zero stress cracked corn and multiple stress cracked corn was smaller (0.8%) than would be expected if stress cracking were an indicator of damage to the wet‐milling characteristics of the corn.     

Hydrolysis and Fermentation of Pericarp and Endosperm Fibers Recovered from Enzymatic Corn Dry‐Grind Process

A modified dry‐grind corn process has been developed that allows recovery of both pericarp and endosperm fibers as coproducts at the front end of the process before fermentation. The modified process is called enzymatic milling (E‐Mill) dry‐grind process. In a conventional dry‐grind corn process, only the starch component of the corn kernel is converted into ethanol. Additional ethanol can be produced from corn if the fiber component can also be converted into ethanol. In this study, pericarp and endosperm fibers recovered in the E‐Mill dry‐grind process were evaluated as a potential ethanol feedstock. Both fractions were tested for fermentability and potential ethanol yield. Total ethanol yield recovered from corn by fermenting starch, pericarp, and endosperm fibers was also determined. Results show that endosperm fiber produced 20.5% more ethanol than pericarp fiber on a g/100 g of fiber basis. Total ethanol yield obtained by fermenting starch and both fiber fractions was 0.370 L/kg compared with ethanol yield of 0.334 L/kg obtained by fermenting starch alone.     

Characterization of polymeric proteins from vitreous and floury sorghum endosperm

Differences in protein content and composition between vitreous and floury endosperm were investigated using a number of different techniques. Differences in protein cross-linking between vitreous and floury endosperm were investigated using differential solubility, size exclusion chromatography (SEC), and analysis of sulfhydryl content and composition. Vitreous endosperm was found to have higher levels of total protein and kafirins, but floury endosperm had a higher proportion of gamma-kafirins than the vitreous. Floury endosperm was found to have higher levels of SDS-soluble proteins than SDS-insoluble proteins extracted using sonication than vitreous endosperm. Conversely, vitreous endosperm had a greater proportion of the insoluble proteins. SEC analysis of the polymeric proteins revealed that the insoluble proteins had more polymeric proteins than did the soluble proteins, indicating greater cross-linking and a larger Mw distribution. Vitreous endosperm was also found to have a greater percentage (i.e., a higher ratio of disulfide to total sulfhydryls) of disulfide bonds than floury endosperm. These results show that the proteins in vitreous endosperm have a higher degree of cross-linking and a greater Mw distribution than those found in floury endosperm.     

双胚苗水稻种子的扫描电镜观察

以同源四倍体双胚苗水稻品系(D07-04-01)及其衍生后代(01-04-01,D07-02-01,DP07-04-01)为研究材料,利用扫描电镜技术和X射线衍射技术对稻米的垩白性状、淀粉粒的形态特征和淀粉的晶体特性进行了初步研究。研究结果表明,与其他材料相比,双胚苗二倍体品系D07-02-01的垩白粒率、垩白度和垩白大小均最小,稻米的自然横断面中部无明显辐射状,裂痕少且浅,"粗短形"的不规则多边形胚乳细胞与淀粉粒分布均匀,多面体状淀粉粒呈现典型的晶体结构,数目多且排列致密,球形单粒淀粉粒和块状不规则的复粒淀粉体数目比较少,相对结晶度高,直链淀粉含量低,即外观品质和食味品质均比其他四倍体品系好。