The controlled evolution of a polymer single crystal

We present a method for controlling the initiation and kinetics of polymer crystal growth using dip-pen nanolithography and an atomic force microscope tip coated with poly-dl-lysine hydrobromide. Triangular prisms of the polymer epitaxially grow on freshly cleaved mica substrates, and their in-plane and out-of-plane growth rates can be controlled by raster scanning the coated tip across the substrate. Atomic force microscope images were concomitantly recorded, providing a set of photographic images of the process as it spans the nanometer- to micrometer-length scales as a function of environmental conditions.     

输气管道裂纹动态扩展的数值模拟

作为输气管道止裂控制的重要依据,必须要求其裂纹驱动力小于管道材料的断裂韧性,在这种情况下进行裂纹动态扩展的数值模拟就显得非常重要.建立了输气管道裂纹动态扩展的有限元模型,用弹塑性、大位移四边形的壳体单元离散管道.裂纹尖端后面的气体压力简化为指数衰减模式.裂纹的开裂采用节点力释放方法来模拟,即根据裂纹扩展速度,依次解除裂纹尖端的节点连接.裂纹驱动力用能量释放率G和裂纹尖端张开角CTOA两个断裂力学参量表示.分析了裂纹驱动力随内压的变化规律.提出的计算模型可为输气管道的止裂设计提供分析工具.     

改性甘蔗膳食纤维对猪肉肌原纤维蛋白凝胶特性的影响

【目的】 探究肌原纤维蛋白凝胶网络结构—膳食纤维-肌原纤维蛋白的填充结构—复合凝胶断裂应力应变三者之间的相互关系,阐释改性甘蔗膳食纤维对肌原纤维蛋白凝胶特性的作用机制,为甘蔗膳食纤维作为脂肪替代物在低脂营养香肠中的应用提供理论依据。【方法】 本试验利用碱性过氧化氢法对甘蔗膳食纤维进行改善,以添加不同比例和粒径的膳食纤维——肌原纤维蛋白为模拟体系,其中未添加甘蔗膳食纤维的试验组为对照组;添加1.0%、2.0%和3.0%的50目甘蔗膳食纤维的试验组分别命名T150、T250和T350;添加1.0%、2.0%和3.0%的100目甘蔗膳食纤维的试验组分别命名T100、T200和T300。利用流变仪测定模拟体系的动态流变特性,利用质构仪测定复合蛋白的凝胶离心损失和断裂形变时应力应变,利用扫描电镜和图像分别分析肌原纤维蛋白凝胶网络微观结构及微观结构的分维维度和缺项值,通过石蜡切片观察膳食纤维在肌原纤维蛋白凝胶基质中的空间分布。【结果】 复合蛋白凝胶的离心损失随着膳食纤维添加比例和粒径增大而显著降低。复合蛋白凝胶的储能模量（G'）随着膳食纤维添加比例和粒径增大而显著提高。复合蛋白凝胶断裂形变时的应力应变结果显示,膳食纤维提高了复合凝胶断裂形变时的应力,而降低了应变。石蜡切片显示膳食纤维和肌原纤维蛋白属于热力不相溶体系,两者之间没有发生离子或共价交联,膳食纤维只是以简单的物理填充形式镶嵌在肌原纤维蛋白凝胶基质中,并形成大量大小和形状各异的空洞。扫描电镜显示未变性对照组的肌原纤维蛋白凝胶网络结构中布满了相互交错的水沟壑,这些沟壑的存在严重阻碍蛋白疏水基团之间的交联,进而导致肌原纤维蛋白凝胶网络结构比较疏松;膳食纤维能够减少蛋白三维网络结构中相互交错的水沟壑,肌原纤维蛋白凝胶网络结构更加致密均一。图像处理软件分析结果显示,添加3.0% 50目甘蔗膳食纤维的肌原纤维蛋白凝胶网络结构的分维维度（1.8670）最高（P<0.05）,而缺项值（0.19）最低（P<0.05）。【结论】 甘蔗膳食纤维-肌原纤维蛋白复合凝胶体系是以热诱导凝胶蛋白网络结构为骨架结构,以甘蔗膳食纤维作为填充相、蛋白基质为连续相形成的填充复合物。从骨架结构角度,甘蔗膳食纤维的物化特性显示其粒径大小与持水力成正比,添加3% 50目甘蔗膳食纤维能够完全消除蛋白基质中的水壑并促进蛋白交联从而形成致密的凝胶网络结构,具有最高断裂形变时的应力。从填充结构角度看,50目甘蔗膳食纤维的体积巨大,在蛋白基质中会形成体积较大的空穴,其非弹性属性导致复合蛋白凝胶断裂形变时的应变显著降低。因此,添加100目甘蔗膳食纤维作为脂肪替代物能够显著提高复合蛋白凝胶的断裂应力,同时极大限度的保持复合蛋白凝胶的弹性。     

Influence of solid friction on polymer relaxation in gel electrophoresis

Solid friction between a charged polymer and fixed gel points can dramatically affect polymer mobility in gel electrophoresis. The effect is present when a polymer chain is entangled over many gel points along a portion of its length, leading to significantly different behavior than predicted by conventional theory: the mobility of the chain decreases and exhibits a stronger length dependence, which separates long linear charged polymers of different molecular weights.     

木材年轮间细胞尺寸数学关系的建模理论

在总结国内外木材年轮细胞几何尺寸计算理论的基础上,研究木材年轮间相关参数与细胞断面形状数学关系的基础理论。通过细胞模型的几何尺寸定量计算细胞与年轮的相关参数,定性地解释木材生长变化的年轮间细胞变化的几何特征。由于绝大多数木材年轮的相关参数随细胞壁尺寸变化而改变,在微观观察年轮间的细胞几何尺寸变化可以定量地描述木材材性的变化。在宏观分析同一树种年轮的不同变化时,采用细胞尺寸差异比较,根据细胞模型形状计算出各树种和材种间尺寸和密度的不同,根据细胞密度显著的变化从微观解释木材强度的变化,将使我们从微观理论的高度来认识木材宏观性质的变化,为木材年轮细胞描述理论开创新的研究领域。     

多变量时序相空间重构中嵌入维和时间延迟的选择

提出了一种用于多变量时序相空间重构的嵌入维和时间延迟联合算法,它利用不同嵌入维和时间延迟重构相空间后所得的预测误差进行比较,最小的误差所对应的嵌入维和时间延迟作为最佳的嵌入维和时间延迟。仿真结果表明,该算法有效地克服了虚假邻点法和误差最小法中必须先选取时间延迟的缺点,大大提高了预测的精度。     

Single-molecule optomechanical cycle

Light-powered molecular machines are conjectured to be essential constituents of future nanoscale devices. As a model for such systems, we have synthesized a polymer of bistable photosensitive azobenzenes. Individual polymers were investigated by single-molecule force spectroscopy in combination with optical excitation in total internal reflection. We were able to optically lengthen and contract individual polymers by switching the azo groups between their trans and cis configurations. The polymer was found to contract against an external force acting along the polymer backbone, thus delivering mechanical work. As a proof of principle, the polymer was operated in a periodic mode, demonstrating for the first time optomechanical energy conversion in a single-molecule device.     

Delay time of hemoglobin S polymerization prevents most cells from sickling in vivo

A laser photolysis technique has been developed to assess the quantitative significance of the delay time of hemoglobin S gelation to the pathophysiology of sickle cell disease. Changes in the saturation of hemoglobin S with carbon monoxide produced by varying the intensity of a photolytic laser beam were used to simulate changes in the saturation of oxyhemoglobin S produced by variations in oxygen pressure. The presence of polymer at steady-state saturation with carbon monoxide was determined by measurement of the kinetics of gelation after complete photodissociation. The kinetics are a very sensitive probe for polymer since small amounts of polymerized hemoglobin increase the rate of nucleation sufficiently to eliminate the delay period. First, the equilibrium gelation properties of partially photodissociated carbonmonoxyhemoglobin S were shown to be the same as partially oxygenated hemoglobin S, and the method was then used to determine the effect of saturation on the formation and disappearance of polymers in individual sickle cells. The saturation at which polymers first formed upon deoxygenation was much lower than the saturation at which polymers disappeared upon reoxygenation. The results indicate that at venous saturations with oxygen, gelation takes place in most cells at equilibrium, but is prevented from occurring in vivo because the delay times are sufficiently long that most cells return to the lungs and are reoxygenated before polymerization has begun.     

长输管道的韧性设计

为保证长输管道系统的安全可靠，韧性设计是管道设计的重要指标，足够的韧性可以延缓或阻止断裂事件的进程。管道韧性设计基本出发点是安全性和经济性，综合平衡这两方面因素，并在断裂力学的基础上，提出了管道韧性设计的基本原则，即开裂控制原则，裂纹扩展的止裂原则和封口形原则。开裂控制原则提出了根据ＣＶ与钢管全壁厚临界缺陷尺寸的关系曲线，来确定相应管道对于开裂控制的韧性设计要求；裂纹扩展的止裂原则是根据Ｗ．Ａ．ｍ     

单链环状DNA添加剂抑制基因表达序列分析Ditag聚合酶链反应引物多聚体生成

[目的]研究利用单链环状DNA抑制聚合酶链反应（PCR）副产物的作用效果。[方法]设计并合成单链环状DNA,并以具同样序列发卡状结构的单链DNA为对照组,在基因表达序列分析（SAGE）Ditag PCR反应中加入上述不同浓度的DNA,利用电泳技术检测不同结构（环状/单链）以及不同浓度单链DNA对PCR多聚体附产物的抑制作用。[结果]发卡状结构的单链DNA无法抑制PCR引物多聚体副产物的产生;而在70～150 nmol/L终浓度范围内,单链环状DNA可以抑制SAGE Ditag PCR反应中引物多聚体的生成,并且不影响SAGE不同tag间的表达丰度差异。[结论]单链环状DNA可以作为PCR反应中引物多聚体生成的有效抑制剂。     

魔芋胶对猪肉肌原纤维蛋白凝胶特性和保水特性的调控机制:基于相分离行为和水相稳定

【目的】研究魔芋胶对猪肉肌原纤维蛋白微观结构和相分离结构的影响,进而阐释魔芋胶对肌原纤维蛋白凝胶特性和保水特性的调控机制,为魔芋胶在低脂香肠中的应用提供理论支撑。【方法】试验以添加不同比例魔芋胶-肌原纤维蛋白为模拟体系,测定模拟体系的质构和发生断裂形变时的应力应变、复合凝胶的水分分布和持水力,观察魔芋胶和肌原纤维蛋白的相分离行为以及肌原纤维蛋白凝胶网络的微观结构。【结果】当魔芋胶的添加比例<0.8%时,随着添加比例的提高,复合蛋白凝胶的凝胶强度、储能模量终值和发生断裂形变时的应力分别显著提高到179.21 g、1 192 Pa和9 139.37 Pa(P<0.05)。当魔芋胶添加比例≥0.8%时,随着添加比例的提高,复合蛋白凝胶的凝胶强度、储能模量、断裂形变时的应力和应变分别显著降至83.03 g、566 Pa、4 964.07 Pa和0.64(P<0.05)。低场核磁结果显示在魔芋胶添加比例<0.8%时,复合凝胶体系不易流动水的弛豫时间和自由水所占百分比随添加比例的提高显著降低（P<0.05）,而不易流动水所占百分比显著提高（P<0.05）,同时复...     

Atomic force microscopy of an organic monolayer

Atomic force microscope images of polymerized monolayers of n-(2-aminoethyl)-10,12-tricosadiynamide revealed parallel rows of molecules with a side-by-side spacing of approximately equal to 0.5 nanometer. Forces used for imaging (10(-8) newton) had no observable effect on the polymer strands. These results demonstrate that atomic force microscope images can be obtained for an organic system.     

农资产品品牌连动力——概念与量表开发初探

基于文献研究和当前农资购销中出现的特定现象提出了农资产品品牌连动力概念,并从农户角度出发,初步构建了农资品牌连动力测量量表,对农资品牌连动力测量维度及各维度所代表的力的大小进行实证分析.结果表明,农资产品品牌连动力可以分为引荐力、店铺信誉力、其他产品信誉力和行动力4个方面,4种力量的大小顺序依次为行动力、店铺信誉力、其他产品信誉力、引荐力.经检验,构建的量表具有较高的信度和效度,对相关研究有一定的借鉴意义,为品牌关系及农资产品品牌研究提供了一个新的研究工具.     

KGM/XG复合凝胶的制备及性能研究

[目的]确定KGM／XG复合凝胶的最佳合成条件。[方法]以魔芋葡甘聚糖（KGM）和黄原胶（XG）为主要原料合成了生物可降解复合凝胶KGM／XG,探讨了KGM和XG的共混比例及反应温度对凝胶平衡溶胀比和凝胶强度的影响。[结果]KGM／XG复合凝胶的溶胀比在溶胀初期增加很快,随着溶胀时间的延长,溶胀比增加变慢,最后达到平衡;凝胶的平衡溶胀比随着反应温度的升高逐渐增加,而KGM含量对凝胶平衡溶胀比影响不大;凝胶强度随XG含量的增加和反应温度的升高逐渐增加,当XG含量为70％、反应温度为75℃时,凝胶强度最大。[结论]KGM／XG复合凝胶的最佳合成温度为75℃,XG的适宜含量为70％。     

甲基丙烯酰氧乙基三甲基氯化铵/丙烯酰胺共聚物溶液性质研究

利用甲基丙烯酰氧乙基三甲基氯化铵(DMC)和丙烯酰胺(AM)合成了阳离子聚合物P(DMCAM), IR和1H NMR谱图证实了提纯产物为DMC和AM的共聚物.通过粘度法对聚合物溶液的基本性质进行研究,得出以下结论:聚合物溶液的特性粘数随聚合物浓度增加先降低后增加,提出了外加盐对聚合物溶液粘度产生影响的模型;比浓粘度随盐中阳离子半径的增加而减小,而随阴离子半径的增大而增大;所合成的聚合物在酸中较稳定,在碱中很容易降解;DMC单体的加入大大提高了聚合物的耐温性能;该聚合物的pH值在4～9范围内对膨润土模拟污水有很好的絮凝能力,并能满足目前油田中碳酸盐岩中高温油水井酸化缓速的要求.     

管线钢应力诱导型氢致开裂分形试验

以酸性气田集输管网中16MnR 和20 号钢为研究对象,开展应力诱导型氢致开裂分形试验,以验证相关理论模型的正确性。试验制备了两种管线钢的双悬臂梁试件,并将其浸入不同H2S 体积摩尔浓度的腐蚀溶液环境中,通过断口数据取样分析及计算,验证了管线钢氢致开裂的断口形貌具有分形特征,以及应力强度因子与分形维数具有对数正比趋势的关系,同时验证了氢致开裂判据模型、氢致开裂分形扩展速率模型、氢致开裂分形物理机制模型的正确性,可为在役管道氢环境下的裂纹扩展速率的预测提供参考依据。     

Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy

Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Dextran filaments linked to a gold surface were probed with the atomic force microscope tip by vertical stretching. At low forces the deformation of dextran was found to be dominated by entropic forces and can be described by the Langevin function with a 6 angstrom Kuhn length. At elevated forces the strand elongation was governed by a twist of bond angles. At higher forces the dextran filaments underwent a distinct conformational change. The polymer stiffened and the segment elasticity was dominated by the bending of bond angles. The conformational change was found to be reversible and was corroborated by molecular dynamics calculations.     

Designing responsive buckled surfaces by halftone gel lithography

Self-actuating materials capable of transforming between three-dimensional shapes have applications in areas as diverse as biomedicine, robotics, and tunable micro-optics. We introduce a method of photopatterning polymer films that yields temperature-responsive gel sheets that can transform between a flat state and a prescribed three-dimensional shape. Our approach is based on poly(N-isopropylacrylamide) copolymers containing pendent benzophenone units that allow cross-linking to be tuned by irradiation dose. We describe a simple method of halftone gel lithography using only two photomasks, wherein highly cross-linked dots embedded in a lightly cross-linked matrix provide access to nearly continuous, and fully two-dimensional, patterns of swelling. This method is used to fabricate surfaces with constant Gaussian curvature (spherical caps, saddles, and cones) or zero mean curvature (Enneper's surfaces), as well as more complex and nearly closed shapes.     

梨果肉质地性状分析

【目的】比较不同梨品种的果肉质地特性,探讨反映梨果实质地状况的评价参数,为研究梨的内在品质提供依据。【方法】应用质构仪质地多面分析法（TPA：质地参数包括脆度、硬度、弹性、回复性、凝聚性、咀嚼性）和穿刺试验（Puncture test：质地参数包括破裂力、破裂位移、破裂能、屈服力、屈服位移和屈服能）对成熟期采收的14个梨品种的果实果肉质地进行测定,通过多元分析得出质地参数之间的关系。【结果】基于TPA和穿刺试验的分析结果表明,不同梨品种之间果肉质地之间有一定的差异。与‘鸭梨’、‘丰水’、‘美人酥’等相比,‘粉酪’、‘晚秀’、‘南水’等品种具有较高的果肉硬度、脆度和咀嚼性;与‘鸭梨’、‘丰水’、‘黄金’等相比,‘粉酪’、‘晚秀’、‘满天红’等品种具有较高的破裂力、破裂能、屈服力和屈服能。相对来说,不同品种之间的果肉破裂位移和屈服位移的差别较小。相关分析表明,除弹性、屈服位移和破裂位移外,梨果肉质地参数中脆度、硬度、回复性、凝聚性、咀嚼性、屈服力、屈服能、破裂力、破裂能之间相关性显著,大多呈正相关关系;聚类分析将14个品种分为松软（如‘丰水’、‘黄金’、‘黄冠’等）、硬脆（如‘晚秀’）、坚硬（如‘粉酪’）等3种不同的果肉质地类型;主成分分析表明,前3个主成分对梨果肉质地的贡献率达到92.196%,第1主成分反映了果肉的咀嚼特性;第2主成分反映了果肉的弹性和屈服性;第3主成分反映了果肉的破裂特性;并且,在梨果肉质地中,果肉硬度、破裂力、脆度等对质地的影响较大,弹性和破裂位移次之。【结论】不同梨品种之间的果肉质地存在差异;梨果肉大多数的TPA参数与穿刺试验参数呈显著正相关;果肉硬度、破裂力、脆度是影响梨果肉质地的重要参数。     

热磨法木片断裂力学模型及磨片参量的影响因素1）

将热磨机磨片把木片原料研磨为纤维的过程转化为木片断裂的形式,运用断裂力学理论对其研究。当磨片研磨木片时,木片的破坏简化为Ⅱ－Ⅲ复合型（滑开型＋撕开型）裂纹的扩展问题,建立木片断裂过程的力平衡方程,研究木片断裂力学模型,分析纤维研磨过程中磨片施力方式与木片原料研磨之间的关系;运用含斜裂缝有限板裂缝尖端的应力强度因子计算公式,推导热磨法木片断裂的断裂判据,并对磨片参量影响的因素进行分析,为磨片的设计提供理论依据。