共查询到20条相似文献，搜索用时 421 毫秒
1.
Verhage M Maia AS Plomp JJ Brussaard AB Heeroma JH Vermeer H Toonen RF Hammer RE van den Berg TK Missler M Geuze HJ Südhof TC 《Science (New York, N.Y.)》2000,287(5454):864-869
Brain function requires precisely orchestrated connectivity between neurons. Establishment of these connections is believed to require signals secreted from outgrowing axons, followed by synapse formation between selected neurons. Deletion of a single protein, Munc18-1, in mice leads to a complete loss of neurotransmitter secretion from synaptic vesicles throughout development. However, this does not prevent normal brain assembly, including formation of layered structures, fiber pathways, and morphologically defined synapses. After assembly is completed, neurons undergo apoptosis, leading to widespread neurodegeneration. Thus, synaptic connectivity does not depend on neurotransmitter secretion, but its maintenance does. Neurotransmitter secretion probably functions to validate already established synaptic connections. 相似文献
2.
【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。 相似文献
3.
本研究针对含分布式电源的配电网故障恢复提出一种将孤岛划分作为网络重构子优化模块的方案。在重构过程中根据DG的类型和与主网的连通状态,将不能并网的分布式电源进行孤岛划分,最大程度恢复失电负荷,并用二进制粒子群算法和遗传算法的混合算法寻找最优恢复路径。算例结果证明了该策略的优越性。 相似文献
4.
对白色棉、棕色棉和绿色棉纤维进行了电镜观察,结果表明:3种颜色纤维的结构由外到内依次为初生壁、次生壁和中腔.在白色纤维的超微结构中未发现染色较深的物质; 在绿色棉纤维中,纤维的次生壁内层存在大量染色深的条纹,这些条纹可能是色素沉积的结果,类似沉积的日轮;在棕色棉纤维的中腔内,存在大量染色深的物质,而且这些物质主要沉积在中腔壁上,这些染色较深的物质可能是棕色棉纤维的色素物质,同时发现棕色棉纤维具有分叉结构. 与白色纤维比较,彩色纤维表现出的品质较差,可能与纤维素含量低及色素物质的沉积有关. 相似文献
5.
A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar (0110) surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in electromechanically coupled sensors, transducers, and resonators. 相似文献
6.
Scanning tunneling microscopy of nucleic acids 总被引：1，自引：0，他引：1
The scanning tunneling microscope (STM) has been used to measure properties of poly(rA).poly(rU) and DNA, such as helical pitch, half-period oscillations that were interpreted as the alternation between the major and minor grooves, and interhelical spacing. Average pitches were measured by two-dimensional Fourier transforms and by topographic profiles along the fiber axes. Values were typically 7 percent less than standard dimensions of A-form RNA and B-form DNA fibers. This result is compatible with the mild dehydration that occurred under air-drying conditions. More extensive dehydration typically led to 19 percent shrinkage. Analysis of specific regions allowed local variations in helical pitch as small as 1 angstrom to be detected, thus demonstrating that the STM can visualize functionally significant modulations of nucleic acid structure. 相似文献
7.
In search of the first flower: A jurassic angiosperm, archaefructus, from northeast china 总被引：1，自引：0，他引：1
Angiosperm fruiting axes were discovered from the Upper Jurassic of China. Angiosperms are defined by carpels enclosing ovules, a character demonstrated in this fossil. This feature is lacking in other fossils reported to be earliest angiosperms. The fruits are small follicles formed from conduplicate carpels helically arranged. Adaxial elongate stigmatic crests are conspicuous on each carpel. The basal one-third of the axes bore deciduous organs of uncertain affinities. No scars of subtending floral organs are present to define the individual fertile parts as floral units, but the leaf-like structures subtending each axis define them as flowers. These fruiting axes have primitive characters and characters not considered primitive. 相似文献
8.
Host-gut microbiota metabolic interactions 总被引：1，自引：0，他引：1
Nicholson JK Holmes E Kinross J Burcelin R Gibson G Jia W Pettersson S 《Science (New York, N.Y.)》2012,336(6086):1262-1267
The composition and activity of the gut microbiota codevelop with the host from birth and is subject to a complex interplay that depends on the host genome, nutrition, and life-style. The gut microbiota is involved in the regulation of multiple host metabolic pathways, giving rise to interactive host-microbiota metabolic, signaling, and immune-inflammatory axes that physiologically connect the gut, liver, muscle, and brain. A deeper understanding of these axes is a prerequisite for optimizing therapeutic strategies to manipulate the gut microbiota to combat disease and improve health. 相似文献
9.
利用新旧图书馆大楼布线系统的比较,并具体对我馆综合布线系统的分析,得出图书馆大楼应采用综合布线系统的发展方向。 相似文献
10.
为阐明羊驼绒毛生长发育提供组织学基础,同时也为毛用动物的遗传改良提供重要的理论依据,通过制作霍奎耶羊驼皮肤组织切片,在显微镜下观察其毛囊兴盛期结构,结果表明霍奎耶羊驼的毛囊结构同其他动物一样,由毛球、连接组织鞘、内根鞘、外根鞘和毛干几部分组成.兴盛期毛囊直径从上到下逐渐增大,末端膨大为毛球,呈一漏斗状,毛球内陷深入形成毛乳头.毛囊群中毛囊的数量较多,且由少量的结缔组织分为两小群. 相似文献
11.
本实验用形态学方法研究6例小型猪脑硬膜外异网的形态构造，并追踪了进入和传出硬膜外异网的血管。小型猪硬膜外异网发达，分前异网和后异网。前异网位于海绵窦内，包括颅内部和颅外部，由颈内动脉和脑膜中动脉、眼外动脉、上颌动脉的异网支共同形成，在异网的前内侧部这些吻合支又聚集形成颈内动脉颅内段自海绵窦传出，并参与组成大脑动脉环。后异网由髁动脉、枕动脉和椎动脉共同形成，通过基底动脉与大脑动脉环连接，但与同侧前异网未见直接联系。异网的血管支都是具有内、外两弹性层的肌型中小动脉。异网血管支的外层是海绵窦的内膜层。 相似文献
12.
Janes KA Albeck JG Gaudet S Sorger PK Lauffenburger DA Yaffe MB 《Science (New York, N.Y.)》2005,310(5754):1646-1653
Signal transduction pathways control cellular responses to stimuli, but it is unclear how molecular information is processed as a network. We constructed a systems model of 7980 intracellular signaling events that directly links measurements to 1440 response outputs associated with apoptosis. The model accurately predicted multiple time-dependent apoptotic responses induced by a combination of the death-inducing cytokine tumor necrosis factor with the prosurvival factors epidermal growth factor and insulin. By capturing the role of unsuspected autocrine circuits activated by transforming growth factor-alpha and interleukin-1alpha, the model revealed new molecular mechanisms connecting signaling to apoptosis. The model derived two groupings of intracellular signals that constitute fundamental dimensions (molecular "basis axes") within the apoptotic signaling network. Projection along these axes captures the entire measured apoptotic network, suggesting that cell survival is determined by signaling through this canonical basis set. 相似文献
13.
低掺量油菜秸秆纤维混凝土力学性能试验研究 总被引：1，自引：1，他引：0
为了探索秸秆纤维对混凝土力学性能的影响机理,研究了在水灰比为0.50、强度等级为C35条件下,不同油菜秸秆纤维长度和油菜秸秆体积掺量的混凝土力学性能。通过测试混凝土的抗压、劈裂抗拉、抗折强度,分析油菜秸秆纤维对混凝土力学性能的影响规律,并使用扫描电镜验证分析结果。结果表明:混凝土的抗压、劈裂抗拉、抗折强度随着油菜秸秆纤维长度的增加和掺量的提高均呈现先增大后减小的趋势;当纤维长度30～40 mm,体积掺量0.1%时,抗压强度为47.43 MPa,比对照组提高16.45%,当纤维长度20～30 mm,体积掺量0.2%时,混凝土的劈裂抗拉和抗折强度为3.71 MPa、9.1 MPa,比对照组提高9.12%、6.64%,扫描电镜对比观察0.2%和0.4%纤维体积掺量的混凝土内部结构,证实0.2%掺量混凝土的纤维-混凝土交界面无大面积孔隙,纤维上水泥浆体均匀分布,与混凝土间形成良好的吸附黏结力与机械啮合力,混凝土内部纤维填充了有害孔隙,无纤维结团现象,减少了应力集中,增强了混凝土的力学性能。 相似文献
14.
Meltability is one of the most important properties of Mozzarella cheese, as it is generally used in pizza and other foods. Mozzarella was prepared by no salted and immature production technology, and the effect of different addition amounts of salt on the meltability of mozzarella cheese was measured by Schreiber method and small amplitude oscillatory shear analysis（SAOSA） method. The results showed that different adding amounts of NaCl had significant influence on the meltability of Mozzarella cheese, and 2% NaCl addition was the best condition. The results measured by the methods of Schreiber and SAOSA were basically same： adding different amounts of NaCl had significant influence on the hardness and elasticity of mozzarella cheese, but no significant influence on the sticky. It was a good microscopic structure arrangement of Mozzarella cheese with 2% NaCl addition. Scanning electron micrographs showed that a space grid structure formed by casein had changed, and formed many uniform molecular holes. The results indicated that different addition amounts of salt had influence on meltability of no salted immature Mozzarella cheese, and this technology could be drastically shorten the processing time. 相似文献
15.
[目的]应用组织切片方法来研究褶皱臂尾轮虫消化系统的组织结构特点。[方法]运用连续石蜡切片及HE染色技术,用光学显微镜对褶皱臂尾轮虫（Brachionus plicatilis）消化系统组织结构进行研究。[结果]褶皱臂尾轮虫消化管管壁结构比较简单。没有结缔组织纤维膜或浆膜,上皮的游离端往往着生有长而密集的纤毛。除了在口沟部位有类似于骨骼肌的肌肉分布以外,其他各段都没有肌肉层,只有一层上皮细胞。[结论]石蜡切片技术可作为判断轮虫生理生长状态的一种有效方法。 相似文献
16.
为研究新型RC网格式框架结构承载力、滞回曲线、骨架曲线、延性、刚度和耗能能力等受力性能，进行了3榀1/5缩尺墙体模型在低周反复水平荷载作用下的试验.试验结果表明：新型RC网格式框架结构表现出框架结构的受力特性，试件各层均出现反弯点，为剪切型破坏；滞回曲线饱满，有较强的耗能能力；延性比常规框架好；试件屈服后，刚度退化较快，临近破坏时，刚度退化缓慢.考虑材料、几何和接触非线性，运用有限元软件ANSYS对相同条件下填充磷石膏的网格式框架结构墙体进行计算，有限元计算屈服时墙体顶点最大水平位移比试验大约5.8%，与试验结果吻合较好.新型RC网格式框架结构是介于框架结构和密肋网格式剪力墙结构受力性能之间的一种结构形式，适用于建造高层住宅及办公建筑等. 相似文献
17.
18.
Promoting functional plasticity in the damaged nervous system 总被引：3，自引：0，他引：3
Damage to the central and peripheral nervous system often produces lasting functional deficits. A major focus of neuroscience research has been to enhance functional restitution of the damaged nervous system and thereby produce recovery of behavioral or physiological processes. Promising procedures include surgical, physical, and chemical manipulations to reduce scar formation and minimize the disruption of support elements, administration of growth-stimulating substances, tissue grafts to bridge gaps in fiber pathways, and embryonic brain tissue grafts to provide new cells with the potential to generate fiber systems. Two elements are required for functional nervous system repair: (i) neurons with the capacity to extend processes must be present, and (ii) the regenerating neurites must find a continuous, unbroken pathway to appropriate targets through a supportive milieu. 相似文献
19.
通过对流脂材解剖性质研究发现,雪压杉木林分树干大量流脂与形成层受压产生应激性反应及形成异常结构有关.杉木树干韧皮纤维分布密度自外向内逐渐增大,雪压后形成的韧皮部环绕形成层呈若干个同心圆,木质部射线在形成层处发生转折,导致输导组织产生瓶颈效应,刺激了非正常组织即韧皮部创伤树脂道的形成;木质部管胞内壁产生皱缩现象;轴向薄壁... 相似文献
20.
Paus T Zijdenbos A Worsley K Collins DL Blumenthal J Giedd JN Rapoport JL Evans AC 《Science (New York, N.Y.)》1999,283(5409):1908-1911
Structural maturation of fiber tracts in the human brain, including an increase in the diameter and myelination of axons, may play a role in cognitive development during childhood and adolescence. A computational analysis of structural magnetic resonance images obtained in 111 children and adolescents revealed age-related increases in white matter density in fiber tracts constituting putative corticospinal and frontotemporal pathways. The maturation of the corticospinal tract was bilateral, whereas that of the frontotemporal pathway was found predominantly in the left (speech-dominant) hemisphere. These findings provide evidence for a gradual maturation, during late childhood and adolescence, of fiber pathways presumably supporting motor and speech functions. 相似文献