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1.
微米木纤维定向重组细胞纤维含量的定量求解理论研究   总被引:25,自引:0,他引:25  
马岩 《生物数学学报》2002,17(3):353-357
本文采用人造板微观力学和木材细胞学理论,提出了一种利用木纤维细胞壁厚的数学求解方法,应用本文提出的理论,可以根据纤维、木质素、细胞直径和排列的程度,建立理想状态下微纤丝的含量和分布情况,为人造板力学运用数学手段深入到细胞结构研究的深度提供了一种新的理论和方法,并且可以为定量解释人造板力学规则细胞出现不同剖分方法后,材性与性能提高的理论原因提供定量解释的数学手段。  相似文献   

2.
原木形状分段描述方法的数学描述理论研究   总被引:4,自引:0,他引:4  
马岩 《生物数学学报》2006,21(3):435-440
为制材、木材检尺等特殊行业需要的原木数控检测提供数学描述理论,提出的这些理论将为数控检测的数学模型建立提供具体的数学方法,为原木形状的视频再现提供编程的数学工具.本文提出的理论还将为数控下锯法提供理论依据,与制材工艺结合起来,将使传统原木检测数字化,为科学管理原木和数字化统计与检尺控制提供了理论,本文是木材工业中用数学描述检测过程的开始.通过本文的研究,可以推进木材工业检测过程数学描述研究的开展.  相似文献   

3.
马岩 《生物数学学报》2003,18(4):473-476
为船舶、乐器等特殊行业需要的弦切板数控加工提供数学描述理论,提出的这些理论将为数控加工的数学模型建立提供基础理论,为板材纹理的视频再现提供数学方法.本文提出的理论还将为三角形下锯法提供理论依据,与制材工艺结合起来,将使传统加工工艺数学化,为科学管理和数字化控制提供了理论.本文是木材工业中用数学描述加工过程的开始,可以推进木材工业加工过程数学描述研究的开展.  相似文献   

4.
本文为制材、剩余物利用等行业需要的板皮数控加工提供数学描述理论,提出的这些理论将为板皮裁边的数控加工数学模型建立提供编程的数学方程,为板材最优下锯的视频再现提供数学方法.本文提出的理论还将为锯切、板皮材积精确检测提供理论依据,与制材工艺结合起来,将使传统加工工艺数学化,为科学管理和数字化控制提供了理论.本文是木材工业中用板皮数学描述加工过程的开始.通过本文的研究,可以推进木材工业加工过程数学描述研究的开展.  相似文献   

5.
马岩 《生物数学学报》2005,20(2):245-250
为家具、乐器、考古鉴定等特殊行业需要对木材的材种和板材的下锯位置及板材进行识别提供数学方法,利用一般喷漆成品木材端面纹理往往可以显现的特点识别木材年轮宽度、锯材在原木中的下锯位置、原木椭圆度等参数.提出这些数学理论将为木材几何参数识别的数学模型建立提供工具,还将为珍贵树种木材识别提供理论依据,为古代家具品质鉴别提供科学的方法,这些理论将使传统人工识别工艺数学化,实现科学考古和鉴定数字化。  相似文献   

6.
根据木材的细胞结构,应用类比推理方法,推导木材的径向导热系数的数学表达式,从中得出木材径向导热系数仅是木材孔隙率函数的结论.孔隙率越大,导热系数越小,并应用该表达式计算20种木材的径向导热系数,理论值的最大误差不超过14%,平均误差在5%以内。  相似文献   

7.
应用碱性成纤维细胞生长因子(FGF-2)体外诱导P19细胞向心肌细胞分化,摸索适宜P19细胞向心肌细胞分化条件。将P19细胞接种于铺有0.5%软琼脂的培养皿中,用含FGF-2的分化培养基培养P19细胞,24h后即可见多个悬浮的细胞团形成,大部分形状较规则,直径随时间延长不断增大,至第4天形成细胞聚集体/EBs,形状规则、体积较大,少量EB呈囊性,隐约可见内细胞团样结构。  相似文献   

8.
FDA-PI双色荧光分光光度法检测细胞活性变化   总被引:7,自引:0,他引:7  
本文建立了FDA-PI双色荧光分光光度法来推测细胞活性的变化,通过图谱初步地观察,进一步测定荧光测值,可以定性和定量地进行分析,此方法简便易行,直观,为测量细胞活性的变化提供一种良好的新方法。  相似文献   

9.
本文评述了理论生物学的两个基础实验。一是用离子束辐照加速大肠杆菌进化的方法研究原核基因组的进化方向,证明进化中的缺失偏好性和编码信息量扩增律不矛盾。二是提出用导热法测量细胞的熵产生,比较研究了癌细胞和正常细胞的熵产生和外加电场的关系,证明在一定强度的电场作用下正常细胞的熵产生可以明显超过癌细胞,从而实现改变两类细胞间熵流方向的目的。  相似文献   

10.
T细胞和APC细胞相互作用形成免疫突触涉及到连续发生的一系列的分子识别事件,最初APC细胞在趋化因子的作用下向T细胞移动,相遇后在抗原非依赖性的弱的黏附力作用下发生最初的黏附,同时伴随着TCR在APC表面俘获特异性抗原;抗原识别之后,由多种机制使T细胞和APC紧密接触并维持一段时间,随后分开,最终引起T细胞的增殖和分化。对免疫突触形成过程中的分子识别机制目前尚无定论,拓扑模式和数学模式的解释,脂筏和细胞骨架蛋白的重排以及接头蛋白的连接为免疫突触形成中分子的识别提供了一定的依据。  相似文献   

11.
Force field-based simulations have been employed to model the mechanical properties of a range of undeformed molecular polymeric honeycombs having conventional and re-entrant hexagon pores. The conventional and re-entrant hexagon honeycombs are predicted to display positive and negative in-plane Poisson's ratios, respectively, confirming previous simulations. The structure, and mechanical and mass transport properties of a layered re-entrant honeycomb ((2,8)-reflexyne) were studied in detail for a uniaxial load applied along the x 2 direction. The mechanical properties are predicted to be stress- (strain-) dependent and the trends can be interpreted using analytical expressions from honeycomb theory. Transformation from negative to positive Poisson's ratio behaviour is predicted at an applied stress of σ2 = 2 GPa. Simulations of the loading of C60 and C70 guest molecules into the deformed layered (2,8)-reflexyne host framework demonstrate the potential for tunable size selectivity within the host framework. The entrapment and release of guest molecules is attributed to changes in the size and shape of the pores in this host–guest system.  相似文献   

12.
Recent work has indicated that the shape and size of a cell can influence how a cell spreads, develops focal adhesions, and exerts forces on the substrate. However, it is unclear how cell shape regulates these events. Here we present a computational model that uses cell shape to predict the magnitude and direction of forces generated by cells. The predicted results are compared to experimentally measured traction forces, and show that the model can predict traction force direction, relative magnitude, and force distribution within the cell using only cell shape as an input. Analysis of the model shows that the magnitude and direction of the traction force at a given point is proportional to the first moment of area about that point in the cell, suggesting that contractile forces within the cell act on the entire cytoskeletal network as a single cohesive unit. Through this model, we demonstrate that intrinsic properties of cell shape can facilitate changes in traction force patterns, independently of heterogeneous mechanical properties or signaling events within the cell.  相似文献   

13.
Summary A chromaticity diagram which plots the 3 photoreceptor excitations of trichromatic colour vision systems at an angle of 120° is presented. It takes into acount the nonlinear transduction process in the receptors. The resulting diagram has the outline of an equilateral hexagon. It is demonstrated by geometrical means that excitation values for any type of spectrally opponent mechanism can be read from this diagram if the weighting factors of this mechanism add up to zero. Thus, it may also be regarded as a general representation of colour opponent relations, linking graphically the Young-Helmholtz theory of trichromacy and Hering's concept of opponent colours. It is shown on a geometrical. basis that chromaticity can be coded unequivocally by any two combined spectrally opponent mechanisms, the main difference between particular mechanisms being the extension and compression of certain spectral areas. This type of graphical representation can qualitatively explain the Bezold-Brücke phenomenon. Furthermore, colour hexagon distances may be taken as standardized perceptual colour distance values for trichromatic insects, as is demonstrated by comparison with behavioural colour discrimination data of 3 hymenopteran species.  相似文献   

14.
毛乌素沙地农牧生态系统能值分析与耦合关系   总被引:1,自引:0,他引:1  
胡兵辉  廖允成 《生态学报》2011,31(9):2559-2566
针对毛乌素沙地脆弱农业生态系统生产力实际,根据复合生态系统耦合理论,借助能值理论及分析方法,选择毛乌素沙地偏农区的榆阳区和偏牧区的乌审旗为比较研究对象,对两地近27a的农牧耦合系统初级生产力、次级生产力及系统耦合状况进行了对比分析,探讨性提出了区域农牧系统耦合程度的演变规律。结果表明,榆阳区是偏农型的农牧耦合产业发展模式,乌审旗是偏牧型的牧农耦合产业发展模式;榆阳区有以耗粮型生猪、禽类生产为主的势头,乌审旗有以节粮型草食动物生产为主的势头;榆阳区和乌审旗的初级生产力、次级生产力及A(有效能值利用率)、B(单位低质能产品转化成高质能产品率)、SCD(系统耦合度)值均沿时间序列增大,且SCD值有呈三阶段型增长的规律性。依据研究结果,最后提出了毛乌素沙地农牧生态系统耦合发展的途径,以期能为沙地农牧生态系统稳健发展提供可靠的理论支撑与政策导向。  相似文献   

15.
The motility of some kinds of bacteria depends on their spiral form, as does the virulence of certain pathogenic species. We propose a novel mechanism for the development of spiral shape in bacteria and the supercoiling of chains ('filaments') of many cells. Recently discovered actin-like proteins lying just under the cell wall form fibers that play a role in maintaining cell shape. Some species have a single actin-like fiber helically wrapped around the cell, while others have two fibers wrapped in the same direction. Here, we show that if these fibers elongate more slowly than growth lengthens the cell, the cell both twists and bends, taking on a spiral shape. We tested this mechanism using a mathematical model of expanding fiber-wound structures and via experiments that measure the shape changes of elongating physical models. Comparison of the model with in vivo experiments on stationary phase Caulobacter crescentus filaments provide the first evidence that mechanical stretching of cytoskeletal fibers influences cell morphology. Any hydraulic cylinder can spiral by this mechanism if it is reinforced by stretch-resistant fibers wrapped helically in the same direction, or shortened by contractile elements. This might be useful in the design of man-made actuators.  相似文献   

16.
湿地公园研究体系构建   总被引:10,自引:1,他引:9       下载免费PDF全文
王立龙  陆林 《生态学报》2011,31(17):5081-5095
湿地公园是湿地保护性利用新方式,也是生态旅游和生态文明建设新载体,目前国内外兴起湿地公园建设热潮,为湿地保护性利用带来了新机遇。但作为新兴研究领域,目前湿地公园专题研究滞后于其建设与发展,研究基础理论薄弱、研究内容系统性不强、研究方法简单、研究体系不完整,对公园建设的实践指导不足。构建湿地公园研究体系具有重大的理论意义和实践价值。 在对国内外研究总结分析的基础上,力图从研究理论体系、研究内容指标体系和研究方法体系等层面对湿地公园研究体系进行初步构建。提出湿地公园生态系统的概念,并将其组成结构研究体系、功能研究体系、影响评价体系和管理体系等作为研究内容的指标体系;对现有研究方法述评分析,构建了以基础理论探讨、规划研究、试验研究和空间分析为主的研究方法体系;指出了未来应注重的研究方法及发展趋势;最后结合部分实证研究对体系进行了充实完善。以望为推动湿地公园专题研究进程做出贡献,为湿地公园科学管理提供参考。  相似文献   

17.

Recent research has shown that motile cells can adapt their mode of propulsion to the mechanical properties of the environment in which they find themselves—crawling in some environments while swimming in others. The latter can involve movement by blebbing or other cyclic shape changes, and both highly-simplified and more realistic models of these modes have been studied previously. Herein we study swimming that is driven by membrane tension gradients that arise from flows in the actin cortex underlying the membrane, and does not involve imposed cyclic shape changes. Such gradients can lead to a number of different characteristic cell shapes, and our first objective is to understand how different distributions of membrane tension influence the shape of cells in an inviscid quiescent fluid. We then analyze the effects of spatial variation in other membrane properties, and how they interact with tension gradients to determine the shape. We also study the effect of fluid–cell interactions and show how tension leads to cell movement, how the balance between tension gradients and a variable bending modulus determine the shape and direction of movement, and how the efficiency of movement depends on the properties of the fluid and the distribution of tension and bending modulus in the membrane.

  相似文献   

18.
Eukariotic cell motility is a complex phenomenon, in which the cytoskeleton and its major constituent, actin, play an essential role. Actin forms polymers of long, stiff filaments that are cross-linked into an anisotropic network inside a thin sheet-like cellular protrusion, the lamellipod. At the leading edge of this structure, polymerization of actin filaments creates the force that pushes out the membrane and leads to translocation of a motile cell. Dynamics of the actin network account for changes in cell shape, crawling motion and turning of the cell in response to external cues. Regulating the dynamics of the cytoskeleton, and playing a central role in signal transduction in the cell, are Cdc42, Rac and Rho (GTPases of the rho family, collectively known as the small G-proteins) and the actin nucleating complex, Arp2/3.In this paper, we use a multiscale modelling approach in a 2D model of a motile cell. We describe the mutual interactions of the small G-proteins, and their effects on capping and side-branching of actin filaments. We incorporate the pushing exerted by oriented actin filament ends on the cell edge, and a Rho-dependent contraction force. Combining these biochemical and mechanical aspects, we investigate the dynamics of a model epidermal fish keratocyte through in silico experiments. Our model gives insight into how, in response to some cue, a cell can polarize, form a leading edge, and move; concomitantly it explains how a keratocyte cell can maintain its shape and polarity, even after removal of the initial stimulus, and how it can change direction quickly in response to changes in its environment. We show that establishment of polarity stems from interactions of Cdc42, Rac and Rho, while maintenance and robustness of polarity is due to the rapid cytosolic diffusion of the inactive (GDI-bound) forms of the small G-proteins. Our model produces a cell shape that closely resembles the keratocytes and correct speeds for biologically reasonable parameter values. Movies of the simulations can be obtained from http://theory.bio.uu.nl/stan/keratocyte.  相似文献   

19.
了解红火蚁Solenopsis invicta Buren复眼形态结构及其与不同性别、品级的关系,为探索其基于视觉行为习性的、有效的非化学防控措施提供新思路和依据。采用扫描电镜技术,比较研究红火蚁工蚁、有翅雌蚁、雄蚁的复眼形态差异。结果表明:(1)工蚁复眼圆形,略外凸,小眼数约110个;雌蚁复眼长椭圆形,外凸,小眼数约510个;雄蚁复眼近半球形,小眼数约805个;(2)工、雌和雄蚁复眼中心区域小眼排列较紧密,多为较规则的五、六边形,边缘区域小眼排列不紧密,多为不规则的四至六边形,且少量相邻小眼的间距较大。工蚁、雌蚁和雄蚁复眼小眼面积大小依次为500,360,348.61μm2,同品级内小眼面大小相差不大;(3)雌、雄蚁复眼中心区域近背区小眼间着生少量感觉毛,感觉毛长度和直径依次为:雌蚁17.5~90.2,2.16~4.29μm,雄蚁17.5~27.9,1.41~2.52μm。表明雌蚁、雄蚁复眼及视力较发达,工蚁则较弱,不同性别或品级个体复眼的形状、小眼数目和形状、表面被物均有较大差异和区域性分化。  相似文献   

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