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应用原子力显微镜对经化学方法预处理的玉米染色体超微结构进行了研究。原子力显微镜观察的结果揭示,经30%醋酸处理的玉米染色体表面呈现出不均一的颗粒状结构。当缩小扫描范围后,在染色体表面发现直径分别为30和100 nm的两种染色质纤丝。100 nm的染色质纤丝由30 nm染色质纤丝螺旋缠绕而成。在经25%胰酶处理的玉米染色体上发现了两种类似的螺旋状染色质纤丝结构,其直径分别为30和100~150 nm。较细的染色质纤丝螺旋缠绕成较粗的纤丝,进而构成整个染色体。经低离子浓度溶液抽提,用原子力显微镜观察到了玉米染色体的染色体骨架结构。这种染色体骨架呈不规则的纤维网状,这些网状纤维在染色体中部显得较为紧密,在染色体的边缘则显得较松散。这一结果暗示染色体是由不同级别的染色质纤丝螺旋缠绕构成,为染色体的多级螺旋结构假说提供了新的证据。同时发现染色体骨架并不是呈轴样的结构存在,而是保留了染色体的基本形态,这种骨架形状也许是由分散在染色体中的染色体骨架蛋白在低离子浓度溶液抽提的过程中凝缩形成的。 相似文献
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首次使用LED作为光源,研究不同光照条件及GA3对菟丝子(Cuscuta spp.)弯钩打开、缠绕发生与吸器形成的影响.结果表明,光照信号作为一个必要条件参与了菟丝子对寄主的识别及缠绕发生的调控,而化学信号可能起到一定的促进作用;GA3参与了对菟丝子缠绕发生的调控,但对弯钩打开没有明显的作用.除了典型的光敏色素作用外,还有另一类光反应(HER)参与了上述过程,这类光反应可由879 nm远红光引发,证明菟丝子存在HER,还有Pfr向Pr的暗转化过程,在缠绕发生过程中光敏色素和隐花色素发生相互作用. 相似文献
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攀爬植物的卷须是对机械刺激极为敏感的器官。拟南芥(Arabidopsisthaliana)小G蛋白能够响应机械刺激调控自身发育,但小G蛋白信号是否在卷须感受机械刺激发生缠绕过程中发挥作用目前尚不清楚。该研究以黄瓜(Cucumissativus)为实验材料,对其卷须受机械刺激缠绕过程中小G蛋白活性进行了探讨。ROP活性检测结果表明,在卷须缠绕过程中小G蛋白CsROP6的活性显著增强;同时,质谱鉴定结果显示,卷须缠绕过程中生长素的含量明显增加。进一步的实验表明,外源生长素处理能明显增强CsROP6的活性,暗示黄瓜卷须在缠绕过程中受机械刺激可能通过生长素增强ROP活性,且机械刺激激活小G蛋白信号在不同植物中存在一定的保守性。 相似文献
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质谱流式技术(mass cytometry)是利用质谱原理对单细胞进行多参数检测的流式技术,能够在单细胞水平实现超过50种标志物的同时测量,显著增强了对细胞生长进程和复杂细胞系统的评估能力。该文简要介绍了质谱流式技术的基本工作原理,并从金属元素标记、质量分析器、高维单细胞数据处理等方面展开论述,阐明设计新型金属元素标签和选择飞行时间质谱的必要性,归纳分析高维单细胞数据的算法并总结各种算法的优点和局限性。 相似文献
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《生物数学学报》2017,(4)
本文研究了下列缠绕方程组解的性质:N(S)=K_0,N(S+M)=K_1,N(S+M+M)=K_2,N(S+M+M+M)=K_3.通过控制变量的方法,将某个K_i(i=0,1,2,3)的向量表示中的元素换成变量,研究变量在满足何条件时,该缠绕方程组系统有唯一解,从而找出其他K_i满足该缠绕方程组系统并使该缠绕方程组只有一个解.此时这个缠绕方程组系统得到了很好的应用,相当于通过对一个DNA分子在酶作用下拓扑结构改变的研究,得到了另外一个DNA分子或多个DNA分子在酶促反应下进行n次连续的特异性位点重组时拓扑结构的变化,这样可以避免逐个研究,大大减少了工作量. 相似文献
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This paper proposes a class-based multipath routing algorithm to support Quality of Service (QoS). The algorithm is called
Two-level Class-based Routing with Prediction (TCRP). Since frequently flooding routing information is very expensive for
dynamic routing, the TCRP is designed to have the traffic load information monitored in one stable period as a guide to control
traffic forwarding in the next stable period. The monitoring function is implemented by adopting the leaky bucket mechanism.
In TCRP, the path selection function can utilize resources on multipath to achieve load balancing, increase network throughput
and reduce the queuing delay. The extensive simulation is conducted to analyze the performance of the TCRP algorithm. The
simulation results show that the TCRP can reduce packet drops and increase network throughput in any size network topology.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Claudio E. Torres Louis F. Rossi Jeremy Keffer Ke Li Chien-Chung Shen 《Swarm Intelligence》2010,4(3):221-244
Using the metaphor of swarm intelligence, ant-based routing protocols deploy control packets that behave like ants to discover
and optimize routes between pairs of nodes. These ant-based routing protocols provide an elegant, scalable solution to the
routing problem for both wired and mobile ad hoc networks. The routing problem is highly nonlinear because the control packets
alter the local routing tables as they are routed through the network. We mathematically map the local rules by which the
routing tables are altered to the dynamics of the entire networks. Using dynamical systems theory, we map local protocol rules
to full network performance, which helps us understand the impact of protocol parameters on network performance. In this paper,
we systematically derive and analyze global models for simple ant-based routing protocols using both pheromone deposition
and evaporation. In particular, we develop a stochastic model by modeling the probability density of ants over the network.
The model is validated by comparing equilibrium pheromone levels produced by the global analysis to results obtained from
simulation studies. We use both a Matlab simulation with ideal communications and a QualNet simulation with realistic communication
models. Using these analytic and computational methods, we map out a complete phase diagram of network behavior over a small
multipath network. We show the existence of both stable and unstable (inaccessible) routing solutions having varying properties
of efficiency and redundancy depending upon the routing parameters. Finally, we apply these techniques to a larger 50-node
network and show that the design principles acquired from studying the small model network extend to larger networks. 相似文献
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干湿纺聚乳酸/壳聚糖纤维交织织物作为细胞体外培养载体的实验观察 总被引:1,自引:0,他引:1
在体外培养的条件下观察干湿纺聚乳酸/壳聚糖纤维交织织物与成骨细胞的相容性,探讨其作为人工胸壁支架材料和人工骨支架材料的可行性。将hFOB1.19人SV40转染的成骨细胞与干湿纺聚乳酸/壳聚糖纤维交织织物体外联合培养。用扫描电镜对体外联合培养早期细胞的形态学进行观察。结果表明,成骨细胞与干湿纺聚乳酸/壳聚糖交织织物间黏附良好,具有良好的相容性,干湿纺聚乳酸/壳聚糖纤维交织织物有可能成为一种理想的可用于修复胸壁缺损和骨缺损的成骨细胞载体。 相似文献
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Questions: How important is the choice of flow routing algorithm with respect to application of topographic wetness index (TWI) in vegetation ecology? Which flow routing algorithms are preferable for application in vegetation ecology? Location: Forests in three different regions of the Czech Republic. Methods: We used vegetation data from 521 georeferenced plots, recently sampled in a wide range of forest communities. From a digital elevation model, we calculated 11 variations of TWI for each plot with 11 different flow routing algorithms. We evaluated the performance of differently calculated TWI by (1) Spearman rank correlation with average Ellenberg indicator values for soil moisture, (2) Mantel correlation coefficient between dissimilarities of species composition and dissimilarities of TWI and (3) the amount of variation in species composition explained by canonical correspondence analysis. Results: The choice of flow routing algorithm had a considerable effect on the performance of TWI. Correlation with Ellenberg indicator values for soil moisture, Mantel correlation coefficient and explained variation doubled when the appropriate algorithm was used. In all regions, multiple flow routing algorithms performed best, while single flow routing algorithms performed worst. Conclusions: We recommend the multiple flow routing algorithms of Quinn et al. and Freeman for application in vegetation ecology. 相似文献
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Self Organized Terminode Routing 总被引:2,自引:0,他引:2
We consider the problem of routing in a wide area mobile ad hoc network called Terminode Network. Routing in this network is designed with the following objectives. First, it should scale well in terms of the number of nodes and geographical coverage; second, routing should have scalable mechanisms that cope with the dynamicity in the network due to mobility; and third, nodes need to be highly collaborative and redundant, but, most of all, cannot use complex algorithms or protocols. Our routing scheme is a combination of two protocols called Terminode Local Routing (TLR) and Terminode Remote Routing (TRR). TLR is used to route packets to close destinations. TRR is used to route to remote destinations. The combination of TLR and TRR has the following features: (1) it is highly scalable because every node relies only on itself and a small number of other nodes for packet forwarding; (2) it acts and reacts well to the dynamicity of the network because as a rule multipath routing is considered; and (3) it can be implemented and run in very simple devices because the algorithms and protocols are very simple and based on high collaboration. We performed simulations of the TLR and TRR protocols using the GloMoSim simulator. The simulation results for a large, highly mobile ad hoc environment demonstrate benefits of the combination of TLR and TRR over an existing protocol that uses geographical information for packet forwarding. 相似文献
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The three-dimensional arrangement of the intestinal smooth muscle in the ammocoetes of the lamprey (Lampetra japonica) was examined by scanning electron microscopy (SEM) after removal of the intestinal mucosa. In cross section of the posterior midgut, its wall was composed of the parietal wall and the typhlosolar wall of the spiral fold, lining a horseshoe-shaped space, and had two distinct muscle layers. The fiber extensions of the muscle layers in the two parts of the wall were reversed; internal longitudinal and external circular in the parietal wall, but internal circular and external longitudinal in the typhlosolar wall. The positional exchange of the two layers occurred within the transitional area from the parietal wall to the typhlosolar wall, where an interlacing texture of longitudinal and circular braids of fibers was observed. Furthermore, the external fibers of the longitudinal braid extended successively into the circular braid until the longitudinal braid disappeared. However, any fibrous transition from the circular braid into the longitudinal braid in the typhlosolar wall was not clear in the present study. The internal location of the longitudinal layer at the parietal wall may be optimal for its main function of contracting the intestinal tract longitudinally. In addition, the external (to be precise, the internal to the hematopoietic tissue) longitudinal muscle layer in the typhlosolar wall may play an important role in saving and squeezing out blood into the cardinal intestinal vein by longitudinal contraction of the elongated adjacent hematopoietic tissue mass. 相似文献
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In this paper, we consider fault-tolerant routing algorithms in hypercube multicomputer networks. In particular, one of the most quoted adaptive fault-tolerant routing algorithm for hypercubes in the literature is studied in detail and its limited ability to route messages in the presence of some fault patterns (i.e., combination of node and link faults), is pointed out. A modified algorithm is proposed and its performance, using simulation, is compared to that of the above mentioned algorithm. It is shown that the proposed algorithm outperforms the existing one in terms of its ability to route routable messages around the hypercube in the presence of node and/or links faults. This improvement is achieved while using the same average path length or even improving it. Illustrative examples are shown in support of such improvement. 相似文献
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Stephen C. H. Leung Jiemin Zheng Defu Zhang Xiyue Zhou 《Flexible Services and Manufacturing Journal》2010,22(1-2):61-82
This paper addresses the capacitated vehicle routing problem with two-dimensional loading constraints (2L-CVRP). The 2L-CVRP is a combination of the two most important problems in distribution logistics, which are loading of freight into vehicles, and the successive routing of the vehicles to satisfy customer demand. The objective is to minimize the transportation cost. All vehicles must start and terminate at a central depot, and the transported items carried by the vehicles must be feasibly packed into the loading surfaces of the vehicles. A simulated annealing algorithm to solve the problem is presented, in which the loading component of the problem is solved through a collection of packing heuristics. A novel approach to plan packing is employed. An efficient data structure (Trie) is used to accelerate the algorithm. The extensive computational results prove the effectiveness of the algorithm. 相似文献
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Internal Node and Shortcut Based Routing with Guaranteed Delivery in Wireless Networks 总被引:3,自引:0,他引:3
Several localized position based routing algorithms for wireless networks were described recently. In greedy routing algorithm (that has close performance to the shortest path algorithm, if successful), sender or node S currently holding the message m forwards m to one of its neighbors that is the closest to destination. The algorithm fails if S does not have any neighbor that is closer to destination than S. FACE algorithm guarantees the delivery of m if the network, modeled by unit graph, is connected. GFG algorithm combines greedy and FACE algorithms. Greedy algorithm is applied as long as possible, until delivery or a failure. In case of failure, the algorithm switches to FACE algorithm until a node closer to destination than last failure node is found, at which point greedy algorithm is applied again. Past traffic does not need to be memorized at nodes. In this paper we further improve the performance of GFG algorithm, by reducing its average hop count. First we improve the FACE algorithm by adding a sooner-back procedure for earlier escape from FACE mode. Then we perform a shortcut procedure at each forwarding node S. Node S uses the local information available to calculate as many hops as possible and forwards the packet to the last known hop directly instead of forwarding it to the next hop. The second improvement is based on the concept of dominating sets. Each node in the network is classified as internal or not, based on geographic position of its neighboring nodes. The network of internal nodes defines a connected dominating set, i.e., and each node must be either internal or directly connected to an internal node. In addition, internal nodes are connected. We apply several existing definitions of internal nodes, namely the concepts of intermediate, inter-gateway and gateway nodes. We propose to run GFG routing, enhanced by shortcut procedure, on the dominating set, except possibly the first and last hops. The performance of proposed algorithms is measured by comparing its average hop count with hop count of the basic GFG algorithm and the benchmark shortest path algorithm, and very significant improvements were obtained for low degree graphs. More precisely, we obtained localized routing algorithm that guarantees delivery and has very low excess in terms of hop count compared to the shortest path algorithm. The experimental data show that the length of additional path (in excess of shortest path length) can be reduced to about half of that of existing GFG algorithm. 相似文献
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Huan Chen Lemin Li Jing Ren Yang Wang Yangming Zhao Xiong Wang Sheng Wang Shizhong Xu 《PloS one》2015,10(12)
This paper aims at minimizing the communication cost for collecting flow information in Software Defined Networks (SDN). Since flow-based information collecting method requires too much communication cost, and switch-based method proposed recently cannot benefit from controlling flow routing, jointly optimize flow routing and polling switch selection is proposed to reduce the communication cost. To this end, joint optimization problem is formulated as an Integer Linear Programming (ILP) model firstly. Since the ILP model is intractable in large size network, we also design an optimal algorithm for the multi-rooted tree topology and an efficient heuristic algorithm for general topology. According to extensive simulations, it is found that our method can save up to 55.76% communication cost compared with the state-of-the-art switch-based scheme. 相似文献