Using drift nets to capture early life stages and monitor spawning of the Yangtze River Chinese sturgeon (Acipenser sinensis)

P>A sampling system for capturing sturgeon eggs using a D-shaped bottom anchored drift net was used to capture early life stages (ELS) of Chinese sturgeon, Acipenser sinensis, and monitor annual spawning success at Yichang on the Yangtze River, 1996-2004, before and just after the Three Gorges Dam began operation. Captured were 96 875 ELS (early life stages: eggs, yolk-sac larvae = eleuthero embryos, and larvae); most were eggs and only 2477 were yolk-sac larvae. Most ELS were captured in the main river channel and inside the bend at the Yichang spawning reach. Yolk-sac larvae were captured for a maximum of 3 days after hatching began, indicating quick dispersal downstream. The back-calculated day of egg fertilization over the eight years indicated a maximum spawning window of 23 days (20 October-10 November). Spawning in all years was restricted temporally, occurred mostly at night and during one or two spawning periods, each lasting several days. The brief temporal spawning window may reduce egg predation by opportunistic predators by flooding the river bottom with millions of eggs. During 1996-2002, the percentage of fertilized eggs in an annual 20-egg sample was between 63.5 to 94.1%; however, in 2003 the percentage fertilized was only 23.8%. This sudden decline may be related to the altered environmental conditions at Yichang caused by operation of the Three Gorges Dam. Further studies are needed to monitor spawning and changes in egg fertilization in this threatened population.

基于极小T-不变量增加的Petri网可达性分析

Petri网是一种图形化和数学化的建模工具，具有描述同步、并发、冲突等行为的能力，已经在工作流管理、软件工程、协议验证等众多领域得到了应用。 可达性是描述Petri网状态和行为的一种重要而有效的手段。对于一般Petri网的可达性问题所具有的时间复杂度至少是指数级的。为了简化可达性分析，我们提出了一种基于T-不变量增加的Petri网的可达性分析方法。 对于一类含T-不变量的Petri网，基于T-不变量增加的Petri网的可达性分析过程如下：首先，通过定义一个Petri网的b-路线性约束问题，即对网的状态方程加以适当的约束，求得一组特征解向量。b-路线性约束问题对Petri网的状态方程的解进行了约束，这一过程的作用是将状态方程的无穷解空间缩小为一个有限的解空间，并且这个有限解空间中的每一个特征解向量的分量和不超过 ( 为给定网的变迁个数)；其次，如果求得的特征解向量使得初始状态到目标状态可达，那么可达性问题就可解决，如果不能使得初始状态到目标状态可达，那么在特征解向量的基础上适当添加整数倍极小T-不变量使得这个添加后的特征解向量形式上可达。这个过程需要运用扩展极小T-不变量关系图和扩展借矩阵，并且保证添加极小T-不变量后的特征解向量的分量小于 （我们称满足这个条件的可达为b-路可达），然后再判断这个添加极小T-不变量后的特征解向量的可达性。该方法的优点在于判断的变迁向量较短，从而在一定程度上简化可达性分析的过程。

基于极小T-不变量增加的Petri网可达性分析

Petri网是一种图形化和数学化的建模工具，具有描述同步、并发、冲突等行为的能力，已经在工作流管理、软件工程、协议验证等众多领域得到了应用。 可达性是描述Petri网状态和行为的一种重要而有效的手段。对于一般Petri网的可达性问题所具有的时间复杂度至少是指数级的。为了简化可达性分析，我们提出了一种基于T-不变量增加的Petri网的可达性分析方法。 对于一类含T-不变量的Petri网，基于T-不变量增加的Petri网的可达性分析过程如下：首先，通过定义一个Petri网的b-路线性约束问题，即对网的状态方程加以适当的约束，求得一组特征解向量。b-路线性约束问题对Petri网的状态方程的解进行了约束，这一过程的作用是将状态方程的无穷解空间缩小为一个有限的解空间，并且这个有限解空间中的每一个特征解向量的分量和不超过 ( 为给定网的变迁个数)；其次，如果求得的特征解向量使得初始状态到目标状态可达，那么可达性问题就可解决，如果不能使得初始状态到目标状态可达，那么在特征解向量的基础上适当添加整数倍极小T-不变量使得这个添加后的特征解向量形式上可达。这个过程需要运用扩展极小T-不变量关系图和扩展借矩阵，并且保证添加极小T-不变量后的特征解向量的分量小于 （我们称满足这个条件的可达为b-路可达），然后再判断这个添加极小T-不变量后的特征解向量的可达性。该方法的优点在于判断的变迁向量较短，从而在一定程度上简化可达性分析的过程。

Petri网可达性的综合判定法

Petri网标识的可达性判定问题是进行Petri网分析的基础,而传统的判定方法并不能确保所得结果的可靠性.在揭示Petri网可达性问题的实质之后,讨论了在标识图的同一连通域内标识可达性的判定问题,进而在分析相关原理的基础上提出了一种有效判定Petri网标识可达性的综合判定法.此判定方法综合多种传统判定方法的优点,结合Gr鯾ner基理论,确保了对Petri网标识可达性进行判定所得结果的可靠性.

基于Petri网的Web服务流程建模方法研究

随着网络应用的蓬勃发展,Web服务越来越普及。在实际应用中,往往需要对已有Web服务进行集成。目前通常的企业Web服务集成过程,都是先根据企业的业务流程建立相应的Web服务流程模型,再由此建立应用系统。而目前已有的建模手段的共同问题是：无法确保模型的正确性和与具体业务的紧密吻合。该文提出一种基于Petri网的Web服务流程建模方法。该建模方法通过将Petri网引入建模过程弥补了原建模过程中无法直观感受模型的不足,通过建立一套完备的形式化定义保证了建立模型的正确性,通过将紧同步随机Petri网引入建模过程可以更好的描述实际业务。通过使用该方法, 可以很好地解决现在Web流程建模过程中存在的问题。此方法也为其他领域中的流程建模仿真提供了一种很好的解决问题的方法和思路。

基于有色Petri网的Web服务组合建模与分析

形式化定义了Web服务组合过程中的5种基本逻辑结构,并采用有色Petri网表示,然后将其抽象为服务的代数运算;在此基础上,提出了经过服务运算后得到的服务的性质及组合服务的构造方法;最后通过实例分析,说明该建模方法可以保证组合的服务是正确且可终止的。

Seeding nets with neutral spores of the red alga Porphyra umbilicalis (L.) Kutzing for use in integrated multi-trophic aquaculture (IMTA)

Nets in traditional Porphyra mariculture are seeded with conchospores derived from the conchocelis phase, and spend a nursery period in culture tanks or calm coastal waters until they reach several centimeters in length. Some species of Porphyra can regenerate the foliose phase directly through asexual reproduction, which suggests that the time, infrastructure, and costs associated with conchocelis culture might be avoided by seeding nets with asexual spores. Here, we present work from a short-term mariculture study using nets seeded with asexual spores (neutral spores) of a native Maine species of Porphyra. Porphyra umbilicalis (L.) Kutzing was selected for this proof of concept research because of its reproductive biology, abundance across seasons in Maine, and evidence of its promise as a mariculture crop. We studied the maturation, release, and germination of the neutral spores to develop an appropriate seeding protocol for nets, followed by development of a nursery raceway to provide an easily manipulated environment for the seeded nets. Neutral spores were produced throughout the year on the central Maine coast,however, there was a temporal variability in the number and survival of released neutral spores, depending upon thallus position in the intertidal zone. Small thalli were strictly vegetative, but most thalli reproduced by neutral spores- sexual reproduction was absent. Neutral spores germinated quickly at 10 and 15 'C, but germination was delayed at 5 degrees C. Unlike some algal zygotes and spores, neutral spores of R umbilicalis required light to germinate; however, irradiances of 25 and 100 mu mol photons M-2 S-1 were equally sufficient for germination. Rafts of seeded nets were deployed in Cobscook Bay, Maine, at two distances from salmon aquaculture pens and at a control site on a nearby, fallow aquaculture site (no salmon). There was no difference in nitrogen content of harvested thalli; however, both the density and the surface area of harvested thalli were different among the sites. The possible causes of these differences are discussed in the context of potential use of P umbilicalis in IMTA. (C) 2007 Elsevier B.V. All rights reserved.

Feeding and growth on bivalve biodeposits by the deposit feeder Stichopus japonicus Selenka (Echinodennata : Holothuroidea) co-cultured in lantern nets

Suspension aquaculture of filter-feeding bivalves has been developing rapidly in coastal waters in the world, especially in China. Previous studies have demonstrated that dense populations of filter-feeding bivalves in shallow water can produce a large amount of faeces and pseudofaeces (biodeposits) that may lead to negative impacts on the benthic environment. To determine whether the deposit feeder Stichopus (Apostichopus) japonicus Selenka can feed on bivalve biodeposits and whether the sea cucumber can be co-cultured with bivalves in suspended lantern nets, three experiments were conducted, two in tanks in the laboratory and one in the field. In a 3-month flow-through experiment, results showed that sea cucumbers grew well with specific growth rate (SGR) reaching 1.38% d(-1), when cultured in the bottom of tanks (10 m(3) water volume) where scallops were cultured in suspension in lantern nets. Moreover, results of another laboratory experiment demonstrated that sea cucumbers could survive well on bivalve biodeposits, with a feeding rate of 1.82 +/- 0.13 g dry biodeposits ind(-1) d(-1), absorption efficiency of organic matter in biodeposits of 17.2% +/- 5.5%, and average SGR of 1.60% d(-1). Our longer-term field experiments in two coastal bays (Sishili Bay and Jiaozhou Bay, northern China) showed that S. japonicus co-cultured with bivalves also grew well at growth rates (0.09-0.31 g wet weight ind(-1) d(-1)) depending on individual size. The results suggest that bivalve lantern nets can provide a good habitat for sea cucumbers; and the co-culture of bivalve molluscs with sea cucumbers may provide an additional valuable crop with no additional inputs. (c) 2006 Elsevier B.V. All rights reserved.

基于有限状态机与Petri网的系统分析与设计

从系统组成、功能需求和体系结构方面介绍了航天器空间对接仿真系统的实时多任务控制系统,基于有限状态机和Petri网方法对其进行了单任务级和多任务级的分析建模,并以此为基础完成系统的详细设计,其中应用分叉和资源共享模型实现了系统的同步和互斥问题。实际应用中应用工程化和模块化的方法完成系统设计,系统运行性能良好。试验证明这种分析设计方法合理可行。