热力学遗传算法计算效率的改进

热力学遗传算法(thermodynamical genetic algorithms,简称TDGA)借鉴固体退火过程中能量与熵的竞争模式来协调GA中"选择压力"和"种群多样性"之间的冲突.然而TDGA目前极高的计算代价限制了其应用.为了提高TDGA的计算效率,首先定义一种等级熵(rating-based entropy,简称RE)度量方法,它能以较小的计算成本度量种群中个体适应值的分散程度.然后引入分量热力学替换规则(component thermodynamical replacement,简称CTR),有效地降低了替换规则的复杂度.同时也证明了CTR规则具有驱动种群自由能近似最速下降的能力.在0-1背包问题上的实验结果表明,RE方法和CTR规则在保持TDGA良好的性能与稳定性的同时,极大地提高了其计算效率.     

基于最小熵产生选择策略的遗传算法研究

针对遗传算法(Genetic Algorithm, GA)容易陷入局部最优的问题,借鉴热力学非平衡定态下的最小熵增原理,提出一种基于最小熵增原理的热力学选择策略,使个体的选择不再完全依赖于适应值。通过最小熵产生选择策略使种群在保证收敛速度的同时保持多样性,有效避免了种群陷入局部最优。通过定义个体密度来度量种群多样性,利用精英策略驱动种群熵产生快速下降;当种群多样性过低时,使用基于最小熵产生的选择策略产生新种群以保证种群多样性。在0/1背包问题和数值测试问题上的实验结果均表明,该策略能很好地保证解集分布的均匀性,防止种群陷入局部最优。同时,该策略也可应用于目前较新改进的遗传算法中,对算法效率也有一定的改进,具有很好地普适性。     

具有多形态种群协同进化的多目标优化算法

为提高进化多目标优化算法在维持最优解多样性方面的性能,获得分布更均匀的Pareto非支配解集,文中提出一种具有多形态种群协同进化的多目标优化算法.该算法构建一种多形态种群协同进化架构,通过引入最小向量夹角的相似性度量方法,给出次优非支配个体选择策略,从而提高种群的多样性.算法还提出一种基于排序链表的拥挤个体删除策略,进一步提高解集分布的均匀性和宽广性.与经典算法对比结果表明,文中算法在解的分布性和多样性方面均有较好表现,尤其在解集分布均匀性方面优势较明显.     

一种基于聚集距离的多目标进化算法

在多目标进化算法的研究中,解群体的多样性和运行效率是最重要的两个指标。在进化算法中一般采用构造非支配集的方法来保持算法的运行效率和解集的分布性;采用聚类技术来计算和维持解群体的分布性和多样性。文章提出了用庄家法构造非支配集和基于个体距离的聚类方法的多目标进化算法。经试验证明,该算法能够趋近到Pareto最优解,并且能保证较好的分布度。     

一种基于Pareto排序的混合多目标进化算法

为了改进多目标进化算法的收敛性和解集的多样性,提出一种基于Pareto排序的混合多目标进化算法PHMOEA。在PHMOEA中使用干扰集刺激优化非支配集的构成,改善算法的收敛性和解集的分布性,并根据Pareto等级和精英保留策略改进了交叉算子和变异算子。该算法与著名的NSGA-II和SPEA2多目标进化算法在13个基准测试函数上的对比结果表明,PHMOEA算法不仅多样性较好,而且提高了算法的收敛性,并使获得的最优解集的分布性更均匀,覆盖范围更广。     

一种改进的多目标演化算法

保持解集的多样性和分布性是多目标进化算法的关键之一。在NSGA-II的基础上,提出了一种用混合距离来估计个体的拥挤度,并使用优先队列根据个体的混合距离来逐个删除种群中超出的非劣解以保持解的多样性,实验结果表明,HD-NSGA-II比NSGA-II的解分布的更加合理且分布度有很大的提高。     

用于约束多目标优化问题的热力学遗传算法

为了保持所求得的约束多目标优化问题Pareto最优解的适应度与多样性,在NSGA-Ⅱ基础上提出了一种用于求解有约束的多目标优化问题的热力学遗传算法.结合热力学中自由能与熵的概念,利用热力学中熵与能量的竞争来保持种群的适应度与多样性的平衡,设计了热力学算子.根据非支配排序Pareto分层结构建立分层小生境来改进选择算子,弥补了选择算子不足.实验结果表明:该算法不仅得到的解在空间分布均匀,收敛性好,同时解集具有较广的分布空间.     

基于直觉模糊支配的混合多目标粒子群算法

为提高求解多目标优化问题的精确性和解集分布的均匀性,提出了一种基于直觉模糊支配的混合粒子群算法。通过引入种群全局目标值标量参数、直觉模糊隶属度和排序方法,定义一种新的最优解支配关系;采用基于模拟退火的Meta-Lamarckian局部学习策略,结合粒子群算法,以避免算法陷入局部最优和早熟;此外,定义种群同构因子来衡量种群多样性,以自适应调节惯性权重和加速因子;提出一种递减扰动策略对粒子飞行速度进行扰动;最后,与多种经典多目标优化算法进行仿真测试比较,结果表明该算法在求解精度、解集分布均匀性上具有明显优势。     

多目标进化算法中基于动态聚集距离的分布性保持策略 *

提出了基于动态聚集距离 ( DCD)的分布性保持策略 ,利用个体在不同维目标上聚集距离的差异程度来定义 DCD,并在种群维护中动态地计算 DCD。与目前经典算法 NSGA-II和ε -MOEA进行比较 ,实验结果表明 DCD能在较大程度上提高分布性 ,并得到较好的收敛性。     

NSGA-II中一种改进的分布性保持策略

NSGA-II以其良好的收敛性和时间效率广泛应用于多目标优化中,然而其基于聚集距离的种群维护策略并不能很好地保持解集的分布性。提出一种改进的分布性保持策略,设置随种群密集程度自适应变化的阈值,动态地维护种群,使得分布性优秀的个体有更大的生存机会。与NSGA-II和ε-MOEA在5个测试函数上进行比较实验,结果表明改进算法在有效提高分布性的同时,拥有良好的收敛性。     

IEEE 802.15.4 MAC协议能耗与时延均衡的GTS调度新算法设计

简述了IEEE 802.15.4 MAC协议中超帧结构和保护时隙(GTS)分配机制,分析了星状网络中信标使能模式下设备节点利用GTS方式通信时超帧结构中各参数对能耗与时延性能的影响.在此基础上设计了一种GTS调度新算法,该调度算法对时延期限小的节点优先进行GTS分配并在满足其时延要求情况下,根据业务量调节超帧结构中的超帧序号SO与信标序号BO,使设备节点能耗降到最低,从而实现星状网络中各节点的能耗与时延均衡,并用NS2仿真评估了调度新算法性能,其研究可为无线传感网络的实时应用系统提供参考价值.     

IEEE802.15.4多时隙下GTS性能分析及配置优化

IEEE802.15.4标准的保障时隙(GTS)机制可分配多个时隙,用于保障实时性数据的传输。针对非竞争接入期多时隙下GTS性能分析的不足,利用网络微积分法分析时延和吞吐量服务曲线及其与能耗的关系,改进IEEE802.15.4传感器节点模型,建模仿真研究GTS参数对网络性能(时延、吞吐量及能耗)的影响。仿真结果表明：根据高低突发性数据率的情况,最优化配置下的GTS可以满足实时性数据的传输。     

基于OPNET的无线传感器网络MAC协议研究

在无线传感器网络中,MAC协议是网络高效通信的重要保证。本文利用OPNET仿真平台,对低速无线个域网(LR-WPAN)中IEEE802.15.4的MAC协议的超帧结构和时隙保障(GTS)机制进行研究。仿真实验中构建了小型星型网络,能更清楚地反映网络中的平均能量消耗情况,并通过设置不同的仿真场景,说明了GTS机制能有效节省电源能量,为大型无线传感器网络的设计提供了重要依据。     

A SKOS-based multilingual thesaurus of geological time scale for interoperability of online geological maps

The usefulness of online geological maps is hindered by linguistic barriers. Multilingual geoscience thesauri alleviate linguistic barriers of geological maps. However, the benefits of multilingual geoscience thesauri for online geological maps are less studied. In this regard, we developed a multilingual thesaurus of geological time scale (GTS) to alleviate linguistic barriers of GTS records among online geological maps. We extended the Simple Knowledge Organization System (SKOS) model to represent the ordinal hierarchical structure of GTS terms. We collected GTS terms in seven languages and encoded them into a thesaurus by using the extended SKOS model. We implemented methods of characteristic-oriented term retrieval in JavaScript programs for accessing Web Map Services (WMS), recognizing GTS terms, and making translations. With the developed thesaurus and programs, we set up a pilot system to test recognitions and translations of GTS terms in online geological maps. Results of this pilot system proved the accuracy of the developed thesaurus and the functionality of the developed programs. Therefore, with proper deployments, SKOS-based multilingual geoscience thesauri can be functional for alleviating linguistic barriers among online geological maps and, thus, improving their interoperability.     

An implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks: theory and practice

Timeliness guarantee is an important feature of the recently standardized IEEE 802.15.4 protocol, turning it quite appealing for Wireless Sensor Network (WSN) applications under timing constraints. When operating in beacon-enabled mode, this protocol allows nodes with real-time requirements to allocate Guaranteed Time Slots (GTS) in the contention-free period. The protocol natively supports explicit GTS allocation, i.e. a node allocates a number of time slots in each superframe for exclusive use. The limitation of this explicit GTS allocation is that GTS resources may quickly disappear, since a maximum of seven GTSs can be allocated in each superframe, preventing other nodes to benefit from guaranteed service. Moreover, the GTS may be underutilized, resulting in wasted bandwidth. To overcome these limitations, this paper proposes i-GAME, an implicit GTS Allocation Mechanism in beacon-enabled IEEE 802.15.4 networks. The allocation is based on implicit GTS allocation requests, taking into account the traffic specifications and the delay requirements of the flows. The i-GAME approach enables the use of one GTS by multiple nodes, still guaranteeing that all their (delay, bandwidth) requirements are satisfied. For that purpose, we propose an admission control algorithm that enables to decide whether to accept a new GTS allocation request or not, based not only on the remaining time slots, but also on the traffic specifications of the flows, their delay requirements and the available bandwidth resources. We show that our approach improves the bandwidth utilization as compared to the native explicit allocation mechanism defined in the IEEE 802.15.4 standard. We also present some practical considerations for the implementation of i-GAME, ensuring backward compatibility with the IEEE 801.5.4 standard with only minor add-ons. Finally, an experimental evaluation on a real system that validates our theoretical analysis and demonstrates the implementation of i-GAME is also presented.     

IEEE 802.15.4中信道利用率的分析与改进

在分析IEEE 802.15.4网络中为时延敏感应用提供的保护时隙(GTS)分配策略后,指出GTS分配中信道利用率低等不足。为此,对IEEE 802.15.4中的GTS进行改进。将GTS时隙再次划分为微时隙,与标准GTS申请命令不同,节点无须指定所需的GTS长度,而是提供需要发送的数据数量和数据长度,通过协调节点来决定所分配的GTS长度。仿真实验结果表明,改进后协议能提高信道利用率和网络吞吐量。     

一种基于梯形自调度技术的集群任务调度的实现

通过比较目前几种集群任务调度算法,选择基于集中队列的动态调度算法——梯形自调度算法（TSS）,实现了一个基于集群的任务调度系统GTS。GTS是一个用户级的任务调度系统,它建立于Linux之上,主要负责对用户任务的调度。通过测试,GTS系统可以胜任集群工作站中的任务调度并在结点数较多的情况下大幅度提高应用问题的性能。     

多节点共享保障时隙分配策略

在现代工业无线网络中,IEEE 802.15.4标准以其独特的低功耗、低成本特点被广泛应用。IEEE 802.15.4可以提供最低0.006%的占空比,最大限度降低功耗,同时提供的保障时隙GTS机制为节点提供了实时服务保障。然而,在为大规模节点提供保障时,IEEE 802.15.4提供的GTS机制缺乏灵活性,只能为有限节点提供实时保障服务。本文针对这一问题提出一种多节点共享保障时隙分配策略,允许多个数据流在满足延迟需求前提下,共享同一个GTS减少带宽浪费。分析表明,多节点共享的保障时隙分配策略与普通分配方法相比,可有效提高带宽利用率。     

A parameter identification method for natural gas supply systems under unsteady gas flow

We consider the identification problem for the technical parameters, i.e., hydraulic efficiency coefficients, of gas transmission systems (GTS) under standard unsteady gas flow. Coefficient estimation is reduced to a conditional optimization problem with equality type constraints. We propose an algorithm to solve it. The algorithm’s efficiency has been tested with computational experiments, including a looped gas supply system. The resulting model operates under the current level of GTS information support.     

Influence of hydration volume and ambient temperature on physiological responses while wearing CBRN protective clothing

This study examined a low (L; 5 ml/kg per h) and high (H, 10 ml/kg per h) rate of fluid replacement in moderate (18°C) and hot (30°C) conditions on physiological responses while wearing personal protective equipment (PPE). PPE included the gas-tight suit (GTS), the powered respirator protective suit (PRPS) and the civil responder 1 (CR1). Relative to the moderate condition, physiological responses were greater in the hot condition. The percentage change in body mass was different (p < 0.05) between L and H in the hot (L vs. H, GTS: -0.83 vs. -0.38%; PRPS: -1.18 vs. -0.71%; CR1: -1.62 vs. -0.57%) and moderate conditions, although in GTS and CR1 body mass increased (L vs. H, GTS: -0.48 vs. 0.06%; PRPS: -0.66 vs. -0.11%; CR1: -0.18 vs. 0.67%). Fluid replacement strategies for PPE should be adjusted for environmental conditions in order to avoid >1% body mass loss and/or net body mass gain. STATEMENT OF RELEVANCE: Currently, the UK Emergency Services do not have specific evidence-based fluid replacement guidelines to follow when wearing chemical, biological, radiological and/or nuclear (CBRN) PPE. Although ad libitum fluid replacement is encouraged (when breathing apparatus permits), recommendations from evidence-based findings specific to different PPE and to different environmental conditions are lacking. This study provides novel evidence supporting the need to develop fluid replacement strategies during CBRN deployments in both moderate and hot environmental conditions for CBRN PPE.