基于门限签名方案的BQS系统的服务器协议

利用冗余复制技术,BQS(Byzantine quorum system)系统在异步信道上提供了能容忍f台服务器拜占庭失效的存储服务.COCA系统和CODEX系统设计了一种结合门限签名方案和BQS系统的服务器协议,完成了TSS-BQS(threshold signature schemes-BQS)系统.与普通BQS系统相比,具有更易于支持Proactive Recovery,简化客户端密钥管理和客户端通信的优点.基于相同的系统模型和信道假设,提出了一种新的服务器协议,满足TSS-BQS系统的安全要求;而且与已有协议相比,该协议只需更少的通信轮数,在读/写并发情况下执行效果 更优.     

TSS-BQS系统的Graceful Degradation机制

将门限签名方案分别应用于两种类型的BQS系统(Masking BQS系统和Dissemination BQS系统),可以得到两种TSS- BQS系统(文中称为TSS- mBQS系统和TSS- dBQS系统).TSS-mBQS系统的性能优于TSS- dBQS系统.由此,作者提出了TSS- BQS系统的Graceful Degradation机制:系统由n=3fd+1台服务器组成,在初始阶段以TSS-mBQS状态运行,容忍fm=[fd/2]台Byzantine失效服务器;随着系统运行,可能失效的服务器数量增大,则以降低性能为代价,切换到TSS- dBQS状态,容忍fd台Byzantine失效服务器.在不影响容错能力的前提下,Graceful Degradation机制提高了已有TSS- BQS系统的平均性能.文中完成的Graceful Degradation机制能够在不中断存储服务、不影响客户端的前提下完成状态切换,客户端也不需要知道系统的运行状态(处于TSS- mBQS或TSS- dBQS状态).     

Analyzing User-Perceived Dependability and Performance Characteristics of Voting Algorithms for Managing Replicated Data

User-perceived dependability and performance metrics are very different from conventional ones in that the dependability and performance properties must be assessed from the perspective of users accessing the system. In this paper, we develop techniques based on stochastic Petri nets (SPN) to analyze user-perceived dependability and performance properties of quorum-based algorithms for managing replicated data. A feature of the techniques developed in the paper is that no assumption is made regarding the interconnection topology, the number of replicas, or the quorum definition used by the replicated system, thus making it applicable to a wide class of quorum-based algorithms. We illustrate this technique by comparing conventional and user-perceived metrics in majority voting algorithms. Our analysis shows that when the user-perceiveness is taken into consideration, the effect of increasing the network connectivity and number of replicas on the availability and dependability properties perceived by users is very different from that under conventional metrics. Thus, unlike conventional metrics, user-perceived metrics allow a tradeoff to be exploited between the hardware invested, i.e., higher network connectivity and number of replicas, and the performance and dependability properties perceived by users.     

无线传感器网络中基于代理Quorum的数据分发算法

提出了一种新颖的数据分发机制——match making by geometric structure quorum（MM GSQ). 该机制使用一种称为空间邻居代理quorum的新quorum方法,可充分利用平面图的几何特性,减少quorum的规模. 通过减少传输的消息数和消息碰撞,MM GSQ改善了能量消耗,增加了匹配成功率,而且易于实现. 理论分析和实验结果表明,新quorum方法和MM GSQ与伪quorum方法相比有更好的可伸缩性、更高的能量效率和匹配成功率,特别适用于大规模无线传感器网络数据分发.     

维氏气单胞菌中AHLs介导的群体感应现象及大蒜提取物的干扰作用

以发酵鱼糜中分离的1株维氏气单胞菌为对象,分析该菌中N-酰基高丝氨酸内酯(AHLs)介导的群体感应现象,研究大蒜提取物作为群体感应抑制剂对该菌群体感应及腐败能力的干扰作用.结果表明,维氏气单胞菌至少产生3种AHLs信号分子,即C6-HSL、C7-HSL和C8-HSL.在细菌快速生长阶段,AHLs分子的活性不断增加;当细...     

真菌群体感应分子法尼醇及其作用机制

群体感应(quorum sensing,QS)是取决于细胞密度的微生物通信机制,可调节细菌毒力因子分泌、生物膜形成、感受态和生物发光等行为。真菌群体感应系统10年前在法尼醇控制致病多态性真菌白色念珠菌中的细丝化研究中被发现。研究显示法尼醇作为群体感应分子(QSM)对宿主和其他微生物发挥多种作用;还发现芳香醇酪醇是控制白色念珠菌生长、形态发生和生物膜形成的另一群体感应分子。在酿酒酵母中,发现另两种芳香醇苯乙醇和色氨酸是在氮饥饿条件下调节形态发生的群体感应分子。此外,类似于群体感应的种群密度依赖性行为已在几种其他真菌中描述。本综述总结了目前发现群体感应效应的几种关键真菌物种,并重点阐述了研究较多的白色念珠菌和法尼醇作用的微观机制研究进展。     

钝顶螺旋藻提取物对细菌群体感应的抑制作用

以mini-Tn5突变株Chromobacterium violaceum CV026为报告菌检测系统,研究钝顶螺旋藻甲醇提取物的群体感应抑制活性及对大菱鲆腐败菌Shewanella putrefacens生物膜形成的影响。结果表明:螺旋藻75%甲醇提取物(0.125～1.000g/100mL)不仅能显著降低Chromobacterium violaceum CV026细菌紫色菌素的产生,而且能显著抑制外源信号分子N-已酰化高丝氨酸内酯(10μmol/L C6-HSL)诱导的报告菌紫色菌素的增加。当螺旋藻提取物添加质量浓度为1.000g/100mL时,对报告菌紫色菌素的抑制率达87.67%,对Shewanella putrefacens生物膜的形成抑制率达77.05%,与对照差异均达显著水平(P<0.05)。抑菌实验表明,在给定的质量浓度范围内,螺旋藻提取物对报告菌的生长无显著影响;螺旋藻提取物抑制紫色色素的产生与生物膜的形成不是通过抑制细菌的生长来实现的,而与抑制信号分子诱导的群体感应现象有关;螺旋藻提取物具有较强的细菌群体感应抑制活性,可作为细菌群体感应抑制剂用于新鲜食品及其制品的贮藏与保鲜。     

降解温和气单胞菌AHLs乳酸菌的筛选及在三文鱼保鲜中的应用

从传统发酵食品中筛选对温和气单胞菌（Aeromonas sobria）N-酰基高丝氨酸内酯（N-acyl-homoserine lactones,AHLs）信号分子具有降解活性的乳酸菌,对其进行菌种鉴定,探究乳酸菌产生的群体感应淬灭作用酶存在位置与类型。以三文鱼为载体,通过测定细菌菌落总数、持水力、硫代巴比妥酸（thiobarbituric acid,TBA）值以及挥发性盐基氮（total volatile basic nitrogen,TVB-N）值等指标评价乳酸菌抑制温和气单胞菌致腐能力的效果。结果表明：采用96孔板法结合牛津杯法筛选获得1株对温和气单胞菌AHLs降解活性接近100%的菌株YF-8,经鉴定为戊糖片球菌（Pediococcus pentosaceus）。菌株YF-8淬灭酶存在于胞外上清液中,且在酸性、中性条件下均具有降解活性,初步判定为AHLs酰基转移酶。通过生长曲线确定YF-8淬灭酶粗提物在亚抑菌质量浓度2.0、4.0 mg/mL和6.0 mg/mL时不影响温和气单胞菌生长。此外,感染温和气单胞菌的三文鱼经YF-8淬灭酶粗提物处理过后,细菌菌落总数、持水力、TBA值...     

Simulated Bacterially-Inspired Problem Solving – The Behavioural Domain

Bacterial populations meet the challenges of dynamic spatially heterogeneous environments with fluctuating biotic and abiotic factors in a number of ways. The motivation for the work presented here has been to transfer ideas from bacterial adaptability and evolvability to computational problem solving. Following a brief comment on some examples of the ways bacteria solve problems, a bacterially-inspired computational architecture for simulating aspects of problem solving is described. We then examine three case studies. The first, a study of the mutational impact of a remediation to toxic (fitness-reducing) material, highlights how a sufficiently pre-engineered adaptive system can solve a difficult problem quite easily. The second study looks at why it is difficult to evolve complex problem solving behaviours and how artificial selection mechanisms coupled with pre-engineering the system can help. Specifically, this refers to quorum sensing and tactic behaviours. A further study looked at ways in which a quorum sensing analogue could help computational agents find multiple peaks in a landscape. The paper concludes with a discussion of an investigation of bacteria that had both quorum sensing and tactic capabilities.