Modelling parallel databases with process algebra

With the current interest in using parallel computers as database servers to provide a scaleable parallel application which satisfies a real commercial need, there is a corresponding interest in performance prediction of parallel database systems. Both analytical and simulation approaches have been used and reported in the literature. This paper reports on an investigation into how a stochastic extension to classical process algebra (performance evaluation process algebra, PEPA) may be used for this purpose. This paradigm has a small but powerful set of elements which offers great flexibility for performance modelling. The paper describes how the approach has been adapted to handle database models, including the development of a technique, the decompositional approach, to handle the state-space explosion of parallel database models. It concludes with a comparison between the results obtained using this approach and those obtained using a different analytical approach.     

A low-density polyethylene composite with phosphorus-nitrogen based flame retardant and multi-walled carbon nanotubes for enhanced electrical conductivity and acceptable flame retardancy

Design and exploitation of flame retardant polymers with high electrical conductivity are desired for polymer applications in electronics. Herein, a novel phosphorus-nitrogen intumescent flame retardant was synthesized from pentaerythritol octahydrogen tetraphosphate, phenylphosphonyl dichloride, and aniline. Low-density polyethylene was combined with the flame retardant and multi-walled carbon nanotubes to form a nanocomposite material via a ball-milling and hot-pressing method. The electrical conductivity, mechanical properties, thermal performance, and flame retardancy of the composites were investigated using a four-point probe instrument, universal tensile machine, thermogravimetric analysis, and cone calorimeter tests, respectively. It was found that the addition of multi-walled carbon nanotubes can significantly improve the electrical conductivity and mechanical properties of the low-density polyethylene composites. Furthermore, the combination of multi-walled carbon nanotubes and phosphorus–nitrogen flame retardant remarkably enhances the flame retardancy of matrixes with an observed decrease of the peak heat release rate and total heat release of 49.8% and 51.9%, respectively. This study provides a new and effective methodology to substantially enhance the electrical conductivity and flame retardancy of polymers with an attractive prospect for polymer applications in electrical equipment.     

TiO_2对PP/MPP/PEPA膨胀阻燃体系的协同作用

以TiO2为阻燃协效剂,采用多聚磷酸蜜胺(MPP)和笼状季戊四醇磷酸酯(PEPA)复配阻燃剂,制备了具有良好阻燃性能的无卤阻燃聚丙烯(PP)。研究了TiO2用量对PP阻燃性能和协效作用的影响。结果表明:添加少量的TiO2即可显著提高PP的阻燃性能;当MPP/PEPA/TiO2添加量分别为12%、8%和1%时,阻燃PP的氧指数高达31.5。TGA和FTIR分析及SEM和体式显微镜观测结果表明:添加TiO2可以催化MPP/PEPA间的酯化反应,促进体系成炭,形成更致密的炭层,从而提高材料的阻燃性能。     

ABS/PA6合金的无卤膨胀性阻燃研究

以聚磷酸铵(APP)为酸源, 利用ABS/PA6合金中PA6为炭源对ABS/PA6合金进行膨胀型阻燃研究,探讨了不同成炭协效剂与APP复配对合金阻燃性能的影响,这些成炭协效剂包括季戊四醇笼状磷酸酯(PEPA),热塑性酚醛树脂(TPPFR),环氧树脂(E-44)和分子筛4A. 结果表明,PA6具有较好的成炭作用, 当APP含量为25%时,阻燃合金体系的极限氧指数可达29,UL-94测定达V-1级别,APP含量为35%时,UL-94测定达V-0级别.而以5t%的季戊四醇笼状磷酸酯(PEPA)或环氧树脂(E-44)与20%APP复配, 或以3%分子筛4A与22%APP复配都可以大大提高体系的阻燃性能和高温下的残炭量, 使阻燃体系氧指数达到30以上, UL-94测定达V-0级别. SEM形貌分析显示体系燃烧表面都形成了膨胀、均匀、致密的炭层结构.     

一种基于PEPA流近似方法的动态自省模型

现有的基于自然语言或框图的自省模型已不能满足系统验证和分析的需求.本文采用流近似方法将PEPA转化为常微分方程组(ODEs),提出了一种基于性能评价进程代数(PEPA)语言的动态自省模型,且具有形式化推理验证和量化分析的功能,避免传统马尔可夫链求解方法状态空间爆炸的问题.分析结果显示,缩减被管理组件检测过程的延迟时间、减小执行指令序列长度对于自省效率的提高具有重要作用.     

Component aggregation for PEPA models: An approach based on approximate strong equivalence

Approximate aggregation for PEPA components involves the construction of a smaller component that approximates the behaviour of the original one. Such an approximation at the component level can be very efficient and it can also result in a considerable reduction of the state-space for the underlying continuous-time Markov chain. We propose an approximate PEPA component aggregation strategy that relies on an approximate form of strong equivalence. The notion of strong equivalence captures behavioural similarity between components of different size. This quality renders approximate strong equivalence appropriate as a criterion to aggregate the state-space of PEPA components. We compare our newly proposed approach with previous work on component aggregation, where only a part of the component behaviour has been used as a criterion for aggregation. Our method requires fewer assumptions regarding the form of the components, and is therefore readily applicable to a larger family of PEPA models.     

Early use of PEPA dialyzer for light chains removal and for the recovery from myeloma cast nephropathy: A case report

Chemotherapy and extracorporeal treatment reduce serum free light chains (FLCs) allowing the recovery of acute kidney injury (AKI) caused by myeloma cast nephropathy (MCN). We report the first case of recovery from AKI in a patient with MCN who underwent the removal of FLCs using the PEPA filter, with an undisclosed cut‐off, combined with chemotherapy for multiple myeloma (MM).     

Novel PEPA-functionalized graphene oxide for fire safety enhancement of polypropylene

Polypropylene (PP) is a general-purpose plastic, but some applications are constrained by its high flammability. Thus, flame retardant PP is urgently demanded. In this article, intumescent flame retardant PP (IFRPP) composites with enhanced fire safety were prepared using 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphabicyclo [2.2.2] octane (PEPA) functionalized graphene oxide (PGO) as synergist. The PGO was prepared through a mild chemical reaction by the covalent attachment of a caged-structure organic compound, PEPA, onto GO nanosheets using toluene diisocynate (TDI) as the intermediary agent. The novel PEPA-functionalized graphene oxide not only improves the heat resistance of GO but also converts GO and PEPA from hydrophobic to hydrophilic materials, which leads to even distribution in PP. In our case, 7 wt% addition of PGO as one of the fillers for IFRPP composites significantly reduces its inflammability and fire hazards when compared with PEPA, by the improvement of first release rate peak (PHRR), total heat release, first smoke release rate peak (PSRR) and total smoke release, suggesting its great potential as the IFR synergist in industry. The reason is mainly attributed to the barrier effect of the unburned graphene sheets, which protects by the decomposition products of PEPA and TDI, promotes the formation of graphitized carbon and inhibits the heat and gas release.     

PEPA Queues: Capturing Customer Behaviour in Queueing Networks

Queueing network formalisms are very good at describing the spatial movement of customers, but typically poor at describing how customers change as they move through the network. We present the PEPA Queues formalism, which uses the popular stochastic process algebra PEPA to represent the individual state and behaviour of customers and servers. We offer a formal semantics for PEPA Queues, plus a direct translation to PEPA, allowing access to the existing tools for analysing PEPA models. Finally, we use the ipc/DNAmaca tool-chain to provide passage-time analysis of a dual Web server example.     

Blood compatibility and filtration characteristics of a newly developed polyester polymer alloy membrane

Background: Many synthetic polymeric membranes have been widely used for blood purification therapies for removing larger solutes and for better blood compatibility. Methods: Five different filters with polyester polymer alloy (PEPA) membrane (Nikkiso) that included polyvinylpyrrolidone (PVP), that is, standard‐pore‐size FLX (PEPA with PVP(–)), standard‐pore‐size FDX (PEPA with PVP(+)), new FDX (PEPA with PVP(++)), larger‐pore‐size FDY (PEPA with PVP(+)), and new FDY (PEPA with PVP(++)), were evaluated in terms of in vivo blood compatibility and aqueous in vitro sieving coefficient (s.c.) for albumin. Results: FDY showed excellent small changes in C3a concentration during the treatment right after switching from polysulfone membrane, leaving no significant changes in other blood‐compatible indices. New FDY, in contrast, showed less biocompatible characteristics in terms of C3a, which may be caused by increased use of PVP. FLX (no PVP) showed the highest s.c. for albumin. With a hydrophilic agent (PVP), the s.c. was greatly reduced in FDX. By enlarging the pore diameter in FDY, the s.c. increased in accordance with the enlargement. Generally speaking, polysulfone filters with PVP(+++) reach the peak s.c. value approximately 10 min after starting the experiment. The s.c. of the PEPA membrane with no or small amount of PVP, which showed excellent blood compatibility, never showed peaks, whereas the peak s.c. values were found in new PEPA with increased amount of PVP that showed higher C3a changes. Conclusions: The separation characteristics of aqueous albumin may be related to its blood compatibility.