Fabrication and characterization of graphene-reinforced waterborne polyurethane nanocomposite coatings by the sol–gel method

Functionalized graphene-reinforced polyurethane nanocomposite coatings were prepared using the sol–gel method. This method not only provides a “green” strategy for fabricating the graphene-based nanocomposites, but also realizes the covalent functionalization of graphene nanosheets with polymer matrix. The functionalization of graphene with conjugated organosilanes is favorable for improving mechanical and thermal properties of the nanocomposite coatings, which is mainly attributed to the homogeneous dispersion of functionalized graphene in the polymer matrix and strong interfacial interactions between the two components. A 71% increase in tensile strength and a 86% improvement of Young's modulus are observed by the addition of 2.0 wt.% of functionalized graphene. The experimentally determined Young's modulus corresponds well with the theoretical simulation under the hypothesis that the graphene sheets are randomly dispersed in the polymer matrix.     

Iron-montmorillonite and zinc borate as synergistic agents in flame-retardant glass fiber reinforced polyamide 6 composites in combination with melamine polyphosphate

This paper presents a preliminary investigation on the effects of organically modified iron-montmorillonite (Fe-OMT) and zinc borate (ZnB) on thermal degradation behaviors and flame retardancy of melamine polyphosphate (MPP) flame-retarded glass fiber reinforced polyamide 6 (GFPA6). The samples were characterized using limiting oxygen index (LOI), UL-94 tests, thermogravimetric analysis (TGA), Fourier transform infrared coupled with the thermogravimetric analyzer (TG-FTIR) and Microscale Combustion Calorimeter (MCC) measurements. The residue after LOI test was also analyzed by Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and Raman spectroscopy. A substitution of a certain fraction of MPP with ZnB or Fe-OMT can significantly improve the UL-94 rating of GFPA6/MPP composites from no rating to V0 rating, exhibiting excellent flame retardacny. Based on the investigations, different flame retardant mechanisms were proposed for the two effective flame-retardant formulations.     

基于分类树的OSEK/VDX操作系统一致性测试研究

在深入研究OSEK/VDX操作系统规范的基础上,提出了基于分类树的OSEK/VDX操作系统的一致性测试方法。该方法的核心思想首先是从OSEK规范抽取出测试目的,其次根据规范和测试目的构造分类树和划分分类树的输入域,再次为分类树添加生成规则和限制条件,最后借助CTE XL工具自动生成一致性测试用例。通过对MiniOSEK的一致性测试,验证了使用分类树方法进行OSEK/VDX操作系统一致性测试的有效性与正确性。     

无线传感网络一种能量有效的分布式数据交换协议

随着微处理技术与无线通讯技术的不断发展,无线传感网络的应用逐渐趋于多元化,新的需求不断涌现.例如,单兵作战系统中要求每个士兵都实时掌握其他士兵的位置信息,这称为数据交换问题,即All-to-all通讯模式.已有的研究主要考虑数据收集(All-to-One)和数据分发(One-to-All)这两个方面,这些协议直接用于面向多源多目的的数据交换问题则难以取得较理想的性能.因此,本文提出能量有效的分布式数据交换协议DDET,用于解决传感节点数据请求率不一致的数据交换问题.协议首先收集网络中传感节点的信息,对所有传感节点的本地数据请求率进行排序;其次,在每一轮中,选择数据请求率最大的节点加入到生成树中,使得网络的总能耗最小;最终,利用虚拟减枝法来确定深度最小生成树的树根,以减少网络能耗.实验结果表明,与性能较好的DEIST协议相比,DDRT至少将系统生命期延长了100%,并且节省了3%的系统总能耗.     

基于三线程保护和软件哨兵的防篡改技术

软件哨兵是一种动态防篡改技术,但是哨兵自身安全性无法保障,容易被绕过或移除。针对软件哨兵中存在的安全弊端,着重研究和实现了三线程结构和软件哨兵相结合的动态防篡改技术,利用改进的三线程结构来保护哨兵自身安全。相对于传统的三线程技术,改进后的三线程通过remote线程和watch线程之间的相互监视保护,显著改善了其保护力度,增加了黑客攻击软件哨兵的难度。实验结果表明,采用改进的三线程保护的软件哨兵,不仅能防止软件篡改攻击,还能有效抵抗对哨兵本身的攻击。     

一种MapReduce实时调度算法设计及实现

MapReduce是云计算中重要的批数据处理框架,多任务共享MapReduce机群并满足任务实时性要求是调度算法急需解决的问题。提出两阶段实时调度算法,将调度划分为任务间调度和任务内调度。对于任务间调度,使用抽样法和经验值法确定子任务执行时间,利用该参数建立资源分配模型,动态确定任务优先级进行调度;对于子任务使用延迟调度策略进行调度,保证计算的本地性。实验结果显示,两阶段实时调度算法相比公平调度算法和FIFO算法,在保证吞吐量的同时能够满足任务实时性要求。     

Automated verification of pointer programs in pointer logic

Reasoning about pointer programs is difficult and challenging, while their safety is critical in software engineering. Storeless semantics pioneered by Jonkers provides a method to reason about pointer programs. However, the representation of memory states in Jonkers’ model is costly and redundant. This paper presents a new framework under a more efficient storeless model for automatically verifying properties of pointer programs related to the correct use of dynamically allocated memory such as absence of null dereferences, absence of dangling dereferences, absence of memory leaks, and preservation of structural invariants. The introduced logic-Pointer Logic, is developed to achieve such goals. To demonstrate that Pointer Logic is a useful storeless approach to verification, the Schorr-Waite tree-traversal algorithm which is always considered as a key test for pointer formalizations was verified via our analysis. Moreover, an experimental tool-plcc was implemented to automatically verify a number of non-trivial pointer programs.     

无线传感器网络高覆盖、低延迟途中过滤方法研究

传感器节点可能被攻击者俘获用来发送大量虚假数据,从而耗尽整个网络的资源。途中过滤是应对此类攻击的有效方法。本文研究了途中过滤方法中经常被忽视的两项指标:覆盖性与实时性。本文提出了自适应的分组算法,提高了网络覆盖率;途中节点动态决定先转发后认证还是先认证后转发。如果网络中未发生虚假数据注入攻击,则途中节点首先转发数据报,然后进行验证,可以降低网络延迟;如果网络中发生虚假数据注入攻击,途中检测节点可以快速切换到先认证后转发模式,而其他节点仍然保持先转发后认证模式,提高了数据传输的实时性。我们将本方法与传统方法进行对比,显示本方法在付出有限代价的前提下能够提高覆盖率并降低系统延迟。     

处理指针相等关系不确定的指针逻辑

为类C小语言PointerC设计的指针逻辑是Hoare逻辑的一种扩展,可用来对指针程序进行精确的指针分析,以支持指针相等关系确定的程序的安全性验证.通过增加相等关系不确定的指针类型访问路径集合,可扩展这种指针逻辑,使得扩展后的指针逻辑可以应用于有向图等指针相等关系不确定的抽象数据结构上的指针程序性质　证明.     

一种链状数据结构细粒度自动加锁方法

细粒度锁在并行编程与并发软件设计中起着重要的作用.然而,细粒度锁对程序员具有较高的要求,通常在设计细粒度锁并发程序时会带来算法复杂,编程困难,程序易出错等问题.提出一种链状数据结构的细粒度加锁方法,并实现自动转换含有形状和共享标注的程序为细粒度锁代码的翻译器,为了使生成的代码具有无死锁,引入了一致性加锁协议,实验结果表明,基于本文方法能够自动为链状数据结构操作添加细粒度锁,生成的代码具有较高的并发性.