基于反克隆机制的WSN区域密钥分发

针对无线传感网安全管理领域中存在的密钥生成困难、节点抗俘性能较差等不足,提出了一种基于反克隆机制的WSN区域密钥分发算法。首先,基于区域成型存在的簇头-簇节点的分层特性,采用反克隆机制进行节点层次认证,引入正交机制进行节点密钥分发,降低因簇头-簇成员节点信息交互不畅而导致的安全抖动风险。随后,采取密文非对称传输方式进行密钥冲激响应,通过逆向分发进一步降低密钥被破解的概率,减少安全确认过程中存在的信令频繁收发现象。仿真结果表明：与当前常用的WSN安全领域常用的基于多项式和矩阵的无线传感器网络密钥管理安全方案算法(Polynomial and Matrix Based Key Management Security Scheme in Wireless Sensor Networks, P-MB算法)和基于块LU分解的无线传感器网络密钥预分配算法(Key Pre-distribution Approach Using Block LU Decomposition in Wireless Sensor Network, PD-BLU算法)相比,本算法可显著降低节点被俘获的概率,减少网络信令传...     

User location privacy protection mechanism for location-based services

With the rapid development of the Internet of Things (IoT), Location-Based Services (LBS) are becoming more and more popular. However, for the users being served, how to protect their location privacy has become a growing concern. This has led to great difficulty in establishing trust between the users and the service providers, hindering the development of LBS for more comprehensive functions. In this paper, we first establish a strong identity verification mechanism to ensure the authentication security of the system and then design a new location privacy protection mechanism based on the privacy proximity test problem. This mechanism not only guarantees the confidentiality of the user’s information during the subsequent information interaction and dynamic data transmission, but also meets the service provider’s requirements for related data.     

熔融燃烧法制备四针状纳米氧化锌

将工业纯锌加热熔化后在氧乙炔火焰场中燃烧并冷凝制得四针状纳米ZnO.经XRD分析产物为ZnO无其它物相存在,场发射扫描电镜及透射电镜分析发现产物基本是四针状的纳米ZnO,针脚长度约100～150nm,直径为20～30nm.产物的形貌与收集条件有密切的关系,有水冷却的收集室壁的产物在针脚长度方向上形成台阶,而在燃烧室高温区停留时间过长则会导致产物尺寸长大.最后对用熔融燃烧法制备四针状纳米ZnO的生长过程和机理进行了分析.     

富氧煤粉气流着火机理的实验研究

针对环境氧浓度发生变化时,煤粉气流的反应动力学级数和机理都会发生变化的情况,采用一维火焰炉对神木烟煤在富氧条件下的着火机理进行了实验研究.结果表明:采用着火时烟气中CO和CO2体积分数的变化规律来判断煤粉气流的着火是可行的;当环境中氧气体积分数从21%升高到40%时,神木烟煤的着火完成了从均相着火向多相着火的转变,同时随着着火温度的降低,着火时刻烟气中热解产物的含量迅速降低.     

脱硫型水煤浆燃烧脱硫的机理研究

脱硫型水煤浆燃烧具有较高的脱硫率，为深入研究其机理，采用Ｘ射线衍射仪等手段，结合水煤浆燃烧特点，分析了整个脱硫过程．特别对于水煤浆燃烧脱硫优越于煤粉的原因作了解释，提出脱硫型水煤浆具有较高脱硫率的机理在于：耐高温脱硫产物３ＣａＯ３Ａｌ２Ｏ３Ｃａ－ＳＯ４的形成、增湿活化作用以及较低的燃烧温度     

Transition metal atom doped C2N as catalyst for the oxygen reduction reaction: A density functional theory study

The catalytic mechanism and activity of transition metal atom doped C₂N (M-C₂N, M = Fe, Co, Ni, and Cu) for the oxygen reduction reaction (ORR) are investigated in detail by density functional theory method. All the screened M-C₂N are thermodynamically stable based on the binding energy calculations. The adsorption energy results indicate that the adsorption strength of O₂ and ORR intermediates are decreased in the order of Fe-C₂N ˃ Co-C₂N ˃ Ni-C₂N ˃ Cu-C₂N, in which the adsorption energy values on Cu-C₂N are most close to those on the Pt(111). Based on the relative energy diagram of ORR, the energetically favorable pathway on Fe-C₂N and Co-C₂N is direct 4e⁻ mechanism, in which the O–O bond is directly dissociated after the second electron transfer. While for Ni-C₂N and Cu-C₂N, the most favorable pathway is indirect 4e⁻ mechanism, in which the H₂O₂ is formed as the intermediate product. For all studied M-C₂N, the Ni-C₂N and Cu-C₂N hold better catalytic activity, which could attribute to the contribution of metal atom and part of its activated nitrogen atoms.     

太阳能吸附制冷用复合吸附剂制备及其吸附机理探讨

以乙醇为吸附质，选取13X分子筛、凹凸楱土和氯化锶等为主要吸附材料．通过混合法制备了一系列有着优良吸附能的复合吸附剂。测定了乙醇在主要吸附材料和自制复合吸附剂上的吸附量，用TG-DTA法对主要吸附材料的热稳定性和自制吸附剂DTA脱附乙醇峰端温度进仃了分析.对吸附剂原料复合比例和扩孔剂种类等制备条件进行了实验研究。结果表明：自制复合吸附剂比单一吸附材料对乙醇确着更大的吸附能力；DTA分析的脱乙醇峰端温度明显低于单一吸附材料；加入扩孔剂E1或E2，可增加自制复合吸附剂孔容和孔径，改善其吸附性能；自制复合吸附剂对乙醇的吸附量显著高于活性炭。其中，M4-0003和M1-0001复合吸附剂对乙醇的平衡吸附量约为活性炭的2．5～4倍；M1-0001—乙醇工质对的吸附制冷量是活性炭—乙醇的2～6倍。对吸附剂复合的机理初步探讨表明：增加复合吸附剂弱吸附中心数，可降低其脱附温度。     

Ammonia chemistry below 1400 K under fuel-rich conditions in a flow reactor

The oxidation of NH₃ under fuel-rich conditions and moderate temperatures has been studied in terms of a chemical kinetic model over a wide range of conditions, based on the measurements of Hasegawa and Sato. Their experiments covered the fuels hydrogen (0 to 80 vol%), carbon monoxide (0 to 95 vol%), and methane (0 to 1.5 vol%), stoichiometries ranging from slightly lean to very fuel rich, temperatures from 300 to 1330 K, and NO levels from 0 to 2500 ppm. A detailed reaction mechanism has been established, based on earlier work on ammonia oxidation in flames and on selective noncatalytic reduction of NO by NH₃. The kinetic model reproduces the experimental trends qualitatively over the full range of conditions covered, and often the predictions are in quantitative agreement with the observations. Using reaction path analysis and sensitivity studies, the major reaction paths have been identified. The comparatively low temperatures in the present study, as well as the presence of NO, promote the reaction path NH₃→NH₂→N₂ (directly or via NNH), rather than the sequence NH₃→NH₂→NH→N important in flames. The major conversion of fuel-N species to N₂ occurs by reaction of amine radicals with NO, in particular NH₂+NO. In the presence of CH₄, NO is partly converted to cyanides by reaction with CH₃. The mechanism is recommended for modeling the reduction of NO by primary measures in the combustion of biomass, since it has been validated under conditions resembling the conversion of early nitrogenous volatile species in a staged combustion process. It is also appropriate for studies of NO formation in the combustion of gas from gasifying coal.     

Effects of isothermal treatment parameters on the microstructure of semisolid alloys

Cold-rolled 6061 aluminium alloys are used to prepare semisolid billets by recrystallisation and partial melting. The effects of isothermal treatment parameters on the microstructures were investigated. The results indicated that the high isothermal holding temperature increases the experimental liquid fraction, average grain size and shape factor. A long isothermal holding time also increases the experimental liquid fraction and improves the spheroidisation degree of solid grains, but the average grain size also increases. Moreover, when the isothermal holding time at high temperature is increased, the size of intragranular liquid droplets increases, but their quantity decreases. The optimal isothermal holding temperature and time during semisolid isothermal treatment were 635°C and 5?–?10?min, respectively.