掺Li_2O–B_2O_3–SiO_2玻璃低温烧结MgTiO_3–CaTiO_3陶瓷及其微波介电性能

研究了Li_2O–B_2O_3–SiO_2玻璃(LBS)对MgTiO_3–CaTiO_3(MCT)介质陶瓷烧结特性、相组成和介电性能的影响,分析了MCT陶瓷与银电极的共烧行为。结果表明通过液相烧结,LBS能有效降低MCT烧结温度至890℃。X射线衍射结果显示有Li_2MgTi_3O_8、硼钛镁石以及Li_2TiSiO_5等新相生成。随着LBS添加量的增大,陶瓷致密化温度和饱和体积密度降低,介电常数εr、品质因数与谐振频率乘积Q×f也呈现下降趋势,频率温度系数τf向负值方向移动。添加质量分数为20%的LBS的0.97MgTiO3–0.03CaTiO3陶瓷在890℃烧结4h,获得最佳性能εr=16.4,Q×f=11640GHz,τf=–1.5×10–6/℃。陶瓷与银电极共烧界面结合状况良好,无明显扩散。该材料可用于制造片式多层微波器件。     

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

The effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (t_b) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006     

High PVC film‐forming composite latex particles via miniemulsification,part 1: Preparation

Miniemulsification technology was used to encapsulate TiO₂ particles inside a styrene/n‐butyl acrylate copolymer with high loading levels (11 to 70% PVC (pigment volume concentration)). In this approach, a St/BA copolymer dissolved in toluene in the presence of a costabilizer (hexadecane) was mixed with a dispersion of TiO₂ particles in toluene and sonified, and then emulsified in an aqueous surfactant solution by sonification. The effect of sonification time on both the dispersibility of the TiO₂ particles in the presence of the copolymer and hexadecane and on the encapsulated particle size was investigated. Particle size analysis by dynamic light scattering showed that these composite latexes are quite stable. It was also found that as the TiO₂ loading increased from 11 to 43% PVC, the particle size of the TiO₂ dispersion decreased while the polymer‐encapsulated TiO₂ particle size increased. The effect of surfactant concentration (sodium lauryl sulfate, SLS) on the encapsulated particle size was investigated using four different SLS concentrations in the 11% PVC system. The results showed that as the SLS concentration increased the particle size decreased, as expected. Also it was found that the minimum surfactant concentration that gives stable encapsulated TiO₂ particles is above 10 mM SLS. The role of HD in the recipe was studied for an artificial latex containing no TiO₂ and one prepared at 11% PVC, in terms of particle size before and after solvent stripping, and its effect on the T_g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4504–4516, 2006     

The deposition of coke from methane on a Ni/MgAl2O4 catalyst

Temperature-programmed reaction techniques and Raman spectroscopy were used to characterize coke species deposited on a 5% Ni/MgAl₂O₄ catalyst for dry reforming of methane. The CH₄ temperature-programmed decomposition profiles showed that the ignited decomposition temperatures of CH₄ increased from 273 to 378 °C when MgAl₂O₄ replaced the catalyst support γ-Al₂O₃. The temperature-programmed oxidation, temperature-programmed hydrogenation and temperature-programmed CO₂ reaction profiles showed that there were three carbon species (i.e. C_α, C_β and C_γ) on the catalyst surface. Raman spectroscopy showed that C_γ was graphite-like carbon species, which was responsible for catalyst deactivation. The C_γ species was the most inactive species toward H₂ and O₂, while it was unexpectedly more active toward CO₂. The unique reactivity of CO₂ with different coke specie could be ascribed to the carbonate, bidentate and formate species formation on MgAl₂O₄ surface. These surface species enhanced the oxidation of C_γ species and thus contributed to the high stability of Ni/MgAl₂O₄ catalyst.     

相控阵雷达天线阵面记录回放系统

相控阵雷达广泛应用,其天线阵面对记录回放系统的数据速率要求提升。针对两种传统记录回放系统架构的不足,结合其优点,设计并实现了一种新型的基于FPGA的记录回放系统。该系统设计为板卡的形式,FPGA实现对硬盘的读写操作,采用自定义的文件系统对数据进行管理。经过测试,系统记录速度可以达到292 MB/s,回放速率为340 MB/s。实验结果表明,该记录回放系统性能稳定,通用性好,存储速率满足要求。     

Characteristics of electrical responsive chitosan/polyallylamine interpenetrating polymer network hydrogel

An interpenetrating polymer network (IPN) hydrogel composed of chitosan and polyallylamine exhibited electric‐sensitive behavior. The chitosan/polyallylamine IPN hydrogel was synthesized by radical polymerization using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPAP) and methylene bisacrylicamide (MBAAm) as initiator and crosslinker, respectively. The swelling behavior of the IPN was studied by immersion of the gel samples in aqueous NaCl solutions at various concentrations and pHs. The swelling ratio decreased with increasing concentration and pH of electrolyte solution. The stimuli response of the IPN hydrogel in electric fields was also investigated. When a swollen the IPN was placed between a pair of electrodes, the IPN exhibited bending behavior in response to the applied electric field. The IPN also showed stepwise bending behavior depending on the electric stimulus. In addition, thermal properties of the IPN were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2290–2295, 2002     

A genetic tango attack against the David–Prasad RFID ultra‐lightweight authentication protocol

Radio frequency identification (RFID) is a powerful technology that enables wireless information storage and control in an economical way. These properties have generated a wide range of applications in different areas. Due to economic and technological constrains, RFID devices are seriously limited, having small or even tiny computational capabilities. This issue is particularly challenging from the security point of view. Security protocols in RFID environments have to deal with strong computational limitations, and classical protocols cannot be used in this context. There have been several attempts to overcome these limitations in the form of new lightweight security protocols designed to be used in very constrained (sometimes called ultra‐lightweight) RFID environments. One of these proposals is the David–Prasad ultra‐lightweight authentication protocol. This protocol was successfully attacked using a cryptanalysis technique named Tango attack. The capacity of the attack depends on a set of boolean approximations. In this paper, we present an enhanced version of the Tango attack, named Genetic Tango attack, that uses Genetic Programming to design those approximations, easing the generation of automatic cryptanalysis and improving its power compared to a manually designed attack. Experimental results are given to illustrate the effectiveness of this new attack.     

On reactive routing protocols in ZigBee wireless sensor networks

ZigBee is the primary standard solution for wireless sensor networks, implementing the Ad hoc On‐Demand Distance Vector (AODV) protocol in the network layer and supported by the standard IEEE 802.15.4. This study is focused on mesh topologies and the critical problems encountered when AODV is executed in conjunction with the Carrier Sense Multiple Access with Collision Avoidance protocol. These problems are mainly related to the packet overhead required to carry out route creation. To perform preliminary experiments to be able to implement AODV in a real network, a new metric is proposed herein. This metric uses fuzzy logic to help in the decision‐making process. The objective of the fuzzy routine is to determine, during the route‐discovery process, the best node to forward request/reply packets, with the aim of reducing packet overhead and energy consumption. Moreover, minor changes are also added to the discovery procedure of AODV to improve the performance of the route‐creation process. This intelligent version of AODV has provided promising experimental results, greatly reducing the number of packets required, with the consequent energy saving while selecting the best nodes to be part of the routes.     

Determinants of users’ continuance of social networking sites: A self-regulation perspective

Social networking sites (SNS) have transformed how individuals interact, build and maintain social relationships. We proposed a research model on the determinants of user continuance using Bagozzi's framework of self-regulation as the theoretical foundation. Following the process of appraisal → emotional reactions → coping responses, we developed the model by leveraging findings from social presence and IS continuance research. Based on survey data from Facebook users, we found that appraisal factors (pleasure, awareness, connectedness, and system quality) were strong determinants of emotional reaction (user satisfaction and sense of belonging). User satisfaction and sense of belonging together positively influenced continuance intention.     

NCO含量对聚氨酯-丙烯酸酯复合乳液性能的影响

以甲苯二异氰酸酯(TDI-80)、聚醚二元醇(N210)、二羟甲基丙酸(DMPA)和甲基丙烯酸甲酯(MMA)为主要原料，采用原位乳液聚合法，合成聚氨酯-丙烯酸酯(PUA)复合乳液。在保证DMPA含量、中和度等不变的情况下，研究了NCO／OH物质的量之比对乳液的性能及外观的影响。