Phenol novolac/poly(4- hydroxyphenylmaleimide) blend hardeners for DGEBA-type epoxy resin

Phenol novolac/poly (4-hydroxyphenylmaleimide) (PHPMI) blends were used as an epoxy resin hardener. The curing behavior of the above system and the thermal and mechanical properties of the cured epoxy resin were studied. It was not necessary to use a curing accelerator for this system, because PHPMI caused acceleration of the curing reaction. The curing mechanism of this system was investigated by using model compounds. Test pieces from the neat resins and the glass fiber reinforced resins were evaluated in terms of thermal and mechanical properties, respectively. It was found that heat resistance and mechanical properties were improved by increasing the amount of PHPMI in the hardener.     

自韧Si3N4陶瓷的显微结构及其性能研究

利用热压的方法制得室温断裂韧性和抗弯强度分别为１１．２ＭＰａ·ｍ￣（１／２）、８２３ＭＰａ，高温（１３５０℃）断裂韧性和抗弯强度分别为２３．９ＭＰａ·ｍ￣（１／２）、６３０ＭＰａ的自韧Ｓｉ＿３Ｎ＿４陶瓷。研究了显微结构和力学性能之间的关系。结果表明：玻璃相的含量、β－Ｓｉ＿３Ｎ＿４的长径比等对性能有重要影响。分析了自韧Ｓｉ＿３Ｎ＿４陶瓷的增韧机理，通过ＳＥＭ明显观察到Ｓｉ＿３Ｎ＿４中存在裂纹偏转、分支和β－Ｓｉ＿３Ｎ＿４拔出现象。     

超低膨胀陶瓷K_（2x）Ba_（1－x）Zr_4（PO_4）_6系统的X射线衍射

用高温Ｘ射线衍射方法对磷酸锆钡钾系统陶瓷材料的各向异性热膨胀作了研究．对七个组份试样的７７套高温Ｘ射线衍射图作了仔细的指标化和精密点阵常数测定．点阵常数随温度作非线性变化·对Ｋ_２ｘＢａ_１－ｘＺｒ_４（ＰＯ_４）_６的不同组份不同温度（３００～１３００Ｋ）的热膨胀系数。α_ａ、α_ｃ、　作了测定·该系统零膨胀陶瓷的组份为Ｋ_１．１６Ｂａ_０．４２Ｚｒ_４（ＰＯ_４）_６（ｘ＝０．５８）     

通讯网的演进

在光纤高速传输技术、光交换与智能光网等与宽带接入、多媒体、3G等网络应用技术的推动下，建设基于IPv6协议的IP基础电信网成为可能。现在IP网正在朝着有序的、可管理的、有QoS保障的、可以支持各类业务的综合业务基础网演进。电信网也正在从网络接入层上、从长途网络层面上、从本地网络层面上、从固定网向含3G在内的移动网络等方面向支持IP技术及其综合业务的方面全面推进。     

Ischemia‐reperfusion injury. A phenomenon,that also occurs in the bone

Ischemia‐reperfusion injury of the bone occurs due to traumatic and non‐traumatic alterations affecting blood supply to the bone. It is likely to occur also upon insertion of an implant. Ischemia‐reperfusion injury of the bone has been studied by interruption of blood supply in situ, in limb replantation/transplantation models, in revascularized bone grafts and non‐vascularized bone fragments, as well as in isolated cultured cells. All cells of the bone are affected, including osteoblasts, osteocytes, osteoclasts, chondrocytes, and bone marrow cells. Critical ischemia times for induction of bone cell death, either in the ischemic period or following reperfusion, are in the range of 3 to 7 h. These critical ischemia times are significantly increased by decreasing the temperature from 37 °C to 0–4 °C. Anoxia is the most likely trigger of cell injury in the ischemic phase. In the reperfusion phase, reactive oxygen species are decisively involved in the injurious process. In general, however, the available information on the mechanism of ischemia‐reperfusion injury of the bone is relatively sparse. On the other hand, there are clear similarities to the mechanisms of ischemia‐reperfusion injury known from other organs, and there is a clear potential for protection against ischemia‐reperfusion injury of the bone.     

锗酸铋（Bi4Ge3O12）单晶热物理性质的研究

本文用不同的测试技术和方法测定了锗酸铋(BGO)单晶的比热(300～800K)热膨胀系数(100～1100K)和导温系数(140～700K),进而导出了 BGO 单晶不同温度下的导热系数、定容比热、德拜温度和格虑内森数。本文还对 BGO 单晶热物理性质的变化规律作了理论解释。     

Effects of calcination temperature on phase and microstructure evolution of BaTi4O9 powders

Calcining of the mixture of BaCO₃ and TiO₂ with a ratio 1:4 at different temperatures was carried out to synthesize BaTi₄O₉ powders. Phase evolution of the samples was studied using the differential thermal analysis (DTA) and X-ray diffractometry (XRD). Both techniques confirmed that the formation of BaTi₄O₉ started around 1000 °C. The XRD peaks showed that BaTi₄O₉ was most pronounced at 1250 °C. X-ray line broadening methods were employed to study the variation of particle size and microstrain of the BaTi₄O₉ powders. The Voigt function in a single line and the pseudo-Voigt function in the variance methods were used in our case. We found that both functions resulted in the same trends, i.e., the particle size increased with the temperature with the biggest size of 180 and 160 nm, whilst the microstrain yielded the opposite trend with the lowest values of 6.2 × 10^–3 and 1.1 × 10^–3. The scanning electron microscopy (SEM) study revealed the size of the large particles formed, due to agglomeration, to be about 0.5–1.9 μm. Furthermore, it was shown that irregular shapes of BaTi₄O₉ powders necked to each other appeared at 1000 °C and grew into ellipse and rod shapes at 1250 °C. Electronic Publication     

无线局域网中基于RC4的加密算法的分析与改进

分析RC4加密算法自身的缺陷和无线局域网WEP协议对RC4的误用,介绍了TKIP协议在安全性方面的改进。     

Comparative hall measurements on wet- and dry-oxidized 4H-SiC MOSFETs

Hall measurements have been used to compare the properties of 4H-SiC inversion-mode MOSFETs with “wet” and “dry” gate oxides. While the field-effect mobilities were approximately 3–5 cm²/Vs, the Hall mobilities in 4H-SiC MOSFETs in the wet and dry oxide samples were approximately 70–80 cm²/Vs. The dry-oxidized metal oxide semiconductor field effect transistors (MOSFETs) had a higher transconductance, improved threshold voltage, improved subthreshold slope, and a higher inversion carrier concentration compared to the wet-oxidized MOSFETs. The difference in characteristics between the wet- and the dry-oxidized MOSFETs is attributed to the larger fixed oxide charge in the dry oxide sample and a higher interface trap density in the wet oxide sample.