IPv6在QoS上的三项重要改进

本文主要分析了IPv6相对于IPv4在QoS上所做的基本报头、ICMP控制机制及基本报头中的QoS元素三项改进,从而为有效支持QoS提供理论支持。     

提高定点精度的FPGA信号处理算法

为了满足速度、功耗等诸多限制的要求,数字信号处理算法常使用FPGA实现。而实现时由于硬件特点,通常将浮点运算转换成定点运算,但定点转换设计流程复杂、周期长,且存在数据范围和精度之间的矛盾。利用浮点数的优点,本文改进了基于FPGA的定点数的基本运算规则,有效解决了上述矛盾。本文详细论述了实现移位、加/减、乘、除基本运算模块的方法和步骤,最后以FIR数字滤波器为设计实例。仿真结果表明:改进的定点数算法比定点运算误差小、精度高、数据范围宽,能有效地防止溢出。     

双参数Bézier曲线的升二次扩展

本文以二次Bernstein基函数为例,首次提出了含双参数基函数的新扩展——αβQ—Bern-stein基函数,此类基函数具有新的特点,即基函数的扩展次数一次性升高两次,且包含了二次多项式和带一个参数的三次多项式基函数的所有性质。基于这组基函数定义了αβQ—Bézier曲线,该曲线也含有参数,具有形状可调性,当α与β取某些值时曲线能达到C4连续或在某个端点处C0连续。最后与含两个参数的升一次Bézier曲线进行比较,该曲线具有调节范围广、灵活性更强的优势。     

阻燃型氢氧化镁制备及其影响因素探讨

以七水硫酸镁为原料、氨水为沉淀剂、选择适宜的表面活性剂。以样品XRD图中（001）面与（101）面衍射峰的相对强弱为考察指标，通过单因素实验，分别考察了反应温度、恒温反应时间、陈化时间、表面活性剂用量及氨镁摩尔比等因素对氢氧化镁样品XRD图中（001）面与（101）面衍射峰相对强弱的影响。实验结果表明，制备阻燃氩氧化镁较适宜的工艺条件为：反应温度40℃、恒温反应时间40min、陈化时间120min、表面活性剂A体积用量4ml、氨镁摩尔比6：1.     

Preparation of micro-arc oxidation coatings on magnesium alloy and its thermal shock resistance property

1. Introduction Due to their high specific strength, good electro-magnetic shielding characteristics, high damping characteristics, good cast ability, and excellent pol-ishing capability, magnesium alloys are extensively used in aeronautical, automobile, and electro- communication industries [1-3]. But magnesium has some disadvantages, such as low chemical stability, high negative electric potential, and low hardness, so it is necessary to use surface disposal to accommo-date the demand for re…     

Mg-Nd-Zn-Zr稀土镁合金的热变形行为

采用GLEEBLE-1500热模拟机对Mg-Nd-Zn-Zr稀土镁合金在温度为250～450.℃、应变速率为0.002～0.100.s-1、最大变形程度为60%的条件下, 进行高温压缩模拟实验研究. 分析了实验合金在高温变形时的流变应力和应变速率及变形温度之间的关系, 计算了变形激活能和应力指数, 并研究了在热压缩过程中组织的变化, 为确定该稀土镁合金的挤压温度提供了实验依据. 结果表明: 合金的峰值流变应力随应变速率的增大而增加, 随温度的升高而降低; 合金的变形激活能在300～400.℃内变化不大, 而在400～450.℃时增加很大; 根据实验分析认为该稀土镁合金挤压温度定在350～400.℃左右为宜; 在350.℃左右顺利挤出的实验合金有很好的力学性能: σb=275.5.MPa, δ=13.5%.     

新型铸造镁合金开发现状

总结了近年来镁合金在高温抗蠕变、高韧性、高强度、高耐蚀性、降低成本和改善工艺性六大热点研究方向上取得的典型研究成果，重点阐述了对高温抗蠕变铸造镁合金的研究。并从热力学角度分析了镁合金中可能出现的各相对镁合金高温蠕变过程的影响，叙述了Mg-Al、Mg-Zn和Mg-RE系耐热合金的最新发明。     

分流挤压镁合金管材工艺研究

用分流挤压方法可生产挤压比不大于68，壁厚不小于1．5mm的非薄壁镁合金管材，其表面基本上无烧损、无横裂纹等缺陷。主要工艺参数：挤压筒温度250-350℃，镁棒温度320-380℃，模具预热温度300-380℃。模具及其内残余镁合金重复加热可保证模具多次使用，不用清洗。     

Calcium carbonate and ammonium polyphosphate flame retardant additives formulated to protect ethylene vinyl acetate copolymer against fire: Hydrated or carbonated calcium?

In this study, the effect of the chemical nature of different calcium (Ca)-based minerals as flame retardant additives in combination with ammonium polyphosphate (APP), in 1:1 proportions, on the flame retardancy behavior and performance of ethylene vinyl acetate copolymer was discussed. Combining APP with partly and completely hydrated calcium oxide led to superior flame-retardant function detected in mass loss calorimeter measurements with respect to the corresponding system containing carbonated calcium. This privileged character was attributed to the higher reactivity of hydrated Ca-based fillers toward APP in comparison with Ca carbonate, which induced the formation of an intumescent residue. The difference between reactivity potential of hydrated and dry Ca was demonstrated by the newly formed thermally stable species, and further evidenced by thermogravimetric analysis performed on APP/fillers blends. Moreover, the presence of more crystalline domains in the Ca/phosphorus-based compounds was evidenced by XRD analysis of the mass loss calorimeter test residues. The results of this work highlight the role of blend additive systems on the performance of flame retardancy of polymer materials.     

Thermal cross-linking and anti-meltdrop properties of copolyester containing phosphorus/magnesium salt composites by in situ polymerization

Polyester is widely used in household products because of its good mechanical properties and wears resistance, but polyester is easy to ignite and inclined to produce droplet, so its application range is limited. The cross-linkable magnesium hydroxide nanoparticles were incorporated into flame-retardant polyester, which enables the phosphorus-containing copolyester with thermal cross-linking and anti-meltdrop properties. The nanoparticles were achieved by in situ polymerization and acted as a nucleating agent for improving the crystalline properties of the copolyester. Furthermore, the nanoparticles also enhanced anti-meltdrop properties and reduced the heat and gas release during the combustion process of the copolyester. The maximum heat release rate and total smoke release reduced by 39.8% and 74.4% compared with pure polyester. Specifically, the combustion products of the nanoparticles and phosphorus flame retardant could act a barrier role by covering the carbon layer to isolate air and heat, thereby resulting in excellent anti-meltdrop properties. The simple modification method reported here realizes the collaborative modification of flame retardant and anti-meltdrop properties of phosphorous flame-retardant copolyesters by thermal cross-linking.