Thermal stability of NO 2 ⋅ and NO⋅ radicals formed in an Al23 catalyst during its preparation from a nitrate precursor

During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH₄OH base, NO ₂ ^⋅ radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C, the NO ₂ ^⋅ was reduced to give NO^⋅ and O^- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

ESTIMATION FOR NONNEGATIVE AUTOREGRESSIVE PROCESSES WITH AN UNKNOWN LOCATION PARAMETER

Abstract. Consider an AR(1) process given by X ^t=γ+ø X _t+ Z _t≥ 1. where 0 ≤γ, 0 ≤ø 1 are unknown parameters and the innovations Z _t, ≥ 1, are independently and identically distributed positive random variables. We propose estimates of (γø) which are obtained as the solution to a linear programming problem and establish their strong consistency. When the Z _ts have the exponential distribution. our estimate becomes the conditional maximum likelihood estimate given X ₀. Under the assumption of regular variation of the innovation distribution at its left and right endpoints (assumed to be 0 and ∝ respectively), we establish asymptotic limit laws for the estimates. Consistent estimators for a class of moving-average processes with heavy-tailed innovation distribution are also presented.     

Orientation and relaxation in uniaxially-stretched poly(2,6-dimethyl 1,4-phenylene oxide) — atactic polystyrene blends

Infra-red measurements of the dichroic ratio of atactic polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide) absorption bands provide a valuable method for the determination of orientation as well as relaxation of chains of both polymers during stretching of their compatible blends. Influence of strain rate, temperature of stretching, and molecular weight of the polymers on orientation of both polymer chains in blends containing up to 35% PPO has been studied. Orientation relaxation for both polymers has been analysed using Lodge's constitutive equation. Master curves have been obtained for PPO and PS in the blends at a reference temperature T₀ = T_g + 10°C. Results are interpreted in terms of an hindrance of relaxation of PS chains induced by interaction with a highly-oriented PPO network which slowly relaxes.     

艾立许混捏机在炭阳极生产中的应用

在预焙阳极生产中，卧式连续混捏机曾经大量应用，使用效果良好。目前艾立许混捏机以其简化机械设计、降低维修及操作成本等许多独特的优点，在铝电解炭阳极生产中也得到大量应用。通过对原有卧式混捏机设备增加艾立许冷却系统，可以使两种设备得到最佳组合，可提高阳极质量，取得良好效益。     

基于转轮换型的水轮机增容改造及数值模拟

从青海铁吾电站HL160-WJ-84水轮机运行中的实际问题出发,在明确了水轮机改造的方向和目标后,对新旧型谱系列模型转轮的性能进行了对比分析。基于对比结果,初选出了D06A转轮用于技术改造试验。对改造前后的水轮机全流道进行三维湍流数值计算,给出了水轮机改造前后的水动力学特性差异。同时,对改造前后的水轮机蜗壳、转轮叶片的流态分布状况进行了分析比较,对改造后的水轮机整体水力性能进行预估。分析认为,对于小型卧式HL160机组而言,更换转轮后还需对上冠泄水孔实施改造,以防止对流场造成扰动,降低机组的效率。     

陡坡傍山双层行车结构体系受力特性分析

以山区常见的40°陡坡地形条件下修建4车道高等级公路为例,提出一种环境和经济效益俱佳的新型"桩-锚-框架"复合双层行车结构体系,该体系具有双层行车、山体锚固、边坡支挡和路面支撑等众多功能。采用ABAQUS大型有限元分析软件对该双层行车结构体系进行三维数值模拟,探究其受力特性。研究结果表明:该结构体系具有良好的承载能力和静力稳定性,对陡坡山体有较强的支护作用;支撑柱和横梁的相交位置是整个结构体系应力较集中的部位,应适当增加该节点的配筋量以提高强度、改善节点受力情况。     

厄瓜多尔干旱情况初探及对策分析

厄瓜多尔水资源极其丰沛,但时空分布不均,旱灾时有发生。在分析厄瓜多尔水资源概况和历史主要旱灾情况的基础上,利用Arc GIS软件绘制了干旱湿润指数等值面图,对厄瓜多尔进行干旱等级划分、易旱季节区分、干旱损失分析等。根据厄瓜多尔的干旱情况、目前水资源条件及形势,提出应对干旱的工程与非工程措施。相关经验可供类似条件的国家和地区借鉴。     

碘量法测定二氧化氯要点分析

二氧化氯是一种安全高效的消毒剂。采用国家行业标准中有效二氧化氯含量的测定方法的测量结果差异较大，用碘量法测定稳定态二氧化氯溶液中的有效二氧化氯含量时，活化反应的速度对测定有效二氧化氯的含量有一定影响。通过条件实验确定了碘量法测定有效二氧化氯含量的最佳测试条件，即：活化时间13min，盐酸稀释至与水体积比1：4，参考电压140V，可确保实验结果的平行性和再现性。     

Pozzolanic properties of reject fly ash in blended cement pastes

Low-grade fly ash (reject fly ash, r-FA), a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process, has remained unused due to its high carbon content and large particle size. But it may be used in certain areas, such as in solidification and stabilization processes of hazardous waste and materials for road base or subbase construction, which require relatively lower strength and reactivity. It is therefore necessary to extend research on the properties of r-FA and explore its possible applications. This paper presents experimental results of a study on the mechanical and hydration properties of cementitious materials prepared by blending r-FA with ordinary Portland cement (OPC). Parallel mixes were also prepared with the good ash [i.e., classified fine fly ash (f-FA)] for comparison. Selective chemical activators were added to the mix to study the effects of the activators on the properties of the blend system. The results show that r-FA generally has a lower rate of hydration than f-FA particularly at the early stage of hydration. Adding Ca(OH)₂ alone almost had no effect on accelerating the hydration of r-FA. But adding a small quantity of Na₂SO₄ or K₂SO₄ together with Ca(OH)₂ significantly accelerated the hydration reaction. The results of the compressive strength measurement correlated nicely with the degree of hydration results. It was also found that water-to-binder ratio (w/b) was an important factor in affecting the strength development and the hydration degree of r-FA pastes.