On technical change in the elasticities of resource inputs

This article analyses growth of an economy where the substitutability between non-renewable and renewable resource inputs changes over time. We allow for exogenous technical change in the elasticity of substitution (EoS) between these two types of resources as well as for biased factor-augmenting technical change. Our main results are: (1) sustained technical change in the EoS is enough to overcome resource constraints; (2) productivity-enhancing technical change is most beneficial when directed to the resource which is currently most important for production; (3) the speed of productivity-enhancing technical change is crucial for its usefulness to overcome resource constraints; (4) sustainability depends critically on the type of technical change.     

酵母菌与两种硫杆菌复合对污泥中三价铬的去除

研究了氧化亚铁硫杆菌LX5(Thiobacillus ferrooxidans LX5)、氧化硫硫杆菌TS6(Thiobacillus thiooxidans TS6)和耐酸性酵母菌R30(Rhodotorula sp.R30)对重金属铬(Cr³⁺)的耐受性.结果表明,700mg/L的Cr³⁺对硫杆菌LX5、TS6的生长和氧化活性影响不大,但Cr³⁺浓度大于500mg/L时明显抑制酵母菌R30的生长.酵母菌R30与硫杆菌LX5和TS6复合能明显加速污泥淋滤的进程,最佳复合比为酵母菌R30接种量2.0%,硫杆菌LX5和TS6接种量10%.分别用含酵母菌R30数量为10⁴个/mL和102个/mL的酸化污泥作接种物进行污泥淋滤,发现淋滤过程中pH值下降的速度没有明显差异,而在淋滤起始时添加2.0%的酵母菌R30,则淋滤反应提前36h结束.由此可见,在其它条件相同的污泥淋滤中,污泥中所含耐酸性酵母菌的数量是加快淋滤的关键.     

公路隧道坍塌灾害治理效果的GPR检测技术

以湖南省常吉高速公路度龙田隧道ZK 207+300~255坍塌地质灾害为例,详细地探讨了检测坍塌灾害治理效果的高精度地质雷达(GPR)检测技术。在综合分析和研究隧道坍塌灾害的基本情况及灾害治理措施的基础上,结合现场施工记录,采用GPR检测技术,准确地查清了塌方处理中注浆饱满度情况,检查了塌腔内是否仍存在危害隧道安全的空洞或松散体;同时,对塌方地段加密设置的钢拱架数量与间距也进行了准确的检测和判定。工程实践表明:结合隧道坍塌灾害相关资料及现场调查,GPR可以无损、快速、准确地检测隧道地质灾害治理效果和整治质量,为准确评价地质灾害治理效果提供科学依据,这对于减少工程隐患、确保工程质量、指导隧道施工具有重要的工程应用价值。     

Efficient purification of Al30 by organic complexation method

A method was developed for preparing high purity Al₃₀O₈(OH)₅₆(H₂O)₂₄^18 + (Al₃₀) through elimination of impurities by complexation. Polyaluminum chloride II (PAC₃₀) with Al_c content of 75% was adopted as the source of Al₃₀. The PAC₃₀ was prepared under conditions of total aluminum concentration 0.1?mol/L and OH^?/Al ratio 2.2 to obtain the highest content of Al₃₀. A precipitation/metathesis method, organic solvent precipitation method and organic complexation method were examined to separate and purify Al₃₀. It was found that only by the organic complexation method could high purity Al₃₀ products be obtained in large yield economically. In the experiments, benzoic acid was used as the coordinating reagent to decompose the main impurity AlO₄Al₁₂(OH)₂₄(H₂O)₁₂^7 + (Al₁₃), and the Al₃₀ product could be obtained by precipitation and metathesis operations. It was noteworthy that the decomposition of impurities by benzoic acid could be completed in 2?hr. The Al₃₀ product was characterized by Ferron assay, ²⁷Al-NMR, SEM, XRD and TGA. The results showed that the purity of the Al₃₀ product could exceed 92%.     

混凝土构件空洞模拟检测试验与ARMA功率谱分析

及时发现空洞隐患、确定空洞大小,准确评估不良病害的危害程度对指导施工和提高混凝土结构质量具有重要意义。为实现空洞尺寸的量化,对试验模型中的模拟空洞进行地质雷达检测,应用基于SVD-TLS方法的ARMA功率谱分析对原始数据进行处理。结果表明:地质雷达探测区域覆盖的空洞范围越大,空洞信号越明显。基于SVD-TLS方法的ARMA功率谱分析具有较高的分辨率,可以识别异常反射信息,判断空洞在测线方向的范围;功率谱参数期望值有一定的分布范围,当参数期望值在-0.160以下时,可以基本确定为空洞区域。最后结合工程实例,对地质雷达数据进行功率谱分析,取得了良好的效果。该分析方法为研究混凝土构件内部空洞的检测提供了新途径,一定程度上实现了空洞尺寸的量化。     

利用场地表征参数研究岷漳地区地震动相对变化趋势

近地表场地条件所引起的地震动差别可以造成不同场地上建筑物震害的显著差异。为了在岷漳地区的震害预测和长期发展规划中考虑场地条件差异性,提出联合V_(s30)和地形标度曲率作为场地表征参数来获得研究区地震动相对变化趋势图的方法。研究表明:土质山体土质河谷基岩山体基岩河谷是研究区地震动变化的基本规律,但因覆盖层厚度和地形条件的不同,具体场地的地震动变化也有不同。总体上,地震动峰值加速度的放大程度主要与近地表V_(s30)相关,V_(s30)越大地震动峰值加速度的放大越小,地震频谱受频率标度地形曲率和覆盖层厚度共同影响,分别在相应的特征频率处放大。该研究可为区域地震动预测提供理论依据,为制定区域长期发展规划和建筑抗震设计提供重要的基础资料,基于场地表征参数研究区域地震动相对变化趋势的方法也可应用于地震烈度速报和地震灾害快速评估等领域。     

Fluid30单元在同轴圆柱壳固有特性计算中的适用性分析

目的分析Fluid30单元用于内侧含环形间隙流体同轴圆柱壳固有特性计算的适用性。方法针对内侧含环形间隙流体的同轴圆柱壳模型,分别基于\"Fluid30单元\"和\"理论流体附加质量\"对壳体固有特性进行分析。通过变间隙宽度对比计算,探究壳体固有特性随无量纲半径比的变化规律,分析波动方程离散化对计算结果的影响,判定Fluid30单元的适用范围。结果半径比与固有频率之间呈非线性关系,半径比越小,壳体固有频率越低,固有频率随半径比变化率越大。波动方程离散化引起的误差随半径比减小而增大,以相对误差10%作为Fluid30单元适用性判别标准,(1,2)壳式频率对应的临界半径比为1.20,(1,3)壳式频率对应的临界半径比为1.03,其他壳式频率对应的临界半径比小于1.001。结论不同阶频率的Fluid30单元适用范围不同,当半径比小于临界值时,相关频率应基于理论流体附加质量迭代计算。     

Reforming small-scale mining in sub-Saharan Africa: Political and ideological challenges to a Fair Trade gold initiative

In sub-Saharan Africa, artisanal and small-scale mining (ASM) has caused a range of environmental, social and economic problems. Most of the donor support pledged to improve conditions in the sector to date, however, has failed to facilitate marked improvements, in large part because emphasis has been placed on technical interventions; at the same time, impoverished miners’ needs and concerns have been seriously overlooked. It is against this background that this paper critically examines the underpinnings and potential of “Fair Trade gold” as a solution to many of the problems plaguing the ASM sector and a mechanism for alleviating the hardships of its operators. Unlike the majority of ASM-support support measures implemented in the past, “Fair Trade gold” is entrenched in the discourse of “partnership” and “participation”. To ensure its effectiveness initiatives must be adapted according to the specificities of ASM.     

A review of the PGM industry,deposit models and exploration practices: Implications for Australia's PGM potential

Australia is prospective for platinum group metal (PGM) mineralisation (in particular primary magmatic reef, primary magmatic by-product, late magmatic and hydrothermal, and alluvial placer type) but its known PGM endowment is negligible compared to that of South Africa, Russia, the USA and Canada. Most Australian PGM projects are operated by mid-cap or junior companies and form part of larger, more diverse project portfolios held by these explorers. Most projects were ‘hot’ while market conditions were favourable. However, as other metals became ‘fashionable’ and market conditions for PGM changed, so did the focus of these companies. Pure PGM companies are rare in Australia. The search for and development of PGM-only deposits in Australia are high risk business activities. No new primary PGM deposits have been discovered since the mid to late 1980s and none of the significant deposits that were discovered or evaluated in the 1980s have been mined. This review suggests that at least several A$10 million but more likely several A$100 million were sunk into PGM exploration and development projects but none advanced to the mining stage. The viability of Australian PGM projects is very sensitive to (1) metal prices, (2) the US$/A$ exchange rate, and (3) large capital expenditure requirements relative to the small size of Australian PGM-only deposits. Most PGM-only projects were initiated at times of high PGM prices. However, advanced exploration, feasibility studies and project development always lagged behind the price booms. South Africa, Russia and Canada contain approximately 98% of the known global PGM reserves. This situation has a very negative effect on the Australian PGM industry as the well-endowed nations continue to receive the lion's share of exploration spend and new projects.     

30CrMnSiA钢薄壁筒错距旋压成形工艺研究

通过对30CrMnSiA钢筒体错距旋压试验,系统研究了毛坯厚度、减薄率、旋轮压下量分配、旋压道次及道次间热处理等工艺参数对旋压过程和产品质量的影响。结果表明:较厚的30CrMnSiA钢毛坯,不用道次间热处理,通过两道次或三道次错距旋压,就可获得高质量的薄壁筒。