Fast Summation of Radial Functions on the Sphere

Radial functions are a powerful tool in many areas of multi-dimensional approximation, especially when dealing with scattered data. We present a fast approximate algorithm for the evaluation of linear combinations of radial functions on the sphere . The approach is based on a particular rank approximation of the corresponding Gram matrix and fast algorithms for spherical Fourier transforms. The proposed method takes (L) arithmetic operations for L arbitrarily distributed nodes on the sphere. In contrast to other methods, we do not require the nodes to be sorted or pre-processed in any way, thus the pre-computation effort only depends on the particular radial function and the desired accuracy. We establish explicit error bounds for a range of radial functions and provide numerical examples covering approximation quality, speed measurements, and a comparison of our particular matrix approximation with a truncated singular value decomposition.     

高温加速试验与运行条件下10CrMo910钢组织变化的比较

根据拉尔森-米列尔公式,对主蒸汽管道10CrMo910钢进行无应力和加应力条件下的高温加速试验,并与实际运行15×104h的10CrMo910钢进行显微组织与碳化物变化的分析比较,确定高温加速试验与实际运行是否存在差异.结果表明,加载应力所产生的显微组织变化和合金元素再分配比未加应力显著,但加速试验所产生的显微组织变化和合金元素再分配远没有实际运行的显著.     

SO_4~(2-)/TiO_2-MoO_3-La_2O_3催化合成丁醛乙二醇缩醛

报道了以稀土改性固体超强酸SO42-/TiO2-MoO3-La2O3为多相催化剂,通过丁醛和乙二醇为原料合成丁醛乙二醇缩醛,探讨了SO42-/TiO2-MoO3-La2O3催化剂对缩醛反应的催化活性,较系统地研究了原料量比,催化剂用量,反应时间诸因素对产品收率的影响。实验表明:在n(丁醛):n(乙二醇)=1:1.5,催化剂用量为反应物料总质量分数的0.80%,环己烷为带水剂,反应时间1.0h的优化条件下,丁醛乙二醇缩醛的收率可达81.9%,由此可见:SO42-/TiO2-MoO3-La2O3是合成丁醛乙二醇缩醛的优良催化剂,具有良好的应用前景。     

第二十届国际原电池和蓄电池会议评述

世界小型蓄电池市场现状及发展趋势分析表明,金属氢化物镍蓄电池开始下降,镉镍蓄电池保持稳定,而锂离子蓄电池仍然处于快速增长态势。预计2003年锂离子蓄电池产量将达到12.55亿只,比2002年增长45%,销售额将达36.14亿美元,比2002年增长29%,价格比2002年下降16%;同时,新型电池技术发展也依然强劲,其中呈现了三个热点技术领域,即锂离子蓄电池及相关材料,42V和混合电动车蓄电池,燃料电池。对上述热点领域的技术发展现状及趋势作了评述。     

钛合金在高温高压过热蒸汽中的腐蚀机理研究

研究了T225NG和T42NG合金在高温、高压、过热蒸汽中长时间的氧化腐蚀规律。对试样表面氧化膜元素、相组成及表面形貌进行了测试与分析，给出了两种合金的腐蚀动力学模型．并对两种合金的腐蚀机理进行了初步分析。结果表明，两种钛合金中主元素Ti优先产生氧化腐蚀，合金元素Al和Fe及N、H、C等杂质元素对腐蚀起到促进作用，并在合金表面呈现出典型的结晶学特征。两种钛合金的腐蚀动力学规律均服从Wagner理论中的近抛物线规律。     

42CrMo环件铸辗复合成形的跨尺度建模

基于有限元理论和元胞自动机模型,提出一种宏观与微观尺度相结合的铸态42CrMo合金环件短流程铸辗复合成形工艺混合建模方法。在铸辗复合成形新工艺理论框架下,定义考虑环坯热变形行为和晶粒空间结构的宏观/微观边界转换条件,该边界条件有助于环件的形/性一体化调控。在微观元胞自动机模型框架下,研究晶粒拓扑变形技术,充分考虑晶粒空间重叠的结构问题,通过独立成分分析对晶粒的拓扑结构进行优化。应用混合模型模拟环件短流程铸辗复合成形过程,结果表明,混合建模能根据环件整体和各位置所需表现尺度的不同,应用不同层次的宏微观模型分别模拟,有效提高了铸态环件短流程铸辗复合成形工艺的模拟效能。     

Frequency effect and influence of testing technique on the fatigue behaviour of quenched and tempered steel and aluminium alloy

Influences of testing technique and frequency on the fatigue behaviour of 50CrMo4 and EN AW-5083 were investigated. To clarify the effect of test frequency on the fatigue behaviour, tests with 20 kHz and f < 400 Hz were performed. The frequency effect can be caused by temperature, environment and strain rate. For the aluminium alloy, the influence of environment is responsible for the dependence of fatigue lifetime on the frequency. The fatigue lifetime of the steel showed in both environments similar frequency dependency, i.e. the strain rate is assumed to be responsible for the differences in fatigue lifetime.     

Effects of the German Renewable Energy Act on structural change in agriculture – The case of biogas

The strong political support for biogas production in Germany over the past decade has greatly affected agricultural production, farms and land markets. This paper analyzes the effects of Germany's biogas policies on agricultural development by using the agent-based simulation model AgriPoliS. Particular focus is placed on the effects of the previous German Renewable Energy Act (REA, German “EEG”) of 2012, as well as the latest amendments, which were added in 2014. Our results show that under the previous REA and its predecessors, biogas production provided an attractive investment opportunity, especially for large farms, which led to a boost in biogas production. However, this policy also caused distortions within the agricultural sector, including increasing land rental prices. These effects particularly threatened farms that were not able to invest in biogas, as well as smaller biogas farms. On average, biogas farms could not increase their profitability. The main reason for this effect can be seen in the fact that a significant share of the value added is transferred via increased rental prices to land owners. The amendment of the REA in 2014, which reduced support levels substantially, partly attenuates some of these effects, though the previous policy will cast a long shadow.     

The effect of residential solar photovoltaic systems on home value: A case study of Hawai‘i

An investment in solar photovoltaic (PV) is considered a home improvement, and should be reflected in home sales prices. However, uncertainty about PV policies and information asymmetries may result in an imperfect pass-through. Hawai‘i serves as an illustrative case study to assess the impact of PV on home prices because Hawai‘i has the highest number of PV installations per capita nationwide. Applying a hedonic pricing model using home resale and PV building permit data from 2000 to 2013 for Oʻahu, I find that the presence of PV adds on average 5.4% to the value of a home. The value of PV exceeds total average installed costs because many of Hawai‘i's electricity circuits have reached legal limits for PV installations and thus many neighborhoods could technically no longer install additional PV capacity. Therefore, the value of the system goes beyond its capital investment—on average, by $5000—to incorporate expected electricity savings.     

盐浴软氮化42CrMo的摩擦学性能分析

对42CrMo进行盐浴软氮化处理,分析盐浴软氮化处理对42CrMo试样硬度的影响,研究不同润滑条件下42CrMo试样的摩擦学性能,分析其摩擦磨损机制。结果表明:盐浴软氮化处理过的42CrMo的平均硬度为HV747.33,约是未处理基体的(HV310)的2.5倍;在其他条件相同时,随载荷的增加,干摩擦条件下42CrMo的摩擦因数先增加后减小,边界润滑和油润滑条件下的摩擦因数不断增加;42CrMo在干摩擦条件下的摩擦因数、表面磨痕深度和磨损量均要明显高于边界润滑和油润滑条件下;在干摩擦条件下42CrMo的磨损机制为严重的黏着磨损和塑性变形,边界润滑条件下42CrMo表面磨损减缓,有轻微犁沟;油润滑条件下42CrMo表面为磨粒磨损,无明显变形。