Factorial 2 p–q Plans Robust Against Linear and Quadratic Trends

When the substrate of a 2 ^n–q factorial or fractional factorial experiment may be expected to show trends representable by linear and quadratic terms in time, then certain orderings spaced at equal time-intervals permit better estimation of the effects than do others. Some of these ordered plans are given for p – q = 2, 3, 4, 5. Simple methods are given for computing effects, trends, and efficiencies.     

Thermobaric stratification in very deep Norwegian freshwater lakes

Thermobaric stratification was investigated in very deep lakes of elongated shape. We considered the spring time configuration when large freshwater lakes may have their deepest recirculation. In five very deep freshwater lakes in Norway, profiles were measured in spring 2006 with multiparameter probes. Temperature profiles confirmed thermobaric stratification in all of these lakes, i.e. the temperature profiles crossed the 4 °C line and thus were affected by pressure effects on the temperature of maximum density. Electrical conductance was low in all of the investigated lakes, and vertical gradients were too small to play a role in the density stratification. In all lakes, deep water was well supplied with oxygen. Three out of five lakes showed a temperature gradient close to Eklund's stability theorem. However, the remaining two lakes clearly opposed the theorem. Bottom temperatures were more closely related to lake length than their maximum depths. Oxygen saturation profiles documented recent intensive gas exchange with the atmosphere. They agree well with the possible formation of deep water from density driven flows at horizontal temperature gradients close to 4 °C.     

Bond strength prediction for deformed steel rebar embedded in recycled coarse aggregate concrete

This paper summarizes the results of an experimental investigation into the bond behavior between recycled aggregate concrete (RAC) and deformed steel rebars, with the main variables being the recycled coarse aggregate replacement ratio (RCAr) and water-to-cement ratio of the concrete mixture. The investigation into splitting cracking strength indicates that the degradation of the bond splitting tensile stress of the cover concrete was affected by not only the roundness of the coarse aggregate particles but also the weak interfacial transition zone (ITZ) between the cement paste and the RCA that has a more porous structure in the ITZ than normal concrete. In this study, a linear relationship between the bond strength and the density of the RCA was found, but the high compressive strength reduced the effects of the parameters. To predict the bond strength of RAC using the main parameters, a multivariable model was developed using nonlinear regression analysis. It can be inferred from this study that the degradation characteristic of the bond strength of RAC can be predicted well, whereas other empirical equations and code provisions are very conservative.     

有强内电场的GaN-基阶梯量子阱中的线性与非线性光吸收

采用密度矩阵方法,考察了带强内建电场GaN-基阶梯量子阱中的线性与非线性光吸收系数.基于能量依赖的有效质量方法,在考虑了带的非抛物性情况下,推导了结构中的精确解析的电子本征态,给出了系统中简单解析的线性与非线性光吸收系数表达式.以AlN/GaN/AlxGa1-xN/AlN阶梯量子阱为例进行了数值计算.结果发现阶梯量子阱的阱宽Lw、阶梯垒宽Lb、阶梯垒的掺杂浓度x的减小将提高体系的吸收系数.而且,随着Lw,Lb和x减小,吸收光子的能量有明显的蓝移,总吸收系数的半宽度及饱和吸收强度均减小.计算获得的部分结果与最近的实验观察完全一致.     

Australia's housing choices: Retrospect and prospect

This article identifies issues around the Auckland Region's strategy for urban intensification and discusses the ensuing policy implications. Medium density housing forms an important element of the strategy for growth management. Implications for its success are primarily drawn from research into a major housing development in Waitakere City. It is argued that for ideological, political and technical reasons the strategy could be easily undermined. The article also suggests that something of a paradigm shift is underway in urban planning.     

【城市笔记:之14】记一栋街道办事处建筑

小建筑并不会因其小而没有故事和风采。此篇《小建筑记》所推介的作品,由董春方设计的上海曲阳综治办中心,就安静地颠覆着过去人们对于此类机构性建筑的概念化认识。去岁晚秋,笔者有机会在设计者的引领下实地探访过这个建筑,并针对该建筑所引申出来的设计话题与该建筑师做过深入交谈,特缀文以(?)读者。     

W-Y二元合金力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理方法研究了钇的含量对W-Y二元合金力学性质的影响,精确计算了W_(1-x)Y_x(x=0.0625,0.125,0.25,0.5)合金的力学常数,并对其力学特性进行分析。结果表明,W-Y合金的弹性常数、体模量、杨氏模量以及剪切模量随Y含量(原子分数)的增加而成非单调性减小,表明Y对W材料的合金化降低了材料的机械强度。然而,基于力学特性B/G、泊松比ν和柯西压力C'等分析,Y的合金化对W的延展性和韧性有明显的提高。当Y含量x为0.25时,可有效改善W-Y合金的延展性和抗变形能力。通过态密度分析,W-Y合金的金属性随Y含量的增加先减弱而后增强。     

Silicon in intericosahedra chains of boron carbide

Interaction between boron carbide and silicon was studied at 1400–1700 ℃ in a vacuum. The results at 1400 ℃ suggest that silicon substitutes a single atom of carbon per formula unit B₁₂C₃, producing a phase with increased lattice parameters. Temperature increase improves the degree of transformation, but at 1700 ℃, the product starts to lose silicon. Analysis of DFT formation energies of configurations with B₁₂C₃ and B₁₂C₂Si stoichiometries shows that B₁₂C₂Si may have two ground states with practically equal stability. The first is B₁₁Si(C-B-C) with silicon in icosahedral polar position, and the second is B₁₂(C^Si^C), where the silicon is in the middle of an angular chain. The latter is suggested to be more favorable during the synthesis, while the former is very close to equilibrium with its precursor B₁₁C(C-B-C), and its formation may be inhibited. Comparison of XRD patterns for the synthesis products and modeled structures seems to confirm this suggestion.