Internal Stresses and the Martensite Start Temperature in Alumina-Zirconia Composites: Effects of Composition and Microstructure

n alumina-based composites containing ceria-stabilized tetragonal zirconia, the martensite start temperature ( M_s ) of the tetragonal-to-monoclinic zirconia phase transformation exhibits a grain size dependence that becomes increasingly pronounced as the zirconia content decreases. Neutron diffraction experiments confirm earlier dilatometry measurements of M _s in composites containing ≥20 vol% ZrO₂ and were instrumental in obtaining M _s values in lower zirconia content (i.e., 10 vol%) composites. The dependence of M _s on zirconia content is related to the internal stresses that arise from differences in thermal expansion coefficients between the two phases. Neutron diffraction measurements show that the internal tensile stresses in the zirconia grains increase with decreasing zirconia content. The measured internal stresses are in quantitative agreement with predictions based on models assuming isolated ZrO₂ particles at low zirconia contents and a continuous ZrO₂"matrix" phase at higher zirconia contents. This assumption is consistent with the observed microstructural development in which the low zirconia contents result in isolated zirconia grains, whereas higher zirconia contents result in more interconnected zirconia grains.     

Solidification Behavior of Undercooled Liquid Aluminum Oxide

Solidification of aluminum oxide from undercooled melts was investigated in containerless experiments. Specimens were levitated in a gas jet, stabilized with an acoustic positioning device, and melted with cw CO₂ laser beams. Cooling curves were obtained by optical pyrometry when the laser intensity was reduced. The materials examined were high-purity Verneuil sapphire, 99.5% polycrystalline alumina, and oxide materials recovered from the effluent of an aluminum-fueled rocket motor. The degree of undercooling, the apparent temperature behavior during the thermal arrest on solidification, and the structure of the materials formed were different in argon and oxygen atmospheres. Undercooling of the sapphire and alumina materials was 360 ± 10 K in an oxygen atmosphere and approximately 450 K in argon. Melting and solidification of high-purity sapphire resulted in a dendritic and porous polycrystalline material in oxygen. Dense, larger crystals were obtained in argon. Products formed from 99.5% alumina were discolored and the cores were white, indicating impurity segregation effects. More reproducible behavior was observed for the sapphire and 99.5% alumina than for the tungstencontaminated rocket motor effluent materials.     

Foundations of topological characterization of surface texture

More than a hundred years ago Maxwell proposed dividing a landscape into regions consisting of hills or alternatively consisting of dales. A hill is a set of points from which maximum uphill paths lead to one particular peak, and a dale is the set of points from which maximum downhill paths lead to one particular pit.Starting with Maxwell's ideas this paper sets out to develop the foundations of topological characterization of surface texture. This leads to a system of surface texture characterization which is complementary to published areal parameters based on the mean line system. In a similar manner that R&W system is complementary to the mean line system for profiles (the dale is the areal equivalent of a motif on a profile).An important example of a true areal characterization contained within this system is the connectability of surface valleys. This is important for applications such as lubrication and paintability of a surface. It is also important for characterizing extruded aluminium that has been anodized. The anodizing has cracks (connected valleys) and isolated pits, both of which require characterizing separately for production control.     

Predicting disinfection by-product formation potential in water

Formation of regulated and non-regulated disinfection by-products (DBPs) is an issue at both potable water and wastewater treatment plants (W/WWTPs). Water samples from W/WWTPs across the USA were collected and DBP formation potentials (DBPFPs) in the presence of free chlorine and chloramine were obtained for trihalomethane (THM), haloacetic acid (HAA), haloacetonitrile (HAN), and N-nitrosodimethylamine (NDMA). With nearly 200 samples covering a range of dissolved organic carbon (0.6-23 mg/L), ultraviolet absorbance (0.01-0.48 cm⁻¹ at 254 nm wavelength), and bromide (0-1.0 mg/L) levels, power function models were developed to predict the carbonaceous DBP (C-DBP) and nitrogenous DBP (N-DBP) precursors spanning 3 orders of magnitudes. The predicted THM and HAA formation potentials fitted well with the measured data (analytical variance of less than 22%). Inclusion of dissolved organic nitrogen (DON) into the HANFP model improved the predictions. NDMAFP was the most difficult one to predict based upon the selected water quality parameters, perhaps suggesting that bulk measurements such as DOC or UVA₂₅₄ were not appropriate for tracking NDMAFP. These are the first such DBPFP models for wastewater systems, and among the few models that consider both C-DBPs and N-DBPs formation potentials from the same water sources.     

Using legitimacy dialogues to explore responses to flooding issues in a UK catchment

A growing awareness of the potential impacts of climate change has led to the consideration of a variety of future outcomes by water supply companies, regulators and local authorities within England and Wales. These strategies recognise the possibility of episodes of flooding within catchments, with the Environment Agency's fourth Periodic Review requiring water companies to explore future demand and supply scenarios up to 2030. However, there is a gap in the literature concerning how those tasked to implement water policy, and those subject to it, view these change scenarios. This paper outlines a study undertaken within the River Nene catchment, exploring how water resource governance bodies and water users respond to flooding issues. In particular, the research focuses on the twin concepts of legitimacy and dialogue as a means to assess the boundaries of stakeholder engagement with these strategic change scenarios.     

The awareness and practice of value management by South African consulting engineers: Preliminary research survey findings

The awareness of value management (VM) and the nature and extent of its practice by professional civil, electrical and mechanical engineers in the South African construction industry are investigated using a web-based, online questionnaire survey as the first part of a more extensive investigation. A primary objective of the early study is to test the UK-based assertion of Kelly et al. [Kelly, J., Male, S., Graham, D., 2004. Value Management of Construction Projects. Blackwell, Oxford] that VM is an established service with commonly understood tools, techniques and styles. The survey findings suggest that, while awareness of VM is reasonably prevalent among South African engineers, its practice is considerably less extensive. Where VM is undertaken, almost no attempt is made to benchmark VM activities against international standards nor does its use appear to conform to any standard methodology. Engineers prefer other ways of delivering value to projects, and do not generally employ VM to facilitate the client briefing process. The findings are important given the increasing globalization of construction services, especially given the international ties between designers, project managers and other professionals. Professional engineering associations in South Africa should adopt a proactive role in promoting the use of VM by engineers, possibly through continuing professional development programmes.     

Managing risks in public-private partnership formation projects

While sourcing by means of Public-Private Partnerships has been lauded over recent years, increasingly risks appear to jeopardise public organisations' unique societal tasks. Integrated Risk Management has not yet been applied to public organisations getting involved in PPP in the sense of understanding risk management capabilities. This article explores risk awareness and risk management practices underpinning maintenance partnership formation by means of a dual case study of two PPP projects and a short industry survey. The results suggest that organisations face several “intolerable risks” linked to project governance and project management responsibilities: insufficient representation of qualified employees, absence of a shared performance system, assignment of responsibilities and decision-making authority, impractical or inappropriate partnership agreement, and timing of the partnership initiative. Cross-case analysis revealed the role of different levels of risk awareness and senior management involvement. Drawing on these findings, a framework for risk management for PPP formation projects is developed.     

An analysis of construction productivity differences between Canada and the United States

Comparisons of industry sectors in advanced economies since the 1960s show that the construction sector has lagged in productivity growth rates, especially in the United States. Although the US and Canadian economies are highly integrated, Canada’s experience differs in key ways. Analysis of these differences offers insight into fundamental construction productivity drivers. Three levels of analyses of construction productivity in the US are provided in this study. The first analysis compared international levels of labour productivity growth. The second compared construction productivity between the US and Canada, and the third analysed cost estimating data from RS Means estimating manuals to measure the changes in labour and partial factor productivity in the US from 1995 to 2009. Statistical significance testing indicates that labour productivity remained nearly constant in the building sub-sector and that partial factor productivity has improved at an annual compound rate of 0.66%. This supports previous findings that US construction has stagnated but is still improving in Canada, with wage differentials and training systems as potential drivers of this difference. While growth rates of productivity seem to decline with higher absolute levels of productivity, there is no evidence that high absolute productivity levels preclude significant growth.     

ASHRAE Standard 170-2013简介

介绍了该标准修订的主要内容,包括:手术分类、湿度控制下限、病房通风要求、通风空调系统、能量回收、空气过滤要求。手术室分类由三类调整为两类。治疗室设计相对湿度的下限降至20%。病房最低换气次数要求由6h-1改为4h-1。调整了关于管道回风、多区域空调新风量计算、室内循环机组使用、风管衬里方面的规定。明确了医疗护理设施系统的能量回收利用及空气过滤的具体要求。     

Core–periphery dynamics in the Portland, Oregon, region: 1982–2006

The relative strength of positive and negative spillovers of urban development is a long-standing and contested issue in regional and development economics, and the search for spread and backwash effects of development in urban core economies goes back at least 50 years. Using data from IMPLAN and the Bureau of Economic Analysis to develop multiregional input–output models, we developed estimates of core–periphery economic interdependence (sales and purchases of goods and services and commuting of workers between the core and the periphery) of the Portland, Oregon, region for 1982 and 2006. We explored whether the changing flows of sales and purchases, spillovers and commuting between 1982 and 2006 suggested a dominance of spread effects or backwash effects. We found increased commuting between periphery and core, decreased core–periphery transactions, and smaller core-to-periphery spillovers and periphery-to-core spillovers in both goods and services. Our findings do not point to a clear dominance of spread or backwash effects. Results showing smaller core-to-periphery and periphery-to-core multipliers/spillovers suggest that spread effects related to trade in goods and services weakened between 1982 and 2006. Our findings of increased commuting are consistent with enhanced spread effects in labor markets.