有条件的正态应力、强度模式结构可靠性的经典精确下限

结构可靠性的估计问题是机械可靠性的主要问题之一。强度、应力均为正态变量的结构模式是一种较常见的模式,由此研究这一模式结构可靠性的区间估计问题,给出正态强度、应力的分布参数均未知,但它们的方差之比为已知常数时,结构可靠性的经典精确置信下限。其下限满足一个含有非中心t分布的方程,借助于已有的非中心t分布分位数表可以方便地计算得到。     

Bevk Perovic arhitekti

An exciting new crop of young Slovenian architects is coming out of Ljubljana. Valentina Croci explores the work of Bevk Perovic arhitekti, a practice whose finely honed hybrid approach owes as much to the contextualism of the great Ljubljanan master Joze Plecnik, as Vasa Perovic's exposure to contemporary Dutch architectural thought and design at the Berlage Institute in Amsterdam. Copyright © 2005 John Wiley & Sons, Ltd.     

Zur Entwicklung der Steifigkeitsmatrizen für dünnwandige Stäbe

On the development of stiffness matrices for thin‐walled members. A glance into the early development of element stiffness matrices for thin‐walled members is given in the present paper and their most mature shapes are shown. Those shapes, the most general and later reduced to two particular forms, refer to the specifics of the classical Vlasov theory of thin‐walled bars [1] as well as to the Bornscheuer systematics of the cross‐sectional properties involved [2]. Appropriate modifications of the relevant matrices are performed and their coordinate system dependence is demonstrated.     

Sediment mercury dynamics and historical trends of mercury deposition in the St. Lawrence River area of concern near Cornwall, Ontario, Canada

The St. Lawrence River near Cornwall, Ontario was designated an Area of Concern by the International Joint Commission in 1985. Sediments from this area have historically been contaminated with mercury (Hg), and although concentrations have decreased since the 1970s, they still remain high. Nine sediment cores were collected from three sites within the Area of Concern in 2004/05 to determine the variability in historical profiles of Hg deposition to the river. Sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and cores were analyzed for ²¹⁰Pb to determine chronologies of sedimentation at these sites. Mercury diffusion rates in pore waters within the sediment column were determined to be very low (between 0 and 2.15 ng cm^− 2 year^− 1, n = 3) compared to the recent Hg sedimentation rates at these sites (183 ± 30 ng cm^− 2 year^− 1 SE, n = 9) determined by multiplying surface Hg concentrations with ²¹⁰Pb-derived sedimentation rates. These results indicate that Hg profiles in these cores accurately depict historical releases of Hg to the river bed. The influence of federal regulations in the early 1970s to restrict Hg emissions to the river was apparent in these dated sediment cores, as were the closures of several local industries in the mid 1990s. Mercury accumulation rates prior to 1970 were 60 times higher than those occurring after 1995. Methyl mercury showed surface enrichment in most of these sediment cores providing evidence that mercury methylation occurred most rapidly near the sediment surface.     

历史城市与设计创新——俄罗斯天然气工业城概念性方案设计国际竞赛概述

2006年在俄罗斯圣彼得堡市进行的天然气工业城概念性方案设计国际竞赛,无论是项目本身还是参赛者名单都极具影响。在这样一座几个世纪来都严格遵守旧城保护政策的历史名城,建造现代理念的高层建筑吸引了众多国际建筑大师前来参与,他们的设计理念为圣彼得堡城市规划及建筑的发展带来了新的尝试与思考。本文对这次竞赛的过程及参赛方案进行了概要论述。     

Comparison of storm intensity and application timing on modeled transport and fate of six contaminants

Hundreds, if not thousands, of fish kills and kills of other aquatic organisms occur following storms in the US each year, but they are difficult to quantify, investigate, or manage due to the transient nature of major storms and the other priorities following them. Methods are needed to better understand the causes of these kills. The Pesticide Root Zone Model and the Exposure Analysis Modeling System were used to compare risk to resident biota in estuarine headwaters in two locations under various conditions. Contaminants were selected using a landuse-based preliminary risk assessment approach. Atrazine, fipronil, and imidacloprid were compared for potential impacts on important prey species, including copepods and grass shrimp, in Lake Bethel in Volusia County, Florida. Carbaryl, diquat dibromide, and fluoranthene were compared for potential impacts on salmon and other aquatic species in Johnson Creek, near Portland, Oregon. Predictions of contaminant concentrations in groundwater runoff, surface water, benthic sediments, and pelagic biota tissue were obtained based upon watershed characteristics, storm types, and contaminant chemistry and application. For all six contaminants, the simulated concentrations were highest following the 100-yr storms and lowest following the 2-yr storms. Aqueous concentrations ranged between 84 and 2100% higher in 100-yr compared to two-yr storms. Most atrazine and carbaryl concentrations were highest if applied one day before the storm while fipronil, imidacloprid, and diquat dibromide were highest if applied 16 days prior to the storm. Carbaryl and fluoranthene concentrations were highest in the forested segment of the watershed while diquat dibromide concentrations were highest in the agricultural segment. In Florida simulations, groundwater and surface water concentrations generally were highest for atrazine, followed by imidacloprid, and then fipronil. Atrazine poses the highest risk to algae and copepods due to its mobility and high allowable application rates. Fipronil and imidacloprid, though highly toxic, were not predicted to occur at high enough concentrations to pose a risk. In Oregon simulations, groundwater and surface water concentrations generally were highest for carbaryl, followed by fluoranthene, and then diquat dibromide. For salmonids, fluoranthene poses a higher risk than carbaryl, whereas it is unlikely that diquat dibromide will affect salmonids in this system. For crustaceans, carbaryl poses the greatest risk, followed by fluoranthene. Diquat dibromide was determined to pose little risk. These tests demonstrate the use of preliminary risk assessment, along with transport and fate modeling, to characterize risks to aquatic organisms without the need for in situ chemical measurements.     

包装用BA/St改性水性聚氨酯及其粘接性能的研究

以丙烯酸丁酯(BA)和苯乙烯(St)为改性剂、双丙酮丙烯酰胺(DAAM)为交联剂,采用自由基引发聚合工艺,制备出高性能的BA/St改性水性聚氨酯(WPU)包装用胶粘剂。采用红外光谱(FT-IR)仪和粒度分析仪对乳液的结构和性能进行了分析,讨论了R值(即-NCO/-OH的物质的量比)、改性剂、St和交联剂用量对胶粘剂粘接强度的影响。试验结果表明:当R=1.1、w(改性剂BA/St)=28%(相对于WPU而言)、w(St)=30%(相对于BA/St而言)和w(DAAM)=2%时,乳液的粘接性能最佳;由该乳液配制的胶粘剂可以满足多种复合软包装膜的使用要求。     

St14双相钢板成形性能研究

研究了Ｓｔ１４钢的双相处理工艺、双相组织、力学性能成形极限图及实冲情况。结果表明,通过在（ａ＋γ）两相区温度加热的淬火处理获得了铁素体加马氏体的双相钢钢板,实冲壳体时具有良好的成形性能。     

汽车用高强度钢板BH340与普通冷轧钢板St13点焊性能对比分析

采用不同点焊工艺参数对BH340钢板和St13钢板进行了点焊工艺实验，并对不同工艺条件下两种钢板的焊接接头进行了组织、性能对比分析。结果表明：在试验范围内，焊接电流为4kA、焊接时间为10周波时，BH340钢板点焊性能较好；在相同的焊接工艺参数下，BH340钢板焊接接头的显微组织比St13钢板细小且均匀，焊接接头的拉剪载荷明显高于St13；点焊后St13钢板和BIF340钢板疲劳特性不存在太大差异。     

J55钢级焊接油井管在线控冷工艺的研究

针对一种J55钢级焊接油井管的生产工艺新流程,在搭建的冷却工艺试验平台上研究了冷却速率、加热速率和喷淋方式对钢管微观组织和机械性能的影响。结果表明:热张力减径工序后采用加速冷却,有利于钢管机械性能的提高;提高焊管热张力减径前的再加热速率,有利于钢管机械性能的提高;切圆喷淋的冷却方式能大大提高钢管的冷却均匀性。