Semantics for consistent activation in context-oriented systems

ContextContext-oriented programming languages provide dedicated programming abstractions to define behavioral adaptations and means to combine those adaptations dynamically according to sensed context changes. Some of these languages feature programming abstractions to explicitly define interaction dependencies among contexts. However, the semantics of context activation and the meaning of dependency relations have been described only informally, which in some cases has led to incorrect specifications, faulty implementations and inconsistent system behavior.ObjectiveWith the aim of avoiding faulty implementations and inconsistencies during system execution, this paper proposes both a formal and run-time model of contexts, context activation and context interaction.MethodAs a formal and computational basis, we introduce context Petri nets, a model based on Petri nets, which we found to match closely the structure of contexts in context-oriented systems. The operational semantics of Petri nets permits the modeling of run-time context activations. Existing Petri net analyses allow us to reason about system properties. As validation, we carried out small and medium-sized case studies.ResultsIn the cases explored, context Petri nets served effectively as underlying run-time model to ensure that declared context interaction constraints remain consistent during context manipulation. Moreover, context Petri nets enabled us to analyze certain properties regarding the activation state of particular contexts.ConclusionContext Petri nets thus proved to be appropriate to encode and manage the semantics of context activation, both formally and computationally, so as to preserve the consistency of context-oriented systems.     

四川盆地中三叠统雷口坡组天然气来源及勘探方向

四川盆地中三叠统雷口坡组天然气勘探近年来取得重要突破后继而成为业内关注的热点，但对气源的认识存在较大的分歧。基于天然气地球化学特征开展的成因鉴别和气源对比研究表明，雷口坡组天然气既有主要来自下伏上二叠统龙潭组/吴家坪组烃源岩（磨溪雷一段气藏），断裂下盘须一段烃源岩有一定贡献（中坝雷三段气藏）或供烃条件（川西雷四段气藏），也有主要来自须家河组烃源岩，雷口坡组自身烃源岩有一定贡献（元坝和龙岗雷四段气藏）。雷口坡组气藏具有3种不同的源储组合，其天然气勘探方向具有差异。上二叠统龙潭组烃源岩作为主力烃源岩构成下生上储型，切穿龙潭组至雷口坡组的深断裂周缘的正向构造是寻找雷口坡组规模性气藏的最有利区。上三叠统须家河组底部烃源岩和雷口坡组顶部储层可以构成旁生侧储型，岩溶残丘或岩溶斜坡局部构造高点是这类组合较有利的发育部位。雷口坡组自身构成自生自储型，这类组合往往作为辅助参与气藏形成。     

加热炉换热工艺特性分析软件进展

为便于对目前各类化工加热炉工艺特性设计技术软件技术进展的了解,通过7个换热特性专题分析软件的内容简介,综述了特性分析技术软件在工业炉工艺设计专业的应用,提出了当前加热炉软件技术发展中,设备结构和工艺两者结合发展面临的3个工程课题,分别是加热炉预热段、辐射段和对流段整体一体化、炉管振动计算、新智能技术的引入。     

环境设计,永恒的主题——广州市芳村花园居住小区规划设计心得

该文从三个方面介绍了广州市芳村花园如何以居住环境设计为创造点，实现“以人为本，回归自然”的设计理念。     

建筑设计基本过程研究

论文在对建筑设计过程相关理论研究成果的归纳比较基础上，引出关于设计过程基本问题的思考，并通过建立设计过程的三维模型、设计过程的特性以及设计阶段和设计程序的分析研究，力求理解和把握建筑设计过程。     

墙板模型高层结构空间分析程序BSSA的特点和应用

本文阐述了墙板单元模型高层结构程序BSSA的主要特点,并通过对典型考题和体型复杂的工程实例的计算分析,指出薄壁柱单元模型程序在一些工程计算中存在的局限性,对于重要工程必须采用不同力学模型的程序进行计算互校,确保工程安全可靠。     

Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish

Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.     

The effects of land use on fluvial sediment chemistry for the conterminous U.S. - results from the first cycle of the NAWQA Program: trace and major elements, phosphorus, carbon, and sulfur

In 1991, the U.S. Geological Survey (USGS) began the first cycle of its National Water Quality Assessment (NAWQA) Program. The Program encompassed 51 river basins that collectively accounted for more than 70% of the total water use (excluding power generation), and 50% of the drinking water supply in the U.S. The basins represented a variety of hydrologic settings, rock types (geology), land-use categories, and population densities. One aspect of the first cycle included bed sediment sampling; sites were chosen to represent baseline and important land-use categories (e.g., agriculture, urban) in each basin. In total, over 1200 bed sediment samples were collected. All samples were size-limited (< 63 µm) to facilitate spatial and/or temporal comparisons, and subsequently analyzed for a variety of chemical constituents including major (e.g., Fe, Al,) and trace elements (e.g., Cu, Zn, Cd), nutrients (e.g., P), and carbon. The analyses yielded total (≥ 95% of the concentrations present), rather than total-recoverable chemical data.Land-use percentages, upstream underlying geology, and population density were determined for each site and evaluated to asses their relative influence on sediment chemistry. Baseline concentrations for the entire U.S. also were generated from a subset of all the samples, and are based on material collected from low population (≤ 27 p km^− 2) density, low percent urban (≤ 5%), agricultural or undeveloped areas. The NAWQA baseline values are similar to those found in other national and global datasets. Further, it appears that upstream/underlying rock type has only a limited effect (mostly major elements) on sediment chemistry. The only land-use category that appears to substantially affect sediment chemistry is percent urban, and this result is mirrored by population density; in fact, the latter appears more consistent than the former.     

超高层建筑的建筑设计理念--对天津经济技术开发区CBD超高层建筑国际招标方案的评析

超高层建筑是城市综合实力的体现,在中国,超高层建筑设计是一项崭新的设计内容,是一个复杂的系统工程,针对建筑的形式特点,应有相应的设计理念和技术手段.本文通过对天津经济技术开发区CBD超高层建筑国际设计方案的评析,总结出其标志性、生态化、亲人性、功能性与文化性的设计特点,并且针对项目用地、交通组织和经济核算等问题进行了探讨.     

采用卡尔曼滤波的电子稳定性程序分析

汽车的横摆加速度过大会引起过度转向和过多不足转向等危险工况。采用线性二自由度车辆模型计算目标横摆角速度和目标质心侧偏角,运用卡尔曼滤波理论实时估算汽车的质心侧偏角并结合横摆角速度传感器对车辆稳定状态进行监测,提出了基于横摆角速度和质心侧偏角的ESP控制方法,着重介绍了ESP逻辑判断准则,应用Matlab/Simulink软件实现相应的电子稳定控制策略,同时利用AMESim软件中的15自由度整车模型建立AMESim-Simulink联合仿真模型,仿真结果验证了所提出的质心侧偏角估算的可行性及稳定性控制策略的有效性。