Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees

Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, projections, coprojections, intersection, and difference; this for Boolean queries and path queries on labeled and unlabeled structures. In all cases, we present the complete Hasse diagram. In particular, we establish, for each query language fragment that we study on trees, whether it is closed under difference and intersection.     

A continuous network location problem for a single refueling station on a tree

This article considers the continuous version of the refueling station location problem on a tree network, which is a common structure in numerous toll roads worldwide, so as to locate a single alternative-fuel refueling station to maximize the traffic flow covered in round trips/day. Two reduction properties regarding the problem size and some optimality conditions are derived. Based on these conditions, an exact polynomial algorithm is developed to determine the set of optimal locations for the refueling station. A small tree network example is solved to illustrate the algorithm.     

考虑布线资源松弛的X结构Steiner最小树算法

为了进一步考虑X结构,并充分利用障碍内可用布线资源,文中提出考虑布线资源松弛的X结构Steiner最小树算法.为了能够求解离散问题,在粒子的更新操作中引入交叉算子和变异算子.通过构建查找表,为整个算法流程提供快速的信息查询.提出角点选取策略,通过引入一些障碍角点,使粒子满足约束.最后构建精炼策略,进一步提高最终布线树的质量.实验表明,文中算法充分利用障碍内可用布线资源,有效缩短总布线长度,取得较佳的总布线长度.     

Second-order kinetic model for the sorption of cadmium onto tree fern: a comparison of linear and non-linear methods

A comparison was made of the linear least-squares method and a trial-and-error non-linear method of the widely used pseudo-second-order kinetic model for the sorption of cadmium onto ground-up tree fern. Four pseudo-second-order kinetic linear equations are discussed. Kinetic parameters obtained from the four kinetic linear equations using the linear method differed but they were the same when using the non-linear method. A type 1 pseudo-second-order linear kinetic model has the highest coefficient of determination. Results show that the non-linear method may be a better way to obtain the desired parameters.     

路易斯·|·小康与密克维·以色列犹太教会堂

密克维·以色列犹太教会堂因其涉及与犹太神秘主义的联系、对历史形式的参照、有关废墟包裹在建筑周围的表达、对光线和空间的微妙处理、建筑与仪式的契合等诸多重要命题,在路易斯小康建筑思想的发展中担当了重要的角色,本文介绍了该方案的三个阶段以及它所展现的这几个方面。     

上海市春季彩叶树种类及应用调查

以上海市春季彩叶树种为研究对象,通过观察记录、比较分析,总结出上海地区春季应用的彩叶树种类,旨在为“彩色上海”园林景观设计提出春季彩叶树种应用的可行性建议。介绍了上海市春季彩叶树种类及其应用现状,并对今后上海市彩叶树种的引种、应用及栽培管理提出建议,为彩叶树种的进一步研究提供依据。     

Atmospheric deposition of nitrogen at five subtropical forested sites in South China

Elevated concentrations of reactive nitrogen (N) in precipitation have been reported for many cities in China. Due to increased use of fossil fuels and expansion in agriculture, further increases in deposition of ammonia (NHx) and reactive N oxides (NOy) are predicted. Increased deposition of reactive N is likely to affect N dynamics and N runoff in forest ecosystems. Yet, in China little work has been done to quantify the levels of atmospheric N deposition in such systems. Here, we assess the deposition of inorganic N (ammonium, NH4+ and nitrate, NO3-) for five subtropical forest ecosystems in remote and urban areas of South China. Annual volume-weighted concentrations in bulk precipitation range from 0.18 to 1.55 mg NH4+ -N L(-1) and from 0.12 to 0.74 mg NO3- -N L(-1). These values are large and several times greater than those reported for remote sites of the world. The fluxes of total inorganic N (TIN) in wet-only deposition range from 0.8 to 2.3 g N m(-2) yr(-1), with NH4+ -N contributing 54% to 77%. Both the tree canopy and the ground vegetation layer are important in determining the net N flux reaching the forest floor, but the net effect varies from site to site. At TieShanPing (TSP), close to Chongqing city, and at CaiJiaTang (CJT), near Shaoshan (Hunan province), the canopy represents a net source of N, probably due to dry deposition. At the other three sites (LiuChongGuan (LCG), LeiGongShan (LGS), both in Guizhou province, and LiuXiHe (LXH) in Guangdong), a net loss of reactive N from precipitation water occurs in the canopy, probably due to uptake processes. The total annual atmospheric TIN load is estimated to range from at least 0.8 g N m(-2) yr(-1) to 4.0 g N m(-2) yr(-1), with a considerable contribution from dry deposition. Concentrations and fluxes of inorganic N in tree canopy throughfall are greater than those in North America. Also the contribution of NH4+ -N to TIN fluxes in throughfall (40% to 70%) is greater than in North America. Our sites have N deposition levels and NH4+ -N contributions similar to those found in Northwest and central Europe. The TIN loads at TSP and CJT far exceed 2.5 g N m(-2) yr(-1), which is the N deposition load above which NO3- leaching is expected in temperate and boreal forests.     

民国时期行道树种植观念之形成与普及探述

我国近代城市中种植行道树的观念形成于民初、并在1920年代后期得以深入人心,成为道路建设和城市生活必不可少的部分。本文考察近代城市行道树种植制度的起源与发展:其起源于19世纪50年代巴黎改造和维也纳等欧洲城市拆墙辟道运动,同时被引入美国城市公园运动并成为城市美化运动的标志之一。西方的这些经验在20世纪初传入日本后,行道树成为模仿西方城市意象的重要道具,同时满足了防灾需求。我国近代的行道树种植观念即在此影响下形成。民国的行道树文献带着普及知识、规训市民行为、强化民族主义意识等多重目的,从一个侧面反映了我国近代国家建构的进程。考察行道树种植观念的形成是研究我国近代城市规划和景观设计思想史的样例。     

基于FTA和AMESim的四通均流阀可靠性提升研究

四通均流阀能够将入口流量均等分成四路,驱动四路不同的负载保证同步动作。采用故障树分析法(Fault Tree Analysis,FTA),对该阀件的失效模式进行研究;通过AMESim仿真,进一步对故障模式进行验证,提出相应的改进措施,并试制样机进行可靠性试验,提高了阀件的性能,对其他阀件的可靠性设计有一定的借鉴作用。     

The Trees of the Sacred Natural Sites of Zagori,NW Greece

Cultural landscapes can often be identified by the presence of sacred trees which have been retained and can be recognised as distinctive veteran trees. The characteristics of these trees such as huge size and longevity give them an enduring presence in the landscape, while their conceptualisation as the ‘domesticated’ wild, transform them into symbols of spirituality and local history. In Zagori, NW Greece, trees gain sanctity by virtue of proximity or connection with sacred sites often associated with churches. In these sites, trees can grow into natural shapes as a result of strong taboos, which prevent use for private needs. There is an association between tree species and the nature of the sacred site: broadleaved oaks and maples are associated with outlying churches; plane trees are located in central squares, next to the church and provide a focal point for community life, while in cemeteries native evergreens are nowadays replaced by planted conifers. In the present day local communities appreciate sacred trees as living elements of their collective memory and local history.