On Combinatorial Approximation of Covering 0-1 Integer Programs and Partial Set Cover

The problems dealt with in this paper are generalizations of the set cover problem, min{cx | Ax b, x {0,1}ⁿ}, where c Q₊ⁿ, A {0,1}^{m × n}, b 1. The covering 0-1 integer program is the one, in this formulation, with arbitrary nonnegative entries of A and b, while the partial set cover problem requires only m–K constrains (or more) in Ax b to be satisfied when integer K is additionall specified. While many approximation algorithms have been recently developed for these problems and their special cases, using computationally rather expensive (albeit polynomial) LP-rounding (or SDP-rounding), we present a more efficient purely combinatorial algorithm and investigate its approximation capability for them. It will be shown that, when compared with the best performance known today and obtained by rounding methods, although its performance comes short in some special cases, it is at least equally good in general, extends for partial vertex cover, and improves for weighted multicover, partial set cover, and further generalizations.     

"巴楚文化"的称谓不宜再使用

指出了在古代巴、楚两个民族交错杂居的长江三峡地区 ,不宜用“巴楚文化”来作为这一地区的地域文化名称。因巴文化和楚文化各有特点 ,虽有一些相互影响或部分融合现象 ,但尚不构成一种新的文化 ,故仍不宜随意命名。同时 ,对“三峡地区是楚文化的摇篮”的提法 ,也认为不妥。对有的学者还用“巴楚文化”这一词汇来涵盖从古到今的地域文化 ,更觉不宜     

热印多层次图像的热印头电阻值离散性校正

研究了影响热敏图像层次的主要因素。通过对实验数据的分析，提出了热印头热印电阻值离散性校正的软件和硬件实施方法。     

Urban tree cover: an ecological perspective

Analysis of urban tree cover is generally limited to inventories of tree structure and composition on public lands. This approach provided valuable information for resource management. However, it does not account for all tree cover within an urban landscape, thus providing insufficient information on ecological patterns and processes. We propose evaluating tree cover for an entire urban area that is based on patch dynamics. Treed patches are classified by their origin, structure, and management intensity. A patch approach enables ecologists to evaluate ecological patterns and processes for the entire urban landscape and to examine how social patterns influence these ecological patterns and processes.     

Methods for spatial and temporal land use and land cover assessment for urban ecosystems and application in the greater Baltimore-Chesapeake region

Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods: (1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A geographic information system (GIS) integrates core analyses with historic data on land use change to yield a comprehensive land use and land cover framework and rates of change. These data resources establish the regional foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological and social patterns and processes for varying degrees of urbanization.     

一类其R-投射模是投射的环(Ⅱ)

本文研究了所有R-投射模都是投射模的环(RP-环),得出了它的几个等价条件,证明了:S=R_n为RP-环当且仅当R为RP-环;sum from i=1 to nR_1为RP-环当且仅当每个R_i为RP-环,讨论了RP-环的左投射维数.     

护士长的管理理念和管理艺术

为了提高护士长的管理技巧,医院的护理部要在医院管理中,对全院护士长进行护士长管理技巧的培训。采取的方法有:外请专家讲课、集体培训、跟班指导、个别交谈的方式,这样,会使护士长的管理技巧迅速提高,成为适应医疗改革中的合格管理者。     

浅谈商品房预售若干法律问题

目前，我国房地产市场的商品房买卖中，以预售商品房居多。由于商品房预售在我国还刚刚起步，实践中，应把握有关商品房预售的若干法律问题     

歌唱行腔过程中语言的特点及运用

从汉语的语音结构特点出发，分别从字头、字腹、字尾三个方面阐述在声乐的演唱过程中，怎样按照汉语拼音的声母、韵母和韵尾的固有特点去学习掌握咬字、吐字和运字行腔的方法和规律真正做到字正腔圆、声情并茂。     

Z2—商的秩为2的超椭圆曲面的斜率

设S是一般型的超椭圆曲面，f:S→C是亏格g的超椭圆纤维化。我们证明了如果S的极大挠2商为Z2^2那么λ（f)≥4，等号成立当且仅当S的奇异性指数除s3外全部为0。