Algebraic surfaces of general type withK 2=2p g−1,p g≥5

This paper mainly deals with minimal algebraic surfaces of general type withK ²=2p _g–1. We prove that forp _g7 all these surfaces are birational to a double cover of some rational surfaces, and all but a finite classes of them have a unique fibration of genus 2; then we study their structures by determining their branch loci and singular fibres. We study similarly for surfaces withp _g=5, 6. Lastly we show that whenp _g13 all these surfaces are simply-connected.     

The Fossils in Shangxi Group and Its Implication for Tectonics, Southern Anhui, China

The Shangxi Group is the local name in southern Anhui Province and it is believed to be the equivalence of the well-known Banxi Group in Hunan Province, southern China. So the area occupied by the Shangxi Group was regarded as a part of the "Jiangnan old land" of Presinian till it was challenged by the present authors years ago. After we postulated that there may be some strata of Palaeozoic Era in Shangxi Group, some microfossils and then macrofossils of Palaeozoic were found in some part of it. The macrof os-sils, Lingula sp. , Conulariid and the microfossils indicate that most units of the Shangxi Group are Palaeozoic strata. Based on the discovery of these fossils and the recognition of the tectonic-setting of the different tectono-petrologic units in the Shangxi Group, three different stratigraphic sequences (island-arc volcanics, back-arc sediments and the cover of passive margin of Yangtze Continental Plate) are established and the tectonic evolution of them is postulated in the present paper. Al     

合肥董铺岛目测云量统计及其与仪器测量资料的对比

利用合肥董铺岛1999～2004年目测的云量测量资料,统计分析了年、季、月总云量的平均和概率分布。结果表明：夏季云量偏多,平均每天有80%,秋季云量最少,平均每天不足50%,十一月份的无云天为全月的25%,六月份100%云量的天数占全月的57%。这可能与本地区雨季和下垫面的影响及东亚季风有关。同时对目测与全天空成象仪在2004年4月～2005年4月的所测云量资料作了相关性分析,两者测量的月总云量的相关系数都大于0．75,但仪器对大气层水汽和气溶胶等悬浮粒子(即雾气)真实的识别性不够,两者之间平均约有1%～7%的差异。     

On the Computational Complexity of the Minimum Committee Problem

Two special cases of the Minimum Committee Problem are studied, the Minimum Committee Problem of Finite Sets (MCFS) and the Minimum Committee Problem of a System of Linear Inequalities(MCLE). It is known that the first of these problems is NP-hard (see (Mazurov et al., Proc. Steklov Inst. Math., 1:67–101, 2002)). In this paper we show the NP-hardness of two integer optimization problems connected with it. In addition, we analyze the hardness of approximation to the MCFS problem. In particular, we show that, unless NP⊂TIME(n ^O(loglogn )), for every ε>0 there are no approximation algorithms for this problem with approximation ratio (1–ε)ln (m–1), where m is the number of inclusions in the MCFS problem. To prove this bound we use the SET COVER problem, for which a similar result is known (Feige, J. ACM, 45:634–652, 1998). We also show that the Minimum Committee of Linear Inequalities System (MCLE) problem is NP-hard as well and consider an approximation algorithm for this problem.      

土地利用现状管理信息系统中土地利用多级变更模型的建立及其事务处理机制设计

土地利用变更模型及其事务处理机制是土地利用现状管理信息系统的核心．传统变更模型所支持的变更操作粒度较为单一、事务完整性差、时空语义表现过于单薄．在分析了土地利用变更特点和存在问题的基础上，提出了一种土地利用多级变更模型LU-MCM（1and use multi—level change model），模型以土地利用变迁过程为变更对象，并进一步将之划分为多级变更逻辑单元进行组合描述，而所需解决的长事务处理机制则通过扩展的多粒度树状事务模型实现．土地利用现状管理信息系统的设计和实现证明，该模型对土地利用变迁过程表达效果较好，为土地利用变更数据管理提供了思路．     

On finite edge transitive graphs and rotary maps

It is shown that every connected vertex and edge transitive graph has a normal multicover that is a connected normal edge transitive Cayley graph. Moreover, every chiral or regular map has a normal cover that is a balanced chiral or regular Cayley map, respectively. As an application, a new family of half-transitive graphs is constructed as 2-fold covers of a family of 2-arc transitive graphs admitting Suzuki groups.     

Canonical covers and dimension of Z-sets in the Hilbert cube

In this paper we characterize the finite dimensionality of a compact Z-set in the Hilbert cube in terms of the existence of a particular canonical cover in its complement.

     

Relations between Clar structures, Clar covers, and the sextet-rotation tree of a hexagonal system

Sextet rotations of the perfect matchings of a hexagonal system H are represented by the sextet-rotation-tree R(H), a directed tree with one root. In this article we find a one-to-one correspondence between the non-leaves of R(H) and the Clar covers of H, without alternating hexagons. Accordingly, the number (nl) of non-leaves of R(H) is not less than the number (cs) of Clar structures of H. We obtain some simple necessary and sufficient conditions, and a criterion for cs=nl, that are useful for the calculation of Clar polynomials. A procedure for constructing hexagonal systems with cs<nl is provided in terms of normal additions of hexagons.     

Very large cliques are easy to detect

It is known that, for every constant k?3, the presence of a k-clique (a complete sub-graph on k vertices) in an n-vertex graph cannot be detected by a monotone boolean circuit using much fewer than n^k gates. We show that, for every constant k, the presence of an (n-k)-clique in an n-vertex graph can be detected by a monotone circuit using only a logarithmic number of fanin-2 OR gates; the total number of gates does not exceed O(n²logn). Moreover, if we allow unbounded fanin, then a logarithmic number of gates is enough.     

移动数据通信技术应用与发展

本阐述了蜂窝数字分组数据（ＣＤＰＤ）系统技术的产生与发展、特点、网络结构和技术应用。