Partial t-Spreads in PG(2t+1,q)

This article first of all discusses the problem of the cardinality of maximal partial spreads in PG(3,q), q square, q>4. Let r be an integer such that 2rq+1 and such that every blocking set of PG(2,q) with at most q+r points contains a Baer subplane. If S is a maximal partial spread of PG(3,q) with q ²-1-r lines, then r=s( +1) for an integer s2 and the set of points of PG(3,q) not covered byS is the disjoint union of s Baer subgeometriesPG(3, ). We also discuss maximal partial spreads in PG(3,p ³), p=p ₀ ^h , p ₀ prime, p ₀ 5, h 1, p 5. We show that if p is non-square, then the minimal possible deficiency of such a spread is equal to p ²+p+1, and that if such a maximal partial spread exists, then the set of points of PG(3,p ³) not covered by the lines of the spread is a projected subgeometryPG(5,p) in PG(3,p ³). In PG(3,p ³),p square, for maximal partial spreads of deficiency p ²+p+1, the combined results from the preceding two cases occur. In the final section, we discuss t-spreads in PG(2t+1,q), q square or q a non-square cube power. In the former case, we show that for small deficiencies , the set of holes is a disjoint union of subgeometries PG(2t+1, ), which implies that 0 (mod +1) and, when (2t+1)( -1) <q-1, that 2( +1). In the latter case, the set of holes is the disjoint union of projected subgeometries PG(3t+2, ) and this implies 0 (mod q ^2/3+q ^1/3+1). A more general result is also presented.     

Normal Spreads

In Dedicata 16 (1984), pp. 291–313, the representation of Desarguesian spreads of the projective space PG(2t – 1, q) into the Grassmannian of the subspaces of rank t of PG(2t – 1, q) has been studied. Using a similar idea, we prove here that a normal spread of PG(rt – 1,q) is represented on the Grassmannian of the subspaces of rank t of PG(rt – 1, q) by a cap V _{r, t} of PG(r ^t – 1, q), which is the GF(q)-scroll of a Segre variety product of t projective spaces of dimension (r – 1), and that the collineation group of PG(r ^t – 1, q) stabilizing V _{r, t} acts 2-transitively on V _{r, t} . In particular, we prove that V _{3, 2} is the union of q ² – q + 1 disjoint Veronese surfaces, and that a Hermitan curve of PG(2, q ²) is represented by a hyperplane section U of V _{3, 2}. For q 0,2 (mod 3) the algebraic variety U is the unitary ovoid of the hyperbolic quadric Q ⁺ (7, q) constructed by W. M. Kantor in Canad. J. Math., 5 (1982), 1195–1207. Finally we study a class of blocking sets, called linear, proving that many of the known examples of blocking sets are of this type, and we construct an example in PG(3, q ²). Moreover, a new example of minimal blocking set of the Desarguesian projective plane, which is linear, has been constructed by P. Polito and O. Polverino.     

日历中一种周期现象的解析

指出日历中的国庆日与中秋节重合这种现象发生的周期性.从公历和农历的历法依据——回归年和朔望月出发,利用辗转相除法以及连分数等数学方法对农历的置闰月规律加以推演,进而得出两种历法运行的会合周期.同时对其会合周期的差异性加以分析.     

我国煤矿瓦斯爆炸的研究现状与发展方向

从爆炸机理、爆炸传播、影响因素和技术措施四个方面介绍了瓦斯爆炸事故的研究现状基于瓦斯爆炸机理，指出了瓦斯爆炸事故的研究中存在的问题和发展方向。     

Scattered Spaces with Respect to a Spread in PG(n,q)

A scattered subspace of PG(n-1,q) with respect to a (t-1)-spread S is a subspace intersecting every spread element in at most a point. Upper and lower bounds for the dimension of a maximum scattered space are given. In the case of a normal spread new classes of two intersection sets with respect to hyperplanes in a projective space are obtained using scattered spaces.     

以8051为核的SOC中的万年历的设计

简要介绍了片上系统（SOC）的设计方法和发展状况．重点讨论了以DW8051单片机为内核的SOC中的万年历电路的设计．给出了该万年历的功能、嵌入到DW8051的方法、电路结构和模拟仿真结果．     

On the Spectrum of the Sizes of Maximal Partial Line Spreads in <Emphasis Type="Italic">PG</Emphasis>(2<Emphasis Type="Italic">n</Emphasis>,<Emphasis Type="Italic">q</Emphasis>), <Emphasis Type="Italic">n</Emphasis> ≥ 3

A lot of research has been done on the spectrum of the sizes of maximal partial spreads in PG(3,q) [P. Govaerts and L. Storme, Designs Codes and Cryptography, Vol. 28 (2003) pp. 51–63; O. Heden, Discrete Mathematics, Vol. 120 (1993) pp. 75–91; O. Heden, Discrete Mathematics, Vol. 142 (1995) pp. 97–106; O. Heden, Discrete Mathematics, Vol. 243 (2002) pp. 135–150]. In [A. Gács and T. Sznyi, Designs Codes and Cryptography, Vol. 29 (2003) pp. 123–129], results on the spectrum of the sizes of maximal partial line spreads in PG(N,q), N 5, are given. In PG(2n,q), n 3, the largest possible size for a partial line spread is q^2n-1+q^2n-3+...+q³+1. The largest size for the maximal partial line spreads constructed in [A. Gács and T. Sznyi, Designs Codes and Cryptography, Vol. 29 (2003) pp. 123–129] is (q²ⁿ⁺¹–q)/(q²–1)–q³+q²–2q+2. This shows that there is a non-empty interval of values of k for which it is still not known whether there exists a maximal partial line spread of size k in PG(2n,q). We now show that there indeed exists a maximal partial line spread of size k for every value of k in that interval when q 9.J. Eisfeld: Supported by the FWO Research Network WO.011.96NP. Sziklai: The research of this author was partially supported by OTKA D32817, F030737, F043772, FKFP 0063/2001 and Magyary Zoltan grants. The third author is grateful for the hospitality of Ghent University.     

水族数学史研究

本文在调查、搜集、整理有关水族数学史方面资料的基础上,对水族的数学发展史从如下四个方面作了初步研究:(1)水族古歌、古文字与水语中所反映的数概念及实物、木刻的记数方法;(2)数的四则运算;(3)水族某些古文字的字形、民间乐器、石棺古墓、民间工艺品中所反映的几何观念;(4)度量、方位及水历中的数学问题。     

<授时历>与仲康日食推算

《书经》所载“仲康日食”的时间确定问题一直是夏年代学中的一个难题 基于华夏历史时期天文家们的研究成果 ,尤其是根据复原了的元代《授时历》交食推步术及有关史料 ,重新考察这次日食事件及古代的推步结果 ,确认了郭守敬等用《授时历》推算出的“仲康日食”发生的日期当是公元前 2 12 8年 10月 13日 ;提供了由《授时历》方法编算的 - 2 2 0 0至 - 1799年日食典 ;为进一步的研究准备了条件     

Results on Maximal Partial Spreads in PG(3, p 3) and on Related Minihypers

This article classifies all {(q + 1), 3, q}-minihypers, small, q = p ^h ₀, h 1, for a prime number p ₀ 7, which arise from a maximal partial spread of deficiency . When q is a third power, the minihyper is the disjoint union of projected PG(5, )'s; when q is a square, also Baer subgeometries PG(3, ) can occur. This leads to a discrete spectrum for the small values of the deficiency of the corresponding maximal partial spreads.