Small complete caps in PG(N,q), q even

A new family of small complete caps in PG(N,q), q even, is constructed. Apart from small values of either N or q, it provides an improvement on the currently known upper bounds on the size of the smallest complete cap in PG(N,q): for N even, the leading term is replaced by with , for N odd the leading term is replaced by with . © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 420–436, 2007     

On Cyclic Caps in Projective Spaces

Let H be a subgroup of a cyclic Singer group of PG (n,q). In this paper we study the following problem: When is a point orbit of H a cap? A necessary and sufficient condition for this is derived and used to give a short proof of some results by Ebert [6] and to show that small orbits are typically caps.     

Constructions of Small Complete Caps in Binary Projective Spaces

In the binary projective spaces PG(n,2) k-caps are called large if k > 2^n-1 and smallif k ≤ 2^n-1. In this paper we propose new constructions producing infinite families of small binary complete caps.AMS Classification: 51E21, 51E22, 94B05     

Small complete caps in Galois affine spaces

Some new families of caps in Galois affine spaces AG(N, q) of dimension N≡ 0(mod 4) and odd order q are constructed. Such caps are proven to be complete by using some new ideas depending on the concept of a regular point with respect to a complete plane arc. As a corollary, an improvement on the currently known upper bounds on the size of the smallest complete caps in AG(N, q) is obtained. This research was performed within the activity of GNSAGA of the Italian INDAM, with the financial support of the Italian Ministry MIUR project “Strutture geometriche, combinatorica e loro applicazioni”, PRIN 2004–2005.     

复射影空间中具有常数量曲率的完备全实子流形

本文研究了复射影空间中具有常数量曲率的完备全实子流形的问题.利用丘成桐的广义极大值原理和自伴随算子,获得了这类子流形的某些内蕴刚性定理.     

Diffeomorphism classification of smooth weighted complete intersections

Xn(d1, . . . , dr-1, dr; w) and Xn(e1, . . . , er-1, dr; w) are two complex odd-dimensional smooth weighted complete intersections defined in a smooth weighted hypersurface Xn+r-1(dr; w). We prove that they are diffeomorphic if and only if they have the same total degree d, the Pontrjagin classes and the Euler characteristic, under the following assumptions: the weights w = (ω0, . . . , ωn+r) are pairwise relatively prime and odd, νp(d/dr) ≥ 2n+1/ 2(p-1) + 1 for all primes p with p(p-1) ≤ n + 1, where νp(d/dr) satisfies d/dr =Ⅱp prime pνp (d/dr).     

New Families of Complete Caps, and the Asymptotic Size of the Largest Caps, of Quadrics over Prime Fields

A cap of a quadric is a set of its points whose pairwise joins are all chords. Such a cap is complete if it is not part of a larger one. Few examples of complete caps are known except for quadrics in low dimensions. In this paper, we consider the case when the coordinate field is GF(p), with p an odd prime, and construct, in each projective space GF(n,p) with n p – 1 and n – 2(mod p), a cap on one of its nonsingular quadrics. We use this in two ways. Firstly, we combine its size with the recent Blokhuis–Moorhouse upper bound for quadric caps to show that the size of the largest cap of any nonsingular quadric in PG(N,p) is asymptotic to Np – 1/(p – 1) ! as N tends to infinity. Secondly, by establishing situations when our cap is complete, we produce various infinite families of complete quadric caps over GF(p) for each p. Earlier work determined all complete caps of all nonsingular quadrics over GF(2).     

Projective Modules and Complete Intersections

Let A be a Noetherian ring of dimension n and P be a projective A module of rank n having trivial determinant. It is proved that if n is even and the image of a generic element g P^* is a complete intersection, then [P] = [Q A] in K₀(A) for some projective A module Q of rank n – 1. Further, it is proved that if n is odd, A is Cohen–Macaulay and [P] = [Q A] in K₀(A) for some projective A module Q of rank n – 1, then P has a unimodular element.     

Nonexistence of [n, 5, d]q Codes Attaining the Griesmer Bound for q4 ?2q2 ?2q+1 ≤ d≤ q4?2q2 ?q

We prove that there does not exist a [q⁴+q³−q²−3q−1, 5, q⁴−2q²−2q+1]_q code over the finite field for q≥ 5. Using this, we prove that there does not exist a [g_q(5, d), 5, d]_q code with q⁴ −2q² −2q +1 ≤ d ≤ q⁴ −2q² −q for q≥ 5, where g_q(k,d) denotes the Griesmer bound.MSC 2000: 94B65, 94B05, 51E20, 05B25     

Vanishing of Tate Homology — An Application of Stable Homology for Complexes

It has been proved that the vanishing of Tate homology is a sufficient condition for the derived depth formula to hold in [J. Pure Appl. Algebra, 219, 464–481(2015)]. In this paper, we investigate when Tate homology vanishes by studying the stable homology theory for complexes. Properties such as the balancedness and vanishing of stable homology for complexes are studied. Our results show that the vanishing of this homology can detect finiteness of homological dimensions of complexes and regularness of rings.     

On Equitorsion Holomorphically Projective Mappings of Generalized Kählerian Spaces

In this paper we investigate holomorphically projective mappings of generalized Kählerian spaces. In the case of equitorsion holomorphically projective mappings of generalized Kählerian spaces we obtain five invariant geometric objects for these mappings.