26,764 research outputs found
Arcs with large conical subsets in Desarguesian planes of even order
We give an explicit classification of the arcs in PG (2, q) (q even) with a large conical suset and excess 2, i.e., that consist of q/2 + 1 points of a conic and two points not on that conic. Apart from the initial setup,the methods used are similar to those for the case of odd q, published earlier
A geometric approach to Mathon maximal arcs
In 1969 Denniston gave a construction of maximal arcs of degree d in
Desarguesian projective planes of even order q, for all d dividing q. In 2002
Mathon gave a construction method generalizing the one of Denniston. We will
give a new geometric approach to these maximal arcs. This will allow us to
count the number of isomorphism classes of Mathon maximal arcs of degree 8 in
PG(2,2^h), h prime.Comment: 20 page
On sizes of complete arcs in PG(2,q)
New upper bounds on the smallest size t_{2}(2,q) of a complete arc in the
projective plane PG(2,q) are obtained for 853 <= q <= 4561 and q\in T1\cup T2
where T1={173,181,193,229,243,257,271,277,293,343,373,409,443,449,457,
461,463,467,479,487,491,499,529,563,569,571,577,587,593,599,601,607,613,617,619,631,
641,661,673,677,683,691, 709},
T2={4597,4703,4723,4733,4789,4799,4813,4831,5003,5347,5641,5843,6011,8192}.
From these new bounds it follows that for q <= 2593 and q=2693,2753, the
relation t_{2}(2,q) < 4.5\sqrt{q} holds. Also, for q <= 4561 we have t_{2}(2,q)
< 4.75\sqrt{q}. It is showed that for 23 <= q <= 4561 and q\in T2\cup
{2^{14},2^{15},2^{18}}, the inequality t_{2}(2,q) < \sqrt{q}ln^{0.75}q is true.
Moreover, the results obtained allow us to conjecture that this estimate holds
for all q >= 23. The new upper bounds are obtained by finding new small
complete arcs with the help of a computer search using randomized greedy
algorithms. Also new constructions of complete arcs are proposed. These
constructions form families of k-arcs in PG(2,q) containing arcs of all sizes k
in a region k_{min} <= k <= k_{max} where k_{min} is of order q/3 or q/4 while
k_{max} has order q/2. The completeness of the arcs obtained by the new
constructions is proved for q <= 1367 and 2003 <= q <= 2063. There is reason to
suppose that the arcs are complete for all q > 1367. New sizes of complete arcs
in PG(2,q) are presented for 169 <= q <= 349 and q=1013,2003.Comment: 27 pages, 4 figures, 5 table
New sizes of complete arcs in PG(2,q)
New upper bounds on the smallest size t_{2}(2,q) of a complete arc in the
projective plane PG(2,q) are obtained for 853<= q<= 2879 and q=3511,4096,
4523,5003,5347,5641,5843,6011. For q<= 2377 and q=2401,2417,2437, the relation
t_{2}(2,q)<4.5\sqrt{q} holds. The bounds are obtained by finding of new small
complete arcs with the help of computer search using randomized greedy
algorithms. Also new sizes of complete arcs are presented.Comment: 10 page
Generalised Veroneseans
In \cite{ThasHVM}, a characterization of the finite quadric Veronesean
by means of properties of the set of its tangent
spaces is proved. These tangent spaces form a {\em regular generalised dual
arc}. We prove an extension result for regular generalised dual arcs. To
motivate our research, we show how they are used to construct a large class of
secret sharing schemes
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