New constructions for covering designs

A $(v,k,t)$ {\em covering design}, or {\em covering}, is a family of $k$-subsets, called blocks, chosen from a $v$-set, such that each $t$-subset is contained in at least one of the blocks. The number of blocks is the covering's {\em size}, and the minimum size of such a covering is denoted by $C(v,k,t)$. This paper gives three new methods for constructing good coverings: a greedy algorithm similar to Conway and Sloane's algorithm for lexicographic codes~\cite{lex}, and two methods that synthesize new coverings from preexisting ones. Using these new methods, together with results in the literature, we build tables of upper bounds on $C(v,k,t)$ for $v \leq 32$, $k \leq 16$, and $t \leq 8$.

Group divisible designs, GBRDSDS and generalized weighing matrices

We give new constructions for regular group divisible designs, pairwise balanced designs, generalized Bhaskar Rao supplementary difference sets and generalized weighing matrices. In particular if p is a prime power and q divides p - 1 we show the following exist; (i) GDD (2(p2+p+1), 2(p2+p+1), rp2,2p2, λ1 = p2λ, λ2 = (p2-p)r, m=p2+p+1,n=2), r_+1,2; (ii) GDD(q(p+1), q(p+1), p(q-1), p(q-1),λ1=(q-1)(q-2), λ2=(p-1)(q-1)2/q,m=q,n=p+1); (iii) PBD(21,10;K),K={3,6,7} and PDB(78,38;K), K={6,9,45}; (iv) GW(vk,k2;EA(k)) whenever a (v,k,λ)-difference set exists and k is a prime power; (v) PBIBD(vk2,vk2,k2,k2;λ1=0,λ2=λ,λ3=k) whenever a (v,k,λ)-difference set exists and k is a prime power; (vi) we give a GW(21;9;Z3)

Some new results on skew frame starters in cyclic groups

In this paper, we study skew frame starters, which are strong frame starters that satisfy an additional "skew" property. We prove three new non-existence results for cyclic skew frame starters of certain types. We also construct several small examples of previously unknown cyclic skew frame starters by computer

The Economics of the Restatement and of the Common Law

The common law process appears to have checks and balances that prevent the self-interest of a particular embedded actor (judge or lawyer) from having a substantial distortive effect. The question that follows is whether the Restatement project is also immune, to the same extent as the common law, from the self-interested incentives of actors involved in its creation. I argue that the Restatement process is far more vulnerable to distortion from self-interest than is the common law process

The Economics of the Restatement and of the Common Law

The common law process appears to have checks and balances that prevent the self-interest of a particular embedded actor (judge or lawyer) from having a substantial distortive effect. The question that follows is whether the Restatement project is also immune, to the same extent as the common law, from the self-interested incentives of actors involved in its creation. I argue that the Restatement process is far more vulnerable to distortion from self-interest than is the common law process

Uniform Mixing on Cayley Graphs over Z_3^d

This thesis investigates uniform mixing on Cayley graphs over Z_3^d. We apply Mullin's results on Hamming quotients, and characterize the 2(d+2)-regular connected Cayley graphs over Z_3^d that admit uniform mixing at time 2pi/9. We generalize Chan's construction on the Hamming scheme H(d,2) to the scheme H(d,3), and find some distance graphs of the Hamming graph H(d,3) that admit uniform mixing at time 2pi/3^k for any k≥2. To restrict the mixing time, we derive a sufficient and necessary condition for uniform mixing to occur on a Cayley graph over Z_3^d at a given time. Using this, we obtain three results. First, we give a lower bound of the valency of a Cayley graph over Z_3^d that could admit uniform mixing at some time. Next, we prove that no Hamming quotient H(d,3)/ admits uniform mixing at time earlier than 2pi/9. Finally, we explore the connected Cayley graphs over Z_3^3 with connected complements, and show that five complementary graphs admit uniform mixing with earliest mixing time 2pi/9