OGO-2 Magnetic Field Observations During the Magnetic Storm of March 13-15, 1966

Magnetic disturbances examined for correlation of surface and satellite magnetic field measurement

Subalgebras of FA-presentable algebras

Automatic presentations, also called FA-presentations, were introduced to extend finite model theory to infinite structures whilst retaining the solubility of fundamental decision problems. This paper studies FA-presentable algebras. First, an example is given to show that the class of finitely generated FA-presentable algebras is not closed under forming finitely generated subalgebras, even within the class of algebras with only unary operations. However, it is proven that a finitely generated subalgebra of an FA-presentable algebra with a single unary operation is itself FA-presentable. Furthermore, it is proven that the class of unary FA-presentable algebras is closed under forming finitely generated subalgebras, and that the membership problem for such subalgebras is decidable.Comment: 19 pages, 6 figure

A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer

The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures

Context-free rewriting systems and word-hyperbolic structures with uniqueness

This paper proves that any monoid presented by a confluent context-free monadic rewriting system is word-hyperbolic. This result then applied to answer a question asked by Duncan & Gilman by exhibiting an example of a word-hyperbolic monoid that does not admit a word-hyperbolic structure with uniqueness (that is, in which the language of representatives maps bijectively onto the monoid)

INCORPORATING THE 1990 FARM BILL INTO FARM-LEVEL DECISION MODELS: AN APPLICATION TO COTTON FARMS

A five-year, 0.1, mixed integer programming model was developed to analyze the effects of 1990 Farm Bill legislation on the crop-mix decisions made on cotton farms. Results showed that, when compared to the 1985 Farm Bill, the 1990 Farm Bill can result in higher whole-farm income despite new "triple base" provisions limiting payment acres. The increase in income results from elimination of limited cross-compliance provisions and the change to a three-year base calculation. The model was also used to assess the likely impact of possible changes in the current legislation.Cotton farms, Farm programs, Programming models, Agricultural and Food Policy, Crop Production/Industries,

Graphs and principal ideals of finite commutative rings

In \cite{ABM}, Afkhami and Khashyarmanesh introduced the cozero-divisor graph of a ring, $\Gamma\u27(R)$, which examines relationships between principal ideals. We continue investigating the algebraic implications of the graph by developing the reduced cozero-divisor graph, which is a simpler analog

Markov semigroups, monoids, and groups

A group is Markov if it admits a prefix-closed regular language of unique representatives with respect to some generating set, and strongly Markov if it admits such a language of unique minimal-length representatives over every generating set. This paper considers the natural generalizations of these concepts to semigroups and monoids. Two distinct potential generalizations to monoids are shown to be equivalent. Various interesting examples are presented, including an example of a non-Markov monoid that nevertheless admits a regular language of unique representatives over any generating set. It is shown that all finitely generated commutative semigroups are strongly Markov, but that finitely generated subsemigroups of virtually abelian or polycyclic groups need not be. Potential connections with word-hyperbolic semigroups are investigated. A study is made of the interaction of the classes of Markov and strongly Markov semigroups with direct products, free products, and finite-index subsemigroups and extensions. Several questions are posed.Comment: 40 pages; 3 figure

SplashKit: A Development Framework for Motivating and Engaging Students in Introductory Programming

Learning to program is known to be challenging for many students. Upon entry, students often have poor perceptions of their capabilities with some anxiety around the challenges they expect to face in learning to code. Lowering the barriers to entry will help ease students into programming and enable a broader range of student to continue programming. SplashKit is an educationally focused development framework designed to aid the teaching of programming by empowering students to create interesting and dynamic programs from their first programming tasks. This paper explores how SplashKit can be used in tertiary education to underpin a range of introductory programming approaches