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The well-known Steiner problem on networks is an NP-complete problem for which there are many deterministic algorithms and heuristics. In this paper a new approach to the directed version of this problem is made by applying the ideas of statistical mechanics through the use of the method of simulated annealing. Two different types of cooling algorithms are tailored to the Directed Steiner Problem. Computations are done on a test bed of 480 random graphs in order to study the performance of these algorithms. In addition to the quality of the final answers, the study looks at the distribution of first occurrences during the execution of the cooling schedules of answers that are within 3% of the optimum. The study suggests that these near-optimal answers appear according to an approximately exponential distribution and that they can be obtained in polynomial time. Experiments also indicate that for random graphs annealing usually gives near-optimal answers in less time than does branch and bound. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.

Alfalfa (Medicago sativa L.) breeders have made substantial progress in recent years to develop cultivars with resistance to Aphanomyces root rot (ARR, caused by Aphanomyces euteiches), yet data showing the agronomic benefits of this resistance under natural field conditions are limited. Two trials were seeded into naturally infested soils with alfalfa cultivars ranging from susceptible to highly resistant to ARR. The trials provided a test of the hypothesis that ARR‐resistant cultivars would provide improved performance. In one test, the combination of high rainfall during the 4 wk following seeding on a soil with a slow percolation rate led to a severe outbreak of ARR, with symptoms typical of a syndrome commonly observed in commercial alfalfa fields in Kentucky. Under these conditions, the ARR‐resistant cultivars provided dramatically improved seedling health, yield, and persistence. Cultivars having a resistance (R) or high resistance (HR) rating provided the most consistent performance. In the other test, a near‐normal rainfall amount on a deep soil with good internal drainage led to moderate disease pressure. In that case, the ARR‐resistant cultivars exhibited a slight improvement in seedling health, but yield trends were not as clear as in the former trial. Based on these findings and previous research, we conclude that the use of cultivars with R or HR ratings to ARR may solve a common stand‐establishment problem in spring‐seeded alfalfa in Kentucky.

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Our entering freshmen have little experience with the underlying concepts of computer science and information technology, and they are not familiar with the process of absorbing new information through listening and reading and cooperating with other well-trained individuals to increase their knowledge and skills in a subject. Simply making group assignments requiring research papers and presentations does not enable students to appreciate this process which is a characteristic of all fields of scientific inquiry today. Most of our upper division courses have team projects, but student culture resists effective teamwork. We have established a course for freshman entitled "Thinking, Speaking, and Writing in Computer Science" in which we try to lay the groundwork for group work in later classes by fostering a sense of interdependence among team members, accountability of individual students to the team in the form of preparation and completion of project tasks, frequent meetings to promote team goals, the development of social skills required for collaboration, and the value of group discussion of strategies in problem solving. Although the course has been in existence only two years, our department has observed that students are finding that following this approach to learning leads to improved academic performance, and that students are becoming more adept in learning skills as they realize the benefits that accrue from our approach to intelligent interaction with their peers and instructors.