Heuristics in Job Shop Scheduling

The problem is that of scheduling jobs with diverse routings on the productive facilities in a shop such that the respective due dates are met, or failing this, the sum of lateness times is minimized. The approach is simulative in that the operation of the shop is simulated in a Fortran program, but in addition to the straightforward use of priority rules for determining sequences of jobs on the machines, a number of heuristics or rules of thumb are incorporated. Both the static and dynamic problems are investigated. The efficacy of a small number of heuristics in combination with certain priority rules is demonstrated.

Spiny plants, mammal browsers, and the origin of African savannas

Savannas first began to spread across Africa during the Miocene. A major hypothesis for explaining this vegetation change is the increase in C4 grasses, promoting fire. We investigated whether mammals could also have contributed to savanna expansion by using spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852 tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for the same tree species, we found that spinescence evolved at least 55 times. The diversification of spiny plants occurred long after the evolution of Afrotherian proboscideans and hyracoids. However, it is remarkably congruent with diversification of bovids, the lineage including the antelope that predominantly browse these plants today. Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas and probably, in different environmental conditions. Spiny savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.We thank the Government of Canada through Genome Canada and the Ontario Genomics Institute (2008-OGI-ICI-03), the International Development Research Centre (Canada), the University of Johannesburg Analytical Facility (South Africa), the South African National Research Foundation, and the Royal Society (United Kingdom) for financial support and various local and international authorities who granted plant collection permits. T.C.-D., G.P.H., and W.J.B. thank the Mellon Foundation, the Claude Leon Foundation, and the National Research Foundation for financial support.http://www.pnas.orghb2017Plant Scienc

Traversing the Topical Landscape

In light of recent theoretical and empirical developments in the areas of reading, writing, and learning, this article proposes a view of literacy learning in which various forms of reading and writing are conceptualized as unique ways of thinking about and exploring a topic of study en route to acquiring knowledge. Throughout this article, we take the theoretical position that a topic of study is analogous to a conceptual “landscape” about which knowledge is best acquired by “traversing” it from a variety of perspectives. In this system, different forms of reading and writing represent the “traversal routes” through which an individual can explore a given content domain. Specifically, we wish to argue that more complex or diverse combinations of different forms of reading and writing provide a learner with the means to conduct a more critical inquiry of a topic by virtue of the multiple perspectives or ways of “seeing” and thinking that these reading and writing exchanges permit. Finally, in light of this theoretical orientation, we contend that the ability to direct dynamically one's own reading and writing engagements en route to learning is central to conducting an inquiry of this nature. This perspective suggests a reexamination of a line of research that has pursued the question of how writing in combination with reading influences thinking and learning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68664/2/10.1177_0741088389006003001.pd