Optimal Imperfect Periodic Preventive Maintenance for Systems in Time-Varying Environments

2012 ◽  
Vol 61 (2) ◽  
pp. 426-439 ◽  
Author(s):  
Xiaofei Lu ◽  
Maoyin Chen ◽  
Min Liu ◽  
Donghua Zhou
Keyword(s):  
Preventive Maintenance ◽  
Time Varying ◽  
Periodic Preventive Maintenance ◽  
Varying Environments

scholarly journals Physical interactions reduce the power of natural selection in growing yeast colonies

2018 ◽  
Vol 115 (45) ◽  
pp. 11448-11453 ◽  
Author(s):  
Andrea Giometto ◽  
David R. Nelson ◽  
Andrew W. Murray
Keyword(s):  
Natural Selection ◽  
Continuum Model ◽  
Microbial Populations ◽  
Mechanical Forces ◽  
Time Varying ◽  
Drug Resistant ◽  
Yeast Strains ◽  
Physical Interactions ◽  
Varying Environments ◽  
Doubling Times

Microbial populations often assemble in dense populations in which proliferating individuals exert mechanical forces on the nearby cells. Here, we use yeast strains whose doubling times depend differently on temperature to show that physical interactions among cells affect the competition between different genotypes in growing yeast colonies. Our experiments demonstrate that these physical interactions have two related effects: they cause the prolonged survival of slower-growing strains at the actively-growing frontier of the colony and cause faster-growing strains to increase their frequency more slowly than expected in the absence of physical interactions. These effects also promote the survival of slower-growing strains and the maintenance of genetic diversity in colonies grown in time-varying environments. A continuum model inspired by overdamped hydrodynamics reproduces the experiments and predicts that the strength of natural selection depends on the width of the actively growing layer at the colony frontier. We verify these predictions experimentally. The reduced power of natural selection observed here may favor the maintenance of drug-resistant cells in microbial populations and could explain the apparent neutrality of interclone competition within tumors.

Time-Varying Environments and Noise

2000 ◽  
pp. 307-330
Author(s):  
Zbigniew Michalewicz ◽  
David B. Fogel
Keyword(s):  
Time Varying ◽  
Varying Environments
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