Causes and biophysical consequences of cellulose production by Pseudomonas fluorescens SBW25 at the air-liquid interface

Cellulose over-producing wrinkly spreader mutants of Pseudomonas fluorescens SBW25 have been the focus of much investigation, but conditions promoting the production of cellulose in ancestral SBW25, its effects and consequences have escaped in-depth investigation through lack of in vitro phenotype. Here, using a custom built device, we reveal that in static broth microcosms ancestral SBW25 encounters environmental signals at the air-liquid interface that activate, via three diguanylate cyclase-encoding pathways (Wsp, Aws and Mws), production of cellulose. Secretion of the polymer at the meniscus leads to modification of the environment and growth of numerous micro-colonies that extend from the surface. Accumulation of cellulose and associated microbial growth leads to Rayleigh-Taylor instability resulting in bioconvection and rapid transport of water-soluble products over tens of millimetres. Drawing upon data we build a mathematical model that recapitulates experimental results and captures the interactions between biological, chemical and physical processes.IMPORTANCE This work reveals a hitherto unrecognized behaviour that manifests at the air-liquid interface, which depends on production of cellulose, and hints to undiscovered dimensions to bacterial life at surfaces. Additionally, the study links activation of known diguanylate cyclase-encoding pathways to cellulose expression and to signals encountered at the meniscus. Further significance stems from recognition of the consequences of fluid instabilities arising from surface production of cellulose for transport of water-soluble products over large distances

Experimental and Analytical Investigation of the Transonic and Supersonic Divergence Characteristics of a Delta-Plan-Form All- Movable Control

The static aeroelastic divergence characteristics of a delta-planform model of the canard control surface of a proposed air-to-ground missile have been studied both analytically and experimentally in the Mach number range from 0.6 to 3.0. The experiments indicated that divergence occurred at a nearly constant value of dynamic pressure at Mach numbers up to 1.2. At higher Mach numbers somewhat higher values of dynamic pressure were required to produce divergence. The analysis and the experiment indicate that the camber stiffness of the control surface and the stiffness of the control actuator are both important in divergence of surfaces of this type

Balls, Strikes, and Norms: Rule Violations and Normative Rules Among Baseball Umpires

This study investigated the use of normative rules by baseball umpires. Normative rules are informal standards of conduct that deviate from the official rules of sport. Sixteen umpires, 25 coaches, and 27 baseball players defined the official upper and lower boundaries of the strike zone, marked these official boundaries on a Strike Zone Form, and marked where they actually call, or believe umpires call, the boundaries. Umpires were significantly more knowledgeable about rules than players were. Umpires reported setting the upper boundary of the strike zone significantly lower (an average of 2.64 inches) than the official rule specifies. Coaches and players reported that umpires lower the boundaries, but players overestimated how much umpires deviate from the rule-book boundaries. Results suggest that umpires consciously violate official rules. The ethical implications of these findings are discussed

Judgment Bias in Baseball Umpires First Base Calls: A Computer Simulation

Tested 39 baseball umpires and 39 undergraduates, using a computer simulation of 1st-base calls to determine the role of the prior entry phenomenon in close plays. Because umpires are directed to focus their attention on an auditory stimulus (ball hitting the glove), they may experience prior entry of the auditory stimulus, resulting in safe runners being called out. There were more errors when runners were just safe and safe because of a tie than when runners were just out, indicating that prior entry occurred in the simulations. This was more pronounced among umpires than controls

Faculty survey on upper-division thermal physics content coverage

Thermal physics is a core course requirement for most physics degrees and encompasses both thermodynamics and statistical mechanics content. However, the primary content foci of thermal physics courses vary across universities. This variation can make creation of materials or assessment tools for thermal physics difficult. To determine the scope and content variability of thermal physics courses across institutions, we distributed a survey to over 140 institutions to determine content priorities from faculty and instructors who have taught upper-division thermodynamics and/or statistical mechanics. We present results from the survey, which highlight key similarities and differences in thermal physics content coverage across institutions. Though we see variations in content coverage, we found 9 key topical areas covered by all respondents in their upper-division thermal physics courses. We discuss implications of these findings for the development of instructional tools and assessments that are useful to the widest range of institutions and physics instructors.Comment: Physics Education Research Conferenc