Investigation of pressure predication methods for low flow radial impellers, phase III FINAL report, Jun. 1963 - Feb. 1966

Pressure predication methods for low flow radial impellers using Fortran progra

Evolutionary Dynamics on Protein Bi-stability Landscapes Can Potentially Resolve Adaptive Conflicts

Experimental studies have shown that some proteins exist in two alternative native-state conformations. It has been proposed that such bi-stable proteins can potentially function as evolutionary bridges at the interface between two neutral networks of protein sequences that fold uniquely into the two different native conformations. Under adaptive conflict scenarios, bi-stable proteins may be of particular advantage if they simultaneously provide two beneficial biological functions. However, computational models that simulate protein structure evolution do not yet recognize the importance of bi-stability. Here we use a biophysical model to analyze sequence space to identify bi-stable or multi-stable proteins with two or more equally stable native-state structures. The inclusion of such proteins enhances phenotype connectivity between neutral networks in sequence space. Consideration of the sequence space neighborhood of bridge proteins revealed that bi-stability decreases gradually with each mutation that takes the sequence further away from an exactly bistable protein. With relaxed selection pressures, we found that bi-stable proteins in our model are highly successful under simulated adaptive conflict. Inspired by these model predictions, we developed a method to identify real proteins in the PDB with bridge-like properties, and have verified a clear bi-stability gradient for a series of mutants studied by Alexander et al. (Proc Nat Acad Sci USA 2009, 106:21149–21154) that connect two sequences that fold uniquely into two different native structures via a bridge-like intermediate mutant sequence. Based on these findings, new testable predictions for future studies on protein bi-stability and evolution are discussed

Molecular dynamics simulation of polyacrylamide adsorption on calcite

In poorly consolidated carbonate rock reservoirs, solids production risk, which can lead to increased environmental waste, can be mitigated by injecting formation-strengthening chemicals. Classical atomistic molecular dynamics (MD) simulation is employed to model the interaction of polyacrylamide-based polymer additives with a calcite structure, which is the main component of carbonate formations. Amongst the possible calcite crystal planes employed as surrogates of reservoir rocks, the (1 0 4) plane is shown to be the most suitable surrogate for assessing the interactions with chemicals due to its stability and more realistic representation of carbonate structure. The molecular conformation and binding energies of pure polyacrylamide (PAM), hydrolysed polyacrylamide in neutral form (HPAM), hydrolysed polyacrylamide with 33% charge density (HPAM 33%) and sulfonated polyacrylamide with 33% charge density (SPAM 33%) are assessed to determine the adsorption characteristics onto calcite surfaces. An adsorption-free energy analysis, using an enhanced umbrella sampling method, is applied to evaluate the chemical adsorption performance. The interaction energy analysis shows that the polyacrylamide-based polymers display favourable interactions with the calcite structure. This is attributed to the electrostatic attraction between the amide and carboxyl functional groups with the calcite. Simulations confirm that HPAM33% has a lower free energy than other polymers, presumably due to the presence of the acrylate monomer in ionised form. The superior chemical adsorption performance of HPAM33% agrees with Atomic Force Microscopy experiments reported herein

Origins of Chevron Rollovers in Non-Two-State Protein Folding Kinetics

Chevron rollovers of some proteins imply that their logarithmic folding rates are nonlinear in native stability. This is predicted by lattice and continuum G\=o models to arise from diminished accessibilities of the ground state from transiently populated compact conformations under strongly native conditions. Despite these models' native-centric interactions, the slowdown is due partly to kinetic trapping caused by some of the folding intermediates' nonnative topologies. Notably, simple two-state folding kinetics of small single-domain proteins are not reproduced by common G\=o-like schemes.Comment: 10 pages, 4 Postscript figures (will appear on PRL

‘It Brings Light to What You Really Put into Your Body’: A Focus Group Study of Reactions to Messages about Nicotine Reduction in Cigarettes

Objective: In 2017, the U.S. Food and Drug Administration (FDA) announced a proposed regulation to lower nicotine in cigarettes to minimally addictive levels to help smokers quit. We sought to explore effective message strategies communicating about nicotine reduction in cigarettes across the different key audiences that the regulation is most likely to influence. Methods: We designed four types of messages: efficacy messages, risk messages, a message about alternative sources of nicotine, and a compensation message. Sixteen virtual focus groups were conducted in Atlanta and San Francisco in April-May 2020. Data were analyzed in NVivo 12.0 using a thematic analysis approach. Findings: Exclusive smokers were receptive to both efficacy messages and risk messages. Dual users were the only group that was open to resorting to alternative sources of nicotine. Former smokers were critical of these messages as promoting the new kinds of cigarettes and potentially encouraging initiation and relapse of smoking. Nonsmokers felt that efficacy messages downplayed the risks of smoking and did not scare people away from smoking. Presenting information that very low nicotine cigarettes (VLNCs) still contain harmful chemicals made smokers question continued smoking in the absence of nicotine and view VLNCs as harmful. Conclusions: Messages communicating about nicotine reduction in cigarettes might help to motivate smokers to quit and can correct the misperceptions that VLNCs are less harmful. The FDA should consider specific target audiences and use different messages that complement each other in communicating about this regulation