Simulation of weak polyelectrolytes: A comparison between the constant pH and the reaction ensemble method

The reaction ensemble and the constant pH method are well-known chemical equilibrium approaches to simulate protonation and deprotonation reactions in classical molecular dynamics and Monte Carlo simulations. In this article, we show similarity between both methods {under certain conditions}. We perform molecular dynamics simulations of a weak polyelectrolyte in order to compare the titration curves obtained by both approaches. Our findings reveal a good agreement between the methods when the reaction ensemble is used to sweep the reaction constant. Pronounced differences between the reaction ensemble and the constant pH method can be observed for stronger acids and bases in terms of adaptive pH values. These deviations are due to the presence of explicit protons in the reaction ensemble method which induce a screening of electrostatic interactions between the charged titrable groups of the polyelectrolyte. The outcomes of our simulation hint to a better applicability of the reaction ensemble method for systems in confined geometries and titrable groups in polyelectrolytes with different pK$_\text{a}$ values.Comment: 3 figure

Use of live freshwater zooplankton for startfeeding Atlantic salmon in net pens

The experiment was carried out 1984 in a coastal lake near Bergen, Norway. A total of four (later doubled) groups of Atlantic salmon (Salmo salar) fry were startfed with live zooplankton delivered by a pump. Small fine-meshed net pens were used. Supplemental feed were offered and promoted additional growth, but after the startfeeding phase

Halibut behaviour as a means of assessing suitability of ongrowth systems

Halibut behaviour in net pens has been studied using direct observation, underwater video and/or hydroacoustic equipment. Rearing experience includes a wide range of fish weights (50-10.000 g) and fish densities (4-150 kg/m2). Individual halibut is able to change their coloration on the ocular side from their whitespotted benthic camouflage to the uniformly brown-grey pelagic camouflage within a minute and vice-a-versa. The proportion of fish with pelagic camouflage on/near the bottom was high in the net pens with high densities, and such groups also showed suboptimal growth. The results also indicated an increase in pelagic swimming activity in the net pens with the highest densities. High light levels and low temperatures decreased the pelagic swimming activity of the fish. Halibut in net pens reared at low densities did not spread evenly on the bottom, but were usually found in clumps