Under physiological conditions, multicomponent biological membranes undergo structural changes which help define how the membrane functions. An understanding of biomembrane structure-function ...relations can be based on knowledge of the physical and chemical properties of pure phospholipid bilayers. Here, we have investigated phase transitions in dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) bilayers. We demonstrated the existence of several phase transitions in DPPC and DOPC mica-supported bilayers by both atomic force microscopy imaging and force measurements. Supported DPPC bilayers show a broad L
β
–L
α
transition. In addition to the main transition we observed structural changes both above and below main transition temperature, which include increase in bilayer coverage and changes in bilayer height. Force measurements provide valuable information on bilayer thickness and phase transitions and are in good agreement with atomic force microscopy imaging data. A De Gennes model was used to characterize the repulsive steric forces as the origin of supported bilayer elastic properties. Both electrostatic and steric forces contribute to the repulsive part of the force plot.
Microplastics are small plastic fragments that have been found around the world, however, research into microplastics in Africa and freshwater systems remains insufficient. In this study, the ...snapshot microplastic profile of an urban stream was assessed in the Braamfontein Spruit, located in Johannesburg the largest city in South Africa. The abundance of microplastics was determined in water, Chironomus sp. larvae and sediment, while in situ parameters were taken to investigate their relationship to the microplastic profile of the different matrices. Microplastics were detected in water (mean of 705 particles mˉ3), Chironomus sp. larvae (mean of 53.4 particles gˉ1 wet weight) and sediment (mean of 166.8 particles kgˉ1 dry weight). The study found evidence of how urban stream characteristics such as a weir, stream depth and velocity could affect the abundance and dispersion of microplastics. The results indicate that areas of increased depth and decreased flow allowed microplastics to settle down to the sediment where benthic macroinvertebrates could ingest these fragments. Large obstructions like a weir also increased microplastic counts in sediment and invertebrates above the obstruction, with a decrease of fragments after the obstruction, however, microplastics in surface water were able to flow over the obstruction and increase in abundance downstream. This study concludes that first order urban streams such as the Braamfontein Spruit may be contributing large numbers of microplastics to higher order streams and large rivers in times of increased flow.
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•Microplastics had a 100% prevalence in Chironomid larvae groups.•Stream characteristics could influence microplastic distribution.•Microplastic abundances varied depending on what matrix was being analysed.•A weir decreased microplastic loads downstream in sediment and invertebrates.
We use a generic model for type-I excitability (known as the SNIPER or SNIC model) to describe the local dynamics of nodes within a network in the presence of non-zero coupling delays. Utilising the ...method of the Master Stability Function, we investigate the stability of the zero-lag synchronised dynamics of the network nodes and its dependence on the two coupling parameters, namely the coupling strength and delay time. Unlike in the FitzHugh-Nagumo model (a model for type-II excitability), there are parameter ranges where the stability of synchronisation depends on the coupling strength and delay time. One important implication of these results is that there exist complex networks for which the adding of inhibitory links in a small-world fashion may not only lead to a loss of stable synchronisation, but may also restabilise synchronisation or introduce multiple transitions between synchronisation and desynchronisation. To underline the scope of our results, we show using the Stuart-Landau model that such multiple transitions do not only occur in excitable systems, but also in oscillatory ones.
We show that for large coupling delays the synchronizability of delay-coupled networks of identical units relates in a simple way to the spectral properties of the network topology. The master ...stability function used to determine stability of synchronous solutions has a universal structure in the limit of large delay: it is rotationally symmetric around the origin and increases monotonically with the radius in the complex plane. We give details of the proof of this structure and discuss the resulting universal classification of networks with respect to their synchronization properties. We illustrate this classification by means of several prototype network topologies.
Peatland drainage causes peat degradation, which results in high greenhouse gas emissions and ongoing subsidence of the ground surface. To avoid further land degradation, the rewetting of peatlands ...is essential. The new land use concept of paludiculture - the use of wet and rewetted peatlands for agriculture and forestry - now offers possibilities for landowners and land managers to continue using these sites under wet conditions. But new challenges arise due to the limited bearing capacity of wet soils, which restricts accessibility for machinery. Whilst many site-specific technical solutions for harvesting on wet peatland are available, it remains unclear whether current machinery is suitable for use in the large-scale implementation of paludiculture. Repeated crossings of the same ground can easily disturb the upper peat layer and cause serious problems for the removal of biomass. In this article we present available machinery and approaches to biomass harvesting; and explore how the number of transport runs required for biomass removal varies with productivity of the site, cargo capacity and working width of the harvesting machinery. The results are used in a discussion of logistics and infrastructure requirements to facilitate the implementation of paludiculture. Whilst there is still considerable scope for improvement of harvesting technologies, our results show that a peat-conserving harvest from wet and rewetted peatlands is possible with adjustments to harvesting technique, logistics and site infrastructure.
Microplastics are defined as plastics smaller than 5 mm down to 0.05 mm. These plastics enter the environment and undergo certain physical changes, most notably density changes and a relative ...increase of surface size. Microplastics can then release or absorb toxicants from the surrounding environment. These plastics may then enter the food chain from producers to top predators. In this study, microplastics were investigated in four study sites in the upper Vaal River, South Africa. The goal of the study was to determine the levels of plastics in water, sediment and a top predator, the benthic fish
Clarias gariepinus
. In this study, a 10% KOH digestion of water and fish, and density separation of sediment with NaCl (1.2 g cm
3
) was used to extract microplastics for identification. Microplastics were detected in water (3, 300 particles m
−
³), fish (7.47 particles per fish) and sediment (46.7 particles kg
−1
). Microplastic intake was not attributed to the microplastic shape or size of the fish that ingested it. This highlights the need to understand how niche-specific microplastic concentrations are, which will not only aid in quantifying microplastics accurately in the environment but to better understand how they may influence various ecosystems.
.
Time-delayed feedback control (TDFC) is transferred to the optical domain and applied to complex multisection semiconductor lasers as used in optical communication. Pyragas-type control is provided ...by purely optical feedback from an external Fabry-Pérot interferometer. This all-optical setup needs no time-consuming signal processing and, thus, has practically no speed limit. Proof-of-principle experiments demonstrate noninvasive stabilization of unstable steady states, chaos control, and suppression of noise-induced oscillations on picosecond time scales. A Lang-Kobayashi type model with optical TDFC is investigated taking into account the dynamic details of the device as well as all-optical time-delayed feedback. The parameter regimes that allow for stabilization of stationary emission are mapped out in good agreement with the experiments. Including noise, an analytical expression for the power spectral density is derived, which is confirmed by the experimental all-optical suppression of noise-induced relaxation oscillations.
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