Ocean pollution by microplastics, i.e. small pieces of plastic of less than 5 mm, is one of the major concerns for the future of our planet. Secondary microplastics formation is due to fragmentation ...of macroplastic waste. This fragmentation can be attributed to environmental loadings such as waves, winds and tides, coupled with a change in mechanical properties of polymers induced by UV and seawater ageing. This study aims to characterize and understand changes in the mechanical behaviour of Polyethylene Terephthalate (PET) induced by hydrolysis, especially for high degradation levels. Thin films (200 μm) of PET were aged in water at temperatures from 110 °C to 80 °C for up to 150 days. Embrittlement occurs with chain scission during hydrolysis when molar mass of the polymer falls below 17 kg/mol. When the polymer is brittle, i.e. for high levels of degradation, the stress at break decreases linearly with the molar mass, and can be described by a simple mathematical expression.
•Aging of PET in water at temperatures ranging from 80 to 110 °C up to 150 days.•Embrittlement of PET due to hydrolysis of the amorphous phase.•Significant decrease in mechanical properties once the polymer is in the brittle state.•Identification of a critical molar mass M'c.•Linear relationship between the stress at failure and the molar mass when the polymer is in the brittle state.
A transformation in energy structures and governance models are required to meet the needs of communities living in rural and remote areas and particularly for those subject to energy and economic ...poverty. New models must be reflexive to global climate concerns, align with social, economic and environmental agendas of national, state, and local governments, and be compatible with embedded energy infrastructure. Decentralised solar solutions are a resilient technology which can support energy transformation to spatially, economically and socially disadvantaged communities yet the deployment of this technology is hamstrung by path dependencies including policy frameworks, business models and infrastructure. In this study, the multi-level perspective has been used to examine energy transformation within rural and remote communities in India through interviews with regime and niche level actors. We identify various barriers impeding successful deployment of decentralised solar PV including a disconnect between policy makers and implementers, poor coordination within and between actors, and limited institutional focus and competence. To support a successful transition to off-grid solar based regimes for rural and remote communities, participants suggested strong political determination, setting enabling policy frameworks, and implementing a collaborative ecosystem with businesses, system suppliers, financial intermediaries, distribution companies, civil society and end users.
Antifreeze proteins (AFPs) are found in a variety of marine cold‐water fishes where they prevent freezing by binding to nascent ice crystals. Their diversity (types I, II, III and antifreeze ...glycoproteins), as well as their scattered taxonomic distribution hint at their complex evolutionary history. In particular, type I AFPs appear to have arisen in response to the Late Cenozoic Ice Age that began ~ 34 million years ago via convergence in four different groups of fish that diverged from lineages lacking this AFP. The progenitor of the alanine‐rich α‐helical type I AFPs of sculpins has now been identified as lunapark, an integral membrane protein of the endoplasmic reticulum. Following gene duplication and loss of all but three of the 15 exons, the final exon, which encoded a glutamate‐ and glutamine‐rich segment, was converted to an alanine‐rich sequence by a combination of frameshifting and mutation. Subsequent gene duplications produced numerous isoforms falling into four distinct groups. The origin of the flounder type I AFP is quite different. Here, a small segment from the original antiviral protein gene was amplified and the rest of the coding sequence was lost, while the gene structure was largely retained. The independent origins of type I AFPs with up to 83% sequence identity in flounder and sculpin demonstrate strong convergent selection at the level of protein sequence for alanine‐rich single alpha helices that bind to ice. Recent acquisition of these AFPs has allowed sculpins to occupy icy seawater niches with reduced competition and predation from other teleost species.
The recent assembly of the herring genome suggests this fish acquired its antifreeze protein gene by horizontal transfer and then passed a copy on to the smelt. The direction of gene transfer is ...confirmed by some accompanying transposable elements and by the breakage of gene synteny.
Kinetic hydrate inhibitors (KHIs) are used commercially to inhibit gas hydrate formation and growth in pipelines. However, improvement of these polymers has been constrained by the lack of verified ...molecular models. Since antifreeze proteins (AFPs) act as KHIs, we have used their solved x-ray crystallographic structures in molecular modeling to explore gas hydrate inhibition. The internal clathrate water network of the fish AFP Maxi, which extends to the protein’s outer surface, is remarkably similar to the {100} planes of structure type II (sII) gas hydrate. The crystal structure of this water web has facilitated the construction of in silico models for Maxi and type I AFP binding to sII hydrates. Here, we have substantiated our models with experimental evidence of Maxi binding to the tetrahydrofuran sII model hydrate. Both in silico and experimental evidence support the absorbance-inhibition mechanism proposed for KHI binding to gas hydrates. Based on the Maxi crystal structure we suggest that the inhibitor adsorbs to the gas hydrate lattice through the same anchored clathrate water mechanism used to bind ice. These results will facilitate the rational design of a next generation of effective green KHIs for the petroleum industry to ensure safe and efficient hydrocarbon flow.
Antifreeze proteins (AFPs) are characterized by their ability to adsorb to the surface of ice crystals and prevent any further crystal growth. AFPs have independently evolved for this purpose in a ...variety of organisms that encounter the threat of freezing, including many species of polar fish, insects, plants and microorganisms. Despite their diverse origins and structures, it has been suggested that all AFPs can organize ice-like water patterns on one side of the protein (the ice-binding site) that helps bind the AFP to ice. Here, to test this hypothesis, we have solved the crystal structure at 2.05 Å resolution of an AFP from the longhorn beetle, Rhagium mordax with five molecules in the unit cell. This AFP is hyperactive, and its crystal structure resembles that of the R. inquisitor ortholog in having a β-solenoid fold with a wide, flat ice-binding surface formed by four parallel rows of mainly Thr residues. The key difference between these structures is that the R. inquisitor AFP crystallized with its ice-binding site (IBS) making protein-protein contacts that limited the surface water patterns. Whereas the R. mordax AFP crystallized with the IBSs exposed to solvent enabling two layers of unrestricted ordered surface waters to be seen. These crystal waters make close matches to ice lattice waters on the basal and primary prism planes.
Tuberculosis at extremes of age SCHAAF, H. Simon; COLLINS, Andrea; BEKKER, Adrie ...
Respirology (Carlton, Vic.),
July 2010, Letnik:
15, Številka:
5
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Although tuberculosis (TB) has its highest burden among young adults, especially since the advent of HIV infection, two other groups with low immunity, the very young (<1 year) with immature ...immunity and the elderly (>65 years) with waning immunity, are vulnerable groups not to be forgotten. This review describes the epidemiology, clinical aspects, public health aspects and outcome of TB in patients at the extremes of age. The epidemiology differs therein that TB in infants occurs in developing countries with high incidences of TB and HIV, while TB in the elderly occurs in developed countries with ageing populations. The clinical presentation may be non‐specific, history of contact with TB is often not known and TB is often not considered at these age extremes, and when the diagnosis is considered, disease progression may already be advanced. Anti‐TB treatment regimens are the same as in other age groups, but drug dosages may need adjustment according to weight, renal function, liver function and other potentially complicating factors. Adverse events are more difficult to observe and both the young and the elderly are reliant on others for adherence to treatment. Mortality at both age extremes is higher than in the general TB population. For all the above reasons, public health measures to: prevent transmission of infection; identify those infected and providing preventive therapy; high index of suspicion in order to make an early diagnosis; and timely initiation of treatment are important in both the very young and the elderly.
Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties. In these ...materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p-n junction solar cell. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol-gel thin-film deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric-electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10(-4) to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7-4 electronvolts) of ferroelectric oxides, which allow the use of only 8-20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: KNbO31 - xBaNi1/2Nb1/2O3 - δx (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1-3.8 electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.
Local government uses the development approval process to place responsibility for stormwater treatment with private landholders through the installation of stormwater quality improvement devices on ...their land. This source control strategy can complement publicly owned and managed centralized solutions to improve urban water quality outcomes. The maintenance of decentralized solutions for waterway health is compromised by the motivation of individuals whose professed value of cleaner waterways is not evident in their individual lot-based actions. This exploratory research makes four policy and governance observations: waterway policy should consider property scale and ownership type when allocating responsibility for stormwater treatment; devices need to be integrated within the landscape and be publicly visible; education and regulation are advised in order to better support devices placed in private ownership; and policy will be more likely to achieve cleaner waterways if it aligns the motivations of waterway scientists, maintenance actors and property owners.
PDF
