Effect of Polymer Chemistry on the Linear Viscoelasticity of Complex Coacervates

Complex coacervates can form through the electrostatic complexation of oppositely charged polymers. The material properties of the resulting coacervates can change based on the polymer chemistry and the complex interplay between electrostatic interactions and water structure, controlled by salt. We examined the effect of varying the polymer backbone chemistry using methacryloyl- and acryloyl-based complex coacervates over a range of polymer chain lengths and salt conditions. We simultaneously quantified the coacervate phase behavior and the linear viscoelasticity of the resulting coacervates to understand the interplay between polymer chain length, backbone chemistry, polymer concentration, and salt concentration. Time-salt superposition analysis was used to facilitate a broader characterization and comparison of the stress relaxation behavior between different coacervate samples. Samples with mismatched polymer chain lengths highlighted the ways in which the shortest polymer chain can dominate the resulting coacervate properties. A comparison between coacervates formed from methacryloyl vs acryloyl polymers demonstrated that the presence of a backbone methyl group affects the phase behavior, and thus the rheology in such a way that coacervates formed from methacryloyl polymers have a similar phase behavior to those of acryloyl polymers with ∼10× longer polymer chains

Methane emission by Camelids

Methane emissions from ruminant livestock have been intensively studied in order to reduce contribution to the greenhouse effect. Ruminants were found to produce more enteric methane than other mammalian herbivores. As camelids share some features of their digestive anatomy and physiology with ruminants, it has been proposed that they produce similar amounts of methane per unit of body mass. This is of special relevance for countrywide greenhouse gas budgets of countries that harbor large populations of camelids like Australia. However, hardly any quantitative methane emission measurements have been performed in camelids. In order to fill this gap, we carried out respiration chamber measurements with three camelid species (Vicugna pacos, Lama glama, Camelus bactrianus; n = 16 in total), all kept on a diet consisting of food produced from alfalfa only. The camelids produced less methane expressed on the basis of body mass (0.3260.11 L kg21 d21) when compared to literature data on domestic ruminants fed on roughage diets (0.5860.16 L kg21 d21). However, there was no significant difference between the two suborders when methane emission was expressed on the basis of digestible neutral detergent fiber intake (92.7633.9 L kg21 in camelids vs. 86.2612.1 L kg21 in ruminants). This implies that the pathways of methanogenesis forming part of the microbial digestion of fiber in the foregut are similar between the groups, and that the lower methane emission of camelids can be explained by their generally lower relative food intake. Our results suggest that the methane emission of Australia’s feral camels corresponds only to 1 to 2% of the methane amount produced by the countries’ domestic ruminants and that calculations of greenhouse gas budgets of countries with large camelid populations based on equations developed for ruminants are generally overestimating the actual levels

Support Letters from Fort Worth Consortium Members [1988-1989]

Photocopies of five letters, each from a different consortium leader, showing support and continued interest in the North Texas Institute for Educators on the Visual Arts program. Two have stamps marking the date they were received, and the Kimbell Art Museum included a side note of corrected information they wished to be included in the proposal

Production risk, inter-annual food storage by households and population-level consequences in seasonal prehistoric agrarian societies

Using complementary behavioural and population ecological models, we explore the role of production risk, normal surplus and inter-annual food storage in the adaptations of societies dependent on seasonal agriculture. We find that (a) household-level, risk-sensitive adaption to unpredictable environmental variation in annual agricultural yields is a sufficient explanation for the origins of normal agrarian surplus and, consequently, of household-level incentives for inter-annual food storage; and, (b) at the population level, density-dependent Malthusian processes tightly constrain the circumstances under which this same mechanism can be effective in smoothing inter-annual fluctuations in household food availability. Greater environmental variation and higher levels of fixed set-asides such as seed requirements or transfer obligations to political authorities lead to more severe, periodic famines; however, outside of famine events, these same factors improve average population welfare by suppressing population density to levels at which Malthusian constraints have lessened impact. The combination of behavioural and population ecological modelling methods has broad and complementary potential for illustrating the dynamic properties of complex, coupled human–natural systems

Thelytoky in Taeniogonalos venatoria Riek (Hymenoptera: Braconidae) with notes on its distribution and first record of the male sex

The Trigonalyidae, which have previously been thought to reproduce arrhenotokously like most parasitic Hymenoptera, are added to the list of families from which thelytoky (true parthenogenesis) is recorded. This has been inferred for Taeniogonalos venatoria Riek on the basis of a male:female sex ratio in the field ranging from about 1:250 to 0:1500. The rare male of this species is described for the first time, and the known distribution of the species extended to include South Australia. The host range of T. venatoria, which parasitises widely dispersing pergid sawfly larvae, is proposed as a possible reason for its thelytokous mode of reproduction