Effects of enchained ester groups on the living carbocationic polymerization of vinyl ethers

A series of chloro - substituted 4-(ethenyloxy)butyl benzoate and acetate monomers were polymerized in toluene at -20 and 4o C using an HCl etherate / ethylaluminum dichloride (EtAlCl2) initiator system in the presence and absence of an externally added esters. The systems were evaluated in accordance with established criteria to determine the degree of “livingness” of each system in the presence and absence of the added ester. The effects of the enchainment of the of the ester moiety was studied by comparison with the polymerization characteristics of 4-(ethenyloxy)butane in the presence and absence of the externally added ester corresponding to the enchained ester moiety. The effect of the “intramolecular” ester on the living nature of the system was studied and it was determined that the enchained ester moiety is less effective in inducing a living system than the equivalent ester added externally. Further, it was determined that the degree to which an enchained or externally added ester is able to induce “livingness” in a system is directly proportional to the pKa of the conjugate carboxylic acid of the ester

Stabilizing corn supplies by storage

Farmers, acting as individuals, ordinarily carry over some of their surplus corn from big crop years to small crop years. This storage has had the effect of reducing fluctuations in corn supplies, on the average, by one-fifth. The best place to store the surplus corn from big crops is right on the farm where it was grown; The costs of this storage average about 3 cents per bushel per year

The Enigmatic Radio Afterglow of GRB 991216

We present wide-band radio observations spanning from 1.4 GHz to 350 GHz of the afterglow of GRB 991216, taken from 1 to 80 days after the burst. The optical and X-ray afterglow of this burst were fairly typical and are explained by a jet fireball. In contrast, the radio light curve is unusual in two respects: (a) the radio light curve does not show the usual rise to maximum flux on timescales of weeks and instead appears to be declining already on day 1 and (b) the power law indices show significant steepening from the radio through the X-ray bands. We show that the standard fireball model, in which the afterglow is from a forward shock, is unable to account for (b) and we conclude that the bulk of the radio emission must arise from a different source. We consider two models, neither of which can be ruled out with the existing data. In the first (conventional) model, the early radio emission is attributed to emission from the reverse shock as in the case of GRB 990123. We predict that the prompt optical emission would have been as bright (or brighter) than 8th magnitude. In the second (exotic) model, the radio emission originates from the forward shock of an isotropically energetic fireball (10^54 erg) expanding into a tenuous medium (10^-4 cm^-3). The resulting fireball would remain relativistic for months and is potentially resolvable with VLBI techniques. Finally, we note that the near-IR bump of the afterglow is similar to that seen in GRB 971214 and no fireball model can explain this bump.Comment: ApJ, submitte

Sn/Mn/Bi2O3 ternary pyrotechnic time delay compositions

Please read abstract in the article.Supporting Information: Particle size distribution; Powder X-ray diffractograms of the burn residues; Mixture model details (PDF)Video of a burn event in a lead tube filled with the composition Bi2O3:Mn:Sn = 63.7:22.5:13.8 (MP4)The University of Pretoriahttps://pubs.acs.org/journal/ascecg2021-08-31hj2021Chemical Engineerin

The Molecular Ecology of the Extinct New Zealand Huia

The extinct Huia (Heteralocha acutirostris) of New Zealand represents the most extreme example of beak dimorphism known in birds. We used a combination of nuclear genotyping methods, molecular sexing, and morphometric analyses of museum specimens collected in the late 19th and early 20th centuries to quantify the sexual dimorphism and population structure of this extraordinary species. We report that the classical description of Huia as having distinctive sex-linked morphologies is not universally correct. Four Huia, sexed as females had short beaks and, on this basis, were indistinguishable from males. Hence, we suggest it is likely that Huia males and females were indistinguishable as juveniles and that the well-known beak dimorphism is the result of differential beak growth rates in males and females. Furthermore, we tested the prediction that the social organisation and limited powers of flight of Huia resulted in high levels of population genetic structure. Using a suite of microsatellite DNA loci, we report high levels of genetic diversity in Huia, and we detected no significant population genetic structure. In addition, using mitochondrial hypervariable region sequences, and likely mutation rates and generation times, we estimated that the census population size of Huia was moderately high. We conclude that the social organization and limited powers of flight did not result in a highly structured population

The Broadband Afterglow of GRB980329

We present radio observations of the afterglow of the bright gamma-ray burst GRB980329 made between one month and several years after the burst, a re-analysis of previously published submillimeter data, and late-time optical and near-infrared (NIR) observations of the host galaxy. From the absence of a spectral break in the optical/NIR colors of the host galaxy, we exclude the earlier suggestion that GRB980329 lies at a redshift of z >~5. We combine our data with the numerous multi-wavelength observations of the early afterglow, fit a comprehensive afterglow model to the entire broadband dataset, and derive fundamental physical parameters of the blast-wave and its host environment. Models for which the ejecta expand isotropically require both a high circumburst density and extreme radiative losses from the shock. No low density model (n << 10 cm^{-3}) fits the data. A burst with a total energy of ~ 10^{51} erg, with the ejecta narrowly collimated to an opening angle of a few degrees, driven into a surrounding medium with density ~ 20 cm^{-3}, provides a satisfactory fit to the lightcurves over a range of redshifts.Comment: 27 pages, incl. 6 figures, minor revisions (e.g. added/updated references) Accepted by Ap

Calcium sulfate as a possible oxidant in “green” siliconbased pyrotechnic time delay compositions

Chemical time delay detonators are used to control blasting operations in mines and quarries. Slow burning Si-BaSO4 pyrotechnic delay compositions are employed for long time delays. However, soluble barium compounds may pose environmental and health risks. Hence inexpensive anhydrous calcium sulfate was investigated as an alternative “green” oxidant. EKVI simulations indicated that stoichiometry corresponds to a composition that contains less than 30 wt. % Si. However combustion was only supported in the range of 30-70 wt. % Si. In this range the bomb calorimeter data and burn tests indicate that the reaction rate and energy output decrease with increasing silicon content. The measured burn rates in rigid aluminium elements ranged from 6.9 to 12.5 mm s1. The reaction product was a complex mixture that contained crystalline phases in addition to an amorphous calcium containing silicate phase. A reaction mechanism consistent with these observations is proposed.Supported in part by AEL Mining Service and by the National Research Foundation of South Africa (Grant 83874).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-40872016-08-31hb201

The effect of additives on the burning rate of silicon-calcium sulfate pyrotechnic delay compositions

The effect of fuel particle size as well as the influence of inert and reactive additives on the burning rate of the Si-CaSO4 composition was evaluated. The burning rate decreased with increase in fuel particle size, while the enthalpy remained constant. Addition of fuels to the base composition increased the burning rate, with an increase from 12.5 mm s-1 to 43 mm s-1 being recorded upon 10 wt. % Al addition. Ternary mixtures of silicon, calcium sulfate and an additional oxidizer generally decreased the burning rate, with the exception of bismuth trioxide where it increased. The Si-CaSO4 formulation was found to be sensitive to the presence of inert material, addition of as little as 1 wt. % fumed silica stifled combustion in the aluminium tubes.This work is based on the research supported in part by AELMining Service and by the National Research Foundation of SouthAfrica (Grant 83874).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-40872017-08-31hb2016Chemical Engineerin

Suppressing hydrogen evolution by aqueous silicon powder dispersions by controlled silicon surface oxidation

Aqueous silicon dispersions are used to produce pyrotechnic time delay compositions. The propensity of silicon to react with water and to produce hazardous hydrogen gas must be suppressed. To this end, the effect of air heat treatment temperature on the rate of corrosion of silicon was investigated. It was found that four hour heat treatments at temperatures below 350 °C provided significant passivation. This is attributed to the removal of the hydroxyl groups present on the SiO2 surface scale layer. It was found that thickening the silica layer, by heat treatment at higher temperatures, causes a further reduction in the amount of hydrogen released. However, differential thermal analysis (DTA) studies showed that excessive silicon surface oxidation increased the ignition temperature and reduced the heat release of a near-stoichiometric silicon-lead chromate pyrotechnic composition.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-4087hb2013ai201