Gas-phase sorption-desorption of propargyl bromide and 1,3-dichloropropene on plastic materials

The goal of this research was to provide information for choosing appropriate materials for studying gas-phase concentrations of propargyl bromide (3BP) and 1,3-dichloropropene (1,3-D) in laboratory experiments. Several materials were tested and found to sorb both gas-phase chemicals in the following order: stainless steel (SS) < Teflon polytetrafluoroethylene (PTFE-FEP) approximately flexible polyvinyl chloride (PVC) approximately acrylic < low-density polyethylene (PE) < vinyl approximately silicone < polyurethane foam (PUF). Sorption of SS was insignificant and PUF sorbed all the fumigant that was applied. For the other materials, linear sorption coefficients (Kd) for 3BP ranged from 3.0 cm3 g(-1) for PVC to 215 cm3 g(-1) for silicone. Freundlich sorption coefficients for 1,3-D ranged from 11.5 to 371 cm3 g(-1). First-order desorption rate constants in an open system ranged from 0.05 to 1.38 h(-1) for 3BP and from 0.07 to 1.73 h(-1) for 1,3-D. In a closed system, less than 2% of sorbed fumigant desorbed from vinyl while up to 99% desorbed from PVC within 24 h when equilibrated at the highest headspace concentration. Sorption of both fumigants was linearly related to the square root of time except for vinyl and silicone. This may indicate non-fickian diffusion of fumigant into the polymer matrix. Vinyl, silicone, PE, and PUF should be avoided for quantitative study of organic gases, except possibly as a trapping medium. Use of PTFE, PVC, and acrylic may require correction for sorption-desorption and diffusion.     

Two-dimensional NMR Spectroscopy

The Science of Nature -     

The effect of elevated UV-B (280–320 nm) radiation levels on Silene vulgaris: A comparison between a highland and a lowland population

Highland (altitude 1600 m above sea level) and lowland (altitude −2 m below sea level) populations of the perennial herb Silene vulgaris (Moench) Garcke, were tested on their response to elevated levels of UV-B radiation. Highland populations typically receive high natural UV-B fluxes, whereas lowland populations receive a lower natural UV-B dose. Adaptation to high UV-B levels of the highland population is to be expected. Experimental comparison of growth rates, gas exchange rates, transpiration and biochemical parameters using adult plants as well as seedlings did not show a difference in the response to elevated UV-B levels between the two populations. Individuals of both populations were relatively insensitive to elevated UV-B radiation. The response of alpine and lowland populations of Silene vulgaris is discussed in relation to the dispersal of this species after the last ice age.     

Bimodality of the combined removal and signs-of-activities estimator for sampling closed animal populations

The possibility of a bimodal log-likelihood function arises with certain data when the combined removal and signs-of-activities estimator is used. Bimodal log-likelihoods may, in turn, yield disjoint confidence intervals for certain confidence levels. The hypothesis that bimodality is caused by the violation of the equal catchability assumption of the removal model, leading to the combination of contradictory data/models in the combined estimator is set forth. Simulations exploring the effect of the violation of removal model assumptions on estimation and inference showed that the assumption of unequal capture probability influenced the frequency of bimodal likelihoods; similarly, extreme parameter values for probability of capture influenced the number of excessively large confidence intervals produced. A sex-specific combined estimator is developed as a remedial model tailored to the problem. The simulations suggest that both the signs-of-activities estimator and the sex-specific estimator perform equally well over the range of simulations presented, though the signs-of-activities estimator is easier to implement.