Kinetics of the reactions of Cl atoms with 2-buten-1-ol, 2-methyl-2-propen-1-ol, and 3-methyl-2-buten-1-ol as a function of temperature

The reactions of three structurally similar unsaturated alcohols, 2-buten-1-ol (crotyl alcohol), 2-methyl-2-propen-1-ol (MPO221) and 3-methyl-2-buten-1-ol (MBO321) with Cl atoms, have been investigated for the first time, using a 400 l Teflon reaction chamber coupled with gas chromatograph-coupled with flame-ionization detection (GC-FID). The experiments were performed at atmospheric pressure and at temperatures between 255 and 298 K, in air or nitrogen as the bath gas. The obtained kinetic data were used to derive the Arrhenius expressions , , (in units of cm³ molecule⁻¹ s⁻¹). Finally, atmospheric lifetimes of those unsaturated alcohols with respect to OH, NO₃, O₃ and Cl have been calculated.     

Light curve morphology study of UW CrB – evidence for a 5 d superorbital period

Since its discovery in 1990, UW CrB (also known as MS1603+2600) has remained a peculiar source without firm classification. Our current understanding is that it is an accretion disc corona (ADC) low-mass X-ray binary. In this paper, we present results from our photometric campaign dedicated to studying the changing morphology of the optical light curves. We find that the optical light curves show remarkable evidence for strongly evolving light curve shapes. In addition, we find that these changes show a modulation at a period of ∼5 d. We interpret these changes as either due to strong periodic accretion disc warping or due to other geometrical changes because of disc precession at a period of 5 d. Finally, we have detected 11 new optical bursts, the phase distribution of which supports the idea of a vertically extended asymmetric accretion disc.     

A test of Sporormiella representation as a predictor of megaherbivore presence and abundance

Spores of the dung fungus Sporormiella have been suggested to indicate the presence, perhaps also the abundance of past megaherbivore populations. Nonetheless, basic studies demonstrating a correlation between Sporormiella concentration in lacustrine sediments and modern herbivore abundance are lacking. This study of Sporormiella representation in grazed and ungrazed landscapes provides supporting evidence for the application of Sporormiella as an indicator of megaherbivore presence and abundance in ancient landscapes. However, Sporormiella representation is spatially sensitive to the distance from the dung source. In lakes where Sporomiella are abundant in shoreline sediments, they decline sharply with increasing distance from the lake edge. Although this study provides supporting evidence for the application of Sporormiella as a proxy for herbivore presence and abundance, independent proxies should be applied in conjunction with Sporormiella to control for changes in lake size.     

Economic benefit of the protection program for the Steller sea lion

This paper examines willingness to pay (WTP) for an endangered species across geographically nested samples using the Contingent Valuation Method (CVM). The three samples range from (1) the boroughs that contain critical habitat for the Steller sea lion to (2) the state that contains these boroughs to and (3) the entire United States. Depending on the assumptions of the model, WTP varies tremendously from sample to sample. WTP for the United States is the highest and it is the lowest for the boroughs. The null hypotheses that mean WTP estimates are greater then zero were rejected for the boroughs and the state but were not rejected for the United States based on the 95% confidence intervals.     

A New Method for Determining Compound Specific Carbon Isotope of Chlorinated Solvents in Porewater

A new method for the extraction of chlorinated solvents (CSs) from porewater with dimethylacetamide (DMA) used as a solvent and the determination of δ¹³C by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) with solid-phase microextraction (SPME) are presented. This method was used for the determination of δ¹³C of chloroethenes and chloromethanes. The extraction of the CSs from porewater with DMA led to a minimal loss of mass of solvent and chlorinated compounds. The accuracy of the method was verified with the analysis of the pure injected compounds using elemental analyzer—isotope ratio mass spectrometry (EA-IRMS). It has been effectively applied in a study area in saturated soil samples of a pollutant source zone of perchloroethylene (PCE) and trichloroethylene (TCE). The limit of quantification of the new method was 0.034 μg/g for PCE and TCE for 10–20 g of soil sample. This new method allows for compound-specific isotope analysis of CSs in porewater, which can be beneficial in sites where the identification of contamination sources and the behavior of the contaminants are not clear.     

Ecological distribution of Stephanodiscus niagarae Ehrenberg in central Mexico and niche modeling for its last glacial maximum habitat suitability in the Nearctic realm

Journal of Paleolimnology - Stephanodiscus niagarae Ehrenberg is currently restricted to specific regions of central Mexico, however, during the late Pleistocene, it had a wider distribution in the...