Rate constants for the reaction of NO and HO2 with peroxy radicals formed from the reaction of OH, Cl or NO3 with alkenes, dienes and α,β-unsaturated carbonyls

Rate constants for the gas-phase reaction of NO and HO2 radicals with 33 peroxy radicals are presented. The peroxy radicals are derived from the addition of either OH, Cl, or NO3 radicals, followed by addition of O2, to a series of alkenes: tetrachloroethene, ethene, 2,3-dimethyl but-2-ene, butadiene, 2,3,4,5-tetramethyl hexa-2,4-diene, 1,1,2,3,4,4-hexachlorobutadiene, but-1-ene-3-one (methyl vinyl ketone) and 2,3-dimethylpen-2-ene-4-one. The rate constants were predicted using a correlation between the singly occupied molecular orbital (SOMO) energy of the peroxy radical and the logarithm of the rate constant for reaction with NO or HO2. A discussion of the accuracy of the method and the trends in the reactivity of the titled peroxy radicals is given. Peroxy radicals derived from halogenated alkenes have larger values of rate constants for reaction with NO relative to reaction with HO2, indicating that they are more likely to react with NO, rather than HO2, in the atmosphere. The reverse is true for peroxy radicals derived from alkylated alkenes

A Survey of the Math Blogosphere

This article provides an overview of different types of mathematical blogs currently available. There are over twenty blogs highlighted, ranging from the technical to the recreational, from those sponsored by national mathematical organizations to those run by individuals--including students

Kinetics and mechanism of the reaction between atomic chlorine and dimethyl selenide; comparison with the reaction between atomic chlorine and dimethyl sulfide

Dimethyl selenide is the most abundant gaseous selenium species in marine environments. In this work, the value of the rate coefficient for the gas-phase reaction between dimethyl selenide and Cl atoms has been determined for the first time. The value of the second-order rate coefficient obtained was (5.0±1.4)×10–10 cm3 molecule–1 s–1. The very fast nature of the reaction means that, when estimating the lifetime of dimethyl selenide in the atmosphere, loss due to reaction with Cl atoms should be considered along with loss due to reaction with O3 and with OH and NO3 radicals. Analysis of the available kinetic data suggests that at 760 Torr the dominant reaction pathway for the reaction of Cl atoms with dimethyl selenide will be the addition of Cl to the Se atom forming an adduct of the type CH3Se(Cl)CH3. Theoretical calculations, at the B3LYP/6-311++G(2df,p)//B3LYP/6-311++G(d,p) level of theory, show that at 298 K the value of rH for the formation of the adduct is –111.4 kJ mol–1. This value may be compared to –97.0 kJ mol–1, the value calculated for rH for the formation of the analogous sulfur adduct, CH3S(Cl)CH3, following the reaction between Cl atoms and dimethyl sulfide. Variational RRKM theory was used to predict the thermal decomposition rates of the two adducts back to starting materials. The estimated rate constant for the decomposition of the selenium adduct to the reactants is 5×10–5 s–1, compared to 0.02 s–1 in the case of the sulfur adduct. However, our calculations suggest that the CH3Se(Cl)CH3 adduct, which is initially formed highly excited, will not be stabilised under atmospheric conditions, but rather will decompose to yield CH3SeCl and CH3, a process that is calculated to be exothermic with respect to the initial reactants by 5.8 kJ mol–1. The formation of CH3SCl and CH3 from the sulfur adduct, on the other hand, is endothermic by 20.8 kJ mol–1 with respect to the initial reactants, and is thus not expected to occur

Colorectal Cancer Brochure Development for African Americans

Introduction: African Americans are more likely to die from colorectal cancer (CRC) than any other racial/ethnic group in the United States. Unfortunately, African Americans are also less likely to undergo screening for CRC than their White counterparts. Focus groups methodology was used to refine educational brochures designed to increase CRC screening among African Americans. Methods: Two series of focus groups were completed, with a total of seven groups and 39 participants. Six different brochures (stage-matched and culturally sensitive) designed to promote CRC screening among African Americans were evaluated. Results: All participants thought that the brochures motivated them to talk with their health care providers about screening. Cost, pain, medical mistrust and fear were identified as major barriers and the brochures were modified to address these concerns. Conclusions: Focus groups methodology with African Americans can be used to inform brochures designed to increase African Americans CRC screening that addresses their major concerns

A scattering of orders

A linear ordering is scattered if it does not contain a copy of the rationals. Hausdorff characterised the class of scattered linear orderings as the least family of linear orderings that includes the class $\mathcal B$ of well-orderings and reversed well-orderings, and is closed under lexicographic sums with index set in $\mathcal B$. More generally, we say that a partial ordering is $\kappa$-scattered if it does not contain a copy of any $\kappa$-dense linear ordering. We prove analogues of Hausdorff's result for $\kappa$-scattered linear orderings, and for $\kappa$-scattered partial orderings satisfying the finite antichain condition. We also study the $\mathbb{Q}_\kappa$-scattered partial orderings, where $\mathbb{Q}_\kappa$ is the saturated linear ordering of cardinality $\kappa$, and a partial ordering is $\mathbb{Q}_\kappa$-scattered when it embeds no copy of $\mathbb{Q}_\kappa$. We classify the $\mathbb{Q}_\kappa$-scattered partial orderings with the finite antichain condition relative to the $\mathbb{Q}_\kappa$-scattered linear orderings. We show that in general the property of being a $\mathbb{Q}_\kappa$-scattered linear ordering is not absolute, and argue that this makes a classification theorem for such orderings hard to achieve without extra set-theoretic assumptions