Competitive partitioning of rotational energy in gas ensemble equilibration

A wide-ranging computational study of equilibration in binary mixtures of diatomic gases reveals the existence of competition between the constituent species for the orbital angular momentum and energy available on collision with the bath gas. The ensembles consist of a bath gas AB(v;j), and a highly excited minor component CD(v';j'), present in the ratio AB:CD = 10:1. Each ensemble contains 8000 molecules. Rotational temperatures (T(r)) are found to differ widely at equilibration with T(r)(AB)/T(r)(CD) varying from 2.74 to 0.92, indicating unequal partitioning of rotational energy and angular momentum between the two species. Unusually, low values of T(r) are found generally to be associated with diatomics of low reduced mass. To test effects of the equi-partition theorem on low T(r) we undertook calculations on HF(6;4) in N(2)(0;10) over the range 100-2000 K. No significant change in T(r)(N2)/T(r)(HF) was found. Two potential sources of rotational inequality are examined in detail. The first is possible asymmetry of -Δj and +Δj probabilities for molecules in mid- to high j states resulting from the quadratic dependence of rotational energy on j. The second is the efficiency of conversion of orbital angular momentum, generated on collision with bath gas molecules, into molecular rotation. Comparison of these two possible effects with computed T(r)(AB)/T(r)(CD) shows the efficiency factor to be an excellent predictor of partitioning between the two species. Our finding that T(r) values for molecules such as HF and OH are considerably lower than other modal temperatures suggests that the determination of gas ensemble temperatures from Boltzmann fits to rotational distributions of diatomics of low reduced mass may require a degree of caution

The influence of an ecosystem engineer on nutrient subsidies and fish invasions in southwestern Montana

Streams and associated riparian zones are among the world\u27s most highly valued yet threatened ecosystems. Interest in using the ecosystem engineering behavior of beaver tomeet watershed conservation goals is becoming more pervasive, owing to substantive work documenting the physical effects of beaver impoundments on freshwater ecosystems. However, it is unclear how beaver modify ecological processes linking abiotic factors to changes in the surrounding biotic community. I investigated how beaver impoundments influence local food web processes, as well as impact native fish species threatened by nonnative invasions. I showed that beaver impoundments enhanced aquatic resource availability to terrestrial consumers. Beaver impounded watersheds had increased densities of emerging aquatic macroinvertebrates and higher levels of aquatic carbon in terrestrial consumer tissues, resulting in higher terrestrial consumer abundances. Beaver impoundments also had measurable effects on invasion dynamics between nonnative brook charr and native cutthroat trout populations. Brook charr are native to the eastern U.S., and are a key factor in native cutthroat declines in western watersheds. Streams with beaver had potential negative impacts for cutthroat, with higher brook charr densities, and increased spatial overlap between these species. In contrast, young-of-theyear cutthroat in invaded streams maintained high growth rates with beaver present, but showed growth reductions without beaver. Thus beaver conveyed both negative and positive impacts to cutthroat trout. At the population level, I found that cutthroat in the non-beaver invaded watershed exhibited low survival rates, negative population growth, and a short median time to extinction. With beaver present in invaded streams, cutthroat exhibited 40 % higher survival rates relative to the non-beaver control. This led to cutthroat population growth rates 5 - 20 % higher than in non-beaver streams, with longer median times to extinction. Therefore, beaver impoundments had positive implications for cutthroat persistence in brook charr invaded streams. My research links the habitat altering effects of beaver to changing ecological processes that influence community and population structure of other elements of the system, with implications for persistence of native species. Understanding the ecosystem effects of a highly interactive species like beaver is crucial to predicting repercussions of using beaver in a restoration context

PIKETTY REVISITED: THE MEANING OF CAPITAL IN THE TWENTY-FIRST CENTURY

Thomas Piketty had himself a moment. It did not come easily or quickly. When the academic economist first published his massive text, Capital in the Twenty-First Century, in French in 2013, summarizing over a decade of his and others’ work on capital and its unequal ownership across time and cultures, he encountered a friendly but muted reception on the continent.1 No bother: Prophets are typically without honor in their own native land. Piketty’s time came in the following year, the spring of 2014, when the English translation of his magnum opus appeared.2 Spurred on by favorable reviews from the likes of Nobel Laureate Paul Krugman (“Capital in the Twenty- First Century . . . is a bona fide phenomenon,” Krugman declared in the New York Times), the nearly seven hundred page economics book made surprising and sustained appearances on all forms of best-seller lists.3 Overnight, Piketty became the unlikeliest of oxymorons: a “Rock-Star Economist,” and a wealthy one at that.4 It might have seemed that, in the millennia-long battle to get the rich to pay their fair share of a just society’s burdens, a glimmer of hope had sprung forth. Years later, what has become of that hope? Academics have debated Piketty’s work, as academics do.5 Critics have criticized and defenders have defended Piketty’s sense of the facts of capital (it is held unequally, and inequality is getting worse); the normative ramifications of those facts (Piketty thinks they are bad); and what, if anything, to do about them (Piketty says tax the rich).6 Piketty himself has followed up with a sequel, Capital and Ideology, weighing in at over 1000 pages, roughly half again longer than Capital in the Twenty- First Century.