Large amplitude electrothermal waves in a nonequilibrium plasma

Steady, one-dimensional current streamers have been observed in nonequilibrium plasma subjected to crossed E and B fields. Their half-width and amplitude agree with a nonlinear model of electrothermal waves

Slave Against Slave: Plantation Violence In The Old South

The Nuance of Violence: Reassessing Intraracial Conflict on the Plantation No matter how well researched, no matter how beautifully written, our understanding of American slavery often takes the form of furtive glimpses through moving keyholes. When we are granted a view, our subject quickly disap...

Sparks from a Busy Anvil

According to the February 4, 1939 issue of The Baptist Examiner, Gilpin had two radio programs each Sunday signing on the station every Sunday morning and signing it off every Sunday night (p. 1). Sparks is a collection of 13 radio sermons, preached on station WCMI between May 30 and August 22, 1937.https://mds.marshall.edu/gilpin_johnr/1000/thumbnail.jp

Comparison of Two Detailed Models of Aedes aegypti Population Dynamics

The success of control programs for mosquito-­borne diseases can be enhanced by crucial information provided by models of the mosquito populations. Models, however, can differ in their structure, complexity, and biological assumptions, and these differences impact their predictions. Unfortunately, it is typically difficult to determine why two complex models make different predictions because we lack structured side-­by-­side comparisons of models using comparable parameterization. Here, we present a detailed comparison of two complex, spatially explicit, stochastic models of the population dynamics of Aedes aegypti, the main vector of dengue, yellow fever, chikungunya, and Zika viruses. Both models describe the mosquito?s biological and ecological characteristics, but differ in complexity and specific assumptions. We compare the predictions of these models in two selected climatic settings: a tropical and weakly seasonal climate in Iquitos, Peru, and a temperate and strongly seasonal climate in Buenos Aires, Argentina. Both models were calibrated to operate at identical average densities in unperturbedconditions in both settings, by adjusting parameters regulating densities in each model (number of larval development sites and amount of nutritional resources). We show that the models differ in their sensitivityto environmental conditions (temperature and rainfall) and trace differences to specific model assumptions.Temporal dynamics of the Ae. aegypti populations predicted by the two models differ more markedly under strongly seasonal Buenos Aires conditions. We use both models to simulate killing of larvae and/or adults with insecticides in selected areas. We show that predictions of population recovery by the models differ substantially, an effect likely related to model assumptions regarding larval development and (director delayed) density dependence. Our methodical comparison provides important guidance for model improvement by identifying key areas of Ae. aegypti ecology that substantially affect model predictions, and revealing the impact of model assumptions on population dynamics predictions in unperturbed and perturbed conditions.Fil: Legros, Mathieu. University of North Carolina; Estados UnidosFil: Otero, Marcelo Javier. Universidad de Buenos Aires; ArgentinaFil: Romeo Aznar, Victoria Teresa. Universidad de Buenos Aires; ArgentinaFil: Solari, Hernan Gustavo. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Gould, Fred. National Institutes of Health; Estados UnidosFil: Lloyd, Alun L.. National Institutes of Health; Estados Unido

Landscape evolution at extensional relay zones

It is commonly argued that the extensional relay zones between adjacent crustal-scale normal fault segments are associated with large catchment-fan systems that deliver significant amounts of sediment to hanging wall basins. This conceptual model of extensional basin development, while useful, overlooks some of the physical constraints on catchment evolution and sediment supply in relay zones. We argue that a key factor in the geomorphic evolution of relay zones is the interplay between two different timescales, the time over which the fault array develops, and the time over which the footwall catchment-fan systems are established. Results of numerical experiments using a landscape evolution model suggest that, in isolated fault blocks, footwall catchment evolution is highly dependent on the pattern and rate of fault array growth. A rapidly linked en echelon fault geometry gives rise to capture of relay zone drainage by aggressive catchment incision in the relay zone and to consequent increases in the rate of sediment supply to the hanging wall. Capture events do not occur when the fault segments are allowed to propagate slowly toward an en echelon geometry. In neither case, however, are large relay zone catchment-fan systems developed. We propose several physical reasons for this, including geometric constraints and limits on catchment incision and sediment transport rates in relay zones. Future research efforts should focus on the timescales over which fault array development occurs, and on the quantitative variations in catchment-fan system morphology at relay zones

Complex population dynamics as a competition between multiple time-scale phenomena

The role of the selection pressure and mutation amplitude on the behavior of a single-species population evolving on a two-dimensional lattice, in a periodically changing environment, is studied both analytically and numerically. The mean-field level of description allows to highlight the delicate interplay between the different time-scale processes in the resulting complex dynamics of the system. We clarify the influence of the amplitude and period of the environmental changes on the critical value of the selection pressure corresponding to a phase-transition "extinct-alive" of the population. However, the intrinsic stochasticity and the dynamically-built in correlations among the individuals, as well as the role of the mutation-induced variety in population's evolution are not appropriately accounted for. A more refined level of description, which is an individual-based one, has to be considered. The inherent fluctuations do not destroy the phase transition "extinct-alive", and the mutation amplitude is strongly influencing the value of the critical selection pressure. The phase diagram in the plane of the population's parameters -- selection and mutation is discussed as a function of the environmental variation characteristics. The differences between a smooth variation of the environment and an abrupt, catastrophic change are also addressesd.Comment: 15 pages, 12 figures. Accepted for publication in Phys. Rev.

Experimental and Theoretical Studies of Electrothermal Waves

Experimental and theoretical studies have been made of the electrothennal waves occurring in a nonequilibrium electrical discharge in a potassium-seeded argon plasma. The studies presented in this paper refer to discharges in transverse gas flow and magnetic field. The behavior of these discharges as determined by photographs, photomultiplier measurements, and voltage probes is discussed and the results interpreted in terms of a steady, one-dimensional theory. A single discharge was found to operate in one of three modes-the shorted, transition, or normal mode-depending on the length of the ionization transient. An extension of the one-dimensional theory to the inlet problem predicts the approximate length of this transient and thus provides criteria for the existence of each mode. The normal mode was studied in a duct with a series of circuits discharging in parallel across a gas flow. Here, a regular set of steady, one-dimensional streamers was found in the center of the duct between hot boundary regions along each electrode wall. The properties of the one-dimensional streamers are shown to agree in detail with values predicted from the one-dimensional theory. A scheme is then presented for calculation of the effective conductivity of a duct using the amplitude of conductivity fluctuations predicted by this theory