An impact sensitivity study of reactive materials

The impact sensitivity of a potassium chlorate, stabilized red phosphorous, Quso, and magnesium oxide mixture in a 34/14/4/2 ratio has been found to be about 18 ł 5 gram-centimeters for a 50% sensitivity to initiation. Chi-square tests at the 95% confidence level have determined that it is not possible to reject the hypothesis that the distribution is either normally distributed or log-normally distributed within the 50% range. Humidity, aging, and some additives were found to desensitize the mixture. Energy versus drop weight and test height curves show that momentum considerations are crucial over large test ranges in studies of impact sensitivity. Drop weight velocity and energy delivered to the reactants were determined to be the critical parameters. Sensitivity data for phosphorous and potassium chlorate mixtures and copper chlorotetrazole are presented and interpreted. A method for appraising the performance of the impact apparatus is included --Abstract, page ii

Phenotypically Plastic Responses to Predation Risk Are Temperature Dependent

Predicting how organisms respond to climate change requires that we understand the temperature dependence of fitness in relevant ecological contexts (e.g., with or without predation risk). Predation risk often induces changes to life history traits that are themselves temperature dependent. We explore how perceived predation risk and temperature interact to determine fitness (indicated by the intrinsic rate of increase, r) through changes to its underlying components (net reproductive rate, generation time, and survival) in Daphnia magna. We exposed Daphnia to predation cues from dragonfly naiads early, late, or throughout their ontogeny. Predation risk increased r differentially across temperatures and depending on the timing of exposure to predation cues. The timing of predation risk likewise altered the temperature-dependent response of T and R0. Daphnia at hotter temperatures responded to predation risk by increasing r through a combination of increased R0 and decreased T that together countered an increase in mortality rate. However, only D. magna that experienced predation cues early in ontogeny showed elevated r at colder temperatures. These results highlight the fact that phenotypically plastic responses of life history traits to predation risk can be strongly temperature dependent

Stochasticity directs adaptive evolution toward nonequilibrium evolutionary attractors

Stochastic processes such as genetic drift may hinder adaptation, but the effect of such stochasticity on evolution via its effect on ecological dynamics is poorly understood. Here we evaluate patterns of adaptation in a population subject to variation in demographic stochasticity. We show that stochasticity can alter population dynamics and lead to evolutionary outcomes that are not predicted by classic eco-evolutionary modeling approaches. We also show, however, that these outcomes are governed by nonequilibrium evolutionary attractors— these are maxima in lifetime reproductive success when stochasticity keeps the ecological system away from the deterministic equilibrium. These NEEAs alter the path of evolution but are not visible through the equilibrium lens that underlies much evolutionary theory. Our results reveal that considering population processes during transient periods can greatly improve our understanding of the path and pace of evolution

Ecological boundaries and constraints on viable eco-evolutionary pathways [Pre-print]

Evolutionary dynamics are subject to constraints ranging from limitations on what is physically possible to limitations on the pathways that evolution can take. One set of evolutionary constraints, known as ‘demographic constraints’, constrain what can occur evolutionarily due to the population demographic or population dynamical consequences of evolution leading to conditions that make populations susceptible to extinction. These demographic constraints can limit the strength of selection or rates of environmental change populations can experience while remaining extant and the trait values a population can express. Here we further hypothesize that the population demographic and population dynamical consequences of evolution also can constrain the eco-evolutionary pathways that populations can traverse by defining ecological boundaries represented by areas of likely extinction. We illustrate this process using a model of predator evolution. Our results show that the populations that persist over time tend to be those whose eco-evolutionary dynamics have avoided ecological boundaries representing areas of likely extinction due to stochastic deviations from a deterministic eco-evolutionary expectation. We term this subset of persisting pathways viable eco-evolutionary pathways. The potential existence of ecological boundaries constraining evolutionary pathways has important implications for predicting evolutionary dynamics, interpreting past evolution, and understanding the role of stochasticity and ecological constraints on eco-evolutionary dynamics

Ecological boundaries and constraints on viable eco-evolutionary pathways

Evolutionary dynamics are subject to constraints ranging from limitations on what is physically possible to limitations on the pathways that evolution can take. One set of evolutionary constraints, known as ‘demographic constraints’, constrain what can occur evolutionarily due to the demographic or dynamical consequences of evolution leading to conditions that make populations susceptible to extinction. These demographic constraints can limit the strength of selection or the rates of environmental change populations can experience while remaining extant and the trait values a population can express. Here we further hypothesize that the population demographic and dynamic consequences of evolution also can constrain the eco-evolutionary pathways that populations can traverse by defining ecological boundaries represented by areas of likely extinction. We illustrate this process using a model of predator evolution. Our results show that the populations that persist over time tend to be those whose eco-evolutionary dynamics have avoided ecological boundaries representing areas of likely extinction due to stochastic deviations from a deterministic eco-evolutionary expectation. We term this subset of persisting pathways viable eco-evolutionary pathways. The potential existence of ecological boundaries constraining evolutionary pathways has important implications for predicting evolutionary dynamics, interpreting past evolution, and understanding the role of stochasticity and ecological constraints on eco-evolutionary dynamics

Predator-Dependent Functional Responses Alter the Coexistence and Indirect Effects among Prey that Share a Predator

Predator functional responses describe predator feeding rates as a function of prey abundance and are central to pred-ator–prey theory. Despite ample evidence that functional responses also depend on predator abundance, theory incor-porating predator-dependent functional responses has focused almost exclusively on specialist predator–prey pairs or linear food chains. This leaves a large gap in our knowledge as many predators feed on multiple prey, and in so doing, generate indirect effects among prey that can alter their coexistence. Here we investigate how predator-dependent functional responses in a one predator–two prey model alter the coexistence among prey and their net effects on one another. We use two different functional response forms (the Beddington–DeAngelis and Crowley–Martin functional responses) and consider situations in which the prey do not directly interact and in which they directly compete with one another. We find that predator dependence can facilitate, hinder, or have no effect on prey coexistence depending on whether prey compete directly and the role of predation in mediating coexistence among the prey in the absence of predator dependence. We also show that the negative net effects of prey on one another are generally weakened by predator dependence and can become positive under the Crowley–Martin functional response. Together, these results suggest that predator dependence may have widespread effects on ecological communities by altering the coexistence among prey species and the strength and signs of the interactions among them

Gravid Tetragnathid Spiders Show an Increased Functional Response

Spiders in the genus Tetragnatha feed on emerging aquatic insects, including mosquitoes and midges, but there is little known about the foraging behavior of these spiders. We hypothesized that female spiders actively developing egg sacs would increase food consumption to provide more energy to produce and provision their eggs. We tested this hypothesis by measuring foraging rates of Tetragnatha spiders kept in jars and provisioned with different levels of midges. We then tested for a difference in the functional response of spiders that did or did not lay egg sacs in their jars. Egg-laying and non-egg-laying spiders showed significantly different functional responses, indicating that Tetragnatha spiders can change their behavior or web structure to increase their foraging rate, presumably to accommodate increased energy demand for reproduction

Continuously operating 4He evaporation refrigerator

Journal ArticleA simple and compact device was developed to provide continuous, self-regulating refrigeration at approximately 1.3 K. The temperature of the device remains nearly constant, independent of external power, up to a critical power. For a molar flow rate of 10^-4 moles/sec, the refrigerator can absorb 4.5 mW. Such a refrigerator should be suitable for condensing 3He in a 3He-4He dilution refrigerator