9,749 research outputs found

    A technique for determining daytime atmospheric oxide above 50 km from backscattered ultraviolet measurements

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    Airglow from gamma band resonance fluorescence of nitric oxide near 255 nm is calculated at several solar zenith angles. Data from the Nimbus 4 BUV wavelengths 273.5 to 287.6 nm is used to estimate the Rayleigh and ozone scattering contributions to the BUV 255.5 nm data and the remaining signal is attributed to NO airglow. The low solar zenith angle contributions by NO is less than 0.5%, and the high latitude/high zenith angle contribution exceeds 5%. This technique allows for estimating NO content above 50 km, as well as partitioning that content between the mesosphere and thermosphere

    Measuring the muon's anomalous magnetic moment to 0.14 ppm

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    The anomalous magnetic moment (g-2) of the muon was measured with a precision of 0.54 ppm in Experiment 821 at Brookhaven National Laboratory. A difference of 3.2 standard deviations between this experimental value and the prediction of the Standard Model has persisted since 2004; in spite of considerable experimental and theoretical effort, there is no consistent explanation for this difference. This comparison hints at physics beyond the Standard Model, but it also imposes strong constraints on those possibilities, which include supersymmetry and extra dimensions. The collaboration is preparing to relocate the experiment to Fermilab to continue towards a proposed precision of 0.14 ppm. This will require 20 times more recorded decays than in the previous measurement, with corresponding improvements in the systematic uncertainties. We describe the theoretical developments and the experimental upgrades that provide a compelling motivation for the new measurement.Comment: 5 pages, 1 figure, presented at International Nuclear Physics Conference 2010 (INPC 2010

    A Double Hurdle Model of Preferences for a Proposed Capacity Reduction Program in the Atlantic Shark Fishery

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    The Atlantic shark fishery is considered to be overcapitalized. One approach to capacity management is the purchase and permanent retirement of fishing vessels, fishing permits, or both under voluntary buyback programs. Representatives of the commercial shark fishery have proposed such an approach to manage the overcapacity in their fishery in the Gulf of Mexico and Atlantic regions. This program would allow owners to submit willingness-to-accept (WTA) bids for their permits and vessels. This study uses econometric modeling to explain the potential participation and bid amounts from a survey of permit owners.Resource /Energy Economics and Policy,

    Mesoscopic Transport: The Electron-Gas Sum Rules in a Driven Quantum Point Contact

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    The nature of the electron gas is characterized, above all, by its multi-particle correlations. The conserving sum rules for the electron gas have been thoroughly studied for many years, and their centrality to the physics of metallic conduction is widely understood (at least in the many-body community). We review the role of the conserving sum rules in mesoscopic transport, as normative criteria for assessing the conserving status of mesoscopic models. In themselves, the sum rules are specific enough to rule out any such theory if it fails to respect the conservation laws. Of greater interest is the capacity of the compressibility sum rule, in particular, to reveal unexpected fluctuation effects in nonuniform mesoscopic structures.Comment: TeX, 11pp, no fi

    Dependence of Galaxy Shape on Environment in the Sloan Digital Sky Survey

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    Using a sample of galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 4, we study the trends relating surface brightness profile type and apparent axis ratio to the local galaxy environment. We use the SDSS parameter `fracDeV' to quantify the profile type. We find that galaxies with M_r > -18 are mostly described by exponential profiles in all environments. Galaxies with -21 < M_r < -18 mainly have exponential profiles in low density environments and de Vaucouleurs profiles in high density environments. The most luminous galaxies, with M_r < -21, are mostly described by de Vaucouleurs profiles in all environments. For galaxies with M_r < -19, the fraction of de Vaucouleurs galaxies is a monotonically increasing function of local density, while the fraction of exponential galaxies is monotonically decreasing. For a fixed surface brightness profile type, apparent axis ratio is frequently correlated with environment. As the local density of galaxies increases, we find that for -20 < M_r < -18, galaxies of all profile types become slightly rounder, on average; for -22 < M_r < -20, galaxies with exponential profiles tend to become flatter, while galaxies with de Vaucouleurs profiles become rounder; for M_r < -22, galaxies with exponential profiles become flatter, while the de Vaucouleurs galaxies become rounder in their inner regions, yet exhibit no change in their outer regions. We comment on how the observed trends relate to the merger history of galaxies.Comment: 23 pages, 7 figures, accepted by Ap

    Self-Medication and Homeostatic Behaviour in Herbivores: Learning about the Benefits of Nature’s Pharmacy

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    Traditional production systems have viewed animals as homogeneous ‘machines’ whose nutritional and medicinal needs must be provided in a prescribed manner. This view arose from the lack of belief in the wisdom of the body to meet its physiological needs. Is it possible for herbivores to select diets that meet their needs for nutrients and to write their own prescriptions? Our research suggests it is. Herbivores adapt to the variability of the external environment and to their changing internal needs not only by generating homeostatic physiological responses, but also by operating in the external environment. Under this view, food selection is interpreted as the quest for substances in the external environment that provide homeostatic utility to the internal environment. Most natural landscapes are diverse mixes of plant species that are literally nutrition centres and pharmacies with vast arrays of primary (nutrient) and secondary (pharmaceutical) compounds vital in the nutrition and health of plants and herbivores. Plant-derived alkaloids, terpenes, sesquiterpene lactones and phenolics can benefit herbivores by, for instance, combating internal parasites, controlling populations of fungi and bacteria, and enhancing nutrition. Regrettably, the simplification of agricultural systems to accommodate inexpensive, rapid livestock production, coupled with a view of secondary compounds as toxins, has resulted in selecting for a biochemical balance in forages favouring primary (mainly energy) and nearly eliminating secondary compounds. There is a global need to create a more sustainable agriculture, with less dependence on external finite resources, such as fossil fuels and their environmentally detrimental derivatives. Self-medication has the potential to facilitate the design of sustainable grazing systems to improve the quality of land as well as the health and welfare of animals. Understanding foraging as the dynamic quest to achieve homeostasis will lead to implementing management programs where herbivores have access not only to diverse and nutritious foods but also to arrays of medicinal plants

    Is Doping of Cognitive Performance an Anti‐Herbivore Adaptation? Alkaloids Inhibiting Acetylcholinesterase as a Case

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    Historically, people who study interactions between plants and herbivores focused on the ecological costs and benefits of synthesizing secondary metabolites. These compounds have diverse functions including defenses against herbivores. Some plants produce alkaloids that act as acetylcholinesterase inhibitors, increasing both the level and duration of action of the neurotransmitter acetylcholine with potential toxic effects in insects and mammals. Yet, among a number of neuroactive plant chemicals, alkaloids that inhibit acetylcholinesterase (AIA) display nootropic activities, that is, positively affect cognition, learning, and memory in mammals. This creates a paradox: Neuroactive AIA, expected to punish herbivores, enhance cognition, learning, and memory. A prevailing view is AIA are pesticides that adversely affecting the nervous systems of herbivorous insects, and the positive influences in mammals are merely a by‐product of other functions. We review literature on the behavioral ecology of diet choice, food‐aversion learning, and neurophysiological actions of AIA in mammals to provide a more comprehensive view of the adaptive significance of AIA. These compounds act as anti‐herbivory defenses that influence flavor (taste plus odor) preference/aversion, the formation of memories, and the feeding behavior of mammalian herbivores. Thus, what appears from an insect standpoint to be an enigma makes sense for mammals: AIA enable mammalian herbivores to quickly learn and remember specific plant(s) and the locations where they ate those plant(s). We provide examples of AIA, synthesized by over 200 plant species in 16 families, which affect learning and memory in mammals. Using 36 examples of acetylcholinesterase inhibitors synthesized by plants in 58 families, we also show that acetylcholinesterase blockers contribute to anti‐herbivore chemical defense by affecting food‐aversion learning and memory in mammalian herbivores. We provide an evolutionary rationale for why natural selection may favor synthesis of chemicals that positively affect mental functions of herbivores. Our hypothesis, which challenges the current view that plant chemical defenses are aimed solely at destabilizing herbivore physiology, facilitates a broader understanding of diet preferences and feeding behavior in mammalian herbivores

    Preference for Wheat Straw by Lambs Conditioned with Intraruminal Infusions of Starch

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    We hypothesized that feed preference depends on the interplay between flavour and postingestive effects, and we tested two predictions based on this hypothesis: (1) lambs acquire preferences for poorly nutritious feeds paired with starch; and (2) preferences persist when starch is no longer administered. Twenty lambs were randomly allocated to two groups and conditioned as follows: on odd-numbered days, lambs in group 1 received onion-flavoured wheat straw and lambs in group 2 received oregano-flavoured wheat straw. On even-numbered days, the flavours were switched and starch (2.5-9.4% of the digestible energy received/d) was infused into the rumen of all animals during straw consumption. Four periods of 8 d of conditioning were performed and on the 9th day of each period all animals were offered a choice between onion- and oregano-flavoured straw. After conditioning, starch administration was suspended and lambs were offered onion- and oregano-flavoured straw at weekly intervals for 8 weeks (extinction). Lambs strongly preferred the flavoured straw paired with starch, and this preference persisted during extinction. Thus, these results suggest that the postingestive effects of energy play an important role in the development of feed preferences of ruminants

    Ultra-Efficient Cooling of Resonators: Beating Sideband Cooling with Quantum Control

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    The present state-of-the-art in cooling mechanical resonators is a version of "sideband" cooling. Here we present a method that uses the same configuration as sideband cooling --- coupling the resonator to be cooled to a second microwave (or optical) auxiliary resonator --- but will cool significantly colder. This is achieved by varying the strength of the coupling between the two resonators over a time on the order of the period of the mechanical resonator. As part of our analysis, we also obtain a method for fast, high-fidelity quantum information-transfer between resonators.Comment: 4 pages, revtex4-1, 2 png figure
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