57,180 research outputs found

    \u3ci\u3eUrophora Affinis\u3c/i\u3e and \u3ci\u3eU. Quadrifasciata\u3c/i\u3e (Diptera: Tephritidae) Released and Monitored by USDA, APHIS, PPQ as Biological Control Agents of Spotted and Diffuse Knapweed

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    USDA, APHIS, PPQ has distributed the seedhead gall flies Urophora affinis and U. quadrifasciata (Diptera: Tephritidae) as classical biological agents of the introduced weeds spotted and diffuse knapweed (Centaurea maculosa and C. diffusa, respectively) (Asteraceae) in the United States. From 1987 to 1996, Urophora spp. have been released in 97 counties in 14 midwestern and western states. Established populations of U. affinis and U. quadrifasciata are confirmed in 85 and 95 counties, respectively, among all 14 states. These include the first reports of successful establishment of Urophora spp. in Arizona (two counties), Colorado (eight counties), Michigan (one county), Minnesota (six counties), Nebraska (four counties), Nevada (two counties), North Dakota (one county), South Dakota (four coun­ties), Utah (three counties), and Wisconsin (two counties). The first confirmed establishment of U. quadrifasciata in Indiana and Michigan is also reported

    Infall near clusters of galaxies: comparing gas and dark matter velocity profiles

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    We consider the dynamics in and near galaxy clusters. Gas, dark matter and galaxies are presently falling into the clusters between approximately 1 and 5 virial radii. At very large distances, beyond 10 virial radii, all matter is following the Hubble flow, and inside the virial radius the matter particles have on average zero radial velocity. The cosmological parameters are imprinted on the infall profile of the gas, however, no method exists, which allows a measurement of it. We consider the results of two cosmological simulations (using the numerical codes RAMSES and Gadget) and find that the gas and dark matter radial velocities are very similar. We derive the relevant dynamical equations, in particular the generalized hydrostatic equilibrium equation, including both the expansion of the Universe and the cosmological background. This generalized gas equation is the main new contribution of this paper. We combine these generalized equations with the results of the numerical simulations to estimate the contribution to the measured cluster masses from the radial velocity: inside the virial radius it is negligible, and inside two virial radii the effect is below 40%, in agreement the earlier analyses for DM. We point out how the infall velocity in principle may be observable, by measuring the gas properties to distance of about two virial radii, however, this is practically not possible today.Comment: 7 pages, 3 figures, to appear in MNRA

    Atomic kinetic energy, momentum distribution and structure of solid neon at zero-temperature

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    We report on the calculation of the ground-state atomic kinetic energy, EkE_{k}, and momentum distribution of solid Ne by means of the diffusion Monte Carlo method and Aziz HFD-B pair potential. This approach is shown to perform notably for this crystal since we obtain very good agreement with respect to experimental thermodynamic data. Additionally, we study the structural properties of solid Ne at densities near the equilibrium by estimating the radial pair-distribution function, Lindemann's ratio and atomic density profile around the positions of the perfect crystalline lattice. Our value for EkE_{k} at the equilibrium density is 41.51(6)41.51(6) K, which agrees perfectly with the recent prediction made by Timms {\it et al.}, 41(2)41(2) K, based on their deep-inelastic neutron scattering experiments carried out over the temperature range 4204 - 20 K, and also with previous path integral Monte Carlo results obtained with the Lennard-Jones and Aziz HFD-C2 atomic pairwise interactions. The one-body density function of solid Ne is calculated accurately and found to fit perfectly, within statistical uncertainty, to a Gaussian curve. Furthermore, we analyze the degree of anharmonicity of solid Ne by calculating some of its microscopic ground-state properties within traditional harmonic approaches. We provide insightful comparison to solid 4^4He in terms of the Debye model, in order to size the relevance of anharmonic effects in Ne.Comment: 20 pages, 7 figures. To be published in Physical Review

    Study of Civil Markets for Heavy-Lift Airships

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    The civil markets for heavy lift airships (HLAs) were defined by first identifying areas of most likely application. The operational suitability of HLAs for the applications identified were then assessed. The operating economics of HLAs were established and the market size for HLA services estimated by comparing HLA operating and economic characteristics with those of competing modes. The sensitivities of the market size to HLA characteristics were evaluated and the number and sizes of the vehicles required to service the more promising markets were defined. Important characteristics for future HLAs are discussed that were derived from the study of each application, including operational requirements, features enhancing profitability, military compatibility, improved design requirements, approach to entry into service, and institutional implications for design and operation

    Modal cut-off and the V-parameter in photonic crystal fibers

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    We address the long-standing unresolved problem concerning the V-parameter in a photonic crystal fiber (PCF). Formulate the parameter appropriate for a core-defect in a periodic structure we argue that the multi-mode cut-off occurs at a wavelength lambda* which satisfies V_PCF(lambda*)=pi. Comparing to numerics and recent cut-off calculations we confirm this result.Comment: 3 pages including 2 figures. Accepted for Optics Letter

    The application of the global isomorphism to the study of liquid-vapor equilibrium in two and three dimensional Lenard-Jones fluids

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    We analyze the interrelation between the coexistence curve of the Lennard-Jones fluid and the Ising model in two and three dimensions within the global isomorphism approach proposed earlier [V. L. Kulinskii, J. Phys. Chem. B \textbf{114} 2852 (2010)]. In case of two dimensions we use the exact Onsager result to construct the binodal of the corresponding Lennard-Jones fluid and compare it with the results of the simulations. In the three dimensional case we use available numerical results for the Ising model for the corresponding mapping. The possibility to observe the singularity of the binodal diameter is discussed.Comment: 9 pages, 2 figure

    21 Layer troposphere-stratosphere climate model

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    The global climate model is extended through the stratosphere by increasing the vertical resolution and raising the rigid model top to the 0.01 mb (75 km) level. The inclusion of a realistic stratosphere is necessary for the investigation of the climate effects of stratospheric perturbations, such as changes of ozone, aerosols or solar ultraviolet irradiance, as well as for studying the effect on the stratosphere of tropospheric climate changes. The observed temperature and wind patterns throughout the troposphere and stratosphere are simulated. In addition to the excess planetary wave amplitude in the upper stratosphere, other model deficiences include the Northern Hemisphere lower stratospheric temperatures being 5 to 10 C too cold in winter at high latitudes and the temperature at 50 to 60 km altitude near the equator are too cold. Methods of correcting these deficiencies are discussed
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