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Sceloporus olivaceus
Number of Pages: 4Integrative BiologyGeological Science
Barbaetis: A New Genus of Eastern Nearctic Mayflies (Ephemeroptera: Baetidae)
The new genus Barbaetis Waltz and McCafferty, and new species Barbaetis benfieldi Kennedy are described from larvae collected from the New River, Virginia. Barbaetis is easily told from Baetis by the presence of procoxal osmobranchia. Cladistics of B. benfieldi, related Pseudocloeon species, and the lutheri and pavidus complexes of Baetis are presented and indicate the need for further taxonomic revision. The habitat of B. benfieldi is described in terms of several ecological parameters. The new species demonstrates a univoltine life history with postembryonic development restricted to a short springtime period
The DCU laser ion source
Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I ⌠108â1011âWâcmâ2) and fluences (F = 0.1â3.9âkJâcmâ2) from a Q-switched ruby laser (full-width half-maximum pulse duration ⌠35âns, λ = 694ânm) were used to generate a copper plasma. In âbasic operating mode,â laser generated plasma ions are electrostatically accelerated using a dc HV bias (5â18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ⌠600âÎŒA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L = 48âmm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a âcontinuous einzel arrayâ were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at âhigh pressure.â In âenhanced operating mode,â peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+âCu6+) increased considerably in this mode of operation
Study of 42 and 85 GHz coupled cavity traveling-wave tubes for space use
Designs were formulated for four CW, millimeter wavelength traveling-wave tubes having high efficiency and long life. Three of these tubes, in the 42 to 44 GHz frequency region, develop power outputs of 100 to 300 watts with overall efficiencies of typically 45 percent. Another tube, which covers the frequency range of 84 to 86 GHz, provides a power output of 200 watts at 25 percent efficiency. The cathode current density in each design was 1A/sq cm. Each tube includes: metal-ceramic construction, periodic permanent magnet focusing, a two step velocity taper, an electron beam refocusing section, and a radiation cooled three-stage depressed collector. The electrical and mechanical design for each tube type is discussed in detail. The results of thermal and mechanical analyses are presented
Some remarks on the isoperimetric problem for the higher eigenvalues of the Robin and Wentzell Laplacians
We consider the problem of minimising the th eigenvalue, , of
the (-)Laplacian with Robin boundary conditions with respect to all domains
in of given volume . When , we prove that the second
eigenvalue of the -Laplacian is minimised by the domain consisting of the
disjoint union of two balls of equal volume, and that this is the unique domain
with this property. For and , we prove that in many cases a
minimiser cannot be independent of the value of the constant in the
boundary condition, or equivalently of the volume . We obtain similar
results for the Laplacian with generalised Wentzell boundary conditions .Comment: 16 page
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