951 research outputs found
Verification of computer-aided designs of traveling-wave tubes utilizing novel dynamic refocusers and graphite electrodes for the multistage depressed collector
A computational procedure for the design of TWT-refocuser-MDC systems was used to design a short dynamic refocusing system and highly efficient four-stage depressed collector for a 200-W, 8- to 18-GHz, TWT. The computations were carried out with advanced, multidimensional computer programs which model the electron beam as a series of disks of charge and follow their trajectories from the RF input of the TWT, through the slow-wave structure and refocusing section, to their points of impact in the depressed collector. Secondary emission losses in the MDC were treated semi-quantitatively by injecting a representative beam of secondary electrons into the MDC analysis at the point of impact of each primary beam. A comparison of computed and measured TWT and MDC performance showed very good agreement. The electrodes of the MDC were fabricated from a particular form of isotropic graphite that was selected for its low secondary electron yield, ease of machinability, and vacuum properties. This MDC was tested (at CW) for more than 1000 hr with negligible degradation in TWT and MDC performances
Direct Detection of Products from the Pyrolysis of 2-Phenethyl Phenyl Ether
The pyrolysis of 2-phenethyl phenyl ether (PPE, C_6H_5C_2H_4OC_6H_5) in a hyperthermal nozzle (300-1350 °C)
was studied to determine the importance of concerted and homolytic unimolecular decomposition pathways.
Short residence times (<100 μs) and low concentrations in this reactor allowed the direct detection of the
initial reaction products from thermolysis. Reactants, radicals, and most products were detected with
photoionization (10.5 eV) time-of-flight mass spectrometry (PIMS). Detection of phenoxy radical, cyclopentadienyl
radical, benzyl radical, and benzene suggest the formation of product by the homolytic scission of
the C_6H_5C_2H_4-OC_6H_5 and C_6H_5CH_2-CH_2OC_6H_5 bonds. The detection of phenol and styrene suggests
decomposition by a concerted reaction mechanism. Phenyl ethyl ether (PEE, C_6H_5OC_2H_5) pyrolysis was also
studied using PIMS and using cryogenic matrix-isolated infrared spectroscopy (matrix-IR). The results for
PEE also indicate the presence of both homolytic bond breaking and concerted decomposition reactions.
Quantum mechanical calculations using CBS-QB3 were conducted, and the results were used with transition
state theory (TST) to estimate the rate constants for the different reaction pathways. The results are consistent
with the experimental measurements and suggest that the concerted retro-ene and Maccoll reactions are
dominant at low temperatures (below 1000 °C), whereas the contribution of the C_6H_5C_2H_4-OC_6H_5 homolytic
bond scission reaction increases at higher temperatures (above 1000 °C)
Nonlinear Scattering of a Bose-Einstein Condensate on a Rectangular Barrier
We consider the nonlinear scattering and transmission of an atom laser, or
Bose-Einstein condensate (BEC) on a finite rectangular potential barrier. The
nonlinearity inherent in this problem leads to several new physical features
beyond the well-known picture from single-particle quantum mechanics. We find
numerical evidence for a denumerably infinite string of bifurcations in the
transmission resonances as a function of nonlinearity and chemical potential,
when the potential barrier is wide compared to the wavelength of oscillations
in the condensate. Near the bifurcations, we observe extended regions of
near-perfect resonance, in which the barrier is effectively invisible to the
BEC. Unlike in the linear case, it is mainly the barrier width, not the height,
that controls the transmission behavior. We show that the potential barrier can
be used to create and localize a dark soliton or dark soliton train from a
phonon-like standing wave.Comment: 15 pages, 15 figures, new version includes clarification of
definition of transmission coefficient in general nonlinear vs. linear cas
Dynamics and energetics of the South Pacific Convergence Zone during FGGE SOP-1 and South Pacific Convergence Zone and global-scale
Significant accomplishments (papers published, conference presentations, and education degrees) are presented. The focus of the current research is outlined. Plans for the coming year are discussed briefly
Theology, News and Notes - Vol. 21, No. 03
Theology News & Notes was a theological journal published by Fuller Theological Seminary from 1954 through 2014.https://digitalcommons.fuller.edu/tnn/1051/thumbnail.jp
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Progress Relating to Civilian Applications During August 1961
Progress is reported on development studies on reactor materials and components, fuels, fuel elements, gaspressure bonding of ceramic fuel elements, uranium carbides, growth of UO/sub 2/ single crystals, radioisotope and radiation applications, materials evaluations, coated-particle fuel materials, corrosion in fiuoride-volatility processes, cold-bonding processes, radiation effects on MGCR fuel materials, radiation effects on SM-2 fuels, gas-cooled reactor program, and gas-pressure bonding of beryllium-clad fuel elements. (B.O.G.
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