In the present work, a performance of ASTM A439 Austenitic Ductile Iron type D5S at high temperature in the oxidizing environment was investigated. The obtained results revealed that exposure at ...temperatures 800?C, 850?C, and 900?C resulted in relatively high mass gain and an extensive oxide scale spallation from the samples? surfaces during cooling. However, the material exposed at 950?C revealed a better oxidation resistance and no oxide scale spallation. The material exposed at 1000?C showed the best oxidation resistance among the studied samples. The surfaces and cross-sectional investigation revealed that the material exposed at 950?C formed mostly Ni/Cr/Mn-mixed protective oxide scale and local formation of Fe-rich nodules. In comparison with the sample exposed at 1000?C, a smaller amount of Fe-rich nodules per area unit was observed and most of the surface was covered by Ni/Cr/Mn-mixed protective scale. The latter was explained by the change in the calculated diffusion coefficients in the alloy for Ni and Fe, namely up to 900?C the diffusion coefficient for Fe was much higher than for Ni, while above 900?C the diffusion coefficient for Ni becomes higher than for Fe. This phenomenon was correlated with a phase transformation from ?-Fe into ?-Fe resulting in the diffusion coefficient change.
We describe a hybrid free-electron laser (FEL) inverse Compton scattering (ICS) system that can be operated at very high repetition rates and with higher average gamma-ray fluxes than possible from ...ICS systems driven by J kHz laser systems. Also, since the FEL system can generate 100 mJ class photon pulses at UV wavelengths, the electron beam energy can be lower than for systems driven with ∼micron wavelength lasers for attaining gamma rays of similar energy.
A sheet-beam traveling-wave amplifier has been proposed as a high-power generator of radio frequency (RF) from 95 to 300 GHz, using a microfabricated RF slow-wave structure (Carlsten, 2002). The ...planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power, high-average power, and wide bandwidths. Simulations of nominal designs using a vane-loaded waveguide as the slow-wave structure have indicated gains in excess of 1 dB/mm, with extraction efficiencies greater than 20% at 95 GHz with a 120-kV, 20-A electron beam. We have identified stable sheet beam formation and transport as the key enabling technology for this type of device. Also, due to the high aspect ratio in the slow-wave structure, the RF coupling is complicated and requires multiple input and output couplers. The RF mode must be transversely flat over the width of the electron beam, which impacts both the vane design and the input and output coupling. We report on new insights on stable sheet-beam transport and RF mode control in the slow-wave structure.
Using the health belief model (HBM) and theory of planned behavior (TPB) as theoretical frameworks, the objectives of this study were: (a) to identify correlates of human papillomavirus (HPV) ...vaccination intentions and (b) to explore differences between correlates of HPV vaccination intentions and uptake.
Undergraduate women (N = 447) who did not intend to receive (n = 223), intended to receive (n = 102), or had received (n = 122) the HPV vaccine were surveyed. Logistic regressions were conducted to examine the correlates of vaccination intentions and uptake.
Negative health consequences of the vaccine, physician's recommendation, positive attitudes toward the vaccine, and subjective norms were significant correlates of vaccination intentions. When comparing correlates of vaccination intentions to correlates of vaccination uptake, physician's recommendation, subjective norms, and perceived susceptibility to HPV were unique correlates of uptake.
Differences between correlates of vaccination intentions and uptake suggest that social influences of liked and trusted individuals may make an important and unique contribution in motivating young women to receive the HPV vaccine beyond other variables from the HBM and TPB. Future utilization of longitudinal designs is needed to understand which factors may cause individuals to decide to receive the HPV vaccine.
This paper describes the design, fabrication, and initial testing of a Ka-band dielectric-loaded traveling-wave tube (TWT) with very high bandwidth. Applications for high-power mm-wave sources span ...radar (including imaging), biology, medicine, communications, national security, and other areas. Specifically, to achieve long-range, cm-scale imaging using synthetic aperture radar techniques, a radio-frequency (RF) source with an average power level of 1 kW and a bandwidth of 10 GHz will be required. We developed a novel Ka-band TWT architecture that approaches these requirements. To achieve a very wide bandwidth, we proposed to use a dielectric-lined waveguide slow-wave structure. A dielectric constant of larger than 13 is needed for the resonance with a 20-keV electron beam. In our design, we have used <inline-formula> <tex-math notation="LaTeX">\varepsilon = 20 </tex-math></inline-formula> magnesium-calcium-titanate (MCT) ceramics. The two halves of the dielectric are shaped to ensure that the TM 11 -like mode has a flat electric field profile along the beam slot to accommodate transport of a 5-A sheet electron beam. The gain for the structure peaks at 33.25 GHz and is predicted to be 2.3 dB/cm with a total gain of 30 dB. The structure was fabricated and cold tested. Although the results of the cold test were inconclusive, we discuss possible reasons for discrepancies between simulations and measurements and propose simplifications to the tube's geometry for future studies.
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