Depth / Conversion Characterization of Electron-beam Initiated Polymerization
Confocal Raman microscopy was used to determine polymer conversion as a function of depth into electron-beam cured coating samples. Samples were irradiated in atmospheres with varying levels of oxygen. As expected, conversion near the surface increased as the level of oxygen was decreased. Samples were also irradiated under well-inerted conditions while varying the accelerating potential (voltage) of the electron beam. The results show low conversion near the sample bottom at the lower voltages. This lower conversion is consistent with inadequate energy penetration predicted by Monte Carlo simulations.
Pulsed electron beam curing of polymer coatings
Pulsed electron beam (PEB) curing is significantly more energy efficient and speedy than continuous EB curing, as Weiss and Dunn (2002) showed in a pioneering work. It exploits the inherently heterogeneous nature of energy deposition along electron tracks to compartmentalize free radical initiation sites, thereby suppressing second-order termination reactions in favor of first-order propagation. Appropriately timed pulses thus allow heterogeneous polymerization in a single phase, enabling in-line curing of polymeric coatings from monomers at relatively high process speeds. That is beyond the capabilities of conventional electron beams.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.