The molecular‐weight distribution (MWD), obtained by pulsed laser polymerization (PLP) at the high termination rate limit has been considered for investigating termination kinetics. The proposed methodology takes into account both the composite model for termination and the chain‐length dependencies of propagation for short‐chain and long‐chain radicals. Power‐law expressions are used to represent propagation and termination of long‐chain radicals (where k and k represent the maximum “virtual” rate coefficients for monomeric radicals, and α and β capture the chain‐length dependencies for propagation and termination), with the combined value of (β − α) evaluated from the MWD, after correcting for the influence of the kinetics of short‐chain radicals. A novel method is also developed for determining the mode of termination, δ, from MWDs produced by PLP at the high termination rate limit. Simulations for methyl methacrylate (MMA) polymerization at 25 °C confirm that the method can be applied robustly in the presence of complicating factors such as chain transfer to monomer and SEC broadening. The analysis of an experimental MWD obtained for MMA polymerization at 25 °C results in estimates of 0.14 ± 0.03 for (β − α) and 0.75 ± 0.04 for δ.
We give an algorithm for finding finite element approximations to surfaces of prescribed variable mean curvature, which span
a given boundary curve. We work in the parametric setting and prove optimal estimates in the H1 norm. The estimates are verified computationally. 相似文献
A capacitively-coupled RF argon discharge at a pressure of 10 mTorr with a plate separation of 7.5 cm has been studied both experimentally and using a one-dimensional particle in cell simulation with Monte Carlo collisions. A magnetic field of 0 to 60 G is applied in the direction parallel to the capacitor plates. In the simulation it was found that as the magnetic field was increased such that the electron cyclotron orbit radius of the hot electrons became smaller than of the order of the discharge length, the electron heating in the bulk of the discharge increased. The dominant electron heating mechanism was observed to change from a stochastic sheath to a bulk ohmic electron heating mode, with a variation of field from a to 10 G. This was accompanied by a drop in the plasma density at small magnetic fields, which was also observed experimentally. At higher magnetic fields the plasma density was found to increase, A detailed discussion of the simulation results is presented drawing comparisons with the experimental results, with which there is good agreement, and a simple magnetohydrodynamic model for the bulk heating 相似文献
Efficient ring cleavage of 9,10-dibromocamphor (3) provides a monocyclic hydroxyacid (5) which can serve as an intermediate in a new enantiospecific synthesis of estrone. 相似文献
Dopant-assisted atmospheric pressure chemical ionization (dAPCI) is a soft ionization method rarely used for gas chromatography-mass spectrometry (GC-MS). The current study combines GC-dAPCI with tandem mass spectrometry (MS/MS) for analysis of a complex mixture such as lignin pyrolysis analysis. To identify the structures of volatile lignin pyrolysis products, collision-induced dissociation (CID) MS/MS using a quadrupole time-of-flight mass spectrometer (QTOFMS) and pseudo MS/MS through in-source collision-induced dissociation (ISCID) using a single stage TOFMS are utilized. To overcome the lack of MS/MS database, Compound Structure Identification (CSI):FingerID is used to interpret CID spectra and predict best matched structures from PubChem library. With this approach, a total of 59 compounds were positively identified in comparison to only 22 in NIST database search of GC-EI-MS dataset. This study demonstrates the effectiveness of GC-dAPCI-MS/MS to overcome the limitations of traditional GC-EI-MS analysis when EI-MS database is not sufficient.
