No abstract

In this article, the thermal history and cooling rate experienced by gas-atomized Al-based amorphous powders were studied via numerical simulations. Modeling simulations were based on the assumption of Newtonian cooling with forced convection, as well as an energy balance, which involves gas dynamics, droplet dynamics, and heat transfer between gas and droplet. To render the problem tractable, phase transformations, crystal nucleation, and growth were not taken into account in the analysis of the solidification of Al droplets; instead, an energy balance approach was formulated and used. The numerical results and associated analysis were used to optimize processing parameters during gas atomization of Al-based amorphous powder. The results showed that the cooling rate of droplets increases with decreasing powder size and can reach in excess of 10 5 K/s for powder <20 lm in diameter. Gas composition has a more significant influence on cooling rate than gas pressure, and 100 pct He has the highest cooling effect. The results also showed that the cooling rate increases with increasing melt superheat temperature.

The analysis of isomeric glycans is a challenging task. In this work, a new strategy was developed for isomer-specific glycan profiling using nanoLC-MS with PGC as the stationary phase. Native glycans were derivatized in the presence of methylamine and trispyrrolidinophosphonium hexafluorophosphate and reduced by the ammonia-borane complex. Methylamidation stabilized the retention time and peak width and improved the detection sensitivity of sialylated glycans to 2-80-fold in comparison to previous ESI-MS methods using the positive-ion mode. Up to 19 tetrasialylated glycan species were identified in the derivatized human serum sample, which were difficult to detect in the sample without derivatization. Furthermore, due to high detection sensitivity and chromatographic resolution, more isomeric glycans could be identified from the model glycoprotein Fetuin and the human serum sample. As a result, up to seven isomers were observed for the disialylated biantennary glycan released from Fetuin, and three of them were identified for the first time in this study. Using the developed analytical strategy, a total of 293 glycan species were obtained from the human serum sample, representing an increase of over 100 peaks in comparison to the underivatized sample. The strategy greatly facilitates the profiling of isomeric glycans and the analysis of trace-level samples.

No abstract

No abstract