Water-phase synthesis of cationic silica/polyamine nanoparticles

Functionalizing surfaces with amine groups through the hydrolytic condensation of aminotrialkoxysilanes is a typical approach when modifying silica particles for use in bioimaging, enzyme immobilization, and other applications. This processing step can be eliminated if amine-functionalized silica particles are directly prepared without using aminotrialkoxysilanes. Here, a one-pot, ambient-condition, water-phase method to synthesize silica-based nanoparticles (NPs) that present surface amine groups is described. The formation mechanism involves the electrostatic crosslinking of cationic polyallylamine hydrochloride by citrate anions and the infusion of the formed polymer/salt aggregates by silicic acid. The particles were unimodal with average diameters in the range of 40 to 100 nm, as determined by the size of the templating polymer/salt aggregates. Colorimetric analysis using Coomassie brilliant blue and zeta potential measurements confirmed the presence of surface amine groups of the hybrid silica/polymer NPs. Surface charge calculations indicated the hybrid NPs had a lower amine surface density than aminopropyltriethoxysilane-functionalized silica (0.057 #/nm 2 vs. 0.169 #/nm 2 at pH 7)

Search for High-Mass Protostellar Objects in Cold IRAS Sources

We present the results of CS J=2-1 mapping observations towards 39 massive star-forming regions selected from the previous CO line survey of cold IRAS sources with high-velocity CO flows along the Galactic plane (Yang et al. 2002). All sources are detected in CS J=2-1 showing the existence of CS clumps around the IRAS sources. However, one-third of the sources are not deeply embedded in the dense clumps by comparison of the central powering IRAS sources and the morphologies of CS clumps. Physical parameters of the dense molecular clumps are presented. We have identified 12 high-mass protostellar object (HMPO) candidates by checking the association between the dense cores and the IRAS sources, the detection of water maser, and the radio properties towards the IRAS sources. We find that the HMPO sources are characterized by low FIR luminosity to virial mass ratios since they are in very early evolutionary stages when the massive protostars have not reached their full luminosities, which are typical for zero-age main sequence stars. Large turbulent motion in the HMPO sources may be largely due to the large kinetic energy ejected by the central protostars formed in the dense clumps. However, alternative means or undetected outflows may also be responsible for the turbulence in the clumps.Comment: 20 pages, 4 figures, accepted for publication in A

Determinants of banking crisis in developing countries

This paper identifies determinants associated with probability of banking crisis in developing countries. By using data sample of more than 80 developing countries around the world from 1974 to 2002, the results from our mutivariate logit economitric model indicate that systemic banking crisis tend to erupt as macro-conditions are weak, especially when economies experience low GDP growth and high inflation. Moreover, also find that the banking sector becomes sensitive to the crisis as the credit growth booming. Besides, other financial macro variables such as high real interest rate and exchange rate are also confirmed to be associated with risk of crisis

Influence of edge crack on frequencies of thin plate in bending

This paper investigates the influence of crack location and crack length on changes in natural frequencies of bending thin plate. To perform this analysis, a computing program called CRACK-PLATE, using the finite element method based on the Ressner-Mindlin' theory of plate is developed. In order to achieve a high accuracy, an isoparametric element of Barsoum is combined with an 8-node quadrilateral isoparametric element. The numerical results show that the natural frequencies are very sensitive to the crack presence in the bending thin plate. This study is a basis for crack identification based on natural frequencies of plates