Chemical characterization of extra layers at the interfaces in MOCVD InGaP/GaAs junctions by electron beam methods

Electron beam methods, such as cathodoluminescence (CL) that is based on an electron-probe microanalyser, and (200) dark field and high angle annular dark field (HAADF) in a scanning transmission electron microscope, are used to study the deterioration of interfaces in InGaP/GaAs system with the GaAs QW on top of InGaP. A CL emission peak different from that of the QW was detected. By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface. The nature and composition of the interlayer(s) are determined by HAADF. Such changes of the nominal GaAs QW can account for the emission observed by CL

NMR assignments and the acid-base characterization of the pomegranate ellagitannin punicalagin in the acidic pH-range.

In exploring the capability of nuclear magnetic resonance (NMR) spectroscopy for pomegranate juice analysis, the eight aromatic singlet resonances of alpha- and beta-punicalagin were clearly identified in the 1H NMR spectra of juice samples. The four downfield resonances were found to be sensitive to small pH changes around pH 3.50 where the NMR spectra of the juice samples were recorded. To understand this unusual behavior, the 1H and 13C resonance assignments of the punicalagin anomers were determined in aqueous solution and pH titrations with UV and 1H NMR detection carried out to characterize the acid-base properties of punicalagin over the pH range 2-8. Simultaneous fitting of all of the pH-sensitive 1H NMR signals produced similar but significantly different pK a values for the first two deprotonation equilibria of the gallagic acid moiety of the punicalagin alpha- (pK a1 = 4.57 +/- 0.02, pK a2 = 5.63 +/- 0.03) and beta- (pK a1 = 4.36 +/- 0.01, pK a2 = 5.47 +/- 0.02) anomers. Equivalent pK a values, (alpha : 6.64 +/- 0.01, beta : 6.63+/- 0.01) were measured for the third deprotonation step involving the ellagic acid group, in good agreement with a prior literature report. The punicalagin anomer equilibrium readjusts in parallel with the proton dissociation steps as the pH is raised such that beta-punicalagin becomes the most abundant anomer at neutral pH. The unusual upfield shifts observed for the glucose H3 and H5 resonances with increasing pH along with the shift in the alpha/beta anomer equilibrium are likely the consequence of a conformational rearrangement

The interaction of enoxaparin and fondaparinux with calcium.

The main sites of calcium binding were determined for the low molecular weight heparin drug enoxaparin and the synthetic pentasaccharide Arixtra (fondaparinux). [1H,13C] HSQC pH titrations were carried out to characterize the acid-base properties of these samples both in the presence and absence of calcium. The differences in the titration curves were used to determine the structural components of enoxaparin and fondaparinux responsible for Ca2+ binding. In enoxaparin both unsubstituted and 2-O-sulfated iduronic acid residues are important in calcium binding and the presence of the 2-O-sulfo group does not seem to influence the Ca2+ binding capability of the iduronate ring. In fondaparinux changes in chemical shifts upon Ca2+ binding were smaller than observed for enoxaparin, and were observed for both the glucuronic acid and 2-O-sulfated iduronic acid residues. In enoxaparin significant perturbations of the chemical shift of the N-sulfoglucosamine anomeric carbon in residues connected to 2-O-sulfated iduronic acid were detected on Ca2+ binding, however it was not possible to determine whether these changes reflect direct involvement in calcium complexation or result from through space interactions or conformational changes

Advanced image retrieval technology in future mobile teaching and learning

Advanced image retrieval technology has been widely adopted in many industries and areas. This technology is also adopted in higher education by some educators and researchers in recent years. With the introduction of mobile technology, it has been adopted in mobile teaching and learning in different disciplines. The image retrieval technology can improve learning efficiency, improve memory by providing similar learning contents, and engage students in learning. However, it is also limited by some software and hardware barriers on mobile devices, such as computing capability, screen size, and quality of wireless connections. Although it is believed to have both advantages and disadvantages in mobile learning, the adoption of the advanced image retrieval technology greatly enhanced the capability of image searching and learning experience by students and educators. The advanced image retrieval technology is believed to play a more important role in future mobile teaching and learning in different industries and businesses as well as in higher education