We investigated the CO sensing mechanism of SnO2 (110) surface by density functional theory calculation. The CO sensing mechanism of SnO2 surface strongly depends upon the concentration of oxygen in the ambient atmosphere. For very high oxygen concentration where oxygen species O2 – or O– are not adsorbed on the stoichiometric SnO2 (110) surface, there is the direct interaction between CO and the stoichiometric surface through the CO adsorption on Sn site or formation of CO2, accompanying the release of electrons to the surface. For the considerable high oxygen concentration, the oxygen species O2 – and O– adsorbed on the oxygen-deficient SnO2 (110) surface grab electrons mainly from Sn atoms of SnO2 (110) surface. When SnO2 (110) surface is exposed to CO reducing gas, the interactions between CO and preadsorbed oxygen species (O2 –, O–) as well as some lattice atoms at certain sites on SnO2 surface lead to the releasing of electrons back to semiconductor SnO2. At very low oxygen concentration, the structural reconstruction is induced by the direct interaction between CO and SnO2 subreduced surface with the removing of 2-fold-coordinated bridging oxygen rows, accompanying the electron transfer from CO to the surface without the formation of CO2 in the sensing response process.

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Direct genetic manipulations have shown that telomerasemediated telomere elongation plays a key role in determining cellular replicative capacity and senescence. The mechanisms regulating the production of an active telomerase enzyme are still predominantly unknown, although roles for transcriptional control of hTERT, alternative-splicing of hTERT transcripts, and post-translational phosphorylation of hTERT protein have been advocated. Here we show that hTERT is alternatively spliced in specific patterns by different tissue types during human development. Alternative splicing often prohibits the expression of hTERT protein containing functional reverse transcriptase domains. In these instances, telomerase activity is absent, leading to shortening of telomeres. The specific pattern of hTERT mRNA variants in human development provides evidence that alternative splicing is non-random and participates in the regulation of telomerase activity.