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.
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.
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