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High precision time difference measurement between satellite and earth is an important part of space-based time-frequency system application in the future. With the on-orbit operation of high-precision atomic clocks, the accuracy of satellite-ground time difference measurement link has become the bottleneck of space-based time-frequency distribution. In this paper, the basic principle of two-way time difference measurement is derived. The system error and equipment error involved are analyzed, and the error control strategy is given. The above work will provide engineering guidance for high-precision two-way time difference measurement in the design of satellite-ground links.

The mitochondrial permeability transition (PT) is a Ca2+-dependent permeability increase of the inner membrane, mediated by the permeability transition pore (PTP). Depending on open time and channel size, the PTP can participate in Ca2+ homeostasis or cell death. In the 1990s, through the use of modifiers of SH groups and of relatively specific histidine and arginine reagents, a few discrete regulatory sites of the PTP have been defined. Recent evidence suggests that PTP forms from F-ATP synthase. The first part of my work was focused on the identification of the arginine residue(s) conferring PTP regulation by glyoxals within the general hypothesis that the PTP originates from F-ATP synthase. Eriksson and co-workers discovered the PTP-modulatory effects of arginine-selective reagents, and focused on the structure-function relationship of arginine-glyoxal adducts in the regulation of PTP opening and closure in rat liver mitochondria. Phenylglyoxal (PGO) is the most extensively used arginine-specific reagent. I have observed for the first time that PGO affects the PT in a species-specific manner (inhibition in mouse and yeast, induction in human and Drosophila mitochondria), indicating that the ability to modulate the PTP by PGO has been conserved but differs across species. I have been able to show that the effect of PGO on the PT is specifically mediated by Arg 107 of subunit g, the only arginine residue of this subunit that has been conserved across species. Yeast mitochondria lacking subunit g or bearing a subunit g R107A mutation were totally resistant to PT inhibition by PGO. Taking advantage of the species-specific differences but conserved reactivity with PGO, I have observed that substitution of yeast subunit g with its human counterpart confers the “human” phenotype to yeast, suggesting that the species-specific effect of PGO is more likely to depend on structural differences between the yeast and human F-ATP synthase than on the R107-PGO adduct as such. This finding is a step forward in the molecular understanding of PTP regulation, and further supports the hypothesis that the PTP forms from F-ATP synthase. The second part of my work was dedicated to reinvestigate the role of Ca2+ as a permissive factor for PTP opening. The most recent hypothesis about the mechanism of PTP formation is that interaction of Ca2+ with the metal binding site of β subunit (which usually contributes to coordinate the binding of Mg-ATP) causes a conformational change that is propagated to the inner membrane through the lateral stalk, which eventually leads to PTP formation. Yet a PT occurred in the absence of added Ca2+ with several inducers including p-hydroxyphenylgloxal (OH-PGO), one of the arginine reagents that favors PTP opening in rat liver mitochondria; and phenylarsine oxide (PhAsO), a dithiol cross-linker that is a potent PTP inducer. I have observed that pore opening can occur in presence of EGTA after the treatment of mitochondria with OH-PGO and PhAsO, but also that the inducing effect is prevented by depletion of matrix Ca2+ with the ionophore A23187 or by chelation of matrix Ca2+ with BAPTA. These observations indicate that in the absence of matrix Ca2+ PTP cannot be activated by OH-PGO and PhAsO. Another part of my work was to test whether charged amino acids of yeast subunits e and g are involved in their interaction, thus playing a role in the dimerization of F-ATP synthase. I have identified Arg 8 of subunit e as a critical residue in mediating e-g interactions, most likely through an electrostatic bond with Glu 83 of subunit g. We have also observed that dimers purified after blue-native electrophoresis from mutants of Arg 8 show decreased PTP channel conductance and activity, indicating that this residue might directly participate in generating the full conductance channel.