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Existing high‐precision inter‐satellite radio frequency (RF) measurement systems were mostly based on two‐satellite formations, and there lacks further research on measurement schemes for multi‐satellite formations. The frequency division multiple access (FDMA) and the code division multiple access based schemes are widely used, but not applicable for distributed applications due to their poor scalability. The time division multiple access (TDMA) based scheme can overcome this weakness, and has been applied in the global positioning system (GPS) IIR/IIF inter‐satellite link. However, the atomic clock used in GPS is not suitable for microsatellites. If a miniaturised frequency source instead of the atomic clock is utilised, the two way ranging (TWR) method adopted in this system would encounter a sharp decrease of measurement accuracy. To this end, this Letter aims to propose a novel TDMA based distributed RF measurement scheme for multi‐microsatellite formations. A TDMA based distributed broadcast protocol is employed in the media access control layer, closely integrated with the asymmetric double‐sided two‐way ranging method adopted in the physical layer. Numerical and simulation results demonstrate the superiority of the proposed scheme over the conventional TDMA scheme. The proposed scheme can be recommended for future multi‐microsatellite formation missions. [ABSTRACT FROM AUTHOR]

Increasingly high bandwidths are desired in modern navigation and autonomous RF ranging signal design to achieve better pseudo-noise (PN) ranging accuracy. However, fulfilling the Nyquist criterion for such high-bandwidth signals would be a challenging issue for system design. Considering that the Nyquist criterion is not a necessary condition for PN code tracking, sub-Nyquist sampling can be adopted as a feasible solution to this issue. Nevertheless, it is at the expense of an increase in thermal noise caused by tracking error. This problem is particularly prominent for tracking weak signals such as navigation signals, which limits the applicability of this sampling scenario. As far as high-precision autonomous PN ranging is concerned, however, the tracking error due to digital implementation is not negligible and even becomes the dominating factor instead of thermal noise. This means that the performance loss incurred by sub-Nyquist sampling can be eliminated under high-signal-to-noise ratio conditions. Exploiting this fact, this Letter proposes a novel PN code tracking approach based on sub-Nyquist and non-commensurate sampling, providing a solution to achieving high-ranging accuracy while breaking the bounds of the Nyquist sampling theorem without performance degradation. The approach is very attractive for precise PN ranging applications demanding miniaturised implementation. [ABSTRACT FROM AUTHOR]

Gold codes are widely used for pseudo‐noise (PN) ranging, and non‐commensurate sampling is an effective solution to improving the tracking performance of digital code tracking loops. However, the sequence transition density of gold codes is low, which limits the achievable ranging accuracy. Here, the authors present a non‐commensurate sampling and double‐loop‐based regenerative PN code tracking approach. With this approach, the tracking of the original regenerative code is equivalent to that of its clock component, and the sequence transition density is maximised. Thus, the tracking error is apparently reduced and optimal tracking performance is achieved. In the double‐loop structure, a unified tracking loop is employed to facilitate performance comparison. Simulation results demonstrate the performance improvement of the proposed approach over the traditional gold code tracking scheme, and the relationship between the non‐commensurate sampling parameters and the achievable tracking accuracy. The approach is especially suitable for precision ranging applications, and can be extended to other applications involving accurate signal tracking in digital equipment. [ABSTRACT FROM AUTHOR]

R4239 --> Regulation of cellular signaling responses through post‐translational modification of proteins is essential for many processes in cardiomyocytes. Ubiquitination of protein contributes both to proteasome‐mediated degradation of specific proteins as well as to modification of protein function as a component of cell signaling responses. The tripartite motif (TRIM) family of E3 ligases have been linked to regulation of many cellular function in cardiomyocytes. Previous studies show that TRIM72 (or MG53) is required for effective sarcolemmal membrane repair in cardiomyocytes. The membrane repair process is a highly conserved pathway were membrane disruptions trigger a robust exocytotic response that leads to formation of a membrane repair patch that can restore membrane integrity. Compromised membrane integrity can result in cardiomyopathy in multiple mouse models. While TRIM72 clearly contributes to sarcolemmal membrane repair the molecular mechanism of its function is not clear. In these studies, we resolve that acute activation of the PI3K‐Akt signaling axis is essential for membrane repair in cardiomyocytes and that TRIM72 function through interaction with the PI3K‐Akt pathway. Overexpression of TRIM72 results in an increased activation of PI3K and AKT and increases rates of exocytosis. This effect can be blocked either through pharmacological inhibition or dominant negative genetic approaches disrupting PI3K‐Akt signaling. These manipulations compromise basal sarcolemmal membrane repair and also block the elevated membrane repair following TRIM72 overexpression. Conversely, pharmaceutical activation of the PI3K‐Akt1 pathway can increase membrane repair in failing mouse hearts and myocardium from failing human hearts to compensate for reduced repair responses observed in failing cardiomyocytes. Mouse studies with trans‐aortic constriction surgery show that increasing membrane repair in failing hearts can minimize the pathology associated with heart failure in this model. These results show that TRIM72 mediated membrane repair acts through the PI3K/Akt pathway and that targeting membrane repair has therapeutic potential for the treatment of heart failure. [ABSTRACT FROM AUTHOR]

Noncommensurate sampling is an effective solution for improving the tracking performance of digital code tracking loops. So far there has been a lack of a generalised method for designing the parameters of this sampling scenario. A simple approach to choosing the parameters of noncommensurate sampling is presented, which is based on the analysis of the quantitative relationship among the chip phase delay discrimination, the sampling ratio and the correlation length. Numerical and simulation results show that optimal phase delay discrimination and thereby superior tracking accuracy can be achieved with the proposed approach. This approach is especially suitable for precision ranging applications, and can be extended to other applications involving accurate signal tracking in digital equipment. [ABSTRACT FROM AUTHOR]