Frequency Division Control of Line-of-Sight Tracking for Space Gravitational Wave Detector.

The space gravitational wave detector uses the inter-satellite laser interferometer to measure a change in distance with ultra-high precision at the picometer level. Its special differential wavefront sensing technology based on laser interference is used to obtain the ultra-high-precision relative attitude between spacecrafts. In order to acquire the measurement, it is necessary to maintain high-precision attitude pointing and alignment for the optical path line-of-sight of the detector. This paper proposes a frequency division control method. More specifically, we chose the telescope attitude control loop frequency division as it is the faster response part, mainly relative to the high-frequency band within the measurement bandwidth. The spacecraft attitude frequency division is mainly in the low-frequency band within the measurement bandwidth. Finally, a high-precision simulation analysis is carried out. The results show that compared with traditional methods, the use of frequency division control design can significantly improve the attitude and pointing stability of the system and provide control support for systems requiring high pointing coordination accuracy, such as space gravity wave detectors.

Dietary pectin caused great changes in bile acid profiles of Pelteobagrus fulvidraco.

To reveal the impact of dietary fiber (DF) on the bile acid (BA) profiles of fish, yellow catfish (Pelteobagrus fulvidraco) were fed a diet containing 300 g kg-1 dextrin (CON diet, control) or pectin (a type of soluble DF, PEC diet) for 7 days, and then the BA profiles were analyzed by UHPLC-MS/MS. A total of 26 individuals of BAs were detected in the fish body, with 8, 10, 14, and 22 individuals of BAs detected in the liver, serum, bile, and hindgut digesta, respectively. The conjugated BAs (CBAs) of fish were dominated by taurine CBAs (TCBAs). The concentrations of free BAs (FBAs) and the value of FBAs/CBAs in the bile of fish fed the PEC diet were nearly 5 and 7 times higher, respectively than those in fish fed the CON diet. The value of glycine CBAs/TCBAs in the liver, serum and bile of fish fed the PEC diet was significantly lower, and in the hindgut digesta was higher than that of fish fed the CON diet (P < 0.05). These results suggested that dietary pectin greatly changed the BA profiles of Pelteobagrus fulvidraco, attributed to inhibition of reabsorption of BAs. Therefore, attention should be paid to the impact on BA homeostasis when replacing fishmeal with DF-rich plant ingredients in the fish diet.

Extension of cell membrane boosting squalene production in the engineered Escherichia coli.

Squalene is a lipophilic and non-volatile triterpene with many industrial applications for food, pharmaceuticals, and cosmetics. Metabolic engineering focused on optimization of the production pathway suffer from little success in improving titers because of a limited space of the cell membrane accommodating the lipophilic product. Extension of cell membrane would be a promising approach to overcome the storage limitation for successful production of squalene. In this study, Escherichia coli was engineered for squalene production by overexpression of some membrane proteins. The highest production of 612 mg/L was observed in the engineered E. coli with overexpression of Tsr, a serine chemoreceptor protein, which induced invagination of inner membrane to form multilayered structure. It was also observed an increase in unsaturated fatty acid in membrane lipids composition, suggesting cellular response to maintain membrane fluidity against squalene accumulation in the engineered strain. This study potentiates the capability of E. coli for squalene production and provides an effective strategy for the enhanced production of such compounds.

Relative attitude stability analysis of double satellite formation for gravity field exploration in space debris environment.

Spacecraft operating in low orbit are at risk of being hit by space debris. In the debris environment, the impact of debris is likely to cause the double satellite formation to exit science mode or even lead to the divergence of the control system, thus affecting the scientific exploration mission. In this paper, the attitude stability of the double satellite formation for gravity field in the near circular and polar orbit in the space debris environment is studied. Firstly, based on Lyapunov control and LQR, two sets of control models of stochastic collision for two satellites aligned with each other were proposed, and the actuators were modelled and assigned. Secondly, models of collision probability and momentum are developed. The distribution law of space debris is obtained according to the international common debris software. Meanwhile, probability density function of two independent collisions is gained. Finally, through Monte Carlo simulation and statistics, the changes of relative attitude and thrust torque are simulated when the satellite obtains the angular momentum for a short period of time due to being impacted by space debris. During the 10-year mission period, the number of times that the space debris impact makes the satellite attitude out of the science mode and the number of times that the control system diverges are obtained, which provides a reference for the normal manner of the double satellite formation for gravity field exploration.

[Construction and optimization of squalene epoxide synthetic pathway in Escherichia coli].

Triterpenoids are a class of natural products of great commercial value that are widely used in pharmaceutical, health care and cosmetic industries. The biosynthesis of triterpenoids relies on the efficient synthesis of squalene epoxide, which is synthesized from the NADPH dependent oxidation of squalene catalyzed by squalene epoxidase. We screened squalene epoxidases derived from different species, and found the truncated squalene epoxidase from Rattus norvegicus (RnSETC) showed the highest activity in engineered Escherichia coli. Further examination of the effect of endogenous cytochrome P450 reductase like (CPRL) proteins showed that overexpression of NADH: quinone oxidoreductase (WrbA) under Lac promoter in a medium-copy number plasmid increased the production of squalene epoxide by nearly 2.5 folds. These results demonstrated that the constructed pathway led to the production of squalene epoxide, an important precursor for the biosynthesis of triterpenoids.