The vibration with large amplitude and low frequency of the flexible space structures is prone to affect the attitude stability and pointing precision of the spacecraft. To mitigate the vibration of ...the flexible space structures, a multi-point decentralized control strategy using reaction wheel (RW) actuators is proposed and investigated in this paper. The motion equations of the solar array with multiple RW actuators are derived in modal coordinate representation. To suppress the overall response of the structure, the decentralized control strategy using RW actuators is designed based on the natural frequencies and mode shapes. The stability and the effect of closed-loop dynamic system is theoretically proved. The comparative studies under sun-pointing of the solar array and the rest-to-rest orbital maneuver conditions are presented to show the control performance of the RW actuators. The results indicate that, with 2% increase in total mass from the addition of the actuators, the vibration attenuation time can be decreased by 85.25% and 94.16% for the vibration excited by the sun-pointing and the rest-to-rest orbital maneuver, respectively. The experimental results demonstrate the effectiveness of the proposed decentralized control method. Theoretical analysis, numerical simulation and experimental study are conducted to demonstrate the validity of the proposed vibration mitigation approach and its potential application in the spacecraft design.
Additive manufacturing (AM) technology develops rapidly and is widely used in various fields. However, high surface roughness of metal components produced by representative AM processes for metallic ...materials such as laser-based powder bed fusion (L-PBF) is an important problem that needs to be solved. In this work, electrorheological (ER) fluid–assisted ultrasonic polishing is proposed to improve surface finish of metal AM parts. The principle of how an ER fluid works on the polishing process is discussed by calculating the electric field distribution and forces exerted on the abrasive particles. The effects of different field intensities caused by different voltages and electrode gaps on the ultrasonic polishing of AM surfaces are discussed by both experiments and simulations. The motion behaviors of abrasive particles after applying ER fluid are also studied by experimental observations. According to the simulation and experimental results, increasing voltage and reducing electrode gap can improve the electric field intensity, which improves the ER effect and makes a more stable aggregation of abrasive particles in the machining zone. Average surface roughness Ra is reduced to 2.74 μm from the initial value of 5.6 μm after 20 min ER fluid–assisted ultrasonic polishing under the voltage of 2000 V and the electrode gap of 3 mm. Ra improvement of the surface polished with ER effect is 11% higher than that without ER effect. The results show that in a certain range, ER effect can improve the ultrasonic polishing capability and a better surface finish can be obtained.
Hepatocyte growth factor (HGF) is a multifunctional growth factor that promotes various biological processes. However, the effect of HGF on bone metabolism in rheumatoid arthritis (RA) remains ...unknown. Here, we investigated the role of HGF in regulating osteoclastogenesis and bone resorption in RA.
The expression of HGF in RA patients and collagen-induced arthritis (CIA) mice was examined. The role of HGF on osteoclastogenesis was analysed by osteoclastogenesis and bone resorption assays. The effect of HGF inhibition was evaluated in a CIA mice model. The mechanism of HGF in regulating osteoclastogenesis and bone resorption was explored by a series of in vitro studies.
HGF was overexpressed in CIA and RA. HGF stimulated osteoclastogenesis in vitro. SU11274, a selective small molecule blocker of c-Met, impeded the effect of HGF on osteoclastogenesis and bone resorption. HGF regulated osteoclastogenesis by JNK and AKT-GSK-3β-NFATc1 signallings. SU11274 protected CIA mice from pathological bone loss.
These data strongly suggest that the highly expressed HGF in the joint tissues contributes to bone loss in RA. Inhibition of HGF/c-Met could effectively alleviate pathological bone loss and inflammatory symptoms in CIA mice. HGF/c-Met may be used as a new target for the treatment of bone loss in RA.
In this paper, a graph convolutional network is constructed and applied for bearing fault diagnosis. Specifically, the constant-Q transform (CQT) is first adopted for spectral analysis of vibration ...signals, where the frequencies are distributed in the logarithmic scale. Varied frequency resolutions can be obtained to satisfy the spectral resolution requirement and reduce signal dimension. Afterwards, the CQT spectrum is modeled by a graph, where nodes are frequency bins and edges reflect the inner relationship of different bins. There are edges between the fundamental and harmonic components. Then, a two-layer graph convolutional network (GCN) is utilized to assess the significance of vibration sources within the mixed signals. Finally, the bearing faults are determined according to the output of the GCN. To the best of our knowledge, this is the first work to model the vibration signal in this graph structure. The advantage of this approach lies in the simplification of edge definitions, facilitating shared connectivity relationships between the fundamental frequency and harmonics. Its performance was compared with another state-of-the-art fault diagnosis model. Experimental results demonstrate that the proposed model obtains higher accuracy, and it is more effective in extracting discriminative features.
This paper compares data from linearized and nonlinear Zebiak-Cane model, as constrained by observed sea surface temperature anomaly （SSTA）, in simulating central Pacific （CP） and eastern Pacific ...（EP） E1 Nino. The difference between the temperature advections （determined by subtracting those of the linearized model from those of the nonlinear model）, referred to here as the nonlinearly induced temperature advection change （NTA）, is analyzed. The results demonstrate that the NTA records warming in the central equatorial Pacific during CP E1 Nino and makes fewer contributions to the structural distinctions of the CP E1 Nino, whereas it records warming in the eastern equatorial Pacific during EP E1 Nino, and thus significantly promotes EP E1 Nino during E1 Nino-type selection. The NTA for CP and EP E1 Nino varies in its amplitude, and is smaller in CP E1 Nino than it is in EP E1 Nino. These results demonstrate that CP E1 Nino are weakly modulated by small intensities of NTA, and may be controlled by weak nonlinearity; whereas, EP E1 Nino are significantly enhanced by large amplitudes of NTA, and are therefore likely to be modulated by relatively strong nonlinearity. These data could explain why CP E1 Nino are weaker than EP E1 Nino. Because the NTA for CP and EP E1 Nino differs in spatial structures and intensities, as well as their roles within different E1 Nino modes, the diversity of E1 Nino may be closely related to changes in the nonlinear characteristics of the tropical Pacific.
Epigallocatechin-3-gallate (EGCG), a frequently studied catechin in green tea, has been shown involved in the anti-proliferation and apoptosis of human nasopharyngeal carcinoma (NPC) cells. However, ...the underlying molecular mechanism of the apoptotic effects of EGCG has not been fully investigated. Recent literature emphasized the importance of Sirtuin 1 (SIRT1), an NAD
-dependent protein deacetylase, in regulating cellular stress responses, survival, and organismal lifespan. Herein, the study showed that EGCG could significantly inhibit cell proliferation and promote apoptosis of 2 NPC (CNE-2 and 5-8F) cell lines. Moreover, it was also found that SIRT1 is down-regulated by EGCG, and the SIRT1-p53 signaling pathway participates in the effects of EGCG on CNE-2 and 5-8 F cells. Taken together, the findings of this study provided evidence that EGCG could inhibit the growth of NPC cell lines and is linked with the inhibition of the SIRT1-p53 signaling pathway, suggesting the therapeutic potential of EGCG in human NPC.
Major hurricanes (MHs) in the eastern North Pacific (ENP) in 1970–2020 are clustered into 3 categories with different quantity, intensity, lifetime, and track. MHs in all three clusters are more ...active in the Pacific Decadal Oscillation (PDO) warm than cold phases. However, only the relationship between MHs in the western part of ENP (cluster A) and El Niño Southern Oscillation (ENSO) is significantly modulated by the PDO. This cluster is more active during El Niño than La Niña years in the PDO cold phases, which results from the local sea surface temperature (SST) warm anomalies caused by the combined influences of ENSO and the PDO. Warmer SST can make a stronger ascending flow, and strengthen the local activity of MHs by leading to anomalous atmospheric circulation. In the PDO warm phases, however, there is no distinct local SST anomalies between two ENSO phases. Therefore, the modulation of PDO on ENSO and cluster A only occurs in the PDO negative phases. In the region of the eastern part of ENP where two other clusters are located, the PDO hardly modulates the relationship between ENSO and MHs activity as the PDO exerts little influences on the ENSO-related SST patterns in both the positive and negative phases. The conclusion is also supported by first mode of empirical orthogonal functions analysis for interannual MHs activity. Therefore, the PDO modulation cannot be ignored when predicting the activity of tropical cyclones in the ENP, especially for MHs with strong wind and rainstorm.
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