Reduction of satellite flywheel microvibration using rubber shock absorbers

Microvibration of flywheels strongly affects the imaging quality of space cameras. A passive vibration method is used in this study to reduce the effect of microvibration. A rubber shock absorber was designed and installed on a satellite. The angular displacement of the second mirror was measured via a fiber optic gyroscopic method. The measured data were imported into MATLAB and analyzed by different methods. The data was plotted as a root-mean-square graph of angular displacement at different speeds along the x-axis, a waterfall plot of the attenuation of force in the x direction, the vibration spectrum between the frequency and displacement amplitude, and the time domain response of the inverse Fourier transform of the spectrum. The results show that the microvibration of the flywheel causes significant vibration of the imaging system, and that adding a rubber shock absorber can reduce the vibration. The proposed method is a new attempt to analyze microvibration, and can be applied to the engineering design of flywheels

Development and validation of a predictive nomogram for lower extremity deep vein thrombosis dislodgement in orthopedic patients

ObjectiveTo analyze the risk factors of lower extremity deep venous thrombosis (DVT) detachment in orthopedic patients, and to establish a risk nomogram prediction model.MethodsThe clinical data of 334 patients with orthopedic DVT admitted to the Third Hospital of Hebei Medical University from January 2020 to July 2021 were retrospectively analyzed. General statistics included gender, age, BMI, thrombus detachment, inferior vena cava filter window type, filter implantation time, medical history, trauma history, operation, use of tourniquet, thrombectomy, anesthesia mode, anesthesia grade, operative position, blood loss during operation, blood transfusion, immobilization, use of anticoagulants, thrombus side, thrombus range, D-dimer content before filter implantation and during removal of inferior vena cava filter. Logistic regression was used to perform univariate and multivariate analysis on the possible factors of thrombosis detachment, screen out independent risk factors, establish a risk nomogram prediction model by variables, and internally verify the predictability and accuracy of the model.ResultsBinary logistic regression analysis showed that Short time window filter (OR = 5.401, 95% CI = 2.338–12.478), lower extremity operation (OR = 3.565, 95% CI = 1.553–8.184), use of tourniquet (OR = 3.871, 95% CI = 1.733–8.651), non-strict immobilization (OR = 3.207, 95% CI = 1.387–7.413), non-standardized anticoagulation (OR = 4.406, 95% CI = 1.868–10.390), distal deep vein thrombosis (OR = 2.212, 95% CI = 1.047–4.671) were independent risk factors for lower extremity DVT detachment in orthopedic patients (P < 0.05). Based on these six factors, a prediction model for the risk of lower extremity DVT detachment in orthopedic patients was established, and the risk prediction ability of the model was verified. The C-index of the nomogram model was 0.870 (95% CI: 0.822–0.919). The results indicate that the risk nomogram model has good accuracy in predicting the loss of deep venous thrombosis in orthopedic patients.ConclusionThe nomogram risk prediction model based on six clinical factors, including filter window type, operation condition, tourniquet use, braking condition, anticoagulation condition, and thrombosis range, has good predictive performance

Space advanced technology demonstration satellite

The Space Advanced Technology demonstration satellite (SATech-01), a mission for low-cost space science and new technology experiments, organized by Chinese Academy of Sciences (CAS), was successfully launched into a Sun-synchronous orbit at an altitude of similar to 500 km on July 27, 2022, from the Jiuquan Satellite Launch Centre. Serving as an experimental platform for space science exploration and the demonstration of advanced common technologies in orbit, SATech-01 is equipped with 16 experimental payloads, including the solar upper transition region imager (SUTRI), the lobster eye imager for astronomy (LEIA), the high energy burst searcher (HEBS), and a High Precision Magnetic Field Measurement System based on a CPT Magnetometer (CPT). It also incorporates an imager with freeform optics, an integrated thermal imaging sensor, and a multi-functional integrated imager, etc. This paper provides an overview of SATech-01, including a technical description of the satellite and its scientific payloads, along with their on-orbit performance

A Review of Lightweight Design for Space Mirror Core Structure: Tradition and Future

With the continuous improvement of the imaging quality requirement of the space optical system, the large-aperture mirror becomes the research focus. However, the increase of the aperture will increase the whole weight which results in high launch cost and degrades the mirror surface figure accuracy. Therefore, the lightweight design method of the mirror structure is of great importance. In recent years, many space telescope system schemes have demonstrated the progress of the structural lightweight design of mirrors, such as Spitzer, SOFIA, JWST, etc. This article reviews the main content and innovations of the research on the structural designs of mirrors including conventional machining designs and topology optimization structures. Meanwhile, some emerging designs (e.g., lattices and Voronoi structures) considering additive manufacturing (AM) are also introduced. Several key elements of different structural design approaches for lightweight mirrors are discussed and compared, such as material, lightweight ratio, design methods, surface figure, etc. Finally, future challenges, trends, and prospects of lightweight design for mirrors are discussed. This article provides a reference for further related research and engineering applications

Uniqueness Theorems on Entire Functions and Their Difference Operators or Shifts

We study the uniqueness problems on entire functions and their difference operators or shifts. Our main result is a difference analogue of a result of Jank-Mues-Volkmann, which is concerned with the uniqueness of the entire function sharing one finite value with its derivatives. Two relative results are proved, and examples are provided for our results

Optimizing both the CoMo/Al2O3 catalyst and the technology for selectivity enhancement in the hydrodesulfurization of FCC gasoline

Herein, a series of alumina supports were prepared by rehydration-dehydration of the traditional gamma-Al2O3 under different hydrothermal temperatures. After loading CoMo species, it was found the selectivity factor of corresponding CoMo/Al2O3 catalysts was improved greatly from 1.21 to 2.51 with the increased hydrothermal temperature of alumina supports in the hydrodesulfurization (HDS) of a model fluid catalytic cracking (FCC) naphtha. The improved HDS selectivity is attributed to the weakened metal-support interaction and lowered dispersion of MoS2 particles, resulting in catalysts with larger edge-to-corner ratios of CoMoS slabs ((f(e)/f(c))(CoMo)). Besides, the recombination mercaptans formed by reaction of produced H2S and olefins were found as a big challenge to reach a high HDS conversion (S < 10 ppm) when only using the selective HDS catalyst (one-unit process). Therefore, a two-unit process has been developed by using a selective HDS catalyst to remove the most of the refractory sulfur compounds firstly, after which using another mercaptan-removing catalyst to deal with the recombination mercaptans specially. The catalytic results show that the two-unit process has a smaller olefin loss (4.38 v%) than that of one-unit process (7.08 v%) when reducing the sulfur concentration of a heavy FCC fraction to less than 10 ppm, thus resulting in a 0.7 unit less of the research octane number loss. The present work shows that high HDS conversion and low olefin hydrogenation conversion in selective HDS of FCC gasoline can be achieved through optimization design of both the selective HDS catalyst and the whole technology

Morphology-performance relation of (Co)MoS2 catalysts in the hydrodesulfurization of FCC gasoline

The morphology-performance relation is of great importance for designing a catalyst with high performance in the selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline. Herein, we report a simple one-pot hydrothermal method to prepare the unsupported MoS2 catalysts with controlled morphology by adjusting the pH values and using different precursors. It is found that smaller MoS2 crystallites are produced when the pH value decreases in the synthetic process. With the increased MoS2 crystallite size, the HDS selectivity factor (SF) increases from 1.46 to 1.52 for non-promoted MoS2 catalysts, and from 13.96 to 19.69 for Co-promoted MoS2 catalysts. On the other hand, for MoS2 catalysts with similar stacking, the MoS2 with longer slab length exhibits improved HDS selectivity (SF from 2.90 to 2.99). These results confirm that the slab length instead of the stacking for MoS2 particles is more important to influence the HDS selectivity. Due to the fact that the corner sites could catalyze both HDS and HYD reactions while edge sites only catalyze the HDS reaction, thus increasing the edge/corner ratio by preparing (Co)MoS2 catalysts with longer MoS2 slab length is an efficient way to improve the selectivity in the selective HDS of FCC gasoline

Direct thermolysis of CO2 into CO and O-2

Most of the solar-driven thermochemical CO2 dissociation reactions have been focused on two-step processes. In this study, a one step CO2 thermolysis process was considered. It was found that direct thermolysis of CO2 obviously occurred at temperatures as low as 1200 degrees C within a corundum tube. The reaction rate could be enhanced by several times in the presence of metal oxides, which may be attributed to the catalysis of oxygen vacancies in the metal oxides