The research on a novel levitation stage using ultrasonic and aerodynamic driving method

Acoustic/ultrasonic levitation is now widely used in industrial production processes employed in semiconductor, bioengineering nano-scale electronics and other industries where precise positioning is required. This paper describes the development of a new mixed levitation stage combining the ultrasonic and aerodynamic concepts. It is shown that the combination of these two levitation methods improves the levitation stability by reducing the system vibration caused by air vortices and hammer vibration. The proposed structure of the mixed levitation stage is described. The effect of ultrasonic levitation height and the aerodynamic levitation height is analyzed to determine their influence on the supporting ability of the mixed levitation stage. Both the experiments and modeling for the mixed levitation stage are conducted. The supporting ability of the mixed levitation stage is examined by varying the supporting masses and supporting states. A 3D computation model of the mixed levitation stage is constructed and is analyzed using the computational fluid dynamics (CFD) software. The computational and experimental results show that the levitation height of the mixed levitation is close to the sum of the ultrasonic levitation and the aerodynamic levitation heights; this result confirms that the mixed levitation promotes the supporting ability of the working stage

Research on modeling and dynamic characteristics of complex coaxial rotor system

To make up deficiency of the finite element method in predicting nonlinear dynamic characteristics of coaxial rotor systems, nonlinear dynamic model of a coaxial rotor system was established with a method combining the finite element method and the fixed interface modal synthesis method. Then an implicit time domain method was presented to solve the nonlinear equations of motion thus dynamic characteristics of the rotor system can be obtained. The computational efficiency of this method largely depends on the number of degrees of freedom with nonlinear forces acting on. With nonlinear forces of squeeze film damper and intermediate bearing considered, nonlinear dynamic response characteristics of the coaxial rotor system under multiple unbalance forces were studied in this work. The results showed that the unbalance excitation frequencies are dominant in the responses of the rotor system. Besides, due to coupling effect of the intermediate bearing some combinations of the unbalance excitation frequencies were also observed in the spectrogram. Stability and periodicity of the rotor system was investigated with bifurcation diagram, Poincare map and phase diagram. It was found that the rotor system executes multiple periods orbital motion under relatively low rotational speeds. With the increasing of rotational speed, the rotor system would execute quasi-periodic motion, chaotic motion and periodic motion again. The quasi-periodic motion and chaotic motion are closely related with the SFD. Finally, under relatively low speed, the nonlinear model was validated by comparing the simulation results with the experimental data. The proposed modeling and solving method is expected to provide theoretical and engineering basis for improving prediction of nonlinear dynamic characteristics of complex rotor systems

Up-regulation of hypoxia inducible factor-1α by cobalt chloride correlates with proliferation and apoptosis in PC-2 cells

<p>Abstract</p> <p>Background</p> <p>The exact mechanism of the effects of hypoxia on the proliferation and apoptosis in carcinoma cells is still conflicting. This study investigated the variation of hypoxia-inducible factor-1α(HIF-1α) expression and the apoptosis effect of hypoxia stimulated by cobalt chloride (CoCl₂) in pancreatic cancer PC-2 cells.</p> <p>Methods</p> <p>PC-2 cells were cultured with different concentration (50-200 μmol/L) of CoCl₂after 24-120 hours to simulate hypoxia in vitro. The proliferation of PC-2 cells was examined by MTT assay. The cellular morphology of PC-2 cells were observed by light inverted microscope and transmission electron microscope(EM). The expression of HIF-1α on mRNA and protein level was measured by semi-quantitive RT-PCR and Western blot analysis. Apoptosis of PC-2 cells were demonstrated by flow cytometry with Annexin V-FITC/PI double staining.</p> <p>Results</p> <p>MTT assay showed that the proliferation of PC-2 cells were stimulated in the first 72 h, while after treated over 72 h, a dose- dependent inhibition of cell growth could be observed. By using transmission electron microscope, swollen chondrosomes, accumulated chromatin under the nuclear membrane and apoptosis bodies were observed. Flow cytometer(FCM) analysis showed the apoptosis rate was correlated with the dosage of CoCl₂. RT-PCR and Western blot analysis indicated that hypoxia could up-regulate the expression of HIF-1α on both mRNA and protein levels.</p> <p>Conclusion</p> <p>Hypoxic microenvironment stimulated by CoCl₂could effectively induce apoptosis and influence cell proliferation in PC-2 cells, the mechanism could be related to up-expression of HIF-1α.</p

Genetic characterization of H1N2 influenza a virus isolated from sick pigs in Southern China in 2010

In China H3N2 and H1N1 swine influenza viruses have been circulating for many years. In January 2010, before swine were infected with foot and mouth disease in Guangdong, some pigs have shown flu-like symptoms: cough, sneeze, runny nose and fever. We collected the nasopharyngeal swab of all sick pigs as much as possible. One subtype H1N2 influenza viruses were isolated from the pig population. The complete genome of one isolate, designated A/swine/Guangdong/1/2010(H1N2), was sequenced and compared with sequences available in GenBank. The nucleotide sequences of all eight viral RNA segments were determined, and then phylogenetic analysis was performed using the neighbor-joining method. HA, NP, M and NS were shown to be closely to swine origin. PB2 and PA were close to avian origin, but NA and PB1were close to human origin. It is a result of a multiple reassortment event. In conclusion, our finding provides further evidence about the interspecies transmission of avian influenza viruses to pigs and emphasizes the importance of reinforcing swine influenza virus (SIV) surveillance, especially before the emergence of highly pathogenic FMDs in pigs in Guangdong

Differential gene expression and potential regulatory network of fatty acid biosynthesis during fruit and leaf development in yellowhorn (Xanthoceras sorbifolium), an oil-producing tree with significant deployment values

Xanthoceras sorbifolium (yellowhorn) is a woody oil plant with super stress resistance and excellent oil characteristics. The yellowhorn oil can be used as biofuel and edible oil with high nutritional and medicinal value. However, genetic studies on yellowhorn are just in the beginning, and fundamental biological questions regarding its very long-chain fatty acid (VLCFA) biosynthesis pathway remain largely unknown. In this study, we reconstructed the VLCFA biosynthesis pathway and annotated 137 genes encoding relevant enzymes. We identified four oleosin genes that package triacylglycerols (TAGs) and are specifically expressed in fruits, likely playing key roles in yellowhorn oil production. Especially, by examining time-ordered gene co-expression network (TO-GCN) constructed from fruit and leaf developments, we identified key enzymatic genes and potential regulatory transcription factors involved in VLCFA synthesis. In fruits, we further inferred a hierarchical regulatory network with MYB-related (XS03G0296800) and B3 (XS02G0057600) transcription factors as top-tier regulators, providing clues into factors controlling carbon flux into fatty acids. Our results offer new insights into key genes and transcriptional regulators governing fatty acid production in yellowhorn, laying the foundation for efforts to optimize oil content and fatty acid composition. Moreover, the gene expression patterns and putative regulatory relationships identified here will inform metabolic engineering and molecular breeding approaches tailored to meet biofuel and bioproduct demands

Taking the pulse of COVID-19: A spatiotemporal perspective

The sudden outbreak of the Coronavirus disease (COVID-19) swept across the world in early 2020, triggering the lockdowns of several billion people across many countries, including China, Spain, India, the U.K., Italy, France, Germany, and most states of the U.S. The transmission of the virus accelerated rapidly with the most confirmed cases in the U.S., and New York City became an epicenter of the pandemic by the end of March. In response to this national and global emergency, the NSF Spatiotemporal Innovation Center brought together a taskforce of international researchers and assembled implemented strategies to rapidly respond to this crisis, for supporting research, saving lives, and protecting the health of global citizens. This perspective paper presents our collective view on the global health emergency and our effort in collecting, analyzing, and sharing relevant data on global policy and government responses, geospatial indicators of the outbreak and evolving forecasts; in developing research capabilities and mitigation measures with global scientists, promoting collaborative research on outbreak dynamics, and reflecting on the dynamic responses from human societies.Comment: 27 pages, 18 figures. International Journal of Digital Earth (2020