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| 1 | Positioning accuracy assessment for the 4GEO/5IGSO/2MEO constellation of COMPASS显示文摘Determined to become a new member of the well-established GNSS family,COMPASS(or BeiDou-2) is developing its capabilities to provide high accuracy positioning services.Two positioning modes are investigated in this study to assess the positioning accuracy of COMPASS' 4GEO/5IGSO/2MEO constellation.Precise Point Positioning(PPP) for geodetic users and real-time positioning for common navigation users are utilized.To evaluate PPP accuracy,coordinate time series repeatability and discrepancies with GPS' precise positioning are computed.Experiments show that COMPASS PPP repeatability for the east,north and up components of a receiver within China's Mainland is better than 2 cm,2 cm and 5 cm,respectively.Apparent systematic offsets of several centimeters exist between COMPASS precise positioning and GPS precise positioning,indicating errors remaining in the treatments of COMPASS measurement and dynamic models and reference frame differences existing between two systems.For common positioning users,COMPASS provides both open and authorized services with rapid differential corrections and integrity information available to authorized users.Our assessment shows that in open service positioning accuracy of dual-frequency and single-frequency users is about 5 m and 6 m(RMS),respectively,which may be improved to about 3 m and 4 m(RMS) with the addition of differential corrections.Less accurate Signal In Space User Ranging Error(SIS URE) and Geometric Dilution of Precision(GDOP) contribute to the relatively inferior accuracy of COMPASS as compared to GPS.Since the deployment of the remaining 1 GEO and 2 MEO is not able to significantly improve GDOP,the performance gap could only be overcome either by the use of differential corrections or improvement of the SIS URE,or both. | ZHOU ShanShi CAO YueLing ZHOU JianHua HU XiaoGong TANG ChengPan LIU Li GUO Rui HE Feng CHEN JunPing WU Bin | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，12： | 31 |
| 2 | Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system显示文摘A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR. | ShanShi Zhou XiaoGong Hu Li Liu Rui Guo LingFeng Zhu ZhiQiao Chang ChengPan Tang XiuQiang Gong Ran Li Yang Yu | 2016 | Science China(Physics,Mechanics & Astronomy)2016，59，10： | 6 |
| 3 | Alginate core-shell microcapsule reduces the DMSO addition-induced osmotic damage to cells by inhibiting cellular blebs显示文摘In cryopreservation,the addition of cryoprotectant can change the intra-and extra-cellular osmotic pressure,affect the cell morphology,and induce blebs on the plasma membrane.In this study,the blebs of cells microencapsulated in the alginate microsphere induced by osmotic shock were studied,and the effects of microencapsulation on bleb size and cell viability were determined.Firstly,a coaxial co-flow focusing device was applied to generate cell-laden microcapsules using alginate hydrogel in this paper.Then,cellular blebs induced by DMSO with various concentrations under microencapsulation were compared with that when non-encapsulated,and the dynamic process of cellular bleb was investigated.Finally,the qualitative relationship between bleb size and cell viability in the presence of DMSO was built,and thus the effects of microencapsulation on bleb size and viability were evaluated.The results show that the bleb size is smaller and the cell viability is higher,and cell microencapsulation can significantly inhibit the excessively large blebs generated on the cell membrane and reduce the osmotic damage to cells when loading cryoprotectant and then to improve cell viability during cryopreservation.This work can provide insights for optimizing cryoprotectant-loading protocols,offer a new avenue to study cell blebbing,and advance future research on cryopreservation of rare cells and biomaterials. | Chengpan Li Jing Liu Qiang Wu Xiangyu Chen Weiping Ding | 2021 | Chinese Journal of Chemical Engineering2021，34，5： | 1 |
| 4 | Microneedle array facilitates hepatic sinusoid construction in a large-scale liver-acinus-chip microsystem显示文摘Hepatic sinusoids play a key role in maintaining high activities of liver cells in the hepatic acinus.However,the construction of hepatic sinusoids has always been a challenge for liver chips,especially for large-scale liver microsystems.Herein,we report an approach for the construction of hepatic sinusoids.In this approach,hepatic sinusoids are formed by demolding a self-developed microneedle array from a photocurable cell-loaded matrix in a large-scale liver-acinus-chip microsystem with a designed dual blood supply.Primary sinusoids formed by demolded microneedles and spontaneously self-organized secondary sinusoids can be clearly observed.Benefiting from significantly enhanced interstitial flows by formed hepatic sinusoids,cell viability is witnessed to be considerably high,liver microstructure formation occurs,and hepatocyte metabolism is enhanced.In addition,this study preliminarily demonstrates the effects of the resulting oxygen and glucose gradients on hepatocyte functions and the application of the chip in drug testing.This work paves the way for the biofabrication of fully functionalized large-scale liver bioreactors. | Shibo Li Chengpan Li Muhammad Imran Khan Jing Liu Zhengdi Shi Dayong Gao Bensheng Qiu Weiping Ding | 2023 | Microsystems & Nanoengineering2023，9，3： | 0 |
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