North/South Station Keeping of the GEO Satellites in Asymmetric Configuration by Electric Propulsion with Manipulator

Geosynchronous orbit (GEO) is a very important strategic resource. In order to maximize the utilization of the GEO resources, the use of all-electric propulsion GEO platforms can greatly extend the service life of satellites. Therefore, this paper proposes a control scheme of the north/south station keeping (NSSK) by using electric propulsion with a manipulator. First, on the basis of the traditional calculation method of the semi-diurnal period of the orbital inclination, the calculation method of the semi-monthly period and the semi-annual period of the orbital inclination are proposed. The new method can reduce the fuel consumption and reduce the control amount and control frequency of the station keeping (SK). Secondly, a fuel-optimized NSSK algorithm by using electric propulsion with a manipulator is proposed. The algorithm can not only be applied to a large initial orbital inclination but also can unload the large angular momentum of the asymmetric satellites while keeping the north/south station, thereby avoiding the loss of control of the satellite’s attitude. The research results of this paper provide a new idea for the SK control of the GEO satellites and have great engineering application value

North/South Station Keeping of the GEO Satellites in Asymmetric Configuration by Electric Propulsion with Manipulator

Geosynchronous orbit (GEO) is a very important strategic resource. In order to maximize the utilization of the GEO resources, the use of all-electric propulsion GEO platforms can greatly extend the service life of satellites. Therefore, this paper proposes a control scheme of the north/south station keeping (NSSK) by using electric propulsion with a manipulator. First, on the basis of the traditional calculation method of the semi-diurnal period of the orbital inclination, the calculation method of the semi-monthly period and the semi-annual period of the orbital inclination are proposed. The new method can reduce the fuel consumption and reduce the control amount and control frequency of the station keeping (SK). Secondly, a fuel-optimized NSSK algorithm by using electric propulsion with a manipulator is proposed. The algorithm can not only be applied to a large initial orbital inclination but also can unload the large angular momentum of the asymmetric satellites while keeping the north/south station, thereby avoiding the loss of control of the satellite’s attitude. The research results of this paper provide a new idea for the SK control of the GEO satellites and have great engineering application value

Magnetostratigraphic dating of the Xiashagou Fauna and implication for sequencing the mammalian faunas in the Nihewan Basin, North China

The Nihewan Basin sedimentary sequences in northern China are rich in mammalian fossil and Paleolithic sites, thus providing insights into our understanding of Quaternary land mammal biochronology and early human settlements in East Asia. Here we present high-resolution magnetostratigraphic results that place stringent age controls on the Xiashagou (XSG) Fauna (that is, the well-known Nihewan Fauna sensu stricto) in the Nihewan Basin, northern China. Results show that the XSG sequence recorded the Brunhes normal chron, the Matuyama reverse chron and the late Gauss normal chron. The XSG Fauna resides in the Matuyama reverse chron (between the pre-Reunion Matuyama chron and the post-Olduvai Matuyama chron), yielding an estimated age of ca. 2.2–1.7 Ma. The Pliocene–Pleistocene boundary (Gauss/Matuyama boundary) is located in the lower part of the XSG section. The combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern Nihewan Basin can be placed between the Gauss–Matuyama geomagnetic reversal and the Matuyama–Brunhes geomagnetic reversal (2.58–0.78 Ma), leading to a time range of ca. 2.6–0.8 Ma for the Nihewan mammalian faunas

Random source for generating Airy-like spectral density in the far field

A stationary beam forming an Airy-like spectral density in the far field is analyzed theoretically and experimentally. The Schell-model source that radiates such a beam is an extended version of a recently introduced source [O. Korotkova, et al., Opt. Lett.43, 4727 (2018)10.1364/OL.43.004727; X. Chen, et al., Opt. Lett.44, 2470 (2019)10.1364/OL.44.002470, in 1D and 2D, respectively]. We show, in particular, that the source degree of coherence, being the fourth-order root of a Lorentz-Gaussian function and having linear and cubic phase terms, may be either obtained from the Fourier transform of the far-field Airy-like pattern or at the source using the sliding function method. The spectral density of the beam is analyzed on propagation through paraxial ABCD optical systems, on the basis of the generalized Collins integral, by means of the derived closed-form expression. We show that the distribution of the side lobes in the Airy beam spectral density can be controlled by the parameters of the source degree of coherence. Further, an experiment involving a spatial light modulator (SLM) is carried out for generation of such a beam. We experimentally measure the complex degree of coherence of the source and observe the gradual formation of a high-quality Airy-like spectral density towards the far field. In addition, the trajectory of the intensity maxima of the beam after a thin lens is studied both theoretically and experimentally. The random counterpart of the classic, deterministic Airy beam may find applications in directed energy, imaging, beam shaping, and optical trapping

Magnetostratigraphic dating of the Shixia red sediments and implications for formation of Nihewan paleo-lake, North China

The sedimentary sequence in Nihewan Basin, northern China, is rich in mammalian fossils and Paleolithic sites. Extensive magnetostratigraphic investigations have been carried out in the Nihewan sediments, but precise age control on the earliest Nihewan red sediments, which have a fluvio-lacustrine origin in the upper part and an eolian origin in the lower part, has remained unavailable. The formation process of Nihewan paleo-lake, therefore, remains unclear. Here we contribute to understanding the age of the early Nihewan reworked and eolian red clays by presenting detailed magnetostratigraphic and rock magnetic results from the Shixia section coupled with geochemical and petrographic analyses. Magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the Shixia sedimentary sequence recorded part of the Gilbert Chron with the onset of deposition of the Nihewan Formation occurring prior to the Gilbert-Gauss geomagnetic reversal at 3.6 Ma. With tectonic development of a graben basin, early red clay was deposited first in Nihewan Basin during the Early Pliocene before giving way to lacustrine environments in Nihewan paleo-lake. Geochemical and petrographic results indicate a wind-blown origin for the lower red clay deposits, which have been reworked and mixed with conglomerates produced by local tectonic activity to produce the basal Nihewan sediments. Later formation of carbonate nodules has given rise to the sediments that are now exposed in Nihewan Basin.This work was supported financially by the National Natural Science Foundation of China (41274001 and 40904016), the Ministry of the Land and Resources of China (201211005), and the Ministry of Science and Technology of China (2014FY110300). C.D. acknowledges further support from the NSFC grants 41690110 and 41621004

Magnetostratigraphic dating of the Shanshenmiaozui mammalian fauna in the Nihewan Basin, North China

Timing of the mammalian faunas in the Nihewan Basin, North China has provided insights into our understanding of Quaternary biochronology and biostratigraphy in East Asia. Here we contribute to this topic with detailed magnetostratigraphic investigation, coupled with mineral magnetic measurements on a fluvio-lacustrine sequence in this basin, which contains the Shanshenmiaozui mammalian fauna. Magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the Shanshenmiaozui sedimentary sequence recorded the Brunhes chron, the Jaramillo subchron, and the late Matuyama chron. Stratigraphic correlation in terms of lithology, magnetic susceptibility and magnetic polarity sequences between the Shanshenmiaozui, Xiaochangliang and Dachangliang sections indicates that the Shanshenmiaozui mammalian fossil layer is younger than the Xiaochangliang and Dachangliang artefact layers, which have been previously estimated to be about 1.36 Ma. The age of the Shanshenmiaozui mammalian fossil layer at the bottom of the section is estimated to be about 1.2 Ma. The new magnetostratigraphy of the Shanshenmiaozui section provides useful constraints on lithostratigraphic and biostratigraphic correlations in the Nihewan Basin

DNA polymerase β deficiency promotes the occurrence of esophageal precancerous lesions in mice

Esophageal mucosa undergoes mild, moderate, severe dysplasia, and other precancerous lesions and eventually develops into carcinoma in situ, and understanding the developmental progress of esophageal precancerous lesions is beneficial to prevent them from developing into cancer. DNA polymerase β (Polβ), a crucial enzyme of the base excision repair system, plays an important role in repairing damaged DNA and maintaining genomic stability. Abnormal expression or deletion mutation of Polβ is related to the occurrence of esophageal cancer, but the role of Polβ deficiency in the esophageal precancerous lesions is still unclear. Here, esophageal mucosa Polβ-knockout mice were used to explore the relationship of Polβ deficiency with esophageal precancerous lesions. First, we found the degree and number of esophageal precancerous lesions in Polβ-KO mice were more serious than those in Polβ-Loxp mice after N-nitrosomethylbenzylamine (NMBA) treatment. Whole exome sequencing revealed that deletion of Polβ increased the frequency of gene mutations. Gene expression prolife analysis showed that the expression of proteins correlated to cell proliferation and the cell cycle was elevated in Polβ-KO mice. We also found that deletion of Polβ promoted the proliferation and clone formation as well as accelerated cell cycle progression of human immortalized esophageal epithelial cell line SHEE treated with NMBA. Our findings indicate that Polβ knockout promotes the occurrence of esophageal precancerous lesions

Magnetostratigraphic dating of the Shanshenmiaozui mammalian fauna in the Nihewan Basin, North China

Timing of the mammalian faunas in the Nihewan Basin, North China has provided insights into our understanding of Quaternary biochronology and biostratigraphy in East Asia. Here we contribute to this topic with detailed magnetostratigraphic investigation, coupled with mineral magnetic measurements on a fluvio-lacustrine sequence in this basin, which contains the Shanshenmiaozui mammalian fauna. Magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the Shanshenmiaozui sedimentary sequence recorded the Brunhes chron, the Jaramillo subchron, and the late Matuyama chron. Stratigraphic correlation in terms of lithology, magnetic susceptibility and magnetic polarity sequences between the Shanshenmiaozui, Xiaochangliang and Dachangliang sections indicates that the Shanshenmiaozui mammalian fossil layer is younger than the Xiaochangliang and Dachangliang artefact layers, which have been previously estimated to be about 1.36 Ma. The age of the Shanshenmiaozui mammalian fossil layer at the bottom of the section is estimated to be about 1.2 Ma. The new magnetostratigraphy of the Shanshenmiaozui section provides useful constraints on lithostratigraphic and biostratigraphic correlations in the Nihewan Basin

126W fiber laser at 1018nm and its application in tandem pumped fiber amplifier

<p> We report on a 126W fiber laser operating at 1018 nm with an optical efficiency of 75%. The optimal length for such a fiber laser is theoretically analyzed using steady-state rate equations including amplified spontaneous emission. Excellent agreement on the maximum output power is achieved between the numerical result and the experimental counterpart. Furthermore, a monolithic tandem pumped fiber amplifier is established by using conventional 30/250 mu m double clad ytterbium-doped fiber, and 185W output power with 85% optical efficiency is realized.</p