Identification and pathogenicity of Aeromonas veronii isolated from sexually mature female Hypophthalmichthys molitrix

An outbreak of bacterial septicemia in female silver carp *Hypophthalmichthys molitrix*, which caused significant death of the fish in the Yantian Reservoir, was investigated. The pathogen was isolated from diseased fish and identified as *Aeromonas veronii* utilizing biochemical characteristics and molecular methods analyses. An artificial infection experiment indicated that the strain caused 100% mortality of juvenile silver carp and mature female fish with eggs but no death of the mature male fish. Silver carp challenged with *A. veronii* showed similar clinical signs with naturally infected fish. The histopathological study revealed that *A. veronii* infection caused the increment of hemosiderin granules and the vacuole formation in tissues of the spleen and livers, as well as the collapse, deformation, and disintegration of egg cells. The ACP, AKP, and CAT enzyme activities in the serum of both naturally and artificially infected silver carp were decreased significantly with the severe infection. In this study, *A. veronii* was isolated and identified as the primary bacterial pathogen causing the mass death of sexually mature female silver carp with eggs in Yantian Reservoir

Simulation of CSST’s astrometric capability

Introduction: The China Space Station Telescope (CSST) will enter a low Earth orbit around 2024 and operate for 10 years, with seven of those years devoted to surveying the area of the median-to-high Galactic latitude and median-to-high Ecliptic latitude of the sky. To maximize the scientific output of CSST, it is important to optimize the survey schedule. We aim to evaluate the astrometric capability of CSST for a given survey schedule and to provide independent suggestions for the optimization of the survey strategy.Methods: We first construct the astrometric model and then conduct simulated observations based on the given survey schedule. The astrometric solution is obtained by analyzing the simulated observation data. And then we evaluate the astrometric capability of CSST by analyzing the properties of the astrometric solution.Results: The accuracy of parallax and proper motion of CSST is better than 1 mas (⋅ yr−1) for the sources of 18–22 mag in g band, and about 1∼10 mas (⋅ yr−1) for the sources of 22–26 mag in g band, respectively. The results from real survey could be worse since the assumptions are optimistic and simple.Discussion: Optimizing the survey schedule can improve the astrometric accuracy of CSST. In the future, we will improve the astrometric capability of CSST by continuously iterating and optimizing the survey schedule

Solar microwave millisecond spike at 2.84 GHz

Using the high time resolution of 1 ms, the data of solar microwave millisecond spike (MMS) event was recorded more than two hundred times at the frequency of 2.84 GHz at Beijing (Peking) Observatory since May 1981. A preliminary analysis was made. It can be seen from the data that the MMS-events have a variety of the fast activities such as the dispersed and isolated spikes, the clusters of the crowded spikes, the weak spikes superimposed on the noise background, and the phenomena of absorption. The marked differences from that observed with lower time resolution are presented. Using the data, a valuable statistical analysis was made. There are close correlations between MMS-events and hard X-ray bursts, and fast drifting bursts. The MMS events are highly dependent on the type of active regions and the magnetic field configuration. It seems to be crucial to find out the accurate positions on the active region where the MMS-events happen and to make co-operative observations at different bands during the special period when specific active regions appear on the solar disk

The First Photometric and Orbital Period Investigation of an Extremely Low Mass Ratio Contact Binary with a Sudden Period Change, TYC 4002-2628-1

Photometric observations for the totally eclipsing binary system TYC 4002-2628-1, were obtained between November 2020 and November 2021. To determine the stellar atmospheric parameters, a spectral image was taken with the 2.16 m telescope at National Astronomical Observatory of China (NAOC). TYC 4002-2628-1 is a low-amplitude (about 0.15 mag for $V$ band), short-period (0.3670495 d), contact eclipsing binary with a total secondary eclipse. Intrinsic light curve variations and the reversal of the O'Connell effect are detected in the light curves, which may be due to spot activity. Based on the photometric solutions derived from the multi-band time series light curves, TYC 4002-2628-1 is an extremely low mass ratio contact binary with a mass ratio of $q\sim$ 0.0482 and a fill-out factor of $f\sim5\%$. By analyzing the $O-C$ variations, we find that its orbital period remains unchanged when BJD < 2458321 . Then the orbital period changed suddenly around BJD 2458743 and has an increasing rate of $dP/dt=1.62\times{10^{-5}}day\cdot yr^{-1}=140$ $second\cdot century^{-1}$ . If confirmed, TYC 4002-2628-1 would be the contact binary with the highest orbital period increasing rate so far. By investigating the ratio of orbital angular momentum to the spin angular momentum ( $J_{orb}$/$J_{spin}$ $<3$) , the instability mass ratio ($q_{inst}/q=1.84$) and the instability separation ($A_{inst}/A=1.35$), TYC 4002-2628-1 can be regarded as a merger candidate.Comment: 9 page

Tectonic controls on block rotation and sheeted sill emplacement in the Xigaze Ophiolite (Tibet): the construction mode of slow-spreading and ultraslow-spreading oceanic crusts

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 22(3), (2021): e2020GC009297, https://doi.org/10.1029/2020GC009297.The internal structure of oceanic crusts is not well understood due to the limitation of deep drilling. However, that of ophiolites, i.e., on-land ancient analogs of oceanic lithosphere, could be precisely mapped and measured. The Xigaze ophiolite in Tibet has been regarded as “peculiar”, due to the sheeted sill complex in its upper crust, and non-sheeted diabase sills/dikes crosscutting its mantle and lower crust, which are geometrically different from the primarily vertical sheeted dike complex. Based on extensive field observations, here we present petrological and geochemical data for the Xigaze ophiolite to decipher the origin of sheeted sill complex and its implications for the construction of oceanic crusts. Diabases in the Xigaze ophiolite could be subdivided into sheeted sills, Group 1 non-sheeted dikes, and Group 2 non-sheeted sills, based on their orientations. These diabases cut other lithologies, and hence belong to the latest-stage products. Based on petrological, geochemical, and structural data, we highlight the important role of detachment fault in the generation of sheeted and non-sheeted sills. During the formation of oceanic crust, large block exhumation, multi-stage rotations, and foundering are argued here as key mechanisms for the generation of Xigaze sheeted and non-sheeted dikes/sills, all of which are in the evolution of detachment fault systems. These processes are also not uncommon for asymmetrical segments at modern slow-spreading and ultraslow-spreading ridges, but are rare at symmetrical segments. Due to the evolution of detachment fault, the internal structures of (ultra)slow-spreading ridges are more complex than those at fast-spreading ridges.This study was financially supported by the National Natural Science Foundation of China (42025201 and 41802062), Key Research Program of Frontier Sciences from CAS (QYZDB-SSW-DQC032), Major Research project on Tethys Geodynamic System from NSFC (91755000), and Open Fund Project of State Key Laboratory of Lithospheric Evolution (201707).2021-07-2

Soft-sediment deformation structures related to volcanic earthquakes of the Lower Cretaceous Qingshan Group in Lingshan Island, Shandong Province, East China

Abstract The study on soft-sediment deformation structures (SSDS) of Lingshan Island has been one of the hot topics of sedimentology researches in China in recent years, and SSDS developed in turbidite system in the Laiyang Group are widely known by domestic researchers. However, few studies were conducted on the SSDS in fan delta system in the Qingshan Group, Lingshan Island. This study analyzes the classification and characteristics of SSDS especially their lithofacies association and lithologic characteristics through field outcrops investigation and thin section analysis as well. A conclusion was acquired that the paleoenvironment was a fan delta system with occurrence of several volcanic eruptions, where the water became gradually shallower. The SSDS types in the Qingshan Group includes load and flame structure, ball and pillow structure, water-escape structure, hydroplastic deformation structure, plastic sandstone breccia structure, volcanic drop stone and V-shaped ground fissure mainly caused by volcanic earthquakes of three types: (1) seismic waves, (2) gravity and inertia effect of pyroclastic flows, (3) instant differential air pressure; which is different from slumping and tectonic earthquakes occurred in the Laiyang Group. In addition, with the lithofacies association analysis between pyroclastic flow and SSDS beds, a distribution model of SSDS related to volcanic earthquakes can be established: SSDS types changed gradually with their distance further away from the volcanic activity core. Brittle deformation which was common in the proximal zone disappeared gradually; liquefied and plastic SSDS continued to dominate in the medial zone; and slightly liquefied SSDS were developed in the distal zone. Meanwhile, the scale and size of SSDS is negatively correlated with the distance of SSDS depositional locations from the volcanic vent