The PandaX-4T experiment, a four-ton scale dark matter direct detection experiment, is being planned at the China Jinping Underground Laboratory. In this paper we present a simulation study of the expected background in this experiment. In a 2.8-ton fiducial mass and the signal region between 1 to 10 keV electron equivalent energy, the total electron recoil background is found to be 4.9 · 10 −5 (kg · day · keV) −1 . The nuclear recoil background in the same region is 2.8 · 10 −7 (kg · day · keV) −1 . With an exposure of 5.6 ton-years, the sensitivity of PandaX-4T could reach a minimum spin-independent dark matter-nucleon cross section of 6 · 10 −48 cm 2 at a dark matter mass of 40 GeV/c 2 .

We report the dark matter search results obtained using the full 132 ton·day exposure of the PandaX-II experiment, including all data from March 2016 to August 2018. No significant excess of events is identified above the expected background. Upper limits are set on the spin-independent dark matter-nucleon interactions. The lowest 90% confidence level exclusion on the spin-independent cross section is 2.2 × 10−46 cm2 at a WIMP mass of 30 GeV/c2.

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The main purpose of data hiding is to hide secret data imperceptibly into multimedia, ensuring secure data transmission. Existing magic matrix-based data hiding schemes cannot achieve satisfactory visual quality for a given low payload because they adopt a single-layer embedding (i.e., the fixed-sized reference matrix (RM) embedding), rather than adaptive multi-layer embedding (i.e., variable-sized RM embedding). To this end, we propose an adaptive data hiding scheme by constructing multi-layer RM using mini-Sudoku. Our scheme can adjust the number of layers (e.g., one, two, or more) of the RM to obtain the desired payload (i.e., low, moderate, or large payloads). In addition, our method also has the capability of obtaining the optimal number of layers of RM achieving the highest visual quality for a given payload. For each pixel pair, our scheme selects the optimal pair having the smallest Euclidean distance with this pair as its stego pair, resulting in a large decrease in distortion. Experimental results show that our proposed scheme can obtain various payloads, and more importantly, it can achieve better or comparable rate-distortion performance than several existing magic matrix-based data hiding schemes.

China’s first solar mission, the Advanced Space-based Solar Observatory (ASO-S), is now changing from Phase B to Phase C. Its main scientific objectives are summarized as ‘1M2B’, namely magnetic field and two types of bursts (solar flares and coronal mass ejections). Among the three scientific payloads, Hard X-ray Imager (HXI) observes images and spectra of X-ray bursts in solar flares. In this paper, we briefly report on the progresses made by the HXI science team (data and software team) during the design phase (till May 2019). These include simulations of HXI imaging, optimization of HXI grids, development of imaging algorithms, estimation of orbital background, as well as in-orbit calibration plan. These efforts provided guidance for the engineering, improved HXI’s imaging capability and reduced the cost of the instrument.