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A bstract PandaX-4T is a ton-scale dark matter direct detection experiment using a dual-phase TPC technique at the China Jinping Underground Laboratory. Various ultra-low background technologies have been developed and applied to material screening for PandaX-4T, including HPGe gamma spectroscopy, ICP-MS, NAA, radon emanation measurement system, krypton assay station, and alpha detection system. Low background materials were selected to assemble the detector. Surface treatment procedures were investigated to further suppress radioactive background. Combining measured results and Monte Carlo simulation, the total material background rates of PandaX-4T in the energy region of 1–25 keV ee are estimated to be (9.9 ± 1.9) × 10 − 3 mDRU for electron recoil and (2.8 ± 0.6) × 10 − 4 mDRU for nuclear recoil. In addition, nat Kr in the detector is estimated to be < 8 ppt.

Liquefied natural gas (LNG), an increasingly widely applied clean fuel, releases a large number of cold energy in its regasification process. In the present paper, the existing power generation cycles utilizing LNG cold energy are introduced and summarized. The direction of cycle improvement can be divided into the key factors affecting basic power generation cycles and the structural enhancement of cycles utilizing LNG cold energy. The former includes the effects of LNG-side parameters, working fluids, and inlet and outlet thermodynamic parameters of equipment, while the latter is based on Rankine cycle, Brayton cycle, Kalina cycle and their compound cycles. In the present paper, the diversities of cryogenic power generation cycles utilizing LNG cold energy are discussed and analyzed. It is pointed out that further researches should focus on the selection and component matching of organic mixed working fluids and the combination of process simulation and experimental investigation, etc.

In this paper, a numerical model considering phase change and external heat leakage is established to study the pressure variation and temperature distribution of marine Liquefied Natural Gas (LNG) fuel tanks under sinusoidal sloshing excitation. The Volume of Fluid (VOF) method, coupled with the mesh motion treatment, is adopted to predict the movement of the vapor-liquid interface. The sinusoidal sloshing excitation is realized by a User-Defined Function (UDF). The feasibility of the numerical model is verified by comparisons with related fluid sloshing experiments. The thermal physical process in the LNG fuel tank under sloshing conditions and the static condition are compared, and the effects of sloshing amplitude and frequency on the pressure and temperature distribution of the tank are also studied. The results show that when the external sloshing excitation frequency is close to the first natural frequency of the LNG fuel tank, the tank pressure will drop rapidly in a short time, resulting in the shutdown of Natural Gas (NG) engine. Meanwhile, the influence of the sloshing excitation on the mass transfer is theoretically analyzed by the definition of the sloshing Nusselt number.

Liquefied natural gas (LNG) is becoming an ideal alternative fuel for vessels because of its environmental and economic advantages. As LNG is a cryogenic fuel stored around -163 °C, the LNG fuel tank is a highly non-equilibrium thermodynamic system especially during bunkering and pressurization processes. The accurate prediction of the thermodynamic behaviors inside the LNG fuel tank is critical for the system design and operation. In this study, a fast and effective analytical model of bunkering and pressurization for marine LNG fuel tank was developed. The Norwegian car ferry MF Korsfjord was chosen as a benchmark case to confirm the validity of the model. The top spray filling process, the pressurization process, and the fuel gas supply process of the MF Korsfjord were simulated. The model prediction showed good agreement with the measured data. Besides, cryogenic liquid sloshing inside the fuel tank was investigated as well. The results showed that the sloshing had a severe impact on the tank pressure, especially when the resonance condition of the tank was met, resulting in the shutdown of gas engines in extreme situations.

Compared with the traditional engines, the thermo-acoustic engines are relatively new and can act as the linear compressors for refrigerators. Many institutes have shown great interest in this kind of machine for its absence of moving mechanical part. In this paper, the influence of the dimensions of the main parts of the small- scale Stifling thermo-acoustic engine was numerically simulated using a computer code called DeltaEC. The resonator and the resonator cavity were found to be the most convenient and effective in improving the perfor- mance of the engine. Based on the numerical simulation, a small-scale Stifling thermo-acoustic engine were constructed and experimentally investigated. Currently, with a resonator length of only 1 m, the working frequency of the engine was decreased to 90 Hz and the onset temperature difference was decreased to 198.2 K.

It is commonly conjectured that dark matter is a charge neutral fundamental particle. However, it may still have minute photon-mediated interactions through millicharge 1 , 2 or higher-order multipole interactions 3 – 10 , resulting from new physics at a high energy scale. Here we report a direct search for effective electromagnetic interactions between dark matter and xenon nuclei that produce a recoil of the latter from the PandaX-4T xenon-based detector 11 , 12 . Using this technique, the first constraint on the charge radius of dark matter is derived with the lowest excluded value of 1.9 × 10 −10  fm 2 for a dark matter mass of 40 giga electron volts per speed of light in a vaccum squared (GeV/ c 2 ), more stringent than that for neutrinos by four orders of magnitude. Constraints on the magnitudes of millicharge, magnetic dipole moment, electric dipole moment and anapole moment are also improved substantially from previous searches 13 , 14 , with corresponding tightest upper limits of 2.6 × 10 −11  e, 4.8 × 10 −10  Bohr magnetons, 1.2 × 10 −23  ecm and 1.6 × 10 −33  cm 2 , respectively, for a dark matter mass of 20–40 GeV/ c 2 . A direct search for effective electromagnetic interactions between dark matter and xenon nuclei that produce a recoil of the latter is carried out and the first constraint on charge radius of dark matter is derived.

Pulsating heat pipe (PHP), or oscillating heat pipe (OHP), a novel type of highly efficient heat transfer component, has been widely applied in many fields, such as in space-borne two-phase thermal control systems, in the cooling of electronic devices and in energy-saving technology, etc. In the present paper, the characteristics and working principles of the PHPs are introduced and the current researches in the field are described from the viewpoint of experimental tests, theoretical analyses as well as practical applications. Besides, it is found that the state-of-the-art experimental investigations on the PHPs are mainly focused on the flow visualization and the applications of nanofluids and other functional fluids, aiming at enhancing the heat transfer performance of the PHPs. In addition, it is also pointed out that the present theoretical analyses of the PHP are restricted by further development of two-phase flow theories, and are concentrated in the non-linear analyses. Numerical simulations are expected to be another research focus, in particular of the combination of the nanofluids and functional fluids.

We propose a major upgrade to the existing PandaX-4T experiment at the China Jinping Underground Laboratory. The new experiment, PandaX-xT, will be a multi-ten-tonne liquid xenon, ultra-low background, and general-purpose observatory. The full-scaled PandaX-xT contains a 43-t liquid xenon active target. Such an experiment will significantly advance our fundamental understanding of particle physics and astrophysics. The sensitivity of dark matter direct detection will be improved by nearly two orders of magnitude compared to the current best limits, approaching the so-called “neutrino floor” for a dark matter mass above 10 GeV/c 2 , providing a key test to the Weakly Interacting Massive Particle paradigm. By searching for the neutrinoless double beta decay of 136 Xe isotope in the detector, the effective Majorana neutrino mass can be measured to a 10–41 meV/c 2 sensitivity, providing a key test to the Dirac/Majorana nature of neutrinos. Astrophysical neutrinos and other ultra-rare interactions can also be measured and searched for with an unprecedented background level, opening up new windows of discovery. Depending on the findings, PandaX-xT will seek the next stage upgrade utilizing isotopic separation of natural xenon.