In Press
In Press catalogue

Vol.73 No.14
20240720
2024, 73 (14): 140201.
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2024, 73 (14): 140701.
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2024, 73 (14): 142501.
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Experimental study of physical quantities after fission provides crucial insights into the fission process, which is an indispensable way to test the fission theory. The characteristics of primary fission products before beta decay are of great value in unraveling fission kinematics and nuclear energy applications. However, the measurement of the fragment charge has always been challenging. Multiparameter studies related to nuclear charge remain relatively scarce. The deexcitation of the primary fission products may undergo internal conversion and is often accompanied by characteristic Xray emissions. Therefore, the correlated measurement of fragment kinetic energy and K Xrays for ^{252}Cf spontaneous fission is conducted. A silicon surface barrier detector is used to measure the fragment kinetic energy, while two lowenergy highpure germanium detectors are utilized for K Xray measurement. Identification of fission fragments with Z = 39–62 is realized through characteristic K Xrays with a charge resolution of ΔZ ≈ 0.7. Fission fragment K Xray yields exhibit a strong charge correlation, with an oddeven effect factor of about 13%. Based on K Xrays, the postneutronemission average kinetic energy, average total kinetic energy $(\langle \rm TKE\rangle) $ , and its dispersion ($ {\sigma }_{{\mathrm{T}}{\mathrm{K}}{\mathrm{E}}} $ ) of fission fragments are determined each as a function of nuclear charge. The kinetic energy distribution of light fragments shows a pronounced oddeven effect, with evenZ elements exhibiting kinetic energy enhanced by about 0.48 MeV compared with oddZ fragments. The peak of the $(\langle\rm TKE\rangle) $ distribution is nearly Z = 52–53, while the minimum of the $ {\sigma }_{{\mathrm{T}}{\mathrm{K}}{\mathrm{E}}} $ appears near Z = 56, indicating the significant influence of deformed shells in the highly asymmetric fission region. The postneutron kinetic energy distribution of fission fragments from ^{252}Cf (sf) is calculated by using the GEF model and CGMF model. The CGMF model effectively reproduces the overall trend of kinetic energy as a function of charge number, while the results of the GEF calculation are systematically higher than the experimental values. Nonetheless, these two phenomenological models make it difficult to quantitatively describe the kinetic energy distribution of fission fragments accurately. In this study, the insights into K Xray emissions and kinetic energynuclear charge relationships provide valuable reference data for independently measuring the fission yields and verifying the theoretical models of fission.
2024, 73 (14): 143101.
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The crystal structure, molecular structure, electronic structure and mechanical properties of molecular perovskite highenergetic material (H_{2}dabco)[K(ClO_{4})_{3}] (DAP2) under hydrostatic pressure ranging from 0 to 50 GPa are calculated and studied based on density functional theory. And the influences of pressure on its stability and impact sensitivity of DAP2 are investigated. As the external pressure gradually increases, both the lattice parameters and the volume of DAP2 crystal exhibit a monotonic decreasing trend. In the entire pressure range, the unit cell volume shrinks by up to 40.20%. By using the Birch Munnaghan equation of state to fit PV relation, the bulk modulus B_{0} and its firstorder derivative B_{0}’ with respect to pressure are obtained to be 23.4 GPa and 4.9 GPa, respectively. The observations of the characteristic bond length and bond angle within the crystal indicate that the cagelike structure of organic cation H_{2}dabco^{2+} undergoes distortion at 25 GPa. Further analysis of the average fractional coordinates of the centerofmass and Euler angles for H_{2}dabco^{2+} and KO_{12} polyhedron shows that within a pressure range from 0 to 50 GPa, both the average fractional coordinates of the centerofmass and the Euler angles exhibit fluctuations at 25 GPa, but the overall amplitude of these fluctuations is very small. Based on this finding, it is speculated that the space group symmetry of the crystal may remain unchanged in the entire pressure range. In terms of electronic structure, with the increase of pressure, the band gap value increases rapidly and reaches a maximum value at about 20 GPa, followed by a slow decreasing trend. Based on the firstprinciples band gap criterion and the variation of the band gap under different pressures, it is demonstrated that below 20 GPa, the impact sensitivity of DAP2 gradually decreases with pressure increasing; however, when the pressure exceeds 20 GPa, the impact sensitivity exhibits a slow increasing trend. In addition, the elastic constants C_{ij,} Young’s modulus (E), bulk modulus (B), shear modulus (G), and Cauchy pressure (C_{12} – C_{44}) all increase with pressure rising, indicating that the rigidity and ductility of the crystal under pressure are significantly strengthened. According to the mechanical stability criterion, the crystal maintains the mechanical stability throughout the pressure range.
2024, 73 (14): 144102.
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In general, more attention is paid to how to improve the characteristic parameters of plasma in plasma applications. However, in some cases, it is necessary to produce plasma with lowelectron density, such as in the laboratory simulation of ionospheric plasma in space science. In this study, a lowdensity plasma is generated by electron beams passing through a silicon nitride transmission window under low pressure condition. The transmission properties of electron beam passing through silicon nitride films are investigated by Monte Carlo simulation, and the plasma feature is studied by a planar Langmuir probe and a digital camera. It is found that the plasma exhibits a conical structure with its apex located at the transmission window. At a constant pressure, the cone angle of conical plasma decreases with the electron energy increasing. This is qualitatively consistent with the Monte Carlo simulation result. The frequency of electronneutral collisions increases as the working pressure rising, which leads the plasma cone angle to increase. When the beam current is reduced from 10 μA to 0.5 μA at 40 keV, the electron density decreases, in a range between 10^{5} and 10^{6} cm^{–3}, while the electron temperature does not change significantly but approaches 1 eV. It can be inferred that the electron density decreases with the distance z from the transmission window in the incident direction of the electron beam. A lowdensity plasma of less than 10^{5} cm^{–3} can be obtained further away from the transmission window.
2024, 73 (14): 144203.
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2024, 73 (14): 144401.
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Compared to the classical Fourier’s law, the phonon hydrodynamic model has demonstrated significant advantages in describing ultrafast phonon heat transport at the nanoscale. The gateallaround fieldeffect transistor (GAAFET) greatly optimizes its electrical performance through its threedimensional channel design, but its nanoscale characteristics also lead to challenges such as selfheating and localized overheating. Therefore, it is of great significance to study the internal heat transport mechanism of GAAFET devices to obtain the thermal process and heat distribution characteristics. Based on this, this paper conducts theoretical and numerical simulation analyses on the phonon heat transfer characteristics within nanoscale GAAFET devices. Firstly, based on the phonon Boltzmann equation, the phonon hydrodynamic model and boundary conditions are rigorously derived, establishing a numerical solution method based on finite elements. For the novel GAAFET devices, the effects of factors such as surface roughness, channel length, channel radius, gate dielectric, and interface thermal resistance on their heat transfer characteristics are analyzed. The research results indicate that the larger the surface roughness, the smaller the channel length and the channel radius, the larger the interface thermal resistance leads to the higher hot spot peak temperature. The nonFourier heat analysis method based on the phonon hydrodynamic model and temperature jump condition within the continuous medium framework constructed in this paper can accurately predict the nonFourier phonon heat conduction process inside GAAFET and reveal the mechanisms of resistive scattering and phonon/interface scattering. This work provides important theoretical support for further optimizing the thermal reliability design of GAAFET, improving its thermal stability, and operational performance.
2024, 73 (14): 144402.
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Thermophotovoltaic (TPV) device converts thermal radiation into electricity output through photovoltaic effect. Highefficiency TPV devices have extensive applications in gridscale thermal storage, fullspectrum solar utilization, distributed thermalelectricity cogeneration, and waste heat recovery. The key to highefficiency TPV devices lies in spectral regulation to achieve bandmatching between thermal radiation of the emitters and electron transition of the photovoltaic cells. The latest advances in nanophotonics, materials science, and artificial intelligence have made milestone progress in spectral regulation and recording power conversion efficiency of up to 40% of TPV devices. Here we systematically review spectral regulation in TPV devices at the emitter end as well as the photovoltaic cell end. At the emitter end, spectral regulation is realized through thermal metamaterials and rareearth intrinsic emitters to selectively enhance the inband radiation and suppress the subbandgap radiation. At the photovoltaic cell end, spectral regulation mainly focuses on recycling the subbandgap thermal radiation through optical filters and back surface reflectors located at the front and back of the photovoltaic cells, respectively. We emphasize the lightmatter interaction mechanisms and material systems of different spectral regulation strategies. We also discuss the spectral regulation strategies in nearfield TPV devices. Finally, we look forward to potential development paths and prospects of spectral regulation to achieve scalable deployment of future TPV devices.
2024, 73 (14): 144701.
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In this paper, the motion of a circular particle in a liddriven square cavity with the powerlaw fluid is studied by using the diffuse interface lattice Boltzmann method, and the study mainly considers the effects of the particle's initial position, the powerlaw index, the Reynolds number, and the particle size. The numerical results show that the circular particle is first in a centrifugal motion under the effect of inertia, and it finally moves steadily on the limit cycle. Furthermore, it is also found that the initial position of the particle has no influence on the limit cycle. For a shearthinning fluid flow, the limit cycle moves towards the bottom right corner of the square cavity. Moreover, the particle velocity is small, and the period of the particle motion is long. On the other hand, in the case of shearthickening fluid flow, the limit cycle moves towards the top left corner of the cavity. In addition, the particle velocity is large, and the period of the particle motion is short.With the increase of Reynolds number, the limit cycle moves towards the bottom right corner of the square cavity, which is caused by a strong fluid flow field. Meanwhile, the particle velocity becomes larger, and the period of the particle motion is shorter. With the increase of particle size, the effect of confinement of the cavity boundary becomes significant, and the circular particle is pushed towards the center of the cavity. In this case, the limit cycle shrinks towards the center of the cavity. The circular particle squeezes the secondary vortices, especially when the circular particle is located in the bottom left, bottom right and top left corners. Additionally, the appearance of the circular particle has a significant influence on the position of the primary vortex, which changes periodically near the position of the primary vortex without the particle. It is also observed that the influence of the circular particle becomes more significant as its size increases and the powerlaw index decreases.
2024, 73 (14): 146302.
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Transition metal dichalcogenides (TMDs) is an important member of twodimensional material family, which has various crystal structures and physical properties, thus providing a broad platform for scientific research and device applications. The diversity of TMD's properties arises not only from their relatively large family but also from the variety of their crystal structure phases. The most common structure of TMD is the trigonal prismatic phase (H phase) and the octahedral phase (T phase). Studies have shown that, in addition to these two highsymmetry phases, TMD has other distorted phases. Distorted phase often exhibits different physical properties from symmetric phases and can perform better in certain systems. Because the structural differences between different distorted phases are sometimes very small, it is experimentally challenging to observe multiple distorted phases coexisting. Therefore, it is meaningful to theoretically investigate the structural stability and physical properties of different distorted phases. In this study, we investigate the structure and phase transition of monolayer RuSe_{2} through firstprinciples calculation. While confirming that its ground state is a the dimerized phase ($T^\prime$ phase), we find the presence of another energetically competitive trimerized phase ($T^{\prime\prime\prime}$ phase). By comparing the energy values of four different structures and combining the results of phonon spectra and molecular dynamics simulations, we predict the stability of the $T^{\prime\prime\prime}$ phase at room temperature. Because the H phase and T phase of twodimensional RuSe_{2} have already been observed experimentally, and considering the fact that $T^{\prime\prime\prime}$ phase has much lower energy than the H and T phases, it is highly likely that the $T^{\prime\prime\prime}$ phase exists in experiment. Combining the calculations of the phase transition barrier and the molecular dynamics simulations, we anticipate that applying a slight stress to the $T^\prime$ phase structure at room temperature can induce a lattice transition from $T^\prime$ phase to $T^{\prime\prime\prime}$ phase, resulting in significant changes in the band structure and carrier mobility, with the bandgap changing from an indirect bandgap of 1.11 eV to a direct bandgap of 0.71 eV, and the carrier mobility in the armchair direction increasing from $ 0.82 \times 10^3 \, {\rm cm}^{2}{\cdot}{\rm V}^{1}{\cdot}{\rm s}^{1}$ to $3.22 \times 10^3 \, {\rm cm}^{2}{\cdot}{\rm V}^{1}{\cdot}{\rm s}^{1}$ , an approximately threefold enhancement. In this work, two possible coexisting distorted phases in monolayer RuSe_{2} are compared with each other and studied, and their electronic structures and carrier mobilities are analyzed, thereby facilitating experimental research on twodimensional RuSe_{2} materials and their applications in future electronic devices.
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