Search

【Objective】 Using a water environment numerical model to study the process of hydrodynamic and water quality changes in a seasonal ice-covered reservoir, revealing the variation patterns during the open water and ice-covered periods. 【Method】 In this paper, Xinlicheng Reservoir, a plain reservoir in the cold region of Northern China, was taken as the research object, and a three-dimensional hydrodynamic water quality model was built based on water environment hydrodynamics. The water temperature and TP concentration of a complete water period which include open water stage and ice-covered stage were simulated and analyzed, and the parameters of the model were calibrated and validated. 【Result】 The statistical analysis results show that the mean relative error (MRE) between the simulated and measured water level values of Xinlicheng Reservoir is 4.47%, and the water temperature MRE value was 12.5%. The MRE of TP concentration at all 3 sampling points are less than 20%. 【Conclusion】 The results can objectively reflect the changes in hydrodynamics force, water temperature and TP concentration of Xinlicheng Reservoir during the open water and ice covered periods, and can provide reliable reference and application value for the water environment management of Xinlicheng Reservoir.

In this paper, we innovatively stack multiple resonant units of photoconductive silicon to design an ultra-broadband metamaterial absorber. By manipulating the conductivity of the silicon with a pump beam, adjustments are made to the amplitude of the wide absorption spectrum spanning 6.6 THz, enabling functional switching from total reflection to near-perfect ultra-broadband absorption. By integrating vanadium dioxide as an intermediary layer, a dual-mode switchable absorber is realized, offering dual control functionalities. Temperature changes enable the absorber to switch between dual-band absorption and ultra-broadband absorption, while variations in pump beam intensity allow for further amplitude adjustments within the absorption spectrum. Impedance matching theory and near-field analysis provide the necessary physical foundation for understanding broadband absorption. Structural parameters, incident angle, and polarization angle of the incident electromagnetic waves are also studied to demonstrate the device's robustness. Our proposed absorbers not only greatly broaden the absorption bandwidth of silicon-based absorbers, but also offer versatility, polarization insensitivity, and robustness over a wide range of incidence angles. Moreover, our design ideas are useful for broadening the bandwidth and enhancing absorption, which enables wider applications in ultra-broadband terahertz absorption and promises extensive prospects. [ABSTRACT FROM AUTHOR]

A tunable dual broadband switchable terahertz absorber based on vanadium dioxide and graphene is proposed. The tunability of graphene and the phase transition properties of vanadium dioxide are used to switch broadband absorption between low-frequency and high-frequency, as well as the absorption rate tuning function. The simulation results indicate that when vanadium dioxide is in the insulating phase and the graphene Fermi energy is 0.7 eV, the absorber achieves low-frequency broadband absorption within the range of 2.6–4.2 THz with an absorptance greater than 90%; when vanadium dioxide is in the metallic phase and the graphene Fermi energy is 0 eV, the absorber achieves high-frequency broadband absorption within the range of 4.9–10 THz with an absorptance greater than 90%. Furthermore, the absorptance can be tuned by adjusting the conductivity of vanadium dioxide or the Fermi energy of graphene. Due to the central symmetry of the proposed structure, the absorber is completely insensitive to polarization. For TE and TM polarized waves, both low and high-frequency broadband absorption are maintained over a range of incident angles from 0° to 50°. The simple structure, tunable absorption rate, insensitivity to polarization angle and incident angle properties are advantages of our proposed absorber. It has broad application prospects in adjustable filters and electromagnetic shielding. [ABSTRACT FROM AUTHOR]

This paper proposes a simulated design for a versatile terahertz absorber that can be actively tuned. The absorber utilizes the unique tuning capabilities of graphene and vanadium dioxide, enabling it to alternate between ultra-broadband absorption, broadband absorption, and almost complete reflection. In the metallic phase of vanadium dioxide, coupled with a graphene Fermi level at 0 eV, the absorber achieves ultra-broadband absorption. This spans an extensive frequency range from 3.85 THz to 9.73 THz, exhibiting an absorption rate surpassing 90%. As we shift to the insulating phase of vanadium dioxide and adjust the graphene Fermi level to 1 eV, the absorber operates in a broadband absorption mode. This mode spans 2.98 THz to 4.63 THz, demonstrating an absorption rate exceeding 90%. In the insulating state of vanadium dioxide with a graphene Fermi level at 0 eV, the absorber metamorphoses into a nearly total reflector. Its maximum absorption rate is a mere 0.52%. The unique adjustability of vanadium dioxide and graphene independently enables the fine-tuning of absorption rates for both ultra-broadband and broadband absorption without encountering interference. Additionally, thanks to the central symmetry inherent in the proposed structure, the absorber exhibits insensitivity to alterations in polarization angles and remains stable under a broad range of incident angles. With these benefits, the absorber shows promising potential for applications in electromagnetic stealth, wireless communication, and so on.

The hybrid perovskite CH3NH3PbX3 (X = Cl, Br, I) is a promising material for developing novel optoelectronic devices. Due to its intrinsic non-layered crystal structure, it remains challenging to synthesize two-dimensional (2D) single-crystalline CH3NH3PbX3 with nanoscale thickness. Here, we report a bottom-up approach to fabricate large CH3NH3PbX3 2D crystals via liquid-phase growth on a mica substrate. The strong potassium-halogen interactions at the perovskite/mica interface decrease the interface energy, driving the striking in-plane growth of the perovskite. The grown 2D CH3NH3PbBr3 crystal was characterized as 8 nm in thickness and hundreds of micrometers in lateral size. Weak exciton binding energy was crucial for improving the photoelectric performance of 2D CH3NH3PbBr3. A visible-light photodetector with a metal/insulator/perovskite configuration was finally achieved with a photoresponsivity of 126 A W-1 and a bandwidth exceeding 80 kHz. Our work proves that the liquid-phase growth on mica is a controllable method to grow 2D hybrid CH3NH3PbX3 perovskites, which can facilitate both device applications and fundamental investigations.