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Previous studies have reported that reactions between selenium (Se) and metal substrates can lead to the formation of monolayer materials, but no studies have reported on the thickness that can be achieved for ordered films formed by this method. Here, we report that 2D layered Cu2Se can be successfully fabricated on the Cu(111) surface through Se deposition at room temperature using molecular beam epitaxy (MBE). Using aberration-corrected scanning transmission electron microscopy (STEM), we obtained the first cross-sectional STEM image with atomic resolution. This image serves as direct evidence supporting the validity of the theoretical model for layered Cu2Se. Our findings demonstrate that the ordered structure can achieve a thickness of approximately 38 nm under room temperature conditions, altering the prevailing perception of the formation of monolayer or few-layer structures through the reaction between Se and Cu(111) substrate. Our work provides valuable insights for the synthesis of layered Cu2Se with specific thicknesses, a novel two-dimensional semiconductor material, which holds potential applications in future electronic devices. [ABSTRACT FROM AUTHOR]

In order to improve the quality of quick-frozen diced mango, a cylindrical quick-frozen container with dry ice spray is designed, the temperature field and velocity field of diced mango sprayed by dry ice in quick-freezing tank are simulated by COMSOL Multiphysics. The effects of different inlet velocities (0.15, 0.20, 0.25, 0.30, 0.35 and 0.40m/s), on the quick-freezing process of diced mango are studied. The results show that with the increase of the inlet velocity of dry ice, the time for diced mango to meet the requirements of quick freezing is continuously shortened, and the outlet solid fraction fluctuates within a certain range. When the inlet velocity is 0.25m/s, the inlet radius is 15mm and the size of diced mango is 10mm, the quick-freezing effect is the best. By the experimental verification, the average errors of surface temperature and core temperature of diced mango to meet the requirements of quick freezing are 3.9% and 3.8% respectively. The results lay a foundation for the popularization and application of dry ice spray quick frozen diced mango.

The effective assessment of risk and speed limitations in ice are critical for the route planning of polar cruise ships. While the Polar Operational Limit Assessment Risk Indexing System (POLARIS) is widely used to evaluate the operational risk in ice, its scope of assessment is limited to the ship's assigned ice class. For a specific ship with a given ice class, the propulsion performance under varying ice conditions is more essential for assessing the besetting risk and finding an optimal route. To establish a more detailed risk evaluation method for a PC6 class polar cruise ship, propulsion performance under various ice conditions is obtained via model tests in an ice tank. During the tests, the tow force, propeller torque, and thrust are measured under different ship velocities and propeller rotation rates, and the relations between required delivered power (P) and ship velocity (V) under the tested ice thicknesses and concentrations are obtained and extended to other ice conditions by curve fitting. A new risk index outcome, RIO*, is proposed after POLARIS according to the optimized load ranges of the ship's rated power. Four risk levels, including low, medium, high, and unnavigable, are classified with the required propulsion power in ice being 50%, 85%, 100%, and >100% of the rated power, respectively. The recommended speed limit for each risk level is proposed based on the economical service speed of 11 kn, the operational limit of 3 kn by POLARIS and the minimum speed of 0.5 kn to avoid besetting, respectively. Based on the RIO* and P–V relations, the speed map for varying ice thicknesses and concentrations can be calculated. On these bases, a route planning simulation for the present polar cruise ship is performed. Results of the case study show that 29% of the simulated area is identified as "unnavigable" by the present procedure, while only 8% is detected by POLARIS. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms. High-performance catalysts with the absolute value of Gibbs free energy (∣∆GH∣) close to zero, is one of the ultimate goals in the catalytic field. Here, we report the formation of monolayer titanium selenide (TiSe2) with line defects. The low-temperature scanning tunneling microscopy/spectroscopy (STM/S) measurements revealed the structure and electronic states of the line defect. Density functional theory (DFT) calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results. Further, DFT calculations show that monolayer TiSe2 with line defects have good catalytic activity for hydrogen evolution reaction (HER). If the defects are decorated with single Pt atom, the HER catalytic activity will be enhanced dramatically (∣∆GH∣ = 0.006 eV), which is much better than Pt metal (∣∆GH∣ = 0.09 eV). Line defects in monolayer TiSe2/Au(111) provide a wonderful platform for the design of high-performance catalysts. [ABSTRACT FROM AUTHOR]