Effect of Surface Termination with Oxygen and Fluorine on the Electronic Structures and optical spectra of Mn2N Based MXenes

The extensive applications of MXenes, a novel type of layered materials known for their favorable characteristics, have sparked significant interest. This research focuses on investigating the impact of surface functionalization on the behavior of Mn2NX2 (X = O, F) MXenes monolayers using the "Density functional theory (DFT) based full-potential linearized augmented-plane-wave (FP-LAPW)" method. We observe and elucidate the variations in the physical properties of the Mn2NX2 by employing different surface terminations with F and O functional groups. We found that O-termination results in half-metallic behavior, whereas the N-termination evolves metallic characteristics within these MXene systems. Similarly, surface termination has effectively influenced their optical absorption efficiency. For instance, Mn2NO2 and Mn2NF2 effectively absorb UV light of magnitude 50.15×104 cm-1 and 37.71×104 cm-1, respectively. Additionally, they demonstrated prominent refraction and reflection characteristics, comprehensively discussed in the present work. Our predictions offer valuable perspectives into the optical and electronic characteristics of Mn2NX2-based MXenes, presenting the promising potential for implementing them in diverse optoelectronic devices.

An optical mechanism-based deep learning approach for deriving water trophic state of China's lakes from Landsat images

Widespread eutrophication has been considered as the most serious environment problems in the world. Given the critical roles of lakes in human society and serious negative effects of water eutrophication on lake ecosystems, it is thus fundamentally important to monitor and assess water trophic status of lakes. However, a reliable model for accurately estimating the trophic state index (TSI) of lakes across a large-scale region is still lacking due to their high complexity. Here, we proposed an optical mechanism-based deep learning approach to remotely estimate TSI of lakes based on Landsat images. The approach consists of two steps: (1) determining the optical indicators of TSI and modeling the relationship between them, and (2) developing an approach for remotely deriving the determined optical indicator from Landsat images. With a large number of in situ datasets measured from lakes (2804 samples from 88 lakes) across China with various optical properties, we trained and validated three machine learning methods including deep neural network (DNN), k-nearest neighbors (KNN) and random forest (RF) to model TSI with the optical indicators and TSI and derive the determined optical indicator from Landsat images. The results showed that (1) the total absorption coefficients of optically active constituents at 440 nm (at-w(440)) performs best in characterizing TSI, and (2) DNN outperforms other models in the inversion of both TSI and at-w(440). Overall, our proposed optical mechanism-based deep learning approach demonstrated a robust and satisfactory performance in assessing TSI using Landsat images (root mean squared error (RMSE) = 5.95, mean absolute error (MAE) = 4.81). This highlights its merit as a nationally-adopted method in lake water TSI estimation, enabling the convenience of the acquisition of water eutrophic information in large scale, thereby assisting us in managing lake ecology. Therefore, we assessed water TSI of 961 lakes (>10 km2) across China using the proposed approach. The resulting at-w(440) and TSI ranged from 0.01 m-1 to 31.42 m-1 and from 6 to 96, respectively. Of all these studied lakes, 96 lakes (11.40 %) were oligotrophic, 338 lakes were mesotrophic (40.14 %), 360 lakes were eutrophic (42.76 %), and 48 were hypertrophic (5.70 %) in 2020.

Gamma-ray, fast neutron and ion shielding characteristics of low-density and high-entropy Mg-Al-Ti-V-Cr-Fe-Zr-Nb alloy systems using Phy-X/PSD and SRIM programs

This study aimed to assess the radiation shielding properties of ten low-density high-entropy alloys (LWHEAs) using Phy-X/PSD software to analyze various shielding parameters, such as attenuation coefficients (μ m and μ), mean free path (λ), effective atomic number (Z eff ), and removal cross-section (Σ R ), in the energy range of Image 1 to Image 2. A comprehensive evaluation was performed to compare the attenuation outcomes provided by HEAs with a range of shielding materials documented in the literature. The study also calculated the build-up factors (BUFs) of the alloys by using the GP-fitting interpolation method. The stopping power of the alloys against H 1 / H e + 2 ions was analyzed using the SRIM Monte Carlo code, considering total stopping power (TSP) and projected range (PR). The results indicated that HEA8 (A l 3.88 C r 14.95 M o 27.58 N b 26.71 T i 13.76 Z r 13.11 ) had the best performance in terms of shielding against γ-rays, fast neutrons, and H 1 / H e + 2 ions, as it achieved the highest values of parameters such as μ m , μ, Z eff , and Σ R , along with the lowest values of HVL, TVL, λ, BUFs (Image 3 Image 4), TSP, and PR. On the other hand, HEA10 (M g 10.77 A l 11.96 M n 24.35 F e 24.75 C u 28.17 ) had the lowest BUFs in both lower (Image 5 Image 4) and higher (Image 6 Image 4) energy regions. The order of μ m for the alloys was found to be HEA5 < HEA6 < HEA9 < HEA7 < HEA10 < HEA4 < HEA2 < HEA3 < HEA1 < HEA8 . The study concluded that LWHEAs possess superior radiation shielding properties compared to conventional materials, making them a promising new class of materials for radiation shielding applications.

Barothermal Theory of Two Devices for Measuring Absorption Coefficients

Two devices are proposed for measuring absorption coefficients in weakly absorbing materials. The first device measures cylindrical samples and the second device measures flat plate or disk samples. This paper reports on the derivations for the steady-state and transient solutions to the heat diffusion equations which describe the barothermal behavior of the two proposed devices. In addition, Green's function techniques are used to describe the cyclic heating and cooling of the cylinders and plates.