First-Principles Investigation of Phase Stability, Electronic Structure and Optical Properties of MgZnO Monolayer

MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using density functional theory calculations, we investigated the phase stability, electronic structure and optical properties of MgxZn1−xO monolayer with Mg concentration x range from 0 to 1. Our calculations show that MgZnO monolayer remains the graphene-like structure with various Mg concentrations. The phase segregation occurring in bulk systems has not been observed in the monolayer due to size effect, which is advantageous for application. Moreover, MgZnO monolayer exhibits interesting tuning of electronic structure and optical properties with Mg concentration. The band gap increases with increasing Mg concentration. More interestingly, a direct to indirect band gap transition is observed for MgZnO monolayer when Mg concentration is higher than 75 at %. We also predict that Mg doping leads to a blue shift of the optical absorption peaks. Our results may provide guidance for designing the growth process and potential application of MgZnO monolayer

Effect of Bi on graphite morphology and mechanical properties of heavy section ductile cast iron

To improve the mechanical properties of heavy section ductile cast iron, bismuth (Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the five castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture

First-Principles Investigation of Phase Stability, Electronic Structure and Optical Properties of MgZnO Monolayer

MgZnO bulk has attracted much attention as candidates for application in optoelectronic devices in the blue and ultraviolet region. However, there has been no reported study regarding two-dimensional MgZnO monolayer in spite of its unique properties due to quantum confinement effect. Here, using density functional theory calculations, we investigated the phase stability, electronic structure and optical properties of MgxZn1−xO monolayer with Mg concentration x range from 0 to 1. Our calculations show that MgZnO monolayer remains the graphene-like structure with various Mg concentrations. The phase segregation occurring in bulk systems has not been observed in the monolayer due to size effect, which is advantageous for application. Moreover, MgZnO monolayer exhibits interesting tuning of electronic structure and optical properties with Mg concentration. The band gap increases with increasing Mg concentration. More interestingly, a direct to indirect band gap transition is observed for MgZnO monolayer when Mg concentration is higher than 75 at %. We also predict that Mg doping leads to a blue shift of the optical absorption peaks. Our results may provide guidance for designing the growth process and potential application of MgZnO monolayer

Influence of Doping Tb on the Mechanical Properties and Martensitic Transformation of Ni-Mn-Sn Magnetic Shape Memory Alloys

Brittleness and low working temperature are two key factors that restrict the application of Ni-Mn-Sn alloys. Element doping is an effective means to improve performance of materials. In present paper, martensitic transformation (MT) and mechanical properties of Ni48Mn39Sn13−xTbx (x = 0, 0.5, 1, 2, and 5 at.%) alloys are investigated. It is found that the Tb addition refines significantly the grains and causes the formation of a Tb-rich phase. All the samples undergo the martensitic transformation from parent phase to martensite. And the martensitic transformation characteristic temperatures increase remarkably from −60.7 °C for x = 0 to 364.1 °C for x = 5. The appropriate amount of Tb addition in Ni48Mn39Sn13−xTbx (x = 0, 0.5, 1, 2, and 5 at.%) alloys significantly enhances the compressive strength and improves the ductility, which can be ascribed to the grain refinement. The compressive stress of 571.8 MPa and strain 22.0% are obtained in the Ni48Mn39Sn11Tb2 alloy. Then the mechanical properties decrease with the further increased Tb content. Simultaneous improving of martensitic transformation temperature and mechanical properties in Ni-Mn-Sn magnetic alloy are achieved by Tb doping

Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study

Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications

Electronic and Magnetic Properties of Rare-Earth Metals Doped ZnO Monolayer

The structural, electronic, and magnetic properties of rare-earth metals doped ZnO monolayer have been investigated using the first-principles calculations. The induced spin polarization is confirmed for Ce, Eu, Gd, and Dy dopings while the induced spin polarization is negligible for Y doping. The localized f states of rare-earth atoms respond to the introduction of a magnetic moment. ZnO monolayer undergoes transition from semiconductor to metal in the presence of Y, Ce, Gd, and Dy doping. More interestingly, Eu doped ZnO monolayer exhibits half-metallic behavior. Our result demonstrates that the RE-doping is an efficient route to modify the magnetic and electronic properties in ZnO monolayer

VALUE OF DEEP CONVOLUTIONAL NEURAL NETWORK BASED ON SINGLE MRI IMAGES IN DIAGNOSIS OF ANTERIOR CRUCIATE LIGAMENT TEARS OF THE KNEE

Objective To establish a deep convolutional neural network (DCNN) model based on the single MRI image of the knee, and to investigate its value in the diagnosis of anterior cruciate ligament (ACL) tears. Methods Knee MRI images were collected from 1 663 subjects from the GreatPACS image archiving and communication system in No. 971 Hospital of People’s Liberation Army Navy from January 1, 2017 to June 30, 2022, and one image was selected from the MRI images of each patient and was annotated as normal ACL or ACL tears by an orthopedic specialist, which obtained 1 111 images with normal ACL and 552 images with ACL tears. The images were randomly assigned to the training set (1 383 images) and the test set (280 images) at a ratio of 83% and 17%, respectively, to train and test the DCNN model established for the intelligent diagnosis of ACL. The performance of the model was evaluated by positive predictive value (PPV), negative predictive value (NPV), accuracy, sensitivity, specificity, and area under the ROC curve (AUC). Results A DCNN model was successfully established for the intelligent diagnosis of ACL. The test results of this model showed a PPV of 52.99%, an NPV of 88.96%, an accuracy of 73.93%, a sensitivity of 77.50%, and a specificity of 72.50%, with an AUC of 0.602. Conclusion The DCNN model based on single MRI images can help clinicians with the diagnosis of ACL tears

Designing a New Ni-Mn-Sn Ferromagnetic Shape Memory Alloy with Excellent Performance by Cu Addition

Both magnetic-field-induced reverse martensitic transformation (MFIRMT) and a high working temperature are crucial for the application of Ni-Mn-Sn magnetic shape memory alloys. Here, by first-principles calculations, we demonstrate that the substitution of Cu for Sn is effective not only in enhancing the MFIRMT but also in increasing martensitic transformation, which is advantageous for its application. Large magnetization difference (ΔM) in Ni-Mn-Sn alloy is achieved by Cu doping, which arises from the enhancement of magnetization of austenite due to the change of Mn-Mn interaction from anti-ferromagnetism to ferromagnetism. This directly leads to the enhancement of MFIRMT. Meanwhile, the martensitic transformation shifts to higher temperature, owing to the energy difference between the austenite L21 structure and the tetragonal martensite L10 structure increases by Cu doping. The results provide the theoretical data and the direction for developing a high temperature magnetic-field-induced shape memory alloy with large ΔM in the Ni-Mn-Sn Heusler alloy system

Magnetic-induced dual-function tunable THz polarization conversion metamaterial based on Ni-Mn-Sn shape memory alloy films

Due to the improvement in miniaturization and practicability of polarization conversion devices, the terahertz polarization control technology has been paid more and more attention. Nevertheless, a critical factor in restricting its development is short of dynamic and multifunctional materials. Ferromagnetic shape memory alloys (FSMAs) provide a novelty solution for tunable metamaterials because of their excellent recovery deformation, non-contact control, and fast response. Here, a new magnetic-induced tunable THz metamaterial is proposed, composed of Ni-Mn-Sn FSMAs resonator in strip structure, polyimide dielectric, and metal copper substrate. Numerical results reveal that the polarization converter can realize any in a broad band between 1.04 and 1.96 THz by applying different magnetic fields to adjust the elastic deformation of Ni-Mn-Sn. Notably, the device can also realize line circularly polarized light conversion in the range of 0.87–0.92 THz and 2.07–2.12 THz. Compared to the current state-of-the-art double functional polarization converter, the THz converter proposed in this work offers benefits in many respects, including the 61.3% relative bandwidth and high conversion efficiency. Our study provides an excellent strategy to develop actively tunable and multifunctional THz compact devices