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PtSe 2 and CuSe monolayers obtained by selenization of a metal substrate are shown to intrinsically form periodic patterns by varying the amount of Se atoms deposited. These patterns are used for the localized absorption of molecules and nanoclusters. Two-dimensional (2D) materials have been studied extensively as monolayers 1 , 2 , 3 , 4 , 5 , vertical or lateral heterostructures 6 , 7 , 8 . To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules 9 , 10 . Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe 2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.

When a crystal is subjected to a periodic potential, under certain circumstances it can adjust itself to follow the periodicity of the potential, resulting in a commensurate state. Of particular interest are topological defects between the two commensurate phases, such as solitons and domain walls. Here we report a commensurate–incommensurate transition for graphene on top of hexagonal boron nitride (hBN). Depending on the rotation angle between the lattices of the two crystals, graphene can either stretch to adapt to a slightly different hBN periodicity (for small angles, resulting in a commensurate state) or exhibit little adjustment (the incommensurate state). In the commensurate state, areas with matching lattice constants are separated by domain walls that accumulate the generated strain. Such soliton-like objects are not only of significant fundamental interest, but their presence could also explain recent experiments where electronic and optical properties of graphene-hBN heterostructures were observed to be considerably altered. A single layer of graphene on top of a hexagonal boron-nitride sheet can stretch to form a commensurate structure, or not — depending on the rotation angle between the two layers. In the case of commensurability, strain gets concentrated in domain walls, resulting in soliton-like structures.

A new rheocasting process, low superheat pouring with a shear field (LSPSF), to achieve sound semisolid slurry is reported. Results show that a fully grain refined spherical structure can be obtained using proper processing conditions within 25 s. The efficient grain refinement should be attributed to the continuous nucleation events, enhanced crystal separation from the nucleation sites and crystal survival, as a consequence of low superheat pouring combined with localised rapid cooling and positive mixing-shearing during the initial stage of solidification. The discussion based on the morphological instability theory indicates that the combined effects of both low cooling and high grain density can enhance the stabilisation of solid/liquid interface and promote grains to grow spherically to a larger size scale. Suppressing dendrite growth and coarsening through the overlapping of diffusion fields and the Gibbs-Thomson effect are the main dynamic conditions that lead to the formation of spherical primary a α-Al particles.

A novel mechanical vibration for refining microstructure is reported where vibration energy was directly exerted into a molten alloy by a vibrating horn, and the vibrating horn was melted during vibration. Effects of vibration intensity and melt superheat on the microstructure and mechanical properties of AZ31 magnesium alloy were investigated. It is confirmed that the melting of the vibrating horn could effectively extract the superheat and latent heat from the interior of the molten alloy, leading to rapid cooling during the initial stage of solidification, and the cooling rate is strongly dependent on the vibration acceleration and melt superheat. This study showed that it was difficult to refine the solidified microstructure when the treated alloy was kept in the full liquid state within the entire vibrating duration. A significantly refined microstructure was obtained by applying mechanical vibration during the nucleation stage, and a globular microstructure could form in a few seconds after solidification. When the molten alloy was treated from 920 K to 903 K (647 °C to 630 °C), with increasing vibration acceleration from 2.5 to 19 m s −2 , the coarse dendritic microstructure of the produced AZ31 billets transformed into a well-refined, reasonably uniform, and non-dendritic one, and mechanical properties were improved significantly. Moreover, the mechanisms of microstructure formation are discussed.

The desired starting material for semi-solid processing is the semi-solid slurry in which the solid phase is present as fine and globular particles. A modified solid–liquid mixing (SLM) is reported wherein semi-solid slurry can be produced by mixing a solid alloy block into a liquid alloy, and mechanical vibration is utilized to enhance the mixing. Effects such as liquid alloy temperature, mass ratio, and mixing intensity on the microstructure and the cooling curves during SLM were evaluated. 2D and 3D microstructure analysis of treated A356 aluminum alloy shows that microstructure can be refined significantly with a considerable morphology change in primary Al phase. It is critical that the temperature of mixture after mixing is lower than its liquidus temperature to obtain a valid SLM process. Specially, mixing intensity is identified as a primary factor for a favorable microstructure of semi-solid slurry.

Dark hollow focus plays an important role in many optical systems. In this paper, dark hollow focal shaping of spirally polarized axisymmetric Bessel-modulated Gaussian beam is investigated by vector diffraction theory in detail. Results show that the dark hollow focus can be altered considerably by beam parameter and spiral parameter that indicates polarization spiral degree. One dark hollow focus and two dark hollow foci pattern may occur for certain spiral parameter, and the transverse size of dark hollow focus can be less than the diffraction limit size of bright focus. In addition, there may also appear two triangle dark hollow foci that are connected by one dark line focus.

In a multi-agent system, there are many intelligent agents distributed in the network. To connect with these agents easily and arbitrarily, wireless ad hoc network is a candidate. Wireless ad hoc network is a distinct network environment with characteristics in self-organisation, dynamical network topologies and easy construction. To provide such networks with secure communication, many researchers tried different ways to create the session key(s). However, there are some drawbacks in session key generation procedure, and the robust session key could not be created. The authors propose a cluster-based secure communication mechanism in wireless ad hoc networks. The proposal applies the Diffie-Hellman key exchange protocol for the session key creation. It helps the clusterhead to reduce the communication overload to avoid the time synchronisation problem in nodes authentication and to preserve the complete secrecy requirements.

The rapid development in electronic commerce and information technology drives the traditional physical product trading evolved to digital product trading. With the effect of the multi-agents system in the Internet environment and the promotions of Government, digital product industry grows fast. The authors proposed a digital product transaction mechanism for electronic auction in the multi-agents system environment. The research introduced a convenient platform to protect the privacies of both buyers and sellers, and track digital product further in an electronic auction environment. In addition, by using simple cryptography techniques supplemented with encryption, the authors ensure the security of information transactions, thereby providing a mechanism of safe and fair digital product electronic auction.

Objective To explore the differences in the effectiveness of various teaching methods combining online and offline modes in paediatric medical education. Methods Fourth-year medical paediatric students at our university in 2020 were randomly divided into three groups: a control group, experimental group 1, and experimental group 2, with 30 students in each group. The control group received traditional teaching, experimental group 1 received a combination of online and offline teaching using two methods simultaneously, and experimental group 2, in addition to the methods used in experimental group 1, engaged in real-case teaching in the ward. The teaching outcomes were evaluated through theoretical exams, clinical skills assessments, and questionnaires. Results Experimental groups 1 and 2 were superior to the control group concerning theoretical examination and overall scores ( P  < 0.05). Experimental group 2 was superior to experimental group 1 and the control group in clinical skills examination scores ( P  < 0.05). The satisfaction rate for the questionnaire was highest in experimental group 2 ( P  < 0.05). Conclusion The combined use of various teaching methods with online and offline modes is more effective than using traditional teaching methods only in paediatric education. It enhances the overall competence of paediatric students, especially in terms of improving clinical skills, and is well-received by both students and teachers.