Identification of different oxygen species in oxide nanostructures with O-17 solid-state NMR spectroscopy

Nanostructured oxides find multiple uses in a diverse range of applications including catalysis, energy storage, and environmental management, their higher surface areas, and, in some cases, electronic properties resulting in different physical properties from their bulk counterparts. Developing structure-property relations for these materials requires a determination of surface and subsurface structure. Although microscopy plays a critical role owing to the fact that the volumes sampled by such techniques may not be representative of the whole sample, complementary characterization methods are urgently required. We develop a simple nuclear magnetic resonance (NMR) strategy to detect the first few layers of a nanomaterial, demonstrating the approach with technologically relevant ceria nanoparticles. We show that the (17)O resonances arising from the first to third surface layer oxygen ions, hydroxyl sites, and oxygen species near vacancies can be distinguished from the oxygen ions in the bulk, with higher-frequency (17)O chemical shifts being observed for the lower coordinated surface sites. H(2)(17)O can be used to selectively enrich surface sites, allowing only these particular active sites to be monitored in a chemical process. (17)O NMR spectra of thermally treated nanosized ceria clearly show how different oxygen species interconvert at elevated temperature. Density functional theory calculations confirm the assignments and reveal a strong dependence of chemical shift on the nature of the surface. These results open up new strategies for characterizing nanostructured oxides and their applications

Time-Average Heat Transfer Coefficient for Steam-Air Condensation during the Dropping of Containment Pressure

The passive containment cooling system (PCCS) has been applied in the new generation nuclear power plant. Previous studies mainly focused on steady-state heat transfer, but the actual heat transfer of PCCS is the transient process. Thus, investigating the transient heat transfer during the containment pressure dropping is necessary. The present study proposes a time-average condensation heat transfer coefficient (time-average condensation HTC) to characterize the intensity of transient condensation heat transfer. The time-average condensation HTC is defined as the heat absorbed per unit heat transfer area and per unit wall subcooling in a unit time. Experiments were performed to research the effect of initial gas-mixture pressure and air mass fraction on transient HTC. The result showed that the more significant gas-mixture pressure and lower air mass fraction could promote the transient-state heat transfer, especially the low air mass fraction. Based on the experimental result, a detailed empirical correlation for the time-average heat transfer coefficient is developed with an error of ±20%. Another simplified empirical correlation that only includes air mass fraction is also proposed to predict the transient heat transfer roughly. Besides, research on self-sustaining stability is also conducted to evaluate the stable operation characteristic of PCCS. The system can respond quickly and then run to a new steady state after interference during the long-term operation of PCCS. The phenomenon above implies that PCCS has good self-sustaining stability

The MD simulation of friction heat dissipation and generation in high-speed dry sliding system

3D non-equilibrium molecular dynamics simulations are performed to investigate the friction heat dissipation and generation of high-speed sliding system. A sliding simulation model with two blocks is built. The friction heat generation with different materials, different velocities are studied. The mechanism of the heat dissipation at the interface is investigated. The heat partition of different friction system is obtained. The results show that more friction heat will be produced with higher sliding velocity. But in the case with more plastic deformation, less friction heat will be generated. The heat partition is mainly influenced by the friction material and the velocity ratio. The material which has the similar thermodynamic properties will be easier to produce phonon with similar spectrum

Theoretical Study on the Dynamic Characteristics of Marine Stern Bearing Considering Cavitation and Bending Deformation Effects of the Shaft

When the ship runs, owing to the superposition of the gravity of the shaft and resistance of water, with the increment in rotational speeds, the shaft will produce different degrees of bending deformation, which immensely reduces the power transmission efficiency. Based on the aforementioned problem, the present study focuses on the influences of bending deformation of the shaft with a cavitation effect on the dynamic characteristics of the stern bearing. The mixed lubrication model with bending deformation and cavitation effect is established. At present, the deflection curve equation is employed, the finite perturbation method is applied to calculate the dynamic coefficient, and the cavitation pressure is determined by the numerical method. According to the analysis, the variation laws of equivalent stiffness and natural frequency are exhibited. It is shown that the equivalent stiffness is more affected by the speeds, especially at low speeds; There is a critical speed between 130 rpm and 150 rpm, which makes the natural frequency strike the maximum value. Finally, the research results provide a theoretical basis for the ships to avoid large vibration during navigation

Theoretical Study on the Dynamic Characteristics of Marine Stern Bearing Considering Cavitation and Bending Deformation Effects of the Shaft

When the ship runs, owing to the superposition of the gravity of the shaft and resistance of water, with the increment in rotational speeds, the shaft will produce different degrees of bending deformation, which immensely reduces the power transmission efficiency. Based on the aforementioned problem, the present study focuses on the influences of bending deformation of the shaft with a cavitation effect on the dynamic characteristics of the stern bearing. The mixed lubrication model with bending deformation and cavitation effect is established. At present, the deflection curve equation is employed, the finite perturbation method is applied to calculate the dynamic coefficient, and the cavitation pressure is determined by the numerical method. According to the analysis, the variation laws of equivalent stiffness and natural frequency are exhibited. It is shown that the equivalent stiffness is more affected by the speeds, especially at low speeds; There is a critical speed between 130 rpm and 150 rpm, which makes the natural frequency strike the maximum value. Finally, the research results provide a theoretical basis for the ships to avoid large vibration during navigation

Research on 3D Path Planning of Quadrotor Based on Improved A* Algorithm

Considering the complexity of the three-dimensional environment and the flexibility of the quadrotor aircraft, using the traditional A* algorithm for global path planning has the disadvantages of less search direction, more expanded nodes, and a longer planning path. Therefore, an improved A* algorithm is proposed, which is improved from two aspects. Firstly, a two-layer extended neighborhood strategy is proposed, which can increase the search direction and make better use of the flexibility of the aircraft. Secondly, the heuristic function is improved to make the heuristic function value closer to the actual planning path distance, which can reduce the expansion nodes and optimize the planning path. Finally, the path planning simulation of the improved A* algorithm is carried out and the results show that the path planned by the improved algorithm is shorter and the expanded nodes are fewer, which can guide the quadrotor to reach the destination better

Improving Nelumbo nucifera genome assemblies using high-resolution genetic maps and BioNano genome mapping reveals ancient chromosome rearrangements

individuals and validated by adding 197 simple sequence repeat (SSR) markers. Additionally, a BioNano optical map covering 86.20% of the 'Chinese Tai-zi' genome was constructed. The draft assembly of 'Chinese Tai-zi' was improved based on the BioNano optical map, showing an increase of the scaffold N50 from 0.989 Mb to 1.48 Mb. Using a combination of multiple maps, 97.9% of the scaffolds in the 'Chinese Tai-zi' draft assembly and 97.6% of the scaffolds in the 'China Antique' draft assembly were anchored into pseudo-chromosomes, and the centromere regions along the pseudo-chromosomes were identified. An evolutionary scenario was proposed to reach the modern N. nucifera karyotype from the seven ancestral eudicot chromosomes. The present study provides the highest-resolution linkage map, the optical map and chromosome level genome assemblies for N. nucifera, which are valuable for the breeding and cultivation of N. nucifera and future studies of comparative and evolutionary genomics in angiosperms. This article is protected by copyright. All rights reserved

Supramolecular Chemistry of Cucurbiturils: Tuning Cooperativity with Multiple Noncovalent Interactions from Positive to Negative

Rational control of the cooperativity of multiple noncovalent interactions often plays an important role in the design and construction of supramolecular self-assemblies and materials, especially in precision supramolecular engineering. However, it still remains a challenge to control the cooperativity of multiple noncovalent interactions through tuning the hydrophobic effect. In this work, we demonstrate that the binding cooperativity of cucurbit[8]­uril­(CB[8])-mediated homoternary complexes is strongly influenced by the amphiphilicity of guest molecule side groups on account of an interplay between both classical (entropy-driven) and nonclassical (enthalpy-driven) hydrophobic effects. To this end, we rationally designed and prepared a series of guest molecules bearing a benzyl group as the CB[8] homoternary binding motif with various hydrophilic and hydrophobic side groups for cooperative control. By gradually tuning side groups of the guest molecules from hydrophilic to hydrophobic, we are able to control the binding from positive to negative cooperativity. An advanced molecular recognition process and self-assembling system can be developed by adjusting the positive and negative cooperativity. The ability to regulate and control the binding cooperativity will enrich the field of supramolecular chemistry, and employing cooperativity-controlled multiple noncovalent interactions in precision supramolecular engineering is highly anticipated