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Five new coordination polymers, namely [Ln(L)(NO3)2] n (Ln = La (1), Pr (2) and Sm (3)), [Eu(L)(NO3)2·1.5H2O] n (4) and [Tb(L)(OAc)2(H2O)·3H2O] n (5) (HOAc = CH3COOH), were synthesised by reaction of lanthanide nitrates with 1,3-bis(4-carboxybenzyl)benzimidazolium chloride (H2L+Cl−) under solvothermal conditions. All the coordination polymers were characterised by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, elemental analysis and single crystal X-ray diffraction. Complexes 1 – 5 exhibit two different 2-D structures due to the variation in reaction temperature. Complexes 1 – 4 are isostructural and crystallised in the monoclinic system, C 2/ c space group, showing a two-dimensional layer with Ln chains linked by L− ligands. Complex 5 crystallised in the P 21/ n space group, featuring a 2-D layer different from 1 – 4 with Tb dimers linked by L− ligands through carboxylates. Further, the luminescence properties of complexes 3 – 5 were investigated. In addition, the fluorescence lifetime and quantum efficiency of complex 4 were measured. Five two-dimensional complexes were obtained and the structures of 1 – 4 differ from that of 5 owing to the distinct coordination modes of the ligand H2L+Cl− at specific reaction temperatures. Further, the luminescence properties of complexes 3 – 5 were investigated. Additionally, the fluorescence lifetime of complex 4 was tested. (Image credit: Li-Xin You.) [ABSTRACT FROM AUTHOR]

BACKGROUND Polymetallic nodules are predominant in deep sea sedimentary mineral resources due to the enrichment of many critical metals. Polymetallic nodules are loose and porous, which is the critical material feature that contributes the adsorption of trace metals from seawater and pore water and then enrichment and mineralization. Therefore, specific surface area (SSA) is one of the key factors for studying the ore-forming process of polymetallic nodules. At present, the methods for SSA determination are well-developed. However, they are less applied in the analysis of the specific surface of polymetallic nodules, and the pretreatment conditions are not constant according to various research targets. OBJECTIVES In order to explore the pretreatment conditions for the BET SSA analysis of polymetallic nodules, and provide necessary parameters for the study of the enrichment of trace metals in polymetallic nodules. METHODS Polymetallic nodules from the Atlantic, Indian, and Pacific oceans were collected. The pretreatment conditions including temperature, duration, and particle size for SSA analysis of polymetallic nodules were studies by applying temperature programming, heating accumulation, and particle size comparing methods. RESULTS The results showed that the analysis values of SSA reached plateau when the heating temperature ranged from 210℃to 350℃. The analysis values of SSA remained constant after heating for 3 hours by a step of 1 hour at 210℃. The SSA values of samples with a size of several millimeters were 1.027-28.535m2/g higher compared with those of the same samples crushed into microns. CONCLUSIONS Reliable SSA values can be obtained when the polymetallic nodules with sizes of several millimeters are heated in a vacuum system for 3 hours at 210℃, which is the pretreatment condition for analyzing SSA of mineralization-related polymetallic nodules.

Tribological properties of oleic acid modified natural serpentine ultrafine mineral powders as lubricating oil additive were investigated by a reciprocating sliding wear tester. The effects of the four factors including load, reciprocating frequency, sliding time and concentration of serpentine on the properties of serpentine additive were analyzed. Results indicate that the anti-wear and friction-reducing properties of the base oil are significantly improved by the addition of the modified serpentine powders. The order that affects the friction-reducing performance of the serpentine additive is:concentration, reciprocating frequency, load, sliding time, and the optimal tribological conditions are 100 N, 5 Hz, 180 min, 0.5%(mass fraction). While that affects the anti-wear property is:load, concentration, reciprocating frequency, sliding time, and the optimal conditions are 100 N, 50 Hz, 180 min, 0.3%. Serpentine minerals forms a tribofilm consisting of various oxides, graphite and organic compounds on the friction surface, which is the key to improving anti-wear and friction-reducing properties.

Small vertical-axis wind turbines are a promising solution for affordable and clean energy, but their noise emissions present a challenge to public acceptance. Numerous blade designs have been aimed at reducing noise but often come with a decrease in wind turbine aerodynamic efficiency. In this study, the acoustic power and torque of a 5 kW vertical-axis wind turbine (VAWT) were simulated by using different mesh sizes and turbulence models. The simulated torque and noise of the turbine have significant sensitivity to the mesh size, so suitable mesh sizes were determined for the near-wall and rotating regions that can be used as a design reference for future turbines with similar operating conditions. The selection of the turbulence model was found to affect the predicted torque by about 10 % and the predicted tip noise by about 2 dB. The selected mesh size and turbulence model were then applied to simulating the effectiveness of three common noise mitigation techniques: a mask, deflector, and wall roughness. The results showed that deflectors are suitable for noise reduction of small VAWTs. This paper provides valuable information on simulating noise propagation from small VAWTs and the optimal noise reduction techniques. [ABSTRACT FROM AUTHOR]

Traditional electronic strain sensors based on metal and semiconductor materials have poor flexibility and wear-ability, which are not applicable for stretchable sensors. With the development of flexible electronic materials, wearable electronic devices show great market prospects. Flexible strain sensors have many unique advantages, such as good biocompatibility, wearable, stretchability and elasticity, which become a hotspot of research. The research progress is the preparation technology, performance and application of PDMS based piezoresistive and capacitive flexible strain sensors were summarized in this paper. Finally, challenges, important directions and perspectives related to PDMS flexible strain sensors were prospected.