Experimental Study on Shear Mechanical Properties and Section Morphology of Coal Samples

The mechanical properties of rocks under cyclic and dynamic loading are important research topics for solving the structural stability of large engineering rocks. As underground mining in coal mines goes deeper, ground stresses are increasing and instability damage of coal rocks by shear loading is frequent. Therefore, in order to investigate the shear mechanical properties and section morphological characteristics of intact coal samples in the direct shear test, the RDS-200 rock direct shear instrument was used to carry out direct shear tests on intact coal samples under different normal stresses, and the shear section was scanned for three-dimensional morphology. The results show that: 1) from the strength characteristics, the peak shear strength of the coal samples increased linearly with increasing normal stress, and the residual shear strength increased logarithmically. 2) In terms of deformation characteristics, the peak shear displacement of the coal sample increases linearly with increasing normal stress, the pre-peak shear stiffness increases logarithmically, and the residual normal displacement decreases linearly. 3) From the morphological characteristics of the shear surface, with the increase of normal stress, the section transitions from high-order undulating to flattening type. The maximum height of the fracture surface profile and kurtosis coefficient of the shear section decreased linearly, and the profile area ratio and root mean square of slope decreased as a power function, i.e. the higher the normal stress, the smaller the undulation of the section, the sharpness of the roughness shape and the roughness coefficient JRC, and the flatter and smoother the section. The findings of this study can help to provide some reference for the evaluation of shear instability occurring in coal bodies under different normal stresses.

Thermo-Economic Performance of Geothermal Driven High-Temperature Flash Tank Vapor Injection Heat Pump System:A Comparison Study

Process heating constitutes a significant share of final energy consumption in the industrial sector around the world.In this paper,a high-temperature heat pump(HTHP)using flash tank vapor injection technology(FTVI)is proposed to develop low-temperature geothermal source for industrial process heating with temperature above 100°C.With heat sink output temperatures between 120°C and 150°C,the thermo-economic performance of the FTVI HTHP system using R1234ze(Z)as refrigerant is analyzed and also compared to the single-stage vapor compression(SSVC)system by employing the developed mathematical model.The coefficient of performance(COP),exergy efficiency(ηexe),net present value(NPV)and payback period(PBP)are used as performance indicators.The results show that under the typical working conditions,the COP andηexe of FTVI HTHP system are 3.00 and 59.66%,respectively,and the corresponding NPV and PBP reach 8.13×106 CNY and 4.13 years,respectively.Under the high-temperature heating conditions,the thermo-economic performance of the FTVI HTHP system is significantly better than that of the SSVC system,and the larger the temperature lift,the greater the thermo-economic advantage of the FTVI HTHP system.Additionally,the FTVI HTHP system is more capable than the SSVC system in absorbing the financial risks associated with changes of electricity price and natural gas price.

Surface ligand modified cesium lead bromide/silica sphere composites for low-threshold upconversion lasing

In recent years,all-inorganic halide perovskite quantum dots(QDs)have drawn attention as promising candidates for photodetectors,light-emitting diodes,and lasing applications.However,the sensitivity and instability of perovskite to moisture and heat seriously restrict their practical application to optoelectronic devices.Recently,a facile ligand-engineering strategy to suppress aggregation by replacing traditional long ligands oleylamine(OAm)during the hot injection process has been reported.Here,we further explore its thermal stability and the evolution of photoluminescence quantum yield(PLQY)under ambient environment.The modified CsPbBr_(3)QDs film can maintain 33%of initial PL intensity,but only 17%is retained in the case of unmodified QDs after 10 h continuous heating.Further,the obtained QDs with higher initial PLQY(91.8%)can maintain PLQY to 39.9%after being continuously exposed in air for 100 days,while the PLQY of original QDs is reduced to 5.5%.Furthermore,after adhering CsPbBr3 QDs on the surface of a micro SiO_(2)sphere,we successfully achieve the highly-efficient upconversion random laser.In comparison with the unmodified CsPbBr_(3)QDs,the laser from the modified CsPbBr_(3)QDs presents a decreased threshold of 79.81μJ/cm^(2)and higher quality factor(Q)of 1312.This work may not only provide a facile strategy to synthesize CsPbBr_(3) QDs with excellent photochemical properties but also a bright prospect for high-performance random lasers.

Nonlinear optical properties of CsPbCl_(x)Br_(3-x)nanocrystals embedded glass

All-inorganic perovskite has attracted significant attention due to its excellent nonlinear optical characteristics.Stable and low-toxic perovskite materials have great application prospects in optoelectronic devices.Here,we study the nonlinear optical properties of CsPbCl_(x)Br_(3-x)(x=1,1.5,2)nanocrystals(NCs)glass by open-aperture Z-scan.It is found that the two-(2 PA)and three-photon absorption(3 PA)intensity can be adjusted by the treatment temperature and the ratio of halide anions.The perovskite NCs glass treated at a high temperature has better crystallinity,resulting in stronger nonlinear absorption performance.In addition,the value of the 2 PA parameter of CsPbCl_(1.5)Br_(1.5)NCs glasses decreases when the incident pump intensity increases,which is ascribed to the saturation of 2 PA and population inversion.Finally,the research results show that the 2 PA coefficient(0.127 cm GW-1)and 3 PA coefficient(1.21×10^(-5)cm^(3)GW-2)of CsPbCl_(1)Br_(2)NCs glass with high Br anion content are larger than those of CsPbCl_(2)Br_(1)and CsPbCl_(1.5)Br_(1.5)NCs glasses.This is mainly due to the greater influence of Br anions on the symmetry of the perovskite structure,which leads to the redistribution of delocalized electrons.The revealed adjustable nonlinear optical properties of perovskite NCs glass are essential for developing stable and high-performance nonlinear optical devices.