A novel binary effective medium model to describe the prepeak stressstrain relationship of combined bodies of rock-like material and rock

Combined bodies of rock-like material and rock are widely encountered in geotechnical engineering,such as tunnels and mines.The existing theoretical models describing the stress-strain relationship of a combined body lack a binary feature.Based on effective medium theory,this paper presents the governing equation of the“elastic modulus”for combined and single bodies under triaxial compressive tests.A binary effective medium model is then established.Based on the compressive experiment of concretegranite combined bodies,the feasibility of determining the stress threshold based on crack axial strain is discussed,and the model is verified.The model is further extended to coal-rock combined bodies of more diverse types,and the variation laws of the compressive mechanical parameters are then discussed.The results show that the fitting accuracy of the model with the experimental curves of the concretegranite combined bodies and various types of coal-rock combined bodies are over 95%.The crack axial strain method can replace the crack volumetric strain method,which clarifies the physical meanings of the model parameters.The variation laws of matrix parameters and crack parameters are discussed in depth and are expected to be more widely used in geotechnical engineering.

Analysis of Pesticide Residues in Vegetables by Enzyme Inhibition Colorimetric Kit

[Objectives]The paper was to understand the detection effect of commercial enzyme inhibition colorimetric kit.[Methods]Six brands of kits were used to detect pesticide residues in vegetables.The detection results were compared with those of 50 kinds of organophosphorus pesticides and 10 kinds of carbamate pesticides detected by chromatography and mass spectrometry.According to different thresholds,the test results of different kits were evaluated,and the false positive rate,false negative rate and coincidence rate of each kit were obtained.The test results of commercial enzyme inhibition colorimetric kits were compared and analyzed.[Results]The detection effect of kit D was the best among the 6 brands of kits,and the coincidence rate was the highest under the 7 thresholds.There was a certain relationship between the detection effect of commercial enzyme inhibition colorimetric kit and the determination threshold of positive samples.The false positive rate decreased with the increase of determination threshold,and the false negative rate increased with the increase of determination threshold,but the coincidence rate with chromatography and mass spectrometry can not reach 100%.When the threshold was set to 20%,the effect was the best.The coincidence rate of 3 brands of kits with the results of chromatography and mass spectrometry was the highest,and none of the 6 kits involved in the comparison had the lowest coincidence rate under this threshold.[Conclusions]It is suggested to modify the threshold values in national standard and trade standard.