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The ultimate particle size distribution of uniform and gap-graded soils is examined on specimens of carbonate sand that were subjected to large strains in a ring shear apparatus. The gap-graded soils were seen to retain a memory of their initial grading even at large strains. The particle size distributions were plotted in double logarithmic graphs either by mass or by number computed assuming different shapes. It was not possible to find linear subsets of the data, and since the samples were found experimentally to have converged to an ultimate grading, this suggests that the initial bimodal distribution prevented reaching an ultimate fractal distribution. Plots of the probability density functions of the particle sizes before and after shearing show the evolution of the gap-graded soils from a bimodal to a multi-modal distribution. This is accompanied by an evolution of the shape of the particles, visible in microphotographs and projections of the grains before and after test.

Background Toddalia asiatica root bark as an effective hemostatic natural medicine or Chinese materia medica was applied in China for long history, its complex drug action mechanisms and unclear substance basis have been constraining the development of this drug.ResultsAn intelligentized strategy by LC-ESI Q-TOF MSE was presented in this study for rapid identification of hemostatic chemical constituents from this natural medicine. Chromatographic separation was performed on a C18 column (150 mm × 2.1 mm, 1.8 μm), the MSE data in both negative and positive ion modes were acquired to record the high-accuracy MS and MS/MS data of all precursor ions. To reduce the false positive identifications, structural confirmation was conducted by comparison with the isolated reference standards (tR and MS, MS/MS data) or matching with natural product databases. Bioassay-guided fractionation of the extract of T. asiatica root bark was also carried out.ConclusionsAs a consequence, 31 natural compounds in T. asiatica root bark got putatively characterized. There were four main coumarins, isopimpinellin (Cp.23), pimpinellin (Cp.24), coumurrayin (Cp.30) and phellopterin (Cp.34) isolated and identified from T. asiatica root bark. The present study provided candidate strategy that helps to effectively identify the primary natural compounds of TCM or other complex natural medicines, and then promote development and application of natural medicines and their medicinal resources.

Based on the deep study of the mechanism of coal spontaneous combustion, this paper proposes new efficient inhibitors preventing coal spontaneous combustion from the perspective of inhibition of free-radical chain reactions. Chifeng coal samples were used as the research object, and six different types of antioxidants were selected as the inhibitor for low-temperature oxidation experiments. A comparison study of the gas product concentration before and after inhibition was conducted; its inhibition mechanism was also studied and analyzed. On the basis of this, the specific indicators, such as cross-point temperature (CPT), apparent activation energy, active functional groups, and an inhibitory rate at 100 °C were used to compare the inhibition effect of antioxidants. The experiments indicate that, except for oxygen-scavenger ascorbic acid, another five antioxidants (butylated hydroxytoluene, BHT; triphenyl phosphite, TPPI; 2,2,6,6-tetramethyl-1-piperidine-noxyl free radical, TEMPO; edetic acid, EDTA; and phytic acid, PA) exhibit a good inhibition effect, and the order of inhibitory effect is R TEMPO > R BHT > R EDTA > R TPPI > R PA , indicating that TEMPO has the best inhibition effect with the activation energy of coal oxidation increased by 14.79 kJ•mol −1 , and the inhibition rate reached 73.08%. The research results provide new ideas for the prevention and control of coal spontaneous combustion.

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