The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased.
Journal of Geographical Sciences - Mountains in western China, hosted rich biodiversity and millions of people and inhabitant with vital ecosystem services, had experienced the most serious... 相似文献
Through theoretical analysis and computer simulation,this short communication comments on theresidual bilinearization(RBL)method and compares it with non-bilinear rank annihilation(NBRA)forthe treatment of second-order calibration with non-bilinear data.It is found that these two methods aremathematically equivalent but have different noise propagation properties.The second-order advantage,namely quantitation in the presence of unknown interferences,can be carried over to non-bilinear dataonly if there exists a net analyte rank(NAR)for the analyte of interest. 相似文献
Multivariate outliers in environmental data sets are often caused by atypical measurement error in a singlevariable.From a quality assurance perspective it is important to identify these variables efficiently so thatcorrective actions may be performed.We demonstrate a procedure for using two multivariate tests toidentify which variable‘caused’each outlier.The procedure is tested with simulated data sets that havethe same correlation structure as selected water chemistry variables from a survey of lakes in the WesternUnited States.The success rates are evaluated for three of the variables for sample sizes of 50 and 100,significance levels of 0.01 and 0.05 and various amounts of mean shift.The procedure works best forhighly correlated variables. 相似文献
For ease in discerning an Antarctic circumpolar wave in the perimeter of the ice pack, we construct a time series of the sea ice extents (essentially the area within the ice perimeter) in 1-degree longitudinal sectors for the period 1978–1996, as observed with the multichannel microwave imagers on board the NASA Nimbus 7 and the DOD (Dept. of Defense) DMSP (Defense Meteorological Satellite Program) F8. F11, and F13 satellites. After converting the time series into complex numbers by means of a Hilbert transform, we decompose the time series of the 360 sectors into its complex principal components (CPCs), effectively separating the spatial and temporal values. Then we decompose the real and imaginary parts of the temporal portions of the first three CPCs (complex principal compenents) by Empirical Mode Decomposition into their intrinsic modes, each representing a narrow frequency band, resulting in a collection of three CPCs for each intrinsic mode. Finally, we reconstruct the data in two different ways. First, we low-pass filter the data by combining all of the intrinsic modes of each CPC with periods longer than two years, which we designate as low-pass filtered. Next, we select the intrinsic mode of each CPC with periods of approximately four years, which we designate the quasiquadrennial (QQ) modes. The low-pass filtered time series shows eastward propagating azimuthal motion in the Ross and Weddell Seas, but no clearly circumpolar motion. The QQ time series, on the other hand, clearly shows castward propagating circumpolar waves, but with occasional retrograde motion to the west. 相似文献
As a solid reservoir, a glacier can regulate regional water resources. The annual net mass balance directly reflects the
fluctuation of the glacier and climate variability. Based on 51 years of mass balance observation data, the mass balance of
Tianshan Mountains Urumqi Glacier No. 1 experienced a nine times positive balance fluctuation and nine times negative
balance fluctuation. There were 35 and 16 negative and positive balance years, respectively. From 1996/97 to 2008/09, 12
consecutive negative balance years were observed at Tianshan Mountains Urumqi Glacier No. 1. These results demonstrate
that the Urumqi Glacier No. 1 is experiencing a strong negative balance, and the strongest negative balance, -931
mm w.e. (mm water equivalent), during the observation period occurred in 2008. In addition, the cumulative mass balance
reached 13,709 mm w.e. in 2008. However, in 2009, the mass balance was positive at 63 mm w.e. The equilibrium-line altitude
changes with the fluctuation in the mass balance, and the effective mass balance gradient is 7.4 mm/m. In this paper,
the headwaters of the Urumqi River were analyzed using meteorological data from 1958 to 2009, including the average
seasonal temperature and precipitation. The results showed that the main factor associated with the mass balance variation
of Glacier No. 1 is the fluctuation in the summer air temperature, followed by changes in the precipitation. 相似文献
Inequality has been the subject of intense debates in China, but inequality across cities remains less studied. This article investigates economic inequality based on prefectural-level cities during the period from 1990 to 2010. Statistical analyses indicate that interregional inequality among cities has increased, which is mostly attributable to widening intraregional inequality, especially within the western region. The high gross domestic product (GDP) per capita clusters emerged in the Pearl River Delta in the 1990s, spread to the Yangtze River Delta in the 2000s, and then reached north China in the 2010s. In contrast, the number of low GDP per capita clusters significantly increased in the central and western regions in the 2010s. In addition, the significance of national development zones and foreign direct investment indicates the greatest effect of globalization on the increasing intercity inequality. Decentralization also contributes to the intercity inequality of China. We suggest that in addition to national programs aimed at reducing the inequality between the eastern region and the rest of China, efforts are needed to reduce inequality within each region through provincial and local government policies, especially in western China. Key Words: China, cluster, decentralization, globalization, regional inequality, urban inequality.相似文献