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To solve multitarget tracking (MTT) problems with coloured measurement noise, this study proposes a Poisson multi‐Bernoulli mixture filter with coloured measurement noise (PMBM‐CMN) and a robust PMBM‐CMN filter. By using the measurement differencing method and state augmentation approach, the proposed PMBM‐CMN filter transforms a state estimation problem with coloured measurement noise into a problem with white measurement noise. However, covariances of the true process and measurement noise in the proposed PMBM‐CMN filter are time‐varying and unknown, which may degrade the filtering performance. Therefore, a robust PMBM‐CMN filter is proposed for estimating the augmented state, including the kinematic state, the predicted state covariance, and the white measurement noise covariance. For linear Gaussian systems, the augmented state is modelled as a Gaussian inverse Wishart inverse Wishart (GIWIW) distribution. The variational Bayesian method is also employed to guarantee the conjugacy of the GIWIW density. Simulation results demonstrate the ability of the PMBM‐CMN filter to solve MTT problems with coloured measurement noise and show that the robust PMBM‐CMN filter based on the GIWIW model (GIWIW‐PMBM‐CMN) has the best overall performance in comparison with existing state‐of‐the‐art filters. [ABSTRACT FROM AUTHOR]

To explore the influence of initial damage on the dynamic characteristics of rock mass, the Φ 50 mm split Hopkinson pressure bar (SHPB) test system was used, and the uniaxial impact compression tests on yellow sandstone specimens with different damage degrees were conducted, and then the variation law of mechanical properties of rock specimens with the initial damage was determined. The test results show that the dynamic stress-strain curve of rock specimens with initial damage can be roughly divided into compaction stage, elastic deformation stage, crack evolution stage, and strain-softening stage; the higher the initial damage degree of rock mass, the more significant the compaction stage. With the increase of the initial damage degree, the dynamic elastic modulus and peak stress of rock mass decrease gradually in a power number, while the peak strain of rock mass increases exponentially. With the increase of the initial damage degree, both the reflected energy ratio and the dissipated energy ratio decrease linearly, while the transmitted energy ratio increases linearly; the increasing rate of the transmitted energy ratio is greater than the decreasing rate of the reflected energy ratio. [ABSTRACT FROM AUTHOR]

Rockburst frequently occurred in an unstable or violent manner, which posed great safety risk and economic loss in deep underground engineering. The water injection into rock stratum was one of the most effectively ways to reduce rockburst by weakening rock mechanics. However, the moisture content was an important index related to rock mechanical properties. Many previous studies focused on the relationship between the moisture contents and macromechanical properties of rock materials under static load and seldom explored the impact of moisture variation on the mechanical properties and brittle-ductile transition characteristics of rock materials under dynamic loads. In this paper, we studied the dynamic mechanical properties of sandstone with different moisture contents under the same strain rate by the Split Hopkinson Pressure Bar (SHPB) experimental system. The relationship between dynamic mechanical properties of sandstone and moisture content was studied, and a dynamic ductility coefficient was proposed, which could be determined by the ratio between the peak strain and the yield strain. Then, it was used to assess the critical moisture content of the brittle-ductile transition of the sandstone. Through scanning electron microscopy (SEM) examination, the microstructure of sandstones with different moisture contents was inspected at magnifications of 500, 2000, and 5000 times, respectively. We showed that as the moisture content increased, the dynamic peak strength and elastic modulus decreased at different degrees, whereas the dynamic peak strain and ductility coefficient exhibited a nonlinear increase, respectively. When the moisture content reached 2.23%, the variation ratio of the dynamic ductility coefficient commenced to increase obviously, indicating that the sandstone began to transit from brittle behavior to ductile behavior. When the sample magnification was 500 times, the microstructure of the sandstone samples with zero and 2.01% to 2.40% moisture content mainly displayed the step pattern and river pattern, respectively, showing that the damage mode was brittle fracture. When the moisture content ranged from 2.49% to 2.58%, the microstructure of the sample included a large number of dimple clusters with local snake patterns and belonged to ductile fracture. When the sample magnification was 2000 and 5000 times, the microstructure was mainly brittle fracture with a moisture content lower than 2.23%. The microstructure of the sample with moisture content of 2.23% exhibited brittle-ductile composite fracture form, whereas others exhibited obviously ductile fracture. These characteristics were fundamentally consistent with the results reflected by the dynamic ductility coefficient. Our findings could provide a theoretical basis for mitigating coal and rock bursts by injecting water methods in underground coal mines. [ABSTRACT FROM AUTHOR]

Solid backfill coal mining (SBCM) is a green mining technology which can effectively alleviate the environmental problems induced by traditional coal mining techniques, such as surface subsidence, water resources loss, coal gangue occupation, and pollution. In this study, a multilayer Winkler foundation beam model for the overburden key strata is proposed, and the model with two key strata is solved. The subsidence, rotating angle, inner force, and stress of the overburden key strata are systematically analyzed under various backfill elastic modulus, mining height, and soft layer thickness. The results show that the subsidence of the key strata exhibit "basin"-shape curves, and the backfill elastic modulus, mining height, and the thickness of the soft strata have significant influences on the subsidence of the key strata. The shear stress, horizontal stress, and vertical stress of key stratum can be effectively reduced by increasing the backfill elastic modulus. The increase of mining height has little influence on the stress of key stratum that close to the coal seam (key stratum #1), but has a significant effect on the stress of key stratum that above the soft layers (key stratum #2). On the contrary, the effect of increasing soft layer thickness on the stress of key stratum is opposite to that of increasing mining height. In addition, the shear failure of key stratum #1 at mining boundary and the tensile failures on both sides of mining boundary should be preferentially considered in SBCM engineering design. Due to the low shear stress level of key stratum #2, the tensile failure on both sides of the mining boundary should be mainly considered. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) direction-of-arrival (DOA) estimation with arbitrary planar sparse array has attracted more interest in massive multiple-input multiple-output application. The research on this issue recently has been advanced with the development of atomic norm technique, which provides super resolution methods for DOA estimation, when the number of snapshots is limited. In this paper, we study the problem of 2D DOA estimation from the sparse array with the sensors randomly selected from uniform rectangular array. In order to identify all azimuth and elevation angles of the incident sources jointly, the 2D atomic norm approach is proposed, which can be solved by semidefinite programming. However, the computational cost of 2D atomic norm is high. To address this issue, our work further reduces the computational complexity of the problem significantly by utilizing the atomic norm approximation method based on the concept of multiple measurement vectors. The numerical examples are provided to demonstrate the practical ability of the proposed method to reduce computational complexity and retain the estimation performance as compared to the competitors. [ABSTRACT FROM AUTHOR]

In order to explore the influence of the porosity change on the mechanical properties and energy dissipation of concrete materials in the construction of sponge city, we design concrete with porosity of 12%, 15%, 18% and 21% respectively. Uniaxial compression tests are performed on the four kinds of porosity concrete by using a universal testing machine. The stressstrain curvesis obtained from these tests. The following results are obtained by analyzing the test data: with the increase of porosity, the elastic modulus, peak stress and Poisson's ratio of concrete gradually decreased, and the peak strain increased gradually:with the increase of porosity, the total absorption energy and elastic energy of the concrete gradually decrease, and the dissipation energy first decreases and then increases. [ABSTRACT FROM AUTHOR]

Rockburst frequently occurs in deep underground engineering, which poses a threat to safety and causes economic losses. Water injection into surrounding rock masses is an effective method for preventing rockburst, and the moisture content of rocks is significant for assessing the probability of rockburst. However, the majority of studies focus on the relationship between the macromechanical properties of rock masses under static loads and the moisture content of rock masses and seldom explore the impact of moisture variation (under dynamic loads) on the mechanical properties and energy dissipation. In this paper, the mechanical properties and energy dissipation of sandstone with different moisture contents have been experimentally investigated by the split Hopkinson pressure bar (SHPB) test. The test results indicate that the peak strength, dynamic elastic modulus, and unloading elastic modulus of sandstone in dry conditions are considerably larger than those in moisture conditions, and the three parameters linearly decrease as the moisture content increases from 0% to 2.58%. The distribution law of sandstone fragments with different moisture contents has been investigated by sieving test fragments with different grain sizes of grading sieves. The results show that the percentage of large grain size fragments incrementally decreases, and the percentage of small grain size fragments incrementally increases with moisture contents from 0% to 2.58%. When the moisture content ranges from 2.01%∼2.58%, the fractal dimension linearly increases, which indicates that the higher the moisture content is, the larger the dimension of the broken sandstone is. The calculation results for energy indicate that the sandstone energy attains the peak value with 0% moisture content. When the moisture content ranges from 2.01%∼2.58%, the reflected energy increases, and the transmitted energy and dissipated energy linearly decrease. In addition, the surface energy of the sandstone with different moisture contents has been investigated by converting fragments into spheres with the corresponding size. The results indicate that the smallest surface area of sandstone is obtained in dry conditions, but its surface energy in dry conditions is larger than that in moisture conditions. When the moisture ranges from 0% to 2.58%, due to 3% illite and 2% chlorite clay minerals reacting with different proportions of moisture, the surface areas of sandstone fragments linearly increase and the surface energy of sandstone linearly decreases. [ABSTRACT FROM AUTHOR]

The instability of layer-crack plate structure in coal wall is one of the causes of rock burst. In the present paper, we investigate the formation and instability processes of layer-crack plate structure in coal wall by experiments and theoretical analysis. The results reveal that layer-crack plate structure formed near the free surface of the coal wall during the loading. During the formation of the layer-crack plate structure, the lateral displacement curve of the coal wall experiences a jagged variation, which suggests the nonlinear instability failure of the coal wall with a sudden release of the elastic energy. Then, a dynamic model for the stability analysis of the layer-crack plate structure was proposed, which takes consideration of the dynamic disturbance factor. Based on the dynamic model, the criterion for dynamic instability of the layer-crack plate structure was determined and demonstrated by an example. According to the analytical results, some control methods of dynamic stability of the layer-crack plate structure was put forward. [ABSTRACT FROM AUTHOR]

Many projects such as the underground gasification of coal seams and coal-bed methane mining (exploitation) widely involve the dynamic problems of coal measures sandstone achieved via thermal treatment. This study examines the dynamic mechanical properties of coal measures sandstone after thermal treatment by means of an MTS653 high-temperature furnace and Split Hopkinson pressure bar test system. Experimental results indicate that 500 °C is a transition point for the dynamic mechanical parameters of coal measures sandstone. The dynamic elastic modulus and peak strength increase linearly from 25 to 500 °C while the dynamic peak strain decreases linearly over the same temperature range. The dynamic elastic modulus and peak strength drop quickly from 500 to 800 °C, with a significant increase in the dynamic peak strain over the same temperature range. The rock mechanics are closely linked to material composition and mesoscopic structure. Analysis by X-ray diffraction and scanning electron microscopy indicate that the molecules inside the sandstone increase in density due to the thermal expansion of the material particles, which effectively improves the deformation resistance and carrying capacity of the sandstone and reduces the likelihood of axial deformation. With heat treatment that exceeds 500 °C, the dynamic mechanical properties rapidly weaken due to the decomposition of kaolinite; additionally, hot cracking of the mineral particles within the materials arises from coal sandstone internal porosity, and other defects gradually appear. [ABSTRACT FROM AUTHOR]

The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures ranging from room temperature to 800°C Results show that (1) the peak strength and elastic modulus of marble fluctuate at the temperature from normal to 400°C; and they decrease gradually over 400°C (2) With the rise of the temperature, the peak strength and elastic modulus of limestone show downward trend from normal temperature to 200°C have little change from 200°C to 600°C and decrease sharply over 600°C (3) The peak strength of sandstone shows a downward trend while a little change for elastic modulus at normal temperature to 200°C and from 200°C to 600°C, the peak strength of sandstone increases while a little change for elastic modulus; the peak strength and elastic modulus decrease rapidly at the temperature over 600°C. (4) The peak strain of limestone shows little change at normal temperature to 600°C, however, the peak strain increases rapidly over 600°C; and for marble and sandstone, the peak strain decreases with the rise of the temperature from normal temperature to 200°C, the peak strain increases rapidly over 200°C. The result can provide valuable references for the rock engineering design at high temperature. [ABSTRACT FROM AUTHOR]

2-Aryl-spiro-[5,5]-1,3,2-dioxaphosphorinane-2-sufides were prepared by the cyclization reaction of Lawesson's reagent with pentaerythritol and monobenzalpentaerythritol, respectively. [ABSTRACT FROM AUTHOR]