Constitutive Model and Fracture Failure of Sandstone Damage under High Temperature-Cyclic Stress.

Deformation and damage characteristics of high-temperature rocks during underground coal gasification are the fundamental mechanical problems encountered in coal-bed gasification production. In order to study the characteristics of deformation and damage processes of rocks under the joint action of high temperature and high stress, a damage intrinsic model under the joint action of high temperature-cyclic loading is needed. In this paper, we used the damage mechanics theory to establish the damage instantiation model of rocks under the joint action of high temperature loads based on the Mohr-Coulomb strength criterion. It was found that the higher the temperature, the lower the strength of sandstone, the lower the peak stress, and the higher the peak strain, the peak stress decreased from 95.6 MPa at room temperature to 74.8 MPa at 400 °C to 49.5 MPa at 800 °C, and the peak strain increased from room temperature to 400 °C to 800 °C by 27.9% and 33.4%, respectively. With the increase in temperature, the internal microcracks of sandstone increased and expanded, which caused the degree of damage to intensify, and the macroscopic expression was the reduction in strength and stiffness of the sandstone. The rock went through four stages from loading to damage, including damage weakening, plastic deformation, strain softening, and residual deformation. The four types of fractures that led to the overall rupture of the rock were open fracture, secondary coplanar fracture, secondary inclined fracture, and oblique fracture. The damage intrinsic model constructed in this paper could better reflect the damage process of thermally damaged sandstone under the action of periodic loading, and had certain rationality. The damage intrinsic evolution curve, as well as the damage mechanism of sandstone under the action of macroscopic high temperature-loading, were discussed from the perspective of microscopic damage evolution, and the fracture extension pattern and penetration mechanism of the rock under different temperatures were analyzed. The research results provide an important reference for the design and engineering application of gasifiers in coal-bed underground gasification projects.

A Total Lp-Norm Optimization for Bearing-Only Source Localization in Impulsive Noise with SαS Distribution.

This paper considers the problem of robust bearing-only source localization in impulsive noise with symmetric α-stable distribution based on the Lp-norm minimization criterion. The existing Iteratively Reweighted Pseudolinear Least-Squares (IRPLS) method can be used to solve the least LP-norm optimization problem. However, the IRPLS algorithm cannot reduce the bias attributed to the correlation between system matrices and noise vectors. To reduce this kind of bias, a Total Lp-norm Optimization (TLPO) method is proposed by minimizing the errors in all elements of system matrix and data vector based on the minimum dispersion criterion. Subsequently, an equivalent form of TLPO is obtained, and two algorithms are developed to solve the TLPO problem by using Iterative Generalized Eigenvalue Decomposition (IGED) and Generalized Lagrange Multiplier (GLM), respectively. Numerical examples demonstrate the performance advantage of the IGED and GLM algorithms over the IRPLS algorithm.

X-ray Pulsar-Based Navigation Considering Spacecraft Orbital Motion and Systematic Biases.

The accuracy of X-ray pulsar-based navigation is greatly affected by the Doppler effect caused by the spacecraft orbital motion and the systematic biases introduced by the pulsar directional error, spacecraft-borne clock error, etc. In this paper, an innovative navigation method simultaneously employing the pulse phase (PP), the difference of two neighbor PPs (DPP) and the Doppler frequency (DF) of X-ray pulsars as measurements is proposed to solve this problem. With the aid of the spacecraft orbital dynamics, a single pair of PP and DF relative to the spacecraft's state estimation error can be estimated by using the joint probability density function of the arrival photon timestamps as the likelihood function. The systematic biases involved to the PP is proved to be nearly invariant over two adjacent navigation periods and the major part of it is eliminated in the DPP; therefore, the DPP is also exploited as additional navigation measurement to weaken the impact of systematic biases on navigation accuracy. Results of photon-level simulations show that the navigation accuracy of the proposed method is remarkably better than that of the method only using PP, the method using both PP and DF and the method using both PP and DPP for Earth orbit.

An Energy Efficient Synchronization Protocol for Target Tracking in Wireless Sensor Array Networks.

Time synchronization is an important middleware function that supports the Quality of Service (QoS) of systems in wireless sensor array networks. Instead of providing high synchronization accuracy for all application scenarios, we argue that synchronization protocols should be application specific. In this paper, we exploit the synchronization requirements of target-tracking systems in wireless sensor array networks and propose an energy-efficient Sensor Array Synchronization Protocol (SASP), which provides the required synchronization accuracy to guarantee the QoS. Specifically, when no target appears, to guarantee system lifetime, coarse synchronization is achieved with little overhead by piggybacking time information onto periodical network maintenance packets. Once targets appear, SASP achieves high inter-array and relatively higher intra-array synchronization accuracy rather than the traditional network-wide high accuracy on average. In this way, it guarantees reliable communication and accurate data fusion, while reducing energy consumption. Theoretical analysis and extensive evaluations show the effectiveness of the proposed protocol.

An Unbalanced Weighted Sequential Fusing Multi-Sensor GM-PHD Algorithm.

In this paper, we study the multi-sensor multi-target tracking problem in the formulation of random finite sets. The Gaussian Mixture probability hypothesis density (GM-PHD) method is employed to formulate the sequential fusing multi-sensor GM-PHD (SFMGM-PHD) algorithm. First, the GM-PHD is applied to multiple sensors to get the posterior GM estimations in a parallel way. Second, we propose the SFMGM-PHD algorithm to fuse the multi-sensor GM estimations in a sequential way. Third, the unbalanced weighted fusing and adaptive sequence ordering methods are further proposed for two improved SFMGM-PHD algorithms. At last, we analyze the proposed algorithms in four different multi-sensor multi-target tracking scenes, and the results demonstrate the efficiency.

Source Localization in Acoustic Sensor Networks via Constrained Least-Squares Optimization Using AOA and GROA Measurements.

A constrained least-squares (CLS) 3D source localization method is presented for acoustic sensor networks with sensor position errors. The proposed approach uses angles of arrivals (AOAs) and gain ratios of arrival (GROAs) measured simultaneously at each node to estimate the source position jointly. Compared to AOA-only localization methods, the GROAs can be used in conjunction with AOA measurements so as to get more accurate results by exploiting the geometrical relationship between these two measurements. Compared to time difference of arrival localization methods, the proposed algorithm does not require accurate time synchronization over different nodes. The theoretical mean-square error matrices of the proposed approach are derived and they are exactly equal to the Cramér-Rao bound for Gaussian noise under the small error condition. Simulations validate the performance of the proposed estimator.

A novel aliasing-free subband information fusion approach for wideband sparse spectral estimation.

Wideband sparse spectral estimation is generally formulated as a multi-dictionary/multi-measurement (MD/MM) problem which can be solved by using group sparsity techniques. In this paper, the MD/MM problem is reformulated as a single sparse indicative vector (SIV) recovery problem at the cost of introducing an additional system error. Thus, the number of unknowns is reduced greatly. We show that the system error can be neglected under certain conditions. We then present a new subband information fusion (SIF) method to estimate the SIV by jointly utilizing all the frequency bins. With orthogonal matching pursuit (OMP) leveraging the binary property of SIV's components, we develop a SIF-OMP algorithm to reconstruct the SIV. The numerical simulations demonstrate the performance of the proposed method.

Wireless Sensor Array Network DoA Estimation from Compressed Array Data via Joint Sparse Representation.

A compressive sensing joint sparse representation direction of arrival estimation (CSJSR-DoA) approach is proposed for wireless sensor array networks (WSAN). By exploiting the joint spatial and spectral correlations of acoustic sensor array data, the CSJSR-DoA approach provides reliable DoA estimation using randomly-sampled acoustic sensor data. Since random sampling is performed at remote sensor arrays, less data need to be transmitted over lossy wireless channels to the fusion center (FC), and the expensive source coding operation at sensor nodes can be avoided. To investigate the spatial sparsity, an upper bound of the coherence of incoming sensor signals is derived assuming a linear sensor array configuration. This bound provides a theoretical constraint on the angular separation of acoustic sources to ensure the spatial sparsity of the received acoustic sensor array signals. The Cram e ´ r-Rao bound of the CSJSR-DoA estimator that quantifies the theoretical DoA estimation performance is also derived. The potential performance of the CSJSR-DoA approach is validated using both simulations and field experiments on a prototype WSAN platform. Compared to existing compressive sensing-based DoA estimation methods, the CSJSR-DoA approach shows significant performance improvement.

[Basic experimental and clinical research on peritoneal dialysis in the past 16 years].

To summarized the experiences from our basic experimental and clinical research on peritoneal dialysis. In the past 16 years, peritoneal fibrosis rat models and rabbit models of peritonitis were first established successfully in our laboratory in China. Peritoneal mesothelial cells were also separated and identificated. Besides, we assessed the biocompatibility of peritoneal dialysis fluid and analyzed the molecular mechanism of peritoneal mesothelial cell injury. We demonstrated the key role of transforming growth factor-beta1 (TGF-beta1), connective tissue growth factor (CTGF) and peroxisome proliferative activated receptor-gamma (PPAR-gamma) in the pathogenesis of peritoneal fibrosis, as well as their regulation of molecular mechanism. Furthermore, we transfected the plasmids encoding TGF-beta1-shRNA or pCTGF-shRNA into peritoneal cells and tissues by nanocarrier technologies. In clinical research, the positioning of peritoneal dialysis catheters, peritoneal dialysis treatment modalities and the prevention and treatment of its complications were studied. The characteristics and mechanism of solute transport in peritoneal dialysis was also explored.

[Effect of mannitol on vasoactive substances].

OBJECTIVE: To observe the changes of vasoactive substances in rabbits administered with mannitol at different dosages and to investigate the mechanism of acute renal failure (ARF) induced by massive mannitol administration. METHODS: Eighteen healthy male New Zealand rabbits were randomly divided into 3 groups: a minor mannitol group (n=6, mannitol 8 g/kg within 2 hours), a control group (n=6, saline of the same volume), and a massive mannitol group with free water taking (n=6, mannitol 40~60 g/kg within 3 days). The changes of renin, angiotensin-I (ang-I), angiotensin-II (ang-II), endothelin (ET), and atrial natriuretic factor(ANF) in the serum were observed. RESULTS: No significant changes in the renin, ang-I, ang-II, ET, and ANF in the serum were found between the minor mannitol group and the saline control group (P> 0.05). In the massive mannitol group with free water taking, renin, ang-I, and ang-II in the serum increased significantly compared with the other 2 groups; ET in the serum decreased significantly compared with the saline control group (P< 0.05); no significant changes in the ANF in the serum were found compared with the other 2 groups(P> 0.05). CONCLUSION: ARF induced by massive mannitol administration is associated with a significant change of vasoactive substances.