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Nuclear magnetic resonance (NMR) technology can directly detect hydrogen signals in hydrogen-containing fluids, such as water and hydrocarbon. It can provide quantitative characterization of the fluid content and surrounding environment, thus finding extensive application in oil and gas exploration field. However, when measured samples containing ultra-fast relaxation components, such as shale oil and gas, the reliability of measurement results tends to be very low because only a small number of front-end signals in Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can be obtained for the fast relaxation components. To address this problem, a multiple micro echo interval measurement (MCTEM) method was proposed in this research. In the measurement stage, the proposed method acquired more NMR front-end signals. In the inversion stage, multiple echo data were adopted for the joint inversion. It contributed to forming an accurate fast relaxation T2 spectrum. MCTEM method was validated through numerical simulations and rock physics experiments. It was concluded from the results that MCTEM method could improve the problem of peak disappearance for fast relaxation components in T2 spectrum caused by long echo interval. MCTEM method could enhance the measurement accuracy of fast relaxation signals effectively.

In order to improve the reliability of two-dimensional nuclear magnetic resonance (2D NMR) measurement in shale oil reservoirs, the T2-T1 2D NMR response characteristics and influencing factors of shale oil reservoirs were analyzed in three scenarios: laboratory core analysis, wellsite mobile full-diameter core scanning and logging. For different application scenarios, the optimization method of T2-T1 NMR measurement parameters for shale oil reservoirs were proposed. Laboratory core measurements require attention to the choice of echo interval time (TE) and number of echo groups, in addition to the different magnetic field strengths and measurement sequences. When scanning full-diameter cores at the well site, it is necessary to focus on TE and minimum waiting time (Tw). To ensure the convergence in T1 dimension of quickly relaxed component, the minimum Tw should be set to at least 1 ms. NMR logging is limited by the acquisition conditions. It is necessary to focus on the distribution range and smoothing factor in data processing to interpret and modify data with different signal-to-noise ratios. A poor shale oil reservoir with NMR porosity less than 5% is difficult to ensure the accuracy of NMR results for its low signal-to-noise ratio. The systematic analysis of T2-T1 2D NMR measurement parameters provides a reference for the optimization of 2D NMR detection methods for shale oil reservoirs, which helps to improve the accuracy of NMR measurements and obtain more reliable reservoir information.

Multi Core Fiber (MCF) is an important transmission medium of Space Division Multiplexing (SDM) technology, which can significantly enhance the communication capacity of existing optical fiber. However, MCF has the problems of high structural complexity, difficult to test, and no test standard for parameters. According to the structural characteristics, combined with the technical experience in the development, this paper standardize the splicing method and the parameters testing method of MCF, which lays the foundation for the large-scale commercialization of MCF in the future.

Bag-of-Tasks (BoT) applications consisting of multiple tasks are widely used in various fields.Different from the traditional deadline constraint in scheduling problems,a due date constraint allows the BoT applications to finish more than a predetermined due date,but would result in the tardiness penalty.In this case,in order to reduce the total cost,the efficient harmony search (EHS) algorithm is proposed to optimize the scheduling tasks in hybrid clouds.The algorithm obtains the initial task sequence by random search and fine tuning.By improving the harmony search steps and the way of generating new harmony memory,a large number of high-quality harmony can be obtained in one search process,which greatly improves the efficiency of harmony search and speeds up the convergence speed of the algorithm.Through continuous iteration,the global optimal solution is obtained,that is to say,BoT application scheduling scheme has the lowest total cost.Experimental results show that compared with other algorithms,the proposed algorithm has significant improvement in performance,which can effectively reduce the total cost of scheduling BoT applications.

At present, resonance demodulation and data envelopment analysis, etc are usually used for health evaluation and remaining life prediction of bearings, but there are some problems such as difficulty in extracting health degree, single fault prediction type, and lack of reliable models. Aiming at these deficiencies, this paper proposes a method which realizes bearing health assessment and remaining life prediction through two-stage cascaded long short term memory neural network. In this paper, the bearing data set of Xi'an Jiaotong University is used for experimental comparison. The results show that, compared with the resonance demodulation method, the monotonicity, robustness and trend of the health degree curve are comprehensive in the health degree evaluation of single fault data using this method. The evaluation indicators increase by 12%, 24.8% and 5% respectively, and the comprehensive evaluation index in the composite fault data increases by 15.1%, and the remaining service life can be predicted according to the health evaluation curve, which proves that the method is effective in health evaluation and remaining life.

Ground penetrating radar (GPR) is a non-destructive exploration technology that utilizes high-frequency ultra-wideband signals to detect the distribution of subsurface objects and media. Benefiting from the advantages of non-destructiveness, high efficiency, and high resolution, GPR has been widely applied in underground defect detection task of urban roads. Illustrating the radar echo wave of subsurface structure, GPR B-scan images are a main means to detect underground disaster; however, compared to natural images, automatic interpretation of GPR B-scan ones is a more challenging task because of same objects with different spectra, different objects with same spectrum as well as heavy noise pollution. Aiming to improve the accuracy of subsurface disasters detection methods, a disasters classification network, i.e., MA-ResNeXt, based on ResNetXt50 is proposed by combining multi-dimensional attention mechanism, atrous space pyramid pool and multi-scale feature extraction structure. The proposed network is trained and tested on real GPR B-scan images of three common subsurface disasters, e.g., void, cavity underneath pavement (CUP) and loosely infilled void (LIV). The comparison results show that classification accuracy of the proposed network approaches 98.2%, and illustrate that the network can effectively realize accurate classification of underground disasters. [ABSTRACT FROM AUTHOR]

The lower limit temperature in the crop water stress index (CWSI) model refers to the canopy temperature (Tc) or the canopy-air temperature differences (dT) under well-watered conditions, which has significant impacts on the accuracy of the model in quantifying plant water status. At present, the direct estimation of lower limit temperature based on data-driven method has been successfully used in crops, but its applicability has not been tested in forest ecosystems. We collected continuously and synchronously Tc and meteorological data in a Quercus variabilis plantation at the southern foot of Taihang Mountain to evaluate the feasibility of multiple linear regression model and BP neural network model for estimating the lower limit temperature and the accuracy of the CWSI indicating water status of the plantation. The results showed that, in the forest ecosystem without irrigation conditions, the lower limit temperature could be obtained by setting soil moisture as saturation in the multiple linear regression model and the BP neural network model with soil water content, wind speed, net radiation, vapor pressure deficit and air temperature as input parameters. Combining the lower limit temperature and the upper limit temperature determined by the theoretical equation to normalize the measured Tc and dT could realize the non-destructive, rapid, and automatic diagnosis of the water status of Q. variabilis plantation. Among them, the CWSI obtained by combining the lower limit temperature determined by the dT under well-watered condition calculated by the BP neural network model and the upper limit temperature was the most suitable for accurate monitoring water status of the plantation. The coefficient of determination, root mean square error, and index of agreement between the calculated CWSI and measured CWSI were 0.81, 0.08, and 0.90, respectively. This study could provide a reference method for efficient and accurate monitoring of forest ecosystem water status. [ABSTRACT FROM AUTHOR]

In order to study the effect of echo time (TE) on nuclear magnetic resonance (NMR) porosity in tight oil (gas) and shale reservoir, multi-TE NMR experiments and NMR numerical simulations were performed on CuSO4 solutions with specific transversal relaxation time (T2). The results showed that the normalization NMR porosity of different T2 relaxation components remained 100% in the low TE region, and rapidly decreased with increasing TE. When TE was greater than certain value, the normalization NMR porosity dropped to zero. However, the TE value at which the normalization NMR porosity began to decrease and the TE value at which the normalization NMR porosity dropped to zero were different for different NMR relaxation component. Moreover, the whole NMR measurement was divided into lossless zone, fast decay zone, invalid parameter zone and instrument blind zone, based on the relationships between the normalization NMR porosity of different relaxation component and TE. For each specific relaxation component, a logarithmic relationship was demonstrated between the loss of relaxation component and TE in the fast decay zone. A method for NMR porosity correction was given.

Microporosity in the body and platform of the three different compositions complex nickel-based single crystal castings solidified by high rate solidification (HRS) process was investigated by the X-ray tomography (XRT). The results show that the solidification range and the dendrite tortuosity have a strong effect on the formation of microporosity. In the body of the casting, the arrangement mode of dendrites among three different compositions castings is the same. Due to the largest solidification range of the first generation single crystal SX1, its porosity volume fraction is the largest. The difference of solidification range in the second generation single crystal SX2 and the third generation single crystal SX3 is not obvious, thus, their porosity volume fraction is mostly influenced by the eutectic volume fraction. With the increase of single crystal generation, the level of refractory elements will be increased, also the eutectic fraction of the body increases. Therefore, the size of interdendritic zone in the final solidification stage is increased, and the pressure drop in liquid phase is reduced, leading to the decrease of porosity volume fraction. The porosity in the platform is mostly decided by the dendrite tortuosity compared with that in the body. In the platform of the first generation single crystal SX1, there is no obvious difference in the dendrite tortuosity, thus, the volume fraction of porosity is similar to that in the body. Due to the larger dendrite tortuosity in the second generation single crystal SX2 and the third generation single crystal SX3, the corresponding porosity volume fraction is increased.

Two-dimensional (2D) NMR logging activation sets are acquisition means aiming at obtaining specific formation information, affecting the adaptability of NMR instruments to different types of reservoirs and the reliability of the original data. In this work, a software with the visualization function for designing 2D NMR logging activation sets was developed using the C# language, based on the component elements and working mechanism of activation. The software supported the design of activation sets for 2D NMR logging and NMR core analyzer. Meanwhile, the software provided three kinds of parameter editing methods, observation mode optimization and graphical display functions, and thus realized flexible adjustment of the activation sets. It solved the problems in the former mainstream 2D NMR logging activation sets, such as low signal-to-noise ratio of the raw data, incomplete loading of fluid relaxation characteristics due to inadequately fixed acquisition parameters and inflexible adjustment etc. In addition, the software also provided outputs for acquisition parameters and acquisition timing.

Microporosity in the body and platform of the three different compositions complex nickel-based single crystal castings solidified by high rate solidification (HRS) process was investigated by the X-ray tomography (XRT). The results show that the solidification range and the dendrite tortuosity have a strong effect on the formation of microporosity. In the body of the casting, the arrangement mode of dendrites among three different compositions castings is the same. Due to the largest solidification range of the first generation single crystal SX1, its porosity volume fraction is the largest. The difference of solidification range in the second generation single crystal SX2 and the third generation single crystal SX3 is not obvious, thus, their porosity volume fraction is mostly influenced by the eutectic volume fraction. With the increase of single crystal generation, the level of refractory elements will be increased, also the eutectic fraction of the body increases. Therefore, the size of interdendritic zone in the final solidification stage is increased, and the pressure drop in liquid phase is reduced, leading to the decrease of porosity volume fraction. The porosity in the platform is mostly decided by the dendrite tortuosity compared with that in the body. In the platform of the first generation single crystal SX1, there is no obvious difference in the dendrite tortuosity, thus, the volume fraction of porosity is similar to that in the body. Due to the larger dendrite tortuosity in the second generation single crystal SX2 and the third generation single crystal SX3, the corresponding porosity volume fraction is increased.

The effect of different process parameters on solidification of industrial gas turbine hollow blades via HRS (High Rate Solidification) and LMC (Liquid Metal Cooling) was studied by ProCAST software. The results show that the paste zone via LMC process is much narrower than that by HRS process and the shape of the S/L (solid/liquid) interface is more flat. The axial thermal gradient of the blade by LMC process is about three times higher than that by HRS process. The cooling rate of the blade is 0.3-2.00℃/s by LMC process, which is far higher than that by HRS process (0.05-0.16℃/s). In LMC process, low holding temperature can still ensure high temperature gradient and cooling rate of the blade; while in order to avoid blocking of stray grains to the initial grains at the platform of the blade, HRS process should adopt high holding temperature and lower withdrawal rate. The calculated and the measured results show that compared with the blade prepared by HRS process, the PDAS (primary dendrite arm spacing) is much finer in the blade prepared by LMC process.

Objective A titanium personalized orthodontic bracket is designed and manufactured using the technol⁃ ogy of computed tomography (CT), computer aided design (CAD), finite element analysis (FEA), and selective laser melt⁃ ing (SLM) to well match the patient tooth so as to realize mold ⁃free manufacturing. Methods A model of a titanium personalized orthodontic bracket which is built by CT scanning machine and Pro/E software, is imported into Ansys soft⁃ ware to carry out finite element simulation analysis with nonlinear contact method. Then, the titanium personalized orth⁃ odontic bracket is proposed after the model data above is imported to SLM molding equipment via titanium powder melt⁃ ed with layer by layer using a high⁃speed scanning galvanometer. Results The maximum equivalent stress of the titani⁃ um personalized orthodontic bracket is distributed uniformly and reasonably, the titanium personalized orthodontic bracket formed by SLM molding equipment can provide high accuracy and there is a high similarity between the bottom of the orthodontic bracket and the tooth surface shape. Conclusion The combination of CT, CAD, FEA, SLM technolo⁃ gy can fulfill model⁃free manufacturing of the personalized orthodontic bracket and thus shorten the manufacturing cycle.

The rock mechanism under frozen condition has played down the significance on the design of frozen wall thickness and section height of the ultra-deep shaft in Western of China.This paper investigated the particle size and voids distribution principles using magnified image technique, which is on the typical medium size sandstone within the deep water-rich stratum during a coal mining construction with artificial freezing skill in Ordos of China.The frozen medium size sandstone have been studied with triaxial compression test under the temperature of-5℃,-10℃,-15℃, and Brazilian Split test at 26℃,-10℃ and-20℃.The test results indicated that the compressive strength improved linearly up to maximum of 27.29%when temperature dropped down, and this effect was weakened with the increase of the confining pressure.So did the internal frictional angle and cohesion, which ended up with the biggest rise of 12.54%and 18.69%.The tensile strength jumped from 0.73 MPa at 26℃ up to 1.59 MPa at-10℃, as of 118.18%extra, followed with declining when the temperature reduced more.The strength property of medium sandstones have been further improved with only cer-tain extent during lowering the temperature, therefore the design criteria of frozen wall thickness should rather be governed by the purpose of sealing water than over cooling control.

A new method is proposed to evaluate the process parameters by the solid-liquid interface position, thermal gradient angle and the axial thermal gradient. The effects of the process parameters on the solid-liquid interface position, thermal gradient angle and the axial thermal gradient were simulated by ProCAST using LMC(Liquid Metal Cooling) and HRS(High Rate Solidification) processes. The results show that HRS process is little affected by the mold thickness, the dominant heat transfer factor in HRS is radiation from the mold surface, and the dominant heat transfer factor in LMC either mold thermal conductivity or mold-metal interface heat transfer; increasing furnace temperature is beneficial to increase the axial thermal gradient; the withdrawal rate is the most important process parameter which significantly affects the thermal field during solidification, as the withdrawal rate increases, the axial thermal gradient first increases and then decreases, therefore, it is necessary to apply different withdrawal rates for different alloys. After holding 10min at different pouring temperatures, a uniform temperature is achieved, and it has slight influence on the subsequent solidification. It has been put forward that the solid-liquid interface position, thermal gradient angle and the axial thermal gradient can be utilized as a serial of efficient analysis standards for optimization of process conditions independent of casting geometry.

Taking slope unit as evaluation unit, through establishing the evaluation index system of three factors including regional geological environment background, resource damage and geological hazard, the evaluation indexes are quantified and weighted to make the zoning evaluation of mine geological environment in Xuchang City by layer overlapping analysis of GIS technology. The zoning results are consistent with the current survey, which verifies the practicability of the method and provides reference for planning and treatment of mine geological environment in the area. [ABSTRACT FROM AUTHOR]

Multi--robot cooperation is widely used in cooperative handling, stamping, welding and other fields, with higher precision and more flexibility. The interpolation algorithm and the force/position control performance determine the smoothness of the trajectories and the stability of the cooperative operation, and also directly affect the bearing capacity and the operation quality. In this paper, the force/position control technology in the process of two robots cooperative handling was studied. First, the clamping characteristics and stress state of two robots cooperative handling were analyzed, and the ideal mathematical model of cooperative handling system was established. Next, according to the mathematical model of the second--order damping system of the master--slave robot, the master--slave cooperative control mode was adopted to design the force/position control strategies respectively. The optimized fuzzy self--tuning position control based on the ideal position was presented for the master robot, and the damping control with the optimized bacterial foraging algorithm based on the force optimization of position deviation of the master robot was presented for the slave robot, and the design of the controller was carried out. Then, the main body of the algorithm and its cost function were programed in MATLAB, and the control system was established in Simulink. Finally, the whole controller was simulated. The simulation results were as follows. The maximum position error of the master was 1.53 mm, and the maximum force error of the slave was 0.038 N. The position error of tracking down between the slave and the master was within 0.18 mm, and the slave could quickly correct the master--slave speed deviation within 0.2 s. The simulation results showed that compared with the conventional PD control method, the proposed controller could reduce the maximum tracking error by 40% and effectively eliminate the zero--crossing oscillations of the force tracking. This method could significantly improve the dynamic performance of the system. [ABSTRACT FROM AUTHOR]

Spatially colored noise would lead to performance degradation or even invalidation of multiple input multiple output (MIMO) radar algorithms. For the problem of joint direction of departure (DOD) and direction of arrival (DOA) estimation in bistatic MIMO radar with spatially colored noise, the reason for the failure of the existing algorithms is analyzed. Taking the low-rank property of the noiseless covariance matrix, the sparse feature of the colored noise covariance matrix as well as the multidimensional structure characteristic of the MIMO radar data after matched filtering into consideration, a tensor analysis-based angle estimation is introduced. Firstly, a covariance tensor for the angle estimation is constructed. The colored noise is suppressed via removing the entities that affected by the noise covariance measurement. Then the noiseless covariance tensor is recovered via tensor completion. Thereafter, the factor matrices corresponding to DOD and DOA are achieved via parallel factor (PARAFAC) decomposition. Finally, the DOD and DOA are fitted using least squares algorithm. Simulation results show that the proposed algorithm is not sensitive to the spatially colored noise, and it is free-from the aperture loss. The proposed algorithm performs more accurate estimation performance than the existing matrix and tensor approaches. [ABSTRACT FROM AUTHOR]

BACKGROUND: Periprosthetic infection of the knee is one of the most serious complications after total knee arthroplasty. Second-stage revision is recognized as the "gold standard" of treatment. The placement of antibiotic cement spacer during the interval of the second operation not only increases the concentration of antibiotics, but also increases the joint activity of patients. At present, the fabrication methods of spacer are different. There are some shortcomings such as low articular surface fit, low fabrication accuracy, unstable structure and low strength, which cannot well fit the patient's physiological structure. How to design personalized spacer and maintain knee joint stability after surgery is a difficulty in its clinical application. OBJECTIVE: To design the structure of personalized spacer using finite element analysis and to make a spacer by three-dimensional printing technology for applied clinically. METHODS: Based on CT data of knee joint from patients undergoing total knee arthroplasty, the prosthesis, femur and tibia were reconstructed by Mimics software. According to the amount of osteotomy and the shape of the prosthesis, a personalized spacer structure was designed. The stress of the spacer in different gaits was analyzed by finite element method. The silicone mould of the occupier was fabricated by three-dimensional printing technology and used in clinical application. RESULTS AND CONCLUSION: (1) According to the amount of osteotomy and the shape of knee prosthesis, the structure of femoral side occupier and the tibial side occupier were designed. In order to prevent the dislocation of the spacer, the groove depth of the tibial side occupier was (4-6 mm) and the anterior end height was (10-14 mm). (2) The results of finite element analysis showed that the maximum stress of the femoral side occupier was 13.6 MPa at 90 degrees of flexion, and that of the tibial side occupier was 7.99 MPa at 90 degrees of flexion. The stress was reasonable and the structural strength of the spacer meets the requirements. (3) Silica gel mould of spacer was made by three-dimensional printing technology. The surface of spacer was smoother and the fit degree was increased. (4) The clinical results showed that the personalized spacer had good joint mobility and stability. (5) The spacer made by this method is fast, simple and saves operation time. It provides a new choice for clinical application of knee joint spacer. [ABSTRACT FROM AUTHOR]

This study estimated stem density by combining distance sampling with stand spatial structure investigation techniques. We tested the statistical performance of two investigative methods (selecting the fourth-or sixth-nearest tree to the sample location) and three different density estimators (Prodan, Persson and Thompson). Different spatial distribution patterns influenced the performance of these estimators. Prodan-s estimator was unbiased for uniform patterns, and it produced increasing bias with increasing spatial clustering. Persson's estimator produced consistent positive bias for uniform and random patterns, with the smallest bias for clustered patterns. Thompson-s estimator was robust for random or near-random patterns, and it produced positive and negative bias for uniform and clustered patterns, respectively. No significant performance difference was found between selecting the fourth- and the sixth-nearest trees with the same sample size of 49. Thus, we could combine distance sampling with spatial structure investigation techniques. [ABSTRACT FROM AUTHOR]

2, 2-Dinitro-l-butanol was obtained using 1-nitropropane as a raw material through the reaction of the oxidative-nitration and methylolation. 2,2-Dinitrobutyl acrylate was prepared from 2,2- dinitro-l-butanol and acrylic acid through direct esterification. The energetic binder poly (2, 2- dinitrobutyl acrylate) was synthesized by the free radical polymerization of 2,2-dinitrobutyl acrylate in toluene and using azobisiosbutyronitrile as initiator. The polymerization rate equation was determined experimentally. The structure and thermal properties of poly (2, 2-dinitrobutyl acrylate) were also characterized by the methods of FTIR, ¹HNMR, TG, DSC. The results show that the polymerization rate equation for 2, 2-dinitrobutyl acrylate is Rp = k[M]1, 27 [I]0, 63 , which displays that the chain termination reaction is the coexistence mode of mono- and bi-molecular termination, and the initiating process is dependent on monomer concentration. The thermal decomposition temperature of poly (2,2- dinitrobutyl acrylate) is 260°C with mass loss of 21%. [ABSTRACT FROM AUTHOR]

An algorithm of terrain hazard assessment for soft landing based on information fusion is presented. Firstly, two types of terrain features are extracted from the gray images of landing navigation camera and the elevation data of Lidar respectively. Then, fuzzy variables and membership functions on terrain features are presented, and local terrain hazard assessments are realized by fuzzy inference. Finally, the global terrain hazard is assessed based on the decision-class fusion of weighted means, and the safe landing sites are obviously showed. The simulation experiments using 3D digital terrain image have validated the proposed algorithm effectively. [ABSTRACT FROM AUTHOR]

Soil samples were collected from the Eucalyptus plantations in the north, east, and west Guangdong and Pearl River Delta region to study their organic carbon content and density, and the main factors affecting the organic carbon density. In the plantations, the soil organic carbon content and density in A and B horizons were significantly different, with the values of (23. 94 ±2. 97) g ∙ kg-1 and (9. 68 ± 1. 05) g ∙ kg-1, and (27. 64±7. 72) t ∙ hm-2 and ( 108. 36±9. 37) t ∙ hm-2, respectively. In 0-50 cm soil layer, the organic carbon density was 66. 72 ±6. 53 t ∙ hm-2, being slightly higher than that in Masson pine and Chinese fir plantations in Guangdong. In both A and B horizons of Eucalyptus plantations, soil organic carbon density was significantly positively correlated with altitude, soil total porosity, capillary porosity, capillary moisture capacity, and total nitrogen content. Soil capillary porosity, capillary moisture capacity, and pH value were the main factors affecting the soil organic carbon density. [ABSTRACT FROM AUTHOR]