Abstract: A combination of passive shimming procedures is employed in the design of a unilateral Nuclear Magnetic Resonance magnet. The first shimming procedure used movable permanent magnets to correct the inhomogeneity of the B0 field to a relatively low level. In the second shimming procedure, the small iron pieces were used as shimming units, and their sizes and locations were predicted by using an integer programming method. Finally, the distribution of the shimming pieces was optimized and a special mathematic model was established. This hybrid technique provides a computational algorithm for optimizing the B0 homogeneity and for minimizing the number of…iron shimming pieces. A prototype unilateral NMR magnet has been built with this method. The B0 field measurement results were compared before and after the shimming. Employing this hybrid shimming method improved the uniformity of the B0 field from 4200 ppm to 796 ppm with only one iteration.
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Abstract: Because of the need for rapid detection and location of diseases in clinical applications, this work proposes a composite measurement of magnetic induction tomography (MIT) and electrical impedance tomography (EIT). This paper is composed of the following aspects: portable and integral hardware design, stable dual constant-current sources, the composite detection method, cross-plane data acquirement, 3-dimensional image reconstruction and so on. A qualitative evaluation of conductivity, resolution and relative position error were taken by combining the EIT and MIT methods via the experiment model. The sensitivities of both methods were analyzed to improve the imaging results. The reconstruction results reveal that…the system is capable of obtaining better physiological measurements, which is very useful in clinical monitoring, quick medical diagnosing and preliminary screening of community health.
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Keywords: Bioelectrical impedance measurement, magnetic induction tomography, cross evaluation and imaging, 3-dimensional image
Abstract: This paper presents a simple design for a nuclear magnetic resonance (NMR) sensor and its application for detecting turbine oil in two power stations. The magnet, which is composed of two identical cuboid permanent magnet blocks and two iron shimming sheets of a special shape, generates a relatively homogeneous static magnetic B0 field (∼ 364 ppm) on a 10 × 10 mm2 region of interest. In the vertical direction, it produces a constant gradient of ∼15.5 T/m within 5 mm which allows for self-diffusion measurements and 1 dimensional imaging. This NMR sensor can produce a deep penetration depth into the…samples with relatively strong and uniform B0 strength. The NMR sensor was specially designed for assessing the aging status of turbine oil in a power station, and a group of turbine oil of different service times was measured. Results demonstrate that an increase in the service time of the turbine oils clearly decreases transverse relaxation time T2 . This portable sensor can be used in fields and provide quantitative evaluation parameters of the aging status of turbine oil during periodic inspection.
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Abstract: Root is the administrative privilege on Android, which is however inaccessible on stock Android devices. Due to the desire for privileged functionalities and the reluctance of rooting their devices, Android users seek for no-root approaches, which provide users with part of root privileges without rooting their devices. Existing no-root approaches require users to launch a separate service via Android Debug Bridge (ADB) on an Android device, which would perform user-desired tasks. However, it is unusual for a third-party Android application to work with a separate native service via sockets, and it requires the application developers to have extra knowledge such…as Linux programming in application development. In this paper, we propose a feasible no-root approach based on new functionalities added on Android, which creates no separate service but an ADB loopback. To ensure such no-root approach is not misused in a proactive instead of reactive manner, we examine its dark side. We find out that while this approach makes it easy for no-root applications to work, it may lead to a “permission explosion ,” which enables any third-party application to attain shell permissions beyond its granted permissions. The permission explosion can further lead to exploits including privacy leakage, account takeover, application UID abuse, and user input inference. A practical experiment is carried out to evaluate the situation in the real world, which shows that many real-world applications from Google Play and four third-party application markets are indeed vulnerable to these exploits. To mitigate the dark side of the new no-root approach and make it more suitable for users to adopt, we identify the causes of the exploits, and propose a permission-based solution. We also provide suggestions to application developers and application markets on how to prevent these exploits.
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Abstract: When the current distribution changes due to the breakage in the grounding grid, the magnetic field in the vicinity of the grounding grid will change, hence the magnetic field on the ground above the grounding can be used to detect the breakage of the grounding. In the paper, the magnetic field forward problem of the grounding grid is described firstly, and simulations were carried out when the breakage was located at different position. Results indicate that the maximum change of the magnetic flux density occurs at different measuring point when the breakage was located at different position. To achieve a…more convenient method to detect the grounding grid fault, the magnetic field inverse problem of the grounding grid is presented, which is the process to calculate the current flowing in the grounding grid according to the magnetic field strength, and the method based on the global regularization and Damped Gauss-Newton method to solve the inverse problem is described, with which the ill-posed and ill-conditioning characteristic of the inverse problem can be diminished. Then the fault state of the grounding grid can be confirmed in the following way. Firstly, inject a 10∼30A current into the grounding grid, measure the magnetic field strength or the magnetic flux density at the measuring points on the ground above the grounding grid, then the current distribution can be obtained by solving the inverse problem. If the parameters of the soil are known, the resistance distribution can be obtained, with which the fault state of the grounding grid and the location of the fault can be confirmed. An equivalent model to verify the inverse problem was set up, and results indicate that the global regularization can diminish the ill-posed and ill-conditioning characteristic of the inverse problem.
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Keywords: Grounding grid, magnetic field, forward problem, inverse problem
Abstract: This paper addresses the augmentation of a conventional plane electrode arrays electrical impedance tomography (EIT) system to form a combined electrode arrays EIT system. This enhances the system performs of providing more accordant information of objects. The system is built up of 65 electrodes, composing of 4 horizontal and 8 axial intercrossing image planes. A phantom experiment has been taken and the measurements been processed by Tikhonov Regularization algorithm and reconstructed by the data obtained from the corresponding model. From comparing the reconstructed volume of anomaly with the target, the results indicate that the described method augments the EIT 3-D…rebuilding to a distinguishable level. The qualitative results illustrate the feasibility of this composite approach in exploiting sensitivity in 3-D space with expectable spatial resolution and positioning accuracy. Moreover, this method effectively reduces the amount of computation and demonstrates the practical potential of EIT for clinical inspection and monitoring.
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Abstract: A new numerical integral method of the Hankel transform which included the dual Bessel function in the integrand was presented. Because of the strong-oscillation and slow-decay properties of the Bessel functions, it is impossible to use a normal numerical integration method. In our method, the integral interval [0, ∞) is divided into two parts: [0, λ _0 ] and [λ _0 , ∞). In [0, λ _0 ], the integration can be calculated using a Gauss-Legendre quadrature method between the adjacent zero points. And in [λ _0 , ∞), the Hankel transform is converted to the Fourier cosine or sine…transform, and can be calculated with a polygonal approximation algorithm. The proper value of the dividing point of λ _0 was discussed. The simulation results of the test functions show that the algorithm is correct and accurate. Finally, the forward problem of the multi-layer medium magnetic induction tomography was calculated with this new method, and the eddy current distribution in the model and the induced voltages in the detection coils were simulated.
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Abstract: In the MLPG method of this paper, only the boundary integrations over local subdomains is involved, which make the MLPG method is very easy to carry out because the local sub-domains are chosen in MLPG method as simple circular or rectangular ranges. In order to simplify the MLPG method, the radius of local sub-domains has been adjusted for the nodes close to the global boundary but not exactly on the boundary. In addition, the boundary conditions including the essential and natural boundary are imposed directly by the nodes which are exactly on the global boundary. Two electromagnetic models have been…studied in this paper to investigate the accuracy and computational efficiency of the MLPG method. The results, which are compared with the solutions obtained from the MLPG in the reference and the FEM, show that the MLPG method in this paper can obtain more accurate results by using fewer nodes.
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Keywords: Local Petrov-Galerkin method, meshless, electromagnetic problems
Abstract: Feature selection is an essential part in the data preprocessing. In the text classification, most of the previous feature selection algorithms rarely consider the redundancy between features. This paper focuses on eliminating redundancy. After modifying the formula of feature correlation of original fast correlation-based filter (FCBF) and updating the algorithm strategy, we propose a new approach named improved feature size customized fast correlation-based filter (IFSC-FCBF). In addition, we combine IFSC-FCBF with Naive Bayes (NB) classifier for text classification, and test it in four typical text corpus data sets. The results demonstrate that with the same feature size, IFSC-FCBF method has…the advantages of higher accuracy and shorter running time than other methods.
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Keywords: Feature selection, Naive Bayes, text classification, FCBF, IFSC-FCBF
Abstract: As the environment issue is put on the agenda, air pollution also concerns a lot. Nitrogen oxide (NOx) an is important factor which affects air pollution and is also the main gas emissions of the smoke and waste gas of FCC unit in petrochemical industry. It is important to accurately predict the NOx emission in advance for petrochemical industry to avoid air pollution incidents. In this paper, convolutional neural network (CNN) and long short-term memory (LSTM) are combined to predict the NOx emission in Fluid Catalytic Cracking unit (FCC unit). Convolutional-LSTM (CLSTM) is able to extract the spatial and temporal…features which are essential information in the prediction of the NOx emission. The features in the factors of production which would affect the NOx emission are extracted by CNN which prepares time series data for LSTM. The LSTM layer is connected after CNN to model the irregular trends in time series. CNN, Multi-layer perception (MLP), rand forest (RF), support vector machine (SVM) and LSTM are implemented as baseline models. The results from the proposed CLSTM model showed better performance than all the baseline models. The mean absolute error and root mean square error for CLSTM were calculated with the values of 16.8267 and 23.7089 which are the lowest among all the models. The Pearson correlation coefficient and R2 for the proposed CLSTM model are calculated with the value of 0.9263, 0.8237 which are the highest among all the models. Furthermore, the residual graphs indicate the well matched performance between the observations and the predictions. The study provides a model reference for forecasting the NOx concentration emitted by FCC unit in petrochemical industry.
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