A new data-driven predictor, PSO-XGBoost, used for permeability of tight sandstone reservoirs: A case study of member of chang 4+5, western Jiyuan Oilfield, Ordos Basin

Lithology identification of igneous rocks based on XGboost and conventional logging curves, a case study of the eastern depression of Liaohe Basin

On the basis of introducing the basic categories of atmospheric refraction and their existing conditions, the forming processes of three kinds of atmospheric duets are expounded. Several main characteristics of atmospheric duct are summarized and analyzed, and field sounding data from the WEstern North-Pacific cloud-radiation EXperiment (WENPEX) and meteorological data around the Xisha sea area are used to validate these characteristics. Meanwhile the sensitivities of the evaporation duct height to the variations of atmospheric humidity, the air-sea temperature difference, and horizontal wind speed are examined. With the analysis of the effect of atmospheric duct on the propagation of electromagnetic wave, the maximum trapped-wavelength and the critical emitting angle of elevation for electromagnetic wave which can form duct propagation are derived.At the same time the four kinds of necessary conditions for electromagnetic wave to form duct propagation are brought forward. The effects of atmospheric duct on ultrashort wave propagation,radar observation, short wave communication etc. are also discussed.

Analysis on characteristics of atmospheric duct and its effects on the propagation of electromagnetic wave

Evaporation ducts have a significant impact on electromagnetic (EM) wave propagation. The accurate prediction of EM propagation loss (PL) is important for the practical application of EM systems. However, the random weather processes and interaction of air-sea variables will cause complex spatial and temporal fluctuations in PL, especially for an over-the-horizon link. The physics prediction models show some limitations in practice. This article proposes a data-driven PL prediction method based on the gated recurrent unit network (GRU-PL). An X-band EM propagation system was developed and deployed for one month to collect PL of a 53 km link in the South China Sea for model training and testing. The GRU-PL model uses the air-sea variables as inputs and outputs the predicted PL. The root-mean-square error (RMSE) of the GRU-PL model is 7.04 dB, decreasing by 57.2% compared with the classical method. Furthermore, a method, which uses the inversion evaporation duct heights (EDHs) as the output to train the GRU network and then uses the parabolic equation model to predict the PL based on the GRU predicted EDHs, is also discussed. The RMSE is 7.3 dB. This method shows good potential in PL prediction of dynamically changing EM propagation links. 

Prediction of Over-the-Horizon Electromagnetic Wave Propagation in Evaporation Ducts Based on the Gated Recurrent Unit Network Model

Multi-stage residual life prediction of aero-engine based on real-time clustering and combined prediction model

Evaporation duct is a specific atmospheric structure at sea, which has an important influence on the propagation path of electromagnetic waves (EW). Considering the limit of existing evaporation duct height (EDH) prediction models and aiming at proposing more accurate and stronger generalization ability of EDH models, we applied eXtreme Gradient Boosting (XGBoosting) algorithm to the field of evaporation duct for the first time. And we proposed the new EDH prediction model using XGBoost algorithm (XGB model). Simultaneously, traditional Paulus-Jeske (PJ) model and deep learning Multilayer Perceptron (MLP) model were introduced into the experiment to make a comparison. In terms of comprehensive performance, XGB model is optimal in all sub-regions and total area. Finally, cross-learning experiments were carried out to test the generalization ability of XGB model. The results show that the generalization ability of XGB model is better than that of MLP model.

XGB Model : Research on Evaporation Duct Height Prediction Based on XGBoost Algorithm

Abstract. Indoor point cloud data is easy to obtain and contains a large amount of data, but there is no connectivity, no structural attributes, and no semantic information between point clouds. It is very difficult to extract interior components. In order to solve the problem that it is difficult to extract the closed door in the indoor point cloud, and the indoor scanning point cloud data is noisy and redundant, a point cloud segmentation method is proposed to reduce the amount of data and the impact of noise. Because most of the indoor components are not on the same horizontal plane, different component information can be obtained by slicing the point cloud at different heights. In these slices, the component that always exists is the wall. By comparing other data with the point cloud data with a more complete wall, the required component can be extracted. The experimental results show that this method can accurately extract the indoor door component information and beam component information, providing a data basis for building model refinement.


/pdf/point-cloud-slicing-based-extraction-of-indoor-components-2gbhw6x4.pdf

Point cloud slicing-based extraction of indoor components

Positive and negative voltages/currents may present long-term unbalance after single-pole breakage faults in ring flexible DC distribution networks, which endangers the safe and stable operation of the system, whereas little research on it has been implemented. Therefore, characteristics of the single-pole breakage fault are studied. First, by establishing the equivalent model of the system before and after the fault, the voltage and current characteristics of the single-pole breakage fault on the DC line, the tie line between the sending-end converter and the DC bus, and that between the receiving-end converter and the DC bus were analyzed. Then, the influence of system grounding mode on the characteristics of the single-pole breakage fault was discussed. In addition, the impact of sudden load change on the fault characteristics was studied. Finally, the model of a ring flexible DC distribution system was built in PSCAD/EMTDC to verify the theoretical analysis. 

Single-pole break fault characteristic analysis for ring flexible DC distribution grids

Obstructive sleep apnea (OSA) is a common sleep-disordered-breathing with decreased or even suspended ventilation due to upper airway obstruction, which is characterized by intermittent hypoxia and sleep fragmentation. OSA can damage a variety of organ systems, especially the cardiovascular system, seriously affecting the quality of life of patients. Therefore, more attention is paid to the precise assessment of the impairments of the organ systems caused by OSA and the evaluation of indicators, in order to carry out preventive measures as soon as possible. However, due to the limitations of traditional indicators such as apnea-hypopnea index (AHI) in assessing the severity of disease, it is necessary to explore other alternative indicators to obtain multi-dimensional characteristics of OSA. A promising parameter, hypoxic burden (HB) can better quantify the severity of OSA and capture the disease load of OSA. This review mainly focused on the basic concept, main features, calculating method of HB and its clinical significance in predicting the adverse consequences of OSA, aiming at a better management of patients with OSA.

[Value of hypoxic burden in evaluating the impairments of organ systems in obstructive sleep apnea].

A Study on a Semi-empirical Model for the Local Loss Coefficient of Small Angle Contraction Pipes

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