Search

With the rapid growth of power demand, the conductor ampacity calculation method based on the dynamic thermal rating (DTR) becomes more and more important. Based on the shortcomings of the current DTR models, a new DTR model that does not need to measure the wind speed and the operating state of conductor is proposed, which is called the equivalent heat transfer (EHT) model. However, there are still shortcomings in the accuracy of the EHT model in application. In this paper, the EHT model is improved at first according to the consideration of the effect of air physical parameters and the redetermination of the experimental parameters of the EHT equipment. Then, the operation of EHT equipment is simulated through the established experimental platform. The improved EHT model is verified by the IEEE standard. Finally, the sensitivity analysis of the improved EHT model is carried out. The results show that the improved EHT model is greatly improved on application accuracy compared to the original EHT model. Moreover, the improved EHT model can choose the steady-state temperature at any position on the surface of the aluminum ball to calculate the conductor ampacity, and the relative error does not exceed 6%. The improved EHT model is reliable and can meet the safe operation requirements of the power system in practical engineering applications.

BackgroundCystic lesions are frequently observed in knee joint diseases and are usually associated with joint pain, degenerative disorders, or acute injury. Magnetic resonance imaging-based, artificial intelligence-assisted cyst detection is an effective method to improve the whole knee joint analysis. However, few studies have investigated this method. This study is the first attempt at auto-detection of knee cysts based on deep learning methods.MethodsThis retrospective study collected data from 282 subjects with knee cysts confirmed at our institution from January to October 2021. A Squeeze-and-Excitation (SE) inception attention-based You only look once version 5 (SE-YOLOv5) model was developed based on a self-attention mechanism for knee cyst-like lesion detection and differentiation from knee effusions, both characterized by high T2-weighted signals in magnetic resonance imaging (MRI) scans. Model performance was evaluated via metrics including accuracy, precision, recall, mean average precision (mAP), F1 score, and frames per second (fps).ResultsThe deep learning model could accurately identify knee MRI scans and auto-detect both obvious cyst lesions and small ones with inconspicuous contrasts. The SE-YOLO V5 model constructed in this study yielded superior performance (F1 = 0.879, precision = 0.887, recall = 0.872, all class mAP0.5 = 0.944, effusion mAP = 0.945, cyst mAP = 0.942) and improved detection speed compared to a traditional YOLO model.ConclusionThis proof-of-concept study examined whether deep learning models could detect knee cysts and distinguish them from knee effusions. The results demonstrated that the classical Yolo V5 and proposed SE-Yolo V5 models could accurately identify cysts.

BACKGROUND We aimed to develop and evaluate a deep learning-based method for fully automatic segmentation of knee joint MR imaging and quantitative computation of knee osteoarthritis (OA)-related imaging biomarkers. MATERIAL AND METHODS This retrospective study included 843 volumes of proton density-weighted fat suppression MR imaging. A convolutional neural network segmentation method with multiclass gradient harmonized Dice loss was trained and evaluated on 500 and 137 volumes, respectively. To assess potential morphologic biomarkers for OA, the volumes and thickness of cartilage and meniscus, and minimal joint space width (mJSW) were automatically computed and compared between 128 OA and 162 control data. RESULTS The CNN segmentation model produced reasonably high Dice coefficients, ranging from 0.948 to 0.974 for knee bone compartments, 0.717 to 0.809 for cartilage, and 0.846 for both lateral and medial menisci. The OA-related biomarkers computed from automatic knee segmentation achieved strong correlation with those from manual segmentation: average intraclass correlations of 0.916, 0.899, and 0.876 for volume and thickness of cartilage, meniscus, and mJSW, respectively. Volume and thickness measurements of cartilage and mJSW were strongly correlated with knee OA progression. CONCLUSIONS We present a fully automatic CNN-based knee segmentation system for fast and accurate evaluation of knee joint images, and OA-related biomarkers such as cartilage thickness and mJSW were reliably computed and visualized in 3D. The results show that the CNN model can serve as an assistant tool for radiologists and orthopedic surgeons in clinical practice and basic research.

Prosthesis-associated infections and aseptic loosening are major causes of implant failure. There is an urgent need to improve the antibacterial ability and osseointegration of orthopedic implants. Zinc oxide nanoparticles (ZnO-NPs) are a common type of zinc-containing metal oxide nanoparticles that have been widely studied in many fields, such as food packaging, pollution treatment, and biomedicine. The ZnO-NPs have low toxicity and good biological functions, as well as antibacterial, anticancer, and osteogenic capabilities. Furthermore, ZnO-NPs can be easily obtained through various methods. Among them, green preparation methods can improve the bioactivity of ZnO-NPs and strengthen their potential application in the biological field. This review discusses the antibacterial abilities of ZnO-NPs, including mechanisms and influencing factors. The toxicity and shortcomings of anticancer applications are summarized. Furthermore, osteogenic mechanisms and synergy with other materials are introduced. Green preparation methods are also briefly reviewed.

Due to the complexity of high-squint synthetic aperture radar (SAR) mounted on maneuvering platforms, the traditional geometric model and imaging algorithms cannot be directly applied in the diving or climbing stage for the existence of vertical velocity. Aiming at this issue, an equivalent geometric model of maneuvering high-squint-mode SAR is constructed, and a modified wavenumber-domain imaging algorithm combined with the proposed equivalent range model is proposed in this article. First, the disadvantages of the conventional range model are analyzed in detail and an equivalent range model is proposed to describe the motion characteristic of squint SAR in maneuvering mode, which maintains the azimuth-shift invariance along the flight direction in the new slant range plane. Then, to achieve the requirement of maneuvering SAR real-time processing, a modified wavenumber-domain imaging algorithm with a high usage of the spectrum by axis rotation for high-squint SAR data is proposed. Further, since the equivalent model may introduce the severe distortion in the imaging plane, a novel geometric correction method based on inverse projection is performed to obtain the ground imagery with a little distortion. Finally, simulation and real-data processing results validate the superiority of the proposed algorithm.

Sag calculation plays an important role in overhead line design. Since the tensile stress of aluminium conductor steel reinforced (ACSR) is required for the sag calculation, an analysis on sag behaviour when considering the tensile stress distribution can be very useful to improve the accuracy of sag results. First, this paper analyses the ACSR tensile stress distribution arising from the temperature maldistribution through proposing a new calculation formula. A finite-element analysis (FEA) model of ACSR is conducted for the solution of the new formula. By using the results, the error and limitations of the existing sag calculation methods for ACSR are discussed. As the critical point of sag calculation, knee-point temperature is solved iteratively involving the tensile stress maldistribution phenomenon in aluminium wires. Based on this iterative solution, an improved analytical method for the ACSR sag calculation considering the creep effect is presented and also compared with the hybrid sag method. The results show that these two methods are basically coincident without the consideration of creep effect, while there are non-negligible differences between them as the creep strain is involved. Compared with the existing analytical methods, the improved sag calculation method proposed in this paper can be applied in more extensive situations.

The rupture accident of overhead ground wire (OGW) may happen when the overhead transmission line gets struck by lightning, especially in the case of a large lightning current. This may trigger a short-circuit fault of the overhead transmission line and cause serious harm to the safety and stable operation of the power grid. The Lightning samples are very limited and it is difficult to simulate the actual lightning current in the laboratory accurately. Besides, the standard are short of the consideration to the thermo-mechanical properties of OGW under lightning current. Therefore, it is of considerable significance to study the reason and process of rupture accident of OGW caused by lightning strike. In this paper, a rupture accident of 220 kV OGW happened in Qingyuan, Guangdong Province due to a large lightning strike (475.9kA) is investigated. Firstly, the rupture process of OGW is preliminarily inferred through the fractography analysis of the broken OGW samples. Then, a three-dimensional thermoelectric coupling simulation model of OGW is established, and the melting area and average temperature of each wire of OGW under a lightning strike are calculated. Based on the fractography analysis results and the simulation results of the OGW samples, and taking the correlation between the temperature and the tensile strength of metal material into consideration, a more detailed discussion on the rupture process of OGW is conducted. Finally, the rationality of wire diameter selection for OGW is demonstrated by calculating the residual tensile strength of each wire of OGW under different lightning current. The method for analyzing the rupture accident of OGW caused by lightning strike presented in this paper, which is based on various influencing factors, can provide reference and suggestions for the investigation and solution in similar cases.

Prosthesis-associated infections are one of the main causes of implant failure; thus it is important to enhance the long-term antibacterial ability of orthopedic implants. Titanium dioxide nanotubes (TNTs) are biomaterials with good physicochemical properties and biocompatibility. Owing to their inherent antibacterial and drug-loading ability, the antibacterial application of TNTs has received increasing attention. In this review, the process of TNT anodizing fabrication is summarized. Also, the mechanism and the influencing factors of the antibacterial property of bare TNTs are explored. Furthermore, different antibacterial strategies for carrying drugs, as well as modifications to prolong the antibacterial effect and reduce drug-related toxicity are discussed. In addition, antibacterial systems based on TNTs that can automatically respond to infection are introduced. Finally, the currently faced problems are reviewed and potential solutions are proposed. This review provides new insight on TNT fabrication and summarizes the most advanced antibacterial strategies involving TNTs for the enhancement of long-term antibacterial ability and reduction of toxicity.

Since cable insulation with low thermal conductivity occupies a large proportion of high-voltage cable, an optimization analysis on dynamic thermal behavior of cable insulation can be very useful to improve the accuracy of cable dynamic thermal rating. In this paper, the dynamic thermal analysis of cable insulation is carried out by combining the theoretical method and finite-element analysis (FEA) method. Based on the analysis, it is proved that using IEC recommended transient thermal model of cable insulation will bring certain error to cable dynamic temperature evaluation, especially at the early stage of cable temperature rise. Moreover, in this paper, an implementable optimization method for transient thermal model of cable insulation is developed. The improvement of the optimized model compared with the IEC model on cable dynamic thermal rating is verified by the FEA method. The results confirm that the optimized model can better model the dynamic thermal behavior of cable than the IEC model and the improvement is more obvious for dynamic thermal rating of cable with high voltage level and under large load. The methodology developed in this paper can pave a way for electricity utilities to increase cable utilization while still ensuring cable reliability.

With the increase in electricity demand, the ampacity calculation based on the dynamic thermal rating (DTR) technology is increasingly significant for assessing and improving the power transfer capacity of the existing overhead conductors. However, the DTR models now available present some inadequacies in measurement techniques related to wind speed. Therefore, it is essential to propose a new model instead of wind speed measuring in DTR technology. In this paper, the influence analysis of various weather parameters on the conductor ampacity is carried out by using the real weather data. Based on the analysis, it is confirmed that the impact of wind speed is significant, especially in the case of the low wind speed. Moreover, an equivalent heat transfer (EHT) model for DTR technology is proposed instead of wind speed measuring. For this EHT model, the calculation of conductor ampacity is realized through investigating the correlation of heat losses between the heating aluminum (Al) ball and conductor. Finally, combined with the finite element method (FEM), the EHT model proposed in this paper is verified by the Institute of Electrical and Electronic Engineers (IEEE) standard. The results indicate that the error of the EHT model is less than 6% when employing the steady thermal behavior of the Al ball to calculate the ampacity. The EHT model is useful in the real-time thermal rating of overhead conductors. It can increase the utilization of overhead conductors while also avoiding the limitation of the existing measurement techniques related to wind speed.

Prosthesis-associated infections and aseptic loosening are major causes of implant failure. There is an urgent need to improve the antibacterial ability and osseointegration of orthopedic implants. Zinc oxide nanoparticles (ZnO-NPs) are a common type of zinc-containing metal oxide nanoparticles that have been widely studied in many fields, such as food packaging, pollution treatment, and biomedicine. The ZnO-NPs have low toxicity and good biological functions, as well as antibacterial, anticancer, and osteogenic capabilities. Furthermore, ZnO-NPs can be easily obtained through various methods. Among them, green preparation methods can improve the bioactivity of ZnO-NPs and strengthen their potential application in the biological field. This review discusses the antibacterial abilities of ZnO-NPs, including mechanisms and influencing factors. The toxicity and shortcomings of anticancer applications are summarized. Furthermore, osteogenic mechanisms and synergy with other materials are introduced. Green preparation methods are also briefly reviewed.

In the ground wire-clamp system, aluminum armor tape (AAT) or armor rod (AR) is commonly adopted to avoid the wear damage of ground wire. While under the short-circuit current, damage or even breakage of ground wire in suspension clamp due to overheat may occur. However, there still lacks attention on the investigation about this type of damage. In this paper, a finite element (FE) modeling method of the ground wire-clamp system, which was applicable to two cases with AAT and AR, was proposed to discuss the transient thermal and mechanical behaviors. In the modeling of contact points, an improved contact bridge model considering the contact shape characteristics was proposed. The transient temperature rise experiments for ground wire-clamp systems with AAT and AR were carried out to verify the accuracy of models. The results shows that the improved contact bridge model is conducive to obtaining the accurate calculation results. For the analysis of this type of damage, the generated thermal stress cannot be ignored. In engineering, the ground wire twinned by AAT is at risk of overheat or even breakage under the short-circuit current, while using AR can prevent the ground wire in the suspension clamp from damage of overheat.

This paper presents a maritime moving target detection technique with multiple BeiDou satellites as opportunistic transmitters. Due to the restrained power budget from BeiDou satellites, a long integration time is indispensable. And the use of multiple satellite transmitters enhances the target detection performance. In this paper, first, the keystone transform (KT) is applied on each individual echo to correct range cell migration (RCM). Then, a long-time integration method based on dechirp processing and Fourier transform is utilized, concentrating each echo into Doppler centroid (DC) and Doppler frequency rate (DFR) domain. Finally, to integrate the echoes from multiple satellite transmitters, spherical intersection (SX) method is used to localize the target, followed with the compensation of DC shifts. The effectiveness of the maritime moving target detection technique is shown by simulations.

Linear frequency modulated interrupted continuous wave (LFMICW) technique is developed to solve the isolation of LFMCW radar. However, there is a range aliasing problem where apply the LFMICW radar for high-resolution and long-range situation. The range aliasing will bring false targets into the range profile, which makes it difficult to detect the target. In this paper, a method of staggered interrupted frequency square wave to eliminate range aliasing is adopted and applied to the MTD-frequency domain pairing velocity measurement and ranging method for the LFMICW radar. The effectiveness of the method is verified by simulation.

A proper biological microenvironment conducive to tissue repair and regeneration, while the bioimplant interface directly affects the local microenvironment. In this study, to improve the biological microenvironment, a nanosized tantalum boride (Ta-B) was coated on a titanium alloy substrate (Ti6Al4V, TC4) using magnetron cosputtering. The sample surface was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). To investigate the effects of tantalum boride coating on the microenvironment, rabbit bone marrow stromal cells (BMSCs), and RAW 264.7 cells were respectively seeded on the sample surface and relevant experiments were conducted in vitro. The pure tantalum coating (Ta) and naked TC4 were prepared as controls. Our results showed that the Ta-B coating enhanced cell proliferation and adhesion and inhibited the inflammatory response. Findings of alkaline phosphatase (ALP) staining, alizarin red staining and real-time PCR for osteoblastic gene expression indicated that Ta-B and Ta coating improve the osteogenesis, in which Ta-B coating showed higher osteogenesis than Ta coating. Thus, this study suggests that Ta-B coating with excellent biocompatibility could have new applications for wound healing in bone tissue engineering.

With appropriate geometry configurations, bistatic synthetic aperture radar (SAR) can break through the limitations of monostatic SAR on forward-looking imaging. Thanks to such a capability, bistatic forward-looking SAR (BFSAR) has extensive potential applications. In BFSAR, the compensation of the spatially variant motion errors is of great significance to get a well-focused image. In this paper, a motion compensation method based on keystone transform and modified autofocus back-projection is presented to deal with this problem. Keystone transform is applied to remove the spatial variation of range cell migration (RCM) and the first-order term of RCM errors simultaneously, prepares for the following modified autofocus back-projection, which can eliminate the high-order term of azimuth phase errors. Simulation results verify the validity and efficiency of the presented method.

For bone tissue engineering, the porous scaffold should provide a biocompatible environment for cell adhesion, proliferation, and differentiation and match the mechanical properties of native bone tissue. In this work, we fabricated porous polyetherimide (PEI) scaffolds using a three-dimensional (3D) printing system, and the pore size was set as 800 μm. The morphology of 3D PEI scaffolds was characterized by the scanning electron microscope. To investigate the mechanical properties of the 3D PEI scaffold, the compressive mechanical test was performed via an electronic universal testing system. For the in vitro cell experiment, bone marrow stromal cells (BMSCs) were cultured on the surface of the 3D PEI scaffold and PEI slice, and cytotoxicity, cell adhesion, and cell proliferation were detected to verify their biocompatibility. Besides, the alkaline phosphatase staining and Alizarin Red staining were performed on the BMSCs of different samples to evaluate the osteogenic differentiation. Through these studies, we found that the 3D PEI scaffold showed an interconnected porous structure, which was consistent with the design. The elastic modulus of the 3D PEI scaffold (941.33 ± 65.26 MPa) falls in the range of modulus for the native cancellous bone. Moreover, the cell proliferation and morphology on the 3D PEI scaffold were better than those on the PEI slice, which revealed that the porous scaffold has good biocompatibility and that no toxic substances were produced during the progress of high-temperature 3D printing. The osteogenic differentiation level of the 3D PEI scaffold and PEI slice was equal and ordinary. All of these results suggest the 3D printed PEI scaffold would be a potential strategy for bone tissue engineering.

Prosthesis-associated infections are one of the main causes of implant failure; thus it is important to enhance the long-term antibacterial ability of orthopedic implants. Titanium dioxide nanotubes (TNTs) are biomaterials with good physicochemical properties and biocompatibility. Owing to their inherent antibacterial and drug-loading ability, the antibacterial application of TNTs has received increasing attention. In this review, the process of TNT anodizing fabrication is summarized. Also, the mechanism and the influencing factors of the antibacterial property of bare TNTs are explored. Furthermore, different antibacterial strategies for carrying drugs, as well as modifications to prolong the antibacterial effect and reduce drug-related toxicity are discussed. In addition, antibacterial systems based on TNTs that can automatically respond to infection are introduced. Finally, the currently faced problems are reviewed and potential solutions are proposed. This review provides new insight on TNT fabrication and summarizes the most advanced antibacterial strategies involving TNTs for the enhancement of long-term antibacterial ability and reduction of toxicity.

The Dice loss function is widely used in volumetric medical image segmentation for its robustness against the imbalance between the numbers of foreground and background voxels. However, it is not able to differentiate hard examples from easy ones, which usually comprise the majority of training examples and therefore dominate the loss function. In this work, we propose a novel loss function, termed as Gradient Harmonized Dice Loss, to both address the quantity imbalance between classes and focus on hard examples in training, with further generalization to multi-class segmentation. The proposed loss function is employed in a 3D fully convolutional neural network for multiple object segmentation of MRI knee joint images and validated on both public SKI10 dataset and 637 MRI knee scans collected from local hospitals. The experimental results show that the Gradient Harmonized Dice Loss outperforms the popular loss functions, such as Dice loss and Focal loss, and achieves the state-of-the-art results on the validation data of SKI10.

For bone tissue engineering, the porous scaffold should provide a biocompatible environment for cell adhesion, proliferation, and differentiation and match the mechanical properties of native bone tissue. In this work, we fabricated porous polyetherimide (PEI) scaffolds using a three-dimensional (3D) printing system, and the pore size was set as 800 μm. The morphology of 3D PEI scaffolds was characterized by the scanning electron microscope. To investigate the mechanical properties of the 3D PEI scaffold, the compressive mechanical test was performed via an electronic universal testing system. For the in vitro cell experiment, bone marrow stromal cells (BMSCs) were cultured on the surface of the 3D PEI scaffold and PEI slice, and cytotoxicity, cell adhesion, and cell proliferation were detected to verify their biocompatibility. Besides, the alkaline phosphatase staining and Alizarin Red staining were performed on the BMSCs of different samples to evaluate the osteogenic differentiation. Through these studies, we found that the 3D PEI scaffold showed an interconnected porous structure, which was consistent with the design. The elastic modulus of the 3D PEI scaffold (941.33 ± 65.26 MPa) falls in the range of modulus for the native cancellous bone. Moreover, the cell proliferation and morphology on the 3D PEI scaffold were better than those on the PEI slice, which revealed that the porous scaffold has good biocompatibility and that no toxic substances were produced during the progress of high-temperature 3D printing. The osteogenic differentiation level of the 3D PEI scaffold and PEI slice was equal and ordinary. All of these results suggest the 3D printed PEI scaffold would be a potential strategy for bone tissue engineering.

In urban underground environment, a short-conduit is commonly used to provide mechanical protection for the cable. The cable section buried in the short-conduit may experience excessive thermal stresses. However, the thermal rating for the cable in the short-conduit is not specialized in the IEC 60287. It has not been sufficiently addressed in the literature either. This paper proposes a quasi-three-dimensional thermal model for the cable installed in the short-conduit. A simplified model for efficiently and effectively solving the proposed model is then developed. Based on the simplified thermal model, an improved method for assessing the real-time ampacity of the cable installed in the short-conduit is implemented. The performance of the improved method with respect to the IEC method on thermal rating for the cable installed in the short-conduit is verified by the Finite Element Analysis (FEA). The results show that the improved method outperforms the IEC method when the conduit length is less than five meters. The method is useful in real-time thermal rating of the short-conduit cables and paves a way to increase the utilization of cables installed in short-conduits while still ensuring their reliability.

For cable termination, which is regarded as a key segment of power grid connecting cable lines with other electrical equipments, its insulation parts withstand much higher electric field strength than the average electric field strength of overall cable line. The excessive local electric field strength may result in the appearance of cable termination breakdown fault which can cause serious harm to the power supply reliability of whole transmission line. Historical statistics show that the breakdown location of cable termination is not confined to the vicinity of stress cone. However, the existing researches have not attached enough importance to the breakdown faults at the tail pipe of cable termination. Thus, it is of considerable significance to study the mechanism of breakdown fault at the tail pipe of cable termination. In this paper, a breakdown fault case of cable termination tail pipe on a 110 kV transmission line is investigated. Firstly, the disassembly inspection is applied to cable terminations of this fault line, and the possible breakdown reasons are preliminarily inferred. Then, a three-dimensional electric field simulation model of intact cable termination is established, and the mechanism of creeping discharge and air discharge inside the tail pipe occurred at the initial stage of breakdown fault is explained by this model. Subsequently, by setting defects on cable insulation surface in the simulation model of intact cable termination and varying the size of defects, the process of cable insulation damage inside the tail pipe formed in the initial stage developing into a penetrating cable insulation damage is simulated. Finally, the mechanism of breakdown fault case of cable termination tail pipe is concluded, and some improvement measures for the installation of cable terminations are proposed to reduce the incidence probability of such breakdown fault at the tail pipe of cable termination. The method for analyzing the breakdown fault case of cable termination tail pipe presented in this paper, which combines the disassembly inspection and simulation analysis, can provide reference and suggestions for the investigation and solution in similar cases.

Rupture accidents of overhead conductors may occur due to its complex operating environment. If wires rupture happens, the overhead conductors can be repaired by full-tension splice (FTS) in practical engineering to restore the mechanical strength and ampacity required. However, with time increases, ageing will occur on the overhead conductors. There may exist potential of rupture in the repaired segment of the conductor. Once the conductor is broken, the reliability of transmission line will be seriously destroyed. Therefore, it is of great importance to investigate the rupture reason and process of conductor repaired by FTS. In this paper, a rupture accident of 110 kV overhead conductor repaired by FTS is discussed. Firstly, the fractography analysis for the conductor sample is conducted, and the rupture reason is preliminarily inferred according to the rupture feature of the sample. Then, the current density distributions in the repaired segment of new conductor and aged conductor are compared by a finite element analysis (FEA) model of electromagnetic field. Also, the reason of high temperature produced in the conductor sample during rupture process is determined. Subsequently, to analyze the relationship between temperature and equivalent plastic strain, a FEA model of structure field for the steel core of conductor is established. Finally, combined with the fractography test results and simulation results, the rupture mechanism of conductor repaired by FTS is summarized in detail. The analytical method and conclusions proposed in this paper can provide references and suggestions for the study of similar conductor rupture accident and optimization of repaired process.

It is a major problem that ground wire breakage occurs due to the high temperature rise. And it is of great significance to study temperature rise characteristics of its hotspot. A 3-D finite element model of contact fracture between the ground wire and preformed armor rod is set up in the paper and firstly the equivalent method of contact resistance is analyzed and determined. Based on this model, influence of skin effect on contact resistance of contact fracture area is studied. Furthermore, effect of contact resistance and short circuit current on transient temperature rise in the contact fracture area are also analyzed. It can be concluded that the deeper the degree of skin effect, the greater the contact resistance and temperature rise. And with the combined effect of contact resistance and short circuit current, the possibility of direct fusing of the ground wire is proved. Moreover, temperature rise ratio of the ground wire which is away from contact fracture is much less than that of contact fracture area.

Overhead earth wire breakage accident may occur frequently, which can seriously affect the reliable operation of the power grid. The main reason of the earth wire breakage is the contact resistance inside the clamp as short-circuit current flows through it. To understand the mechanism of the earth wire breakage, this paper conducts the theoretical study on the skin effect and contact resistance of the wire suspension string with winding preformed armor rods. The temperature rise experiments using of the new and old earth wire suspension string are performed to verify the theoretical analysis. The results show that the hotspots locate in the fracture of the preformed armor rods and the inside the clamp when short-circuit current flows through the earth wire suspension string. The reason could be the increase of the contact resistances in these two locations due to rust of the suspension string. Comparing with the earth wire suspension string without wrapping preformed armor rods, the number of hotspots in the earth wire may increase and accordingly the possibility of earth wire breakage can increase.

Image formation from squinted sliding spotlight synthetic aperture radar (SAR) is limited by azimuth spectral folding and severe two dimension coupling. This paper presents an Extended Wavenumber Domain Algorithm (WDA) for highly squinted sliding spotlight SAR data processing. This algorithm adopts azimuth deramping approach to overcome the azimuth spectral folding phenomenon. The chirp rate for azimuth deramping and the principle of choosing pulse repetition frequency (PRF) is presented to accommodate the characteristic of Doppler history. Subsequently, the full focusing is implemented by WDA. Instead of the conventional Stolt mapping in WDA, a modifled Stolt mapping is introduced in order to enlarge the range extension of focused image and enable to update the Doppler parameters along range. To conflrm the correctness of the implementation of modifled Stolt mapping and the azimuth position of target in focused image, related compensation terms are developed. Point target simulation results are presented to validate the efiectiveness of extended WDA to process highly squinted sliding spotlight SAR data.

This paper improved polar format algorithm (PFA) based on nonuniform azimuth sampling for squint spotlight synthetic aperture radar (SAR) imaging. The range resampling for chirped signal is carried out by chirp z transform (CZT). The novel nonuniform azimuth sampling during the echo data collection enables the utilizing of CZT in azimuth resampling. According to the data collection geometry, the precise expression of phase error induced by wavefront curvature is deduced, and then the overlapped subaperture approach (OSA) is adopted to correct the geometric distortion and defocus arising from the effect of wavefront curvature. Simulation results confirm the validity of the presented approach.