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  • 1
    In: Electronics, MDPI AG, Vol. 11, No. 12 ( 2022-06-11), p. 1857-
    Abstract: The next-generation communication base station antennas represented by phased array antennas are towards high frequency, high gain, high density, and high pointing accuracy. The influence of mechanical structure factors on communication system channel quality is obviously increasing, and the electromechanical coupling problem is becoming more prominent. To effectively guarantee the realization of 5G/6G communication in complex working environments and accelerate the commercial process of future communication systems, an electromechanical coupling channel capacity model is established in comprehensive consideration of the positional shift, attitude deflection, and temperature change of the communication base station phased array antennas. It can be used to rapidly evaluate the communication index degradation of RF devices within the heating environment. Moreover, a sensitivity model of the electric field strength and array antenna channel capacity to the random position error of each element is constructed. The influence of the random positioning error of each element on the communication indicators is analyzed and compared under different working conditions. The simulation results show that the proposed model can effectively provide a theoretical basis and guiding role for the design and manufacture of high-frequency array base station antennas.
    Type of Medium: Online Resource
    ISSN: 2079-9292
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2662127-7
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  • 2
    In: Electronics, MDPI AG, Vol. 9, No. 8 ( 2020-07-28), p. 1211-
    Abstract: Active phased array antennas (APAAs) can suffer from the effects of harsh thermal environments, which are caused by the large quantity of power generated by densely packed T/R modules and external thermal impacts. The situation may be worse in the case of limited room and severe thermal loads, due to heat radiation and a low temperature sink. The temperature field of the antenna can be changed. Since large numbers of temperature-sensitive electronic components exist in T/R modules, excitation current output can be significantly affected and the electromagnetic performance of APAAs can be seriously degraded. However, due to a lack of quantitative analysis, it is difficult to directly estimate the effect of temperature on the electromagnetic performance of APAAs. Therefore, this study investigated the electromagnetic performance of APAAs as affected by two key factors—the uniformly distributed temperature field and the temperature gradient field—based on different antenna shapes and sizes, to provide theoretical guidance for their thermal design.
    Type of Medium: Online Resource
    ISSN: 2079-9292
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2662127-7
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  • 3
    In: Materials, MDPI AG, Vol. 15, No. 9 ( 2022-05-08), p. 3380-
    Abstract: In order to explore the feasibility of underwater wet laser welding of the TC4 titanium alloy, research on the underwater laser self-fusion welding process was carried out. The weld structure and mechanical properties in both the air environment and the underwater environment were compared and analyzed. The results show that increasing the laser power and reducing the welding speed are beneficial to obtain a larger water depth threshold. Off-focus amount has little effect on water depth threshold; when the laser power is 3000 W and the welding speed is 5 mm/s, and the water depth exceeds 7 mm, a continuous weld cannot be formed. Compared with welding in the air, underwater welding has narrower weld width, smaller heat affected zone and finer crystal grains. The weld structure is mainly composed of α′ martensite and secondary acicular α′ phase, it is distributed in a net basket shape and the grain size at the top of the weld is finer. The hardness of the weld center is above 600 HV0.1, and the residual stress of the underwater welding weld is approximately symmetrically distributed. There is a large tensile stress along the welding direction at the weld, reaching 458 MPa. The larger residual tensile stress leads to the decrease of weld tensile strength, the tensile strength and elongation of the middle sample are only 52% and 77% of the base metal. Furthermore, the fracture mode is typical brittle fracture.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 4
    Online Resource
    Online Resource
    MDPI AG ; 2021
    In:  ISPRS International Journal of Geo-Information Vol. 10, No. 11 ( 2021-10-20), p. 714-
    In: ISPRS International Journal of Geo-Information, MDPI AG, Vol. 10, No. 11 ( 2021-10-20), p. 714-
    Abstract: Due to the increasingly complex objects and massive information involved in spatial statistics analysis, least squares support vector regression (LS-SVR) with a good stability and high calculation speed is widely applied in regression problems of geospatial objects. According to Tobler’s First Law of Geography, near things are more related than distant things. However, very few studies have focused on the spatial dependence between geospatial objects via SVR. To comprehensively consider the spatial and attribute characteristics of geospatial objects, a geospatial LS-SVR model for geospatial data regression prediction is proposed in this paper. The 0–1 type and numeric-type spatial weight matrices are introduced as dependence measures between geospatial objects and fused into a single regression function of the LS-SVR model. Comparisons of the results obtained with the proposed and conventional models and other traditional models indicate that fusion of the spatial weight matrix can improve the prediction accuracy. The proposed model is more suitable for geospatial data regression prediction and enhances the ability of geospatial phenomena to explain geospatial data.
    Type of Medium: Online Resource
    ISSN: 2220-9964
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2655790-3
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  • 5
    In: Micromachines, MDPI AG, Vol. 13, No. 9 ( 2022-08-27), p. 1412-
    Abstract: With the constant increase in communication requirements in modern society, the number and type of antennas on communication platforms have been increasing at an accelerating rate. This has led to a continuous increase in platform volume and weight, and the electromagnetic environment of antenna operating has increasingly worsened, seriously restricting the further development of communication systems. As a new communication system antenna type, a reconfigurable microstrip antenna can reconstruct operating frequencies, beam directions, etc., by changing the antenna structure to provide the good multifunction characteristics of a single antenna, avoiding the electromagnetic compatibility issues caused by numerous system antennas. At present, most of the research on reconfigurable antennas judges the influence of structural characteristics on electromagnetic characteristics by simulation, which has imposed restrictions on their development and application. Therefore, a reconfigurable antenna with a resonant frequency of 8.66 GHz and 15.26 GHz and a reconfigurable antenna with maximum radiation directions of 36.2° and −36.5° are designed in this paper, and the electromechanical coupling theory of the reconfigurable antennas is studied. The resonance frequency coupling model and the pattern function coupling model considering the structural deformation of a reconfigurable microstrip antenna are established. Within the applicable range of antenna structural parameters, the relative error between the resonance frequency coupling model and the pattern function coupling model is less than 5%, which meets practical engineering application requirements. Finally, the method is shown by experimentation to verify the accuracy and validity of the proposed electromechanical coupling model.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2620864-7
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  • 6
    Online Resource
    Online Resource
    MDPI AG ; 2023
    In:  Remote Sensing Vol. 15, No. 19 ( 2023-09-29), p. 4771-
    In: Remote Sensing, MDPI AG, Vol. 15, No. 19 ( 2023-09-29), p. 4771-
    Abstract: The simulation and prediction of coastline changes are of great significance for the development and scientific management of coastal zones. Coastline changes are difficult to capture completely but appear significantly periodic over a long time series. In this paper, the transformer model is used to learn the changing trend of the coastline so as to deduce the position of the coastline in the coming year. First, we use the distance regularization level set evolution (DRLSE) model for instantaneous waterline extraction (IWE) from preprocessed Landsat time-series images from 2010–2020 in Weitou Bay, China. Then, tidal correction (TC) is performed on the extracted instantaneous waterline dataset to obtain coastlines projected to a single reference tidal datum. Finally, the coastline datasets from 2010–2019 are used for model training, and the coastline in 2020 is used for accuracy assessment. Three precision evaluation methods, including receiver operating characteristic curve matching, the mean offset, and the root mean square error, were used to verify the predicted coastline data. The receiver operating characteristic curve was specifically designed and improved to evaluate the accuracy of the obtained coastline. Compared with the support vector regression (SVR) and long–short-term memory (LSTM) methods, the results showed that the coastline predicted by the transformer model was the closest to the accurate extracted coastline. The accuracies of the correct values corresponding to SVR, LSTM, and transformer models were 88.27%, 94.08%, and 98.80%, respectively, which indicated the accuracy of the coastline extraction results. Additionally, the mean offset and root mean square error were 0.32 pixels and 0.57 pixels, respectively. In addition, the experimental results showed that tidal correction is important for coastline prediction. Moreover, through field investigations of coastlines, the predicted results obtained for natural coastlines were more accurate, while the predicted results were relatively poor for some artificial coastlines that were intensely influenced by human activities. This study shows that the transformer model can provide natural coastline changes for coastal management.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2513863-7
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  • 7
    In: Micromachines, MDPI AG, Vol. 13, No. 6 ( 2022-06-08), p. 908-
    Abstract: Surface mount technology (SMT) plays an important role in integrated circuits, but due to thermal stress alternation caused by temperature cycling, it tends to have thermo-mechanical reliability problems. At the same time, considering the environmental and health problems of lead (Pb)-based solders, the electronics industry has turned to lead-free solders, such as ternary alloy Sn-3Ag-0.5Cu (SAC305). As lead-free solders exhibit visco-plastic mechanical properties significantly affected by temperature, their thermo-mechanical reliability has received considerable attention. In this study, the interface delamination of an SMT solder joint using a SAC305 alloy under temperature cycling has been analyzed by the nonlinear finite element method. The results indicate that the highest contact pressure at the four corners of the termination/solder horizontal interface means that delamination is most likely to occur, followed by the y-direction side region of the solder/land interface and the top arc region of the termination/solder vertical interface. It should be noted that in order to keep the shape of the solder joint in the finite element model consistent with the actual situation after the reflow process, a minimum energy-based morphology evolution method has been incorporated into the established finite element model. Eventually, an Improved Efficient Global Optimization (IEGO) method was used to optimize the geometry of the SMT solder joint in order to reduce the contact pressure at critical points and critical regions. The optimization result shows that the contact pressure at the critical points and at the critical regions decreases significantly, which also means that the probability of thermal-induced delamination decreases.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2620864-7
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  • 8
    Online Resource
    Online Resource
    MDPI AG ; 2020
    In:  Electronics Vol. 9, No. 4 ( 2020-04-13), p. 642-
    In: Electronics, MDPI AG, Vol. 9, No. 4 ( 2020-04-13), p. 642-
    Abstract: There are a large number of interconnections in the microwave module, among which the lead wire interconnection is widely used. Under the environmental load, the solder joint of the lead wire interconnection often appears to have cracks and other defects, which directly affect the return loss and insertion loss when transmitting electrical signals through solder joints, and indirectly affect the performance of the microwave module. For this reason, the segmented modeling method is realized by segmenting the lead wire interconnection structure into two parts in this paper, and the equivalent circuit model of the lead wire interconnection with the cracked solder joint is established using the equivalent circuit method. The correlation mechanism of the shape of the solder joint of the lead wire interconnection is studied, and formulas for predicting electrical performance based on return loss and insertion loss are derived. This paper realizes the prediction of the electrical performance of the lead wire interconnection with the defect, and can provide a reference for engineers and technicians.
    Type of Medium: Online Resource
    ISSN: 2079-9292
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
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  • 9
    In: Microorganisms, MDPI AG, Vol. 9, No. 12 ( 2021-11-26), p. 2443-
    Abstract: Carbapenem-resistant pathogens mediated by metallo-beta-lactamases (MBLs) have spread worldwide, where NDM-1 is a typical and key MBL. Here, we firstly discussed the distribution characterization of NDM-1, which produces multidrug-resistant Proteus mirabilis among broilers in China. From January to April 2019, 40 (18.1%, 40/221) blaNDM-1-carrying P. mirabilis strains were recovered from commercial broilers in slaughterhouse B in China. All the isolates were resistant to imipenem, meropenem and other β-lactams. These isolates belong to five clusters identified via pulsed field gel electrophoresis (PFGE). Further studies on twenty representative strains revealed that seven blaNDM-1 genes were located on plasmids with sizes of 104.5–138.9 kb. Notably, only three strains (PB72, PB96 and PB109) were successfully transferred to Escherichia coli J53, while the other four isolates were located in nontransferable plasmids. The rest were harbored in chromosomes. Ulteriorly, based on whole genome sequencing (WGS), these twenty isolates showed four typical phylogenetic clades according to single nucleotide polymorphisms (SNPs) of a core genome and presented four main genomic backbone profiles, in which type II/III strains shared a similar genetic context. All of the above is evidence of blaNDM-1 transmission and evolution in P. mirabilis, suggesting that the prevalence may be more diverse in broiler farms. Accordingly, as intestinal and environmental symbiotic pathogens, blaNDM-1-positive P. mirabilis will pose greater threats to the environment and public health.
    Type of Medium: Online Resource
    ISSN: 2076-2607
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2720891-6
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  • 10
    In: Cancers, MDPI AG, Vol. 14, No. 17 ( 2022-08-25), p. 4111-
    Abstract: Recurrent nasopharyngeal carcinoma (NPC), which occurs in 10–20% of patients with primary NPC after the initial treatment modality of intensity-modulated radiation therapy (IMRT), is one of the major causes of death among NPC patients. Patients with recurrent disease without distant metastases still have a chance to be saved, but re-treatment often carries more serious toxicities or higher risks. For this group of patients, both otolaryngologists and oncologists are committed to developing more appropriate treatment regimens that can prolong patient survival and improve survival therapy. Currently, there are no international guidelines for the treatment of patients with recurrent NPC. In this article, we summarize past publications on clinical research and mechanistic studies related to recurrent NPC, combined with the experience and lessons learned by our institutional multidisciplinary team in the treatment of recurrent NPC. We propose an objective protocol for the treatment of recurrent NPC.
    Type of Medium: Online Resource
    ISSN: 2072-6694
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2527080-1
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