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Existing testing methods inadequately capture the internal stress state of concrete, a vital structural safety metric, resulting in a divergence between measured and actual internal stress states, especially in larger structures. There is an urgent need for innovative theoretical and technical approaches that can directly, accurately, and instantly reflect the internal stress state of concrete, meeting the growing demand for such detection. This paper conducts experimental research on the internal stress detection of concrete based on the principle of displacement current. Firstly, the theoretical relationship between the internal stress and oscillation frequency of concrete is established. Secondly, two dielectric plates are embedded in the concrete specimen as a sensing unit, and an LC oscillation circuit is connected externally to express the internal stress state of the concrete in the form of oscillation frequency. The research findings suggest that there is a decrease in the oscillation frequency as the dielectric constant of the concrete increases. Additionally, a significant change in the oscillation frequency is observed because of the dielectric polarization effect that takes place during the pouring and curing of the concrete specimen. The concrete age starts from about 25 days, and its oscillation frequency gradually stabilizes; the internal stress of the concrete is proportional to the oscillation frequency, and they show a good correlation in the experiment.

As the main driving force for the digital transformation of the construction industry, the uncertainty of digital technology in the application process has seriously hindered the high-quality development of the construction industry. In order to promote the wide application of digital technology in the construction industry and clarify the key uncertainties in its application process, this paper identifies the uncertainty index system of digital technology application based on the LDA topic model and literature analysis; the DEMATEL-ISM method is used to construct the multilevel hierarchical structure model of the uncertainty indicators in the application of digital technology to study the mutual influence among the indicators and to find the key uncertainty indicators. The research results show that the uncertainty indicators of the application of digital technology in the construction industry are divided into five levels: policy, industry, personnel, economy and law, and that the perfection of the policy guarantee system is the key uncertainty indicator for the investment return period of digital technology application. The standard contract model for digital technology is a direct uncertainty indicator for the application of digital technology in the construction industry. The results of this study help researchers and practitioners to focus on the key barriers and provide a list of key elements for construction companies to promote the application of next-generation digital technologies to improve digitalization of the construction industry. This study also provides a policy reference to further promote the digital transformation of the construction industry.

The availability of multiple illuminators in the multi-static airborne passive synthetic radar (SAR) system can provide the improved SAR imaging capability. The reflection coefficients of targets in the observed scene are different due to diverse observation angles and carrier frequencies in multi-static scenarios. To tackle this problem, the study firstly introduces the forward signal model of multi-static airborne passive SAR system and then formulates the imaging problem as an joint sparsity optimisation problem of multiple measurement vectors. Under the distributed greedy sparse recovery framework, the study finally proposes the cross-validation-based simultaneous orthogonal matching pursuit (SOMP) imaging algorithm for multi-static airborne passive SAR system. The proposed imaging algorithm can avoid the requirement of sparsity level of the observed scene and achieve the accurate imaging reconstruction of the observed scene. The simulation results have verified the effectiveness and validity of the proposed imaging method.