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This letter presents a novel approach to constructing 1-bit coding unit cells for metasurface design and utilizes a genetic algorithm to effectively reduce the radar cross section (RCS) of the antenna over a wide frequency range. Unlike previous methods, this approach allows for manipulation of the coding state of unit cells by modifying the sheet impedance of resistive graphene rather than altering conventional metallic structures. The 1-bit coding units “0” and “1” can be achieved by utilizing graphene Rs values of 10 and 1000 Ω/sq, respectively, resulting in a reflection response with a phase difference of π and relatively large amplitude. The measurement results were compared with full-wave simulation ones to benchmark the performance of the proposed antenna. The antenna achieves more than 10 dB RCS reduction band from 12.5 to 27.7 GHz with a fractional bandwidth of 75.6%. The proposed design exhibits promising potential applications in stealth technology for intricate entities.

Rail vehicles generate huge longitudinal impact loads in collisions. If unreasonable matching exists between the compressive strength of the intermediate coupler and the structural strength of the car body, the risk of car body structure damage and train derailment will increase. Herein, a four-stage rigid–flexible coupling finite element model of the coupler is established considering the coupler buckling load. The influence of the coupler buckling load on the train longitudinal–vertical–horizontal buckling behavior was studied, and the mechanism of the train horizontal buckling instability in train collisions was revealed. Analysis results show that an intermediate coupler should be designed to ensure that the actual buckling load is less than the compressive load when the car body structure begins to deform plastically. The actual buckling load of the coupler and the asymmetry of the structural strength of the car body in the lateral direction are two important influencing factors for the lateral buckling of a train collision. If the strength of the two sides of the car body structure in the lateral direction is asymmetrical, the deformation on the weaker side will be larger, and the end of the car body will begin to deflect under the action of the coupler force, which in turn causes the train to undergo sawtooth buckling.

ABSTRACTWhen a train is in a nonbraking state during an actual collision, the wheelset rotational movement aggravates the wheel–rail impact and increases the wheel lift and risk of overriding. Based on the principle of equal initial collision kinetic energy, the idea of using wheelset translation instead of rotation is proposed. Moreover, the calculation formula for a mass equivalent coefficient is deduced. From the perspective of the dynamic transmission relationship between the car body, bogie, and wheelset, the mechanism of the wheelset lift are investigated. The research results show that without considering the rotational kinetic energy of wheelset, the difference of collision response can be effectively reduced by increasing the translational mass of wheelset by 10%. The vertical speed lift displacement and inclined lift displacement of the bogie have the largest contribution to the wheel lift. When the wheelset rotation is not considered, the wheel lift is significantly reduced.

This study comprehensively analyzes the failure behavior of metro vehicle end structures (VESs) during collisions, using the common material SUS301L-MT in a stainless steel metro and its VES as the research object. First, constitutive and failure tests are performed on the material, the macro–micro characterization of its mechanical properties is performed, and the failure strains and morphologies under various stress states are obtained and discussed. Subsequently, two failure criteria, Von Mises (VM) and Generalized Incremental Stress State Dependent Damage Model (GISSMO), are calibrated and established. Finally, the crashworthiness evaluation indexes of the VES are defined, and vertical offset collisions of metro VESs for different speed levels are numerically analyzed. The results show that the stress triaxiality significantly affects the failure strain of stainless steel SUS301L-MT, with the maximal difference for different stress states reaching 51.10%. SUS301L-MT stainless steel exhibits strain-rate strengthening and yield hysteresis effects. Overall, the numerical results for the VM criterion are worse than for the GISSMO criterion, which more accurately describes the collision behavior of metro VESs under complex stress states.

Synthetic transmit aperture (STA) imaging benefits from the two-way dynamic focusing to achieve optimal lateral resolution and contrast resolution in the full field of view, at the cost of low frame rate (FR) and low signal-to-noise ratio (SNR). In our previous studies, compressed sensing-based STA (CS-STA) and minimal ${l}_{{2}}$ -norm least squares (LS-STA) methods were proposed to recover the complete STA dataset from fewer Hadamard-encoded (HE) plane wave (PW) transmissions. Results demonstrated that, compared with STA imaging, CS/LS-STA can maintain the high resolution of STA in the full field of view and improve the contrast in the deep region with increased FR. However, these methods would introduce errors to the recovered STA datasets and subsequently produce severe artifacts to the beamformed images, especially in the shallow region. Recently, we discovered that the theoretical explanation for the error introduced in the LS-STA-based recovery is that the LS-STA method neglects the null space component of the real STA dataset. To deal with this problem, we propose to train a convolutional neural network under the null space learning framework (CNN-Null) to estimate the missing null space component) for high-accuracy recovery of the STA dataset from fewer HE PW transmissions. The mapping between the low-quality STA dataset (i.e., the range space component of the real STA dataset recovered using the LS-STA method) and the missing null space component of the real STA dataset was learned by the network with the high-quality STA dataset (obtained using full HE STA (HE-STA) imaging) as training labels. The performance of the proposed CNN-Null method was compared with the baseline LS-STA, conventional STA, and HE-STA methods, in terms of the visual quality, the normalized root mean square error (NRMSE), the generalized contrast-to-noise ratio (gCNR), and the lateral full-width at half-maximum (FWHM). The results demonstrate that the proposed method can greatly improve the recovery accuracy of the STA datasets (lower NRMSE) and, therefore, effectively suppress the artifacts presented in the images (especially in the shallow region) obtained using the LS-STA method (with a gCNR improvement of 0.4 in the cross-sectional carotid artery images). In addition, the proposed method can maintain the high lateral resolution of STA with fewer (as low as 16) PW transmissions, as LS-STA does.

Rising damp is one of the main problems affecting historical masonry structures worldwide, as it affects the appearance of heritage architecture and reduces strength. In this study, to reproduce the pathologies as much as possible and explain the mechanism, the aging test was set up with the climate data (temperature, humidity, etc.) derived from the real environment in nature at the location of the White Temple Tower, which was the object of this study. The tests mimicked the temperature, humidity, and types of salt solutions as closely as possible. Unlike the traditional aging test (producing specimens in accordance with some standards), two samples of blue brick carvings and blue brick cubes were used for the test. The results show that brick carvings suffered more severe surface degradation than brick cubes under various circumstances. Brick specimens' mechanical characteristics, such as wave velocity and compressive strength, were greatly diminished, and there was a fluctuating trend in surface hardness and color difference. The data indicate a size effect on the weathering between brick carvings and brick cubes, with the former displaying a faster rate of weathering under identical conditions. The experiment successfully simulates some of the phenomena observed in the field and provides an idea for studying the weathering of brick artifacts.

Grouting technology is the primary method for repairing cracks in earthen sites. However, there has been a long-standing lack of effective methods for evaluating grouting effectiveness. This paper proposes a field evaluation method based on P-wave velocity. This method explicitly discusses two scenarios where the P-wave velocity of the grout is either higher or lower than that of the soil, using the depth ℎ of the “hypothetical crack” as the evaluation indicator. The experimental results indicate that specimens with 20% and 40% defects show increases in ℎ values of 0.0113 m and 0.0166 m, respectively. Laboratory tests have demonstrated that this method can accurately evaluate grouting effectiveness and is not affected by the P-wave velocity of the soil. The application of this evaluation method to three typical earthen sites resulted in more reliable and easily quantifiable evaluation outcomes. By considering the width of grout, the method provides a more intuitive comparison of reparation effectiveness. The study demonstrates the feasibility of the proposed method, thereby facilitating effective crack reparation in earthen sites.

Grout injection is an effective technique for repairing cracks in earthen sites. This study aims to address the challenges of Calcined Ginger Nuts (CGN)-based grout and enhance its engineering performance by investigating the compatibility of different superplasticizers. We examined the effects of Polycarboxylate Superplasticizer (PCE) and Naphthalene Superplasticizer (PNS) on the properties of CGN-based grout, focusing on fluidity, rheological properties, mechanical strength, volume stability, color difference, and pore structure. The engineering applicability of the optimized CGN-based grout with superplasticizers was assessed using COMSOL Multiphysics. The results show that fluidity increased with higher dosages of PCE and PNS. The grout containing these superplasticizers behaved as a shear-thinning fluid, following the power law model. Specifically, the consistency coefficient of grout with 0.5 wt% PCE and PNS decreased by 39.73% and 64.83%, respectively. Additionally, 2.9 wt% PCE and PNS reduced volume shrinkage rate by 6.86% and 6.27%, respectively. Initially, increasing the dosage of PCE and PNS improved compressive and flexural strength, but these properties later declined. XRD analysis revealed that PNS above 1.1 wt% and PCE weakened the hydration reaction, while both superplasticizers promoted carbonation. Mercury Intrusion Porosimetry (MIP) showed that 1.1 wt% PCE and PNS reduced the proportion of capillary pores by 13.79% and 10.11%, respectively. Based on these findings, 0.5 wt% PNS demonstrated the best compatibility with CGN-based grout, whereas PCE showed poor compatibility. Numerical simulations using COMSOL Multiphysics confirmed that 0.5 wt% PNS provided superior grouting effectiveness. Therefore, the CGN based grout with 0.5wt% PNS demonstrates excellent engineering performance and applicability. This study offers valuable insights into optimizing CGN-based grout for the preservation of earthen sites.

ABSTRACTMultitemporal interferometric synthetic aperture radar (MT-InSAR) technique is an important approach for surface deformation monitoring. Nonlocal adaptive multilooking approach has potential benefits for the filtering and coherence estimation in the data preprocessing steps of MT-InSAR technique. The kernel of nonlocal adaptive multilooking approach lies in the selection of statistically homogeneous pixels (SHPs). Various amplitude-based strategies, such as DespecKS and its variations, have been proposed for selecting SHPs. However, the detection rates of these methods are usually unsatisfactory in the case of small data sets. To overcome this limitation, SHPs are selected based on the adaptive joint data vector, which encompasses both time dimensional samples and spatial information. In this letter, the outliers of the time dimensional samples are removed first based on a revised boxplot method. Additionally, image segmentation and L1 norm are both introduced to adaptively construct joint data vector in the preset window. Experiments on five TSX images are used to verify the reliability and efficiency of the proposed algorithm.

The underdetermined model in the hybrid massive multiple-input and multiple-output (MIMO) brings challenges to channel estimation. This paper proposes a low rank Hankel matrix reconstruction based method for this problem. First, the channel is modelled as a superposition of finite complex exponential functions based on the millimetre wave (mmWave) channel sparsity in angular domain. Then, channel estimation is converted into seeking a low rank Hankel matrix of the channel. For the low rank matrix reconstruction, an inequality constrained nuclear norm minimisation problem is built, and an efficient Alternating Direction Method of Multipliers (ADMM) based algorithm is derived for solving this problem. The new method estimates the channel using only one pilot. It is gridless, efficient, free of path number estimation, and has no minimum angle separation requirement. Its performances are verified by simulations and compared with representative algorithms.

In this paper, a new switch-based multi-polarised receiver architecture and two compatible Direction-of-Arrival (DOA) estimation algorithms are proposed for the partially polarised signals. In the receiver, each polarised element in an antenna is connected to a common Radio Frequency (RF) chain via a switch, which reduces the number of RF chains. For DOA estimation, an ESPRIT-based algorithm and a joint annihilation-based algorithm are proposed. The ESPRIT-based algorithm is based on summing the covariance matrices of different polarised outputs, and the joint annihilation-based algorithm is based on annihilating different polarised outputs by a common filter. Compared with other algorithms, the ESPRIT-based algorithm, which only takes about 91 us to perform one estimation, is more efficient and the joint annihilation-based algorithm, which can approach the Cramer-Rao Lower Bound (CRLB), is more accurate. It is also concluded that the tri-polarised Uniform Linear Array (ULA) can offer more accurate estimation than the dual-polarised ULA.

With the increase of energy consumption, the shortage of fossil resource, and the aggravation of environmental pollution, the development of cost-effective and environmental friendly bio-based energy storage devices has become an urgent need. As the second most abundant natural polymer found in nature, lignin is mainly produced as the by-product of paper pulping and bio-refining industries. It possesses several inherent advantages, such as low-cost, high carbon content, abundant functional groups, and bio-renewable, making it an attractive candidate for the rechargeable battery material. Consequently, there has been a surge of research interest in utilizing lignin or lignin-based carbon materials as the components of lithium-ion (LIBs) or sodium-ion batteries (SIBs), including the electrode, binder, separator, and electrolyte. This review provides a comprehensive overview on the research progress of lignin-derived materials used in LIBs/SIBs, especially the application of lignin-based carbons as the anodes of LIBs/SIBs. The preparation methods and properties of lignin-derived materials with different dimensions are systemically discussed, which emphasizes on the relationship between the chemical/physical structures of lignin-derived materials and the performances of LIBs/SIBs. The current challenges and future prospects of lignin-derived materials in energy storage devices are also proposed.

ABSTRACTThis paper summarizes the research on passive safety of rail vehicles from the perspective of Crash Energy Management (CEM) in recent decades, which covers the analysis of main crashworthiness standards, as well as the latest research progress in theoretical methods, numerical simulation, and experimental technology of rail vehicles crashworthiness. According to the research status of each subject, some weak links and potential research suggestions are pointed out, such as the requirements of CEM in standards, the influence mechanism of the coupler under different collision speeds, structural compatibility and standardization of anti-climbers, the establishment of vehicle structure crashworthiness design method in design-simulation-test closed-loop system, etc. In the future, under the support of mature CEM theory, more detailed and reliable numerical simulation models, more comprehensive vehicle crash test data, and higher computer computing efficiency, the passive safety of rail vehicles will be guaranteed to the maximum extent.

During the process of archaeological excavation in the regions of Southeast China, collapse of test square usually occurs due to poor site-specific conditions. In this paper, the fast Lagrangian analysis of continua in three dimensions (FLAC3D) is employed to reveal the behaviors of test square. Taking the archaeological works in Liangzhu prehistoric earthen sites as the research background, the paper first introduces the geological setting, excavation procedure and monitoring scheme of the studied test square. Then, the deformation of four sides of the test square is modeled using FLAC3D. By comparison, it shows that the numerical results are consistent with the results from field monitoring. The result suggests that the numerical simulation can be effectively applied to representing the actual behaviors of the test square, which is helpful for determination of excavation scheme and stability evaluation of the test square during archaeological excavation.

The work reported here is a systematic study to evaluate the compatibility of using PS-F (potassium silicate with high modulus – fly ash) slurry in the conservation of adobe structures. Firstly, the optimum mixing proportion (0.47) was determined by flow meter. Then the experimental program was divided into two parts: one part studied changes in physical and mechanical properties with increase in setting time by means of the measurement of moisture content, compressive and flexural strength, elastic-wave velocity, density, and porosity; the other part studied the durability of PS-F slurry through temperature and humidity cycles, freeze–thaw cycles, water stability, tensile testing, and alkali resistivity tests. The results show that the consolidation process with the slurry can meet the requirements of conservation applications and provide a timely anchoring force, and the slurry and soil mass of adobe-based structures have good compatibility in physical and mechanical properties. In addition, the slurry can strongly resist freeze–thaw cycles, temperature-moisture cycles, and tensile stress and has a relatively weak resistance to alkali solutions and water immersion. In conclusion, PS-F with a mixing ratio of 0.47 is a suitable slurry for conservation of adobe structures.