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The acoustic wave transmission manipulation ability is the most important performance for the acoustic metamaterials. To manipulate the acoustic transmission, the combination acoustic metamaterials structures are involved, and the two-directional acoustic penetration cloaking scheme are constructed. The combination acoustic metamaterials include chiral metamaterials and self-collimation metamaterials, the acoustic wave transmission path are manipulated to bypass from the acoustic scattering target in the penetration cloaking, and the target scattering stealth problem are effectively solved. In the end, the acoustic transmission manipulation performances are verified by numerical analysis with a finite-width acoustic metamaterial structure plates. The results provide technical support for design and application for acoustic transmission manipulation with acoustic metamaterials.

Background and Purpose Methods Results Conclusion Paramagnetic rim lesions (PRLs) are an MRI biomarker of chronic inflammation in people with multiple sclerosis (MS). PRLs may aid in the diagnosis and prognosis of MS. However, manual identification of PRLs is time‐consuming and prone to poor interrater reliability. To address these challenges, the Automated Paramagnetic Rim Lesion (APRL) algorithm was developed to automate PRL detection. The primary objective of this study is to evaluate the accuracy of APRL for detecting PRLs in a multicenter setting.We applied APRL to a multicenter dataset, which included 3‐Tesla MRI acquired in 92 participants (43 with MS, 14 with clinically isolated syndrome [CIS]/radiologically isolated syndrome [RIS], 35 without RIS/CIS/MS). Subsequently, we assessed APRL's performance by comparing its results with manual PRL assessments carried out by a team of trained raters.Among the 92 participants, expert raters identified 5637 white matter lesions and 148 PRLs. The automated segmentation method successfully captured 115 (78%) of the manually identified PRLs. Within these 115 identified lesions, APRL differentiated between manually identified PRLs and non‐PRLs with an area under the curve (AUC) of .73 (95% confidence interval [CI]: [.68, .78]). At the subject level, the count of APRL‐identified PRLs predicted MS diagnosis with an AUC of .69 (95% CI: [.57, .81]).Our study demonstrated APRL's capability to differentiate between PRLs and lesions without paramagnetic rims in a multicenter study. Automated identification of PRLs offers greater efficiency over manual identification and could facilitate large‐scale assessments of PRLs in clinical trials. [ABSTRACT FROM AUTHOR]

The band structure properties of phononic crystal is important to evaluate the vibration and noise reduction of acoustic metamaterials. Taking the 2D hexachiral phononic crystal as an example, the band structure and Dirac cone properties were investigated by numerical analysis, and the four-fold accidental degenerate Dirac point was obtained in the center of Brillouin zone. By adjusting the design parameters of ligament structure, a double Dirac cone was broken and a novel directional band gap was formed. The influence of geometric parameters on the directional band gaps width was investigated, and the band structure inversion problem was further discussed. This research can provide support for the application of hexachiral phononic crystal in elastic wave manipulation and acoustic topological insulator.

Objectives Reducing the weight of the cross-deck is an important method for reducing the weight and center of gravity of a trimaran. Structural strength analysis is used as the premise for judging whether a weight reduction method is feasible.Methods Based on the loading characteristics of a trimaran, a new dispersed cross-deck structure is proposed in which most of the unnecessary panels are removed. The finite element (FE) direct calculation method is adopted to analyze the structural strength of the dispersed cross-deck, and its strength is then compared with that of the traditional integral cross-deck.Results The results show that using the dispersed cross-deck can reduce the structural weight and center of gravity of a trimaran by 6.75% and 5.54% respectively on the premise of meeting the structural strength requirements.Conclusions Using the dispersed cross-deck can greatly reduce the structural weight and vertical location of the center of gravity, which provides new approaches for the structural design of trimarans.

In the present work, to improve the accuracy of the numerical model, the structural model updating problem is investigated in consideration of the influence of pre-stress. In order to eliminate the influence of complex pre-stress on the calculation scale and calculation precision for the continuous structures, the structural dynamic model updating is implemented by using the structural optimization strategy. The optimization function is established, in which the residual value of natural frequency parameter between the finite element model with/without complex pre-stress distribution is defined as objective function under certain constraints. Finally, the thin cylindrical shell structure with welding residual stress distribution, for example, the structural model updating is carried out, and the numerical results verify the feasibility and effectiveness of the proposed method.

In this study, the dynamic characteristic problem of riser structure with complex pre-stress distribution is investigated. At first, the differential equation of the riser structure with complex pre-stress distribution is derived. The analytical expression of the free vibration of a riser structure with complex pre-stress distribution is discussed by using the orthogonal property of the trigonometric series. A top-tensioned riser (TTR) for example, the influences of the amplitude and direction of complex pre-stress on natural frequency and mode shape characteristics are compared. This study provides a new method for addressing the riser structure response problem with complex loading.

The influence of the complex pre-stress on the circular plate is investigated herein, with which to solve the non-uniform pre-stress distribution problem. According to the strain–stress equation, the motion differential equations of the circular thin plate with complex pre-stress distribution are derived. Based on the Rayleigh–Ritz theory of energy method, the complex pre-stress distribution function and vibration-displacement function are expanded into the cosine trigonometric series, and the approximate analytical solutions of structural free vibration for circular plate are proposed. A circular plate with simply supported boundary condition, for example, the effectiveness of the proposed method is confirmed through numerical calculations and the finite element method verification. The influence of different type’s distribution of welding residual stress on the natural frequency and mode shape for circular plate structure are compared. The proposed approach in present article can be used in arbitrary pre-stress distribution problem.

[Objectives] The mounting structure of a ship is an important piece of equipment for vibration reduction. In order to improve the vibration reduction effect of the mounting structure, damping material is often pasted onto its surface.[Methods] The vibration level difference of the mounting structure's acceleration parameters is defined as the evaluation index. Based on the Solid Isotropic Material with Penalization(SIMP) model, a topological optimization model of free damping material distribution is established. In the optimization formulation, the constraints ensure the optimal distribution of damping material on the surface of the structure while the total volume of damping material is certain. Finally, based on the Finite Element Model (FEM) of the structure, the optimal damping materials for the laying scheme are ascertained. The results of topological optimization are tested and verified by the model test.[Results] The optimal free damping material distribution of amounting structure is obtained.[Conclusions] The research results have value as a reference for the design of the mounting structures of ships and the application of composite materials.

Objective: To determine early magnetic resonance imaging (MRI) features of new multiple sclerosis (MS) lesions that will develop into paramagnetic rim lesions (PRLs), which have been associated with progressive tissue injury in MS. Methods: New contrast‐enhancing lesions observed on routine clinical MRI were imaged at 7 T within 4 weeks of observation, and 3 and 6 months later. The 6‐month MRI was used to classify PRL status (PRL or non‐PRL). The relationship between early lesion characteristics and subsequent PRL status was assessed using generalized linear mixed effects models. Random forest classification was performed to classify early predictors of subsequent PRL status. Results: From 93 contrast‐enhancing lesions in 23 MS patients, 37 lesions developed into a PRL. In lesions that developed into PRLs compared with those that did not, the average lesion T1 on the initial 7 T MRI was 1994 ms compared with 1,670 ms (p‐value <0.001), and the average volume was 168.7 mL compared with 44 mL (p‐value <0.001) in lesions that did not. These volume differences were also found on 3 T scans (p‐value <0.001), and for intensity‐normalized T1‐w (p‐value = 0.011) and fluid‐attenuated inversion recovery (p‐value = 0.005). The area under the receiver operating characteristic curve for the random forest classification with leave‐one‐out cross‐validation was found to be 0.86 using initial 7 T features. Interpretation: New MS lesions that evolve into PRLs can be identified early in lesion evolution. These findings suggest that biological mechanisms underlying PRL development begin early, which has important implications for clinical trials targeting PRLs development and subsequent therapeutics. ANN NEUROL 2023;94:736–744 [ABSTRACT FROM AUTHOR]