Over the past decade, RNA sequencing (RNA-seq) has become an indispensable tool for transcriptome-wide analysis of differential gene expression and differential splicing of mRNAs. However, as next-generation sequencing technologies have developed, so too has RNA-seq. Now, RNA-seq methods are available for studying many different aspects of RNA biology, including single-cell gene expression, translation (the translatome) and RNA structure (the structurome). Exciting new applications are being explored, such as spatial transcriptomics (spatialomics). Together with new long-read and direct RNA-seq technologies and better computational tools for data analysis, innovations in RNA-seq are contributing to a fuller understanding of RNA biology, from questions such as when and where transcription occurs to the folding and intermolecular interactions that govern RNA function.

RNA sequencing: the teenage years

Time-reassigned synchrosqueezing transform: The algorithm and its applications in mechanical signal processing

Foreword Chapter 1 Introduction to SHM (Daniel L Balageas) Chapter 2 Vibration-based techniques for SHM (Claus-Peter Fritzen) Chapter 3 Fiber-optics sensors (Alfredo Guemes and Jose M Menendez) Chapter 4 SHM with piezoelectric sensors (Philippe Guy and Thomas Monnier) Chapter 5 SHM using electrical resistance (Michelle Salvia and Jean-Christophe Abry) Chapter 6 Low frequency electromagnetic techniques (Michel B Lemistre) Chapter 7 Capacitive methods for SHM in civil engineering (Xavier Derobert and Jean Iaquinta) Short Bibliographies of the Contributors Index

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Structural health monitoring

Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws.

Structural Health Monitoring (SHM) and Determination of Surface Defects in Large Metallic Structures using Ultrasonic Guided Waves.

This review introduces several areas of importance in acoustic emission (AE) technology, starting from signal attenuation. Signal loss is a critical issue in any large-scale AE monitoring, but few systematic studies have appeared. Information on damping and attenuation has been gathered from metal, polymer, and composite fields to provide a useful method for AE monitoring. This is followed by discussion on source location, bridge monitoring, sensing and signal processing, and pressure vessels and tanks, then special applications are briefly covered. Here, useful information and valuable sources are identified with short comments indicating their significance. It is hoped that readers note developments in areas outside of their own specialty for possible cross-fertilization.

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Review on Structural Health Evaluation with Acoustic Emission

Structural Health Monitoring (SHM) allows the integrity of a system to be monitored in situ, detecting weaknesses as they form. Due to the waveguide nature of cylindrical structures, ultrasonic waves can be used to detect defects in cables over large distances. Considering that common power line cables consist of several individual wires, a straightforward energy-based approach is chosen to simplify the model development. The purpose of this investigation is to extend the current coupling model to include n wires and to verify this model for a seven-wire cable, experimentally. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Inter‐wire Coupling Model Development for Health Monitoring of Cable Structures


 This work is concerned the with analysis of the convergence of guided waves in pipes to Lamb waves in plates for isotropic materials. The main goal is to be able to define a threshold frequency above which it is reasonable to approximate waves propagating in a pipe with a certain wall thickness to radius ratio as Lamb waves. The study involves a detailed comparison of velocity differences for symmetric and antisymmetric waves in plates versus longitudinal and flexural modes in pipes. Phase and group velocities of pipes with various wall thickness-to-radius ratios are compared to a plate of corresponding thickness. An empirical convergence criterion is defined to determine the frequency above which a pipe will have a plate-like response. It is shown that “convergence” may already be reached at frequencies commonly used for nondestructive testing purposes. Analytical considerations are supported and validated by experimental results, showing good agreement of predicted and measured wave velocities.

Guided Waves in Pipes Versus Lamb Waves in Plates - A Convergence Analysis

In order to support the continued trend of increased use of composite materials in many industries, efficient testing systems need to be developed. That is, existing visual inspection techniques may be inadequate as they do not allow for the detection of internal flaws such as delaminations. The contributions of this paper to the nondestructive testing (NDT) community are threefold: it provides 1) an overview of an opportunity for undergraduate engineering education in form of a class project, 2) a description and demonstration of a newly developed multi-axis positioning system for air-coupled transducers and 3) the application to the characterization of composites. A competition-based course project was designed for an undergraduate machine design class. The objective of the project was to design a low-cost, multi-axis positioning system for NDT experiments. The winning design was built and features an innovative robotic arm with many custom-made components, including a 2-D goniometric stage for orienting air-coupled ultrasound transducers. The system allows for automated and accurate positioning to acquire detailed wave propagation and scattering data from NDT experiments on composite specimens. The NDT positioning system’s capabilities are demonstrated via dispersion characterization problems on metal and composite specimens. Specifically, a pitch-catch methodology is employed where one stationary transducer is complemented by a roving transducer positioned with the robotic arm. Several datasets are collected and different signal processing techniques are employed in an effort to characterize the studied specimens. The results are compared to the existing literature and simulation data, showing good agreement.

Automated nondestructive testing of composites using air-coupled guided ultrasound

In order to support the continued trend of increased use of composite materials especially in aviation, efficient testing systems need to be developed. The anisotropic material properties of composites allow for high specific stiffnesses and strengths. However, some failure modes in composite structures cannot be identified through visual inspection and to ensure the health of the structures, a time-consuming and costly inspection approach must be taken. Often, this approach includes disassembly and premature part replacements. Thus, complete nondestructive inspection (NDI) and monitoring of composite structures in aviation is virtually nonexistent. Hence, there is a need to introduce an autonomous inspection method to reduce time and cost, while increasing aircraft reliability. To this end, several recent advancements of a mobile robotic platform and related algorithms for Lamb wave-based inspection of aircraft surfaces are presented here. The robots are envisioned to be operated in a low cardinality swarm, where each robot employs guided ultrasound technology to collaboratively inspect plate-like components. For the purpose of implementing a fully autonomous platform, simultaneous localization and mapping (SLAM) methods are combined with Lamb wave-based NDI techniques. Specifically, it is demonstrated that a novel Lamb wave-based edge seeking and tracing methodology can contribute to increasing testing efficiency, with the overarching goal of creating a full map of the tested structure including all potential flaws. 

Recent advancements on autonomous Lamb wave-based nondestructive inspection

High-intensity focused ultrasound (HIFU) has been studied for the purpose of developing a variety of medical therapies. Numerical and laboratory work has led to many clinical trials as well as first approved therapies, such as in the case of prostate cancer. However, little research has been performed to validate numerical simulations and in-vivo HIFU treatments in the presence of bones. To this end, recent advancements on visualization and optical measurements using schlieren techniques are presented in this work. In laboratory experiments, HIFU is induced in a tank filled with distilled water, and the incident waves are scattered at a bone phantom plate. Advanced filtering and computer vision techniques are adopted and their general feasibility is demonstrated for unobstructed and partially obstructed HIFU wave fields. In particular, it is shown that low-amplitude reflected wave peaks can be tracked despite their superposition with high-amplitude incident waves. 

Christoph Schaal

Papers

Inter‐wire Coupling Model Development for Health Monitoring of Cable Structures

Guided Waves in Pipes Versus Lamb Waves in Plates - A Convergence Analysis

Automated nondestructive testing of composites using air-coupled guided ultrasound

Recent advancements on autonomous Lamb wave-based nondestructive inspection

Visualization and analysis of the scattering of high-intensity focused ultrasound at bone phantoms