Accurate Ultrasonic Thickness Measurement for Arbitrary Time-Variant Thermal Profile.

Ultrasonic thickness measurement of mechanical structures is one of the most popular and commonly used nondestructive methods for various kinds of process control and corrosion monitoring. With ultrasonic propagation speed being temperature-dependent, the thickness measurement can be performed reliably only when the thermal profile is completely known. Most conventional techniques assume the temperature of the test structure is uniform and at room temperature across its thickness.

Multi-level structural damage characterization using sparse acoustic sensor networks and knowledge transferred deep learning.

Standard structural health monitoring techniques face well-known difficulties for comprehensive defect diagnosis in real-world structures that have structural, material, or geometric complexity. This motivates the exploration of machine-learning-based structural health monitoring methods in complex structures. However, creating sufficient training data sets with various defects is an ongoing challenge for data-driven machine (deep) learning algorithms.

Large-area inspection of defects in metal plates using multi-mode guided acoustic waves and sparse sensor networks.

Various types of defects can be induced during the manufacturing or operation of engineering structures. For effective detection and characterization of the defects in large engineering structures, this paper proposes a large-area inspection technique that combines multi-mode guided acoustic waves with sparse sensor networks. The basic sparse sensor network employed in this study is composed of one transmitter and three receivers, distributed in a square lattice on the test plates.

Void-Engineered Metamaterial Delay Line with Built-In Impedance Matching for Ultrasonic Applications.

Metamaterials exhibit unique ultrasonic properties that are not always achievable with traditional materials. However, the structures and geometries needed to achieve such properties are often complex and difficult to obtain using common fabrication techniques. In the present research work, we report a novel metamaterial acoustic delay line with built-in impedance matching that is fabricated using a common 3D printer.

Ultrasonic Testing of Mechanical Changes in a Water-Filled Pipe with Multi-Mode and Broadband Signals and Two-Level Compensation.

Ultrasonic testing (UT) has been widely used for the Nondestructive Evaluation (NDE) of pipes due to its many favorable characteristics. However, one of the main challenges in the general use of UT for real-world pipelines is the sensitivity of this method to environmental and operational condition changes. This paper proposes a new UT method with enhanced compensation for environmental effects and operational condition changes.

Thermodynamics, dynamics, and structure of supercritical water at extreme conditions.

Molecular dynamics (MD) simulations to understand the thermodynamic, dynamic, and structural changes in supercritical water across the Frenkel line and the melting line have been performed. The two-phase thermodynamic model [J. Phys.

Electrical conductivity, ion pairing, and ion self-diffusion in aqueous NaCl solutions at elevated temperatures and pressures.

We have performed classical molecular dynamics (MD) simulations of aqueous sodium chloride (NaCl) solutions from 298 to 674 K at 200 bars to understand the influence of ion pairing and ion self-diffusion on electrical conductivity in high-temperature/high-pressure salt solutions. Conductivity data obtained from the MD simulation highlight an apparent anomaly, namely, a conductivity maximum as temperature increases along an isobar, which has been also observed in experimental studies. By examining both velocity autocorrelation and cross-correlation terms of the Green-Kubo integral, we quantitatively demonstrate that the conductivity anomaly arises mainly from a competition between the single-ion self-diffusion and the contact ion pair formation.

Size-dependent silicon epitaxy at mesoscale dimensions.

New discoveries on collective processes in materials fabrication and performance are emerging in the mesoscopic size regime between the nanoscale, where atomistic effects dominate, and the macroscale, where bulk-like behavior rules. For semiconductor electronics and photonics, dimensional control of the architecture in this regime is the limiting factor for device performance. Epitaxial crystal growth is the major tool enabling simultaneous control of the dimensions and properties of such architectures.

Hybrid photovoltaics based on semiconductor nanocrystals and amorphous silicon.

Semiconductor nanocrystals (NCs) are promising materials for applications in photovoltaic (PV) structures that could benefit from size-controlled tunability of absorption spectra, the ease of realization of various tandem architectures, and, perhaps, increased conversion efficiency in the ultraviolet region through carrier multiplication. The first practical step toward utilization of the unique properties of NCs in PV technologies could be through their integration into traditional silicon-based solar cells. Here, we demonstrate an example of such hybrid PV structures that combine colloidal NCs with amorphous silicon.