Material characterisation by enhanced resolution in non-stationary thermal wave imaging

In the recent past, quadratic frequency-modulated thermal wave imaging (QFMTWI) has been advanced with a chirp z-transform (CZT)-based processing approach to facilitate enhanced subsurface anomaly detection, depth quantification and material property estimation with enhanced depth resolution. In the present study, the applicability of CZT-based phase analysis for foreign object defect detection in a structural steel sample using QFMTWI is validated through finite element-based numerical modelling rather than experimental verification due to limited available resources. Furthermore, the enhanced defect detection capability of the CZT phase approach is qualitatively compared with the frequency- and time-domain phase approaches using the defect signal-to-noise ratio (SNR) as a quality metric. Also, an empirical relationship between the observed phases and the thermal reflection coefficient is obtained, which recommends the CZT phase as a prominent approach for foreign material defect detection.

A Numerical Study of Optimization Methods for Phase-Only Optical Pulse-Shaping

The field of optical pulse-shaping and its applications is introduced, with a focus on time-domain approaches. A numerical investigation of all-fiber, time-domain, phase-only filtering is conducted for arbitrary temporal pulse synthesis. The theoretical phase modulation function required for generating use- specific target-intensity profiles is calculated using different optimization methods including a Brute Force Monte Carlo search, the Simulated Annealing method and the Genetic Algorithm method. The convergence speed, computational complexity and accuracy of these methods is compared under binary phase-only modulation, where the Genetic algorithm was found to outperform other methods.

A multi-step nucleation process determines the kinetics of prion-like domain phase separation

Compartmentalization by liquid-liquid phase separation (LLPS) has emerged as a ubiquitous mechanism underlying the organization of biomolecules in space and time. Here, we combine rapid-mixing time-resolved small-angle X-ray scattering (SAXS) approaches to characterize the assembly kinetics of a prototypical prion-like domain with equilibrium techniques that characterize its phase boundaries and the size distribution of clusters prior to phase separation. We find two kinetic regimes on the micro- to millisecond timescale that are distinguished by the size distribution of clusters. At the nanoscale, small complexes are formed with low affinity. After initial unfavorable complex assembly, additional monomers are added with higher affinity. At the mesoscale, assembly resembles classical homogeneous nucleation. Careful multi-pronged characterization is required for the understanding of condensate assembly mechanisms and will promote understanding of how the kinetics of biological phase separation is encoded in biomolecules.

Intelligent Fluorescence Image Analysis of Giant Unilamellar Vesicles and Protein Liquid Phase Droplets by Whole Z-stack Analysis

Fluorescence image analysis in biochemical science often involves the complex tasks of identifying samples for analysis and calculating the desired information from the intensity traces. Analyzing giant unilamellar vesicles is one of these tasks. Researchers need to identify many vesicles to statistically analyze the degree of molecular interaction or state of molecular organization on the membranes. This analysis is complicated, requiring a careful manual examination by researchers, so automating the analysis can significantly aid in improving its efficiency and reliability. We developed an intelligent analysis routine based on the 3D information of whole z-stack images. The program identifies the valid vesicles to analyze and calculates the desired data automatically. The program can examine the amount of protein binding on the membranes and determine the state of domain phase separation by calculating the fluorescence intensity trace along the membranes. We also show that the method can easily be applied to similar analyses, such as intensity analysis of phase-separated protein droplets. A deep learning-based classification approach enables the identification of vesicles even from relatively complex samples. We demonstrate that the proposed artificial intelligence-assisted classification can further enhance the accuracy of the analysis close to the performance of manual examination.

A time-domain phase diagram of metastable states in a charge ordered quantum material

Metastable self-organized electronic states in quantum materials are of fundamental importance, displaying emergent dynamical properties that may be used in new generations of sensors and memory devices. Such states are typically formed through phase transitions under non-equilibrium conditions and the final state is reached through processes that span a large range of timescales. By using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), the evolution of the metastable states in the quasi-two-dimensional dichalcogenide 1T-TaS2 is mapped out on a temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from 10-12 to 103 s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram and opening the way to understanding of the complex ordering processes in metastable materials.

Progress on Forcing Pulsations for Acoustic, Thermoacoustic or Flow Control Purpose in a Pressurised Vessel by Means of a Siren

A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under combustor field conditions. Its principle relies on a sonic jet sheared periodically by a cogged wheel rotating at a given speed. Developed for experiments in combustion stability, it offers an alternative to loudspeakers when the use of these is made difficult because of aggressive flow conditions (e.g. elevated conditions of pressure and temperature, presence of impurities in the gas). While the siren was designed for laboratory applications, its technology is a promising candidate for effective flow control on gas turbine fleets. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly and identifies a zone of combustion instability during a sensitivity analysis where the flame is exposed to calibrated perturbations. Regarding control applications, it can act out of phase for damping purposes in the low-frequency domain (phase control), or transfer the acoustic energy to a higher and less harmful sub-harmonic (modal control). Since a chocked nozzle is involved, the siren’s actuation is decoupled from the flow condition downstream, which is convenient for control. Following-up to previous works where a siren model was introduced with the capacity to vary the amplitude of pulsation independently from the frequency [GT2011-45071], this paper describes into details new features as follows. First, the performance of the apparatus was improved to visit frequencies in the 0–6 kHz range so that the operation is extended to frequencies met by precessing vortex cores in a burner or tangential instabilities in an annular combustor. Next, the discharge configuration is tested and validated as an alternative to the conventional blow-down operation with the siren placed upstream of the pressurised test cell. There, the siren is placed downstream of the test cell, deriving a small part of the pressurised air in the plenum. Finally, a new calibration procedure for fast pressure probes and accelerometers is presented and tested. A multi-modal excitation is introduced where more than one frequency peak is being produced and where the excited frequencies create a kind of a chord. In conclusion the siren is recommended as an effective flow controller, and as a broadband and powerful calibrator.