Numerical and Experimental Investigation on Parameter Identification of Time-Varying Dynamical System Using Hilbert Transform and Empirical Mode Decomposition

This paper proposes an approach to identifying time-varying structural modal parameters using the Hilbert transform and empirical mode decomposition. Definition of instantaneous frequency and instantaneous damping ratio based on Hilbert transform for single-degree-of-freedom (SDOF) system is first introduced. The following is the definition of Hilbert damping spectrum from which the time-varying damping ratio of multi-degree-of-freedom (MDOF) system can be calculated. Identification procedures for both instantaneous frequency and damping ratios based on their definition are then introduced. Applicability of the proposed identification algorithm has been validated through several numerical examples. The instantaneous frequency and damping ratios of SDOF system under free vibration and under sinusoidal and white noise excitation have been identified. The proposed method is also applied to MDOF system with slow and sudden changing structural parameters. The results demonstrate that when the system modal parameters are slowly changing, the instantaneous frequency could be easily and well identified with satisfied accuracy for all cases. However, the instantaneous damping ratio could be extracted only when the system is lightly damped. The damping results are better for free vibration situation than for the forced vibration cases. It is also shown that the suggested method can easily track the abrupt change of system modal parameter under free vibration. The proposed method is then applied to a 12-story short-lag shear wall structure model tested on a shaking table. The instantaneous dynamic properties of the structure were identified and were then introduced as known parameters into a finite element model. Comparisons with the numerical results using constant structural parameters demonstrate that the calculated structural responses using the identified time-varying parameters are much closer to the experimental results

Wetting layer evolution and its temperature dependence during self assembly of InAs/GaAs quantum dots

For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy (RDS) and analyzed with a rate equation model. The WL thicknesses showed a monotonic increase at relatively low growth temperatures but a first increase and then decrease at higher temperatures, which were unexpected from the thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD growth was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was also given. Those results gave hints of the kinetic aspects of QD self-assembly.Comment: 13 pages, 3 figure

One-Step Rapid and Scalable Flame Synthesis of Efficient WO3 Photoanodes for Water Splitting

Photoelectrochemical water splitting is a promising approach for the carbon‐free production of hydrogen using sunlight. Here, robust and efficient WO3 photoanodes for water oxidation were synthesized by the scalable one‐step flame synthesis of nanoparticle aerosols and direct gas‐phase deposition. Nanostructured WO3 films with tunable thickness and band gap and controllable porosity were fabricated by controlling the aerosol deposition time, concentration, and temperature. Optimal WO3 films demonstrate superior water oxidation performance, reaching a current density of 0.91 mA at 1.24 V vs. reversible hydrogen electrode (RHE) and an incident photon‐to‐current conversion efficiency (IPCE) of ca. 61 % at 360 nm in 0.1 m H2SO4. Notably, it is found that the excellent performance of these WO3 nanostructures arises from the high in situ restructuring temperature (ca. 1000 °C), which increases oxygen vacancies and decreases charge recombination at the WO3/electrolyte interface. These findings provide a scalable approach for the fabrication of efficient photoelectrodes based on WO3 and other metal oxides for light‐driven water splitting.A.T. gratefully acknowledges the support of the Australian Research Council (AR; DP150101939, ARC DE160100569), and a Westpac 2016 Research Fellowship

Performance evaluation: Identifying barriers and enablers for landscape architecture practice

Performance evaluation is crucial for environmental design and sustainable development, especially so for architecture and landscape architecture. However, such performance evaluations remain rare in practice. It is argued that the concerns over potential negative evaluations and a lack of funding are the two main barriers preventing the undertaking of performance evaluations. This research investigated how these two barriers were overcome in practice by studying 41 evaluation cases in the New Zealand landscape architecture field, as well as several international and architectural case studies for comparison. A range of enablers for performance evaluation practices were identified by this research, including funding sources and models that were not documented by existing literature, as well as two strategies for handling the risks of negative evaluation. All of the identified enablers share the same underlying logic—the benefits and costs of an evaluation should be well-regulated by certain mechanisms to keep the benefits of an evaluation greater than, or at least balanced with, the costs, for all the parties involved in the evaluation

Design of a Fibrin Microthread Bundling Device

Fibrin microthreads are a biological material being used for targeted cell delivery, but exhibit variance in their mechanical properties. A mechanical microthread bundling device was designed to produce consistent and reproducible bundles. The mechanical properties, cell seedability, and twist consistency of prototype bundles were compared to hand-made samples. Hand-made samples were calculated to have a YS, UTS, and E of 0.390 ± 0.190, 1.066 ± 0.678, and 0.405 ± 0.168 MPa, respectively. Prototype produced bundles had a YS, UTS, and E of 0.196 ± 0.050, 0.537 ± 0.181, and 0.269 ± 0.158 MPa respectively. Prototype bundles were found to have an average of 1.65 ± 0.5 twists per cm. Average values and standard deviations for bundle mechanics were found to be lower for prototype bundles