We apply wavelet analyses to study how the Covid pandemic influenced the volatility of commodity prices, covering various classes of commodities. We document the intervals of low, medium, and high ...coherence between the coronavirus panic index and the moves of the commodity prices. The low coherence intervals indicate the diversification potential of commodity investments during a systemic pandemic such as Covid-19. We document differences in the observed patterns per commodity category and evidence their potential role for designing cross-assets hedge strategies based on investments in commodities.
•We examine the impact of Covid fueled panic on the volatility of commodity prices.•Wavelet coherence and phase-difference methods are used to study interdependencies.•For diverse commodities, we find low coherence intervals, implying hedge potential.•Energy, agricultural stuff, and precious metals are attractive diversifying hedges.•Non-precious metals offer the best diversification during the recovery from crisis.
A body of work using the continuous wavelet transform has been growing. We provide a self‐contained summary on its most relevant theoretical results, describe how such transforms can be implemented ...in practice, and generalize the concept of simple coherency to partial wavelet coherency and multiple wavelet coherency, moving beyond bivariate analysis. We also describe a family of wavelets, which emerges as an alternative to the popular Morlet wavelet, the generalized Morse wavelets. A user‐friendly toolbox, with examples, is attached to this paper.
We perform time-frequency wavelet-based analysis to explore how the media coverage of the Covid-19 pandemic influenced the volatility of the Islamic equity indices, covering various sectors of ...economic activity. Our results show that the coherence between the Media Coverage Index and the moves of the Islamic stocks varies from low and medium to high levels. We attribute the intervals of low coherence to the diversification potential of Islamic equity investments during a systemic pandemic such as Covid-19. We document differences in the patterns exhibited by various indices per sector, showing their potential role for designing hedging strategies across sectors, based on stocks of companies which comply with Shariah.
•Impact of the Covid-19 media coverage on DJ Islamic equity volatility is studied.•We apply wavelet method and reveal intervals of low, medium, and high coherence.•We observe differences in the coherence patterns per sector of economic activity.•The “brick-and-mortar” and service-oriented sectors responses to Covid differ.•Faith-based investments offer attractive hedging attributes during systemic crises.
•The mechanism of the bimodal coupling phase difference varying along the span is revealed.•The phase difference of vibration increases from the mid-span to the bridge tower.•The vibration track of ...the main girder and main cable are elliptical and asynchronous along the span.
The research on vibration characteristics of long-span bridges is of great importance to flutter analysis, yet the literature is limited which concerns the phase difference characteristic of the full bridge. This study thus aims to investigate the vibration phase difference characteristics and mechanism along the main span during flutter. The time-domain flutter analysis was conducted in a long-span suspension bridge. The results manifest that the vibration in different directions at the same position and the vibration in the same direction at different positions of the main girder and the main cable all exist phase difference, which varies along the main span. The deduced phase difference equation reveals that the variable of the distance from mid-span is in cosine term of the denominator, making the increasing of the distance resulting in the growth of phase difference. Due to the variation of phase difference, the vibration of the main girder and main cable along the span is asynchronous. The motion trajectories of individual points are elliptic and vary along the main span. These findings can help understand the flutter performance and mechanism of long-span bridges.
We apply wavelet analyses to examine the impact of the Covid-19 fueled panic on the volatility of major fiat and cryptocurrency markets during January–May, 2020. There is high coherence between moves ...of the Coronavirus Panic Index and the price moves in Euro, British pound, and Renminbi currencies as well as movements of the Bloomberg Galaxy Crypto Index. The main conclusions for each index pair are quite similar and corroborate with our thesis that the cross-currency hedge strategies, which could work under normal market conditions, are likely to fail during the periods of global crisis, e.g., such as the Covid-19 pandemic. However, we document some important differences in currency markets behavior, which potentially could be used to design effective cross-currency hedges capable of withstanding adverse impacts of global financial and economic turmoil. Our findings could be of use for future development of financial policies and currency markets regulation rules.
•We examine the impact of the Covid-19 panic on the volatility of fiat currency and cryptocurrency markets.•We apply wavelet coherence and wavelet phase difference techniques to identify interdependencies.•There is high coherence between the Coronavirus Panic Index and the EUR, GBP, RMB.•There is high coherence between the Panic Index and the eleven major cryptocurrencies.•The cross-currency hedges for normal market conditions may fail during periods of global crisis.
Wave phase difference is a fundamental property that characterises the relative behaviour of transmitted signals. It has significant roles in signal wave analysis and in interpreting various ...propagation phenomena, which are crucial when designing wireless links and various applications in signal processing techniques, optics, and acoustics. This study investigated the concept of phase difference significance based on high frequencies (i.e., 1.0, 2.4, 10.0, and 20.0 GHz). Several phase difference models and their shortcomings were reviewed to emphasise the need for greater accuracy and precision in quantifying phase differences. The outcomes revealed that 1 GHz contributed to the lowest phase difference among the other frequencies. A constructive signal may be deployed to provide a better link build-up. Overall, determining the importance of phase difference in GHz and identifying the signal attitude substantially contribute to the advancement of wave analysis, while simultaneously encouraging further exploration in this domain.
Fiber-optic hydrophone (FOH) has been widely applied for underwater target signal detection, while the environmental influences and device instability often introduce light intensity disturbance, ...which makes it difficult for the target signal to be accurately restored. This paper demonstrates, for the first time, a novel self-phase difference ellipse fitting demodulation scheme with sinusoidal excitation (SPD-Fe) to address the above challenges. In the proposed SPD-Fe scheme, a pair of interference pulses for target signal demodulation are generated by one single pulse bisection, frequency shifting, time delay processing and interfering at two arms of FOH. By applying ellipse fitting, the nonlinear distortion of demodulation results introduced by the light intensity disturbance can be eliminated. Additional sinusoidal excitation not only resolves the issue of insufficient fitting data when the amplitude of the target signal is too low, but also ensures that the FOH is all-optical structure. Experimental results show that SPD-Fe scheme accurately demodulates a low-amplitude target signal in the presence of light intensity disturbance, with Signal-to-Noise and Distortion Ratio (SINAD) of 46.17 dB. Meanwhile, the nonlinear distortion is eliminated, with Total Harmonic Distortion (THD) of 0.08%. With excellent stability, simple hardware architecture and all-optical FOH structure, SPD-Fe scheme has potential applications in underwater acoustic target detection and characteristic measurement.
A novel radio frequency identification (RFID)-based mobile robot global localization method combining two kinds of RFID signal information, i.e., phase difference and readability, is proposed. ...Specifically, a phase difference model and a classification logic strategy based on readability are built and integrated into a particle filter localization algorithm. Compared with existing RFID localization methods, the proposed localization method can achieve competitive localization performance in an environment with a relatively sparse reference tag distribution and without the need for offline phase drift calibration. A series of real experimental tests were performed, and the results show that the proposed method can localize a mobile robot with centimeter-level position accuracy and satisfactory attitude angle accuracy when the distance between adjacent reference tags is approximately 60 cm, even if all RFID devices are commercial off-the-shelf (COTS). The proposed method provides a promising option for mobile robot localization applications, such as path tracking of mobile robots. Note to Practitioners -Mobile robot localization is a key technology for its location-based services. Considering that radio frequency identification (RFID) is entirely unaffected by light interference and has a globally unique ID, RFID has been regarded as a localization sensor with broad application prospects. This article proposes an RFID-based mobile robot global localization method combining phase difference and readability, by which the mobile robot can be accurately localized in an environment with a relatively sparse reference tag distribution and without the need for offline phase drift calibration. The experimental results indicate that the proposed method can localize the mobile robot with good performance, including centimeter-level position accuracy and satisfactory attitude angle accuracy. The proposed method can effectively contribute to many practical applications, such as the path tracking of a mobile robot.
•An optical structure of dual-period liquid crystal phase grating with excellent performance is proposed.•Optimal parameter selections for the liquid crystal phase grating are thoroughly ...discussed.•Comprehensive simulations are carried out on the liquid crystal phase grating, elucidating its operational behavior.•A tunable LC phase grating shows great potential for diffractive optics components.
The liquid crystal (LC) phase grating is highly sought-after in a myriad of applications, ranging from telecommunications to sensing technologies. However, achieving both rapid response times and high phase differences simultaneously remains a formidable challenge. Here, a novel single-sided dual-period LC phase grating structure with high phase difference and fast-response is proposed. The grating's substrate is comprised of a composite electrode, incorporating strip electrodes and a common electrode. By applying varied voltages across different electrode modules, distinct periods and diffraction angles are attained. Simulation results indicate that this approach yields phase differences of 1.61π for large-period LC phase grating and 1.17π for small-period ones. Moreover, the measured rise and decay time for the former is 8.15 ms and 4.10 ms, and for the latter is 8.84 ms and 4.12 ms, respectively. The proposed LC phase grating, with its simplicity and ease of operation, holds substantial potential for application across a broad spectrum of fields, highlighting its considerable room for development.
In this paper, a numerical crack growth analysis is conducted by using the Maximum Tangential Stress (MTS) criterion and its extension, which considers the contact stress between the crack surfaces. ...Moreover, fretting fatigue is a multiaxial non-proportional loading problem, and most components are subjected to asynchronous loads. Therefore, this paper mostly focuses on the influence of loading phase difference (Φ) on the crack propagation behavior. Meanwhile, for the fretting fatigue problem, as there is a relationship between the crack initiation and propagation, the effect of initiation characteristics, including crack initiation position and direction is studied under different loading phase differences using Linear Elastic Fracture Mechanics (LEFM) theory. It is observed that the predicted crack path and lifetime by using the extended MTS criterion and Paris’ law is in good agreement with the experimental results in the literature. It is found that the phase difference has a strong effect on the crack propagation behavior. Furthermore, we found that the crack initiation position has a greater influence on crack propagation behavior than the crack initiation direction.
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