Dataset Information

Testing for multiple bubbles in the copper price: Periodically collapsing behavior.

ABSTRACT: This study investigates whether multiple bubbles exist in the copper price on the basis of the Generalized Supremum Augmented Dickey-Fuller (GSADF) approach (Phillips et al., 2013). This technique delivers date-stamping strategies for the emergence as well as collapse of explosive bubble episodes and is best suited for practical application to time series. The results reveal that four explosive bubbles are detected over the period of 1980-2019 when copper price deviates from fundamental value. Besides, this finding is in accordance with the asset pricing model (Gürkaynak, 2008), which generally considers both fundamental and bubble components in the presence of asset prices. Based on the empirical results, the multiple emergence and collapse of multiple price bubbles are attributed to speculation, depreciation of the U.S. dollar, an imbalance between supply and demand, and financial crises. Policymakers should actively recognize bubble episodes and monitor their evolution, which could be conducive to achieving the effective stabilization of the international copper price. To reduce excess price fluctuations and explosive copper bubbles, authorities should impose restrictions on excessive speculative behaviors under extreme market conditions.

SUBMITTER: Su CW

PROVIDER: S-EPMC7147841 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Testing for multiple bubbles in the copper price: Periodically collapsing behavior.

Su Chi-Wei CW Wang Xiao-Qing XQ Zhu Haotian H Tao Ran R Moldovan Nicoleta-Claudia NC Lobonţ Oana-Ramona OR

Resources policy 20200121

This study investigates whether multiple bubbles exist in the copper price on the basis of the Generalized Supremum Augmented Dickey-Fuller (GSADF) approach (Phillips et al., 2013). This technique delivers date-stamping strategies for the emergence as well as collapse of explosive bubble episodes and is best suited for practical application to time series. The results reveal that four explosive bubbles are detected over the period of 1980-2019 when copper price deviates from fundamental value. B ...[more]

PMID: 34170991

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Project description:In electrochemical processes, gas bubbles on the electrode can cause an increase in both overpotential and ohmic voltage drop which leads to higher energy consumption. Applying power ultrasound during water electrolysis can help to reduce the overpotential, enhance mass transfer, and save energy. In this study, we investigated the effect of ultrasound (20 kHz) on the hydrogen evolution reaction (HER) on a stainless steel plate with varying concentrations of NaOH solutions at 298 K, using linear sweep voltammetry (LSV). We especially focused on understanding the bubble behavior on the stainless steel plate during HER using high-speed imaging in ultrasonic field. When ultrasound was applied to solutions with NaOH concentrations of 0.1, 0.5, 1 M, the current density increased by about 9.0, 5.9, 2.8 %, respectively. As the ultrasound irradiation began, the bubbles tended to hover around on the electrode surface, coalescing with other bubbles, rather than rising. When the size of the coalesced bubbles became too large to stay on the surface of the electrode, they were expelled from the ultrasonic field. The repeated collapse and coalescence of these bubbles was observed while they were rising. The velocity increased about 2 times when ultrasound irradiation began, and increased by more than 6 times in the ultrasonic field. More nucleation of bubbles was observed on the electrode in the ultrasonic field. Using ultrasound reduced the critical diameter of bubbles which detached from the electrode, from 58.0 to 15.9 μm, and the residence time of the bubbles, from 533 to 118 ms. Further, when the ultrasound was applied, the mean diameter of bubbles decreased from 71.8 to 17 μm. Hence, bubble coverage on the electrode surface decreased from 8.3 to 1 % despite an increase in the total number of bubbles. As a result, ultrasound was found to be effective for hydrogen production during water electrolysis, increasing current by the faster removal of gas from the stainless steel plate.

Dataset Information

Testing for multiple bubbles in the copper price: Periodically collapsing behavior.

Publications

Testing for multiple bubbles in the copper price: Periodically collapsing behavior.

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