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Axi-symmetric solutions for active vector models generalizing 3D Euler and electron???MHD equations
No full textWe study systems interpolating between the 3D incompressible Euler and electron???MHD equations, given by ???tB+V??????B=B??????V,V=????????(?????)???aB,??????B=0,where B is a time-dependent vector field in R3. Under the assumption that the initial data is axi-symmetric without swirl, we prove local well-posedness of Lipschitz continuous solutions and existence of traveling waves in the range 1/2<a[removed
Phase-leg power equalization method of modular multilevel converter with APOD strategy under unbalanced fault condition
No full textAn active power oscillation damping (APOD) control is one of the representative unbalanced fault compensa-tion strategies. Recently, various studies have been performed on the effect of the APOD with the internal power dynamic analysis of a Modular Multilevel Converter (MMC); however, most of the papers have considered only the active power component for analyzing the internal dynamics of the MMC. During the APOD operation, while reactive power is supplied to the grid for the voltage compensation, phase-leg power imbalance can be aggravated. To enhance stability and reliability, the phase-leg power imbalance phenomenon should be sufficiently considered at the development stage of the controller. This research discovers that the phase-leg power imbalance rate could be determined by the magnitude and phase of the negative sequence component of the grid voltage and the amount of reactive power. In addition, the unbalanced power component can be accurately calculated only based on the grid voltage information and the reactive power reference. Also, this paper proposes a phase-leg power equalization method (PPEM) using unbalanced power component estimation. Furthermore, an improved control structure is also proposed to achieve more accurate phase -leg power equalization using the internal leg-energy dynamics analysis. The effectiveness of the proposed methods is verified through high-fidelity PSCAD/EMTDC time-domain simulations using Point-to-Point (PTP) MMC-HVDC system and Hardware-in-the-Loop Simulation (HILS) with the MMC-MVDC system
Performance and stability enhancement of methanogenic granular sludge process: Feed pre-acidification and magnetite-embedded granule formation
No full textRecently, inducing the formation of conductive magnetite-embedded granules (MEGs) by self-embedding sub-micron magnetite particles into anaerobic granules has been demonstrated to be effective in enhancing methanation and improving sludge stability in upflow anaerobic sludge blanket (UASB) reactors. However, MEGs still suffer structural and functional destabilization at high organic loading rates (OLRs) due to the excessive secretion of extracellular polymeric substances (EPS), resulting in a significant washout of active microbes. This is particularly true when treating carbohydrate-rich wastewater that is prone to producing excessive EPS. In order to address this issue, this study explored the potential of combining MEG-UASB process with feed pre-acidification as a means of improving the methanogenic treatment performance and stability of whey, a carbohydrate-rich dairy effluent. Two UASB reactors, one with MEGs and one without, were operated to treat pre-acidified whey at increasing OLRs of 2-11 g chemical oxygen demand/L center dot d. Feed pre-acidification was effective in preventing granule destabilization and maintaining stable UASB performance with or without MEGs. Meanwhile, the reactor with MEGs (JM) showed significantly better performance and stability than the one without MEGs (JC), especially at high OLRs, which was likely because MEGs improved sludge retention and promoted electro-syntrophic methanogenic activity. Accordingly, JM sludge exhibited greater electron transfer capability and a more pronounced enrichment of electroactive microbes than JC sludge. External voltage application (0.6 V) did not relieve but rather aggravated the process upset under overloading conditions for both reactors. The overall results suggest that the MEG-UASB process coupled with pre-acidification holds promise for efficient and stable treatment of carbohydrate-rich wastewater
Social construction of fire accidents in battery energy storage systems in Korea
No full textRenewable energy (RE) has the potential to become an essential part of the national policy for energy transition. The government of the Republic of Korea has sought to solve the problem of RE intermittency and achieve flexible grid management by leveraging a powerful policy drive for battery energy storage system (B-ESS) technology. However, from 2017 to 2019, over two dozen B-ESS fire accidents occurred across Korea. Consecutive fires in B-ESSs, which were expected to be game-changers in energy transition, have instead become an issue of social concern. This study aims to analyze the influence of various social factors on fire accidents, for which previous studies could not provide sufficient explanation. A literature analysis and qualitative interviews revealed the social construction process of B-ESS fires through stakeholder interaction. The economic incentive schemes of B-ESS and insufficient safety regulations has had a significant influence on the interactions of relevant social groups (RSGs), and several factors in the environment, organizations, and cognition/choice of RSGs have exacerbated fire risks. This research provides a clearer understanding of the adverse outcomes of adopting new energy technologies
Challenges in engineering direct interspecies electron transfer for enhanced methanogenesis
No full textInterspecies electron transfer (IET) between fatty acid-oxidizing bacteria and hydrogenotrophic methanogens is key to stable and efficient methanogenesis in the anaerobic digestion (AD) process. Recently discovered direct IET (DIET) enables energetically and kinetically advantageous methanogenesis and facilitating cell-to-cell electrical connections using conductive additives (mostly metal- or carbon-based) has been recognized a promising approach to enhancing methanogenesis. Over the last decade, extensive efforts have been made to understand the mechanism and role of DIET in AD and to use it to improve AD performance and stability. However, challenges and limitations remain and must be addressed for the practical application of DIET-AD technology, for example, (i) how to prevent the washout loss of particulate conductive materials in continuous operation, (ii) how to further promote DIET so as to achieve better and more stable methanogenic performance, and (iii) how to evaluate the effects of DIET promotion separately from enhanced biomass retention by adding conductive materials with high specific surface areas. This paper discusses these challenges in both research and practical application of engineering DIET in AD using conductive additives, as well as the efforts to address them. Reviewing current technologies and recent advances to tackle the challenges and improve the practicability of the DIET-AD process, it has been suggested that significant further research is needed, especially on the retention of conductive additives and their biocompatibility and interactions with microorganisms. DIETAD technology is still in its early stages, and ongoing efforts are required to improve its scalability and economic feasibility at the industrial scale
Low-Voltage Hydrogen Production via Hydrogen Peroxide Oxidation Facilitated by Oxo Ligand Axially Coordinated to Cobalt in Phthalocyanine Moiety
No full textA cobalt phthalocyanine having an electron-poor CoN4 (+& delta;) in its phthalocyanine moiety was presented as an electrocatalyst for hydrogen peroxide oxidation reaction (HPOR). We suggested that hydrogen peroxide as an electrolysis medium for hydrogen production and therefore as a hydrogen carrier, demonstrating that the electrocatalyst guaranteed high hydrogen production rate by hydrogen peroxide splitting. The electron deficiency of cobalt allows CoN4 to have the highly HPOR-active monovalent oxidation state and facilitates HPOR at small overpotentials range around the onset potential. The strong interaction between the electron-deficient cobalt and oxygen of peroxide adsorbates in CoOOH- encourages an axially coordinated cobalt oxo complex (OCoN4) to form, the OCoN4 facilitating the HPOR efficiently at high overpotentials. Low-voltage oxygen evolution reaction guaranteeing low-voltage hydrogen production is successfully demonstrated in the presence of the metal-oxo complex having electron-deficient CoN4. Hydrogen production by 391 mA cm(-2) at 1 V and 870 mA cm(-2) at 1.5 V is obtained. Also, the techno-economic benefit of hydrogen peroxide as a hydrogen carrier is evaluated by comparing hydrogen peroxide with other hydrogen carriers such as ammonia and liquid organic hydrogen carriers
Advocacy, Ecotourism, and Biopolitics of Whale Conservation in Ecuador
No full textWhale-watching tourism in Ecuador thrives through the spectacular image of a flagship species, the humpback whale. Seemingly, it is an example of an industry regulated and managed in accordance with sustainable principles of nature conservation, thanks to the work of Ecuadorian scientists who advocate for policies to protect whales from harmful exploitation. However, does the use of the whale as an icon of conservation result in its utilization as a mere commodity for profit? Through ethnographic fieldwork including interviews, observations, and textual analysis, it is shown that the Ecuadorian practices of whale conservation have resulted in the whale becoming a subject of governance, by which the wild animals are recognized as entities worthy of ethical treatment. Using the humpback whale as a flagship species, the Ecuadorian scientists practice biopolitics through the strategies of categorizing, monitoring, and regulating human interactions with the whale population. The success of this approach to wildlife governance highlights the role of NGO-affiliated scientists as knowledge producers and policy advocates
An emerging Asian aerosol dipole pattern reshapes the Asian summer monsoon and exacerbates northern hemisphere warming
No full textSince the early 2010s, anthropogenic aerosols have started decreasing in East Asia (EA) while have continued to increase in South Asia (SA). Yet the climate impacts of this Asian aerosol dipole (AAD) pattern remain largely unknown. Using a state-of-the-art climate model, we demonstrate that the climate response is distinctly different between the SA aerosol increases and EA aerosol decreases. The SA aerosol increases lead to similar to 2.7 times stronger land summer precipitation change within the forced regions than the EA aerosol decreases. Contrastingly, the SA aerosol increases, within the tropical monsoon regime, produce weak and tropically confined responses, while the EA aerosol decreases yield a pronounced northern hemisphere warming aided by extratropical mean westerly and positive air-sea feedbacks over the western North Pacific. By scaling the observed instantaneous shortwave radiative forcing, we reveal that the recent AAD induces a pronounced northern hemisphere extratropical (beyond 30 degrees N) warming (0.024 +/- 0.010 degrees C decade(-1)), particularly over Europe (0.049 +/- 0.009 degrees C decade(-1)). These findings highlight the importance of the pattern effect of forcings in driving global climate and have important implications for decadal prediction
A USB Sensor/Actuator Development Platform for Plug&Play in Raspberry-Pi
No full textIoT ?????? ????????? ?????? ?????????????????? ????????? ????????? ????????????-????????? ??????????????? ????????????. ????????? ???????????? ????????????-????????? ????????? ????????? Plug??? ??? ????????? ????????? ????????? ?????????????????? ???????????? Play????????? ?????? ????????? ????????? ?????????. ????????? ??????/????????? Plug&Play ????????? ????????? ????????? ????????? ??????/???????????? ????????? ?????????????????? ????????? ????????? ?????????. ??? ??????????????? ??????/???????????? ????????????-????????? USB ????????? Plug??? ??? ??????/???????????? ????????? ???????????? ???????????? ???????????? ??????????????? ???????????? ???????????? Play?????? ????????? ????????????. ??????, ??? ???????????? USB ??????/???????????? ??????????????? ???????????? ?????? ???????????? ???????????? ?????? ????????? ???????????????. USB ??????/???????????? ?????? ??? ????????? ??? ?????? ???????????? ???????????? ????????? ??? ??????/???????????? ??????????????? ???????????? ???????????? ?????? ?????? ???????????? ????????? ???????????????. USB ?????? /???????????? ???????????? ????????? ???????????? ?????? ???????????? ??????????????? ???????????? ?????????
