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Does the introduction of US spot Bitcoin ETFs affect spot returns and volatility of major cryptocurrencies?
(Elsevier, 2025-06) Vassilios, Babalos; Bouri, Elie; Gupta, Rangan; rangan.gupta@up.ac.za
This paper provides the first empirical evidence of whether the introduction of US spot Bitcoin ETFs affected the returns and volatility of major cryptocurrencies. Using data from December 18, 2017 to March 15, 2024, we apply an event-study methodology within a GARCH-based framework. Our results reveal a significant effect of the introduction of spot Bitcoin ETFs on cryptocurrency returns and volatility. The analysis shows a positive impact for Bitcoin, Ethereum, and Litecoin spot price returns around the event date. The volatility of Bitcoin and Ripple spot markets decreased following the introduction of spot Bitcoin ETFs, which supports the stabilization hypothesis for these two cases. We also examine the volatility spillovers using a wavelet coherence approach, and reveal significant volatility spillovers from Grayscale Bitcoin ETF to Bitcoin futures and to a lesser extend to the Bitcoin spot market. Our findings enhance the limited understanding of the price discovery and functioning of the cryptocurrency markets, which could be useful for investors, regulators, and policymakers.
HIGHLIGHTS
• Study the impact of introduction of Spot Bitcoin ETFs on the cryptocurrency market.
• Apply event study methodology within a GARCH framework.
• Find a positive impact for Bitcoin, Ethereum, and Litecoin spot price returns.
• Volatility of Bitcoin and Ripple decreased, supporting the stabilization hypothesis.
• Wavelet coherence analysis reveals volatility spillovers from Bitcoin ETF to Bitcoin futures.
Design and fabrication of porous three‐dimensional Ag-doped reduced graphene oxide (3D Ag@rGO) composite for interfacial solar desalination
(Nature Research, 2024-06-14) Bezza, Fisseha Andualem; Iwarere, Samuel Ayodele; Brink, Hendrik Gideon; Chirwa, Evans M.N.; evans.chirwa@up.ac.za
Solar-driven interfacial desalination technology has shown great promise in tackling the urgent global water scarcity crisis due to its ability to localize heat and its high solar-to-thermal energy conversion efficiency. For the realization of sustainable saline water desalination, the exploration of novel photothermal materials with higher water vapor generation and photothermal conversion efficiency is indispensable. In the current study, a novel 3D interconnected monolithic Ag-doped rGO network was synthesized for efficient photothermal application. The Ultraviolet–Visible-Near Infrared (UV–Vis-NIR) and FTIR analyses demonstrated that the controlled hydrothermal reduction of GO enabled the restoration of the conjugated sp2 bonded carbon network and the subsequent electrical and thermal conductivity through a significant reduction of oxygen-containing functional groups while maintaining the hydrophilicity of the composite photothermal material. In the solar simulated interfacial desalination study conducted using 3.5 wt.% saline water, the average surface temperatures of the 3D material increased from 27.1 to 54.7 °C in an hour, achieving an average net dark-excluded evaporation rate of 1.40 kg m−2 h−1 and a photothermal conversion efficiency of ~ 97.54% under 1 sun solar irradiance. In the outdoor real-world application test carried out, the surface temperature of the 3D solar evaporator reached up to 60 °C and achieved a net water evaporation rate of 1.50 kg m−2 h−1 under actual solar irradiation. The 3D interwoven porous hierarchical evaporator displayed no salt precipitation over the 54-h period monitored, demonstrating the promising salt rejection and real-world application potential for efficient desalination of saline water.
Assessment of domestic pig-bushpig (Potamochoerus larvatus) interactions through local knowledge in rural areas of Madagascar
(Nature Research, 2024-07-15) Rakotoarivony, Rianja; Kassie, Daouda; Andriamahefa, Alpha; Andria‑Mananjara , Diana; Rakotoarinoro , Mihaja; Ramaroson, Herilantonirina Solotiana; Raliniaina , Modestine; Rasamoelina , Miatrana; Gomez‑Vazquez, Jose Pablo; Jori, Ferran J.
In many parts of the world, domestic and wild animal populations interact at the interface between natural and agricultural ecosystems. Introduced with the first inhabitants arriving from eastern Africa, the bushpig (Potamochoerus larvatus) is the largest living terrestrial mammal in Madagascar. Bushpigs are regularly reported close to human settlements where they damage crops and gardens. As domestic pigs are often raised in free-ranging conditions around the villages, bushpigs and domestic pigs can interact leading to the transmission and circulation of shared swine pathogens that impact both animal and human health. In this study, we characterized the socio-ecological context of bushpig-domestic pig interactions in two different regions of western Madagascar. We conducted participatory mapping sessions and focus group interviews with 65 hunters, 80 pig farmers and 96 crop farmers in 20 fokontany, the smallest administrative unit in Madagascar. After discussing with participants, we gathered information about the spatialization of interactions and their potential geographical drivers. We explored data by performing multiple correspondence analysis and hierarchical clustering on principal components. Based on the reported occurrence or absence of bushpig-domestic pig interactions we were able to classify areas with high or intermediate levels of interactions or no interactions at all. Interactions between the two pig species were reported in only 25% of the fokontany assessed. Even though both suid species were attracted to fruit trees, crops, and water sources, only indirect interactions in those spots were reported. Direct interactions were reported in 10% of cases and referred to interspecific sexual and/or agonistic behavior. The participatory methods used to acquire local knowledge about natural events were confirmed as valuable, low-cost exploratory methods to characterize areas with wild-domestic animal interactions. The results of this study will help plan future studies to characterize the interface between the two species from an ecological or epidemiological perspective using more sensitive and sophisticated ecological approaches.
Application of geospatial technology and decision model in the development of improved food security index
(Nature Research, 2024-12-04) Chukwuma, Emmanuel Chibundo; Afolabi, O.O.D.; Okonkwo, C.C.; Olamigoke, O.O.; Okonkwo, C.E.
Most developing countries are currently experiencing a severe food security crisis. A good policy to mitigate food insecurity is dependent on accurate assessment. Therefore, an improved assessment of food situation is important in implementing food security measures. Existing food security assessments are limited in integrating localized variables, often needing more context-specific information. This study proposes a new food security index (Hybrid Food Security Index-HFSI), the Nigerian state was used as a case study. Data used include; food consumption, poverty levels, variability in food prices, inflation, climate variability data and the status of road infrastructure. The study also integrated a hybrid Multi-criteria Criteria Decision Model (MCDM) and geo-spatial technology. The geo-spatial presentation of food security across Nigeria shows that food security is generally better in the Southern part of the country than in the Northern region. Broadly, indicators’ performance primarily improves from the country’s North to South, which suggests that Northern states tend to be less food secure than Southern states. According to the Fuzzy-DEMATEL-ANP model, the Poverty level indicator significantly impacts the food security situation in all focused states, as it received the highest priority weight of 0.1487. The study recommends intensifying poverty alleviation programs to improve food security, and women’s development programs should be prioritized. This study provides policymakers and stakeholders with evidence-based assessments to address food security challenges in Nigeria.
Accuracy of self‑collected versus healthcare worker collected specimens for diagnosing sexually transmitted infections in females : an updated systematic review and meta‑analysis
(Nature Research, 2024-05-07) Jaya, Ziningi Nobuhle; Mapanga, Witness; Dlangalala, Thobeka Nomzamo; Thembane, Nokukhanya; Kgarosi, Kabelo; Dzinamarira, Tafadzwa; Mashamba‑Thompson, Tivani Phosa; u21848522@tuks.ac.za
The use of self-collected specimens as an alternative to healthcare worker-collected specimens for diagnostic testing has gained increasing attention in recent years. This systematic review aimed to assess the diagnostic accuracy of self-collected specimens compared to healthcare worker-collected specimens across different sexually transmitted infections (STIs) including Chlamydia trachomatis (CT), human papillomavirus (HPV), Mycoplasma genitalium (MG), Neisseria gonorrhoea (NG), Treponema pallidum and Trichomonas vaginalis (TV) in females. A rigorous process was followed to screen for studies in various electronic databases. The quality of included studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. There were no studies on syphilis that met the criteria for inclusion in the review. A total of six studies for chlamydia, five studies for HPV, four studies for MG, and seven studies for gonorrhoea and trichomoniasis were included in the review. However, not all studies were included in the sub-group meta-analysis. The analysis revealed that self-collected specimens demonstrated comparable diagnostic accuracy to healthcare worker-collected specimens across most STIs. This indicates that the diagnostic accuracy of self-collected specimens can provide accurate results and enhance access to diagnostic testing, potentially improving healthcare service delivery. Future research should further explore the diagnostic accuracy of self-collected specimens in larger and more diverse populations.