Volume-12, Issue-5, May 2026

Abstract

This paper examines the evolution of the global zirconium ore trade network using a matrix of bilateral trade relationships from 2014 to 2023, selecting 2014, 2017, 2020, and 2023 as cross-sectional years. Focusing on the countries that account for the top 80% of the global zirconium ore trade volume, this study employs the Quadratic Assignment Procedure (QAP) to systematically analyze the key factors driving trade volumes and their temporal evolution across four dimensions: economic scale, factor endowments, geographical distance, and institutional quality. The study yields four main findings: (1) Overall, the network exhibits the characteristic of "expanding in scale but becoming increasingly sparse." While the number of participating countries has increased, network density and centrality have declined, and the network’s small-world properties have weakened under the influence of external shocks. (2) Trade flows are highly concentrated with a shifting center of gravity. China has emerged as a major transshipment hub with strong resource allocation capabilities, acting as the primary core of the network, while emerging hubs exemplified by the Netherlands have concurrently risen. (3) The community structure has evolved toward multipolarity and regionalization. It has gradually restructured from an early tripolar structure centered around China, Italy, and South Africa into a more decentralized multipolar configuration anchored by China, Spain, and South Africa, accompanied by frequent shifts in regional sub-centers. (4) The trade-driving mechanisms are characterized by a combination of economic complementarity and resource endowment orientation. QAP regression analysis reveals that differences in per capita GDP and urbanization levels are the primary positive drivers of bilateral trade. Furthermore, the zirconium ore trade has transcended the geographical distance and linguistic-cultural barriers typical of traditional gravity models, demonstrating the hallmark features of cross-regional, long-distance allocation. Conversely, disparities in government effectiveness and significant differences in economic size constitute barriers to trade.

Keywords: global zirconium ore trade; complex networks; international trade networks; QAP analysis; influencing factors.

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Abstract

Underwater data collectors are devices designed to acquire information from beneath the ocean surface, providing valuable insight to subsurface conditions that are hard to measure by conventional surface instruments such as buoys and ship-based sensors.

The proposed data collector is optimized for Singapore waters and integrates an expanded sensor suite, including conductivity, temperature, and depth (CTD) sensors, a hydrophone, and an echosounder. The system is designed with a reduced size and weight (0.9 m length, 10.2 kg) compared to current underwater data collectors such as Argo floats (Argo: 1.3 m length, 40 kg) and has an extended deployment time of 10 years (~3500 profiles, assuming daily profiling), compared to 3–5 years (~100–200 profiles at 10-day cycles) for Argo systems. This extended operational lifespan is enabled by rechargeable batteries and solar energy harvesting.

The system architecture includes a buoyancy engine for depth control, sensor integration for data acquisition, power system design, and solar energy harvesting. The resulting data collector is lightweight, man-portable, and readily deployable. The sensor suite includes conductivity, temperature and depth sensors for inferring sound velocity of the ocean waters at that location and depth, an echosounder for determining seabed depth, and a hydrophone to listen to the ocean soundscape and for underwater sound pollution monitoring. Experimental validation demonstrates accurate sensor measurements, stable depth control, and effective solar energy harvesting, with example quantitative results provided in Section V.

The system is intended for the collection of oceanographic data, with an emphasis on real-time measurements of ocean conditions (data transmitted upon each surfacing). The enhanced data collector will facilitate oceanographic research by providing real-time data on ocean conditions, sound pollution monitoring and sediment movement information.

Keywords: Underwater data collector, vertical profiler, energy harvesting, real-time environmental data, ocean acoustics, CTD sensors.

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Abstract

Conventional routes were achieved for the synthesis of methylthiazolidin-4-one derivatives starting through reaction of substituted salicylaldehyde and acetoacetic ester, which gives acetyl-coumarin. Upon further reaction with benzene-1,4-diamine, it was converted into imine, subsequently cyclized into a thiazole-amine in the presence of thioglycolic acid. The final derivatives were cyclized by a three-component one-pot reaction of amine, substituted aldehyde, and ketone, yielding 2-(8-fluoro-2-oxo-2H-chromen-3-yl)-3-(4-(2-(4-hydroxy-3-methoxyphenyl)-4,5-diphenyl-4,5-dihydro-1H-imidazol-1-yl)phenyl)-2-methylthiazolidin-4-one derivatives. The structures of the novel synthesized derivatives were established by elemental analysis, UV, FT-IR, ¹H-NMR, and mass spectra. The obtained derivatives displayed excellent to moderate antimicrobial activity. 

Keywords: Benzil, thioglycolic acid, coumarin, acetoacetic ester, substituted salicylaldehyde, benzene-1,4-diamine, acetic acid.

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Abstract

A convenient protocol for the synthesis of oxoazetidinyl-phenothiazinone derivatives has been initiated with the reaction of resorcinol and acetoacetic ester to yield coumarin. In another reaction, Schiff bases were prepared by the condensation of substituted-salicylaldehyde with benzidine and substituted-salicylaldehyde with benzene-1,4-diamine, subsequently cyclized with chloroacetyl chloride to form β-lactam-amine. Further, the amine reacted with coumarin in the presence of ZnCl₂ to form prefinal derivatives. The interaction of biphenylyl-azetidin-2-one or phenyl-azetidin-2-one with sulphur powder and iodine afforded the final phenothiazinone derivatives. The structures of the synthesized derivatives were determined by elemental analysis, UV-visible, FT-IR, ¹H-NMR, and mass spectra. The obtained derivatives exhibited excellent to moderate antimicrobial activity. 

Keywords: Phenothiazinone, acetoacetic ester, coumarin, benzidine, benzene-1,4-diamine, salicylaldehyde.

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