Albert S. Kim

This study quantitatively evaluates Ukraine’s agricultural virtual water footprint over two decades (2001–2021), focusing on ten representative crops with varying water demands. We assess the environmental and economic implications of virtual water flows and emphasize the need for more sustainable agricultural water management. Our findings reveal a shift in Ukraine toward water-intensive crops despite their high-water requirements, highlighting critical trends in production and trade. While crops like sunflowers and maize generate higher economic returns per unit of weight, less water-intensive crops such as wheat and barley exhibit greater profitability per unit of water consumed, albeit with lower trade volumes. These insights challenge prevailing agricultural practices and underscore the necessity for a more strategic approach that balances economic productivity with responsible water stewardship. Our study provides a data-oriented framework for optimizing water use in Ukrainian agriculture, offering essential guidance for policy interventions and sustainable development.

A heiau is a Hawaiian pre-Christian place of worship composed of rocks and holding historical and cultural significance, with a variety of uses ranging from worship to rituals. The scientific origins of Hawaiian heiau have yet to be fully inspected in the literature. This paper covers Hāpaialiʻi heiau on the island of Hawai‘i and its main function as a seasonal calendar through continuous observation of the sunrise and sunset locations over the sea horizon. Understanding the calendar functionality of the heiau contributes an essential step towards understanding Hawaiians’ use of indigenous science. This study mathematically investigates the sacred structure’s functionality with numerical accuracy and scientific rigour. A brief overview of the history of the Kahaluʻu area and the surrounding heiau provides important context for the heiau’s significance. This study reports and analyses the heiau’s relevant history, cultural significance and reconstruction by Kamehameha Schools. The importance of the calendar lies in the determination of the responsibilities for the current season, indicating which crops are to be harvested and which fish are in the mating season. In the mathematical analysis, the coordinates of the stones within the heiau are independently measured using Google Earth and Google Maps. The relative distances and angles between the internal stones are calculated using Google Sheets and Matlab to discover the underlying sciences possibly used by ancient native Hawaiians.

Ocean thermal energy conversion (OTEC) aims to use the temperature difference between surface and deep seawater to generate electricity and (possibly) freshwater

As of April 30, 2020, the number of cumulative confirmed coronavirus disease 2019 (COVID-19) cases exceeded 3 million worldwide and 1 million in the US with an estimated fatality rate of more than 7 percent. Because the patterns of the occurrence of new confirmed cases and deaths over time are complex and seemingly country-specific, estimating the long-term pandemic spread is challenging. I developed a simple transformation algorithm to investigate the characteristics of the case and death time series per nation, and described the universal similarities observed in the transformed time series of 19 nations in the Group of Twenty (G20). To investigate the universal similarities among the cumulative profiles of confirmed cases and deaths of 19 individual nations in the G20, a transformation algorithm of the time series data sets was developed with open-source software programs. The algorithm was used to extract and analyze statistical information from daily updated COVID-19 pandemic data sets from the European Centre for Disease Prevention and Control (ECDC). Two new parameters for each nation were suggested as factors for time-shifting and time-scaling to define reduced time, which was used to quantify the degree of universal similarities among nations. After the cumulative confirmed case and death profiles of a nation were transformed by using reduced time, most of the 19 nations, with few exceptions, had transformed profiles that closely converged to those of Italy after the onset of cases and deaths. The initial profiles of the cumulative confirmed cases per nation universally showed 3 – 4 week latency periods, during which the total number of cases remained at approximately ten. The latency period of the cumulative number of deaths was approximately half the latency number of cumulative cases, and subsequent uncontrollable increases in human deaths seemed unavoidable because the coronavirus had already widely spread. Immediate governmental actions, including responsive public-health policy-making and enforcement, are observed to be critical to minimize (and possibly stop) further infections and subsequent deaths. In the pandemic spread of infectious viral diseases, such as COVID-19 studied in this work, different nations show dissimilar and seemingly uncorrelated time series profiles of infected cases and deaths. After these statistical phenomena were viewed as identical events occurring at a distinct rate in each country, the reported algorithm of the data transformation using the reduced time revealed a nation-independent, universal profile (especially initial periods of the pandemic spread) from which a nation-specific, predictive estimation could be made and used to assist in immediate public-health policy-making.

Computational fluid dynamics (CFD) simulations were employed in this paper to analyze the dynamic flow patterns within extremely thin slit spaces of two corrugated heat exchanger (HEx) plates. The entire plates are 1.0 m long and wide and 6.5 mm high, and the top and bottom parts consist of six unit plates of the same size (1.0 m long and 16.7 cm wide). A digital geometry of the assembled HEx was prepared as a stereolithography (STL) file (exported from AutoCAD), having excessive geometrical complexity. In this work, a numerical algorithm to reconstruct the STL file is developed, which converts a complex STL file consisting of skew triangles to one having a simple grid structure and an even size-distribution of surface triangles. The whole STL file is split into 36 square pieces (SPs), and each SP is meshed individually using NETGEN, and these meshes are merged as one for OpenFOAM-based CFD simulations. Finally, the flow and pressure profiles are obtained in the low Reynolds number region. The current CFD method with the split-and-merge scheme will be continuously used for the design and optimization for ocean thermal energy conversion technology in the future.

Transient mass-transfer phenomena occurring in natural and engineered systems consist of convection, diffusion, and reaction processes. The coupled phenomena can be described by using the unsteady convection-diffusion-reaction (CDR) equation, which is classified in mathematics as a linear, parabolic partial-differential equation. The availability of analytic solutions is limited to simple cases, e.g., unsteady diffusion and steady convective diffusion. The CDR equation has been considered analytically intractable, depending on the initial and boundary conditions. If spatial adsorption and desorption of matter are super-positioned in the CDR equation as sink and source functions, respectively, then the governing equation becomes an unsteady convection-diffusion-reaction-source (CDRS) equation, of which general solutions are unknown. In this study, a general 1D analytic solution of the CDRS equation is obtained by using a one-sided Laplace transform, by assuming constant diffusivity, velocity, and reactivity. This paper also provides a general formalism to derive 1D analytic solutions for Dirichlet/Dirichlet and Dirichlet/Neumann boundary conditions. Derivations of the analytic solutions are found to be straightforward if a combination of the source function and the initial concentration provide a non-zero singularity pole of inverse Laplace transform.