Advances in Carbon Xerogels: Structural Optimization for Enhanced EDLC Performance.

This review explores the recent progress on carbon xerogels (CXs) and highlights their development and use as efficient electrodes in organic electric double-layer capacitors (EDLCs). In addition, this work examines how the adjustment of synthesis parameters, such as pH, polymerization duration, and the reactant-to-catalyst ratio, crucially affects the structure and electrochemical properties of xerogels. The adaptability of xerogels in terms of modification of their porosity and structure plays a vital role in the improvement of EDLC applications as it directly influences the interaction between electrolyte ions and the electrode surface, which is a key factor in determining EDLC performance. The review further discusses the substantial effects of chemical activation with KOH on the improvement of the porous structure and specific surface area, which leads to notable electrochemical enhancements. This structural control facilitates improvement in ion transport and storage, which are essential for efficient EDLC charge-discharge (C-D) cycles. Compared with commercial activated carbons for EDLC electrodes, CXs attract interest for their superior surface area, lower electrical resistance, and stable performance across diverse C-D rates, which underscore their promising potential in EDLC applications. This in-depth review not only summarizes the advancements in CX research but also highlights their potential to expand and improve EDLC applications and demonstrate the critical role of their tunable porosity and structure in the evolution of next-generation energy storage systems.

Correlation between oxygen flow-controlled resistive switching and capacitance behavior in gallium oxide memristors grown via RF sputtering.

We studied on the bipolar resistive switching (RS)-dependent capacitance of Ga2O3 memristors, grown using controlled oxygen flow via a radio frequency sputtering process. The Ag/Ga2O3/Pt memristor structure was employed to investigate the capacitance changes associated with RS behavior and oxygen concentration. In the low-resistance state (LRS), capacitance increased by over 60 times compared to the high-resistance state (HRS). Furthermore, in the HRS state, increasing the oxygen flow from 0 to 0.3 sccm resulted in an 80 % decrease in capacitance, while in the LRS state, capacitance increased by 128 %. These results indicate that RS-dependent capacitance in Ga2O3 memristors is influenced by the density of oxygen vacancies. The presence of oxygen vacancies affects charge storage capacity and capacitance, with higher oxygen concentrations leading to reduced capacitance in HRS and increased capacitance in LRS. The results contribute to the understanding of the capacitance behavior in Ga2O3 memristors and highlight the significance of oxygen vacancies in their operation.

An Evolutionary Strategy for Spawning Habitat Selection by Pseudopungtungia tenuicorpa.

In this study, we hypothesized that the limited geographical distribution of Pseudopungtungia tenuicorpa in South Korea is closely related to the local abundance of their preferred spawning habitats. Eggs of P. tenuicorpa were most frequently observed in cracks smaller than 5 cm, followed by the nests of other fish, such as Coreoperca herzi. Although eggs of P. tenuicorpa were also found in cracks larger than 6 cm, most of them were consumed or damaged by other fish. However, the number of P. tenuicorpa eggs spawned in cracks smaller than 5 cm remained similar to the number of eggs at the time of initial spawning, even after 9 days. The strong preference of P. tenuicorpa for cracks smaller than 5 cm was found to influence the geographical distribution of P. tenuicorpa in South Korea. In the upper reaches of the Han River, the ratio of cracks smaller than 5 cm is higher than that in the Geum River and in the Nakdong River, which contributes to the stable population growth of P. tenuicorpa there. In the future, management strategies to maintain/restore cracks smaller than 5 cm should be reviewed for the preservation of this endemic fish in South Korea.

Complete mitochondrial genome of Ischnura asiatica (Brauer, 1865) assembled from next-generation sequencing data.

Ischnura asiatica (Brauer, 1865) is a freshwater damselfly belonging to the family Coenagrionidae that is distributed across most of Korea, primarily in areas with low water flow, such as ponds and wetlands. The complete mitochondrial genome of I. asiatica was sequenced by next-generation sequencing. The circular mitochondrial genome was found to be 15,769 bp long, with of 13 protein-coding, two ribosomal RNA, and 22 transfer RNA genes (GenBank accession no. OM310774). Maximum likelihood, phylogenetic analysis showed that this species clustered with other species belonging to the family Coenagrionidae. This study contributes to the phylogeny of damselflies and other members of the family Coenagrionidae.

Behavioral Avoidance Response of Daphnia to Fungal Infection Caused by Metschnikowia Species in a Temperate Reservoir.

Morphological or behavioral defense mechanisms are important evolutionary strategies for the survival of prey. Studies have focused on predation and competition, but infection has been overlooked, despite being a determining factor of distribution and species diversity of prey. We hypothesized that the winter migration of Daphnia pulicaria is a community defense strategy to avoid fungal infection. To test this hypothesis, environmental variables and the Cladocera community, including D. pulicaria, were monitored in three study sections of the Anri Reservoir in the Republic of Korea during September 2010-August 2015. During three winter seasons, the density of infected D. pulicaria increased in all study sections, and they migrated from the central to the littoral area. Most of the infected individuals had dormant eggs in sexually reproducing mothers. However, when the proportion of non-infected individuals was higher than that of infected individuals, winter migration was not observed. Additional microcosm experiments showed that dormant eggs of D. pulicaria obtained from ice crystals in the littoral area had lower hatching and infection rates than those obtained from mothers moving from other zones. Therefore, the migration of D. pulicaria during winter is an active response to avoid intergenerational fungal infection.

Hydrological Characteristics and Trophic Status as Dominant Drivers of Rotifer Community Composition in Artificially Created Riverine Wetlands.

Hydrological characteristics of freshwater ecosystems are powerful determinants of the distribution of biological communities and changes in environmental factors. This study identified relationships between the wetland environment, rotifer community, and hydrological factors for 48 wetlands, to determine their impact on wetland conservation and management. Different hydrological factors produced different wetland environments, which influenced the rotifer community composition. The wetlands with "poor" "in/outflow function" and "shore stability" levels showed high conductivity, turbidity, depth, and concentrations of total nitrogen, total phosphorus, and chlorophyll a. In contrast, the dissolved oxygen levels and velocity were the highest in wetlands with "good" in/outflow function and shore stability variables. The nutritional status of each wetland affected the composition of the rotifer community. Some genera (Keratella, Brachionus, Anuraeopsis, Trichocerca, and Philodina) were found in wetlands with high concentrations of total nitrogen, total phosphorus, and chlorophyll a, and high turbidity and depth. In contrast, Ascomorpha and Ploesoma were found in wetlands with high dissolved oxygen levels and flow velocity. High densities of Lepadella, Lecane, and Testudinella were found in wetlands completely covered by macrophytes. The rotifer community distribution can be used to understand the trophic, current functional, and environmental status of wetlands.

Invasion and Dispersion of the Exotic Species Procambarus clarkii (Decapoda Cambaridae) in Yeongsan River Basin, South Korea.

The introduction of exotic species negatively affects the distribution and interactions within local biological communities in an ecosystem and can threaten ecosystem health. This study aimed to provide the basic data required to manage P. clarkii in the Yeongsan River basin. We identified the dispersion pattern and evaluated the ecosystem risk of this newly introduced species. The distribution survey investigated Procambarus clarkii populations at 25 sites in the Yeongsan River basin over a four-year period. The initial introduction occurred in Jiseok Stream. The larvae of P. clarkii were most abundant in areas with a dense aquatic plant cover, whereas adults preferred silt/clay areas. The alterations in the water flow by the river refurbishment project (carried out in 2012) increased their preferred habitats and contributed to P. clarkii dispersion. However, stable isotope analysis showed that the dispersion has had little effect on the freshwater ecosystem. The interrelationship between P. clarkii (i.e., larvae and adults) and other biological communities has been limited. Although the rapid dispersion by P. clarkii in the Yeongsan River basin has not impacted the freshwater ecosystem, further ecological information is required on how to manage P. clarkii beyond this early stage of invasion.

Changes in Antibiotic-Resistance Genes Induced by the Grazing Effect in Three Cladoceran Species.

The acquisition of Antibiotic-Resistance Genes (ARGs) by natural bacteria caused by antibiotic abuse is causing serious problems for human and animal welfare. Here, we evaluated the influence of three cladoceran species on Antibiotic-Resistant Bacteria (ARB) and tetracycline-resistance gene (tet(A)) copies, and discussed the effect of these biological interactions on the distribution and diffusion of ARGs in freshwater ecosystems. Bacterial community and tet(A) abundances in water samples collected from wetlands were strongly influenced by cladoceran presence. The presence of Daphnia obtusa dramatically decreased ARB and tet(A) abundance compared to that with other cladoceran species (Chydorus sphaericus and Simocephalus vetulus). Interestingly, we found a high abundance of Flavobacteriales in the microbiomes of cladoceran species. Considering that Flavobacteriales species are potential carriers of the tet(A) gene, their adsorption and assimilation with cladocerans could significantly impact the reduction of tet(A) in water. Field surveys also showed that tet(A) abundance could be low if the dominance of D. obtusa in each wetland was high. This study highlighted the need for ecological interactions and a broad range of niches in the food web when discussing the fate of ARGs in freshwater ecosystems.

The Use of Winter Water Temperature and Food Composition by the Copepod Cyclops vicinus (Uljanin, 1875) to Provide a Temporal Refuge from Fish Predation.

Frequent predation induces various defense strategies in prey, including morphological changes or migration patterns in zooplankton. We hypothesized that the winter dominance of Cyclops vicinus in the Upo Wetlands, South Korea, is an evolved temporal defense mechanism to avoid fish predation. Long-term data (2014-2019) showed that fish consumed the most cyclopoid copepods from spring to autumn. Lepomis macrochirus preferentially consumed C. vicinus; thus, C. vicinus density was lower from spring to autumn. However, C. vicinus was abundant in winter when fish consumed fewer copepods. Nauplii density began to increase in late autumn (October-November), and their population growth was fueled through consumption of Cyclotella sp. and Rhodomonas sp. Culture experiments showed that Cyclotella sp. contributed more to the growth stage (copepodite or subadult) after nauplii than Rhodomonas sp. C. vicinus density was lower in the winters of 2013 and 2016 when the densities of these phytoplankton prey species were lower. In summary, although winter conditions were suitable for copepod survival and population growth, C. vicinus relied heavily on the diversity and species composition of its food sources. The winter dominance of C. vicinus could increase regional biodiversity and contribute significantly to the stability of the freshwater food web.

Habitat Preferences and Trophic Position of Brachydiplax chalybea flavovittata Ris, 1911 (Insecta: Odonata) Larvae in Youngsan River Wetlands of South Korea.

In freshwater ecosystems, habitat heterogeneity supports high invertebrate density and diversity, and it contributes to the introduction and settlement of non-native species. In the present study, we identified the habitat preferences and trophic level of Brachydiplax chalybea flavovittata larvae, which were distributed in four of the 17 wetlands we examined in the Yeongsan River basin, South Korea. Larval density varied across four microhabitat types: open water area, and microhabitats dominated by Myriophyllum aquaticum, Paspalum distichum, and Zizania latifolia. Microhabitats dominated by M. aquaticum had the highest larval density, followed by those dominated by P. distichum. The larvae were more prevalent in silt sediments than in plant debris or sand. Stable isotope analysis showed that B. chalybea flavovittata is likely to consume, as a food source, other species of Odonata larvae. We conclude that successful settlement of B. chalybea flavovittata can be attributed to their habitat preferences. As temperature increases due to climate change, the likelihood of B. chalybea flavovittata spreading throughout South Korea increases. We, therefore, recommend continued monitoring of the spread and ecological impacts of B. chalybea flavovittata.

Coordinated Metacommunity Assembly and Spatial Distribution of Multiple Microbial Kingdoms within a Lake.

Freshwater planktonic communities comprise a tremendous diversity of microorganisms. This study investigated the distribution patterns of microbial kingdoms (bacteria, fungi, protists, and microbial metazoans) within a lake ecosystem. Water samples were collected from 50 sites along the shoreline in a lake during an early eutrophication period, and MiSeq sequencing was performed with different marker genes. Metacommunity analyses revealed a bimodal occupancy-frequency distribution and a Clementsian gradient persisting throughout all microbial kingdoms, suggesting similar regional processes in all kingdoms. Variation partitioning revealed that environmental characteristics, macrophyte/macroinvertebrate composition, space coordinates, and distance-based Moran's eigenvector maps (dbMEM) together could explain up to 29% of the community variances in microbial kingdoms. Kingdom synchrony results showed strong couplings between kingdoms (R2 ≥ 0.31), except between Fungi and Metazoa (R2 = 0.09). Another variation partitioning revealed that microbial kingdoms could well explain their community variances up to 73%. Interestingly, the kingdom Protista was best synchronized with the other kingdoms. A correlation network showed that positive associations between kingdoms outnumbered the negative ones and that the kingdom Protista acted as a hub among kingdoms. Module analysis showed that network modules included multi-kingdom associations that were prevalent. Our findings suggest that protists coordinate community assembly and distribution of other kingdoms, and inter-kingdom interactions are a key determinant in shaping their community structures in a freshwater lake.

Maturation of Adipocytes is Suppressed by Fluid Shear Stress.

Preadipocytes are mechano-responsive cells and their differentiation to adipocytes may be regulated by various types of physical stimulation. Understanding the mechanism of differentiation, which increases the number of adipocytes and lipid accumulation is important in the study of obesity-related diseases. In this study, we investigated the effects of physical stimulation at different stages of adipogenic differentiation using physiological levels of fluid shear stress. Preadipocytes were treated with dexamethasone, 3-isobutyl-1-methylxanthine and insulin for 3 days (induction period) and incubated for additional 6 days for maturation. Fluid shear stress of 1 Pa at 1 Hz was applied for 1 h at different stages of differentiation. Fluid shear stress applied at the maturation period significantly reduced the expressions of C/enhancer binding protein (EBP)α and peroxisome proliferator-activated receptor (PPAR)γ2 leading to reduced lipid accumulation. Fluid shear stress applied at the early or late stages of the induction period only decreased peroxisome proliferator-activated receptor γ2 expression without any significant changes in lipid accumulation. Stimulation at multiple days during the induction period did not result in changes in lipid accumulation compared to stimulation at a single day. These results suggest that lipid droplet accumulation is effectively decreased by fluid shear stress applied during the cell maturation period. Understanding the cellular response to physical stimulation throughout the entire adipocyte differentiation period may be important in controlling adipogenesis by physical stimulation.

Effects of algal food quality on sexual reproduction of Daphnia magna.

The objective of our study was to investigate sexual reproduction of Daphnia magna associated with mating behaviors and hatching rates, according to different algal food sources. Since a diatom is known to contain more abundant long-chain poly unsaturated fatty acids (PUFAs), we hypothesized that the diatom-consuming D. magna would exhibit more successful reproduction rates. Upon the hypothesis, we designed three experiments using two algal species, a green alga (Chlorella vulgaris) and a diatom (Stephanodiscus hantzschii). From the results, we found that the mating frequency and copulation duration increased in the treatment with S. hantzschii, resulting in a significant increase of hatching rates of resting eggs. In the other two repetitive mating strategies (e.g., one female vs. multiple males, and one male vs. multiple females), we found that the hatching rates of resting eggs were greater in the S. hantzschii treatment. In addition to the mating strategy, male body size significantly increased in the diatom treatment, hence average diameter of penis was also statistically different among the treatments (greater diameter in the S. hantzschii treatment). To examine the effect of algal food quality, we estimated quantity of fatty acids in the two algal species. Our result showed that S. hantzschii had a higher proportion of long-chain PUFAs than C. vulgaris. Furthermore, a stable isotope analysis revealed that carbon and nitrogen originated from S. hantzschii were more assimilated to D. magna. In summary, our study manifested that diatom consumption of D. magna leads to more successful sexual reproduction. We then discussed how the diatom consumption of zooplankton influences food web dynamics in a freshwater ecosystem.

Mating behavior of Daphnia: impacts of predation risk, food quantity, and reproductive phase of females.

High predation risk and food depletion lead to sexual reproduction in cyclically parthenogenetic Daphnia. Mating, the core of sexual reproduction, also occurs under these conditions. Assessment of the environmental conditions and alteration of mating efforts may aid in determining the success of sexual reproduction. Here, we evaluated the impacts of predation risk, food quantity, and reproductive phase of females on the mating behavior of Daphnia obtusa males including contact frequency and duration using video analysis. Mating-related behavior involved male-female contact (mating) as well as male-male contact (fighting). Mating frequency increased while unnecessary fighting decreased in the presence of predation risk. In addition, low food concentration reduced fighting between males. Males attempted to attach to sexual females more than asexual females, and fighting occurred more frequently in the presence of sexual females. Duration of mating was relatively long; however, males separated shortly after contact in terms of fighting behavior. Thus, assessment of environmental factors and primary sexing of mates were performed before actual contact, possibly mechanically, and precise sex discrimination was conducted after contact. These results suggest that mating in Daphnia is not a random process but rather a balance between predation risk and energetic cost that results in changes in mating and fighting strategies.

Population growth of the Cladoceran, Daphnia magna: a quantitative analysis of the effects of different algal food.

In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.