Longitudinal Gradient Research Articles

Long-term prediction of algal chlorophyll based on empirical models and the machine learning approach in relation to trophic variation in Juam Reservoir, Korea

This study analyzed spatiotemporal variation and long-term trends in water quality indicators and trophic state conditions in an Asian temperate reservoir, Juam Reservoir (JR), and developed models that forecast algal chlorophyll (CHL-a) over a period of 30 years, 1993–2022. The analysis revealed that there were longitudinal gradients in water quality indicators along the reservoir, with notable influences from tributaries and seasonal variations in nutrient regimes and suspended solids. The empirical model showed phosphorus was found to be the key determinant of algal biomass, while suspended solids played a significant role in regulating water transparency. The trophic state indices indicated varying levels of trophic status, ranging from mesotrophic to eutrophic. Eutrophic states were particularly observed in zones after the summer monsoons, indicating a heightened risk of algal blooms, which were more prevalent in flood years. The analysis of trophic state index deviation suggested that phosphorus availability strongly influences the reservoir trophic status, with several episodes of non-algal turbidity at each site during Mon. Increases in non-algal turbidity were more prevalent during the monsoon in flood years. This study also highlighted overall long-term trends in certain water quality parameters, albeit with indications of shifting pollution sources towards non-biodegradable organic matter. According to the machine learning tests, a random forest (RF) model strongly predicted CHL-a (R2 = 0.72, p < 0.01), except for algal biomass peaks (>60 μg/L), compared to all other models. Overall, our research suggests that CHL-a and trophic variation are primarily regulated by the monsoon intensity and predicted well by the machine learning RF model.

Nonuniformity in stress transfer across FRP width of FRP-concrete interface

The nonuniformity of stress and strain analysis is an important consideration that describes the bond behavior between concrete and externally bonded fiber reinforced polymer (FRP) laminates. The interfacial stress transfer between FRP and concrete generates a longitudinal strain gradient in the longitudinal (or FRP fiber) direction. Most of the available studies in this area have focused on nonuniformity in the longitudinal direction. In this paper, the nonuniformity in the FRP width direction is investigated by studying the strain distribution using digital image correlation (DIC) full-field optical techniques. In the direction along the FRP width, there is an area in the middle that has consistent strain and stress, while the edge regions have strain and stress gradients. During the complete debonding process, the width of the central area is found to be insignificantly affected by the concrete strength but significantly affected by the FRP stiffness. The fracture characteristics below the central region are purely Mode II fracture. However, the complex curved cracks and high in-plane shear strains at the interface near the FRP edge regions show a mixed mode with Modes II and III. This boundary effect results in a significant difference in the bond–slip characteristics of FRP along the width direction. The maximum bond stress of the central region is higher than that of the edge region. However, for FRP with higher stiffness, the inhomogeneity of the stress distribution is weakened. Moreover, it is reasonable to find that calculating the sum of the bearing capacity of the single FRP strips along the width direction is close to the experimental bond strength. Based on the research findings in this study, it is qualitatively recommended that the width factor model in calculating FRP-concrete bond strength should include the significant effect of FRP stiffness.

Hydrochemical and isotopic characteristics of water sources for biological activity across a massive evaporite basin on the Tibetan Plateau: Implications for aquatic environments on early Mars

Covered by vast eolian landforms, gravel deposits, and playas, the worldwide typical evaporite deposit land, Qaidam Basin, in northwestern China is analogous to early Mars when the aridification process had lasted for millions of years since the end of a wetter climate. This study aims to investigate the chemical and isotopic characteristics of waters in an evaporite-rich environment, as well as the habitable conditions therein, that have undergone a transformation similar to early Mars. In May 2023, a total of 26 water samples were collected across the representative central axis of a longitudinal aridity gradient in the Qaidam Basin, including categories of meteoric water, freshwater, standing water accumulated after precipitation, salty lacustrine water, and hypersaline brines to inspect compounds made up of carbon, nitrogen, phosphorus, sulfur, halogen, and metallic elements. As evaporation intensified, the salt types transformed from HCO3-Ca·Na to Cl·SO4-Na or ClMg. The dominance of carbonate will gradually be replaced by sulfate and chloride, leaving much more dilute and less detectable contents. The presence of trace ClO4−, ClO3−, ClO2−, and BrO3− was confirmed in a few of the sampled Qaidam waters, indicating the preservation of oxyhalides in waters within an arid region and possibly the presence of relevant microbial enzymes. The isotopes of water, carbonaceous, and nitrogenous compounds provide valuable references for either abiogenic or biogenic signatures. With undetectable amount, phosphorus was found to be the limiting nutrient in evaporative aquatic environments but not necessarily antibiosignatures. Overall, these results suggest that the paleo-lacustrine environments on Mars are more likely to preserve biosignatures if they feature the dominance of carbonate minerals, bioavailable nitrate, phosphorus, and organic carbon, the presence of thermodynamically unstable oxyhalides, and isotope ratios that point to the involvement of biological activity.

Assessing the modulation of outer bank erosion by slump blocks: A case study from Marqu Meadow, China

The outer bank slump blocks play a fundamental role in modulating the rate of bank erosion, and consequently, have a profound influence on many geomorphic and ecologic processes in meandering streams, e.g., channel evolution and habitat creation. To date, no adequate research has been developed regarding how these blocks, partially strengthened by roots of herbaceous plants, impact the near-bank flow velocity, bank erosion, and migration of streambanks. This paper analyzes 246 slump blocks in a meandering stream on the Marqu Meadow, China. Aerial surveys were conducted once a year from 2018 to 2021 and the lateral migration rates (M) of streambanks are estimated by superimposing the current-year drone imagery onto its previous-year counterpart. When compared to the outer bank segments lacking slumps, our research findings indicate that the bank segments exhibiting slumps demonstrate a reduction of 57 % and 43 % in the maximum and average bank erosion rates, respectively. Overall, the wider blocks provide stronger bank protection; nevertheless, they may also introduce or enhance local scouring in their vicinity, thereby increasing the heterogeneity of bank erosion rates. To elucidate this complex influence mechanism, we simulate the three-dimensional flow velocity field of a ~100 m meandering bend containing three slump blocks using the MIKE-3 model. Furthermore, we compare one-year bank migration distance with and without the blocks by correlating the lateral migration distance of outer banks to the longitudinal gradient of near-bank velocity. The paper provides valuable insights into the complex interplay between flow dynamics and streambank behavior in real-world settings, thereby enhancing the effectiveness of future management and restoration practices.

Role of Longitudinal Temperature Gradients in Eliminating Interleaving Inclusions in Casting of Monocrystalline Silicon Ingots

Infrared analysis reveals the presence of interwoven inclusions, primarily comprised of silicon nitride and silicon carbide, in the casting process of monocrystalline silicon ingots. This study investigates how the longitudinal temperature gradient affects the removal of inclusions during the casting of monocrystalline silicon ingots through simulations and comparative experiments. Two monocrystalline silicon ingots were cast, each using different longitudinal temperature gradients: one employing smaller gradients and the other conventional gradients. CGSim (Version Basic CGSim 23.1) simulation software was utilized to analyze the melt flow and temperature distribution during the growth process of quasi–monocrystalline silicon ingots. The findings indicate that smaller longitudinal temperature gradients lead to a more robust upward flow of molten silicon at the solid–liquid interface, effectively carrying impurities away from this interface and preventing their inclusion formation. Analysis of experimental photoluminescence and IR results reveals that although inclusions may not be observed, impurities persist but are gradually displaced to the top of the silicon melt through a stable growth process.

Plant dispersal in the Devonian world (c. 419–359 Ma)

AbstractDispersal, whether active or passive, plays a crucial role in biogeography by facilitating the movement of propagules away from their original location. Botanical geographical zonation, resulting from the co‐evolution of plants and their environment, has been established since the remarkable plant diversification during the Devonian Period (c. 419–359 Ma). However, a significant knowledge gap exists in understanding plant dispersal between living and fossil organisms due to the rarity of opportunities for tracing plant dispersal in geological history. In this study, we present evidence of two plant dispersal routes and verify their occurrence through the examination of geographical zonation, changes in plant diversity, and latitudinal and longitudinal gradients during the Devonian. We analyse global occurrence data from widely‐distributed and extensively‐studied Devonian plants. The two dispersal routes, namely clockwise and anticlockwise, connect the South China and Euramerica–Siberia realms. These routes clearly demonstrate inland and inter‐land dispersal models, closely linked to Devonian sea–land topography and dispersal vectors such as wind and ocean currents. Moreover, these models probably apply to all Devonian plants. Our comprehensive synthesis of plant dispersal in deep time reveals that propagule diversity and dispersal vectors have progressively increased and become more complex over time, facilitating plant colonization and diversity changes. Importantly, our study unveils the dispersal models of fossil plants, demonstrating the equivalent models observed in extant plants that have been established since the Devonian Period.

Application of environmental DNA metabarcoding to identify fish community characteristics in subtropical river systems

AbstractFish are vital in river ecosystems; however, traditional investigations of fish usually cause ecological damage. Extracting DNA from aquatic environments and identifying DNA sequences offer an alternative, noninvasive approach for detecting fish species. In this study, the effects of environmental DNA (eDNA), coupled with PCR and next‐generation sequencing, and electrofishing for identifying fish community composition and diversity were compared. In three subtropical rivers of southern China, fish specimens and eDNA in water were collected along the longitudinal (upstream–downstream) gradient of the rivers. Both fish population parameters, including species abundance and biomass, and eDNA OTU richness grouped 38 sampling sites into eight spatial zones with significant differences in local fish community composition. Compared with order‐/family‐level grouping, genus‐/species‐level grouping could more accurately reveal the differences between upstream zones I−III, midstream zones IV−V, and downstream zones VI–VIII. From the headwaters to the estuary, two environmental gradients significantly influenced the longitudinal distribution of the fish species, including the first gradient composed of habitat and physical water parameters and the second gradient composed of chemical water parameters. The high regression coefficient of alpha diversity between eDNA and electrofishing methods as well as the accurate identification of dominant, alien, and biomarker species in each spatial zone indicated that eDNA could characterize fish community attributes at a level similar to that of traditional approaches. Overall, our results demonstrated that eDNA metabarcoding can be used as an effective tool for revealing fish composition and diversity, which is important for using the eDNA technique in aquatic field monitoring.

Two orthogonal differentiation gradients locally coordinate fruit morphogenesis

Morphogenesis requires the coordination of cellular behaviors along developmental axes. In plants, gradients of growth and differentiation are typically established along a single longitudinal primordium axis to control global organ shape. Yet, it remains unclear how these gradients are locally adjusted to regulate the formation of complex organs that consist of diverse tissue types. Here we combine quantitative live imaging at cellular resolution with genetics, and chemical treatments to understand the formation of Arabidopsis thaliana female reproductive organ (gynoecium). We show that, contrary to other aerial organs, gynoecium shape is determined by two orthogonal, time-shifted differentiation gradients. An early mediolateral gradient controls valve morphogenesis while a late, longitudinal gradient regulates style differentiation. Local, tissue-dependent action of these gradients serves to fine-tune the common developmental program governing organ morphogenesis to ensure the specialized function of the gynoecium.

Assessment of the changes in growth, photosynthetic traits and gene expression in Cynodon dactylon against drought stress

Drought stress considered a key restrictive factor for a warm-season bermudagrass growth during summers in China. Genotypic variation against drought stress exists among bermudagrass (Cynodon sp.), but the selection of highly drought-tolerant germplasm is important for its growth in limited water regions and for future breeding. Our study aimed to investigate the most tolerant bermudagrass germplasm among thirteen, along latitude and longitudinal gradient under a well-watered and drought stress condition. Current study included high drought-resistant germplasm, “Tianshui” and “Linxiang”, and drought-sensitive cultivars; “Zhengzhou” and “Cixian” under drought treatments along longitude and latitudinal gradients, respectively. Under water deficit conditions, the tolerant genotypes showed over-expression of a dehydrin gene cdDHN4, antioxidant genes Cu/ZnSOD and APX which leads to higher antioxidant activities to scavenge the excessive reactive oxygen species and minimizing the membrane damage. It helps in maintenance of cell membrane permeability and osmotic adjustment by producing organic osmolytes. Proline an osmolyte has the ability to keep osmotic water potential and water use efficiency high via stomatal conductance and maintain transpiration rate. It leads to optimum CO2 assimilation rate, high chlorophyll contents for photosynthesis and elongation of leaf mesophyll, palisade and thick spongy cells. Consequently, it results in elongation of leaf length, stolon and internode length; plant height and deep rooting system. The CdDHN4 gene highly expressed in “Tianshui” and “Youxian”, Cu/ZnSOD gene in “Tianshui” and “Linxiang” and APX gene in “Shanxian” and “Linxiang”. The genotypes “Zhongshan” and “Xiaochang” showed no gene expression under water deficit conditions. Our results indicate that turfgrass show morphological modifications firstly when subjected to drought stress; however the gene expression is directly associated and crucial for drought tolerance in bermudagrass. Hence, current research has provided excellent germplasm of drought tolerant bermudagrass for physiological and molecular study and future breeding.

Longitudinal changes on ecological diversity of Neotropical fish along a 1700 km river gradient show declines induced by dams

In naturally flowing waters, communities are expected to increase their taxonomic and functional diversity as well as increase the complexity of food web architecture along the longitudinal gradient from headwaters to mouth. However, these theories do not necessarily apply to dammed rivers. We analysed fish communities at 12 locations along the 1700 km stretch of the transnational Uruguay River. We determined species richness, beta-diversity and its components (turnover and nestedness), trophic diversity, and isotopic niches at community level, with particular focus on areas upstream and downstream of the four existing dams. We estimated trophic diversity metrics based on diet analysis, and isotopic niche breadth based on Bayesian isotopic niche models. We detected consistent longitudinal changes, supporting predictions from the River Continuum Concept. However, taxonomic richness, trophic diversity, and isotopic niche decreased abruptly immediately downstream of dams, and the component contributing the most to beta diversity was turnover, with the highest values occurring mainly after the cascade of dams in the upper Uruguay River, fitting expectations from the Serial Discontinuity Concept. The dam-free stretches of the Uruguay River allowed the recovery of ecological diversity as fish richness and trophic and isotopic niche increased. The negative impacts of dams should urgently be considered in the Neotropics, where many large dams are projected.

Fish assemblage structure and habitat relationships of a large floodplain river in western North America

AbstractUnderstanding complex river floodplains is critical to conserve species of fish and their ecological functions. In 2011 through 2013, longitudinal gradients in fish assemblage were investigated in the Willamette River in western United States. Of 36,586 individual fish collected, 93% were native and 7% non‐native. The best predictors of fishes collected with a boat electrofisher were percent embeddedness, macrophytes, longitudinal river distance, average depth, and velocity. Habitat type (mainstem or slough) was also a significant predictor. The best predictor of fishes collected in nearshore habitats with a backpack electrofisher were longitudinal river distance, velocity, and percent embeddedness. Fish communities differed significantly between mainstem and slough habitat. Overall, 25 of 40 species had high fidelities to mainstem or slough habitats. Native species showed a high fidelity to both mainstem and slough habitats while non‐native species were significantly related only to slough habitats. Environmental characteristics strongly influenced fish assemblage structure in this large floodplain river. Maintaining and restoring mainstem and off‐channel habitats are critical for maximizing native species resilience in the face of non‐native species encroachment and a changing environment. Restoring the natural flow regime to the degree possible is needed to increase connectivity between the floodplain and mainstem and provide thermal and flood refuges for native fishes. Understanding habitat relationships provides essential context for fish conservation and management by resource agencies and landowners.

Spatiotemporal variability and drivers of water microchemistry in the upper Nu-Salween river: With implications for fish habitat conservation

Microchemical maps, also known as “chemoscapes”, hold immense potential for reconstructing fish habitat utilization and guiding conservation efforts. This approach relies on matching the microchemical composition of fish calcified structures (e.g., otoliths) with the surrounding water's microchemistry. However, applying this method faces a major challenge: a clear understanding of the spatiotemporal variability and drivers of water microchemistry, particularly in vast, free-flowing river ecosystems like the Nu-Salween River, Southeast Asia's longest free-flowing river. We analyzed the spatiotemporal variability and influencing factors of water microchemistry (i.e., Na:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Zn:Ca, Se:Ca, Sr:Ca, and Ba:Ca) in the upper Nu-Salween River, based on a two-year sampling. Five elemental ratios (excluding Na:Ca, Mg:Ca, and Zn:Ca) in water demonstrated significant spatiotemporal variability, with Cu:Ca having the largest spatial variation, and Mn:Ca and Sr:Ca showing the greatest temporal variation. More specifically, four elemental ratios (Cu:Ca, Se:Ca, Sr:Ca, and Ba:Ca), exhibited significant variations along the longitudinal gradient, and Mn:Ca, Cu:Ca, Sr:Ca, and Ba:Ca, showed significant differences between mainstreams and tributaries. Temporally, Mn:Ca, Cu:Ca, and Ba:Ca displayed higher values and variations during the wet season, opposing the seasonal patterns of Na:Ca, Mg:Ca, and Sr:Ca. The four-element (Ba:Ca, Sr:Ca, Mg:Ca, and Mn:Ca) forest model showed the highest classification accuracy of 93%. Linear mixed-effects models showed that spatial factors have the largest influence on the variances in water microchemistry (56.36 ± 28.64%). Our study highlights the feasibility and reliability of utilizing microchemistry to reconstruct fish habitat utilization, thereby unveiling promising avenues for a more accurate understanding of fish life history in large rivers characterized by high heterogeneity in water microchemistry. By proportionally accounting for contribution of different factors to water microchemistry variability and relating them to microchemical composition of fish calcified structures, key fish habitats (e.g., spawning grounds) and migratory routes can be more precisely identified and thus protected.

Peristaltic mechanism of Ellis fluid with viscous dissipation and thermal radiation induced by cilia wave

Bioheat transfer analysis in tissue has attracted the attention of numerous researchers due to its widespread potential applications in the medical field, mainly in thermotherapy and the human thermoregulation system. Also, temperature regulation of the human body primarily occurs through bioheat transfer. Due to the widespread biomedical applications of bio-heat transfer, we aim to investigate the movement of biofluid and bioheat in human organs with the influences of thermal radiation and ciliary waves. The mathematical model for Ellis fluid flow through a tube includes the metachronal wave of cilia motion and convective conditions. The governing equations are created based on mass, momentum conservation, and energy. The current problem is displayed and exact solutions are managed under long wavelength [Formula: see text] and low Reynolds number [Formula: see text] approximations. An analytical approach is employed to derive expressions for longitudinal velocity, temperature, pressure gradient, and stream function as a function of the parameters of the problem. The physical behavior of the peristaltic motion of the Ellis fluid is explained in detail and illustrated graphically for various parameter values. The results of the current study provide potential information for advancement in the biomedical industry, particularly in the development of biomedical devices and processes.

Research and Optimization of Four Serpentine-Wave Flow Fields in PEMFC

The layout of the cathode flow field largely determines the net output power of the proton exchange membrane fuel cell (PEMFC). To make the normal mass transfer effect best, the longitudinal channel was waved based on four serpentine flow channels, and the effects of sag depth and longitudinal channel width on the output efficiency of the cell were explored. The results show that the wave channel design systematically enhances the forced convection between adjacent channels, which can prevent a large zone of oxygen starvation zone at the outlet of the channel. The increase of the normal velocity in the gas transmission process will inevitably induce a significant enhancement of the mass transfer effect and obtain a higher current density in the reaction zone. For the longitudinal channel width, it is found that increasing its size in the effective range can greatly reduce the channel pressure drop without reducing the output power, thereby improving the overall efficiency. When the sag depth and longitudinal channel width gradient are 0.6 mm and 0.2 mm respectively, PEMFC can obtain the best comprehensive performance.

Microstructure and residual stress distribution of electron beam-welded joints of a 50 mm-thick TA15 titanium alloy plate

Abstract Vacuum electron beam welding was applied to a 50 mm-thick TA15 titanium alloy plate. Microstructure observation and microhardness testing were performed. Meanwhile, the residual stress on the surface at different distances from the weld centre was measured via the hole drilling method. A finite element model for electron beam welding of the TA15 titanium alloy plate was constructed on commercial finite element software. Experimental results showed that the microstructure of the weld zone consisted of a basket martensitic phase. The highest microhardness in the weld zone was 409 HV, and the microhardness of the base metal was the lowest. The maximum gradient change area was located at the HAZ near the base metal. The peak value of longitudinal residual stress from the simulation was 880 MPa, which was in the weld metal. The sharp change area of longitudinal residual stress gradient was located in the base metal near HAZ.

Harmful blooms across a longitudinal gradient in central Europe during heatwave: Cyanobacteria biomass, cyanotoxins, and nutrients

Climate change has increased the frequency, duration and intensity of heatwaves in Europe. These extreme events result in alterations of physical, chemical, and biological properties of lakes that may synergistically promote cyanobacterial dominance. In our study we focused on cyanobacterial blooms in lakes distributed over a longitudinal gradient in Central Europe during one of the “top ten European heat waves” in summer 2015. 92 lakes were included in the study, located across three climatic subregions: cool northern lakes, situated in Lithuania, temperate northern lakes in Poland, and warm northern lakes in Croatia. The objective of the study was to determine if cyanobacterial biomass, predominant species, and cyanotoxin concentration differed, across the south-north gradient, as a function of water temperature, total phosphorus, and total nitrogen. Statistical significance of observed patterns was tested using the Kruskal-Wallis rank sum test and the generalized linear model. We found the lowest average epilimnion temperature, but the highest average cyanobacterial biomass in the northern, ‘cool’ lakes while the highest average temperature with the lowest average cyanobacterial biomass in the southern, ‘warm’ lakes. The concentration of cyanotoxins was also the highest in the ‘cool’ lakes. Total phosphorus and total nitrogen correlated significantly with cyanobacterial biomass, cyanotoxins concentration and biomass of some cyanobacterial species (mainly Planktothrix agardhii), regardless of the latitude. Only in the ‘cool’ lakes concentration of cyanotoxins (microcystins and anatoxin-a) correlated significantly with cyanobacterial biomass and the biomass of some dominant cyanobacterial species (P. agardhii). Our results emphasized the differences of heat weaves impact on lakes of various latitudes, with the strongest increase in toxic cyanobacterial blooms in northern ‘cool’ lakes, situated in high latitudes. On the other hand, nutrients directly enhanced blooms across all the studied latitudes of Central Europe. The cyanobacteria species dominating in blooms might be recognized as ecological indicators of climate change, especially in the north-eastern part of Europe.

Trophic Fish Structure Along the Beaches of The Brazilian Amazon River

Purpose: This study analyzes fish communities' diet and trophic structure on beaches along the Amazon River. Methods: 41 beaches were studied, and fish were collected with 12x3m trawl nets and 5mm mesh between nodes. The stomachs were analyzed using the frequency of occurrence and points method. The dietary index was calculated using the preponderance index (PI). Using IP values, the following trophic categories were established: detritivore, hematophagous, herbivorous, benthic invertivore, pelagic invertivore, terrestrial invertivore, scavenger, and piscivore. Species richness and abundance of fish in trophic categories were related to the longitudinal variation of the sampled sites through linear regression 1,166 stomachs from 119 species were analyzed. Results and discussion: The abundance and richness of detritivore species and the richness of scavengers showed a negative relationship throughout the floodplain, while the number of aquatic invertivore species showed a positive relationship. Implications of the research: The existing differences in beach water quality create a longitudinal conductivity gradient, transparency, and suspended material, gradually altering the environment and composition of the ichthyofauna and the trophic structure along the Amazon River. Originality/value: Ecological studies relating the trophic structure of fish to a large-scale longitudinal gradient are scarce in the Amazon River floodplain, which makes this article an essential piece for better understanding Amazonian systems by characterizing the trophic structure of fish from beaches in a longitudinal gradient of the Amazon River in Brazilian territory.

Driving factors of colored dissolved organic matter dynamics across a complex urbanized estuary

The role of estuaries in sourcing and transforming dissolved organic matter - the largest reservoir of organic carbon in the ocean - still presents many unknowns for coastal biogeochemical cycles, and is further complicated by increasing human pressures and a changing climate. Here, we examined the major drivers of colored dissolved organic matter (CDOM) dynamics in Long Island Sound (LIS), a heavily urbanized estuary of National Significance with a storied water quality past. A comprehensive new optical dataset, including measurements of CDOM absorption and fluorescence signatures, was integrated with biological and hydrological measurements to capture the spatiotemporal heterogeneities of LIS, including its urban-to-rural gradient, dynamic river mouths, and blue carbon ecosystems across seasons, following episodic storm events, and over five years. Results reveal longitudinal gradients in both DOM amount and quality. While carbon-rich and humic terrigenous DOM was dominant in the heavily riverine-influenced Central to Eastern LIS, an uncoupling between CDOM absorption (aCDOM) and dissolved organic carbon (DOC) concentration in Western LIS, and a stronger correlation with Chlorophyll-a, indicated increased autochthonous CDOM production. Closer to the New York City urban core, aCDOM was highly correlated to turbidity, consistent with increased wastewater influences. Fluorescence PARAFAC analysis provided strong evidence for seasonal processing of CDOM in LIS, related to increased summertime photochemical degradation of humic-like components and shoulder-season microbial processing. Riverine CDOM export was influenced by discharge amount, residence time, and coastal wetlands acting as additional sources of strongly humic and aromatic organic matter. These measurements allowed us to assess how hydrologic, biological, and anthropogenic processes impact DOM dynamics and, subsequently, biogeochemical variability and trophic status in this complex urbanized estuary, with implications for water quality management and policy. Results discussed here are applicable beyond LIS, as urbanized estuaries globally face similar hydrological and anthropogenic forcings.

Magnetoinduced spin Nernst effect in topological nodal-line semimetals

The spin Nernst effect (SNE) of a topological nodal-line semimetals (TNLSMs) nanowire in a four-terminal cross-bar device is studied. Based on the nonequilibrium Green’s function method combining with the tight-binding Hamiltonian, the spin Nernst coefficients Ns3z, Ns3x and Ns3y of the two thermal transport models (kz-y case and kx-y case) under a perpendicular magnetic field are obtained. The traditional SNE describes the transverse voltage and spin current caused by the longitudinal thermal gradient. The transverse spin current is generated by the spin–orbit interaction rather than the perpendicular magnetic field. Here we find that the spin Nernst coefficients are equal to zero at the zero-magnetic field, but have finite values for non-zero magnetic fields in TNLSMs. The spin Nernst coefficient is closely related to the strength of the magnetic field and temperature. With the increase of the magnetic field strength, the peak height of the spin Nernst coefficient increases. These results indicate that the SNE is induced by the perpendicular magnetic field in the present TNLSMs system, which can be considered as an anomalous spin Nernst phenomenon. In addition, we find that Ns3z displays a series of peaks when the transmission coefficient TLR jumps from one integer plateau to another, and the spin Nernst coefficient Ns3i (i=x,y,z) is an odd function of the Fermi energy EF with Ns3z/x/y(−EF)=−Ns3z/x/y(EF) in connection mode kz-y. For the kx-y connection mode, due to the presence of the mass term m opening the energy gap, a sudden jump of the transmission coefficient TLR in the vicinity of the energy gap edge causes a very larger peak for the spin Nernst coefficient Ns3z/x/y, and the symmetrical properties of the spin Nernst coefficient Ns3z/x/y are completely broken in the strong magnetic field. These results indicate that the spin Nernst coefficient in TNLSMs strongly depends on the thermal gradient direction and the transverse lead connection direction. The spin Nernst coefficient in TNLSMs has strongly spatial anisotropy, which can be used as the characterization of the experimental detection of TNLSMs.

Numerical prediction of thermal conductivity and thermal expansion coefficient of glass fiber-reinforced polymer hybrid composites filled with hollow spheres

The optimal performance of composites enriched with hollow spheres has been reported in contemporary literature, whereas their thermal properties have received less attention. In this regard, a finite element method (FEM)-based micromechanical model has been developed systematically to investigate the role of intra-matrix embedding of hollow spheres on the thermal conductivity and coefficient of thermal expansion (CTE) of unidirectional fiber-reinforced hybrid composites. In so doing, the concept of representative volume element (RVE) considers microstructures comprising an epoxy matrix, E-glass fiber, and E-glass hollow spheres, assuming perfect bonding (ideal interface) between the components and modified approximate periodic boundary conditions. By computing the longitudinal and transverse temperature gradients generated due to the application of uniform heat flux as well as the geometrical variation in RVE owing to temperature enhancement, thermal conductivity and CTE have been respectively determined. Comprehensive evaluations have been conducted to examine the effects of microstructural-level features, including fiber volume content and orientation, plus volume content and thickness of hollow spheres, on the effective thermal conductivity and CTE of pseudo-porous ternary E-glass/epoxy composites.