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Topo-Bathymetric LiDAR for Monitoring River Morphodynamics and Instream Habitats—A Case Study at the Pielach River
摘要： Airborne LiDAR Bathymetry (ALB) has been rapidly evolving in recent years and now allows fluvial topography to be mapped in high resolution (>20 points/m2) and height accuracy (<10 cm) for both the aquatic and the riparian area. This article presents methods for enhanced modeling and monitoring of instream meso- and microhabitats based on multitemporal data acquisition. This is demonstrated for a near natural reach of the Pielach River, with data acquired from April 2013 to October 2014, covering two flood events. In comparison with topographic laser scanning, ALB requires a number of specific processing steps. We present, firstly, a novel approach for modeling the water surface in the case of sparse water surface echoes and, secondly, a strategy for improved filtering and modeling of the Digital Terrain Model of the Watercourse (DTM-W). Based on the multitemporal DTM-W we discuss the massive changes of the fluvial topography exhibiting deposition/erosion of 103 m3 caused by the 30-years flood event in May 2014. Furthermore, for the first time, such a high-resolution data source is used for monitoring of hydro-morphological units (mesohabitat scale) including the consequences for the target fish species nase (Chondrostoma nasus, microhabitat scale). The flood events caused a spatial displacement of the hydro-morphological units but did not effect their overall frequency distribution, which is considered an important habitat feature as it documents resilience against disturbances.
关键词： microhabitat monitoring,airborne LiDAR bathymetry,mesohabitat monitoring,digital terrain modeling,fluvial change detection,water surface modeling
更新于2025-09-04 15:30:14
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Combining Multispectral Imagery with in situ Topographic Data Reveals Complex Water Level Variation in China’s Largest Freshwater Lake
摘要： Lake level variation is an important hydrological indicator of water balance, biodiversity and climate change in drainage basins. This paper illustrates the use of moderate-resolution imaging spectroadiometer (MODIS) data to characterize complex water level variation in Poyang Lake, the largest freshwater lake in China. MODIS data were used in conjunction with in situ topographic data, otherwise known as the land-water contact method, to investigate the potential of this hybrid water level spatiotemporal variability measurement technique. An error analysis was conducted to assess the derived water level relative to gauge data. Validation results demonstrated that the land-water contact method can satisfactorily capture spatial patterns and seasonal variations in water level fluctuations. The correlation coefficient ranged from 0.684 to 0.835, the root-mean-square-error from 0.79 m–1.09 m, and the mean absolute bias error from 0.65 m to 0.86 m for five main gauge stations surrounding the lake. Additionally, seasonal and interannual variations in the lake’s water level were revealed in the MODIS-based results. These results indicate that the land-water contact method has the potential to be applied in mapping water level changes in Poyang Lake. This study not only provides a foundation for basic hydrological and ecological studies, but is also valuable for the conservation and management of water resources over gauge-sparse regions in Poyang Lake.
关键词： Poyang Lake,water level,in situ topographic data,spatiotemporal variation,MODIS
更新于2025-09-04 15:30:14
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Efficiency of evacuated tube solar collector using WO3/Water nanofluid
摘要： The thermal performance of the evacuated tube solar collector with WO3/Water Nanofluid was studied in this paper. The WO3 nanoparticles were spherical with 90 nm diameter Three different volume fraction of WO3 nanoparticles of 0.014%, 0.028%, and0.042% were examined at several mass flux rates of 0.013 kg/s.m2, 0.015 kg/s.m2 and 0.017 kg/s.m2. The stability of the nanofluid was checked. Experiments were performed in Budapest, Hungary on the latitude of 47°280N and longitude of 19°030E. The results showed that the temperature difference of the fluid increased up to 21% with adding WO3 nanoparticles. The maximum heat gain at the solar irradiance of 900 W/m2 was raised up to 23% when WO3 nanoparticles were used. The proportion of the growth of the heat removable factor for nanofluids comparing to water at the same mass flux rate is between 1.05 and 1.16. The results indicated that the efficiency of the evacuated tube solar collector enhanced with more nanoparticles added. The thermal-optical efficiency of the evacuated tube solar collector reached 72.8%.
关键词： WO3/Water nanofluid,Solar collector,Efficiency,Evacuated tube
更新于2025-09-04 15:30:14
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Dynamics of Molecules Physically Adsorbed onto Metal Oxide Nanoparticles: Similarities between Water and a Flexible Polymer
摘要： Water at interfaces is considered present and important within almost all physical processes. Interfacial water shows nonbulk properties, however, its structure/organization and dynamics are on a still open debate. In parallel to that, the interfacial polymer in nanocomposites exhibits modi?ed structure and dynamics, the latter characteristic being widely considered responsible for the improved nanocomposite properties. One of the most suitable tools for studying dynamics of a variety of small molecules and macromolecules is broadband dielectric spectroscopy (BDS), mainly due to its high resolving power. BDS is employed here in combination with isothermal hydration and has proved quite illuminating in recording for the ?rst time striking similarities in the dynamics behavior between water molecules and ?exible polydimethylsiloxane macromolecules, when the latter molecules are individually adsorbed physically on the attractive surfaces of metal oxide nanoparticle. The qualitative similarities between water and polymer interfacial dynamics, for example, in their exhibiting time-scale and the elevation of the respective activation energy upon increasing of interfacial molecules fraction, lay most probably at the origins of the same main surface-adsorbed molecule interaction, i.e.. the hydrogen bonding. Whereas, the quantitative di?erences in molecular dynamics, e.g., slower, more energetically demanding, and cooperative interfacial dynamics for the polymer than for water, arise from the di?erent scale of the two molecular motions (<1 nm for water and ≥1 nm for the polymer) and/or from alternations in interfacial layer density.
关键词： dielectric spectroscopy,water,nanoparticles,polydimethylsiloxane,interfaces,dynamics,hydrogen bonding
更新于2025-09-04 15:30:14
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Evaluation of electroless Pt deposition and electron beam Pt evaporation on p-GaAs as a photocathode for hydrogen evolution
摘要： This study examines the changes in the photoelectrochemical (PEC) properties with Pt morphology after wet (electroless Pt deposition) and dry (e-beam Pt evaporation) deposition of Pt on p-GaAs. The Pt morphology and composition of the p-GaAs surface differed depending on the Pt deposition method, which in turn affected the optical and PEC properties of Pt on the GaAs electrode. Thus, the findings of this study can help in gaining a clearer understanding of the manner in which these changes affect the operation of a GaAs PEC water-splitting electrode.
关键词： Electrocatalyst,Electron beam evaporation,Gallium arsenide,Water splitting,Electroless deposition,Platinum
更新于2025-09-04 15:30:14
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Bimetallic PtAu Alloy Nanoparticles-Integrated g-C <sub/>3</sub> N <sub/>4</sub> Hybrid as an Efficient Photocatalyst for Water-to-Hydrogen Conversion
摘要： Herein, we report the synthesis of metal (Pt and Au) and metal alloy (PtAu) nanoparticles (NPs) integrated graphitic carbon nitride (g?C3N4) hybrid using a facile solvothermal route for water splitting application. The metal and metal alloy NPs with varying percentages of Pt and Au are found to be in the size range of 3?5 nm and uniformly distributed on the g?C3N4 sheets. The metal and metal alloy NPs act as cocatalyst for g?C3N4 to enhance the photocatalytic activity for hydrogen (H2) generation through higher light absorption and efficient charge separation. The alloy composition plays an important role to maximize the photoactivity, with an optimized PtAu/g?C3N4 sample delivered 1009 μmol g?1 h?1 of H2. The visible light assisted photocatalytic H2 evolution is further investigated with the optimized PtAu alloy NPs integrated g?C3N4. This study presents a robust, stable, and easily synthesizable PtAu/g?C3N4 hybrid material as a promising photocatalyst for H2 generation through water splitting.
关键词： alloy nanoparticles,heterostructure,g?C3N4,water splitting,bimetallic,photoelectrochemical
更新于2025-09-04 15:30:14
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Energy Level Engineering in Transition-Metal Doped Spinel-Structured Nanosheets for Efficient Overall Water Splitting
摘要： Unraveling the role of transition-metal doping on affecting the native spinel-structured nanosheets’ water splitting remains a grand challenge. In this work, a series of spinel-structured nanosheets wrapped hollow nitrogen-doped carbon polyhedrons was constructed, and doped transition-metal domains were deliberately introduced on the surface. Theoretical investigations show that their energy level can be finely tuned via direct transition-metal doping engineering. As a prototype, Fe-doped NiCo2O4 nanosheets wrapped hollow nitrogen-doped carbon polyhedron (Fe-NiCo2O4@HNCP) exhibits outstanding bifunctional electrocatalytic performances with low overpotentials (η = 270 mV for OER, η = 84 mV for HER), low Tafel slopes (b = 42 mV dec-1 for OER, b = 47 mV dec-1 for HER), and high durability. The enhanced performance is attributed to the synergistic effects of energy level matching for electron transfer, and partial charge delocalization-induced rich active sites for reactant adsorption via thermodynamic and kinetic acceleration. This work may open a new pathway to design highly active and stable transtion-metal doped electrocatalysts by manipulated energy levels for efficient overall water splitting.
关键词： energy level engineering,water splitting,electrocatalysts,spinel-structured nanosheets,transition-metal doping
更新于2025-09-04 15:30:14
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Suppression of poisoning of photocathode catalysts in photoelectrochemical cells for highly stable sunlight-driven overall water splitting
摘要： A photoelectrochemical (PEC) cell composed of two semiconductor electrodes, a photocathode, and a photoanode is a potentially effective means of obtaining hydrogen through spontaneous overall water splitting under light irradiation. However, the long-term stability (that is, operation for more than one day) of a PEC cell has not yet been demonstrated. In addition to the corrosion of both photoelectrodes, the gradual migration of heavy metal cations from the photoanode into the electrolyte can also result in degradation of the cell by contamination of the photocathode surface. In the present work, BiVO4-based photoanodes were used in conjunction with two different modifications: dispersion of a chelating resin in the electrolyte and coating of the photoanode surface with an anion-conducting ionomer. The chelating resin was found to capture Bi3+ cations in the electrolyte before they became deposited on the cathode surface. Consequently, a PEC cell incorporating a BiVO4-based photoanode and a (ZnSe)0.85(CuIn0.7Ga0.3Se2)0.15-based photocathode showed stable overall water splitting over a span of two days under simulated sunlight. To the best of our knowledge, this represents the longest period over which stable PEC cell performance has been established. A considerable decrease in the performance of the BiVO4-based photoanode was still observed due to the continuous dissolution of Bi species, but surface coating of the photoanode with an anion-conducting ionomer prevented the movement of Bi3+ ions into the electrolyte because of the selective conduction of ions. The coating also served as a protective layer that improved the durability of the photoanode. This study therefore suggests a simple yet effective method for the construction of stable PEC cells using semiconductor photoelectrodes.
关键词： chelating resin,photoanode,stability,BiVO4,anion-conducting ionomer,water splitting,photoelectrochemical cell,photocathode
更新于2025-09-04 15:30:14
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Direct comparison of pulsed spark discharges in air and water by synchronized electrical and optical diagnostics
摘要： In this study, a direct comparison was made between pulsed spark discharges in air and water in sub-mm gaps. The discharges were ignited at atmospheric pressure in the same discharge arrangement for air and water, using a solid-state microsecond pulse source with ≈1 μs voltage rise time (Umax up to 37 kV). Fast voltage and current measurements were synchronized with iCCD imaging with high spatial resolution on symmetrical half-sphere tungsten electrodes (electrode gaps of up to 0.7 mm for air and 0.3 mm for water). The breakdown voltage and electrical ?eld strength, maximal current, transferred charge, consumed electrical energy and discharge emission structure (e.g. discharge channel diameters) was obtained for all cases. Using the synchronization of the electrical data and the iCCD imaging, current and energy densities were estimated for the sparks in air and water. It was found that the breakdown voltage, the discharge current, the transferred charge, and the consumed electrical energy increase with the gap distance, and that this dependency is much stronger for discharges in water (compared to air). Due to the use of the same discharge arrangement and the same applied voltage, the di?erence in the discharge characteristics was directly quanti?ed.
关键词： energy density,spark discharges,water,optical diagnostics,breakdown voltage,electrical diagnostics,air,discharge current
更新于2025-09-04 15:30:14
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Ag@Fe <sub/>3</sub> O <sub/>4</sub> Core–Shell Surface-Enhanced Raman Scattering Probe for Trace Arsenate Detection
摘要： Developing an effective and reliable method for trace arsenic (As) detection is a prerequisite for improving the safety of drinking water. In this paper, we designed and prepared Ag@Fe3O4 core–shell nanoparticles (NPs), which were then used as Surface-Enhanced Raman Scattering (SERS) probe for trace arsenate (As(V)) detection. The Ag@Fe3O4 core–shell NPs were prepared by in situ growth of Fe3O4 NPs on the surface of AgNPs, which can effectively combine the strong adsorption ability of Fe3O4 nanoshells to As(V) with high SERS activity of Ag nanocores to decrease the detection limit. By use of Ag@Fe3O4 core–shell NPs for As(V) detection, the detection limit can be as low as 10 (cid:2)g/L, and a good linear relationship between the SERS intensity of As(V) and their concentrations in the range from 10 to 500 (cid:2)g/L was achieved. Furthermore, Ag@Fe3O4 core–shell NPs could be regenerated through desorption of As(V) from Fe3O4 nanoshells in NaOH solution, and then used for recyclic SERS detection. Therefore, it has been demonstrated for the ?rst time that multifunctional Ag@Fe3O4 core–shell SERS probe could be applied to realize the highly sensitive and reversible detection of As(V).
关键词： Drinking Water,Core–Shell,Fe3O4,Heavy Metals,Trace Detection
更新于2025-09-04 15:30:14