Areal Coverages Research Articles

How Do Weak, Misaligned Tropical Cyclones Evolve Toward Alignment? A Multi‐Case Study Using the Hurricane Analysis and Forecast System

AbstractThis study simulates five initially weak, moderately sheared tropical cyclones (TCs) from the 2020–2021 North Atlantic basin hurricane seasons using the Hurricane Analysis and Forecast System (HAFS). Four of the five simulations rapidly evolve from misaligned vortices with asymmetric precipitation and thermodynamic distributions toward more aligned and symmetric configurations. The displaced low‐level (LLC) and mid‐level circulations (MLC) non‐monotonically progress toward alignment with periods of reformation, precession, and advection. Beginning 12–18 hr pre‐alignment, TCs have increasingly greater mid‐tropospheric humidity and areal coverages of precipitation downshear left than the simulation that fails to align. Alignment precedes the most sustained symmetrization of favorable thermodynamics and precipitation, but deep convection (not necessarily symmetric) plays a critical role in alignment. Ida (2021), a high impact US storm, undergoes a vortex‐scale evolution where an increase in areal coverage and intensity of deep convection promotes a reformation of the vortex into a smaller compact core with a closed MLC (a closed LLC does not immediately form). This convective behavior downtilt helps to reshape the irrotational velocity field in the lower troposphere toward the reformed vortex. The increasingly convergent flow of favorable boundary layer thermodynamics within the inflow region thereby increases the instability, which maintains the persistent intense convection. The confluent flow ultimately promotes an advection of the pre‐existing LLC toward the reformed vortex resulting in alignment. Tilt reductions are also shown to be temporally linked with the diurnal cycle, wherein convection preferentially increases near the center during the early morning hours (local time).

Regional Geoengineering Using Tiny Glass Bubbles Would Accelerate the Loss of Arctic Sea Ice

AbstractArctic sea ice might be preserved if its albedo could be increased. To this end, it has been proposed to spread hollow glass microspheres (HGMs) over the ice. We assess the radiative forcing that would result, by considering the areal coverages and spectral albedos of eight representative surface types, as well as the incident solar radiation, cloud properties, and spectral radiative properties of HGMs. HGMs can raise the albedo of new ice, but new ice occurs in autumn and winter when there is little sunlight. In spring the ice is covered by high‐albedo, thick snow. In summer the sunlight is intense, and the snow melts, so a substantial area is covered by dark ponds of meltwater, which could be an attractive target for attempted brightening. However, prior studies show that wind blows HGMs to the pond edges. A thin layer of HGMs has about 10% absorptance for solar radiation, so HGMs would darken any surfaces with albedo >0.61, such as snow‐covered ice. The net result is the opposite of what was intended: spreading HGMs would warm the Arctic climate and speed sea‐ice loss. If non‐absorbing HGMs could be manufactured, and if they could be transported and distributed without contamination by dark substances, they could cool the climate. The maximum benefit would be achieved by distribution during the month of May, resulting in an annual average radiative forcing for the Arctic Ocean of −3 Wm−2 if 360 megatons of HGMs were spread onto the ice annually.

Features of MCSs in the Central United States Using Simulations of ERA5-Forced Convection-Permitting Climate Models

Abstract In this work, we characterized the occurrences and conditions before the initiations of mesoscale convective systems (MCSs) in the central United States, using 15 years of observations and convection-permitting climate model simulations. The variabilities of MCSs in summer were obtained using high-resolution (4 km) observation data [Stage-IV (stIV)] and ECMWF Re-Analysis v5 (ERA5)-forced Weather Research and Forecasting (WRF) Model simulations (E5RUN). MCSs were identified using the object tracking algorithm MODE-time domain (MTD). MTD-determined MCSs were divided into daytime short-lived MCSs (SLM12), daytime long-lived MCSs (LLM12), nighttime short-lived MCSs (SLM00), and nighttime long-lived MCSs (LLM00). E5RUN showed skill to simulate MCSs by obtaining similar statistics in occurrences, areal coverages, and propagation speeds compared to those of stIV. We calculated the 15 parameters using sounding data from E5RUN before an MCS was initiated (−1, −3, −6, and −9 h) at each location of an MCS. The parameters were tested to figure out the significance of predicting the longevities of MCSs. The key findings are 1) LLM12 showed favorable thermodynamic variables compared to that of SLM12 and 2) LLM00 showed significant conditions of vertically rotating winds and sheared environments that affect the longevity of MCSs. Moreover, storm-relative helicity of 0–3 km, precipitable water, and vertical wind shear of 0–6 km are the most significant parameters to determine the longevities of MCSs (both daytime and nighttime MCSs). Significance Statement The purpose of this study is to understand the features of mesoscale convective systems (MCSs) in observational data and convection-permitting climate model simulations. We tested long-term simulations using new forcing data (ERA5) to see the benefits and limitations. We designed a novel approach to obtain the distributions of meteorological parameters (instead of obtaining one value for one event of MCS) before initiations of MCSs to understand preconvective conditions (times from −9 to −1 h from initiation). We also divided MCSs into daytime/nighttime and short-/long-lived MCSs to help predict MCSs longevity considering the initiation times. Our results provide hints for the forecasters to predict MCS longevity based on preconvective conditions from parameters discussed in this work.

Reduced Soil Gross N2O Emission Driven by Substrates Rather Than Denitrification Gene Abundance in Cropland Agroforestry and Monoculture

AbstractConversion of monoculture to agroforestry (integrating trees with crops) is promoted as a promising management in reducing N2O emissions from croplands. How agroforestry influences gross N2O emission (N2O + N2 from N2O reduction) and uptake (N2O reduced to N2) compared to monoculture is unknown. We used the 15N2O pool dilution technique to quantify these processes using soil cores (top 5 cm) incubated in the field with monthly measurements over two growing seasons (2018–2019) at two sites (each with paired agroforestry and monoculture) and one site with monoculture only. The unfertilized tree rows showed the lowest gross N2O emissions (P ≤ 0.002). Although tree rows occupied only 20% in agroforestry, gross N2O emissions tended to decrease by 6–36% in agroforestry (0.98–1.02 kg N2O‐N ha−1 yr−1) compared to monoculture (1.04–1.59 kg N2O‐N ha−1 yr−1). Gross N2O emissions were influenced by soil mineral N, soil respiration, and moisture content rather than by denitrification gene abundance. Soil gross N2O uptake was highest in the tree row and decreased with distance into crop rows (P = 0.012). The agroforestry tended to increase gross N2O uptake by 27–42% (0.38–0.44 kg N2O‐N ha−1 yr−1) compared to monoculture (0.30–0.31 kg N2O‐N ha−1 yr−1). In tree rows, soil gross N2O uptake correlated with nirK gene abundance which was indirectly influenced by the low mineral N‐to‐soil CO2‐C ratio. Adjusting the tree and crop areal coverages of agroforestry and optimizing fertilization can further augment the benefits of agroforestry in reducing emission and increasing uptake of N2O in soils.

Electron microscopy characterization of the tribolayer formation mechanism in sintered Cu-based composites under dry sliding

In this study, the effect of Cu matrix grain size in sintered Cu-based composites on the microstructural evolution of tribolayers and the resulting tribological properties were investigated. We observed that the hardness of composite and wear dynamics of the Cu composite significantly affected the composition and stability of the tribolayers. As a result, the characters of tribolayers are divided into Fe oxides or Cu with different areal coverages of the surrounding amorphous phase by electron microscopy study. Also, we figured out the self-lubricating property of the tribolayer plays a critical role in deciding the tribological properties such as friction coefficient or wear resistance. Based on analysis, we determined the optimal sintering conditions of the Cu-based composites as 800 °C and 40 MPa for their industrial application; the composite sintered under these conditions possessed an ultrathin and robust tribolayer with high C content.

A semi-quantitative landslide risk assessment of central Kahramanmaraş City in the Eastern Mediterranean region of Turkey

Landslides are one of the most destructive natural hazards in Turkey. In addition to loss of lives, there were many negative impacts of landslides on properties and the environment. To minimize the losses and damages related to landslides, a series of labour-intensive studies starting from landslide inventory to landslide risk mapping is required. Thus, this study aims to assess the landslide risk by a semi-quantitative approach in a landslide-prone area located in the Eastern Mediterranean region of Turkey. This region has been suffering from landslides with its high population and industrial characteristics. A total of 215 deep-seated rotational earth slides were mapped during field studies. Then, landslide-susceptibility mapping was performed by frequency ratio and logistic regression methods. For the hazard stage, the susceptibility map and the triggering indicator maps were used to produce a Landslide Hazard Index (LHI) map. As for the vulnerability analysis, a relative evaluation was performed by considering land use, infrastructure and population density data. All maps were combined at the final stage to produce a Landslide Risk Index (LRI) map of the study area. It was revealed that areal coverages of the produced LRI map were 21.4% very low (VL), 10.8% as low (L), 37.4% as medium (M), 24.8% as high (H) and 5.6% as very high (VH) LRI, respectively. The so-produced LRI map would be beneficial for further and detailed risk analyses to be performed in the future since it highlights the landslide risk hotspots in a regional scale.

Characterizing Peatland Microtopography Using Gradient and Microform-Based Approaches

Peatlands represent an important component of the global carbon cycle, storing 180–621 Gt of carbon (C). Small-scale spatial variations in elevation, frequently referred to as microtopography, influence ecological processes associated with the peatland C cycle, including Sphagnum photosynthesis and methane flux. Microtopography can be characterized with measures of topographic variability and by using conceptual classes (microforms) linked to function: most commonly hummocks and hollows. However, the criteria used to define these conceptual classes are often poorly described, if at all, and vary between studies. Such inconsistencies compel development of explicit quantitative methods to classify microforms. Furthermore, gradient-based characterizations that describe spatial variability without the use of microforms are lacking in the literature. Therefore, the objectives of this study were to (1) calculate peatland microtopographical elevation gradients and measures of spatial variability, (2) develop three microform classification methods intended for specific purposes, and (3) evaluate and contrast classification methods. Our results suggest that at spatial scales much larger than microforms, elevation distributions are unimodal and are well approximated with parametric probability density functions. Results from classifications were variable between methods and years and exhibited significant differences in mean hollow areal coverages of a raised ombrotrophic bog. Our results suggest that the conceptualization and classification of microforms can significantly influence microtopographic structural metrics. The three explicit methods for microform classification described here may be used and built upon for future applications.

3D Printer-Based Encapsulated Origami Electronics for Extreme System Stretchability and High Areal Coverage.

Stretchability and areal coverage of active devices are critical design considerations of stretchable or wearable photovoltaics and photodetections where high areal coverages are required. However, simultaneously maximizing both properties in conventional island-bridge structures through traditional two-dimensional manufacturing processes is difficult due to their inherent trade-offs. Here, a 3D printer-based strategy to achieve extreme system stretchability and high areal coverage through combining fused deposition modeling (FDM) and flexible conductive nanocomposites is reported. Distinguished from typical approaches of using conductive filaments for FDM which have a flexibility dilemma and conductivity trade-offs, the proposed axiomatic approach to embed a two-dimensional silver nanowire percolation network into the surfaces of flexible 3D printed structures offers sufficient conductivity and deformability as well as additional benefits of electrical junction enhancement and encapsulation of silver nanowires. Kirigami/origami-pattern-guided three-dimensional arrangements of encapsulated interconnections provide efficient control over stretchability and areal coverage. The suggested process enables a perovskite solar module with an initial areal coverage of ∼97% to be electrically and mechanically reversible with 400% system stretchability and 25 000% interconnect stretchability under the 1000 cycle test, by folding down or hiding the origami-applied interconnects under the islands. This 3D printing strategy of potentially low cost, large size capabilities, and high speed is promising for highly flexible future energy conversion applications.

GIS-Supported Airfield Selection near Zhongshan Station, East Antarctica, based on Multi-Mission Remote Sensing Data

As Antarctica attracts increasing attention in global climate change studies, the demand for field expeditions has increased in recent decades. Aircraft has become the most efficient mode of transportation because of the advantages of short travel times over long distances, access to unreachable locations and capability to carry different types of sensors to obtain large areal coverages. However, few studies have been published regarding Antarctic airfield site selection for heavy-wheeled aircraft. In this paper, we present methods and results of blue-ice airfield preliminary selection near Zhongshan station, East Antarctica. The geographic information system (GIS)-based method is supported by multi-mission high-resolution images from the ZY-3, WorldView-2 and Landsat-8 satellites along with existing remote sensing products. Ground truth observations were integrated with satellite panchromatic and spectral information to identify runway candidate areas. The information inferred by remote sensing data, including firn type, ice movement, surface slope and ice fracture, is used for evaluation of the airfield selection rules. Finally, the rankings and recommendations of runway candidates were performed in a GIS analysis environment. The site selection approach developed in this paper can be applied in preconstruction studies of other similar cryosphere environments to provide appropriate candidates for a final stage field investigation.

Interfacial Junctions Control Electrolyte Transport through Charge-Patterned Membranes.

Distinct transport mechanisms emerge when nanostructured substrates are patterned with multiple chemistries. For example, charge-patterned mosaic membranes possess surfaces functionalized with discrete domains of both positive and negative charge. These oppositely charged domains provide pathways for both the cation and anion from a dissolved salt to permeate through the membrane without violating the macroscopic constraint of electroneutrality. Here, by systematically varying the geometry and size of the charge pattern, we elucidate the molecular interactions that promote the transport of salts under the action of pressure-driven flow. For patterns that consist of equivalent areal coverages of positively charged and negatively charged domains, the effects of the geometric parameters were encapsulated in a single variable, the interfacial packing density, that quantified the fraction of the membrane surface covered by junctions between oppositely charged domains. Experimentally, the transport of symmetric electrolytes (i.e., KCl and MgSO4) increased with the value of the interfacial packing density, while the interfacial packing density did not significantly affect the transport of asymmetric electrolytes (i.e., K2SO4 and MgCl2). Simulations of the electrical potential near the membrane surface demonstrate that for symmetric electrolytes the structural charge heterogeneity reduces the barrier to ion partitioning, thereby promoting salt transport through the membranes. For asymmetric electrolytes, the charge heterogeneity skews the local availability of ions from the stoichiometric ratio of the salt, thus hindering salt transport. These findings demonstrate the promise of accessing transport mechanisms, which could find utility in a diverse range of chemical separations and sensing applications, through chemical patterning of membranes.

Using Radar-Derived Parameters to Develop Probabilistic Guidance for Lightning Cessation within Isolated Convection near Cape Canaveral, Florida

Abstract Thunderstorms in central Florida frequently halt outdoor activities, requiring that one wait some prescribed time after an assumed last flash before safely resuming activities. The goal of this research is to develop a high-skill probabilistic method that can be used in high pressure real-world operations to terminate lightning warnings more quickly while maintaining safety. Probabilistic guidance tools are created for isolated warm season storms in central Florida using dual-polarized radar data at 1-min intervals. The parameters examined are maximum reflectivity and graupel presence at the 0°, −5°, −10°, −15°, and −20°C levels as well as composite reflectivity. Random samples of the radar data are used to train a generalized linear model (GLM) to make a probabilistic prediction whether a given flash is the storm’s last flash. The most statistically significant predictors for lightning cessation are found to be the storm’s maximum reflectivity in the composite and the 0°C levels, along with graupel presence or absence at the −5°, −10°, −15°, and −20°C levels. Statistical verification is used to analyze the performance of the two GLMs at different probability thresholds (95.0%, 97.5%, and 99.0%). When applying the cessation guidance as though storms are occurring in real time, results showed ~99% of the storms produced no additional lightning after the GLM suggested cessation had already occurred. Although these results are encouraging, the procedure must be tested on much larger datasets having different convective modes and different areal coverages to prove its value compared to operational forecasters.

Lagrangian simulation of ice particles and resulting dehydration in the polar winter stratosphere.

Polar stratospheric clouds (PSCs) and cold stratospheric aerosols drive heterogeneous chemistry and play a major role in polar ozone depletion. The Chemical Lagrangian Model of the Stratosphere (CLaMS) simulates the nucleation, growth, sedimentation, and evaporation of PSC particles along individual trajectories. Particles consisting of nitric acid trihydrate (NAT), which contain a substantial fraction of the stratospheric nitric acid (HNO3), were the focus of previous modeling work and are known for their potential to denitrify the polar stratosphere. Here, we carried this idea forward and introduced the formation of ice PSCs and related dehydration into the sedimentation module of CLaMS. Both processes change the simulated chemical composition of the lower stratosphere. Due to the Lagrangian transport scheme, NAT and ice particles move freely in three-dimensional space. Heterogeneous NAT and ice nucleation on foreign nuclei as well as homogeneous ice nucleation and NAT nucleation on preexisting ice particles are now implemented into CLaMS and cover major PSC formation pathways.We show results from the Arctic winter 2009/2010 and from the Antarctic winter 2011 to demonstrate the performance of the model over two entire PSC seasons. For both hemispheres, we present CLaMS results in comparison to measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the Microwave Limb Sounder (MLS). Observations and simulations are presented on season-long and vortex-wide scales as well as for single PSC events. The simulations reproduce well both the timing and the extent of PSC occurrence inside the entire vortex. Divided into specific PSC classes, CLaMS results show predominantly good agreement with CALIOP and MIPAS observations, even for specific days and single satellite orbits. CLaMS and CALIOP agree that NAT mixtures are the first type of PSC to be present in both winters. NAT PSC areal coverages over the entire season agree satisfactorily. However, cloud-free areas, next to or surrounded by PSCs in the CALIOP data, are often populated with NAT particles in the CLaMS simulations. Looking at the temporal and vortex-averaged evolution of HNO3, CLaMS shows an uptake of HNO3 from the gas into the particle phase which is too large and happens too early in the simulation of the Arctic winter. In turn, the permanent redistribution of HNO3 is smaller in the simulations than in the observations. The Antarctic model run shows too little denitrification at lower altitudes towards the end of the winter compared to the observations. The occurrence of synoptic-scale ice PSCs agrees satisfactorily between observations and simulations for both hemispheres and the simulated vertical redistribution of water vapor (H2O) is in very good agreement with MLS observations. In summary, a conclusive agreement between CLaMS simulations and a variety of independent measurements is presented.

Kirigami-inspired, highly stretchable micro-supercapacitor patches fabricated by laser conversion and cutting

The recent developments in material sciences and rational structural designs have advanced the field of compliant and deformable electronics systems. However, many of these systems are limited in either overall stretchability or areal coverage of functional components. Here, we design a construct inspired by Kirigami for highly deformable micro-supercapacitor patches with high areal coverages of electrode and electrolyte materials. These patches can be fabricated in simple and efficient steps by laser-assisted graphitic conversion and cutting. Because the Kirigami cuts significantly increase structural compliance, segments in the patches can buckle, rotate, bend and twist to accommodate large overall deformations with only a small strain (<3%) in active electrode areas. Electrochemical testing results have proved that electrical and electrochemical performances are preserved under large deformation, with less than 2% change in capacitance when the patch is elongated to 382.5% of its initial length. The high design flexibility can enable various types of electrical connections among an array of supercapacitors residing in one patch, by using different Kirigami designs.

Flexible Semiconductor Technologies with Nanoholes-Provided High Areal Coverages and Their Application in Plasmonic-Enhanced Thin Film Photovoltaics

Mechanical flexibility and advanced light management have gained great attentions in designing high performance, flexible thin film photovoltaics for the realization of building-integrated optoelectronic devices and portable energy sources. This study develops a soft thermal nanoimprint process for fabricating nanostructure decorated substrates integrated with amorphous silicon solar cells. Amorphous silicon (a-Si:H) solar cells have been constructed on nanoholes array textured polyimide (PI) substrates. It has been demonstrated that the nanostructures not only are beneficial to the mechanical flexibility improvement but also contribute to sunlight harvesting enhancement. The a-Si:H solar cells constructed on such nanopatterned substrates possess broadband-enhanced light absorption, high quantum efficiency and desirable power conversion efficiency (PCE) and still experience minimal PCE loss even bending around 180°. The PCE performance without antireflection coatings increases to 7.70% and it improves 40% compared with the planar devices. Although the advantages and feasibility of the schemes are demonstrated only in the application of a-Si:H solar cells, the ideas are able to extend to applications of other thin film photovoltaics and semiconductor devices.

Drought Occurrences and Their Characteristics across Selected Spatial Scales in the Contiguous United States

An understanding of drought occurrences and their characteristics such as intensity, duration, frequency, and areal coverage, and their variations on different spatial scales, is crucial to plan for droughts in different regions and in different sized areas. This study investigated the variations of spatio-temporal characteristics of droughts under selected spatial scales: National (Contiguous U.S.), regional (High Plains), state (North Dakota, ND), climatic division (South Central, ND), and county (Grant, ND). Weekly drought area coverage data for the period spanning the years 2000–2014 from the U.S. Drought Monitor of the National Drought Mitigation Center were used. The study captured the areal coverages and occurrence frequency of droughts with different intensity levels for the years 2000 to 2014 for the contiguous U.S. Year to year variability in spatial distribution of the areal coverages of droughts with different intensity levels were also analysed. The study further investigated how the weekly percentage area under different intensity categories varied along time, and extracted the spatio-temporal characteristics of different drought intensity categories at different spatial scales. The study identified areas that are frequently affected by droughts of different intensity categories in the U.S. at the national scale, and reported the spatial scale dependence of drought characteristics.

Theoretical and experimental study of 2D conformability of stretchable electronics laminated onto skin

Smoothly attaching the stretchable epidermal electronic devices (EEDs) onto the skin surface is highly desired to improve the measurement accuracy of electrophysiological signal. The paper presents an analytical approach to study interfacial mechanics of the 2D planar EEDs on the checkerboard buckling patterns of human skin. Energy variation method is proposed to determine a criterion whether EEDs laminate conformally onto the skin surface under undeformed and stretched cases. EEDs with low bending stiffness (thin, soft devices/backing layer), smooth and soft skin, and strong adhesion promote conformal contact. Furthermore, the adhesion energy at the EED/skin interface is measured by the homemade peeling experiment platform with different substrate thicknesses and areal coverages. The upper limit of the areal coverage for EED conformal contact with the skin is proposed with given EED/skin properties. Conformability of EEDs are validated by experiments with different substrate thickness, areal coverage and external loadings. It provides a design guideline for EED to conformally contact with the skin surface for more accurate biological signal monitoring.

Influence of Crassostrea gigas on the permeability and microstructure of the surface layer of concrete exposed to the tidal zone of the Yellow Sea

Concrete exposed to the tidal zone of the Yellow Sea and bearing Crassostrea gigas (CG) with differing areal coverages was investigated for evidence of biologically induced corrosion prevention. The experimental results indicated that both the chloride ion profile and the neutralization depth of the concrete decreased with increasing CG coverage. Moreover, the water absorption rate and the chloride ion permeability of concrete with the original surface intact also declined with increasing degrees of CG coverage. However, the water absorption rates of three concrete samples with 2 mm of the surface layer removed were similar, as was their chloride ion permeability. Mercury intrusion porosimetry tests indicated that CG significantly reduced the pore structure of the concrete surface layer. SEM observation revealed that the CG cementation membrane and left valve were tightly glued to the concrete surface and had a dense structure. Concrete durability indices showed that high CG coverage greatly improved concrete durability.

A hierarchical computational model for stretchable interconnects with fractal-inspired designs

Stretchable electronics that require functional components with high areal coverages, antennas with small sizes and/or electrodes with invisibility under magnetic resonance imaging can benefit from the use of electrical wiring constructs that adopt fractal inspired layouts. Due to the complex and diverse microstructures inherent in high order interconnects/electrodes/antennas with such designs, traditional non-linear postbuckling analyses based on conventional finite element analyses (FEA) can be cumbersome and time-consuming. Here, we introduce a hierarchical computational model (HCM) based on the mechanism of ordered unraveling for postbuckling analysis of fractal inspired interconnects, in designs previously referred to as ‘self-similar’, under stretching. The model reduces the computational efforts of traditional approaches by many orders of magnitude, but with accurate predictions, as validated by experiments and FEA. As the fractal order increases from 1 to 4, the elastic stretchability can be enhanced by ~200 times, clearly illustrating the advantage of simple concepts in fractal design. These results, and the model in general, can be exploited in the development of optimal designs in wide ranging classes of stretchable electronics systems.

Relating land use patterns to stream nutrient levels in red soil agricultural catchments in subtropical central China.

Land use has obvious influence on surface water quality; thus, it is important to understand the effects of land use patterns on surface water quality. This study explored the relationships between land use patterns and stream nutrient levels, including ammonium-N (NH4 (+)-N), nitrate-N (NO3 (-)-N), total N (TN), dissolved P (DP), and total P (TP) concentrations, in one forest and 12 agricultural catchments in subtropical central China. The results indicated that the TN concentrations ranged between 0.90 and 6.50 mg L(-1) and the TP concentrations ranged between 0.08 and 0.53 mg L(-1), showing that moderate nutrient pollution occurred in the catchments. The proportional areal coverages of forests, paddy fields, tea fields, residential areas, and water had distinct effects on stream nutrient levels. Except for the forest, all studied land use types had a potential to increase stream nutrient levels in the catchments. The land use pattern indices at the landscape level were significantly correlated to N nutrients but rarely correlated to P nutrients in stream water, whereas the influence of the land use pattern indices at the class level on stream water quality differentiated among the land use types and nutrient species. Multiple regression analysis suggested that land use pattern indices at the class level, including patch density (PD), largest patch index (LPI), mean shape index (SHMN), and mean Euclidian nearest neighbor distance (ENNMN), played an intrinsic role in influencing stream nutrient quality, and these four indices explained 35.08 % of the variability of stream nutrient levels in the catchments (p<0.001). Therefore, this research provides useful ideas and insights for land use planners and managers interested in controlling stream nutrient pollution in subtropical central China.

Modeling the Performance of an Integrated Photoelectrolysis System with 10 × Solar Concentrators

Two designs for an integrated photoelectrolysis system that uses a 10× concentrating solar collector have been investigated in detail. The system performance was evaluated using a multi-physics model that accounted for the properties of the tandem photoabsorbers, mass transport, and the electrocatalytic performance of the oxygen-evolution and hydrogen-evolution reactions (OER and HER, respectively). The solar-to-hydrogen (STH) conversion efficiencies and the ohmic losses associated with proton transport in the solution electrolyte and through the membrane of the photoelectrolysis system were evaluated systematically as a function of the cell dimensions, the operating temperatures, the bandgap combinations of the tandem cell, and the performance of both the photoabsorbers and electrocatalysts. Relative to designs of optimized systems that would operate without a solar concentrator, the optimized 10× solar concentrator designs possessed larger ohmic losses and exhibited less uniformity in the distribution of the current density along the width of the photoelectrode. To minimize resistive losses while maximizing the solar-to-hydrogen conversion efficiency, ηSTH, both of the designs, a two-dimensional “trough” design and a three-dimensional “bubble wrap” design, required that the electrode width or diameter, respectively, was no larger than a few millimeters. As the size of the electrodes increased beyond this limiting dimension, the ηSTH became more sensitive to the performance of the photoabsorbers and catalysts. At a fixed electrode dimension, increases in the operating temperature reduced the efficiency of cells with smaller electrodes, due to degradation in the performance of the photoabsorber with increasing temperature. In contrast, cells with larger electrode dimensions showed increases in efficiency as the temperature increased, due to increases in the rates of electrocatalysis and due to enhanced mass transport. The simulations indicted that cells that contained 10% photoabsorber area, and minimal amounts of Nafion or other permselective membranes (i.e. areal coverages and volumetric fractions of only a few percent of the cell), with the remaining area comprised of a suitable, low-cost inert, non porous material (flexible polymers, inert inorganic materials, etc.) should be able to produce high values of ηSTH, with ηSTH = 29.8% for an optimized design with a bandgap combination of 1.6 eV/0.9 eV in a tandem photoabsorber system at 350 K.