Managed aquifer recharge (MAR) systems can be operated intermittently through wetting-drying cycles to simultaneously improve the water supply and quality. Although MAR can naturally attenuate ...considerable amounts of nitrogen, the dynamic processes and control mechanisms of nitrogen removal by intermittent MAR remain unclear. This study was conducted in laboratory sandy columns and lasted for 23 d, including four wetting periods and three drying periods. The hydraulic conductivity, oxidation reduction potential (ORP), and leaching concentrations of ammonia nitrogen and nitrate nitrogen of MAR systems were intensively measured to test the hypothesis that hydrological and biogeochemical controls play an essential role in regulating nitrogen dynamics at different stages of wetting-drying cycles. Intermittent MAR functioned as a sink for nitrogen while providing a carbon source to support nitrogen transformations; however, it occasionally became a source of nitrogen under intense flushes of preferential flow. Nitrogen dynamics were primarily controlled by hydrological processes in the initial wetting phase and were further regulated by biogeochemical processes during the subsequent wetting period, supporting our hypothesis. We also observed that a saturated zone could mediate nitrogen dynamics by creating anaerobic conditions for denitrification and buffering the flush effect of preferential flow. The drying duration can also affect the occurrence of preferential flow and nitrogen transformations, which should be balanced when determining the optimal drying duration for intermittent MAR systems.
•Intermittent managed aquifer recharge overall functioned as a sink for nitrogen.•Nitrogen dynamics and their controls vary with different stages of recharging.•Saturated zone can create an anerobic condition for denitrification.•Drying duration can mediate control mechanisms and thus nitrogen dynamics.
This paper proposes a fault simulation test method suitable for five divisions of power supply area. Distribution network structures are classified according to different power supply areas and more ...active interference is injected into test cases, which makes fault scenarios more diverse. Besides, to evaluate the whole process of fault isolation and recovery, the index of fault isolation and index of fault restoration are presented separately, and power recovery rate is provided to evaluate the load transfer capability. In the end, two typical test cases are displayed to clarify the whole test procedure and the use of evaluation method.
•Polysaccharides from angelica and astragalus (AAP) were extracted according to Danggui Buxue Decoction.•AAP was at first isolated and purified.•The characterization of AAP-2A was elucidated and the ...structure of AAP-2A was deduced.•The ultramicrostructure of AAP-2A was described.•AAP-2A presented better antioxidant activities when compared with AAP.
In the present study, structural characterization and antioxidant activity of a fraction (AAP-2A) of polysaccharides from angelica and astragalus (AAP) were investigated. Characteriztion assay showed that AAP-2A had molecular weight (Mw), root-mean square (RMS) radius and polydispersity index (Mw/Mn) of 2.252×103kDa, 28.4nm and 1.038, respectively. There were infrared characteristic absorption peaks of polysaccharides in FT-IR spectroscopy. AAP-2A was composed of rhamnose (Rha), galactose (Gal), arabinose (Ara) and glucose (Glc) with a molar ratio of 1:2.13:3.22:6.18 in GC analysis. Methylation analysis combined with NMR spectroscopic analysis demonstrated that a preliminary structure of AAP-2A was proposed as follows: 1,3-linked Rhap, 1,3-linked Galp, 1,3-linked Araf, 1,5-linked Araf, 1,3,5-linked Araf, 1,4-linked Glcp and 1,4,6-linked Glcp interspersed with terminal Glcp. AAP-2A exhibited a surface with a sheet-like appearance in scanning electron microscope and stronger antioxidant capacity compared with AAP.
•Formulated continuous approximation model for optimizing AB-type skip-stop service under heterogeneous demand.•Developed an efficient algorithm that solves the model to near-optimality.•Proposed a ...recipe for fitting the continuous approximation solution to real settings.•AB-type service outperforms all-stop service under various operating conditions.
Transit vehicles operating under skip-stop service visit only a subset of the stops residing along a corridor. It is a strategy commonly used to increase vehicle speeds and reduce patron travel times. The present paper develops a continuous approximation model to optimally design a select form of skip-stop service, termed AB-type service. The model accounts for demand patterns that slowly vary over space. An efficient heuristic is developed to obtain solutions. These are shown to be near-optimal for a variety of numerical examples. Results also indicate that optimal AB-type designs outperform optimized all-stop service in a variety of cases. The AB-type service is found to be especially competitive when travel demands are high, trip origins are unevenly distributed along a corridor, and patrons have relatively high values of time. In these cases, AB-type service is found to reduce system costs by as much as 8%.
•Formulated continuous approximation model for planning the coordinated skip-stop services.•Modeled general coordination plans in which headways have integer common multiples.•The coordination brings ...2–3% additional benefit to skip-stop services.•The common-headway plan works robustly better than others under various scenarios.
This paper develops a continuum approximation model for simultaneously designing and coordinating an AB-type skip-stop service, which had been successfully operated in many places (e.g., Chicago, Philadelphia, and Portland in US and Santiago in Chile). The model accounts for spatially heterogeneous demand patterns in transit corridors. Thanks to the parsimonious property, a solution algorithm is developed using calculus of variations and direct search method. In numerical experiments, a variety of scenarios were examined with respect to 14 operational schemes (i.e., the all-stop scheme, the uncoordinated skip-stop scheme, and the coordinated ones of 12 coordination plans), 2 transit modes (i.e., regular bus and rail), and 3 demand patterns (i.e., uniform, low-varied and high-varied demand). The results indicate: (i) the additional benefit of schedule coordination is 2–3% for uncoordinated skip-stop services, which eventually may add up to 6% cost saving as against the traditional all-stop service; (ii) among all coordination plans, the simplest common-headway plan often works best in all tested scenarios; and (iii) for rail system, the operation of the coordinated skip-stop service is very costly due to the requirement of building an extra track, and positive benefit only emerges in the very busy corridors. Lastly, a case study in Chengdu (China) using real surveyed demand data illustrates the application of our model.
Differing from the conventional fixed-route transit, Demand Responsive Connector (DRC) is scheduled to pick up passengers based on requests, and delivers them to a common destination (e.g., a metro ...station). The demand for DRC is affected by not only the fare and travel time, but also time reliability. The latter' impact is non-negligible because of the uncertainty nature of DRC on collecting the temporally and spatially distributed passengers. This paper explicitly introduces an elastic demand function embedded with a time deviation penalty model. Based on that, one-vehicle and two-vehicle DRC models are formulated to maximize the social welfare. The decision variables include fare, service area, and operating cycle time. Augmented Lagrange Multiplier Method is applied to solve the optimization problem. Simulation is performed to verify the validity of the models. In numerical studies, sensitivity analysis unveils the influences of several key parameters, e.g., potential demand density, vehicle capacity, line-haul distance and elasticity factors. By comparison, threshold values of demand density are revealed for the applicability of the one-vehicle and two-vehicle schemes. The proposed model provides a decision-making tool for DRC operators considering local conditions.
This paper proposes a fault simulation test method suitable for five divisions of power supply area. Distribution network structures are classified according to different power supply areas and more ...active interference is injected into test cases, which makes fault scenarios more diverse. Besides, to evaluate the whole process of fault isolation and recovery, the index of fault isolation and index of fault restoration are presented separately, and power recovery rate is provided to evaluate the load transfer capability. In the end, two typical test cases are displayed to clarify the whole test procedure and the use of evaluation method.
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•Artificially-labeled 15N data aids the nitrogen transformation module verification.•A coupled model quantifies N leaching from multiple sources in bioretention systems.•Submerged ...zone weakens immediate leaching and improves nitrogen removal efficiency.
Bioretention systems are a typical stormwater management technology intended to reduce runoff and non-point source pollution. Multiple sources can contribute to nitrogen (N) leaching from bioretention systems, including the current rainfall-runoff (i.e., immediate leaching), recent rainfall-runoffs (i.e., fast leaching) and long-ago legacy N (i.e., slow leaching), however, there is a lack of methods to quantify these contributions. Here, a process-based Bioretention System (BRS) model for N leaching simulations was verified with artificially-labeled 15N data besides N data to reduce predictive uncertainties. The BRS model was then coupled with an Nitrogen Source Apportionment (NSA) module for N leaching tracking to quantify the contributions from different sources. Results from a bioretention system showed that additional 15N data reduced the predictive uncertainty of total N (TN) concentrations by 23 %. Immediate leaching, fast leaching and slow leaching increased, decreased and remained steady during the leaching process and accounted for 79.54 ± 5.08 %, 2.80 ± 1.74 % and 17.66 ± 4.11 % of N leaching, respectively. The dominant immediate leaching can be significantly weakened by a submerged zone, a shorter antecedent dry period (ADP), a lower rainfall intensity or influent concentration. This study provides a framework to quantify N leaching from multiple sources with implications for long-term N leaching management.
•A general bimodal transit network with intersecting local and express lines is optimized.•The continuum models for transit network design account for realistic route choices.•The intersecting ...network outperforms unimodal networks for moderate to high demand.•Designing two modes separately would undermine the benefits of the bimodal network.
The urban transit system in a real city usually has two major components: a sparse express (e.g. rail) network and a dense local (e.g. bus) network. The two networks intersect and interweave with each other throughout the city to furnish various route options for serving transit patrons with distinct ODs. The optimal design problem of this bimodal transit system, however, has not been well explored in the literature, partly due to the difficulty of modeling the patrons’ complex route choice behavior in the bimodal networks. In light of this, we formulate parsimonious continuum models for minimizing the total cost of the patrons and the transit agency for an intersecting bimodal transit network in a grid city, where the perpendicular local and express lines intersect at transfer stops. Seven distinct route types are identified in this network, which represent realistic intra- and inter-modal route options. A lower-level assignment problem between these routes is embedded in the upper-level network design optimization problem. We develop an efficient method to find near-optimal designs of the intersecting network. Numerical results unveil a number of insightful findings, e.g., that sizable cost savings are observed for the intersecting bimodal design as compared to the single-mode designs for moderate to high demand levels, and that only moderate benefits are observed as compared to the trunk-feeder designs under certain operating conditions. We also show that the conventional practice of designing the local and express networks separately would greatly undermine the benefit of the bimodal system.
Sodium-ion batteries have great potential to become large-scale energy storage devices due to their abundant and low-cost resources. However, the lack of anode and cathode materials with both high ...energy density and long-term cycling performance significantly affects their commercial applications. In this work, uniform CoTe2 nanoparticles are generated from the tellurization of Co nanoparticles, which were coated with polyvinylpyrrolidone in a three-dimensional (3D) porous carbon matrix (CoTe2@3DPNC). Finally, a dual-type carbon confinement structure is formed after tellurization during which citric acid is adopted as the source of the inner carbon scaffold. The hierarchical carbon matrix not only builds a robust and fast ion/electronic conductive 3D architecture but also mitigates the volume expansion and aggregation of CoTe2 during sodium insertion/extraction. Remarkably, the CoTe2@3DPNC electrode displays a high reversible capacity (216.5 mAh g–1/627.9 mAh cm–3 at 0.2 A g–1 after 200 cycles) and outstanding long-term cycling performance (118.1 mAh g–1/342.5 mAh cm–3 even at 5.0 A g–1 after 2500 cycles). Kinetics tests and capacitance calculations clearly reveal a battery-capacitive dual-model Na-storage mechanism. Furthermore, ex situ XRD/SEM/TEM demonstrate superior stability during sodium insertion/extraction. This work provides a valuable strategy for the rational structural design of long-life electrodes for advanced rechargeable batteries.
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