Researchers and practitioners highlight the unreliability of travel as a potential weak link in the transportation system which may inhibit individuals’ accessibility and urban economic activity. ...With the trend towards increasing traffic congestion, the outlook suggests that travel conditions will become structurally less reliable over time, but that not all places will be equally affected. But is travel time unreliability a problem? This study uses global positioning systems travel survey data for Chicago to build a regional model of travel time unreliability. The results suggest that unreliability varies spatially during different time periods, but that the average overall network unreliability varies little across times in the day. Using the Chicago Metropolitan Agency for Planning (CMAP)’s 2007 Travel Tracker Survey, a household travel diary survey including both GPS and non-GPS components, we estimate a mode choice model for work trips to explore the influence of unreliability on travel behavior. The results suggest that unreliable auto travel conditions induce mode switching to transit and that the influence is strongest when service by train is already faster than by car. This further suggests that auto travel unreliability may have the strongest influence in metropolitan regions with highly-competitive transit systems. Nevertheless, the influence of travel unreliability is limited and is not the underlying driver of travel decision-making.
In order to investigate the role of high-speed rail (HSR) investment in aiding the transformation process of urban agglomeration economies, this study focuses on three fundamental questions through ...an observation of more than 100 French cities. First, how has HSR investment impacted the reshaping of accessibility patterns in France? Using rail travel timetables from 1982 to 2009, I adopt gravity models to identify the spatial distribution of accessibility in France. I find that although the introduction of HSR improved the level of mobility and accessibility both between Paris and other cities and among cities in general, this was unequal and depended upon the location of cities relative to the newly built HSR line. Second, does HSR investment induce agglomeration economies? If so, how? I use commune-level panel data to study the economic performance of HSR cities by using a matched-pair analysis and various regression models with instrumental variables. I find that the key determinant for boosting agglomeration economies is the level of HSR train frequencies to/from Paris, rather than travel-time savings. Moreover, panel estimation shows that the evidence for the economic impact of HSR investment is mixed and location specific. However, the impact of HSR on the knowledge-based job market is positive. Finally, what is the effect of the spatial competition of HSR investment on the location choices of French firms? I develop a survey and in-depth interview approaches to conclude that most firms in France do not believe HSR itself can influence location choice or make a significant contribution to company growth. Instead, factors related to land value appear to be the most influential determinant in the distribution and relocation of firms, particularly knowledge-based firms. In conclusion, the evidence suggests that investment in HSR needs to be considered rationally, and factors such as the optimal competitive advantage of HSR and daily HSR train frequencies should be taken into account. In addition, regardless of where an HSR station is located, a well-developed and efficient local transportation service will maximize the benefits of the HSR service itself and expand the market coverage.
In this paper, system description of a photovoltaic powered three-phase Neutral-Point-Clamped (NPC) inverter is firstly analyzed for the sake of establishing simulation. Based on perturbation & ...observation method for maximal power point tracking and proportional-integral control, the simulation is carried out to explore the operational system behaviors. The curves of output variables and their phase trajectories are comparatively depicted. Based on sampled multivariate time series, mutual information and false nearest neighbor methods are introduced to determine the delay time and embedding dimension for reconstructing the phase space, based on which, the largest Lyapunov exponent and fractional dimension are calculated to characterize the chaotic behavior of this photovoltaic powered three-level inverter. The simulation results also show that the system parameter variation has significant impacts on the operational performance of inverter system, which implies that suitable control method is required to eliminate unexpected influences.
Additive manufacturing of structural materials Liu, Guo; Zhang, Xiaofeng; Chen, Xuliang ...
Materials science & engineering. R, Reports : a review journal,
July 2021, 2021-07-00, 20210701, Volume:
145
Journal Article
Peer reviewed
Open access
Additive manufacturing (AM), also known as three-dimensional (3D) printing, has boomed over the last 30 years, and its use has accelerated during the last 5 years. AM is a materials-oriented ...manufacturing technology, and printing resolution versus printing scalability/speed trade-off exists among various types of materials, including polymers, metals, ceramics, glasses, and composite materials. Four-dimensional (4D) printing, together with versatile transformation systems, drives researchers to achieve and utilize high dimensional AM. Multiple perspectives of the AM of structural materials have been raised and illustrated in this review, including multi-material AM (MMa-AM), multi-modulus AM (MMo-AM), multi-scale AM (MSc-AM), multi-system AM (MSy-AM), multi-dimensional AM (MD-AM), and multi-function AM (MF-AM). The rapid and tremendous development of AM materials and methods offers great potential for structural applications, such as in the aerospace field, the biomedical field, electronic devices, nuclear industry, flexible and wearable devices, soft sensors, actuators, and robotics, jewelry and art decorations, land transportation, underwater devices, and porous structures.
Single atom nanozymes are the artificial enzymes with enzyme-like activity, which have attracted a great deal attention in recent years due to their unique merits such as remarkable stability, ...excellent atom utilization and low cost. Herein, a convenient and sensitive colorimetric strategy was developed for the sensing of galactose based on Fe–N–C single-atom nanozyme (Fe-SAzyme). The Fe-SAzyme was prepared through “isolation-pyrolysis” method that exhibited intrinsic peroxidase mimicking activity, which can quickly catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce blue-colored oxTMB in the presence of hydrogen peroxide (H2O2). Galactose can be oxidized by galactose oxidase (Gal Ox) to generate H2O2, and Fe-SAzyme can be utilized for quantitative colorimetric detection of galactose. A good linearity between absorbance and the galactose concentration in the range of 50–500 μM was obtained with a detection limit of (LOD) 10 μM. The Fe-SAzyme based colorimetric strategy offered a rapid, convenient and economic way for galactose quantification detection, which could be used as an alternative method for galactosemia diagnosis.
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•The Fe-SAzyme was synthesized by low-cost precursors and simple procedure.•The Fe-SAzyme displayed high stability and excellent peroxidase-like activity.•A convenient and economic colorimetric detection method for H2O2 and galactose has been successfully established.•This proposed strategy exhibited satisfactory performance for galactose assay in human serum samples.
In order to explore the spatiotemporal evolution of land use function and its driving factors in China, taking both sides of the Hu Line as an example, we used Exploratory Spatial Data Analysis and ...Geographically Weighted Regression methods to reveal dynamic evolution law, spatial characteristics and influencing factors of the "Production-Living-Ecology" functions of 288 prefecture-level cities on both sides of the Hu Line. The results show that: (1) In the temporal dimension, the coordination of "Production-Living-Ecology" functions of land use in China has been improved, and the Hu Line can be roughly used as the boundary of China's territorial space use. (2) In the spatial dimension, there is a significant positive spatial correlation between "Production-Living-Ecology" functions of land use in China, and the coordination gap between "Production-Living-Ecology" functions of land use on both sides of the Hu Line is gradually narrowing. (3) In terms of influencing mechanism, the coordination of "Production-Living-Ecology" functions is mainly driven by internal factors and is supplemented by external ones. The influence pattern of most driving factors is consistent with the layout characteristics of "strong east and weak west" of the Hu Line.
•This study constructs evaluation index system of ecological city.•Urban ecological level in cities of Yellow River Basin are calculated and analyzed.•Obstacle factors are analyzed by the obstacle ...diagnosis model.•The setting of indicators fully reflects the concept of high quality.
Taking the cities along the Yellow River Basin (YRB) as research objects, the entropy-TOPSIS model is used to evaluate urban ecological level; and the main obstacle factors that restrict the improvement of urban ecological level are analyzed through the obstacle diagnosis model. The results show that ecological level of the cities along the YRB has been steadily increasing, and there is a significant correlation with the city size and watershed location, and the gap between cities has declined; the spatial pattern is characterized by “high in head and tail, low in center”. The number of full-time teachers in colleges, the number of college students, living area per capita, and garden space per capita are the main obstacle factors for most cities; the environmental foundation, infrastructure, public services, economic potential, and innovation vitality are the main obstacle factors for the criterion layer. In the future, we should adhere to the concept of basin-based governance, make full use of a series of strategic overlapping effects such as the development of urban agglomerations, the strategy of strengthening the transportation nation, and the construction of ecological civilization, relying on strategies such as green economic transformation, industrial structure upgrade, and ecological corridor construction to build the YRB's ecological economic culture and to create high-quality ecological cities.
3D printing of various polymers has attracted great attention and developed rapidly in recent years. Digital light processing (DLP) has recently emerged as a fast growing 3D printing technique due to ...its high resolution and high speed. However, the lack of printable high-performance materials limits its broad applications. In addition, with the increasing adoption of DLP 3D printing, the efficient recycling of printed thermosetting materials is highly desired. Herein, we proposed a two-stage curing approach involving dynamic reactions by using the acrylate-epoxy hybrid resin for the recyclable DLP 3D printing of high-performance thermosetting polymers. Bond exchange reactions (BERs) could establish covalent bonds between the acrylate network and the epoxy network, thus partially triggering the copolymerization. The resulting new polymers exhibited excellent mechanical properties. A small-molecule assisted BER method was then used to efficiently depolymerize the thermosetting printed parts into soluble oligomers, which were formulated with fresh photopolymers for the next round of printing. The reprinted samples still showed good mechanical properties comparable to the virgin ones. In addition, the new polymers demonstrated potential applications in 4D printing of smart actuators. This work opens a novel avenue for green manufacturing technologies.
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•Digital light processing 3D printing of recyclable thermosetting polymers.•A two-stage curing approach involving dynamic reactions to improve performance.•Recycle printed parts by using small-molecule assisted bond exchange reactions.•Reprinted polymers exhibit comparable mechanical properties to the virgin ones.•4D printing of smart actuators by using the shape memory effect.
Zinc ion capacitors (ZICs) hold great promise in large-scale energy storage by inheriting the superiorities of zinc ion batteries and supercapacitors. However, the mismatch of kinetics and capacity ...between a Zn anode and a capacitive-type cathode is still the Achilles’ heel of this technology. Herein, porous carbons are fabricated by using tetra-alkali metal pyromellitic acid salts as precursors through a carbonization/self-activation procedure for enhancing zinc ion storage. The optimized rubidium-activated porous carbon (RbPC) is verified to hold immense surface area, suitable porosity structure, massive lattice defects, and luxuriant oxygen functional groups. These structural and compositional merits endow RbPC with the promoted zinc ion storage capability and more matchable kinetics and capacity with a Zn anode. Consequently, RbPC-based ZIC delivers a high specific energy of 178.2 W h kg–1 and a peak power density of 72.3 kW kg–1. A systematic ex situ characterization analysis coupled with in situ electrochemical quartz crystal microbalance tests reveal that the preeminent zinc ion storage properties are ascribed to the synergistic effect of the dual-ion adsorption and reversible chemical adsorption of RbPC. This work provides an efficient strategy to the rational design and construction of high-performance electrodes for ZICs and furthers the fundamental understanding of their charge storage mechanisms or extends the understanding toward other electrochemical energy storage devices.
Zinc‐ion capacitors (ZICs) are promising technology for large‐scale energy storage by integrating the attributes of supercapacitors and zinc‐ion batteries. Unfortunately, the insufficient ...Zn2+‐storage active sites of carbonaceous cathode materials and the mismatch of pore sizes with charge carriers lead to unsatisfactory Zn2+ storage capability. Herein, new insights for boosting Zn2+ storage capability of activated nitrogen‐doped hierarchical porous carbon materials (ANHPC‐x) are reported by effectively eliminating the micropore confinement effect and synchronously elevating the utilization of active sites. Therefore, the best‐performed ANHPC‐2 delivers impressive electrochemical properties for ZICs in terms of excellent capacity (199.1 mAh g−1), energy density (155.2 Wh kg−1), and durability (65 000 cycles). Systematic ex situ characterizations together with in situ electrochemical quartz crystal microbalance and Raman spectra measurements reveal that the remarkable electrochemical performance is assigned to the synergism of the Zn2+, H+, and SO42− co‐adsorption mechanism and reversible chemical adsorption. Furthermore, the ANHPC‐2‐based quasi‐solid‐state ZIC demonstrates excellent electrochemical capability with an ultralong lifespan of up to 100 000 cycles. This work not only provides a promising strategy to improve the Zn2+ storage capability of carbonaceous materials but also sheds lights on charge‐storage mechanism and advanced electrode materials’ design for ZICs toward practical applications.
The Zn2+ storage capability of carbonaceous materials is boosted by eliminating the micropore confinement effect and synchronously enhancing the utilization of active sites. Systematic ex situ characterizations coupled with in situ electrochemical quartz crystal microbalance and Raman spectra certify that the excellent Zn2+ storage capability is attributed to the synergistic effect of Zn2+, H+, and SO42– co‐adsorption mechanism and invertible chemical adsorption.
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