Traffic congestion is one of the key issues relating to sustainability and livability in many large cities. In particular, the situation in the growing megacities of developing countries has been ...worsening and is now attracting considerable attention from researchers and politicians. An understanding of the spatio-temporal patterns of this congestion is necessary in order to formulate effective policies to relieve it. Much of the research to date has focused on single districts for relatively short periods (days or weeks) using GPS, while long-term analysis of spatial and temporal patterns of traffic congestion at the city level has been rare. The aim of this paper is to help fill this gap in the literature by applying a big data analytic approach to a sample of 10.16 million records of traffic congestion indexes for 233 roads in the Beijing area over a six-month period. This analysis revealed four typical traffic congestion patterns in Beijing, which can be described as the weekend mode, holiday mode, weekday mode A, and weekday mode B. Each of these patterns possesses unique spatial and temporal characteristics. Compared with working days, on which congestion is regular and agglomerated, weekends and holidays are characterized by long-lasting congestion peaks throughout the day. Non-commuting travel on weekends and holidays, including trips for tourism, shopping, entertainment, and children's after-school activities, are major contributors to traffic congestion of the weekend and holiday mode. Owing to poor jobs-housing balance, the suburban new towns and job centres had relatively higher congestion than other areas. These findings shed significant light on geographical patterns of traffic congestion in growing megacities.
•Traffic congestion is a key issue relating to urban sustainability.•This paper apples a big data analytic approach to a sample of 10.16 million records of traffic congestion.•There are four typical traffic congestion patterns in Beijing.•No-commuting travels on weekends and holidays are major contributors to traffic congestion.•The suburban new towns and job centres had relatively higher congestion.
Abstract
In this article, we prove that the Swan conductor of an étale sheaf on a smooth variety defined by Abbes and Saito’s logarithmic ramification theory can be computed by its classical Swan ...conductors after restricting it to curves. It extends the main result of Barrientos 7 for rank $1$ sheaves. As an application, we give a logarithmic ramification version of generalizations of Deligne and Laumon’s lower semi-continuity property for Swan conductors of étale sheaves on relative curves to higher relative dimensions in a geometric situation.
In this study, the effect of different modeling hypotheses for the plastic deformation of lath martensite was investigated through an integrated experimental–numerical approach. The local plastic ...strain distribution of a dual-phase steel with a coarse microstructure was quantified by high-resolution digital image correlation analysis. The same area was reproduced in a crystal plasticity finite element model using the electron backscatter diffraction measurement of the specimen surface prior deformation. Different modeling hypotheses in terms of in-lath and out-of-lath slip strength as well as boundary and bulk elements were explored. It was found that early plastic deformation in lath martensite grains predominantly took place at various interfaces in the form of slip bands parallel to the in-lath slip planes in blocks exhibiting high in-lath Schmid factor. A comparison between experiment and simulations suggested that assuming a lower strength and hardening rate for in-lath slip systems of boundary elements better reproduced the plastic strain fields in martensite grains. However, the different models showed limited effect on the strain distribution within ferrite grains and on the local stress–strain path at void nucleation sites. This suggested that the main factor affecting early strain concentration and subsequent damage initiation in ferrite grains was the phase morphology and strength contrast.
Statistical analysis of slip system identification and quantitative study on local plasticity is crucial to understand the collective deformation by the sub-grain-scale slip activities in ...polycrystalline metallic materials. In this study, an automated framework for identifying slip system and assessing strain localization of slip bands termed ASSISL (automated Slip System Identification and Strain Localization analysis of slip bands) is introduced, using the results from high resolution digital image correlation (HR-DIC), and is demonstrated on 1591 primary α grains of a bimodal Ti-6Al-4V alloy under tensile loading. The framework includes: (1) alignment of electron backscattered diffraction (EBSD) maps with strain field maps from HR-DIC through treatment of EBSD distortion, (2) slip band orientations identification from strain field map of each grain through a Radon-transform-based algorithm, (3) slip system assignment with combined Schmid factor and critical resolved shear stress analysis, (4) quantification of plasticity by slip activities which provides information on the numbers, positions and mean strain of slip bands in each grain. The confidence of ASSISL is validated through comparing current statistical results with existing literature, as well as examining reasons for grains assigned with wrong slip systems, which accounts for 9.6 percent (153 out of 1591) of the primary α grains. A comparison between ASSISL and other HR-DIC-based slip identification methods is also conducted. This framework provides a method for analyzing slip activities in a large number of grains of polycrystalline metals in a time-saving and automated fashion.
•An automated slip analysis framework termed ASSISL using strain field maps from HR-DIC is developed.•Statistical analysis obtained from ASSISL is demonstrated on 1591 primary α grains of a Ti-6Al-4V alloy.•Comparisons among ASSISL and other HR-DIC-based slip system identification methods are presented.•ASSISL could be applied to other metals for automated slip trace and strain localization analysis.
Rechargeable aluminum-ion batteries (RAIBs) are regarded as the next generation of low-cost and high-capacity electrical energy storage systems. Compared to graphene-based cathodes, metal ...dichalcogenide cathodes can potentially provide RAIBs with higher capacities. However, metal dichalcogenides suffer from poor cycling performance, hindering the further development of high-capacity RAIBs. Thus, to further improve the performance of RAIBs, it is imperative to gain a deep understanding of the mechanisms behind the energy-storage and capacity-deterioration characteristics of these materials. In this work, we conducted detailed characterization to acquire a deep understanding of the energy storage mechanism of a CoSe2-based cathode. The characterization results revealed that energy storage involved incorporation of Al3+ into CoSe2 to generate AlmConSe2 (i.e., partial substitution of Co2+ by Al3+) and elemental Co, while capacity deterioration resulted from the dissolution of active cobalt species into the electrolyte and the pulverization of the CoSe2 phase. The understanding of the capacity-deterioration mechanism allowed us to design a two-step concept for a new type of RAIB composite cathode material. Thus, we employed a conductive wrapping layer of reduced graphene oxide (rGO) to protect CoSe2/carbon nanodice composites from cobalt dissolution and CoSe2 pulverization while also improving the conductivity of the materials. This novel design resulted in a CoSe2/carbon nanodice@rGO composite material with an outstanding cycling performance (after 500 cycles) of 143 mA h g−1 at 1000 mA g−1, which is one of the best performances for a metal-based RAIB cathode material reported to date. These findings are of great significance for the further development of high-capacity RAIBs.
As an emerging post‐lithium battery technology, aluminum ion batteries (AIBs) have the advantages of large Al reserves and high safety, and have great potential to be applied to power grid energy ...storage. But current graphite cathode materials are limited in charge storage capacity due to the formation of stage‐4 graphite‐intercalated compounds (GICs) in the fully charged state. Herein, we propose a new type of cathode materials for AIBs, namely polycyclic aromatic hydrocarbons (PAHs), which resemble graphite in terms of the large conjugated π bond, but do not form GICs in the charge process. Quantum chemistry calculations show that PAHs can bind AlCl4− through the interaction between the conjugated π bond in the PAHs and AlCl4−, forming on‐plane interactions. The theoretical specific capacity of PAHs is negatively correlated with the number of benzene rings in the PAHs. Then, under the guidance of theoretical calculations, anthracene, a three‐ring PAH, was evaluated as a cathode material for AIBs. Electrochemical measurements show that anthracene has a high specific capacity of 157 mAh g−1 (at 100 mA g−1) and still maintains a specific capacity of 130 mAh g−1 after 800 cycles. This work provides a feasible “theory guides practice” research model for the development of energy storage materials, and also provides a new class of promising cathode materials for AIBs.
Polycyclic aromatic hydrocarbons (PAHs) with a small conjugate system were proposed as potential aluminium ion battery (AIB) cathode materials through quantum chemistry calculations and experimental verification. Electrochemical evaluations demonstrate that PAHs break through the limitation of graphite to form stage‐4 graphite‐intercalated compounds (GICs) at the fully charged state and exhibit outstanding electrochemical performance.
With the challenge to reach targets of carbon emission reduction at the regional level, it is necessary to analyze the regional differences and influencing factors on China’s carbon emission ...efficiency. Based on statistics from 2005 to 2015, carbon emission efficiency and the differences in 30 provinces of China were rated by the Modified Undesirable Epsilon-based measure (EBM) Data Envelopment Analysis (DEA) Model. Additionally, we further analyzed the influencing factors of carbon emission efficiency’s differences in the Tobit model. We found that the overall carbon emission efficiency was relatively low in China. The level of carbon emission efficiency is the highest in the East region, followed by the Central and West regions. As for the influencing factors, industrial structure, external development, and science and technology level had a significant positive relationship with carbon emission efficiency, whereas government intervention and energy intensity demonstrated a negative correlation with carbon emission efficiency. The contributions of this paper include two aspects. First, we used the Modified Undesirable EBM DEA Model, which is more accurate than traditional methods. Secondly, based on the data’s unit root testing and cointegration, the paper verified the influencing factors of carbon emission efficiency by the Tobit model, which avoids the spurious regression. Based on the results, we also provide several policy implications for policymakers to improve carbon emission efficiency in different regions.
Ultrafine grained medium Mn steel exhibits simultaneous high strength and ductility, however, often showing Lüders deformation and discontinuous yielding phenomena. The connections between martensite ...transformation and Lüders deformation as well as the localized failure behavior are quantitatively investigated through high resolution digital image correlation, enabled by nanoscale strain distribution and microstructural alignment. At a low global tensile strain level, strain localization happens in austenite domain resulted from a sequential slip deformation and martensite transformation, which then triggers the yielding of ferrite by generating thin strain channels to connect adjacent hotspots. This microscopic deformation mode promotes the formation of macroscopic deformation bands, resulting in Lüders band initiation and propagation. When increasing the applied load, the externally imposed strain is accommodated by ferrite instead, resulting in pronounced strain partitioning. The triple grains boundary having no further strain hardening capacity is favorable for void initiation and propagation.
There are a few existing studies on whether domestic migration improves China's pension system's fiscal sustainability in the context of rapid urbanization and industrialization. In this paper, we ...systematically investigate the impact of migration on the solvency of the worker's old-age insurance for urban employees by constructing actuarial and econometric models. We use panel data from 2002 to 2018, collected from 31 provinces in China. The results show that the association between migration and the solvency of pensions is an inverted-U shape along the urbanization process. Further regional comparison showed that the above-stated inverted-U curve is more pronounced in the central and western regions. We also established that the number of participants and the contribution base are the main contributors to these results. Our conclusions are important for future population policies and public pension systems in China.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Quantum critical points often arise in metals perched at the border of an antiferromagnetic order. The recent observation of singular and dynamically scaling charge conductivity in an ...antiferromagnetic quantum critical heavy fermion metal implicates beyond-Landau quantum criticality. Here we study the charge and spin dynamics of a Kondo destruction quantum critical point (QCP), as realized in an SU(2)-symmetric Bose-Fermi Kondo model. We find that the critical exponents and scaling functions of the spin and single-particle responses of the QCP in the SU(2) case are essentially the same as those of the large-N limit, showing that 1/N corrections are subleading. Building on this insight, we demonstrate that the charge responses at the Kondo destruction QCP are singular and obey ω/T scaling. This property persists at the Kondo destruction QCP of the SU(2)-symmetric Kondo lattice model.
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