[en] A large amount of carbon dioxide emissions have drawn more and more attention recently. Existing regional research is mainly based on the classification of geographical location, without considering the differences in urbanization. Using panel data of 30 provinces in China during the period of 1997–2014, this paper investigates the impact of population, per capita GDP, energy intensity, urbanization, industry proportion and tertiary industry proportion on CO₂ emissions. Taking into account regional differences, 30 provinces in China are divided into four regions according to the features of “urbanization–CO₂ emissions.” The results show that the impacts of population and per capita GDP on CO₂ emissions in the LU–LC region are higher than the other three regions. The energy intensity has positive effect on CO₂ emissions in the four regions. The impact of energy intensity on CO₂ emissions in HU–HC and HU–LC regions is greater than the other two regions. Meanwhile, the impact of urbanization on CO₂ emissions differs across regions. The urbanization has a significant negative effect on CO₂ emissions in the HU–LC region, indicating the urbanization increases CO₂ emissions. However, the urbanization has a positive effect on CO₂ emissions in the LU–HC region, indicating the urbanization increases CO₂ emissions in the region. The impact of industry proportion is not statistically significant in all the regions, while the impact of tertiary industry proportion on CO₂ emissions is negatively significant in the HU–LC and LU–HC regions, which indicates that the adjustment and upgrading of industrial structure play important roles in the decrease in carbon emissions.

[en] Highlights: • Analysis of purge strategy optimization with anode recirculation is presented. • Optimal purge duration is defined as purge stops when voltage starts falling. • Optimal purge duration and energy efficiency are predicted by modelling. • Energy efficiency increases with reducing purge interval in the simulated range. • 3% bleed rate is optimal for energy efficiency for the simulated conditions. Anode recirculation increases hydrogen utilization but also causes nitrogen crossover and accumulation in proton exchange membrane fuel cell (PEMFC) anode. Purge is necessary to remove the impurity. Voltage-based and nitrogen-based are the two basic purge strategies. For voltage-based purge, purge interval is defined by the voltage drop rate of the voltage peak. The voltage recovers first and then drops in the excess purge duration, so the optimal purge duration is defined as the purge stops when the voltage starts falling. The optimal purge duration is mainly determined by scavenging velocity, and it decreases with increasing scavenging velocity. Energy efficiency and fuel loss rate both increase with decreasing purge interval for the simulated operating conditions. Scavenging velocity significantly affects the fuel loss rate but has little effect on energy efficiency under the optimal purge duration. For nitrogen-based purge, the effect of purge duration on energy efficiency is much less significant than purge interval. Due to the difficulty of the real-time nitrogen fraction measurement, the voltage-based purge is more recommended. An optimal bleed rate for energy efficiency exists and 3% bleed rate is the optimal for the simulated operating conditions.

[en] Highlights: • A quasi-2D transient model of PEMFC with anode recirculation is developed. • Anode recirculation leads to certain level of self-humidification. • Nitrogen accumulation causes performance decrease especially at anode downstream. • Current distribution non-uniformity of co-flow is improved by anode recirculation. • Anode recirculation avoids the severe fuel starvation compared to dead-ended anode. - Abstract: Anode recirculation of proton exchange membrane fuel cell (PEMFC) is considered as an effective way for self-humidification and efficient hydrogen utilization, but nitrogen crossover presents a problem. To investigate the transient characteristics of PEMFC with anode recirculation, a comprehensive quasi-2D non-isothermal transient model is developed. The simulation results show that for a PEMFC initially operated with dry hydrogen, anode recirculation leads to certain level of performance increase in the beginning due to self-humidification effect, and then the performance decreases caused by nitrogen crossover, hydrogen dilution and the increase of anode activation loss. The nitrogen accumulation in anode downstream is severer than upstream, and the performance decline rate decreases with increasing cathode inlet velocity under the simulated operating conditions. The performance and current density distribution uniformity of counter-flow configuration is better than co-flow under low inlet humidity, but the difference becomes smaller with anode recirculation. Anode recirculation and dead-ended anode (DEA) operation both have self-humidification effect, and compared to DEA, the advantages of anode recirculation can be summarized as lower performance decline rate, less chance of local hydrogen starvation and better current density distribution uniformity.

[en] This paper focuses on the lifetime characteristics of pulse capacitors applied in millisecond pulse discharge through the establishment of the repetition-frequency lifetime test platform. The pulsed power charger adopts the mode of constant current charging and the output power is 30 kW with the voltage range between 0 kV and 12 kV. The switch of the pulse discharge circuit is a thyristor whose repetition frequency is up to 100 Hz. The discharge waveform can be adjusted by load resistance and load inductance. The effect of the charging time, hold time, intervals and repetition frequency on the lifetime characteristic of pulse capacitors can be sufficiently studied. Meanwhile, failure mechanisms of pulse capacitors in specific working conditions can be investigated. (authors)

[en] A dynamic hysteretic sensing model has been developed to predict the dynamic responses of the magnetic induction, the stress, and the output voltage for a bending-mode Galfenol unimorph transducer subjected simultaneously to acceleration and bias magnetic field. This model is obtained by coupling the hysteretic Armstrong model and the structural dynamic model of the Galfenol unimorph beam. The structural dynamic model of the beam is founded based on the Euler-Bernouli beam theory, the nonlinear constitutive equations, and the Faraday law of electromagnetic induction. Comparisons between the calculated and measured results show the model can describe dynamic nonlinear voltage characteristics of the device, and can predict hysteretic behaviors between the magnetic induction and the stress. Moreover, the model can effectively analyze the effects of the bias magnetic field, the acceleration amplitude, and frequency on the root mean square voltage of the device

[en] We analyze the role of nuclear modifications of parton distributions, notably, the nuclear shadowing and antishadowing corrections, in the production of lepton pairs from decays of neutral Z and γ* gauge bosons in proton-lead and lead-lead collisions at the LHC. Using the Collins-Soper-Sterman resummation formalism that we extended to the case of nuclear parton distributions, we observed a direct correlation between the predicted behavior of the transverse momentum and rapidity distributions of the produced vector bosons and the pattern of quark and gluon nuclear modifications. This makes the production of Z/γ* in pA and AA collisions at the LHC a useful tool for constraining nuclear PDFs in the small-x shadowing and moderate-x antishadowing regions. (orig.)

[en] Design and synthesis of integrated, interconnected porous structures are critical to the development of high-performance supercapacitors. We develop a novel and facile synthesis technic to construct three-dimensional carbon-bubble foams with hierarchical pores geometry. The carbon-bubble foams are fabricated by conformally coating, via catalytic decomposition of ethanol, a layer of carbon coating onto the surfaces of pre-formed ZnO foams and then the removal of the ZnO template by a reduction-evaporation process. Both the wall thickness and the pore size can be well tuned by adjusting the catalytic decomposition time and temperature. The as-synthesized carbon-bubble foams electrode retains 90.3% of the initial capacitance even after 70 000 continuous cycles under a high current density of 20 A g⁻¹, demonstrating excellent long-time electrochemical and cycling stability. The symmetric device displays rate capability retention of 81.8% with the current density increasing from 0.4 to 20 A g⁻¹. These achieved electrochemical performances originate from the unique structural design of the carbon-bubble foams, which provide not only abundant transport channels for electron and ion but also high active surface area accessible by the electrolyte ions. (paper)

[en] Highlights: • HGNs were prepared by dual-electrochemical and microwave-assisted expansion of graphite. • The methods can realize cost-effective production of high-quality HGNS. • The obtained HGNS with ultralow defects and higher electrical conductivity. Holey graphene nanosheets (HGNS) contain nanoholes on the surface of graphene sheets and these nanoholes can provide the rich mass transfer channel for the electrons and the ions, thus induce more hole edge defects, controllable band gap and better mechanical stability. Here, HGNS were massive production by dual-electrochemical intercalation and microwave-assisted expansion of graphite. The final obtained HGNS contain few layer graphene (5–10 layers), with ultralow defects (I_D/I_G < 0.07) and higher electrical conductivity (691S/cm). The holey anodic graphene nanosheets demonstrate a narrow peak of pore size distribution centering at around 1.13 nm, 3 nm and a broad range from 3 nm to 252 nm centered at 68 nm, which denoting the characters of micropore, mesoporous and macropore structure. The holey cathodic graphene nanosheets with the feature of mesoporous and macropore structure in which the pore size in the range of 2 nm-252 nm centered at 3.18 nm, 68 nm.

[en] Highlights: • Modeling of operating condition effect on anode recirculation PEMFC is presented. • An appropriate low cathode humidity is proposed for low nitrogen crossover rate. • High anode stoichiometry can improve fuel distribution and mitigate voltage decline. • Increasing anode and cathode inlet pressure by similar amount is recommended. -- Abstract: We investigate different operating conditions effects, including cathode relative humidity, anode stoichiometry and inlet pressure, on PEMFC with anode recirculation by conducting dynamic simulations. The performance improvement caused by the self-humidification effect is about 6.5% with dry cathode inlet, and it is very slight with fully humidified cathode inlet. Nitrogen fraction in the anode is low in the first 20 min under a low cathode relative humidity. A 0.3–0.6 cathode relative humidity might be suitable for the simulated cases. Generally, the fuel cell benefits from increasing anode stoichiometry by enhancing the self-humidification effect, decreasing the performance decline rate and ameliorating hydrogen distribution along the channel. Increasing anode inlet pressure and cathode inlet pressure play the mitigated and exacerbated role on voltage decline, respectively. However, increasing cathode inlet pressure can significantly improve output performance especially under a low cathode relative humidity. We suggest an appropriate low cathode relative humidity, increasing anode stoichiometry, and increasing anode and cathode inlet pressure by similar amount for PEMFC with anode recirculation.

[en] Highlights: • 60 MN horizontal extruder and Φ360 mm circular container are used to manufacture 316 L N L-shape stainless steel. • Location holes and dowel pins are used to fix die and cushion, keyway and flat key are used to fix cushion and bolster. • The properties of products at room temperature of 300 K and low temperature of 4.2 K all satisfy the requirements of SCC box. • SCC box case is manufactured by bending, machining and welding processes, which passes X-ray, UT and PT tests. - Abstract: 316 L N L-shape stainless steel is used in ITER Side Correction Coil (SCC) box. Finite Element Method (FEM) simulation is adopted to analyze metal flow characteristics, forecast extrusion force and ascertain extruder tonnage of 316 L N L-shape stainless steel during extrusion process. Based on simulation results, 316 L N round forged billet is used to manufacture L-shape stainless steel by extrusion process. The extrusion process includes circular furnace preheating, induction heating, glass lubrication, mould design and deformation design. 316 L N L-shape stainless steel is manufactured by Φ360 mm circular container and 60 MN horizontal extruder successfully. Mechanical properties and microstructure of 316 L N L-shape stainless steel all accord with the requirements of ITER SCC box. SCC box case is manufactured by bending, machining and welding processes. X-ray, ultrasonic testing (UT) and penetration testing (PT) are used to inspect the welding quality of SCC box case. The SCC box case passes the acceptance of ITER project expert group, this result verifies that the extrusion process and manufacture process are reasonable and feasible.