Search

In the era of big data, the necessity for in-memory computing has become increasingly pressing, rendering memristors a crucial component in next-generation computing architectures. The self-rectifying memristor (SRM), in particular, has emerged as a promising solution to mitigate the sneak path current issue in crossbar architectures. In this work, a Pt/HfO2/WO3−x/TiN SRM structure is reported with an impressive rectification ratio above 106. To elucidate the underlying mechanisms, we systematically investigate the impact of the WO3−x resistive layer thickness modulation on the device's conductive behavior. Our findings reveal that the abundant traps in the WO3−x resistive layer and the excellent insulating property of HfO2 synergistically suppress negative current while promoting positive current. According to the simulation, the crossbar array based on the proposed SRMs can realize an array scale of over 21 Gbit. Furthermore, artificial synapses fabricated using these SRMs demonstrate a remarkable linearity of 0.9973. In conclusion, our results underscore the great potential of these SRMs for the ultra-large-scale integration of neuromorphic hardware, providing a guide for future ultra-high-energy efficiency hardware with minimal circuit overhead. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) were synthesised utilising a one-pot green synthesis process using phytonutrients obtained from Houttugniae herba (HH) as a reductant and stabiliser. The proposed technique was fast, simple, eco-friendly, and cost-effective, and it does not require any additional processing or toxic ingredients to reduce and stabilise the AgNPs. All parameters (concentration of HH, reaction duration, temperature, and pH) involved in the reduction/stabilisation reaction were evaluated using a one-factor-at-a-time (OFAT) technique in a set of the experimental array to establish an optimal reaction state. Intense yellow colour and a prominent peak at 411 nm in the UV–vis absorption spectra indicated the growth of AgNPs in the reaction system. The produced AgNPs deploying optimum parameters were nearly spherical, with nanometre size (16.28 ± 4.48 nm), highly crystalline (d-spacing = 0.234 and 0.258 nm), and well stabilised (zeta potential = −26.4 mV). The measurement and analysis also yielded that the AgNPs were formed by an oxidation-reduction reaction between plant-derived phytonutrients and metal precursors and subsequently stabilised by the encapsulation of phytonutrients. The biogenic AgNPs exhibited remarkable antibacterial effectiveness against gram-positive and gram-negative bacteria. In addition, the AgNPs demonstrated significant catalytic degradation and mineralisation of industrially essential di-azo dyes with a degradation efficiency of nearly 100% within 20 min. The present investigation shows a simple and environmentally friendly way to synthesise AgNPs, which might be feasible to meet the current need for bacterial reduction and textile wastewater treatment. [ABSTRACT FROM AUTHOR]

The oxygen discharge process significantly affects the electrochemical performance of a proton exchange membrane water electrolyzer (PEMWE), which requires an optimal structure of the flow field implemented in the bipolar plate (BP) component. In this study, we numerically investigated the two-phase (liquid water and oxygen) flow in the PEMWE's channel region with different outlet manifold structures utilizing the volume of fluid (VOF) model. Then, the oxygen volume fraction at the liquid/gas diffusion layer (L/GDL) surface, i.e., the interface of the channel and L/GDL, obtained by the liquid water and oxygen flow model was incorporated into a three-dimensional (3D) PEMWE model, which made it possible to predict the influence of the outlet manifold structure on the multiple transfers inside the whole electrolyzer as well as the electrochemical performance. The results indicate that the existence of oxygen in the flow field significantly decreased the electrolyzer voltage at a fixed operation current density and deteriorated the uniform distribution of the oxygen amount, current density (corresponding to the electrochemical reaction rate) and temperature in the membrane electrode assembly (MEA), indicating that the rapid oxygen removal from the flow field is preferred in the operation of the electrolyzer. Moreover, slight increases in the width of the outlet manifold were helpful in relieving the oxygen accumulation in the anode CL and, hence, improved the electrolyzer performance with more uniform distribution characteristics. [ABSTRACT FROM AUTHOR]

Background: As the second largest leafy vegetable, cabbage (Brassica oleracea L. var. capitata) is grown globally, and the characteristics of the different varieties, forms, and colors of cabbage may differ. In this study, five analysis methods—variance analysis, correlation analysis, cluster analysis, principal component analysis, and comprehensive ranking—were used to evaluate the quality indices (soluble protein, soluble sugar, and nitrate), antioxidant content (vitamin C, polyphenols, and flavonoids), and mineral (K, Ca, Mg, Cu, Fe, Mn, and Zn) content of 159 varieties of four forms (green spherical, green oblate, purple spherical, and green cow heart) of cabbage. Results: The results showed that there are significant differences among different forms and varieties of cabbage. Compared to the other three forms, the purple spherical cabbage had the highest flavonoid, K, Mg, Cu, Mn, and Zn content. A scatter plot of the principal component analysis showed that the purple spherical and green cow heart cabbage varieties were distributed to the same quadrant, indicating that their quality indices and mineral contents were highly consistent, while those of the green spherical and oblate varieties were irregularly distributed. Overall, the green spherical cabbage ranked first, followed by the green cow heart, green oblate, and purple spherical varieties. Conclusions: Our results provide a theoretical basis for the cultivation and high-quality breeding of cabbage. [ABSTRACT FROM AUTHOR]

Background: As the second largest leafy vegetable, cabbage (Brassica oleracea L. var. capitata) is grown globally, and the characteristics of the different varieties, forms, and colors of cabbage may differ. In this study, five analysis methods—variance analysis, correlation analysis, cluster analysis, principal component analysis, and comprehensive ranking—were used to evaluate the quality indices (soluble protein, soluble sugar, and nitrate), antioxidant content (vitamin C, polyphenols, and flavonoids), and mineral (K, Ca, Mg, Cu, Fe, Mn, and Zn) content of 159 varieties of four forms (green spherical, green oblate, purple spherical, and green cow heart) of cabbage. Results: The results showed that there are significant differences among different forms and varieties of cabbage. Compared to the other three forms, the purple spherical cabbage had the highest flavonoid, K, Mg, Cu, Mn, and Zn content. A scatter plot of the principal component analysis showed that the purple spherical and green cow heart cabbage varieties were distributed to the same quadrant, indicating that their quality indices and mineral contents were highly consistent, while those of the green spherical and oblate varieties were irregularly distributed. Overall, the green spherical cabbage ranked first, followed by the green cow heart, green oblate, and purple spherical varieties. Conclusions: Our results provide a theoretical basis for the cultivation and high-quality breeding of cabbage. [ABSTRACT FROM AUTHOR]

Next‐generation ultrahigh power density proton exchange membrane fuel cells rely not only on high‐performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double‐cell structure is believed to increase the power density from 4.4 to 6.52 kW L−1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0 kW L−1. [ABSTRACT FROM AUTHOR]

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L–1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization. [ABSTRACT FROM AUTHOR]

Appropriate nucleo-cytoplasmic partitioning of proteins is a vital regulatory mechanism in phytohormone signaling and plant development. However, how this is achieved remains incompletely understood. The Karyopherin (KAP) superfamily is critical for separating the biological processes in the nucleus from those in the cytoplasm. The KAP superfamily is divided into Importin α (IMPα) and Importin β (IMPβ) families and includes the core components in mediating nucleocytoplasmic transport. Recent reports suggest the KAPs play crucial regulatory roles in Arabidopsis development and stress response by regulating the nucleo-cytoplasmic transport of members in hormone signaling. However, the KAP members and their associated molecular mechanisms are still poorly understood in maize. Therefore, we first identified seven IMPα and twenty-seven IMPβ genes in the maize genome and described their evolution traits and the recognition rules for substrates with nuclear localization signals (NLSs) or nuclear export signals (NESs) in plants. Next, we searched for the protein interaction partners of the ZmKAPs and selected the ones with Arabidopsis orthologs functioning in auxin biosynthesis, transport, and signaling to predict their potential function. Finally, we found that several ZmKAPs share similar expression patterns with their interacting proteins, implying their function in root development. Overall, this article focuses on the Karyopherin superfamily in maize and starts with this entry point by systematically comprehending the KAP-mediated nucleo-cytoplasmic transport process in plants, and then predicts the function of the ZmKAPs during maize development, with a perspective on a closely associated regulatory mechanism between the nucleo-cytoplasmic transport and the phytohormone network. [ABSTRACT FROM AUTHOR]

Accurate lung tumor segmentation has great significance in the treatment planning of lung cancer. However, robust lung tumor segmentation becomes challenging due to the heterogeneity of tumors and the similar visual characteristics between tumors and surrounding tissues. Hence, we developed an improved 3D dense connected UNet (I-3D DenseUNet) to segment various lung tumors from CT images. The nested dense skip connection adopted in the I-3D DenseUNet aims to contribute similar feature maps between encoder and decoder sub-networks. The dense connection used in encoder-decoder blocks also encourages feature propagation and reuse. A robust data augmentation strategy was employed to alleviate over-fitting based on a 3D thin plate spline (TPS) algorithm. We evaluated our method on 938 lung tumors from three datasets consisting of 421 tumors from the Cancer Imaging Archive (TCIA), 450 malignant tumors from the Lung Image Database Consortium (LIDC), and 67 tumors from the private dataset. Experiment results showed an excellent Dice similarity coefficients (DSC) of 0.8316 for the TCIA and LIDC and 0.8167 for the private dataset. The proposed method presents a strong ability in lung tumor segmentation, and it has the potential to help radiologists in lung cancer treatment planning. [ABSTRACT FROM AUTHOR]

A template-engaged multistep synthesis process is developed to fabricate ultrathin carbon nanosheets assembled hierarchical nanoboxes embedded with dense Mo-N 4 active sites, which exhibited excellent activity and superb stability for oxygen reduction reaction. [Display omitted] • Unique hierarchical SA-Mo-C nanoboxes were fabricated via a template-engaged multistep synthesis process. • Comprehensive characterizations including EXAFS reveal Mo-N 4 atomic sites were formed and densely dispersed in the SA-Mo-C nanoboxes. • SA-Mo-C nanoboxes exhibited better ORR performance compared to commercial Pt/C catalysts. Construction of single-atom catalysts (SACs) with maximally exposed active sites remains a challenging task mainly because of the lack of suitable host matrices. In this study, hierarchical N -doped carbon nanoboxes composed of ultrathin nanosheets with dispersed atomic Mo (denoted as hierarchical SA-Mo-C nanoboxes) were fabricated via a template-engaged multistep synthesis process. Comprehensive characterizations, including X-ray absorption fine structure analysis, reveal the formation of Mo-N 4 atomic sites uniformly anchored on the hierarchical carbon nanoboxes. The prepared catalysts offer structural and morphological advantages, including ultrathin nanosheet units, unique hollow structures and abundant active Mo-N 4 species, that result in excellent activity with a half-wave potential of 0.86 V vs. RHE and superb stability for the oxygen reduction reaction in 0.1 M KOH; thus, the catalysts are promising air–cathode catalysts for Zn-air batteries with a high peak power density of 157.6 mW cm−2. [ABSTRACT FROM AUTHOR]

Background: Type 2C protein phosphatase (PP2C) is a negative regulator of ABA signaling pathway, which plays important roles in stress signal transduction in plants. However, little research on the PP2C genes family of cucumber (Cucumis sativus L.), as an important economic vegetable, has been conducted. Results: This study conducted a genome-wide investigation of the CsPP2C gene family. Through bioinformatics analysis, 56 CsPP2C genes were identified in cucumber. Based on phylogenetic analysis, the PP2C genes of cucumber and Arabidopsis were divided into 13 groups. Gene structure and conserved motif analysis showed that CsPP2C genes in the same group had similar gene structure and conserved domains. Collinearity analysis showed that segmental duplication events played a key role in the expansion of the cucumber PP2C genes family. In addition, the expression of CsPP2Cs under different abiotic treatments was analyzed by qRT-PCR. The results reveal that CsPP2C family genes showed different expression patterns under ABA, drought, salt, and cold treatment, and that CsPP2C3, 11–17, 23, 45, 54 and 55 responded significantly to the four stresses. By predicting the cis-elements in the promoter, we found that all CsPP2C members contained ABA response elements and drought response elements. Additionally, the expression patterns of CsPP2C genes were specific in different tissues. Conclusions: The results of this study provide a reference for the genome-wide identification of the PP2C gene family in other species and provide a basis for future studies on the function of PP2C genes in cucumber. [ABSTRACT FROM AUTHOR]

Although every glioma patient varies in tumor size, location, histological grade and molecular biomarkers, non-tumoral morphological abnormalities are commonly detected by a statistical comparison among patient groups, missing the information of individual morphological alterations. In this study, we introduced an individual-level structural abnormality detection method for glioma patients and proposed several abnormality indexes to depict individual atrophy patterns. Forty-five patients with a glioma in the frontal lobe and fifty-one age-matched healthy controls participated in the study. Individual structural abnormality maps (SAM) were generated using patients' preoperative T1 images, by calculating the degree of deviation of voxel volume in each patient with the normative model built from healthy controls. Based on SAM, a series of individual abnormality indexes were computed, and their relationship with glioma characteristics was explored. The results demonstrated that glioma patients showed unique non-tumoral atrophy patterns with overlapping atrophy regions mainly located at hippocampus, parahippocampus, amygdala, insula, middle temporal gyrus and inferior temporal gyrus, which are closely related to the human cognitive functions. The abnormality indexes were associated with several molecular biomarkers including isocitrate dehydrogenase (IDH) mutation, 1p/19q co-deletion and telomerase reverse transcriptase (TERT) promoter mutation. Our study provides an effective way to access the individual-level non-tumoral structural abnormalities in glioma patients, which has the potential to significantly improve individualized precision medicine. [ABSTRACT FROM AUTHOR]

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan's full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity. [ABSTRACT FROM AUTHOR]

• A novel airfoil flow field is proposed for fuel cells. • Airfoil flow field can enhance mass transfer while maintain low pressure drop. • Fuel cell with airfoil flow field is evaluated via experimental test and simulation. • Airfoil flow field increases the fuel cell's maximum power density effectively. • Airfoil flow field promotes the uniform distributions in fuel cells. Optimal configuration of bipolar plate (BP) embedding flow field is of great significance in improving the power density and durability of proton exchange membrane fuel cells (PEMFCs). Inspired by the airfoil in aircraft dividing the airflow into two streams causing pressure difference, a novel airfoil flow field (AFF) is designed to enhance the mass transfer capacity in channel and across the rib between two adjacent channels, which hardly increases the pressure drop in channel, unlike many baffle designs. The performance improvement achieved by implementing AFF in PEMFC is compared with common parallel flow field (PFF) and the wave flow field (WFF) by experimental test with respect to polarization curve and electrochemical loss and numerical simulation via a three-dimensional (3D) PEMFC model. The experimental results indicate that the novel AFF exhibits best fuel cell performance at various operation conditions (e.g. relative humidity, air stoichiometric ratio) mainly benefitted from the enhanced oxygen transfer, which contributes to the improvement of maximum power density by 8.85 % and 14.37 % compared to PFF and WFF, respectively. The modeling results indicate that the pressure drop increase in AFF is negligible compared with PFF, and is even slightly lower than WFF, indicating high practicability. Moreover, the utilization of AFF also helps the uniformity of oxygen concentration, current density and temperature in PEMFC. [ABSTRACT FROM AUTHOR]

Flexible capture has high applicability in the removal of space debris. In this paper, a novel adhesive capture mechanism is proposed, the multibody dynamic modeling method of the capture system is detailed, and an investigation of the adhesive capture process by numerical simulation is presented. First, the passive trigger mechanism of the capture device is described. Second, based on the classical rigid body mechanics and the fully parameterized ANCF beam element, the multibody model of the capture device is detailed. A contact detection algorithm is proposed to take the failure of adhesive connection into account, and its robustness and effectiveness are demonstrated. Finally, investigations of the dynamics during the capture process in two typical capture conditions are described and the impact of some system parameters on the capture effectiveness is discussed. The simulation results provide key parameters for the selection of the adhesive material and show the practical applicability of the capture mechanism. [ABSTRACT FROM AUTHOR]

The tethered-net is one of the most promising flexible space debris cleaning technologies to be developed in recent years. Momentum and geometric analysis were used to select four characteristic parameters of the tethered-net ejection system—the radius of the circumcircle of the net, the ratio of the bullet mass to the net mass, the ejection velocity of the bullet, and the ejection angle—to establish a set of formulas that describe the kinematics of the net deployment. The net deployment performance evaluation criteria were obtained with a concise analytical form. The calculation results of this set of analytical formulas are in good agreement with the numerical simulation results of the mass-spring model. Furthermore, this set of analytical formulas reveals some intrinsic characteristics of the net deployment dynamics. For example, the flying distance of the net from the start of ejection to the largest area is mainly determined by the radius of the circumcircle of the net and ejection angle. It is believed that the analytic formulas proposed are suitable for the preliminary design of a tethered-net system, especially when numerical simulation is time consuming. [ABSTRACT FROM AUTHOR]

Segmented proton exchange membrane (PEM) fuel cells are widely implemented in measuring their internal spatially distributed variables (e.g. current density and temperature). However, the difference between the segmented and ordinary fuel cells in spatial distribution characteristics has not been fully understood. In this work, we studied the spatial distribution characteristics in segmented fuel cells (cell area: 366.6 cm2) utilizing a three-dimensional (3D) large-scale fuel cell model that considers the full morphologies of metallic bipolar plates (BPs) and dot-matrix hydrogen, air and coolant flow distribution zones, including the current density, temperature, water content, etc., and compared with those in ordinary fuel cells. It is found that placing a segmented print circuit board (PCB) next to the bipolar plate (BP) component has little influence on fuel cell performance and internal distribution characteristics, whereas the measured current density distribution in the PCB still has inconsistency with that in the ordinary fuel cell, indicating that the influence of segmentation on electron conduction cannot be neglected. In the fuel cell with segmented BP and PCB, the fuel cell performance decreases significantly mainly due to increased electrical and ionic ohmic loss. In addition, the BP's segmentation significantly influences on the water and thermal state inside the whole fuel cell, leading to inconsistency in the measured temperature, relative humidity (RH) and current density distributions with ordinary fuel cells. [ABSTRACT FROM AUTHOR]

It is well-known that flow field design is of primary importance to optimization of proton exchange membrane (PEM) fuel cell. Traditional channel-rib flow fields, e.g. parallel or serpentine channels, always lead to non-uniform distributions of reactant gas, liquid, current density and so on between the channel and rib regions. Metal foam materials with high porosity (>90%) have been proposed as alternative flow fields for PEM fuel cells. In this study, influences of metal foam flow field on the transport phenomena coupled with the electrochemical reactions in PEM fuel cell are investigated using a three-dimensional (3D) multi-phase non-isothermal model. Specifically, the full morphology of metal foam flow field is taken into account in the 3D simulation after validated against experimental permeability data. The full morphology inclusion enables capture of the detailed gas flow from the flow field into the gas diffusion layer (GDL) and the current collection at the metal foam/GDL interface. In addition, compared with the conventional channel-rib flow fields, the metal foam design greatly increases fuel cell performance in the high current density regime. In addition, the oxygen and current density distributions in PEM fuel cell with the metal foam flow field are more uniform than those in the conventional one. Though the current collection area at the GDL surface is much smaller in the metal foam flow field, the relevant Ohmic loss won't increase significantly due to the improved physical contact by the fine pore structure of metal foam over the GDL. Image 1 • Full morphology of a foam flow field is included in 3D PEM fuel cell simulation. • Using metal foam flow field improves oxygen and current density distributions. • Metal foam flow field enhances gas flow towards CL due to the solid ligaments. • Small-pore metal foams help reduce the Ohmic loss at the GDL/metal foam interface. [ABSTRACT FROM AUTHOR]

The discrete-time fault-tolerant control method for permanent magnet synchronous motors (PMSMs) is investigated for the first time in this paper based on adaptive fuzzy theory, where the designed controllers consider faults containing both loss of effectiveness and bias. Firstly, with the help of Euler method, the discrete-time model of PMSMs is obtained. Secondly, adaptive fuzzy theory is used to realize fault-tolerant control of PMSMs. Next, dynamic surface control is used to resolve the problems of "explosion of complexity" and noncausal in discrete-time systems caused by backstepping. It is proved that the proposed method can guarantee all signals and states in the closed-loop system are semi-global uniform ultimate bounded when the faults occur and the position tracking error can converge to a small neighborhood of the origin. Finally, simulation results show that the proposed control method has strong fault-tolerant performance and robustness. [ABSTRACT FROM AUTHOR]

The Dadiwan F901 site, boasting a history of over 5000 years, stands as the largest and most intricately crafted large-scale housing structure from China's prehistoric era. The early renovation efforts, incorporating a sealed glass curtain wall, led to a continuous rise in relative humidity within the site, triggering outbreaks of microbial diseases. Subsequent measures successfully restored stability to the thermal and humid environment. This paper employs on-site real-time environmental monitoring and numerical simulation methods to assess the ventilation effectiveness and relative humidity changes before and after multiple interior modifications of the Dadiwan F901 site museum. The results indicate that the fully enclosed glass curtain wall can suppress the dependence of indoor humidity fluctuations on external weather fluctuations but has generated unintended consequences, leading to increased air relative humidity and even reaching saturation in the museum space. The strategic deployment of louvered windows and duct fans proved effective in enhancing internal airflow dynamics and overall air exchange capacity. It was possible to ensure that the relative humidity inside the site remained at approximately 70%, meeting the essential requirements for the preservation of cultural relics. This study is of great significance for alleviating the deterioration problem of enclosed exhibition halls of earthen relics. [ABSTRACT FROM AUTHOR]

Calcium‐ion batteries (CIBs) are considered as potential next‐generation energy storage systems due to their abundant reserves and relatively low cost. However, irreversible structural changes and weak conductivity still hinder in current CIBs cathode materials. Herein, an organic molecular intercalation strategy is proposed, in which V2O5 regulated with quinoline, pyridine, and water molecules are studied as cathode material to provide fast ion diffusion channels, large storage host, and high conductivity for Ca ions. Among them, V2O5‐quinoline (QVO) owns the largest interplanar spacing of 1.25 nm and the V‐O chains are connected with organic molecular by hydrogen bond, which stabilizes the crystal structure. As a result, QVO exhibits a specific capacity of 168 mAh g−1 at 1 A g−1 and capacity retention of 80% after 500 cycles at 5 A g−1 than the other materials. Furthermore, X‐Ray diffraction and X‐ray absorption spectroscopy results reveal a reversible order‐disorder transformation mechanism of Ca2+ for QVO, which can make full use of the abundant active sites for high capacity and simultaneously achieve fast reaction kinetics for excellent rate performance. These results demonstrate that QVO is a promising cathode material for CIBs, providing more choices for the development of high‐performance CIBs. [ABSTRACT FROM AUTHOR]

Flow field design and optimization are critical for the proton exchange membrane (PEM) fuel cells to meet the requirement of ultra-high power density commercial applications. However, the multi-physics transport mechanism inside such large-scale PEM fuel cells has not been fully understood. In this study, we have developed a three-dimensional (3D) PEM fuel cell model. It is first validated against the experimental data obtained from a small-size cell. Thereafter, based on this model, the performance characteristics of a large fuel cell (cell area: 245.76 cm2) assembled with a partially narrow flow field are elucidated, while the full bipolar plate (BP) and cell morphology are also considered. It is found that the partially narrow flow field can not only significantly increase the net power density of PEM fuel cells, but also effectively improve the uniform distribution of species with the staggered partially narrow (SPN) zone arrangement between adjacent channels. While this flow field can improve the cell performance, the blindly increasing of the narrow zone numbers may play a negative impact on the net power density due to the dramatic increase in pressure drop. Finally, the partially narrow channel can indeed provide improved drainage capacity. • Liquid water cooling is considered in the large-scale 3D model of PEM fuel cell. • Comprehensive comparison between the partially narrow and parallel flow fields. • The partially narrow channel has the advantage of enhancing oxygen convection. • The drainage mechanism of the partially narrow channel is clearly presented. [ABSTRACT FROM AUTHOR]

• The full-morphology simulation of the large-scale automobile PEM fuel cell is proposed. • All components, the realistic morphology of distribution area and the coolant flow is fully considered. • The advantages and disadvantages and its influence on physical and chemical processes of double-cell structure are deeply analyzed. • Novel double-cell structure can significantly improve power density (almost 20%) under actual operating conditions. The structural design of PEM fuel cell is crucial to improving its power density, and the cell structure largely depends on the bipolar plate (BP). This study compares the conventional single-cell structure and double-cell structure through three-dimensional (3D) large-scale (cell area: 312 cm2) full-morphology simulation. As for the double-cell structure, the channels are arranged in a dislocation manner and there is one cooling flow field per two cells. For the structure of the BP, we also fully considered the realistic morphology of distribution area and the coolant flow. It is found that the heat dissipation effect of double-cell structure is worse but the performance is very close compared to single-cell structure. Moreover, its volumetric power density is significantly improved (∼ 20%) due to the reduction in height. It is also found that increasing the velocity of coolant in the double-cell structure increases the performance first and then decreases. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A process was developed to selectively extract V from V-bearing ferro-phosphorus. • The mechanism of selective vanadium extraction was discussed in detail. • Pressure hydrogen reduction was first used for V precipitation from the leachate. Abstract A novel process involving roasting with additives, water leaching, and vanadium precipitation by high-pressure hydrogen reduction is proposed to selectively extract vanadium from vanadium-bearing ferro-phosphorus. The optimum conditions of roasting and leaching are obtained as follows: roasting temperature of 850 °C, Na 2 CO 3 dosage of 30 wt%, CaCO 3 dosage of 30 wt%, roasting time of 1 h, leaching time of 2 h and a leaching liquid–solid ratio of 1 mL/g. A V 2 O 3 product having a purity of 99.92% is precipitated from the leaching solution by a high-pressure hydrogen reduction. The total recovered vanadium is up to 92.3%. X-ray diffraction (XRD) analysis of the raw ore, roasted ore, and leaching residue shows that the additive of Na 2 CO 3 during roasting can react with the vanadium-bearing compounds and transform it into water-soluble NaVO 3 , while the additive of CaCO 3 can solidify phosphorus-bearing and chromium-bearing compounds into non-water-soluble phosphates of Ca 3 (PO 4) 2 and Cr 3 (PO 4) 2. Moreover, the iron-bearing compounds are converted into non-water-soluble Fe 2 O 3 and Na 3 Fe 2 (PO 4) 3. Thus, vanadium can be selectively extracted through the subsequent water leaching and high pressure hydrogen reduction process. Compared with the traditional process, this process is more efficient and environmentally friendly owing to the high recovery of vanadium, the non-used roasting additive of sodium chloride and the adopted eco-friendly vanadium precipitation method. [ABSTRACT FROM AUTHOR]

A full-duplex ultra-dense network (FDUDN) has been envisioned as a promising network paradigm for spectrum efficiency enhancement. This paper presents a novel joint spectrum and power management scheme, which maximizes the total capacity of the FDUDN, under given quality-of-service and cross-tier interference constraints. The proposed scheme is decomposed into inter-cell and intra-cell allocation. A novel approach, which performs initial capacity-maximization allocation and successive adjustment based on the constraints, is proposed for the allocation of the inter-cell subchannels. The inter-cell power control is formulated as a non-convex optimization problem, and variable substitution is used to transform it into a convex one. Furthermore, we solve this problem through a low-complexity heuristic scheme, which utilizes the water-filling theorem in inter-cell power allocation. Finally, a time-sharing relaxation method is adopted to solve the intra-cell subchannel allocation problem and reduce the computation complexity. The Computer simulation demonstrates the enhancement effect of the proposed scheme in terms of the capacity, spectrum efficiency, and power efficiency. [ABSTRACT FROM AUTHOR]

Highlights • Comfort index is proposed to evaluate water and thermal characteristics. • Comfort index is helpful to improve the water and thermal management. • Cathode water flooding and anode membrane drying are determined quantitatively. • Various operation conditions and design parameters are studied by comfort index. Abstract Water and thermal management is of great importance to proton exchange membrane fuel cell. A comfort index is proposed to comprehensively evaluate the water and thermal characteristics in proton exchange membrane fuel cell. It refers to the concept of comfort index in meteorology and selects the cathode liquid water accumulation and anode membrane drying as two basic factors so as to prevent water flooding and low proton conductivity simultaneously. The anode and cathode comfort degrees corresponding to the anode membrane drying and cathode liquid water accumulation, respectively, are quantified and fitted at various operation conditions, of which the parameters in the calculation process are determined utilizing a carefully validated quasi-two-dimensional model. The influences of cathode stoichiometric ratio, operating pressure, coolant temperature difference, cathode relative humidity, coolant temperature, anode recirculating ratio, current density and membrane thickness at wide-range temperature are studied in detail by the comfort index. It is found that the comfort index usually first increases and then decreases with the increment of temperature, because the low water saturation pressure at low temperature makes the water condensation easier and thus leads to water flooding. Compared to analytical simulation models, the comfort index is able to instantly obtain the quantified water and thermal characteristics in proton exchange membrane fuel cell, which is of great significance to the stack design and in-situ system controlling in practical design. [ABSTRACT FROM AUTHOR]

Highlights • Large-scale multi-phase simulations of PEMFC are conducted. • Realistic flow fields with distribution zone next to inlet and outlet are designed. • Effects of surface tension, wall adhesion and gravity in flow fields are included. • Counter-flow is more helpful to PEMFC compared to co-flow arrangement. • Coolant flow direction is suggested to be the same with air under counter-flow. Abstract Limited by the computational efficiency and stability, traditional 3D (three-dimensional) CFD (computational fluid dynamics) simulations of PEMFC (proton exchange membrane fuel cell) are always in single-channel scale, which neglect the realistic flow field structures in commercial PEMFC. In this study, a large-scale PEMFC (109.93 cm2), which is a repeated unit in commercial stacks and includes realistic anode and cathode flow fields, is investigated in detail utilizing a comprehensive 3D multi-phase model. In particular, the Eulerian-Eulerian model is chosen for the solution of gas and liquid two-phase flow in flow fields and the surface tension, wall adhesion, drag force and gravity are all taken into consideration. The gas concentration and liquid water amount in each channel of flow field are studied to test the influence of flow field. Moreover, it is proved that increasing operating pressure is helpful to improve PEMFC performance by increasing the reactant gas concentration and membrane water content significantly. Besides, counter-flow arrangement of hydrogen and air facilitates uniform distribution of membrane content and electrochemical reaction. And in this case, the coolant flow direction designed to be the same with that of air is beneficial to PEMFC performance. [ABSTRACT FROM AUTHOR]

Summary: A three‐dimensional (3D) multi‐phase numerical model of proton exchange membrane fuel cell (PEMFC) is built. The catalyst layer (CL) spherical agglomerate model is used to replace traditional homogenous model, which can predict the concentration loss in PEMFC more accurately. Utilizing this multi‐phase model, the PEMFC with 3D fine mesh flow field is investigated at length, and the liquid water distribution in 3D flow field is qualitatively compared with the experimental image in previous literature. It is found that the 3D fine mesh flow field can improve the reactant gas supply from flow field to porous electrodes significantly and facilitate liquid water removal in PEMFC simultaneously. Therefore, it reduces the concentration loss of PEMFC effectively without increasing the pumping power loss thanks to the greatly increased mass transfer area between gas diffusion layer (GDL) and flow field and vertical flow design of hydrogen and air, which also make the reaction rate distribution in CL more uniform. However, the decreased contact area between GDL and bipolar plate in 3D flow field may decrease PEMFC performance at the current densities where ohmic loss is dominated, but its effect is insignificant. A comprehensive three‐dimensional (3D) multi‐phase computational fluid dynamics numerical model is developed, in which the spherical agglomerate model of catalyst layer is introduced to better reflect the concentration loss in proton exchange membrane fuel cell (PEMFC). Utilizing this model, the PEMFC with 3D fine mesh flow field is simulated in detail, and the liquid water distribution in 3D fine mesh flow field is qualitatively compared with the experimental image in previous literature. [ABSTRACT FROM AUTHOR]

Highlights • A 3D multi-phase model of PEMFC coupling E-E model and two-fluid model is developed. • The water condensation and evaporation in PEMFC channels is taken into account. • The gravity force in the whole PEMFC is also incorporated in this model. • Partial low temperature and velocity may result in local liquid water accumulation. • The wave-like channel can improve PEMFC performance due to the enhanced convection. Abstract A 3D (three-dimensional) multi-phase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the Eulerian-Eulerian model is utilized to solve the gas and liquid two-phase flow in channels, while the two-fluid model is adopted in porous electrodes. Hence, the surface tension, wall adhesion and drag force in channels are all included. Besides, the gravity effects in the whole PEMFC are also taken into consideration. It is found that the water vapor concentration in cathode channel at high inlet humidity (e.g. 1.0) will be much higher than the saturation concentration if neglecting the water vapor condensation. In addition, the liquid water condensed from vapor in channel is mainly blown to side walls, rather than only exist on the bottom surface. The effect of water condensation and evaporation in channel is found to be lower than that in porous electrodes because of the much higher gas velocity in channel. Besides, the partial low temperature is likely to cause local liquid water accumulation in both anode and cathode channels and porous electrodes. Meanwhile, the wave-like channel is found to be able to remove the liquid water effectively due to the enhanced convection effect. Meanwhile, the simulation results in this study show that the serpentine flow field is much more beneficial to the liquid water removal and reactant gas distribution than parallel flow field, which results in the much higher performance. [ABSTRACT FROM AUTHOR]

The 3D (three-dimensional) multi-phase CFD (computational fluid dynamics) model is widely utilized in optimizing water and thermal management of PEM (proton exchange membrane) fuel cell. However, a satisfactory 3D multi-phase CFD model which is able to simulate the detailed gas and liquid two-phase flow in channels and reflect its effect on performance precisely is still not developed due to the coupling difficulties and computation amount. Meanwhile, the agglomerate model of CL (catalyst layer) should also be added in 3D CFD model so as to better reflect the concentration loss and optimize CL structure in macroscopic scale. Besides, the effect of thermal management is perhaps underestimated in current 3D multi-phase CFD simulations due to the lack of coolant channel in computation domain and constant temperature boundary condition. Therefore, the 3D CFD simulations in cell and stack levels with convection boundary condition are suggested to simulate the water and thermal management more accurately. Nevertheless, with the rapid development of PEM fuel cell, current 3D CFD simulations are far from practical demand, especially at high current density and low to zero humidity and for the novel designs developed recently, such as: metal foam flow field, 3D fine mesh flow field, anode circulation etc. [ABSTRACT FROM AUTHOR]

Abstract: Aqueous Zn‐ion batteries (ZIBs) have received incremental attention because of their cost‐effectiveness and the materials abundance. They are a promising choice for large‐scale energy storage applications. However, developing suitable cathode materials for ZIBs remains a great challenge. In this work, pioneering work on the designing and construction of aqueous Zn//Na0.33V2O5 batteries is reported. The Na0.33V2O5 (NVO) electrode delivers a high capacity of 367.1 mA h g−1 at 0.1 A g−1, and exhibits long‐term cyclic stability with a capacity retention over 93% for 1000 cycles. The improvement of electrical conductivity, resulting from the intercalation of sodium ions between the [V4O12]n layers, is demonstrated by single nanowire device. Furthermore, the reversible intercalation reaction mechanism is confirmed by X‐ray diffraction, Raman, X‐ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis. The outstanding performance can be attributed to the stable layered structure and high conductivity of NVO. This work also indicates that layered structural materials show great potential as the cathode of ZIBs, and the indigenous ions can act as pillars to stabilize the layered structure, thereby ensuring an enhanced cycling stability. [ABSTRACT FROM AUTHOR]

A comprehensive 3D (three-dimensional) multiphase model of PEMFC (proton exchange membrane fuel cell) is developed, in which the gas and liquid two-phase flow in channel and porous electrodes are investigated in detail. In the simulation of gas and liquid two-phase flow in channels, the effect of surface tension, wall adhesion and gravity is taken into account, including the influence of pressure difference between the inlet and outlet on inlet reactant gas concentration; while in porous electrodes, the anisotropy of GDL (gas diffusion layer) and liquid saturation jump at the interface of two different porous layers (e.g. GDL and MPL (micro-porous layer)) are also considered in this model. It is found that the amount of liquid water in channels increases with the increment of current density. In addition, increasing the contact angle at GDL/channel interface is found to be able to improve the performance of PEMFC by facilitating the water removal process in channels. Moreover, it can be concluded that adding baffles in cathode channel not only increases the oxygen concentration in porous electrodes but also facilitates the water removal process, both of which prevent PEMFC from concentration loss effectively. [ABSTRACT FROM AUTHOR]

A three-dimensional multiphase numerical model for proton exchange membrane fuel cell (PEMFC) is developed to study the fuel cell performance and water transport properties with low external humidification. The results show that the sufficient external humidification is necessary to prevent the polymer electrolyte dehydration at low current density, while at high current density, the water produced in cathode CL is enough to humidify the polymer electrolyte instead of external humidification by flowing back and forth between the anode and cathode across the membrane. Furthermore, a steady anode circulation status without external humidification is demonstrated in this study, of which the detailed internal water transfer path is also illustrated. Additionally, it is also found that the water balance under the counter-flow arrangement is superior to co-flow at low anode external humidification. [ABSTRACT FROM AUTHOR]

The Berezitovoe deposit is a large-sized Au-Ag-Zn-Pb deposit in the east of the Selenga-Stanovoi superterrane, Russia. Au-Ag orebodies are hosted by tourmaline-garnet-quartz-muscovite metasomatic rocks; Zn-Pb orebodies are hosted by granodiorites, porphyritic granites and tourmaline-garnet-quartz-muscovite metasomatic rocks. These orebodies are surrounded by wall rocks dominated by the Tukuringra Complex granodiorites, porphyritic granites, and gneissic granodiorites. The alteration includes silicification and garnet, sericitization chloritization, carbonatization and kaollinization. LA-ICP-MS U-Pb zircon dating indicates that the gold mineralization can be divided into two stages in the Berezitovoe polymetallic gold deposit (at 363.5 ± 1.5 Ma, and 133.4 ± 0.5). Hornblende-plagioclase gneisses of the Mogocha Group in the study area underwent Paleoproterozoic metamorphism (at 1870 ± 7.8 and 2400 ± 13 Ma), gneissic granodiorite of the Tukuringra Complex yields a late Paleozoic magmatic age (at 379.2 ± 1.1 Ma), and subalkaline porphyritic granitoid of the Amudzhikan Complex yield late Mesozoic magmatic ages (133-139 and 150-163 Ma). Granodiorites of the Tukuringra Complex in the study area have high concentrations of SiO2 (average of 60.9 wt%), are aluminum-oversaturated (average A/CNK of 1.49), are enriched in the large ion lithophile elements (e.g., K, Rb, and Ba), U, Th, and Pb, are depleted in high field strength elements (e.g., Ta, Nb, and Ti), and have slightly negative Eu and no Ce anomalies in chondrite-normalized rare earth element diagrams. Fluid inclusions from quartz veins include three types: aqueous two-phase, CO2-bearing three-phase, and pure CO2. Aqueous two-phase inclusions homogenize at 167°C-249°C and have salinities of 4.32%-9.47% NaCl equivalent, densities of 0.86-0.95 g/cm3, and formed at depths of 0.52-0.94 km. In comparison, the CO2-bearing three-phase inclusions have homogenization temperatures of 265°C-346°C, salinities of 7.14%-11.57% NaCl equivalent, and total densities of 0.62-0.67 g/cm3. The geochemical and zircon U-Pb data and the regional tectonic evolution of the study area, show that the Berezitovoe polymetallic gold deposit formed in an island arc or active continental margin setting, most probably related to late Paleozoic subduction of Okhotsk Ocean crust beneath the Siberian Plate. [ABSTRACT FROM AUTHOR]

In cognitive heterogeneous network, when multitudes of femtocells coexist, effective resource management become important to enhance network performance. Based on the base station location and terminal distribution density, we propose spectrum management and power configuration scheme for femtocells deployment network. In the beginning, we consider two femtocells adjacent network and propose the resource management scheme. The scheme allocates time frequency resource by adopting complete reusing and private usage in non-overlapping and overlapping areas respectively. Subsequently the scheme optimizes base station power under the constraints of cross-tier interference and maximal transmission power to maximize network capacity. According to the analysis of the power variation effect to femtocell coverage, a near-optimal solution of the transmission power is derived, and the corresponding power configuration scheme is proposed. After then we extend the spectrum and power management to multiple femtocells coexisting networks, and propose the management scheme applied for multiple femtocells deployment networks. The simulation results indicate that in capacity performance, the proposed power solution is close to the optimal solution, and the proposed resource management outperforms the existing schemes. [ABSTRACT FROM AUTHOR]

The effect of ionomer/carbon (I/C) ratio on proton exchange membrane (PEM) fuel cell cold start is investigated experimentally with theoretical water transport analysis. The scanning electron microscope (SEM) images show larger agglomerates and smaller effective reaction area by increasing the I/C ratio from 0.7 to 1.7. For normal operation, increasing the I/C ratio can improve the humidity tolerance, especially in the cathode. For cold start >−10 °C, a lower I/C ratio leads to better performance because the core reaction area is shifted towards the membrane, leading to more membrane water absorption and slower ice formation. For <−15 °C, the total water production is low and almost the same for the different I/C ratios because the ice formation takes place before effective membrane water absorption; and although the cathode catalyst layer (CL) and micro-porous layer (MPL) can provide sufficient space to store all the ice, higher I/C ratios (e.g. 1.2) still cause more ice formation in GDL and flow channel because the core reaction area becomes closer to GDL. The results show that the CL design has significant effect on the cold start performance, and there is a potential for further improvement. [ABSTRACT FROM AUTHOR]

In situ X-ray diffraction (XRD), as a widely used tool in probing the structure evolution in electrochemical process as well as the energy storage and capacity fading mechanism, has shown great effects with optimizing and building better batteries. Based on the research progresses of in situ XRD in recent years, we give a review of the development and the utilization of this powerful tool in understanding the complex electrochemical mechanisms. The studies on in situ XRD are divided into three sections based on the reaction mechanisms: alloying, conversion, and intercalation reactions in lithium-ion batteries. The alloying reaction, in which lithium ions insert into Si, Sb, and Ge is firstly reviewed, followed by a discussion about the recent development of in situ XRD on conversion reaction materials (including metal oxides and metal sulfides) and intercalation reaction materials (including cathode materials and some structure-stable anode materials). As for sodium-ion batteries, we divide these researches on structure evolution into two categories: cathode and anode materials. Finally, the future development of in situ XRD is discussed. [ABSTRACT FROM AUTHOR]

In this study, the gas liquid two-phase flow of low-temperature fuel cells is simulated to study the water removal process in the anode channel utilizing VOF (volume of fluid) method. It is found that the water removal process in the cathode channel is easier compared to that in the anode under the same operating condition and inlet velocity. Increasing the humidification rate and contact angle is helpful for water removal. Moreover, further simulations show that in the semicircle-U channel, the water can be removed successfully, but it will be stuck in the corner in the rectangular-U channel, which can be prevented by changing the contact angle of specific walls into extremely hydrophilic or hydrophobic. Extremely hydrophilic wall would make the entire water pave on the wall and smash into little droplets which is not only helpful in water removal and evaporation but also prevents the water from blocking the holes on the Gas Diffusion Layer (GDL). And different hydrophilic/hydrophobic levels also influence the water removal. [ABSTRACT FROM AUTHOR]

A comprehensive mathematical model is proposed to calculate the optimal leg length and cross-section area of TEG unit to maximize the peak output power. The model shows that for a TEG unit, there exists an optimal ratio of leg length and leg cross-section area corresponding to the maximum peak output power with a convective thermal boundary condition, and the optimal leg length and cross-section area can be further calculated based on the optimal ratio. The mathematical model is also validated in this paper, and the corresponding error is within a reasonable range. Moreover, the effects of the leg length and leg area on the peak output power, the peak output power density and the efficiency of TEG unit with different thermal boundary conditions are also discussed. This study will provide guidance for the structure design optimization of TEG unit. [ABSTRACT FROM AUTHOR]

We derive a power factor and an efficiency factor for comprehensive evaluation of thermoelectric generator (TEG) materials, and approve that only using the power factor (or efficiency factor) is sufficient to determine the output power (or thermoelectric conversion efficiency) potential of a material. We also show that the effect of thermal conductivity is underestimated in the traditionally used figure of merit. In fact, the traditionally used power factor and figure of merit are simplified versions of the new factors for the special “constant surface temperatures” condition (the heat transfer coefficients on the hot and cold sides are infinitely large), which rarely occurs in practical applications. These two new factors can be conveniently used for material evaluation and design optimization, for example, to determine the optimal interface temperature and length ratio of a segmented TEG. [ABSTRACT FROM AUTHOR]

In cognitive heterogeneous networks, when multiple adjacent femtocells are deployed, uncontrolled transmission power can lead to severe mutual interference. In order to reduce interference while satisfying capacity requirements, we propose a power management scheme for an adjacent femtocell network. Firstly, we build an interference model for adjacent femtocells, in which distance-dependent interference to terminals within the whole femtocell coverage area is considered. Then, we calculate the total capacity of adjacent femtocells based on the mutual interference and formulate a non-convex optimization problem to maximize the capacity under the transmission power constraints. To solve the non-convex problem, we divide it into two convex subproblems and solve them with the Lagrange dual theory and linear programming method. Finally, we derive the closed-form expression of the optimal power configuration to maximize capacity while minimizing energy consumption simultaneously. The simulation results indicate that the proposed power scheme demonstrates obvious improvement in terms of capacity and power economization, compared with the maximal power configuration method. [ABSTRACT FROM AUTHOR]

A comprehensive method for indicating the length ratio of segmented thermoelectric generator (TEG) is proposed to increase the output power and thermoelectric conversion efficiency. It is found that for a segmented TEG, there is an optimal length ratio corresponding to the highest maximum output power or thermoelectric conversion efficiency, which is not only dependent on the material properties but also the heat transfer conditions and geometry structure. The optimal length ratios corresponding to the output power and thermoelectric conversion efficiency are different. This method is also validated, and the error is within a reasonable range, indicating that this method can be used accurately and time-efficiently for the design of segmented TEGs. [ABSTRACT FROM AUTHOR]

A hot-dip galvanized steel fastener on an electromagnetic product was found to be seriously corroded after 16 years of storage in a room environment. Its surface had become rough and lost its metallic luster, and large amounts of corrosion products had accumulated on the surface, with color ranging from light yellow to red brown. To determine the corrosion mechanism, the manufacturing process and storage information of the fastener were first investigated. Pieces of the corroded fastener were sampled; at the same time, the same kind of steel before and after galvanization was prepared as two control samples. The micromorphology and composition of the surface and corrosion were analyzed by scanning electron microscopy, X-ray energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. Based on these analyses, as well as the manufacturing process and storage information, the corrosion mechanism was identified to be that zinc plating first reacted with oxygen, water vapor, and carbon dioxide in the atmosphere to form Zn(OH), ZnCO, and Zn(CO)(OH). Subsequently, the iron under the zinc plating reacted with oxygen and water vapor to form Fe(OH), Fe(OH) or FeO. [ABSTRACT FROM AUTHOR]

• Full-scale 3D simulation for air-cooled PEM fuel cell stack was presented; • The stack polarization curve and temperature distribution were validated; • Oxygen content becomes lower at a higher temperature site in the stack; • Thermal behavior has a decisive effect on the distributions of temperature, gas, etc.; • Increasing the air flow rate benefits the uniform distribution of oxygen, water, etc. This study presents one of the first full-scale stack three-dimensional (3D) simulations for proton exchange membrane (PEM) fuel cell to investigate temperature distribution, cell/stack performance, and impact of air cooling. The stack consists of 30 cells with the active area of 50 mm × 200 mm for each fuel cell. The manifold and all the basic components are included in the computational domain, while the flow field structure is treated as porous media in order to reduce the computational burden. The model predictions are validated against the experimentally measured voltage and detailed temperature distribution under different currents. It is found that significant differences in temperature are present between the fuel cells at the two sides and that in the middle, and the oxygen content becomes lower at a higher temperature site due to the local increased water vapor concentration. As a consequence, thermal behavior has a decisive effect on the distributions of temperature, reactant concentration, membrane hydration, current density, etc., inside this air-cooled stack. It is also found that increasing the cooling air flow rate not only decreases the stack temperature, but also reduces the temperature variation, which further benefit the uniform distributions of oxygen, water vapor, etc. in the stack. [ABSTRACT FROM AUTHOR]

The conjugate addition reaction of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloid derivatives (QD-R″) is investigated using density functional theory calculations in this paper. The geometry optimizations and frequency calculations were carried out at the B3LYP/6-31G( d, p) level, and the accurate energetic parameters were obtained by the B3LYP/6-311++G(2 df,2 p) method. Our calculations find that cinchona alkaloids with -NCONHPh and -NH electron-withdrawing substituents in the quinuclidine show stronger activation on the system than that with -CH electron-donating substituent. The NBO charge analysis for the tertiary amine nitrogen of the quinuclidine affirms that the electron-withdrawing substituents decrease the negative charges on the tertiary amine nitrogen atom, which is favorable for the second proton transfer from the catalyst to α-carbon of 1-nitroprop-1-ene. As a result, the calculations show that the charge distribution of the tertiary amine nitrogen affects the catalytic efficiency of the system. Furthermore, a detailed analysis of the effects of the solvent on the system further revealed the regularity. [ABSTRACT FROM AUTHOR]

The distributions of bird species have changed over the past 50 years in China. To evaluate whether the changes can be attributed to the changing climate, we analyzed the distributions of 20 subspecies of resident birds in relation to climate change. Long-term records of bird distributions, gray relational analysis, fuzzy-set classification techniques, and attribution methods were used. Among the 20 subspecies of resident birds, the northern limits of over half of the subspecies have shifted northward since the 1960s, and most changes have been related to the thermal index. Driven by climate change over the past 50 years, the suitable range and latitude or longitude of the distribution centers of certain birds have exhibited increased fluctuations. The northern boundaries of over half of the subspecies have shifted northward compared with those in the 1960s. The consistency between the observed and predicted changes in the range limits was quite high for some subspecies. The changes in the northern boundaries or the latitudes of the centers of distribution of nearly half of the subspecies can be attributed to climate change. The results suggest that climate change has affected the distributions of particular birds. The method used to attribute changes in bird distributions to climate change may also be effective for other animals. [ABSTRACT FROM AUTHOR]

The coupling vibration of a blade-disk-shaft unit is generally studied on the assumption that all the blades are identical. However, the mistuning feature always occurs due to manufacturing tolerances and other reasons in engineering practice. Therefore, a shaft-disk-blades coupling model with the random mistuning feature is derived based on our previous work. Then the statistical analysis on vibration characteristics of a blade-disk-shaft unit is performed. The uncertainty effects of blade parameters on coupling characteristics between the subcomponents are exhibited. The Monte Carlo simulation and statistical theory are used to capture the probability distributions of coupling characteristics. The natural frequency distributions of coupling modes are obtained under different mistuning levels and evaluated through confidence intervals. Then the mode shapes, obtained by eigenvector, are plotted to derive the evolution law of coupling mode type in a random mistuning system. At last, the localization factor is defined, then its statistical results are obtained to evaluate the mode localization magnitude under different mistuning levels. [ABSTRACT FROM AUTHOR]

Viruses have demonstrated strong potential for the therapeutic targeting of glioblastoma stem cells (GSCs). In this study, the use of a herpes simplex virus carrying endostatin–angiostatin (VAE) as a novel therapeutic targeting strategy for glioblastoma-derived cancer stem cells was investigated. We isolated six stable GSC-enriched cultures from 36 human glioblastoma specimens and selected one of the stable GSCs lines for establishing GSC-carrying orthotopic nude mouse models. The following results were obtained: (a) VAE rapidly proliferated in GSCs and expressed endo–angio in vitro and in vivo 48 h and 10 d after infection, respectively; (b) compared with the control gliomas treated with rHSV or Endostar, the subcutaneous gliomas derived from the GSCs showed a significant reduction in microvessel density after VAE treatment; (c) compared with the control, a significant improvement was observed in the length of the survival of mice with intracranial and subcutaneous gliomas treated with VAE; (d) MRI analysis showed that the tumor volumes of the intracranial gliomas generated by GSCs remarkably decreased after 10 d of VAE treatment compared with the controls. In conclusion, VAE demonstrated oncolytic therapeutic efficacy in animal models of human GSCs and expressed an endostatin–angiostatin fusion gene, which enhanced antitumor efficacy most likely by restricting tumor microvasculature development. [ABSTRACT FROM AUTHOR]

In this article, the failure phenomena of softening and flow of crosslinked epoxy resin encapsulant during a long-term storage were analyzed by means of fault tree analysis, Fourier transform infrared spectroscopy, x-ray energy dispersive spectrum, and differential scanning calorimetry coupled with thermogravimetric analysis. Based on the results of those analyses, the reason of failure is identified to be that the epoxy resin was not cured completely during manufacturing, and the resulting imperfect three-dimensional crosslinked network was hydrolyzed because of the humidity in the environment during a long-term storage. Hence, the depolymerized polymers became softened gradually, and the seriously softened polymers flowed slowly because of creeping, an inherent property of the polymer materials. [ABSTRACT FROM AUTHOR]

Abstract: A novel porous CuOx/CeO2 co-loaded ZrO2–TiO2 (ZT) nanocomposite with tunable pore structure and high surface area was prepared by a simple surfactant-free solvothermal method. The pore structure could be well controlled by adjusting the ratio of ethanol to H2O during the solvothermal process. Both copper oxides and ceria species could be homogeneously loaded into porous ZT nanocomposite by either incorporation into ZT framework or dispersion into the pore channels. Two kinds of novel catalysts with different pore structures have been synthesized and exhibit excellent soot catalytic combustion performance, owing to the porous structure and the active components of CuOx/CeO2. [Copyright &y& Elsevier]