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Fig Schematic of cation transport mechanism: driven by a concentration gradient. The schematic diagram is not to scale. During the operation of PEM fuel cells, a large amount of water is generated at the cathode, while the anode side remains relatively dry. Under the influence of a water concentration gradient, Cr3+ migrates through the PEM from the cathode catalyst layer to the anode catalyst layer. [Display omitted] • Cr3+ and its concentration significantly affect the performance of PEM fuel cells. • The charge transfer impedance and mass transfer resistance increase with the increasing degree of Cr3+ contamination. • Cr3+ contamination slows down ORR kinetics and reduces the limiting diffusion current density. • The presence of Cr3+ affects the durability and stability of the PEM fuel cell. • Cr3+ migrates from the cathode to the anode catalyst layer across the membrane during the operation of the PEM fuel cell. It is known that contamination ions stemming from the corrosive deterioration of vital subassemblies, such as bipolar plates (BPs) and sealing gaskets, exert a profound influence on the performance and durability degradation of PEM fuel cells. The impacts of Cr3+ on the catalyst layers (CLs) and single-cell performance were investigated by immersing the cathode catalyst layer (CCL) and anode catalyst layer (ACL) in a Cr3+ solution with different concentrations for contamination treatment. During the fuel cell test, polarization curves (PCs), electrochemical impedance spectroscopy (EIS), H+ transfer impedance, and cyclic voltammetry (CV) curve results were recorded. The effects of Cr3+ contamination on the kinetic for oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) were analyzed in a three-electrode system. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to explore the degradation mechanisms of Cr3+ contamination on fuel cell activity. The results indicate that the presence of Cr3+ increased the ohmic impedance from 0.200 Ω cm2 to 0.449 Ω cm2, resulting in a voltage attenuation rate as high as 55.21 %. Moreover, the presence of Cr3+ slowed the ORR reaction rate and changed the ORR reaction pathway. Cr3+ contamination caused irreversible damage to PEMFC performance and durability. [ABSTRACT FROM AUTHOR]

• An accurate admittance model for the grid-connected converter with droop control is proposed. • The frequency coupling phenomenon is induced by the asymmetry of the droop controller for the grid-connected converter. • The outer control loop will impact the frequency-coupled phenomenon, but has slight effects on positive and negative sequence admittance of VSCs. • The proportional gain of the current control loop impacts obviously the frequency coupling phenomenon. The droop control scheme is widely applied for the paralleled operation of the grid-connected converter. Yet, the frequency-domain admittance model for the grid-connected converter with droop control is still inaccurate due to the complex coupling relation of the droop control loop, the voltage control loop, and the current control loop. To address this problem, the coupling relationship of these control loops is analyzed in this paper, and then an accurate admittance model for the grid-connected converter with droop control is proposed based on the complex vector modeling method in both dq -frame and αβ -frame. The influence of different control parameters on the admittance model is analyzed further. The proposed model accurately describes the admittance characteristics of the grid-connected converter with droop control, and reveals the frequency coupling phenomenon caused by the droop control loop. The frequency response measured by frequency scan and simulation results verify the effectiveness of the established model. Finally, the impedance interactive stability analysis results show that the grid-connected converter with droop control is prone to instability in stiff grid conditions. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

In this study, Ni/W–TiN composites were fabricated by the pulse current electrodeposition (PCE) method. The effects of TiN concentration on the microstructure, microhardness, and wear properties of the resulting composites were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), microhardness tester, and friction wear testing. Among the four obtained composites, Ni/W–TiN composite prepared at 8 g/L showed the densest and finest surface structure. The TiN contents in obtained Ni/W–TiN composites at 8 and 16 g/L were estimated to 8.1 and 5.4 wt%, respectively. The average Ni/W grain diameter in Ni/W–TiN composite obtained at 8 g/L TiN was recorded as 84.7 nm. The protrusion and depression heights of the composite deposited at 8 g/L were 81.8 and 45.4 nm, respectively. This composite also processed an average microhardness of 897.6 HV, with only a few shallow and narrow scratches on its worn surface, demonstrating its prominent wear resistance when compared to the other three composites. [ABSTRACT FROM AUTHOR]

Multivariate distribution models for geo-material parametric data play a crucial role in reliability-based design. Currently, two major models are commonly used: the conventional multivariate normal distribution model and the copula model (including subtypes like the elliptical copula model and Vine copula model). This study aims to assess the performance of different models including three specific copula models (Gaussian copula, t copula, and D-Vine copula models) and the conventional normal distribution model. To this end, this study employs an incomplete database comprising 693 data samples related to lacustrine soils near Dianchi Lake in Kunming city, China. Results indicate that copula models generally exhibit lower model uncertainty compared to the conventional multivariate normal distribution model. Using Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC), the elliptical copula ranks first, followed by Gaussian copula, with D-Vine copula ranking third. For a balanced evaluation of performance and complexity, the conventional multivariate normal distribution model is favored. This study provides valuable insights for selecting appropriate models for geo-material parametric data, aiding reliability-based design in geotechnical engineering. Additionally, it is demonstrated that sampling with replacement in the Bootstrapping technique has only a slight effect on the estimation of correlation matrices for the incomplete database. [ABSTRACT FROM AUTHOR]

Uniform dispersion of pristine graphene in polymers has always been a difficulty in the research and industry. In this paper, a simple but effective method was used to uniformly disperse the pristine graphene in NR matrix to prepare an NR/pristine graphene composite. The conductivity of this composite with 5 wt% graphene loading fraction was ∼0.005 S/m, around 4 orders of magnitude higher than that prepared by other methods with a similar loading fraction. The gauge factor (GF) of the strain sensor using the as-prepared composite as the component could be as high as 46, taking a lead positon in the reported strain sensors. Owing to the high sensibility, the sensor was suitable to be used for the detection of very subtle motions such as breathing or heartbeat. In a wrist-pulse testing, premature beats, less forceful heartbeats, and the "P""T""D″ waves of the heartbeats could be precisely monitored and distinguished. Swallowing and vocalization could also be efficiently detected by attaching the sensor on the subject's throat. Image 1 • Convenient method to uniformly disperse pristine graphene in natural rubber matrix was proposed. • Pressing treatment affected the conductivity and sensitivity of the composite. • The conductivity of composite with 5 wt% graphene loading fraction was around 0.005 S/m. • The GF of the strain sensor was as high as 46. [ABSTRACT FROM AUTHOR]

The foregut theory posits that the proximal small intestine plays an important role in the improvement of type 2 diabetes (T2D) after Roux-en-Y gastric bypass (RYGB). To study the possible role of proximal jejunum in the treatment of T2D after RYGB via the analysis of DNA methylation and transcriptome. Laboratory of Shanghai Diabetes Institute, China. Two batches of T2D rats undergoing surgeries (RYGB and a sham operation as control) were established independently. The proximal jejuna from one batch were used for the methylated DNA immunoprecipitation sequencing and transcriptome sequencing. Those from another batch were used for DNA methylation analysis via a MassARRAY (Agena Bioscience, San Diego, CA, United States) platform and quantitative polymerase chain reaction to verify the results of high-throughput sequencing analysis. The transcriptome sequencing results showed that the genes differentially expressed (P <.05) in the RYGB- and sham-operated groups were significantly enriched in the gene ontology biological processes associated with fatty acid metabolism and lipid transport. The methylated DNA immunoprecipitation sequencing analysis showed that there were 1973 genes with significantly differentially methylated CpG sites located within gene promoters between the 2 groups (P <.05 and fold change > 2). The Mogat3 in the proximal jejunum after RYGB was hypermethylated in the promoter region and its transcription level was significantly reduced. The results of the high-throughput sequencing were validated via methylation quantitative analysis and quantitative polymerase chain reaction in a new set of samples. RYGB could change DNA methylation and gene expression profiles in the proximal jejunum in T2D rats. Mogat3 potentially contributes to the beneficial effects caused by RYGB. 1. RYGB significantly altered gene expression patterns in the proximal jejunum of diabetic rats. 2. RYGB could change DNA methylation patterns in the proximal jejunum of diabetic rats. 3. Mogat3 was significantly hypermethylated in gene promoter region and poorly expressed in the proximal jejunum after RYGB, potentially contributing to the beneficial effects caused by bariatric surgery. [ABSTRACT FROM AUTHOR]