A novel densely connected neural network for proton exchange membrane fuel cell fault diagnosis

It is of great significance to perform proton exchange membrane fuel cell (PEMFC) fault diagnosis and take action timely to mitigate or even eliminate the faults, which can strengthen PEMFC reliability and durability. In previous studies, cell voltage is extensively used for PEMFC fault diagnosis. However, there exists similar cell voltage drop phenomenon as different PEMFC faults occur, especially for faults like flooding and air starvation having extremely similar voltage dynamic variation, which makes it difficult to capture the features sensitive to faults. Moreover, cell voltages collected from different MEAs follow different distributions even in the same operation condition, which challenges the diagnosis consistency of fault diagnosis methods. In this paper, in order to break through the hindrances, a novel densely connected neural network codenamed Inc-DenseNet is proposed for PEMFC fault diagnosis, which integrates advantages of InceptionNet and DenseNet to extract more specific and robust features from cell voltage. In the analysis, the collected PEMFC voltage signal is transformed into 2D image data, which is then used to train the Inc-DenseNet. Results demonstrate that with the trained Inc-DenseNet, the diagnostic accuracy for four PEMFC states of health (normal, flooding, dehydration, air starvation) can reach 95.3%, especially for flooding and air starvation. In addition, by using the voltage datasets collected from two different MEAs, the generalization capacity of the Inc-DenseNet is proved. With the findings, the proposed network Inc-DenseNet can not only achieve high-precision fault diagnosis, but also has a high computing efficiency, which makes it promising in real-time PEMFC fault diagnosis in the future.     

Glucose Oxidase‐Instructed Multimodal Synergistic Cancer Therapy

Over the past 3 years, glucose oxidase (GOx) has aroused great research interest in the context of cancer treatment due to its inherent biocompatibility and biodegradability, and its unique catalytic properties against β‐d ‐glucose. GOx can effectively catalyze the oxidation of glucose into gluconic acid and hydrogen peroxide. This process depletes oxygen levels, resulting in elevated acidity, hypoxia, and oxidative stress in the tumor microenvironment. All of these changes can be readily harnessed to develop a multimodal synergistic cancer therapy by combining GOx with other therapeutic approaches. Herein, the representative studies of GOx‐instructed multimodal synergistic cancer therapy are introduced, and their synergistic mechanisms are discussed systematically. The current challenges and future prospects to advance the development of GOx‐based nanomedicines in this cutting‐edge research area are highlighted.     

离子液体添加到废旧发动机油引起的摩擦学性能"再生"

目的 探究离子液体(IL)对废旧发动机油摩擦学性能的影响.方法 在四球试验机上,评价了添加剂对摩擦力的影响,随后利用SEM、EDS和粗糙度轮廓仪表征了磨斑形貌、表面化学成分和粗糙度变化;利用点接触光干涉油膜厚度测量装置,研究了添加剂对成膜特性的影响.结果 在40℃和100℃下,添加离子液体的发动机油摩擦系数相较于废旧油均有所下降,分别在0.095和0.085左右,尤其是在100℃下,其摩擦系数(≈0.085)还低于新鲜润滑油(≈0.09).其次,钢球的磨斑直径也均有所减小.在"轻度"和"严重"乏油的弹流润滑(Starved EHL)条件下,补加离子液体至废旧发动机油中,废旧机油可获得较好的成膜特性,其中心膜厚可增加约20 nm.结论 在边界润滑下加入IL,废旧发动机油重新获得了良好的摩擦磨损性能,高温摩擦过程中,IL在金属表面发生了复杂的化学反应,生成了一层低剪切强度的反应膜.在乏油状态下,油性添加剂IL具有较强的极性,容易在接触表面形成一层稳定的吸附膜,改变接触区润滑油的压力分布,进而引起入口区润滑油的有效黏度远大于其表观黏度,提升了废旧油的成膜能力,从而使其重新获得了较好的润滑性能.     

Dynamic characteristics and mitigations of hydrogen starvations in proton exchange membrane fuel cells during start-ups

Hydrogen starvation during a start-up process in proton exchange membrane (PEM) fuel cells could result in drastic local current density variations, reverse cell voltage and irreversible cell damages. In this work, variations of local current densities and temperatures are measured in situ under both potentiostatic and galvanostatic modes. Experimental results show that when the cell starts up under potentiostatic mode with hydrogen starvation, current density undershoots occur in the downstream; while under the galvanostatic mode, local current density in the downstream almost drops to zero, but the current density near the outlet remains almost constant. The phenomenon of near constant current density near the outlet leads to a novel approach to alleviate hydrogen starvations - a hydrogen reservoir is added at the anode outlet. Experimental results show that the exit hydrogen reservoir can significantly reduce the zero current region and alleviate hydrogen starvations. A non-dimensional current-density variation coefficient is proposed to measure the magnitude of local current density changes during starvations. Experimental results show that the exit hydrogen reservoir can significantly reduce the current-density variations coefficient over the entire flow channel, indicating that adding an exit reservoir is an effective approach in mitigating hydrogen starvations.     

Triacylglycerol Production in the Snow Algae Chlamydomonas nivalis under Different Nutrient Conditions

Eukaryotic microalgae have been known for high competency in the accumulation of triacylglycerol (TAG), a representative class of storage lipid. The snow algal species, Chlamydomonas nivalis, is a unique green eukaryotic microalga that can grow and survive in a wide range of temperatures. Although a few metabolomic studies of C. nivalis were conducted, no study has reported on TAG accumulation in C. nivalis. Herein, the present work aimed to investigate TAG production in C. nivalis under nutrient-starved conditions at 22 °C. Compared to phosphorus starvation, C. nivalis under nitrogen starvation showed a less severe growth defect, greater capacity for TAG production, and simple acyl composition in TAG enriched with 18:1. These features suggest that C. nivalis may be a significant model species to investigate glycerolipid metabolism for basic and applied research.     

Study of failure mechanisms of the reversal tolerant fuel cell anode via novel in-situ measurements

Cell voltage reversal resulting from hydrogen starvation at anode is one of the factors that exacerbate the overall degradation of polymer electrolyte fuel cells (PEFCs). An effective material-based mitigation strategy against cell reversal is to add oxygen evolution reaction (OER) catalysts into the anode to make reversal-tolerant-anodes (RTAs). However, RTAs still suffer from an eventual sudden death, and the failure mechanisms of this sudden death have not been well studied thus far. Here we show a novel in-situ measurement technique with a distinctive partition membrane electrode assembly (MEA) to research the failure mechanism of RTAs. It is observed for the first time that the failure of RTAs is mainly attributed to the destruction of electron conducting paths caused by carbon corrosion from catalyst layers (CLs), gas diffusion layers (GDLs) and bipolar plates (BPs), rather than deactivation of the OER catalyst. As a verification, the application of additional OER catalysts on the GDL is found to effectively prolong the reversal tolerant time. These results add significant new insights into the failure mechanism of the RTA MEA and will be of practical importance in directing to design advanced MEAs and BPs that can withstand cell voltage reversal.     

New research programme of JAEA/CLADS to reduce the knowledge gaps revealed after an accident at Fukushima-1: introduction of boiling water reactor mock-up assembly degradation test programme

ABSTRACT

The new R&D programme of JAEA/CLADS tests complements the previous investigations related to BWR severe accidents. A series of tests aim at closing the gaps in understanding of the Fukushima Dai-Ichi degradation sequence at each unit. The paper emphasises the problem of control blade degradation, which influences the accident progression at an early stage and shows the approach for thorough investigation of this problem.     

Dislocation starvation and exhaustion hardening in Mo alloy nanofibers

The evolution of defects in Mo alloy nanofibers with initial dislocation densities ranging from 0 to ∼1.6 × 10¹⁴ m⁻² were studied using an in situ “push-to-pull” device in conjunction with a nanoindenter in a transmission electron microscope. Digital image correlation was used to determine stress and strain in local areas of deformation. When they had no initial dislocations the Mo alloy nanofibers suffered sudden catastrophic elongation following elastic deformation to ultrahigh stresses. At the other extreme fibers with a high dislocation density underwent sustained homogeneous deformation after yielding at much lower stresses. Between these two extremes nanofibers with intermediate dislocation densities demonstrated a clear exhaustion hardening behavior, where the progressive exhaustion of dislocations and dislocation sources increases the stress required to drive plasticity. This is consistent with the idea that mechanical size effects (“smaller is stronger”) are due to the fact that nanostructures usually have fewer defects that can operate at lower stresses. By monitoring the evolution of stress locally we find that exhaustion hardening causes the stress in the nanofibers to surpass the critical stress predicted for self-multiplication, supporting a plasticity mechanism that has been hypothesized to account for the rapid strain softening observed in nanoscale bcc materials at high stresses.     

Enhanced hydrogen production by means of sulfur-deprived Chlamydomonas reinhardtii cultures grown in pretreated olive mill wastewater

Under sulfur-deprived conditions, the metabolism of Chlamydomonas reinhardtii switches to the photoproduction of hydrogen. This process is sustained by both photosystem II-driven water splitting and by the fermentation of stored carbohydrates. We investigated the possibility of using diluted pretreated olive mill wastewaters (OMW), which contain organic acids and sugars, as a substrate on which to grow Chlamydomonas, in order to obtain suitable biomass to produce hydrogen. The cells grown on a mixture of pretreated OMW and TAP (tris-acetate-phosphate) (50% dilution) were found to be richer in carbohydrates and exhibited a greater production of hydrogen (150 ml H₂ l⁻¹ culture), compared to the control cells (100 ml H₂ l⁻¹ culture). In these cultures, the hydrogen production process was characterized by a shorter aerobic phase and a longer hydrogen-production period. The results offer a useful perspective for the utilization of olive mill wastewaters, which constitute an environmental problem, particularly in Mediterranean areas, and for increasing the output for hydrogen production with Chlamydomonas.