A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

A qualitative account of the causes and effects of performance degradation and failure in hydrogen-fuelled polymer electrolyte fuel cells (PEFCs) is given in the present review. The purpose of the review is to establish a backbone understanding of the phenomenological processes that occur within the PEFC, how they interact, how they are influenced through elements of design, manufacturing and operation, and ultimately how they result in performance degradation and cell failure. In the current work, 22 common faults are identified which are induced by 48 frequent causes. The major PEFC components considered here that are susceptible to faults are the polymer electrolyte-based membrane, the anode and cathode catalyst layers, gas diffusion and microporous layers, seals and the bipolar plate. Faults pertaining to these components can cause irreversible increases in activation, mass transportation, ohmic and fuel efficiency losses, or indeed cause catastrophic cell failure

Onset of cellular instabilities in spherically propagating hydrogen-air premixed laminar flames

Using high-speed Schlieren and Shadow photography, the instabilities of outwardly propagating spherical hydrogen-air flames have been studied in a constant volume combustion bomb. Combustion under different equivalence ratios (0.2 w 1.0), temperatures (298 K w 423 K) and pressures (1.0 bar w 10.0 bar) is visualized. The results show that flames experience both unequal diffusion and/or hydrodynamic instabilities at different stages of propagation. The critical flame radius for such instabilities is measured and correlated to the variations of equivalence ratio, temperature and pressure. Analysis revealed that equivalence ratio affects unequal diffusion instability via varying the Lewis number, Le; increased temperature can delay both types of instabilities in the majority of tests by promoting combustion rate and changing density ratio; pressure variation has minor effect on unequal diffusion instability but is responsible for enhancing hydrodynamic instability, particularly for stoichiometric and near-stoichiometric flames

A proposed agglomerate model for oxygen reduction in the catalyst layer of proton exchange membrane fuel cells

Oxygen diffusion and reduction in the catalyst layer of PEM fuel cell is an important process in fuel cell modelling, but models able to link the reduction rate to catalyst-layer structure are lack; this paper makes such an effort. We first link the average reduction rate over the agglomerate within a catalyst layer to a probability that an oxygen molecule, which is initially on the agglomerate surface, will enter and remain in the agglomerate at any time in the absence of any electrochemical reaction. We then propose a method to directly calculate distribution function of this probability and apply it to two catalyst layers with contrasting structures. A formula is proposed to describe these calculated distribution functions, from which the agglomerate model is derived. The model has two parameters and both can be independently calculated from catalyst layer structures. We verify the model by first showing that it is an improvement and able to reproduce what the spherical model describes, and then testing it against the average oxygen reductions directly calculated from pore-scale simulations of oxygen diffusion and reaction in the two catalyst layers. The proposed model is simple, but significant as it links the average oxygen reduction to catalyst layer structures, and its two parameters can be directly calculated rather than by calibration

Jablotron 100-Based Corporation Access System

Bakalářská práce se zabývá problematikou návrhu a realizace přístupového systému podniku s elektronickým zabezpečovacím systémem Jablotron 100 a jeho propojením s jinými systémy. Byl navržen a naprogramován můstek s API rozhraním pro ovládání systému Jablotron 100. Tento můstek byl použit pro realizaci webového uživatelského rozhraní k ovládání přístupového systému. Dále byl vytvořen koncept získávání dat docházky ze systému Jablotron 100.This bachelor thesis deals with the design and implementation of an enterprise access control system based on the electronic security system Jablotron 100 and its connection with external systems. The bridge with an API interface for controlling the Jablotron 100-based corporation access system has been designed and programmed. This bridge was used to implement the web user interface to control the access system. Furthermore, the concept of collecting attendance data from the Jablotron 100-based system was created.

node_shenzhen.csv

The nodes of road network graph in Shenzhen cit

node_jinan.csv

The nodes of road network graph in Jinan cit

edge_jinan.csv

The edges of road network graph in Jinan cit

traj_jinan.csv

Vehicle trajectories in Jinan city on October 17, 202

Trends of ductility at 5°C.

In recent years, diatomite has been successfully adopted in asphalt modification to overcome the problems of polymer modified asphalt, because of the advantages in wide sources, low price, and worthy technical characteristics. Although the improvement of the high-temperature performance of the modified diatomite asphalt has been verified in previous studies, the diatomite will bring negative impact on the low-temperature resistance. Hence, the objective of this study is to seek a new channel to improve the comprehensive performance of the diatomite modified asphalt binder. Considering the advantage of the SBR in improving the low-temperature performance of asphalt binder, the diatomite/SBR composite modified asphalt binder (DSA) and the corresponding preparation technology are developed to obtain an improved comprehensive performance via the orthogonal experiment method in this study. Moreover, the modification mechanisms of the DSA are revealed using fluorescence microscopy (FM) tests, Gel permeation chromatography (GPC) tests, and Fourier transform infrared spectroscopy (FTIR) tests.</div

Descriptive statistics of main variables.

Share repurchase is not only an important financial policy of the company, but also a financial policy with a very wide range of influence. A scientific and reasonable share repurchase policy has a significant financial effect in terms of an equity structure optimization, capital structure adjustment, cash holding control, and even management compensation system design. The long-standing share repurchase in the U.K. and U.S. companies and the recent practice of share repurchase by Chinese listed companies imply an important financial proposition: share repurchase is a high-quality financial policy that, when properly applied, will help reduce the cost of capital. The data in this study show that share repurchases can reduce the level of firms’ cost of capital and play an important role in enhancing their competitiveness. This study also finds that Chinese listed companies, when formulating and implementing share repurchase programs, do not subjectively view share repurchases as a policy tool to adjust cash holdings and capital structure. In addition, they do not view share repurchases as an alternative to cash dividends but use equity incentives for management as the main intention for share repurchases. This decision-making concept is not conducive to the rational use of share repurchase policies in the long run and should be a cause for concern in the business community. Finally, the leverage and the cash holding path are the main motives affecting share repurchases and are the important fundamental mechanisms in this study, while the mediating mechanism test finds that share repurchases mainly reduce the cost of capital through two information perspectives of analyst following and stock liquidity. The heterogeneity analysis shows that the role of share repurchases in reducing the cost of capital is more obvious in enterprises with fierce product market competition, high institutional investor shareholding.</div