Effects of basic gas diffusion layer components on PEMFC performance with capillary pressure gradient

The gas diffusion layer (GDL) is composed of a substrate and a micro-porous layer (MPL), and is treated with polytetrafluoroethylene (PTFE) to promote water discharge. Additionally, the MPL mainly consists of carbon black and PTFE. In other words, the optimal design of these elements has a dominant effect on the polymer electrolyte membrane fuel cell (PEMFC) performance. For the GDL, it is crucial to prevent water flooding, and the water flux within the GDL is strongly affected by the capillary pressure gradient. In this study, the PEMFC performance was systematically investigated by varying the substrate PTFE content, MPL PTFE content, and MPL carbon loading per unit area. The effects of each experimental variable on the PEMFC performance and especially on the capillary pressure gradient were quantitatively analyzed when the GDLs were manufactured by the doctor blade manufacturing method. The experimental results indicated that as the PTFE content of the anode and cathode GDL increased, the PEMFC performance deteriorated due to the deformation of the porosity and tortuosity of the GDL. Additionally, the PEMFC performance improved as the MPL PTFE content of the cathode GDL increased at low relative humidity (RH), but the PEMFC performance tendency was reversed at high RH. Further, the MPL carbon loading of 2 mg/${\text{cm}}^2$ demonstrated the best performance, and the advantages and disadvantages of the MPL carbon loading were identified. In addition, the effects of each experimental variable on liquid water, water vapor, and gas permeability were investigated.     

An engineering approach to the design of a BcN control network

A broadband convergence network (BcN), which enables the convergence of communications and broadcasting services, the convergence of voice, video, and data services, and the integration of wired and wireless technology in order to provide high-quality broadband multimedia services, is an implementation example of a next generation network (NGN). To rapidly provide various new application services, a simple but feature-rich control network that performs all demanded control functions required for the provision of service is indispensable. However, there are few studies on control networks for BcN or NGN, and therefore we need to carefully consider the architecture and functions of the control network. The main purpose of this paper is therefore to present a BcN control network architecture and its design methodology. The network design process includes capacity and expense calculation process of control systems and control links, which enables the estimation of the overall network building cost. A reliability analysis for the control network is performed in detail based on various system redundancy policies. The proposed design methodology is expected to be utilized in the design of BcN control networks prior to field deployment.     

A Review of the Pharmacological Activities and Recent Synthetic Advances of γ-Butyrolactones

γ-Butyrolactone, a five-membered lactone moiety, is one of the privileged structures of diverse natural products and biologically active small molecules. Because of their broad spectrum of biological and pharmacological activities, synthetic methods for γ-butyrolactones have received significant attention from synthetic and medicinal chemists for decades. Recently, new developments and improvements in traditional methods have been reported by considering synthetic efficiency, feasibility, and green chemistry. In this review, the pharmacological activities of natural and synthetic γ-butyrolactones are described, including their structures and bioassay methods. Mainly, we summarize recent advances, occurring during the past decade, in the construction of γ-butyrolactone classified based on the bond formation in γ-butyrolactone between (i) C5-O1 bond, (ii) C4-C5 and C2-O1 bonds, (iii) C3-C4 and C2-O1 bonds, (iv) C3-C4 and C5-O1 bonds, (v) C2-C3 and C2-O1 bonds, (vi) C3-C4 bond, and (vii) C2-O1 bond. In addition, the application to the total synthesis of natural products bearing γ-butyrolactone scaffolds is described.     

Effects of ratio variation in substrate and micro porous layer penetration on polymer exchange membrane fuel cell performance

A gas diffusion layer (GDL) facilitates the diffusion of reactant gas and the discharge of the generated water. The GDL performs various functions, such as conducting heat and electrons generated by electrochemical reactions and providing mechanical support for the catalyst layer. In this study, the effects of ratio variation in the substrate and microporous layer (MPL) penetration region on the proton exchange membrane fuel cell (PEMFC) performance were investigated. Furthermore, the reasons for these performance tendencies are explained based on the thermogravimetric analysis, contact angle, scanning electron microscopy, mercury porosimetry, electrical resistance, electrochemical impedance spectroscopy, and capillary pressure gradient. The experimental results indicate that the MPL penetration ratio within 15–20% of the total GDL thickness and the combined ratio of the MPL and MPL penetration within 35–40% is the best for the overall PEMFC performance. In addition, when the substrate ratio is excessively low, water flooding substantially occurs in the substrate, and this accumulated water functions as a back pressure, causing severe capillary condensation in the MPL penetration region and thus depriving the supply of the reactant gas.     

Decontamination of uranium-contaminated waste oil using supercritical fluid and nitric acid

The waste oil used in nuclear fuel processing is contaminated with uranium because of its contact with materials or environments containing uranium. Under current law, waste oil that has been contaminated with uranium is very difficult to dispose of at a radioactive waste disposal site. To dispose of the uranium-contaminated waste oil, the uranium was separated from the contaminated waste oil. Supercritical R-22 is an excellent solvent for extracting clean oil from uranium-contaminated waste oil. The critical temperature of R-22 is 96.15 °C and the critical pressure is 49.9 bar. In this study, a process to remove uranium from the uranium-contaminated waste oil using supercritical R-22 was developed. The waste oil has a small amount of additives containing N, S or P, such as amines, dithiocarbamates and dialkyldithiophosphates. It seems that these organic additives form uranium-combined compounds. For this reason, dissolution of uranium from the uranium-combined compounds using nitric acid was needed. The efficiency of the removal of uranium from the uranium-contaminated waste oil using supercritical R-22 extraction and nitric acid treatment was determined.     

An experimental study on after-fracture redundancy of continuous span two-girder bridges

This paper presents the results of an experimental test and numerical analysis of the after-fracture redundancy of two-girder continuous span bridges. Two test specimens that are commonly composed of two steel-plate girders and concrete deck have a fractured section in one of the two girders, which is artificially set up by making an entire cut along the web and bottom flange of the girder. To demonstrate the effect of bottom lateral bracings on the after-fracture redundancy of two-girder bridge system, one of the two test specimens includes a lateral bracing system between the girder bottom flanges but the other does not. The bend-loading test was conducted on the bridge specimens up to the collapse state. The test results revealed that the ultimate bending behaviors of the bridge specimens are considerably different from each other and the load carrying capacity could be increased as much as 20% when the bottom lateral bracings are installed. The numerical analysis of the test specimens indicates that the bottom lateral bracings play a substantial role in the load redistribution process from the severely fractured girder to the intact girder, making a considerable contribution to the load-carrying capacity of the after-fracture two-girder bridges. In the last part, the after-fracture redundancy was quantitatively evaluated for a prototype example bridge and some conclusions were drawn.     

Effects of microporous layer penetration ratio and substrate carbonization temperature on the performance of proton exchange membrane fuel cells

The gas diffusion layer (GDL) is composed of a microporous layer (MPL) and a substrate; this substrate is generally fabricated from carbon fiber, carbonized resin, and polytetrafluoroethylene. When the MPL penetrates deeper into the substrate, the porosity and pore size of the GDL decrease, and the tortuosity increases; this leads to a reduction in the water discharge capability of the GDL. In this study, the MPL penetration ratio over the total GDL thickness was controlled using three different substrate manufacturing methods. These manufacturing methods for preventing the MPL from penetrating deeper into the substrate were based on the carbon fiber content within the substrate, the amount of carbonized resin coating on the substrate, and the approach used for loading the MPL. Furthermore, the GDLs were manufactured at different carbonization temperatures to investigate the effects of the carbonization temperature of the substrate on the performance of the proton-exchange membrane fuel cell.