排序方式: 共有12条查询结果,搜索用时 15 毫秒
1.
Junhyun Cho Hwanyeong Oh Jaeman Park Kyoungdoug Min Eunsook Lee Jy-Young Jyoung 《International Journal of Hydrogen Energy》2014
The mass transport characteristics of a gas diffusion layer (GDL) predominantly affect the performance of a proton exchange membrane (PEM) fuel cell. However, studies examining the transient response related to the GDL are insufficient, although the dynamic behavior of a PEM fuel cell is an important issue. In this study, the effects of the design of a micro porous layer (MPL) on the transient response of a PEM fuel cell are investigated. The MPL slurry density and multiple functional layers are treated as the variable design parameter. The results show that the transient response is determined by the capillary pressure gradient through the GDL. The trade-off relation for the PEM fuel cell performance under low and high humidity conditions due to the hydrophobic GDL is mitigated by designing a reverse capillary pressure gradient in the MPL. 相似文献
2.
Junhyun Cho Hwanyeong Oh Jaeman Park Kyoungdoug Min Eunsook Lee Jy-Young Jyoung 《International Journal of Hydrogen Energy》2014
Although characteristics of the gas diffusion layer (GDL) affect the performance of a proton exchange membrane fuel cell (PEMFC), mass transfer mechanisms inside the GDL and the performance of the PEMFC have not been directly correlated. To determine the design parameters of the GDL, the effects of substrate design of the GDL on performance of a PEMFC are investigated. By adding an active carbon fiber (ACF), which has a high surface area, the substrate is designed to have a different pore size structure. The results show that steady-state and transient responses are determined by capillary pressure gradient characteristics of the GDL made by pore size distribution of the substrate. The small macro-pore functions as water-retaining passage and the large macro-pore functions as water-removal passage. It is concluded that both small and large macro-pore must be present on the substrate to facilitate its function in a wide range of operating conditions. 相似文献
3.
We have investigated the mixing phenomena in a stratified two-layer fluid system where a layer of fresh water is initially
put on top of salty water. When this stabilized system by a salt gradient is heated from below, it becomes unstable by an
onset of convection in the lower layer due to the thermal buoyancy effect. Thereafter the heat and salt is ready to diffuse
into the upper layer through the adjacent diffusive interface. To examine quantitatively the merging process of the two layers
as the destabilizing temperature gradient gets more dominant, we have measured many profiles of temperature and salinity in
both layers by using accurate micro-scale measurement probes. Each run of experiment with several different initial concentrations
of salt is followed until there appears a sudden overturning into a perfect mixing state. The order of thermal Rayleigh number
has been kept as order of 107 around which we have observed uniform temperature and salt profiles in the upper layer without
any external mixing force. Since the employed measuring probes shows good reproducibility and very fast response time to the
variations of the temperature and salt concentration, the mixing phenomena with the double-diffusive convection has been pursued
easily. 相似文献
4.
5.
Sang Hyeon Hong Mikyung Shin Eunsook Park Ji Hyun Ryu Jason A. Burdick Haeshin Lee 《Advanced functional materials》2020,30(26)
The development of bioadhesives has become an emerging research field for tissue sealants, wound dressings, and hemostatic agents. However, assembling hydrogels using bioadhesive‐mediated attachment remains a challenging task. Significantly high water content (>90%) in hydrogels compared to that of biological tissues is the main cause of failure. Considering that hydrogels are primary testing scaffolds mimicking in vivo environments, developing strategies to assemble hydrogels that exhibit diverse properties is important. Self‐healing gels have been reported, but such gels often lack biocompatibility, and two gel pieces should be identical in chemistry for assembly, thus not allowing co‐existence of diverse biological environments. Herein, a mussel‐mimetic cis‐diol‐based adhesive, alginate‐boronic acid, that exhibits pH‐responsive curing from a viscoelastic solution to soft gels is developed. Associated mechanisms are that 1) polymeric diffusion occurs at interfaces utilizing intrinsic high water content; 2) the conjugated cis‐diols strongly interact/entangle with hydrogel chains; 3) curing processes begin by a slight increase in pH, resulting in robust attachment of diverse types of hydrogel building blocks for assembly. The findings obtained with alginate‐boronic acid glues suggest a rational design principle to attach diverse hydrogel building blocks to provide platforms mimicking in vivo environments. 相似文献
6.
For communication between heterogeneous conference systems, it is important to build a conference control protocol independent from signaling protocols. We simulate an XML‐based conference control that is under consideration as a standard mechanism. We describe the framework and operations for easy implementation in heterogeneous conference systems. The simulation results show that the proposed control protocol provides a consistent service for an increasing number of conferences and participants in small to mid‐size centralized conferencing. 相似文献
7.
Junhyun ChoTaehun Ha Jaeman ParkHan-Sang Kim Kyoungdoug Min Eunsook LeeJy-Young Jyoung 《International Journal of Hydrogen Energy》2011,36(10):6090-6098
The transient response characteristics and durability problems of proton-exchange membrane fuel cells are important issues for the application of PEM fuel cells to automotive systems. The gas diffusion layer is the key component of the fuel cell because it directly influences the mass transport mechanism. In this study, the effects of GDL degradation on the transient response of the PEM fuel cell are systematically studied using transient response analysis under different stoichiometric ratios and humidity conditions. With GDLs aged by the accelerated stress test, the effects of hydrophobicity and structural changes due to carbon loss in the GDL on the transient response of PEM fuel cells are determined. The cell voltage is measured according to the sudden current density change. The degraded GDLs that had uneven hydrophobicity distributions cause local water flooding inside the GDL and induce lower and unstable voltage responses after load changes. 相似文献
8.
Seok Joo Koh Eunsook Kim Juyoung Park Shin Gak Kang Ki Shik Park Chee Hang Park 《ETRI Journal》2001,23(3):111-120
For scalable multicast transport, one of the promising approaches is to employ a control tree known as acknowledgement (ACK) tree which can be used to convey information on reliability and session status from receivers to a root sender. The existing tree configuration has focused on a ‘bottom‐up’ scheme in which ACK trees grow from leaf receivers toward a root sender. This paper proposes an alternative ‘top‐down’ configuration where an ACK tree begins at the root sender and gradually expands by including non‐tree nodes into the tree in a stepwise manner. The proposed scheme is simple and practical to implement along with multicast transport protocols. It is also employed as a tree configuration in the Enhanced Communications Transport Protocol, which has been standardized in the ITU‐T and ISO/IEC JTC1. From experimental simulations, we see that the top‐down scheme provides advantages over the existing bottom‐up one in terms of the number of control messages required for tree configuration and the number of tree levels. 相似文献
9.
Haesung A. Lee Eunsook Park Haeshin Lee 《Advanced materials (Deerfield Beach, Fla.)》2020,32(35):1907505
Polydopamine coating, the first material-independent surface chemistry, and its related methods significantly influence virtually all areas of material science and engineering. Functionalized surfaces of metal oxides, synthetic polymers, noble metals, and carbon materials by polydopamine and its related derivatives exhibit a variety of properties for cell culture, microfluidics, energy storage devices, superwettability, artificial photosynthesis, encapsulation, drug delivery, and numerous others. Unlike other articles, this review particularly focuses on the development of material science utilizing polydopamine and its derivatives coatings at the Korea Advanced Institute of Science and Technology for a decade. Herein, it is demonstrated how material-independent coating methods provide solutions for challenging problems existed in many interdisciplinary areas in bio-, energy-, and nanomaterial science by collaborations and independent research. 相似文献
10.
Eunsook Kim Shin Gak Kang Jongwon Choe 《Communications Letters, IEEE》2002,6(10):464-466
A session tree based mechanism provides an efficient method to avoid well-known feedback implosion. However, it is not easy to configure an efficient session tree for IP multicast because it does not provide any explicit membership and routing topology information to the upper layer protocol. Incongruity between a session tree built on the transport layer and the corresponding routing tree on the network layer would incur large cost to handle control messages. This problem can be solved if a router that knows the information of routing topology can support the configuration of a session tree. Thus this letter proposed a router-assistant mechanism which minimizes the change of router functions and allows the routers to assist in providing a reliable multicast transport service 相似文献