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Electrically insulating graphene oxide with various oxygen-functional groups is a novel material as an active layer in resistive switching memories via reduction process. Although many research groups have reported on graphene oxide-based resistive switching memories, revealing the origin of conducting path in a graphene oxide active layer remains a critical challenge. Here nanoscale conductive graphitic channels within graphene oxide films are reported using a low-voltage spherical-aberration-corrected transmission electron microscopy. Simultaneously, these channels with reduced graphene oxide nanosheets induced by the detachment of oxygen groups are verified by Raman intensity ratio map and conductive atomic force microscopy. It is also clearly revealed that Al metallic protrusions, which are generated in the bottom interface layer, assist the local formation of conductive graphitic channels directly onto graphene oxide films by generating a local strong electric field. This work provides essential information for future carbon-based nanoelectronic devices.

Determining the presence of conducting filaments in resistive random access memory with nanoscale thin films is vital to unraveling resistive switching mechanisms. Bistable resistive switching within graphene-oxide (GO)-based resistive memory devices, recently developed by many research groups, has been generally explained by the formation and rupture of conducting filaments induced by the diffusion of metal or oxygen ions. Using a low-voltage spherical aberration-corrected transmission electron microscopy (TEM), we directly observe metallic nanofilaments formed at the amorphous top interface layer with the application of external voltages in an Al/GO/Al memory system. Atomic-resolution TEM images acquired at an acceleration voltage of 80 kV clearly show that the conducting nanofilaments are composed of nanosized aluminum crystalline within the amorphous top interface layer after applying a negative bias (ON state). Simultaneously, we observe the change in the crystallinity of GO films by the back-diffusion of oxygen ions. The oxygen-deficient regions are clearly confirmed by energy-filtered TEM oxygen elemental mapping. This work could provide strong evidence to confirm the resistive switching mechanism previously suggested by our group.

This study represents the effective fire and smoke control in the case of fire in deep underground tunnels, even if the exhaust system can be calculated, the optimal smoke capacity can be determined by establishing technical standards for the transverse ventilation system focusing on the design as a basis for deriving the parameters for utilization. Numerical analyses were performed using the FDS program as a function of the unsteady flow in a deep underground tunnel fire. The analysis results were calculated within 250 m smoke using an inside wind velocity of 0m/s when the capacity of smoke was exhausted, 80 m 3 /s, whereas in case of an internal wind velocity of 3m/s, the

Recently, high-thermal-conductivity graphene and carbon nanotube nanoparticles have attracted particularly close attention from researchers. In the present study, the thermal conductivity and viscosity properties of two kinds of graphene and carbon nanotube nanofluids added to distilled water - two graphenes and carbon nanotubes of differing size - were compared and analyzed. The thermal conductivities of the nanofluids, formulated in the usual manner by adding graphene and carbon nanotube to distilled water and subjecting the mixture to ultrasonic dispersion, were measured by the transient hot-wire method, and the viscosities were determined using a rotational digital viscometer. As a result, we concluded that the nanofluid of small particle diameter of graphene have outstanding properties as heat transfer media, due to their excellent thermal conductivity and viscosity, compared with the other nanofluid.

Nanofluids using Carbon Nanotubes have a excellent thermal characteristic. In this study, for increasing the efficiency of solar collector, the thermal conductivity and viscosity of Ethanol-Oxidized Multi-walled Carbon Nanofluids were measured. Nanofluids were manufactured by ultra-sonic dispersing Oxidized Multi-walled Carbon Nanotubes(OMWCNTs) in ethanol at the rates of 0.0005 ~ 0.1 vol%. The thermal conductivity and viscosity of manufactured nanofluids were measured at the low temperature(), the room temperature() and the high temperature(). For measuring thermal conductivity and viscosity, we used transient hot-wire method and rotational digital viscometer, respectively. As a result, under given temperature conditions, thermal conductivity of the 0.1 vol% nanofluids improved 33.74% (), 33.14% () and 32.36% (), and its viscosity increased by 37.93% (), 31.92% () and 29.42% () than the base fluids.

The co-generation system consisted of gas a turbine, a steam turbine, heat recovery steam generator and a heat exchangers for district heating was investigated in the present study. A back-pressure steam turbine (non-condensing type) was used. A partial load analysis according to the outdoor temperature in winter was conducted and optimal thermal load and power conditions was examined using the commercial computing software Thermoflex. As a result, under a constant thermal load, the power outputs of gas turbine and overall system increased as an outdoor temperature decreased. On the other hand, the reduction in exhaust gas temperature led to the decrease in output of steam turbine. Considering the portion of gas turbine in overall system in terms of the power output, it can be known that the tendency in power output of overall system was similar to that of the gas turbine.

Recently it is widely conducted about the usage of regenerative energy produced during brake periods of railway vehicles. The storage system for regenerative energy using super-capacitor (EDLC:Electric Double Layer Capacitor) is one of those research areas. In the storage systems of the regenerative energy, super-capacitor (EDLC) is used for storage device of modular energy. It is critical to estimate the proper replacement moment for the existed super-capacitor (EDLC) due to the safety of the system. However, there is no standard method to predict the expected life of super-capacitor (EDLC). In this paper, therefore, we propose the method to estimate expected life of super-capacitor by evaluating of internal heating which caused by regenerative current pattern of railway vehicles. With that, we improve the reliability of whole system. Furthermore, it is also addressed to prove that our research is reasonable.

The tunnel, a type of road structure contains more risk than open road due to its characteristic of confined space. When a fire occurs in a tunnel, reduction of visibility, diffusion of toxic gas, temperature rise and oxygen depletion happen as well as psychological impact to the tunnel users,hence, endangering tunnel user's life. Fire in tunnel also damages integrity of tunnel structure, infrastructures and vehicles and financial cost due to the repair and lost business by tunnel closure will be enormous. If a fire occurs in tunnel, control and extraction of the smoke are carried out using the ventilation system. In a longitudinally ventilated tunnel, the principle of smoke management is to push the smoke to the downstream of fire preventing back-layering of smoke to the escape route and safe area. The aim of this study is to find out influence of the jet fan to the smoke dispersion phenomena in the longitudinally ventilated tunnel fire by quantitative measurements. For the study, the scale model experiments are carried out and in order to find out the smoke flow pattern, the PIV technique which uses the Ar-ion laser as a light source is applied. It is expected this study will contribute to understand the smoke dispersion phenomena along with the critical velocity profile of fully developed flow and asymmetric flow. Finally this study will suggest the minimum jet fan installation distance for the stable control of the smoke layer. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".