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Park J.,Korea Institute of Industrial Technology
Journal of Lightwave Technology | Year: 2010

We demonstrate that large-area organic light-emitting diodes (OLEDs) exhibit slow dynamic response due to their capacitor-like behaviors. In particular, the discharge dynamics of large-area OLEDs is observed to be relatively slower, compared with the charge dynamics. To find ways to increase the response speed of large-area OLEDs, we make an in-depth study of transient electroluminescence (EL) of OLEDs in response to voltage pulses (i.e., pulse separation), device configurations (i.e., device length), and various material parameters (e.g., carrier mobility, exciton lifetime, and energy level offset). The EL response speed can be increased by applying high bias voltage and reducing the device length. Meanwhile, the pulse separation affects the response speed of the second pulse. As the pulse separation is decreased, the ratio of the delay time of the second pulse to the delay time of the first pulse is found to be reduced, whereas the ratio of the peak luminance of the second pulse to the peak one of the first pulse is getting increased. We have also shown that the dependence of the delay time on the carrier mobility, exciton lifetime, and energy level offset is less pronounced. This study may provide design guidelines of OLEDs for practical applications including ac-driven displays and next-generation visible-light communications (VLCs). © 2010 IEEE.

Jin S.H.,Korea Advanced Institute of Science and Technology | Kim D.H.,Korea Institute of Industrial Technology | Jun G.H.,Korea Advanced Institute of Science and Technology | Hong S.H.,Korea Advanced Institute of Science and Technology | Jeon S.,Korea Advanced Institute of Science and Technology
ACS Nano | Year: 2013

The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1-3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (ca. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the amine-functionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization. © 2012 American Chemical Society.

Kwon J.-W.,Korea Institute of Industrial Technology | Chwa D.,Ajou University
IEEE Transactions on Robotics | Year: 2012

This paper proposes a hierarchical formation control using a target tracking control law based on the vector field method such that a decentralized and flexible formation control can be achieved without additional motion planning. Previously, many researchers have dealt with the control laws for the rigid formation, where the line of sight toward the leader is controlled for the leader-follower formation control. However, a width change or a collision of the formation can occur since a limited motion of the rigid formation can occur when the formation control maintains the line of sight. Therefore, the formation of multiple mobile robots is required to be flexible, keeping the width and curvature of the formation. To this end, a formation control law based on a vector field method is proposed, and a hierarchical formation structure is introduced in such a way that it consists of a line formation and a column formation based on the leader-follower formation strategy. First, a subgroup, which consists of several robots, is generated using the line formation, and then, the overall formation structure is constructed from several subgroups using the column formation. Finally, we show the stability of the whole formation. The stability analysis and simulation results of the proposed hierarchical formation control using this vector field method are included to demonstrate the practical applicability of the proposed method. © 2012 IEEE.

An electromagnetic wave shielding sheet including a carbon composite fiber and manufactured by electrospinning, and a method of manufacturing the same are disclosed. More particularly, an electromagnetic wave shielding sheet includes a carbon composite fiber having a core-shell structure and a resin, and the core-shell structure includes an outer shell including a carbon fiber, and a core including metal nano particles arranged in a length direction of the carbon fiber in the outer shell. The electromagnetic wave shielding sheet includes metal nano particles as electromagnetic wave shielding materials in a carbon fiber, and the oxidation of a metal may be prevented, conductivity in a length direction of the carbon fiber may be secured, and the sheet may be applied to various industrial fields as an electromagnetic shielding material.

Korea Institute of Industrial Technology | Date: 2014-05-27

Disclosed are a magnesium mother alloy, a manufacturing method thereof, a metal alloy using the same, and a method of manufacturing the metal alloy. In particular, there are provided a magnesium mother alloy with improved oxidation and ignition properties, and a manufacturing method thereof, and also provided a metal alloy with low cost that is suitable for design purposes using the magnesium mother alloy, and a method of manufacturing the metal alloy. The magnesium mother alloy includes a plurality of magnesium grains, and scandium dissolved in the magnesium grains, or a scandium compound crystallized at grain boundaries which are not inside but outside the magnesium grains. Also, the metal alloy suitable for design purposes is manufactured at low cost by adding the magnesium mother alloy containing scandium into a magnesium alloy or an aluminum alloy.

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