Youngho Park

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Terminal-based quality of Service (QoS) measurement method for the wireless internet services is proposed. Based on application interface method, which mechanism is sharing the service quality measurement data between the applications, we derive realistic system parameters such as average access time and throughput, and then propose a terminal-based quality(More)
The numerical estimation of seismic isolation (SI) system with frictional bearing implies an exact solution of pertinent equations of motion. Rigid-perfectly plastic model is widely used technique to approximate the relationship of frictional force-displacement. This paper presents a direct treatment of equations of motion with prediction scheme for(More)
A novel simulation model for the dose distribution of moving targets for high-energy photons was analyzed using the EGSnrc Monte Carlo simulation. We provide here a fundamental numerical framework for the calculation of doses delivered to moving tissues in respiratory systems with improved accuracy. A spherical object with periodic motions inside a water(More)
We propose and demonstrate evanescently-decoupled, solid-angle-optimized distributed Bragg reflectors (DBRs) for AlGaInP light-emitting diodes (LEDs). The thickness of each DBR layer is tuned to the wavelength slightly longer than the emission peak of the active medium in order to maximize the radiated power integrated over the top surface. In addition, to(More)
A new fully secure ciphertext-policy attributed based encryption (CP-ABE) scheme with high expressibity access policy is presented. Our CP-ABE scheme uses tree-based access structure which includes AND, OR, threshold and NOT gates which granted high degree of expressibility for encryptor to make an access policy. Moreover, our scheme achieves full security(More)
PURPOSE To measure the absorbed dose rate to water of (60)Co gamma rays of a Gamma Knife Model C using water-filled phantoms (WFP). METHODS AND MATERIALS Spherical WFP with an equivalent water depth of 5, 7, 8, and 9 cm were constructed. The dose rates at the center of an 18-mm helmet were measured in an 8-cm WFP (WFP-3) and two plastic phantoms. Two(More)