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백정우,안수한 한국통계학회 2014 Journal of the Korean Statistical Society Vol.43 No.3
In this paper, we analyze Markov modulated fluid flow processes with one-sided phtypejumps using the completed graph and also through the limits of coupled queueingprocesses to be constructed. For the models, we derive various results on time-dependentdistributions and distributions of first passage times, and present the Riccati equations thattransform matrices of the first return times to 0 satisfy. The Riccati equations enable usto compute the transform matrices using Newton’s method which is known very fast andstable. Finally,wepresent some duality results between the model with ph-type downwardjumps and the model with ph-type upward jumps. This paper contains extended results ofAhn (2009) and probabilistic interpretations given by the completed graphs.
A production–inventory system with a Markovian service queue and lost sales
백정우,문승기 한국통계학회 2016 Journal of the Korean Statistical Society Vol.45 No.1
We study an (s, S) production–inventory system with an attached Markovian service queue. A production facility gradually replenishes items in the inventory based on the (s, S) scheme, and the production process is assumed to be a Poisson process. In addition to the production–inventory system, c servers process customers that arrive in the system according to the Poisson process. The service times are assumed to be independent and identically distributed exponential random variables. The customers leave the system with exactly one item at the service completion epochs. If an item is unavailable, the customers cannot be served and must wait in the system. During this out-of-stock period, all newly arriving customers are lost. A regenerative process is used to analyze the proposed model. We show that the queue size and inventory level processes are independent in steadystate, and we derive an explicit stationary joint probability in product form. Probabilistic interpretations are presented for the inventory process. Finally, using mean performance measures, we develop cost models and show numerical examples.
Markov-modulated fluid flow model with server maintenance period
백정우,이호우,안수한 한국통계학회 2020 Journal of the Korean Statistical Society Vol.49 No.2
We consider a Markov-modulated fluid flow model with server maintenance period. As soon as the fluid level reaches zero, the server begins a maintenance period of a random length. During the maintenance period, fluid arrives from outside depending on the state of the background Markov process and the level increases either vertically or linearly. This model can be applied to various real-world systems such as inventory systems and production systems. We first derive the distribution of the fluid level and the mean performance measures. Then, we present some numerical examples to show the effect of the maintenance time.
Switchable Printed Yagi-Uda Antenna with Pattern Reconfiguration
백정우,표성민,이태학,김영식 한국전자통신연구원 2009 ETRI Journal Vol.31 No.3
A switchable Yagi-Uda antenna prototype with radiation pattern reconfiguration is presented in this letter. The proposed reconfigurable antenna is based on the concept of switching between the reflector and director of a Yagi-Uda antenna using a radio frequency PIN diode. As a result, the minimum/maximum radiation can be steered towards desired signals or away from interfering signals in opposite directions. The measured 10 dB impedance bandwidth and gain are 210 MHz (7%) and 8.02 dBi at 3 GHz, respectively. Details of the antenna design and its performance are described and empirically analyzed.
백정우,심재우,박진홍 한국물리학회 2015 Current Applied Physics Vol.15 No.7
Although numerous studies have been previously reported for the formation of Ge pen junctions, there is still a lack of research on Ge junctions formed by solid-phase diffusion doping, which typically uses the diffusion phenomenon of phosphorus (P) atoms from InGaP for the fabrication of a Ge n+/p subcell in a III eV multi-junction cell. Here, we investigate the characteristics of Ge n+/p junctions achieved by the InGaP-based diffusion technique at 450-650 ℃ with SIMS, ECV, and J-V analyses. In addition, through a multiple error function fitting method, diffusivity, peak position, and activation energy values are accurately estimated from raw In/Ga/P/Ge SIMS profiles. The extracted activation energy values for In/Ga/ P atoms are much lower than previously reported, indicating that a faster diffusion phenomenon occurs during the simultaneous diffusion of In/Ga/P into Ge. A non-annealed InGaP-deposited junction shows Ohmic behavior with a high current density because of leakage currents by many interfacial point defects. Although numerous studies have been previously reported for the formation of Ge pen junctions, there is still a lack of research on Ge junctions formed by solid-phase diffusion doping, which typically uses the diffusion phenomenon of phosphorus (P) atoms from InGaP for the fabrication of a Ge n+/p subcell in a III eV multi-junction cell. Here, we investigate the characteristics of Ge n+/p junctions achieved by the InGaP-based diffusion technique at 450-650 ℃ with SIMS, ECV, and J-V analyses. In addition, through a multiple error function fitting method, diffusivity, peak position, and activation energy values are accurately estimated from raw In/Ga/P/Ge SIMS profiles. The extracted activation energy values for In/Ga/ P atoms are much lower than previously reported, indicating that a faster diffusion phenomenon occurs during the simultaneous diffusion of In/Ga/P into Ge. A non-annealed InGaP-deposited junction shows Ohmic behavior with a high current density because of leakage currents by many interfacial point defects. After a 550 ℃ anneal, the current density is reduced by 3-4 orders of magnitude and a small on/ off-current ratio is obtained. Compared to this 550 ℃ annealed junction, a current density increases ~10 times in the 650 ℃ sample due to an increased n-type carrier concentration.