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응급실을 내원한 구강악안면외과 안면골 골절 환자의 변화에 대한 비교 연구
신상훈,성화식,강영훈,황대석,김용덕,김욱규,김종렬,정인교 부산대학교 병원 암연구소 2008 부산대병원학술지 Vol.- No.24
Although there have been many clinical studies about the facial trauma in the recent as well as in the past, severity and frequency of facial trauma are reported multifarious. It seemed to be because of variety of social, cultural, and environmental factors, and the view point of investigators. In this study, we investigated about the patients visiting emergency room during recent 4 years(2004-2007), and compared with retrospective study during former 10 years(1992-1996, 1999-2003) in Dept. OMS Pusan National University Hospital. We assessed the cause, type, demographic, etc, and analyzed alterations of facial bone fractures during past 3 periods. The results were as follows. The total number of patients was increased. 429 patients treated for maxillofacial fractures between January 1992 and December 1996, 466 patients treated between January 1992 and December 1996 and 764 patients treated between January 2004 and December 2007. The male-to-female ratio were 4.6:1, 3.9:1, and 4.16:1, respectively. Patient in the age groups of 10-19 years and 20-29 years increased in the latter two periods. Assaults and falls are decreased gradually, but slip down s are increased. Traffic accidents are still major cause of facial trauma. The mandibular fractures showed the highest incidence thorought three periods. Symphysis fractures of mandible was increased and condyle fractures of mandible was drecreased in the third period.
POWER TAIL ASYMPTOTIC RESULTS OF A DISCRETE TIME QUEUE WITH LONG RANGE DEPENDENT INPUT
Hwang, Gang-Uk,Sohraby, Khosrow Korean Mathematical Society 2003 대한수학회지 Vol.40 No.1
In this paper, we consider a discrete time queueing system fed by a superposition of an ON and OFF source with heavy tail ON periods and geometric OFF periods and a D-BMAP (Discrete Batch Markovian Arrival Process). We study the tail behavior of the queue length distribution and both infinite and finite buffer systems are considered. In the infinite buffer case, we show that the asymptotic tail behavior of the queue length of the system is equivalent to that of the same queueing system with the D-BMAP being replaced by a batch renewal process. In the finite buffer case (of buffer size K), we derive upper and lower bounds of the asymptotic behavior of the loss probability as $K\;\longrightarrow\;\infty$.
Design and Analysis of Optimal Random Access Policies in Cognitive Radio Networks
Gang Uk Hwang,Roy, S. IEEE 2012 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.60 No.1
<P>In this paper, we consider a time slotted cognitive radio network where multiple secondary users (SUs) contend to access wireless channels. We propose and analyze a channel access policy where each secondary user stochastically determines whether to access a wireless channel (or not) based on a given access probability. In our analysis we consider two extreme cases - where all SUs a) possess full information and b) have no information regarding idle channels. We propose to obtain the access probabilities that minimize the steady-state queue length tail probabilities in the two extreme cases based on Effective Bandwidth theory. Our analysis provides an insight on how to design optimal channel access policies in the two extreme cases. We also show how the optimal channel access policies of two extreme cases are related with each other. Some numerical examples are provided to validate our analysis and investigate the performance behaviors of the optimal channel access policies.</P>
PERFORMANCE OF THE IEEE 802.11 DISTRIBUTED COORDINATE FUNCTION
Gang Uk Hwang,Min Young Chung,Yutae Lee 한국산업응용수학회 2005 한국산업응용수학회 학술대회 논문집 Vol.- No.-
In this paper, we consider a cluster of N identical IEEE 802.11 DCF (Distributed Coordinate Function) terminals with RTS/CTS mechanism, each of which is assumed to be saturated. For performance analysis, we propose a simple and efficient mathematical model to derive the statistical characteristics of the cluster such as the inter-transmission time distribution of packets and the service time distribution (the inter-transmission time distribution of successful transmissions) of the IEEE 802.11 DCF cluster. We provide simulation results to show the validity of our analytic results and show that analytic results and simulation results are well matched.
MAC DELAY ANALYSIS OF THE IEEE 802.11 DISTRIBUTED COORDINATE FUNCTION
Gang Uk Hwang,Min Young Chung,Yutae Lee 한국산업응용수학회 2006 한국산업응용수학회 학술대회 논문집 Vol.1 No.1
In this paper, we consider a cluster of N identical IEEE 802.11 DCF (Distributed Coordinate Function) terminals with RTS/CTS mechanism, each of which is assumed to be saturated. we develop a mathematical model for the packet transmission processes of the IEEE 802.11 cluster and analyze the MAC (Medium Access Control) delay of the IEEE 802.11 DCF under saturation. Since the packet delay of a terminal largely depends on the medium access delay, we believe our model and anaysis will be quite useful in practice. Simulation results are provided to show the validity of our analytic results.
An Efficient Power Saving Mechanism for Delay-Guaranteed Services in IEEE 802.16e
PARK, Yunju,HWANG, Gang Uk The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.1
<P>As the IEEE 802.16e Wireless Metropolitan Access Network (WMAN) supports the mobility of a mobile station (MS), increasing MS power efficiency has become an important issue. In this paper, we analyze the sleep-mode operation for an efficient power saving mechanism for delay-guaranteed services in the IEEE 802.16e WMAN and observe the effects of the operating parameters related to this operation. For the analysis we use the <I>M</I>/<I>GI</I>/1/<I>K</I> queueing system with multiple vacations, exhaustive services and setup times. In the analysis, we consider the power consumption during the wake-mode period as well as the sleep-mode period. As a performance measure for the power consumption, we propose the power consumption per unit time per effective arrival which considers the power consumption and the packet blocking probability simultaneously. In addition, since we consider delay-guaranteed services, the average packet response delay is also considered as a performance measure. Based on the performance measures, we obtain the optimal sleep-mode operation which minimizes the power consumption per unit time per effective arrival with a given delay requirement. Numerical studies are also provided to investigate the system performance and to show how to achieve our objective.</P>