• 한국전자파학회논문지
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• 제10권6호
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• pp.959-967
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• 1999

본 논문에서는 등간격 선형어레이로 입사하는 다중 인코히어런트 평면파의 도래각을 추정하기 위하여 신 호부각법과 결합된 선형예측방법을 제안한다. 선호부각법의 기본 개념은 Frobenius norm변에서 주어진 추정 행렬에 가장 가까이에 있는 주어진 rank의 공분산 행렬을 찾는 것이다. 선형예측방법은 높은 분해능을 보이나 낮은 신호대 잡음비 환정에서 낮은 통계적 성능을 보이는 것으로 알려져 있다. 이 문제를 해결하기 위하여 선형예측방볍에 신호부각법을 적용하였다. 낮은 신호대 잡음비 환경에서도 제안된 선호부각 선형예측 방법의 성능이 기존의 선형예측방법보다 우수한 통계적 성능을 제공함을 컴퓨터 시율레이션을 통하여 알 수 있었다.

• Journal of applied mathematics & informatics
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• 제39권5_6호
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• pp.601-616
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• 2021

Retrial queueing models have been studied extensively in the literature. These have many practical applications, especially in service sectors. However, retrial queueing models have their own limitations. Typically, analyzing such models involve level-dependent quasi-birth-and-death processes, and hence some form of a truncation or an approximate method or simulation approach is needed to study in steady-state. Secondly, in general, the customers are not served on a first-come-first-served basis. The latter is the case when a new arrival may find a free server while prior arrivals are waiting in the retrial orbit due to the servers being busy during their arrivals. In this paper, we take a different approach to the study of multi-server retrial queues in which the signals are generated in such a way to provide a reasonably fair treatment to all the customers seeking service. Further, this approach makes the study to be level-independent quasi-birth-and-death process. This approach is different from any considered in the literature. Using matrix-analytic methods we analyze MAP/M/c-type retrial queueing models along with Poisson signals in steady-state. Illustrative numerical examples including a comparison with previously published retrial queues are presented and they show marked improvements in providing a quality of service to the customers.

• Smart Structures and Systems
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• 제24권2호
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• pp.173-182
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• 2019

Due to the degradation of beamforming properties at angles close to $0^{\circ}$ to $180^{\circ}$, linear array does not have a complete $180^{\circ}$ inspection range but a smaller one. This paper develops a improved sensor array with two additional sensors above and below the linear sensor array, and presents time difference and two dimensional multiple signal classification (2D-MUSIC) based impact localization for omni-directional localization on composite structures. Firstly, the arrival times of impact signal observed by two additional sensors are determined using the wavelet transform and compared, and the direction range of impact source can be decided in general, $0^{\circ}$ to $180^{\circ}$ or $180^{\circ}$ to $360^{\circ}$. And then, 2D-MUSIC based spatial spectrum formula using uniform linear array is applied for locate accurate position of impact source. When the arrival time of impact signal observed by two additional sensors is equal, the direction of impact source can be located at $0^{\circ}$ or $180^{\circ}$ by comparing the first and last sensor of linear array. And then the distance is estimated by time difference algorithm. To verify the proposed approach, it is applied to a quasi-isotropic epoxy laminate plate and a stiffened composite panel. The results are in good agreement with the actual impact occurring position.

• Journal of Trauma and Injury
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• 제34권2호
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• pp.105-111
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• 2021

Purpose: Open extremity fractures require prompt antibiotic medication and initial debridement surgery to reduce the infection rate and restore functional stabilization. We aimed to report the effects and positive outcomes of a trauma team approach on the management of open extremity fractures in polytrauma patients. Methods: This retrospective review included all polytrauma patients with open extremity fractures admitted between March 2009 and December 2019. Patients were divided into two groups according to whether they were treated before or after the implementation of the trauma team approach (March 2014). We analyzed the outcomes in each group with respect to the time interval until the doctor's arrival, total length of stay in the emergency department, the time interval until initial antibiotic treatment and operation, whether the initial operation was performed within 24 hours, and the rate of deep infections. Results: A total of 123 patients met the inclusion criteria. There were no statistically significant differences in demographic characteristics. The time interval until the doctor's arrival (64.12±49.2 minutes vs. 19.82±15.23 minutes; p=0.035) and initial antibiotic treatment (115.47±72.12 minutes vs. 48.78±30.12 minutes; p=0.023) significantly improved after implementing the trauma team approach. The union rate was not significantly different. However, the time interval until initial debridement, opportunity for initial debridement within 24 hours, and the rate of deep infections demonstrated better results. Conclusions: The reduced time interval until initial antibiotic treatment and debridement could be attributed to the positive effect of the trauma team approach on the management of open extremity fractures in polytrauma patients.

• 전자공학회논문지B
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• 제32B권7호
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• pp.989-1002
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• 1995

In this paper, we propose a new algorithm, so called the Signal Decorrelation via Virtual Translation of Array (SDVTA) algorithm, for estimating the directions of arrival(DOA's) of narrowband coherent signals incident on a general array. An effective procedure is composed of transforming the steering matrix of the original array into that of the virtually translated sensor array and taking the average of the transformed covariance matrices in order to decorrelate the coherent signals. The advantage of this approach is in that 1) it can estimate the DOA's of m-1 coherent signals(M : the number of array sensors) since the effective aperture size is never reduced. 2) a geometry of array is unrestricted for solving the narrowband coherency problem. 3) the efficiency of signal decorrelation does not depend on the phase differences between coherent signals unlike the Coherent Signal Subspace Method (CSM). Simulation results are illustrated to demonstrate the superior performance of this new algorithm in comparison with the normal MUSIC and examine the comparative performance with the various choices of the optimal transformation matrix under coherent signal environments.

• 한국정보통신학회논문지
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• 제18권9호
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• pp.2109-2116
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• 2014

본 논문은 무선랜 시스템에서 성능 향상을 위해, 안테나 빔을 전 방향으로 방사하는 기존의 방법과는 달리, 접속한 단말이 존재하는 방향으로만 안테나 빔을 방사하는 빔포밍 시스템을 설계 및 구현하였다. 해당 시스템은 패치형 배열 안테나를 통해 통신을 하며, DSP(Digital Signal Processor)에서 패킷 타입과 단말의 정보를 퀄컴사의 상용 칩으로부터 제공받아 FPGA(Field Programmable Gate Array)로 전송하는 방식으로 동작한다. DSP와 FPGA의 통신 방식은 데이터 송수신시 생기는 지연을 최소화하기 위해 PCI express(Peripheral Component Interconnect express)를 사용하였다. 단말 고유의 MAC(Media Access Control) 주소를 FPGA에서 저장하고 데이터베이스화함으로써 단말들의 위치를 관리할 수 있도록 하였다. 따라서 해당하는 단말로 패킷을 전송할 때, 추정한 위치로 빔을 방사하여 T/P(throughput)를 높일 수 있다. 단말의 위치는 패치형 배열 안테나를 통해 수신한 단말의 SINR(Signal to Interface plus Noise Ratio)을 프리앰블 구간에서 극대화하는 알고리즘을 사용하여 추정하였다. 제안하는 빔포밍 시스템을 Verilog HDL(Hardware Description Language)을 이용하여 FPGA와 퀄컴사의 상용 칩과 연동하여 구현하였으며 실제 운용 환경에서 시험을 통해 구현된 장비가 일반 AP(Access Point) 보다 더 높은 성능을 보이며 통신하는 것을 확인하였다.

• 대한장애인치과학회지
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• 제6권2호
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• pp.116-119
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• 2010

Trauma to the lips and tongue can occur by accidental self-biting after dental treatment. After local anesthesia, it is likely that the patient may feel painless even in biting the tongue. In case of young children and disabled patients, the dentists should be careful not to bite the tongue. In this report, we present a case of deep lingual laceration due to biting the tongue in the course of dental treatment under general anesthesia. A 33 year-old male was transferred to our hospital to treat tongue laceration. Before 2 hour on arrival, he had received dental care under general anesthesia at a dental hospital for the disabled because of cooperation difficulty and cerebral palsy. During recovery from general anesthesia, he tried to bite his own tongue involuntary. The doctors and nurses tried to prevent the patient from being injured. Despite these efforts, massive bleeding occurred from the injured sites of the tongue. Because we could not communicate with him, we decided to evaluate the extent of the injury and treat the injured sites under general anesthesia. The laceration wound was sutured for nearly 1 hr general anesthesia. During recovery we inserted mouth prop into the oral cavity to prevent further injuries from tongue biting. After full recovery from general anesthesia he didn't try to bite his tongue. After 4 hour admission, he was discharged without other complications.

• 한국정보전자통신기술학회논문지
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• 제8권4호
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• pp.275-280
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• 2015

본 논문에서는 수정된 MUSIC 도래 방향 추정 알고리즘에 대해서 연구 하였다. 수정된 MUSIC 알고리즘은 특이 값 행렬과 베이즈 방법을 적용시켜 공 분산행렬을 최적화 시키고 가중치를 갱신하여 원하는 신호를 추정하는 방법이다. 그리고 MUSCI 알고리즘의 신호 부 공간 방법을 적용시켜 원하는 신호를 정확히 추정하였다. 무상관 신호가 수신 시스템에 입사하면 기존의 MUSIC알고리즘으로 원하는 신호를 추정 할 수 있다. 그러나 일반적으로 수신 시스템에는 상관성 신호가 입사하므로 기존의 MUSIC알고리즘으로 원하는 도래 방향 신호를 추정할 수 있는 능력이 현저히 떨어진다. 모의실험을 통해서 상관성 신호인 경우에 본 연구에서 제안된 MUSIC알고리즘과 기존의 MUSIC알고리즘의 성능을 비교 분석한다.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1616-1625
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• 2019

Measuring occurrence times of random events, aimed to determine the statistical properties of the governing stochastic process, is a basic topic in science and engineering, and has been the subject of numerous mathematical modeling approaches. Often, true statistical properties deviate from measured properties due to the so called dead time phenomenon, where for a certain time period following detection, the detection system is not operational. Understanding the dead time effect is especially important in radiation measurements, often characterized by high count rates and a non-reducible detector dead time (originating in the physics of particle detection). The effect of dead time can be interpreted as a suitable rarefied sequence of the original time sequence. This paper provides a limit theorem for a high rate (diffusion-scale) counter with extendable (Type II) dead time, where the underlying counting process is a renewal process with finite second moment for the inter-event distribution. The results are very general, in the sense that they refer to a general inter arrival time and a random dead time with general distribution. Following the theoretical results, we will demonstrate the applicability of the results in three applications: serially connected components, multiplicity counting and measurements of aerosol spatial distribution.

• 산업경영시스템학회지
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• 제14권24호
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• pp.149-154
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• 1991

The one of the important problems in the design of queueing systems is the decision of the order of service stations. The object of this problem is the decision of the order that minimizes the expected sojourn time per customer in the given arrival process and service time distributions. In this paper, the tandem queueing system in series is studied with the emphasis on the optimal order of the tandem queueing system which has three stations with single servers. In one system, customers arrive at the first station with Poisson process. This system is composed of service stations with a constant, a general distribution and a Exponential distribution is studied. To select the optimal order after the orders of each pair of two stations is decided, it is compared the two orders of system. With this results, total expected delay of the systems which has three stations is compared. The result is the best that service station with constant time is on the first place, then the service station with general distribution and the service station with Exponential distribution is followed. And the other system is consist of service stations with a constant and two probabilistic distributions. In this case, two probabilistic distributions has a non-overlapping feature. It is the optimal order that the service station with constant time is on the first place then the service station with longer service time and the service station with shorter service time is followed.