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김효수,조경임 대한심장학회 2013 Korean Circulation Journal Vol.43 No.5
Background and Objectives: An association between chronic stress and cardiovascular diseases has been described, but the underlying mechanisms have not been fully elucidated. We investigate the impact of perceived stress on the left ventricular (LV) and endothelial functions in postmenopausal women. Subjects and Methods: We investigated 64 consecutive postmenopausal women (mean age 56.7±9.7 years) with atypical chest pain and chronic stress. Patients with coronary heart disease were excluded. Global and segmental longitudinal deformation parameters of LV were used as parameters to assess myocardial function and brachial flow-mediated dilatation (FMD) was used to assess the endothelial function, and patients were analyzed by the Symptom Checklist 90 Revised (SCL-90-R) to determine emotional stress. The study partici-pants were divided into two groups, based on global severity index (GSI): ≥50 (group A, n=27) or <50 (group B, n=37). Results: Although there were no significant differences in LV geometry or myocardial performance indices between the groups, global LV strain was significantly reduced in group A compared to group B (-16.6 ±2.7% vs. -19.1±1.9%, p=0.001). There were also significant differ-ences in the value of reactive FMD (6.6±2.2% vs. 9.5±2.9%, p<0.001), and same result was observed for nitroglycerine-induced dilatation (14.6±4.7% vs. 18.0±5.8%, p=0.016). Multivariate linear regression analysis showed that GSI was the only significant attributor to global LV strain (β=0.149, p=0.008) and reactive FMD (β=-0.200, p=0.041). Conclusion: Chronic emotional stress may exert negative effects on the LV and endothelial functions, which may be associated with the severity of stress. This study provides a possible mechanism by which stress is associated with an increased risk of cardiovascular dys-function.
하향링크 무선 통신 시스템에서의 Inter-cell DCA 알고리즘
김효수,김동회,박승영 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.7
In OFDMA (Orthogonal Frequency Division Multiple Access) system that frequency reuse factor is 1, as the same channels in the neighborhood cells creates inter-cell co-channel interference which provides a resource underutilization problem, channel allocation schemes to minimize inter-cell interference have been studied. This paper proposes a new CNIR (Carrier to Noise and Interference Ratio)-based distributed Inter-cell DCA (Dynamic Channel Allocation) algorithm in the OFDMA environment with frequency reuse factor of 1. When a channel allocation is requested, if there is not a free channel in home cell or the available free channels in home cell do not satisfy a required threshold value, the proposed Inter-cell DCA algorithm finds CNIR values of available free channels in the neighborhood cells and then allocates a free channel with maximum CNIR value. Through the simulationresults, we find that the proposed scheme decreases both new call block rate and forced termination rate due to new call generation at the same time because it increases channel allocation probability. 주파수 재 사용률이 1인 OFDMA(Orthogonal Frequency Division Multiple Access) 시스템에서는 인접한 셀에서 동일채널을 사용하는 것은 셀 간 간섭(Inter-cell-Interference)이 발생하므로 셀 간 간섭을 최소로 하는 채널할당이 이루어져야 한다. 본 논문에서는 OFDMA환경에서 새로운 최대 CNIR(Carrier to Noise and Interference Ratio) 기반의 분산형 Inter-cell DCA (Dynamic Channel Allocation) 알고리즘을 제안한다. 제안된 Inter-cell DCA 알고리즘은 자신의 셀에서 채널할당 요구 시 자신의 셀 내에서 채널이 포화상태이거나 할당 가능한 채널이 남아 있지만 주변 셀 간섭으로 인해 기준 CNIR 문턱치 값을 만족하지 못할 경우에도 인접한 셀의 할당 가능한 채널들의 CNIR을 검색하여 최대값을 갖는 채널을 할당하는 방법이다. 제안된 방법은 채널 할당 확률을 높여 신규호 블록율과 신규호 생성에 의한 기존채널의 강제 종료율을 동시에 감소시켜 시스템 수율을 향상시킬 수 있음을 시뮬레이션을 통해 확인하였다.