• Journal of Communications and Networks
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• 제18권3호
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• pp.340-350
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• 2016

The performance of large-scale cognitive radio (CR) networks with secondary users sustained by opportunistically harvesting radio-frequency (RF) energy from nearby primary transmissions is investigated. Using an advanced RF energy harvester, a secondary user is assumed to be able to collect ambient primary RF energy as long as it lies inside the harvesting zone of an active primary transmitter (PT). A variable power (VP) transmission mode is proposed, and an energy-based opportunistic spectrum access (OSA) strategy is considered, under which a secondary transmitter (ST) is allowed to transmit only if its harvested energy is larger than a predefined transmission threshold and it is outside the guard zones of all active PTs. The transmission probability of the STs is derived. The outage probabilities and the throughputs of the primary and the secondary networks, respectively, are characterized. Compared with prior work, the throughput can be increased by as much as 29%. The energy-based OSA strategy can be generally applied to a non-CR setup, where distributed power beacons (PBs) are deployed to power coexisting wireless signal transmitters (WSTs) in a wireless powered sensor network.

• Journal of Communications and Networks
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• 제15권1호
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• pp.102-110
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• 2013

This paper considers a cooperative orthogonal frequency division multiple access (OFDMA)-based cognitive radio network where the primary system leases some of its subchannels to the secondary system for a fraction of time in exchange for the secondary users (SUs) assisting the transmission of primary users (PUs) as relays. Our aim is to determine the cooperation strategies among the primary and secondary systems so as to maximize the sum-rate of SUs while maintaining quality-of-service (QoS) requirements of PUs. We formulate a joint optimization problem of PU transmission mode selection, SU (or relay) selection, subcarrier assignment, power control, and time allocation. By applying dual method, this mixed integer programming problem is decomposed into parallel per-subcarrier subproblems, with each determining the cooperation strategy between one PU and one SU. We show that, on each leased subcarrier, the optimal strategy is to let a SU exclusively act as a relay or transmit for itself. This result is fundamentally different from the conventional spectrum leasing in single-channel systems where a SU must transmit a fraction of time for itself if it helps the PU's transmission. We then propose a subgradient-based algorithm to find the asymptotically optimal solution to the primal problem in polynomial time. Simulation results demonstrate that the proposed algorithm can significantly enhance the network performance.

• ETRI Journal
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• 제43권3호
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• pp.436-446
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• 2021

In this paper, we propose an energy-efficient unmanned aerial vehicle (UAV) relaying network. In this network, the channels between UAVs and ground transceivers are model-free. A UAV acting as a flying relay explores better channels to assist in efficient data delivery between two ground nodes. The full-duplex relaying mode is applied for potential energy efficiency (EE) improvements. With the genetic algorithm, we manage to optimize the UAV trajectory for any arbitrary radio map scenario. Numerical results demonstrate that compared to other schemes (eg, fixed trajectory/speed policies), the proposed algorithm performs better in terms of EE. Additionally, the impact of self-interference on average EE is also investigated.

• 종양간호연구
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• 제12권1호
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• pp.20-26
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• 2012

Purpose: The purpose of this study was to identify the stress and the coping strategies in breast cancer patients and their spouses. Methods: The stress level was measured by the Stress Questionnaire of Andersson & Albertsson (2000). The coping strategies were measured by the modified Lazarus & Folkman's Ways of Coping Questionnaire. The data were collected by a survey sampling 49 couples from one hospital in Seoul. The data were analyzed by t-test, ANOVA and paired t-test. Results: There was no significant differences between the stress level of breast cancer patients and their spouses. The problem-focused coping of breast cancer patients was significant higher than their spouses. The cancer patients and their spouses used problem-focused coping mode more than emotion-focused coping mode. In the problem-focused coping mode, breast cancer patients used two coping strategies - 'seeking information' and 'cognitive reconstruction' - significantly more than their spouses. In emotion-focused coping mode, the breast cancer patients used one coping strategy, 'emotional expression', significantly more than the their spouses. Conclusion: Further study needs to attempt to develop nursing interventions that could improve positive coping strategies.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권2호
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• pp.550-565
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• 2018

Cognitive radio technology is still the key technology of future mobile communication systems. Previous studies have focused on improving spectrum utilization and less energy consumption. In this paper, we propose an Overhead Reduced Scheme (ORS) for green cooperative spectrum sensing. Compared to traditional cooperative sensing scheme, ORS scheme divides the sensing time into three time slots and selects the best multi-mode user to report decisions. In consideration of reporting channel deviation, we derive closed-form expressions for detection probability and false alarm probability of ORS scheme based on Rayleigh fading channel. Simulation results show that ORS scheme can improve the perception accuracy while reducing the perceived delay and energy consumption in the process of perception, so as to realize the green communication.

• 한국정보통신학회논문지
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• 제17권6호
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• pp.1318-1323
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• 2013

본 논문은 비 슬롯 모드 인지 무선망에서 기회적 스펙트럼 접속 방식의 성능을 시뮬레이션을 통해 비교 분석한다. 비교 분석할 두 가지 기회적 스펙트럼 방식은 다음과 같다. 첫 번째 방식은 어떤 채널에서 전송을 성공한 경우 동일한 채널을 다시 센싱하고, 실패한 경우 가장 오래전에 선택했던 채널을 센싱하는 방식이다. 두 번째 방식은 어떤 채널에서 전송에 실패한 경우 동일한 채널을 다시 센싱하고, 성공한 경우 가장 오래전에 선택했던 채널을 센싱하는 방식이다. 본 논문에서는 일차 사용자가 채널을 점유하는 기간에 따라 두 방식 사이의 성능을 비교한다.

• Molecules and Cells
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• 제43권3호
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• pp.276-285
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• 2020

Circadian rhythm is an endogenous oscillation of about 24-h period in many physiological processes and behaviors. This daily oscillation is maintained by the molecular clock machinery with transcriptional-translational feedback loops mediated by clock genes including Period2 (Per2) and Bmal1. Recently, it was revealed that gut microbiome exerts a significant impact on the circadian physiology and behavior of its host; however, the mechanism through which it regulates the molecular clock has remained elusive. 3-(4-hydroxyphenyl)propionic acid (4-OH-PPA) and 3-phenylpropionic acid (PPA) are major metabolites exclusively produced by Clostridium sporogenes and may function as unique chemical messengers communicating with its host. In the present study, we examined if two C. sporogenes-derived metabolites can modulate the oscillation of mammalian molecular clock. Interestingly, 4-OH-PPA and PPA increased the amplitude of both PER2 and Bmal1 oscillation in a dose-dependent manner following their administration immediately after the nadir or the peak of their rhythm. The phase of PER2 oscillation responded differently depending on the mode of administration of the metabolites. In addition, using an organotypic slice culture ex vivo, treatment with 4-OH-PPA increased the amplitude and lengthened the period of PER2 oscillation in the suprachiasmatic nucleus and other tissues. In summary, two C. sporogenes-derived metabolites are involved in the regulation of circadian oscillation of Per2 and Bmal1 clock genes in the host's peripheral and central clock machineries.

• 유통과학연구
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• 제12권6호
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• pp.67-79
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• 2014

Purpose - This study aims to accomplish three major research goals. First, it strives to change consumers' focus from peripheral routes to a central route of public service advertising related to the good health policy, without problematic effects, by influencing consumers' knowledge or involvement. Second, this study examines the elaboration likelihood model (ELM) and construal level theory (CLT). Specifically, we consider that the central route of ELM might correspond with the focal goal of CLT. Third, this study analyzes ELM through CLT. That is, ELM predicted that low involvement would take the peripheral route, and high involvement would take the central route. Research design, data, and methodology - This study consisted of three experiments. The first experiment had a 2×2 between-subject design. The subjects were university students and the research period was approximately one year. The first independent variable was the involvement of the overweight issue; this variable was measured and split by the median. The second independent variable was the temporal distance (near vs. distant future); this variable was manipulated. The second experiment also had a 2×2 between-subject design. The first variable was the involvement of cervical adenocarcinoma prevention, and was considered already manipulated by sex. Specifically, males had a low involvement of the disease, but females had high involvement. The second independent variable was priming (power vs. submissive). Power priming would induce abstract thinking, but submissive priming would take concrete processing. The third experiment had a 2×2×2 between-subject design. The first variable was cognitive depletion, and was manipulated by memorizing 9-digit numbers. The second and third independent variables were involvement and abstract thinking induction, such as prior experiments. Data were collected through questionnaires, and were analyzed by an SPSS program. Major hypotheses were tested by examining the interaction effects through ANOVA. Results - Major findings are as follows. First, even for low-involved consumers in the overweight category, distant future manipulation induced them to focus not on the peripheral route but on the central route of the public service advertisement. This result does not correspond to the typical ELM prediction. Second, under power priming, low-involved males of the cervical adenocarcinoma category focused on the peripheral route because of the induction to abstract thinking. This result replicated the first experiment, and confirmed the theoretical robustness. Third, high-involved females focused not on the central but on the peripheral route under the mixed condition of cognitive depletion and near future manipulation. Depletion consumed cognitive resources, and the processing mode of consumers changed from systematic to heuristic. Conclusions - ELM needs to be complemented through CLT in context of public service good health advertising. Specifically, the involvement of ELM may impact consumers' thinking mode (abstract vs. concrete), and the interaction effects may influence consumers' focus on advertising (central vs. peripheral route). This study's limitations were bounded subjects, limited stimuli, and somewhat weak external validity.

• 공학교육연구
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• 제12권4호
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• pp.150-158
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• 2009

본 연구의 목적은 비실시간 온라인 토론에서 학습자의 자기조절학습전략이 토론 만족도와 참여 메시지 유형에 미치는 효과를 살펴보는 것이다. 본 연구의 결과 분석을 통해 도출된 결론은 다음과 같다. 우선, 비실시간 온라인 토론에서 자기조절학습전략이 토론 만족도에 영향을 주는 것으로 나타났다. 다음으로, 자기조절학습전략이 인지적 차원의 참여 유형 형태에 영향을 주는 것으로 나타났다. 이상의 연구결과를 통해, 비실시간 온라인 토론에서 학습자의 인지적 차원의 참여와 토론 만족 수준의 향상을 위해 자기조절학습전략을 활용할 것이 제안되었다.

• 한국조사연구학회지:조사연구
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• 제1권1호
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• pp.21-43
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• 2000

전화면접을 개별직접면접에 대한 매력적 대안이 될 수 있지만 두 가지 자료 수집방식에서 동일한 결과를 얻을 수 있는지에 대하여는 많은 의문이 제기되어 왔다. 이러한 의문에 대답하기 위해서는 i)전화면접에 대한 피면접자의 선호도, 면접의 속도, 개방질문에 대한 응답의 상세성, 미응답 항목의 비율 등 직접효과 ii) 통계적 추정량 iii) 면접자의 차이와 자료수집양식 등의 관점에서 경험적 문헌검토를 하였다. 이러한 차이는 전화면접에 대한 사회적 소망성 효과, 서베이 질문에 대한 인지능력 및 양식효과와 면접자 효과로 설명될 수 있다.