Welcome to Epidemiology and Health

The Korean Society of Epidemiology publishes a scholarly journal titled 'Korean Journal of Epidemiology', which announces and discusses the results of epidemiological studies from the past 30 yr. Since its first publication in 1979, the journal has contributed to the advancement of epidemiology as well as the prevention and control of disease, and the promotion of health in Korea

Resource allocation for maximizing outage throughput in OFDMA systems with finite-rate feedback

Previous works on orthogonal frequency division multiple access (OFDMA) systems with quantized channel state information (CSI) were mainly based on suboptimal quantization methods. In this paper, we consider the performance limit of OFDMA systems with quantized CSI over independent Rayleigh fading channels using the rate-distortion theory. First, we establish a lower bound on the capacity of the feedback channel and build the test channel that achieves this lower bound. Then, with the derived test channel, we characterize the system performance with the outage throughput and formulate the outage throughput maximization problem with quantized channel state information (CSI). To solve this problem in low complexity, we develop a suboptimal algorithm that performs resource allocation in two steps: subcarrier allocation and power allocation. Using this approach, we can numerically evaluate the outage throughput in terms of feedback rate. Numerical results show that this suboptimal algorithm can provide a near optimal performance (with a performance loss of less than 5%) and the outage throughput with a limited feedback rate can be close to that with perfect CSI.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000294918800001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicTelecommunicationsSCI(E)1ARTICLEnul

Visually Guided Inter-limb Adaptation During Walking In Children And Adults

Voluntary visually guided movements must be constantly adapted to maintain accuracy. Here we applied principles of visuomotor adaptation to drive inter-limb adaptation of joint kinematics during voluntary, visually guided walking. We tested whether step length symmetry could be adapted and stored after training with mismatched visual feedback on two legs. 17 healthy children (9M/8F, 6-15 yrs) and 8 healthy adults (7M/1F, 26±6 yrs) were tested. We created a computer task where subjects modified step length trial-by-trial to hit virtual targets while walking on a treadmill. The relationship between screen-space and treadmill-space was defined by a visuomotor gain for each leg. Each test consisted of a baseline period (same gain on both legs), an adaptation period (one high gain, one low gain) and a post-adaptation period (same gain). The ‘fast leg’ and ‘slow leg’ refers to the leg adapted with the higher and lower gain, respectively. During the adaptation period, the leg adapted with the higher gain appeared to move fast, and the other leg appeared to move slowly on display. All healthy children and adults tested could rescale step length to maintain endpoint accuracy during visually guided walking. Step length gradually became more asymmetric during adaptation. The fast leg shortened step length (to correct overshoot), and the slow leg lengthened step length (to correct undershoot). In the post-adaptation period, step length asymmetry persisted (after-effect) despite the fact that the gains have returned to normal. The presence of an after-effect indicates storage of a new inter-limb visuomotor calibration. The after-effect was partially washed out after one minute of post-adaptation walking. This study suggests that visually guided inter-limb adaptation can alter step length, a major determinant of gait stability and energetic costs. This may open up new opportunities to correct abnormal, asymmetric walking patterns in children and adults with neurological damage

Matching People And Groups: Recruitment And Selection In Online Games

Massively multiplayer online games (MMOGs) have great potential as sites for research within the social and behavioral sciences and human-computer interaction. This is because “guilds” — semi-persistent groups in online games — are much like groups in real organizations. In this paper, we examine how groups and individuals find appropriate matches and whether appropriate matches lead newcomers to stay longer in their groups in an online game environment. Results from archival data, observation, and survey in the game World of Warcraft (WoW) indicate that different selection methods lead to person-group fit for social and task-oriented characteristics and good fit leads recruits to stay longer in their group. In particular, recruitment of new members to task-oriented guilds was most successful when brief interactions were used whereas recruitment to social-oriented guilds was most successful when probationary periods and referrals were used