• Journal of Korea Multimedia Society
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• v.14 no.1
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• pp.54-75
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• 2011

PoC(Push-to-talk Over Cellular) is an integrated technology of group voice calls, video calls and internet based multimedia services. If a PoC user can not participate in the PoC session for various reasons such as an emergency situation, lack of battery capacity, then the user can use the PoC Box which has a similar functionality to the MM Box in the MMS(Multimedia Messaging Service). The RTSP(Real-Time Streaming Protocol) method is recommended to be used when there is a transmission session between the PoC box and a terminal. Since the existing VOD service uses a wired network, the packet size of RTSP-based VOD service is huge, however, the PoC service has wireless communication environments which have general characteristics to be used in RTSP method. Packet loss in a wired communication environments is relatively less than that in wireless communication environment, therefore, a buffering latency occurs in PoC service due to a play-out delay which means an asynchronous play of audio & video contents. Those problems make a user to be difficult to find the information they want when the media contents are played-out. In this paper, the following techniques and methods were proposed and their performance and superiority were verified through testing: cross-over dual reception buffering technique, advance partition multi-reception buffering technique, and on-demand multi-reception buffering technique, which are designed for effective picking up of information in media content being transmitted in short amount of time using RTSP when a user searches for media, as well as for reduction in playback delay; and same-priority packetization transmission method and priority-based packetization transmission method, which are media data packetization methods for transmission. From the simulation of functional evaluation, we could find that the proposed multiple receiving buffering and packetizing methods are superior, with respect to the media retrieval inclination, to the existing single receiving buffering method by 6-9 points from the viewpoint of effectiveness and excellence. Among them, especially, on-demand multiple receiving buffering technology with same-priority packetization transmission method is able to manage the media search inclination promptly to the requests of users by showing superiority of 3-24 points above compared to other combination methods. In addition, users could find the information they want much quickly since large amount of informations are received in a focused media retrieval period within a short time.

• Progress in Medical Physics
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• v.20 no.3
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• pp.132-138
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• 2009

Studies on target motion in 4-dimensional radiotherapy are being world-widely conducted to enhance treatment record and protection of normal organs. Prediction of tumor motion might be very useful and/or essential for especially free-breathing system during radiation delivery such as respiratory gating system and tumor tracking system. Neural network is powerful to express a time series with nonlinearity because its prediction algorithm is not governed by statistic formula but finds a rule of data expression. This study intended to assess applicability of neural network method to predict tumor motion in 4-dimensional radiotherapy. Scaled Conjugate Gradient algorithm was employed as a learning algorithm. Considering reparation data for 10 patients, prediction by the neural network algorithms was compared with the measurement by the real-time position management (RPM) system. The results showed that the neural network algorithm has the excellent accuracy of maximum absolute error smaller than 3 mm, except for the cases in which the maximum amplitude of respiration is over the range of respiration used in the learning process of neural network. It indicates the insufficient learning of the neural network for extrapolation. The problem could be solved by acquiring a full range of respiration before learning procedure. Further works are programmed to verify a feasibility of practical application for 4-dimensional treatment system, including prediction performance according to various system latency and irregular patterns of respiration.

• Nuclear Medicine and Molecular Imaging
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• v.43 no.5
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• pp.459-467
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• 2009

Purpose: The maximum likelihood-expectation maximization (ML-EM) is the statistical reconstruction algorithm derived from probabilistic model of the emission and detection processes. Although the ML-EM has many advantages in accuracy and utility, the use of the ML-EM is limited due to the computational burden of iterating processing on a CPU (central processing unit). In this study, we developed a parallel computing technique on GPU (graphic processing unit) for ML-EM algorithm. Materials and Methods: Using Geforce 9800 GTX+ graphic card and CUDA (compute unified device architecture) the projection and backprojection in ML-EM algorithm were parallelized by NVIDIA's technology. The time delay on computations for projection, errors between measured and estimated data and backprojection in an iteration were measured. Total time included the latency in data transmission between RAM and GPU memory. Results: The total computation time of the CPU- and GPU-based ML-EM with 32 iterations were 3.83 and 0.26 see, respectively. In this case, the computing speed was improved about 15 times on GPU. When the number of iterations increased into 1024, the CPU- and GPU-based computing took totally 18 min and 8 see, respectively. The improvement was about 135 times and was caused by delay on CPU-based computing after certain iterations. On the other hand, the GPU-based computation provided very small variation on time delay per iteration due to use of shared memory. Conclusion: The GPU-based parallel computation for ML-EM improved significantly the computing speed and stability. The developed GPU-based ML-EM algorithm could be easily modified for some other imaging geometries.

• Journal of Korea Game Society
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• v.4 no.4
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• pp.11-18
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• 2004

The on-line games in the past were played by only two persons exchanging data based on one-to-one connections, whereas recent ones (e.g. MMORPG: Massively Multi-player Online Role-playings Game) enable tens of thousands of people to be connected simultaneously. Specifically, Korea has established an excellent network infrastructure that can't be found anywhere in the world. Almost every household has a high-speed Internet access. What made this possible was, in part, high density of population that has accelerated the formation of good Internet infrastructure. However, this rapid increase in the use of on-line games may lead to surging traffics exceeding the limited Internet communication capacity so that the connection to the games is unstable or the server fails. expanding the servers though this measure is very costly could solve this problem. To deal with this problem, the present study proposes the load distribution technology that connects in the form of local clustering the game servers divided by their contents used in each on-line game reduces the loads of specific servers using the load balancer, and enhances performance of sewer for their efficient operation. In this paper, a cluster system is proposed where each Game server in the system has different contents service and loads are distributed efficiently using the game server resource information such as CPU utilization. Game sewers having different contents are mutually connected and managed with a network file system to maintain information consistency required to support resource information updates, deletions, and additions. Simulation studies show that our method performs better than other traditional methods. In terms of response time, our method shows shorter latency than RR (Round Robin) and LC (Least Connection) by about 12%, 10% respectively.

• Sleep Medicine and Psychophysiology
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• v.4 no.1
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• pp.57-65
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• 1997

As jet lag of modern travel continues to spread, there has been an exponential growth in popular explanations of jet lag and recommendations for curing it. Some of this attention are misdirected, and many of those suggested solutions are misinformed. The author reviewed the basic science of jet lag and its practical outcome. The jet lag symptoms stemed from several factors, including high-altitude flying, lag effect, and sleep loss before departure and on the aircraft, especially during night flight. Jet lag has three major components; including external de synchronization, internal desynchronization, and sleep loss. Although external de synchronization is the major culprit, it is not at all uncommon for travelers to experience difficulty falling asleep or remaining asleep because of gastrointestinal distress, uncooperative bladders, or nagging headaches. Such unwanted intrusions most likely to reflect the general influence of internal desynchronization. From the free-running subjects, the data has revealed that sleep tendency, sleepiness, the spontaneous duration of sleep, and REM sleep propensity, each varied markedly with the endogenous circadian phase of the temperature cycle, despite the facts that the average period of the sleep-wake cycle is different from that of the temperature cycle under these conditions. However, whereas the first ocurrence of slow wave sleep is usually associated with a fall in temperature, the amount of SWS is determined primarily by the length of prior wakefulness and not by circadian phase. Another factor to be considered for flight in either direction is the amount of prior sleep loss or time awake. An increase in sleep loss or time awake would be expected to reduce initial sleep latency and enhance the amount of SWS. By combining what we now know about the circadian characteristics of sleep and homeostatic process, many of the diverse findings about sleep after transmeridian flight can be explained. The severity of jet lag is directly related to two major variables that determine the reaction of the circadian system to any transmeridian flight, eg., the direction of flight, and the number of time zones crossed. Remaining factor is individual differences in resynchmization. After a long flight, the circadian timing system and homeostatic process can combine with each other to produce a considerable reduction in well-being. The author suggested that by being exposed to local zeit-gebers and by being awake sufficient to get sleep until the night, sleep improves rapidly with resynchronization following time zone change.

• Sleep Medicine and Psychophysiology
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• v.14 no.1
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• pp.20-25
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• 2007

The present study compared the actigraphic indices between both wrist actigraphies (WATGs), and the sleep estimates between each WATG and nocturnal polysomnography (NPSG) to assess their differences and consistencies. We studied 22 right-handed subjects (mean age $43.9{\pm}13.3\;years$, M：F=14：8) with untreated primary sleep disorders (primary insomnia=8, simple snorer=2, obstructive sleep apnea=12) undergone by overnight both WATGs and NPSG, simultaneously. Comparison and correlation were analyzed between right and left wrist actigraphic data. In the sleep estimates of both WATGs and NPSG, each WATG was compared and correlated with NPSG in sleep period time (SPT), total sleep time (TST), sleep latency (SL), sleep efficiency (SE) and wake time (WT). Sleep indices between both WATGs showed significant positive correlations with no correlations in SL and fragmentation index (FI). There were no differences in sleep indices between both WATGs. SPTs of both WATGs, SL of left WATG, and TST of right WATG showed positively significant correlations, and SE of right WATG did negatively significant correlation in sleep indices between each WATG and NPSG. As each WATG was compared to PSG, SPTs of both WATGs and WT of right WATG were decreased, and TST and SE of right WATG and SL of left WATG were increased. Inconsistent SL and FI between both WATGs indicate that the activities between both WATGs can differentially happen during wake or arousal. Inconsistent sleep estimates between each WATG and NPSG may indicate the limited usefulness in measuring and analyzing one-night sleep by using WATG.

• The KIPS Transactions:PartA
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• v.13A no.2 s.99
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• pp.123-136
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• 2006

The prefetching technique is an effective way to reduce the latency caused memory access. However, excessively aggressive prefetch not only leads to cache pollution so as to cancel out the benefits of prefetch but also increase bus traffic leading to overall performance degradation. In this thesis, a prefetch filtering scheme is proposed which dynamically decides whether to commence prefetching by referring a filtering table to reduce the cache pollution due to unnecessary prefetches In this thesis, First, prefetch hashing table 1bitSC filtering scheme(PHT1bSC) has been shown to analyze the lock problem of the conventional scheme, this scheme such as conventional scheme used to be N:1 mapping, but it has the two state to 1bit value of each entries. A complete block address table filtering scheme(CBAT) has been introduced to be used as a reference for the comparative study. A prefetch block address lookup table scheme(PBALT) has been proposed as the main idea of this paper which exhibits the most exact filtering performance. This scheme has a length of the table the same as the PHT1bSC scheme, the contents of each entry have the fields the same as CBAT scheme recently, never referenced data block address has been 1:1 mapping a entry of the filter table. On commonly used prefetch schemes and general benchmarks and multimedia programs simulates change cache parameters. The PBALT scheme compared with no filtering has shown enhanced the greatest 22%, the cache miss ratio has been decreased by 7.9% by virtue of enhanced filtering accuracy compared with conventional PHT2bSC. The MADT of the proposed PBALT scheme has been decreased by 6.1% compared with conventional schemes to reduce the total execution time.