• Journal of Chest Surgery
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• v.55 no.2
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• pp.101-107
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• 2022

Background: Spread through air spaces (STAS) has recently emerged as a prognostic factor in lung adenocarcinoma, but little is known about the association of STAS and its grade with recurrence in neuroendocrine tumors (NETs). This study investigated the prognostic effect of STAS grade in NETs after curative resection. Methods: Seventy-seven patients were retrospectively reviewed, including 9 with typical carcinoid (TC), 6 with atypical carcinoid (AC), 26 with large cell neuroendocrine carcinoma (LCNEC), and 36 with small cell carcinoma (SCC). STAS was defined as the presence of floating tumor cells within air spaces in the lung parenchyma beyond the edge of the main tumor. STAS was classified as grade 1 or 2 depending on whether it was found within or beyond one ×10 objective lens field away from the main tumor margin, respectively. Results: Fifty-four patients (70%) had STAS, including 22% with TC, 50% with AC, 69% with LCNEC, and 86% with SCC. Patients with STAS had more nodal metastasis, lymphatic and vascular invasion, tumor necrosis, and tumor subtypes other than TC. Among STAS cases, grade 2 STAS was present in 33% of AC, 78% of LCNEC, and 87% of SCC. The 5-year recurrence-free survival (RFS) rate was 81%, 63%, and 35% in patients with no STAS, grade 1, and grade 2 STAS, respectively. Multivariate analysis found that grade 2 STAS was an independent negative prognostic factor for RFS. Conclusion: Although STAS itself was not associated with a poor prognosis, grade 2 STAS was an independent negative prognostic factor for RFS.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.237-245
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• 2007

In this paper, a modified PCF (Point Coordination Function) MAC (Medium Access Control) Protocol is proposed to support the multiple direct link communication between STAs (STAtions) in infrastructure mode IEEE 802.11 wireless LANs. By the proposed MAC protocol, the direct link communication between STAs, which are located within the communication range of each other, is allowed without the use of AP (Access Point) as a relay. Moreover, when multiple direct data communication between STAs can be simultaneously performed with a sufficiently small interference, multiple simultaneous direct link communication is allowed for the efficient use of radio bandwidth. AP polls STAs to grant the transmission opportunities using the direct link communication by transmitting the polling frames to STAs. An efficient polling method for granting the transmission opportunities to STAs is proposed to reduce the number of the polling frame transmissions and enhance the PCF MAC performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1873-1879
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• 2007

As the mobile terminal which uses P2P service increases and it comes to be applied to many fields, mobile agent technology has been applied to P2P and its innovative services has been offered to various fields. However, free mobility of mobile agent technology works like worm, the problem which is contaminated by malicious attacker's attack quickly has appeared and fundamental solution has not been developed yet. This paper proposes STAS (Security Tracking and Auditing Server) system which can offer verification for security of mobile agent in structured P2P environments. Mobile Agent will send data value to STAS via peer so that STAS can verify secure audit and integrity and Mobile agent initiator will obtain the final value of the data from STAS. It can minimize overload of mobile terminal which is occurred by verification of mobile agent and its accomplishment.

• Journal of Korean Institute of Industrial Engineers
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• v.37 no.2
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• pp.89-95
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• 2011

The distributed coordination function (DCF) and point coordination function (PCF) protocols are the basic MAC protocols for legacy IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g and IEEE 802.11n wireless LANs. When the DCF protocol is used for the various versions of IEEE 802.11 wireless LANs, the MAC performance seriously degrades due to the collisions among the stations (STAs) as more and more STAs attempt to transmit their data frames. On the other hand, the PCF MAC performance becomes poor when many STAs exist in IEEE 802.11 wireless LANs, however, only small number of STAs actually attempt to transmit their data frames. In this paper, we propose the algorithm for improving the MAC performance by selectively using the DCF and PCF protocols according to the state of IEEE 802.11 wireless LANs. Numerical examples are presented to show the MAC performance improvement by the selective use of the DCF and PCF protocols according to the network state.

• Journal of the Korean Vacuum Society
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• v.16 no.1
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• pp.7-14
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• 2007

A new horizontal neutron reflectometer has been designed and now under construction at the HANARO, 30 MW research reactor, in Daejon, Korea. We performed simulations of neutron ray-tracing to evaluate the performance of all of the optical components of the instrument with a Monte Carlo technique using McStas. The feasible wavelength of the incident neutron beam is $2.5{\AA}$. It produces a q-range up to $0.126{\AA}^{-1}$ with a supermirror as a deflector. Our studies showed improvement of the performance of the guide tube and monochromators. Although the performance is limited in q-range, it promises to be the first reflectometer in Korea for the study of free surfaces, which is currently in demand.

• The KIPS Transactions:PartA
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• v.16A no.2
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• pp.69-78
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• 2009

One of the most effective way to improve cache performance is to exploit both temporal and spatial locality given by any program executive characteristics. In this paper we present a high performance and low power cache structure with a bank selection mechanism that enhances exploitation of spatial and temporal locality. The proposed cache system consists of two parts, i.e., a main direct-mapped cache with a small block size and a fully associative buffer with a large block size as a multiple of the small block size. Especially, the main direct-mapped cache is constructed as two banks for low power consumption and stores a small block which is selected from fully associative buffer by the proposed bank selection algorithm. By using the bank selection algorithm and three state bits, We selectively extend the lifetime of those small blocks with high temporal locality by storing them in the main direct-mapped caches. This approach effectively reduces conflict misses and cache pollution at the same time. According to the simulation results, the average miss ratio, compared with the Victim and STAS caches with the same size, is improved by about 23% and 32% for Mibench applications respectively. The average memory access time is reduced by about 14% and 18% compared with the he victim and STAS caches respectively. It is also shown that energy consumption of the proposed cache is around 10% lower than other cache systems that we examine.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2007.11a
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• pp.330-340
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• 2007

IEEE 802.11 wireless LANs employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, we propose a dynamic contention window control algorithm using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.32 no.3
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• pp.10-19
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• 2009

Wireless LAN systems have been widely implemented for supporting the wireless internet services especially in the hotspot areas such as hospitals, homes, conference rooms, and so on. Compared with wired LAN systems, wireless LAN systems have the advantages of the users' mobility support and low implementation and maintenance costs. IEEE 802.11 wireless LAN systems employ the backoff algorithm to avoid contentions among STAs when two or more STAs attempt to transmit their data frames simultaneously. The MAC efficiency can be improved if the CW values are adaptively changed according to the channel state of IEEE 802.11 wireless LANs. In this paper, a dynamic contention window control algorithm is proposed using the genetic algorithm to improve the MAC throughput of IEEE 802.11 wireless LANs.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.99-109
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• 2007

IEEE 802.lie is being proposed to improve QoS by IEEE 802.11 working group. HCCA (HCF Controlled Channel Access) a centralized polling based mechanism of IEEE 802.11e, needs a scheduling algorithm that decides on how the available radio resources are allocated to the polled STAs. In IEEE 802.l1e standard Reference Scheduler is presented. Reference Scheduler Polls all STAs in a polling list by the same interval that causes ineffectively frequent polling. It increases not only the overhead but it decreases the TXOP (Transmission Opportunity) utilization. In this paper, we propose the scheduling and admission control algorithm that poll stations depending on the MSI (Maximum Service Interval)o( stations to solve these shortcomings. In our proposed algorithm a station is polled by an interval close to its MSI, so polling overhead decrease and TXOP utilization increases than Reference Scheduler. Simulation results show that our algorithm outperforms Reference Scheduler. Our algorithm maintains higher aggregate throughput and services mere stations than Reference Scheduler.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.11B
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• pp.974-979
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• 2004

In the IEEE 802.1 Ib, DCF provides contention based services and PCF provides contention free services for QoS suppof. DCF uses CSMA/CA (Carrier Sense Multiple Access/collision Avoidance) as an access protocol. In this paper, an enhanced PCF, which gives weights to channels with heavy traffic load, was proposed. The weight is depending on the partial queue length information from STAs. NS-2 simulation results show that the proposed scheme is an promising approach for enhancing the PCF.