• Journal of Ecology and Environment
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• 제36권2호
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• pp.117-123
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• 2013

This study investigated the impact of the fire disturbance and the pattern of recovery of soil dwelling oribatid mite communities with respect to the resilience from the fire disturbance. Oribatid mites are important decomposer animals of plant debris in soil with the feeding habits of saprophagy and mycophagy. Massive wild fire reduced soil oribatid mite abundance and diversity. The impact varied relative to the intensity of the disturbance. The proportion of the species common to the non-disturbed natural site increased as the time after the disturbance elapsed, which implying some degree of naturalness occurring in reorganization phase of the oribatid mite community. From the sites with different degree of fire impact, we found higher diversity in intermediately disturbed sites than in severely disturbed or non-disturbed site, supporting the intermediate disturbance hypothesis. Also this study showed that with differential degree of disturbance plots, resilience pattern after the disturbance can be explored even with shorter period research relative to the ecological succession of community.

• Journal of Communications and Networks
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• 제12권6호
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• pp.616-623
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• 2010

In this paper, exact closed-form expressions for outage probability and bit error probability (BEP) are presented for multi-hop decode-and-forward (DF) relaying schemes in conjunction with cooperative diversity, in which selection combining technique is employed at each node. We have shown that the proposed protocol offers remarkable diversity advantage over direct transmission as well as the conventional DF relaying schemes with the same combining technique. We then investigate the system performance when different diversity schemes are employed. It has been observed that the system performance loss due to selection combining relative to maximal ratio combining is not significant. Simulations are performed to confirm our theoretical analysis.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• 제2권2호
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• pp.129-138
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• 2021

Living modified organisms (LMOs) are managed by seven government agencies according to their use in South Korea. The Ministry of Environment is responsible for LMOs used for environmental remediation. This study aimed to develop guidelines for assessing potential risks posed by transgenic plants used for remediation to insect ecosystems by investigating arthropod communities in sunflower fields. A total of 2,350 insects and spiders belonging to 134 species of 10 orders and 71 families were collected from sunflower fields over four growth stages ranging from anthesis to seed maturity. At the R3 phase of flower-bud formation, Chironomidae sp. of a decomposer insect guild presented the highest density, while Apis mellifera of a pollinator guild was the most abundant in the R5.8 phase of flowering. During the R7 seed-filling phase and the R9 phase of seed maturity, herbivorous Pochazia shantungensis predominated. During the R9 phase, richness and diversity indices of arthropod communities were distinctly lower whereas their dominance indices were significantly higher than those at other phases. In addition, the composition of arthropod communities was strongly correlated not only with the sampling date, but also with the sampling method depending on the growth stage of sunflowers. Our results suggest that appropriate sampling timing and methods should be considered in advance and that long-term field trials that cover a variety of environmental conditions should be carried out to evaluate potential risks to insect ecosystems.

• ETRI Journal
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• 제28권5호
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• pp.680-683
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• 2006

One objective in developing the next generation of wireless communication systems is to increase data rates and reliability. A promising way to achieve this is to combine multiple-input and multiple-output signal processing with a space-time coding scheme, which offers higher coding and diversity gains and improves the spectrum efficiency and reliability of a wireless communication system. It is noted, however, that time delay differences and phase differences among different channels increase symbol interference and degrade system performance. In this letter, we investigate phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for the Rayleigh fading model to minimize their effects.

• 한국광학회:학술대회논문집
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• 한국광학회 2002년도 하계학술발표회
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• pp.174-175
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• 2002

One-dimensional semiconductor nanowires and nanorods have attracted increasing interest due to their unique physical properties and diversity for potential electronic and photonic device applications., Unlike the conventional nanowires fabricated by metal catalyst-assisted vapor-liquid-solid (VLS) method, we developed metalorganic vapor-phase epitaxial (MOVPE) growth for which no catalyst is needed. The structural and photoluminecent properties will also be discussed. (omitted)

• Journal of electromagnetic engineering and science
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• 제9권1호
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• pp.39-45
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• 2009

In this paper, we discuss hardware design and deployment issues in current passive UHF RFID systems. Using the link budget concept, the methodology to calculate forward- and reverse-link interrogation range is shown. Then, we consider hardware issues: phase diversity, phase noise with range correlation, and TX leakage problems. Finally, three interference problems when deploying RFID systems are presented.

• Journal of Communications and Networks
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• 제15권3호
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• pp.276-282
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• 2013

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading code from a random information source, rather than using the traditional pseudo-random noise (PN) codes. In this paper, we present our study of the SESS system performance under pulsed-noise jamming and show that iterative detection can significantly improve the bit error rate (BER) performance. The jamming performance of the SESS with correlation detection is verified to be similar to that of the conventional direct sequence spread spectrum (DSSS) system. On the other hand, the time diversity detection of the SESS can completely mitigate the effect of jamming by exploiting the inherent temporal diversity of the SESS system. Furthermore, iterative detection with multiple iterations can not only eliminate the jamming completely but also achieve a gain of approximately 1 dB at $10^{-3}$ BER as compared with the binary phase shift keying (BPSK) system under additive white gaussian noise (AWGN) by effectively combining the correlation and time diversity detections.

• 한국전자파학회논문지
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• 제12권4호
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• pp.630-643
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• 2001

본 논문에서는 다중경로 레일리 페이딩 환경에서 하이브리드 SC/MRC-$L_{c}/L$ 다이버시티 수신 Multi-Carrier DS-CDMA 시스템의 성능을 해석하고, 이를 광대력 DS-CDMA 시스템의 성능과 비교, 분석하였다 Multi-Ca-rrier DS-CDMA 시스템에서는 각 반속파의입력 다이버시티 가지 L 개중에서 $L_{c}$ 개를 선택하여 최대비 합성하며, 하이브리드 SC/MRC 다이버시티의 출력 신호에 대하여 각각 반송파별로 상관기를 이용하여 동조 복조 및 역확산을 수행한다. 분석 결과, 하이브리드 SC/MRC-$L_{c}/L$ 다이버시티 수신 광대역 DS-CDMA 시스템은 모든 다이버시티 가지에 대해 비트 동기나 위상 동기가 요구되지 않으므로 시스템의 구조가 간단하며, 비트 동기나 위상 동기가 요구되는 최대비 합성 다이버시티 수신보다는 오율 성능이 떨어지지만, 선택 다이버시티 수신보다는 오율 성능이 좋음을 알 수 있었다. 그리고, 각 다이버시티 가지로부터 이득을 얻게 되므로 하이브리드 SC/MRC-$L_{c}/L$ 수신시 Multi-Carrier DS_CDMA 시스템은 다중경로 페이딩 채널에서 기존의 광대역 DS-CDMA 시스템보다 성능이 개선된다. 무선 데이터 통신에서 요구되는 오율 $10^{-6}$을 목표로 했을 때 4개의 반송파를 이용하는 경우 하이브리드 SC/MRC-2/4 다이버시티 수신시, 하이브리드 SC/MRC-2/3 다이버시티 수신할 때 보다 사용자를 17명 더 증가시킬 수 있음을 알 수 있었다. 이로서 하이브리드 SC/MRC-$L_{c}/L$ 다이버시티 수신시 입력 다이버시티 가지(L)를 증가시킴으로써 다이버시티 가지의 선택의 폭을 늘릴 수 있어서, 이득을 얻게 된다는 것을 알 수 있었다.

• 한국결정학회지
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• 제12권2호
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• pp.81-87
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• 2001

We have studied the effect of sintering temperature and time on the cation ordering and second phase formation in Ba(Mg/sub 1/3/Nb/sub 2/3/)O₃(BMN) microwave ceramics by using transmission electron microscopy. The relationship between the structural-chemical behavior arid microwave dielectric properties has also been investigated. It is revealed that according to the sintering conditions the BMN ceramics show very diverse local ordering behavior, such as the development of domain twinning and "core-shell"-structured grains and the formation of local disordered domains, though having 1 : 2 cation ordering structure basically. The disordered structure is found in Mg-excess region. Such local chemical variation seems to be caused by the formation of BaNb₂O/sub 6/-like second phase in its neigh-boring grain boundary. The microwave dielectric quality factor of the ceramics decreases greatly with the increase of the structural-chemical inhomogeneity and diversity.

• 전기학회논문지
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• 제65권12호
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• pp.2177-2182
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• 2016

Using the existing exact but quite complicated symbol error rate (SER) expressions for M-ary phase shift keying (M-PSK) and M-ary differential phase shift keying (M-DPSK), we derive effective and concise closed-form asymptotic SER formulas especially in Rician-Nakagami fading channels. The derived formulas can be utilized to efficiently verify the achievable error rate performances of M-PSK and M-DPSK systems for the Rician-Nakagami fading environments. In addition, by exploiting the modulation gains directly obtained from the asymptotic SER formulas, we also theoretically demonstrate that M-DPSK suffers an asymptotic SER performance loss of 3.01dB with respect to M-PSK for a given M in Rician-Nakagami fading channels at high signal-to-noise ratio (SNR).