• 한국통신학회논문지
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• 제18권5호
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• pp.643-649
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• 1993

본 논문에서는 백색 가우스 잡음 Co-channel 간섭이 존재하는 채널에서의 2진 펄스 진폭변조 통신 시스템에서 주기적으로 삽입되는 프레임 동기 문제를 다루었다. Co-channel 간섭이 존재함으로서 발생되는 Correlation Rule의 성능 저하를 보이고 백색 가우스 잡음과 Co-channel 간섭이 존재하는 채널에서의 최대 프레임 동기 공식을 유도하였다. 최대 추정 동기 공식은 신호 에너지에 있어 Correlation Rule 보다 약 1dB 정도의 성능 향상을 보였다. 특히, 신호대잡음비가 0dB 이상일 경우 최대 추정 동기 공식은 최대 2dB 정도의 성능향상을 보였다.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.276.2-278
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• 2000

In a recent years, a number of approaches have been studied, including passive, active, and hybrid mode-locking of semi-conductor lasers for short pulse generation and research has been devoted to achieve low timing-jitter operation since the timing jitter is unfavorable for system applications. Among the methods of mode locking, passive mode locking does not need external rf drives, and therefore the operation and fabrication procedures are simplified. In spite of these attractive advantages of passive mode-locked laser, it has critical drawbacks such as large timing jitter and the difficulty in synchronization with external circuits. Their inherent large timing jitter value was shown to be suppressed to certain levels by means of hybrid mode-locking technique$^{(1)}$ , where the saturable absorber section was modulated by an external signal with the cavity round trip frequency. Furthermore, the subharmonic mode-locking (SHML) technique alleviates the restrictions of high speed driving electronics. It has been demonstrated experimentally$^{(1)}$ that the hybrid subharmonic mode-locking technique has lead to significant reduction of the timing jitter. (omitted)

• 한국광학회지
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• 제9권2호
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• pp.104-110
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• 1998

Cu 도핑된(0.04 wt.%) 광굴절 (K/sub 0.5/Na/sub 0.5/)/sub 0.2/(Sr/sub 0.61/Ba/sub 0.39/)/sub 0.9/Nb/sub 2/O/sub 6/ 결정에서 두 빔간의 에너지 교환특성을 632.8 nm He-Ne 레이저 파장에서 해석하고 측정하였다. 또한 신호빔 혹은 기준빔이 고주파에서 진폭 변조될 때 광유기된 굴절율 부피 격자의 코히어런트한 2광파 결합 특성을 해석하고 실험하였으며, 코히어런트 광통신 시스템 및 광신호처리 분야에서 동적 광굴절 결합기및 펄스 shaping 소자로 활용하기 위한 예비 실험 결과를 제시했다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.681-684
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• 2005

본 논문은 (3$^{n-1}$+2) 레벨 형성법에 기반한 멀티레벨 인버터를 제안한다. PWM 인버터, LEVEL 인버터와 다단 변압기로 구성되는 이 회로는 양질의 출력전압을 형성하기 위해서 이차측이 직렬로 결합된 다단 변압기를 이용하게 된다. 변압기 권선비의 적절한 선택을 통해 입력전압의 정수비 형태로 주어지는 출력전압레벨을 형성할 수 있다. 제안된 방식으로 11레벨, 29레벨 시작품을 제작하여 실험을 통해 타당성을 검증한다.

• ETRI Journal
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• 제45권1호
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• pp.163-170
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• 2023

We report an electroabsorption modulator (EAM)-integrated distributed Bragg reflector laser diode (DBR-LD) capable of supporting a high data rate and a wide wavelength tuning. The DBR-LD contains two tuning elements, plasma and heater tunings, both of which are implemented in the DBR section, which have blue-shift and red-shift in the Bragg wavelength through a current injection, respectively. The light created from the DBR-LD is intensity-modulated through the EAM voltage, which is integrated monolithically with the DBRLD using a butt-joint coupling method. The fabricated chip shows a threshold current of approximately 8 mA, tuning range of greater than 30 nm, and static extinction ratio of higher than 20 dB while maintaining a side mode suppression ratio of greater than 40 dB under a window of 1550 nm. To evaluate its modulation properties, the chip was bonded onto a mount including a radiofrequency line and a load resistor showing clear eye openings at data rates of 25 Gb/s nonreturn-to-zero and 50 Gb/s pulse amplitude modulation 4-level, respectively.

• 한국전자파학회논문지
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• 제26권11호
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• pp.999-1011
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• 2015

전자전(Electronic Warfare) 상황에서 레이다는 재머에 의해 전파교란공격(ECM: Electronic Counter Measures)을 받게 된다. Linear-FM 신호는 도플러 특성이 우수하고, 신호의 구현이 용이하여 레이다에서 주로 사용되어 왔지만, 반복된 패턴에 의해 피탐 확률이 높고, 신호 특성변수 추정이 가능하여 기만재밍에 취약하다. 최근 제안된 APCN(Advanced Pulse Compression Noise) 신호는 랜덤 진폭과 랜덤 위상코드로 이루어진 신호로서, 저피탐 성능이 우수한 신호이다. 하지만, APCN 신호를 비롯한 일반적인 위상코드 신호는 도플러 특성이 좋지 않으므로, 주파수 천이에 의해 신호수신 성능이 저하될 수 있다. 따라서 본 논문에서는 도플러 특성을 개선하기 위한 방안으로 랜덤 위상천이 및 부호율 천이(RPCR: Random Phase and Code Rate transition) 레이다 신호 파형을 제안하고, 도플러 성능과 저피탐 성능을 분석하였다. Ambiguity 함수를 이용하여 부호율 천이에 의한 도플러 특성 개선을 제시하며, WHT(Wigner-Hough Transform)을 이용한 신호 특성 변수 추정 실험을 통해 RPCR 신호의 저피탐 성능을 분석하고, 전파교란대응책(ECCM: Electronic Counter Counter Measures)으로의 가능성을 확인한다.

• 대한약리학회지
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• 제23권2호
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• pp.57-75
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• 1987

Two modalities of gonadotropin secretion, pulsatile gonadotropin and preovulatory gonadotropin surge, have been identified in the mammals. Pulsatile gonadotropin secretion is modulated by the pulsatile pattern of GnRH release and complex ovarian steroid feedback actions. The neural mechansim that regulates the pulsatile release of GnRH in the hypothalamus is called "GnRH pulse generator". Ovarian steroids, estradiol and progesterone, appear to exert thier feedback effects both directly on the pituitary to modulate gonadotropin release and on a hypothalamic site to modulate GnRH release; estradiol primarily affects the amplitude while progesterone decreases the frequency of the pulsatile GnRH. Steroid hormones are known to affect catecholamine transmission in brain. MBH-POA is richly innervated by NE systems and close apposition of NE terminals and GnRH cell bodies occurs in the MBH as well as in the POA. NE normally facilitates pulsatile LH release by acting through ${\alpha}-receptor$ mechanism. However, precise nature of facilitative role of NE transmission in maintaining pulsatile LH has not been clearly understood. Close apposition of DA and GnRH terminals in ME might permit DA to influence GnRH release. Action of DA transmission probably is mediated by axo-axonic contacts between GnRH and DA fibers in the ME. Dopamine transmission does not normally regulate pulsatile LH release, but under certain conditions, increased DA transmission inhibit LH pulse. Endogenous opioid acts to suppress the secretion of GnRH into hypophysial portal circulation, thereby inhibiting gonadotropin secretion. However, an interaction between endogenenous opioid peptides and gonadotropin release is a complex one which involves ovarian hormones as well. LH secretion appears to be most suppressed by endogenenous opioids during the luteal phase, at a time of elevated progesterone secretion. The arcuate nucleus contains not only cell bodies for GnRH and ${\beta}-endorphin$ but also a dense aborization of fibers suggesting that GnRH release is changed by the interactions between GnRH and ${\beta}-endorphin$ cell bodies within the arcuate nucleus. The frequency and amplitude of pulsatile LH release seem to be increased during the preovulatory gonadotropin surge. Estradiol exerts positive feedback action on the hypothalamo-pituitary axis to trigger preovulatory LH surge. GnRH is also crucial hormonal stimulus for preovulatory LH surge. It is unlikely, however, that increased secretion of GnRH during the preovulatory gonadotropin surge represents an obligatory neural signal for generation of the LH discharge in primates including human. Modulation of preovulatory LH surge by catecholamines has been studied almost exclusively in rats. NE and E may be involved in distinct way to accumulate GnRH in the MBH and its release into the hypophysial portal system during the critical period for LH surge on proestrus in rats. However, the mechanisms whereby augmented adrenergic transmission may facilitate the formation and accumulation of GnRH in the ME-ARC nerve terminals before the LH surge have not been clearly understood.

• 한국통신학회논문지
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• 제36권1A호
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• pp.8-18
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• 2011

발광 다이오드와 같은 광원을 이용하여 조명과 통신의 두가지 기능을 동시에 이용할 수 있는 가시광 무선 통신은 최근 초고속 개인용 무선 네트워크에서 각광을 받고 있다. 광원의 제한된 대역폭으로 인하여 무선 광채널에서 전송률을 향상시키는 것이 이슈로 대두되는 가운데, 본 논문에서는 전송률을 향상시키는 기법으로써 다중 입출력 무선 광채널에서 두 개의 데이터 스트림을 지원하기 위해 고유값 분해를 이용한 공간 다중화 시스템을 설계한다. 채널의 변화에 따라 적응적 변조 기법을 적용하여 주파수 효율을 높이기 위해 펄스 진폭 변조 기법을 이용한다. 본 논문에서는 세기 변조를 이용한 변조 기법의 세 가지 제한 조건인 비음수성, 총 광출력값, 비트 오류율에 대하여 주파수 효율성을 향상시키기 위해 광출력값, 오프셋값, 변조 크기를 적응적으로 할당하기 위한 기법을 이론적으로 제안한다. 모의 실험 결과를 통해 본 논문의 제안 기법이 각 데이터 스트림에 광출력값을 동일하게 할당하는 기법에 비해 성능 향상을 이룰 수 있다는 것을 보인다.

• ALGAE
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• 제27권2호
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• pp.125-134
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• 2012

Germanium dioxide ($GeO_2$) has been used for many years in the cultivation of red and green algae as a means of controlling the growth of diatoms. Brown algae are sensitive to $GeO_2$, however, the basis of this sensitivity has not been characterized. Here we use embryos of $Fucus$ $vesiculosus$ to investigate morphological and physiological impacts of $GeO_2$ toxicity. Morphometric features of embryos were measured microscopically, and physiological features were determined using pulse amplitude modulated (PAM) fluorometry. At 5 mg $L^{-1}$ $GeO_2$, embryos grew slower than controls and developed growth abnormalities. After 24 h, initial zygote divisions were often oblique rather than transverse. Rhizoids had inflated tips in $GeO_2$ and were less branched, and apical hairs were deformed, with irregularly aligned, spheroidal cells. Minimum fluorescence ($F_0$) showed minor differences over the 10 days experiment, and pigment levels (chlorophylls $a$, $c$ and total carotenoids) showed no difference after 10 days. Optimum quantum yield increased from ca. 0.52 at 24 h to 0.67 at 5 days, and $GeO_2$-treated embryos had higher mean values (significant at 3 and 5 days). Optimum quantum yield of photosystem II (${\Phi}_{PSII}$) was stable in control thalli after 5 days, but declined significantly in $GeO_2$. Addition of silica (as $SiO_2$) did not reverse the effects of $GeO_2$. These results suggest that $GeO_2$ toxicity in brown algae is associated with negative impacts at the cytological level rather than metabolic impacts associated with photosynthesis.

• Journal of Power Electronics
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• 제17권4호
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• pp.1048-1057
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• 2017

An indirect matrix converter (IMC) is a modern power generation system that enables a direct ac/ac conversion without the need for any bulky and limited lifetime electrolytic capacitor. This system also allows four-quadrant operation, generation of sinusoidal output voltage waveforms with variable frequency and amplitude, and control of input power factor. This study proposes a pulse-width modulation-based sliding-mode controller to achieve unity input-power factor operation of the IMC independently of the active power exchanged with the grid, as well as a fast dynamic response. The designed equivalent control law determines, at each sampling period, the appropriate q-axis component of the modulated input current to be injected into the grid through the LC input filter. An integral term of the error is included in the expression of the sliding surface to increase the accuracy of the control method. A double space vector modulation method is used to synthesize the direction of the space vector of the input currents as required by the sliding-mode controller and the space vectors of the target output voltages. Simulation and experimental results are provided to show the effectiveness and evaluate the performance of the proposed control method.