• Structural Engineering and Mechanics
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• 제11권5호
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• pp.565-574
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• 2001

Experimental investigation into the behaviour of half-scale brick masonry panels were conducted under cyclic loading normal to the bed joint and parallel to the bed joint. For each cycle, full reloading was performed with the cycle peaks coinciding approximately with the envelope curve. Unloading, however, was carried out fully to zero stress level and partially to two different stress levels of 25 percent and 50 percent of peak stress. Stability point limit exhibits a unique stress-strain curve for full unloading but it could not be established for partial unloading. Common point limit was established for all unloading-reloading patterns considered, but its location depends on the stress level at which unloading is carried to. Common point curves were found to follow an exponential formula, while residual strains versus envelope strains can be expressed by a polynomial function of a single term. The relation between residual strain and envelope strain can be used to determine the stress level at which deterioration due to cyclic loading began.

• 한국통신학회논문지
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• 제30권9A호
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• pp.795-802
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• 2005

바이너리 CDMA(B-CDMA) 기술은 CDMA 신호의 크기를 일정하게 유지시키는 새로운 변조 기법이다. 다중코드CDMA 신호를 일정한 레벨의 신호로 양자화한 후 변조함으로써 B-CDMA 기술은 CDMA 신호가 가지는 장점들을 유지하는 동시에 최대전력 대 평균전력의 비율을 감소시킨다. 본 논문에서는 확산인자가 현저히 작지 않은 가정 하에 B-CDMA시스템의 성능을 다중 경로 페이딩 환경에서 분석한다. 수학적 분석 결과는 컴퓨터 모의실험을 통하여 검증된다.

• Journal of electromagnetic engineering and science
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• 제15권2호
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• pp.63-75
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• 2015

The CMOS power amplifier (PA) is a promising solution for highly-integrated transmitters in a single chip. However, the implementation of PAs using the CMOS process is a major challenge because of the inferior characteristics of CMOS devices. This paper focuses on improvements to the efficiency and linearity of CMOS PAs for modern wireless communication systems incorporating high peak-to-average ratio signals. Additionally, an envelope tracking supply modulator is applied to the CMOS PA for further performance improvement. The first approach is enhancing the efficiency by waveform engineering. In the second approach, linearization using adaptive bias circuit and harmonic control for wideband signals is performed. In the third approach, a CMOS PA with dynamic auxiliary circuits is employed in an optimized envelope tracking (ET) operation. Using the proposed techniques, a fully integrated CMOS ET PA achieves competitive performance, suitable for employment in a real system.

• Wind and Structures
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• 제16권1호
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• pp.61-91
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• 2013

An analytical model of internal pressure response of a leaky and quasi-statically flexible building with a dominant opening is provided by including the effect of the envelope external pressure fluctuations on the roof, in addition to the fluctuating external pressure at the dominant opening. Wind tunnel experiments involving a flexible roof and different building porosities were carried out to validate the analytical predictions. While the effect of envelope flexibility is shown to lower the Helmholtz frequency of the building volume-opening combination, the lowering of the resonant peak in the internal and net roof pressure coefficient spectra is attributed to the increased damping in the system due to inherent background leakage and envelope flexibility. The extent of the damping effects of "skin" flexibility and background leakage in moderating the internal and net pressure response under high wind conditions is quantified using the linearized admittance functions developed. Analytical examples provided for different combinations of background leakage and envelope flexibility show that alleviation of internal and net pressure fluctuations due to these factors by as much as 40 and 15% respectively is possible compared to that for a nominally sealed rigid building of the same internal volume and opening size.

• 천문학회보
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• 제40권2호
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• pp.42.1-42.1
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• 2015

We model the Spectral Energy Distribution (SED) of Class 0 protostar L1527 IRS using a radiative transfer code RADMC-3D. In addition to the photometry data from literatures, we include the Herschel/PACS data which well covers the far-infrared SED peak of L1527 IRS, providing precise constraints to the density structure and other physical properties of its circumstellar envelope. Previously, Tobin et al. (2013) presented a dust continuum modeling results using a rotating and infalling envelope (Terebey and Shu, & Cassen 1984 ; TSC envelope), which originally describes a power-law density profile (${\rho}{\propto}r-{\alpha}$) with the power-law index (${\alpha}$) of 1.5. However, we find that Herschel/PACS data are better fitted with a shallower power-law density profile. This smaller power-law might be attributed to a inner envelope. Thus, we fit the SED of L1527 IRS with a Bonnor-Ebert sphere, which is a combination of the inner flat-topped and the outer power-law (${\alpha}=2$) density profiles. This Bonnor-Ebert sphere is often used to explain the density profile of prestellar cores, which is considered the earliest stages of star formation. The well-fitted SED with a Bonnor-Ebert sphere suggests that L1527 IRS might have collapsed from a Bonnor-Ebert sphere rather than a singular isothermal sphere.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.276-279
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• 2003

The phase change upon reflection from target surfaces in white-light interferometer induces measurement errors when target surfaces are composed of dissimilar materials. We prove that this phase change on reflection considered of the polarization of the white-light causes the shift of both envelope peak position and fringe peak position of several tens of nanometer. In addition, we propose a new equation of white-light interference fringe pertinent to the polarization of source.

• 한국인터넷방송통신학회논문지
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• 제11권5호
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• pp.47-52
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• 2011

본 논문에서는 주행 중 타이어와 노면이 마찰하면서 발생하는 초음파 신호에서 이물질로 인해 야기되는 우성주기를 검출하여 타이어 손상 유무를 판별하는 알고리즘에 대해 연구하였다. 손상된 타이어에서 획득한 초음파 신호의 포락선에 대해 전력스펙트럼을 산출하고 통계적 처리에 의한 임계값을 설정함으로써 우성주기를 판별하는 알고리즘을 제안하였다. 모의실험 결과, 시속 80km/h로 주행 시 초음파 신호의 포락선에 대해 전력스펙트럼의 피크주기 97.6ms에 비해 제안된 알고리즘의 우성주기는 100ms로서 포락선 피크의 평균주기 101.24ms를 기준으로 하였을 때 더 정확한 주기 측정 결과를 보였다.

• 천문학회보
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• 제45권1호
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• pp.70.1-70.1
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• 2020

A type IIb supernova (SN IIb) is the result of core-collapse of a massive star which lost most of its hydrogen-rich envelope during its evolution. The pre-SN progenitor properties, such as the total radius and the mass of the hydrogen-rich envelope, can widely vary due to the mass-loss history of the progenitors. Optical light curves of SNe IIb are dominated by energy released by the hydrogen recombination and the radioactive decay of 56Ni in the early and late epochs respectively. This may result in distinctive double peaked light curves like the one observed in SN 1993J. The first peak, caused by the hydrogen recombination, can be modelled with numerical simulations providing information on the pre-SN progenitor properties. We compare two radiation-hydrodynamics codes, STELLA and SNEC, that are frequently used in SNe modelling, and investigate the effect of opacity treatment on the temporal evolution of the color temperature of SNe and eventually on the optical light curves. We find that with a proper treatment of the scattering opacity, SNe IIb models exploded from the progenitor models evolved with latest stellar evolution model hardly match the observational data. We also discuss the smaller scale features found in the models during hydrogen recombination phase.

• Journal of electromagnetic engineering and science
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• 제14권1호
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• pp.1-8
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• 2014

A differential-cascode CMOS power amplifier (PA) with a supply modulator for envelope tracking (ET) has been implemented by 0.18 ${\mu}m$ RF CMOS technology. The loss at the output is minimized by implementing the output transformer on a FR-4 printed circuit board (PCB). The CMOS PA utilizes the $2^{nd}$ harmonic short at the input to enhance the linearity. The measurement was done by the 10MHz bandwidth 16QAM 6.88 dB peak-to-average power ratio long-term evolution (LTE) signal at 1.85 GHz. The ET operation of the CMOS PA with the supply modulator enhances the power-added efficiency (PAE) by 2.5, to 10% over the stand-alone CMOS PA for the LTE signal. The ET PA achieves a PAE of 36.5% and an $ACLR_{E-UTRA}$ of -32.7 dBc at an average output power of 27 dBm.

• 대한전자공학회논문지TC
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• 제41권2호
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• pp.65-70
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• 2004

본 논문에서는 비선형 RF(Radio Frequency) 증폭기의 선형화를 위한 새로운 구조의 전치왜곡 선형화기를 제안한다. 전치 왜곡에 이용되는 3차 비선형 성분은 RF 신호의 포락선(envelope) 전력을 이용하여 발생시킨다. 3차 왜곡 성분 발생기(3rd order distortion generator)는 FET로 구성되었고, 왜곡 신호 발생 후 남아 있는 주 신호 성분 제거를 위해 평형 결합 구조를 제시하였다. 발생된 3차 혼변조 신호는 RF 대역에서 진폭과 위상을 조절함으로써 최적의 선형화 조건을 만족시킨다. 2-tone 실험결과 증폭기의3차 흔변조특성이 30～40㏈ 개선되었다. IS-95 CDMA 신호 실험 결과 인접 채널 전력 비(ACPR)가 약 l0㏈이상 개선됨을 확인하였다.