• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4387-4404
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• 2015

The energy-efficient design of sensing-based spectrum sharing of a multi-input and multi-output (MIMO) cognitive radio (CR) system with imperfect multiple antenna spectrum sensing is investigated in this study. Optimal resource allocation strategies, including sensing time and power allocation schemes, are studied to maximize the energy efficiency (EE) of the secondary base station under the transmit power and interference power constraints. EE problem is formulated as a nonlinear stochastic fractional programming of a nonconvex optimal problem. The EE problem is transformed into its equivalent nonlinear parametric programming and solved by one-dimension search algorithm. To reduce searching complexity, the search range was founded by demonstration. Furthermore, simulation results confirms that an optimal sensing time exists to maximize EE, and shows that EE is affected by the spectrum detection factors and corresponding constraints.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1402-1411
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• 2018

Nuclear-related facilities can be detrimentally affected by ground vibrations due to the collapse of adjacent cooling towers in nuclear power plants. To reduce this hazard risk, a design-oriented acceleration response spectrum (ARS) was proposed to predict the dynamic responses of nuclear-related facilities subjected to ground vibrations. For this purpose, 20 computational cases were performed based on cooling tower-soil numerical models developed in previous studies. This resulted in about 2664 ground vibration records to build a basic database and five complementary databases with consideration of primary factors that influence ground vibrations. Afterwards, these databases were applied to generate the design-oriented ARS using a response spectrum analysis approach. The proposed design-oriented ARS covers a wide range of natural periods up to 6 s and consists of an ascending portion, a plateau, and two connected descending portions. Spectral parameters were formulated based on statistical analysis. The spectrum was verified by comparing the representative acceleration magnitudes obtained from the design-oriented ARS with those from computational cases using cooling tower-soil numerical models with reasonable consistency.

• 한국재료학회지
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• 제20권7호
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• pp.364-369
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• 2010

A $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor powder with stuffed tridymite structure was synthesized by glycine-nitrate combustion method. The luminescence, formation process and microstructure of the phosphor powder were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The XRD patterns show that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was an amorphous phase. However, a crystalline $SrAl_2O_4 $ phase was formed by calcining at $1200^{\circ}C$ for 4h. From the SEM analysis, also, it was found that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was in irregular porous particles of about 50 ${\mu}m$, while the calcined phosphor was aggregated in spherical particles with radius of about 0.5 ${\mu}m$. The emission spectrum of as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor did not appear, due to the amorphous phase. However, the emission spectrum of the calcined phosphor was observed at 520 nm (2.384eV); it showed green emission peaking, in the range of 450~650 nm. The excitation spectrum of the $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor exhibits a maximum peak intensity at 360 nm (3.44eV) in the range of 250~480 nm. After the removal of the pulse Xe-lamp excitation (360 nm), also, the decay time for the emission spectrum was very slow, which shows the excellent longphosphorescent property of the phosphor, although the decay time decreased exponentially.

• 한국지반공학회논문집
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• 제39권12호
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• pp.7-22
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• 2023

본 연구에서는 입력가속도의 한계 범위를 흙의 상대밀도, 지하수위, 지반 조건을 고려하여 시간이력해석과 응답스펙트럼해석으로 분석하였다. 시간이력해석은 FLAC3D로 응답스펙트럼해석은 FB-Multipier를 이용하여 여러 지반 조건에 대한 수치해석을 실시하였다. 말뚝 주변 지반은 탄소성 물질로 가정하였다. FLAC3D 해석의 주변 지반은 Mohr-Coulomb과 Finn 모델로 설정하였고, FB-Multiplier 해석은 비선형 p-y 곡선을 이용하여 해석하였다. 비선형 지반 거동을 갖는 가속도의 한계범위는 주변 지반의 상대밀도에 비례함을 보였다. 해석 결과 SP soil이 SM soil보다 지반의 가속도의 한계범위가 훨씬 크고 지하수위는 지반조건에 관계없이 입력가속도의 한계범위를 감소시키는 경향이 있음을 알 수 있다. 또한 가속도의 한계 범위는 주로 전단탄성계수의 영향을 받는 것으로 나타났다.

• Journal of Biosystems Engineering
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• 제27권2호
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• pp.117-124
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• 2002

This research was conducted to develop a method to remove the effect of surface temperature of Shingo pears for sugar content measurement. Sugar content was measured by a near-infrared spectrum analysis technique. Reflected spectrum and sugar content of a pear were used for developing regression models. For the model development, reflected spectrums having wavelengths in the range of 654 to 1,052nm were used. To remove the effect of surface temperature, special sample preparation techniques and partial least square (PLS) regression models were proposed and tested. 71 Shingo pears stored in a cold storage, which had 2$^{\circ}C$ inside temperature, were taken out and left in a room temperature for a while. Temperature and reflected spectrum of each pear was measured. To increase the temperature distribution of samples, temperature and reflected spectrum of each pear was measured four times with one hour twenty minutes interval. During the experiment, temperature of pears increased up to 17 $^{\circ}C$. The total number of measured spectrum was 284. Three groups of spectrum data were formed according to temperature distribution. First group had surface temperature of 14$^{\circ}C$ and total number of 51. Second group consisted of the first and the fourth experiment data which contained the minimum and the maximum temperatures. Third group consisted of 155 data with normal temperature-distribution. The rest data set were used for model evaluation. Results shelved that PLS model I, which was developed by using the first data group, was inadequate for measuring sugar content of pears which had different surface temperatures from 14$^{\circ}C$. After temperature compensation, sugar content predictions became close to the measured values. Since using many data which had wide range of surface temperatures, PLS model II and III were able to predict sugar content of pears without additional temperature compensation. PLS model IV, which included the surface temperatures as an independent variable. showed slightly improved performance(R$^2$=0.73). Performance of the model could be enhanced by using samples with more wide range of temperatures and sugar contents.

• 한국해양공학회지
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• 제28권3호
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• pp.185-192
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• 2014

The riser systems for floating offshore structures are known to experience tri-modal dynamic responses. These are owing to the combined loadings from the low-frequency response due to riser tension behavior, middle-range frequency response coming from winds and waves, and high-frequency response due to vortex induced-vibration. In this study, fatigue damage models were applied to predict the fatigue damages in a well-separated tri-modal spectrum, and the resultant fatigue damages of each model were compared with the most reasonable fatigue damage calculated by the inverse Fourier transform of the spectrum, rain-flow counting method, and Palmgren-Miner rule as a reference. The results show that the fatigue damage models developed for a wide-band spectrum are applicable to the tri-modal spectrum, and both the Benasciutti-Tovo and JB models could most accurately predict the fatigue damages of the tri-modal spectrum responses.

• 한국수학교육학회지시리즈A:수학교육
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• 제60권4호
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• pp.543-554
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• 2021

동적 기하 환경은 학생들의 기하 문제 해결에 긍정적인 역할을 한다. 학생들은 드래깅을 통해 변화 속에서 불변성을 추측할 수 있으며, 분석법은 기하 문제를 해결하는 데 도움을 준다. 하지만 드래깅 활동과 분석법을 활용한 문제 해결은 제한점이 있으며, 연속 스펙트럼은 대안이 될 수 있다. 학생들은 코딩이 결합된 동적 기하 환경에서 프로그래밍을 통해 연속 스펙트럼을 구현할 수 있다. 이에 본 연구에서는 동적 기하 환경의 문제 해결에서 연속 스펙트럼을 활용하는 방안을 제시하였다. 학생들은 문제 해결의 이해 단계에서 시각적으로 표현된 문제 상황을 통해 즉각적으로 이해하고, 계획 단계에서 해결 전략을 수립하고, 반성 단계에서 결과의 점검 및 일반화하는 데 도움을 줄 수 있다.

• 한국전자파학회논문지
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• 제24권8호
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• pp.820-830
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• 2013

스마트 장비의 보급에 따라 무선 통신 트래픽은 급격히 증가하여, 제한된 주파수 자원을 효율적으로 사용하기 위한 주파수 공동사용 정책과 주파수 공동기술에 대한 도입이 매우 필요한 상황이다. 본 연구에서는 이러한 요구에 대처하기 위하여 공공 및 국가안전 관련 지정/승인 무선국과 허가 무선국을 중심으로 공동사용 가능 주파수 대역을 발굴하였다. 발굴된 공동사용 후보 주파수 대역은 기존의 무선국 데이터베이스를 기초로 중심주파수, 대역폭, 무선국 사용 지역 등을 고려하여 검토되었다. 결과적으로 1~4.5 GHz의 주파수 대역에서 지역적으로 공동사용이 가능한 주파수 대역을 약 901 MHz 발굴하였으며, 발굴된 대역은 향후 공동사용을 통한 M2M, WiFi 서비스 등에 활용될 것으로 예상된다.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2002년도 Proceedings
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• pp.228-230
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• 2002

The relative electron density resolution was discussed by the noise power spectrum (NPS) in the heavy ion CT image. The heavy ion beam $\^$12/C accelerated up to 400MeV/u by RIMAC was used in this study. The two-dimensional (2-D) NPS in the CT image was obtained from the one-dimensional (1-D) NPS of the measured residual range distribution of water phantom for single projection, and the noise variance in the CT image was calculated from 2-D NPS. The technique used in the reconstruction was the filtered back-projection method with Shepp-Logan filter. The calculated value suggests the result of our previous works using the density resolution phantom, assuming that the relative electron density resolution is twice the standard deviation. Therefore, the estimation of the noise in CT images by 2-D NPS obtained the measured residual range distribution is the useful method.

• 한국음향학회지
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• 제40권4호
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• pp.304-313
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• 2021

본 논문은 2020년 11월 동해에서 실시한 장거리 수중음향통신의 해상실험 결과를 제시한다. 하나의 이동하는 송신기와 16개의 수직 배열 수신기들을 통해 신호를 수집하였으며, 송신기와 수신기 사이의 거리는 약 20 km정도였다. 실험에 적용된 신호는 기존의 직접수열 대역확산 방식과 각 심볼마다 다수의 순환된 Pseudo Noise(PN) 시퀀스를 중첩함으로써 전송률을 높이는 중첩된 직접수열 대역확산 방식이다. 실험결과 채널 부호화 기법이 적용되지 않은 비부호화 비트 오류율에 있어서 기존의 직접수열 대역확산 방식은 16채널 평균 0.0005로 나타났으며, 중첩된 직접수열대역확산 방식은 0.00124을 보였다.