유사-파워스펙트럼 추정자를 사용한 각파워스펙트럼 측정법 소개

박찬경 ( Chan-gyung Park ) 전북대학교 과학교육연구소 2017 科學敎育論叢 Vol.42 No.1

각파워스펙트럼은 구면 상에 펼쳐진 요동의 특성을 기술하는 대표적인 통계량이다. 구면 상의 일부 영역에서만 요동이 관측될 경우, 탐사 영역의 기하학적 효과에 의해 요동의 구면조화함수 계수들은 서로 결합하고, 이로부터 계산한 각파워스펙트럼은 변형되어 유사-파워스펙트럼으로 나타난다. 이 논문에서는 유사-파워스펙트럼 추정자를 사용하여 통계적으로 등방한 요동의 부분적 자료로부터 각파워스펙트럼을 측정하는 방법을 소개한다. 이를 위해 제한된 탐사영역에 의한 각파워스펙트럼의 성분 간 결합 관계를 구면조화함수와 위그너 3j 기호를 사용해 유도하고 유사-파워스펙트럼으로부터 보정된 각파워스펙트럼을 얻는 과정을 상세히 기술한다. The angular power spectrum is a typical statistical quantity that describes the property of fluctuations on a sphere. For fluctuations observed on a partial region on the sphere, the spherical harmonic coefficients of the fluctuations are coupled together due to the geometrical effect of the survey region and thus the angular power spectrum is deformed into the pseudo-power spectrum. This paper introduces the method of measuring the angular power spectrum from the partial data of statistically isotropic fluctuations. For this purpose, we derive the mode-mode coupling of the angular power spectrum due to the limited survey region using the spherical harmonics and Wigner 3j symbols, and describe in detail how the corrected angular power spectrum is obtained from the pseudo-power spectrum.

Consumed-Power and Load Characteristics of Potato Harvesting Operation in Dry Field

Ju-Yeon Lee(이주연),Seok-Joon Hwang(황석준),Ju-Seok Nam(남주석),Jeong-Gil Kim(김정길) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.1

This study analyzed the load and the consumed power characteristics of a potato harvesting operation in a dry field. The potato harvesting operation was performed using an underground crop harvester mounted on an agricultural tractor with a rated engine power of 23.7 kW. The rotational speeds and the torque of the engine output shaft, rear axle, and power take-off (PTO) shaft were measured under various working conditions. The load spectrum and the consumed power were analyzed using the measured data. The results show that the consumed power of the rear axle increased as the working speed increased, while that of the PTO shaft decreased. The consumed power of the engine output shaft showed a similar trend with that of the PTO shaft, but the torque deviation was larger in the load spectrum. The results of previous studies were used to compare herein the consumed power and the load characteristics of the harvesting, rotary, and plow operations in a dry field. PTO and tractive power were highly consumed in the plow and rotary operations, respectively. The consumed power of the PTO shaft and the rear axle in the harvesting operation were 29–41% and 18–23% of the engine power, respectively. Compared to those in the rotary and plow operations, the engine power was relatively evenly distributed to the PTO shaft and rear axle in the harvesting operation.

Cooperative Power Control Scheme for a Spectrum Sharing System

Ban, Tae-Won,Jung, Bang-Chul The Korea Institute of Information and Commucation 2011 Journal of information and communication convergen Vol.9 No.6

In this paper, we investigate a power control problem which is very critical in underlay-based spectrum sharing systems. Although an underlay-based spectrum sharing system is more efficient compared to an overlay-based spectrum sharing system in terms of spectral utilization, some practical problems obstruct its commercialization. One of them is a real-time-based power adaptation of secondary transmitters. In the underlay-based spectrum sharing system, it is essential to adapt secondary user's transmit power to interference channel states to secure primary users' communication. Thus, we propose a practical power control scheme for secondary transmitters. The feedback overhead of our proposed scheme is insignificant because it requires one-bit signaling, while the optimal power control scheme requires the perfect information of channel states. In addition, the proposed scheme is robust to feedback delay. We compare the performance of the optimal and proposed schemes in terms of primary user's outage probability and secondary user's throughput. Our simulation results show that the proposed scheme is almost optimal in terms of both primary user's outage probability and secondary user's throughput when the secondary user's transmit power is low. As the secondary user's transmit power increases, the primary user's outage probability of the proposed scheme is degraded compared with the optimal scheme while the secondary user's throughput still approaches that of the optimal scheme. If the feedback delay is considered, however, the proposed scheme approaches the optimal scheme in terms of both the primary user's outage probability and secondary user's throughput regardless of the secondary user's transmit power.

방사선 디텍터의 Noise Power Spectrum

이은애(Eunae Lee),김동식(Dong Sik Kim) 대한전자공학회 2017 전자공학회논문지 Vol.54 No.3

NNPS(normalized noise power spectrum)는 획득한 x선 영상에서 평판형 방사선 디텍터의 잡음 특성을 spectrum을 관찰하기 위해 측정한다. 그러나 NNPS 측정은 획득한 영상에 따라 일관적이지 못한 성질을 가지고 있어서 안정된 측정이 필요하다. 디텍터의 NNPS 측정은 표본 periodogram을 구하여 평균을 내는 방법을 사용하는데, 일반적으로 표본의 개수를 충분히 늘리면 정확하면서 안정된 값을 구할 수 있다. 본 논문에서는 periodogram과 같은 표본 spectrum의 평균으로 유한한 개수의 영상이 주어졌을 때 일관적이고 효율적인 NNPS 값을 제공 할 수 있는 두 가지 방법을 제안하고 그 성능을 비교하고 분석했다. 실제 두 종류의 방사선 디텍터로부터 획득한 x선 영상을 사용하여 제안한 방법을 실험하였으며, 주어진 영상을 사용하여 표본 spectrum의 최대 가지 수를 갖는 조합으로 NNPS를 구하고 평균을 내는 방법이 기존 방법에 비하여 안정된 NNPS 측정이 가능함을 보였다. In order to observe the noise property of the flat-panel digital radiography detector, measuring the normalized noise power spectrum (NNPS) from acquired x-ray images is conducted. However, the conventional NNPS measurement has an unstable property depending on the acquired image. Averaging the sample periodograms of the input image is usually performed to estimate the NNPS values and increasing the number of samples can provide a reliable NNPS measurement. In this paper, for a finite number of images, two measurement methods, which are based on averaging spectra, such as the image periodogram, are proposed and their performances are analyzed. Using x-ray images acquired from two types of radiography detectors, the two spectrum averaging methods are compared and it is shown that averaging spectra based on the maximal number of combinations of the image pairs provides the best performance in measuring NNPS.

Power Allocation in Heterogeneous Networks: Limited Spectrum-Sensing Ability and Combined Protection

Yuehuai Ma,Youyun Xu,Dongmei Zhang 한국통신학회 2011 Journal of communications and networks Vol.13 No.4

In this paper, we investigate the problemof power alloca-tion in a heterogeneous network that is composed of a pair of cog-nitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to charac-terize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situ-ations is introduced to protect the primary network from unac-ceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the com-bined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the pro-posed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.

디지털 의료영상에서 위너스펙트럼(Wiener spectrum)의 보정방법

김정민(Jung-Min Kim) · 이기성(Ki-Sung Lee) · 김유현(You-Hyun Kim) 대한방사선과학회(구 대한방사선기술학회) 2009 방사선기술과학 Vol.32 No.1

노이즈를 평가하는 방법은 Root Mean Square(RMS) 입상도, 자기상관함수, 위너스펙트럼이 있다. RMS입상도는 광자데이터의 표준편차로 나타내며, 자기상관함수는 거리변화에 따른 1차원함수를 중적분하여 얻어진다. 그리고 자기상관함수를 푸리에 변환하면 노이즈 파워 스펙트럼이 되고, 화상에서는 이것을 위너스펙트럼이라고 한다. 위너스펙트럼은 노이즈 자체만을 표현할 뿐 아니라 해상특성을 나타내는 Modulation Transfer Function(MTF)과 함께 Detective Quantum Efficiency(DQE)를 산출하는 중요한 요소가 된다. 제시된 위너스펙트럼의 평가기술은 교육현장에서 그 개념을 교육하거나 임상 환경에서 시설에 알맞은 디지털 영상 검출기를 선택하고 디지털 영상 시스템의 영상품질을 유지 보수하는데 도움이 될 것으로 기대한다. Noise evaluation for an image has been performed by root mean square (RMS) granularity, autocorrelation function (ACF), and Wiener spectrum. RMS granularity stands for standard deviation of photon data and ACF is acquired by integration of 1 D function of distance variation. Fourier transform of ACF results in noise power spectrum which is called Wiener spectrum in image quality evaluation. Wiener spectrum represents noise itself. In addition, along with MTF, it is an important factor to produce detective quantum efficiency (DQE). The proposed evaluation method using Wiener spectrum is expected to contribute to educate the concept of Wiener spectrum in educational organizations, choose the appropriate imaging detectors for clinical applications, and maintain image quality in digital imaging systems.

유도모터의 스위칭 소음저감을 위한 2상 및 3상 RCD-PWM기법의 파워 스펙트럼

정영국,위석오,임영철 전력전자학회 2004 전력전자학회 논문지 Vol.9 No.2

This paper proposes a two-phase RCD-PWM scheme which is much better than a three-phase RCD-PWM scheme from the standpoint of the broadening and linearizing effect of the power spectrum. To implement the proposed scheme and conventional scheme, the experiment based on the SAB-C167 micro-controller was executed. Based on the space vector modulation technique, the duty ratio of the pulses is calculated using the SAB-C167 and each of PWM pulses is located randomly in each switching interval. The power spectrum of the output voltage, output current, the d.c link current and the acoustic noise radiated from inverter drives are experimentally investigated. Then, the performance of the proposed scheme was compared and discussed with the conventional scheme. 본 연구에서는 3상 RCD(Random Pulse Centered Displacement) PWM기법에 비하여 구현이 용이하고 스위칭 주파수의 정수배 스펙트럼의 광대역화와 선형화의 효과가 우수한, 2상 RCD-PWM을 제안하였으며, 그 파워 스펙트럼을 비교하고 있다. 종전의 3상 RCD-PWM과 제안된 2상 RCD-PWM을 구현하기 위하여, 16비트 고성능 마이크로 컨트롤러 SAB-C167이 사용되었다. SAB-C167에 의하여 각 변조 구간에서의 듀티비를 구한 후, 선형 랜덤 발생기를 이용하여 균일한 확률 분포로 각 상의 펄스의 위치를 재배치하였다. 제안된 2상 RCD-PWM에 의한 모터 전압과 전류 그리고 직류링크 전류의 파워 스펙트럼 및 모터의 가청 스위칭 소음 효과를 종전의 3상 RCD-PWM과 비교 검토하였다.

Power Allocation in Heterogeneous Networks: Limited Spectrum-Sensing Ability and Combined Protection

Ma, Yuehuai,Xu, Youyun,Zhang, Dongmei The Korea Institute of Information and Commucation 2011 Journal of communications and networks Vol.13 No.4

In this paper, we investigate the problem of power allocation in a heterogeneous network that is composed of a pair of cognitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to characterize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situations is introduced to protect the primary network from unacceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the combined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the proposed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.

Electroencephalogram Power Spectra in Thioacetamide-induced Hepatic Encephalopathy

김지희,최원진,박정숙,이향이,하정희,이만기,Lee, Chi-Hui,Choi, Won-Jin,Park, Jung-Sook,Lee, Hyang-Yi,Ha, Jeoung-Hee,Lee, Maan-Gee The Korean Society of Pharmacology 1996 대한약리학잡지 Vol.32 No.3

흰쥐에 thioacetamide(TAA)를 투여하면 간성뇌장애가 유발된다. 두가지 행동 상태(꼬리 접촉자극 및 미자극)와 세 단계의 신경학적 이상의 단계(정상, 약한 운동실조, 심한 운동실조)별로 뇌파를 기록하였고, 뇌파 스펙트럼 및 대역 분석을 통하여 간성뇌장애 진행동안 뇌파의 정량적인 변동을 관찰하였다. 정상 쥐에서 자극은 $theta(3.5{\sim}8\;Hz)$ 및 $gamma(30{\sim}50\;Hz)$ 대역의 power을 증가시켰다. 운동실조가 있는 쥐에서 이러한 변화가 일어나지 못하였다. 꼬리 자극을 하는 상태에서 theta 대역의 변화는 gamma 대역의 변화 보다 더욱 일찍 관찰되었다. 신경학적 행동 단계가 심해짐에 따라서 $beta3(21{\sim}30\;Hz)$ 및 gamma 대역에서 power가 점차적으로 감소하였다. 또한 간성뇌장애의 신경학적 증상은 benzodiazepine계 물질에 의하여 야기된다는 가설이 있으므로 beta power의 증가가 관찰될 것으로 기대하였으나 이 연구에서는 관찰하지 못하였다. 이 결과들로 미루어 볼때 이 연구에 사용된 스펙트럼 및 대역 분석이 간성뇌장애동안 신경학적 증상의 정도를 정량화 할 수 있다고 생각된다. During the development of hepatic encephalopathy after thioacetamide (TAA) injection to rat, EEG was recorded at two different states: without or with tactile stimulation of tail at regular intervals. Calculations based on the spectral and band analysis were used. The changes in the power spectra and bands were examined in 3 different behavioral stages: normal, mild ataxia and severe ataxia. In normal rats, the stimulation produced the increase in the power of the theta $(3.5{\sim}8\;Hz)$ and the gamma $(30{\sim}50\;Hz)$ bands. These changes could not be produced in rats with the mild and severe ataxia. The changes in the power of the theta band occurred earlier than those of the beta3 and the gamma bands in the stimulated state. Gradual decreases in the spectral power of the beta3 $(21{\sim}30\;Hz)$ and the gamma bands were correlated with the progress of the stages from normal condition to mild to severe ataxia in both unstimulated and stimulated states. The results indicate that the spectral and band analysis used in this study can quantify the severity of the neurological malfunction during HE.

Thioacetamide 유발 간성뇌장애에서 뇌파 Power Spectra

김지희(Chi Hui Kim),최원진(Won Jin Choi),박정숙(Jung Sook Park),이향이(Hyang Yi Lee),하정희(Jeoung Hee Ha),이만기(Maan Gee Lee) 대한약리학회 1996 대한약리학잡지 Vol.32 No.3

흰쥐에 thioacetamide(TAA)를 투여하면 간성뇌장애가 유발된다. 두가지 행동 상태(꼬리 접촉자극 및 미자극)와 세 단계의 신경학적 이상의 단계(정상, 약한 운동실조, 심한 운동실조)별로 뇌파를 기록하였고, 뇌파 스펙트럼 및 대역 분석을 통하여 간성뇌장애 진행동안 뇌파의 정량적인 변동을 관찰하였다. 정상 쥐에서 자극은 theta(3.5 ~ 8 Hz) 및 gamma(30 ~ 50 Hz) 대역의 power을 증가시켰다. 운동실조가 있는 쥐에서 이러한 변화가 일어나지 못하였다. 꼬리 자극을 하는 상태에서 theta 대역의 변화는 gamma 대역의 변화 보다 더욱 일찍 관찰되었다. 신경학적 행동 단계가 심해짐에 따라서 β3(21 ~ 30 Hz) 및 gamma 대역에서 power가 점차적으로 감소하였다. 또한 간성뇌장애의 신경학적 증상은 benzodiazepine계 물질에 의하여 야기된다는 가설이 있으므로 beta power의 증가가 관찰될 것으로 기대하였으나 이 연구에서는 관찰하지 못하였다. 이 결과들로 미루어 볼때 이 연구에 사용된 스펙트럼 및 대역 분석이 간성뇌장애동안 신경학적 증상의 정도를 정량화 할 수 있다고 생각된다. During the development of hepatic encephalopathy after thioacetamide (TAA) injection to rat, EEG was recorded at two different states: without or with tactile stimulation of tail at regular intervals. Calculations based on the spectral and band analysis were used. The changes in the power spectra and bands were examined in 3 different behavioral stages: normal, mild ataxia and severe ataxia. In normal rats, the stimulation produced the increase in the power of the theta (3.5 ~ 8 Hz) and the gamma (30 ~ 50 Hz)$ bands. These changes could not be produced in rats with the mild and severe ataxia. The changes in the power of the theta band occurred earlier than those of the beta3 and the gamma bands in the stimulated state. Gradual decreases in the spectral power of the beta3 (21 ~ 30 Hz) and the gamma bands were correlated with the progress of the stages from normal condition to mild to severe ataxia in both unstimulated and stimulated states. The results indicate that the spectral and band analysis used in this study can quantify the severity of the neurological malfunction during HE.