• 천문학회보
• /
• 제40권1호
• /
• pp.76.2-76.2
• /
• 2015

We present the results of the Westerbork Synthesis Radio Telescope (WSRT) HI imaging study of seven late-type galaxies. They are located in the outskirts of the Virgo cluster, possibly along a filament connected to Virgo from the north-west. Most galaxies in this region are found to be HI-rich, containing more HI gas compared to field galaxies with similar size and optical luminosity. The positions of the sample with respect to the cluster and their high HI mass-to-light ratios suggest that the selected galaxies might be accreting more gas from their surroundings while falling into the cluster. By high-resolution HI imaging, we aim to find evidence that galaxies are pre-processed by gas accretion from the intergalactic medium and/or gas-rich neighbors. We probe the detailed HI morphology/kinematics and the star formation properties of the sample. All of these galaxies are found with a large HI disk which is quite extended compared to their stellar disk. Together with kinematical peculiarities, this strongly suggests that cold gas accretion is responsible for active star formation in these galaxies.

• 자원ㆍ환경경제연구
• /
• 제15권3호
• /
• pp.405-423
• /
• 2006

본 연구는 자본과 노동의 요소투입물 증가가 환경오염의 증가를 유발하고 기술축적자체도 환경오염을 유발한다는 가설모형을 설정하고, 사회계획자모형과 환경오염방지활동이 이루어지지 않는 시장경제모형을 구축하여 이론모형을 도출한다. 도출된 이론모형을 이용하여 환경오염변수와 경제성장률(또는 국민소득 수준) 간에 선형이 아닌 비선형동학(nonlinear dynamics) 관계가 존재하는지를 분석하기 위하여 변수의 부드러운 곡면전환이 이루어지는 평활전이자기회귀모형(Smooth Transition Autoregressive : STAR)을 사용하였다. 서울시 산업생산지수와 대기오염도를 이용한 실증분석에서 경제성장률과 환경오염변수 간에 비선형 동태적인 관계와 비선형 그랜저 인과관계가 존재하는 것으로 나타나 서울지역에서의 환경쿠즈네츠곡선가설이 성립하고 있음을 간접적으로 확인하였다. 그러나 그 해석에는 한계가 있음을 지적하였다.

• 천문학회보
• /
• 제36권2호
• /
• pp.74.1-74.1
• /
• 2011

To probe the connection between starburst and AGN activity, we investigate the relation between the 3.3 micron~PAH emission and AGN properties based on the new AKARI observations and the data collected from the literature. Using a sample of low-z Type I AGN, we measure the global 3.3 micron PAH luminosity from the AKARI slit-less spectroscopy. The 3.3 ${\backslash}$micron~PAH emissions are detected for 7 out of 26 target galaxies, but we find no strong correlation between the 3.3 ${\backslash}$micron~PAH emission and AGN luminosity, suggesting that global star formation may not be tightlyrelated with AGN activity. In contrast the to global star formation, the nuclear 3.3 micron~PAH emission luminosity, which are measured from ground-based long slit spectroscopy with a narrow slit, correlates with AGN luminosity. These results imply that starburst and AGN activity are directly connected at the nuclear region.

• 천문학논총
• /
• 제30권2호
• /
• pp.133-137
• /
• 2015

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy's supermassive black hole (SMBH) Sgr $A^{\ast}$. We resolved several molecular gas streams orbiting the center on ${\gtrsim}10$ pc scales. Some of these gas streams appear connected to the well-known 2-4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates inflow via exterior gas filaments/arms, and ultimately feeds gas toward Sgr $A^{\ast}$. Our high resolution GBT+JVLA $NH_3$ images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ${\gtrsim}100$ times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I $CH_3OH$ masers and some $H_2O$ masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.

• 대한기계학회논문집B
• /
• 제29권10호
• /
• pp.1092-1100
• /
• 2005

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{o}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, smoke particles produced from mosquito coils. The experimental data were obtained at 9 points dividing the test sections by 400 3m. Experimental and numerical results can be summarized as follows. 1) Reynolds number, Re was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and secondary flows. 2) The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number. Especially, fluid dynamic phenomenon called conner impact were observed at dimensionless axial position, x/D$_{h}$=50.

• 대한기계학회논문집B
• /
• 제28권9호
• /
• pp.1058-1065
• /
• 2004

In the present study, characteristics of steady state laminar flows of a straight duct connected to a 180$^{\circ}$ curved duct were examined in the entrance region through experimental and numerical analyses. For the analysis, the governing equations of laminar flows in the Cartesian coordinate system were applied. Flow characteristics such as velocity profiles, and secondary flows were investigated numerically and experimentally in a square cross-sectional straight duct by the PIV system and a CFD code(STAR CD). For the PIV measurement, working fluid produced from mosquito coils smoke. The experimental data were obtained at 9 points dividing the test sections by 400 mm. Experimental and numerical results can be summarized as follows. Critical Reynolds number, Recr which indicates transition from laminar steady flow to transition steady flow was 2,150. As Reynolds number, Re, was increased, dimensionless velocity profiles at the outer wall were increased due to the effect of the centrifugal force and the secondary flows. The intensity of a secondary flow became stronger at the inner wall rather than the outer wall regardless of Reynolds number.

• Journal of Power Electronics
• /
• 제15권1호
• /
• pp.256-267
• /
• 2015

Grid-connected transformerless photovoltaic (PV) inverters (TPVIs) are increasingly dominating the market due to their higher efficiency, lower cost, lighter weight, and reduced size when compared to their transformer based counterparts. However, due to the lack of galvanic isolation in the low voltage grid interconnections of these inverters, the PV systems become vulnerable to leakage currents flowing through the grounded star point of the distribution transformer, the earth, and the distributed parasitic capacitance of the PV modules. These leakage currents are prohibitive, since they constitute an issue for safety, reliability, protection coordination, electromagnetic compatibility, and module lifetime. This paper investigates a wide range of multi-kW range power rating TPVI topologies and classifies them in terms of their leakage current attributes. This systematic classification places most topologies under a small number of classes with basic leakage current attributes. Thus, understanding and evaluating these topologies becomes an easy task. In addition, based on these observations, new topologies with reduced leakage current characteristics are proposed in this paper. Furthermore, the important efficiency and cost determining characteristics of converters are studied to allow design engineers to include cost and efficiency as deciding factors in selecting a converter topology for PV applications.

• 한방안이비인후피부과학회지
• /
• 제29권4호
• /
• pp.1-13
• /
• 2016

Objectives : The purpose of this study is to compare hair and alopecia of Korean Medicine with those of western medicine. Methods : We studied relationships between hair and essense(精), qi(氣), blood(血), five vicera(五臟) and meridians(經絡) through literature review about hair and alopecia. We compared Korean medicine with western medicine on physiology of hair and treatment of alopecia based on the study. Results & Conclusion : 1. Congenital essense(先天之精) is related with genetic factor and acquired essence(後天之精) is connected with nutritional factor. Defending function of Defense qi(衛氣) is related with immune reaction and qi stagnation(氣鬱) is associated with stress reaction. Atrophy of vascular tissues observed in alopecia scalp means deep relationship between blood(血) and alopecia, further deficiency of blood can cause telogen effluvium. 2. Kidney qi(腎氣) is related with inhibiting combination of Androgen receptor and Dihydrotestosterone(DHT) or activating hair growth factior. Pi(脾) is connected with alopecia seborrheica caused by damp-heat(濕熱) and alopecia areata caused by excessive prudence(思慮過度). Heart(心) is associated with atrophy in vascular tissue of scalp and liver(肝) is connected with metabolism. 3. Armpit hair and pubic hair as secondary sex characteristics are realated with Yangming Meridian(陽明經) and beard and hair at crown part where Type II $5{\alpha}$-reductase is activated much are associated with Taiyang Meridian(太陽經). 4. Juglandis Semen pharmacopuncture and Ganoderma lucidum pharmacopucture have better effects on inhibit $5{\alpha}$-reductase than Finasteride. Minoxidil and PRP are similar with promoting blood flow and removing stasis(活血祛瘀). Seven-star needling(七星針) is similar with microneedling. 5. Alopecia can be caused by due to lack of circulation Views we need solution to improve circulation coincide in opinion with Korean Medicine and Western medicine.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.553-558
• /
• 2002

Physical sensor model in pushbroom satellite images can be made from sensor modeling by rotation parameters and attitude parameters on the satellite track. These parameters are determined by the information obtained from GPS, INS, or star tracker. Provided from satellite image, an auxiliary data error is connected directly with an error of rotation parameters and attitude parameters. This paper analyzed how obtaining satellite images influenced errors of rotation parameters and attitude parameters. furthermore, for detailed analysis, this paper generated simulated satellite image, which was changed variously by rotation parameters and attitude parameters of satellite sensor model. Simulated satellite image is generated by using high-resolution digital aerial image and DEM (Digital Elevation Model) data. Moreover, this paper determined correlation of rotation parameter and attitude parameters through error analysis of simulated satellite image that was generated by various rotation parameters and attitude parameters.

• Journal of Power Electronics
• /
• 제10권5호
• /
• pp.538-547
• /
• 2010

This paper deals with a stand-alone wind energy conversion system (WECS) with an isolated asynchronous generator (IAG) and voltage and frequency (VF) control feeding three-phase four-wire loads. The reference generator currents are estimated using the instantaneous symmetrical component theory to control the voltage and frequency of an IAG system. A three-leg voltage source converter (VSC) with an isolated star/delta transformer is used as an integrated VSC. An integrated VSC with a battery energy storage system (BESS) is used to control the active and reactive powers of the WECS. The WECS is modeled and simulated in MATLAB using the Simulink and the Sim Power System (SPS) toolboxes. The proposed VF controller functions as a voltage and frequency regulator, a load leveler, a load balancer and a harmonic eliminator in the WECS. A comparison is made on the rating of the VSC with and without ac capacitors connected at the terminals of an IAG. Simulation and test results are presented to verify the control algorithm.