• 천문학회보
• /
• 제36권2호
• /
• pp.53.1-53.1
• /
• 2011

We analyze the halo and galaxy catalogs from the Millennium simulations at redshifts z=0, 0.5, 1 to determine the alignment profiles of cluster galaxies in terms of the matter density correlation coefficient and discuss a cosmological implication our result has for breaking parameter degeneracies. For each selected cluster, we measure the alignment between the major axes of the pseudo inertia tensors from all satellites within cluster's virial radius and from only those satellites within some smaller radius. Then we average the measured values over the similar-mass sample to determine the cluster galaxy alignment profile as a function of top-hat scale difference at each redshift. It is shown that the alignment profile of cluster galaxies is well approximated by a power-law of the nonlinear density correlation coefficient that is independent of the power spectrum normalization and bias factor. The alignment profile of cluster galaxies is found to have higher amplitude and lower power-law index when averaged over the larger-mass sample and to have rather weak redshift-dependence. This result is consistent with the picture that the satellite galaxies retain the memory of the external tidal fields right after merging and infalling into the clusters but they gradually lose the initial alignment tendency as the cluster's relaxation proceeds. Demonstrating that the nonlinear density correlation coefficient varies sensitively with the density parameter and neutrino mass fraction, we discuss a potential power of the cluster galaxy alignment profile as an independent probe of cosmology.

• 한국생물공학회:학술대회논문집
• /
• 한국생물공학회 2003년도 생물공학의 동향(XII)
• /
• pp.611-614
• /
• 2003

p-KG03의 고유점도는 65.22 및 50.75 $d{\ell}/g$ 이며, 사슬강도성은 0.170이였고, 특성화 농도는 0.114 g/l이었다. p-KG03은 non-Newtonic fluid로 Power-Low Model에 의한 pseudoplastic한 물성을 갖으며, 유체성으로 p-KG03 1%의 constancy index (K)는 2,172 cp, flow behavior index (n)는 0.52이었다. 특히 pH, 염 및 열에 안정하며 기존 다당류와의 혼합이용 가능성이 있을 것으로 생각된다.

• 동력기계공학회지
• /
• 제7권4호
• /
• pp.67-73
• /
• 2003

The entry guidance design involves trajectory optimization and generation of a drag acceleration profile as the satisfaction of trajectory conditions during the entry flight. The reference trajectory is parameterized and optimized as piecewise linear functions of the velocity. A regularization technique is employed to achieve desired properties of the optimal drag profile. The regularized problem has smoothness properties and the minimization of performance index then prevents the drag acceleration from varying too fast, thus eliminating discontinuities. This paper shows the trajectory control using the simple control law as well as the information of reference drag acceleration.

• 한국에너지공학회:학술대회논문집
• /
• 한국에너지공학회 1993년도 추계학술발표회 초록집
• /
• pp.31-36
• /
• 1993

Three different methods were employed to measure the degree of aerial oxidation in coal and the resulting oxidation/weathering indices were applied to obtain kinetic parameters of aerial oxidation processes, The index (i.e., slurry pH, Free Swelling Index, weight gain) values were subjected to kinetic analysis based on power-law Arrhenius type reaction model. The results show that activation energy of the aerial oxidation in 20-29$0^{\circ}C$ is in the range of 12-16 ㎉/㏖ and the agreement among three techniques is remarkable. The first order kinetic model is suitable in describing low temperature aerial oxidation process, except in the FSI case where the zero order expression is the best one.

• 한국수자원학회논문집
• /
• 제49권5호
• /
• pp.451-458
• /
• 2016

본 연구에서는 미계측유역에서의 빈도홍수량을 추정하기 위해 지역홍수빈도분석의 표준방법인 지수홍수법을 이용하였다. 이를 위해 충주댐 상류유역을 대상으로 공간확장한 22개 지점의 연최대홍수량 자료을 활용하였으며, 구축된 다지점의 자료계열을 이용하여 지수홍수법의 주요인자인 평균홍수량의 지역화 과정를 수행하였다. 지역화를 위한 방법으로는 홍수량과 유역면적과의 관계가 멱함수 법칙(power law)를 따른다는 이론에 근거한 경험관계를 유도하였다. 충주댐 상류유역 전체를 하나의 그룹, 3개의 중권역을 각각 하나의 그룹으로 구분하여 분석하였다. 도출된 결과에 따르면 평균홍수량과 유역면적과의 관계를 멱함수 법칙으로 설명할 수 있었다. 또한, 미계측 지점의 홍수량 추정시에는 가까운 계측지점 즉, 직상하류 유역의 비유량의 관계를 사용하는 것이 타당함을 증명하였다. 따라서, 미계측 유역을 위한 지역빈도해석은 지역홍수빈도해석 절차 자체도 중요하지만, 지역의 세밀한 구분과 그에 따른 지역화 경험관계 개발과정도 중요한 절차임을 확인할 수 있었다.

• 한국주조공학회지
• /
• 제38권5호
• /
• pp.95-102
• /
• 2018

The dependence of the tensile properties on variations in the porosity of A356 aluminium alloys was investigated in terms of the quality index of the tensile properties based upon the ultimate tensile strength and elongation as well as the variation of the strength coefficient and strain-hardening exponent with regard to a T6 treatment. The test specimens were prepared by low-pressure die-casting and a subsequent T6 treatment, and the experimental results of a tensile test carried out at room temperature were compared to the theoretical description using a modified constitutive model. The nominal value of the quality index of A356 alloys increases gradually with a lapse of the ageing time upon a T6 treatment, despite the fact that this value is temporarily decreased during the initial stage of ageing from a solutionised condition. Additionally, the quality index depends practically upon the porosity variation with a power law relationship without regard to whether in solutionised or artificial aged conditions. The theoretical description indicates that the strength coefficient directly determines the nominal level of the quality index. Moreover, the overall dependence of the quality index on the porosity variation is remarkably weakened with an increase in the tensile strain, whereas the quality index depends sensitively upon the porosity variation with a low value of the strain-hardening exponent.

• 천문학회보
• /
• 제40권1호
• /
• pp.49.3-50
• /
• 2015

Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling timescale is shorter than the dynamical timescale, electrons are cooled down below the minimum injection energy. It has been believed that such fast-cooling electrons have a power-law distribution in energy with an index -2, and their synchrotron radiation has a photon spectral index -1.5. On the other hand, in a transient expanding astrophysical source, such as a gamma-ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast-cooling electrons can have a harder energy spectrum. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon spectral index has a typical value -1 could be due to synchrotron radiation in this moderately fast-cooling regime.

• 대한기계학회논문집
• /
• 제7권3호
• /
• pp.270-277
• /
• 1983

Plastic plane stress solutions are given for a center cracked strip, characterized by the Ramberg-Osgood plastic index, under bi-axial tension. Using a power law hardening stress-strain relation, an incremental plasticity finite element formulation is developed, and simple formulation is given for computing J-integral with nodal displacements. The near tip angular distribution of von Mises effective stress doesn't differ significantly in magnitude according to the change of loading stress and bi-axial load combination factor. But, for smaller plastic index, the location of its maximum value moves vertically at a head of crack. J-integral value, in the plastic zone near crack tip, decreases with load combination factor for large and small plastic index.

• 천문학회보
• /
• 제41권1호
• /
• pp.36.2-37
• /
• 2016

We study the long-term radio variability of 43 radio bright AGNs by exploiting the data base of the University of Michigan Radio Astronomy Observatory (UMRAO) monitoring program. The UMRAO database provides high quality lightcurves spanning 25 - 32 years in time at three observing frequencies, 4.8, 8, and 14.5 GHz. We model the periodograms (temporal power spectra) of the observed lightcurves as simple power-law noise (red noise, spectral power $P(f){\propto}f^{-{\beta}}$ using Monte Carlo simulations, taking into account windowing effects (red-noise leak, aliasing). The power spectra of 39 (out of 43) sources are in good agreement with the models, yielding a range in power spectral index (${\beta}$) from ${\approx}1$ to ${\approx}3$. We find a strong anti-correlation between ${\beta}$ and the fractal dimension of the lightcurves, which provides an independent check of the quality of our modelling of power spectra. We fit a Gaussian function to each flare in a given lightcurve to obtain the flare duration. We discover a correlation between ${\beta}$ and the median duration of the flares. We use the derivative of a lightcurve to obtain a characteristic variability timescale which does not depend on the assumed functional form of the flares, incomplete fitting, and so on. We find that, once the effects of relativistic Doppler boosting on the observed timescales are corrected, the variability timescales of our sources are proportional to the black hole mass to the power of ${\alpha}=1.70{\pm}0.49$. We see an indication for AGNs in different regimes of accretion rate, flat spectrum radio quasars and BL Lac objects, having different scaling relations with ${\alpha}{\approx}1$ and ${\approx}2$, respectively. We find that modelling the periodograms of four of our sources requires the assumption of broken powerlaw spectra. From simulating lightcurves as superpositions of exponential flares we conclude that strong overlap of flares leads to featureless simple power-law periodograms of AGNs at radio wavelengths in most cases (The paper is about to be submitted to ApJ).

• 천문학회보
• /
• 제43권1호
• /
• pp.56.1-56.1
• /
• 2018

Tidal disruption events (TDEs) provide evidence for quiescent supermassive black holes (SMBHs) in the centers of inactive galaxies. TDEs occur when a star on a parabolic orbit approaches close enough to a SMBH to be disrupted by the tidal force of the SMBH. The subsequent super-Eddington accretion of stellar debris falling back to the SMBH produces a characteristic flare lasting several months. The theoretically expected bolometric light curve decays with time as proportional to $t^{-5/3}$. However, the light curves observed in most of the optical-UV TDEs deviate from the $t^{-5/3}$ decay rate especially at early time, while the light curves of some soft-X-ray TDEs are overall in good agreement with the $t^{-5/3}$ law. Therefore, it is required to construct the theoretical model for explaining these light curve variations consistently. In this paper, we revisit the mass fallback rates analytically and semi-analytically by taking account of the structure of the star, which is simply modeled by the polytrope. We find the relation between a polytropic index and the power law index of the mass fallback rate. We also discuss whether and how the decay curves, which we derived, fit the observed ones.