• Title/Summary/Keyword: Power index law

Search Result 264, Processing Time 0.033 seconds

Dynamic of behavior for imperfect FGM plates resting on elastic foundation containing various distribution rates of porosity: Analysis and modeling

  • Kablia, Aicha;Benferhat, Rabia;Tahar, Hassaine Daouadji
    • Coupled systems mechanics
    • /
    • v.11 no.5
    • /
    • pp.389-409
    • /
    • 2022
  • During the manufacture of FGM plates, defects such as porosities can appear. Those can change the entire behavior of these plates. This paper aims to investigate the free vibration characteristics of porous functionally graded (FG) plates resting on elastic foundations. The Young's modulus of the plate is assumed to vary continuously through the thickness according to a power-law formulation, and the Poisson ratio is held constant. Different types of porosity distribution rates are considered. To examine the accuracy of the present formulation, several comparison studies are investigated. Effects of variation of porosity distribution rate, foundation parameter, power-law index and thickness ratio on the fundamental frequency of plates have been investigated.

Modeling the tidal connection between in and around galaxy clusters

  • Song, Hyun-Mi;Lee, Joung-Hun
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.36 no.2
    • /
    • 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.

  • PDF

Rheological Properties of Exopolysaccharide p-KG03 Produced by Marine Microalgae Gyrodinium impudicum strain KG03

  • Im, Jeong-Han;Kim, Seong-Jin;Park, Gyu-Jin;An, Se-Hun;Lee, Hyeon-Sang;Lee, Hong-Geum
    • 한국생물공학회:학술대회논문집
    • /
    • 2003.04a
    • /
    • pp.611-614
    • /
    • 2003
  • The rheological properties of exopolysaccharide, p-KG03, produced by marine microalgae Gyrodinium impudicum strain KG03 had been studied. The intrinsic viscosity of this p-KG03 was calculated to 65.22 and 50.75 $d{\ell}/g$ using Huggins and Kramer equations (xanthan gum 24.41 and 24.03). Aqueous dispersions at p-KG03 concentrations ranging from 0.1 to 1.0 % (w/w) showed marked shear-thinning properties as Power-Law behavior. In aqueous dispersions of p-KG03 1.0 %, consistency index (K) and flow behavior index (n) were 2,172 and 0.52. The apparent viscosity and the influence of shear rate on different conditions as p-KG03 concentrations, pH, NaCl, $CaCl_2$ and temperature in aqueous solutions were measured. And p-KG03 had mixed with aqueous solutions of xanthan gum and gellan gum, and invested the change of mixed aqueous solution behavior.

  • PDF

Reference Trajectory Design for Atmosphere Re-entry of Transportation Mechanical Structure (수송기계구조물의 대기권 재진입 기준궤도 설계)

  • Park, J.H.;Eom, W.S.
    • Journal of Power System Engineering
    • /
    • v.7 no.4
    • /
    • 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.

  • PDF

Determination of Kinetic Parameters in Coal Weathering Processes

  • Yun, Yongseung
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
    • /
    • 1993.11a
    • /
    • 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.

  • PDF

Regional frequency analysis using spatial data extension method : II .Flood frequency inference for ungaged watersheds (공간확장자료를 이용한 지역빈도분석 : II. 미계측 유역의 홍수빈도 추론)

  • Kim, Nam Won;Lee, Jeong Eun;Lee, Jeongwoo;Jung, Yong
    • Journal of Korea Water Resources Association
    • /
    • v.49 no.5
    • /
    • pp.451-458
    • /
    • 2016
  • In order to infer regional flood frequency for ungauged watersheds, index flood method was applied for this study. To pursuit this given purpose, annual peak flood data for 22 watersheds located at the upstream of the Chungju Dam watershed were obtained from the spatial extension technique. The regionalization of mean annual flood was performed from extended flood data at 22 points. Based on the theory that flood discharge and watershed size follows the power law the regionalization generated the empirical relationship. These analyses were executed for the full size of the Chungju Dam watershed as one group and three different mid-size watersheds groups. From the results, the relationship between mean annual flood and watershed sizes follow the power law. We demonstrated that it is appropriate to use the relationship between specific flood discharges from the upper and lower watersheds in terms of estimating the floods for the ungaged watersheds. Therefore, not only the procedure of regional frequency analysis but also regionalizaion analaysis using finer discretization of the regions interest with respect to the regional frequency analyisis for the ungauged watersheds is important.

Effect of Porosity on Quality Index of Tensile Property of A356 Casting Alloys (A356합금의 품질지수에 미치는 미소기공율의 영향)

  • Lee, Choong-Do
    • Journal of Korea Foundry Society
    • /
    • v.38 no.5
    • /
    • 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.

Radiation mechanism of gamma-ray burst prompt emission

  • Uhm, Z. Lucas;Zhang, Bing
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.40 no.1
    • /
    • 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.

  • PDF

Finite Element Analysis on the Small Scale Yielding of a Crack Tip in Plane Stress (平面應力狀態 에서 균열先端 의 小規模降伏 에 관한 有限要素解析)

  • 임장근;맹주성;김병용
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.7 no.3
    • /
    • 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.

The long-term centimeter variability of active galactic nuclei: A new relation between variability timescale and black hole mass

  • Park, Jongho;Trippe, Sascha
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.41 no.1
    • /
    • 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).

  • PDF