• 천문학회보
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• 제45권1호
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• pp.68.3-69
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• 2020

We develop a series of N-body data challenges, functional to the final analysis of the extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16) galaxy sample, primarily based on high-fidelity catalogs constructed from the Outer Rim simulation. We generate synthetic galaxy mocks by populating Outer Rim halos with a variety of halo occupation distribution (HOD) schemes of increasing complexity, spanning different redshift intervals. We then assess the performance of three complementary redshift space distortion (RSD) models in configuration and Fourier space, adopted for the analysis of the complete DR16 eBOSS sample of Luminous Red Galaxies (LRGs). We find that all the methods are mutually consistent, with comparable systematic errors on the Alcock-Paczynski parameters and the growth of structure, and robust to different HOD prescriptions - thus validating the robustness of the models and the pipelines used for the baryon acoustic oscillation (BAO) and full shape clustering analysis. Our study is relevant for the final eBOSS DR16 'consensus cosmology', as the systematic error budget is informed by testing the results of analyses against these high-resolution mocks. In addition, it is also useful for future large-volume surveys, since similar mock-making techniques and systematic corrections can be readily extended to model for instance the DESI galaxy sample.

• Journal of Power Electronics
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• 제18권6호
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• pp.1901-1911
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• 2018

This study presents a circuit model for simulating the switching transients of insulated-gate bipolar transistors (IGBTs) with inductive load switching. The modeling approach used in this study considers the behavior of IGBTs and freewheeling diodes during the transient process and ignores the complex semiconductor physics-based relationships and parameters. The proposed circuit model can accurately simulate the switching behavior due to the detailed consideration of device-circuit interactions and the nonlinear nature of model parameters, such as internal capacitances. The developed model is incorporated in an IGBT loss calculation module of an electromagnetic transient simulation program to enable the estimation of switching losses in voltage source converters embedded in large power systems.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1219-1224
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• 2018

We investigate the evolutionary dynamics and the phase transitions of the island model which consists of subdivided populations of individuals confined to two islands. In the island model, the population is subdivided so that migration acts to determine the evolutionary dynamics along with selection and genetic drift. The individuals are assumed to be haploid and to be one of two species, X or Y. They reproduce according to their fitness values, die at random, and migrate between the islands. The evolutionary dynamics of an individual based model is formulated in terms of a master equation and is approximated by using the diffusion method as the multidimensional Fokker-Planck equation (FPE) and the coupled non-linear stochastic differential equations (SDEs) with multiplicative noise. We analyze the infinite population limit to find the phase transitions from the monomorphic state of one type to the polymorphic state to the monomorphic state of the other type as we vary the ratio of the fitness values in two islands and complete the phase diagram of our island model.

• Wind and Structures
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• 제26권3호
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• pp.147-161
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• 2018

For wind engineering applications downbursts are, presently, almost exclusively modeled, both experimentally and numerically, as transient impinging momentum jets (IJ), even though that model contains none of the physics of real events. As a result, there is no connection between the IJ-simulated downburst wind fields and the conditions of formation of the event. The cooling source (CS) model offers a significant improvement since it incorporates the negative buoyancy forcing and baroclinic vorticity generation that occurs in nature. The present work aims at using large-scale numerical simulation of downburst-producing thunderstorms to develop a simpler model that replicates some of the key physics whilst maintaining the relative simplicity of the IJ model. Using an example of such a simulated event it is found that the non-linear scaling of the velocity field, based on the peak potential temperature (and, hence, density) perturbation forcing immediately beneath the storm cloud, produces results for the radial location of the peak radial outflow wind speeds near the ground, the magnitude of that peak and the time at which the peak occurs that match well (typically within 5%) of those produced from a simple axi-symmetric constant-density dense source simulation. The evolution of the downdraft column within the simulated thunderstorm is significantly more complex than in any axi-symmetric model, with a sequence of downdraft winds that strengthen then weaken within a much longer period (>17 minutes) of consistently downwards winds over almost all heights up to at least 2,500 m.

• 비파괴검사학회지
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• 제28권6호
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• pp.524-530
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• 2008

The spin valve tunneling magnetoresistance (SV-TMR) sensor performance is analyzed using Stoner-Wohlfarth model for the detection of eddy current signals in nondestructive testing applications. The SV-TMR response in terms of the applied AC magnetic field dominantly generates the second harmonic amplitude in hard axis direction. The second harmonic eddy current signal detection using SV-TMR sensor shows higher performance than that of the coil sensor at lower frequencies. The SV-TMR sensor with high sensitivity gives a good solution to improve the low frequency performance in comparison with the inductive coil sensors. Therefore, the low frequency eddy current techniques based on SV-TMR sensors are specially useful in the detection of hidden defects, and it can be applied to detect the deeply embedded flaws or discontinuities in the conductive materials.

• The Journal of the Acoustical Society of Korea
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• 제25권3E호
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• pp.110-114
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• 2006

In a previous theoretical paper, we have derived a unified formula by considering 2-D coupled mode vibrations. The unified formula for electromechanical coupling coefficient of piezoelectric resonator was verified experimentally. The capacitance change near the resonant frequency was investigated to estimate the effective coupling coefficient of the resonator instead of the conventional method based on I-D model. The susceptance spectra were measured for the seven samples of piezoelectric resonator with different aspect ratio. Excellent agreement between theoretical and experimental results was obtained.

• 에너지공학
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• 제23권4호
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• pp.215-222
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• 2014

A theory-based methodology for describing the thermodynamic properties of molecular nitrogen is presented. The results obtained indicate a successful application of a fully consistent statistical method for the description of a molecular system in different phase states. The method employs a density of states equation for solid nitrogen and a perturbation potential for gaseous and liquid nitrogen. The main characteristics of the calculation method include the need for a minimal number of initial data and the absence of fitting parameters. The adequacy of the physical model that is the basis for the method allows a description of existing experimental data and the peculiarities of the thermodynamic properties.

• 천문학회보
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• 제35권1호
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• pp.75.1-75.1
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• 2010

The first near-infrared (NIR) spectroscopic survey of SDSS-selected blue early-type galaxies (BEGs) has been conducted using the AKARI/IRC. The NIR spectra of 36 BEGs are successfully secured, which are well balanced in their SF/Seyfert/LINER type composition. For high signal-to-noise ratio, we stack the BEG spectra all and in bins of several properties: color, specific star formation rate and optically-determined spectral type. We estimate the NIR continuum slope and the 3.3 micron PAH emission equivalent width in the stacked BEG spectra, and compare them with those of SSP model galaxies and known ULIRGs. We first report the NIR spectral features of BEGs and discuss the nature of BEGs based on the comparison with other objects.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1560-1565
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• 2003

Tapping mode atomic force microscopy (TM-AFM) utilizes the dynamic response of a resonating probe tip as it approaches and retracts from a sample to measure the topography and material properties of a nanostructure. We present recent results based on nonlinear dynamical systems theory, computational continuation techniques and detailed experiments that yield new perspectives and insight into AFM. A dynamic model including van der Waals and Derjaguin-Muller-Toporov (DMT) contact forces demonstrates that periodic solutions can be represented with respect to the approach distance and excitation frequency. Turning points on the surface lead to hysteretic amplitude jumps as the tip nears/retracts from the sample. Experiments are performed using a tapping mode tip on a graphite sample to verify the predictions.

• Current Optics and Photonics
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• 제2권4호
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• pp.378-382
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• 2018

In most previous investigations of plasmonic and metamaterial applications, the metallic film has been regarded as a perfect electrical conductor. Here we demonstrate the resonance characteristics of THz metamaterials fabricated from metal film that has a finite dielectric constant, using finite-difference time-domain simulations. We found strong redshift and spectral broadening of the resonance as we decrease the metal's plasma frequency in the Drude free-electron model. The frequency shift can be attributed to the effective thinning of the metal film, originating from the increase in penetration depth as the plasma frequency decreases. On the contrary, only peak broadening occurs with an increase in the scattering rate. The metal-thickness dependence confirms that the redshift and spectral broadening occur when the effective metal thickness drops below the skin-depth limit. The electromagnetic field distribution illustrates the reduced field enhancement and reduced funneling effects near the gap area in the case of low plasma frequency, which is associated with reduced charge density in the metal film.