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Ulju, South Korea

Park K.,Gwangju University | Kyung G.,UNIST
International Journal of Advanced Manufacturing Technology | Year: 2014

This paper proposes a method to optimize both the total cost and order fill rates in a supply chain using the particle swarm optimization (PSO) method. This method automatically adjusts the initial inventory levels of all tiers involved in a supply chain by considering information quality level (IQL), which is determined by the degree of availability of lead time history data. Analyses of variance are used to examine if there are any effects of IQL on the total cost and order fill rates. The results show that the proposed method finds better solutions which provide a lower inventory level while maintaining higher order fill rates than when PSO is not applied. © 2013 Springer-Verlag London. Source

Kang H.,Pusan National University | Petrosian V.,Stanford University | Ryu D.,UNIST | Jones T.W.,University of Minnesota
Astrophysical Journal | Year: 2014

We consider a phenomenological model for the thermal leakage injection in the diffusive shock acceleration (DSA) process, in which suprathermal protons and electrons near the shock transition zone are assumed to have the so-called κ-distributions produced by interactions of background thermal particles with pre-existing and/or self-excited plasma/MHD waves or turbulence. The κ-distribution has a power-law tail, instead of an exponential cutoff, well above the thermal peak momentum. So there are a larger number of potential seed particles with momentum, above that required for participation in the DSA process. As a result, the injection fraction for the κ-distribution depends on the shock Mach number much less severely compared to that for the Maxwellian distribution. Thus, the existence of κ-like suprathermal tails at shocks would ease the problem of extremely low injection fractions, especially for electrons and especially at weak shocks such as those found in the intracluster medium. We suggest that the injection fraction for protons ranges 10-4-10-3 for a κ-distribution with 10 ≲ κp ≲ 30 at quasi-parallel shocks, while the injection fraction for electrons becomes 10-6-10-5 for a κ-distribution with κe ≲ 2 at quasi-perpendicular shocks. For such κ values the ratio of cosmic ray (CR) electrons to protons naturally becomes K e/p ∼ 10-3-10 -2, which is required to explain the observed ratio for Galactic CRs. © 2014. The American Astronomical Society. All rights reserved.. Source

Kim J.-Y.,UNIST | Jang D.,California Institute of Technology | Greer J.R.,California Institute of Technology
Advanced Functional Materials | Year: 2011

Homogeneous plasticity in metallic glasses is generally only observed at high temperatures or in very small structures (less than ≈100 nm), so their applications for structural performance have been very limited. Here, nanolaminates with alternating layers of Cu50Zr50 metallic glass and nanocrystalline Cu are synthesized and it is found that samples with an optimal composition of 112-nm-thick metallic-glass layers and 16-nm-thick Cu layers demonstrate a maximum strength of 2.513 GPa, a value 33% greater than that predicted by the rule-of-mixtures and 25% better than that of pure Cu 50Zr50 metallic glass. Furthermore, ≈4% strain at fracture is achieved, suppressing the instantaneous catastrophic failure often associated with metallic glasses. It is postulated that this favorable combination of high strength and deformability is caused by the size-dependent deformation-mode transition in metallic glasses, from highly localized plasticity, leading to immediate failure in larger samples to homogeneous extension in the smaller ones. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Kang H.,Pusan National University | Ryu D.,UNIST
Astrophysical Journal | Year: 2015

In order to understand certain observed features of arc-like giant radio relics such as the rareness, uniform surface brightness, and curved integrated spectra, we explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud containing fossil relativistic electrons. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. Three types of fossil electron populations are considered: a delta-function like population with the shock injection momentum, a power-law distribution, and a power law with an exponential cutoff. The surface brightness profile of the radio-emitting postshock region and the volume-integrated radio spectrum are calculated and compared with observations. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed μs∼3X103km s-1 and sonic Mach number Ms∼3. These shocks produce curved radio spectra that steepen gradually over (0.1-10)vbrwith a break frequency vbr∼1GHz if the duration of electron acceleration is∼6080 Myr. However, the abrupt increase in the spectral index above∼1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons withγe≳104. © 2015. The American Astronomical Society. All rights reserved. Source

Hessari P.,UNIST
Computers and Mathematics with Applications | Year: 2014

The first order system least squares method for the Stokes equation with discontinuous viscosity and singular force along the interface is proposed and analyzed. First, interface conditions are derived. By introducing a physical meaningful variable such as the velocity gradient, the Stokes equation transformed into a first order system of equations. Then the continuous and discrete norm least squares functionals using Legendre and Chebyshev weights for the first order system are defined. We showed that continuous and discrete homogeneous least squares functionals are equivalent to appropriate product norms. The spectral convergence of the proposed method is given. A numerical example is provided to support the method and its analysis. © 2014 Elsevier Ltd. All rights reserved. Source

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