• Membrane and Water Treatment
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• v.8 no.1
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• pp.51-71
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• 2017

Antimicrobial polyethersulfone ultrafiltration membranes containing zerovalent iron ($Fe^0$) and magnetite ($Fe_3O_4$) nanoparticles were synthesized via phase inversion method using polyethersulfone (PES) as membrane material and nano-iron as nanoparticle materials. Zerovalent iron nanoparticles (nZVI) were prepared by the reduction of iron ions with borohydride applying an inert atmosphere by using $N_2$ gases. The magnetite nanoparticles (nMag) were prepared via co-precipitation method by adding a base to an aqueous mixture of $Fe^{3+}$ and $Fe^{2+}$ salts. The synthesized nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction, and dynamic light scattering analysis. Moreover, the properties of the synthesized membranes were characterized by scanning electron microscopy energy dispersive X-ray spectroscopy and atomic force microscopy. The PES membranes containing the nZVI or nMag were examined for antimicrobial characteristics. Moreover, amount of iron run away from the PES composite membranes during the dead-end filtration were tested. The results showed that the permeation flux of the composite membranes was higher than the pristine PES membrane. The membranes containing nano-iron showed good antibacterial activity against gram-negative bacteria (Escherichia coli). The composite membranes can be successfully used for the domestic wastewater filtration to reduce membrane biofouling.

• Journal of Internet Computing and Services
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• v.14 no.3
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• pp.67-79
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• 2013

In wireless networks, efficient mobility management to support of mobile users is very important. Several mobility management schemeshave been proposed with the aim of reducing the signaling traffic of MN(Mobile Node). Among them, PMIPv6 (Proxy Mobile IPv6) is similar with host-based mobility management protocols but MN does not require any process for mobility. By introducing new mobile agent like MAG (Mobile Access Gateway) and LMA (Local Mobility Anchor), it provides IP mobility to MN. In this paper, we propose the analytical model to evaluate the mean signalingdelay and the mean bandwidth according to the type of MN mobility. As a result of mathematical analysis, MF-PMIP (Multicasting-based FastPMIP) outperforms compared to F-PMIP and PMIP in terms of parameters for the performance evaluation.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.6
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• pp.383-389
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• 2001

We report on the design, fabrication, and characterization of 0.35${\mu}{\textrm}{m}$-gate AIGaAs/InGaAs PHEMTs for millimeter-wane applications. The epi-wafer structures were designed using ATLAS for optimum DC and AC characteristics, 0.351m-gate AIGaAs/rnGaAs PHEMTs having different gate widths and number of fingers were fabricated using electron beam lithography Dependence of RF characteristics of PHEMT on gate finger with and number of gate fingers have been investigated. PHEMT haying two 0.35$\times$60${\mu}{\textrm}{m}$$^2$ gate fingers showed the knee voltage, pinch-off voltage, drain saturation current density, and maximum transconductance of 1.2V, -1.5V, 275㎃/mm, and 260.17㎳/mm, respectively. The PHEMT showed fT(equation omitted)(current gain cut-off frequency) of 45㎓ and fmax(maximum oscillation frequency) of 100㎓. S$_{21}$ and MAG of the PHEMT were 3.6dB and 11.15dB, respectively, at 35㎓

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.337-349
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• 2013

In this paper, we propose a new mobility management scheme, called i-FP(intelligent Fast PMIPv6). Our proposed i-FP scheme is addressed for solving the existing local mobility management problems from legacy frameworks. To move MN(Mobile Node) to other networks in one domain, i-FP employs three network entities which are extended from PMIPv6(Proxy Mobile IPv6), LMA(Local Mobility Anchor), MAG(Mobile Access Gateway) and MN. In i-FP, the three network entities can reduce the handover delay time of MNs. Also, i-FP uses an IP header swapping mechanism to avoid the traffic overhead and improve the throughput of network. To evaluate the performance of i-FP, we analyze our i-FP, HMIPv6(Hierarchical Mobile IPv6) and PMIPv6 which are legacy protocols of local mobility management in terms of various parameters. Finally, our i-FP scheme shows good performance(reduction of routing hops 10.2%, signaling costs 58.5% and handover delay 16.3%) than other network schemes for the total cost.

• KIPS Transactions on Computer and Communication Systems
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• v.1 no.3
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• pp.219-228
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• 2012

As the wireless Internet become more widely accessible, variety of Internet services can be used without limitation of location. However, existing mobility management methods such as MIP and PMIP of IETF requires the load of heavy protocol stack on the mobile nodes or the addition of components such as LMA and MAG. In this paper, we proposed the location management technique in the PMIPv6 and Fast Handover technique. according to the moving pattern of the node, the location management technique proposed in order to adjust the paging area dynamically. The Fast Handover technique applied MIH technology and it reduced the handover signal processing time between heterogeneous network. The location management cost in the environment which the node moves in order to evaluate this and handover delay time was calculate. The proposal technique was efficiently more evaluated than PMIPv6 with the smallest 29% and maximum 83%.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.77.3-77.3
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• 2019

We present an analysis of the stellar population of compact elliptical galaxies (cEs) in various environments. Following conventional selection criteria of cEs, we created a list of cE candidates in the redshift range of z < 0.05 using SDSS DR12 catalog. We finally selected cEs with low-luminosity (Mg > 18.7 mag), small effective radius (Re < 600 pc), and high velocity dispersion (> 60 kms-1). We divide our cE sample into those inside and outside of the one virial radius of the bright (Mr < -21 mag) nearby host galaxy which is then defined as cEs with (cEw) and without (cEw/o) host galaxy, respectively. We investigated the stellar population properties of cEs based on the Hb, Mgb, Fe 5270, and Fe 5335 line strengths from the OSSY catalog. We found that cEw has a systematically higher metallicity than cEw/o. In the velocity dispersion-Mgb distribution, while cEw/o follows the relation of early-type galaxies, cEw are found to have a systematically higher metallicity than cEw/o at a given velocity dispersion. The different feature in the metallicity between cEw and cEw/o can suggest that two different scenarios can be provided in the formation of cEs. cEw would be the remnant cores of the massive progenitor galaxies that their outer parts have been tidally stripped by massive neighbor galaxies (i.e., nurture origin). On the other hand, cEw/o are likely to be faint-end of early-type galaxies maintaining in-situ evolution (i.e., nurture origin).

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.37.3-38
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• 2016

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ($M_{1450}$ > -24 mag) at z > 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z ~ 6 in a $12.5deg^2$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at ${\sim}8443{\AA}$, with emission lines redshifted to $z=5.944{\pm}0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59{\pm}0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z ~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars. This suggest that the number of $M_{1450}$ ~ -23 mag quasars at z ~ 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.50.3-50.3
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• 2020

We present deep UBVIc and Hα photometry for the young open cluster IC 1590 which is at the center of the HII region NGC 281. From Ha index, 39 Hα emission stars and 15 Hα emission candidates are selected. The reddening law toward IC 1590 is slightly abnormal (RV,cl = 3.6 ± 0.2). The distance modulus of IC 1590 obtained from the reddening-free (Q', QVλ) diagrams is 12.4 ± 0.1 mag (d = 3.02 ± 0.14 kpc), which is consistent with distance d = 2.91 ± 0.42 kpc from the parallax of Gaia DR2 catalogue within the error range. We also determined the age and mass function of IC 1590 using the stellar evolution models and PMS evolutionary tracks. The median age of PMS stars is 2.4 ± 2.2 Myr. The initial mass function (IMF) of IC 1590 is the Salpeter-type IMF with a slope of �� = -1.26 ± 0.14 for m > 1 M⊙ stars.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.301-303
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• 2012

We present the result of our near infrared J- (${\lambda}=1.25{\mu}m$), H- (${\lambda}=1.63{\mu}m$), and $K_s$-band (${\lambda}=2.14{\mu}m$) imaging of ultraluminous ($L_{IR}$ > $10^{12}L_{\odot}$) and luminous ($L_{IR}=10^{11-12}L_{\odot}$) infrared galaxies (ULIRGs and LIRGs), to investigate their relationship through properties of their host galaxies. We find that (1) for single-nucleus ULIRGs and LIRGs, their spheroidal host galaxies have similar properties, but ULIRGs display a substantially higher level of nuclear activity than LIRGs, suggesting that their infrared luminosity difference comes primarily from the different level of current nuclear activity. We infer that LIRGs and ULIRGs have similar progenitor galaxies, follow similar evolutionary processes, and may evolve into optically-selected QSOs. (2) Largely-separated multiple-nuclei ULIRGs have significantly brighter host galaxies than single-nucleus ULIRGs and LIRGs in $K_s$-band, indicating that multiple-nuclei ULIRGs have a bias towards mergers of intrinsically large progenitor galaxies, in order to produce high infrared luminosity ($L_{IR}$ > $10^{12}L_{\odot}$) even at the early merging stage. (3) We derive dust extinction of host galaxies of ULIRGs and LIRGs to be $A_V$ ~ 14 mag in the optical or equivalently $A_K$ ~ 0.8 mag in the near-infrared $K_s$-band, based on the comparison of host galaxy's luminosities in the J-, H-, and $K_s$-bands.

• Journal of Digital Contents Society
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• v.11 no.3
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• pp.341-348
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• 2010

Unlike host-based IPv6 mobility support protocols such as Mobile IPv6 (MIPv6), Hierarchical Mobile IPv6 (HMIPv6), and Fast handover for Mobile IPv6 (FMIPv6), Proxy Mobile IPv6 (PMIPv6) is expected to accelerate the real deployment of IPv6 mobility support protocol by using only collaborative operations between the network entities without mobile node (MN) being involved. In this paper, we analyze and compare the handover latency of network-based IPv6 mobility support protocol (i.e., PMIPv6) with the representative host-based IPv6 mobility support protocols such as MIPv6, HMIPv6, and FMIPv6. Analytical results show that the handover latency of PMIPv6 is considerably lower than those of MIPv6 and HMIPv6, and the handover latency of PMIPv6 becomes lower than that of FMIPv6 in case the wireless link delay is greater than the delay between mobile access gateway (MAG) and local mobility anchor (LMA).