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Search Results: 1 - 10 of 220 matches for " Jonghwa Eom "
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Phase Dependent Thermopower in Andreev Interferometers
Jonghwa Eom,Chen-Jung Chien,Venkat Chandrasekhar
Physics , 1998, DOI: 10.1103/PhysRevLett.81.437
Abstract: We report measurements of the thermopower S of mesoscopic Andreev interferometers, which are hybrid loops with one arm fabricated from a superconductor (Al), and one arm from a normal metal (Au). S depends on the phase of electrons in the interferometer, oscillating as a function of magnetic flux with a period of one flux quantum (= h/2e). The magnitude of S increases as the temperature T is lowered, reaching a maximum around T = 0.14 K, and decreases at lower temperatures. The symmetry of S oscillations with respect to magnetic flux depends on the topology of the sample.
Temperature evolution of the quantum Hall effect in the FISDW state: Theory vs Experiment
Victor M. Yakovenko,Hsi-Sheng Goan,Jonghwa Eom,Woowon Kang
Physics , 1999, DOI: 10.1051/jp4:19991049
Abstract: We discuss the temperature dependence of the Hall conductivity $\sigma_{xy}$ in the magnetic-field-induced spin-density-wave (FISDW) state of the quasi-one-dimensional Bechgaard salts (TMTSF)_2X. Electronic thermal excitations across the FISDW energy gap progressively destroy the quantum Hall effect, so $\sigma_{xy}(T)$ interpolates between the quantized value at zero temperature and zero value at the transition temperature T_c, where FISDW disappears. This temperature dependence is similar to that of the superfluid density in the BCS theory of superconductivity. More precisely, it is the same as the temperature dependence of the Fr\"ohlich condensate density of a regular CDW/SDW. This suggests a two-fluid picture of the quantum Hall effect, where the Hall conductivity of the condensate is quantized, but the condensate fraction of the total electron density decreases with increasing temperature. The theory appears to agree with the experimental results obtained by measuring all three components of the resistivity tensor simultaneously on a (TMTSF)_2PF_6 sample and then reconstructing the conductivity tensor.
Phase coherent transport in Kondo/superconducting hybrid structures
Jonghwa Eom,Yun-Sok Shin,Hu-Jong Lee,Wang-Hyun Park,Taegon Kim,Jonghan Song
Physics , 2003,
Abstract: We present measurements of the transport properties of hybrid structures consisting of a Kondo AuFe film and a superconducting Al film. The temperature dependence of the resistance indicates the existence of the superconducting proximity effect in the Kondo AuFe wires over the range of $\sim0.5$ $\mu$m. Electronic phase coherence in the Kondo AuFe wires has been confirmed by observing the Aharanov-Bohm effect in the magnetoresistance of the loop structure. The amplitude of the magnetoresistance oscillations shows a reentrant behavior with a maximum at $\sim$ 870 mK, which results from an interplay between the Kondo effect and the superconducting proximity effect.
Electrical spin injection and detection in an InAs quantum well
Hyun Cheol Koo,Hyunjung Yi,Jae-Beom Ko,Joonyeon Chang,Suk-Hee Han,Donghwa Jung,Seon-Gu Huh,Jonghwa Eom
Physics , 2006, DOI: 10.1063/1.2430688
Abstract: We demonstrate fully electrical detection of spin injection in InAs quantum wells. A spin polarized current is injected from a NiFe thin film to a two-dimensional electron gas (2DEG) made of InAs based epitaxial multi-layers. Injected spins accumulate and diffuse out in the 2DEG, and the spins are electrically detected by a neighboring NiFe electrode. The observed spin diffusion length is 1.8 um at 20 K. The injected spin polarization across the NiFe/InAs interface is 1.9% at 20 K and remains at 1.4% even at room temperature. Our experimental results will contribute significantly to the realization of a practical spin field effect transistor.
Quantificational analysis of NPT-II protein from genetically modified Vitis vinifera L.
SH Eom, BI Reisch
African Journal of Biotechnology , 2010,
Abstract: Widely distributed inhibitors in grapevine extracts make it difficult to improve analytical procedures for protein detection. In this study, acidity in grapevine extracts was one of the major factors inhibiting the detection of neomycin phosphotransferase II via enzyme-linked immunosorbent assay. Leaf and berry extracts with low pH (3.0 – 4.0) strongly inhibited NPT-II detection, while root and xylem sap extracts (normally pH 5.5 to 7.0) allowed the successful detection of NPT-II. The other inhibitory effect against the detection was successfully solved by heat treatment to samples extracted. Boiling leaf extract prior to ELISA, in conjunction with pH adjustment (to 7.0) was essential to improve NPT-II detection, while with berry extracts only pH adjustment was required. In the basis of above results, NPT-II protein contents in transgenic grapevine tissues possessing a NPT-II gene were successfully measured. The results here may be useful to help in evaluation of the bio-safety whether the transgenic grapevines were released or contaminated on the grapevine cultivation area by NPT-II protein detection.
The association of Alu repeats with the generation of potential AU-rich elements (ARE) at 3' untranslated regions.
Hyeong Jun An, Doheon Lee, Kwang Hyung Lee, Jonghwa Bhak
BMC Genomics , 2004, DOI: 10.1186/1471-2164-5-97
Abstract: Interspersed in the human genome, Alu repeats occupy 5% of the 3' UTR of mRNA sequences. Alu has poly-adenine (poly-A) regions at its end, which lead to poly-thymine (poly-T) regions at the end of its complementary Alu. It has been found that AREs are present at the poly-T regions. From the 3' UTR of the NCBI's reference mRNA sequence database, we found nearly 40% (38.5%) of ARE (Class I) were associated with Alu sequences (Table 1) within one mismatch allowance in ARE sequences. Other ARE classes had statistically significant associations as well. This is far from a random occurrence given their limited quantity. At each ARE class, random distribution was simulated 1,000 times, and it was shown that there is a special relationship between ARE patterns and the Alu repeats.AREs are mediating sequence elements affecting the stabilization or degradation of mRNA at the 3' untranslated regions. However, AREs' mechanism and origins are unknown. We report that Alu is a source of ARE. We found that half of the longest AREs were derived from the poly-T regions of the complementary Alu.Varying more than ten-fold, messenger RNA degradation is essential for the regulation of gene expression [1,2]. Differential mRNA decay rates were determined by specific cis-acting sequences within mRNA. For example, the mRNA sequences of yeast, many mammalians, and other eukaryotes contain AU-rich elements or AREs at their 3' untranslated regions (UTR) [3,4]. For example, in yeast, AREs stimulated the shortening of poly adenine (poly A), and two kinds of degradation pathways followed. One is 5'-to-3' exonuclease access by removal of the 5' cap structure. The other is 3'-to-5' digestion by a complex of exonucleases called exosome [5,6]. Genes required for these steps have been identified in yeast and were found to be conserved among eukaryotes. Although the mechanisms of AREs enhanced mRNA degradation are unknown, several groups provided evidence that 3'-to-5' degradation by the exosome may be
Is HAPS Viable for the Next-Generation Telecommunication Platform in Korea?
Kim Jonghwa,Lee Deokjoo,Ahn Jaekyoung,Ahn Do-Seob
EURASIP Journal on Wireless Communications and Networking , 2008,
Abstract: HAPS is a promising technology capable of providing broadband multimedia services as an alternative to the satellite communication system or terrestrial network. In this study, economic aspects of HAPS service are analyzed, HAPS services are defined, and revenues from the defined services are forecasted assuming nine scenarios. Capital expenditure as well as operating expenditure is estimated. To evaluate the profitability of HAPS service, the net present value (NPV), payback period, and the internal rate of return (IRR) are calculated. The results show that HAPS is economically justifiable in all the scenarios. Assuming that ARPU for the service is $35 per month in the average scenario, NPV is calculated as $2964 million, IRR becomes 31.9%, and payback occurs in 2017, which implies that HAPS service is profitable in Korea. In addition, the results of the sensitivity analysis show that the results are fairly robust.
Is HAPS Viable for the Next-Generation Telecommunication Platform in Korea?
Jonghwa Kim,Deokjoo Lee,Jaekyoung Ahn,Do-Seob Ahn
EURASIP Journal on Wireless Communications and Networking , 2008, DOI: 10.1155/2008/596383
Abstract: HAPS is a promising technology capable of providing broadband multimedia services as an alternative to the satellite communication system or terrestrial network. In this study, economic aspects of HAPS service are analyzed, HAPS services are defined, and revenues from the defined services are forecasted assuming nine scenarios. Capital expenditure as well as operating expenditure is estimated. To evaluate the profitability of HAPS service, the net present value (NPV), payback period, and the internal rate of return (IRR) are calculated. The results show that HAPS is economically justifiable in all the scenarios. Assuming that ARPU for the service is $35 per month in the average scenario, NPV is calculated as $2964 million, IRR becomes 31.9%, and payback occurs in 2017, which implies that HAPS service is profitable in Korea. In addition, the results of the sensitivity analysis show that the results are fairly robust.
Three-dimensional metamaterials with an ultra-high effective refractive index over broad bandwidth
Jonghwa Shin,Jung-Tsung Shen,Shanhui Fan
Physics , 2008, DOI: 10.1103/PhysRevLett.102.093903
Abstract: The authors introduce a general mechanism, based on electrostatic and magnetostatic considerations, for designing three-dimensional isotopic metamaterials that possess an enhanced refractive index over an extremely large frequency range. The mechanism allows nearly independent control of effective electric permittivity and magnetic permeability without the use of resonant elements.
One-Way Optical Transition based on Causality in Momentum Space
Sunkyu Yu,Xianji Piao,KyungWan Yoo,Jonghwa Shin,Namkyoo Park
Physics , 2014, DOI: 10.1364/OE.23.024997
Abstract: The concept of parity-time (PT) symmetry has been used to identify a novel route to nonreciprocal dynamics in optical momentum space, imposing the directionality on the flow of light. Whereas PT-symmetric potentials have been implemented under the requirement of V(x) = V*(-x), this precondition has only been interpreted within the mathematical frame for the symmetry of Hamiltonians and has not been directly linked to nonreciprocity. Here, within the context of light-matter interactions, we develop an alternative route to nonreciprocity in momentum space by employing the concept of causality. We demonstrate that potentials with real and causal momentum spectra produce unidirectional transitions of optical states inside the k-continuum, which corresponds to an exceptional point on the degree of PT-symmetry. Our analysis reveals a critical link between non-Hermitian problems and spectral theory and enables the multi-dimensional manipulation of optical states, in contrast to one-dimensional control from the use of a Schrodinger-like equation in previous PT-symmetric optics.
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