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Search Results: 1 - 10 of 25290 matches for " Jhinhwan Lee "
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A high-resolution cross-sectional analysis for Fourier-transform scanning tunneling spectroscopy and fully-phased Green-function-based quasiparticle scattering theories
Jhinhwan Lee
Physics , 2012,
Abstract: The Fourier-transform scanning tunneling spectroscopy (FTSTS) contains rich signals related to the quasiparticle scattering interference and/or the density-wave-like orders which are crucial in interpretation of the ground states and the phase transitions in quasi-2D strongly correlated electron systems such as cuprate and pnictide high-Tc superconductors. The octet model has been used to describe the FTSTS data according to the simplified banana band model of cuprates in superconducting ground state and worked well deep inside the superconducting dome, but away from the superconducting ground state the description starts to show severe limitations, such as appearance of particle-hole asymmetry of the quasiparticle band as will be discussed later. The first efforts to describe the FTSTS signals based on the fully-phased Green's function-based quasiparticle scattering interference theory, however lacked the full similarity to the FTSTS data, in part due to the lack of accurate information on the tunneling and scattering matrix elements. In this paper we discuss how the noise due to the potential disorder and the various artifacts in the raw FTSTS data can be handled by a simple cross-sectional analysis with an isotropic Gaussian averaging and modeling the set-point effect by an energy-independent and position-dependent factor to the density of states function. The result shows that in the cross-sectional presentation an enhanced correlation exists between the FTSTS data and the theoretical simulation even without the accurate model for the tunneling and the scattering matrix elements and without the assumption for particle-hole symmetry, suggesting that it can be a new starting point of a more robust quantum physical analysis framework appropriate for the phase transition study in the high-Tc superconductors and other strongly correlated electron systems.
Prediction of ultra-high ON/OFF ratio nanoelectromechanical switching from covalently-bound C60 chains
Han Seul Kim,Jhinhwan Lee,Yong-Hoon Kim
Physics , 2013, DOI: 10.1016/j.carbon.2013.09.054
Abstract: Applying a first-principles computational approach, we have systematically analyzed the effects of [2+2] cycloaddition oligomerization of fullerene C60 chains on their junction electronic and charge transport properties. For hypothetical infinite C60 chains, we first establish that the polymerization can in principle increase conductance by several orders of magnitude due to the strong orbital hybridizations and band formation. On the other hand, our simulations of the constant-height scanning tunneling microscope (STM) configuration shows that, in agreement with the recent experimental conclusion, the junction electronic structure and device characteristics are virtually unaffected by the C60 chain oligomerization. We further predict that the switching characteristics including even the ON/OFF-state assignment will sensitively depend on the substrate metal species due to the Fermi-level pinning at the substrate-side contact and the subsequent energy level bending toward the STM tip-side contact. We finally demonstrate that a force-feedbacked nanoelectromechanical approach in which both of the C60-electrode distances are kept at short distances before and after switching operations can achieve a metal-independent and significantly improved switching performance due to the Fermi-level pinning in both contacts and the large intrinsic conductance switching capacity of the C60 chain oligomerization.
Real Space Imaging of One-Dimensional Standing Waves: Direct Evidence for a Luttinger Liquid
Jhinhwan Lee,Sebastian Eggert,H. Kim,S. -J. Kahng,H. Shinohara,Y. Kuk
Physics , 2004, DOI: 10.1103/PhysRevLett.93.166403
Abstract: Electronic standing waves with two different wavelengths were directly mapped near one end of a single-wall carbon nanotube as a function of the tip position and the sample bias voltage with highresolution position-resolved scanning tunneling spectroscopy. The observed two standing waves caused by separate spin and charge bosonic excitations are found to constitute direct evidence for a Luttinger liquid. The increased group velocity of the charge excitation, the power-law decay of their amplitudes away from the scattering boundary, and the suppression of the density of states near the Fermi level were also directly observed or calculated from the two different standing waves.
Spectroscopic Fingerprint of Phase-Incoherent Superconductivity in the Cuprate Pseudogap State
Jhinhwan Lee,K. Fujita,A. R. Schmidt,Chung Koo Kim,H. Eisaki,S. Uchida,J. C. Davis
Physics , 2009, DOI: 10.1126/science.1176369
Abstract: A possible explanation for the existence of the cuprate "pseudogap" state is that it is a d-wave superconductor without quantum phase rigidity. Transport and thermodynamic studies provide compelling evidence that supports this proposal, but few spectroscopic explorations of it have been made. One spectroscopic signature of d-wave superconductivity is the particle-hole symmetric "octet" of dispersive Bogoliubov quasiparticle interference modulations. Here we report on this octet's evolution from low temperatures to well into the underdoped pseudogap regime. No pronounced changes occur in the octet phenomenology at the superconductor's critical temperature Tc, and it survives up to at least temperature T ~ 1.5Tc. In the pseudogap regime, we observe the detailed phenomenology that was theoretically predicted for quasiparticle interference in a phase-incoherent d-wave superconductor. Thus, our results not only provide spectroscopic evidence to confirm and extend the transport and thermodynamics studies, but they also open the way for spectroscopic explorations of phase fluctuation rates, their effects on the Fermi arc, and the fundamental source of the phase fluctuations that suppress superconductivity in underdoped cuprates.
How Cooper pairs vanish approaching the Mott insulator in Bi2Sr2CaCu2O8+d
Y. Kohsaka,C. Taylor,P. Wahl,A. Schmidt,Jhinhwan Lee,K. Fujita,J. W. Alldredge,Jinho Lee,K. McElroy,H. Eisaki,S. Uchida,D. -H. Lee,J. C. Davis
Physics , 2008, DOI: 10.1038/nature07243
Abstract: The antiferromagnetic ground state of copper oxide Mott insulators is achieved by localizing an electron at each copper atom in real space (r-space). Removing a small fraction of these electrons (hole doping) transforms this system into a superconducting fluid of delocalized Cooper pairs in momentum space (k-space). During this transformation, two distinctive classes of electronic excitations appear. At high energies, the enigmatic 'pseudogap' excitations are found, whereas, at lower energies, Bogoliubov quasi-particles -- the excitations resulting from the breaking of Cooper pairs -- should exist. To explore this transformation, and to identify the two excitation types, we have imaged the electronic structure of Bi2Sr2CaCu2O8+d in r-space and k-space simultaneously. We find that although the low energy excitations are indeed Bogoliubov quasi-particles, they occupy only a restricted region of k-space that shrinks rapidly with diminishing hole density. Concomitantly, spectral weight is transferred to higher energy r-space states that lack the characteristics of excitations from delocalized Cooper pairs. Instead, these states break translational and rotational symmetries locally at the atomic scale in an energy independent fashion. We demonstrate that these unusual r-space excitations are, in fact, the pseudogap states. Thus, as the Mott insulating state is approached by decreasing the hole density, the delocalized Cooper pairs vanish from k-space, to be replaced by locally translational- and rotational-symmetry-breaking pseudogap states in r-space.
Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states
M. J. Lawler,K. Fujita,Jhinhwan Lee,A. R. Schmidt,Y. Kohsaka,Chung Koo Kim,H. Eisaki,S. Uchida,J. C. Davis,J. P. Sethna,Eun-Ah Kim
Physics , 2010, DOI: 10.1038/nature09169
Abstract: In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within CuO2 unit cell. We analyze spectroscopic-imaging scanning tunneling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+{\delta} and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90o -rotational symmetry within every CuO2 unit cell.
The Relationship between Visual Satisfaction and Water Clarity and Quality Management in Tourism Fishing Ports  [PDF]
Lee-Hsueh Lee
Journal of Water Resource and Protection (JWARP) , 2016, DOI: 10.4236/jwarp.2016.88064
Abstract: Visual satisfaction of the tourists with a water body is strongly influenced by water clarity, which is in turn influenced by a number of water quality parameters. Visual satisfaction thus stands to benefit from having a water quality management tool that results in better water clarity. A Clarity Suitability Index of Water Quality (CSIWQ), derived from clarity suitability curves of selected water quality parameters, can allow estimation of optimal values for these parameters, while ensuring high visual satisfaction among tourists. The present study used sampling and survey methodologies to investigate water clarity and quality at five tourism fishing ports; simultaneously, tourists’ visual satisfaction with a water body was assessed through a questionnaire based on their perceptions. The relationship between tourists’ visual satisfaction and water clarity was found to be positive and strong, with water clarity having predictive power of 74.2%. The study showed that DO, BOD, TP, and SS were the most critical parameters for water clarity. A continued product approach of CSIWQ was found to be most appropriate for describing the relationship between water clarity and these four parameters. This enabled a CSIWQ Index value to be calculated. With a CSIWQ value of 0.6, water clarity would be more than 2.08 m, and tourists would experience very high satisfaction. CSI curves showed that DO would preferably be 9.0 mg/L, and BOD, TP, and SS less than 0.5 mg/L, 0.12 mg/L, and 45.0 mg/L, respectively. The model thus produced valuable insights for assessing and improving water quality and ensuring high levels of visual satisfaction among tourists in tourism fishing ports. This model identified only four parameters but could be improved by ensuring that other water quality parameters were included, to encourage an increase in the number of tourists and to include monitoring of more pollutant sources.
Appearance’s Aesthetic Appreciation to Inform Water Quality Management of Waterscapes  [PDF]
Lee-Hsueh Lee
Journal of Water Resource and Protection (JWARP) , 2017, DOI: 10.4236/jwarp.2017.913103
Abstract:
The appearance of the water is just one aspect of a waterscape that can be appreciated aesthetically. Water appearance is affected by water clarity and water colour. Here, an aesthetic assessment model of waterscape was suggested. In the model, water clarity and colour have direct effects, whereas water quality and phytoplankton biomass have indirect effects, on tourists’ aesthetic assessment of water bodies. The preferred water colour is aquamarine to blue, regardless of depth of clarity. Water colour ranges from pastel yellow to yellow-green are not favoured by tourists. Four water-quality parameters were correlated with water clarity and phytoplankton biomass. The coefficient of indirect effect of river pollution index on tourists’ aesthetic valuation of aquamarine to blue water colour was -0.457, and for pastel yellow to yellowgreen, it was -0.209. The research results showed observation of water colour could not only reflect waterscape aesthetic value, but also serve as a guide of judging water quality, and the status of phytoplankton benefited to simplify the process of water-quality management for waterscape.
Abdominal Fat Reduction through Cryolipolysis  [PDF]
Doyeop Lee, Kyurae Lee
Journal of Biosciences and Medicines (JBM) , 2018, DOI: 10.4236/jbm.2018.69005
Abstract: Although several studies showed the efficacy and safety from this procedure, the comparative assessment of adipose tissue by cryolipolysis has not been studied until now. Therefore we investigated the quantitative change of cross sectional areas of abdominal SAT (subcutaneous adipose tissue) and VAT (visceral adipose tissue) following cryolipolysis. A prospective study for twelve subjects with a single session of cryolipolysis on abdomen was performed. We assessed for their height, weight, and waist circumferences, body contours by photographs, and the cross sectional areas of visceral and subcutaneous adipose tissues were measured at umbilicus level by computerized tomography for 2 months. The cross sectional areas in SAT reduced from 243.3 ± 24.7 to 238.5 ± 40.7 cm2 at 2 months post-treatment. Those of VAT reduced from 141.3 ± 46.4 to 125.1 ± 42.8 cm2 at 2 months post-treatment. Cross sectional areas of VAT, and waist circumferences were significantly reduced by 16.2 cm2, 4.1 cm respectively. Additionally visual improvement without unexpected adverse events was noted. In conclusion a single session cryolipolysis demonstrated to reduce visceral adipose tissue as well as waist circumferences tissue for 2 months. Further controlled study would be needed to evaluate for reduction of visceral adipose tissue by cryolipolysis.
Exponential Ergodicity and β-Mixing Property for Generalized Ornstein-Uhlenbeck Processes  [PDF]
Oesook Lee
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.21004
Abstract: The generalized Ornstein-Uhlenbeck process is derived from a bivariate Lévy process and is suggested as a continuous time version of a stochastic recurrence equation [1]. In this paper we consider the generalized Ornstein-Uhlenbeck process and provide sufficient conditions under which the process is exponentially ergodic and hence holds the expo-nentially β-mixing property. Our results can cover a wide variety of areas by selecting suitable Lévy processes and be used as fundamental tools for statistical analysis concerning the processes. Well known stochastic volatility models in finance such as Lévy-driven Ornstein-Uhlenbeck process is examined as a special case.
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