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Search Results: 1 - 10 of 341290 matches for " H. C. Chung "
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Large-N solutions of the Heisenberg and Hubbard-Heisenberg models on the anisotropic triangular lattice: application to Cs$_2$CuCl$_4$ and to the layered organic superconductors $κ$-(BEDT-TTF)$_2$X
C. H. Chung,J. B. Marston,Ross H. McKenzie
Physics , 2000, DOI: 10.1088/0953-8984/13/22/311
Abstract: We solve the Sp(N) Heisenberg and SU(N) Hubbard-Heisenberg models on the anisotropic triangular lattice in the large-N limit. These two models may describe respectively the magnetic and electronic properties of the family of layered organic materials $\kappa$-(BEDT-TTF)$_2$X. The Heisenberg model is also relevant to the frustrated antiferromagnet, Cs$_2$CuCl$_4$. We find rich phase diagrams for each model. The Sp(N) antiferromagnet is shown to have five different phases as a function of the size of the spin and the degree of anisotropy of the triangular lattice. The effects of fluctuations at finite-N are also discussed. For parameters relevant to Cs$_2$CuCl$_4$ the ground state either exhibits incommensurate spin order, or is in a quantum disordered phase with deconfined spin-1/2 excitations and topological order. The SU(N) Hubbard-Heisenberg model exhibits an insulating dimer phase, an insulating box phase, a semi-metallic staggered flux phase (SFP), and a metallic uniform phase. The uniform and SFP phases exhibit a pseudogap. A metal-insulator transition occurs at intermediate values of the interaction strength.
Simple Time-Domain Expressions for Prediction of Crosstalk on Coupled Microstrip Lines
C. C. Chai;B. K. Chung;H. T. Chuah
PIER , 2003, DOI: 10.2528/PIER02060902
Abstract: This paper presents an improved variant of timedomain method for predicting crosstalk on parallel-coupled matched terminated microstrip lines. This method derives simple near-end and far-end time-domain crosstalk expressions which are applicable to lossless case with significant harmonic frequency < 1 GHz. The expressions are in polynomial form with geometrical dimensions of the structure and stimulus information as the only required entry parameters. They are simpler as compared to other methods because the difficult-to-determine distributed electrical parameters of the coupled lines are not needed. A look-up table for the polynomial coefficients is generated for easy application of this technique. The expressions are applicable for board thickness of 4-63 mils, 30-70Ω line characteristic impedance, 0.5-4.0 (where is the line width) inner edge to edge separation, and 3-5 dielectric constant. For significant harmonic frequency > 1 GHz, the effect of both losses and dispersion on the crosstalk levels is accounted for by investigating the gradient of the distorted driving signal. The peak crosstalk levels are then predicted by modifying the time derivative term in the lossless expressions. In addition, the far-end crosstalk is proved to saturate at half of the magnitude of the driving signal entering the active line. The saturation phenomenon is studied from the viewpoint of difference in odd-mode and even-mode propagation velocities.
Non-equilibrium frequency-dependent noise through a quantum dot: A real time functional renormalization group approach
C. P. Moca,P. Simon,C. H. Chung,G. Zarand
Physics , 2010, DOI: 10.1103/PhysRevB.83.201303
Abstract: We construct a real time current-conserving functional renormalization group (RG) scheme on the Keldysh contour to study frequency-dependent transport and noise through a quantum dot in the local moment regime. We find that the current vertex develops a non-trivial non-local structure in time, governed by a new set of RG equations. Solving these RG equations, we compute the complete frequency and temperature-dependence of the noise spectrum. For voltages large compared to the Kondo temperature, $eV \gg k_BT_K$, two sharp anti-resonances are found in the noise spectrum at frequencies $\hbar \omega = \pm e V$, and correspondingly, two peaks in the ac conductance through the dot.
A Chinese Information Processing System
C.Y.Chung,H.R.Hwa
计算机科学技术学报 , 1986,
Abstract: The Chinese information processing system(CIPS)introduced in this paper can producegraphs,tables,flowcharts,mathematical equations,forms and also provides typesettingfacilities.The system can process not only Chinese text but also English text or a mixture ofthem.It is written in C language and runs on VAX Ⅱ/780 under Unix operating system.TheCIPS system is very easy to use and provides user-defined macro which allows abbreviationsof commonly used Chinese phrases and reduce the complexity of Chinese characters coding.
Raman Spectra of Triplet Superconductor in Sr$_2$RuO$_4$
Hae-Young Kee,K. Maki,C. H. Chung
Physics , 2002, DOI: 10.1103/PhysRevB.67.180504
Abstract: We study the Raman spectra of spin-triplet superconductors in Sr$_2$RuO$_4$. The p-wave and f-wave symmetries are considered. We show that there is the clapping mode with frequency of $\sqrt{2} \Delta(T)$ and $1.02 \Delta(T)$ for p-wave and f-wave superconductors, respectively. This mode is visible as a huge resonance in the B1g and B2g modes of Raman spectra. We discuss the details of the Raman spectra in these superconducting states.
Effect of Ring Exchange on Orbital Antiferromagnet
C. H. Chung,Hae-Young Kee,Yong Baek Kim
Physics , 2002, DOI: 10.1103/PhysRevB.67.224405
Abstract: We study the effect of four-particle ring exchange process on orbital antiferromagnetic state that occurs in some correlated electron systems in two dimensions. The primary question is whether the ring exchange process enhances or suppresses the orbital antiferromagnetic ordering. Using the fact that the orbital antiferromagnetic state arises in the large-N limit of the SU(N) generalization of the t-J model, we consider the large-N limit of the t-J-$K$ model where $K$ represents the four-particle ring exchange term. The phase diagrams in the large-N mean field theory are obtained for the half-filling and finite hole concentrations at zero temperature. It is found that the ring exchange in general favors dimerized states or the inhomogeneous orbital antiferromagnetic state, and suppresses the homogeneous orbital antiferromagnetic state. We compare our results with other related models of strongly correlated systems with ring exchange processes.
Quantum Phases of the Shastry-Sutherland Antiferromagnet
C. H. Chung,J. B. Marston,Subir Sachdev
Physics , 2001, DOI: 10.1103/PhysRevB.64.134407
Abstract: We study possible paramagnetic phases of antiferromagnets on the Shastry-Sutherland lattice by a gauge-theoretic analysis of fluctuations in a theory with Sp(2N) symmetry. In addition to the familiar dimer phase, we find a confining phase with plaquette order, and a topologically ordered phase with deconfined S=1/2 spinons and helical spin correlations. The deconfined phase is contiguous to the dimer phase, and in a regime of couplings close to those found in the insulator SrCu2(BO3)2. We suggest that a superconductor obtained by doping this insulator with mobile charge carriers will be an attractive candidate for observing the anomalous magnetic flux properties associated with topological order.
A NEW GA APPROACH FOR OPTIMAL CONTROL SETTING DETERMINATION OF UPFC IN POWER SYSTEM OPERATION
T.S.Chung,H.C.Leung
电力系统自动化 , 2002,
Abstract: Thispaperpresentsanew,hybridgeneticalgorithm(GA)approachtosolveoptimalpowerflow(OPF)inpowersystemincorporatingflexibleACtransmissionsystems(FACTS).AversatileFACTSdevice,UPFC(unifiedpowerflowcontroller),isconsidered.Inthesolutionprocess,GA,coupledwithfullACpowerflow,selectsthebestregulationtominimizethetotalcostandkeepthepowerflowswithintheirsecuritylimits.TheoptimizationprocesswithGAispresentedwithcasestudyexamplesusingIEEEtestsystemtodemonstrateitsapplicability.Theresultsarepresentedtoshowthefeasibilityandpotentialofthisnewapproach.
Functionalization of Polypropylene with High Dielectric Properties: Applications in Electric Energy Storage  [PDF]
T. C. Mike Chung
Green and Sustainable Chemistry (GSC) , 2012, DOI: 10.4236/gsc.2012.22006
Abstract: Biaxial-oriented polypropylene (BOPP) thin films are currently used as dielectrics in state-of-the-art capacitors that show many advantages, such as low energy loss and high breakdown strength, but a limited energy density (<2 J/cm3). This paper reviews some of our experimental results in functionalization of polypropylene with the objective to increase its electric energy density and maintain all desirable properties. A family of PP copolymers with various moieties, such as OH, O-Si(CH3)3, long chain branching, and cross-linking structure, have been systematically synthesized and studied to examine their dielectric properties (i.e. dielectric constant, dielectric loss, breakdown strength, polarization under various temperatures and electric fields). Evidently, a high molecular weight poly(propylene-co-hexen-6-ol) copolymer (PP-OH) containing 4.2 mol% of polar OH groups shows a dielectric constant (ε) of about 4.6 (more than 2 times of BOPP)—which is independent on a wide range of temperatures and frequencies—and high breakdown strength > 600 MV/m. The PP-OH dielectric demonstrates a linear reversible charge storage behavior with high releasing energy density > 7 J/cm3 (2 - 3 times of BOPP) after an applied electric field at E = 600 MV/m, without showing any significant increase of energy loss and remnant polarization at zero electric field. On the other hand, a cross-linked polypropylene (x-PP) exhibits an ε ~ 3, which is independent of a wide range of temperatures and frequencies, slim polarization loops, high breakdown strength (E = 650 MV/m), narrow breakdown distribution, and reliable energy storage capacity > 5 J/cm3 (double that of state-of-the-art BOPP capacitors), without showing any increase in energy loss.
Electronic and optical properties in graphane
M. H. Lee,H. C. Chung,J. M. Lu,C. P. Chang,M. F. Lin
Physics , 2014,
Abstract: We develop the tight-binding model to study electronic and optical properties of graphane. The strong sp3 chemical bondings among the carbon and hydrogen atoms induce a special band structure and thus lead to the rich optical excitations. The absorption spectrum hardly depends on the direction of electric polarization. It ex- hibits a lot of shoulder structures and absorption peaks, which arise from the extreme points and the saddle points of the parabolic bands, respectively. The threshold op- tical excitations, only associated with the 2px and 2py orbitals of the carbon atoms, are revealed in a shoulder structure at ?3.5 eV. The ?rst symmetric absorption peak, appearing at ~11 eV, corresponds to energy bands due to the considerable hybridiza- tion of carbon 2pz orbitals and H 1s orbitals. Also, some absorption peaks at higher frequencies indicate the bonding of 2s and 1s orbitals. These results are in sharp contrast to those of the sp2 graphene systems.
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