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Search Results: 1 - 10 of 338540 matches for " C. H. Woo "
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Consistent histories: Description of a world with increasing entropy
C. H. Woo
Electronic Journal of Differential Equations , 2000,
Abstract: A distinction is made between two kinds of consistent histories: (1) robust histories consistent by virtue of decoherence, and (2) verifiable histories consistent through the existence of accessible records. It is events in verifiable histories which describe amplified quantum fluctuations. If the consistent-histories formalism is to improve on the Copenhagen interpretation by providing a self-contained quantum representation of the quasi-classical world, the appropriate quantum state must track closely all macroscopic phenomena, and the von Neumann entropy of that quantum state ought to change in the same direction as the statistical entropy of the macro-world. Since the von Neumann entropy tends to decrease under successive branchings, the evolution of an entropy-increasing quasi-classical world is not described by a process of branchings only: mergings of previously separate histories must also occur. As a consequence, the number of possible quasi-classical worlds does not have to grow indefinitely as in the many-world picture.
Consistent-Histories Description of A World of Increasing Entropy
C. H. Woo
Physics , 1999,
Abstract: A distinction is made between two kinds of consistent histories: (1) robust histories consistent by virtue of decoherence, and (2) verifiable histories consistent through the existence of accessible records. It is events in verifiable histories which describe amplified quantum fluctuations. If the consistent-histories formalism is to improve on the Copenhagen interpretation by providing a self-contained quantum representation of the quasi-classical world, the appropriate quantum state must track closely all macroscopic phenomena, and the von Neumann entropy of that quantum state ought to change in the same direction as the statistical entropy of the macro-world. Since the von Neumann entropy tends to decrease under successive branchings, the evolution of an entropy-increasing quasi-classical world is not described by the process of branchings only: mergings of previously separate histories must also occur. As a consequence, the number of possible quasi-classical worlds does not have to grow indefinitely as in the many-world picture.
Interatomic exchange coupling of BCC iron
Hai Wang,Pui-Wai Ma,C. H. Woo
Physics , 2010, DOI: 10.1103/PhysRevB.82.144304
Abstract: We performed first-principle calculations on the exchange interaction (EI) between atoms in BCC-Fe strained volumetrically. Our results show that the volume-dependence of the EI deviates considerably from the Bethe-Slater curve. This behavior is discussed in terms of the on-site and/or inter-site direct exchange interactions between electrons.
Monte-Carlo Simulation of Pulsed Laser Deposition
Pui-Man Lam,S. J. Liu,C. H. Woo
Physics , 2002, DOI: 10.1103/PhysRevB.66.045408
Abstract: Using the Monte Carlo method, we have studied the pulsed laser deposition process at the sub-monolayer regime. In our simulations, dissociation of an atom from a cluster is incorporated. Our results indicate that the pulsed laser deposition resembles molecular beam epitaxy at very low intensity, and that it is characteristically different from molecular beam epitaxy at higher intensity. We have also obtained the island size distributions. The scaling function for the island size distribution for pulsed laser deposition is different from that of molecular beam epitaxy.
Wave Propagation in Lossy and Superconducting Circular Waveguides
K. H. Yeap,C. Y. Tham,K. C. Yeong,H. J. Woo
Radioengineering , 2010,
Abstract: We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly.
Spinons in the strongly correlated copper oxide chains in SrCuO2
I. A. Zaliznyak,H. Woo,T. G. Perring,C. L. Broholm,C. D. Frost,H. Takagi
Physics , 2003, DOI: 10.1103/PhysRevLett.93.087202
Abstract: We have investigated the spin dynamics in the strongly correlated chain copper oxide SrCuO$_2$ for energies up to $\gtrsim 0.6$ eV using inelastic neutron scattering. We observe an acoustic band of magnetic excitations which is well described by the "Muller-ansatz" for the two-spinon continuum in the S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the continuum extends up to $\approx 360$ meV, which corresponds to an exchange constant $J = 226(12)$ meV. Our finding that an effective Heisenberg spin Hamlitonian adequately describes the spin sector of this 1D electron system, even though its energy scale is comparable to that of charge excitations, provides compelling experimental evidence for spin-charge separation.
Two- and three-dimensional computation of solitary wave runup on non-plane beach
B. H. Choi, E. Pelinovsky, D. C. Kim, I. Didenkulova,S.-B. Woo
Nonlinear Processes in Geophysics (NPG) , 2008,
Abstract: Solitary wave runup on a non-plane beach is studied analytically and numerically. For the theoretical approach, nonlinear shallow-water theory is applied to obtain the analytical solution for the simplified bottom geometry, such as an inclined channel whose cross-slope shape is parabolic. It generalizes Carrier-Greenspan approach for long wave runup on the inclined plane beach that is currently used now. For the numerical study, the Reynolds Averaged Navier-Stokes (RANS) system is applied to study soliton runup on an inclined beach and the detailed characteristics of the wave processes (water displacement, velocity field, turbulent kinetic energy, energy dissipation) are analyzed. In this study, it is theoretically and numerically proved that the existence of a parabolic cross-slope channel on the plane beach causes runup intensification, which is often observed in post-tsunami field surveys.
An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines
Zhiyuan Ma,Feng Ni,Grace H. C. Woo,Sie-Mun Lo
Beilstein Journal of Organic Chemistry , 2012, DOI: 10.3762/bjoc.8.93
Abstract: Intramolecular inverse electron demand cycloadditions of isatin-derived 1,2,4-triazines with acetylenic dienophiles tethered by amidations or transesterifications proceed in excellent yields to produce lactam- or lactone-fused α-carbolines. Beginning with various isatins and alkynyl dienophiles, a pilot-scale library of eighty-eight α-carbolines was prepared by using this robust methodology for biological evaluation.
Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. II. Analysis with the Yale models
J. -H. Woo,C. Gallart,P. Demarque,S. Yi,M. Zoccali
Physics , 2002, DOI: 10.1086/345959
Abstract: We present an analysis of CMDs of three intermediate-age LMC clusters, namely NGC 2173, SL 556 and NGC 2155. The main goal of our project is to investigate the amount of convective core overshoot necessary to reproduce the CMDs of relatively metal-poor, intermediate age stellar populations. We conclude that a moderate amount of overshoot and some fraction of binary stars are essential for reproducing the observed shapes around the turnoff in the CMD's of all three clusters: unresolved binary stars fill in the expected core contraction gap, and make a unique sequence near the gap, which cannot be reproduced by single stars alone, even with a larger amount of overshoot. From our overall analysis such as, shape of isochrones, star counts, color distribution, and synthetic CMD comparisons, we conclude that overshoot ~ 20% of the local pressure scale height best reproduces the CMD properties of all three clusters. The best age estimates are 1.5, 2.1 and 2.9 Gyr for NGC 2173, SL 556 and NGC 2155, respectively.
High Energy Spin Excitations in Electron-Doped Superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-δ}$ with $T_c=21$ K
Stephen D. Wilson,Shiliang Li,H. Woo,Pengcheng Dai,H. A. Mook,C. D. Frost,Seiki Komiya,Yoichi Ando
Physics , 2006, DOI: 10.1103/PhysRevLett.96.157001
Abstract: We use high-resolution inelastic neutron scattering to study the low-temperature magnetic excitations of electron-doped superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$ ($T_c=21\pm 1$ K) over a wide energy range (4 meV$\le\hbar\omega\le 330$ meV). The effect of electron-doping is to cause a wave vector ($Q$) broadening in the low-energy ($\hbar\omega\le 80$ meV) commensurate spin fluctuations at ($\pi$,$\pi$) and to suppress the intensity of spin-wave-like excitations at high energies ($\hbar\omega\ge 100$ meV). This leads to a substantial redistribution in the spectrum of the local dynamical spin susceptibility $\chi^{\prime\prime}(\omega)$, and reveals a new energy scale similar to that of the lightly hole-doped YB$_2$Cu$_3$O$_{6.353}$ ($T_c=18$ K).
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