Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films

A long standing problem of domain switching process - how domains nucleate - is examined in ultrathin ferroelectric films. We demonstrate that the large depolarization fields in ultrathin films could significantly lower the nucleation energy barrier (U*) to a level comparable to thermal energy (kBT), resulting in power-law like polarization decay behaviors. The "Landauer's paradox": U* is thermally insurmountable is not a critical issue in the polarization switching of ultrathin ferroelectric films. We empirically find a universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure

Conceptual study of electron ripple injection for tokamak transport control

A non-intrusive method for inducing radial electric field based on electron ripple injection is under development by the Princeton CDX-U group. The radial electric field is known to play an important role in the L-H and H-VH mode transition according to the recent theoretical and experimental research. It is therefore important to develop a non-intrusive tool to control the radial electric field profile in tokamak plasmas. The present technique utilizes externally-applied local magnetic ripple fields to trap electrons at the edge, allowing them to penetrate towards the plasma center via {gradient}B and curvature drifts, causing the flux surfaces to charge up negatively. Electron cyclotron resonance heating is utilized to increase the trapped population and the electron drift velocity by raising the perpendicular energy of trapped electrons. In order to quantify the effects of cyclotron resonance heating on electrons, the temperature anisotropy of resonant electrons in a tokamak plasma is calculated. For the calculation of anisotropic temperatures, energy moments of the bounce-averaged Fokker-Planck equation with a bi-Maxwellian distribution function for heated electrons are solved, assuming a moderate wave power and a constant quasilinear diffusion coefficient. Simulation using a guiding-center orbit model have been performed to understand the behavior of suprathermal electrons in the presence of ripple fields. Examples for CDX-U and ITER parameters are given

Spin-3/2 Baryons in Lattice QCD

We present first results for masses of spin-3/2 baryons in lattice QCD, using a novel fat-link clover fermion action in which only the irrelevant operators are constructed using fat links. In the isospin-1/2 sector, we observe, after appropriate spin and parity projection, a strong signal for the J^P=3/2^- state, and find good agreement between the 1/2^+ mass and earlier nucleon mass simulations with a spin-1/2 interpolating field. For the isospin-3/2 Delta states, clear mass splittings are observed between the various 1/2^+/- and 3/2^+/- channels, with the calculated level orderings in good agreement with those observed empirically

Strange meson-nucleon states in the quark potential model

The quark potential model and resonating group method are used to investigate the $\bar{K}N$ bound states and/or resonances. The model potential consists of the t-channel and s-channel one-gluon exchange potentials and the confining potential with incorporating the QCD renormalization correction and the spin-orbital suppression effect in it. It was shown in our previous work that by considering the color octet contribution, use of this model to investigate the $KN$ low energy elastic scattering leads to the results which are in pretty good agreement with the experimental data. In this paper, the same model and method are employed to calculate the masses of the $\bar{K}N$ bound systems. For this purpose, the resonating group equation is transformed into a standard Schr\"odinger equation in which a nonlocal effective $\bar{K}N$ interaction potential is included. Solving the Schr\"odinger equation by the variational method, we are able to reproduce the masses of some currently concerned $\bar{K}N$ states and get a view that these states possibly exist as $\bar{K}N$ molecular states. For the $KN$ system, the same calculation gives no support to the existence of the resonance $\Theta ^{+}(1540)$ which was announced recently.Comment: 15 pages, 4 figure

Cold testing of quasi-optical mode converters using a generator for non-rotating high-order gyrotron modes

In this paper, we test the performance of a quasi-optical, internal-gyrotron mode converter. When cold testing mode converters, a rotating higher-order mode is commonly used. However, this requires a nontrivial design and precise alignment. We thus propose a new technique for testing gyrotron mode converters by using a simple, non-rotating, higher-order mode generator. We demonstrate the feasibility of this technique for a W-band gyrotron quasi-optical mode converter by examining the excitation of a TE6,2 mode from a non-rotating mode generator. Our results demonstrate that this new cold-test scheme is an easy and efficient method for verifying the performance of quasi-optical mode converters.open0

Test of the Kolmogorov-Johnson-Mehl-Avrami picture of metastable decay in a model with microscopic dynamics

The Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the time evolution of the order parameter in systems undergoing first-order phase transformations has been extended by Sekimoto to the level of two-point correlation functions. Here, this extended KJMA theory is applied to a kinetic Ising lattice-gas model, in which the elementary kinetic processes act on microscopic length and time scales. The theoretical framework is used to analyze data from extensive Monte Carlo simulations. The theory is inherently a mesoscopic continuum picture, and in principle it requires a large separation between the microscopic scales and the mesoscopic scales characteristic of the evolving two-phase structure. Nevertheless, we find excellent quantitative agreement with the simulations in a large parameter regime, extending remarkably far towards strong fields (large supersaturations) and correspondingly small nucleation barriers. The original KJMA theory permits direct measurement of the order parameter in the metastable phase, and using the extension to correlation functions one can also perform separate measurements of the nucleation rate and the average velocity of the convoluted interface between the metastable and stable phase regions. The values obtained for all three quantities are verified by other theoretical and computational methods. As these quantities are often difficult to measure directly during a process of phase transformation, data analysis using the extended KJMA theory may provide a useful experimental alternative.Comment: RevTex, 21 pages including 14 ps figures. Submitted to Phys. Rev. B. One misprint corrected in Eq.(C1

An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium

We explore the splitting between flavour singlet and non-singlet mesons in charmonium. This has implications for the hyperfine splitting in charmonium