Impact of energetic particle orbits on long range frequency chirping of BGK modes

Long range frequency chirping of Bernstein-Greene-Kruskal modes, whose existence is determined by the fast particles, is investigated in cases where these particles do not move freely and their motion is bounded to restricted orbits. An equilibrium oscillating potential, which creates different orbit topologies of energetic particles, is included into the bump-on-tail instability problem of a plasma wave. With respect to fast particles dynamics, the extended model captures the range of particles motion (trapped/passing) with energy and thus represents a more realistic 1D picture of the long range sweeping events observed for weakly damped modes, e.g. global Alfven eigenmodes, in tokamaks. The Poisson equation is solved numerically along with bounce averaging the Vlasov equation in the adiabatic regime. We demonstrate that the shape and the saturation amplitude of the nonlinear mode structure depends not only on the amount of deviation from the initial eigenfrequency but also on the initial energy of the resonant electrons in the equilibrium potential. Similarly, the results reveal that the resonant electrons following different equilibrium orbits in the electrostatic potential lead to different rates of frequency evolution. As compared to the previous model [Breizman B.N. 2010 Nucl. Fusion 50 084014], it is shown that the frequency sweeps with lower rates. The additional physics included in the model enables a more complete 1D description of the range of phenomena observed in experiments.Comment: Submitted to Nuclear Fusion 25/01/201

Market concentration, risk-taking, and bank performance: evidence from emerging economies

This paper investigates the relationship between market concentration, risk-taking, and bank performance using a unique dataset of the BRIC banks over the period 2003-2010. We find a negative association between market concentration and performance, in support of the “quiet life” hypothesis. We also find that banks taking a lower level of risks perform better, in favour of prudential practice. Moreover, the BRICs’ banking sectors were all negatively affected by the 2007-2008 global financial crisis with China and Russia being the least and most affected, respectively. On average Chinese and Brazilian banks outperform Indian and Russian ones, indicating that China and Brazil have more favourable institutional infrastructure. These results are robust to alternative model specifications and estimation techniques. Our analysis may have important policy implications for bankers and regulators in the BRICs and other developing and transition countries

Multi-Resolution Successive Iteration (MRSI) for Non-Cartesian SENSE Reconstruction

An improved reconstruction strategy ¡ª the multi-resolution successive iteration (MRSI) method is proposed for non-Cartesian SENSE. The conjugate gradient (CG) reconstruction is performed in several successive phases with different level of resolution. In such a fashion, the iteration approaches the desired image with increasing resolution. In vivo results show that the total reconstruction time can be significantly reduced with this novel method.published_or_final_versio

Tunable loop microstrip (TLM) coil array with decoupling capacitors

The tunable loop microstrip (TLM) coil array with capacitive decoupling circuits can achieve more than -20dB element isolation. The decoupling circuit is quite simple and easy to be adjusted, so it is suitable for array with large number of elements. It is not only used for receive-only mode, but an excellent choice for transceiver as well for parallel MRI.published_or_final_versio

A novel RF coil: tunable loop microstrip (TLM) coil

A new tunable loop microstrip (TLM) RF coil for MRI is presented. It is a novel approach to use tuning capacitor on microstrip ring resonator. The resonant frequency and Q are analyzed based on microstrip theory. The experiment results show its advantages of higher Q and less frequency shift with loading effect than conventional microstrip coils terminated with open or short circuit. Because of its tunable characteristics, this new TLM coil can be easily applied to high and particularly to ultra-high filed MRI systems.published_or_final_versio

Microstrip Loop Array (MLA) for Parallel Imaging

The microstrip loop array (MLA), an improved version of planar strip array, is proposed which take advantage of loop geometry. Without much loss of the well-decoupling benefit of strip line arrays, the proposed microstrip loop arrays have well-localized sensitivity profiles which are more suitable for parallel imaging. Simulation and experiment results show that microstrip loop coils have sensitivity profiles like conventional loop coils, while the mutual coupling is 10-20dB less at same distances. A sensitivity-encoded cardiac imaging was performed to demonstrate the suitability of MLA for parallel imaging.published_or_final_versio

A novel RF coil: tunable loop microstrip (TLM) coil

A new tunable loop microstrip (TLM) RF coil for MRI is presented. It is a novel approach to use tuning capacitor on microstrip ring resonator. The resonant frequency and Q are analyzed based on microstrip theory. The experiment results show its advantages of higher Q and less frequency shift with loading effect than conventional microstrip coils terminated with open or short circuit. Because of its tunable characteristics, this new TLM coil can be easily applied to high and particularly to ultra-high filed MRI systems.published_or_final_versio

Improved Iterative Non-Cartesian SENSE Reconstruction using Inner-regularization

The conjugate-gradient (CG)-based non-Cartesian SENSE reconstruction in many cases exhibits unstable convergence behavior. This is because the generalized encoding matrix (GEM) is usually seriously ill-conditioned due to the large dimension and the mixed encoding scheme. To overcome this difficulty, an improved iterative SENSE approach is presented. During a so-called Lanczos iteration process, inner-regularization can be incorporated into the reconstruction without touching the iteration process. With inner-regularization adaptively applied for every iteration loop, the convergence behavior of iterative SENSE can be significantly improved and noise booming can be avoided.published_or_final_versio

Optimization of Regularization Parameter for GRAPPA Reconstruction

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