Strong "quantum" chaos in the global ballooning mode spectrum of three-dimensional plasmas

The spectrum of ideal magnetohydrodynamic (MHD) pressure-driven (ballooning) modes in strongly nonaxisymmetric toroidal systems is difficult to analyze numerically owing to the singular nature of ideal MHD caused by lack of an inherent scale length. In this paper, ideal MHD is regularized by using a $k$-space cutoff, making the ray tracing for the WKB ballooning formalism a chaotic Hamiltonian billiard problem. The minimum width of the toroidal Fourier spectrum needed for resolving toroidally localized ballooning modes with a global eigenvalue code is estimated from the Weyl formula. This phase-space-volume estimation method is applied to two stellarator cases.Comment: 4 pages typeset, including 2 figures. Paper accepted for publication in Phys. Rev. Letter

Investigating Problem-Based Learning Tutorship in Medical and Engineering Programs in Malaysia

Although Malaysia was the first country in Asia to adopt problem-based learning (PBL), the impact that this has had on its tutors remains largely unexplored. This paper details a qualitative study of the changing perceptions of teaching roles in two groups of problem-based learning tutors in two institutional contexts—one in medicine located in Kuala Lumpur and one in engineering located in Johor Bahru. Using Interpretive Phenomenological Analysis, the authors attempt to describe the way in which the two groups have experienced their changing professional world, and the mental processes through which they rationalize the transformation of Malaysia’s educational landscape. This paper discusses four themes of analysis: (1) Tutor perceptions are embedded in the context of Malaysian hierarchical social structures, (2) tutors recount a rewarding but challenging move to PBL, (3) tutors display widely different attitudes towards the role of expertise in PBL, and (4) tutors attempt to construct explanations and rationalize their emotional experiences with PBL

The role of the orbitofrontal cortex in regulation of interpersonal space: Evidence from frontal lesion and frontotemporal dementia patients

Interpersonal distance is central to communication and complex social behaviors but the neural correlates of interpersonal distance preferences are not defined. Previous studies suggest that damage to the orbitofrontal cortex (OFC) is associated with impaired interpersonal behavior. To examine whether the OFC is critical for maintaining appropriate interpersonal distance, we tested two groups of patients with OFC damage: Patients with OFC lesions and patients with behavioral variant frontotemporal dementia. These two groups were compared to healthy controls and to patients with lesions restricted to the dorsolateral prefrontal cortex. Only patients with OFC damage showed abnormal interpersonal distance preferences, which were significantly different from both controls and patients with dorsolateral prefrontal damage. The comfortable distances these patients chose with strangers were significantly closer than the other groups and resembled distances normally used with close others. These results shed light on the role of the OFC in regulating social behavior and may serve as a simple diagnostic tool for dementia or lesion patients

Boosting Long-term Memory via Wakeful Rest: Intentional Rehearsal is not Necessary, Automatic Consolidation is Sufficient.

<div><p>People perform better on tests of delayed free recall if learning is followed immediately by a short wakeful rest than by a short period of sensory stimulation. Animal and human work suggests that wakeful resting provides optimal conditions for the consolidation of recently acquired memories. However, an alternative account cannot be ruled out, namely that wakeful resting provides optimal conditions for intentional rehearsal of recently acquired memories, thus driving superior memory. Here we utilised non-recallable words to examine whether wakeful rest boosts long-term memory, even when new memories could not be rehearsed intentionally during the wakeful rest delay. The probing of non-recallable words requires a recognition paradigm. Therefore, we first established, via Experiment 1, that the rest-induced boost in memory observed via free recall can be replicated in a recognition paradigm, using concrete nouns. In Experiment 2, participants heard 30 non-recallable non-words, presented as ‘foreign names in a bridge club abroad’ and then either rested wakefully or played a visual spot-the-difference game for 10 minutes. Retention was probed via recognition at two time points, 15 minutes and 7 days after presentation. As in Experiment 1, wakeful rest boosted recognition significantly, and this boost was maintained for at least 7 days. Our results indicate that the enhancement of memory via wakeful rest is <i>not</i> dependent upon intentional rehearsal of learned material during the rest period. We thus conclude that consolidation is <i>sufficient</i> for this rest-induced memory boost to emerge. We propose that wakeful resting allows for superior memory consolidation, resulting in stronger and/or more veridical representations of experienced events which can be detected via tests of free recall and recognition.</p></div

Anderson localization of ballooning modes, quantum chaos and the stability of compact quasiaxially symmetric stellarators

The radially local magnetohydrodynamic(MHD) ballooning stability of a compact, quasiaxially symmetric stellarator (QAS), is examined just above the ballooning beta limit with a method that can lead to estimates of global stability. Here MHDstability is analyzed through the calculation and examination of the ballooning modeeigenvalue isosurfaces in the 3-space (s,α,θk); s is the edge normalized toroidal flux, α is the field linevariable, and θk is the perpendicular wave vector or ballooning parameter. Broken symmetry, i.e., deviations from axisymmetry, in the stellarator magnetic field geometry causes localization of the ballooning mode eigenfunction, and gives rise to new types of nonsymmetric eigenvalue isosurfaces in both the stable and unstable spectrum. For eigenvalues far above the marginal point, isosurfaces are topologically spherical, indicative of strong “quantum chaos.” The complexity of QAS marginal isosurfaces suggests that finite Larmor radius stabilization estimates will be difficult and that fully three-dimensional, high-nMHD computations are required to predict the beta limit.Research supported by U.S. DOE Contract No. DEAC02-76CH0373. John Canik held a U.S. DOE National Undergraduate Fellowship at Princeton Plasma Physics Laboratory, during the summer of 2000

Predictive use of the Maximum Entropy Production principle for Past and Present Climates

In this paper, we show how the MEP hypothesis may be used to build simple climate models without representing explicitly the energy transport by the atmosphere. The purpose is twofold. First, we assess the performance of the MEP hypothesis by comparing a simple model with minimal input data to a complex, state-of-the-art General Circulation Model. Next, we show how to improve the realism of MEP climate models by including climate feedbacks, focusing on the case of the water-vapour feedback. We also discuss the dependence of the entropy production rate and predicted surface temperature on the resolution of the model

Randomised comparison of 5 years of adjuvant tamoxifen with continuous therapy for operable breast cancer. The Scottish Cancer Trials Breast Group.

In 1985 a second randomisation was initiated for women in the treatment arm of the Scottish Tamoxifen Trial either to stop tamoxifen at 5 years or to continue indefinitely. A preliminary analysis of outcome in 342 patients at a median follow-up of 6 years suggests that a worthwhile gain in disease control from continuing adjuvant tamoxifen beyond 5 years is unlikely. [Hazard ratio for events (relapse or death without relapse) is 1.27, 95% CI = 0.87 - 1.85.] There is a suggestion that therapy for longer than 5 years may increase the risk of endometrial carcinoma (P = 0.064)

Dissipation processes in the Tongue of the Ocean

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 3159–3170, doi:10.1002/2015JC011165.The Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively understudied region in terms of both its biological and physical oceanographic characteristics. A prey-field mapping cruise took place in the fall between 15 September 2008 and 1 October 2008, consisting of a series of transects and “clovers” to study the spatial and temporal variability. The region is characterized by a deep scattering layer (DSL), which is preyed on by nekton that serves as the food for beaked whale and other whale species. This study marks the first of its kind where concurrent measurements of acoustic backscatter and turbulence have been conducted for a nekton scattering layer well below the euphotic zone. Turbulence data collected from a Deep Microstructure Profiler are compared to biological and shear data collected by a 38 kHz Simrad EK 60 echo sounder and a hydrographic Doppler sonar system, respectively. From these measurements, the primary processes responsible for the turbulent production in the TOTO region are assessed. The DSL around 500 m and a surface scattering layer (SSL) are investigated for raised ε values. Strong correlation between turbulence levels and scattering intensity of prey is generally found in the SSL with dissipation levels as large as ∼10−7 W kg−1, 3 orders of magnitude above background levels. In the DSL and during the diel vertical migration, dissipation levels ∼10−8 W kg−1 were observed.U.S. Office of Naval Research Grant Number: N00014-08-1-1162-0

Universal trapping scaling on the unstable manifold for a collisionless electrostatic mode

An amplitude equation for an unstable mode in a collisionless plasma is derived from the dynamics on the two-dimensional unstable manifold of the equilibrium. The mode amplitude $\rho(t)$ decouples from the phase due to the spatial homogeneity of the equilibrium, and the resulting one-dimensional dynamics is analyzed using an expansion in $\rho$. As the linear growth rate $\gamma$ vanishes, the expansion coefficients diverge; a rescaling $\rho(t)\equiv\gamma^2\,r(\gamma t)$ of the mode amplitude absorbs these singularities and reveals that the mode electric field exhibits trapping scaling $|E_1|\sim\gamma^2$ as $\gamma\rightarrow0$. The dynamics for $r(\tau)$ depends only on the phase $e^{i\xi}$ where $d\epsilon_{{k}} /dz=|{\epsilon_{{k}}}|e^{-i\xi/2}$ is the derivative of the dielectric as $\gamma\rightarrow0$.Comment: 11 pages (Latex/RevTex), 2 figures available in hard copy from the Author ([email protected]); paper accepted by Physical Review Letter