Observation of Three-dimensional Long-range Order in Smaller Ion Coulomb Crystals in an rf Trap

Three-dimensional long-range ordered structures in smaller and near-spherically symmetric Coulomb crystals of ^{40}Ca^+ ions confined in a linear rf Paul trap have been observed when the number of ions exceeds ~1000 ions. This result is unexpected from ground state molecular dynamics (MD) simulations, but found to be in agreement with MD simulations of metastable ion configurations. Previously, three-dimensional long-range ordered structures have only been reported in Penning traps in systems of ~50,000 ions or more.Comment: 5 pages; 4 figures; to appear in Phys. Rev. Lett.; changed content

Fuel-Supply-Limited Stellar Relaxation Oscillations: Application to Multiple Rings around AGB Stars and Planetary Nebulae

We describe a new mechanism for pulsations in evolved stars: relaxation oscillations driven by a coupling between the luminosity-dependent mass-loss rate and the H fuel abundance in a nuclear-burning shell. When mass loss is included, the outward flow of matter can modulate the flow of fuel into the shell when the stellar luminosity is close to the Eddington luminosity $L_{\rm Edd}$. When the luminosity drops below $L_{\rm Edd}$, the mass outflow declines and the shell is re-supplied with fuel. This process can be repetitive. We demonstrate the existence of such oscillations and discuss the dependence of the results on the stellar parameters. In particular, we show that the oscillation period scales specifically with the mass of the H-burning relaxation shell (HBRS), defined as the part of the H-burning shell above the minimum radius at which the luminosity from below first exceeds the Eddington threshold at the onset of the mass loss phase. For a stellar mass M_*\sim 0.7\Msun, luminosity L_*\sim 10^4\Lsun, and mass loss rate |\dot M|\sim 10^{-5}\Msun yr$^{-1}$, the oscillations have a recurrence time $\sim 1400$ years $\sim 57\tau_{\rm fsm}$, where $\tau_{\rm fsm}$ is the timescale for modulation of the fuel supply in the HBRS by the varying mass-loss rate. This period agrees with the $\sim$ 1400-year period inferred for the spacings between the shells surrounding some planetary nebulae, and the the predictied shell thickness, of order 0.4 times the spacing, also agrees reasonably well.Comment: 15 pages TeX, 1 ps figure submitted to Ap

Disentangling the effects of age and mild traumatic brain injury on brain network connectivity:A resting state fMRI study

INTRODUCTION: Cognitive complaints are common shortly after mild traumatic brain injury (mTBI) but may persist up to years. Age-related cognitive decline can worsen these symptoms. However, effects of age on mTBI sequelae have scarcely been investigated. METHODS: Fifty-four mTBI patients (median age: 35 years, range 19-64 years, 67% male) and twenty age- and sex-matched healthy controls were studied using resting state functional magnetic resonance imaging in the sub-acute phase. Independent component analysis was used to identify intrinsic connectivity networks (ICNs). A multivariate approach was adopted to evaluate the effects of age and group on the ICNs in terms of (static) functional network connectivity (FNC), intensities of spatial maps (SMs) and time-course spectral power (TC). RESULTS: We observed significant age-related changes for a) FNC: changes between 10 pairs of ICNs, mostly involving the default mode (DM) and/or the cognitive-control (CC) domains; b) SMs: intensity decrease in clusters across three domains and intensity increase in clusters across two domains, including the CC but not the DM and c) TC: spectral power decrease within the 0-0.15 Hz range and increase within the 0.20-0.25 Hz range for increasing age within networks located in frontal areas, including the anterior DM. Groups only differed for TC within the 0.065-0.10 Hz range in the cerebellar ICN and no age × group interaction effect was found. CONCLUSIONS: We showed robust effects of age on connectivity between and within ICNs that are associated with cognitive functioning. Differences between mTBI patients and controls were only found for activity in the cerebellar network, increasingly recognized to participate in cognition. Our results suggest that to allow for capturing the true effects related to mTBI and its effects on cognitive functioning, age should be included as a covariate in mTBI studies, in addition to age-matching groups

Best network chirplet-chain: Near-optimal coherent detection of unmodeled gravitation wave chirps with a network of detectors

The searches of impulsive gravitational waves (GW) in the data of the ground-based interferometers focus essentially on two types of waveforms: short unmodeled bursts and chirps from inspiralling compact binaries. There is room for other types of searches based on different models. Our objective is to fill this gap. More specifically, we are interested in GW chirps with an arbitrary phase/frequency vs. time evolution. These unmodeled GW chirps may be considered as the generic signature of orbiting/spinning sources. We expect quasi-periodic nature of the waveform to be preserved independent of the physics which governs the source motion. Several methods have been introduced to address the detection of unmodeled chirps using the data of a single detector. Those include the best chirplet chain (BCC) algorithm introduced by the authors. In the next years, several detectors will be in operation. The joint coherent analysis of GW by multiple detectors can improve the sight horizon, the estimation of the source location and the wave polarization angles. Here, we extend the BCC search to the multiple detector case. The method amounts to searching for salient paths in the combined time-frequency representation of two synthetic streams. The latter are time-series which combine the data from each detector linearly in such a way that all the GW signatures received are added constructively. We give a proof of principle for the full sky blind search in a simplified situation which shows that the joint estimation of the source sky location and chirp frequency is possible.Comment: 22 pages, revtex4, 6 figure

Lie algebras and 3-transpositions

We describe a construction of an algebra over the field of order 2 starting from a conjugacy class of 3-transpositions in a group. In particular, we determine which simple Lie algebras arise by this construction. Among other things, this construction yields a natural embedding of the sporadic simple group \Fi{22} in the group $^2E_6(2)$.Comment: 23 page

Pressure-induced metallization and structural phase transition of the Mott-Hubbard insulator TiOBr

We investigated the pressure-dependent optical response of the low-dimensional Mott-Hubbard insulator TiOBr by transmittance and reflectance measurements in the infrared and visible frequency range. A suppression of the transmittance above a critical pressure and a concomitant increase of the reflectance are observed, suggesting a pressure-induced metallization of TiOBr. The metallic phase of TiOBr at high pressure is confirmed by the presence of additional excitations extending down to the far-infrared range. The pressure-induced metallization coincides with a structural phase transition, according to the results of x-ray powder diffraction experiments under pressure.Comment: 4 pages, 3 figure

Full Elite Sets for Multi-Objective Optimisation

Copyright © 2002 Springer. The final publication is available at link.springer.com5th International Conference on Adaptive Computing in Design and Manufacture (ACDM 2002), Exeter, UK, 16-18 April, 2002Multi-objective evolutionary algorithms frequently use an archive of non-dominated solutions to approximate the Pareto front. We show that the truncation of this archive to a limited number of solutions can lead to oscillating and shrinking estimates of the Pareto front. New data structures to permit efficient query and update of the full archive are proposed, and the superior quality of frontal estimates found using the full archive is illustrated on test problems

The broad differential diagnosis of encephalitis:a case report

A 31-year-old previously healthy woman presented with hallucinations and altered mental status, which was eventually found to be due to anti-N-methyl-D-aspartate receptor encephalitis. In this case report, we discuss the broad differential diagnosis of encephalitis with infectious and autoimmune causes. Furthermore, we consider empirical treatment options in case a definite diagnosis is hard to be made