Atmospheric tomography with separate minimum variance laser and natural guide star mode control

This paper introduces a novel, computationally efficient, and practical atmospheric tomography wavefront control architecture with separate minimum variance laser and natural guide star mode estimation. The architecture is applicable to all laser tomography systems, including multi conjugate adaptive optics (MCAO), laser tomography adaptive optics (LTAO), and multi object adaptive optics (MOAO) systems. Monte Carlo simulation results for the Thirty Meter Telescope (TMT) MCAO system demonstrate its benefit over a previously introduced “ad hoc” split MCAO architecture, calling for further in-depth analysis and simulations over a representative ensemble of natural guide star (NGS) asterisms with optimized loop frame rates and modal gains

Real-time turbulence profiling with a pair of laser guide star Shack–Hartmann wavefront sensors for wide-field adaptive optics systems on large to extremely large telescopes

Real-time turbulence profiling is necessary to tune tomographic wavefront reconstruction algorithms for wide-field adaptive optics (AO) systems on large to extremely large telescopes, and to perform a variety of image post-processing tasks involving point-spread function reconstruction. This paper describes a computationally efficient and accurate numerical technique inspired by the slope detection and ranging (SLODAR) method to perform this task in real time from properly selected Shack–Hartmann wavefront sensor measurements accumulated over a few hundred frames from a pair of laser guide stars, thus eliminating the need for an additional instrument. The algorithm is introduced, followed by a theoretical influence function analysis illustrating its impulse response to high-resolution turbulence profiles. Finally, its performance is assessed in the context of the Thirty Meter Telescope multi-conjugate adaptive optics system via end-to-end wave optics Monte Carlo simulations

Constrained matched filtering for extended dynamic range and improved noise rejection for Shack-Hartmann wavefront sensing

We recently introduced matched filtering in the context of astronomical Shack-Hartmann wavefront sensing with elongated sodium laser beacons [Appl. Opt. 45, 6568 (2006)]. Detailed wave optics Monte Carlo simulations implementing this technique for the Thirty Meter Telescope dual conjugate adaptive optics system have, however, revealed frequent bursts of degraded closed loop residual wavefront error [Proc. SPIE 6272, 627236 (2006)]. The origin of this problem is shown to be related to laser guide star jitter on the sky that kicks the filter out of its linear dynamic range, which leads to bursts of nonlinearities that are reconstructed into higher-order wavefront aberrations, particularly coma and trifoil for radially elongated subaperture spots. An elegant reformulation of the algorithm is proposed to extend its dynamic range using a set of linear constraints while preserving its improved noise rejection and Monte Carlo performance results are reported that confirm the benefits of the method

Temporal precedence of emotion over attention modulations in the lateral amygdala: Intracranial ERP evidence from a patient with temporal lobe epilepsy

Previous fMRI studies have reported mixed evidence for the influence of selective attention on amygdala responses to emotional stimuli, with some studies showing "automatic" emotional effects to threat-related stimuli without attention (or even without awareness), but other studies showing a gating of amygdala activity by selective attention with no response to unattended stimuli. We recorded intracranial local field potentials from the intact left lateral amygdala in a human patient prior to surgery for epilepsy and tested, with a millisecond time resolution, for neural responses to fearful faces appearing at either task-relevant or task-irrelevant locations. Our results revealed an early emotional effect in the amygdala arising prior to, and independently of, attentional modulation. However, at a later latency, we found a significant modulation of the differential emotional response when attention was directed toward or away from fearful faces. These results suggest separate influences of emotion and attention on amygdala activation and may help reconcile previous discrepancies concerning the relative responsiveness of the human amygdala to emotional and attentional factors

Free-energy model for fluid helium at high density

We present a semi-analytical free-energy model aimed at characterizing the thermodynamic properties of dense fluid helium, from the low-density atomic phase to the high-density fully ionized regime. The model is based on a free-energy minimization method and includes various different contributions representative of the correlations between atomic and ionic species and electrons. This model allows the computation of the thermodynamic properties of dense helium over an extended range of density and temperature and leads to the computation of the phase diagram of dense fluid helium, with its various temperature and pressure ionization contours. One of the predictions of the model is that pressure ionization occurs abruptly at \rho \simgr 10 g cm$^{-3}$, {\it i.e.} P\simgr 20 Mbar, from atomic helium He to fully ionized helium He$^{2+}$, or at least to a strongly ionized state, without He$^{+}$ stage, except at high enough temperature for temperature ionization to become dominant. These predictions and this phase diagram provide a guide for future dynamical experiments or numerical first-principle calculations aimed at studying the properties of helium at very high density, in particular its metallization. Indeed, the characterization of the helium phase diagram bears important consequences for the thermodynamic, magnetic and transport properties of cool and dense astrophysical objects, among which the solar and the numerous recently discovered extrasolar giant planets.Comment: Accepted for publication in Phys. Rev.

The effect of social security payroll tax reductions on employment and wages: an evaluation of the 2003 French reform

public policy evaluation, payroll tax cuts, labour cost, semi-parametric estimations