Internetwork and intranetwork communications during bursting dynamics: Applications to seizure prediction

We use a simple dynamical model of two interacting networks of integrate-and-fire neurons to explain a seemingly paradoxical result observed in epileptic patients indicating that the level of phase synchrony declines below normal levels during the state preceding seizures (preictal state). We model the transition from the seizure free interval (interictal state) to the seizure (ictal state) as a slow increase in the mean depolarization of neurons in a network corresponding to the epileptic focus. We show that the transition from the interictal to preictal and then to the ictal state may be divided into separate dynamical regimes: the formation of slow oscillatory activity due to resonance between the two interacting networks observed during the interictal period, structureless activity during the preictal period when the two networks have different properties, and bursting dynamics driven by the network corresponding to the epileptic focus. Based on this result, we hypothesize that the beginning of the preictal period marks the beginning of the transition of the epileptic network from normal activity toward seizing

High-density lipoprotein: does it have a dark side?

There are proven pleiotropic anti-atherogenic actions of high-density lipoprotein (HDL). However, in systemic inflammation, HDL can have pro-inflammatory properties that may contribute to accelerated atherosclerosis, likely mediated by a change in the structure of HDL to pro-inflammatory HDL (PiHDL). Validation of the technically challenging assay for PiHDL, and confirmation of an association of PiHDL in multiple populations with known risk for atherosclerosis will eventually provide a useful biomarker. Identification of PiHDL in patients with rheumatic disease may help identify patients at risk of accelerated atherosclerosis, and focus our therapeutic interventions

Dissecting Massive YSOs with Mid-Infrared Interferometry

The very inner structure of massive YSOs is difficult to trace. With conventional observational methods we often identify structures still several hundreds of AU in size. But we also need information about the innermost regions where the actual mass transfer onto the forming high-mass star occurs. An innovative way to probe these scales is to utilise mid-infrared interferometry. Here, we present first results of our MIDI GTO programme at the VLTI. We observed 10 well-known massive YSOs down to scales of 20 mas. We clearly resolve these objects which results in low visibilities and sizes in the order of 30 - 50 mas. Thus, with MIDI we can for the first time quantify the extent of the thermal emission from the warm circumstellar dust and thus calibrate existing concepts regarding the compactness of such emission in the pre-UCHII region phase. Special emphasis will be given to the BN-type object M8E-IR where our modelling is most advanced and where there is indirect evidence for a strongly bloated central star.Comment: 8 pages, 6 figures, proceedings contribution for the conference "Massive Star Formation: Observations confront Theory", held in September 2007 in Heidelberg, Germany; to appear in ASP Conf. Ser. 387, H. Beuther et al. (eds.

PYRAMIR: Calibration and operation of a pyramid near-infrared wavefront sensor

The concept of pyramid wavefront sensors (PWFS) has been around about a decade by now. However, there is still a great lack of characterizing measurements that allow the best operation of such a system under real life conditions at an astronomical telescope. In this article we, therefore, investigate the behavior and robustness of the pyramid infrared wavefront sensor PYRAMIR mounted at the 3.5 m telescope at the Calar Alto Observatory under the influence of different error sources both intrinsic to the sensor, and arising in the preceding optical system. The intrinsic errors include diffraction effects on the pyramid edges and detector read out noise. The external imperfections consist of a Gaussian profile in the intensity distribution in the pupil plane during calibration, the effect of an optically resolved reference source, and noncommon-path aberrations. We investigated the effect of three differently sized reference sources on the calibration of the PWFS. For the noncommon-path aberrations the quality of the response of the system is quantified in terms of modal cross talk and aliasing. We investigate the special behavior of the system regarding tip-tilt control. From our measurements we derive the method to optimize the calibration procedure and the setup of a PWFS adaptive optics (AO) system. We also calculate the total wavefront error arising from aliasing, modal cross talk, measurement error, and fitting error in order to optimize the number of calibrated modes for on-sky operations. These measurements result in a prediction of on-sky performance for various conditions

Detecting Extrasolar Planets with Integral Field Spectroscopy

Observations of extrasolar planets using Integral Field Spectroscopy (IFS), if coupled with an extreme Adaptive Optics system and analyzed with a Simultaneous Differential Imaging technique (SDI), are a powerful tool to detect and characterize extrasolar planets directly; they enhance the signal of the planet and, at the same time, reduces the impact of stellar light and consequently important noise sources like speckles. In order to verify the efficiency of such a technique, we developed a simulation code able to test the capabilities of this IFS-SDI technique for different kinds of planets and telescopes, modelling the atmospheric and instrumental noise sources. The first results obtained by the simulations show that many significant extrasolar planet detections are indeed possible using the present 8m-class telescopes within a few hours of exposure time. The procedure adopted to simulate IFS observations is presented here in detail, explaining in particular how we obtain estimates of the speckle noise, Adaptive Optics corrections, specific instrumental features, and how we test the efficiency of the SDI technique to increase the signal-to-noise ratio of the planet detection. The most important results achieved by simulations of various objects, from 1 M_J to brown dwarfs of 30 M_J, for observations with an 8 meter telescope, are then presented and discussed.Comment: 60 pages, 37 figures, accepted in PASP, 4 Tables adde

The Impact of Adaptive Optics on Star Formation Research

In this paper, we discuss the benefits of ground-based, adaptive optics (AO) aided observations for star formation research. After outlining the general advantages, we present results obtained during the ALFA science demonstration programme in 1999. These results underline the absolute necessity of AO assistance for almost any kind of observations regarding star formation regions.Comment: 10 pages, 8 figures (partially converted to bitmap), to appear in SPIE Proceedings 4007, Astronomical Telescopes and Instrumentation 2000, Munich, German

VLTI observations of IRS~3: The brightest compact MIR source at the Galactic Centre

The dust enshrouded star IRS~3 in the central light year of our galaxy was partially resolved in a recent VLTI experiment. The presented observation is the first step in investigating both IRS~3 in particular and the stellar population of the Galactic Centre in general with the VLTI at highest angular resolution. We will outline which scientific issues can be addressed by a complete MIDI dataset on IRS~3 in the mid infrared.Comment: 4 pages, 3 figures, published in: The ESO Messenge

Online conferences – Towards a new (virtual) reality

The recent article: Nature 579, 327–328 (2020), ending with the phrase: “You can’t just suddenly make a conference be online.”, has motivated us to write about the practicalities and philosophy of running online events, drawing on our extensive experience running an annual online computational chemistry conference. Our goals for this online conference series have always been: (1) Availability; (2) Community building and (3) Supporting young scientists. In this article, we highlight the motivations behind our initiative, how this has influenced the organisation of our online meeting, and discuss the benefits as well as the drawbacks of virtual meetings. Virtual conferences may not fully replace in-person meetings, but they are rapidly becoming an accepted alternative format. We discuss the hybrid online/in-person conference format as a future possibility that may offer an opportunity to reduce the environmental impact and accessibility barriers associate with in-person meetings without comprising networking and community-building opportunities

Ground truth deficiencies in software engineering: when codifying the past can be counterproductive

Many software engineering tools build and evaluate their models based on historical data to support development and process decisions. These models help us answer numerous interesting questions, but have their own caveats. In a real-life setting, the objective function of human decision-makers for a given task might be influenced by a whole host of factors that stem from their cognitive biases, subverting the ideal objective function required for an optimally functioning system. Relying on this data as ground truth may give rise to systems that end up automating software engineering decisions by mimicking past sub-optimal behaviour. We illustrate this phenomenon and suggest mitigation strategies to raise awareness

High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments

We present high-resolution infrared imaging of the massive star-forming region around the O-star Herschel 36. Special emphasis is given to a compact infrared source at 0".25 southeast of the star. The infrared source, hereafter Her 36 SE, is extended in the broad-band images, but features spatially unresolved Br gamma line emission. The line-emission source coincides in position with the previous HST detections in H alpha and the 2 cm radio continuum emission detected by VLA interferometry. We propose that the infrared source Her 36 SE harbors an early B-type star, deeply embedded in a dusty cloud. The fan shape of the cloud with Herschel 36 at its apex, though, manifests direct and ongoing destructive influence of the O7V star on Her 36 SE