Wavefront sensing with a brightest pixel selection algorithm

Astronomical adaptive optics systems with open-loop deformable mirror control have recently come on-line. In these systems, the deformable mirror surface is not included in the wavefront sensor paths, and so changes made to the deformable mirror are not fed back to the wavefront sensors. This gives rise to all sorts of linearity and control issues mainly centred on one question: Has the mirror taken the shape requested? Non-linearities in wavefront measurement and in the deformable mirror shape can lead to significant deviations in mirror shape from the requested shape. Here, wavefront sensor measurements made using a brightest pixel selection method are discussed along with the implications that this has for open-loop AO systems. Discussion includes elongated laser guide star spots and also computational efficiency.Comment: 10 pages, 12 figures, accepted by MNRA

Sulfonium Salts as Leaving Groups for Aromatic Labelling of Drug-like Small Molecules with Fluorine-18.

Positron emission tomography (PET) is unique in that it allows quantification of biochemical processes in vivo, but difficulties with preparing suitably labelled radiotracers limit its scientific and diagnostic applications. Aromatic [(18)F]fluorination of drug-like small molecules is particularly challenging as their functional group compositions often impair the labelling efficiency. Herein, we report a new strategy for incorporation of (18)F into highly functionalized aromatic compounds using sulfonium salts as leaving groups. The method is compatible with pharmacologically relevant functional groups, including aliphatic amines and basic heterocycles. Activated substrates react with [(18)F]fluoride at room temperature, and with heating the reaction proceeds in the presence of hydrogen bond donors. Furthermore, the use of electron rich spectator ligands allows efficient and regioselective [(18)F]fluorination of non-activated aromatic moieties. The method provides a broadly applicable route for (18)F labelling of biologically active small molecules, and offers immediate practical benefits for drug discovery and imaging with PET

Ultimate performance of Quantum Well Infrared Photodetectors in the tunneling regime

Thanks to their wavelength diversity and to their excellent uniformity, Quantum Well Infrared Photodetectors (QWIP) emerge as potential candidates for astronomical or defense applications in the very long wavelength infrared (VLWIR) spectral domain. However, these applications deal with very low backgrounds and are very stringent on dark current requirements. In this paper, we present the full electro-optical characterization of a 15 micrometer QWIP, with emphasis on the dark current measurements. Data exhibit striking features, such as a plateau regime in the IV curves at low temperature (4 to 25 K). We show that present theories fail to describe this phenomenon and establish the need for a fully microscopic approach

An aperture masking mode for the MICADO instrument

MICADO is a near-IR camera for the Europea ELT, featuring an extended field (75" diameter) for imaging, and also spectrographic and high contrast imaging capabilities. It has been chosen by ESO as one of the two first-light instruments. Although it is ultimately aimed at being fed by the MCAO module called MAORY, MICADO will come with an internal SCAO system that will be complementary to it and will deliver a high performance on axis correction, suitable for coronagraphic and pupil masking applications. The basis of the pupil masking approach is to ensure the stability of the optical transfer function, even in the case of residual errors after AO correction (due to non common path errors and quasi-static aberrations). Preliminary designs of pupil masks are presented. Trade-offs and technical choices, especially regarding redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea

Detection of the Sgr A* activity at 3.8 and 4.8 microns with NACO

L'-band (lambda=3.8 microns) and M'-band (lambda=4.8 microns) observations of the Galactic Center region, performed in 2003 at VLT (ESO) with the adaptive optics imager NACO, have lead to the detection of an infrared counterpart of the radio source Sgr A* at both wavelengths. The measured fluxes confirm that the Sgr A* infrared spectrum is dominated by the synchrotron emission of nonthermal electrons. The infrared counterpart exhibits no significant short term variability but demonstrates flux variations on daily and yearly scales. The observed emission arises away from the position of the dynamical center of the S2 orbit and would then not originate from the closest regions of the black hole.Comment: 5 pages, 3 figures, accepted in Astronomy & Astrophysic

Magnetic and electronic properties of lithium cobalt oxide substituted by nickel

[Abstract] We measured susceptibility, electron-spin resonance, magnetization and electrical conductivity of LiCo1−yNiyO2 powders synthesized by wet-chemistry method using succinic acid as chelating agent. We found unusual properties in the nickel-rich LiCo0.2Ni0.8O2, which shows several resonance lines as a function of the temperature in the range 3.5–300 K. The signal at low magnetic field is attributed to the magnetic domains in the nanostructured sample. The two other lines correspond to the typical ferromagnetic signal observed in powdered compounds. In the temperature range 120–300 K, the unique ESR line centered at 315 mT is the paramagnetic signal with a gyromagnetic factor g=2.12, which is in good agreement with the presence of a high concentration of Ni3+ (3d7) ions. In the nickel-rich oxide, LiNi0.8Co0.2O2, the magnetic data are qualitatively well-described by the model proposed by Drillon and Panissod for a 3D ferromagnetic order.Spanish and French Foreign Office; HF 1999-0101Spanish and French Foreign Office; PAI Picasso 00717T

Adaptive Optics for Astronomy

Adaptive Optics is a prime example of how progress in observational astronomy can be driven by technological developments. At many observatories it is now considered to be part of a standard instrumentation suite, enabling ground-based telescopes to reach the diffraction limit and thus providing spatial resolution superior to that achievable from space with current or planned satellites. In this review we consider adaptive optics from the astrophysical perspective. We show that adaptive optics has led to important advances in our understanding of a multitude of astrophysical processes, and describe how the requirements from science applications are now driving the development of the next generation of novel adaptive optics techniques.Comment: to appear in ARA&A vol 50, 201

A fast ILP-based Heuristic for the robust design of Body Wireless Sensor Networks

We consider the problem of optimally designing a body wireless sensor network, while taking into account the uncertainty of data generation of biosensors. Since the related min-max robustness Integer Linear Programming (ILP) problem can be difficult to solve even for state-of-the-art commercial optimization solvers, we propose an original heuristic for its solution. The heuristic combines deterministic and probabilistic variable fixing strategies, guided by the information coming from strengthened linear relaxations of the ILP robust model, and includes a very large neighborhood search for reparation and improvement of generated solutions, formulated as an ILP problem solved exactly. Computational tests on realistic instances show that our heuristic finds solutions of much higher quality than a state-of-the-art solver and than an effective benchmark heuristic.Comment: This is the authors' final version of the paper published in G. Squillero and K. Sim (Eds.): EvoApplications 2017, Part I, LNCS 10199, pp. 1-17, 2017. DOI: 10.1007/978-3-319-55849-3\_16. The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-55849-3_1

The FALCON concept: multi-object spectroscopy combined with MCAO in near-IR

A large fraction of the present-day stellar mass was formed between z=0.5 and z~3 and our understanding of the formation mechanisms at work at these epochs requires both high spatial and high spectral resolution: one shall simultaneously} obtain images of objects with typical sizes as small as 1-2kpc(~0''.1), while achieving 20-50 km/s (R >= 5000) spectral resolution. The obvious instrumental solution to adopt in order to tackle the science goal is therefore a combination of multi-object 3D spectrograph with multi-conjugate adaptive optics in large fields. A partial, but still competitive correction shall be prefered, over a much wider field of view. This can be done by estimating the turbulent volume from sets of natural guide stars, by optimizing the correction to several and discrete small areas of few arcsec2 selected in a large field (Nasmyth field of 25 arcmin) and by correcting up to the 6th, and eventually, up to the 60th Zernike modes. Simulations on real extragalactic fields, show that for most sources (>80%), the recovered resolution could reach 0".15-0".25 in the J and H bands. Detection of point-like objects is improved by factors from 3 to >10, when compared with an instrument without adaptive correction. The proposed instrument concept, FALCON, is equiped with deployable mini-integral field units (IFUs), achieving spectral resolutions between R=5000 and 20000. Its multiplex capability, combined with high spatial and spectral resolution characteristics, is a natural ground based complement to the next generation of space telescopes.Comment: ESO Workshop Proceedings: Scientific Drivers for ESO Future VLT/VLTI Instrumentation, 10 pages and 5 figure