125 research outputs found
Atmospheric refractivity effects on mid-infrared ELT adaptive optics
We discuss the effect of atmospheric dispersion on the performance of a
mid-infrared adaptive optics assisted instrument on an extremely large
telescope (ELT). Dispersion and atmospheric chromaticity is generally
considered to be negligible in this wavelength regime. It is shown here,
however, that with the much-reduced diffraction limit size on an ELT and the
need for diffraction-limited performance, refractivity phenomena should be
carefully considered in the design and operation of such an instrument. We
include an overview of the theory of refractivity, and the influence of
infrared resonances caused by the presence of water vapour and other
constituents in the atmosphere. `Traditional' atmospheric dispersion is likely
to cause a loss of Strehl only at the shortest wavelengths (L-band). A more
likely source of error is the difference in wavelengths at which the wavefront
is sensed and corrected, leading to pointing offsets between wavefront sensor
and science instrument that evolve with time over a long exposure. Infrared
radiation is also subject to additional turbulence caused by the presence of
water vapour in the atmosphere not seen by visible wavefront sensors, whose
effect is poorly understood. We make use of information obtained at radio
wavelengths to make a first-order estimate of its effect on the performance of
a mid-IR ground-based instrument. The calculations in this paper are performed
using parameters from two different sites, one `standard good site' and one
`high and dry site' to illustrate the importance of the choice of site for an
ELT.Comment: 11 pages, to be published in SPIE Proceedings vol. 7015, Adaptive
Optics Systems, eds. N. Hubin, C.E. Max and P.L. Wizinowich, 200
Refractive Index of Humid Air in the Infrared: Model Fits
The theory of summation of electromagnetic line transitions is used to
tabulate the Taylor expansion of the refractive index of humid air over the
basic independent parameters (temperature, pressure, humidity, wavelength) in
five separate infrared regions from the H to the Q band at a fixed percentage
of Carbon Dioxide. These are least-squares fits to raw, highly resolved spectra
for a set of temperatures from 10 to 25 C, a set of pressures from 500 to 1023
hPa, and a set of relative humidities from 5 to 60%. These choices reflect the
prospective application to characterize ambient air at mountain altitudes of
astronomical telescopes.Comment: Corrected exponents of c0ref, c1ref and c1p in Table
Recommended from our members
Simple DFT-LSDA modeling of the molecular-like aspects of ultra-thin film properties
Ordered ultra-thin films (UTF`s) are atomic n-layers (n = 1,2,3,...) with translational symmetry in-plane and molecular-like inter-planar spacings. Though commonly used (especially at relatively large n-values) as models of crystalline surfaces, they are intrinsically interesting and of growing technological significance as the basic building blocks of multi-layer electronic devices. Predicting the structure and properties of even a simple diatomic 1-layer means addressing aspects of molecular binding (and boundary conditions) in the context of an extended, periodically bounded system. At the level of refinement provided by the local spin density approximation to Density Functional Theory, the baseline standard of today`s predictive, chemically specific solid-state calculations, a number of technical and fundamental issues arise. The authors focus on treatment of the isolated atoms, on basis sets, and on numerical precision, as illustrated by the Fe atom and BN 1- and 2-layer calculations. Computational requirements are illustrated by a brief summary of recently completed calculations on crystalline sapphire, {alpha}-Al{sub 2}O{sub 3}, which used the same code
Probing embryonic tissue mechanics with laser hole-drilling
We use laser hole-drilling to assess the mechanics of an embryonic epithelium
during development - in vivo and with subcellular resolution. We ablate a
subcellular cylindrical hole clean through the epithelium, and track the
subsequent recoil of adjacent cells (on ms time scales). We investigate dorsal
closure in the fruit fly with emphasis on apical constriction of amnioserosa
cells. The mechanical behavior of this epithelium falls between that of a
continuous sheet and a 2D cellular foam (a network of tensile interfaces).
Tensile stress is carried both by cell-cell interfaces and by the cells' apical
actin networks. Our results show that stress is slightly concentrated along
interfaces (1.6-fold), but only in early closure. Furthermore, closure is
marked by a decrease in the recoil power-law exponent - implying a transition
to a more solid-like tissue. We use the site- and stage-dependence of the
recoil kinetics to constrain how the cellular mechanics change during closure.
We apply these results to test extant computational models.Comment: 23 pages with 9 figures (require color
A mathematical and computational review of Hartree-Fock SCF methods in Quantum Chemistry
We present here a review of the fundamental topics of Hartree-Fock theory in
Quantum Chemistry. From the molecular Hamiltonian, using and discussing the
Born-Oppenheimer approximation, we arrive to the Hartree and Hartree-Fock
equations for the electronic problem. Special emphasis is placed in the most
relevant mathematical aspects of the theoretical derivation of the final
equations, as well as in the results regarding the existence and uniqueness of
their solutions. All Hartree-Fock versions with different spin restrictions are
systematically extracted from the general case, thus providing a unifying
framework. Then, the discretization of the one-electron orbitals space is
reviewed and the Roothaan-Hall formalism introduced. This leads to a exposition
of the basic underlying concepts related to the construction and selection of
Gaussian basis sets, focusing in algorithmic efficiency issues. Finally, we
close the review with a section in which the most relevant modern developments
(specially those related to the design of linear-scaling methods) are commented
and linked to the issues discussed. The whole work is intentionally
introductory and rather self-contained, so that it may be useful for non
experts that aim to use quantum chemical methods in interdisciplinary
applications. Moreover, much material that is found scattered in the literature
has been put together here to facilitate comprehension and to serve as a handy
reference.Comment: 64 pages, 3 figures, tMPH2e.cls style file, doublesp, mathbbol and
subeqn package
Взаимосвязь показателей кровообращения мышц бедра и плеча с координационной точностью при совершенствовании ударных баллистических движений
В работе была исследована взаимосвязь показателей кровообращения мышц бедра и плеча с координационной точностью при совершенствовании ударных баллистических движений. Для этого было сформировано две группы: в экспериментальной группе в качестве предупреждения травматизма кисти использовались боксерские перчатки (10 унций), а в контрольной - снарядные перчатки. В результате после нанесения одиночного акцентированного прямого удара правой рукой в голову по боксерскому мешку в течение раунда было получено, что в экспериментальной группе происходило увеличение интенсивности кровенаполнения задней поверхности правого бедра и увеличение венозного оттока. Можно предположить, что спортсмены экспериментальной группы больше опираются на правую ногу в заключительной фазе ударного действия, что является более правильно с биомеханической точки зрения нанесения ударов. Интенсивность кровенаполнения и венозного оттока плеча в экспериментальной группе, наоборот, падала. Это позволяет сделать предположение о том, что мышцы плеча при выполнении ударных движений лишь незначительно задействуются спортсменами старших спортивных разрядов в завершающей фазе ударного действия. Данный факт им позволяет наносить удары с большей точностью и эффективностью
MATISSE, perspective of imaging in the mid-infrared at the VLTI
International audienceMATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study demonstrates the enormous capability of a new generation mid-infrared beam combiner. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime
The CARMENES search for exoplanets around M dwarfs High-resolution optical and near-infrared spectroscopy of 324 survey stars
The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520–1710 nm at a resolution of at least R >80 000, and we measure its RV, Hα emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, Q, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700–900 nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1 m s−1 in very low mass M dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4 m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3–4 m s−1
The CARMENES search for exoplanets around M dwarfs HD147379 b: A nearby Neptune in the temperate zone of an early-M dwarf
We report on the first star discovered to host a planet detected by radial velocity (RV) observations obtained within the CARMENES survey for exoplanets around M dwarfs. HD 147379 (V = 8.9 mag, M = 0.58 ± 0.08 M⊙), a bright M0.0 V star at a distance of 10.7 pc, is found to undergo periodic RV variations with a semi-amplitude of K = 5.1 ± 0.4 m s−1 and a period of P = 86.54 ± 0.06 d. The RV signal is found in our CARMENES data, which were taken between 2016 and 2017, and is supported by HIRES/Keck observations that were obtained since 2000. The RV variations are interpreted as resulting from a planet of minimum mass mP sin i = 25 ± 2 M⊕, 1.5 times the mass of Neptune, with an orbital semi-major axis a = 0.32 au and low eccentricity (e < 0.13). HD 147379 b is orbiting inside the temperate zone around the star, where water could exist in liquid form. The RV time-series and various spectroscopic indicators show additional hints of variations at an approximate period of 21.1 d (and its first harmonic), which we attribute to the rotation period of the star.FEDER/ERF FICTS-2011-02 fundsMajor Research Instrumentation Programme
and DFG Research Unit FOR2544 “Blue Planets around Red StarsEuropean Research Council (ERC-279347), Deutsche Forschungsgemeinschaft
(RE 1664/12-1, RE 2694/4-1), Bundesministerium für Bildung
und Forschung (BMBF-05A14MG3, BMBF-05A17MG3), Spanish Ministry
of Economy and Competitiveness (MINECO, grants AYA2015-68012-C2-2-P,
AYA2016-79425-C3-1,2,3-P, AYA2015-69350-C3-2-P, AYA2014-54348-C03-
01, AYA2014-56359-P, AYA2014-54348-C3-2-R, AYA2016-79425-C3-3-P and
2013 Ramòn y Cajal program RYC-2013-14875), Fondo Europeo de Desarrollo
Regional (FEDER, grant ESP2016-80435-C2-1-R, ESP2015-65712-C5-
5-R), Generalitat de Catalunya/CERCA programme, Spanish Ministerio de
Educación, Cultura y Deporte, programa de Formación de Profesorado Universitario
(grant FPU15/01476), Deutsches Zentrum für Luft- und Raumfahrt
(grants 50OW0204 and 50OO1501), Office of Naval Research Global (award
no. N62909-15-1-2011), Mexican CONACyT grant CB-2012-183007
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