416 research outputs found
From the optical characteristics of Herschel-hifi to in-orbit spatial response calibration using Mars
Making use of all Mars observations taken by Herschel-HIFI, we present a detailed comparison of the measured and predicted beam profiles observed in space. Starting with a number of instrument beam profile models, including one based on actual wavefront measurements in the 480-1625 GHz frequency range, we developed a forward model predicting the detailed characteristics of the beam profile at the sky. Once convolved with the actual brightness temperature distribution and appearance of Mars, this forward model can be compared in detail with the observed spatial response towards Mars, using the science data of HIFI. Since the HIFI instrument is a single-mode coherent receiver, and given the availability of phase-sensitive measurements at instrument level, the results suggest that it is possible to extract some interesting optical characteristics of the Herschel telescope in addition. We discuss a possible way to extract the location of the telescope focus from these observations, which could provide useful feedback to the thermo-elastic properties of the SiC telescope assembly under zero-g and cryogenic conditions.</p
Open data and smallholder food and nutritional security
This report was commissioned CTA as a member of the GODAN initiative. It aims to provide a better understanding of the actual impact of the open data movement on the food and nutrition security of smallholders and highlight the areas of potential unfilled opportunity
1958 Payton Lectures: Faith and Reason in Philosophy
Fuller Theological Seminary instituted the Payton Lectures in 1948, providing for a series of divinity lectures by a notable scholar outside the regular faculty. The lectureship is named for Dr. John E. and Mrs. Eliza Payton, parents of the late Mrs. Grace Fuller, wife of seminary founder Charles E. Fuller.
El Seminario Teolรณgico de Fuller instituyรณ las Conferencias Payton en 1948, proveyendo una serie de conferencias en divinidades por una persona erudita de renombre fuera de la facultad regular. Las conferencias llevan el nombre del Dr. John E. y la Sra. Eliza Payton, padres de la fallecida Sra. Grace Fuller, esposa del fundador del seminario Charles E. Fuller.
ํ๋ฌ์ ํ๋ํ์์ 1948๋
ํ์ดํผ ๊ฐ์ข๋ฅผ ๊ฐ์คํ์ฌ ์ ๊ท ๊ต์์ง ์ธ์ ์ ๋ช
ํ ํ์์ ์ ํ ๊ฐ์ฐ์ ์ ๊ณตํด์์ต๋๋ค. ๊ฐ์ข์ ๋ช
์นญ์ ํ๊ต ์ค๋ฆฝ์ ์ฐฐ์ค ํ๋ฌ (Charles E. Fuller)์ ์๋ด์ธ ๊ทธ๋ ์ด์ค ํ๋ฌ (Grace Fuller) ๋ถ์ธ์ ์์น ์กด ํ์ดํผ (John E. Payton) ๋ฐ์ฌ์ ์๋ฆฌ์ ํ์ดํผ (Eliza Payton) ๋ถ์ธ์ ์ด๋ฆ์ ๋ฐ๋ผ ๋ถ์ฌ์ก์ต๋๋ค
Modeling the partially coherent behavior of few-mode far-infrared grating spectrometers
Modelling ultra-low-noise far-infrared grating spectrometers has become
crucial for the next generation of far-infrared space observatories.
Conventional techniques are awkward to apply because of the partially coherent
form of the incident spectral field, and the few-mode response of the optics
and detectors. We present a modal technique for modelling the behaviour of
spectrometers, which allows for the propagation and detection of partially
coherent fields, and the inclusion of straylight radiated by warm internal
surfaces. We illustrate the technique by modelling the behaviour of the Long
Wavelength Band of the proposed SAFARI instrument on the well-studied SPICA
mission.Comment: This paper is submitted to Journal Optical Society of America A. When
accepted, the paper can be found here: https://opg.optica.org/josaa/home.cf
Safari:Instrument design of the far-infrared imaging spectrometer for spica
The next great leap forward in space-based far-infrared astronomy will be made by the Japanese-led SPICA mission, which is anticipated to be launched late 2020's as the next large astrophysics mission of JAXA, in partnership with ESA and with key European contributions. Filling in the gap between JWST and ALMA, the SPICA mission will study the evolution of galaxies, stars and planetary systems. SPICA will utilize a deeply cooled 3m-class telescope, provided by European industry, to realize zodiacal background limited performance, high spatial resolution and large collecting area. Making full advantage of the deeply cooled telescope (<6K), the SAFARI instrument on SPICA is a highly sensitive wide-field imaging photometer and spectrometer operating in the 34-210 ฮผm wavelength range. Utilizing Nyquist-sampled focal-plane arrays of very sensitive Transition Edge Sensors (TES), SAFARI will offer a photometric imaging (R โ 2), and a low (R = 100) and medium resolution (R = 2000 at 100 ฮผm) imaging spectroscopy mode in three photometric bands within a 2'x2' instantaneous FoV by means of a cryogenic Mach-Zehnder Fourier Transform Spectrometer. In this paper we will provide an overview of the SAFARI instrument design and system architecture. We will describe the reference design of the SAFARI focal- plane unit, the implementation of the various optical instrument functions designed around the central large-stroke FTS system, the photometric band definition and out-of-band filtering by quasioptical elements, the control of straylight, diffraction and thermal emission in the long-wavelength limit, and how we interface to the large-format FPA arrays at one end and the SPICA telescope assembly at the other end. We will briefly discuss the key performance drivers with special emphasis on the optical techniques adopted to overcome issues related to very low background operation of SAFARI. A summary and discussion of the expected instrument performance and an overview of the astronomical capabilities finally conclude the paper.</p
A Fourier optics approach to evaluate the astrometric performance of MICADO
We present our investigation into the impact of wavefront errors on high
accuracy astrometry using Fourier Optics. MICADO, the upcoming near-IR imaging
instrument for the Extremely Large Telescope, will offer capabilities for
relative astrometry with an accuracy of 50 micro arcseconds ({\mu}as). Due to
the large size of the point spread function (PSF) compared to the astrometric
requirement, the detailed shape and position of the PSF on the detector must be
well understood. Furthermore, because the atmospheric dispersion corrector of
MICADO is a moving component within an otherwise mostly static instrument, it
might not be sufficient to perform a simple pre-observation calibration.
Therefore, we have built a Fourier Optics framework, allowing us to evaluate
the small changes in the centroid position of the PSF as a function of
wavefront error. For a complete evaluation, we model both the low order surface
form errors, using Zernike polynomials, and the mid- and high-spatial
frequencies, using Power Spectral Density analysis. The described work will
then make it possible, performing full diffractive beam propagation, to assess
the expected astrometric performance of MICADO.Comment: 13 pages, 13 figures, to be submitted to the SPIE Astronomical
Telescopes & Instrumentation 2020 conferenc
Full characterization and analysis of a terahertz heterodyne receiver based on a NbN hot electron bolometer
We present a complete experimental characterization of a quasioptical twin-slot antenna coupled small area (1.0ร0.15 ยตm^2) NbN hot electron bolometer (HEB) mixer compatible with currently available solid state tunable local oscillator (LO) sources. The required LO power absorbed in the HEB is analyzed in detail and equals only 25 nW. Due to the small HEB volume and wide antenna bandwidth, an unwanted direct detection effect is observed which decreases the apparent sensitivity. Correcting for this effect results in a receiver noise temperature of 700 K at 1.46 THz. The intermediate frequency (IF) gain bandwidth is 2.3 GHz and the IF noise bandwidth is 4 GHz. The single channel receiver stability is limited to 0.2โ0.3 s in a 50 MHz bandwidth
Complex Beam Mapping and Fourier Optics Analysis of a Wide-Field Microwave Kinetic Inductance Detector Camera
For astronomical instruments, accurate knowledge of the optical pointing and
coupling are essential to characterize the alignment and performance of
(sub-)systems prior to integration and deployment. Ideally, this requires the
phase response of the optical system, which for direct (phase insensitive)
detectors was not previously accessible. Here we show development of the phase
sensitive complex beam pattern technique using a dual optical source heterodyne
technique for a large field of view Microwave Kinetic Inductance Detector
camera at 350 GHz. We show here how you can analyze the measured data with
Fourier optics, which allows integration into a telescope model to calculate
the on sky beam pattern and telescope aperture efficiency prior to deployment
at a telescope.Comment: This is a post-peer-review, pre-copy edit version of an article
published in Journal of Low Temperature Physics. The final authenticated
version is available onlin
Value of symptoms and additional diagnostic tests for colorectal cancer in primary care: systematic review and meta-analysis
Objective To summarise available evidence on diagnostic tests that might help primary care physicians to identify patients with an increased risk for colorectal cancer among those consulting for non-acute lower abdominal symptoms
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