2,426 research outputs found
Quantification of the expected residual dispersion of the MICADO Near-IR imaging instrument
MICADO, a near-infrared imager for the Extremely Large Telescope, is being
designed to deliver diffraction limited imaging and 50 micro arcsecond
(as) astrometric accuracy. MICADO employs an atmospheric dispersion
corrector (ADC) to keep the chromatic elongation of the point spread function
(PSF) under control. We must understand the dispersion and residuals after
correction to reach the optimum performance. Therefore, we identified several
sources of chromatic dispersion that need to be considered for the MICADO ADC.
First, we compared common models of atmospheric dispersion to investigate
whether these models remain suitable for MICADO. We showed that the
differential dispersion between common atmospheric models and integration over
the full atmosphere is less than 10 as for most observations in H-band.
We then performed an error propagation analysis to understand the uncertainty
in the atmospheric dispersion as a function of atmospheric conditions. In
addition, we investigated the impact of photometric color on the astrometric
performance. While the differential refraction between stars within the same
field of view can be significant, the inclusion of an ADC rendered this effect
negligible. For MICADO specifically, we found that the current optomechanical
design dominates the residual dispersion budget of 0.4 milli arcseconds (mas),
with a contribution of 0.31 mas due to the positioning accuracy of the prisms
and up to 0.15 mas due to a mismatch between the dispersive properties of the
glass and the atmosphere. We found no showstoppers in the design of the MICADO
ADC for achieving 50 as relative astrometric accuracy.Comment: Submitted to Monthly Notices of the Royal Astronomical Society.
Contains 11 pages and 12 figure
Demonstration of an imaging technique for the measurement of PSF elongation caused by Atmospheric Dispersion
Elongation of the point spread function due to atmospheric dispersion becomes
a severe problem for high resolution imaging instruments, if an atmospheric
dispersion corrector is not present. In this work we report on a novel
technique to measure this elongation, corrected or uncorrected, from imaging
data. By employing a simple diffraction mask it is possible to magnify the
chromatic elongation caused by the atmosphere and thus make it easier to
measure. We discuss the theory and design of such a mask and report on two
proof of concept observations using the 40 cm Gratama telescope at the
University of Groningen. We evaluate the acquired images using a geometric
approach, a forward modelling approach and from a direct measurement of the
length of the point spread function. For the first two methods we report
measurements consistent with atmospheric dispersion models to within 0.5
arcsec. Direct measurements of the elongation do not prove suitable for the
characterisation of atmospheric dispersion. We conclude that the addition of
this type of diffraction mask can be valuable for measurements of PSF
elongation. This can enable high precision correction of atmospheric dispersion
on future instruments.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Society. Contains 11 pages, 11 figures, 2 table
LVU och Europakonventionen - om lagligheten av att omhÀnderta unga över 18 Är med stöd av LVU
Care provided by the Swedish social services shall, as a starting point, always be based on voluntary participation. Each personâs autonomy and integrity must be respected. However, interventions of these rights may be justified under certain circumstances. By applying the Act containing Special Provisions on the Care of Young Persons (hereinafter LVU), a child may be committed to compulsory care on account of his or her home environment, or because of his or her behaviour. LVU complements the Social Services Act (hereinafter SoL), which regulates voluntary care. Although LVU is primarily applicable in relation to children, young persons between 18 and 20 years may, under certain circumstances, be committed to compulsory care. 3 § LVU sets out the conditions for compulsory care on account of a personâs behaviour. It is on this ground that persons over the age of 18 may be committed to care. Such care may continue until that personâs 21st birthday. The compulsory care, as provided for by LVU, constitutes a significant intervention in a personâs life. The care may be provided in a family home or in an institutionalised accommodation. There are also certain accommodations, in which the young person is put under particular supervision. This form of accommodation may be used for the care of persons over 18 years. The European Convention on Human Rights was incorporated with Swedish law in 1995. Article 5 of the Convention contains the right to liberty and security. The article provides an exhaustive list of exceptions to the prohibition of depravation of liberty. The two categories that are particularly relevant to examine for the purpose of this thesis are, detention of minors, and detention for medical or social reasons, of drug addicts or alcoholics. The purpose of this thesis is to examine the legality of committing persons over the age of 18 to compulsory care in accordance with LVU, in relation to article 5 of the European Convention on Human Rights.Som utgĂ„ngspunkt skall vĂ„rden genom SocialtjĂ€nsten grundas pĂ„ frivillighet, med respekt för varje mĂ€nniskas sjĂ€lvbestĂ€mmanderĂ€tt och integritet. Trots det avsteg frĂ„n frivillighet, och det ingrepp i en persons sĂ„vĂ€l integritet, som sjĂ€lvbestĂ€mmanderĂ€tt ett tvĂ„ngsomhĂ€ndertagande innebĂ€r, anses sĂ„dana ingripanden Ă€ndĂ„ vara försvarliga under vissa omstĂ€ndigheter. Genom tillĂ€mpning av lag (1990:52) med sĂ€rskilda bestĂ€mmelser om vĂ„rd av unga, kan barn tvĂ„ngsvis omhĂ€ndertas pĂ„ grund av sin hemmiljö, alternativt pĂ„ grund av barnets eget beteende. Trots att LVU i första hand Ă€r tillĂ€mplig i förhĂ„llande till barn, kan Ă€ven unga över 18 Ă„r, som Ă€nnu ej har fyllt 20 Ă„r, bli föremĂ„l för ett tvĂ„ngsomhĂ€ndertagande. Det Ă€r 3 § LVU som reglerar möjligheten att omhĂ€nderta en person pĂ„ grund av dennes eget beteende, och det Ă€r denna grund som kan aktualisera vĂ„rd av personer över 18 Ă„r. SĂ„dan vĂ„rd fĂ„r som lĂ€ngst fortgĂ„ fram till dess att den unge fyller 21 Ă„r. Den vĂ„rd som ges i enlighet med LVU innebĂ€r en mycket ingripande Ă„tgĂ€rd i den omhĂ€ndertagne personens liv. VĂ„rden kan ges i ett familjehem, eller i ett hem för vĂ„rd eller boende. Det finns Ă€ven hem med sĂ€rskild tillsyn, som kan aktualiseras för personer som har beretts vĂ„rd pĂ„ grund av sitt eget beteende. Lagen (1994:1219) om den europeiska konventionen angĂ„ende skydd för de mĂ€nskliga rĂ€ttigheterna och de grundlĂ€ggande friheterna, trĂ€dde i kraft den 1 januari 1995, genom vilken Europakonventionen inkorporerades med svensk rĂ€tt. Sedan dess gĂ€ller konventionen som lag hĂ€r i landet. Artikel 5 i Europakonventionen reglerar rĂ€tten till frihet och personlig sĂ€kerhet. I en uttömmande lista framgĂ„r de kategorier under vilka ett frihetsberövande kan anses vara konventionsenligt. De tvĂ„ grunder som Ă€r mest relevanta för detta arbete Ă€r den som behandlar möjligheten att frihetsberöva underĂ„riga för att de skall undergĂ„ skyddsuppfostran, samt grunden för frihetsberövande av missbrukare av alkohol eller droger. Arbetet syftar till att undersöka huruvida svensk lagstiftning i LVU gĂ€llande omhĂ€ndertaganden av unga över 18 Ă„r, Ă€r förenlig med artikel 5 i Europakonventionen
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