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 (${\mu}$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 ${\mu}$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 ${\mu}$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

Hydrogen sulfide in diabetes and cardiovascular disease

In dit proefschrift wordt de rol van waterstofsulfide (H2S) onderzocht in hart- en vaatziekten en diabetes-geassocieerde vaatziekten. H2S is vooral bekend om z'n penetrante geur van rotte eieren en toxiciteit. Maar recent is gebleken dat H2S ook in het menselijk lichaam wordt gemaakt, en in lage concentraties veel gunstige eigenschappen heeft. Uit dit onderzoek is gebleken dat H2S beschermend werkt in een dierexperimenteel model voor een hartinfarct. Tevens werd de uitscheiding van H2S-metaboliet sulfaat gemeten in verschillende patiënten-cohorten, waaruit bleek dat lager H2S is geassocieerd met diabetes, hogere bloeddruk, groter risico op overlijden en het ontstaan van hart- en vaatziekten. Er lijkt echter ook nadeel te zijn van H2S in het kader van hart- en vaatziekten. In vergevorderde atherosclerotische plaques kunnen kleine bloedvaatjes ontstaan, die stabiele plaques kwetsbaarder maken en het risico op hart- of herseninfarct vergroten. H2S stimuleert het ontstaan van nieuwe bloedvaatjes (angiogenese) en wordt lokaal in de atherosclerotische plaque geproduceerd. Als H2S-gerelateerde therapieën worden overwogen, moeten we ons bewust zijn van deze potentieel gevaarlijke bijwerkingIn this thesis, the role of hydrogen sulfide (H2S) is studied in the context of cardiovascular disease and diabetes-associated disease. H2S is best known for its pungent smell of rotten eggs and toxicity. However, recently it has been found that H2S is endogenously produced in the human body, and has – be it at low concentrations - a lot of beneficial properties. In this thesis, we showed that gaseous H2S is protective in an experimental animal model of myocardial infarction. Also, the urinary excretion of H2S-metabolite sulfate was measured in different patients cohorts, which showed that lower urinary sulfate is associated with diabetes, increased blood pressure, greater risk of all-cause mortality, and the onset of cardiovascular disease. However, there is also a potential disadvantage of H2S in the context of cardiovascular diseases. Within advanced atherosclerotic plaques, small blood vessels can be formed. These microvessels are a risk factor for plaque vulnerability, since they are fragile and can cause an intraplaque hemorrhage, with subsequent plaque rupture and risk of myocardial infarction or stroke. H2S promotes the formation of new blood vessels (angiogenesis), and is produced locally in the atherosclerotic plaque. We need to be aware of this potentially dangerous side effect when considering H2S-related therapies in the course of cardiovascular disease

Cryogenic characterisation of a permanent magnet stepper motor and its impact on the MICADO atmospheric dispersion corrector

The MICADO atmospheric dispersion corrector (ADC) will be the first ADC built for an astronomical instrument that has to operate in a cryogenic environment (T = 77 K). A detailed understanding of the system behaviour is necessary to maximise the operational lifetime of the planned design concept and to design a suitable controller. The MICADO ADC design features a friction drive concept that is powered by a commercially available permanent magnet stepper motor (PMSM). Here, we report on an extensive characterisation of this PMSM. By matching the experimental results to an analytical description of PMSMs, we obtain a solid foundation to build a complete dynamical model of the ADC system. A prototype of the ADC design concept had already been built and tested at its operational temperature. The results from these tests allowed us to compare the measured and modelled response and discuss the implications. With respect to the motor characterisation, we find no significant performance difference of the tested stepper motor when operated at room temperature, compared to at 77 K. However, we do find that static friction plays a large role in the precise response of the ADC mechanism