pySPT: a package dedicated to the source position transformation

The modern time-delay cosmography aims to infer the cosmological parameters with a competitive precision from observing a multiply imaged quasar. The success of this technique relies upon a robust modeling of the lens mass distribution. Unfortunately strong degeneracies between density profiles that lead to almost the same lensing observables may bias precise estimate for the Hubble constant. The source position transformation (SPT), which covers the well-known mass sheet transformation (MST) as a special case, defines a new framework to investigate these degeneracies. In this paper, we present pySPT, a Python package dedicated to the SPT. We describe how it can be used to evaluate the impact of the SPT on lensing observables. We review most of its capabilities and elaborate on key features that we used in a companion paper regarding SPT and time delays. pySPT also comes with a sub-package dedicated to simple lens modeling. It can be used to generate lensing related quantities for a wide variety of lens models, independently from any SPT analysis. As a first practical application, we present a correction to the first estimate of the impact on time delays of the SPT, which has been experimentally found in Schneider and Sluse (2013) between a softened power-law and a composite (baryons + dark matter) lenses. We find that the large deviations predicted in Schneider and Sluse (2014) have been overestimated due to a minor bug (now fixed) in the public lens modeling code lensmodel (v1.99). We conclude that the predictions for the Hubble constant deviate by $\sim 7$\%, first and foremost caused by an MST. The latest version of pySPT is available at https://github.com/owertz/pySPT. We also provide tutorials to describe in detail how making the best use of pySPT at https://github.com/owertz/pySPT_tutorials.Comment: 9 pages, 5 figure

Ambiguities in gravitational lens models: impact on time delays of the source position transformation

The central ambition of the modern time delay cosmography consists in determining the Hubble constant $H_0$ with a competitive precision. However, the tension with $H_0$ obtained from the Planck satellite for a spatially-flat $\Lambda$CDM cosmology suggests that systematic errors may have been underestimated. The most critical one probably comes from the degeneracy existing between lens models that was first formalized by the well-known mass-sheet transformation (MST). In this paper, we assess to what extent the source position transformation (SPT), a more general invariance transformation which contains the MST as a special case, may affect the time delays predicted by a model. To this aim we use pySPT, a new open-source python package fully dedicated to the SPT that we present in a companion paper. For axisymmetric lenses, we find that the time delay ratios between a model and its SPT-modified counterpart simply scale like the corresponding source position ratios, $\Delta \hat{t}/ \Delta t \approx \hat{\beta}/\beta$, regardless of the mass profile and the isotropic SPT. Similar behavior (almost) holds for non-axisymmetric lenses in the double image regime and for opposite image pairs in the quadruple image regime. In the latter regime, we also confirm that the time delay ratios are not conserved. In addition to the MST effects, the SPT-modified time delays deviate in general no more than a few percent for particular image pairs, suggesting that its impact on time-delay cosmography seems not be as crucial as initially suspected. We also reflected upon the relevance of the SPT validity criterion and present arguments suggesting that it should be reconsidered. Even though a new validity criterion would affect the time delays in a different way, we expect from numerical simulations that our conclusions will remain unchanged.Comment: 15 pages, 14 figure

Bildgebende Röntgendetektion mit Gasverstärkung durch Mikrostrukturen für Hochgeschwindigkeitsmessungen

Eine Vielzahl biologischer und technischer Anwendungen an Synchrotronstrahlungsquellen erfordert schnelle, bildgebende Röntgendetektoren, die sich durch eine gute Zeit- und Ortsauflösung bei gleichzeitig großer sensitiver Fläche auszeichnen. Aufgrund fehlender kommerziell erhältlicher Systeme für diesen Anwendungsbereich, werden in der vorliegenden Arbeit detaillierte Studien eines neuartigen, gasbasierten Einzelphotonzählers mit Gasverstärkung durch Mikrostrukturen vorgestellt. Diesbezüglich wird die Eignung von MicroCAT- und GEM-Strukturen, ihrer Kombination und Konstellationen von Zweifachund Dreifach-GEMs für den Einsatz in Hochgeschwindigkeitsmessungen, die im Allgemeinen hohe Photonenflüsse erfordern, diskutiert. Da die Hochratenverträglichkeit des Detektors im Wesentlichen durch Raumladungseffekte und durch Totzeit beschränkt ist, konzentrieren sich die Untersuchungen auf die Optimierung des Ladungstransfers und der Signallänge, aber auch auf das Gasverstärkungsverhalten bei unterschiedlichen Gasmischungen und -drücken. Die zweidimensionale Positionsbestimmung eines Ereignisses wird durch ein interpolierendes Auslesekonzept realisiert, das auf resistiver Ladungstrennung basiert und große sensitive Flächen bei gleichzeitig wenigen elektronischen Kanälen ermöglicht. Um von der asynchronen und parallelen Auslesefähigkeit zu profitieren, wird ein neues, speziell an das interpolierende Auslesekonzept angepasstes, elektronisches Datenverarbeitungs- und Auslesesystem entwickelt. Durch die lokal beschränkte Auslese der Orts- und Energieinformationen zeichnet sich dieses System durch eine hohe Ereignisausleserate bei geringer, lokal begrenzter Totzeit aus. Die erfolgreiche Optimierung des hier vorgestellten Detektorsystems für Hochgeschwindigkeitsmessungen führt zu einem flexibel einsetzbaren Werkzeug, das eine Zeitauflösung in der Größenordnung von 100 ns und eine lokale Ratenverträglichkeit von > 10⁶ Photonen s^−1 in punktförmigen Beugungsmaxima bietet. Die globale Ratenverträglichkeit, die direkt proportional zur sensitiven Fläche ist, beträgt mehr als 2 · 10⁵ Photonen cm^−2 s^−1.Many biological and technical applications at synchrotron radiation facilities require fast X-ray imaging detectors with good temporal and spatial resolution and large sensitive area. Motivated by the absence of commercially available detectors for these purposes, this thesis describes detailed studies of a novel gaseous single photon counter with gas amplification by micro pattern devices. In this respect, the suitability of MicroCAT and GEM micro structures, their combination and constellations of double- and triple-GEM stages is investigated for utilisation in high speed measurements, which usually demand high photon fluxes. Since the high rate capability of the detector is mainly limited by space charge effects and by dead time, the studies are focussed on the optimisation of the charge transfer behaviour and the signal lengths but also on the gas gain performance in different gas mixtures and pressures. The truly two-dimensional determination of the event position is realised by an interpolating readout concept based on resistive charge division, providing a large sensitive area with only a few electronic channels at the same time. To fully exploit the asynchronous and parallel readout capability, a newly developed electronic preprocessing and readout system has specially been adapted to the interpolating readout concept, offering low dead times and a high readout speed owing to the use of a locally confined readout of the spatial and energy information. The optimisation of the detector system, presented here, with respect to high speed measurements successfully leads to a flexible tool providing a time resolution of the order of 100 ns and a rate capability > 10⁶ photons s^−1 in diffraction peaks. The total rate capability amounts to more than 2 · 10⁵ photons cm^−2 s^−1 and is proportional to the sensitive area of the detector

A new GIS toolbox for integrating massive heterogeneous GIS data for land use change analysis

Agricultural land use in Germany and related impacts on the environment and the use of natural resources are key research topics at the Thünen-Institute of Rural Studies. As spatial context is essential for the analysis of causal connections, GIS data regarding all necessary information was gathered during different research projects and prepared for processing in a database. In particular, the Integrated Administration and Control System, which was available for certain project purposes for several Federal Laender and years, serves as a very detailed data source for agricultural land use. We use different Open Source GIS software like PostgreSQL/ PostGIS, GRASS and QuantumGIS for geoprocessing, supplemented with the proprietary ESRI product ArcGIS. After introducing the used input data and the general processing approach, this paper presents a selection of geoprocessing routines for which Open Source GIS software was used. As an exemplary ’use case’ for the conclusions from the consecutive statistical analysis, we summarize impacts of increased biogas production on agricultural land use change highlighting the trend in biogas maize cultivation and the conversion of permanent grassland to agricultural cropland

Investigation of the performance of an optimised MicroCAT, a GEM and their combination by simulations and current measurements

A MicroCAT (Micro Compteur A Trous) structure which is used for avalanche charge multiplication in gas filled radiation detectors has been optimised with respect to maximum electron transparency and minimum ion feedback. We report on the charge transfer behaviour and the achievable gas gain of this device. A three-dimensional electron and ion transfer simulation is compared to results derived from electric current measurements. Similarly, we present studies of the charge transfer behaviour of a GEM (Gas Electron Multiplier) by current measurements and simulations. Finally, we investigate the combination of the MicroCAT and the GEM by measurements with respect to the performance at different voltage settings, gas mixtures and gas pressures.Comment: 26 pages, 32 figure

Gas gain and signal length measurements with a triple-GEM at different pressures of Ar-, Kr- and Xe-based gas mixtures

We investigate the gas gain behaviour of a triple-GEM configuration in gas mixtures of argon, krypton and xenon with ten and thirty percent of carbon dioxide at pressures between 1 and 3 bar. Since the signal widths affect the dead time behaviour of the detector we present signal length measurements to evaluate the use of the triple-GEM in time-resolved X-ray imaging.Comment: 19 pages, 21 figures, revised version, accepted for publication in Nucl. Instr. and Meth.

Development of a two-dimensional virtual pixel X-ray imaging detector for time-resolved structure research

An interpolating two-dimensional X-ray imaging detector based on a single photon counter with gas amplification by GEM (gas electron multiplier) structures is presented. The detector system can be used for time-resolved structure research down to the microsecond-time domain. The prototype detector has been tested at the SAXS beamline at ELETTRA synchrotron light source with a beam energy of 8 keV to test its capabilities in the rough beamline environment. The imaging performance is examined with apertures and standard diffraction targets. Finally, the application in a time-resolved lipid temperature jump experiment is presented.Comment: 10 pages, 14 figures, accepted for publication in J. Synchrotron Rad, revised version, paper shortened, minor change

Better Soils for Resilient Agricultural Production

Agriculture plays a pivotal role in improving food security and reducing poverty in Africa, as well as in promoting climate change mitigation and adaptation and general progress on the Sustainable Development Goals (SDGs). In Sub-Saharan Africa (SSA), the agricultural sector employs 70% of the population and is estimated to contribute roughly 15% to GDP. But changing climate conditions and poor agricultural practices lead to soil degradation of up to 65% of agricultural lands in SSA, threatening food security. The “betterSoil” concept is a holistic and systemic approach that stresses the whole, considers essential regional aspects to link economic prosperity and sustainable agricultural practices, and addresses climate change. Its four simple principles – soil management, compost, biochar, and agroforestry – can unlock the potential of soils to restore soil organic matter, to protect soil fertility and biodiversity, and to sequester CO2 for the future build-up of humus in agricultural soils. Better soils can promote economic growth and development, especially in low-income countries hit hardest by climate change. Its four principles support the introduction of climate-positive practices that can be implemented anywhere. To harvest the benefits of large-scale soil improvement, farmers, governments, the African Union, individuals, the private sector, and practitioners must work together to bring theory on better soils into practice.</p

Metabolomics demonstrates divergent responses of two Eucalyptus species to water stress

Past studies of water stress in Eucalyptus spp. generally highlighted the role of fewer than five “important” metabolites, whereas recent metabolomic studies on other genera have shown tens of compounds are affected. There are currently no metabolite profiling data for responses of stress-tolerant species to water stress. We used GC–MS metabolite profiling to examine the response of leaf metabolites to a long (2 month) and severe (Ψpredawn < −2 MPa) water stress in two species of the perennial tree genus Eucalyptus (the mesic Eucalyptus pauciflora and the semi-arid Eucalyptus dumosa). Polar metabolites in leaves were analysed by GC–MS and inorganic ions by capillary electrophoresis. Pressure–volume curves and metabolite measurements showed that water stress led to more negative osmotic potential and increased total osmotically active solutes in leaves of both species. Water stress affected around 30–40% of measured metabolites in E. dumosa and 10–15% in E. pauciflora. There were many metabolites that were affected in E. dumosa but not E. pauciflora, and some that had opposite responses in the two species. For example, in E. dumosa there were increases in five acyclic sugar alcohols and four low-abundance carbohydrates that were unaffected by water stress in E. pauciflora. Re-watering increased osmotic potential and decreased total osmotically active solutes in E. pauciflora, whereas in E. dumosa re-watering led to further decreases in osmotic potential and increases in total osmotically active solutes. This experiment has added several extra dimensions to previous targeted analyses of water stress responses in Eucalyptus, and highlights that even species that are closely related (e.g. congeners) may respond differently to water stress and re-waterin

Biological X-ray diffraction measurements with a novel two-dimensional gaseous pixel detector

In order to exploit the potential of modern X-ray diffraction studies to its full extent, a new generation of appropriate detectors is required. Here, a small prototype (28 × 28 mm2 active area) of a novel two-dimensional pixel detector is presented which satisfies most of the requirements. It is based on a gaseous single-photon counter with asynchronous readout and interpolating position encoding, combining the advantages of a pure pixel readout (high local and global rate capability) with those of a projecting readout (small number of channels). In order to demonstrate the suitability of this detector for X-ray diffraction applications, measurements at a synchrotron radiation source have been performed recording diffraction patterns from different biological samples (rat tail tendon collagen, phospholipid and protein crystal). These measurements have proven the good spatial resolution, the high intensity precision and the high local rate capability. Moreover, the single-photon readout was utilized in order to perform time-resolved measurements in the case of SAXS studies and to apply fine angular slicing in the case of protein crystallography. The detector has a high reliability and robustness, particularly when compared with conventional gaseous detectors, and the technology used can be easily extended to large active areas.Work supported by the European Community (contract No. FMBICT980104 and No. FMBICT961694)