466 research outputs found
Thermodynamic characterization of an engineered tetracycline-binding riboswitch
Riboswitches reflect a novel concept in gene regulation that is particularly suited for technological adaptation. Therefore, we characterized thermodynamically the ligand binding properties of a synthetic, tetracycline (tc)-binding RNA aptamer, which regulates gene expression in a dose-dependent manner when inserted into the untranslated region of an mRNA. In vitro, one molecule of tc is bound by one molecule of partially pre-structured and conformationally homogeneous apo-RNA. The dissociation constant of 770 pM, as determined by fluorimetry, is the lowest reported so far for a small molecule-binding RNA aptamer. Additional calorimetric analysis of RNA point mutants and tc derivatives identifies functional groups crucial for the interaction and including their respective enthalpic and entropic contributions we can propose detailed structural and functional roles for certain groups. The conclusions are consistent with mutational analyses in vivo and support the hypothesis that tc-binding reinforces the structure of the RNA aptamer, preventing the scanning ribosome from melting it efficiently
Digital technologies and the development of the dynamic view of functional thinking
Functional thinking can be characterised by three properties, namely the assignment aspect, the covariation aspect, and the object aspect. Furthermore, static and dynamic views can be distinguished. In this article, an empirical study is presented that investigates the development of the dynamic view when working with linear functions through the use of digital technologies in the context of suitably selected tasks. The results show prerequisites and necessities for the integration of digital technologies into a constructive teaching concept for the development of functional thinking
Influence of Increasing Nutrient Availability on Fern and Lycophyte Diversity
Increased nutrient supply can have drastic effects on natural ecosystems, especially in naturally nutrient-poor ones such as most tropical rainforests. Many studies have focused on the reaction of trees to fertilization, but little is known about herbaceous plants. Ferns are a particularly common group in tropical forests, spanning all vegetation types and zones. Here, we assess how seven years of moderate addition of nitrogen (N), phosphorus (P), and N+P along an elevational gradient (1000â3000 m) have impacted richness and composition of fern and lycophyte assemblages in tropical montane rain forests growing on naturally nutrient deficient soils in the Ecuadorian Andes. We found that fertilization does not affect overall species richness, but that there were strong differences in species abundances (âŒ60% of species), both negative and positive, that were apparently related to the systematic affiliations and ecological properties of the affected species. These diverse responses of ferns to fertilization provide insight into the sensitivity and complexity of the relationships of nutrient availability and community composition in tropical forests
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Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopic analysis
Abstract. Manganese (Mn)-rich natural rock coatings, so-called rock varnishes, are discussed controversially regarding their genesis. Biogenic and abiogenic mechanisms, as well as a combination of both, have been proposed to be responsible for the Mn oxidation and deposition process. We conducted scanning transmission X-ray microscopy - near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) measurements to examine the abundance and spatial distribution of the different oxidation states of Mn within these nano- to micrometer thick crusts. Such microanalytical measurements of thin and hard rock crusts require sample preparation with minimal contamination risk. Focused ion beam (FIB) slicing, a well-established technique in geosciences, was used in this study to obtain 100â200ânm thin slices of the samples for X-ray transmission spectroscopy. However, even though this preparation is suitable to investigate element distributions and structures in rock samples, we observed that, using standard parameters, modifications of the Mn oxidation states occur in the surfaces of the FIB slices. Based on our results, the preparation technique likely causes the reduction of Mn4+ to Mn2+/3+. We draw attention to this issue, since FIB slicing, SEM imaging, and other preparation and visualization techniques operating in the keV range are well-established in geosciences, but researchers are often unaware of the potential for reduction of Mn and possibly other elements in the samplesâ surface layers
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CurcuminoidâBF2 complexes: Synthesis, fluorescence and optimization of BF2 group cleavage
Eight difluoroboron complexes of curcumin derivatives carrying alkyne groups containing substituents have been synthesized following an optimised reaction pathway. The complexes were received in yields up to 98% and high purities. Their properties as fluorescent dyes have been investigated. Furthermore, a strategy for the hydrolysis of the BF2 group has been established using aqueous methanol and sodium hydroxide or triethylamine
OxoplatinâBased Pt(IV) Lipoate Complexes and Their Biological Activity
αâLipoic acid, known for its antiâinflammatory and antioxidant activity, represents a promising ligand for Pt(IV) prodrugs. Three new Pt(IV) lipoate complexes were synthesized and characterized by NMR spectroscopy ( 1 H, 13 C, 195 Pt), mass spectrometry and elemental analysis. Due to the low solubility of the complex containing two axial lipoate ligands, further experiments to examine the biological activity were performed with two Pt(IV) complexes containing just one axial lipoate ligand. Both complexes exhibit anticancer activity and produce reactive oxygen species (ROS) in the cell lines tested. Especially, the monosubstituted complex can be reduced by ascorbic acid and forms adducts with 9âmethylguanine (9MeG), which is favorable for the formation of DNAâcrosslinks in the cells
Nonreciprocal Spin Waves in Nanoscale Domain Walls Detected by Scanning X-ray Microscopy in Perpendicular Magnetic Anisotropic Fe/Gd Multilayers
Spin wave nonreciprocity in domain walls (DWs) allows for unidirectional
signal processing in reconfigurable magnonic circuits. Using scanning
transmission x-ray microscopy (STXM), we examined coherently-excited magnons
propagating in Bloch-like DWs in amorphous Fe/Gd multilayers with perpendicular
magnetic anisotropy (PMA). Near 1 GHz we detected magnons with short
wavelengths down to nm in DWs whose minimum width amounted to
nm. Consistent with micromagnetic simulations, the STXM
data reveal their nonreciprocal magnon band structures. We identified Bloch
points which disrupted the phase evolution of magnons and induced different
adjacent to the topological defects. Our observations provide direct
evidence of nonreciprocal spin waves within Bloch-like DWs, serving as
programmable waveguides in magnonic devices with directed information flow
Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions
[EN] Experiments and numerical simulations were carried out in order to contribute to a better understanding and prediction
of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation
processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a
chamber filled with pure nitrogen at 5 MPa and 293 K and three different test cases were selected such that they
cover regimes in which the thermodynamic non-idealities, in particular the effects that stem from the potential phase
separation, are significant. Simultaneous shadowgraphy and elastic light scattering experiments were conducted to
capture both the flow structure as well as the phase separation. In addition, large-eddy simulations with a vaporliquid
equilibrium model were performed. Both experimental and numerical results show phase formation for the
cases, where the a-priori calculation predicts two-phase flow. Moreover, qualitative characteristics of the formation
process agree well between experiments and numerical simulations and the transition behaviour from a dense-gas
to a spray-like jet was captured by bothThe authors gratefully acknowledge the German Research Foundation (Deutsche Forschungsgemeinschaft) for providing
financial support in the framework of SFB/TRR 40. Financial support was also provided by Munich Aerospace
(www.munich-aerospace.de). Furthermore, the authors thank the Gauss Centre for Supercomputing e.V. (GCS)
(www.gauss-centre.eu) for supporting this project by providing computing time on the GCS Supercomputer SuperMUC
at Leibniz Supercomputing Centre (www.lrz.de).Traxinger, C.; MĂŒller, H.; Pfitzner, M.; Baab, S.; Lamanna, G.; Weigand, B.; Matheis, J.... (2018). Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat PolitĂšcnica de ValĂšncia. 130-137. https://doi.org/10.4995/ILASS2017.2017.4756OCS13013
SatellitengestĂŒtzte Vermessung von stĂ€dtischem GrĂŒn in deutschen StĂ€dten
Urbane GrĂŒnflĂ€chen besitzen vielfĂ€ltige Funktionen und sind als Bereitsteller von Ăkosystemleistungen von zentraler Bedeutung. Sie dienen als NaherholungsflĂ€chen fĂŒr die Stadtbevölkerung, als Lebensraum fĂŒr Flora und Fauna und verbessern die LuftqualitĂ€t. Mit Daten des europĂ€ischen Erdbeobachtungsprogramms Copernicus werden Satellitendaten in einer hohen geometrischen Auflösung sowie mit einer hohen rĂ€umlichen und zeitlichen Abdeckung kostenlos zur VerfĂŒgung gestellt. Die Aufnahmen der Sentinel-2 Satelliten des Copernicus Programms werden in dieser Analyse verwendet, um urbane GrĂŒnflĂ€chen in deutschen StĂ€dten zu kartieren. Um phĂ€nologische EinflĂŒsse abzubilden wird der Jahresgang der Vegetation anhand eines Medianmosaiks bzw. ĂŒber Vegetationsindizes berĂŒcksichtigt. Darauf aufbauend wurde eine Methodik zur Landnutzungs-/Landbedeckungsklassifikation auf Basis von LUCAS Referenzpunkten entwickelt und getestet. Die hohe Gesamtgenauigkeit von 92,3 % zeigt, dass innerstĂ€dtische GrĂŒnflĂ€chen mithilfe flĂ€chendeckender Satellitendaten in hohem Detailgrad erfasst werden können
Which city is the greenest? A multi-dimensional deconstruction of city rankings
The question âwhich city is the greenestâ sounds trivial, but in reality, this question contains statistical ambiguities. In this study, we approach this issue by ranking cities by green space shares. However, we do not base our ranking only on one green parameter and the commonly used administrative boundaries. Instead, we broaden access to rankings through several approaches: First, we calculate two parameters, i.e. green space shares and green space per capita. Second, we apply these parameters for two cases: for all green areas as well as for green
areas with a minimum size of one hectare. The latter are considered to have an impact on near-home recreation and the local climate. Third, we relate these parameters on the one hand to administrative spatial units
constituting the entity âcityâ, but juxtapose these on the other hand with two alternative spatial reference units: a morphological spatial unit that closely encompasses the built-up pattern of the city, and a standardized buffer unit around the city centers. The variability of these manifold rankings obtained by this study makes clear: the rank of one city in a relational system to other cities depends strongly on these parameters and spatial units applied. In our experiments we rank and compare the 80 major cities in Germany. The diversity of results allows to discuss the susceptibility of spatial statistics to ambiguities that may arise from the use of different concepts. By integrating these multidimensional concepts into one final ranking, we propose a strategy for a more holistic and robust approach while revealing uncertainties
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