University of Vienna

About: University of Vienna is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Population & Stars. The organization has 44686 authors who have published 95840 publications receiving 2907492 citations.

Molecfit: A general tool for telluric absorption correction - II. Quantitative evaluation on ESO-VLT/X-Shooterspectra

Abstract: Context. Absorption by molecules in the Earth’s atmosphere strongly affects ground-based astronomical observations. The resulting absorption line strength and shape depend on the highly variable physical state of the atmosphere, i.e. pressure, temperature, and mixing ratio of the different molecules involved. Usually, supplementary observations of so-called telluric standard stars (TSS) are needed to correct for this effect, which is expensive in terms of telescope time. We have developed the software package molecfit to provide synthetic transmission spectra based on parameters obtained by fitting narrow ranges of the observed spectra of scientific objects. These spectra are calculated by means of the radiative transfer code LBLRTM and an atmospheric model. In this way, the telluric absorption correction for suitable objects can be performed without any additional calibration observations of TSS.Aims. We evaluate the quality of the telluric absorption correction using molecfit with a set of archival ESO-VLT/X-Shooter visible and near-infrared spectra. Methods. Thanks to the wavelength coverage from the U to the K band, X-Shooter is well suited to investigate the quality of the telluric absorption correction with respect to the observing conditions, the instrumental set-up, input parameters of the code, the signal-to-noise of the input spectrum, and the atmospheric profiles. These investigations are based on two figures of merit, I off and I res , that describe the systematic offsets and the remaining small-scale residuals of the corrections. We also compare the quality of the telluric absorption correction achieved with molecfit to the classical method based on a telluric standard star.Results. The evaluation of the telluric correction with molecfit shows a convincing removal of atmospheric absorption features. The comparison with the classical method reveals that molecfit performs better because it is not prone to the bad continuum reconstruction, noise, and intrinsic spectral features introduced by the telluric standard star.Conclusions. Fitted synthetic transmission spectra are an excellent alternative to the correction based on telluric standard stars. Moreover, molecfit offers wide flexibility for adaption to various instruments and observing sites.

Kohlenstoffhaltige ternäre Verbindungen (H-Phase)

Abstract: In einer Notiz wurde auf das Bestehen einer neuen ternaren Kristallart in Systemen vom Typus M (Ubergangsmetall)-Me (Metametall)-X (Kohlenstoff) hingewiesen1. Diese Kristallart, deren Zusammensetzung in der Nahe der Kohlenstoffstabilisierten β-Manganphase, z.B. Mo3Al2C2, angenommen wurde, bezeichneten wir mit H-Phase. In der Folge gelang es, diese Phase in einer Reihe von weiteren Dreistoffen aufzufinden und mit Hilfe von Einkristallen im Cr−Al−C-System deren Zusammensetzung und Kristall-Struktur zu ermitteln.

RNAplex: a fast tool for RNA-RNA interaction search.

Abstract: Motivation Regulatory RNAs often unfold their action via RNA-RNA interaction. Transcriptional gene silencing by means of siRNAs and miRNA as well as snoRNA directed RNA editing rely on this mechanism. Additionally ncRNA regulation in bacteria is mainly based upon RNA duplex formation. Finding putative target sites for newly discovered ncRNAs is a lengthy task as tools for cofolding RNA molecules like RNAcofold and RNAup are too slow for genome-wide search. Tools like RNAhybrid that neglects intramolecular interactions have runtimes proportional to O(m x n), albeit with a large prefactor. Still in many cases the need for even faster methods exists. Results We present a new program, RNAplex, especially designed to quickly find possible hybridization sites for a query RNA in large RNA databases. RNAplex uses a slightly different energy model which reduces the computational time by a factor 10-27 compared to RNAhybrid. In addition a length penalty allows to focus the target search on short highly stable interactions. Availability RNAplex can be downloaded at http://www.tbi.univie.ac.at/~htafer/ Supplementary information Supplementary data are available at Bioinformatics online.

Relaxation mechanisms of UV-photoexcited DNA and RNA nucleobases

Abstract: A comprehensive effort in photodynamical ab initio simulations of the ultrafast deactivation pathways for all five nucleobases adenine, guanine, cytosine, thymine, and uracil is reported These simulations are based on a complete nonadiabatic surface-hopping approach using extended multiconfigurational wave functions Even though all five nucleobases share the basic internal conversion mechanisms, the calculations show a distinct grouping into purine and pyrimidine bases as concerns the complexity of the photodynamics The purine bases adenine and guanine represent the most simple photodeactivation mechanism with the dynamics leading along a diabatic ππ* path directly and without barrier to the conical intersection seam with the ground state In the case of the pyrimidine bases, the dynamics starts off in much flatter regions of the ππ* energy surface due to coupling of several states This fact prohibits a clear formation of a single reaction path Thus, the photodynamics of the pyrimidine bases is much richer and includes also nπ* states with varying importance, depending on the actual nucleobase considered Trapping in local minima may occur and, therefore, the deactivation time to the ground state is also much longer in these cases Implications of these findings are discussed (i) for identifying structural possibilities where singlet/triplet transitions can occur because of sufficient retention time during the singlet dynamics and (ii) concerning the flexibility of finding other deactivation pathways in substituted pyrimidines serving as candidates for alternative nucleobases