48 research outputs found
Dihydrogen activation at non-metallic centers
No full textThe work presented in this thesis was dedicated to the development of novel systems based on pyridinium salts for the heterolytic dihydrogen activation and evaluation of their suitability as catalysts for catalytic hydrogenation. These systems contain a pyridinium salt as hydride acceptor and a basic nitrogen or oxygen function as proton acceptor. Initially, an intramolecular system was envisioned, in which the pyridinium salt is linked with a basic amine and the hydrogen cleavage should occur through a concerted transition state. Due to the low stability of the starting materials, mainly decomposition products were observed after test reactions at high temperatures and hydrogen pressures ranging from 50-100 bar.
As a next step, a bimolecular system based on pyridinium salts and sterically hindered alcoxides was evaluated. For this purpose, electrophilic N-acyl ammonium salts and phenolates derived from commercially available BHT derivatives were prepared. However, in the presence of hydrogen gas no reaction was observed and starting materials were recovered.
ITAMI and co-workers demonstrated the formation of pyridylidenes from pyridinium salts in the presence of a strong base. These highly reactive intermediates could then undergo formal addition of H2. Known pyridinium salt/dihydropyridine systems are Hantzsch esters and nicotinamide derivatives. Both classes of pyridinium salts were tested for H2 activation reactions. Although the formation of the corresponding dihydropyridines was observed, deuteration experiments proved that the reaction did not proceed via dihydrogen splitting. Furthermore, the ability of these N protected pyridinium salts to reduce selected substrates was rather poor.
Finally, the activation of dihydrogen was achieved by reaction of a pyridinium salt as described by ITAMI in the presence of base. First, a 1,3,5 triarylpyridinium salt was synthesized, which could be transformed into the corresponding pyridylidene in the presence of LiHMDS. This intermediate was trapped by quenching with S8. Reaction with H2 led to its activation and the corresponding 1,2 dihydropyridine was formed.
Dihydrogen activation was confirmed by reaction with deuterium gas, as the 2H NMR spectra showed the signal of the corresponding CD2 group. Studies towards catalytic applications of that system showed that imine 255 was reduced to the corresponding amine in the presence of stoichiometric amounts of base and 20 mol% of catalyst loading
Unfolding presence: an interpretative phenomenological analysis of photography
No full textNote: This record first appeared under the author\u27s less commonly used primary name of Emma Helena Sawatzky. In order to match the information contained in the thesis itself, the name in the record has been changed to the author\u27s regular name of Helma Sawatzky
The Effect of Propeller Scaling Methodology on the Performance Prediction
No full textIn common model testing practise, the measured values of the self propulsion test are split into the characteristics of the hull, the propeller and into the interaction factors. These coefficients are scaled separately to the respective full scale values and subsequently reassembled to give the power prediction. The accuracy of this power prediction depends inter alia on the accuracy of the measured values and the scaling procedure. An inherent problem of this approach is that it is virtually impossible to verify each single step, because of the complex nature of the underlying problem. In recent years the scaling of the open-water characteristics of propeller model tests attracted a renewed interest, fuelled by competitive tests, which became the norm due to requests of the customer. This paper shows the influence of different scaling procedures on the predicted power. The prediction is compared to the measured trials data and the quality of the prediction is judged. The procedures examined are the standard ITTC 1978 procedure plus derivatives of it, the Meyne method, the strip method developed by the Hamburgische Schiffbau-Versuchsanstalt (HSVA) and the
β
i
-method by Helma
Surprising Behaviour of the Wageningen B-Screw Series Polynomials
No full textUndoubtedly, the Wageningen B-screw Series is the most widely used systematic propeller series. It is very popular to preselect propeller dimensions during the preliminary design stage before performing a more thorough optimisation, but in the smaller end of the market it is often used to merely select the final propeller. Over time, the originally measured data sets were faired and scaled to a uniform Reynolds number of 2 · 106 to increase the reliability of the series. With the advent of the computer, polynomials for the thrust and torque values were calculated based on the available data sets. The measured data are typically presented in the well-known open-water curves of thrust and torque coefficients K T and K Q versus the advance coefficient J . Changing the presentation from these diagrams to efficiency maps reveals some unsuspected and surprising behaviours, such as multiple extrema when optimising for efficiency or even no optimum at all for certain conditions, where an optimum could be expected. These artefacts get more pronounced at higher pitch to diameter ratios and low blade numbers. The present work builds upon the paper presented by the author at the AMT’17 and smp’19 conferences and now includes the extended efficiency maps, as suggested by Danckwardt, for all propellers of the Wageningen B-screw Series
Studies on DNA, complexed by surfactants or modified with pyrene
No full textThis work consists of several parts. It was initiated by Giese’s electon or hole transfer
through DNA using a modified thymidine as a photon triggered radical injector. Taken
the gained knowlegde, that has been collected over years from the series of Tstar
experiments in DNA fragments (oligonucleotides) in solution in account, this work
describes in the first part the changing of the surrounding media. By complexing the
polyanionic backbone of DNA or oligonucleotides with amphiphilic, cationic surfactants
(Surfactant-DNA complex, SDC), water as media could be exchanged by alcohols such
es methanol or propanol. DNA can thereby be dissolved in organic solvents. Surfactants
like dimethylditetradecylammonium chloride (DMDTAB) were used for experiments on
the T star.
During gathering the knowlegde of how to handle the complexes, we started to complex
salmon DNA with a hole series of surfactants of aliphatic as well as aromatic and
polyaromatic nature. Cationic surfactants (trimethylammonim heads) were synthesisied
containing moieties like pyrene, anthracene and substituted derivatives, naphthalimide,
carbazole, umbelliferone, phthalimide and coumarin to change the physical and spectral
properties of the resulting DNA complexes.
The complex of DNA and cetylammonium bromide (CTAB) was spun into fibres with
diameters of 300 - 500 nm by electrospinning. In this way stable, self-assembling
nanomaterials have been produced.
An other part of this work deals with the photophysical and photochemical properties of
DNA, modifed with pyrene. Pyrene has been incorporated as pyrene deoxyribose
nucleoside, replacing only one nucleobase as well as a diamide, replacing the nucleobase
and a sugar moiety into oligomers. This pyrene modified strands have been irradiated
with UV light and the degradation has been analysed using HPLC and Maldi-ToF
Author Correction: A prospective observational study of post-COVID-19 chronic fatigue syndrome following the first pandemic wave in Germany and biomarkers associated with symptom severity (Nature Communications, (2022), 13, 1, (5104), 10.1038/s41467-022-3
No full textIn the author list of this article, the names of the authorswere incorrectly listed with initials and family name only. The incorrect author list read as “C. Kedor, H. Freitag, L. Meyer-Arndt, K. Wittke, L. G. Hanitsch, T. Zoller, F. Steinbeis, M. Haffke, G. Rudolf, B. Heidecker, T. Bobbert, J. Spranger, H. D. Volk, C. Skurk, F. Konietschke, F. Paul, U. Behrends, J. Bellmann-Strobl and C. Scheibenbogen”. The author list has now been amended to include the given and family names in the HTML and PDF versions of the article. The corrected author list reads as “Claudia Kedor, Helma Freitag, Lil Meyer-Arndt, Kirsten Wittke, Leif G. Hanitsch, Thomas Zoller, Fridolin Steinbeis, Milan Haffke, Gordon Rudolf, Bettina Heidecker, Thomas Bobbert, Joachim Spranger, Hans- Dieter Volk, Carsten Skurk, Frank Konietschke, Friedemann Paul, Uta Behrends, Judith Bellmann-Strobl and Carmen Scheibenbogen”
Innovative Strategies to Develop Chemical Categories Using a Combination of Structural and Toxicological Properties
No full text1.AbstractInterest is increasing in the development of non-animal methods for toxicological evaluations. These methods are however, particularly challenging for complex toxicological endpoints such as repeated dose toxicity. European Legislation, e.g. the European Union´s Cosmetic Directive and REACH, demands the use of alternative methods. Frameworks, such as the Read-across Assessment Framework or the Adverse Outcome Pathway Knowledge Base, support the development of these methods. The aim of the project presented in this publication was to develop substance categories for a read-across with complex endpoints of toxicity based on existing databases. The basic conceptual approach was to combine structural similarity with shared mechanisms of action. Substances with similar chemical structure and toxicological profile form candidate categories suitable for read-across. We combined two databases on repeated dose toxicity, RepDose database and ELINCS database to form a common database for the identification of categories. The resulting database contained physicochemical, structural and toxicological data, which were refined and curated for cluster analyses. We applied the Predictive Clustering Tree (PCT) approach for clustering chemicals based on structural and on toxicological information to detect groups of chemicals with similar toxic profiles and pathways/mechanisms of toxicity. As many of the experimental toxicity values were not available, this data was imputed by predicting them with a multi-label classification method, prior to clustering. The clustering results were evaluated by assessing chemical and toxicological similarities with the aim of identifying clusters with a concordance between structural information and toxicity profiles/mechanisms. From these chosen clusters, seven were selected for a quantitative read-across, based on a small ratio of NOAEL of the members with the highest and the lowest NOAEL in the cluster (<5). We discuss the limitations of the approach. Based on this analysis we propose improvements for a follow-up approach, such as incorporation of metabolic information and more detailed mechanistic information. The software enables the user to allocate a substance in a cluster and to use this information for a possible read- across. The clustering tool is provided as a free web service, accessible at http://mlc-reach.informatik.uni-mainz.de
Parallelt. [Übers. des Autors]: Steady and unsteady jet wiping processes
No full textDer Gasdüsenabstreifprozeß kommt bei vielen kontinuierlichen Beschichtungsverfahren zum Einsatz, um die überschüssige Materialmenge, die vom Substrat aus dem Bad ausgetragen wird, zu reduzieren. Typische Anwendungsbereiche sind das Verzinken von Bandblechen und das Beschichten von photographischen Filmen. Das fundamentale Prinzip dieses Verfahrens besteht in dem Auftreffen eines Freistrahls auf einen von einem festen Substrat transportierten Flüssigkeitsfilm.In dieser Arbeit wird dieser Prozeß rein zweidimensionalen untersucht.Unter der Voraussetzung, daß Trägheitseffekte vernachlässigt werden können, werden neben den Einflüssen der Druck- und Schubspannungsverteilung des Freistrahls auf das flüssige Beschichtungsmaterial auch der Einfluß der Oberflächenspannung untersucht. Es zeigt sich, daß eine einzige inhomogene Wellengleichung die Verteilung der Schichtdicke beschreibt. Schlußendlich werden numerische und graphische Ergebnisse für ausgewählte stationäre und instationäre Fälle inklusive der Ausbildung von Unstetigkeiten präsentiert.The jet wiping process is widely used in continuous coating applications to remove the excess amount of liquid entrained by a sheet moving out of a liquid bath. Typical fields of applications are hot dip galvanization of metal strips and coating of photographic films. The process is based on the impact of a gas jet onto the liquid film carried by the solid substrate.In the present study the process is investigated for the case of strictly two-dimensional flow. It is assumed that inertia effects in the film flow can be neglected, whereas the effects of the pressure gradient and the shear stress distribution of the impinging jet and the surface tension of the liquid film are taken into account
A scaling procedure for modern propeller designs
No full textThe extrapolation procedures currently used to scale propeller characteristics tested at
model scale to their full scale performances are either based on a statistical [1], the Lerbs-
Meyne [2] or the recently developed strip method [3].
With the emergence of so-called unconventional propellers and different design strategies
associated with them, it has been questioned whether the assumptions used in these scaling methods
are still universally valid. E.g. with tip and root unloading employed, the circulation
distribution deviates from the optimum, which is assumed by the Lerbs-Meyne method; more modern
profiles show a different camber distribution and hence the drag coefficient must be aligned with
the hydrodynamic inflow angle and not with the pitch to diameter ratio as assumed by the strip
method (and implicitly by the ITTC 1978 method [4]).
The work presented still uses the assumption of the equivalent profile and will
explain a modified scaling procedure showing a way to calculate the hydrodynamic inflow angle
solely from one open-water test conducted at a constant Reynolds number. Finally exemplary results
comparing a propeller of conventional type with a recent propeller designs will also be shown.
The new proposed method shows a superior performance when compared to other scaling
methods
A scaling procedure for modern propeller designs
No full textThe extrapolation procedures currently used to scale propeller characteristics tested at
model scale to their full scale performances are either based on a statistical [1], the Lerbs-
Meyne [2] or the recently developed strip method [3].
With the emergence of so-called unconventional propellers and different design strategies
associated with them, it has been questioned whether the assumptions used in these scaling methods
are still universally valid. E.g. with tip and root unloading employed, the circulation
distribution deviates from the optimum, which is assumed by the Lerbs-Meyne method; more modern
profiles show a different camber distribution and hence the drag coefficient must be aligned with
the hydrodynamic inflow angle and not with the pitch to diameter ratio as assumed by the strip
method (and implicitly by the ITTC 1978 method [4]).
The work presented still uses the assumption of the equivalent profile and will
explain a modified scaling procedure showing a way to calculate the hydrodynamic inflow angle
solely from one open-water test conducted at a constant Reynolds number. Finally exemplary results
comparing a propeller of conventional type with a recent propeller designs will also be shown.
The new proposed method shows a superior performance when compared to other scaling
methods
