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Search Results: 1 - 10 of 2283 matches for " Charlotte Friederike Kuhn "
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Another Base, Another Solvent? Desalinating Iron Finds with Tetramethylammonium Hydroxide Solution
Charlotte Friederike Kuhn,Christian Heinrich Wunderlich,Gerhard Eggert,Thomas Schleid
E-Preservation Science , 2011,
Abstract: The desalination processes commonly applied to improve the corrosion stability of archaeological iron artifacts are based on immersion treatments in aqueous sodium hydroxide solutions. Faster and more efficient chloride extraction in solutions based on organic solvents with a lower surface tension can be expected. Furthermore, the danger of new corrosion forming during the subsequent washing out of residual chemicals from the desalinating solution could be minimised, if organic solvents would replace the water, commonly used for this process. Only alkali metal hydroxide (LiOH and NaOH) solutions in organic solvents have been tested so far. Their comparatively low chloride extraction efficiency was ascribed to the low solubility of the alkali metal hydroxides and the corresponding chlorides in the solvents used. Tetramethylammonium hydroxide (TMAH) is readily soluble in alcohols and has been tested in aqueous and/or methanolic solutions as an alternative. Neither improved overall chloride extraction efficiency, nor a higher chloride extraction rate could be observed using methanolic solutions. However, aqueous TMAH showed a trend towards higher overall chloride extraction efficiency than the common alkaline treatments. These results could be explained by the different solubility of corrosion products, in particular akaganéite, β-FeO(OH), in the tested solutions.
Is there an order-barrier $p\leq2$ for time integration in computational elasto-plasticity?
Bernhard Eidel,Charlotte Kuhn
Mathematics , 2015,
Abstract: This paper is devoted to the question, whether there is an order barrier $p\leq2$ for time integration in computational elasto-plasticity. In the analysis we use an implicit Runge-Kutta (RK) method of order $p=3$ for integrating the evolution equations of plastic flow within a nonlinear finite element framework. We show that two novel algorithmic conditions are necessary to overcome the order barrier, (i) total strains must have the same order in time as the time integrator itself, (ii) accurate initial data must be calculated via detecting the elastic-plastic switching point (SP) in the predictor step. Condition (i) is for a \emph{consistent} coupling of the global boundary value problem (BVP) with the local initial value problems (IVP) via displacements/strains. Condition (ii) generates consistent initial data of the IVPs. The third condition, which is not algorithmic but physical in nature, is that (iii) the total strain path in time must be smooth such that condition (i) can be fulfilled at all. This requirement is met by materials showing a sufficiently smooth elastic-plastic transition in the stress-strain curve. We propose effective means to fulfil conditions (i) and (ii). We show in finite element simulations that, if condition (iii) is additionally met, the present method yields the full, theoretical convergence order 3 thus overcoming the barrier $p\leq 2$ for the first time. The observed speed-up for a 3rd order RK method is considerable compared with Backward Euler.
Local Mechanical Stimuli Regulate Bone Formation and Resorption in Mice at the Tissue Level
Friederike A. Schulte, Davide Ruffoni, Floor M. Lambers, David Christen, Duncan J. Webster, Gisela Kuhn, Ralph Müller
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062172
Abstract: Bone is able to react to changing mechanical demands by adapting its internal microstructure through bone forming and resorbing cells. This process is called bone modeling and remodeling. It is evident that changes in mechanical demands at the organ level must be interpreted at the tissue level where bone (re)modeling takes place. Although assumed for a long time, the relationship between the locations of bone formation and resorption and the local mechanical environment is still under debate. The lack of suitable imaging modalities for measuring bone formation and resorption in vivo has made it difficult to assess the mechanoregulation of bone three-dimensionally by experiment. Using in vivo micro-computed tomography and high resolution finite element analysis in living mice, we show that bone formation most likely occurs at sites of high local mechanical strain (p<0.0001) and resorption at sites of low local mechanical strain (p<0.0001). Furthermore, the probability of bone resorption decreases exponentially with increasing mechanical stimulus (R2 = 0.99) whereas the probability of bone formation follows an exponential growth function to a maximum value (R2 = 0.99). Moreover, resorption is more strictly controlled than formation in loaded animals, and ovariectomy increases the amount of non-targeted resorption. Our experimental assessment of mechanoregulation at the tissue level does not show any evidence of a lazy zone and suggests that around 80% of all (re)modeling can be linked to the mechanical micro-environment. These findings disclose how mechanical stimuli at the tissue level contribute to the regulation of bone adaptation at the organ level.
Changing Spaces for Civil Society Organisations in China  [PDF]
Berthold Kuhn
Open Journal of Political Science (OJPS) , 2018, DOI: 10.4236/ojps.2018.84030
Abstract: Concerns about shrinking spaces for civil society organisations have risen in China over the past years, in particular among international nonprofit organisations. The third sector in China, however, continued its growth in numbers, diversity and activities of organisations, accounting for more than 700,000 registered organisations. Government’s financial support to nonprofits significantly increased through contracting out of services. The new Charity Law contains provisions for public fundraising activities, including for online platforms. International activities of Chinese nonprofits took off in the context of participation in global conferences. Chinese NGOs also started to engage in delivering humanitarian aid to communities in other countries. Assessments on shrinking or changing spaces for civil society in China much depend on the type of organisations in focus. This paper pays attention to discourses related to NGO development in China and sheds light on changing spaces for different types of nonprofits in China, those that are negatively affected by new regulations and different kinds of restrictions and those benefiting from emerging opportunities in the context of growing cooperation with the government or the business sector. Analysis based on interviews and talks with experts in China and abroad shows that advocacy-oriented organisations and those receiving foreign funding tend to face more difficulties. Larger international nonprofits with a long track-record in China, however, are seen to continuing or even expanding their activities.
The Short Series of the Oxygen-Poor Lanthanide Oxide Selenides M10OSe14 with M = La–Nd
Frank A. Weber,Christian M. Schurz,Susanne Frunder,Charlotte F. Kuhn,Thomas Schleid
Crystals , 2012, DOI: 10.3390/cryst2031136
Abstract: Single crystals and phase pure samples of oxygen-poor ternary lanthanide oxide selenides with the composition M 10OSe 14 ( M = La–Nd; tetragonal, I4 1/ acd; a = 1592.0–1559.8 pm, c = 2106.5–2062.9 pm) could be obtained by reacting the corresponding metals, selenium and selenium dioxide as oxygen source. Their crystal structures are isotypic with Pr 10OS 14 and thus contain isolated [O M 4] 10+ tetrahedra ( d(O 2–– M 3+) = 243–248 pm) embedded in a complex anionic {[ M 6Se 14] 10–} lanthanide selenide matrix ( d( M 3+–Se 2–) = 288–358 pm). All three crystallographically independent M 3+ cations exhibit eight contacts to chalcogenide anions (O 2– and/or Se 2–) resulting in the formation of bicapped trigonal prismatic coordination polyhedra. The optical band gaps of the oxide selenides M 10OSe 14 amount to values between 1.89 and 2.04 eV indicating wide band-gap semiconductors.
Synthesis and Plasma Stability of Disulfide-Bridged Cyclic Endomorphin-1 Derivatives  [PDF]
Friederike M. Mansfeld, Istvan Toth
International Journal of Organic Chemistry (IJOC) , 2012, DOI: 10.4236/ijoc.2012.21001
Abstract: Endomorphin-1 is an endogenous opioid peptide that mediates pain relief through interaction with the μ-opioid receptor in the central nervous system. To enhance the metabolic stability of this tetrapeptide, cyclisation through the formation of a disulfide bridge between the side chains of cysteine residues added to the sequence was explored. A further increase in stability was achieved through N-terminal modification with lipoamino acid and lactose succinamic acid, and the inclusion of D-amino acids. The latter also provided an alternative spatial arrangement of the aromatic side chains. The lipidated cyclic derivatives were insoluble in aqueous buffer, however, the cyclic peptides and glycopeptides showed greatly improved stability towards enzymatic degradation in human plasma.
First record of a maternity colony of Nyctalus noctula in Austria: does the European nursing area expand?
Friederike Spitzenberger
Hystrix : the Italian Journal of Mammalogy , 2008, DOI: 10.4404/hystrix-18.2-4406
Abstract: The first maternity colony of Nyctalus noctula in Austria was found in 2006. The possibility of an ongoing expansion of the European nursing area is discussed.
Transylvanian Review of Administrative Sciences , 2008,
Abstract: The paper defines the term “Governance” and explores its characteristics such as participation, legitimacy, transparency, effectiveness and efficiency or accountability. Furthermore, it contains the description of different methods such as Government Business Process Reengineering, Public Private Partnership, New Public Management or the Reform of Public Administration. Also the paper shows procedures and trends in Austria, for example the establishment of E-Government including its legislation and developments of the national infrastructure.
La diáspora china: un acercamiento a la migración china en Colombia
Friederike Fleischer
Revista de Estudios Sociales , 2012,
Abstract: The Chinese diaspora is the largest and most extensive among the world's migrant populations. Recent estimates put the number of Chinese emigrants at 40 million people. Far from being a homogenous group, members of the Chinese diaspora have diverse economic, cultural, social, educational, and personal backgrounds as well as very different life stories and emigration experiences. Despite the growing interest in the Pacific Rim and the constant immigration of Chinese to the Americas through the 20[th] century, there is very little information about their migration to Colombia. This article explores the topic from a historical point of view in order to fill this void. The little that is known about Chinese migrants to Colombia is presented in the context of a discussion on the diaspora in order to highlight the transnationality and multiplicity of identities among this migrant group. The article also examines the similarities and differences between Chinese migration to Colombia and other countries in Latin America and on other continents, relating these particularities to local contexts.
Verhandeln, Verwandeln, Verwirren Change. Exchange. Derange.
Friederike Schneider
querelles-net , 2006,
Abstract: Das Graduiertenkolleg Identit t und Differenz“ der Universit t Trier pr sentiert mit dem vorliegenden Band die Ergebnisse einer Tagung von 2004. Trotz der Heterogenit t der zahlreichen angesprochenen Themen wird die Koh renz dieses umfangreichen Sammelbandes durch die gleichbleibend hohe Qualit t der Beitr ge gew hrleistet. With the collection at hand, the postgraduate working group “Identity and Difference” at the University of Trier present the results of a conference held in 2004. Despite the heterogeneity of the various themes touched upon in this comprehensive volume, the consistent high quality of the contributions ensures its coherence.
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