Freiburg Institute for Advanced Studies FRIAS

Freiburg, Germany

Freiburg Institute for Advanced Studies FRIAS

Freiburg, Germany
Time filter
Source Type

Bermudez A.,Institute Fisica Fundamental | Schaetz T.,Albert Ludwigs University of Freiburg | Schaetz T.,Freiburg Institute for Advanced Studies FRIAS
New Journal of Physics | Year: 2016

We introduce a theoretical scheme that exploits laser cooling and phonon-mediated spin-spin interactions in crystals of trapped atomic ions to explore the transport of energy through a quantum magnet. We show how to implement an effective transport window to control the flow of energy through the magnet even in the absence of fermionic statistics for the carriers. This is achieved by shaping the density of states of the effective thermal reservoirs that arise from the interaction with the external bath of the modes of the electromagnetic field, and can be experimentally controlled by tuning the laser frequencies and intensities appropriately. The interplay of this transport window with the spin-spin interactions is exploited to build an analogue of the Coulomb-blockade effect in nano-scale electronic devices, and opens new possibilities to study quantum effects in energy transport. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Raue A.,Albert Ludwigs University of Freiburg | Kreutz C.,Albert Ludwigs University of Freiburg | Theis F.J.,Helmholtz Center Munich | Timmer J.,Albert Ludwigs University of Freiburg | And 2 more authors.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013

Increasingly complex applications involve large datasets in combination with nonlinear and highdimensional mathematical models. In this context, statistical inference is a challenging issue that calls for pragmatic approaches that take advantage of both Bayesian and frequentist methods. The elegance of Bayesian methodology is founded in the propagation of information content provided by experimental data and prior assumptions to the posterior probability distribution of model predictions. However, for complex applications, experimental data and prior assumptions potentially constrain the posterior probability distribution insufficiently. In these situations, Bayesian Markov chain Monte Carlo sampling can be infeasible. From a frequentist point of view, insufficient experimental data and prior assumptions can be interpreted as non-identifiability. The profile-likelihood approach offers to detect and to resolve non-identifiability by experimental design iteratively. Therefore, it allows one to better constrain the posterior probability distribution until Markov chain Monte Carlo sampling can be used securely. Using an application from cell biology, we compare both methods and show that a successive application of the two methods facilitates a realistic assessment of uncertainty in model predictions. © 2012 The Author(s) Published by the Royal Society. All rights reserved.

Rumi L.,Albert Ludwigs University of Freiburg | Scheuermann G.M.,Albert Ludwigs University of Freiburg | Mulhaupt R.,Freiburg Institute for Advanced Studies FRIAS | Bannwarth W.,Albert Ludwigs University of Freiburg
Helvetica Chimica Acta | Year: 2011

Pd 2+-Exchanged graphite oxide (GO) serves as a precatalyst for the formation of Pd-nanoparticles which are then deposited on the highly functionalized carbonaceous support. This versatile, air-stable, and ligand-free system was applied successfully to Suzuki-Miyaura couplings of some aryl chlorides and to the Mizoroki-Heck as well as the Sonogashira reaction showing relatively high activities and good selectivities. Like with other ligand-free supported systems, the reaction proceeded dominantly by a homogeneous mechanism, but attack of an aryl iodide to Pd-nanoparticles can be excluded as substantial contribution to the entire catalytic process. Beside its straightforward preparation and its stability in air, the system combines the advantages of both homogeneous and heterogeneous catalysis. © 2011 Verlag Helvetica Chimica Acta AG, Zürich, Switzerland.

Stein M.,Albert Ludwigs University of Freiburg | Wieland J.,Albert Ludwigs University of Freiburg | Steurer P.,Albert Ludwigs University of Freiburg | Tolle F.,Albert Ludwigs University of Freiburg | And 4 more authors.
Advanced Synthesis and Catalysis | Year: 2011

Iron nanoparticles (Fe-NP) supported on chemically-derived graphene (CDG) were prepared and identified as an effective catalyst for the hydrogenation of alkenes and alkynes. The catalyst canh easily be separated by magnetic decantation. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA.

Zimmermann A.C.,Freiburg Institute for Advanced Studies FRIAS | Zimmermann A.C.,Albert Ludwigs University of Freiburg | Zarei M.,Freiburg Institute for Advanced Studies FRIAS | Zarei M.,Albert Ludwigs University of Freiburg | And 4 more authors.
Autophagy | Year: 2010

Stress-induced autophagy leads to major cellular remodeling. During autophagy, a new organelle, the autophagosome, is formed that shuttles cellular material to lysosomes for degradation. Quantitative mass spectrometry-based proteomics is a powerful research strategy for the description of spatio-temporal protein dynamics during autophagy. This technique allows the identification of protein-protein interactions and of specific post-translational modifications. In addition, current methods enable the in-depth characterization of cellular as well as organellar composition changes and the global analysis of signaling networks. Thus, a plastic picture of the cell can be drawn. In this review we describe recent advances in MS-based proteomics approaches and their implications for autophagy-related research questions. © 2010 Landes Bioscience.

Zarei M.,Freiburg Institute for Advanced Studies FRIAS | Zarei M.,Albert Ludwigs University of Freiburg | Sprenger A.,Freiburg Institute for Advanced Studies FRIAS | Sprenger A.,Albert Ludwigs University of Freiburg | And 4 more authors.
Journal of Proteome Research | Year: 2012

In large-scale phosphoproteomics studies, fractionation by strong cation exchange (SCX) or electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) is commonly used to reduce sample complexity, fractionate phosphopeptides from their unmodified counterparts, and increase the dynamic range for phosphopeptide identification. However, these procedures do not succeed to separate, both singly and multiply phosphorylated peptides due to their inverse physicochemical characteristics. Hence, depending on the chosen method only one of the two peptide classes can be efficiently separated. Here, we present a novel strategy based on the combinatorial separation of singly and multiply phosphorylated peptides by SCX and ERLIC for in-depth phosphoproteome analysis. In SCX, mostly singly phosphorylated peptides are retained and fractionated while not-retained multiply phosphorylated peptides are fractionated in a subsequent ERLIC approach (SCX-ERLIC). In ERLIC, multiply phosphorylated peptides are fractionated, while not-retained singly phosphorylated peptides are separated by SCX (ERLIC-SCX). Compared to single step fractionations by SCX, the combinatorial strategies, SCX-ERLIC and ERLIC-SCX, yield up to 48% more phosphopeptide identifications as well as a strong increase in the number of detected multiphosphorylated peptides. Phosphopeptides identified in two subsequent, complementary fractionations had little overlap (5%) indicating that ERLIC and SCX are orthogonal methods ideally suited for in-depth phosphoproteome studies. © 2012 American Chemical Society.

Kurek A.,Albert Ludwigs University of Freiburg | Mark S.,University of Heidelberg | Enders M.,University of Heidelberg | Kristen M.O.,Basell Polyolefine GmbH | And 2 more authors.
Macromolecular Rapid Communications | Year: 2010

A ternary blend of the bisiminopyridine chromium (III) (Cr-1) with the bisiminopyridine iron (II) (Fe-2) postmetallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr-3) was supported on mesoporous silica to produce novel multiple single-site catalysts and polyethylene reactor blends with tailor-made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO-treated silica was Fe-2 followed by Cr-1 and Cr-3. Cosupporting does not impair the single-site nature of the blend components producing polyethylene fractions with M̄w = 104 g · mol-1 on Cr-1, M̄w = 3 × 105 g · mol-1 on Fe-2, and M̄w = 3 × 106 g mol-1 on Cr-3. As a function of the Fe-2/Cr-1/Cr-2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor-made polyethylene reactor blends with ultra-broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe-2/Cr-1 was constant, the ultra-high molecular polyethylene (UHMWPE, M̄w 106 g-mol-1) content was varied between 8 and 16 wt.-% as a function of the Cr-3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe-2/Cr-3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr-1. Due to the intimate mixing of low and ultra-high molecular weight polyethylenes (UHMPEs) produced on cosupported single-site catalysts a wide range of melt processable polyethylene reactor blends was obtained. (Figure Presented) © 2010 WlLEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kurek A.,Albert Ludwigs University of Freiburg | Xalter R.,Albert Ludwigs University of Freiburg | Sturzel M.,Albert Ludwigs University of Freiburg | Mulhaupt R.,Albert Ludwigs University of Freiburg | Mulhaupt R.,Freiburg Institute for Advanced Studies FRIAS
Macromolecules | Year: 2013

Highly active single- and dual-site catalysts supported on silica nanofoams (NF) enable the control of both polyethylene (PE) morphology and tailoring of bimodal PE molar mass distribution in catalytic ethylene polymerization. In a templating process, aqueous polystyrene (PS) nano suspensions are mineralized and calcinated at 600 C, thus producing NF with specific surface area of 1200 m2/g and average pore diameter varying between 20 and 80 nm. Mineralization of the aqueous PS nano suspensions in a water-in-oil emulsion affords spherical NF with average diameter of 40 μm and control of pore size. The methylalumoxane- (MAO-) tethered NF immobilizes single-site catalysts such as metallocene (nBuZr), bisiminopyridine iron(II) (Fe) and constrained geometry chinolyl cyclopentadienyl chromium(III) complexes (Cr-1). Immobilization of binary blends of Fe/Cr-1 and nBuZr/Cr-1 affords NF-supported dual-site catalysts. The catalyst activity, PE particle size and molecular weight distribution varies as a function of the NF pore size. Typically, macroporous NF (pore size of 75 nm) are effective supports for Cr-1, producing ultrahigh molecular weight polyethylene (UHMWPE, Mw > 106 g/mol). Dual -site catalysts such as nBuZr/Cr-1 on mesoporous NF (pore size of 20 nm) enable tailoring of bimodal PE molar mass distribution with UHMWPE content increasing with increasing Cr-1/nBuZr molar ratio. © 2013 American Chemical Society.

Leyva-Castillo J.M.,University of Strasbourg | Hener P.,University of Strasbourg | Michea P.,French Institute of Health and Medical Research | Michea P.,University Pierre and Marie Curie | And 6 more authors.
Nature Communications | Year: 2013

Thymic stromal lymphopoietin (TSLP) has emerged as a key initiator in Th2 immune responses, but the TSLP-driven immune cascade leading to Th2 initiation remains to be delineated. Here, by dissecting the cellular network triggered by mouse skin TSLP in vivo, we uncover that TSLP-promoted IL-4 induction in CD4 + T cells in skin-draining lymph nodes is driven by an orchestrated 'DC-T-Baso-T' cascade, which represents a sequential cooperation of dendritic cells (DCs), CD4 + T cells and basophils. Moreover, we reveal that TSLP-activated DCs prime naive CD4 + T cells to produce IL-3 via OX40L signalling and demonstrate that the OX40L-IL-3 axis has a critical role in mediating basophil recruitment, CD4 + T-cell expansion and Th2 priming. These findings thus add novel insights into the cellular network and signal axis underlying the initiation of Th2 immune responses. © 2013 Macmillan Publishers Limited. All rights reserved.

Chandrasekaran S.,TU Hamburg - Harburg | Sato N.,TU Hamburg - Harburg | Sato N.,Toray Industries Inc | Tolle F.,Freiburg Institute for Advanced Studies FRIAS | And 4 more authors.
Composites Science and Technology | Year: 2014

The present study investigates the effect of addition of three different types on carbon nano-fillers on fracture toughness (KIC) and failure mechanism of epoxy based polymer nano-composites. The carbon nano-fillers were dispersed in the epoxy matrix using a three-roll mill and the three nano-fillers used for this experiment were (i) thermally reduced graphene oxide (TRGO); (ii) graphite nano-platelets (GNP); and (iii) multi-wall carbon nano-tubes (MWCNT). The fracture toughness was measured as a function of weight percentage of the filler using single edge notch three-point-bending tests. The toughening effect of TRGO was most significant resulting in 40% increase in KIC for 0.5wt% of filler. On the other hand, the enhancements in toughness were 25% for GNP/epoxy and 8% for MWCNT/epoxy. Investigations on fracture surface revealed that crack pinning or bi-furcation by TRGO and crack face separation initiated from TRGO contributed to enhance the fracture toughness. Based on the observations, a schematic explaining the crack propagation in graphene/epoxy composite and the interaction of crack front with graphene particles was proposed. © 2014 Elsevier Ltd.

Loading Freiburg Institute for Advanced Studies FRIAS collaborators
Loading Freiburg Institute for Advanced Studies FRIAS collaborators