Sequentially Triggered Star Formation in OB Associations

We discuss observational evidence for sequential and triggered star formation in OB associations. We first review the star formation process in the Scorpius-Centaurus OB association, the nearest OB association to the Sun, where several recent extensive studies have allowed us to reconstruct the star formation history in a rather detailed way. We then compare the observational results with those obtained for other OB associations and with recent models of rapid cloud and star formation in the turbulent interstellar medium. We conclude that the formation of whole OB subgroups (each consisting of several thousand stars) requires large-scale triggering mechanisms such as shocks from expanding wind and supernova driven superbubbles surrounding older subgroups. Other triggering mechanisms, like radiatively driven implosion of globules, also operate, but seem to be secondary processes, forming only small stellar groups rather than whole OB subgroups with thousands of stars.Comment: Invited talk at the IAU Symposium 237: "Triggered Star Formation in a Turbulent ISM", Prague, Czech Republic, August 200

Revitalizing Multilateral Governance at the World Trade Organization Report of the High-Level Board of Experts on the Future of Global Trade Governance. Bertelsmann Policy Brief 2018

If international trade is not governed by rules, mere might dictates what is right. The World Trade Organization (WTO) serves as a place where trade policy issues are addressed, disputes arbitrated, legal frameworks derived and enforced. Through these functions, the WTO ensures that the rules of trade policy are inspired by fairness and reciprocity rather than national interest. It is more important than ever to vitalize the global public good that it rep-resents against various threats that have been undermining it. Therefore, the Global Economic Dynamics project of the Bertelsmann Stiftung has called into life a High-Level Board of Experts on the Future of Global Trade Governance. Composed of eminent experts and seasoned trade diplomats, it elaborated a series of feasible policy recommendations that will increase the effectiveness and sali-ence of the WTO. We hope that this Report provides helpful suggestions in a time marked by increasing trade disputes and protectionism and instead contributes to stronger multilateral institutions and fora.1 The Bertelsmann Stiftung owes a debt of gratitude to Prof Bernard Hoekman, the Chairman of the Expert Board and author of this report. His invaluable expertise and experience, guidance and ability to bridge controversial opinions have been crucial in defining the work of the Board. We would also like to express our sincere thanks to all our Board Members, who generously contributed their expertise, time and networks. Without their dedication, this Report would not have been possible. Finally, we would like to thank Robert Koopman and Aik Hoe Lim of the WTO for their support throughout the whole process and Christian Bluth of Bertelsmann Stiftung for managing this common endeavour

Revitalizing Multilateral Governance at the World Trade Organization Policy Brief based on the Report of the High-Level Board of Experts on the Future of Global Trade Governance. Bertelsmann Policy Brief 2018

If international trade is not governed by rules, mere might dictates what is right. The World Trade Organization (WTO) serves as a place where trade policy issues are addressed, disputes arbitrated, legal frameworks derived and enforced. Through these functions, the WTO ensures that the rules of trade policy are inspired by fairness and reciprocity rather than national interest. It is more important than ever to vitalize the global public good that it represents against various threats that have been undermining it. Therefore, the Global Economic Dynamics project of the Bertelsmann Stiftung has called into life a High- Level Board of Experts on the Future of Global Trade ominant view among the members of the Expert Board. Members of the Board participated in meetings on a Governance. Composed of eminent experts and seasoned trade diplomats, it elaborated a series of feasible policy recommendations that will increase the effectiveness and salience of the WTO. We hope that this Report provides helpful suggestions in a time marked by increasing trade disputes and protectionism and instead contributes to stronger multilateral institutions and fora

Economic Integration and the Welfare State

Wirtschaftsintegration, Sozialstaat, Mobilität, Europäische Wirtschafts- und Währungsunion, Economic integration, Welfare state, Mobility, European Economic and Monetary Union

Energy-based comparison between the Fourier--Galerkin method and the finite element method

The Fourier-Galerkin method (in short FFTH) has gained popularity in numerical homogenisation because it can treat problems with a huge number of degrees of freedom. Because the method incorporates the fast Fourier transform (FFT) in the linear solver, it is believed to provide an improvement in computational and memory requirements compared to the conventional finite element method (FEM). Here, we systematically compare these two methods using the energetic norm of local fields, which has the clear physical interpretation as being the error in the homogenised properties. This enables the comparison of memory and computational requirements at the same level of approximation accuracy. We show that the methods' effectiveness relies on the smoothness (regularity) of the solution and thus on the material coefficients. Thanks to its approximation properties, FEM outperforms FFTH for problems with jumps in material coefficients, while ambivalent results are observed for the case that the material coefficients vary continuously in space. FFTH profits from a good conditioning of the linear system, independent of the number of degrees of freedom, but generally needs more degrees of freedom to reach the same approximation accuracy. More studies are needed for other FFT-based schemes, non-linear problems, and dual problems (which require special treatment in FEM but not in FFTH).Comment: 24 pages, 10 figures, 2 table

Enantiomer fractions instead of enantiomer ratios

The use of enantiomer ratios (ERs) to indicate the relative amounts of a pair of enantiomers in a sample has some disadvantages. Enantiomer fractions (EFs) are proposed as all alternative expression to eliminate the difficulties. (C) 2000 Elsevier Science Ltd

Enzymatic catalysis in the synthesis of new polymer architectures and materials

Over the last decade, progress in the research towards enzymatic ring-opening polymerization has lead to novel, biocatalytic, and cleaner processes for the synthesis of polymeric materials. So far, this research has predominantly been focused on how to utilize the enzyme’s selectivity to synthesize and modify polymers, which cannot easily be achieved via chemical routes. However, proper understanding of these processes has not been obtained yet. Additionally, already present polymers have been enzymatically synthesized for biomedical applications, without the use of a metal catalyst, e.g. poly(e-caprolactone). However, only little reports have been published on new materials, which were not readily accessible via traditional polymerization techniques. In this PhD research, the implementation of enzymes into polymer chemistry has been investigated, looking for an answer to the question: Can enzymes open new perspectives in polymer chemistry? Lipase was chosen as the enzyme for enzymatic ring-opening polymerization (e-ROP), as this is well-known in organic synthesis. The lipase that was used in this research is Candida antarctica Lipase B immobilized on an acrylic resin, which is commercially available under the name Novozym 435TM. The aim of this investigation is to (i) obtain insight into the critical parameters of e- ROP of lactones, and (ii) make new materials that are not (directly) accessible via chemical polymerization methods. In order to study the critical parameters of e-ROP of lactones, the present knowledge was investigated in more depth for e-caprolactone (e-CL) as monomer in the enzymatic synthesis of end-functionalized polymer using a functional initiator. It was found that only by optimizing reaction conditions such as temperature, presence of water, monomer concentration, and the type of initiator, well-defined polymeric structures could be obtained, thereby limiting the amount of polymeric side-products (i.e. polymer species that lack the specific end-group functionality). Moreover, the concentrations of end-functionalized polymer and the undesired side-products were quantified for the first time using Liquid Chromatography under Critical Conditions (LCCC). This technique has provided us new insights into the actual enzymatic process at different stages in the polymerization. Water appears to be the primary nucleophile during the initial stages of the reaction, even when all the reaction components are thoroughly dried. Depending on the type of functional initiator that is applied, this nucleophile is incorporated into the polymer, by both transesterification and initiation. Finally, cyclic polymer structures are formed during all stages of the reaction and their concentration depends strongly on the initial monomer concentration Subsequently, e-ROP was used in combination with controlled radical polymerization (atom transfer radical polymerization, ATRP) in order to investigate the compatibility of enzymes with other catalyst systems. All information that was previously obtained was used to synthesize a block copolymer (poly(CL-block-MMA)) by these two polymerization techniques. Ultimately, a cascade chemo-enzymatic polymerization was performed in which the two polymerization techniques were applied simultaneously from a bifunctional initiator to obtain a block copolymer. It was observed that enzymes are slowly deactivated in the presence of transition metals (i.e. copper- and nickel-based ATRP-catalysts), depending on the ligands used to coordinate these metals. Hence, cascade chemo-enzymatic synthesis is only feasible when the two catalysts are applied separately. In order to synthesize novel materials that are not (directly) accessible via chemical polymerization methods, a larger lactone (i.e. ¿-pentadecalactone, PDL) was polymerized using enzymatic ring-opening polymerization. Using chemical, metal-based catalysts, larger lactones cannot be polymerized to high molecular weight polyesters due to their low ringstrain, whereas enzymes have shown surprisingly high activity towards these monomers. The synthesis of this type of monomers opens a novel promising route to the production of biomedical materials. To test the mechanical properties of PPDL, the enzymatic synthesis was scaled up to obtain 30 g of polymer in one batch and optimized to obtain a polymer with a high molecular weight and a relatively narrow molecular weight distribution. The obtained PPDL was melt-spun into fibers, which after drawing show good properties for biomedical applications. In conclusion, it can be stated that enzymes do open new perspectives in polymer science. Careful analysis of the enzymatic process has revealed the critical parameters for proper enzymatic polymer synthesis. Enzymes can be used in combination with other catalysts and polymerization techniques to make polymer architectures that may not be directly available via chemical synthesis. Finally, a new range of monomers can be utilized specifically by enzymes to make novel, tailored biomedical materials