Study of Space Station propulsion system resupply and repair Final report

Resupply and repair capabilities for orbital space station bipropellant propulsion syste

Souvenirs littéraires

2 v

Paris : ses organes, ses fonctions et sa vie dans la seconde moitié du XIX siècle

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 2009T. I (488 p.) -- T. II (472 p.

Redox-responsive degradable PEG cryogels as potential cell scaffolds in tissue engineering

A Michael addition strategy involving the reaction between a maleimide double bond and amine groups is investigated for the synthesis of cryogels at subzero temperature. Low-molecular-weight PEG-based building blocks with amine end groups and disulfide-containing building blocks with maleimide end groups are combined to synthesize redox-responsive PEG cryogels. The cryogels exhibit an interconnected macroporous morphology, a high compressive modulus and gelation yields of around 95%. While the cryogels are stable under physiological conditions, complete dissolution of the cryogels into water-soluble products is obtained in the presence of a reducing agent (glutathione) in the medium. Cell seeding experiments and toxicologic analysis demonstrate their potential as scaffolds in tissue engineerin

Solvent-resistant nanofiltration for product purification and catalyst recovery in Click chemistry reactions

The quickly developing field of "click" chemistry Would undoubtedly benefit from the availability of an easy and efficient technology for product purification to reduce the potential health risks associated with the presence of copper in the final product. Therefore. solvent-resistant nanofiltration (SRNF) membranes have been developed to selectively separate "clicked" polymers from the copper catalyst and solvent. By using these solvent-stable cross-linked polyimide membranes in diafiltration, up to 98% of the initially present copper could be removed through the membrane together with the DMF solvent, the polymer product being almost completely retained. This paper also presents the first SRNF application in which the catalyst permeates through the membrane and the reaction product is retained

Search for quark contact interactions and extra spatial dimensions using dijet angular distributions in proton-proton collisions at √s = 8 TeV

A search is presented for quark contact interactions and extra spatial dimensions in proton-proton collisions at s = 8 TeV using dijet angular distributions. The search is based on a data set corresponding to an integrated luminosity of 19.7 -1 collected by the CMS detector at the CERN LHC. Dijet angular distributions are found to be in agreement with the perturbative QCD predictions that include electroweak corrections. Limits on the contact interaction scale from a variety of models at next-to-leading order in QCD corrections are obtained. A benchmark model in which only left-handed quarks participate is excluded up to a scale of 9.0 (11.7) TeV for destructive (constructive) interference at 95% confidence level. Lower limits between 5.9 and 8.4 TeV on the scale of virtual graviton exchange are extracted for the Arkani-Hamed-Dimopoulos-Dvali model of extra spatial dimensions

Limitations of radical thiol-ene reactions for polymer-polymer conjugation

In this work, we report our findings on the use of radical thiol-ene chemistry for polymer-polymer conjugation. The manuscript combines the results from the Preparative Macromolecular Chemistry group from the Karlsruhe Institute of Technology (KIT) and the Polymer Chemistry Research group from Ghent University (UGent), which allowed for an investigation over a very broad range of reaction conditions. In particular, thermal and UV initiation methods for the radical thiol-ene process were compared. In the KIT group, the process was studied as a tool for the synthesis of star polymers by coupling multifunctional thiol core molecules with poly(n-butyl acrylate) macromonomers (MM), employing thermally decomposing initiators. The product purity and thus reaction efficiency was assessed via electrospray ionization mass spectrometry. Although the reactions with 10 or 5 equivalents of thiol with respect to macromonomer were successful, the coupling reaction with a one-to-one ratio of MM to thiol yielded only a fraction of the targeted product, besides a number of side products. A systematic parameter study such as a variation of the concentration and nature of the initiator and the influence of thiol-to-ene ratio was carried out. Further experiments with poly(styrene) and poly(isobornyl acrylate) containing a vinylic end group confirmed that thermal thiol-ene conjugation is far from quantitative in terms of achieving macromolecular star formation. In parallel, the UGent group has been focusing on photo-initiated thiol-ene chemistry for the synthesis of functional polymers on one hand and block copolymers consisting of poly(styrene) (PS) and poly (vinyl acetate) (PVAc) on the other hand. Various functionalization reactions showed an overall efficient thiol-ene process for conjugation reactions of polymers with low molecular weight compounds (∼90% coupling yield). However, while SEC and FT-IR analysis of the conjugated PS-PVAc products indicated qualitative evidence for a successful polymer-polymer conjugation, 1H NMR and elemental analysis revealed a low conjugation efficiency of about 23% for a thiol-to-ene ratio equal to one. Blank reactions using typical thiol-ene conditions indicated that bimolecular termination reactions occur as competitive side reactions explaining why a molecular weight increase is observed even though the thiol-ene reaction was not successful. The extensive study of both research groups indicates that radical thiol-ene chemistry should not be proposed as a straightforward conjugation tool for polymer-polymer conjugation reactions. Head-to-head coupling is a major reaction pathway, which interrupts the propagation cycle of the thiol-ene process. © 2010 Wiley Periodicals, Inc