1,514 research outputs found
Towards mirror symmetry Ă la SYZ for generalized Calabi-Yau manifolds
Fibrations of flux backgrounds by supersymmetric cycles are investigated. For an internal six-manifold M with static SU(2) structure and mirror hat M, it is argued that the product M Ă hat M is doubly fibered by supersymmetric three-tori, with both sets of fibers transverse to M and hat M. The mirror map is then realized by T-dualizing the fibers. Mirror-symmetric properties of the fluxes, both geometric and non-geometric, are shown to agree with previous conjectures based on the requirement of mirror symmetry for Killing prepotentials. The fibers are conjectured to be destabilized by fluxes on generic SU(3) Ă SU(3) backgrounds, though they may survive at type-jumping points. T-dualizing the surviving fibers ensures the exchange of pure spinors under mirror symmetry
Fractionation of Suwannee River fulvic acid and Aldrich humic acid on -AlO: spectroscopic evidence
International audienceSorptive fractionation of Suwannee River Fulvic Acid (SRFA) and Purified Aldrich Humic Acid (PAHA) on -AlO at pH 6 was probed in the supernatant using different spectroscopic techniques. Comparison of dissolved organic carbon (DOC) analysis with UV/Vis spectrophotometric measurements at 254 nm, including Specific UV absorbance (SUVA) calculation, revealed a decrease in chromophoric compounds for the non sorbed extracts after a 24 h contact time. This fractionation, only observable below a certain ratio between initial number of sites of humic substances and of -AlO, seems to indicate a higher fractionation for PAHA. C(1s) near-edge X-ray absorption fine structure spectroscopy (NEXAFS) confirmed this trend and points to a decrease in phenolic moieties in the supernatant and to an eventual increase in phenolic moieties on the surface. Time-resolved luminescence spectroscopy (TRLS) of Eu(III) as luminescent probe showed a decrease in the ratio between the D0F and D0F transitions for the fractionated organic matter (OM) that is thought to be associated to a lower energy transfer from the OM to Eu(III) due to the loss of polar aromatics. These modifications in the supernatant are a hint for the modification of sorbed humic extracts on the surface
Performance-Optimized Dielectric Elastomer Actuator System with Scalable Scissor Linkage Transmission
Thanks to their outstanding properties, in the last few years Dielectric Elastomer Actuators
(DEAs) have increasingly attracted the interest of the scientific community and generated a surge
in the effort devoted to their industrialization. Compared to conventional actuator systems, DEAs
are based on inexpensive and widely available polymeric materials, which make them potentially
attractive from a market perspective. However, DEA systems with a given layout and dimensions
have a fixed force-stroke response that is only suitable for a specific load profile. This leads to
a wide variety of designs combined with small production volumes and high costs, limiting the
competitive advantage. This work addresses this issue by proposing a combination of DEA systems
with compliant scissor linkage transmission mechanisms, which provide linear stroke and force
scaling and simultaneously maintain performance optimization by leaving the convertible energy
density of the DEA unaffected. For this purpose, three systems are designed, based on a same
strip-shaped DEA combined with inclined buckled beam biasing mechanisms. Two of the systems
are coupled with scissor linkages that offer transmission ratios of 3:1 and 1:3, respectively, to adapt
the system to different load profiles. The system design is explained in detail, and the functional
principle is validated through experiments
Towards New Robust Zn(II) Complexes for the Ring-Opening Polymerization of Lactide Under Industrially Relevant Conditions
The synthesis of bio-based and biodegradable plastics is a hot topic in research due to growing environmental problems caused by omnipresent plastics. As a result, polylactide, which has been known for years, has seen a tremendous increase in industrial production. Nevertheless, the manufacturing process using the toxic catalyst Sn(Oct)2 is very critical. As an alternative, five zinc acetate complexes have been synthesized with Schiff base-like ligands that exhibit high activity in the ring-opening polymerization of non-purified lactide. The systems bear different side arms in the ligand scaffold. The influence of these substituents has been analyzed. For a detailed description of the catalytic activities, the rate constants kapp and kp were determined using in-situ Raman spectroscopy at a temperature of 150 °C. The polymers produced have molar masses of up to 71 000 g molâ1 and are therefore suitable for a variety of applications. Toxicity measurements carried out for these complexes proved the nontoxicity of the systems. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Genomeâwide analysis of acute leukemia and clonally related histiocytic sarcoma in a series of three pediatric patients
Reversible cation exchange on macroscopic CdSe/CdS and CdS nanorod based gel networks
Over the past decades, cation exchange reactions applied to nanoparticles have opened up synthetic pathways to nanocrystals, which were not accessible by other means before. The limitation of cation exchange on the macroscopic scale of bulk materials is given by the limited ion diffusion within the crystal structure. Lyogels or aerogels are macroscopic, highly voluminous, porous materials composed of
interconnected nanoscopic building blocks and hence represent a type of bridge between the macroscopic and the nanoscopic world. To demonstrate the feasibility of cation exchange on such macroscopic nanomaterials, the cation exchange on CdSe/CdS core/shell and CdS nanorod based lyogels to Cu2âxSe/ Cu2âxS and Cu2âxS and the reversible exchange back to CdSe/CdS and CdS lyogels is presented. These copper-based lyogels can also be used as an intermediate state on the way to other metal chalcogenidebased macroscopic structures. By reversed cation exchange back to cadmium an additional proof is given, that the crystal structures remain unchanged. It is shown that cation exchange reactions can also
be transferred to macroscopic objects like aerogels or lyogels. This procedure additionally allows the access of aerogels which cannot be synthesized via direct destabilization of the respective colloidal solutions
Tuning a robust system: N,O Zinc Guanidine Catalysts for the ROP of Lactide
Non-toxic, highly-active and robust complexes are the holy grail as ideal green catalysts for the polymerisation of biobased and biodegrable polylactide. Four new zinc guanidine complexes [ZnCl2(TMG4NMe2asme)], [ZnCl2(TMG5Clasme)], [ZnCl2(TMG5Measme)] and [ZnCl2(TMG5NMe2asme)] with different electron-donating and electron-withdrawing groups on aromatic backbone of the ligand have been synthesised. Ligands are derived from low-cost commercially available compounds and have been converted in a three- or four-step synthesis into the desired ligand in good yields. The compounds have been fully characterised and tested in the ROP of rac-LA in the melt under industrially relevant conditions. The complexes are based on the recently published structure [ZnCl2(TMGasme)] which has shown high activity in the polymerisation of lactide at 150 °C. Different substituents in the para-position to the guanidine moiety significantly increase the polymerisation rate whereas positioning substituents in meta-position causes no change in the reaction rate. With molecular weights over 71 000 g mol-1, the best catalyst produces polymer for several industrial applications and its polymerisation rate approaches the one of Sn(Oct)2. The robust systems are able to polymerise non-purified lactide. The initiation of the polymerisation is suggested to occur by impurities in the monomer
T-duality with H-flux: non-commutativity, T-folds and G x G structure
Various approaches to T-duality with NSNS three-form flux are reconciled.
Non-commutative torus fibrations are shown to be the open-string version of
T-folds. The non-geometric T-dual of a three-torus with uniform flux is
embedded into a generalized complex six-torus, and the non-geometry is probed
by D0-branes regarded as generalized complex submanifolds. The
non-commutativity scale, which is present in these compactifications, is given
by a holomorphic Poisson bivector that also encodes the variation of the
dimension of the world-volume of D-branes under monodromy. This bivector is
shown to exist in SU(3) x SU(3) structure compactifications, which have been
proposed as mirrors to NSNS-flux backgrounds. The two SU(3)-invariant spinors
are generically not parallel, thereby giving rise to a non-trivial Poisson
bivector. Furthermore we show that for non-geometric T-duals, the Poisson
bivector may not be decomposable into the tensor product of vectors.Comment: 25 pages, LaTeX; v2: typos corrected, references adde
Towards mirror symmetry \`a la SYZ for generalized Calabi-Yau manifolds
Fibrations of flux backgrounds by supersymmetric cycles are investigated. For
an internal six-manifold M with static SU(2) structure and mirror \hat{M}, it
is argued that the product M x \hat{M} is doubly fibered by supersymmetric
three-tori, with both sets of fibers transverse to M and \hat{M}. The mirror
map is then realized by T-dualizing the fibers. Mirror-symmetric properties of
the fluxes, both geometric and non-geometric, are shown to agree with previous
conjectures based on the requirement of mirror symmetry for Killing
prepotentials. The fibers are conjectured to be destabilized by fluxes on
generic SU(3)xSU(3) backgrounds, though they may survive at type-jumping
points. T-dualizing the surviving fibers ensures the exchange of pure spinors
under mirror symmetry.Comment: 30 pages, 3 figures, LaTeX; v2: references adde
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