Adaptive chemistry lookup tables for combustion simulations using optimal B-spline interpolants

Flamelet models, which enable the storing of precomputed detailed chemistry into lookup tables, are widely used in combustion simulations. They allow the computation of accurate results at low computational cost, but standard implementations can lead to numerical problems due to a non-smooth representation, and their applicability is limited by memory requirements. Here, the methods used by a newly developed and optimised lookup table generator based on B-spline interpolation are presented. The creation of smooth representations of flamelet solutions requiring less than one fifth of the number of points in each direction compared to the non-smooth representations of standard lookup tables based on linear interpolation is shown to be possible. The new B-spline interpolation based tables are also applied within a large-eddy simulation of the Swirling Methane/Hydrogen Flame 1 and the results are compared to simulations using lookup tables based on linear interpolation or optimised artificial neural networks. Better performance of the B-spline interpolation based tables with respect to physical accuracy and numerical performance is demonstrated.     

Sending femtosecond pulses in circles: highly nonparaxial accelerating beams

We use caustic beam shaping on 100 fs pulses to experimentally generate nonparaxial accelerating beams along a 60° circular arc, moving laterally by 14 μm over a 28 μm propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of nonparaxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic.     

Fluorescent aromatic platforms for cell patterning

This paper describes a simple experimental method of patterning fluorescent organic dyes, fluorescein, and rhodamine on gold substrates by microcontact printing techniques. The development of this step-by-step protocol has allowed us to prepare striped and squared micropatterns with poly(ethylene glycol) (PEG) linkers terminated by these fluorophores using a fast, easy, and inexpensive technique. Although the rest of the surface was covered with aliphatic molecules (methyl terminated), human fibroblasts demonstrated an unexpected response, aligning themselves according to the aromatic patterns, despite the presence of PEG, which is a cell resistant molecule, in the fluorescent regions.     

Live-Cell Localization Microscopy with a Fluorogenic and Self-Blinking Tetrazine Probe

Recent developments in fluorescence microscopy call for novel small-molecule-based labels with multiple functionalities to satisfy different experimental requirements. A current limitation in the advancement of live-cell single-molecule localization microscopy is the high excitation power required to induce blinking. This is in marked contrast to the minimal phototoxicity required in live-cell experiments. At the same time, quality of super-resolution imaging depends on high label specificity, making removal of excess dye essential. Approaching both hurdles, we present the design and synthesis of a small-molecule label comprising both fluorogenic and self-blinking features. Bioorthogonal click chemistry ensures fast and highly selective attachment onto a variety of biomolecular targets. Along with spectroscopic characterization, we demonstrate that the probe improves quality and conditions for regular and single-molecule localization microscopy on live-cell samples.     

Synthesis of amphiphilic polymer networks with guest‐host properties

A modular assembly procedure for producing amphiphilic polymer networks containing specific linker lengths between cyclodextrin (CD) cross‐link sites is described. The linker type and length can be selected to tune the relative hydrophilicity/hydrophobicity of the network, and the size of the guest‐host binding site can be varied by using either α‐, β‐, or γ‐CD as the node. The two‐step, one‐pot reaction sequence produces well‐defined networks with stable ether linkages that can be purified by simple washing and filtration steps. Short ethylene glycol versus long polyethylene oxide linkers result in networks that are generally insoluble in common organic solvents, but which swell to varying degrees in polar protic, polar aprotic, and chlorinated solvents such as water, methanol, ethanol, dimethylsulfoxide, dimethylformamide, methylene chloride, and chloroform. All networks swell in water and present a hydrophobic CD cavity that is available for binding nonpolar molecules. The networks should be applicable to the removal of hydrophobic contaminants, for example, pharmaceutical molecules, from water or wastewater streams. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1824–1831     

Origin and Use of Hydroxyl Group Tolerance in Cationic Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Catalysts

The origin of hydroxyl group tolerance in neutral and especially cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) complexes has been investigated. A wide range of catalysts was prepared and tested. Most cationic complexes can be handled in air without difficulty and display an unprecedented stability towards water and alcohols. NHC complexes were successfully used with substrates containing the hydroxyl functionality in acyclic diene metathesis polymerization, homo‐, cross and ring‐opening cross metathesis reactions. The catalysts remain active even in 2‐PrOH and are applicable in ring‐opening metathesis polymerization and alkene homometathesis using alcohols as solvent. The use of weakly basic bidentate, hemilabile anionic ligands such as triflate or pentafluorobenzoate and weakly basic aromatic imido ligands in combination with a sterically demanding 1,3‐dimesitylimidazol‐2‐ylidene NHC ligand was found essential for reactive and yet robust catalysts.     

Silica-Supported Cationic Tungsten Imido Alkylidene Stabilized by an N-Heterocyclic Carbene Ligand Boosts Activity and Selectivity in the Metathesis of α-Olefins

A well-defined silica-supported cationic W imido alkylidene was prepared through surface organometallic chemistry. This catalyst shows preferential activity towards α- over internal olefins, which is atypical for W-based catalysts, but consistent with the strong σ-donating ability of the NHC ancillary ligand. Complementing the studies on tungsten-based d⁰ metathesis catalysts, the silica-supported cationic W imido alkylidene displays the highest activity among W imido catalysts for α-olefins and shows improved selectivity for this class of olefins compared to Mo-based catalysts.     

Molecular Porous Photosystems Tailored for Long-Term Photocatalytic CO2 Reduction

The molecular-level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long-term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time-resolved spectroscopy.