Fast processes and intermediates in photochemistry of 7-dimethyl-germanorbornadiene

Laser pulse photolysis experiments have shown that the triplet excited-state of 1,2,3,4-tetraphenylnaphthalene (TPN) is one of the primary intermediates of the photochemical transformation of 7,7'-dimethylgerma-1,4,5,6-tetraphenyl-2,3-benzo-norbornadiene (GNB) in hexane solution. The molar absorption of T-T absorption and the quantum yield of the intersystem crossing of TPN were determined from the triplet-triplet energy transfer. The scheme of GNB photocleavage has been suggested where the triplet excited TPN originated from the triplet state of biradical through cleavage of the second C-Ge bond, the latter being generated from the excited singlet state of the initial GNB after the cleavage of the first C-Ge bond and the intersystem crossing. Other channels of GNB's chemical transformation have been discussed.     

A priori information in a regularized sinogram‐based method for removing ring artefacts in tomography

Ring artefacts in X‐ray computerized tomography reconstructions are considered. The authors propose a ring artefact removal method based on a priori information regarding the sinogram including smoothness along the horizontal coordinate, symmetry of the first and the final rows and consideration of small perturbations during acquisition. The method does not require prior reconstruction of the original or corrected sinograms. Its numerical implementation is based on quadratic programming. Its efficacy is examined with regard to experimental data sets collected on graphite and bone.     

Magnetic and structural anomalies of Na<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C<Subscript>60</Subscript> (n = 2, 3)

Sodium fullerides Na _n C60 (n = 2, 3) have been synthesized by a liquid phase reaction and investigated with X-ray diffraction (XRD), nuclear magnetic resonance (NMR), electron paramagnetic resonance, and differential thermal analysis. XRD data indicate that the crystal structure of Na₂C₆₀ at 300 K is face centered cubic (FCC). A phase transition from primitive cubic to FCC crystal structure has been observed in this work in Na₂C₆₀ fulleride at 290 K. The transition is accompanied by the step-like change of paramagnetic susceptibility. The crystal structure of Na₃C₆₀ is more complicated than, and different from, what has been reported in the literature. A nearly seven-fold increase of paramagnetic susceptibility with increasing temperature has been observed in the Na₃C₆₀ fulleride at 240–260 K. In the same temperature range, a new line at about 255 ppm appears in the ²³Na NMR spectrum, indicating a significant increase of electron density near the Na nucleus. The observed effect can be explained by a metal-insulator transition caused by a structural transition.     

Novel Galvanic Nanostructures of Ag and Pd for Efficient Laser Desorption/Ionization of Low Molecular Weight Compounds

A simple approach for synthesis of palladium and silver nanostructures with readily adjustable morphologies was developed using galvanic electrochemical deposition, for application to surface-assisted laser desorption/ionization (SALDI) of small biological molecules. A range of fatty acids, triglycerides, carbohydrates, and antibiotics were investigated to assess the performance of the new materials. Intense analyte cations were generated from the galvanic surfaces upon UV laser irradiation such as potassium adducts for a film thickness <100 nm (originating from impurities of the electrolyte solution) and Pd and Ag cluster ions for films with a thickness >120 nm. Possible laser desorption/ionization mechanisms of these galvanic structures are discussed. The films exhibited self-organizing abilities and adjustable morphologies by changing electrochemical parameters. They did not require any stabilizing agents and were inexpensive and very easy to produce. SALDI analysis showed that the materials were stable under ambient conditions and analytical results with excellent measurement reproducibility and detection sensitivity similar to MALDI were obtained. Finally, we applied the galvanic surfaces to fast screening of natural oils with minimum sample preparation.

A Unified Mechanism on the Formation of Acenes,Helicenes, and Phenacenes in the Gas Phase

A unified low-temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes—polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho-condensed arrangements of fused benzene rings—is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas-phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer-selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free-radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space. Connecting helicene templates to the Origins of Life ultimately changes our hypothesis on interstellar carbon chemistry.     

Synthesis of 2,5,7‐Triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles by Reaction of 5(3)‐Amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with Chalcones

The reaction of 5(3)‐amino‐3(5)‐aryl‐1H‐pyrazole‐4‐carbonitriles with 1,3‐diaryl‐2‐propen‐1‐ones (chalcones) in refluxing DMF leads to 2,5,7‐triaryl‐4,7(6,7)‐dihydropyrazolo[1,5‐a]pyrimidine‐3‐carbonitriles. In DMSO solution, the latter exist in equilibrium of two tautomeric 4,7‐dihydropyrazolo[1,5‐a]pyrimidines and 6,7‐dihydropyrazolo[1,5‐a]pyrimidines in various ratios, depending on the nature of aryl substituents in chalcone building blocks.     

Wave propagation in axially polarized piezoelectric hollow cylinders of sector cross section

In this paper, the problem of electroelastic waves propagating in piezoelectric hollow cylinders of sector cross section is studied for the case when the boundary surfaces of sector cut are covered by non-extensible membranes. The three-dimensional linear equations of motion for the piezoelectric cylinder are analytically integrated and different boundary conditions on the cylindrical surfaces yield frequency equations, which relate the frequencies of elastic waves to their wavenumbers. Numerical results for waveguides with various boundary conditions are presented to illustrate the approach. Analysis of the dispersion spectra is carried out, and cutoff frequencies are obtained and characterized; mode asymptotic behavior and amplitude distributions of wave characteristics are analyzed. The main effects of their transformation by variation of the angular measure and the ratio of inner and outer radii are discussed. The results obtained are in good agreement with the results for the special case of a hollow semicircular cylinder.     

High‐energy optical parametric oscillator for the 6 μm spectral range based on HgGa2S4 pumped at 1064 nm

The defect chalcopyrite crystal HgGa₂S₄ has been employed in a 1064‐nm pumped optical parametric oscillator to generate <7 ns long idler pulses near 6.3 μm with energies as high as 3 mJ, tunable in a broad spectral range from 4.5 to 9 μm.     

Thin Indicator Films to Assess the Residual Strength of a GFRP after a Local Contact Action

Mechanics of Composite Materials - Two types of thin impact indicator films were developed: made of an epoxy composite with hollow glass microspheres and of a selfadhesive thermoplastic with...     

Computational modeling of block-copolymer directed self-assembly

Directed self-assembly (DSA) is a potentially promising method of writing lithographic patterns on a sub-40 nm length-scale. While the utility of DSA has been demonstrated in principle, there are many challenges that need to be solved before its wide adoption in the semiconductor industry. Computational modeling is crucial in addressing many of those challenges, for example, optimizing polymer formulations, producing a better pattern, or predicting the defect density. In particular, the use of mesoscale approaches such as Self-Consistent Field Theory (SCFT), coarse-grained Monte Carlo, coarse-grained Molecular Dynamics, and Dynamic Density Functional Theory (DDFT) to describe polymer morphology—both bulk and in confinement—is now widespread. These models are used to predict phase behavior of block copolymers in thin films (undirected self-assembly), as well as in cases of chemo- and graphoepitaxy (DSA). In the near future, modeling is expected to be an integral part of formulation design and screening process. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 90–95