An alternate route for the synthesis of hybrid mesoporous organosilica with crystal-like pore walls from allylorganosilane precursors

The bridged allylorganosilanes 1,4-bis(diallylethoxysilyl)benzene and 1,4-bis(triallylsilyl)benzene are presented as new precursors for the surfactant-assisted synthesis of ordered mesoporous organosilica with pore walls having crystal-like molecular-scale periodicity. This approach provides a new route to the formation of periodic mesostructures with crystal-like pore walls. The synthesis method presented is applicable to the preparation of mesoporous organosilica with bulky organic groups, the precursors of which are typically impossible to obtain in high purity.     

Annulation reactions of allene-derived 1,3-dipole with 3-substituted-chromones: unusual recognition of 4pi-component in 3-(N-Aryliminomethyl)chromones through

All-carbon dipole derived by the interaction of triphenylphosphine with allenic ester is able to locate the polarized 2pi-component in 3-formylchromones through a regioselective [2 + 3] addition to the C2-C3 pi-bond, which is followed by deformylation leading to novel 3a,9a-dihydro-1-ethoxycarbonyl-1-cyclopenteno[5, 4-b]benzopyran-4-ones. On the contrary, the dipole recognizes azadiene in 3-(N-aryliminomethyl)chromones through [4 + 3] annulation and initially formed adducts undergo tandem rearrangements to afford novel N-aryl-2, 3-dihydro-4-ethoxycarbonylchromano[2,3-b]azepine-6-ones in good yield.     

Spectrophotometric determination of maneb by ternary complex formation with PAR and CTAB

A rapid, simple, direct, and sensitive method has been developed for the determination of maneb (manganese ethylenebisdithiocarbamate) based on the formation of manganese-4-(2′-pyridylazo) resorcinol complex by a ligand displacement reaction, which is rendered water soluble by a cationic surfactant cetyltrimethylammonium bromide (CTAB) by the formation of an ion association complex. Beer's law is obeyed over the concentration range 0.08–2.4 μg/ml of the final solution at 500 nm in pH range 8–12. The molar absorptivity and Sandell's sensitivity are calculated to be 8.84 × 10⁴ l.mol⁻¹.cm⁻¹ and 0.003 μg/cm², respectively. The developed method has been applied to the determination of maneb in commercial formulations, synthetic mixture, grain samples and vegetables.     

Blueshift and spectral features of the gravitational searchlight

It is shown that a photon emitted in the forward direction by a charged particle moving in an equatorial circular orbit centred on a highly collapsed mass M, the radius being slightly in excess of one and a half times the Schwarzschild radius, is strongly blueshifted when it arrives at a distant receiver. A ring shaped emitting region composed of such orbiting particles has a power law spectrum of the formd/ as seen by a distant stationary observer.     

Determination of calcium in uranium by X-ray fluorescence

Summary An X-ray fluorescence method for the analysis of calcium in uranium in the range of 20 to 500 ppm is described. U₃O₈ samples are mixed with boric acid binder and double-layer pellets are prepared. The pellets are analysed using Philips PW 1220 semi-automatic X-ray spectrometer. Calculated lower limits of detection are better than 5 ppm for calcium in uranium.

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Bestimmung von Calcium in Uran durch Röntgenfluorescenz

Zusammenfassung Ein Verfahren für den Bereich von 20–500 ppm wird beschrieben. Die U₃O₈-Proben werden mit BorsÄure als Bindemittel vermischt zu Doppelschicht-Tabletten gepre\t, die mit Hilfe eines halbautomatischen Philips PW 1220 Röntgenspektrometers analysiert werden. Die untere Nachweisgrenze liegt bei 5 ppm Ca.

     

Graphs with prescribed degree sets and girth

For a finite nonempty set of integers, each of which is at least two, and an integern 3, the numberf(;n) is defined as the least order of a graph having degree set and girthn. The numberf(;n) is evaluated for several sets and integersn. In particular, it is shown thatf({3, 4}; 5) = 13 andf({3, 4}; 6) = 18.Research of the third author was partially supported by a Faculty Research Fellowship from Western Michigan University.     

Investigation of Various Pressure Transient Techniques on Permeability Measurement of Unconventional Gas Reservoirs

Chloride ingress into concrete is a major cause for material degradation, such as cracking due to corrosion-induced steel reinforcement expansion. Corresponding transport processes encompass diffusion, convection, and migration, and their mathematical quantification as a function of the concrete composition remains an unrevealed enigma. Approaching the problem step by step, we here concentrate on the diffusivity of cement paste, and how it follows from the microstructural features of the material and from the chloride diffusivity in the capillary pore spaces. For this purpose, we employ advanced self-consistent homogenization theory as recently used for permeability upscaling, based on the resolution of the pore space as pore channels being oriented in all space directions, resulting in a quite compact analytical relation between porosity, pore diffusivity, and the overall diffusivity of the cement paste. This relation is supported by experiments and reconfirms the pivotal role that layered water most probably plays for the reduction of the pore diffusivity, with respect to the diffusivity found under the chemical condition of a bulk solution.     

The first diastereoselective nitroaziridination of N-tosylaldimines with 1-bromonitroalkanes

The first expeditious nitroaziridination of N-tosylaldimines is reported. The protocol involves operationally simple catalyst-free reaction of N-tosylaldimines, 1-bromonitroalkanes and NaOAc to afford 2-nitro-1-tosylaziridines in excellent yields with high Z-diastereoselectivity in a one-pot procedure under ambient conditions.