Neutron decoherence imaging for visualizing bulk magnetic domain structures

Here we introduce a novel neutron imaging method, which is based on the effect that the spatial coherence of the neutron wave front can be changed through small-angle scattering of neutrons at magnetic domain walls in the specimen. We show that the technique can be used to visualize internal bulk magnetic domain structures that are difficult to access by other techniques. The method is transferable to a wide variety of specimens, extendable to three dimensions, and well suited for investigating materials under the influence of external parameters, as, e.g., external magnetic field, temperature, or pressure.     

An efficient one-pot synthesis of strongly fluorescent (hetero)arenes polysubstituted with amino and cyano groups

An efficient one-pot synthesis simultaneously results in three types of densely substituted mono-, di- and tetracyclic π-systems, which can easily be isolated. Each chromophore presents a strong fluorescence emission, either in the red, green or blue part of the spectrum.     

Analytical artifacts produced by a polycarbonate chamber compared to a Teflon chamber for measuring surface mercury fluxes

We found significant differences in mercury fluxes measured with a dynamic surface mercury flux chamber made of Teflon versus one made of polycarbonate. While both materials responded reasonably well when virgin materials were used, the polycarbonate chamber was found to exhibit significant chamber blanks under light after it was exposed to surface mercury fluxes of >100 ng/m²/h. Most significantly, the polycarbonate chamber blocked all wavelengths of light below ∼320 nm. Given that ultraviolet radiation plays an important role in soil mercury flux, the polycarbonate chamber was found to significantly underestimate observed fluxes from background soil in both high light conditions (by 1–4-fold) and under diffuse, low light conditions (by ∼10-fold). These results suggest that Teflon produces fewer analytical artifacts in the surface emission of mercury measured with a flux chamber than polycarbonate.     

Visible light-driven water oxidation by Ir oxide clusters coupled to single Cr centers in mesoporous silica

Visible light-induced water oxidation has been demonstrated at an Ir oxide nanocluster coupled to a single CrVI site on the pore surface of MCM-41 mesoporous silica. The photocatalytic unit was assembled by the reaction of surface Cr=O groups with Ir(acac)3 precursor followed by calcination at 300 degrees C and bond formation monitored by FT-Raman and FT-IR spectroscopy. High-resolution Z-contrast electron micrographs of the calcined material combined with energy-dispersive X-ray spot analysis confirmed the occlusion of Ir oxide nanoparticles inside the mesopores. Oxygen evolution of an aqueous suspension of the IrxOy-CrMCM-41 upon visible light irradiation of the CrVI-O ligand-to-metal charge-transfer absorption was monitored mass-spectrometrically. Comparison of the product yields for samples with low Cr content (Cr/Si 相似文献   

On the construction of independent units in cyclic or radical extensions

A general theorem on independency in a [G]-module is proved where G is a finite cyclic group. If applied to radical algebraic extensions of algebraic number fields, it yields a criterion of independency for systems of (parametric) units which contains as special cases theorems by Frei and Levesque and Halter-Koch and Stender.     

On-line and low-level measurements of β-radiation in HPLC

The use of on-line β-detection in HPLC of radioactive-labelled samples is hampered by the time lag between the (relatively) fast separation and the slow counting. In the present approach, this difficulty is overcome by introducing a storage loop in which the eluate is temporarily stored, interspaced by a non-mixing liquid which may be the scintillator itself. The apparatus developed enables the determination of radiochromatograms which contain a total activity of ～10 Bq.     

Photochemische Reaktionen. 104. Mitteilung [1]. Zur Photospaltung der C,C-Oxiranbindung konjugierter γ, δ-Epoxy-enone: Photolyse von 4-Methyliden-5,6-epoxy-5,6-dihydro-β-jonon

The photoinduced cleavage of the C,C-oxirane bond of γ, δ-epoxy-enones: UV.-irradiation of 4-methylidene-5,6-epoxy-5,6-dihydro-β-ionone On ¹n, π*-excitation (λ ≥ 347 nm, pentane) 5 gives the isomeric bicyclic ether 10 in 75% yield (s. Scheme 2). In methanol the photoconversion of 5 to 10 is strongly reduced (12%) in favour of the formation of the methanol adduct 11 (43%). On photolysis in aqueous acetonitrile 5 is converted to the bicyclic ether 10 (9%), the dihydrofurane 12 (18%) as well as to the triketones 13A and 13B (7%), and 14 (23%). On ¹π, π*-excitation (λ = 254 nm) in pentane no 10 is formed, but 5 isomerizes to the tricyclic cyclopropyl compound 16 (59%), the allenic product 17 (10%), and the cyclopropene compound 18 (12%; s. Scheme 3). Photolysis in methanol furnishes 11 (63%), and 18 (4%), but no tricyclic cyclopropyl compound 16 . In a secondary photoreaction (λ = 254 nm) the dihydrofurane 12 is isomerized to the bicyclic cyclopropyl compound 20 . Evidence is given that the products 11 and 13 are formed by solvent addition to an intermediate ketonium ylide b (s. Scheme 12). The presence of b is further proven by the formation of 12 , a product of an electrocyclization of b . On photofragmentation of b carbenoids d and e are presumably formed (s. Scheme 14). 1,2-Hydrogen shift in d yields the allene derivative 17 , and cyclization of d gives the cyclopropene compound 18 . On the other hand, e cyclizes to the non isolated cyclopropene compound 69 which is transformed to 16 by an intramolecular [4 + 2]-cycloaddition. The present investigation shows that the photochemistry of 5 is determined by photoinduced C,C-bond cleavage of the oxirane ring. This is in sharp contrast to the photochemistry of conjugated γ, δ-epoxy-enones without the additional double bond in ε, ζ-position, where selective photocleavage of the C(λ), O-bond is observed.