Cation assisted binding and cleavage of dinitrogen by uranium complexes

The role of alkali promoters in N₂ cleavage by metal complexes remains poorly understood despite its relevance to the industrial production of ammonia from N₂. Here we report a series of alkali bound-oxo-bridged diuranium(iii) complexes that provide a unique example of decreasing N₂ binding affinity with increasing cation size (from K to Cs). N₂ binding was found to be irreversible in the presence of K. A N₂ complex could be isolated in the solid state in the presence of the Rb cation and crystallographically characterized, but N₂ binding was found to be reversible under vacuum. In the presence of the Cs cation N₂ binding could not be detected at 1 atm. Electrochemical and Computational studies suggest that the decrease in N₂ binding affinity is due to steric rather than electronic effects. We also find that weak N₂ binding in ambient conditions does not prevent alkali assisted N₂ cleavage to nitride from occurring. More importantly, we present the first example of cesium assisted N₂ cleavage leading to the isolation of a N₂ derived multimetallic U/Cs bis-nitride. The nitrides readily react with protons and CO to yield ammonia, cyanate and cyanide.

N₂ binding affinity decreases markedly in a series of isostructural U(iii)–alkali ions complexes with increasing cation size. N₂ binding is undetectable in the Cs analogue, but the first example of cesium-assisted N₂ cleavage to bis-nitride was observed at ambient condition.     

Groups with some restrictions on non-Baer subgroups

Ricerche di Matematica - It is proved that if G is an $$\mathfrak {X}$$ -group of infinite rank whose proper subgroups of infinite rank are Baer groups, then so are all proper subgroups of G, where...     

Experimental mixing parameterization due to multiphase fluid–structure interactions

Experimental estimates of the rate at which energy is extracted from the barotropic tide at corrugated sloping topography are presented. To this end, a series of experimental simulations of the process of generation of internal tides (i.e., internal waves of the tidal frequency) over a corrugated slope in stratified fluid were performed. An oceanic interior is modeled as four-layer stratified fluid. The main focus in these studies was to obtain the relation for the potential energy available for mixing as a function of a slope of a corrugated slope. The available potential energy available for partial mixing to the topographic slope was compared with the available potential energy sufficient for complete mixing of the four layers. The experimental data were compared with the analytic results of a linear theory and found in agreement with a recent theoretically predicted scenario showing that the dominant contribution of the energy distribution in internal wave field resides in waves of the lowest allowed frequency.     

Phonons and related crystal properties in indium phosphide under pressure

Based on the pseudopotential approach, the lattice vibration and polaron properties in InP under pressure up to 8 GPa have been investigated. At zero pressure, our calculated values for all features of interest are in reasonable agreement with data available in literature. Upon compression, the optical phonon modes at Γ point in the Brillouin zone are shifted towards high energies and their frequencies display a blueshift with rising pressure. The splitting of the longitudinal and transverse optical phonons narrows under pressure, indicating thus a decrease of the ionicity of InP crystal with pressure. It is observed that all physical quantities being studied in this contribution behave monotonically upon compression. To the best of the author's knowledge, the pressure dependence of the polaron properties for InP in the present study is reported for the first time.     

Effective masses of electrons, heavy holes and positrons in quasi-binary (GaSb)1−x(InAs)x crystals

The present investigation is focused on the effective masses of electrons, heavy holes and positrons in quasi-binary (GaSb)_1−x(InAs)_x crystals. To the best of our knowledge, this is the first time such quantities have been obtained for such a quasi-binary crystals. Our computations are based on the pseudopotential scheme within the virtual crystal approximation in which the effects of composition disorder are involved, while the positron wave function is evaluated under the point core approximation for the ionic potential. Comparisons are made with the measured values, which are only available for binary parent compounds and showed roughly good agreement. The calculated quantities in the quasi-binary crystals of interest are found to be generally different from those of the conventional quaternary alloys GaInAsSb which may provide more diverse opportunities to describe most carrier transport properties.     

Facile cleavage of N?arylsulfonyl bond of N‐arylsulfonylimidazolidinone with magnesium in methanol

Cleavage of N? arylsulfonyl bond in N‐arylsulfonylimidazolidinones is best carried out selectively with magnesium in methanol.     

Gas sensor using gold doped copper oxide nanostructured thin films as modified cladding fiber

We investigate the spectral response of nanostructured copper oxides thin film. Gold was doped in two different concentrations (2% and 4%) using the spray method. A novel ammonia gas sensor at various concentrations (0-500 ppm) was fabricated by replacing CuO films with a clad region. In addition, the effect of gold doping on structural, optical, and morphological properties has been demonstrated. The study shows that the spectral intensity increases linearly with ammonia concentration. The 4% Au doped CuO presents higher sensitivity compared with 2% doped and pure copper oxides. Time response characteristics of the sensor are also reported.     

Experimental and theoretical study of turning mirrors and beam splitters with optimized waveguide structures

Integrated waveguide turning mirrors (IWTM) based on total internal reflection are investigated theoretically and experimentally. The effects of the mirror surface displacement, the rotation, and the roughness are studied. The loss due to the various spectral components of the roughness is comprehensively analysed. A wide waveguide turning mirror is more influenced by the low-frequency component, which is the major component of the actually fabricated mirror surface, resulting in high radiation loss of an IWTM with long taper, contrary to expectation. The excess radiation loss is about 0.8 dB/mirror and 1.0 dB/mirror for quasi-TE and quasi-TM modes, respectively, in the optimum design, which could be reduced by further minimizing the displacement error of the mirror position. We also designed and fabricated a low-loss beam splitter with modal interference region, the measured excess losses being about 1.2 dB and 1.8 dB for quasi-TE and quasi-TM modes, respectively, which are believed to be the lowest in this kind of beam splitter.