Do Carbenes Have a “Hidden” Carbon(0) Character? Revisiting the Electronic Structure of 2,2′‐Bipyridyl Carbene

Density functional calculations predict that 2,2′‐bipyridyl carbenes have some degree of “hidden” carbon(0) character. This is supported by very high second proton affinity values and bond dissociation energies (BDEs) for the dissociation of one AuCl and one Ni(CO)₂ molecule from [(AuCl)₂(2,2′‐bipyridyl carbene)] and [{Ni(CO)₂}₂(2,2′‐bipyridyl carbene)]. An Arduengo type carbene also showed significant BDE values for gem‐dimetallation, thus indicating the possible existence of carbon(0) character. All of the dimetallated derivatives showed metallophilic interactions.     

Effect of sol–gel-based silica buffer layer on the formation of NaA zeolite membrane

The support substrates were modified with sol?Cgel-based silica coating as intermediate buffer layer followed by NaA zeolite seed (prepared hydrothermally at 85?°C for 3?h) coating with 2?wt% aqueous dispersion. The secondary crystallization of NaA zeolite in the silica-seed-coated supports was carried out hydrothermally through crystal growth process at 65?°C for 4 and 8?h (single-stage each), (6?+?4) and (6?+?6)?h (double-stage each), and (6?+?4?+?2) and (6?+?4?+?4)?h (triple-stage each). The crystallization behaviours of the prepared NaA membranes were studied by X-ray diffraction, and the microstructures of the same films were observed by field emission scanning electron microscope. The efficiency of the membranes was tested with gas permeation study. The double-stage secondary crystallization at 65?°C for (6?+?4)?h showed highly interlocked NaA grains in the membrane and it rendered the permeance values of 3.7?×?10^?8?mol?m^?2?s^?1?Pa^?1 and 15.9?×?10^?8 for single gas, nitrogen (N₂) and hydrogen (H₂) respectively with the ideal selectivity of 4.3.     

Structure of the B2 phase in Ti–25Al–25Mo alloy

The structure of the B2 phase has been investigated in Ti–25Al–25Mo alloy using Rietveld refinement of X-ray and neutron diffraction data in as-cast and solution-treated conditions. Different initial structure models have been used for the refinement. The site occupancy of the various chemical constituents in the B2 phase has been calculated and compared with earlier investigations. The relative merits of neutron diffraction over X-ray diffraction for structural refinement of the B2 phase in Ti–25Al–25Mo alloy have been demonstrated.     

Light and thermally induced metastabilities in electrochemically etched nanocrystalline porous silicon

We observe that light soaking for short durations and thermal quenching in nanocrystalline porous silicon (PS) produce metastable states. These metastable states show higher dark and photo currents, large photoluminescence and a weaker electron spin resonance (ESR) signal. However, long exposures to light produce the opposite effect. The metastable states are stable against sub-band gap light exposures. These metastable states can be removed by annealing at 150°C for 1 h. ESR shows the presence of a-Si phase (g ～ 2.0058, 6.4 G) in PS sample, but it is not sufficient to explain all the experimental results. Rather, our experiments suggest that light soaking causes more than one type of defects in porous silicon. The structural changes involving the movement of hydrogen present at the surface of PS or at the PS/a-Si interface may be responsible for these effects.     

Fuzzy generalized Bi-ideals of Γ-semigroups

In this paper, we introduce the concept of fuzzy generalized bi-ideal of a ??-semigroup, which is an extension of the concept of a fuzzy bi-ideal of a ??-semigroup and characterize regular ??-semigroups in terms of fuzzy generalized biideals.     

Positronium formation in positron-helium collisions with a screened Coulomb interaction

A study is conducted on positronium (Ps) formation in positron-helium collisions under the effect of a Coulomb screening, e⁺ + He(1s ²) ?? Ps(100) + He⁺(100), using the second-order distorted-wave approximation (DWA) and taking into consideration the screened dipole polarisation potential at low and intermediate incident positron energies in the range, 6 ? 500 eV. The theoretical model for the scattering calculation is fairly accurate and predicts a number of interesting features in the total and differential cross sections for the screening parameter, ?? = 0.0?0.4. The existence of resonances in the S-, P-, D- and F-partial waves has been reported in this work. Surface plots of the total and differential cross sections have also been presented to illustrate the interesting nature of the Ps formation in this scattering process.     

Origin of Piezoelectricity in an Electrospun Poly(vinylidene fluoride‐trifluoroethylene) Nanofiber Web‐Based Nanogenerator and Nano‐Pressure Sensor

A single stage electrospinning process can give rise to preferentially oriented induced dipoles in poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] nanofibers. The piezoelectricity of as‐electrospun P(VDF‐TrFE) nanofiber webs opens up new possibilities for their use as a flexible nanogenerators and nano‐pressure sensors. In this work, the origin of the piezoelectricity has been spotlighted by randomization of the induced dipoles at the Curie temperature and analyzed by polarized FT‐IR spectroscopic techniques as well as by detecting the piezoelectric signal from a nano‐pressure sensor.

     

Green photoluminescence from highly oriented ZnO thin film for photovoltaic application

We report here the fabrication of ZnO nanoparticles embedded on glass substrate by sol–gel and spin coating technique. Transmission electron microscope images revealed that the thin film is composed of ZnO nanoparticles. X-ray diffraction data confirms that the fabricated ZnO nanoparticles have hexagonal unit cell structure. The ZnO nanocrystals of the thin film are oriented along the c-axis of the hexagonal unit cell. UV–vis absorption spectroscopy shows that the absorption occurring at 373 nm in the ZnO thin film. The band gap was calculated from the absorption data and found to be 3.76 eV. This band gap enhancement occurs due to size effect in the nanoscale regime. Room temperature photoluminescence spectrum shows strong green emission at 530 nm owing to the singly ionized oxygen vacancy. This green emission was further investigated by annealing the thin film at different temperature. This singular green emission will be very useful in optoelectronic and nanophotonic devices.     

Finite Nilpotent BRST Transformations in Hamiltonian Formulation

We consider the finite field dependent BRST (FFBRST) transformations in the context of Hamiltonian formulation using Batalin-Fradkin-Vilkovisky method. The non-trivial Jacobian of such transformations is calculated in extended phase space. The contribution from Jacobian can be written as exponential of some local functional of fields which can be added to the effective Hamiltonian of the system. Thus, FFBRST in Hamiltonian formulation with extended phase space also connects different effective theories. We establish this result with the help of two explicit examples. We also show that the FFBRST transformations is similar to the canonical transformations in the sector of Lagrange multiplier and its corresponding momenta.