Anderson transition in dilute systems with pure exponential interactions

Summary Assuming a completely disordered lattice it is shown that all the states are localized when the disorder parameterx=a ₀/0 reachesthe value 0.31, wherea is the mean atomic separation anda ₀ is the Bohr radius.     

Conformational behaviour and inclusion compound forming properties of 5,18-disubstituted derivatives of 5, 11, 12, 18-tetrahydrotribenzo[b,f,j][1,4]diazacyclododecine-6, 17-dione

An X-ray structure analysis shows that the 5, 18-dimethyl derivative ($\text{5}$) of the title compound ($\text{4}$) crystallises from xylene as a 1:1 inclusion compound in which the host molecules adopt propeller-like conformations ($\text{7}$ and $\text{7}$*) with almost perfect $\text{C}$₂ symmetry. Dynamic ¹H n.m.r. spectroscopy shows that the 5, 18-dibenzyl derivative ($\text{6}$) of ($\text{4}$) forms a 1:1 inclusion compound with ethanol in the solid state and undergoes ring inversion ($\text{7}$ ? $\text{7}$*) between enantiomeric propeller-like conformations in solution against a barrier of 21.1 kcal mol^?1     

Parametric optimization of heat transfer characteristics for helical coils

Journal of Thermal Analysis and Calorimetry - In this study, helically coiled tubes are used in a shell, and the effects of tube diameter, coil diameter, Reynolds number, Dean number and flow rate...     

Microstructural properties and local atomic structures of cobalt oxide nanoparticles synthesised by mechanical ball-milling process

In this study, facile preparation of pure and nano-sized cobalt oxides particles was achieved using low-cost mechanical ball-milling synthesis route. Microstructural and morphological properties of synthesised products were characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD results indicated that the fabricated samples composed of cubic pure phase CoO and Co₃O₄ nanocrystalline particles with an average crystallite size of 37.2 and 31.8 nm, respectively. TEM images showed that the resulting samples consisted of agglomerates of particles with average diameter of about 37.6 nm for CoO and 31.9 nm for Co₃O₄. Phase purity of the prepared samples was further investigated due to their promising technological applications. Local atomic structure properties of the prepared nanoparticles were probed using synchrotron radiation-based X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). EXAFS data analysis further confirmed the formation of single-phase CoO and Co₃O₄ nanoparticles. In addition, structural properties of cobalt oxide nanoparticles were investigated by performing density functional theory calculations at B3LYP/TZVP level and Born–Oppenheimer molecular dynamics. Theoretical calculations for both prepared samples were found to be consistent with the experimental results derived from EXAFS analysis. Obtained results herein reveals that highly crystalline and pure phase CoO and Co₃O₄ nanoparticles can be synthesised using simple, inexpensive and eco-friendly ball-milling method for renewable energy applications involving fuel cells and water splitting devices.     

Covalent Adaptable Networks with Tunable Exchange Rates Based on Reversible Thiol–yne Cross‐Linking

The design of covalent adaptable networks (CANs) relies on the ability to trigger the rearrangement of bonds within a polymer network. Simple activated alkynes are now used as versatile reversible cross‐linkers for thiols. The click‐like thiol–yne cross‐linking reaction readily enables network synthesis from polythiols through a double Michael addition with a reversible and tunable second addition step. The resulting thioacetal cross‐linking moieties are robust but dynamic linkages. A series of different activated alkynes have been synthesized and systematically probed for their ability to produce dynamic thioacetal linkages, both in kinetic studies of small molecule models, as well as in stress relaxation and creep measurements on thiol–yne‐based CANs. The results are further rationalized by DFT calculations, showing that the bond exchange rates can be significantly influenced by the choice of the activated alkyne cross‐linker.     

Synthesis and characterization of poly(1-vinyl-1,2,4-triazole) (PVTri)-barium hexaferrite nanocomposite

We present a method for the fabrication of PVTri-BaFe₁₂O₁₉ nanocomposites by in-situ polymerization of PVTri in the presence of synthesized BaFe₁₂O₁₉ nanoparticles. Nanoparticles, polymer and nanocomposite were analyzed by XRD, FTIR, TGA, TEM, NMR, GPC and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 17±5 nm. Conjugation of PVTri to nanoparticle surface was assessed to be via carbonyl groups on the polymer. TG analysis revealed that 45 wt% of nanocomposite is inorganic phase (BaFe₁₂O₁₉). It was found out that the ac conductivity of nanocomposite under a certain frequency increases with temperature.     

Surface texturing of Si, porous Si and TiO2 by laser ablation

Excimer laser ablation at 308 nm has been used to texture the surfaces of a variety of materials of interest for optoelectronic and biotechnological applications. Using a range of pre- and post-processing methods, we are able to produce nano-, micro- and meso-scale features over large areas rapidly in materials such as crystalline Si, porous silicon and TiO₂. Texturing of porous silicon leads to the growth of crystalline dendritic structures, which distinguishes them dramatically from the conical pillars formed from crystalline silicon. Regular arrays of Si microdots are formed by irradiating a Si surface pre-covered with a Cr thin film grating. Nano-crystalline porous TiO₂ films are easily ablated or compacted with laser irradiation. However, at low enough laser fluence, surface roughening without complete loss of porosity is possible.     

Step structure on the fivefold Al-Pd-Mn quasicrystal surface, and on related surfaces

We compare step morphologies on surfaces of Al-rich metallic alloys, both quasicrystalline and crystalline. We present evidence that the large-scale step structure observed on Al-rich quasicrystals after quenching to room temperature reflects equilibrium structure at an elevated temperature. These steps are relatively rough, i.e., have high diffusivity, compared to those on crystalline surfaces. For the fivefold quasicrystal surface, step diffusivity increases as step height decreases, but this trend is not obeyed in a broader comparison between quasicrystals and crystals. On a shorter scale, the steps on Al-rich alloys tend to exhibit local facets (short linear segments), with different facet lengths, a feature which could develop during quenching to room temperature. Facets are shortest and most difficult to identify for the fivefold quasicrystal surface.     

Approximate First Integrals of Weakly Nonlinear,Damped-Driven Oscillators with One Degree of Freedom

First-order approximate symmetries of weaklynonlinear, damped-driven oscillators have been determined.First-order approximate first integrals have been obtained byemploying an approximate version of Noether's theorem for the conservativecase. Furthermore, approximate first integrals of the damped case have been obtained based on the first integrals of the conservative case.Approximate first integrals enabled us to identify three types of genericbifurcations. Analytical results have been verified by numerical experiments.