Effect of orientation of lateral methyl substituent on the thermal behaviour of the mesophase in binary systems of 4-substituted phenyl 4ʹ-(4”-alkoxy phenylazo) benzoates

Several binary systems made from two laterally substituted azo/ester isomers, namely 2?- (and 3?-) methyl-4-substituted phenyl 4?-(4?-alkoxyphenylazo) benzoates, where the length of the terminal alkoxy group = 8 and 16 carbons, while the other terminal substituent, X, varies between CH₃O, CH₃, H, Br and CN groups, were investigated using differential scanning calorimetry (DSC) and phases identified by polarised light microscope (PLM). For the sake of comparison, two another binary systems made from 2?- (or 3?-) methyl-4-substituted phenyl 4?-(4?-alkoxyphenylazo) benzoates (n = 8 and X = CH₃) each was mixed with its laterally neat analogue and similarly investigated. Results were discussed on the basis of constructed phase diagrams whereby various mesomorphic properties were observed dependent on X, n, and position of the lateral methyl group. In most of the cases, the mixtures exhibited eutectic compositions, while linear or nearly linear nematic and smectic A-composition temperature dependence were observed.     

Interconnecting networks with optimized service provisioning

Telecommunication Systems - A recent trend of peering at geo-diversified Internet exchange points (IXPs) has empowered decades-old proposal of inter-networking and opened up new avenues of business...     

ARTIFICIAL INTELLIGENCE(AI)-DRIVEN SPECTRUM MANAGEMENT

Recent advances in communication and networking technologies are leading to a plethora of novel wireless services that range from unmanned aerial vehicle(UAV)communication to smart cognitive networks and massive Internet of Things(IoT)systems.Enabling these emerging applications over the fifth generation(5G)of wireless cellular systems requires meeting numerous challenges pertaining to spectrum sharing and management.In fact,most 5G applications will be highly reliant on intelligent spectrum management techniques,which should adapt to dynamic network environments while also guaranteeing high reliability and high quality-of-experience(QoE).     

Compact Patch Antenna Array for 60 GHz Millimeter-Wave Broadband Applications

Wireless Personal Communications - In this study, a wide-band compact patch antenna array is developed for 60 GHz band applications. The antenna array consists of eight identical elements....     

Structural Stabilities and Elastic Thermodynamic Properties of SrTe Compound and SrTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Alloy Under High Pressure

The effect of pressure on the structural, elastic, and thermodynamic properties of SrTe in both B1 (rocksalt) and B2 (CsCl-type) phases and the SrTe_1?x Ca _x alloys with Ca dopant concentrations at x = 0.16667, 0.20, 0.33333, 0.42857, 0.44444 and 0.50 have been investigated using the two new gradient-corrected functional developed by Perdew, J.P.; Burke, K.; Ernzerhof named Density-Gradient Expansion for Exchange in Solids (PBEsol) and generalized Wu–Cohen (WC), in a significant range of pressure from 0 GPa to 30 GPa. The structure parameters, elastic stiffness constants c _ij , the bulk modulus (B), Kleinman parameter (\( \xi \)), shear anisotropies A _shear are also determined. Furthermore, as reported in this study, the aggregate elastic modulus (B, G, E), Poisson’s ratio (ν) and the Lame’s coefficients (λ) are estimated. On the other hand, the ductility, brittleness, longitudinal, transverse sound velocities and the Debye temperature Θ_D(T) are also obtained. Importantly, our results are in reasonable agreement with the available theoretical and experimental data. To the best of our knowledge, this is the first study of the effect of the composition on the properties of the SrTe_1?x Ca _x alloys which may encourage other works for the confirmation of the reported results.     

Controlled electrophoretic deposition of uniquely nanostructured star polymer films

The controlled electrophoretic deposition of polystyrene/divinylbenzene (PS/DVB) star polymer films from a colloidal suspension is reported. Liquid suspensions, containing the PS/DVB star polymer, were prepared by injecting a dichloromethane (DCM) solution of the star polymer into a stratified liquid combination of hexane and DCM. A variety of hexane/DCM volume ratios were examined to identify the optimal solution conditions for electrophoretic deposition; thin films were produced from both unmixed and well-mixed hexane/DCM suspensions. Unmixed suspensions yielded spatially separated thin films, deposited in a controlled fashion, that were dependent on the polarity of the corresponding electrode. Films on the positive electrode differed in thickness, microstructure, and appearance from those formed on the negative electrode. In contrast, films produced from well-mixed hexane/DCM suspensions deposited uniformly across only the negative electrode. Atomic force microscopy studies revealed nanostructured surface morphologies that were unique to each of these films. Additionally, these microscopy studies shed light on the possible conformations of star polymers adsorbed on a surface. By controlling the composition and the mixing state of the solution and by controlling the bias of electrodes, we achieved controlled deposition of star polymer films with a specific nanostructure. These nanostructured films may have broad use in optical and biological device applications.     

Turbo charging time-dependent density-functional theory with Lanczos chains

We introduce a new implementation of time-dependent density-functional theory which allows the entire spectrum of a molecule or extended system to be computed with a numerical effort comparable to that of a single standard ground-state calculation. This method is particularly well suited for large systems and/or large basis sets, such as plane waves or real-space grids. By using a superoperator formulation of linearized time-dependent density-functional theory, we first represent the dynamical polarizability of an interacting-electron system as an off-diagonal matrix element of the resolvent of the Liouvillian superoperator. One-electron operators and density matrices are treated using a representation borrowed from time-independent density-functional perturbation theory, which permits us to avoid the calculation of unoccupied Kohn-Sham orbitals. The resolvent of the Liouvillian is evaluated through a newly developed algorithm based on the nonsymmetric Lanczos method. Each step of the Lanczos recursion essentially requires twice as many operations as a single step of the iterative diagonalization of the unperturbed Kohn-Sham Hamiltonian. Suitable extrapolation of the Lanczos coefficients allows for a dramatic reduction of the number of Lanczos steps necessary to obtain well converged spectra, bringing such number down to hundreds (or a few thousands, at worst) in typical plane-wave pseudopotential applications. The resulting numerical workload is only a few times larger than that needed by a ground-state Kohn-Sham calculation for a same system. Our method is demonstrated with the calculation of the spectra of benzene, C(60) fullerene, and of chlorophyll a.     

A new uranyl niobate sheet in the cesium uranyl niobate Cs9[(UO2)8O4(NbO5)(Nb2O8)2]

A new cesium uranyl niobate, Cs₉[(UO₂)₈O₄(NbO₅)(Nb₂O₈)₂] or Cs₉U₈Nb₅O₄₁ has been synthesized by high-temperature solid-state reaction, using a mixture of U₃O₈, Cs₂CO₃ and Nb₂O₅. Single crystals were obtained by incongruent melting of a starting mixture with metallic ratio=Cs/U/Nb=1/1/1. The crystal structure of the title compound was determined from single crystal X-ray diffraction data, and solved in the monoclinic system with the following crystallographic data: a=16.729(2) Å, b=14.933(2) Å, c=20.155(2) Å β=110.59(1)°, P2₁/c space group and Z=4. The crystal structure was refined to agreement factors R₁=0.049 and wR₂=0.089, calculated for 4660 unique observed reflections with I?2σ(I), collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector.In this structure the UO₇ uranyl pentagonal bipyramids are connected by sharing edges and corners to form a uranyl layer corresponding to a new anion-sheet topology, and creating triangular, rectangular and square vacant sites. The two last sites are occupied by Nb₂O₈ entities and NbO₅ square pyramids, respectively, to form infinite uranyl niobate sheets stacking along the [010] direction. The Nb₂O₈ entities result from two edge-shared NbO₅ square pyramids. The Cs⁺ cations are localized between layers and ensured the cohesion of the structure.The cesium cation mobility between the uranyl niobate sheets was studied by electrical measurements. The conductivity obeys the Arrhenius law in all the studied temperature domains. The observed low conductivity values with high activation energy may be explained by the strong connection of the Cs⁺ cations to the infinite uranyl niobate layers and by the high density of these cations in the interlayer space without vacant site.Infrared spectroscopy investigated at room temperature in the frequency range 400-4000 cm⁻¹, showed some characteristic bands of uranyl ion and niobium polyhedra.