Investigations on mode-division multiplexed free-space optical transmission for inter-satellite communication link

Wireless Networks - Inter-satellite data transmission links are very crucial for providing global inter-connectivity. We report designing and investigations on high date rate inter-satellite...     

Rich vehicle routing problems: From a taxonomy to a definition

Over the last years, several variants of multi-constrained Vehicle Routing Problems (VRPs) have been studied, forming a class of problems known as Rich Vehicle Routing Problems (RVRPs). The purpose of the paper is twofold: (i) to provide a comprehensive and relevant taxonomy for the RVRP literature and (ii) to propose an elaborate definition of RVRPs. To this end, selected papers addressing various cases are classified using the proposed taxonomy. Once the articles have been classified, a cluster analysis based on two discriminating criteria is performed and leads to the definition of RVRPs.     

Effect of Mn and Nb Doped BaTiO3 in the Dielectric Properties in the Ba(Mn1/2Nb1/2)xTi1−xO3

Polycrystalline samples of BaTi_1?x (Mn_0.5Nb_0.5) _x O₃ with x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.175 have been synthesized by the high-temperature solid-state reaction technique. The effects of cationic substitution of manganese and niobium for titanium at B sites of the BaTiO₃ perovskite lattice on symmetry and dielectric properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 K to 500 K and frequency range from 100 Hz to 2 × 10⁵ Hz were studied. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. T _C or T _m decreases when both manganese and niobium are introduced into the lattice of BaTiO₃. High dielectric constant of around 9000 at T _C = 280 K was found for Ba Ti_0.925(Mn_0.5Nb_0.5)_0.075O₃ ceramic. A relaxor ferroelectric with ΔT _m = 60 K and $ \varepsilon_{\rm{r}}^{\prime } $ of about 3500 at 10 kHz with T _m = 150 K was found for the BaTi_0.85(Mn_0.5Nb_0.5)_0.15O₃ sample.     

Structure refinement, dielectric, pyroelectric and Raman characterizations of Ba1−xLax(1−y)/2Euxy/2Nax/2TiO3 solid solution

The perovskite-type oxides Ba_1−xLa_x(1−y)/2Eu_xy/2Na_x/2TiO₃ (0?x?0.5 and xy=0.04) were synthesized and characterized by X-ray diffraction as well as dielectric measurements and Raman spectroscopy. The crystal structure of these ceramics has been determined by the Rietveld refinement powder X-ray diffraction data at room temperature. These compounds crystallize at room temperature in tetragonal space group P4mm for 0?x?0.1 and in the cubic group for 0.2?x?0.5. The phase transition temperature T_C (or T_m) decreases as x content increases. The degree of diffuseness of the phase transition is more pronounced for higher x content, implying the existence of a composition-induced diffuse phase transition of the ceramics with x?0.1. The evolution of the Raman spectra was studied as a function of various compositions at room temperature. The polarization state was checked by pyroelectric measurements.     

Chemical durability of MoO<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and K<Subscript>2</Subscript>O-MoO<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Thermal and chemical durability studies of the phosphate glasses belonging to the binary MoO₃-P₂O₅ and the ternary K₂O-MoO₃-P₂O₅ systems are reported. The chemical resistant attack tests carried out on the free alkaline MoO₃-P₂O₅ glasses show that the glass associated with the P/Mo ratio 2 has the high chemical durability. It shows also a high glass transition temperature value. The above findings are interpreted in terms of the cross-link density of the glasses and the strength of the M-O bonds (M=P, Mo). The influence of K₂O addition on the properties (density, T _g, durability) of this binary high water resistant glass is studied. It is found that the chemical durability along with the other physical properties are reduced by the incroporation of K₂O in the glass matrix. The results were explained by assuming the formation of non-bridging oxygens and weak bonds. The mechanism of the dissolution of these glasses is proposed.     

Dielectric and Raman studies on the solid solution (1−x)BaTiO3/xNaNbO3 ceramics

In order to elucidate the correlation between the relaxor type of phase transition and the percent of the A and B site substitution in the Ba_1−xNa_xTi_1−xNb_xO₃ solid solution, the dielectric permittivity was carried out in the temperature range 80–600 K. All ceramics of these solid solutions present a ferroelectric–paraelectric phase transition with relaxor and classical character depending on the value of x. With increasing x the three phase transition of pure BaTiO₃ are pinched into one rounded dielectric peak, and there is evidence for Vogel–Fulcher type relaxational freezing. Raman spectra of the x=0.3 and x=0.7 compositions taken at various temperatures and measured over the wavenumber range 100–1200 cm⁻¹ confirm that the first order scattering is dominant in phonon bands resulting from both ordered region and disordered matrix.     

Dielectric proprieties of ferroelectric ceramics derived from the system BaTiO3NaNbO3-based solid solutions

Dielectric studies performed on the solid solution Ba_1−xNa_xTi_1−xNb_xO₃ (BNTN) show that all compositions (x= 0.1, 0.15, 0.2, 0.4, 0.5 and 0.025, 0.05, 0.6, 0.7, 0.8) exhibit a ferroelectric–paraelectric phase transition where the Curie temperature is a function of the composition. The specimens with composition BNTN (x= 0.05, 0.1, 0.15, 0.2) have been refined by the Celref method from X-ray powder diffraction data. The evolution of dielectric constant as a function of temperature and frequency in the range 77–500 K and 20–2 × 10⁵ Hz, respectively, show that these ceramics present the classical ferroelectric character when 0x<0.075 and 0.55<x1 and relaxor character when 0.075x0.55.     

Small Iminocoumarin Derivatives as Red Emitters: From Biological Imaging to Highly Photoluminescent Non‐doped Micro‐ and Nanofibres

The fluorescence properties of four derivatives of 3‐thienyl‐2‐(N‐dicyanovinyl)iminocoumarin, bearing a diethylamino group in the 7‐position or a methoxy group in the 6, 7 and 8 positions, were compared in solution and in the solid state. The 7‐diethylamino derivative was strongly fluorescent in various solvents, with marked solvatochromism. Its fluorescence was quenched by aggregation. In contrast, the methoxy derivatives were only moderately or weakly fluorescent in solution, but two of them were strongly photoluminescent in the crystalline state, owing to favourable molecular packing. The 6‐methoxy derivative even exhibited spectacular crystallization‐enhanced emission, examples of which are particularly rare for this type of dyes. Dyes were tested for biological use. The 7‐diethylamino derivative led to particularly strong fluorescence staining of the cytoplasm of HCT‐116 colon cancer cells. No fading was observed over prolonged illumination by the microscope light beam, but a phototoxic effect was detected. The use of the dyes as red‐emitting materials was also investigated. Using easy‐to‐implement preparation methods, the compounds self‐ assembled to give one‐dimensional nano‐ and microsized particles, including millimeter‐long microfibres that exhibited clear wave‐guiding properties. This study shows the value of these low molecular‐weight molecules for the preparation of new orange and red‐emitting fluorescent materials based on totally pure dye.