Bi4LnNb3O15 (Ln = La, Pr, Nd) and Bi4LaTa3O15: New intergrowth Aurivillius related phases

We describe the synthesis and characterization of new intergrowth Aurivillius related phases, Bi₄LnNb₃O₁₅ (Ln = La, Pr, Nd) and Bi₄LaTa₃O₁₅. Both powder X-ray diffraction and electron microscopy investigations show that the compounds adopt orthorhombic structures with the cell parameters a ∼ 5.5 Å, b ∼ 5.5 Å and c ∼ 20.9 Å, suggesting an ordered intergrowth structure that consists of n = 1 [Bi₂NbO₆]⁻ and n = 2 [Bi₂LnNb₂O₉]⁺ Aurivillius fragments which are stacked alternately along the c-axis. The oxides do not show a second harmonic generation (SHG) response toward 1064 nm laser radiation; they do not show a ferroelectric-paraelectric transition either between 30 and 900 °C in dielectric measurements, indicating a centrosymmetric structure. Optical absorption studies show that the intergrowth phases possess considerably smaller band gaps than the parent Nb₂O₅ and Ta₂O₅.     

An experimental investigation on the performance,combustion and emission characteristics of a variable compression ratio diesel engine using diesel and palm stearin methyl ester

An attempt has been made to use biodiesel prepared from non-edible portion of palm oil as fuel of a conventional mono-cylinder compression ignition engine. The present experimental investigation takes into account the combined effect of using blends of diesel–palm stearin biodiesel as fuels and the compression ratio on different performance, combustion and emission characteristics of the said engine. The experiments have been carried out on a single-cylinder, direct injection diesel engine at varying compression ratio of 16:1–18:1 in four steps. It is observed that the brake thermal efficiency reduces by 7.9% when neat biodiesel is used instead of diesel. But, it increases with the increase in compression ratio for all the blends. Brake specific fuel consumption and exhaust gas temperature increase with the addition of biodiesel to diesel and also with the increase in compression ratio. Heat release rate decreases with biodiesel, and it is minimum at the rated compression ratio of 17.5:1 for all the fuels considered here. On the other hand, ignition delay is found to be more with neat diesel, and it increases with the decrease in compression ratio. Significant reductions in emissions of carbon monoxide (CO), hydrocarbon (HC) and smoke are observed with biodiesel, while the emissions of oxides of nitrogen (NO_x) and carbon dioxide (CO₂) increase. The decrease in compression ratio increases the emissions of CO, HC and smoke, but the emissions of NO_x and CO₂ decrease with the decrease in compression ratio.     

Water wave scattering by a pair of thin vertical barriers with submerged gaps

The scattering of obliquely incident water waves by two thin vertical barriers with gaps at different depths has been studied assuming linear theory. Using Havelock’s expansion of water wave potential, the problem is reduced to two pairs of integral equations of the first kind, one pair involving a horizontal component of velocity across the gaps and the other pair involving the difference of potentials across each wall. These two pairs of integral equations can be solved approximately by employing a Galerkin single-term approximation technique to obtain numerical estimates for the reflection and transmission coefficients. These estimates for the reflection and transmission coefficients thus obtained are seen to satisfy the energy identity. The reflection coefficient is plotted against wave number in a number of figures for different values of various parameters involved in the problem. It is observed that the reflection coefficient vanishes at discrete frequencies when the vertical barriers are identical. For nonidentical vertical barriers the reflection coefficient never vanishes, though at some wave number it becomes close to zero. The results for a single barrier and fully submerged two barriers, and for a single barrier with a narrow gap, are also recovered as special cases.     

Rational design of fluorescent phosgene sensors

Phosgene is a very toxic gas, which was used as a chemical weapon in World War I, and is currently widely used in industrial processes. So far, no any phosgene fluorescent sensor has been reported. In this study, we report rational design of unimolecular fluorescent phosgene sensors for the first time. Phosgene was used to initiate intramolecular cyclization and convert nonfluorescent molecules to highly fluorescent products. Bright blue fluorescence of phosgene reaction products can be easily visualized by naked eye. The detection limit for phosgene is as low as 1 nM in solutions at room temperature.     

Synthesis of biocompatible multicolor luminescent carbon dots for bioimaging applications

Water-soluble carbon dots (C-dots) were prepared through microwave-assisted pyrolysis of an aqueous solution of dextrin in the presence of sulfuric acid. The C-dots produced showed multicolor luminescence in the entire visible range, without adding any surface-passivating agent. X-ray diffraction and Fourier transform infrared spectroscopy studies revealed the graphitic nature of the carbon and the presence of hydrophilic groups on the surface, respectively. The formation of uniformly distributed C-dots and their luminescent properties were, respectively, revealed from transmission electron microscopy and confocal laser scanning microscopy. The biocompatible nature of C-dots was confirmed by a cytotoxicity assay on MDA-MB-468 cells and their cellular uptake was assessed through a localization study.     

Space charge limited conduction in CdSe thin films

The current (I)-voltage (V) characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 Å and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study ofI-V curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage (V_t) from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the lnI vs 10³/T plots are found to be within 0.60-0.37 eV. Using the relevant SCLC theory, the carrier concentration, n₀, total trap concentration, N_t, and the ratio of free charge to trapped charge, θ, have been calculated and correlated with ambient temperature and intensity of illumination.     

Energy Bands and Thermoelectricity of Filled Skutterudite $$\mathrm{EuRu}_{4}\mathrm{As}_{12}$$

Density functional theory-based calculations of the elastic and electronic properties with magnetic moments of the filled skutterudite \(\mathrm{EuRu}_{4}\mathrm{As}_{12}\) have been performed in its ferromagnetic ground state. The full-potential linearized augmented plane wave (FP-LAPW) method has been used for the study presented here. The numerical values of the elastic parameters are estimated within the framework of the Voigt–Reuss–Hill approximations. The energy band structure calculation performed near the Fermi energy level shows the metallic nature of the material with a high value of Seebeck coefficient (S). The presence of an exchange splitting of Eu-4f states suggests their appreciable contribution toward the magnetic behavior. The analysis of the thermal transport properties confirms the result obtained from the electronic structure calculation with Seebeck coefficient of \(118\,\,\upmu \hbox {V/K}\) and the figure of merit (ZT) value of 0.51, at room temperature. The estimated values of S and ZT indicate the possibility of the thermoelectric applications of the sample material.     

High molecular weight polyethylene nanospheres: synthesis physical and mechanical properties

The high molecular weight (MW) polyethylene (PE) particles of particle size varied from macro to micron to nanometer were synthesized by Grignard reagent. The microscopy analysis (scanning electron microscope, SEM; transmission electron microscope, TEM; and atomic force microscope, AFM) shows the spherical shape of PE particles. The effects of particle size, varies from macro to nanometer scale on crystal structure, crystallinity (chic), glass transition temperature (Tg), melting temperature (Tm), surface roughness and mechanical properties were studied. Differential scanning calorimetry (DSC) experiments show that the nanoparticles of PE are highly crystalline (chic approximately equal 72%). The crystal length of PE nanoparticles is found to be approximately 14 A. Although the Gibbs-Thomson equation is explained the depression of melting temperature (DeltaTm) by 5 degrees C, the impervious results of Tg are still not fully understood. The low roughness value (2 A) proves the presence of "atomic-scale-chain" folding at the surface of PE nanoparticles. A novel protocol is developed, and the elastic modulus of individual nanospherical PE particles is computed from 'force-distance' mapping curves of AFM. Hemispherical tungsten (W) tip was fabricated from focused ion beam and used as an indenter to measure the mechanical properties. It is found that the nano sized PE particles have higher elastic modulus (E = 1.2-1.4 GPa) compared to the bulk or macro sized PE (E = 0.6-0.7 GPa). The results corroborate the robustness of our experiments, since, the analogous results for macro sized particles match well with the literature.     

A Computational Study of Soot Formation in Methane Air Co-Flow Diffusion Flame Under Microgravity Conditions

An in-house developed code has been used to predict soot formation in a methane air co flow diffusion flame at normal gravity and at lower gravity levels of 0.5 G, and 0.0001 G (microgravity). There is an augmentation of soot formation at lower gravity levels because of lower buoyancy induced acceleration leading to an increased residence time. The peak temperature at microgravity is reduced by about 50 K than that at normal gravity level. The axial velocity under normal gravity and reduced gravity show negative values (relatively small in magnitude) near the wall at axial height beyond 15 cm; but axial velocity is never negative in microgravity condition. Peak value of soot volume fraction at 0.5 G and microgravity multiplies by a factor of ～3 and ～7, respectively of that at normal gravity. The zone of peak soot volume fraction shifts away from the axis towards the wings, as gravity level is lowered. In comparison to soot volume fraction, the factors of amplification of soot number density at reduced gravity and at microgravity are comparatively lower at 1.2 and 1.5 of that at normal gravity respectively. On the other hand, mean soot particle sizes at reduced gravity and microgravity increase to 1.5 and 2 times of that at normal gravity respectively.     

Cytocompatibility property evaluation of gas pressure sintered SiAlON-SiC composites with L929 fibroblast cells and Saos-2 osteoblast-like cells

Although the oxide ceramics have widely been investigated for their biocompatibility, non-oxide ceramics, such as SiAlON and SiC are yet to be explored in detail. Lack of understanding of the biocompatibility restricts the use of these ceramics in clinical trials. It is hence, essential to carry out proper and thorough study to assess cell adhesion, cytocompatibility and cell viability on the non-oxide ceramics for the potential applications. In this perspective, the present research work reports the cytocompatibility of gas pressure sintered SiAlON monolith and SiAlON-SiC composites with varying amount of SiC, using connective tissue cells (L929) and bone cells (Saos-2). The quantification of cell viability using MTT assay reveals the non-cytotoxic response. The cell viability has been found to be cell type dependent. An attempt has been made to discuss the cytocompatibility of the developed composites in the light of SiC content and type of sinter additives.