Mixture of Fuels Approach for the Synthesis of SrFeO3-delta Nanocatalyst and Its Impact on the Catalytic Reduction of Nitrobenzene

A modified solution combustion approach was applied in the synthesis of nanosize SrFeO3-delta (SFO) using single as well as mixture of citric acid, oxalic acid, and glycine as fuels with corresponding metal nitrates as precursors. The synthesized and calcined powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis and derivative thermogravimetric analysis (TG-DTG), scanning electron microscopy, transmission electron microscopy, N-2 physisorption methods, and acidic strength by n-butyl amine titration methods. The FT-IR spectra show the lower-frequency band at 599 cm(-1) corresponds to metal-oxygen bond (possible Fe-O stretching frequencies) vibrations for the perovskite-structure compound. TG-DTG confirms the formation temperature of SFO ranging between 850-900 degrees C. XRD results reveal that the use of mixture of fuels in the preparation has effect on the crystallite size of the resultant compound. The average particle size of the samples prepared from single fuels as determined from XRD was similar to 50-35 nm, whereas for samples obtained from mixture of fuels, particles with a size of 30-25 nm were obtained. Specifically, the combination of mixture of fuels for the synthesis of SFO catalysts prevents agglomeration of the particles, which in turn leads to decrease in crystallite size and increase in the surface area of the catalysts. It was also observed that the present approach also impacted the catalytic activity of the SFO in the catalytic reduction of nitrobenzene to azoxybenzene.

Riemann shock tube: 1D normal shocks in air, simulations and experiments

This paper presents numerical simulation of the evolution of one-dimensional normal shocks, their propagation, reflection and interaction in air using a single diaphragm Riemann shock tube and validate them using experimental results. Mathematical model is derived for one-dimensional compressible flow of viscous and conducting medium. Dimensionless form of the mathematical model is used to construct space-time finite element processes based on minimization of the space-time residual functional. The space-time local approximation functions for space-time p-version hierarchical finite elements are considered in higher order GRAPHICS] spaces that permit desired order of global differentiability of local approximations in space and time. The resulting algebraic systems from this approach yield unconditionally positive-definite coefficient matrices, hence ensure unique numerical solution. The evolution is computed for a space-time strip corresponding to a time increment Delta t and then time march to obtain the evolution up to any desired value of time. Numerical studies are designed using recently invented hand-driven shock tube (Reddy tube) parameters, high/low side density and pressure values, high- and low-pressure side shock tube lengths, so that numerically computed results can be compared with actual experimental measurements.

MULTI-PITCH TRACKING USING GAUSSIAN MIXTURE MODEL WITH TIME VARYING PARAMETERS AND GRATING COMPRESSION TRANSFORM

Grating Compression Transform (GCT) is a two-dimensional analysis of speech signal which has been shown to be effective in multi-pitch tracking in speech mixtures. Multi-pitch tracking methods using GCT apply Kalman filter framework to obtain pitch tracks which requires training of the filter parameters using true pitch tracks. We propose an unsupervised method for obtaining multiple pitch tracks. In the proposed method, multiple pitch tracks are modeled using time-varying means of a Gaussian mixture model (GMM), referred to as TVGMM. The TVGMM parameters are estimated using multiple pitch values at each frame in a given utterance obtained from different patches of the spectrogram using GCT. We evaluate the performance of the proposed method on all voiced speech mixtures as well as random speech mixtures having well separated and close pitch tracks. TVGMM achieves multi-pitch tracking with 51% and 53% multi-pitch estimates having error <= 20% for random mixtures and all-voiced mixtures respectively. TVGMM also results in lower root mean squared error in pitch track estimation compared to that by Kalman filtering.

The key role of polymer grafted nanoparticles in the phase miscibility of an LCST mixture

Blends of bromo-terminated polystyrene (PS-Br) and poly(vinyl methylether) (PVME) exhibit lower critical solution temperatures. In this study, PS-Br was designed by atom transfer radical polymerization and was converted to thiol-capped polystyrene (PS-SH) by reacting with thiourea. The silver nanoparticles (nAg) were then decorated with covalently bound PS-SH macromolecules to improve the phase miscibility in the PS-Br-PVME blends. Thermally induced demixing in this model blend was followed in the presence of polystyrene immobilized silver nanoparticles (PS-g-nAg). The graft density of the PS macromolecules was estimated to be ca. 0.78 chains per nm(2). Although the matrix and the grafted molecular weights were similar, PS-g-nAg particles were expelled from the PS phase and were localized in the PVME phase of the blends. This was addressed with respect to intermediate graft density and favourable PS-PVME contacts from microscopic interactions point of view. Interestingly, blends with 0.5 wt% PS-g-nAg delayed the spinodal decomposition temperature in the blends by ca. 18 degrees C with respect to the control blends. The scale of cooperativity, as determined by differential scanning calorimetry, increased only marginally in the case of PS-g-nAg; however, it increased significantly in the presence of bare nAg particles.

Tunability of monodispersed intermetallic AuCu nanoparticles through understanding of reaction pathways

Synthesis of size selective monodispersed nanoparticles particularly intermetallic with well-defined compositions represents a challenge. This paper presents a way for the synthesis of intermetallic AuCu nanoparticles as a model system. We show that reduction of Au and Cu precursors is sensitive to the ratio of total molar concentrations of surfactant to metal precursors. A careful design of experiments to understand the kinetics of the reduction process reveals initial formation of seed nanoparticles of pure Au. Reduction of Cu occurs on the surface of the seed followed by diffusion to yield AuCu. This understanding allows us to develop a two step synthesis where the precise size controlled seed of Au nanoparticles produced in the first step is used in the second step reaction mixture as an Au precursor to allow deposition and interdiffusion of Cu that yields size selected AuCu intermetallics of sub 10 nm sizes.

Optical diagnostics of fuel-air mixing and vortex formation in a cavity combustor

The current work reports optical diagnostic measurements of fuel-air mixing and vortex structure in a single cavity trapped vortex combustor (TVC). Specifically, the mixture fraction using acetone PLIF technique in the non-reacting flow, and PIV measurements in the reacting flow are reported for the first time in trapped vortex combustors. The fuel-air momentum flux ratio, where the air momentum corresponds to that entering the cavity through a specially-incorporated flow guide vane, is used to characterize the mixing. The acetone PLIF experiments show that at high momentum flux ratios, the fuel-air mixing in the cavity is very minimal and is enhanced as the momentum flux ratio reduces, due to a favourable vortex formation in the cavity. Stoichiometric mixture fraction surfaces show that the mixing causes the reaction surfaces to shift from non-premixed to partially-premixed stratified mixtures. PIV measurements conducted in the non-reacting flow in the cavity further reinforce this observation. The scalar dissipation rates of mixture fraction were compared with the contours of RMS of fluctuating velocity and showed very good agreement. The regions of maximum mixing are observed to be along the fuel air interface. Reacting flow Ply measurements which differ substantially from the non-reacting cases primarily because of the heat release from combustion and the resulting gas expansion show that the vortex is displaced from the centre of the cavity towards the guide vane. Overall, the measurements show interesting features of the flow including the presence of the dual cavity structure and lead to a clear understanding of the underlying physics of the cavity flow highlighting the importance of the fuel-air momentum ratio parameter. (C) 2014 Elsevier Inc. All rights reserved.

Performance study of a cesium iodide photocathode-based UV photon detector in Ar/CH4 mixture

The detection efficiency of a gaseous photomultiplier depends on the photocathode quantum efficiency and the extraction efficiency of photoelectrons into the gas. In this paper we have studied the performance of an UV photon detector with P10 gas in which the extraction efficiency can reach values near to those in vacuum operated devices. Simulations have been done to compare the percentage of photoelectrons backscattered in P10 gas as well as in the widely used neon-based gas mixture. The performance study has been carried out using a single stage thick gas electron multiplier (THGEM). The electron pulses and electron spectrum are recorded under various operating conditions. Secondary effects prevailing in UV photon detectors like photon feedback are discussed and its effect on the electron spectrum under different operating conditions is analyzed. (C) 2014 Chinese Laser Press

Analysis on the atomization characteristics of aviation biofuel discharging from simplex swirl atomizer

The atomization characteristics of aviation biofuel discharging from a simplex swirl atomizer into quiescent atmospheric air are studied. The aviation biofuel is a mixture of 90% commercially available camelina-derived biofuel and 10% VonSol-53 (aromatics). The experiments are conducted in a spray test facility at varying fuel flow rate conditions. The measured characteristics include atomizer flow number, spray cone angle, breakup length of liquid sheet, wavelength of undulations on liquid sheet, and spray droplet size. The characteristics of biofuel sheet breakup are deduced from the captured images of biofuel spray. The measurements of spray droplet size distribution are obtained using Spraytec. The experimentally measured characteristics of the biofuel sheet breakup are compared with the predictions obtained from the liquid film breakup model proposed by Senecal et al. (1999). The measurements of wavelength and breakup length of the biofuel sheet discharging from the simplex swirl atomizer agree well with the model predictions. The model-predicted droplet size for the biofuel spray is significantly higher than the experimentally measured Sauter mean diameter (SMD). The spray droplets formed from the liquid sheet breakup undergo secondary atomization until 35-45 mm from the atomizer exit and thereafter the SMD increases downstream due to the combined effect of fuel evaporation and droplet coalescence. A good comparison is observed between the experimentally measured SMD of the biofuel spray and the predictions obtained using the empirical correlation reported in literature for sprays discharging from simplex swirl atomizers. (C) 2015 Elsevier Ltd. All rights reserved.

On the superposition principle in interference experiments

The superposition principle is usually incorrectly applied in interference experiments. This has recently been investigated through numerics based on Finite Difference Time Domain (FDTD) methods as well as the Feynman path integral formalism. In the current work, we have derived an analytic formula for the Sorkin parameter which can be used to determine the deviation from the application of the principle. We have found excellent agreement between the analytic distribution and those that have been earlier estimated by numerical integration as well as resource intensive FDTD simulations. The analytic handle would be useful for comparing theory with future experiments. It is applicable both to physics based on classical wave equations as well as the non-relativistic Schrodinger equation.

Simplified Mixture Design for Production of Self-Consolidating Concrete

In this work, a methodology to achieve ordinary-, medium-, and high-strength self-consolidating concrete (SCC) with and without mineral additions is proposed. The inclusion of Class F fly ash increases the density of SCC but retards the hydration rate, resulting in substantial strength gain only after 28 days. This delayed strength gain due to the use of fly ash has been considered in the mixture design model. The accuracy of the proposed mixture design model is validated with the present test data and mixture and strength data obtained from diverse sources reported in the literature.

Metal-insulator transition characteristics of vanadium dioxide thin films synthesized by ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture

We report the synthesis of high quality vanadium dioxide (VO2) thin films by a novel spray pyrolysis technique, namely ultrasonic nebulized spray pyrolysis of aqueous combustion mixture (UNSPACM). This simple and cost effective two step process involves synthesis of a V2O5 film on an LaAlO3 substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (p21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal-insulator transition (MIT) was observed at 61 degrees C, where the resistivity changes by four orders of magnitude. Activation energies for the low conduction phase and the high conduction phase were obtained from temperature variable resistance measurements. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 mu m. This indicates the suitability of the films for optical switching applications at infrared frequencies.

A mobile robot with a two-degree-of-freedom suspension for traversing uneven terrain with minimal slip: Modeling, simulation and experiments

It is known in literature that a wheeled mobile robot (WMR) with fixed length axle will slip on an uneven terrain. One way to avoid wheel slip is to use a torus-shaped wheel with lateral tilt capability which allows the distance between the wheel-ground contact points to change even with a fixed length axle. Such an arrangement needs a two degree-of-freedom (DOF) suspension for the vertical and lateral tilting motion of the wheel. In this paper modeling, simulation, design and experimentation with a three-wheeled mobile robot, with torus-shaped wheels and a novel two DOF suspension allowing independent lateral tilt and vertical motion, is presented. The suspension is based on a four-bar mechanism and is called the double four-bar (D4Bar) suspension. Numerical simulations show that the three-wheeled mobile robot can traverse uneven terrain with low wheel slip. Experiments with a prototype three-wheeled mobile robot moving on a constructed uneven terrain along a straight line, a circular arc and a path representing a lane change, also illustrate the low slip capability of the three-wheeled mobile robot with the D4Bar suspension. (C) 2015 Elsevier Ltd. All rights reserved.

Local structure of boundary layer transition in experiments with a single streamwise vortex

Transition induced by an isolated streamwise vortex embedded in a flat plate boundary layer was studied experimentally. The vortex was created by a gentle hill with a Gaussian profile that spanned on half of the width of a flat plate mounted in a low turbulence wind tunnel. PIV and hot-wire anemometry data were taken. Transition occurs as a non-inclined shear layer breaks up into a sequence of vortices, close to the boundary layer edge. The passing frequency of these vortices scales with square of the freestream velocity, similar to that in single-roughness induced transition. Quadrant analysis of streamwise and wall-normal velocity fluctuations show large ejection events in the outer layer. (C) 2015 Elsevier Inc. All rights reserved.

H2O-CH4 and H2S-CH4 complexes: a direct comparison through molecular beam experiments and ab initio calculations

New molecular beam scattering experiments have been performed to measure the total ( elastic plus inelastic) cross sections as a function of the velocity in collisions between water and hydrogen sulfide projectile molecules and the methane target. Measured data have been exploited to characterize the range and strength of the intermolecular interaction in such systems, which are of relevance as they drive the gas phase molecular dynamics and the clathrate formation. Complementary information has been obtained by rotational spectra, recorded for the hydrogen sulfide-methane complex, with a pulsed nozzle Fourier transform microwave spectrometer. Extensive ab initio calculations have been performed to rationalize all the experimental findings. The combination of experimental and theoretical information has established the ground for the understanding of the nature of the interaction and allows for its basic components to be modelled, including charge transfer, in these weakly bound systems. The intermolecular potential for H2S-CH4 is significantly less anisotropic than for H2O-CH4, although both of them have potential minima that can be characterized as `hydrogen bonded'.

Gasification of wood particles in a co-current packed bed: Experiments and model analysis

This study focuses on addressing the propagation front movement in a co-current downdraft gasification system. A detailed single particle modeling analysis extended to the packed bed reactor is used to compare with the experimental measurement as well those available in the literature. This model for biomass gasification systems considered pyrolysis process, gas phase volatile combustion, and heterogeneous char reactions along with gas phase reactions in the packed bed. The pyrolysis kinetics has a critical influence on the gasification process. The propagation front has been shown to increase with air mass flux, attains a peak and then decreases with further increase in air mass flux and finally approaches negative propagation rate. This indicates that front is receding, or no upward movement() bra her it is moving downward towards the char bed. The propagation rate correlates with mass flux as (m) over dot `'(0.883) during the increasing regimes of the front movement The study clearly identifies that bed movement is an important parameter for consideration in a co-current configuration towards establishing the effective bed movement. The study also highlights the importance of surface area to volume ratio of the particles in the packed bed and its influence on the volatile generation. Finally, the gas composition for air gasification under various air mass fluxes is compared with the experimental results. (C) 2016 Elsevier B.V. All rights reserved.