Velocity measurements in a turbulent round jet using PTV: the effect of tracer particles

The effects of different tracer particles used in the PTV technique on the velocity field are investigated. The measurements are taken in a water round jet at a Reynolds number equal to about 40000, a flow field widely examined in the literature, in which strong velocity differences are encountered. The interest is focused onto particles with different density. Although the mean and rms values are almost unaffected, both measurements obtained with light and heavy particles (in comparison to the density of the fluid) reveal a modified velocity field. The moments of velocity differences (structure functions) point out that such a modification is felt within each range of flow scales. Particles with density almost equal to that of the fluid reproduce the flow behaviour over all the scales.     

Searches for new physics at Tevatron: Most recent results

The most recent results obtained from searches of particles and phenomena beyond the Standard Model (new physics) in the D0 and CDF experiments at the Tevatron accelerator (FNAL, USA) on the basis of statistics corresponding to the integrated luminosity of up to 4 fb⁻¹ in 2009 are considered. Particular attention is given to the most recent results on searches for a supersymmetric Higgs boson.     

Properties of droplet formation made by cone jet using a novel capillary with an external electrode

A capillary with an external electrode for cone-jet mode of electrospray has been developed to spot a droplet accurately on a substrate surface. The external electrode is made by gold deposition around tip of a glass capillary. The electrospray was made by applying a positive pulsed dc voltage to the solution in the capillary. Using a positive bias voltage to the external electrode, the meniscus of the solution at the tip deformed to be more sharp, and center of the meniscus was prolonged. This deformation stabilized the trajectory of the jet from the Taylor cone at the tip. From the experimental result, accuracy of positioning of the droplet having 0.3 pL volume was improved with the standard deviation of 1.1 μm, from that of 2.5 μm for conventional capillary without the external electrode.     

Xyloglucan degradation using different radiation sources: a comparative study

Tamarind seed xyloglucan was subjected to different radiation sources-ultrasound, gamma-radiation, and microwave heating, and the effects of these energies upon its molecular and structural properties were characterised by gel permeation chromatography, viscometry, sugar analysis, FT-IR and NMR spectroscopic techniques. In dependence on the degradation methods and experimental conditions used, the decrease of the relative molecular mass (RMM) was accompanied with alteration of the primary structure. Depolymerisation by ultrasound at a frequency of 20 kHz yielded after 120 min products with RMM of about 131 x 10(3) without significant alteration of the primary structure of the polysaccharide. Intense degradation of XG started by microwave heating at pH 1.5 yielding polymers with RMM in the range of higher oligosaccharides, however, with changed sugar composition due to cleavage of the glycosyl side chains. At gamma-irradiation doses >40 kGy, next to chain cleavage, very high-molecular mass components exhibiting UV(254)-absorption were formed, and the RMM decreased to about 50 x 10(3) at the highest applied dose (100 kGy). The results of the comparative study suggest that ultrasonication was the most convenient procedure to decrease the RMM of xyloglucan to 130 x 10(3) and preserve the primary structure of the polysaccharide.     

Infrared line narrowing and cluster absorption in a planar jet

Infrared laser absorption by a planar molecular jet is studied. The absorption lineshape is narrowed by a factor of 2 to 3, as compared to the absorption lineshape in bulk gas. The infrared absorption of CO₂ clusters is observed directly in a jet. The formation of clusters in the jet is monitored for different mixtures and distances from the nozzle.Work supported by Stichting voor Fundamenteel Onderzoek der Materie (FOM)     

Mesh refinement algorithms in an unstructured solver for multiphase flow simulation using discrete particles

This study developed spray-adaptive mesh refinement algorithms with directional sensitivity in an unstructured solver to improve spray simulation for internal combustion engine application. Inadequate spatial resolution is often found to cause inaccuracies in spray simulation using the Lagrangian–Eulerian approach due to the over-estimated diffusion and inappropriate liquid–gas phase coupling. Dynamic mesh refinement algorithms adaptive to fuel sprays and vapor gradients were developed in order to increase the grid resolution in the spray region to improve simulation accuracy. The local refinement introduced the coarse-fine face interface that requires advanced numerical schemes for flux calculation and grid rezoning with moving boundaries. To resolve the issue in flux calculation, this work implemented the refinement/coarsening algorithms into a collocated solver to avoid tedious interpolations in solving the momentum equations. A pressure correction method was applied to address unphysical pressure oscillations due to the collocation of pressure and velocity. An edge-based algorithm was used to evaluate the edge-centered quantities in order to account for the contributions from all the cells around an edge at the coarse-fine interface. A quasi-second-order upwind scheme with strong monotonicity was also modified to accommodate the coarse-fine interface for convective fluxes. To resolve the issue related to grid rezoning, rezoning was applied to the initial baseline mesh only and the new locations of the refined grids were obtained by interpolating the updated baseline mesh. The time step constraints were also re-evaluated to account for the change resulting from mesh refinement. The present refinement algorithm was used in simulating fuel sprays in an engine combustion chamber. It was found that the present approach could produce the same level of results as those using the uniformly fine mesh with substantially reduced computer time. Results also showed that this approach could alleviate the artifacts related to the Lagrangian discrete modeling of spray drops due to insufficient spatial resolution.     

Effect of nonrigid registration algorithms on deformation-based morphometry: a comparative study with control and Williams syndrome subjects

Deformation-based morphometry (DBM) is a widely used method for characterizing anatomical differences across groups. DBM is based on the analysis of the deformation fields generated by nonrigid registration algorithms, which warp the individual volumes to a DBM atlas. Although several studies have compared nonrigid registration algorithms for segmentation tasks, few studies have compared the effect of the registration algorithms on group differences that may be uncovered through DBM. In this study, we compared group atlas creation and DBM results obtained with five well-established nonrigid registration algorithms using 13 subjects with Williams syndrome and 13 normal control subjects. The five nonrigid registration algorithms include the following: (1) the adaptive bases algorithm, (2) the image registration toolkit, (3) The FSL nonlinear image registration tool, (4) the automatic registration tool, and (5) the normalization algorithm available in Statistical Parametric Mapping (SPM8). Results indicate that the choice of algorithm has little effect on the creation of group atlases. However, regions of differences between groups detected with DBM vary from algorithm to algorithm both qualitatively and quantitatively. Some regions are detected by several algorithms, but their extent varies. Others are detected only by a subset of the algorithms. Based on these results, we recommend using more than one algorithm when performing DBM studies.     

Asymmetric mixture of hard particles with Yukawa attraction between unlike ones: a cluster algorithm simulation study

The influence of a Yukawa attraction between unlike species on the structure of an asymmetric mixture of hard particles is investigated. A recently proposed cluster algorithm for the simulation of hard particle fluids is extended in order to treat the Yukawa tail. Starting with nonoverlapping hard core configurations generated by the cluster algorithm, the attractive tail is treated according to a standard Metropolis scheme. Preliminary results on the effect of the Yukawa attraction on the pair distribution of the larger particles and the potential of mean force at infinite dilution confirm important changes in comparison with pure hard sphere mixtures.     

Synthesis of nano-sized antimony-doped tin oxide (ATO) particles using a DC arc plasma jet

Nano-sized antimony-doped tin oxide (ATO) particles were synthesized using DC arc plasma jet. The precursors SnCl₄ and SbCl₅ were injected into the plasma flame in the vapor phase. ATO powder could conveniently be synthesized without any other post-treatment in this study. To control the doping amount of antimony in the ATO particles, the Sb/Sn molar ratio was used as an operating variable. To study the effect of carrier gas on the particle size, argon and oxygen gases were used. The results of XRD and TGA show that all Sb ions penetrated the SnO₂ lattice to substitute Sn ions. With the increased SbCl₅ concentration in source material, the Sb doping level was also increased. The size of the particles synthesized using the argon carrier gas was much smaller than that of the particles prepared using the oxygen carrier gas. For the argon gas, PSA results and SEM images reveal that the average particle size was 19 nm. However, for the oxygen gas, the average particle size was 31 nm.     

Reverse monte carlo method and its implications for generalized cluster algorithms

We describe a novel switching algorithm based on a "reverse" Monte Carlo method, in which the potential is stochastically modified before the system configuration is moved. This new algorithm facilitates a generalized formulation of cluster-type Monte Carlo methods, and the generalization makes it possible to derive cluster algorithms for systems with both discrete and continuous degrees of freedom. The roughening transition in the sine-Gordon model has been studied with this method, and high-accuracy simulations for system sizes up to 1024(2) were carried out to examine the logarithmic divergence of the surface roughness above the transition temperature, revealing clear evidence for universal scaling of the Kosterlitz-Thouless type.     

On correlations between charged and neutral particles in a cluster model

Correlations between charged and neutral pions at high energies are investigated in the framework of a cluster model in which neutral clusters have a decay distribution determined by isospin conservation and statistical independence. For 〈n₀〉_n? an asymptotic expansion around the mean 〈n_?〉 leading asymptotically to a quadratic form in n_? is derived and compared with data.     

A comparative study of jet formation and nanofiber alignment in electrospinning and electrocentrifugal spinning systems

Electrocentrifugal spinning is a recently developed spinning system whose performance is still under investigation by researchers. In this study the process of jet formation in electrocentrifugal spinning is explored and compared to the same process in electrospinning and centrifuge spinning. The results show that the incorporation of the electrical and the centrifugal forces in the electrocentrifugal spinning system leads to the formation of a more stable jet at lower viscosities. It is also shown that the electrocentrifugal spinning method is an efficient technique for the production of aligned nanofiber bundles with enhancement in the mechanical properties.     

Nanosized ceria-based ceramics: a comparative study

Ce_(1−x)Gd/Sm _x O_2−δ (x = 0.05–0.2, GDC/SDC) nanometric powder was prepared by glycine-nitrates combustion synthesis, by strictly following uniformity in the preparation route. The thermochemical properties of the obtained precursor were studied by TGA/DTA. Crystallization of the fluorite phase occurred on heating at 800 °C or higher temperature. The grain size of calcined powder was found to be about 15 nm. Densification was studied as a function of dopant content. SDC was found more sinterable than GDC. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical characterization was carried out using the impedance spectroscopy method in the frequency range of 50 Hz–13 MHz. The bulk conductivity of SDC is higher than GDC pellet for all concentration ranges. The results were analyzed by using the concept of change of the chemical bond ionicity due to the replacement of the host by dopant. Guest/host ionic size, valence mismatch ratio and their consequences are counted semiquantitatively into the configurational and thermal entropy.     

The evolution of a cluster of particles and the invariants of a time-dependent oscillator

A simple physical realization is found for the time-dependent harmonic oscillator equation $\text{q}\text{?}\text{+ φ(t)q = 0}$, for its auxiliary equation $\text{g}\text{?}\text{9 + φ(t)? = h}{}^2\text{?}{}^{\mathrm{?3}}$, and for the Ermakov invariant. Through generalization of the model, a set of invariants is obtained for a system of equations of the form .     

A comparative study between LMS and PSO algorithms on the optical channel estimation for radio over fiber systems

In this paper the particle swarm optimization (PSO) and least mean square (LMS) algorithms are comparatively studied to estimate the optical communication channel parameters for radio over fiber systems. It is observed that especially in low noise one tap optical channels, the convergence of LMS algorithm is approximately same with PSO algorithm. On the other hand, as a communication medium, selecting high noisy fiber optical channels or free space optical channels; PSO reaches better mean square error values. The computational complexity which is one of the most important features for optimization algorithms has also been taken into account.