Search results for "Refinement"

Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under red…

2009

Abstract A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce 0.6 Zr 0.4 O 2 homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs. By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic …

Influence of sol counter-ions on the visible light induced photocatalytic behaviour of TiO2 nanoparticles

2014

Titanium dioxide (TiO2) nanoparticles are attracting increasing interest because of their superior photocatalytic and antibacterial properties. Here, aqueous titanium oxy-hydroxide sols were made, using a green synthesis method, from the controlled hydrolysis/peptisation of titanium isopropoxide. Three different mineral acids were used to peptise the sol (HNO3, HBr and HCl), and provide counter-ions. The influence of nitrate or halide sol counter-ions on size distributions of the starting sols were measured via photon correlation spectroscopy (PCS). Semi-quantitative phase composition analysis (QPA), on the gels thermally treated at 450 and 600 degrees C, was carried out via Rietveld refine…

Anomalous Valence Contrast of Metal Transition in Nanocrystalline Ferrite

2001

Error Estimates and Automatic Adaptive Mesh Refinement for the Metal Forming FEM Analysis

1988

The Authors propose a new technique which enables a estimation of the error inherent with the FEM analysis of metal forming processes. The aim is to evaluate the zones where the error is higher in order to proceed to a refinement of the mesh in such zones, and to obtain a smaller value of the global error. Moreover, to simplify the analyst work in the progressive refinement of the mesh, it has been prepared a software able to read the drawing created by a CAD program and to generate, automatically, all the geometrical and topological data necessary to perform the analysis on Personal Computer. The automatic renumbering of the elements in the refined mesh has been performed with the aim to r…

Outlier recognition in crystal-structure least-squares modelling by diagnostic techniques based on leverage analysis.

2005

The identification of the actual outliers in a least-squares crystal-structure model refinement and their subsequent elimination from the data set is a non-trivial task that has to be carried out carefully when a high level of accuracy of the estimates is required. One of the most suitable tools for detecting the influence of each data entry on the regression is the identification of ;leverage points'. On the other hand, the recognition of the actual statistical outliers is effectively possible by using some diagnostics as a function of the leverage, such as Cook's distance, DFFITS and FVARATIO. The evaluation of these estimators makes it possible to achieve a reliable identification of the…

A normalized iterative Smoothed Particle Hydrodynamics method

2020

Abstract In this paper we investigate on a normalized iterative approach to improve the Smoothed Particle Hydrodynamics (SPH) estimate of a function. The method iterates on the residuals of an initial SPH approximation to obtain a more accurate solution. The iterative strategy preserves the matrix-free nature of the method, does not require changes on the kernel function and it is not affected by disordered data distribution. The iterative refinement is further improved by ensuring linear approximation order to the starting iterative values. We analyze the accuracy and the convergence of the method with the standard and normalized formulation giving evidence of the enhancements obtained wit…

Comparison between adaptive and uniform discontinuous Galerkin simulations in dry 2D bubble experiments

2013

Accepted by the Journal of Computational Physics Adaptive mesh refinement generally aims to increase computational efficiency without compromising the accuracy of the numerical solution. However it is an open question in which regions the spatial resolution can actually be coarsened without affecting the accuracy of the result. This question is investigated for a specific example of dry atmospheric convection, namely the simulation of warm air bubbles. For this purpose a novel numerical model is developed that is tailored towards this specific application. The compressible Euler equations are solved with a Discontinuous Galerkin method. Time integration is done with an IMEXmethod and the dy…

A semi-Lagrangian AMR scheme for 2D transport problems in conservation form

2013

In this paper, we construct a semi-Lagrangian (SL) Adaptive-Mesh-Refinement (AMR) solver for 1D and 2D transport problems in conservation form. First, we describe the a-la-Harten AMR framework: the adaptation process selects a hierarchical set of grids with different resolutions depending on the features of the integrand function, using as criteria the point value prediction via interpolation from coarser meshes, and the appearance of large gradients. We integrate in time by reconstructing at the feet of the characteristics through the Point-Value Weighted Essentially Non-Oscillatory (PV-WENO) interpolator. We propose, then, an extension to the 2D setting by making the time integration dime…

ChemInform Abstract: X-Ray Powder Structure Determination and Thermal Behavior of a New Modification of Pb(II) Selenite.

2010

The crystal structure of a new polymorphic form of lead(II) selenite (PbSeO3) was solved directly from conventional X-ray powder diffraction data. Direct methods and Rietveld refinement techniques were used for the structure determination. The compound crystallizes in the monoclinic space group P21/c (no. 14) with cell dimensions a = 9.1587(1) A, b = 8.0902(1) A, c = 8.7932(1) A, β = 103.032(1)°, and V = 634.76(2) A3. The final refinement gave background excluded Rp = 6.22%, Rwp = 8.81%, and RB = 2.16% by using 45 structural and 15 profile parameters with 10 atoms in an asymmetric unit. The three-dimensional structure consists of 9-coordinated lead atoms, which are linked by three bidentate…

Complex high-pressure polymorphism of barium tungstate

2012

We have studied BaWO 4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO 4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO 4-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure- transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may…