Extended proper orthogonal decomposition: a tool to analyse correlated events in turbulent flows

A tool to analyse correlated events in turbulent flows based on an extended proper orthogonal decomposition (POD) is proposed in this paper. A general definition of extended POD modes is presented and their properties are demonstrated. If the initial POD analysis in a spatio-temporal domain S concerns, for example, velocity—the concept of extended modes can be applied to study the correlation of any physical quantity in any domain with the projection of the velocity field on POD modes in S. The link with particular associations of POD and linear stochastic estimation (LSE) recently proposed is demonstrated at the end of the paper. The method is believed to provide a valuable tool to extend the well-documented POD analysis of eddy structures in turbulent flows, for example, in boundary layers or free shear flows. If extended modes are velocity modes, spatial and temporal interactions between eddy structures can be detected and studied. The rapid development of experimental diagnostic techniques now permit measurements of the concentration in the domain, the velocity of a dispersed phase in the domain or the static pressure at the boundary together with the fluid velocity field. Using this method we are then able to extract objectively the link between the representative groups of velocity modes and the correlated part of the concentration, particle motion or pressure signals.     

Automated topology classification method for instantaneous velocity fields

Topological concepts provide highly comprehensible representations of the main features of a flow with a limited number of elements. This paper presents an automated classification method of instantaneous velocity fields based on the analysis of their critical points distribution and feature flow fields. It uses the fact that topological changes of a velocity field are continuous in time to extract large scale periodic phenomena from insufficiently time-resolved datasets. This method is applied to two test-cases : an analytical flow field and PIV planes acquired downstream a wall-mounted cube.     

Removal of C3F8 Via the Combination of Non-Thermal Plasma, Adsorption and Catalysis

The feasibility of C₃F₈ abatement via combining nonthermal plasma with adsorption and/or catalysis is investigated in this study. In terms of the simultaneous combination of plasma, adsorption and catalysis (CPAC), three different configurations including A/C layer (adsorbent layer prior to catalyst layer), C/A layer (catalyst layer prior to adsorbent layer) and A/C mixture (adsorbent and catalyst are mechanically mixed) are adopted. For all the experimental tests conducted in this study, the gas stream consists of 500 ppm C₃F₈, 2% O₂, and balanced N₂. The experimental results indicate that C₃F₈ removal efficiencies depend on what kind of packing material is adopted (adsorbent, catalyst or both) and how the material is packed within the plasma reactor. The removal efficiencies obtained with different reactors are in the order as: CPAC (A/C layer; AC mixture) > CPA (plasma with adsorbent alone) > CPC (plasma with catalyst alone) > CPAC (C/A layer). The indentified products after treatment include CO₂, CO, N₂O and CF₄. The formation of C₂F₆ is not observed in this study, which is encouraging since the global warming potential of C₂F₆ is actually higher than that of C₃F₈.     

Factors for generalized absolute Cesàro summability

In this paper, a known theorem dealing with ${|C,\alpha |}_k$ summability factors has been generalized for ${|C,\alpha ,\beta |}_k$ summability factors.     

Nanodiamond-based two-step sampling of multiply and singly phosphorylated peptides for MALDI-TOF mass spectrometry analysis

Simultaneous detection of multiply and singly phosphorylated peptides using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is challenging because of suppression effects during ionization. In oder to overcome this problem, this study presents a new approach to improve the detection of phosphopeptides by stepwise enrichment using polyarginine-coated (PA-coated) and titanium dioxide-coated (TiO(2)-coated) nanodiamonds for fractionation of multiply and singly phosphorylated peptides prior to on-probe MALDI MS analysis. The feasibility of this approach was demonstrated using synthetic peptides containing different numbers of phosphate groups, tryptic digests of α-casein, β-casein, and complex protein mixtures. The high specificity of the approach is shown in its effective enrichment and fractionation of phosphopeptides from the digest of β-casein and bovine serum albumin at a molar ratio as low as 1 : 1000, which out-performs the commercial Fe(3+)-IMAC and TiO(2) isolation kits. It offers a simple and effective alternative for the fractionation and identification of multiply and singly phosphorylated peptides by MALDI MS and allows for deduction of more information from limited starting materials.     

Subspace methods for three‐parameter eigenvalue problems

We propose subspace methods for three‐parameter eigenvalue problems. Such problems arise when separation of variables is applied to separable boundary value problems; a particular example is the Helmholtz equation in ellipsoidal and paraboloidal coordinates. While several subspace methods for two‐parameter eigenvalue problems exist, their extensions to a three‐parameter setting seem challenging. An inherent difficulty is that, while for two‐parameter eigenvalue problems, we can exploit a relation to Sylvester equations to obtain a fast Arnoldi‐type method, such a relation does not seem to exist when there are three or more parameters. Instead, we introduce a subspace iteration method with projections onto generalized Krylov subspaces that are constructed from scratch at every iteration using certain Ritz vectors as the initial vectors. Another possibility is a Jacobi–Davidson‐type method for three or more parameters, which we generalize from its two‐parameter counterpart. For both approaches, we introduce a selection criterion for deflation that is based on the angles between left and right eigenvectors. The Jacobi–Davidson approach is devised to locate eigenvalues close to a prescribed target; yet, it often also performs well when eigenvalues are sought based on the proximity of one of the components to a prescribed target. The subspace iteration method is devised specifically for the latter task. The proposed approaches are suitable especially for problems where the computation of several eigenvalues is required with high accuracy. MATLAB implementations of both methods have been made available in the package MultiParEig (see http://www.mathworks.com/matlabcentral/fileexchange/47844-multipareig ).     

Organic deposits on MCM-41 surface after thermal treatment of as-synthesized samples

FT-IR spectroscopy with photoacoustic detector has been applied to investigate organic template transformations during thermal treatment of silica and silica-alumina MCM-41 molecular sieve. The role of surfactant degradation and type of organic deposits on silica surface remaining after surfactant elimination depends on the presence of alumina in MCM-41 pore network.     

300 Femtosecond pulses at 497 nanometer generated by an excimer laser pumped cascade of distributed feedback dye lasers

The setup is a cascade of 3 lasers: A competing cavity dye laser pumped by a XeCl excimer laser, followed by two distributed feedback dye lasers. The typical durations of the pulses from the lasers are 100 ps, 5 ps, and 300 fs, respectively. The output pulses at 497 nm are amplified up to 500 MW. The shortest pulse duration obtained was 198 fs.     

Theory of travelling-wave amplified spontaneous emission

A rate-equation model for describing the travelling-wave amplified spontaneous emission pulses (TWASE) in a transversally excited travelling wave arrangement is given. 6.35 ps long ASE pulses have been obtained by 12 ps long pump pulses. The effect of pump intensity, pump-pulse duration, molecular parameters of the dyes and pump-sweep velocity on the ASE pulses is studied.