A method for interpolating on manifolds structural dynamics reduced‐order models

A rigorous method for interpolating a set of parameterized linear structural dynamics reduced‐order models (ROMs) is presented. By design, this method does not operate on the underlying set of parameterized full‐order models. Hence, it is amenable to an online real‐time implementation. It is based on mapping appropriately the ROM data onto a tangent space to the manifold of symmetric positive‐definite matrices, interpolating the mapped data in this space and mapping back the result to the aforementioned manifold. Algorithms for computing the forward and backward mappings are offered for the case where the ROMs are derived from a general Galerkin projection method and the case where they are constructed from modal reduction. The proposed interpolation method is illustrated with applications ranging from the fast dynamic characterization of a parameterized structural model to the fast evaluation of its response to a given input. In all cases, good accuracy is demonstrated at real‐time processing speeds. Copyright © 2009 John Wiley & Sons, Ltd.     

Wear resistant composite coatings

In the search for wear resistant coatings, nanolaminated composite films composed of alternating metallic and ceramic layers, namely, Al/Al₂O₃ and Ti/TiN were produced using radio frequency magnetron sputtering. The metal layer thickness in the as-sputtered films of Al/Al₂O₃ ranged from 70 to 500 nm, and 150 to 450 nm in Ti/TiN. The non-metals (Al₂O₃ and TiN) layer thicknesses ranged from 10 to 40 nm and total film thicknesses of 10–15 µm. All coatings were characterized and tested for their tribological properties. Friction and wear tests were performed under non-lubricated sliding conditions using a pin-on-disc type tribometer. The coefficient of friction of the composite coatings tested, against a stainless steel pin, varied with the sliding distance. At the early stages of sliding the coefficient of friction rose to a peak, followed by a decrease to a steady-state value. Wear rates and coefficients of friction were related to the hardness and to the structure refinement of the coatings.     

Separation and identification of DNA-carcinogen adduct conformers by polyacrylamide gel electrophoresis with laser-induced fluorescence detection.

We have developed a separation protocol utilizing high-resolution polyacrylamide gel electrophoresis (PAGE) to isolate stable anti-benzo[a]pyrene diol epoxide adducts of oligodeoxynucleotides. Both enantiomers produced multiple adduct species. The distribution of adduct types could be quantitated by densitometry of autoradiograms or Cerenkov counting of eluted oligomers modified by anti-BPDE isomers. Laser-induced fluorescence (LIF) spectra of eluted adducts at 4.2 K (fluorescence line-narrowing spectroscopy) and 77 K revealed that bands corresponded to pure conformers of pyrene chromophore. Carcinogen-modified oligodeoxynucleotides were single-stranded, but there were often considerable stacking interactions between the pyrenyl residues and the oligonucleotide bases, indicating that electrophoresed oligomers were single-stranded but in a native, versus random coil, conformation. The ability to identify and quantitate adducts by PAGE-LIF, coupled with the high resolution and sensitivity of both techniques, makes PAGE and LIF in tandem a potentially powerful tool in the study of chemical carcinogenesis or other ligand-DNA interactions.     

Influence of autogenous cracking on the durability of repairs by cement-based overlays reinforced with metal fibres

The focus of this research is a better understanding of the structural behaviour and durability of metal fibre reinforced concrete repairs. A total of 9 overlaid specimens, with the overlay on the tension face, were tested under deflection controlled three point bending. Three types of overlays were tested: one made with plain mortar (M0) and two with fibre-reinforced mortars (M1 and M2). Mortar M1 was reinforced with 40 kg.m⁻³ of 30-mm-long hooked-ends steel fibres. Mortar M2 was reinforced with 20 kg.m⁻³ of 30-mm-long amorphous metal fibres. During the preparation of the repair layer, the upper face of the repair was notched at mid-length using a shaped PVC plate, fitted to the mould. Because of the specimen curing conditions, the associated drying shrinkage had initiated a crack at the notch tip before the mechanical tests started. In such conditions, the debonding mechanisms are quite representative of the debonding of in situ repairs. It is shown that the debonding of fibre-reinforced repairs is significantly delayed in comparison with plain repairs. This better behaviour is due to the fibres’ ability to restrain the crack opening within the repair layer, which in turn helps to reduce the stresses at the base-repair interface.     

Sensitivity analysis and design optimization of three‐dimensional non‐linear aeroelastic systems by the adjoint method

We consider the problem of optimizing a non‐linear aeroelastic system in steady‐state conditions, where the structure is represented by a detailed finite element model, and the aerodynamic loads are predicted by the discretization of the non‐linear Euler equations. We present a solution method for this problem that is based on the three‐field formulation of fluid–structure interaction problems, and the adjoint approach for coupled sensitivity analysis. We discuss the computational complexity of the proposed solution method, describe its implementation on parallel processors, and illustrate its computational efficiency with the aeroelastic optimization of various wings. Copyright © 2002 John Wiley & Sons, Ltd.     

Mesh partitioning for implicit computations via iterative domain decomposition: Impact and optimization of the subdomain aspect ratio

Optimal domain decomposition methods have emerged as powerful iterative algorithms for parallel implicit computations. Their key preprocessing step is mesh partitioning, where research has focused so far on the automatic generation of load-balanced subdomains with minimum interface nodes. In this paper, we emphasize the importance of the subdomain aspect ratio as a mesh partitioning factor, and highlight its impact on the convergence rate of an optimal domain decomposition based iterative method. We also present a fast optimization algorithm for improving the aspect ratio of existing mesh partitions, and illustrate it with several examples from fluid dynamics and structural mechanics applications. For a stiffened shell problem decomposed by the optimal Recursive Spectral Bisection scheme and solved by the FETI method, this optimization algorithm is shown to improve the solution time by a factor equal to 1·54 and to restore numerical scalability.     

Changes in migraine symptoms from childhood to adolescence

INTRODUCTION: Kaposi's disease is increasingly frequent in transplant recipients. The therapeutic approach in heart transplantation is not fully established. CASE REPORT: A 61-year-old male transplant recipient (June 1992) presented Kaposi's disease on the legs. Immunosuppressive therapy was reduced, cyclosporin by 20 p. 100, withdrawal of azathioprine and 40 p. 100 reduction in prednisone was insufficient to control the disease. Due to the extension of the lesions and the major functional handicap, bleomycin was given and led to complete regression of the lesions within 6 months. DISCUSSION: This case illustrates the difficult therapeutic situation encountered in heart transplant recipients. The situation may be life-threatening with organ rejection. The first step is to reduce immunosuppressive therapy. If this is insufficient or the Kaposi is particularly aggressive, bleomycin may be used. The efficacy of bleomycin observed in our case requires confirmation in multicenter studies.     

A new iterative algorithm for extrapolation of data available in multiple restricted regions with application to radar imaging

A new iterative method for extrapolation of incomplete segmented data available in multiple separated bands is proposed and tested. The method uses the Burg algorithm to find the linear prediction parameters and an iterative procedure to improve the estimation of the linear prediction parameters and the extrapolation of the data. This method is especially effective when the spectra (Fourier transform of the observed data) are in discrete forms, in the context of radar imaging represented here, this means the objects consist of distinctly spaced scattering centers. The advantages of this algorithm are demonstrated using both numerically generated and realistic experimental data pertaining to high resolution radar imaging.