A normal modes technique to reduce the order of poroelastic models: application to 2D and coupled 3D models

A reduced‐order model for structures involving poroelastic materials is proposed in this paper. The approach is based on a separation of the solid and fluid phases of the porous material into separate substructures. For each individual substructure, a decoupled normal mode basis is considered, from which a set of vectors for the decomposition is selected. The preserved modes are completed by an additional family to correct for the influence of the static response of the non‐preserved. It is shown that the only neglected phenomenons in the model are the inertia of the non‐preserved modes and part of their intercoupling. The following three features render the proposed scheme computationally attractive: (i) real valued matrices are involved in the transformations; (ii) the assembly of complex, frequency dependent matrices is only performed at the stage of solving for a particular frequency; and (iii) the number of normal modes required are selected using a novel method. The computational efficacy is demonstrated, on a simple but realistic 3D case, through numerical results obtained using a reduced number of DOFs, showing a significant reduction of computational cost compared with traditional methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Relationship between texture and mechanical properties of granites, central Sweden, by use of image-analysing techniques

Rock texture is of great importance in understanding the mechanical properties of a rock. Los Angeles and studded tyre tests were used to assess the mechanical properties of homogeneous acidic plutonic and volcanic rocks and these properties were related to the rock texture using image analysis and the more common optical microscopy. The image-analysing technique was based on SEM/BSE images, where the perimeter was measured on each mineral phase in order to numerically quantify a texture parameter. The results demonstrate that rocks with high perimeter values have the best resistance to fragmentation and abrasion. A high perimeter corresponds to fine-grained rocks where the minerals occur as individual grains rather than monomineralic aggregates. An increase in grain size and the formation of mineral aggregates of the same phase have a negative effect on the quality of the rock. Electronic Publication     

A finite element approach combining a reduced‐order system,Padé approximants,and an adaptive frequency windowing for fast multi‐frequency solution of poro‐acoustic problems

In this work, a solution strategy is investigated for the resolution of multi‐frequency structural‐acoustic problems including 3D modeling of poroelastic materials. The finite element method is used, together with a combination of a modal‐based reduction of the poroelastic domain and a Padé‐based reconstruction approach. It thus takes advantage of the reduced‐size of the problem while further improving the computational efficiency by limiting the number of frequency resolutions of the full‐sized problem. An adaptive procedure is proposed for the discretization of the frequency range into frequency intervals of reconstructed solution. The validation is presented on a 3D poro‐acoustic example. Copyright © 2013 John Wiley & Sons, Ltd.     

A Cactus‐Derived Toxin‐Like Cystine Knot Peptide with Selective Antimicrobial Activity

Naturally occurring cystine knot peptides show a wide range of biological activity, and as they have inherent stability they represent potential scaffolds for peptide‐based drug design and biomolecular engineering. Here we report the discovery, sequencing, chemical synthesis, three‐dimensional solution structure determination and bioactivity of the first cystine knot peptide from Cactaceae (cactus) family: Ep‐AMP1 from Echinopsis pachanoi. The structure of Ep‐AMP1 (35 amino acids) conforms to that of the inhibitor cystine knot (or knottin) family but represents a novel diverse sequence; its activity was more than 500 times higher against bacterial than against eukaryotic cells. Rapid bactericidal action and liposome leakage implicate membrane permeabilisation as the mechanism of action. Sequence homology places Ec‐AMP1 in the plant C6‐type of antimicrobial peptides, but the three dimensional structure is highly similar to that of a spider neurotoxin.     

Material and knot properties of braided polyester (Ticron®) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures

The purpose of the present study was to investigate in vitro the biomechanical material and knot properties and histomorphometrical knot properties of 3-0 braided polyester suture (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 suture. In Ticron five throws are needed to form a secure knot, and the 1 = 1 = 1 = 1 = 1 and the 2 = 1 = 1 = 1 configurations are recommended. For PLDLA several granny and square knots formed a secure knot, but the 1 = 1 and 1 = 1 = 1 knots were the best. These PLDLA knots had lower yield force and strain at yield point, but higher stiffness than the recommended Ticron knots. The ultimate force values did not differ, but PLDLA knots had significantly higher strain at ultimate point. In the histomorphometrical analysis of the recommended knots, the PLDLA knots had a significantly smaller knot surface area than the Ticron knots. According to these results, PLDLA suture proved to be suitable for flexor tendon repair.     

A comparison of variation management strategies for wind power integration in different electricity system contexts

Variation management strategies improve the capability of the electricity system to meet variations both in the electricity demand and in the generation that relies on variable energy sources. In this work, we introduce a new, functionality‐based, categorization of variation management strategies: shifting (eg, batteries), absorbing (eg, power‐to‐gas), and complementing (dispatchable generation, including reservoir hydropower) strategies. A dispatch model with European coverage (EU‐27 plus Norway and Switzerland) is applied to compare the benefits of shifting and absorbing strategies on wind integration in regions with different amounts of complementing strategies in place. The benefits are measured in terms of the wind value factor, wind owner revenue, and average short‐term generation cost. The results of the modeling show that the reduction in average short‐term generation cost and the increase in revenue earned by the wind owner from shifting strategies, such as the use of batteries, are more substantial at low wind shares than at high wind shares. The opposite situation is found for absorbing strategies, such as power‐to‐gas, which are found to be more efficient at reducing the average generation cost and increasing profit for the wind owner as the wind share increases. In regions that have access to complementing strategies in the form of reservoir hydropower, variation management has a weak ability to reduce the average short‐term generation cost, although it can increase significantly the revenue accrued by the wind power owner.     

Weak formulation of Biot's equations in cylindrical coordinates with harmonic expansion in the circumferential direction

A weak symmetric form of Biot's equation in cylindrical coordinates with a spatial Fourier expansion in the circumferential direction is presented. The solid phase displacement and the pore pressure are used as the dependent variables. The original three‐dimensional boundary value problem is here, due to the orthogonality of the harmonic functions and the rotationally symmetric geometry, decomposed into independent two‐dimensional problems, one for each harmonic function. This formulation provides a computationally efficient procedure for vibroacoustic finite element modelling of rotationally symmetric three‐dimensional multilayered structures including porous elastic materials. By numerical simulations, this method is compared with, and verified against, full three‐dimensional Cartesian coordinate system finite element models. Copyright © 2009 John Wiley & Sons, Ltd.     

Sensitive detection of bacterial DNA by magnetic nanoparticles

This work presents sensitive detection of bacterial genomic DNA using a magnetic nanoparticle-based substrate-free method. For the first time, such a method is employed for detection of a clinically relevant analyte by implementing a solid-phase-based molecular probing and amplification protocol that can be executed in 80 min. The molecular detection and amplification protocol is presented and verified on samples containing purified genomic DNA from Escherichia coli cells, showing that as few as 50 bacteria can be detected. This study moves the use of volume-amplified magnetic nanoparticles one step further toward rapid, sensitive, and selective infectious diagnostics.     

Integration of plug-in hybrid electric vehicles in a regional wind-thermal power system

This study investigates consequences of integrating plug-in hybrid electric vehicles (PHEVs) in a wind-thermal power system supplied by one quarter of wind power and three quarters of thermal generation. Four different PHEV integration strategies, with different impacts on the total electric load profile, have been investigated. The study shows that PHEVs can reduce the CO₂-emissions from the power system if actively integrated, whereas a passive approach to PHEV integration (i.e. letting people charge the car at will) is likely to result in an increase in emissions compared to a power system without PHEV load. The reduction in emissions under active PHEV integration strategies is due to a reduction in emissions related to thermal plant start-ups and part load operation. Emissions of the power sector are reduced with up to 4.7% compared to a system without PHEVs, according to the simulations. Allocating this emission reduction to the PHEV electricity consumption only, and assuming that the vehicles in electric mode is about 3 times as energy efficient as standard gasoline operation, total emissions from PHEVs would be less than half the emissions of a standard car, when running in electric mode.