Endovascular magnetically guided robots: navigation modeling and optimization

This paper deals with the benefits of using a nonlinear model-based approach for controlling magnetically guided therapeutic microrobots in the cardiovascular system. Such robots used for minimally invasive interventions consist of a polymer binded aggregate of nanosized ferromagnetic particles functionalized by drug-conjugated micelles. The proposed modeling addresses wall effects (blood velocity in minor and major vessels' bifurcations, pulsatile blood flow and vessel walls, and effect of robot-to-vessel diameter ratio), wall interactions (contact, van der Waals, electrostatic, and steric forces), non-Newtonian behavior of blood, and different driving designs as well. Despite nonlinear and thorough, the resulting model can both be exploited to improve the targeting ability and be controlled in closed-loop using nonlinear control theory tools. In particular, we infer from the model an optimization of both the designs and the reference trajectory to minimize the control efforts. Efficiency and robustness to noise and model parameter's uncertainties are then illustrated through simulations results for a bead pulled robot of radius 250 μm in a small artery.     

Analytical electron tomography mapping of the SiC pore oxidation at the nanoscale

Silicon carbide is a ceramic material that has been widely studied because of its potential applications, ranging from electronics to heterogeneous catalysis. Recently, a new type of SiC materials with a medium specific surface area and thermal conductivity, called β-SiC, has attracted overgrowing interest as a new class of catalyst support in several catalytic reactions. A primary electron tomography study, performed in usual mode, has revealed a dual surface structure defined by two types of porosities made of networks of connected channels with sizes larger than 50 nm and ink-bottled pores with sizes spanning from 4 to 50 nm. Depending on the solvent nature, metal nanoparticles could be selectively deposited inside one of the two porosities, a fact that illustrates a selective wetting titration of the two types of surfaces by different liquids. The explaining hypothesis that has been put forward was that this selectivity against solvents is related to the pore surface oxidation degree of the two types of pores. A new technique of analytical electron tomography, where the series of projections used to reconstruct the volume of an object is recorded in energy filtered mode (EFTEM), has been implemented to map the pore oxidation state and to correlate it with the morphology and the accessibility of the porous network. Applied, for the first time, at a nanoscale resolution, this technique allowed us to obtain 3D elemental maps of different elements present in the analysed porous grains, in particular oxygen; we found thus that the interconnected channel pores are more rapidly oxidized than the ink-bottled ones. Alternatively, our study highlights the great interest of this method that opens the way for obtaining precise information on the chemical composition of a 3D surface at a nanometer scale.     

Multiple circular nano-inhomogeneities and/or nano-pores in one of two joined isotropic elastic half-planes

The paper considers the problem of multiple interacting circular nano-inhomogeneities or/and nano-pores located in one of two joined, dissimilar isotropic elastic half-planes. The analysis is based on the solutions of the elastostatic problems for (i) the bulk material of two bonded, dissimilar elastic half-planes and (ii) the bulk material of a circular disc. These solutions are coupled with the Gurtin and Murdoch model of material surfaces [Gurtin ME, Murdoch AI. A continuum theory of elastic material surfaces. Arch Ration Mech Anal 1975;57:291–323; Gurtin ME, Murdoch AI. Surface stress in solids. Int J Solids Struct 1978;14:431–40.]. Each elastostatic problem is solved with the use of complex Somigliana traction identity [Mogilevskaya SG, Linkov AM. Complex fundamental solutions and complex variables boundary element method in elasticity. Comput Mech 1998;22:88–92]. The complex boundary displacements and tractions at each circular boundary are approximated by a truncated complex Fourier series, and the unknown Fourier coefficients are found from a system of linear algebraic equations obtained by using a Taylor series expansion. The resulting semi-analytical method allows one to calculate the elastic fields everywhere in the half-planes and inside the nano-inhomogeneities. Numerical examples demonstrate that (i) the method is effective in solving the problems with multiple nano-inhomogeneities, and (ii) the elastic response of a composite system is profoundly influenced by the sizes of the nano-features.     

Identify capacity fading mechanism in a commercial LiFePO4 cell

The capacity fading of an 18650 LiFePO₄-based lithium ion cell was studied using the dynamic stress test (DST) schedule in a cycle life evaluation. Intermittent reference performance tests were conducted to quantify capacity loss and peak power capability degradation with cycle number to the end-of-life. An incremental capacity analysis was applied to identify various contributions to capacity loss, whereas the open circuit voltage measurements were utilized to trace the correct state of charge as the cell degrades in order to accurately correlate the capacity degradation with SOC. Our non-invasive, in situ analyses are in general consistent with current understanding of the degradation mechanism in this chemistry derived from post-mortem analysis. Loss of lithium inventory is the main cause of capacity degradation, in addition to the loss of active materials. The degree of under-discharge and under-charge is quite minimal under the test protocol.     

Nanoparticles: Aspects of Safety and Risk Management

Synthetic nanoparticles are within the scope of the existing chemical law in Europe (REACH). However, the present knowledge is not yet sufficient for the elaboration of nanospecific regulations. Many projects with the aim of completing the necessary scientific and technical basis for the assessment of nanotechnology related risks are under way. Under these circumstances voluntary safety standards by authorities or industry constitute an appropriate tool for the protection of human health and the environment. Received: June 2, 2008; accepted: June 3, 2008.     

High‐throughput measurement of recombination rates and genetic interference in Saccharomyces cerevisiae

Allelic recombination owing to meiotic crossovers is a major driver of genome evolution, as well as a key player for the selection of high‐performing genotypes in economically important species. Therefore, we developed a high‐throughput and low‐cost method to measure recombination rates and crossover patterning (including interference) in large populations of the budding yeast Saccharomyces cerevisiae. Recombination and interference were analysed by flow cytometry, which allows time‐consuming steps such as tetrad microdissection or spore growth to be avoided. Moreover, our method can also be used to compare recombination in wild‐type vs. mutant individuals or in different environmental conditions, even if the changes in recombination rates are small. Furthermore, meiotic mutants often present recombination and/or pairing defects affecting spore viability but our method does not involve growth steps and thus avoids filtering out non‐viable spores.     

Numerical and experimental analysis of the vibration serviceability of the Bears’ Cage footbridge

The Bears’ Cage footbridge is a slender steel structure with a single span. Its dynamic behaviour is predicted based on a refined finite-element (FE) model and the vibration serviceability is assessed according to the current codes of practice. The assessment indicates a high susceptibility to human-induced vibrations with disturbing vibration levels even for sparse pedestrian densities. To validate the predicted behaviour of the structure, an extensive experimental study is performed including static deflection and dynamic vibration tests. The analysis shows that statically, the longitudinal movement of the supports on one side of the span can be considered unconstrained, indicating a behaviour of the sliding pot bearings as designed. Due to the footbridge’s arch-like shape, the longitudinal stiffness of the supports highly influences the natural frequency of the fundamental bending mode. The analysis shows that the longitudinal stiffness of sliding pot bearings and the structural inherent damping ratio of the fundamental mode significantly reduces once an initial friction level in the sliding pot bearings is overcome as the result of a significant movement at the supports. The vibration serviceability is reassessed based on the calibrated FE model and shows that even for high pedestrian densities, maximum vibration comfort is ensured.     

Retrieval of a metabolite from cells with polyelectrolyte microcapsules

To monitor cellular processes in individual cells, it is important to measure the concentrations of intracellular metabolites and to retrieve them for analysis. The use of functionalized polyelectrolyte microcapsules as intracellular sensors for in vivo reporting is persented. Capsules loaded with streptavidin-rhodamine, which was introduced into fibroblasts by electroporation, autonomously escaped from an endocytic compartment and efficiently recruited biotin-fluorescein from the cytosol. This work demonstrates the utility of polyelectrolyte microcapsules for intracellular capture of metabolites and eventually for drug delivery on an organismic level.     

Investigation of fragments size resulting from dynamic fragmentation in melted state of laser shock-loaded tin

The understanding of dynamic fragmentation in shock-loaded metals and the evaluation of geometrical and kinematical properties of the resulting fragments are issues of considerable importance for both basic and applied science, for instance to predict the evolution of engineering structures submitted to high-velocity impact or explosive detonation. Among dynamic failure processes, spall fracture in solid materials has been extensively studied for many years, while scarce data can be found yet about how such phenomenon could evolve after partial or full melting on compression or on release. In this case, the dynamic fragmentation process, which may be referred to as ‘micro-spalling’, takes place in a liquid medium. It results in the formation of a cloud of fine molten droplets, ejected at high-velocity. The present work is devoted to experimental characterization, theoretical modelling and simulation of the ‘micro-spalling’ process in tin, with a specific emphasis on the size of the resulting fragments, namely the melted droplets. Laser-driven shock-loading experiments on tin have been performed. Post-test observations of the recovered fragments provide an insight into the actual fragmentation process and allow to infer the distribution of the fragments size which are found to be mostly sub-micrometric. Fragmentation modelling is based on a widely employed, energetic approach adapted to the case of liquids. This approach is implemented as a failure criterion in an one-dimensional hydrocode including a multiphase equation of state for tin. A fairly good agreement is obtained between experimental and computed sizes range. Some discrepancies are explained by both experimental uncertainties and model limitations which are carefully pointed out and discussed.