Long-Term Neuroelectric Signal Recording from Severed Nerves

Six recording electrode units were implanted around the severed sciatic nerves of rabbits immediately after an axotomy was performed. Voluntary and involuntary motor neuroelectric signals (including individual action potentials) were recorded from the surface of the severed nerve for as long as 142 days after implantation, the average duration being 64 days. In order to study the course of the limited duration of the signal detection, a stimulation electrode was implanted around the sciatic nerve proximal to the lesion; evoked neuroelectric signals were recorded throughout the length of the experiment. The impedance of the recording electrode was also measured throughout the length of the experiment. The behavior of the above parameters, combined with histological observations, indicated that nerve degeneration accounted for the deterioration of signal detection.     

Bearing Capacity of Piled Rafts on Soft Clay Soils

The conventional design of a piled foundation is based on a bearing capacity approach, and neglects the contribution of the raft. As a consequence, piled foundations are usually designed by overconservative criteria. With respect to the conventional approach, a more rational and economical solution could be obtained by accounting for the contribution of the raft toward the overall bearing capacity, but this potential is not exploited due to the lack of theoretical and experimental research on the behavior of piled rafts at failure. Based on both experimental evidence and three-dimensional finite element analyses, a simple criterion is proposed to evaluate the ultimate vertical load of a piled raft as a function of its component capacities, which can be simply evaluated by the conventional bearing capacity theories. The results presented in the paper thus provide a guide to assess the safety factor of a vertically loaded piled raft.     

Investigation of commercial lecithin by 31P NMR in a ternary CUBO solvent

Many different ways have been devised over the years for analysing phospholipids in solution by ³¹P NMR. One promising method entails the use of the so‐called CUBO solvent, a ternary mixture of dimethylformamide, triethylamine and guanidinium hydrochloride. As this interesting system seems to have been overlooked in the literature, we present here a study on the quantification of phospholipids and lysophospholipids contained in 10 samples of commercial lecithin using the CUBO/³¹P NMR method. Cluster analysis and principal component analysis of the NMR data showed clear differences among the samples according to the actual lecithin producer. Multivariate analysis of the chemical and physical parameters of the samples confirmed these differences. Copyright © 2004 Society of Chemical Industry     

Adaptive dynamic programming for model-free tracking of trajectories with time-varying parameters

Recently proposed adaptive dynamic programming (ADP) tracking controllers assume that the reference trajectory follows time-invariant exo-system dynamics—an assumption that does not hold for many applications. In order to overcome this limitation, we propose a new Q-function that explicitly incorporates a parametrized approximation of the reference trajectory. This allows learning to track a general class of trajectories by means of ADP. Once our Q-function has been learned, the associated controller handles time-varying reference trajectories without the need for further training and independent of exo-system dynamics. After proposing this general model-free off-policy tracking method, we provide an analysis of the important special case of linear quadratic tracking. An example demonstrates that our new method successfully learns the optimal tracking controller and outperforms existing approaches in terms of tracking error and cost.     

Influence of uncertainty in selected aerodynamic and structural parameters on the buffeting response of long-span bridges

Multimode-analysis methods for the study and derivation of flutter instability and buffeting response are readily available from the literature and have been successfully applied to the assessment of the susceptibility of long-span bridges to wind loading. In both cases flutter critical velocity and buffeting oscillation are usually estimated from deterministic analyses. However, the probabilistic nature of the problem is latent since uncertainties, especially those associated with the definition of wind and aerodynamic characteristics, are intrinsically present. These quantities include, for example, wind-turbulence power spectral density, static coefficients and aerodynamic derivatives, usually derived from either site observations or experimental analysis. Their effects are often neglected or usually addressed through sensitivity analyses only.While in the past uncertainty in flutter estimates has been analyzed by researchers (for example through reliability analysis), little attention has been devoted to buffeting. In this paper the effects associated with the random nature of wind and structural characteristics are analyzed through the derivation of a closed-form solution associated with the single-mode buffeting problem with selected random parameters. A specific example is provided to clarify the role of wind power spectral density, damping and selected aeroelastic derivatives.     

Beam separator for high-order harmonic radiation in the 3-10 nm spectral region

We present the scheme of a beam separator for ultrashort high-order harmonic radiation below 10 nm. The system consists of a collimating mirror and two plane grazing-incidence gratings in compensated configuration. The first grating acts as the beam separator: it diffracts the extreme ultraviolet (XUV) light into the first order while reflecting the fundamental laser beam into the zero order. The diffracted light goes to a second grating that compensates both for the spectral dispersion and for the temporal broadening of the XUV ultrashort pulse caused by the diffraction at the first grating. The system can be designed for any wavelength in the 3-40 nm region. Since the gratings are operated at extreme grazing incidence, the area of the optical surface illuminated by the fundamental laser pulse is large, and therefore there is no risk of damage of the optical surfaces. The effects on the phase of the ultrashort pulse for narrowband applications are discussed.     

Multiscale investigation of the functional properties of the human femur

The mechanical strength of human bones has often been investigated in the past. Bone failure is related to musculoskeletal loading, tissue properties, bone metabolism, etc. This is intrinsically a multiscale problem. However, organ-level performance in most cases is investigated as a separate problem, incorporating only part (if any) of the information available at a higher scale (body level) or at a lower one (tissue level, cell level). A multiscale approach is proposed, where models available at different levels are integrated. A middle-out strategy is taken: the main model to be investigated is at the organ level. The organ-level model incorporates as an input the outputs from the body-level (musculoskeletal loads), tissue-level (constitutive equations) and cell-level models (bone remodelling). In this paper, this approach is exemplified by a clinically relevant application: fractures of the proximal femur. We report how a finite-element model of the femur (organ level) becomes part of a multiscale model. A significant effort is related to model validation: a number of experiments were designed to quantify the model's sensitivity and accuracy. When possible, the clinical accuracy and the clinical impact of a model should be assessed. Whereas a large amount of information is available at all scales, only organ-level models are really mature in this perspective. More work is needed in the future to integrate all levels fully, while following a sound scientific method to assess the relevance and validity of such an integrated model.     

Biomimetic Mg-substituted hydroxyapatite: from synthesis to in vivo behaviour

The incorporation of magnesium ions (in the range 5–10 mol% in respect to Ca) into the hydroxyapatite structure, which is of great interest for the developing of artificial bone, was performed using magnesium chloride, calcium hydroxide and phosphoric acid, as reactants. Among the synthesized powders, the synthetic HA powder containing 5.7% Mg substituting for calcium was selected, due to its better chemico-physical features, and transformed into granules of 400–600 μm, for biocompatibility tests (genotoxicity, carcinogenicity, toxicity, in vitro cytotoxicity and in vivo skin irritation-sensitization tests). In vivo tests were carried out on New Zealand White rabbits using the granulate as filling for a femoral bone defect: osteoconductivity and resorption were found to be enhanced compared to commercial stoichiometric HA granulate, taken as control.     

A hybrid plasmonic-photonic nanodevice for label-free detection of a few molecules

Noble metal nanowaveguides supporting plasmon polariton modes are able to localize the optical fields at nanometer level for high sensitivity biochemical sensing devices. Here we report on the design and fabrication of a novel photonic-plasmonic device which demonstrates label-free detection capabilities on single inorganic nanoparticles and on monolayers of organic compounds. In any case, we determine the Raman scattering signal enhancement and the device detection limits that reach a number of molecules between 10 and 250. The device can be straightforwardly integrated in a scanning probe apparatus with the possibility to match topographic and label-free spectroscopic information in a wide range of geometries.