An Artificial Disc: Chemical and Biomechanical Analysis

Summary: Degeneration of intervertebral discs is the most common cause of back pain. The first phase of this degenerative process involves the nucleus pulposus. A rapid recovery of this structure can prevent further degradation of the annulus fibrosus. Guar Gum is an hydrophilic polysaccharide extracted from the seed endosperm of a plant. Through a cross-linking procedure a Guar hydrogel was synthesized. The Guar hydrogel could be injected by a syringe and it is a good candidate as a nucleus pulposus substitute. For the preparation of the artificial fibrosus annulus, commercially available polymer materials are tuned to achieve suitable mechanical properties. To achieve this peculiar behaviour, the main strategy investigated is the dispersion of hollow polymer micro spheres in a thermoplastic polymer matrix. Processing conditions and particle content are finely tuned to get the target mechanical behaviour.     

Ultrasonic flaw detection using radial basis function networks (RBFNs)

Ultrasonic flaw detection has been studied many times in the literature. Schemes based on thresholding after a previous matched filter use to be the best solution, but results obtained with this method are only satisfactory when scattering and attenuation are not considered. In this paper, we propose an alternative solution to thresholding detection method. We deal with the usage of different flaw detection methods comparing them with the proposed one. The experiment tries to determinate whether a given ultrasonic signal contains a flaw echo or not. Starting with a set of 24,000 patterns with 750 samples each one, two subsets are defined for the experiments. The first one, the training set, is used to obtain the detection parameters of the different methods, and the second one is used to test the performance of them. The proposed method is based on radial basis functions networks, one of the most powerful neural network techniques. This signal processing technique tries to find the optimal decision criterion. Comparing this method with thresholding based ones, an improvement over 25-30% is obtained, depending on the probability of false alarm. So our new method is a good alternative to flaw detection problem.     

Dynamics of nematic liquid crystal with quenched disorder in the random dilution and random field regimes

By means of specific heat spectroscopy, we have studied the dynamics of nematic 8CB nucleated, in the presence of random disorder, as the temperature is lowered across the isotropic to nematic phase transition such that the crossover region of random dilution to random field regimes of disorder strength is explored. We show, in terms of frequency dependence, hysteretic behavior, and aging effects, that the out-of-equilibrium properties of the nematic nucleated in the random disorder regime are strongly reminiscent of the bulk material while the one grown in the random field regime shows a glassy behavior with aging leading to slower dynamics. The aging effect has been explained in terms of strain relaxation in analogy with observations in other soft glassy colloidal systems.     

Sensitivity analysis of Mixed Tempered Stable parameters with implications in portfolio optimization

Computational Management Science - This paper investigates the use, in practical financial problems, of the Mixed Tempered Stable distribution both in its univariate and multivariate formulation....     

New BEDT-TTF/[Fe(C5O5)3]3- hybrid system: synthesis, crystal structure, and physical properties of a chirality-induced alpha phase and a novel magnetic molecular metal

The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52-=croconate) has been combined with the organic donor BEDT-TTF (=ET=bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced alpha phase, alpha-(BEDT-TTF)5[Fe(C5O5)3].5H2O (1), and one of the few known paramagnetic molecular metals, beta-(BEDT-TTF)5[Fe(C5O5)3].C6H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the alpha or beta packing modes, alternating with layers containing the high-spin S=5/2 Fe(III) anions and solvent molecules. In the alpha phase, the alternation of the chiral [Fe(C5O5)3]3- anions along the direction perpendicular to the BEDT-TTF chains induces an alternation of the tilt angle of the BEDT-TTF molecules, giving rise to the observed alpha phase. The alpha phase presents a semiconductor behavior with a high room-temperature conductivity (6 S.cm-1) and an activation energy of 116 meV. The beta phase presents a metallic behavior down to ca. 120 K, where a charge localization takes place with a reentrance to the metallic state below ca. 20 K followed by a metal-semiconductor transition at ca. 10 K. The magnetic properties are dominated by the paramagnetic S=5/2 [Fe(C5O5)3]3- anion with an extra Pauli-type paramagnetism in the metallic beta phase. The ESR spectra confirm the presence of the high-spin Fe(III)-containing anion and show a progressive localization in the organic sublattice along with an antiferromagnetic coupling below ca. 120 K that, in the metallic beta phase, could be at the origin of the transition from the metallic to the activated conductivity regime. The correlation between crystal structure and conductivity behavior has been studied by means of tight-binding band structure calculations which provide a rationalization of the charge distribution and conductivity results.     

Bilirubin Oxidase‐Based Nanobiocathode Working in Serum‐Mimic Buffer for Implantable Biofuel Cell

Low‐density graphite electrodes have been covalently modified with gold nanoparticles and used as scaffold for the oriented immobilization of Myrothecium verrucaria bilirubin oxidase. The developed nanobioelectrodes have been tested as a biocathode in a human‐serum surrogate buffer that mimics physiological conditions. The nanostructured bioelectrode offered a ?140 µA cm^?2 current density under serum‐mimic conditions at 0.2 V, and was operational during at least 6 days.     

Multiple logic gates based on electrically wired surface-reconstituted enzymes

The electrode functionalized with glucose oxidase (GOx) and microperoxidase-11 (MP-11) performs various Boolean logic operations (OR, XOR, AND-OR) upon addition of glucose and/or H2O2 and application of different potentials. The output signal coming from the electrically wired enzymes is electrochemically readable, allowing interfacing of biochemical computing systems with ordinary electronics.