Growth model for cholesterol accumulation in the wall of a simplified 3D geometry of the carotid bifurcation

Atherosclerosis is one of the leading causes of death in the first world countries nowadays. It is a vascular disease that affects medium and large size arteries, involving the formation of plaques within the artery wall. These plaques result from the accumulation of fat, cholesterol, cell debris, smooth muscle cells and other cells and substances, and may cause temporary or definitive lack of blood supply to an organ.This article proposes a model for cholesterol accumulation and plaque growth. The model is basically a mass balance of low density lipoproteins (LDL) in the intima. The inflow, outflow, oxidation, and consumption of LDL is modeled combining partial models and correlations available in the literature.The model was implemented into an open source finite volume code. Assuming steady blood flow, the code was used to predict lesion formation on a three-dimensional model of the carotid artery bifurcation, a location greatly studied for its role in supplying blood to some parts of the brain and for being related to strokes due to formation of atheromas. The simulation was carried out under physiologic conditions for blood pressure and LDL blood concentration.Results for LDL mass accumulation and intimal thickening over time, plaque shape, and location of thicker spots are reported, showing that the proposed model approximates reasonably well the intimal thickening obtained from post-mortem aortic fatty streaks and from B-mode ultrasonography of the carotid artery of healthy subjects reported by other authors.     

Vitrification of municipal solid waste incineration fly ash: An approach to find the successful batch compositions

Incineration is the most common way to reduce the mass and the volume of municipal solid wastes. One of the most dangerous by-products of the incineration process is fly ash that contains a considerable amount of heavy metals. Therefore, its treatment is crucial to prevent the leaching of heavy metals into the environment. In the present work, two different sources of municipal solid waste incinerator fly ash have been vitrified in order to inhibit the release of potentially toxic heavy metals. Two different sources of silica, i.e. silica sand and glass cullet, have been added to each type of fly ash in an attempt to obtain vitrifiable batches. The standard leaching test on vitrified products was performed according to EN12457-2 confirming no heavy metal leaching and, therefore, they all pass waste acceptance criteria to be classified as an inert material. Furthermore, the previously reported data for vitrification of fly ash was combined with the present work and their compositions were presented in the SiO₂–Al₂O₃–CaO, and SiO₂-ΣM₂O₃-Σ(MO + M₂O) ternary phase diagrams to identify the region in which successful compositions are concentrated. This analysis could facilitate the attempt to find the right composition for vitrification of fly ash.     

Geometric steerable medial maps

To provide more intuitive and easily interpretable representations of complex shapes/organs, medial manifolds should reach a compromise between simplicity in geometry and capability of restoring the anatomy/shape of the organ/volume. Existing morphological methods show excellent results when applied to 2D objects, but their quality drops across dimensions. This paper contributes to the computation of medial manifolds from a theoretical and a practical point of view. First, we introduce a continuous operator for accurate and efficient computation of medial structures of arbitrary dimension. Second, we present a validation protocol for assessing the suitability of medial surfaces for anatomical representation in medical applications. We evaluate quantitatively the performance of our method with respect to existing approaches and show its higher performance for medical imaging applications in terms of medial simplicity and capability of reconstructing the anatomical volume.     

Functionalized liquid polyisoprene as a promising toughening agent for poly(lactic acid): Combining stiffness and toughness

Liquid polyisoprene rubbers (LIR) containing anhydride and carboxylic groups along their chains were successfully employed as toughening agent for poly(lactic acid) (PLA) without great influence on the stiffness of the matrix. In fact, the addition of 5% of these functionalized LIR resulted in an improvement of toughness and impact resistance of more than 2000%, whereas the reduction of the yield stress stayed in the range of 12%. No significant variation of the Young modulus was observed for the modified PLA samples. The effect of the LIR on the rheological and thermal properties of PLA was also investigated. The glass transition temperature obtained from dynamic-mechanical analysis of the PLA matrix was not affected by the addition of 10% of the liquid rubber. The scanning electron microscopy analysis revealed a significant decrease in the rubber domains for the blends containing LIR functionalized with anhydride groups. Finally, the modified PLA with anhydride-functionalized LIR was able to produce transparent film with outstanding mechanical performance than neat PLA, making this material a good option for food packaging.     

Catalytic oxidation of concentrated orange oil phase by synthetic metallic complexes biomimetic to MMO enzyme

BACKGROUND: This paper reports the catalytic oxidation of the concentrated orange oil phase using the complexes [Fe^III(BMPP)Cl(µ‐O)Fe^IIICl₃], [Cu^II(BTMEA)₂Cl]Cl and [Co^II(BMPP)]Cl₂ biomimetic to methane monooxygenase enzyme as catalysts and hydrogen peroxide as oxidant. RESULTS: The reaction products of oil oxidation, mainly nootkatone, were identified by gas chromatography/mass spectrometry. A screening of catalysts was performed through a full 2³ experimental design, varying the temperature from 30 to 70 °C, the catalyst concentration from 7.0 × 10^?4 to 1.5 × 10^?3 mol L^?1 and the oxidant/substrate molar ratio from 1:1 to 3:1. The results of reaction kinetics employing the most promising catalysts showed that conversions to nootkatone of up to 8% were achieved after 16 h at 70 °C. CONCLUSION: The results obtained in this study in terms of nootkatone production should be considered encouraging, since a real, industrially collected, raw material, instead of pure valencene, was employed in the reaction experiments, with a final content about ten times that present in the original concentrated oil. Copyright © 2010 Society of Chemical Industry     

Large anisotropic conductance and band gap fluctuations in nearly round-shape bismuth nanoparticles

Unlike their bulk counterpart, nanoparticles often show spontaneous fluctuations in their crystal structure at constant temperature [Iijima, S.; Ichihashi T. Phys. Rev. Lett.1985, 56, 616; Ajayan, P. M.; Marks L. D. Phys. Rev. Lett.1988, 60, 585; Ben-David, T.; Lereah, Y.; Deutscher, G.; Penisson, J. M.; Bourret, A.; Korman, R.; Cheyssac, P. Phys. Rev. Lett.1997, 78, 2585]. This phenomenon takes place whenever the net gain in the surface energy of the particles outweighs the energy cost of internal strain. The configurational space is then densely populated due to shallow free-energy barriers between structural local minima. Here we report that in the case of bismuth (Bi) nanoparticles (BiNPs), given the high anisotropy of the mass tensor of their charge carriers, structural fluctuations result in substantial dynamic changes in their electronic and conductance properties. Transmission electron microscopy is used to probe the stochastic dynamic structural fluctuations of selected BiNPs. The related fluctuations in the electronic band structure and conductance properties are studied by scanning tunneling spectroscopy and are shown to be temperature dependent. Continuous probing of the conductance of individual BiNPs reveals corresponding dynamic fluctuations (as high as 1 eV) in their apparent band gap. At 80 K, upon freezing of structural fluctuations, conductance anisotropy in BiNPs is detected as band gap variations as a function of tip position above individual particles. BiNPs offer a unique system to explore anisotropy in zero-dimension conductors as well as the dynamic nature of nanoparticles.     

Very high thermopower of Bi nanowires with embedded quantum point contacts

Quantum confinement effects in bismuth (Bi) nanowires (NWs) are predicted to impart them with high thermopower values and hence make them efficient thermoelectric materials. Yet, boundary scattering of charge carriers in these NWs operating in the diffusion transport regime mask any quantum effects and impede their use for nanoscale thermoelectric applications. Here we demonstrate quantum confinement effects in Bi NWs by forming in their structure ballistic quantum point contacts (QPCs) leading to exceptionally high thermopower values (S > 2 mV/K). The power factor, S(2)G, of the QPCs is maximized at G ~ 0.25G(0) (where G(0) is the quantum of conductance) within agreement with a one-band model with step edge characteristics.     

Effect of nanoclay and carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) rubber on the reaction induced phase separation and cure kinetics of an epoxy/cyclic anhydride system

The effects of nano clay, carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) liquid rubber and the combination of both on the cure kinetics of diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin/nadic methyl anhydride were studied. Cure kinetics studies were carried out by performing dynamic and isothermal differential scanning calorimetric (DSC) experiments. The dynamic DSC experiments were carried out at four different heating rates. Dynamic kinetic modeling was performed using Kissinger and Ozawa approaches. Since these methods are based exclusively on the maximum rate of cure, which occurs approximately at the beginning of the cure reaction, the activation energy calculated using these methods is valid only for the initial stage of the cure. The clay (3 phr) filled epoxy system has an activation energy 24 % lower than the unfilled system. The role of the surfactant chemistry on the initial stage of the cure reaction was also studied. A plausible reaction mechanism which involves the effect of the nanoclay surfactant as an accelerator of the cure reaction was proposed. The phase separated CTBN rubber hindered the cure reaction and has 3 % higher activation energy for epoxy/CTBN system than the unfilled system. In the ternary epoxy/3 phr clay/15 phr CTBN system, the accelerating effect of clay on cure was highlighted. The cure activation observed in the presence of clay overshadows the hindrance created by the phase separated CTBN. Isothermal DSC scans were carried out at five different temperatures. The experimental datas showed an autocatalytic behavior of the reaction, and the isothermal modeling was carried out by Kamal autocatalytic model. The results showed a very good agreement within the whole conversion range for the unfilled and all the filled systems. The evolution of the morphology and phase separation was also studied using optical and scanning electron microscope. Faster cure reaction resulted in smaller phase-separated CTBN particles in epoxy/clay/CTBN ternary system as compared with those observed in epoxy/CTBN binary blend.     

Ethylene maleated amorphous propylene compatibilized polyethylene nanocomposites: Stress and temperature effects on nonlinear creep

The effects of stress and temperature on the nonlinear creep behavior of linear low‐density polyethylene (LLDPE) nanocomposites reinforced with montmorillonite‐layered silicate (MLS) nanoclay and compatibilized with an amorphous maleated ethylene copolymer (amEP) is investigated. To study the effect of stress on the creep resistance of these materials, creep tests were conducted at different stress levels (10, 25, and 50% yield stress). The effect of temperature was examined by analyzing the creep and recovery of the films at temperatures in the range of ?100 to 25°C. The individual creep compliance curves for each stress level and temperature were fitted to both the Burgers model and the Kohlrausch‐Williams‐Watts (KWW) function. The results indicate that modification of the polyethylene results in a suppression of relaxation times but the temperature trends are reversed below the β transition temperature. Filled systems exhibited a distribution in relaxation times whose trend matched the relaxation time trends in both Burger and KWW models. POLYM. ENG. SCI., 50:1633–1645, 2010. © 2010 Society of Plastics Engineers