Organic–inorganic bonding in chitosan–silica hybrid networks: Physical properties

Novel biomaterials are needed for bone tissue repair with improved mechanical performance compared to classical bioceramics. The objective of this work was to characterize a hybrid filler material, which is capable to coat as a thin film porous scaffolds improving their mechanical properties for bone tissue engineering. The hybrid filler material is a blend of chitosan and silica network formed through in situ sol–gel using tetraethylortosilicate and 3‐glycidoxypropyltrimethoxysilane (GPTMS) as silica precursors. The hypothesis was that the epoxy ring of GPTMS could react with the amino groups of chitosan in acidic media while it is also reacting the siloxane groups of hydrolyzed silica precursors. The formation of the hybrid organic–inorganic network was assessed by different physical techniques revealing changes in molecular mobility and hydrophilicity upon chemical reaction. Finally, the cytotoxicity of the samples was also evaluated by MTT assay. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1391–1400     

Modeling of non-stationary ground motion using the mean reverting stochastic process

This paper presents a new method for modeling amplitude and frequency non-stationary earthquake ground motions using a scalar first order dynamic mean reverting stochastic differential equation driven by Brownian motion with parametric time varying coefficients. It determines the proper relationship between these time varying parametric coefficients and presents the statistical and probability distribution characteristics of the response solution. It demonstrates the applicability of the method by presenting some simulations of amplitude and frequency non-stationary earthquake ground motions. The verification of the amplitude and frequency non-stationary contents of the mean reverting stochastic ground motions is demonstrated using the Hilbert–Huang transform method. Also a corresponding interpretation between the coefficients of the proposed model and the coefficients of the usual oscillatory second order differential equation driven by white Gaussian noise is presented along with some comments how it can be applied to simulate ground motions consistent with acceleration target records such as boxcar, trapezoidal, other exponential functions, or compound and target records at source, near field, and far field distances.     

Approximate dynamic programming for stochastic linear control problems on compact state spaces

This paper addresses Markov Decision Processes over compact state and action spaces. We investigate the special case of linear dynamics and piecewise-linear and convex immediate costs for the average cost criterion. This model is very general and covers many interesting examples, for instance in inventory management. Due to the curse of dimensionality, the problem is intractable and optimal policies usually cannot be computed, not even for instances of moderate size.     

Estimate of the truncation error of finite volume discretization of the Navier–Stokes equations on colocated grids

A methodology is proposed for the calculation of the truncation error of finite volume discretizations of the incompressible Navier–Stokes equations on colocated grids. The truncation error is estimated by restricting the solution obtained on a given grid to a coarser grid and calculating the image of the discrete Navier–Stokes operator of the coarse grid on the restricted velocity and pressure field. The proposed methodology is not a new concept but its application to colocated finite volume discretizations of the incompressible Navier–Stokes equations is made possible by the introduction of a variant of the momentum interpolation technique for mass fluxes where the pressure part of the mass fluxes is not dependent on the coefficients of the linearized momentum equations. The theory presented is supported by a number of numerical experiments. The methodology is developed for two‐dimensional flows, but extension to three‐dimensional cases should not pose problems. Copyright © 2005 John Wiley & Sons, Ltd.     

Radiatively induced neutrino masses and large Higgs-neutrino couplings in the Standard Model with Majorana fields

The Higgs sector of the Standard Model (SM) with one right-handed neutrino per family is systematically analyzed. In a model with intergenerational independent mixings between families, we can account for very light neutrinos acquiring Majorana masses radiatively at the first electroweak loop level. We also find that in such a scenario the Higgs coupling to the light-heavy neutrinos and to the heavy-heavy ones may be remarkably enhanced with significant implications for the production of these heavy neutrinos at high energy colliders.     

Delayed Capital Injections for a Risk Process with Markovian Arrivals

Methodology and Computing in Applied Probability - In this paper we propose a generalisation to the Markov Arrival Process (MAP) risk model, by allowing for a delayed receipt of required capital...     

Nondestructive detection of damage in aluminum: Electromagenetic discharge imaging

Electromagnetic Discharge Imaging (EDI) is applied for the nondestructive detection of imperfections and inhomogeneities in solids. These imperfections were introduced mechanically by drilling holes of different sizes and chemically by applying corrosive agents to aluminum specimens. The results are influenced by a host of variables associated with the waveform generator, the dielectric air gap and the specimen type. Correlation is thus established between the electromagnetic discharge image and the degree of material damage. Detection of material damage was also made possible even when the specimen surface was a layer of opaque insulation material.     

Structure determination of oligomeric alkannin and shikonin derivatives

Monomeric alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity and comprise the active ingredients for several pharmaceutical preparations. Therefore, the determination of the impurities, degradation products or byproducts in alkannin and shikonin samples is of great importance. Oligomeric alkannin and shikonin are formed during biosynthesis of these bioactive secondary metabolites in Boraginaceaous root plants, during tissue culture production of A/S, during alkaline hydrolysis of A/S esters and also thermal treatment of A/S. In the present study, a dimeric alkannin/shikonin compound was isolated by size exclusion chromatography from alkannin and shikonin commercial samples and its structure was determined by one- and two-dimensional NMR spectroscopy. The structure of the most abundant oligomeric species in these samples, a dimeric naphthoquinone, was established for the fi rst time, indicating that coupling of the side chain of one naphthoquinone unit with the aromatic ring of a second naphthoquinone leads to dimer formation. This type of coupling allows further oligomerization by leaving one isohexenyl side chain available at the second monomer unit.     

On complete intersection toric ideals of graphs

We study the graphs G for which their toric ideals I _G are complete intersections. In particular, we prove that for a connected graph G such that I _G is a complete intersection all of its blocks are bipartite except for at most two. We prove that toric ideals of graphs which are complete intersections are circuit ideals. In this case, the generators of the toric ideal correspond to even cycles of G except of at most one generator, which corresponds to two edge disjoint odd cycles joint at a vertex or with a path. We prove that the blocks of these graphs satisfy the odd cycle condition. Finally, we characterize all complete intersection toric ideals of graphs which are normal.