Cylindrical geometry electroquasistatic dielectrometry sensors

Semianalytical models are used to simulate the response of periodic-field electroquasistatic dielectrometry sensors. Due to the periodic structure of the sensors it is possible to use Fourier transform methods in combination with collocation point numerical techniques to generate accurate sensor simulations much more efficiently than with the more general finite-element methods. The models previously developed for Cartesian geometry sensors have been extended to sensors with cylindrical geometry. This enables the design of families of circularly symmetric dielectrometers with the "model-based" methodology, which requires close agreement between actual sensor response and simulated response. These kinds of sensors are needed in applications where the components being tested have circular symmetry, or if it is important to be insensitive to sensor orientation, in cases where a property shows some anisotropy. It is possible to extend the Fourier Series Cartesian geometry models to this case with the use of Fourier-Bessel Series over a radius large compared to the sensor dimensions. The validity of the cylindrical geometry model is confirmed experimentally, where the combined response of two circularly symmetric dielectric sensors with different depths of sensitivity is used to simultaneously measure the permittivity of a dielectric plate and its lift-off from the electrode surface     

Relations between enzyme activities connected with energy metabolism and parameters of food energy utilization in young and adult rats. Part 2. Enzyme activities related to alpha-glycerophosphate shuttle in various tissues

The possible significance of food composition connected with the alpha-glycerophosphate (alpha GP) shuttle, a putative metabolic pathway of energy dissipation, was investigated at the level of enzyme activities. Liver, adipose tissue, slow-twitch and fast-twitch muscle of weaned male Wistar rats fed ad libitum for seven and for forty weeks a normal-protein (NP), a low-protein (LP), and a high-fat (HF) diet were examined. No striking dietary influences on cytosalic (NAD-linked glycerophosphate dehydrogenase, glyceraldehyde-phosphate dehydrogenase) and mitochondrial (succinate dehydrogenase, cytochrome c oxidase) enzyme activities could be detected, but mitochondrial alpha-glycerophosphate dehydrogenase (m-GPDH) showed an about twofold increase of its activity in the liver of LP-fed animals after seven weeks. A relationship between the "gross efficiency of food energy utilization" and tissue m-GPDH levels could not be established in general. The proposed inducing effect of a LP diet on the magnitude of the GP shuttle observed in the liver of young and adult rats seems to be interconnected reciprocally with the degree of metabolic energy dissipation only under the conditions of growth. The calculated capacities of the alpha GP shuttle are compatible with the assumption of its function as an energy dissipating pathway which is restricted in its magnitude.     

Forward and inverse parameter estimation algorithms of interdigitaldielectrometry sensors

In this paper we extend the continuum model for interdigital dielectrometry sensors and propose a new, direct technique for estimating material electrical properties from measurements. Interdigital sensors consist of alternating pairs of long, thin electrodes on a plane. An ideal model assumes that the periodic structure extends to infinity and the electrodes have no thickness. We extend this ideal analysis to account for the physical thickness of the electrodes. We also present the model in a matrix form which is amenable to linear algebraic analysis techniques. In particular, the `inverse problem' of estimating material properties is formulated as a generalized Eigenvalue problem, which avoids the convergence problems of previous iterative algorithms     

Multi-scale simulations of apatite–collagen composites: from molecules to materials

We review scale-bridging simulation studies for the exploration of atomicto-meso scale processes that account for the unique structure and mechanic properties of apatite-protein composites. As the atomic structure and composition of such complex biocomposites only partially is known, the first part (i) of our modelling studies is dedicated to realistic crystal nucleation scenarios of inorganic-organic composites. Starting from the association of single ions, recent insights range from the mechanisms of motif formation, ripening reactions and the self-organization of nanocrystals, including their interplay with growth-controlling molecular moieties. On this basis, (ii) reliable building rules for unprejudiced scale-up models can be derived to model bulk materials. This is exemplified for (enamel-like) apatite-protein composites, encompassing up to 10⁶ atom models to provide a realistic account of the 10 nm length scale, whilst model coarsening is used to reach μm length scales. On this basis, a series of deformation and fracture simulation studies were performed and helped to rationalize biocomposite hardness, plasticity, toughness, self-healing and fracture mechanisms. Complementing experimental work, these modelling studies provide particularly detailed insights into the relation of hierarchical composite structure and favorable mechanical properties.     

Synthesis and Characterization of Gelatin‐Based Magnetic Hydrogels

A simple preparation of thermoreversible gelatin‐based ferrogels in water provides a constant structure defined by the crosslinking degree for gelatin contents between 6 and 18 wt%. The possibility of varying magnetite nanoparticle concentration between 20 and 70 wt% is also reported. Simulation studies hint at the suitability of collagen to bind iron and hydroxide ions, suggesting that collagen acts as a nucleation seed to iron hydroxide aggregation, and thus the intergrowth of collagen and magnetite nanoparticles already at the precursor stage. The detailed structure of the individual ferrogel components is characterized by small‐angle neutron scattering (SANS) using contrast matching. The magnetite structure characterization is supplemented by small‐angle X‐ray scattering and microscopy only visualizing magnetite. SANS shows an unchanged gelatin structure of average mesh size larger than the nanoparticles with respect to gel concentration while the magnetite nanoparticles size of around 10 nm seems to be limited by the gel mesh size. Swelling measurements underline that magnetite acts as additional crosslinker and therefore varying the magnetic and mechanical properties of the ferrogels. Overall, the simple and variable synthesis protocol, the cheap and easy accessibility of the components as well as the biocompatibility of the gelatin‐based materials suggest them for a number of applications including actuators.     

Extending the scope of ‘in silico experiments’: Theoretical approaches for the investigation of reaction mechanisms, nucleation events and phase transitions

The investigation of the atomistic mechanisms of processes in complex systems constitutes a major challenge to both theory and experiment. While experimental studies offer a wide variety of insights at the macroscopic scale, the atomistic level of detail often remains elusive. On the other hand, molecular simulation approaches may easily achieve microscopic resolution and hence appear particularly suited for detailed mechanistic analyses. However, the computational effort is typically quite considerable and in many cases special simulation strategies are needed to make simulations possible. This review is dedicated to special approaches for tackling the time/length-scale problem inherent to molecular dynamics simulations. Employing these techniques opened a series of new perspectives. The latter are illustrated with the example of recent simulation studies of the atomistic mechanisms involved in complex processes like crystal nucleation, phase transitions and reactions in solution. Along this line, we discuss the reaction mechanisms for He insertion into C₆₀ fullerenes, nucleation events and domain morphogenesis in pressure-induced phase transitions in solids and ion aggregation from solution.     

Lorenz Function of Bi2Te3/Sb2Te3 Superlattices

Combining first-principles density functional theory and semiclassical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi₂Te₃/Sb₂Te₃ superlattices and their bulk constituents. It was found that, already for the bulk materials Bi₂Te₃ and Sb₂Te₃, the Lorenz function is not a clear function of charge carrier concentration and temperature. For electron-doped Bi₂Te₃/Sb₂Te₃ superlattices, large oscillatory deviations of the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.     

Preparation of mesoscopic gold rings and split rings by selective wetting of the contact points between the spheres within colloidal crystals

Rings and split rings of sub-micrometer size are prepared by the infiltration of colloidal crystals of spherical silica particles with diameters of about 1 μm by diluted solutions of tetrachloroauric acid in butanone, followed by the evaporation of the butanone, the annealing of the samples at elevated temperatures and the removal of the silica spheres with hydrofluoric acid. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and electron backscatter diffraction investigations reveal that the obtained rings and split rings are made out of metallic gold.     

Progress report on hair keratin research

Evidence is given for the progress in hair keratin research by bringing out four examples from the recent hair science literature. 1 Kon et al. [1] published a new method of solubilization and fractionation of the matrix and the microfibril proteins and found a significant decrease in the 'intact' microfibril keratin at the tip end of permed hair. 2 Contrary to the previous view of the existence of four major and one minor hair keratin pair, Langbein et al. [2, 3] showed that there are nine type I hair keratins and six type II hair keratins and drew up a two-dimensional catalogue of human hair keratins. 3 To collectively describe the extremely complex expression pattern of human type I and type II hair keratins in the hair follicle, Langbein et al. [2, 3] have summarized the corresponding RNA expression profiles of the various hair keratins schematically. 4 Contrary to the previous assignment of keratins exclusively to the microfibrils in the cortex, the mRNA expression studies of Langbein et al. [2, 3] implied that any hair cuticle cell leaving the living cell compartment contains four different hair keratins.     

Electric Field Effects on the Equilibrium and Small Signal Stabilization of Electrofluidized Beds

A continuum analysis is developed of electric field coupling to a charge-free fluidized bed of polarizable particles, with the electric field at an arbitrary angle to the gas flow. The electric force density and stress tensor is derived from the principle of virtual work and includes polarization and electrostriction forces but neglects Coulombic free charge forces. Effective medium theory for various particle structures derives the effective bed permittivity as a function of particle voidage and is used with the energy method to derive the electric. force density acting on the particles. Necessary force-free boundary conditions at the top free surface of the bed are developed. A linear stability analysis is used to find the conditions for electric field stabilization. Experiments with Rochelle salt show elimination of bubbling with collinear electric field and flow but never complete stabilization with crossed field and flow as predicted by the analysis. There is qualitative agreement between the stability analysis and measurements. Numerical differences are attributed to particle viscosity, which was not included in the fluid model.