A highly oriented cubic phase formed by lipids under shear

We demonstrate the formation of a macroscopically oriented inverse bicontinuous cubic (Q(II)) lipid phase from a sponge (L(3)) phase by controlled hydration during shear flow. The L(3) phase was the monoolein/butanediol/water system; the addition of water reduces the butanediol concentration, inducing the formation of a diamond (Q(II)(D)) cubic phase, which is oriented by the shear flow. The phenomenon was reproduced in both capillary and Couette geometries, indicating that this represents a robust general route for the production of highly aligned bulk Q(II) samples, with applications in nanomaterial templating and protein research.     

Enhanced annuities and the impact of individual underwriting on an insurer’s profit situation

We analyze the effect of enhanced annuities on an insurer engaging in individual underwriting. We use a frailty model for heterogeneity of the insured population and model individual underwriting by a random variable that positively correlates with the corresponding frailty factor. For a given annuity portfolio, we analyze the effect of the quality of the underwriting on the insurer’s profit/loss situation and the impact of adverse selection effects.     

Neumann Problem in Domains with Outlets of Bounded Diameter

We study the Neumann problem for the Laplace equation in domains having quasicylindrical outlets. The aim is to collect and sort known results spread over the literature and to fill in the gaps of the theory which still exist. Namley, solutions with finite Dirichlet integral are found applying on the one hand the Helmholtz decomposition and on the other hand the Riesz representation theorem. We investigate generalizations for the non-Hilbert space setting and collect several types of Saint Venant estimates.     

The shape of the yield and its impact on inventory decisions

We consider an inventory model with stochastic demand, positive lead time and random yield where ordering decisions are made according to a linear inflation rule. In case of a positive lead times the complexity of such inventory systems increases distinctly. Due to positive lead times, the inventory position contains no longer a term for outstanding orders but the estimated quantity of goods to be delivered after a known positive lead time period, which differ from the realized deliveries. Thus, a forecast error occurs in each period. In previous research this forecast error was assumed to be normally distributed which is not an appropriate assumption in case of symmetric yield. Since yield skewness can’t be neglected, we propose to fit a skew normal distribution or a generalized extreme value distribution on the forecast error to account for the yield skewness. A numerical study reveals that the proposed approaches are excellent and outperform existing ones.     

Synthesis and Crystal Structure of RbKLiAlF6 – the First Al‐Elpasolite with Three Different Alkali Metals

The synthesis of RbKLiAlF₆ via a sol‐gel route is described. The crystal structure has been determined using Rietveld‐refinement. It is shown that the compound crystallizes in the hexagonal 12L‐structure of the Cs₂NaCrF₆‐type (space‐group ) with a = 5.7195Å, c = 27.8655(4) Å and therefore belongs to the family of hexagonal elpasolites being the first example for an Al‐elpasolite with three different alkali metals. Further insights regarding structural details could be gained using ⁸⁷Rb MAS NMR spectroscopy.     

Structure of (NH4)3GaF6 investigated by multinuclear magic-angle spinning NMR spectroscopy in comparison with rietveld refinement

The structure of ammonium gallium cryolite (NH(4))(3)GaF(6) was investigated by (19)F and (69,71)Ga magic-angle spinning (MAS) NMR in comparison with X-ray powder diffraction followed by Rietveld refinement. In agreement with previous thermodynamic measurements, NMR experiments on (NH(4))(3)GaF(6) support the model of rigid GaF(6) octahedra. At high spinning speeds (30 kHz), the scalar coupling between the six equivalent (19)F nuclei and (69,71)Ga can be directly observed in the powder spectra. The coupling constants are J(19)F(69)Ga = 197 Hz and J(19)F(71)Ga = 264 Hz. To explain the (71)Ga spectra recorded at 3 kHz a small distribution of quadrupolar frequencies has to be included. The spread of the spinning sidebands hints to a largest nu(Q) value of 28 kHz for (71)Ga. This can be explained by the occurrence of highly symmetric GaF(6) octahedra, which are tilted against the surrounding atoms. In addition, the incomplete motional excitation does not average out the quadrupolar effects. NMR findings are in discrepancy to those of Rietveld refinement. As result it appears that X-ray diffraction is not sensitive enough to deliver proper results.     

Highly Extensible Bio‐Nanocomposite Fibers

Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.

     

Thermosensitive and Dissolution Properties in Nanocomposite Polymer Hydrogels

We investigate the phase transition behavior and dissolution resistant properties of thermo‐sensitive nanocomposite hydrogels made from PEO‐PPO‐PEO triblock copolymer (Pluronic F127) and Laponite silicate nanoparticles. The rapid dissolution properties of F127 copolymer hydrogels usually limit their use as sustained release drug carriers. We overcome this limitation by synergistic combination of nanoparticle gelation characteristics with polymer thermo‐sensitivity. We present a proof of concept that the temperature‐dependent phase transitions can be shifted as a function of hydrogel composition and that the dissolution of the polymer hydrogels as well as the release of a model drug, albumin, can be significantly slowed down by addition of nanoparticles. The dissolution resistant properties generated will prove useful in the future formulation, processing and application of our polymer hydrogels for sustained release drug delivery carriers.