Effect of cholecalciferol on unsaturated model membranes.

Vitamin D plays an important role in many physiological processes, particularly calcium and phosphorous homeostasis. The biochemistry of vitamin D is also complex, encompassing a range of active molecules that may be either endogenous or dietary in origin. The role of lipids and fats in the production, processing and use of vitamin D is an interesting one, with a relative paucity of model studies into the interactions of vitamin D with lipidic systems such as micelles and vesicles. Here, we have studied the effect of vitamin D3 in simple unsaturated phospholipid systems. We used NMR and FTIR spectroscopy to investigate the effect of increasing vitamin D concentration on the structure and dynamics of the lipid chains and interfacial region. In order to link these model studies with more complex biomimetic environments, we compare results in the presence of buffer and vitamin D binding protein. We have also used DLS to determine that vitamin D3-DOPC vesicles can retain their size distribution for varying amounts of time in different conditions. We find that the acyl chain region of vitamin D3-DOPC membranes are generally disordered, and that the addition of buffer and/or protein alters the properties of the interfacial region.

An algorithm for filtering detector instabilities in search of novel non-exponential decay and in conventional half-life determinations.

Recent reports of Solar modulation of beta-decay have reignited interest in whether or not radioactive half-lives are constants. A numerical approach for filtering instrumental effects on residuals is developed, using correlations with atmospheric conditions recorded while counting 204Tl emissions with a Geiger-Müller counter. Half-life oscillations and detection efficiency oscillations can be separated provided their periods are substantially different. A partial uncertainty budget for the 204Tl half-life shows significant decreases to medium-frequency instabilities correlated with pressure and temperature, which suggests that further development may aid general improvements in half-life determinations.

A bi-prism interferometer for hard X-ray photons.

Micro-fabricated bi-prisms have been used to create an interference pattern from an incident hard X-ray beam, and the intensity of the pattern probed with fluorescence from a 30 nm-thick metal film. Maximum fringe visibility exceeded 0.9 owing to the nano-sized probe and the choice of single-crystal prism material. A full near-field analysis is necessary to describe the fringe field intensities, and the transverse coherence lengths were extracted at APS beamline 8-ID-I. It is also shown that the maximum number of fringes is dependent only on the complex refractive index of the prism material.

Kinoform optics applied to X-ray photon correlation spectroscopy.

Moderate-demagnification higher-order silicon kinoform focusing lenses have been fabricated to facilitate small-angle X-ray photon correlation spectroscopy (XPCS) experiments. The geometric properties of such lenses, their focusing performance and their applicability for XPCS measurements are described. It is concluded that one-dimensional vertical X-ray focusing via silicon kinoform lenses significantly increases the usable coherent flux from third-generation storage-ring light sources for small-angle XPCS experiments.

Diamond kinoform hard X-ray refractive lenses: design, nanofabrication and testing.

Motivated by the anticipated advantageous performance of diamond kinoform refractive lenses for synchrotron X-ray radiation studies, this report focuses on progress in designing, nanofabricating and testing of their focusing performance. The method involves using lift-off and plasma etching to reproduce a planar definition of numerically determined kinoform refractive optics. Tests of the focusing action of a diamond kinoform refractive lens at the APS 8-ID-I beamline demonstrate angular control of the focal spot.

Shear modulus and plasticity of a driven charge density wave.

We have probed the effects of transverse variations in pinning strength on charge-density-wave (CDW) structure in NbSe3 by x-ray micro-beam diffraction. In ribbonlike crystals having a large longitudinal step in thickness, the CDW first depins on the thick side of the step, causing rotations of the CDW wave vector. By measuring these rotations as a function of position and electric field, the corresponding shear strains are determined, allowing the CDW's shear modulus to be estimated. These results demonstrate the usefulness of x-ray microdiffraction as a tool in studying collective dynamics in electronic crystals.

Dynamic nuclear polarization by electrical spin injection in ferromagnet-semiconductor heterostructures.

Electrical spin injection from Fe into AlxGa1-xAs quantum well heterostructures is demonstrated in small (<500 Oe) in-plane magnetic fields. The measurement is sensitive only to the component of the spin that precesses about the internal magnetic field in the semiconductor. This field is much larger than the applied field and depends strongly on the injection current density. Details of the observed hysteresis in the spin injection signal are reproduced in a model that incorporates the magnetocrystalline anisotropy of the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamic polarization of nuclei by the injected spins.