On the heterogeneous character of water's amorphous polymorphism

In this letter we report {\it in situ} small--angle neutron scattering results on the high--density (HDA) and low-density amorphous (LDA) ice structures and on intermediate structures as found during the temperature induced transformation of HDA into LDA. We show that the small--angle signal is characterised by two $Q$ regimes featuring different properties ($Q$ is the modulus of the scattering vector defined as $Q = 4\pi\sin{(\Theta)}/\lambda_{\rm i}$ with $\Theta$ being half the scattering angle and $\lambda_{\rm i}$ the incident neutron wavelength). The very low--$Q$ regime ($< 5\times 10^{-2}$ \AA $^{-1}$) is dominated by a Porod--limit scattering. Its intensity reduces in the course of the HDA to LDA transformation following a kinetics reminiscent of that observed in wide--angle diffraction experiments. The small--angle neutron scattering formfactor in the intermediate regime of $5 \times 10^{-2} < Q < 0.5$ \AA$^{-1}$ HDA and LDA features a rather flat plateau. However, the HDA signal shows an ascending intensity towards smaller $Q$ marking this amorphous structure as heterogeneous. When following the HDA to LDA transition the formfactor shows a pronounced transient excess in intensity marking all intermediate structures as strongly heterogeneous on a length scale of some nano--meters

Pressure dependence of diffusion in simple glasses and supercooled liquids

Using molecular dynamics simulation, we have calculated the pressure dependence of the diffusion constant in a binary Lennard-Jones Glass. We observe four temperature regimes. The apparent activation volume drops from high values in the hot liquid to a plateau value. Near the critical temperature of the mode coupling theory it rises steeply, but in the glassy state we find again small values, similar to the ones in the liquid. The peak of the activation volume at the critical temperature is in agreement with the prediction of mode coupling theory

Diffusion and jump-length distribution in liquid and amorphous Cu33_{33}Zr67_{67}

Using molecular dynamics simulation, we calculate the distribution of atomic jum ps in Cu$_{33}$Zr$_{67}$ in the liquid and glassy states. In both states the distribution of jump lengths can be described by a temperature independent exponential of the length and an effective activation energy plus a contribution of elastic displacements at short distances. Upon cooling the contribution of shorter jumps dominates. No indication of an enhanced probability to jump over a nearest neighbor distance was found. We find a smooth transition from flow in the liquid to jumps in the g lass. The correlation factor of the diffusion constant decreases with decreasing temperature, causing a drop of diffusion below the Arrhenius value, despite an apparent Arrhenius law for the jump probability

Field-induced structural aging in glasses at ultra low temperatures

In non-equilibrium experiments on the glasses Mylar and BK7, we measured the excess dielectric response after the temporary application of a strong electric bias field at mK--temperatures. A model recently developed describes the observed long time decays qualitatively for Mylar [PRL 90, 105501, S. Ludwig, P. Nalbach, D. Rosenberg, D. Osheroff], but fails for BK7. In contrast, our results on both samples can be described by including an additional mechanism to the mentioned model with temperature independent decay times of the excess dielectric response. As the origin of this novel process beyond the "tunneling model" we suggest bias field induced structural rearrangements of "tunneling states" that decay by quantum mechanical tunneling.Comment: 4 pages, 4 figures, accepted at PRL, corrected typos in version

Die Biologie der Heilung der Rotatorenmanschettenläsion: Welche Rolle spielen Wachstumsfaktoren heutzutage?

Zusammenfassung: Die Rotatorenmanschettenläsion ist eine häufige Diagnose in der orthopädischen Sprechstunde. Die Rerupturrate ist trotz Weiterentwicklung der Nahtmaterialien und -techniken im offenen und arthroskopischen Bereich nach wie vor hoch. In den letzten Jahren wurden den physiologischen Vorgängen der natürlichen Insertion wie auch den biologischen Eigenschaften der Rotatorenmanschettenheilung in der Forschung vermehrt Aufmerksamkeit geschenkt. Es hat sich gezeigt, dass die Heilung der Sehnen-Knochen-Insertion der Rotatorenmanschette ein komplexes Zusammenspiel von lokalen Zellen, Stammvorläuferzellen, extrazellulärer Matrix sowie von Wachstumsfaktoren und anderen Zytokinen ist. Dementsprechend wurden verschiedene biologische In-vitro- und In-vivo-Therapieverfahren zur potenziellen Verbesserung der Reinsertion entwickelt. Ziel dieses Artikels ist es, einen Überblick über die heutige Evidenz der Augmentation der Rotatorenmanschettenrekonstruktion mit Wachstumsfaktoren zu geben. Weiterhin werden mögliche zukünftige Therapieansätze diskutier

A survey of attitudes toward visual training in the Northwest

A questionnaire was sent to one third of the ophthalmologists and optometrists in Oregon and Washington . It contained questions pertaining to practitioner attitudes toward their educational backgrounds in visual training. Questions dealing with some of the controversial issues in visual training\u27s role in strabismus and amblyopia therapy were also included. Lastly, profile information and data concerning the practice in general was gathered from each survey recipient. The respondent population was divided into groups by profession and extent of VT offered. The different groups responses were then tabulated and statistically compared within and between professions

Voronoi-Delaunay analysis of normal modes in a simple model glass

We combine a conventional harmonic analysis of vibrations in a one-atomic model glass of soft spheres with a Voronoi-Delaunay geometrical analysis of the structure. ``Structure potentials'' (tetragonality, sphericity or perfectness) are introduced to describe the shape of the local atomic configurations (Delaunay simplices) as function of the atomic coordinates. Apart from the highest and lowest frequencies the amplitude weighted ``structure potential'' varies only little with frequency. The movement of atoms in soft modes causes transitions between different ``perfect'' realizations of local structure. As for the potential energy a dynamic matrix can be defined for the ``structure potential''. Its expectation value with respect to the vibrational modes increases nearly linearly with frequency and shows a clear indication of the boson peak. The structure eigenvectors of this dynamical matrix are strongly correlated to the vibrational ones. Four subgroups of modes can be distinguished