Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. I. Experimental

The experimental characterization of the current/outer potential (I/U) behavior during the electrochemical CO oxidation on Pt(100), Pt(110) and Pt(111) is used as the first step towards a thorough investigation of the processes occurring during the electrochemical formic acid oxidation. The CO study is followed by new cyclovoltammetric results during the electrochemical formic acid oxidation on the corresponding Pt single crystals. At high concentrations of formic acid, the cyclovoltammograms revealed a splitting of the large current peak observed on the cathodic sweep into two peaks whose dependence on scan rate and reverse potential was investigated. It turned out that the presence of a sufficiently large ohmic resistance R was crucial for oscillatory instabilities. Given an appropriate resistance, all three Pt surfaces were found to exhibit current oscillations at both low and high formic acid concentrations. On Pt(100) stable mixed-mode oscillations were observed. In addition, the sensitivity of the oscillations to stirring was investigated. Whereas the period-1 oscillations were found to be independent of stirring, the mixed-mode oscillations transformed into simple oscillations with stirring. The mechanism giving rise to instability and oscillations is described

Functional outcome after open and arthroscopic Bankart repair for traumatic shoulder instability

<p>Abstract</p> <p>Purpose</p> <p>Both open and arthroscopic Bankart repair are established procedures in the treatment of anterior shoulder instability. While the open procedure is still considered as the "golden standard" functional outcome is supposed to be better in the arthroscopic procedure. The aim of this retrospective study was to compare the functional outcome between open and arthroscopic Bankart repair.</p> <p>Materials and methods</p> <p>In 199 patients a Bankart procedure with suture anchors was performed, either arthroscopically in presence of an detached, but not elongated capsulolabral complex (40) or open (159). After a median time of 31 months (12 to 67 months) 174 patients were contacted and agreed to follow-up, 135 after open and 39 after arthroscopic Bankart procedure.</p> <p>Results</p> <p>Re-dislocations occurred in 8% after open and 15% after arthroscopic Bankart procedure. After open surgery 4 of the 11 re-dislocations occurred after a new adequate trauma and 1 of the 6 re-dislocations after arthroscopic surgery. Re-dislocations after arthroscopic procedure occured earlier than after open Bankart repair. An external rotation lag of 20° or more was observed more often (16%) after open than after arthroscopic surgery (3%). The Rowe score demonstrated "good" or "excellent" functional results in 87% after open and in 80% patients after arthroscopic treatment.</p> <p>Conclusion</p> <p>In this retrospective investigation the open Bankart procedure demonstrated good functional results. The arthroscopic treatment without capsular shift resulted in a better range of motion, but showed a tendency towards more frequently and earlier recurrence of instability. Sensitive patient selection for arthroscopic Bankart repair is recommended especially in patients with more than five dislocations.</p

Quaternionic Monopoles

We present the simplest non-abelian version of Seiberg-Witten theory: Quaternionic monopoles. These monopoles are associated with Spin^h(4)-structures on 4-manifolds and form finite-dimensional moduli spaces. On a Kahler surface the quaternionic monopole equations decouple and lead to the projective vortex equation for holomorphic pairs. This vortex equation comes from a moment map and gives rise to a new complex-geometric stability concept. The moduli spaces of quaternionic monopoles on Kahler surfaces have two closed subspaces, both naturally isomorphic with moduli spaces of canonically stable holomorphic pairs. These components intersect along Donaldsons instanton space and can be compactified with Seiberg-Witten moduli spaces. This should provide a link between the two corresponding theories. Notes: To appear in CMP The revised version contains more details concerning the Uhlenbeck compactfication of the moduli space of quaternionic monopoles, and possible applications are discussed. Attention ! Due to an ununderstandable mistake, the duke server had replaced all the symbols "=" by "=3D" in the tex-file of the revised version we sent on February, the 2-nd. The command "\def{\ad}" had also been damaged !Comment: LaTeX, 35 page

Stable bundles on hypercomplex surfaces

A hypercomplex manifold is a manifold equipped with three complex structures I, J, K satisfying the quaternionic relations. Let M be a 4-dimensional compact smooth manifold equipped with a hypercomplex structure, and E be a vector bundle on M. We show that the moduli space of anti-self-dual connections on E is also hypercomplex, and admits a strong HKT metric. We also study manifolds with (4,4)-supersymmetry, that is, Riemannian manifolds equipped with a pair of strong HKT-structures that have opposite torsion. In the language of Hitchin's and Gualtieri's generalized complex geometry, (4,4)-manifolds are called ``generalized hyperkaehler manifolds''. We show that the moduli space of anti-self-dual connections on M is a (4,4)-manifold if M is equipped with a (4,4)-structure.Comment: 17 pages. Version 3.0: reference adde

Approximate Hermitian-Yang-Mills structures and semistability for Higgs bundles. II: Higgs sheaves and admissible structures

We study the basic properties of Higgs sheaves over compact K\"ahler manifolds and we establish some results concerning the notion of semistability; in particular, we show that any extension of semistable Higgs sheaves with equal slopes is semistable. Then, we use the flattening theorem to construct a regularization of any torsion-free Higgs sheaf and we show that it is in fact a Higgs bundle. Using this, we prove that any Hermitian metric on a regularization of a torsion-free Higgs sheaf induces an admissible structure on the Higgs sheaf. Finally, using admissible structures we proved some properties of semistable Higgs sheaves.Comment: 18 pages; some typos correcte

In-depth mesocrystal formation analysis of microwave-assisted synthesis of LiMnPO4nanostructures in organic solution

In the present work, we report on the preparation of LiMnPO4 (lithiophilite) nanorods and mesocrystals composed of self-assembled rod subunits employing microwave-assisted precipitation with processing times on the time scale of minutes. Starting from metal salt precursors and H3PO4 as phosphate source, single-phase LiMnPO4 powders with grain sizes of approx. 35 and 65 nm with varying morphologies were obtained by tailoring the synthesis conditions using rac-1-phenylethanol as solvent. The mesocrystal formation, microstructure and phase composition were determined by electron microscopy, nitrogen physisorption, X-ray diffraction (including Rietveld refinement), dynamic light scattering, X-ray absorption and X-ray photoelectron spectroscopy, and other techniques. In addition, we investigated the formed organic matter by gas chromatography coupled with mass spectrometry in order to gain a deeper understanding of the dissolution\u2013precipitation process. Also, we demonstrate that the obtained LiMnPO4 nanocrystals can be redispersed in polar solvents such as ethanol and dimethylformamide and are suitable as building blocks for the fabrication of nanofibers via electrospinning

Solutions of the Strominger System via Stable Bundles on Calabi-Yau Threefolds

We prove that a given Calabi-Yau threefold with a stable holomorphic vector bundle can be perturbed to a solution of the Strominger system provided that the second Chern class of the vector bundle is equal to the second Chern class of the tangent bundle. If the Calabi-Yau threefold has strict SU(3) holonomy then the equations of motion derived from the heterotic string effective action are also satisfied by the solutions we obtain.Comment: 19 pages, late

Stability of vector bundles and extremal metrics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46622/1/222_2005_Article_BF01404460.pd