Force depression following a stretch-shortening cycle is independent of stretch peak force and work performed during shortening

Abstract The steady-state isometric force following active muscle shortening or lengthening is smaller (force depression; FD) or greater (residual force enhancement; RFE) than a purely isometric contraction at the corresponding length. The mechanisms behind these phenomena remain not fully understood, with few studies investigating the effects of FD and RFE in stretch-shortening cycles (SSC). The purpose of this study was to investigate the influence of RFE and peak force at the end of the stretch phase on the steady-state isometric force following shortening. Isometric thumb adduction force measurements were preceded by an isometric, a shortening contraction to induce FD, and SSCs at different stretch speeds (15°/s, 60°/s, and 120°/s). The different peak force values at the end of stretch and the different amounts of work performed during shortening did not influence the steady-state isometric force at the end of the SSC. We conclude that the FD following SSC depends exclusively on the amount of RFE established in the initial stretch phase in situations where the timing and contractile conditions of the shortening phase are kept constant

High Potassium Concentrations Nested in Epitaxial Monolayers of a Flexible Lander-Type Molecule on Ag(111)

The structural, electronic, and optical properties of organic adlayers can be tuned to a large extent by incorporating metal atoms. Naturally, the tunability of those properties is limited by the thermodynamic stability of the intercalated phases obtained and the segregation tendency, which often prevents the nesting of high metal atom concentrations in homogeneous epitaxial compound films. Here, we employ scanning tunneling microscopy and low-energy electron diffraction to investigate monolayers of the polycyclic aromatic hydrocarbon tetraphenyldibenzoperiflanthene (DBP, C64H36) epitaxially grown on Ag(111) and intercalated with potassium. This lander-type molecule contains four phenyl substituents that are nearly perpendicular to the aromatic backbone, and its flexibility enables rather complex adlayer structures. We succeeded in preparing highly ordered (mixed) monolayers with up to six potassium atoms per DBP. For increasing K concentrations, we find that DBP changes its shape from a considerably bent geometry (pristine DBP and K2DBP phases) to a molecule with a planar backbone (K6DBP phase), which is known to occur in free DBP molecules. By means of density functional theory (DFT) calculations, it is elucidated that the added K atoms adsorb underneath the molecule and thereby weaken the direct bonding channels between DBP and Ag while adding new bonding channels via the K atoms. This is accompanied by a gradually increasing charge transfer into the lowest unoccupied molecular orbital of DBP. The combination of structural data, results of different spectroscopy methods, and state-of-the-art DFT calculations leads to a comprehensive view on this rather complex host molecule-guest atom-substrate system

Ordered Superstructures of a Molecular Electron Donor on Au(111)

The molecular donor tetraphenyldibenzoperiflanthene (DBP) forms coverage-dependent superstructures on Au(111). At submonolayer coverage, the molecules align parallel to each other. They arrange in row-like structures, which exhibit a nearly rectangular primitive unit cell. By contrast, the molecular monolayer is characterized by a herringbone-type DBP arrangement spanned by an almost square unit cell containing two molecules. Both superstructures occur simultaneously in a narrow coverage range close to completion of the molecular monolayer. The adsorbate–substrate interaction is similar to other physisorbed molecular films on Au(111), but differs for the two adsorption phases as inferred from the different modification of the Au(111) surface reconstruction. Structural properties were consistently probed in real and reciprocal space by scanning tunneling microscopy and low-energy electron diffraction, respectively

Werkzeugunterstuetzte Parallelisierung von Finite-Element Anwendungen (PARFEM) Abschlussbericht

Goal of the PARFEM project was the development of software tools and methods to support the efficient treatment of large sparse matrices on parallel computers. Also new algorithms for the solution of such systems should be investigated. Portability of all components was an important aspect. Finally, the algorithms and methods should be integrated in the well-known FE software package PERMAS. The parallelization concept for PERMAS is based on the exploitation of task parallelism and not on the usual mesh partitioning (or domain decomposition) technique. The solution of the sparse system leads to the execution on many tasks which operate on independent data and which can be executed in parallel. A task graph controls the data dependency. A scheduler maps those tasks to processors and tries to achieve load balance. As an alternative to the standard direct Cholesky solver parallel preconditioned cg-solvers and parallel multifrontal solvers were implemented and investigated: - Several variants of preconditioners were tested as well as different storage schemes. The optimal variants showed very good speed-up results and the execution time was shorter than the time of the standard direct solver for a large number of processors. The integration into the PERMAS code, however, lead to some loss of scalability. - A parallel multifrontal solver was integrated and parallelized using the tools developed in the project. Speedup figures on an IBM SP2 system were satisfactory. The PARFEM project was very important for the development of the PERMAS code. The tools in PARFEM made it possible to maintain one version of the code for sequential and parallel platforms. Users can use the parallel code without additional training since the user interface was not changed at all. Since portability was very important the project used PARMACS and later MPI as portability platform. The parallel approach could even be executed on workstation clusters although, due to weak communication performance, not very efficiently. (orig.)SIGLEAvailable from TIB Hannover: F98B607+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman