Collective treatment of the giant resonances in spherical nuclei

In a collective treatment the energies of the giant resonances are given by the boundary conditions at the nuclear surface, which is subject to vibration in spherical nuclei. The general form of the coupling between these two collective motions is given by angular-momentum and parity conservation. The coupling constants are completely determined within the hydrodynamical model. In the present treatment the influence of the surface vibrations on the total photon-absorption cross section is calculated. It turns out that in most of the spherical nuclei this interaction leads to a pronounced structure in the cross section. The agreement with the experiments in medium-heavy nuclei is striking; many of the experimental characteristics are reproduced by the present calculations. In some nuclei, however, there seem to be indications of single-particle excitations which are not yet contained in this work

Determination of residual stress in bonded wood components

Climate tests on double-layered samples were performed to detect deformation and induced stress concentrations. The paper is divided into two parts. The first presents experimental results for double-layered specimens. These specimens consisted of two wooden layers (each conditioned at a different climate before bonding) that were bonded using two different adhesives. The displacement field of the specimens was measured by means of digital fringe projection. The second part presents finite element results for two model stages using coupled thermal-mechanical analysis. For the first simple model, both orthotropic properties and the grain orientations were taken into account to investigate the behavior of the layers in principle. The results were compared to those for the experimental set-up. The improved second-stage model considers the adhesive layer between the wooden layers. The experimental and computational results of the improved simulation model are in good agreement. In the future, if inelastic material behavior is considered in a competitively superior manner, even better simulation results can be expecte

Practical considerations for in vivo MRI with higher dimensional spatial encoding

Object: This work seeks to examine practical aspects of in vivo imaging when spatial encoding is performed with three or more encoding channels for a 2D image. Materials and methods: The recently developed 4-Dimensional Radial In/Out (4D-RIO) trajectory is compared in simulations to an alternative higher-order encoding scheme referred to as O-space imaging. Direct comparison of local k-space representations leads to the proposal of a modification to the O-space imaging trajectory based on a scheme of prephasing to improve the reconstructed image quality. Data were collected using a 4D-RIO acquisition in vivo in the human brain and several image reconstructions were compared, exploiting the property that the dense encoding matrix, after a 1D or 2D Fourier transform, can be approximated by a sparse matrix by discarding entries below a chosen magnitude. Results: The proposed prephasing scheme for the O-space trajectory shows a marked improvement in quality in the simulated image reconstruction. In experiments, 4D-RIO data acquired in vivo in the human brain can be reconstructed to a reasonable quality using only 5% of the encoding matrix—massively reducing computer memory requirements for a practical reconstruction. Conclusion: Trajectory design and reconstruction techniques such as these may prove especially useful when extending generalized higher-order encoding methods to 3D image

Charging of dielectric surfaces in contact with aqueous electrolyte -- the influence of CO2_2

The charge state of dielectric surfaces in aqueous environments is of fundamental and technological importance. We use super-heterodyne light scattering in a custom-made cell to study the influence of dissolved CO$_2$ on the charging of three, chemically different surfaces. We compare an ideal, CO$_2$-free reference state to ambient CO$_2$ conditions. Systems are conditioned under conductometric control at different low concentrations of NaCl. As expected for constant charge densities, zeta-potentials drop upon increasing the salt concentration in the reference state. Presence of CO$_2$ leads to an overall lowering of zeta-potentials. Moreover, for the inorganic dielectric, the salt dependent drop is significantly weakened, and it is inversed for the organic dielectrics. We suggest that at ambient conditions, the charge state of dielectric surfaces is related to dielectric charge regulation caused by the salt concentration dependent adsorption/desorption of CO$_2$.Comment: Thoroughly revised version, extended data, improved interpretation, Main text and supplementary materials, 23 Pages, 11 figures, submitted to Angew. Chem. Int E

On the chemical and microstructural requirements for the pesting-resistance of Mo-Si-Ti alloys

In recent publications [Schliephake et al. in Intermetallics 104 (2019) 133-142 and Obert, Kauffmann & Heilmaier in Acta Materialia, 184 (2020) 132-142], an unexpected pesting-stability of fully eutectic and specific eutectic-eutectoid Mo-Si-Ti alloys was found. Several potential reasons were proposed: microstructural length scale being typically very fine due to the eutectic and eutectoid reactions, the phase distribution including the fraction of the eutectic and eutectoid regions, as well as the chemical composition of the individual phases. In the present study, we prove the Ti content to be decisive for the pesting-resistance in air at 800 °C by investigating the microstructure and oxidation behaviour of Mo-Si-Ti alloys with systematically varying nominal Ti content. A critical Ti content of 43 at% was identified. Due to the phase equilibrium, this corresponds to a local Ti content in Mo solid solution of 35 at%. Other microstructural properties such as (i) lamellar size within eutectic and eutectoid regions and (ii) volume fraction of the eutectic and eutectoid regions were demonstrated to have an insignificant influence on the pesting-resistance of the alloys. Rather, the assessment of the oxidation behaviour of the monolithic phase MoSS, which was identified to be crucial for the oxidation behaviour of the Mo-Si-Ti alloys, confirmed an improvement in oxidation behaviour with increasing Ti content

Fluctuations and Ergodicity of the Form Factor of Quantum Propagators and Random Unitary Matrices

We consider the spectral form factor of random unitary matrices as well as of Floquet matrices of kicked tops. For a typical matrix the time dependence of the form factor looks erratic; only after a local time average over a suitably large time window does a systematic time dependence become manifest. For matrices drawn from the circular unitary ensemble we prove ergodicity: In the limits of large matrix dimension and large time window the local time average has vanishingly small ensemble fluctuations and may be identified with the ensemble average. By numerically diagonalizing Floquet matrices of kicked tops with a globally chaotic classical limit we find the same ergodicity. As a byproduct we find that the traces of random matrices from the circular ensembles behave very much like independent Gaussian random numbers. Again, Floquet matrices of chaotic tops share that universal behavior. It becomes clear that the form factor of chaotic dynamical systems can be fully faithful to random-matrix theory, not only in its locally time-averaged systematic time dependence but also in its fluctuations.Comment: 12 pages, RevTEX, 4 figures in eps forma

Surgery of secondary mitral insufficiency in patients with impaired left ventricular function

<p>Abstract</p> <p>Background</p> <p>Secondary mitral insufficiency (SMI) is an indicator of a poor prognosis in patients with ischemic and dilated cardiomyopathies. Numerous studies corroborated that mitral valve (MV) surgery improves survival and may be an alternative to heart transplantation in this group of patients.</p> <p>The aim of the study was to retrospectively analyze the early and mid-term clinical results after MV repair resp. replacement in patients with moderate-severe to severe SMI and left ventricular ejection fraction (LVEF) below 35%.</p> <p>Methods</p> <p>We investigated 40 patients with poor LVEF (mean, 28 ± 5%) and SMI who underwent MV repair (n = 26) resp. replacement (n = 14) at the University Hospital Muenster from January 1994 to December 2005. All patients were on maximized heart failure medication. 6 pts. had prior coronary artery bypass grafts (CABG). Twenty-seven patients were in New York Heart Association (NYHA) class III and 13 were in class IV. Eight patients were initially considered for transplantation. During the operation, 14 pts had CABG for incidental disease and 8 had tricuspid valve repair. Follow-up included echocardiography, ECG, and physician's examination and was completed in 90% among survivors. Additionally, the late results were compared with the survival after orthotope heart transplantation (oHTX) in adults with ischemic or dilated cardiomyopathies matched to the same age and time period (148 patients).</p> <p>Results</p> <p>Three operative deaths (7.5%) occurred as a result of left ventricular failure in one and multiorgan failure in two patients. There were 14 late deaths, 2 to 67 months after MV procedure. Progress of heart failure was the main cause of death. 18 patients who were still alive took part on the follow-up examination. At a mean follow-up of 50 ± 34 (2–112) months the NYHA class improved significantly from 3.2 ± 0.5 to 2.2 ± 0.4 (p < 0.001). The LVEF improved significantly from 29 ± 5% to 39 ± 16 (p < 0.05). There were no differences in survival after MV repair or replacement. The 1-, 3-, 5-year survival rates in the study group were 80%, 58% and 55% respectively. In the group of patients after oHTX the survival was accordingly 72%, 68%, 66% (p > 0.05).</p> <p>Conclusion</p> <p>High risk mitral valve surgery in patients with cardiomyopathy and SMI offers a real mid-term alternative method of treatment of patients in drug refractory heart failure with similar survival in comparison to heart transplantation.</p