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Spherical Shell (spherical + shell)
Selected AbstractsImperfection Sensitivity and Limit Loads of Spherical Shells under Radial PressurePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Jens Pontow The evaluation of the imperfection sensitivity of shell structures and the estimation of their limit loads are widely discussed phenomena. The perturbation energy concept according to Dinkler et al. [1], [2] enables to assess the imperfection sensitivity of shell structures by means of an energy value, the perturbation energy. A buckling criterion may be developed from the comparison between the perturbation energy and experimental data. This paper focuses on the imperfection sensitivity and limit loads of spherical shells of revolution under radial pressure. The investigations include the influence of the meridional angle and different types of boundary conditions. By comparing the numerical results with the German design rule DIN 18800, critical values for the perturbation energy are derived to predict the limit loads. These critical values for the perturbation energy allow to judge whether the German design rule DIN18800 predicts the limit loads of spherical shells under external pressure with varying meridional angles and different boundary conditions with the same reliability in respect of the perturbation energy. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic field annihilators: invisible magnetization at the magnetic equatorGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003S. Maus SUMMARY Some distributions of magnetization give rise to magnetic fields that vanish everywhere above the surface, rendering these distributions of magnetization completely invisible. They are the annihilators of the magnetic inverse problem. Known examples are the infinite sheet with constant magnetization and the spherical shell of constant susceptibility magnetized by an arbitrary internal field. Here, we show that remarkably more interesting annihilators exist for the Earth's dipole-dominated inducing field. Indeed, any susceptibility profile along the magnetic equator can be extended north/south into an annihilator. Consequently, the induced magnetization along the magnetic equator is entirely undetermined by the visible magnetic field. In contrast to the Backus effect, this ambiguity persists even if the full magnetic vector field is known. [source] Dual Templating Synthesis of Mesoporous Titanium Nitride Microspheres,ADVANCED MATERIALS, Issue 31 2009Jin Ho Bang Hierarchically nanostructured titanium nitride is prepared via a novel and facile in situ dual templating approach. No prestructured templates are necessary; instead, a template is generated in situ during the synthesis from a liquid core and the resulting spherical shell, and the template is removed in the final heating without any additional chemical etching. [source] Sodium MRI using a density-adapted 3D radial acquisition techniqueMAGNETIC RESONANCE IN MEDICINE, Issue 6 2009Armin M. Nagel Abstract A density-adapted three-dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k -space sampling than conventional three-dimensional projection reconstruction sequences. The gradients of the density-adapted three-dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k -space is constant. Due to hardware restrictions, an inner sphere of k -space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three-dimensional projection reconstruction sequence trajectories and an enhanced signal-to-noise ratio (SNR) efficiency akin to the commonly used three-dimensional twisted projection imaging trajectories. Benefits for low SNR applications, when compared to conventional three-dimensional projection reconstruction sequences, are demonstrated with the example of sodium imaging. In simulations of the point-spread function, the SNR of small objects is increased by a factor 1.66 for the density-adapted three-dimensional radial projection reconstruction pulse sequence sequence. Using analytical and experimental phantoms, it is shown that the density-adapted three-dimensional radial projection reconstruction pulse sequence allows higher resolutions and is more robust in the presence of field inhomogeneities. High-quality in vivo images of the healthy human leg muscle and the healthy human brain are acquired. For equivalent scan times, the SNR is up to a factor of 1.8 higher and anatomic details are better resolved using density-adapted three-dimensional radial projection reconstruction pulse sequence. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Growth, clustering and morphology of intermetallic alloy core-shell nanodropletsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008A. C. Cefalas Abstract Sm,Fe,Ta,N core-shell (CS) nanospheroids were fabricated from hot liquefied nanodroplets by 157 nm pulse laser deposition in nitrogen gas. The Sm13.8Fe82.2Ta4.0 intermetallic alloy was used as the target. At low laser energy (20 mJ), spherical CS of 1,35 nm radius were fabricated on a Si/Ta substrate forming uniform films. The small nanodroplets were grown in the plume from the gas phase, and the larger ones (>50 nm radius) from the target's hydrodynamic ejection. The critical radius of the droplets and their surface energy per unit area was found to be 7.5 nm and 3.8 ,J/cm2 respectively. A number of CS solidified in the plume and consist of 2.5,5 nm radius crystalline nucleus surrounded by a <35 nm radius amorphous spherical shell. This structure prevents the oxidization of the crystalline nucleus because oxidization is confined on the surface of the CS. Furthermore, multi-crystalline nanodomains (embryos) were identified in a single CS from both homogeneous and heterogeneous nucleation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An icosahedral assembly of the light-harvesting chlorophyll a/b protein complex from pea chloroplast thylakoid membranesACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2004Tomoya Hino When the light-harvesting chlorophyll a/b protein complex (LHC-II) from pea thylakoid membranes is co-crystallized with native lipids, an octahedral crystal that exhibits no birefringence is obtained. Cryogenic electron micrographs of a crystal edge showed the crystal to be made up of hollow spherical assemblies with a diameter of 250,Å. X-ray diffraction data at 9.5,Å resolution revealed the spherical shell of LHC-II to have icosahedral symmetry. A T = 1 icosahedral model of LHC-II, in which the stromal surface of the protein faces outward, was constructed using the previously reported structure of the LHC-II trimer [Kühlbrandt et al. (1994), Nature (London), 367, 614,621]. The present result shows the first example of a well ordered three-dimensional crystal of icosahedral proteoliposomes. [source] Imperfection Sensitivity and Limit Loads of Spherical Shells under Radial PressurePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Jens Pontow The evaluation of the imperfection sensitivity of shell structures and the estimation of their limit loads are widely discussed phenomena. The perturbation energy concept according to Dinkler et al. [1], [2] enables to assess the imperfection sensitivity of shell structures by means of an energy value, the perturbation energy. A buckling criterion may be developed from the comparison between the perturbation energy and experimental data. This paper focuses on the imperfection sensitivity and limit loads of spherical shells of revolution under radial pressure. The investigations include the influence of the meridional angle and different types of boundary conditions. By comparing the numerical results with the German design rule DIN 18800, critical values for the perturbation energy are derived to predict the limit loads. These critical values for the perturbation energy allow to judge whether the German design rule DIN18800 predicts the limit loads of spherical shells under external pressure with varying meridional angles and different boundary conditions with the same reliability in respect of the perturbation energy. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Convective dynamos in spherical wedge geometryASTRONOMISCHE NACHRICHTEN, Issue 1 2010P.J. Käpylä Abstract Self-consistent convective dynamo simulations in wedge-shaped spherical shells are presented. Differential rotation is generated by the interaction of convection with rotation. Equatorward acceleration and dynamo action are obtained only for sufficiently rapid rotation. The angular velocity tends to be constant along cylinders. Oscillatory large-scale fields are found to migrate in the poleward direction. Comparison with earlier simulations in full spherical shells and Cartesian domains is made (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Differential rotation and meridional circulation in global models of solar convectionASTRONOMISCHE NACHRICHTEN, Issue 10 2007M.S. MieschArticle first published online: 27 DEC 200 Abstract In the outer envelope of the Sun and in other stars, differential rotation and meridional circulation are maintained via the redistribution of momentum and energy by convective motions. In order to properly capture such processes in a numerical model, the correct spherical geometry is essential. In this paper I review recent insights into the maintenance of mean flows in the solar interior obtained from high-resolution simulations of solar convection in rotating spherical shells. The Coriolis force induces a Reynolds stress which transports angular momentum equatorward and also yields latitudinal variations in the convective heat flux. Meridional circulations induced by baroclinicity and rotational shear further redistribute angular momentum and alter the mean stratification. This gives rise to a complex nonlinear interplay between turbulent convection, differential rotation, meridional circulation, and the mean specific entropy profile. I will describe how this drama plays out in our simulations as well as in solar and stellar convection zones. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||