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Thin Shell (thin + shell)
Selected AbstractsFormation of Gold and Silver Nanoparticle Arrays and Thin Shells on Mesostructured Silica Nanofibers,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007S. Zhang Abstract Mesostructured silica nanofibers synthesized in high yields with cetyltrimethylammonium bromide as the structure-directing agent in HBr solutions are used as templates for the assembly of Au and Ag nanoparticles and the formation of thin Au shells along the fiber axis. Presynthesized spherical Au and Ag nanoparticles are adsorbed in varying amounts onto the silica nanofibers through bifunctional linking molecules. Nonspherical Au nanoparticles with sharp tips are synthesized on the nanofibers through a seed-mediated growth approach. The number density of nonspherical Au nanoparticles is controlled by varying the amount of seeded nanofibers relative to the amount of supplied Au precursor. This seed-mediated growth is further used to form continuous Au shells around the silica nanofibers. Both the Au- and Ag-nanoparticle/silica-nanofiber hybrid nanostructures and silica/Au core/shell fibers exhibit extinction spectra that are distinct from the spectra of Au and Ag nanoparticles in solution, indicating the presence of new surface plasmon resonance modes in the silica/Au core/shell fibers and surface plasmon coupling between closely spaced metal nanoparticles assembled on silica nanofibers. Spherical Au- and Ag-nanoparticle/silica-nanofiber hybrid nanostructures are further used as substrates for surface-enhanced Raman spectroscopy, and the enhancement factors of the Raman signals obtained on the Ag-nanoparticle/silica-nanofiber hybrid nanostructures are 2,×,105 for 4-mercaptobenzoic acid and 4-mercaptophenol and 7,×,107 for rhodamine,B isothiocyanate. These hybrid nanostructures are therefore potentially useful for ultrasensitive chemical and biological sensing by using molecular vibrational signatures. [source] An Euler system source term that develops prototype Z-pinch implosions intended for the evaluation of shock-hydro methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2009J. W. Banks Abstract In this paper, a phenomenological model for a magnetic drive source term for the momentum and total energy equations of the Euler system is described. This body force term is designed to produce a Z-pinch like implosion that can be used in the development and evaluation of shock-hydrodynamics algorithms that are intended to be used in Z-pinch simulations. The model uses a J × B Lorentz force, motivated by a 0-D analysis of a thin shell (or liner implosion), as a source term in the equations and allows for arbitrary current drives to be simulated. An extension that would include the multi-physics aspects of a proposed combined radiation hydrodynamics (rad-hydro) capability is also discussed. The specific class of prototype problems that are developed is intended to illustrate aspects of liner implosions into a near vacuum and with idealized pre-fill plasma effects. In this work, a high-resolution flux-corrected-transport method implemented on structured overlapping meshes is used to demonstrate the application of such a model to these idealized shock-hydrodynamic studies. The presented results include an asymptotic solution based on a limiting-case thin-shell analytical approximation in both (x, y) and (r, z). Additionally, a set of more realistic implosion problems that include density profiles approximating plasma pre-fill and a set of perturbed liner geometries that excite a hydro-magnetic like Rayleigh,Taylor instability in the implosion dynamics are demonstrated. Finally, as a demonstration of including and evaluating multiphysics effects in the Euler system, a simple radiation model is included and self-convergence results for two types of (r, z) implosions are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] Predatory boreholes in Tournaisian (Lower Carboniferous) spiriferid brachiopodsLETHAIA, Issue 3 2009BERNARD MOTTEQUIN A brachiopod fauna from the uppermost part of the Tournaisian Tournai Formation (Belgium) contains an undetermined species of Crurithyris (Spiriferida, Ambocoeliidae), which displays numerous bored shells. About 8% of the 432 specimens with conjoined valves display single, small (, 1 mm) boreholes, which are smooth-sided, cylindrical or weakly conical, circular to slightly elliptical in plan view, perpendicular to the shell surface and generally complete. Of the 35 bored articulated specimens, 27 were drilled on the ventral valve. Most of the boreholes are located in the posterior half of the shell, and no case of edge-drilling has been observed. The boreholes were drilled by a predator, or possibly a parasite, which selected individuals greater than 2.5 mm long. Crurithyris sp. may have represented an attractive (in terms of energy cost) and easy target for a small-sized predator because of its thin shell and ornament of minute spines. [source] The role of suture complexity in diminishing strain and stress in ammonoid phragmoconesLETHAIA, Issue 1 2008FABIO VITTORIO DE BLASIO Several hypotheses have been put forward to explain the sinuosity and complexity of suture lines in Ammonoidea. At present, the two principal opponent views maintain either that high complexity was a requisite to reinforce the shell in response to hydrostatic pressure, or that complexity augmented the attachment area for muscles. By using finite element calculations and analytical estimates of simplified ammonoid shell geometries, it is shown that complex suture lines reduced dramatically the strain and the stress in the phragmocone. The calculations lend support to the hypothesis that high sinuosity is an evolutionary response to external pressure. Additionally, it is found that without complex septa, the inward deformation of an ammonoid with thin shell would cause it to shrink in response to pressure and to lose buoyancy by a non-negligible amount. [source] Stellar wind/ISM shocks in gravitational potentialsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007A. Hubbard ABSTRACT The geometry of stellar wind bow shocks has been solved analytically in the thin shell, no gravity limit by Wilkin. We determine when, where and how gravity influences those results. In particular, we find that gravity strongly influences weak wind shocks, potentially prevents steady shocks and even pulls shocks back on to the star. [source] Synthesis, characterization, and its PL dynamics of colloidal type II CdTe/CdSe nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Masaru Oda Abstract We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (,1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spontaneous emission from semiconductor nanocrystals in coupled spherical microcavitiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2005Yu. P. Rakovich Abstract We report on the coherent coupling of whispering gallery modes (WGM) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions the splitting of the WGM resonances originating from bonding and anti-bonding branches of the photonic states is observed and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A non-linear triangular curved shell elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 4 2004T. Wenzel Abstract The objective of this paper is to present and test a simple triangular finite shell element that uses five degrees of freedom at each node. The element is characterized by three position vectors and three unit directors. It depicts the plane stress state version of the element presented (Comput. Struct. 1989; 32(2):379). The element is of the ANS-type (assumed natural strain (J. Appl. Mech. 1981; 48:587). All strains inside the element contain dot products of the six actual element nodal vectors. The construction of the element also allows non-linear material behaviour. Since an enhancement of the membrane strains by the EAS (enhanced assumed strain method) is not possible inside a three node triangle element, the membrane strains perform poor. But via the DKT (discrete Kirchhoff theory) the three directors reveal an excellent bending behaviour for thin shells. The main concern of this paper is to test, if superimposing the CST (constant srain) with the classic DKT leads to good results in standard benchmark tests. Copyright © 2004 John Wiley & Sons, Ltd. [source] A quadrilateral thin shell element based on area co-ordinate for explicit dynamic analysisINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2003Zhu Yaqun Abstract The mechanism of explicit dynamic finite element method for shell deformation analysis and the key influential factors on computation precision and efficiency are briefly described. A new area co-ordinate-based quadrilateral thin shell element is put forward and combined with the co-rotational theory and velocity strain formulation in the shell stress and strain analysis. A new local co-ordinate system is constructed in which normal vector is much closer to the material axis. The more accurate integration can be obtained and the hourglass control is avoided. Therefore simulation precision and efficiency of thin shells are improved. Copyright © 2003 John Wiley & Sons, Ltd. [source] A meshfree thin shell method for non-linear dynamic fractureINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2007T. Rabczuk Abstract A meshfree method for thin shells with finite strains and arbitrary evolving cracks is described. The C1 displacement continuity requirement is met by the approximation, so no special treatments for fulfilling the Kirchhoff condition are necessary. Membrane locking is eliminated by the use of a cubic or quartic polynomial basis. The shell is tested for several elastic and elasto-plastic examples and shows good results. The shell is subsequently extended to modelling cracks. Since no discretization of the director field is needed, the incorporation of discontinuities is easy to implement and straightforward. Copyright © 2007 John Wiley & Sons, Ltd. [source] Synthesis, characterization, and its PL dynamics of colloidal type II CdTe/CdSe nanocrystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Masaru Oda Abstract We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (,1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Clonal selection in ,Uzunmusa' hazelnutPLANT BREEDING, Issue 4 2003Abstract Clonal selection was practised in ,Uzunmusa' hazelnut over the past 3 years (1999-2001) to select the highest quality types. Based on an initial assessment of a total of 102 types, 45 were selected for further study. The best types were selection numbers (SN) 397 and 570. The two selected clones have very good characteristics and seem to be superior to the standard clone. The clones had a higher kernel percentage (62.72%), a higher number of nuts per cluster (5.5), thinner shells (0.75 mm) and heavier nuts (2.34 g). On the other hand, the clones seem to be very suitable for the nut industry because of their oil content and size. These types have very thin shells which are suitable for in-shell market. [source] Mechanical Behavior and Stability of the Internal Membrane of the InCor Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 11 2001Pedro Baroni Da Costa Teixeira Abstract: This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths. [source] | |||||||||||||