Single Shells Research Articles

Coupled form-finding and grid optimization approach for single layer grid shells

This paper demonstrates a novel two-phase approach to the preliminary structural design of grid shell structures, with the objective of material minimization and improved structural performance. The two-phase approach consists of: (i) a form-finding technique that uses dynamic relaxation with kinetic damping to determine the global grid shell form, (ii) a genetic algorithm optimization procedure acting on the grid topology and nodal positions (together called the ‘grid configuration’ in this paper). The methodology is demonstrated on a case study minimizing the mass of three 24×24m grid shells with different boundary conditions. Analysis of the three case studies clearly indicates the benefits of the coupled form-finding and grid configuration optimization approach: material mass reduction of up to 50% is achieved.

Stability and Optical Properties of ZnO Nanoparticles Capped by ZnS

ZnO nanoparticles were grown by decomposing of zinc acetate dehydrate. ZnS shells formed on ZnO nanoparticle surfaces in Na2S aqueous solution with the help of ultrasonic at room temperature. The nanoparticle structures and optical properties were characterized. Stability of the shells and effects of capping on the nanoparticle optical properties were studied. Luminescence of the nanoparticles was sensitive to the shell structures and excitation laser density. Single crystal shells could enhance ZnO nanoparticle emission more obviously under higher excitation, but the suppression of the green emission depended on the shell thickness. Single crystal shell could suppress while nanoparticle shells enhance the interface defect vibration. ZnS nanoparticle shells were unstable under exposure to laser light.

Effect of Multiple Delamination on Free Vibration Behaviour of Quasi-Isotropic Composite Conical Shells

In this paper, a finite element method is employed to investigate the free vibration characteristics of single and multiple delaminated graphite-epoxy quasi-isotropic composite conical shells. The generalized dynamic equilibrium equation is derived from Lagrange’s equation of motion neglecting Coriolis effect for moderate rotational speeds. The formulation is based on Mindlin’s theory considering eight-noded isoparametric plate bending element. The multipoint constraint algorithm is employed to ensure the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front. The QR iteration algorithm is utilized for solution of standard eigen value problem. Finite element codes are developed to obtain the natural frequencies of single and multiple delaminated quasi-isotropic composite conical shells. The mode shapes for a typical laminate configuration are also depicted. Numerical results obtained are the first known values which could serve as reference solutions for the future investigators.

Oxide–oxide nanojunctions in coaxial SnO2/TiO2, SnO2/V2O3 and SnO2/(Ti0.5V0.5)2O3 nanowire heterostructures

A single-crystalline shell based on titanium and vanadium binary oxides with karelianite structure (Ti1−xVx)2O3 was successfully deposited onto SnO2 nanowires by sequential chemical vapor deposition (CVD). In comparison to single titanium or vanadium oxide shells, the binary Ti–V metal oxide overlayer overcomes the problems related to lattice mismatch and thermochemical stability, which usually take place in coaxial oxide–oxide heterostructures due to the atomic diffusion between core and shell. The modulation of the titanium content in the binary (Ti1−xVx)2O3 karelianite shell results in a lower mismatch (∼1.5%) and improves the epitaxial relationship with the rutile lattice of SnO2 core nanowires. Therefore, the presence of defects such as dislocations and strain fields, which in principle limit the carrier transport properties affecting the electrical, optical and photocatalytic performance, is strongly reduced. Atomic model simulations confirm that structural characteristics related to lattice mismatch and strain accommodation at the heterojunction influence the thermochemical stability and were corroborated by detailed high resolution transmission electron microscopy analyses of the different core–shell systems.

Epifauna dynamics at an offshore foundation – Implications of future wind power farming in the North Sea

In the light of the introduction of thousands of large offshore wind power foundations into the North Sea within the next decades, this manuscript focuses on the biofouling processes and likely reef effects. The study explores the macrozoobenthos (biofouling) colonization at an offshore platform which is comparable to offshore wind turbine foundations. A total of 183 single samples were taken and the parameters water depth and time were considered comparing biofouling masses and communities. The blue mussel Mytilus edulis, Anthozoa and the Amphipoda Jassa spp. were the dominant species. The community from the 1 m zone and those from the 5 and 20–28 m zones can clearly be differentiated. The 10 m zone community represents the transition between the M. edulis dominated 1 m and 5 m zones and the Anthozoa dominated 20–28 m zone. In the future offshore wind farms, thousands of wind turbine foundations will provide habitat for a hard bottom fauna which is otherwise restricted to the sparse rocky habitats scattered within extensive sedimentary soft bottoms of the German Bight. However, offshore wind power foundations cannot be considered natural rock equivalents as they selectively increase certain natural hard bottom species. The surface of the construction (1280 m²) was covered by an average of 4300 kg biomass. This foundation concentrates on its footprint area (1024 m²) 35 times more macrozoobenthos biomass than the same area of soft bottom in the German exclusive economic zone (0.12 kg m−2), functioning as a biomass hotspot. Concerning the temporal biomass variation, we assume that at least 2700 kg biomass was exported on a yearly basis. 345 × 104 single mussel shells of different sizes were produced during the study period. It is anticipated that the M. edulis abundance will increase in the North Sea due to the expansion of the offshore wind farm development. This will result in the enhanced production of secondary hard substrate (mussel shells) and its associated fauna and will intensify filtration rates of the seawater. This predicted ecological system change is coined the ’Mytilusation’ of the German Bight.

Boron, carbon, and oxygen isotopic composition of brachiopod shells: Intra-shell variability, controls, and potential as a paleo-pH recorder

The boron isotopic composition of biogenic carbonates has been used to reconstruct seawater pH and atmospheric pCO2 on Pleistocene and Cenozoic timescales. Because of their excellent preservation and extensive fossil record throughout the Phanerozoic, brachiopods are a promising candidate for extending the boron isotope record as far back as the Cambrian. Here we present stable carbon, oxygen, and boron isotopic measurements of modern Terebratulid brachiopod calcite in comparison with environmental pH estimates calculated from oceanographic data. Geochemical transects along the length and depth of single shells confirm previously published trends in carbon and oxygen isotopic composition. In the outer surface (primary and outermost secondary layers), δ11B covaries with δ13C and δ18O, with more negative values in the outer and more positive values in the middle of the shell. However, δ11B deviates from δ13C and δ18O in the inner part of the secondary layer, where the δ13C and δ18O values are more positive and near equilibrium, whereas δ11B returns to more negative values. A comparison of different specimens of the species Terebratalia transversa (Sowerby, 1846) and Laqueus californianus (Küster, 1844) microsampled from the middle part of the fibrous secondary layer demonstrates a clear correlation to ambient pH with a sensitivity similar to other empirical calibration curves for cultured planktic foraminifers, corals, and inorganic calcite. The relationship in other species is less clear and significantly offset, necessitating the use of a single species or a cross-calibration method with other species in paleo-pH reconstructions.

Diversity of Bivalve Molluscs in the St Lucia Estuary, with an Annotated and Illustrated Checklist

Bivalves play a vital role in estuarine ecosystems, but are vulnerable to rapid or prolonged changes in the physico-chemical environment. The St Lucia estuarine lake exhibits sub-decadal changes from wet to dry periods, resulting in fluctuating physico-chemical conditions. This paper represents a census of the diversity of bivalve molluscs in this estuary, emphasising changes associated with climate-induced hydrological states. Twenty-four bivalve species were recorded within St Lucia between 1925 and 2011. Twelve that had not been reported previously from St Lucia in the literature were encountered during the present study. These are Anadara natalensis, Anomia achaeus, Arcuatula capensis, Chambardia wahlbergi, Corbicula fluminalis, Dendostrea sandvichensis, Fulvia fragilis, Mactra cuneata, Martesia striata, Meretrix meretrix, Saccostrea forskahlii and Tellina s.l. bertini. Single shells of another two previously unrecorded species, Anodontia edentula and Timoclea lavrani, were also found, although these may have been introduced dead from the ocean through tidal exchange. Meretrix meretrix, an unexpected yet abundant species, represents a new record for South African waters, but the timing and mode of its introduction into the estuary remain unresolved. Extremely large numbers (>100 ind.m-2)of dead specimens of Barnea manilensis were observed in 2011 along the western shoreline of the estuarine lake, which indicates that the species was a major role-player in the settling of suspended silt within the system. Currently, this function appears to be fulfilled only by Solen cylindraceus. Apart from this species, Brachidontes virgiliae, Dosinia hepatica, Macomopsis moluccensis, Salmacoma litoralis and an undescribed Tellina sp. (reported here as T. cf. rousi) are the only bivalves that were found alive in St Lucia during the latest survey, in March 2011.

Diversity of Bivalve Molluscs in the St Lucia Estuary, with an Annotated and Illustrated Checklist

ABSTRACT Bivalves play a vital role in estuarine ecosystems, but are vulnerable to rapid or prolonged changes in the physico-chemical environment. The St Lucia estuarine lake exhibits sub-decadal changes from wet to dry periods, resulting in fluctuating physico-chemical conditions. This paper represents a census of the diversity of bivalve molluscs in this estuary, emphasising changes associated with climate-induced hydrological states. Twenty-four bivalve species were recorded within St Lucia between 1925 and 2011. Twelve that had not been reported previously from St Lucia in the literature were encountered during the present study. These are Anadara natalensis, Anomia achaeus, Arcuatula capensis, Chambardia wahlbergi, Corbicula fluminalis, Dendostrea sandvichensis, Fulvia fragilis, Mactra cuneata, Martesia striata, Meretrix meretrix, Saccostrea forskahlii and Tellina s.l. bertini. Single shells of another two previously unrecorded species, Anodontia edentula and Timoclea lavrani, were also found, althou...

Hybrid systems based on living organisms, polymers, and nanoparticles

The review sums up the achievements of recent years in the field of hybrid systems containing living microorganisms and single mammalian cells, polymers, nanoparticles, and inorganic bio-mimetic shells. The authors paid special attention to the methods of creating and classifying these systems. Several approaches to the formation of hybrid systems were emphasized, including the direct deposition of nanomaterials onto the surface of organisms, the functionalization of organisms by thin polymer films, the polymer-mediated immobilization of nanomaterials, and biomimetic encapsulation. Methods for the practical applications of hybrid systems are suggested. The final chapter describes, approaches to the formation of multicellular clusters of microorganism single cells via the integration of the cells into a synthetic polymer matrix on a structured surface or their three-dimensional self-assembling onto various templates.

Preparation of Various Prussian Blue Analogue Hollow Nanocubes with Single Crystalline Shells

AbstractWe report the preparation of monocrystalline Prussian blue (PB) analogue hollow nanocubes by applying a controlled chemical etching method with assistance of polyvinylpyrrolidone (PVP). The hollow particles obtained possess the original single‐crystalline structures, with retention of the high surface areas. Our synthetic route based on chemical etching is quite simple, and it can be scaled up for mass production.

Spiky Gold Nanoshells: Synthesis and Enhanced Scattering Properties

Gold nanoshells covered with sharp rods called “spiky gold nanoshells” are synthesized by employing a silver-assisted seed-growth method for heterogeneous nanoparticle syntheses at polymer/water interfaces. It is found that silver ions in the growth solution play an important role in forming uniform gold shells as well as regulating the surface morphology. The optical properties of spiky gold nanoshells are investigated by single-particle scattering measurements, single-particle surface-enhanced Raman scattering measurements, and finite-difference time-domain modeling. The scattering intensities from isolated spiky nanoshells are significantly enhanced compared to those of conventional smooth shells. Moreover, due to the abundant hot spots on spiky nanoshells, the SERS signal is readily observed from single spiky shells with a very small intensity variation (35%), whereas there is no detectable signal from isolated smooth shells. These results demonstrate that our synthetic method provides a straightforwa...

The influence of initial geometric imperfections on the buckling load of single and double curvature concrete shells

Several traditional methods are available to address the problem of instability in concrete shells, usually by means of curves representing the influence of the initial geometric imperfections in the buckling load for simple geometries (spheres and cylinders). Although some revisions of these methods have been made, new curves for other geometries have not been stated. In this study, the imperfection sensitivity factor in shell structures with different geometries (spherical dome, barrel vault, and double-curvature ruled surface) is determined graphically. This graphical method is useful to the designer in the early stages of the design of shell structures when dimensioning.

Conditions of Mytilus edulis extracellular body fluids and shell composition in a pH‐treatment experiment: Acid‐base status, trace elements and δ11B

Mytilus edulis were cultured for 3 months under six different seawater pCO2 levels ranging from 380 to 4000 μatm. Specimen were taken from Kiel Fjord (Western Baltic Sea, Germany) which is a habitat with high and variable seawater pCO2 and related shifts in carbonate system speciation (e.g., low pH and low CaCO3 saturation state). Hemolymph (HL) and extrapallial fluid (EPF) samples were analyzed for pH and total dissolved inorganic carbon (CT) to calculate pCO2 and [HCO3−]. A second experiment was conducted for 2 months with three different pCO2 levels (380, 1400 and 4000 μatm). Boron isotopes (δ11B) were investigated by LA‐MC‐ICP‐MS (Laser Ablation–Multicollector–Inductively Coupled Plasma–Mass Spectrometry) in shell portions precipitated during experimental treatment time. Additionally, elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF of specimen from the second experiment were measured via ICP‐OES (Inductively Coupled Plasma–Optical Emission Spectrometry). Extracellular pH was not significantly different in HL and EPF but systematically lower than ambient water pH. This is due to high extracellular pCO2 values, a prerequisite for metabolic CO2 excretion. No accumulation of extracellular [HCO3−] was measured. Elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF increased slightly with pH which is in accordance with increasing growth and calcification rates at higher seawater pH values. Boron isotope ratios were highly variable between different individuals but also within single shells. This corresponds to a high individual variability in fluid B/Ca ratios and may be due to high boron concentrations in the organic parts of the shell. The mean δ11B value shows no trend with pH but appears to represent internal pH (EPF) rather than ambient water pH.

Continuous hollow TiO2 structures with three-dimensional interconnected single crystals and large pore mesoporous shells for high-performance lithium-ion batteries

A continuous hollow TiO2 structure with three-dimensional (3D) interconnected anatase single crystals self-assembled into compact large pore mesoporous shells had been fabricated in this paper. The as-obtained hierarchically micro/nano-structured materials, denoted as CTAB–TiO2, are simply prepared via a hydrothermal method with the assistance of cetyltrimethylammonium bromide (CTAB) micelles. The results show that both CTAB and the thermal treatment played a key role in forming a continuous hollow micro/nano-structure with large mesopores. It has been found that the rate properties and cyclic performance of lithium-ion batteries based on annealed CTAB–TiO2, denoted as A-CTAB–TiO2, were greatly enhanced compared to the CTAB–TiO2 electrodes, this improvement was largely attributed to the reduction of the interfacial resistance due to nanocrystal–nanocrystal contact throughout the electrode films and the increased Li-ion diffusion properties of uniform large pore mesoporous shells (12.8 nm). The low-cost synthesis and excellent electrode properties of the continuous interconnected single crystals with a large pore mesoporous architecture could provide a new direction for developing higher-performance lithium storage electrodes.

The Finite Analysis of the Piezoelectric Shell Stack Transducer

Novel piezoelectric shell stack in radial direction had been developed. The shell stack was composed of inner and outer shells which are bonded with each other by epoxy resin. The vibration and electromechanical characteristics of the piezoelectric shell stack were modeled and simulated by Finite Element Analysis (FEA). The send voltage response (SV) of both single and double shells under water were computed. Particularly the analytical results of shell stack presented in resonance frequency varying with the radius and thickness had been compared with experiments. The computations show agreement with the experimental results, and the errors are less than 1.28%.

Epitaxial TiO2/SnO2 core–shell heterostructure by atomic layer deposition

Taking TiO2/SnO2 core–shell nanowires (NWs) as a model system, we systematically investigate the structure and the morphological evolution of this heterostructure synthesized by atomic layer deposition/epitaxy (ALD/ALE). All characterizations, by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction and Raman spectra, reveal that single crystalline rutile TiO2 shells can be epitaxially grown on SnO2 NWs with an atomically sharp interface at low temperature (250 °C). The growth behavior of the TiO2 shells highly depends on the surface orientations and the geometrical shape of the core SnO2 NW cross-section. Atomically smooth surfaces are found for growth on the {110} surface. Rough surfaces develop on {100} surfaces due to (100) − (1 × 3) reconstruction, by introducing steps in the [010] direction as a continuation of {110} facets. Lattice mismatch induces superlattice structures in the TiO2 shell and misfit dislocations along the interface. Conformal epitaxial growth has been observed for SnO2 NW cores with an octagonal cross-section ({100} and {110} surfaces). However, for a rectangular core ({10} and {010} surfaces), the shell also derives an octagonal shape from the epitaxial growth, which was explained by a proposed model based on ALD kinetics. The surface steps and defects induced by the lattice mismatch likely lead to improved photoluminescence (PL) performance for the yellow emission. Compared to the pure SnO2 NWs, the PL spectrum of the core–shell nanostructures exhibits a stronger emission peak, which suggests potential applications in optoelectronics.

α-Fe2O3 hollow structures: formation of single crystalline thin shells

Novel α-Fe(2)O(3) hollow polyhedra structures with single crystalline thin shells were synthesized by a facile one-pot template-free hydrothermal method, which exhibit high efficiency on the decoloration of RhB aqueous solution in the presence of H(2)O(2). Based on experimental analysis, a plausible growth process is proposed.

Comment on “A study on Holocene foraminifera from the Aral Sea and West Siberian lakes and its implication for migration pathways” by Riedel F., Kossler A., Tarasov P. and Wünnemann B. (Quaternary International 229, 105–111)

Riedel et al. (2011) discuss the processes of foraminifera transportation and colonization, and their implication to the Holocene history ofWestern Siberia and Aral Sea using work by Gusskov et al. (2008) and other papers (see below) as case studies. Upon acquaintance with the arguments presented and their evaluation, it is necessary to give comments and replies to Riedel et al. (2011) due to their views and misrepresentation of our work (see Gusskov et al., 2008). There are two main topics which deserve discussion: 1) transport of living foraminifera by birds and colonization of lacustrine environments; and 2) geological history of the Caspian and Aral seas in relation to the spread of benthic organisms, primarily foraminifera and mollusks. The major issue raised by Riedel et al. (2011) is the possibility of foraminifera transport by birds as concluded (Riedel et al., 2011:109). This is based on studies by different authors (Resig, 1974; Cann and De Deckker, 1981; Patterson, 1987; Almogi-Labin et al., 1992, 1995; Perthuisot, 1995; Boudreau et al., 2001; Abu-Zied et al., 2007; Wennrich et al., 2007; see Riedel et al., 2011:105). In our opinion, the migration of foraminifera by water birds is unproven. First, nobody has ever observed the transport of living foraminifera by waterfowl, to the best of our knowledge, and this is in accord with Riedel et al. (2011:109). Second, the examples of foraminifera existence in inland lakes and other reservoirs used by Riedel et al. (2011) are not convincing, and they can be sub-divided into two groups. As for the first group, in the references cited the transportation by birds of foraminifera is not discussed; these are Resig (1974), and Cann and De Deckker (1981). In the second group, the authors are convinced that birds transported foraminifera; however, they do not consider other ways of their appearance in lakes and other basins, and this should be briefly commented on. Information presented by Patterson (1987) shows that the foraminifera complex in Lake Tecopa (California, USA) does not represent a natural assemblage. This is supported by the distribution of foraminifera in the lake section; the majority of species are represented by single shells. The degree of shell preservation is quite poor, and is most

Mg/Ca ratios of single planktonic foraminifer shells and the potential to reconstruct the thermal seasonality of the water column

Mg/Ca ratios of surface and subsurface dwelling foraminifera provide valuable information about the past temperature of the water column. Planktonic foraminifera calcify over a period of weeks to months. Therefore, the range of Mg/Ca temperatures obtained from single specimens potentially records seasonal temperature changes. We present solution‐derived Mg/Ca ratios for single specimens of the planktonic foraminifera species Globigerinoides ruber (pink), Globigerinoides ruber (white), and Globorotalia inflata from a sediment trap off northwest Africa (20°45.6′N, 18°41.9′W). Cleaning of single specimens was achieved using a flow‐through system in order to prevent sample loss. Mg/Ca ratios of surface dwelling G. ruber (pink) show strong seasonality linked to sea surface temperature. Mg/Ca ratios of G. ruber (white) do not show such seasonality. Subsurface dwelling G. inflata flux is largest during the main upwelling season, but Mg/Ca ratios reflect annual temperatures at intermediate water depths. The sediment trap time series suggests that changes in the range of Mg/Ca ratios exhibited by single specimens of G. ruber (pink) and G. inflata from the sedimentary record should provide information on the past temperature range under which these species calcified. Statistical analysis suggests detectable changes in the Mg/Ca range are ≥0.80 mmol/mol (G. ruber (pink)) and ≥0.34 mmol/mol (G. inflata). For G. ruber (pink), such changes would indicate changes in the seasonal sea surface temperature range >4°C or a shift in the main calcification and reproductive period. For G. inflata, such changes would indicate >1.7°C changes in the thermocline temperature or a change in the depth habitat.

New magic numbers in the continent of isotopes

Recently, Lucas has explained that the magic numbers are really composites of several sub shells filling, rather than being single shells. In addition, his theory leads to the conclusion that protons and neutrons fill sub shells differently, because the protons tend to occupy outer shells first, while neutrons tend to occupy both outer and inner shells. Using a simple modification of Lucas’ geometrical packing scheme, new magic proton and neutron numbers were postulated for the superheavy nuclei, which matched the island of stability distribution to a large extent. These magic numbers were also tested against some nuclei in the peninsula of isotopes, and found to be relevant. Now, in consideration of a suggestion made many years ago by Linus Pauling, new magic numbers between 50 and 82 are postulated in the continent of isotopes, and compared to experimental data. These new numbers have strong support among the three elements considered by Pauling, namely Cadmium, Tin and Tellurium, and the results suggest that the range of isotopes found, their stability, and their lifetimes are strongly affected by the new magic numbers. In addition, if 58 nucleons are taken to be magic, then the double hump fission distribution for heavy isotopes may be explained semi-quantitatively.