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Kinds of Shell Terms modified by Shell Selected AbstractsSupercritical-Fluid-Assisted One-Pot Synthesis of Biocompatible Core(, -Fe2O3)/Shell(SiO2) Nanoparticles as High Relaxivity T2 -Contrast Agents for Magnetic Resonance ImagingADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Elena Taboada Abstract Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(, -Fe2O3)/shell(SiO2), with a diameter of approximately 100,nm and a high magnetization are synthesized by combining sol,gel chemistry and supercritical fluid technology. This one-step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T2 MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation. [source] A Facile Synthesis and Photoluminescent Properties of Redispersible CeF3, CeF3:Tb3+, and CeF3:Tb3+/LaF3 (Core/Shell) Nanoparticles.CHEMINFORM, Issue 27 2006Z. L. Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Cost estimate for biosynfuel production via biosyncrude gasificationBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 1 2009Edmund Henrich Abstract Production of synthetic fuels from lignocellulose like wood or straw involves complex technology. There-fore, a large BTL (biomass to liquid) plant for biosynfuel production is more economic than many small facilities. A reasonable BTL-plant capacity is ,1 Mt/a biosynfuel similar to the already existing commercial CTL and GTL (coal to liquid, gas to liquid) plants of SASOL and SHELL, corresponding to at least 10% of the capacity of a modern oil refinery. BTL-plant cost estimates are therefore based on reported experience with CTL and GTL plants. Direct supply of large BTL plants with low bulk density biomass by trucks is limited by high transport costs and intolerable local traffic density. Biomass densification by liquefaction in a fast pyrolysis process generates a compact bioslurry or biopaste, also denoted as biosyncrude as produced by the bioliq® process. The densified biosyncrude intermediate can now be cheaply transported from many local facilities in silo wagons by electric rail over long distances to a large and more economic central biosynfuel plant. In addition to the capital expenditure (capex) for the large and complex central biosynfuel plant, a comparable investment effort is required for the construction of several dozen regional pyrolysis plants with simpler technology. Investment costs estimated for fast pyrolysis plants reported in the literature have been complemented by own studies for plants with ca. 100 MWth biomass input. The breakdown of BTL synfuel manufacturing costs of ca. 1 , /kg in central EU shows that about half of the costs are caused by the biofeedstock, including transport. This helps to generate new income for farmers. The other half is caused by technical costs, which are about proportional to the total capital investment (TCI) for the pyrolysis and biosynfuel production plants. Labor is a minor contribution in the relatively large facilities. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd [source] ARCHAEOMETRIC STUDY OF SHELLS OF HELICIDAE FROM THE EDERA CAVE (NORTHEASTERN ITALY),ARCHAEOMETRY, Issue 1 2009L. BONIZZONI The Edera Cave, near Aurisina in the Trieste Karst, retains a stratigraphy that extends from the Mesolithic to the modern era. At Sauveterrian layers, many specimens of Helix cincta are present, which are considerably crushed, and a small percentage of which are also blackened. Chemical analyses show that the blackened specimens were exposed to a temperature of between 500 and 550°C, and suggest that many others were destroyed by fire at temperatures of above 700°C. Consequently, only a part of the Helix cincta shells is assumed to be the residue of human meals, since several factors render plausible an accidental combustion of shells already present in the ground before the lighting of Mesolithic hearths. [source] ,CONCHAS LEGERE': SHELLS AS TROPHIES OF REPOSE IN NORTHERN EUROPEAN HUMANISMART HISTORY, Issue 3 20062Article first published online: 1 AUG 200, LEOPOLDINE VAN HOGENDORP PROSPERETTI This paper interprets Hendrick Goltzius's 1603 portrait of a Dutch shell collector as a powerful statement on the cultural and spiritual ambitions of leading citizens in the Dutch city of Haarlem. The focus is on the role of natural philosophy and natural theology in realizing the ideals of the humanist vocation. Within this context the Erasmian adage ,collecting of shells' proves to be a fitting slogan for the pursuit of fruitful repose as the indispensable foundation of a successful commonwealth. [source] A case study of shell at Sakhalin: having a whale of a time?CORPORATE SOCIAL RESPONSIBILITY AND ENVIRONMENTAL MANAGEMENT, Issue 3 2008Subhasis Ray Abstract This is a case study on the world's largest oil and gas project, at the Sakhalin Islands, Russia. Shell is the key promoter of this project. The case highlights the sustainability challenges that Shell faced when working on the mega-project. By their very nature, all such projects involve disruptions in the environmental and social fabric of the project site. NGOs often take up these issues and create international headlines, bringing pressure on the management team. The Russian government also changed its stand over a period of time. While many of these issues are valid in their own way, they often create managerial dilemmas. Traditional management approaches to community development and environmental conservation fell short of stakeholder expectations at Sakhalin. The issue of saving around 100 endangered whales put a cloud of doubt over this $20 billion project. The case highlights strategic issues involved in crafting sustainability strategies at mega-projects, possible pitfalls and the challenge of balancing project execution and stakeholder commitments against an unstable political backdrop. As Shell plans to start many exploration projects in bio-diversity rich parts of the world, the Sakhalin project acts as a pilot to and reminder of social responsibility challenges to big multi-nationals. Copyright © 2007 John Wiley & Sons, Ltd and ERP Environment. [source] Development of an Expert System Shell Based on Genetic Algorithms for the Selection of the Energy Best Available Technologies and their Optimal Operating Conditions for the Process IndustryEXPERT SYSTEMS, Issue 3 2001D.A. Manolas The development of genetic algorithms started almost three decades ago in an attempt to imitate the mechanics of natural systems. Since their inception, they have been applied successfully as optimization methods, and as expert systems, in many diverse applications. In this paper, a genetic-algorithm-based expert system shell is presented that, when combined with a proper database comprising the available energy-saving technologies for the process industry, is able to perform the following tasks: (a) identify the best available technologies (BATs) among the available ones for a given process industry, and (b) calculate their optimal design parameters in such a way that they comply with the energy requirements of the process. By the term BAT is meant the available energy-saving technology, among the existing ones in the market, that is the best for the case. [source] Biological Materials: Mechanical Function of a Complex Three-Dimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider Turtle (Adv. Mater.ADVANCED MATERIALS, Issue 4 20094/2009) The shell of a turtle is required to be a shield that is stiff at high loads, but must provide sufficient flexibility for respiration and locomotion at smaller loads. On p. 407, Peter Fratzl and co-workers show that these seemingly contradictory requirements are met by a self-locking material, whereby stiff bony elements are connected by a much softer suture with a complex three-dimensional shape. [source] Mechanical Function of a Complex Three-Dimensional Suture Joining the Bony Elements in the Shell of the Red-Eared Slider TurtleADVANCED MATERIALS, Issue 4 2009Stefanie Krauss The shell of turtles is a shield which needs to be stiff at high loads but should provide sufficient flexibility for respiration and locomotion at smaller loads. We show that this seemingly contradictory requirement is met by a self-locking material, whereby stiff bony elements are connected by a much softer suture with a complex three-dimensional shape. [source] High-Sensitivity Solid-State Pb(Core)/ZnO(Shell) Nanothermometers Fabricated by a Facile Galvanic Displacement Method,ADVANCED MATERIALS, Issue 24 2008Chiu-Yen Wang Solid-Pb-filled ZnO nanotubes are synthesized and tested for use as nanothermometers. The expansion of the filling with increasing temperature (see figure) , or the corresponding changes in capacitance , can be measured and related to temperature. The advantages of this nanothermometer are extremely low fabrication costs, superior reliability, and lower demands on structural integrity of the outer shell compared to nanothermometers based on liquid fillings. [source] Trapping Metallic Liquid Mercury in a Carbon Shell by the Decomposition of Dimethyl Mercury,ADVANCED MATERIALS, Issue 5 2008A. Gedanken An efficient single-step synthesis of mercury droplets covered with a carbon shell by the thermolysis of dimethyl mercury under its autogenic pressure is described. This is a unique case in which a liquid metal is trapped inside a nano- and micrometer size carbon capsule. The air-stability and the characterization by XRD, TEM, DSC, HRSEM, and HRTEM of this composite are reported. [source] Molecular thermodynamics of asphaltene precipitation in reservoir fluidsAICHE JOURNAL, Issue 1 2000Jianzhong Wu A previously described molecular-thermodynamic framework, based on colloid theory, is used to correlate experimental asphaltene-precipitation data at high-temperature and pressure conditions. In this framework, asphaltenes and resins are represented by pseudopure components, and all other components in a crude oil are presented by a continuous medium that affects van der Waals attractions among asphaltene and resin molecules. Model parameters are evaluated systematically from average properties of asphaltenes and resins in crude oils, and from dispersion-force properties of the oil medium. Given the composition of the medium, and asphaltene and resin concentrations, the molecular-thermodynamic model described here can be used to identify the onset of asphaltene precipitation, and the total amount of precipitation at the given operation conditions. Calculated results for the effects of oil composition and pressure on asphaltene precipitation are in good agreement with at least some experimental measurements for four reservoir fluids, including Texaco, Shell, Weyburn, and North-Sea crude oils. [source] Ethanol Is Self-Administered Into the Nucleus Accumbens Shell, But Not the Core: Evidence of Genetic SensitivityALCOHOLISM, Issue 12 2009Eric A. Engleman Background:, A previous study indicated that selectively bred alcohol-preferring (P) rats self-administered ethanol (EtOH) directly into the posterior ventral tegmental area at lower concentrations than Wistar rats. The present study was undertaken to determine involvement of the nucleus accumbens (Acb) with EtOH reinforcement, and a relationship between genetic selection for high alcohol preference and sensitivity of the Acb to the reinforcing effects of EtOH. Methods:, Adult P and Wistar rats were assigned to groups that self-infused 0 to 300 mg% EtOH into the Acb shell (AcbSh) or Acb Core (AcbC). Rats were placed into 2-lever (active and inactive) operant chambers and given EtOH for the first 4 sessions (acquisition), artificial cerebrospinal fluid (aCSF) for sessions 5 and 6 (extinction), and EtOH again in session 7 (reinstatement). Responding on the active lever produced a 100-nl injection of the infusate. Results:, Alcohol-preferring rats self-infused 75 to 300 mg% EtOH, whereas Wistar rats reliably self-infused 100 and 300 mg% EtOH into the AcbSh. Both P and Wistar rats reduced responding on the active lever when aCSF was substituted for EtOH, and reinstated responding in session 7 when EtOH was restored. EtOH was not self-infused into the AcbC by P or Wistar rats. Conclusions:, The present results indicate that the AcbSh, but not AcbC, is a neuroanatomical structure that mediates the reinforcing actions of EtOH. The data also suggest that, compared to Wistar rats, the AcbSh of P rats is more sensitive to the reinforcing effects of EtOH. [source] Sonochemical Synthesis of Networked Silica Shell with Reduced Microporosity on Titania Nanocores for Photocatalytic Activity ReductionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Ahmed Mohamed El-Toni Silica shells with a high density of networks and reduced microporosity has been formed on titania nanocores via a sonochemical approach in the absence of ammonia as a hydrolyzing catalyst. The TiO2 -silica core-shell nanoparticles were characterized by transmission electron microscopy, energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy (FTIR), and microporosity measurements. The photocatalytic activity of coated titania was also reported. FTIR measurements showed that the silica shell was formed with a high density of networks through the formation of asymmetric Si,O,Si vibration and asymmetric Si,O,Si stretching vibration bonds. Moreover, the thickness and microporosity of the silica shell could be altered by controlling the sonochemical power and time parameters. [source] Sintering Characteristics in the BaTiO3,Nb2O5,Co3O4 Ternary System: II, Stability of So-called "Core,Shell" StructureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Hirokazu Chazono The sintering characteristics and the reaction of additives with BaTiO3 (BT) were examined for two materials having Nb-rich composition (Comp.N) and Co-rich composition (Comp.C) to elucidate the relation between the stability of the core,shell microstructure and the Nb/Co ratio in the BT,Nb2O5,Co3O4 system. TEM observation revealed that the concentration gradient of Nb and Co existed in the shell region although Nb and Co macroscopically distributed homogeneously. X-ray diffraction analysis showed that the shell formation preceded the densification and completed at about 1280°C for both Comp.N and Comp.C as determined from differential scanning calorimetry. A diffusion couple experiment disclosed that Co had a larger diffusivity than Nb and that the diffusion of Co was suppressed when the sample was codoped with a sufficient amount of Nb. On the basis of these experimental results, new mechanisms of the formation and collapse of core,shell structure in the BT,Nb2O5,Co3O4 system were proposed. [source] Russia flexes muscles over oil and gasOIL AND ENERGY TRENDS, Issue 10 2006Article first published online: 13 OCT 200 A new militancy is emerging from Moscow in dealings with foreign companies operating in Russia. The government has severely criticized a number of international oil companies engaged in major oil and gas developments, including Shell, ExxonMobil, BP and Total. In several cases, the companies have been told that their environmental plans covering the development of new fields are unsatisfactory. The latest arguments concern two large oil and gas developments on the Pacific island of Sakhalin. The environmental criticisms, however, are simply the outward sign of a growing sentiment inside Russia that foreign companies have been granted lucrative upstream opportunities on terms that are much too favourable to them. [source] PtSn Intermetallic, Core,Shell, and Alloy Nanoparticles as CO-Tolerant Electrocatalysts for H2 Oxidation,ANGEWANDTE CHEMIE, Issue 18 2010Zhufang Liu Dr. Mehr Ordnung, mehr Toleranz: Intermetallische und legierte PtSn-Nanopartikel (NPs) wurden durch gemeinsame Reduktion von [Pt(acac)2] (acac=Acetylacetonat) und SnCl4 hergestellt. Die intermetallischen NPs können durch potentialdynamische Aktivierung in CO-gesättigter H2SO4 -Lösung in PtSn@Pt-Kern-Schale-NPs umgewandelt werden. Elektrochemische Studien zeigen, dass Kern-Schale- und intermetallische Elektrokatalysatoren eine deutlich höhere CO-Toleranz aufweisen als reines Pt, PtSn- und PtRu-Legierungen. [source] Synthesis of Fe3O4@SiO2@PMMA Core,Shell,Shell Magnetic Microspheres for Highly Efficient Enrichment of Peptides and Proteins for MALDI-ToF MS Analysis,ANGEWANDTE CHEMIE, Issue 3 2010Hemei Chen Sehr bereichernd: Kern-Schale-Schale-Mikrokügelchen aus Fe3O4§SiO2§PMMA (siehe Bild; PMMA=Poly(methylmethacrylat)) wurden durch Kombination eines Sol-Gel-Verfahrens mit einer radikalischen Saatpolymerisation in wässriger Phase synthetisiert. Mithilfe der Mikrokügelchen gelang die effiziente Anreicherung von in niedriger Konzentration vorliegenden Peptiden und Proteinen für die massenspektrometrische Analyse. [source] Zones of Exclusion: Offshore Extraction, the Contestation of Space and Physical Displacement in the Nigerian Delta and the Mexican GulfANTIPODE, Issue 3 2009Anna Zalik Abstract:, This article examines two aid interventions that manifest the merging of community development/relief and industrial security policy in the petroleum offshore of the Nigerian Niger Delta and the Mexican Gulf. In the Nigerian case, the article considers the crisis in the Warri region of Delta State in 2003, the subsequent evacuation of local residents, and the surrounding context of oil-related violence. Simmering since the 1990s, the 2003 Warri conflict displaced thousands due to competing community claims to territory that "hosts" oil installations, Shell and Chevron primarily. In Mexico, the analysis centers on the implementation of 2003 Mexican security legislation, prompted by International Maritime Organization post 9/11 security policy, that amplifies the "Zone of Exclusion" around offshore installations. To offset the loss of livelihoods resulting from the "exclusion zone", Mexican state agencies offered financing to support the conversion of the displaced small-scale fishers to fish farming. The varying forms of displacement prompted by these two "liberating" interventions reflect the socio-historical specificity of territorial relations in the Nigerian and Mexican extractive regimes. These relations constitute divergent extractive settings which have come to play contrasting roles in the global political economy of oil, one highly volatile, the other relatively stable. [source] The effect of environmental factors, depth and position on the growth and mortality of raft-cultured blue mussels (Mytilus edulis L.)AQUACULTURE RESEARCH, Issue 12 2000S Karayücel Abstract One-year-old rope grown blue mussels (Mytilus edulis L.) were grown in experimental lantern nets at two depths (2 and 6 m below the surface) in two different positions (inflow and outflow) off a raft in Loch Etive on the west coast of Scotland. Shell and tissue growth, and mortality were recorded. Water temperature, salinity and food availability were also monitored over the experimental period. There were no significant differences in the length, live weight, wet meat weight, dry meat weight and ash-free dry meat weight between depths (P >,0.05). However, position had a significant effect on these parameters as mussels located at the inflow of the raft differed significantly from those at the outflow of the raft (P <,0.05). Particulate organic matter (POM) and chlorophyll a (Ch a) were significantly higher at the inflow than the outflow of the raft (P <,0.05), but depth had no effect on POM and Ch a (P >,0.05). The results show that food concentration was higher in the inflow of the raft than the outflow. In the light of these results, recommendations for better management of Scottish raft mussel cultivation are discussed. [source] Synthesis of a Carbosilane Dendrimer with the Functional Inner Shell.CHEMINFORM, Issue 45 2004E. A. Vodop'yanov No abstract is available for this article. [source] Preparation of Core,Shell-Structured Nanoparticles (with a Noble-Metal or Metal Oxide Core and a Chromia Shell) and Their Application in Water Splitting by Means of Visible LightCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2010Kazuhiko Maeda Dr. Abstract Core,shell-structured nanoparticles, consisting of a noble metal or metal oxide core and a chromia (Cr2O3) shell, were studied as promoters for photocatalytic water splitting under visible light. Core nanoparticles were loaded by impregnation, adsorption or photodeposition onto a solid solution of gallium nitride and zinc oxide (abbreviated GaN:ZnO), which is a particulate semiconductor photocatalyst with a band gap of approximately 2.7,eV, and a Cr2O3 shell was formed by photodeposition using a K2CrO4 precursor. Photodeposition of Cr2O3 on GaN:ZnO modified with a noble metal (Rh, Pd and Pt) or metal oxide (NiOx, RuO2 and Rh2O3) co-catalyst resulted in enhanced photocatalytic activity for overall water splitting under visible light (,>400,nm). This enhancement in activity was primarily due to the suppression of undesirable reverse reactions (H2,O2 recombination and/or O2 photoreduction) and/or protection of the core component from chemical corrosion, depending on the core type. Among the core materials examined, Rh species exhibited relatively high performance for this application. The activity for visible-light water splitting on GaN:ZnO modified with an Rh/Cr2O3 core,shell configuration was dependent on both the dispersion of Rh nanoparticles and the valence state. In addition, the morphology of the Cr2O3 photodeposits was significantly affected by the valence state of Rh and the pH at which the photoreduction of K2CrO4 was conducted. When a sufficient amount of K2CrO4 was used as the precursor and the solution pH ranged from 3 to 7.5, Cr2O3 was successfully formed with a constant shell thickness (,2,nm) on metallic Rh nanoparticles, which resulted in an effective promoter for overall water splitting. [source] Synthesis of Anatase TiO2 Nanoparticles with ,-Cyclodextrin as a Supramolecular ShellCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2006Landong Li Abstract We report a novel, green hydrothermal-synthesis route to well-dispersed anatase TiO2 nanoparticles with particle sizes of 9,16,nm in the presence of ,-CD (,-cyclodextrin). During the synthesis process, the CD-containing synthesis mixture assembled in both longitudinal and latitudinal directions. Driven by the interaction between molecules, the ,-CDs assembled in the longitudinal direction to form long-chain compounds, whereas in the latitudinal direction, they tended to form regular aggregates through coordination with the Ti species from the hydrolysis of tetrabutyl titanate. In view of the effect of the coordination and the steric hindrance of ,-CDs as a supramolecular shell, homogeneous nuclei and slow growth of TiO2 crystals during the synthesis process was observed, which was responsible for the formation of uniform TiO2 nanoparticles. The low ,-CD dosage and the high product yield (>90,%) demonstrated well the potential of this synthesis route in the large-scale industrial production of anatase nanoparticles. [source] Colours and Metallic Sheen in Beetle Shells , A Biomimetic Search for Material Structuring Principles Causing Light Interference,ADVANCED ENGINEERING MATERIALS, Issue 4 2008T. Lenau Abstract Visual aesthetic has always played a vital role for the success of many products. This includes colours and glossiness and metal appearance which is often achieved using surface coatings. Present coating techniques do, however, have limitations. It is difficult to reach very bright and brilliant colours, colours tend to fade over time and many of the materials and coating technologies pollute and have other environmental problems. Beetles in nature have many of the desired properties: They have appealing brilliant colours and some even with metallic appearance. It is noticeable that the colours are long lasting as some of the beetles we have studied at the zoological museum are more than 200 years old and have colours and brightness as if they were still alive. Furthermore, the beetles in nature are part of sustainable ecosystems, which means that they are made from renewable materials that are broken down and recycled when the beetle dies. Beetles also possess another and very attractive property: Their metallic look originates from structures in organic materials which is both electrically and thermal insulating. The industrial perspective is to be able to manufacture products with attractive metallic surfaces that do not feel so cold to touch as their metallic counterparts and that do not represent an electrical shock hazard. [source] Evolution and development of gastropod larval shell morphology: experimental evidence for mechanical defense and repairEVOLUTION AND DEVELOPMENT, Issue 1 2001Carole S. Hickman SUMMARY The structural diversity of gastropod veliger larvae offers an instructive counterpoint to the view of larval forms as conservative archetypes. Larval structure, function, and development are fine-tuned for survival in the plankton. Accordingly, the study of larval adaptation provides an important perspective for evolutionary-developmental biology as an integrated science. Patterns of breakage and repair in the field, as well as patterns of breakage in arranged encounters with zooplankton under laboratory conditions, are two powerful sources of data on the adaptive significance of morphological and microsculptural features of the gastropod larval shell. Shells of the planktonic veliger larvae of the caenogastropod Nassarius paupertus[Gould] preserve multiple repaired breaks, attributed to unsuccessful zooplankton predators. In culture, larvae isolated from concentrated zooplankton samples rapidly repaired broken apertural margins and restored the "ideal" apertural form, in which an elaborate projection or "beak" covers the head of the swimming veliger. When individuals with repaired apertures were reintroduced to a concentrated mixture of potential zooplankton predators, the repaired margins were rapidly chipped and broken back. The projecting beak of the larval shell is the first line of mechanical defense, covering the larval head and mouth and potentially the most vulnerable part of the shell to breakage. Patterns of mechanical failure show that spiral ridges do reinforce the beak and retard breakage. The capacity for rapid shell repair and regeneration, and the evolution of features that resist or retard mechanical damage, may play a more prominent role than previously thought in enhancing the ability of larvae to survive in the plankton. [source] Nanometer-Scale Mapping of Elastic Modules in Biogenic Composites: The Nacre of Mollusk ShellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Haika Moshe-Drezner Abstract In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D-distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta-chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back-scattered electrons. Based on this comparison, the Young modulus of beta-chitin is extracted. The obtained number, E, = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites. [source] Surface-Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal NanocatalystsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Qiao Zhang Abstract Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk,shell and core,satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework. [source] Nacre in Mollusk Shells as a Multilayered Structure with Strain GradientADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Boaz Pokroy Abstract How do living organisms attain the complicated shapes of grown bio-composites? This question is answered when studying the mechanics of the nacre layer in the bivalve mollusk shells. In this study, the internal strains/stresses across the shell thickness are profiled as a function of depth by strain gauge measurements during controlled etching in the selected areas. Measurements of stress release under etching provide clear evidence that the investigated shells, in fact, are strained multilayered structures, which are elastically bent due to the forces evolving at the organic/inorganic interfaces. The stresses are mostly concentrated in the "fresh" nacre sub-layers near the inner surface of the shell adjacent to the mollusk mantle. This analysis unexpectedly shows that the elastic bending of the nacre layer is due to strain gradients which are originated in the gradual in-depth changes of the thickness of ceramic lamellae. The changes mentioned were directly observed by scanning electron microscopy. By this sophisticated design of the ultra-structure of the nacre layer, the bowed shape of the bivalve shells is apparently achieved. [source] Reactive Template Method to Synthesize Gold Nanoparticles with Controllable Size and Morphology Supported on Shells of Polymer Hollow Microspheres and Their Application for Aerobic Alcohol Oxidation in WaterADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Jie Han Abstract A novel method has been developed to synthesize gold nanoparticles with tunable size and morphology supported on both inner and outer surfaces of poly(o -phenylenediamine) (PoPD) hollow microspheres, which act as both reductant and template/stabilizer. The size of gold nanoparticles supported on shells of PoPD hollow microspheres can be tuned from 3 to 15,nm by changing the concentration of the gold source, HAuCl4. Gold nanorods supported on shells of PoPD hollow microspheres can also be fabricated by introducing a well-known seed-growth strategy. In addition, silver nanoparticles supported on shells of PoPD hollow microspheres can also be successfully fabricated using the same strategy, which indicates the diversity of this proposed method for polymer hollow microspheres supporting noble metal nanoparticles. The products are characterized by X-ray diffraction and contact angle analysis. Furthermore, the catalytic activity of the obtained PoPD-microsphere-supported gold nanoparticles for aerobic alcohol oxidation is investigated. The results demonstrate that such polymer-supported gold nanoparticles can be used as reusable catalysts with high catalytic activity for aerobic alcohol oxidation in water. [source] Formation 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] | |||||||||||||||||||||||||||||||||||||||||||||||||