Search results for "mechanical engineering"

showing 10 items of 4245 documents

Superexchange pathways in oxovanadium(IV) phosphates

1992

Abstract Oxovanadium(IV) phosphates show a diversity of magnetic behaviours that cannot be deduced from their respective structural features only. In part, this is due to the involvement of phosphate bridges in the spin transfer between V(IV) centres, and 31P solid state nuclear magnetic resonance becomes a key tool in determining the exchange mechanisms. The magnetic properties of a wide set of vanadium(IV) containing derivatives can be explained by realizing that a good overlap of the magnetic orbits may be achieved through paths involving phosphorus d orbitals.

chemistry.chemical_classificationMechanical EngineeringMetals and AlloysVanadiumchemistry.chemical_elementOxovanadium IVPhosphatePhysics::Geophysicschemistry.chemical_compoundCrystallographySolid-state nuclear magnetic resonancechemistryAtomic orbitalMechanics of MaterialsSuperexchangeMaterials ChemistrySpin transferInorganic compoundNuclear chemistryJournal of Alloys and Compounds
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The First sulfur-containing twin-DCNQI-type acceptor

1994

chemistry.chemical_classificationMechanics of MaterialsChemistryMechanical EngineeringPolymer chemistryOrganic chemistryGeneral Materials ScienceElectronic structureElectron acceptorSulfur containingAcceptorChemical synthesisAdvanced Materials
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Numerical model for composite material with polymer matrix reinforced by carbon nanotubes

2008

Due to the high stiffness and strength, as well as their ability to act as conductors, carbon nanotubes are under intense investigation as fillers in polymeric materials. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes within the polymer have arisen as particular factors in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the nanocomposite. Here the effects of carbon nanotube curvature and interface interaction with the matrix on the nanocomposite stiffness are investigated using nanomechanical analysis. In particular, the effects of poor bonding and thus poor shear lag load transfer to the carbon nano…

chemistry.chemical_classificationNanocompositeMaterials scienceMechanical EngineeringCarbon nanotube actuatorsComposite numbertechnology industry and agricultureMechanical properties of carbon nanotubesmacromolecular substancesPolymerCarbon nanotubeCondensed Matter::Mesoscopic Systems and Quantum Hall EffectCondensed Matter PhysicsCarbon Nanotube Numerical Simulations Composite Materials Nanotechnology.law.inventionCarbon nanotube metal matrix compositesSettore ING-IND/14 - Progettazione Meccanica E Costruzione Di MacchineCondensed Matter::Materials ScienceCarbon nanobudchemistryMechanics of MaterialslawComposite materialMeccanica
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Photoluminescence waveguiding in CdSe and CdTe QDs–PMMA nanocomposite films

2011

In this paper, active planar waveguides based on the incorporation of CdSe and CdTe nanocrystal quantum dots in a polymer matrix are demonstrated. In the case of doping the polymer with both types of quantum dots, the nanocomposite film guides both emitted colors, green (550 nm, CdTe) and orange (600 nm, CdSe). The optical pumping laser can be coupled not only with a standard end-fire coupling system, but also directing the beam to the surface of the sample, indicating a good absorption cross-section and waveguide properties. To achieve these results, a study of the nanocomposite optical properties as a function of the nanocrystal concentration is presented and the optimum conditions are fo…

chemistry.chemical_classificationNanocompositePhotoluminescenceMaterials scienceCondensed Matter::Otherbusiness.industryMechanical EngineeringDopingPhysics::OpticsBioengineeringGeneral ChemistryPolymerCondensed Matter::Mesoscopic Systems and Quantum Hall EffectCadmium telluride photovoltaicsOptical pumpingCondensed Matter::Materials ScienceNanocrystalchemistryMechanics of MaterialsQuantum dotOptoelectronicsGeneral Materials ScienceElectrical and Electronic EngineeringbusinessNanotechnology
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Metal nanoparticle/polymer superlattice films: Fabrication and control of layer structure

1997

chemistry.chemical_classificationNanostructureFabricationMaterials scienceMechanical EngineeringSuperlatticeNanoparticleNanotechnologyPolymerMetalchemistryMechanics of Materialsvisual_artvisual_art.visual_art_mediumGeneral Materials ScienceSelf-assemblyLayer (electronics)Advanced Materials
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Reversible tuning of a block-copolymer nanostructure via electric fields

2007

Block copolymers consisting of incompatible components self-assemble into microphase-separated domains yielding highly regular structures with characteristic length scales of the order of several tens of nanometres. Therefore, in the past decades, block copolymers have gained considerable potential for nanotechnological applications, such as in nanostructured networks and membranes, nanoparticle templates and high-density data storage media. However, the characteristic size of the resulting structures is usually determined by molecular parameters of the constituent polymer molecules and cannot easily be adjusted on demand. Here, we show that electric d.c. fields can be used to tune the char…

chemistry.chemical_classificationNanostructureMaterials scienceCharacteristic lengthField (physics)Mechanical EngineeringNanoparticleNanotechnologyGeneral ChemistryPolymerCondensed Matter PhysicsDipoleMembranechemistryMechanics of MaterialsElectric fieldGeneral Materials ScienceNature Materials
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Self-assembly of small gold colloids with functionalized gold nanorods.

2007

We present a general strategy to stabilize gold nanorod suspensions with mono- and bifunctional polyethylene glycol (PEG) and to attach a controlled number of nanoparticles or biomolecules. Characterization by gel electrophoresis, transmission electron microscopy (TEM), and optical dark-field microscopy show the specific binding of functionalized nanorods to their target while avoiding nonspecific binding to substrates, matrices, and other particles. Such nanorods are well suited for self-assembly of nanostructures and single-molecule labeling.

chemistry.chemical_classificationNanostructureMaterials scienceMechanical EngineeringBiomoleculeNanoparticleBioengineeringNanotechnologyGeneral ChemistryPolyethylene glycolCondensed Matter Physicschemistry.chemical_compoundchemistryTransmission electron microscopyGeneral Materials ScienceNanorodSelf-assemblyBifunctionalNano letters
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Organolanthanides, catalysts for specific olefin-diene copolymerization: access to new materials

2001

Abstract Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4)2Sm(allyl)]n, and (CMe2C5H4)2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe2C5H4)2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence o…

chemistry.chemical_classificationOlefin fiberDieneMechanical EngineeringMetals and Alloyschemistry.chemical_compoundchemistryPolymerizationMechanics of MaterialsPolymer chemistryMaterials ChemistryCopolymerOrganic chemistryMoietyMetalloceneIsopreneAlkylJournal of Alloys and Compounds
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New Thermoshrinkable Materials of Radiation Modified Polypropylene-Elastomer Composites with Cross-Linking Agents

2014

In this work, electron beam modified heterogeneous composites of isotactic polypropylene (PP) with chlorinated polyethylene (CPE) have been investigated. The PP/CPE blend composites with an excess of elastomer (30/70 wt%) have been modified with trimethylolpropane triacrylate (TMPTA) and bisphenol-A-dimethacrylate (BPDMA) cross-linking agents and have been irradiated with accelerated electrons up to ionizing radiation doses from 25 to 150 kGy. The internal stresses characterizing the thermoshrinkage properties (TMP) thermorelaxation stresses formed in thermal heating and the residual stresses resulting in the process of full setting and cooling of materials have been investigated for radiat…

chemistry.chemical_classificationPolypropyleneMaterials scienceMechanical EngineeringComposite numberPolymerTMPTAElastomerchemistry.chemical_compoundLow-density polyethylenechemistryMechanics of MaterialsResidual stressTacticityGeneral Materials ScienceComposite materialKey Engineering Materials
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Anisotropic Stick-slip friction of highly oriented thin films of poly(tetrafluoroethylene) at the molecular level

1996

Lateral force microscopy (LFM) studies of poly(tetrafluoroethylene) (PTFE) films with molecular resolution are reported. Thin PTFE layers with a high degree of orientation were obtained by pressing and sliding a block of polymer on a clean, heated muscovite mica substrate. LFM nanographs obtained on these films by scanning at directions between ca. 40 and 90° with respect to the film orientation direction, i.e. with respect to the direction of the polymer chains, showed a “stick-slip” type frictional motion of the LFM probe tip at the molecular level. The friction force observed at constant load decreased with decreasing scan angles. Chain-chain packing distances obtained by LFM and contact…

chemistry.chemical_classificationPressingMaterials scienceMechanical EngineeringMuscoviteNanotechnologySurfaces and InterfacesPolymerSlip (materials science)engineering.materialSurfaces Coatings and Filmschemistry.chemical_compoundchemistryMechanics of MaterialsMicroscopyengineeringTetrafluoroethyleneComposite materialThin filmAnisotropyTribology letters
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