| 1. |
- Bolton, Kim, et al.
(författare)
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Carbon Nanotube Growth Mechanisms
- 2007
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Ingår i: Proceedings of Diamond 2007, the 18th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide.
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Konferensbidrag (refereegranskat)abstract
- We have used a variety of computational methods to study key aspects of single-walled carbon nanotube (SWNT) growth. Molecular dynamics (MD) studies based on an empirical force field showed; for example; why SWNT growth occurs in a temperature window and why; for 1-2 nm catalyst particles; the SWNT diameter varies linearly with the size of the particle. In addition; the liquid or solid phase of the catalyst particle is strongly dependent on particle size; and smaller particles (< 1.5 nm) are liquid at typical chemical vapor deposition temperatures whereas larger particles (> 5 nm) are solid. The phase of particles of intermediate sizes depends on the exact temperature and on their carbon content. The effect of substrates on metal-carbide properties and SWNT growth has been studied by combing density functional (DFT) and MD methods. A major effect of flat; inert substrates is to flatten the catalyst particles thereby increasing their melting points. DFT has also been used to study the catalyst-SWNT interaction which is critical for the growth of long SWNTs; and is also being used to study the importance of the SWNT cap structure on its chirality. This knowledge is important; for example; when using SWNTs as seeds for the growth of longer nanotubes.
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| 2. |
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| 3. |
- Larsson, Andreas, et al.
(författare)
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Multi-Scale Simulation for Nanowires and Carbon Nanotubes
- 2008
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Konferensbidrag (refereegranskat)abstract
- With the advent of nanotechnology; semiconductor processing is driving developments in computational chemis-try and computational material science. Describing materials from an atomic perspective allows for simulations that describe the formation of and flow of electrons in nanoscale structures. However; to achieve design for mi-croelectronics technologies requires atomic scale simulations that span varying length and time scales. In this presentation; developments toward a strategy for simulating nanowire and carbon nanotubes; their electronic structure; and electron and phonon transport within a single simulation hierarchy is described.
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| 4. |
- Avan, Evan Y., et al.
(författare)
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Experimental and numerical investigations of oil film formation and friction in a piston ring–liner contact
- 2013
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 227:2, s. 126-140
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Tidskriftsartikel (refereegranskat)abstract
- The piston ring–cylinder liner contact is a major source of the total parasitic losses in an internal combustion engine. The lubrication process of this contact highly influences the amount of friction, oil consumption and wear that occurs. In this work, a reciprocating test rig combined with an ultrasonic film thickness measurement system was developed and then used for tribological investigation of the piston ring–cylinder liner contact under idealised cold conditions. A special piston ring and cylinder liner holder were designed and five sensors were glued on to the back side of the liner specimen. Ultrasonic reflections captured by the sensors, used to obtain the film thickness, and friction were continuously recorded as the piston ring section reciprocated over the liner. Several experiments were performed at different speed and load conditions. Furthermore, a numerical model has been developed to predict film thickness and friction in all lubrication regimes. The experimentally measured film thickness and friction were compared with the output from the numerical model and good correlation was found. The parameters affecting the accuracy of the ultrasound measurements and numerical simulations of film thickness and friction are then discussed.
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| 5. |
- Björling, Marcus, et al.
(författare)
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Towards the true prediction of EHL friction
- 2013
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 66, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- The capability to predict elastohydrodynamic film-thickness and friction from primary measurements of transport properties of liquid has been an elusive goal for tribologists for 50 years. Most comparisons between predictions and experiments involve some amount of tuning of the model in order to match the experimental results. In true prediction, this cannot be done since there are normally no experimental results to compare to. Primary measurements of lubricant transport properties of Squalane were performed, and used in a numerical friction prediction model. Afterwards, friction was measured in a ball-on-disc tribotester. No tuning of the lubricant properties, model or test setup were applied. The current work on EHL-friction is therefore a true representation of the current level of EHL-friction prediction.
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| 6. |
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| 7. |
- Cremona, C., et al.
(författare)
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Improved Assessment Methods for Static and Fatigue Resistance of Old Steel Railway Bridges
- 2007
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Rapport (refereegranskat)abstract
- The present section of Deliverable D.4.3 is dedicated to the static and fatigue assess-ment of old metal bridges. It forms the basis of the Chapter 7 guideline developed in work package 4 (WP4) “Guideline for Load and Resistance Assessment of Existing European Railway Bridges”. This section is divided into four parts related to the four research activities of the WP4 metal subgroup:– Analysis of material properties of existing metal railway bridges, – Fatigue of riveted structure,– Updated assessment methods for riveted structures,– Enhanced non destructive techniques for inspecting riveted structures.
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| 8. |
- Gowda, Vasantha, et al.
(författare)
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DFT calculations in the assignment of solid-state NMR and crystal structure elucidation of a lanthanum(iii) complex with dithiocarbamate and phenanthroline
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:48, s. 19473-19484
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Tidskriftsartikel (refereegranskat)abstract
- The molecular, crystal, and electronic structures as well as spectroscopic properties of a mononuclear heteroleptic lanthanum(iii) complex with diethyldithiocarbamate and 1,10-phenanthroline ligands (3 : 1) were studied by solid-state 13C and 15N cross-polarisation (CP) magic-angle-spinning (MAS) NMR, X-ray diffraction (XRD), and first principles density functional theory (DFT) calculations. A substantially different powder XRD pattern and 13C and 15N CP-MAS NMR spectra indicated that the title compound is not isostructural to the previously reported analogous rare earth complexes with the space group P21/n. Both 13C and 15N CP-MAS NMR revealed the presence of six structurally different dithiocarbamate groups in the asymmetric unit cell, implying a non-centrosymmetric packing arrangement of molecules. This was supported by single-crystal X-ray crystallography showing that the title compound crystallised in the triclinic space group P1[combining macron]. In addition, the crystal structure also revealed that one of the dithiocarbamate ligands has a conformational disorder. NMR chemical shift calculations employing the periodic gauge including projector augmented wave (GIPAW) approach supported the assignment of the experimental 13C and 15N NMR spectra. However, the best correspondences were obtained with the structure where the atomic positions in the X-ray unit cell were optimised at the DFT level. The roles of the scalar and spin-orbit relativistic effects on NMR shielding were investigated using the zeroth-order regular approximation (ZORA) method with the outcome that already the scalar relativistic level qualitatively reproduces the experimental chemical shifts. The electronic properties of the complex were evaluated based on the results of the natural bond orbital (NBO) and topology of the electron density analyses. Overall, we apply a multidisciplinary approach acquiring comprehensive information about the solid-state structure and the metal-ligand bonding of the heteroleptic lanthanum complex.
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| 9. |
- Gowda, Vasantha, et al.
(författare)
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Structural insights into the polymorphism of bismuth(III) di-n-butyldithiocarbamate by X-ray diffraction, solid-state (13C/15N) CP-MAS NMR and DFT calculations
- 2017
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Ingår i: Polyhedron. - : Elsevier. - 0277-5387 .- 1873-3719. ; 129, s. 123-132
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Tidskriftsartikel (refereegranskat)abstract
- Two crystalline polymorphs of a binuclear tris(di-n-butyldithiocarbamato)bismuth(III) complex, I and II, with an empirical formula of [Bi{S2CN(n-C4H9)2}3] were synthesised and characterised by X-ray diffraction (XRD), solid-state NMR and density functional theory (DFT) calculations. At the supramolecular level, these mononuclear molecular units interact in pairs via secondary Bi⋯S bonds, yielding binuclear formations of [Bi2{S2CN(n-C4H9)2}6]. The polymorph I () contains two isomeric non-centrosymmetric binuclear molecules of [Bi2{S2CN(n-C4H9)2}6], which are related to each other as conformers, therefore having four structurally inequivalent bismuth atoms and twelve inequivalent dithiocarbamate ligands. In contrast, the structurally simpler polymorph II (P21/n) exists as a single molecular form of the corresponding centrosymmetric binuclear formation, comprising two structurally equivalent bismuth atoms and three structurally different dithiocarbamate groups. The polymorphs I and II were found to be interconvertible by altering the solvent system during the recrystallisation process. Sun et al. (2012) has reported a crystalline form of the title compound which resembles, but is not identical with, polymorph II. Experimental solid-state 13C and 15N cross-polarisation (CP) magic-angle-spinning (MAS) NMR spectra of both polymorphs I and II were in accord with the direct structural data on these complexes. Assignments of the resonance lines in the solid-state 13C and 15N NMR spectra were assisted by chemical shift calculations of the crystals using periodic DFT.
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| 10. |
- Gustafsson, Ö., et al.
(författare)
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Evaluation of the collection efficiency of upper ocean sub-photic-layer sediment traps : A 24-month in situ calibration in the open Baltic Sea using 234Th
- 2004
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Ingår i: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 2:2, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- The collection efficiency of cylindrical sediment traps of common design was assessed in situ for more than 2 y in an offshore shelf regime using the 234Th proxy and simultaneously collected hydrological and biogeochemical parameters. The traps were found to systematically record an undertrapping bias of 234Th by, on average, a factor of three (range 0.8 to 10). Seasonal variations in trapping efficiency were related to the seasonally varying ballasting properties of the settling particle pool. Sediment trap 234Th fluxes agreed within a factor of two of the estimated 234Th export from the overlying surface waters in the winter-spring periods in both 1999 and 2000 and appeared related to a particle pool that included, presumably rapidly sinking, mineral particles and diatom tests acting as ballast. In contrast, discrimination against slowly settling organic-rich aggregates of apparent exudate origin resulted in undertrapping of 234Th by factors of three to ten throughout the summerfall seasons. These data are consistent with hydrodynamic predictions that the collection efficiency of sinking particles is inversely related to their intrinsic settling velocities. Recognition of changing particle composition along a settling velocity spectrum combine with carbon mass balance restrictions to suggest that these 234Th-based collection efficiencies, ranging from 0.1 to 1, may not be directly applicable to "correct" sediment trap fluxes of other components, such as organic carbon. However, the 234Th-derived insights of settling-velocity-related undertrapping may beneficially be taken into account when interpreting trap records both in studies of biogeochemical element fluxes and in phytoplankton ecology
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