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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
881

Kemilaborationer på gymnasiet : Gymnasieelevers uppfattningar om laborativa moment i kemi

Håkansson, Pelle January 2016 (has links)
Traditionell kemiundervisning innebär att elever utför laborativa moment. Syftet är att främjalärande, introducera kemins arbetssätt samt stärka intresset för kemi. I ljuset av studier somvisar på att svenska elevers resultat och intresse för kemi sjunker, tar denna studie avstamp ifrågan huruvida eleverna uppfattar att deras laborativa moment uppfyller dessa syften. För attbelysa denna frågeställning har jag genomfört en enkätstudie där elevernas åsikter om hurlaborativa moment bidrar till lärande och intresse undersöks. Mina resultat indikerar atteleverna generellt är positivt inställda till hur laborativa moment bidrar till lärande mentveksamma till huruvida laborativa moment bidrar till ett ökat intresse för kemi. Sammantagetbidrar min studie till en ökad insikt om hur vi lärare kan förändra kemiundervisningen för attfrämja elevens lärande samt intresse för kemi.
882

Samband mellan motivationstyper och emotioner för kemilaborationer på gymnasiet / Relations Between Motivation Types and Emotions in the UpperSecondary Chemistry Laboratory

Karlsson, Simon, Krantz Öberg, Victor January 2017 (has links)
Kopplingen mellan positiva emotioner och olika motivationstyper är ett område som är väl beforskat, men trots det finns det luckor. Syftet med denna studie har varit att studera korrelationen mellan positiva emotioner och olika motivationstyper i den laborativa kemiundervisningen, men även studera skillnader i dessa faktorer hos olika elevgrupper. För att svara på dessa frågor genomfördes en enkätstudie där elevernas positiva emotioner och motivationstyper för den laborativa kemiundervisningen undersökts. Resultatet av denna studie indikerar att det finns positiva korrelationer mellan de mer inre motivationstyperna och positiva emotioner, men även att det finns signifikanta skillnader i dessa faktorer hos olika elevgrupper. Vår studie bidrar till en djupare förståelse till lärare för hur elevers motivation hänger samman med deras emotioner och till vad lärare kan ha i beaktning i planeringen av laborativa moment.
883

Charged colloids observed by electrophoretic and diffusion NMR

Thyboll Pettersson, Erik January 2005 (has links)
<p>The thesis deals partly with methodology including construction</p><p>of hardware and new pulse sequences in the field of electrophoretic</p><p>NMR, and partly with practical use of ENMR and</p><p>diffusion NMR in the investigation of charged colloidal systems.</p><p>Several sources of artefacts are investigated, including gas production</p><p>at the electrodes, electroosmosis and Joule heating</p><p>effects that can cause convection. The electrophoretic double</p><p>stimulated-echo pulse sequence is introduced to suppress these</p><p>artefacts and to increase the feasible measuring range to higher</p><p>electric fields and conductivities.</p><p>The interaction between the non-ionic polymer poly(ethylene</p><p>oxide) PEO and differently charged surfactants is investigated</p><p>using the above mentioned methods. The investigated surfactants</p><p>are the anionic sodium dodecyl sulphate (SDS) and</p><p>potassium laurate (KC12), the cationic dodecyltrimethylammonium</p><p>bromide (CTAB) and the non-ionic octyl β-D-glucoside.</p><p>ENMR is also used to investigate two different mixed micelle</p><p>systems, with SDS as the charged surfactant component and</p><p>dodecyl malono-bis-N-methylglucamide (C12BNMG) respectively</p><p>tetra(ethylene oxide) dodecyl ether (C12EO4) as the nonionic</p><p>surfactant component. A method to calculate the degree</p><p>of counter-ion dissociation, αdissociation, as a function of composition</p><p>is demonstrated.</p><p>Finally diffusion NMR is used to compare transport dynamics</p><p>in gel electrolyte systems based on two differently grafted polymers;</p><p>one amphiphilic system containing polymethacrylate</p><p>grafted partly with polyethylene oxide and partly with fluorocarbons</p><p>and the corresponding nonamphiphilic system grafted</p><p>with only polyethylene oxide. Both systems contain the electrolyte</p><p>lithium bis(trifluoromethylsulfonyl) imide salt dissolved in</p><p>γ-butyrolactone. The results show that the system based on the</p><p>amphiphilic polymer has better transport dynamics and therefore</p><p>is more suited as material for battery</p>
884

Structure and Dynamics of the Copper-binding Octapeptide Region in the Human Prion Protein

Riihimäki, Eva-Stina January 2005 (has links)
<p>The copper-binding ability of the prion protein may be closely connected to its function. Identifying the exact function of the prion protein can clarify the underlying mechanism in prion diseases. In this work, the copper-binding octapeptide region in the human prion protein has been studied. The structural characteristics of the binding site are examined by quantum chemical structural optimization. The calculations aim at identifying a substitute for copper(II) to be used in NMR-spectroscopic studies of the copper-binding region. The dynamical and structural features of the peptide region are investigated in molecular dynamics simulations. Aspects of importance in the development of model systems in molecular dynamics simulation are addressed.</p>
885

Novel powder-coating solutions to improved micro-structures of ZnO based varistors, WC-Co cutting tools, and Co/Ni nano-phase films and sponges

Ekstrand, Åsa January 2002 (has links)
Solution chemistry is a versatile and powerful tool in the synthesis of designed, complex nano-level high-tech materials. Normally, the technique is considered too expensive for large-scale production of complex multi-component ceramic materials. This thesis describes the expansion of the useful area of solution processing to multi-component bulk materials such as ZnO-based high-field varistors and WC–Co cutting tools, by developing novel techniques for solution-based coating of conventionally prepared metal and ceramic powders. The chemistry and microstructure development in the preparation of coatings, and the sintering of the coated powders to compacts, were studied in detail by SEM-EDS, TEM-EDS, XRD, IR-spectroscopy, dilatometry, TGA and DSC chemical analysis. ZnO powder with a ca 20 nm thick, homogeneous oxide coat of Bi–Sb–Ni–Co–Mn–Cr–Al oxide was prepared. After sintering to dense varistor bodies, much improved microstructures with much reduced ZnO-grain sizes were obtained. This shows that the oxides added as liquid sintering aid and grain-growth inhibitor become much more active when added homogeneously as a skin on the ZnO powder. After sintering of cobalt-coated WC, much improved micro-structures were obtained with a much more narrow WC grain-size distribution than that obtained from starting powders mixed by a conventional milling route. Coated powders also obviate the need for the extensive milling of WC and Co powders used in conventional mixing. The novel solution route was also applied to preparation of porous sponges and thin films on metal, glass and Al2O3 of sub 20 nm sized Co- or Ni-particles.
886

Phase Formation of Nanolaminated Transition Metal Carbide Thin Films

Lai, Chung-Chuan January 2017 (has links)
Research on inherently nanolaminated transition metal carbides is inspired by their unique properties combining metals and ceramics, such as higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining the metallic conductivity. The interesting properties are related to their laminated structure, composed of transition-metalcarbide layers interleaved by non-transition-metal (carbide) layers. These materials in thin-film form are particularly interesting for potential applications such as protective coatings and electrical contacts. The goal of this work is to explore nanolaminated transition metal carbides from the aspects of phase formation and crystal growth during thin-film synthesis. This was realized by studying phases in select material systems synthesized from two major approaches, namely, fromdirect-deposition and post-deposition treatment. The first approach was used in studies on the Mo-Ga-C and Zr-Al-C systems. In the former system, intriguing properties have been predicted for the 3D phases and their 2D derivatives (socalled MXenes), while in the latter system, the phases are interesting for nuclear applications. In this work, the discovery of a new Mo-based nanolaminated ternary carbide, Mo2Ga2C, is evidenced from thin-film and bulk processes. Its structure was determined using theoretical and experimental techniques, showing that Mo2Ga2C has Ga double-layers in simple hexagonal stacking between adjacent Mo2C layers, and therefore is structurally very similar to Mo2GaC, except for the additional Ga layers. For the Zr-Al-C system, the optimization of phase composition and structure of Zr2Al3C4 in a thin-film deposition process was studied by evaluating the effect of deposition parameters. I concluded that the formation of Zr2Al3C4 is favored with a plasma flux overstoichiometric in Al, and with a minimum lattice-mismatch to the substrates. Consequently, epitaxial Zr2Al3C4 thin film of high quality were deposited on 4H-SiC(001) substrates at 800 °C. With the approach of post-deposition treatment, the studies were focused on a new method of thermally-induced selective substitution reaction of Au for the non-transition-metal layers in nanolaminated carbides. Here, the reaction mechanism has been explored in Al-containing (Ti2AlC and Ti3AlC2) and Ga-containing (Mo2GaC and Mo2Ga2C) phases. The Al and Ga in these phases were selectively replaced by Au while the carbide layers remained intact, resulting in the formation of new layered phases, Ti2Au2C, Ti3Au2C2, Mo2AuC, and Mo2(Au1-xGax)2C, respectively. The substitution reaction was explained by fast outward diffusion of the Al or Ga being attracted to the surface Au, in combination with back-filling of Au, which is chemically inert to the carbide layers,to the vacancies. The substitution reaction was further applied to Ga-containing nanolaminated carbides, (Cr0.5Mn0.5)2GaC and Mo2GaC, motivated by development of novel magnetic nanolaminates. The former experiment resulted in the formation of (Cr0.5Mn0.5)2AuC, where the retained (Cr0.5Mn0.5)2C layers allowed a comparative study on the magnetic properties under the exchange of Ga for Au. After Au substitution, reduction in the Curie temperature and the saturation magnetization were observed, showing a weakened magnetic exchange interaction of the magnetic (Cr0.5Mn0.5)2 Clayers across the Au. In the Mo2GaC case, an Fe-containing MAX phase, Mo2AC with 50 at.% of Fe on the A site, was synthesized through selective substitution of Au-Fe alloy for the Ga layers, showing the first direct evidence for Fe in the MAX-phase structure. The substitution of Fe did not take place on another Mo2GaC sample tested for Fe exchange only, indicating the essential role of Au in catalyzing the Fe-substitution reaction. The knowledge gained from this thesis work contributes to improved approaches for attaining thin films of nanolaminated transition metal carbides with desired phase composition and crystal quality. The reports on the new nanolaminated phases through exchange interactions are likely to expand the family of nanolaminated carbides and advance their properties, and trigger more studies on related (quasi-) 2D materials.
887

An Analysis of NMRD profiles and ESR lineshapes of MRI Contrast Agents

Zhou, Xiangzhi January 2004 (has links)
To optimize contrast agent in MRI scan region, e.g. to enhance paramagnetic relaxation in the MRI scan fields(0.1T-3T), one possible way is to slow down the tumbling of the paramagnetic complex. The effect of slowing down the reorientational motion of the complex to increase relaxivity is obvious and this strategy has already been employed in producing MRI contrast agent that can bind to specific proteins. An example is MS-325 binds to human serum albumin(HSA). The slow down effects on the ligands around paramagnetic ion, and on the zero field splitting(ZFS) interaction are under studies and the physics behind is still not clear. In this thesis, a generalized Solomon-Bloembergen-Morgan(GSBM) theory together with stochastic Liouville approach(SLA), is applied to investigate the mechanism behind the slow down effects. Two gadolinium complexes, MS-325+HSA and Gd(H2O)83++glycerol are studied by means of NMRD and ESR experiments. GSBM is a second order perturbation theory with closed analytical form. The computation based on this theory is fast, but it has its limitation and in the case of Gd(S=7/2) the ZFS strength times its correlation time(Δt.τƒ) should be less than 0.1. In comparison, the SLA is an "exact" theory that can evaluate the validity of GSBM calculation. However, the calculation in SLA is time consuming due to the large matrix it constructed. The major model used in GSBM is a two dynamic model, characterized by transient ZFS Δt and static ZFS Δs and their corresponding correlation time τƒ and τR, while in SLA the model is only described by Δt and τƒ. A combined NMRD and ESR analysis is used to understand the details of ZFS interaction. Both models can reproduce experimental NMRD profiles and model parameters are similar; for ESR linewidths the model parameters are quite different. The fitting results indicate the NMRD profiles are less sensitive to the detail expression of ZFS correlation function. In order to interpret both NMRD and ESR experiments with identical parameters, a more complex ZFS interaction model should be developed.
888

Hur markegenskaper i produktionsskog påverkas av bök från vildsvin (Sus scrofa) i sydvästra Sverige

Petersson, Linn January 2019 (has links)
A balance between large-scale and small-scale disturbance is important for maintaining species diversity on landscape level. Wild boar rooting contributes to small-scale disturbance when leaving patches bare of soil. Knowledge is scarce regarding their impact on soil properties in managed spruce forests in south-west Sweden. Therefore, the objective of this study was to determine the effects of wild boar rooting on soil physical and chemical properties, by taking soil samples from the centre, the edge and outside of disturbed patches. Rooting activities significantly increased soil moisture, organic matter, total N and pH but did not affect total P in this study. Areas with high number of disturbed patches had higher soil moisture and organic matter compared to areas with intermediate and few disturbed patches. These new soil characteristics can favour species diversity and ultimately increase productivity in managed forests. The results of this study indicate that wild boar activity contributes to more positive than negative effects in managed spruce forests and focus should therefore lie on preventing wild boar rooting in other areas more sensitive to this disturbance. It is also important to disseminate information and knowledge about the wild boar's positive and negative impact on managed forests in order to better prevent the negative effects and strengthen the positive ones.
889

Photoredox catalysis with 10-phenyl-10H- phenothiazine and synthesis of a photocatalytic chiral proline-based organocatalyst / Photoredoxkatalys med 10-fenyl-10H-fenotiazin och syntes av en fotokatalytisk, kiral prolin-baserad organokatalysator

Lamprianidis, Panagiotis January 2020 (has links)
Photoredox catalysis applications for the purpose of new synthetic routes in organic and sustainable chemistry are hot topics in organic synthesis today. In the present study, the synthesis of a chiral proline-based organocatalyst functionalized with 10-phenyl-10H phenothiazine (PTH) photocatalytic moietiesis investigated and attempted for the first time. PTH, an organic photocatalyst, isstudied for its photocatalytic activity in different organic reactions, such as dehalogenation of aromatic halides and the pinacol coupling reaction between aromatic aldehydes. These transformations are otherwise difficult to achieve without a suitable catalyst and the reactions were performed with moderate to high yields. / Applikationer av photoredox-katalys med syftet att generera nya syntetiska vägar inom organisk och hållbar kemi är populära ämnen i organisk syntes idag. I denna studien undersöktes för första gången syntesen av en kiral prolinbaserad organokatalysator som är funktionaliserad med fotokatalytiska enheter (10-fenyl-10H-fenotiazin (PTH)). Den fotokatalytiska aktiviteten av PTH studerades för olika organiska reaktioner, såsom t.ex. dehalogenering av aromatiska halider och pinacolkopplingar mellan aromatiska aldehyder. Dessa transformationer är annars svåra att uppnå utan en lämplig fotokatalysator och reaktionerna utfördes med måttliga till höga utbyten.
890

Quantum Chemical Investigations of Phenol and Larger Aromatic Molecules on TiO2 Surface

Karlsson, Maria January 2004 (has links)
<p>Adsorption of organic molecules at a surface of titanium dioxide (101) anatase is studied using quantum-chemical density functional theory. Anatase can be used in solar cells. For the clean anatase surface the band gap is so large that only UV-light can excite electrons. Different groups with conjugated systems are attached to obtain a more suitable band gap. </p><p>Phenol was attached in different positions to a cluster of anatase and geometry optimized using the B3LYP-functional. The geometry that was energetically most favorable was used to put in phenylmethanol, phenylethanol, naphthol, 2-phenanthrol, 1-pyrol and 2-perylol. To give a more realistic model of phenol at anatase, a study of a two- dimensional periodic anatase surface was also made. </p><p>Molecular orbitals were calculated to study the overlap between HOMO and LUMO orbitals. The calculation shows that phenol will remain as a molecule and will not dissociate. The band gap gets smaller when molecules are attached at the cluster and with 2-perylol it reaches the energy of visible light. </p><p>The molecular orbitals for HOMO, LUMO and LUMO of the adsorbed molecule were investigated. HOMO was localized at the molecule, LUMO at the cluster and LUMO of the adsorbed molecule move closer to the energy of LUMO when the number of rings increases.</p>

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