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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.
21

The effect of environment on peptide stability

Bodkin, Michael James January 1996 (has links)
No description available.
22

Kunskapsöverföring - vägen till konkurrenskraft och ökad tillväxt i turistindustrin? : En studie baserad på samarbete mellan universitet och tre turistföretag.

Antonsson, Camilla January 2012 (has links)
Turism är den nya basnäringen i svensk ekonomi. För att företag inom turistindustrin ska bli konkurrenskraftiga och nå ökad tillväxt krävs innovationsprocesser. Tre studentuppsatser från 2007 har legat till grund för den här undersökningen. Syftet med den här studien är att kartlägga hur kunskapsöverföring som överlämnats från universitet till turistföretag bidragit med innovationsprocesser som lett till ökad tillväxt och konkurrenskraft i turistföretag. I samtliga undersökta fall påvisas att den överförda kunskapen varit mer bekräftande än innovativ för uppdragsgivarna. Vidare visar undersökningen att studentuppsatserna som erhållits varit för omfattande och för svåra att ta till sig för merparten av mottagarna. Undersökningen visar att kunskapen i sig, genom studentuppsatserna från universiteten inte varit bristfällig och obrukbar. Istället visar undersökningen att kommunikationen, mottagandet och situationen vid överföringen av uppsatsarbetets resultat varit bristfällig och hämmat implementering av innovationsprocesser.   Resultatet av studien visar att det behövs nya synsätt kring kunskapsöverföring och hur den kommuniceras. Att utveckla ett kunskapsöverföringsprogram, kvalitetssäkra överföringen och fastställa speciella normer för presentationen av utfört uppsatsarbete skulle kunna vara potentiella faktorer som förbättrade processen och medförde att merparten av mottagarna inom turistindustrin skulle kunna ta till sig den överförda kunskapen på ett bättre sätt.
23

Using Simulated Annealing Method to Resolve the Structure of Myoglobin

Chen, Chien-Cheng 17 July 2002 (has links)
The £\-helix structure of protein is very similar to the cylindrical structure. Especially, the Sperm-Whale Myoglobin molecules has 70% £\-helix structure. Therefore, we use simulated annealing method to solve ¡§X-ray phase problem¡¨, and apply Metropolis algorithm to avoid local minimum. We hope that the new method can build £\-helix structure of Sperm-Whale Myoglobin molecule. Therefore, we use multi cylinders as the Myoglobin¡¦s tertiary structure and solve the cylinder¡¦s structure with the simulated annealing method.
24

Modellierung helikaler Transmembranproteine

Gottschalk, Kay-Eberhard. January 2002 (has links) (PDF)
München, Techn. Univ., Diss., 2002.
25

Controlling macromolecular conformation for the nanoscale transmission of information

Le Bailly, Bryden January 2015 (has links)
Helical oligomers made up of the achiral amino acid Aib (2-aminoisobutyric acid) have great potential in relaying stereochemical information over nanometre distances by control of their macromolecular conformation. In a synthetic signalling pathway, the helical domain acts as a transducer, mediating the information flow between an input and an output. This thesis describes the advancement of these helical systems into functioning, dynamic transduction pathways capable of nanoscale information processing by a variety of different means. Through studying the effect of C-terminal chiral amino acids, alanine was found to give maximal control over the helical screw-sense. It was also discovered that the hydrogen bonding preference of the terminal group (ester, amide etc.) determined the screw-sense direction. By modifying the terminus, this directional preference was inverted using light or pH as secondary stimuli. Non-covalent interactions with solvent were found to be important in controlling the flow of information through the helical domain. In less polar solvents (THF, chloroform) a single screw sense can prevail for up to 200 monomers, leading to very low signal loss. A zinc binding site was developed to allow a chiral ligand to act as the input in the signalling process. Both amino and phosphoric acids led to remarkable levels of screw-sense induction. Using the reversible ligand binding interaction a pH switch was set up to moderate the binding of these two ligands, creating a ternary information switch. Significant progress was also made towards a light switch using a spiropyran as a competing ligand. Finally, a novel light-responsive switch capable of releasing a signalling molecule in solution was conceived and developed.
26

Forces modulating the folding of Bacteriorhodopsin

Allen, Samantha Jane January 2002 (has links)
No description available.
27

Analysis of a Helix Antenna Using a Moment Method Approach With Curved Basis and Testing Functions

Caswell, Eric D. 28 September 1998 (has links)
Typically wire antenna structures are modeled by approximating curved structures with straight wire segments. The straight wire approximation yields accurate results, but often requires a large number of segments to adequately approximate the antenna geometry. The large number of straight wire segments or unknowns requires a large amount of memory and time to solve for the currents on the antenna. By using curved segments which exactly describe the contour of the antenna geometry the number of unknowns can be reduced, thus allowing for bigger problems to be solved accurately. This thesis focuses on the analysis of a helix antenna. The Method of Moments is used to solve for the currents on the antenna, and both the triangle basis and pulse testing functions exactly follow the contour of the helix antenna. The thin wire approximation is used throughout the analysis. The helix is assumed to be oriented along the z-axis with an optional perfect electric conductor (PEC) ground plane in the x-y plane. For simplicity, a delta gap source model is used. Straight feed wires may also be added to the helix, and are modeled similarly to the helix by the Method of Moments with triangular basis and pulse testing functions. The primary validation of the curved wire approach is through a comparison with MININEC and NEC of the convergence properties of the input impedance of the antenna versus the number of unknowns. The convergence tests show that significantly fewer unknowns are needed to accurately predict the input impedance of the helix, particularly for the normal mode helix. This approach is also useful in the analysis of the axial mode helix where the current changes significantly around one turn. Because of the varying current distribution, the improvement of impedance convergence with curved segments is not as significant for the axial mode helix. However, radiation pattern convergence improvement is found. Multiple feed structures for the axial mode helix are also investigated. In general, the many straight wire segments, and thus unknowns, that are needed to accurately approximate the current around one turn can be greatly reduced by the using the curved segment method. / Master of Science
28

Polypeptide-Based Nanoscale Materials

Aili, Daniel January 2008 (has links)
Self-assembly has emerged as a promising technique for fabrication of novel hybrid materials and nanostructures. The work presented in this thesis has been focused on developing nanoscale materials based on synthetic de novo designed polypeptides. The polypeptides have been utilized for the assembly of gold nanoparticles, fibrous nanostructures, and for sensing applications. The 42-residue polypeptides are designed to fold into helix-loop-helix motifs and dimerize to form four-helix bundles. Folding is primarily driven by the formation of a hydrophobic core made up by the hydrophobic faces of the amphiphilic helices. The peptides have either a negative or positive net charge at neutral pH, depending on the relative abundance of Glu and Lys. Charge repulsion thus prevents homodimerization at pH 7 while promoting hetero-dimerization through the formation of stabilising salt bridges. A Cys incorporated in position 22, located in the loop region, allowed for directed, thiol-dependent, immobilization on planar gold surfaces and gold nanoparticles. The negatively charged (Glu-rich) peptide formed homodimers and folded in solution at pH < 6 or in the presence of certain metal ions, such as Zn2+. The folding properties of this peptide were retained when immobilized directly on gold, which enabled reversible assembly of gold nanoparticles resulting in aggregates with well-defined interparticle separations. Particle aggregation was found to induce folding of the immobilized peptides but folding could also be utilized to induce aggregation of the particles by exploiting the highly specific interactions involved in both homodimerization and hetero-association. The possibility to control the assembly of polypeptide-functionalized gold nanoparticles was utilized in a colorimetric protein assay. Analyte binding to immobilized ligands prevented the formation of dense particle aggregates when subjecting the particles to conditions normally causing extensive aggregation. Analyte binding could hence easily be distinguished by the naked eye. Moreover, the peptides were utilized to assemble gold nanoparticles on planar gold and silica substrates. Fibrous nanostructures were realized by linking monomers through a disulphide-bridge. The disulphide-linked peptides were found to spontaneously assemble into long and extremely thin peptide fibres as a result of a propagating association mediated by folding into four-helix bundles. / Ingenjörer och vetenskapsmän har ofta inspirerats av naturen i sökandet efter lösningar på tekniska problem. Allt ifrån byggnadskonstruktioner, flygplansvingar, kompositmaterial till kardborrebandet har skapats med utgångspunkt från förebilder i naturen. Många av de material och konstruktioner som återfinns i naturen har åtråvärda egenskaper som är svåra att erhålla i syntetiska matrial med traditionell teknik. Även om vi i flera fall kan härma sammansättningen och formen blir resultatet inte nödvändigtvis det samma. Den största skillnaden mellan syntetiska material och material producerade av levande organismer är hur deras komponenter sinsemellan är organiserade och sammansatta. I syntetiska material är komponenterna ofta inbördes mer eller mindre slumpvis ordnade medan de i biologiska material är organiserade med en oerhörd precision som sträcker sig ända ned på molekyl- och atomnivå. Naturens byggstenar har genom evolutionens gång förfinats för att spontant kunna organisera sig och bilda komplexa material  och strukturer. Denna process, som styrs genom att många svaga krafter inom och mellan byggstenarna samverkar, kallas ofta för självorganisering och är en förutsättning för allt liv. Självorganisering har också blivit en allt viktigare metod inom nanotekniken för att konstruera material och strukturer med nanometerprecision. I den här avhandlingen beskrivs en typ av självorganiserande material där byggstenarna utgörs av nanometerstora guldpartiklar och syntetiska proteiner. De syntetiska proteinerna är designade för att efterlikna naturliga biomolekyler och antar en välbestämd tredimensionell struktur när två av dem interagerar med varandra. Denna interaktion är mycket specifik men kan styras genom att variera kemiska parametrar som surhet och jonstyrka vilket ger en möjlighet att påverka och kontrollera proteinernas struktur. Proteinerna har vidare modifierats för att spontant organisera sig till fibrer som är flera mikrometer långa men endast några nanometer tjocka. Proteinfibrer utgör en mycket viktig typ av strukturer i biologiska system och finns i alltifrån spindelväv till muskler. Syntetiska proteinfibrer är därför både ett intressant modellsystem och ett material med många potentiellt intressanta användningsområden. Genom att fästa de syntetiska proteinerna på ytan av guldnanopartiklar går interaktionerna mellan partiklarna att kontrollera på samma sätt som interaktionerna mellan proteinerna. Krafterna mellan proteinerna och interaktionerna involverade i proteinernas veckning har använts för att reversibelt aggregera och organisera nanopartiklarna. Ett antal olika byggstenar har studerats och utvecklats till något som liknar ett mycket enkelt nano-Lego, som på en given signal spontant bygger ihop sig eller trillar isär. Guldnanopartiklar är intressanta eftersom de är stabila och lätta att modifiera kemiskt men också på grund av deras optiska egenskaper som ger dem en ovanligt vacker vinröd färg. Färgen uppstår på grund av partiklarnas ringa storlek och varierar naturligt med egenskaperna hos den omgivande miljön. Detta gör det enkelt att studera hur partiklarna interagerar eftersom de byter färg när de närmar sig varandra, men gör dem också intressanta för sensortillämpningar. En enkel och robust sensor beskrivs i avhandlingen där syntetiska proteiner, speciellt utformade för att upptäcka och binda andra molekyler, har fästs på nanopartiklarna. Med partiklarnas hjälp går det att med blotta ögat detektera ett mänskligt protein i koncentrationer under ett tusendels gram per liter. En tidig diagnos av sjukdomstillstånd kan i de flesta fall avsevärt underlätta behandlingen och behovet av enkla sensorer för att bestämma närvaro och koncentration av medicinskt intressanta molekyler är därför mycket stort.
29

I. Collagen-like polypeptides. II. Helix-turn-helix peptides and turn mimetics

Dai, Nan 15 August 2008 (has links)
Collagen is one of the most important and abundant proteins in mammals. It consists of three left-handed PPII helixes coiled along a common axis to form a very compact right-handed super helix. The primary structure is shown to be (Gly-Xaa-Yaa)n repeats with high content of prolyl residues at both Xaa and Yaa positions. <i>Cis-trans</i> isomerization of the prolyl amide bonds is one of the rate-limiting steps during collagen triple helix folding. The conformationally locked alkene isosteres Fmoc-Gly-Ψ[(E)CH=C]-Pro-Hyp(tBu)-OH and Fmoc-Pro-Ψ[(E)CH=C]-Pro-OH were designed and synthesized. The synthesis of the Gly-Pro isostere had no stereo-control, and the two diastereomers of the tripeptide isostere Fmoc-Gly-Ψ[(E)CH=C]-Pro-Hyp(tBu)-OBn were separated by normal phase HPLC. Although the stereoselectivity of the asymmetric reduction was not good for the Pro-Pro isostere, the resulting diastereomers was separable by flash chromatography, and the absolute stereochemistry of the two diastereomers was determined by Mosher's method. The Gly-Pro alkenyl peptides, and their control peptide Ac-(Gly-Pro-Hyp)8-Gly-Gly-Tyr-NH2 were synthesized and purified. All three peptides showed a maximum around 225 nm and a minimum close to 200 nm in the CD spectra, which indicated the formation of PPII helixes. The Tm value of the control peptide was determined to be 50.0 °C. The peptide with Gly-Ψ[(E)CH=C]-L-Pro-Hyp as the guest triplet formed a stable triple helix with a Tm value of 28.3 °C. The peptide with Gly-Ψ[(E)CH=C]-D-Pro-Hyp as the guest triplet showed a linear decrease in the ellipticity with increasing temperature, which indicated that no triple helix was formed. The Pro-Pro alkenyl peptide and its control peptide H-(Pro-Pro-Gly)₁₀-OH were synthesized and purified. The T<sub>m</sub> value of control peptide was determined to be 31.6 °C by extrapolation to 0 M TMAO in PBS buffer, which was very close to the measured value of 31.5 °C. The Pro-Pro alkenyl peptide began to show a maximum around 225 nm in the CD spectra when the concentration of TMAO was higher than 2.5 M. After extrapolation to 0 M TMAO, the T<sub>m</sub> value was determined to be –22.0 °C. These results indicate that the backbone inter-chain hydrogen bond is one of the major forces in stabilizing the collagen triple helix, while <i>cis-trans</i> isomerization has limited contribution. The intrinsic properties of the amide bond may have huge influence on the stability of the collagen triple helix. The helix-turn-helix motif is an important tertiary structure in DNA-binding proteins. Stepwise modifications of the Antennapedia HTH peptide (27-55) were performed to improve the helicity and stability. The peptide with more side-chain ion-pairs was over 4 times more helical than the native Antp peptide, while the Ala-based peptide was over 9 times more helical than the native peptide. A 12-membered ring, Fmoc-protected HTH-turn mimic was designed and synthesized, and was ready for solid phase peptide synthesis. The solubility of the cyclic peptide was very poor, and the purification of the final product was very difficult. The solubility problem might also affect solid phase peptide synthesis in the future. / Ph. D.
30

Artificial neural networks in medicine : theory and application in biomedical systems

Thompson, Ian M. January 1997 (has links)
No description available.

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