1,721,112 research outputs found
Energy transfer in individual high aspect-ratio nanostructures via all-optical techniques
Full text linkNanoscale energy transfer in high aspect-ratio nanostructures plays a crucial role in engineering reliable nanostructure-based devices and optimizing heat dissipation. The ultrafast time and micro- to nano-length scales characteristic of nanoscale energy transfer require devising appropriate investigation techniques. This thesis focuses on the mechanical and thermal energy transients occurring in individual MoS2 nanotubes (NTs) and InAs nanowires (NWs), addressing the relevant time and length scales using all-optical microscopy.A nanofabrication protocol is developed to suspend single nanostructures over a trench, while matching the requirements dictated by the spectromicroscopy setup. In addition, to address the role of the environment, configurations in which the nanostructure is supported on polymethyl methacrylate (PMMA) or sapphire substrates are investigated.Energy transfer is investigated in individual multiwall MoS2 NTs. First, the MoS2 NT absolute extinction cross-section per unit length is experimentally retrieved over a wide range of wavelengths and for light polarizations both perpendicular and orthogonal to the NT main axis. The impact of NT diameters and its environment is investigated. Then, analytical and numerical simulations are implemented to disentangle the absorption and scattering contributions to the extinction cross-section. Second, the mechanical properties of MoS2 NTs are investigated, allowing for the identification of their breathing and thickness modes. Finally, supported by analytical models, the thickness of the MoS2 NT shell was accessed, found to be constant (16 nm) with respect to the NT external radius.The mechanical response of individual InAs NWs is also investigated, giving access to their breathing and longitudinal modes, rationalized both by analytical models and numerical simulations, providing a benchmark for the elastic stiffness matrix proposed for wurtzite InAs NWs. The extrinsic and intrinsic attenuation times of the acoustic modes are accessed in the hypersonic frequency range. On the thermal side, a novel method for analyzing heat dissipation out of the NWs starting from time-resolved optical traces affected by reproducibility issues is devised. The extent of the NW-to-substrate contact correlates with the rate of heat dissipation out of the individual NW. Finally, the thermal conductance at the InAs-PMMA interface G~83 MW/m2K is retrieved.Le transfert d'énergie à l'échelle nanométrique dans des nano-objets à rapport d'aspect élevé joue un rôle crucial dans l'ingénierie de dispositifs basés sur des nanostructures et dans l'optimisation de leur dissipation thermique. Les temps ultrarapides et les échelles de longueur caractéristiques du transfert d'énergie à cette échelle nécessitent de techniques appropriées pour l'investigation. Cette thèse traite les phénomènes de transfert d'énergie mécanique et thermique dans des nanotubes (NTs) individuels de MoS2 et des nanofils (NWs) d'InAs, en abordant les échelles de temps et de longueur pertinentes à l'aide de la microscopie tout optique.Un protocole de nanofabrication est développé pour suspendre des nanostructures uniques au-dessus d'une tranchée, en respectant les exigences du système de spectromicroscopie. Pour aborder le rôle de l'environnement, des configurations avec la nanostructure supportée sur du polyméthacrylate de méthyle (PMMA) ou sur du saphir sont étudiées.Le transfert d'énergie est étudié dans des NTs de MoS2. La section efficace d'extinction par unité de longueur d'un NT unique est quantitativement extraite sur une large gamme de longueurs d'onde et pour des polarisations lumineuses perpendiculaires et orthogonales à l'axe principal du NT. L'impact des diamètres des NTs et de leur environnement est examiné. Des simulations analytiques et numériques démêlent les contributions d'absorption et de diffusion à la section efficace d'extinction. Les propriétés mécaniques des NTs de MoS2 sont étudiées, permettant d'identifier leurs modes de respiration et d'épaisseur. La modélisation analytique permet d'accéder à l'épaisseur de la coque du NT, constante (d’environ 16 nm) par rapport au rayon externe du NT.La réponse mécanique des NWs d'InAs est étudiée, donnant accès à leurs modes de respiration et longitudinaux, rationalisés par des modèles analytiques et des simulations numériques, fournissant une référence pour la matrice de rigidité élastique des NW d'InAs. Les temps d'atténuation extrinsèques et intrinsèques des modes acoustiques sont obtenus dans la gamme de fréquences hypersoniques. Du côté thermique, une méthode d'analyse de la dissipation de chaleur des NW à partir de traces optiques est conçue. Le taux de dissipation de chaleur des NWs est corrélé avec l'étendue du contact NW-substrat. Enfin, la valeur de la conductance thermique à l'interface InAs-PMMA (G~83 MW/m²K) est extraite
Expression vector system and a method for optimization and confirmation of DNA delivery and quantification of targeting frequency
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Genome medicine: gene therapy for the millennium, 30 September-3 October 2001, Rome, Italy
No full textThe recent surge of DNA sequence Information resulting from the efforts of agencies interested in deciphering the human genetic code has facilitated technological developments that have been critical in the identification of genes associated with numerous disease pathologies. In addition, these efforts have opened the door to the opportunity to develop novel genetic therapies to treat a broad range of inherited disorders, Through a joint effort by the University of Vermont, the University of Rome, Tor Vergata, University of Rome, La Sapienza, and the CSS Mendel Institute, Rome, an international meeting, 'Genome Medicine: Gene Therapy for the Millennium' was organized. This meeting provided a forum for the discussion of scientific and clinical advances stimulated by the explosion of sequence information generated by the Human Genome Project and the implications these advances have for gene therapy. The meeting had six sessions that focused on the functional evaluation of specific genes via biochemical analysis and through animal models, the development of novel therapeutic strategies involving gene targeting, artificial chromsomes, DNA delivery systems and non-embryonic stem cells, and on the ethical and social implications of these advances
Targeted correction of a defective selectable marker gene in human epithelial cells by small DNA fragments
No full textA novel gene targeting strategy, small fragment homologous replacement (SFHR), has been used to correct specific genomic lesions in human epithelial cells. The frequency of targeting was estimated to be 1-10%. However, given the genomic target, the cystic fibrosis transmembrane conductance regulator (CFTR) gene, it is difficult to accurately quantify targeting frequency. As an alternative to targeting CFTR, targeted correction of a mutant selectable marker or reporter gene would be more amenable to accurate and rapid quantification of gene targeting efficiency. The present study evaluates the conditions that modulate SFHR-mediated correction of a defective Zeocin antibiotic resistance (Zeo(r)) gene that has been inactivated by a 4-bp insertion. The conditions include delivery systems, plasmid-to-fragment ratio, fragment length, and fragment strandedness (single- or double-stranded DNA). Targeting fragments comprise the wild-type Zeo(r) gene sequence and were either 410 (Zeo1) or 458 bp (Zeo3). Expression vectors containing the corrected Zeo(r) gene were isolated as episomal plasmids or were allowed to stably integrate into cultured human airway epithelial cells. Correction of the Zeo(r) gene was phenotypically defined as restoration of resistance to Zeocin in either bacteria or epithelial cell clones. Extrachromosomal gene correction was assayed using polymerase chain reaction amplification, restriction enzyme digestion, DNA sequencing, and Southern blot hybridization analysis of DNA from isolated prokaryotic and eukaryotic clones. Neither random sequence alteration in the target episomal gene nor random integration of the small fragments was detected. Targeted correction efficiencies of up to 4% were attained. These studies provide insight into parameters that can be modulated for the optimization of SFHR-mediated targeting
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