Tesi sul tema "Conductance"
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1
Zhu, Ningjia. "Conductance fluctuations in nanostructures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30431.pdf.
Testo completo
2
Donnermeyer, Achim. "Scanning ion-conductance microscopy". [S.l.] : [s.n.], 2007. http://nbn-resolving.de/urn/resolver.pl?urn=urn:nbn:de:hbz:361-11593.
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3
Zhu, Ningjia. "Conductance fluctuations in nanostructures". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=34492.
Testo completoAbstract (sommario):
In this Ph.D thesis the conductance fluctuations of different physical origins in semi-conductor nanostructures were studied using both diagrammatic analytical methods and large scale numerical techniques. In the "mixed" transport regime where both mesoscopic and ballistic features play a role, for the first time I have analytically calculated the non-universal conductance fluctuations. This mixed regime is reached when impurities are distributed near the walls of a quantum wire, leaving the center region ballistic. I have discovered that the existence of a ballistic region destroys the universal conductance fluctuations. The crossover behavior of the fluctuation amplitude from the usual quasi-1D situation to that of the mixed regime is clearly revealed, and the role of various length scales are identified. My analytical predictions were confirmed by a direct numerical simulation by evaluating the Landauer formula. In another direction, I have made several studies of conductance or resistance oscillations and fluctuations in systems with artificial impurities in the ballistic regime. My calculation gave explanations of all the experimental results concerning the classical focusing peaks of the resistance versus magnetic field, the weak localization peak in a Sinai billiard system, the formation of a chaotic billiard, and predicted certain transport features which were indeed found experimentally. I have further extended the calculation to study the Hall resistance in a four-terminal quantum dot in which there is an antidot array. From my numerical data I analyzed the classical paths of electron motion and its quantum oscillations. The results compare well with recent experimental studies on similar systems. Since these billiard systems could provide quantum chaotic dynamics, I have made a detailed study of the consequence of such dynamics. In particular I have investigated the resonant transmission of electrons in these chaotic systems, and found that the level-s
4
鄭蔚 e Wei Zheng. "Dynamic conductance of nanostructures". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243939.
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5
Fulford, D. J. "Variable conductance heat pipes". Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234584.
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6
Zheng, Wei. "Dynamic conductance of nanostructures /". Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B24367382.
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7
Ayers, George Harold. "Cylindrical thermal contact conductance". Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969/88.
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8
Page, Ashley M. "Multifunctional scanning ion conductance microscopy". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/99668/.
Testo completoAbstract (sommario):
Scanning ion conductance microscopy (SICM) is a nanopipette-based technique that has historically been used for the topographical imaging of soft samples. This thesis demonstrates the development of SICM into a multifunctional tool, capable of providing a host of additional information about both biological and inert samples, whilst maintaining the structural mapping capability for which it is usually employed. Two approaches are taken to extend the functionality of SICM: (i) designing sophisticated potential, and positional, control functions that are then used with traditional single-channel nanopipettes; and (ii) incorporating an ion conductance channel into a multi-barrelled probe. In the single-channel setup, a pulsed-potential profile allows the extraction of surface charge density on extended substrates, and a ramped-potential profile permits spatially resolved mapping of redox reactions on an electrode substrate. When integrated into a more complex probe, SICM is used to study molecular uptake at cellular surfaces, and to print Cu microstructures on a Au substrate. While this thesis is primarily concerned with technique development, the studies herein have broad applications in cell biology, pharmaceuticals, materials science and beyond. In addition to developing imaging modes that allow the extraction of functional information at a surface, this thesis also contributes to the fundamental understanding of the SICM system. Finite element method simulations are performed alongside experimental studies, in order to fully understand the contributions of the pipette geometry, ion current rectification, and pipette-surface interactions on the measured ionic current. The theoretical treatment herein provides a foundation upon which future multifunctional SICM regimes could be designed, extending the scope of this increasingly powerful technique.
9
Fox, Colin. "Conductance imaging : estimation of isotropic conductance perturbations from low-frequency boundary measurements in circular geometries". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303010.
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10
Göppert, Georg. "Single electron tunneling at large conductance". [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=960943420.
Testo completo
11
Asano, Yasuhiro, Yukio Tanaka, Alexander A. Golubov e Satoshi Kashiwaya. "Conductance Spectroscopy of Spin-Triplet Superconductors". American Physical Society, 2007. http://hdl.handle.net/2237/11290.
Testo completo
12
Davies, Owen R. "Electronic structure and conductance of DNA". Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56032/.
Testo completoAbstract (sommario):
In this thesis an efficient method has been developed for calculating the electronic structure and conductance of large biological molecules. The embedding method has been adapted to allow the splitting of large molecules such as DNA into smaller component blocks, completely preserving the information of the macro-system. The computational time required for this method increases as O(N) with the size of the system, instead of the traditional O(N3). The semi-empirical extended Huckel theory is used to describe the electron wavefunctions within a tight-binding scheme, taking the effect of the metal-molecule contacts into account. Presented in this thesis are the results for several different DNA molecules and structures. It has been determined that the transmission through DNA depends sensitively on the energy at which it is evaluated, and the atoms to which the metallic leads are connected. It is also found that poly(G)-poly(C) DNA conducts charge better than DNA with mixed bases, and that energy-minimised DNA with less structural disorder conducts better than DNA obtained from x-ray diffraction experiments. The electrical conduction of DNA that has undergone stretching has been investigated, and the distorted structure gives very small currents. The embedding method has also been applied to the small aromatic molecule OPE, to determine its electronic properties. Metallic conductivity is found for this molecule, and it is able to carry currents 1000 times greater than DNA, giving possible applications in molecular electronics.
13
Martin, Shashi A. "Computation of conductance for ballistic nanostructures". Virtual Press, 1994. http://liblink.bsu.edu/uhtbin/catkey/917024.
Testo completoAbstract (sommario):
Future electronic devices having dimensions on the nanometer scale will rely on the resultant quantum effects for their operation. In this project, these quantum effects were investigated through the theoretical modeling and computer simulation of a confined twodimensional electron gas in a semiconductor heterostructure. Assuming hardwall boundaries and sharp geometrical features, the nanostructure conductance has been calculated by finding transverse eigenvalues and eigenfunctions, computing hopping integrals for a one-dimensional tight binding lattice, determining the Greens' propagators, and then finally evaluating the transmittance. From the transmittance, the conductance was determined.A structured and modular computer program in FORTRAN was developed to investigate the effects of geometrical modifications on the conductance of ballistic nanochannels. The program has been designed in such a way that the user need only supply the nanostructure specifications to an input data file. The program then uses this data file to perform the calculations. A separate, user-friendly program has been developed to form the data file. The program is such that additions and modifications can be easily made in the future.Department of Physics and Astronomy
14
Richards, Owen James. "Advances in scanning ion conductance microscopy". Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648409.
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15
Paulla, Kirti Kant. "Conductance Modulation in Bilayer Graphene Nanoribbons". Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1253023785.
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16
Andersson, Victor. "Thermal Contact Conductance in Aircraft Applications". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-72512.
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17
Seiler, Kurt Massimo. "Anomalous contribution to the magnetic Kapitza conductance /". [S.l.] : [s.n.], 1986. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8071.
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18
Scullion, Lisa. "Single molecular conductance of ethers and peptides". Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539474.
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19
Leary, Edmund. "Single Molecule Conductance of Dithiahexyl-Aryl Compounds". Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507724.
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20
Woodland, Simon. "Measurement and modelling of thermal contact conductance". Thesis, University of Surrey, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510558.
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21
Lee, Young-Su Ph D. Massachusetts Institute of Technology. "Electronic structure and quantum conductance of nanostructures". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37371.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 145-158).
This thesis is dedicated to development and application of a novel large-scale first-principles approach to study the electronic structure and quantum conductance of realistic nanoscale materials. Electron transport at the nanometer scale involves phenomena which are beyond the realm of classical transport theory: the wave character of the electrons becomes central, and the Schrddinger equation needs to be solved explicitly. First-principles calculations can nowadays deal with systems containing hundreds of electrons, but simulations for nanostructures that contain thousands of atoms or more need to rely on parametrized Hamiltonians. The core of our approach lies in the derivation of exact and chemically-specific Hamiltonians from first-principles calculations, in a basis of maximally-localized Wannier functions, that become explicit tight-binding orbitals. Once this optimal basis is determined, the Hamiltonian matrix becomes short-ranged, diagonally-dominant, and transferable - i.e. a large nanostructure can be constructed by assembling together the Hamiltonians of its constitutive building block. This approach is first demonstrated for pristine semiconducting and metallic nanotubes, demonstrating perfect agreement with full first-principles calculations in a complete planewave basis.
(cont.) Then, it is applied to study the electronic structure and quantum conductance of functionalized carbon nanotubes. The first class of functionalizing addends, represented by single-bond covalent ligands (e.g. hydrogens or aryls), turns out to affect very strongly the back-scattering and the conductance, since sp3 rehybridization at the sidewall carbon where a group is attached dramatically perturbs the conjugated [pi]-bonding network. Inspection on the shape and the on-site energy of MLWFs before and after functionalizations leads to the conclusion that the effect of sp3 rehybridization is essentially identical to removing a "half-filled" p-orbital from the [pi]-manifold. In this perspective, the chemical difference between functional groups (e.g. different electronegativity of the residues) is relatively minor, even if, of course, will lead to different doping of the tube. We also find that these single-bond ligands tend to cluster, and are more stable when two groups are located nearby (incidentally, the degree of perturbation at the Fermi level becomes weaker when such paired configuration is assumed). The second class of functionalizing addends, represented by cycloaddition functionalizations (e.g. carbenes and nitrenes), demonstrates a radically different behavior.
(cont.) These addends are bonded to two neighboring sidewall carbon atoms, creating a three-membered ring structure. On narrow-diameter tubes, cleaving of the sidewall bond takes place to release the high strain energy of a three-membered ring. In the process, the two sidewall carbons recover their original sp2 hybridization. This step is crucial, since the quantum conductance of a metallic nanotube then recovers almost perfectly the ideal limit of a pristine tube: the bond cleavage restores a transparent conduction manifold. Bond cleavage is controlled by the chemistry of the functional groups and the curvature of the nanotubes. High-curvature favors bond opening, whereas in graphene the bond is always closed; in between the two limits, chemistry determines the critical curvature at which the open-to-closed transition takes place. The preference for bond opening or closing has been screened extensively for different classes of functional groups, using initially some molecular homologues of the nanotubes. It is found that a subclass of addends, exemplified by dicyanocarbene, can assume both the open and closed form in the same tube around a narrow range of diameters.
(cont.) While these two forms are very similar in energy, and separated by a small barrier (hence they can be considered "fluxional" tautomers), the quantum conductance in the closed case is found to be significantly lower than that in the open case. Interconversion between the two minima could then be directed by optical or electrochemical means, in turn controlling the conductance of the functionalized tubes. We envision thus that this novel class of functionalization will offer a practical way toward non-destructive chemistry that can either preserve the metallic conductance of the tubes, or modulate it in real-time, with foreseeable applications in memories, sensors, imaging, and optoelectronic devices.
by Young-Su Lee.
Ph.D.
22
Euler, Christoph [Verfasser]. "Thermal conductance in spin caloritronics / Christoph Euler". Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2016. http://d-nb.info/1225296560/34.
Testo completo
23
Wright, Matthew Henderson. "Anomalous conductance characteristics of quasiballistic 2D systems". Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611913.
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Havlin, Shlomo, Eduardo López, Sergey V. Buldyrev e H. Eugene Stanley. "Anomalous conductance and diffusion in complex networks". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195170.
Testo completoAbstract (sommario):
We study transport properties such as conductance and diffusion of complex networks such as scale-free and Erdős-Rényi networks.
We consider the equivalent conductance G between two arbitrarily chosen nodes of random scale-free networks with degree distribution P(k) ~ k−⋋ and Erdős-Rényi networks in which each link has the same unit resistance. Our theoretical analysis for scale-free networks predicts a
broad range of values of G (or the related diffusion constant D), with a power-law tail distribution ɸSF(G) ~ G−gG, where gG = 2⋋ − 1. We confirm our predictions by simulations of scale-free networks solving the Kirchhoff equations for the conductance between
a pair of nodes. The power-law tail in ɸSF(G) leads to large values of G, thereby significantly improving the transport in scale-free networks, compared to Erdős-R´nyi networks where the tail of the conductivity distribution decays exponentially. Based on a simple physical “transport backbone” picture we suggest that the conductances of scale-free and Erdős-Rényi networks can be approximated by ckAkB/(kA + kB) for any pair of nodes A and B with degrees kA and kB. Thus, a single parameter c characterizes transport on both scale-free and Erdős-Rényi networks.
25
Havlin, Shlomo, Eduardo López, Sergey V. Buldyrev e H. Eugene Stanley. "Anomalous conductance and diffusion in complex networks". Diffusion fundamentals 2 (2005) 4, S. 1-11, 2005. https://ul.qucosa.de/id/qucosa%3A14337.
Testo completoAbstract (sommario):
We study transport properties such as conductance and diffusion of complex networks such as scale-free and Erdős-Rényi networks.
We consider the equivalent conductance G between two arbitrarily chosen nodes of random scale-free networks with degree distribution P(k) ~ k−⋋ and Erdős-Rényi networks in which each link has the same unit resistance. Our theoretical analysis for scale-free networks predicts a
broad range of values of G (or the related diffusion constant D), with a power-law tail distribution ɸSF(G) ~ G−gG, where gG = 2⋋ − 1. We confirm our predictions by simulations of scale-free networks solving the Kirchhoff equations for the conductance between
a pair of nodes. The power-law tail in ɸSF(G) leads to large values of G, thereby significantly improving the transport in scale-free networks, compared to Erdős-R´nyi networks where the tail of the conductivity distribution decays exponentially. Based on a simple physical “transport backbone” picture we suggest that the conductances of scale-free and Erdős-Rényi networks can be approximated by ckAkB/(kA + kB) for any pair of nodes A and B with degrees kA and kB. Thus, a single parameter c characterizes transport on both scale-free and Erdős-Rényi networks.
26
Demolombe, Sophie. "Cftr : ou cystic fibrosis transmembrane conductance regulator". Paris 11, 1996. http://www.theses.fr/1996PA112463.
Testo completoAbstract (sommario):
La mucoviscidose, maladie genetique grave la plus frequente dans les populations europeenne et nord-americaine, est caracterisee par un defaut de transport d'ions chlore par les cellules epitheliales. Cette affection, transmise selon le mode autosomique recessif, est liee a la mutation du gene cf codant pour la proteine cftr (cystic fibrosis transmembrane conductance regulator) qui exerce un role de canal chlore regule par l'atp intracellulaire et l'ampc. La mutation la plus frequente (70% des alleles mutes) est une deletion de la phenylalanine en position 508 qui conduit a un defaut d'adressage de la proteine neoformee. Par des techniques d'immunomarquages faisant appel a differents anticorps monoclonaux, nous avons montre que l'anomalie moleculaire caracteristique de la mutation f508 est retrouvee dans la lignee cfpac-1 issue d'un carcinome pancreatique preleve chez un patient homozygote pour cette mutation. Cfpac-1 est une lignee cellulaire couramment utilisee pour les investigations biochimiques, physiologiques et pharmacologiques de l'insuffisance cellulaire responsable de la mucoviscidose. Nous avons developpe une nouvelle methode permettant d'evaluer l'efficacite de la complementation par transfert de gene de l'epithelium respiratoire mucoviscidosique. Le principe de cette methode consiste a detecter les proteines cftr recombinantes correctement adressees dans la membrane apicale a l'aide d'un anticorps dirige contre la premiere boucle extracellulaire et utilise sur des cellules vivantes. Cette methode est suffisamment sensible pour etre utilisee sur un petit nombre de cellules prelevees par simple curetage de la surface epitheliale. La fonction de la proteine cftr ne se limite pas a celle de canal chlore. Par un mecanisme inconnu, cftr exerce un role regulateur d'autres canaux ioniques, chlorures et sodiques epitheliaux. Nous avons mis en evidence la regulation par cftr de canaux potassiques epitheliaux rectifiant dans le sens entrant et dont le controle par la voie de l'ampc depend de la presence d'une proteine cftr fonctionnelle. Ces canaux k+ interviendraient dans le controle du potentiel membranaire et participeraient au maintien d'un gradient electro-chimique indispensable a la vectorisation transepitheliale du chlore
27
Wu, Jing. "Conductance Switching of Carbon Based Molecular Heterojunctions". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1227844170.
Testo completo
28
Lu, Zhi. "Optimization approaches for minimum conductance graph partitioning". Thesis, Angers, 2020. http://www.theses.fr/2020ANGE0013.
Testo completoAbstract (sommario):
Le problème de partitionnement de graphe de conductance minimale (MCGPP) est un problème d’optimisation combinatoire NP-difficile avec de nombreuses applications pratiques dans divers domaines tels que la détection communautaire, la bioinformatique et la vision par ordinateur. Etant donnée sa complexité intrinsèque, des approches heuristiques et métaheuristiques constituent un moyen convenable pour résoudre des instances de grande taille. Cette thèse est consacrée au développement d’algorithmes métaheuristiques performants pour le MC-GPP. Plus précisément, nous proposons un algorithme «Stagnation aware Breakout Tabu Search», un algorithme évolutif hybride (MAMC) et un algorithme multiniveaubasé sur le recuit simulé (IMSA). Nous présentons des résultats expérimentaux sur de nombreux graphes de grande dimension de la littérature ayant jusqu’à 23 millions de sommets. Nous montrons la haute performance de nos algorithmes par rapport à l’état de l’art. Nous analysons les éléments algorithmiques et stratégies de recherche pour mettre en lumière leur influence sur la performance des algorithmes proposésThe minimum conductance graph partitioning problem (MC-GPP) is an important NP-hard combinatorial optimization problem with numerous practical applications in various areas such as community detection, bioinformatics, and computer vision. Due to its high computational complexity, heuristic and metaheuristic approaches constitute a highly useful tool for approximating this challenging problem. This thesis is devoted to developing effective metaheuristic algorithms for the MC-GPP. Specifically, we propose a stagnation-aware breakout tabu search algorithm (SaBTS), a hybrid evolutionary algorithm (MAMC), and an iterated multilevel simulated annealing algorithm (IMSA). Extensive computational experiments and comparisons on large and massive benchmark instances (with more than 23 million vertices) demonstrate that the proposed algorithms compete very favorably with stateof- the-art algorithms in the literature. Furthermore, the key issues of these algorithms are analyzed to shed light on their influences over the performance of the proposed algorithms
29
Neslen, Cody R. "Negative Conductance Load Modulation RF Power Amplifier". DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/312.
Testo completoAbstract (sommario):
The number of mobile wireless devices on the market has increased substantially over the last decade. The frequency spectrum has become crowded due to the number of devices demanding radio traffic and new modulation schemes have been developed to accommodate the number of users. These new modulation schemes have caused very poor efficiencies in power amplifiers for wireless transmission systems due to high peak-to-average power ratios (PAPR). This thesis first presents the issue with classical power amplifiers in modern modulation systems. A brief overview of current attempts to mitigate this issue is provided. A new RF power amplifier topology is then presented with supporting simulations.
The presented amplifier topology utilizes the concept of negative conductance and load modulation. The amplifier operates in two stages, a low power stage and a high power stage. A negative conductance amplifier is utilized during peak power transmission to modulate the load presented to the input amplifier. This topology is shown to greatly improve the power added efficiency of power amplifiers in systems with high PAPR.
30
Rzigui, Touhami. "Analyse de la réponse d’un mutant mitochondrial de Nicotiana sylvestris au manque d’eau". Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112144/document.
Testo completoAbstract (sommario):
Pour étudier le rôle de la mitochondrie dans la tolérance à la sécheresse, la réponse à la contrainte hydrique a été comparée entre une lignée sauvage (WT) et un mutant CMSII (Cytoplasmic Male Sterile) de Nicotiana sylvestris. Chez le mutant CMSII, le complexe I mitochondrial est absent et la respiration est assurée par les NAD(P)H déshydrogénases alternes et elle est maintenue à un niveau supérieur de l’ordre de 20 à 30% à celui du WT. La différence observée entre les plantes WT et CMSII met en jeu non seulement le fonctionnement mitochondrial, mais également le fonctionnement des chloroplastes. En effet, l’activité photosynthétique du mutant est plus faible que celui du WT et elle est corrélée avec une plus faible conductance stomatique (gs) et mésophyllienne (gm).Après l’arrêt de l’arrosage, on observe que le contenu relatif en eau (RWC) diminue plus lentement chez les feuilles du CMSII. Ceci n’était pas le résultat d’une plus petite surface de transpiration ou d’une masse racinaire d’absorption plus élevé puisque le rapport partie aérienne/racine et la surface foliaire totale ont été similaires au début de l’expérience chez les deux génotypes. De plus la mutation n’a pas induit des changements au niveau des paramètres hydriques (P0, PTLP, RWCTLP) ni au niveau de la densité stomatique. La tolérance des plantes CMSII a été le plus probablement la conséquence de sa plus faible transpiration en conditions bien hydratées et aux premiers jours de déshydratation et non pas d’une meilleure efficacité d’absorption de l’eau puisque le contenu en eau du sol reste plus élevé chez CMSII après l’arrêt de l’arrosage. La plus faible conductance stomatique chez le CMSII bien hydraté a été expliquée par sa plus faible conductance hydraulique. De plus, contrairement au WT, le niveau des acides aminés totaux diminue au cours de la déshydratation lorsque le contenu en protéines solubles augmente chez les feuilles du CMSII, suggérant une accélération de la remobilisation des acides aminés. D’autre part, il a été aussi montré que le mutant CMSII est capable de s’acclimater mieux à la sécheresse que le WT lorsqu’ils ont été maintenus à un RWC de 80 % sur plusieurs jours. Sous ces conditions, la photosynthèse reste plus élevée chez le mutant que chez le WT. Cette meilleure acclimatation corrèle avec une plus forte photorespiration du CMSII sous conditions bien hydratées et sous conditions d’acclimatation. La photorespiration chez CMSII et le WT a été estimée par le transport électronique dévolu à l’oxygénation de RuBP et en plus par l’accumulation des métabolites impliqués dans la photorespiration. D’une part, l’acclimatation à la sécheresse diminue gm plus fortement chez le WT que chez le CMSII. D’autre part, le WT accumule la glycine ce qui laisse supposer que le glycine décarboxylase mitochondrial est plus affectée chez le WT que chez le CMS et inhibe ainsi la photorespiration. En effet, cette plus faible photorespiration chez le WT affecte les réactions primaires de la photosynthèse par une accumulation d’un gradient de protons estimé par le quenching non-photochimique (NPQ) de la fluorescence chlorophyllienne ce qui induit une diminution du transport électronique des réactions primaires de la photosynthèseTo investigate the role of mitochondria in drought stress, the response to water deprivation was compared between Nicotiana sylvestris wild type (WT) plants and the CMSII respiratory complex I mutant. In CMSII, alternative NAD(P)H-dehydrogenases bypassing complex 1 allow respiration.. The difference of mitochondrial function between WT and CMSII plants affect also photosynthesis. The CMSII has lower photosynthetic actitvity than the WT and lower stomatal (gs) and internal (gm) conductances to CO2. When watering of plants with similar leaf surface and similar shoot/root ratio was stopped the relative water content (RWC) declined faster in WT as compared to CMSII leaves. Furthermore, CMSII and WT leaves had the same osmotic potential at leaf saturation (P0) and at leaf turgor lost pressure (PTLP) and the same stomatal density. The slower decline of RWC in CMSII, compared to WT leaves, was most likely the consequence of the lower stomatal conductance (gs) under well-watered conditions and during the first days after withholding watering, The lower stomatal conductance of well-watered CMSII leaves correlated with a lower hydraulic conductance of leaves. Remarkably, total free amino acid levels declined and total soluble protein content increased in CMSII leaves, while the opposite was observed in WT leaves. This suggests protein synthesis in CMSII but protein degradation in WT leaves during drought stress. We also show that CMSII leaves better acclimate to drought stress than the WT leaves. After several days at 80 % RWC , photosynthesis is higher in the mutant than in WT. As compared to the WT, the mutant shows higher rates of photorespiration before and after acclimation to drought.The strong accumulation of glycine in the WT suggests that photorespiration may be limited at the level of glycine decarboxylase. In addition, after acclimation to drought gm declined markedly in WT but not in CMSII leaves, thus further limiting CO2 supply for photosynthesis in the WT. The resulting lower photosynthesis and photorespiration in WT leaves affect also the primary reaction of photosynthesis by increasing the non-photochemical fluorescence quenching (NPQ) and decreasing linear electron transport
31
Salvi, Michele [Verfasser], e Wolfgang [Akademischer Betreuer] Koenig. "The Random Conductance Model: local times large deviations, law of large numbers and effective conductance / Michele Salvi. Betreuer: Wolfgang Koenig". Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2013. http://d-nb.info/1034952757/34.
Testo completo
32
Ogbazghi, Asmerom Yemane. "Conductance through Nanometer-scale Metal-to-Graphite Contacts". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6872.
Testo completoAbstract (sommario):
The metal/graphite interface is interesting due to the typically large disparity in the characteristics of the electronic structure (e.g.
Fermi wavelength and Fermi energy) and dimensionality (3D in the metal versus quasi-2D in graphite). The goal of this work is to
determine how the contact conductance to graphite depends on the metal contact area for nanometer-scale contacts. From this we deduce the
effect of electronic screening in the graphite. Three different metals were chosen for this work: Solid Cu and Al, and liquid Ga.
Liquid Ga provided a unique opportunity to reduce the effect of mechanical interactions to near zero, while Cu and Al were chosen for
their different electronic structures. At the interface between the metal and graphite, the large Fermi wavevector of Al should allow
phase matching of Al states to those in graphite, while the Cu Fermi surface lies inside of all available graphite wavevector states.
33
Wrathmell, Claire Louise. "Scanning tunnelling microscopy study of tuneable metalloprotein conductance". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491601.
Testo completoAbstract (sommario):
Azurin wild-type and mutant proteins were directly adsorbed onto pristine gold surfaces. Scanning probe and electrochemical characterisation of the metalloprotein arrays indicated robust, high coverage adsorption with good retention of redox activity. Imaging resolution was optimised through extensive pre-testing of tip and substrate preparations. Tunnelling transport was then examined as a function of environmental conditions (ambient/fluid, bias/set point and temperature). The first documented low temperature protein STM under fluid is presented. The role of azurin's metal centre in the tunnelling pathway was probed using electrochemical STM. Striking differences were observed in the imaging ofredox-active Cu azurin, compared to its redox-inactive Zn analogue. The conductance of Cu azurin was shown to be tunable by the substrate potential at the single molecule level. A peak in molecular contrast was resolved at a potential close to azurin's midpoint potential, with a contrast enhancement of over 55 %. Since the contrast of Zn azurin did not vary as a function of substrate potential, this strongly suggests the involvement of Cu-based densities of states in the tunnelling pathway. Single molecule scanning tunnelling spectroscopy of metalloproteins was demonstrated for the first time. Reproducible negative differential resistance (NDR) features were resolved at positive and negative biases in the 1-V spectroscopy of Cu azurin, but not for Zn azurin. Derivative spectra indicated molecular densities of states involved in Cu azurin's tunnelling pathway. Peak to valley ratios of the Cu azurin NDR features were of the same order of magnitude as the degree of contrast switching observed by ECSTM, suggesting the same redox densities of states were being accessed by both techniques. This work has therefore demonstrated metal centre involvement in tunnel transport across azurin, and shown that the tunnelling conductance can be probed and reversibly tuned at the single molecule level.
34
Bogozi, Albert. "Molecular detection using metallic nanowires with quantized conductance". FIU Digital Commons, 2000. http://digitalcommons.fiu.edu/etd/1720.
Testo completoAbstract (sommario):
This thesis studies the adsorption of molecules with different binding strengths onto copper nanowires with prestabilized conductance values fabricated by an electrochemical method. Since the diameters of these wires are comparable to the wavelength of conduction electrons the conductance of the nanowires is quantized, and the adsorption of even a few molecules onto atomically thin wires changes the conductance from integer values to fractional ones. These changes are proportional to the binding strength of the adsorbed molecules. The decrease in conductance is hypothesized to be caused by the scattering of the conduction electrons by the adsorbed molecules. The sensitivity of molecular adsorption-induced conductance change can be used for the development of a chemical sensor. The stabilized copper nanowires obtained in this thesis may also be used for other purposes, such as interconnecting conductors between nanodevices and digital switches in functional nanoelectronic circuitry.
35
Ho, Melisa Wai Yin. "Regulation of chloride conductance in cultured epithelial cells". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq21577.pdf.
Testo completo
36
Belogiannis, Theodoros. "Individual Stress Diagnosis from Skin Conductance sensor signals". Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-19033.
Testo completo
37
Houari, Ahmed. "Numerical studies of conductance fluctuations in disordered metals". Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74576.
Testo completoAbstract (sommario):
We compute conductance fluctuations in a variety of disordered mesoscopic systems through direct numerical evaluation of the Kubo-Greenwood formula for the conductivity.Our model Hamiltonian is quite different from the Anderson tight-binding Hamiltonian which has been most commonly used in studies of electronic structure and properties of disordered systems. It is reminiscent of the Kronig-Penney model in that $ delta$-like atomic potentials are specified by a single parameter.
Our model structures range from substitutional binary alloys to topologically disordered "glasses", and include systems where the disorder is caused by random small displacements of atoms from their crystalline lattice positions.
We test the universal nature of conductance fluctuations for the model with substitutional disorder. We study systems which are always larger than the elastic mean free path, but not always smaller than the localization length of the electron wavefunctions. In those systems where universality is expected, we confirm the ergodic theorem of Lee and Stone and observe the universal amplitudes of the fluctuations both in two-dimensional systems with and without a magnetic field, and in quasi-one-dimensional geometry.
We have also performed the first studies of conductance fluctuations in strongly disordered systems and observed a universal relationship between the amplitude of the fluctuations and the value of the conductance itself: this relationship does not depend upon the nature of the disorder.
38
Tucker, Stephen John. "Studies on the cystic fibrosis transmembrane conductance regulator". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357427.
Testo completo
39
Petej, Ivan. "Coulomb blockade and quantum conductance in ferromagnetic nanostructures". Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270647.
Testo completo
40
唐紅星 e Hongxing Tang. "Mesoscopic conductance through superconductor-normal-metal-superconductor heterostructures". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31219937.
Testo completo
41
Collins, Kimberlee C. (Kimberlee Chiyoko). "Experimental investigations of solid-solid thermal interface conductance". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61600.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 70-84).
Understanding thermal interface conductance is important for nanoscale systems where interfaces can play a critical role in heat transport. In this thesis, pump and probe transient thermoreflectance methods are used to measure the thermal interface conductance between solid materials. Two experimental studies of thermal interface conductance are presented, each revealing the complexity of phonon interactions at interfaces which are inadequately captured by current models of phonon transmissivity. The first study considers interfaces of different metals with graphite, and finds that atomic-scale roughness at the interface could be appreciably influencing the heat transport due to the extreme anisotropy of graphite. The thermal interface conductance of graphite is found to be similar to that of diamond, suggesting that when estimating the thermal interface conductance between metal and multi-walled carbon nanotubes (MWCNTs), a reasonable assumption may be that the conductance with the side walls of the MWCNTs is similar to the conductance with the ends of the MWCNTs. The second study considered aluminum on diamond interfaces where the diamond samples were functionalized to have different chemical surface terminations. The surface termination of the diamond is found to significantly influence the heat flow, with oxygenated diamond, which is hydrophilic, exhibiting four times higher thermal interface conductance than hydrogen-treated diamond, which is hydrophobic. Microstructure analysis determined that the Al film formed similarly, independent of diamond surface termination, suggesting that differences in interface bonding likely caused the observed difference in thermal interface conductance, a phenomenon which is not captured in current models of solid-solid phonon transmissivity.
by Kimberlee Chiyoko Collins.
S.M.
42
Mezaache, El-Hacene. "Contribution à l'étude d'un caloduc à conductance variable". Grenoble INPG, 1987. http://www.theses.fr/1987INPG0071.
Testo completoAbstract (sommario):
Analyse de divers modeles publies, en fonction de leurs applications. Elaboration de 2 modeles applicables a un caloduc stationnaire et a pression uniforme (unidimensionnel,bidimensionnel). Comparaison des resultats de calcul, avec resultats experimentaux d'un caloduc a eau avec helium comme gaz non condensable
43
Wongwanitwattana, Chalermwat. "Low thermal conductance platforms for mK tunnelling coolers". Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/67747/.
Testo completoAbstract (sommario):
The impact of the O2 content in SF6-O2 gas mixtures on the etch rate and sidewall profile of Silicon (Si), Germanium (Ge) and phosphorous doped Germanium (Ge:P) in reactive ion etching has been studied. The characteristics of etch rate and sidewall profile were greatly affected by the O2 content. Below 50% of O2 content, a large variation in Ge etch rates was found compared to that of Si, but for O2 content above 50% the etch rates followed relatively the same trend. Lightly doped Ge showed the highest etch rate at a O2 concentration up to 20%. Sidewall angles range from a minimum of 80° to a maximum of 166°, with O2 concentration of 20% yielding perfect anisotropic mesa etch. Also at this O2 concentration, reasonable Si/Ge selectivity was possible. These observations indicate that by adjusting the O2 concentration, precision plasma etching of Si, Ge and Ge:P was possible. Suspended Ge structures were fabricated: micro wires, spiderweb and the van der Pauw Greek-cross. The micro wires’size could be reduced to fabricate suspended Ge nanowires devices. The suspended spiderweb could be fabricated for bolometers. The van der Pauw Greek-cross structure could reveal the electrical properties of thin expitaxial layer such as resistivity and mobility via hall measurement as a function of temperature. Removal of dislocations was shown to enhance the electrical isolation. Thermal properties of germanium doped with phosphorus (4x1019 cm-3) were investigated in this study. At lowest Tbath of 312 mK , the results indicate that heat flow from hot electrons to phonons was proportional to T7 and the electron-phonon coupling constant is 1.31x109 W/m3 K7 . The temperature dependence of doped Ge was higher than doped Si (which has a T6 temperature dependence) because the band structure was different. Moreover, the heat flow between electrons and phonon that is proportional to T7 could possibly be explained by a combination of strong disorder and surface modes.
44
Zheng, Tao. "Study of Conductance Quantization by Cross-Wire Junction". Thesis, University of North Texas, 2004. https://digital.library.unt.edu/ark:/67531/metadc5540/.
Testo completoAbstract (sommario):
The thesis studied quantized conductance in nanocontacts formed between two thin gold wires with one of the wires coated by alkainthiol self assembly monolayers (SAM), by using the cross-wire junction. Using the Lorenz force as the driving force, we can bring the two wires in contact in a controlled manner. We observed conductance with steps of 2e2 / h. The conductance plateaus last several seconds. The stability of the junction is attributed to the fact that the coating of SAM improves the stability and capability of the formed contact.
45
Strop, Pavel Parker Carl Stevens. "Characterisitics of the mechanosensitive channel of large conductance /". Diss., Pasadena, Calif. : California Institute of Technology, 2002. http://resolver.caltech.edu/CaltechETD:etd-05092002-155216.
Testo completo
46
Mezaache, El-Hacene. "Contribution à l'étude d'un caloduc à conductance variable". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37607985r.
Testo completo
47
Tang, Hongxing. "Mesoscopic conductance through superconductor-normal-metal-superconductor heterostructures /". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20126384.
Testo completo
48
Alsaleh, Dana. "Bifurcations in a model of Per1 neurons". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/bifurcations-in-a-model-of-per1-neurons(0d004fab-c795-4afe-8dc7-6a807e946e2b).html.
Testo completoAbstract (sommario):
Circadian rhythms refer to the physiological and biological processes that fluctuate over a 24-hour period. These rhythms are found in most living things such as animals, plants and fungi. In mammals, circadian rhythms are mainly generated and regulated by the suprachiasmatic nucleus (SCN).The period (Per1) gene in the SCN plays a key role in directing circadian rhythms. Per1 expression increases during the day and decreases at night. The neurons which express the Per1 gene show different behaviours to non-Per1 neurons during the day-night cycle. Per1 neurons are in a state of repetitive firing in the morning while in the late morning they display a bursting behaviour. In the afternoon, Per1 neurons divide into two groups: GA and GB, where GA is in a repetitive firing state and GB is silent. At night, these neurons are generally in a quiescent state but late at night they generate spikes. In this study, a standard Hodgkin-Huxley type model was used to study the behaviours of Per1 neurons over the day-night cycle using bifurcation analysis. In this model, the potassium and calcium currents carry the circadian rhythms which are modelled by their conductance. The currents had a significant impact on Per1 neuron behaviours. Furthermore, by changing some of the model parameters, different bistability mechanisms were examined. The study was extended to explore the effect of noise from other neurons on Per1 neuron behaviours. It was shown that noise plays a crucial role in inducing some of the Per1 neuron behaviours and that some Per1 neuron behaviours are fully induced by this noise, e.g. the late morning and late night behaviours. In contrast, the noise was found not to have any significant effect on other Per1 neuron behaviours other than the two behaviours that are observed in the afternoon.
49
Freyn, Axel. "Effets des interactions électroniques sur la conductance de nanosystèmes". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00347605.
Testo completoAbstract (sommario):
Dans cette thèse, l'effet non-local des interactions locales électron-électron sur le transport est étudié dans des modèles de dimensions réduites. À température nulle, le transport au travers d'une nanostructure où les électrons interagissent peut être décrit par une matrice de diffusion. Néanmoins, si les interactions sont importantes à l'intérieur de la nanostructure, le diffuseur effectif à un corps qui décrit la nanostructure ne dépend pas seulement des paramètres internes de la nanostructure, mais aussi des diffuseurs qui existent dans les conducteurs en contact avec la nanostructure.Ces effets non-locaux induits par l'interaction sont étudiés dans trois modèles différents, en utilisant la théorie Hartree-Fock pour décrire l'interaction.
En regardant deux nanostructures où les électrons interagissent, on montre que les matrices de diffusion des deux nanostructures sont effectivement couplées par les oscillations de Friedel qu'elles engendrent dans les conducteurs externes.
Pour observer les effets non-locaux dans la conductance quantique, il suffit de regarder une seule nanostructure où les électrons interagissent en série avec un diffuseur à un corps. En remplaçant la deuxième nanostructure par une boucle attachée, nous montrons que la matrice de diffusion de la nanostructure dépend du flux magnétique au travers de la boucle.
En étendant l'étude à des modèles bidimensionnels, l'influence de l'effet non-local sur les images obtenues par un microscope à effet de grille est étudiée. En utilisant l'effet non-local, on peut détecter l'importance des interactions locales électron-électron dans ces images.
50
Shevchuk, Andriy. "Development of scanning ion conductance microscopy for biomedical applications". Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/8160.
Testo completo