Submitted by LAÍS MORANDINI CARVALHO null (lais_morandini@yahoo.com.br) on 2018-01-03T14:22:11Z No. of bitstreams: 1 Lais Morandini Carvalho.pdf: 3515290 bytes, checksum: b29a2f58afa414dd9e9f4df531340ca2 (MD5) / Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-04T18:53:50Z (GMT) No. of bitstreams: 1 Carvalho_lm_dr_sjc.pdf: 3515290 bytes, checksum: b29a2f58afa414dd9e9f4df531340ca2 (MD5) / Made available in DSpace on 2018-01-04T18:53:50Z (GMT). No. of bitstreams: 1 Carvalho_lm_dr_sjc.pdf: 3515290 bytes, checksum: b29a2f58afa414dd9e9f4df531340ca2 (MD5) Previous issue date: 2017-11-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nas últimas décadas houve um aumento considerável na utilização dos implantes metálicos para aplicações na área da ortopedia e odontologia, por isso as pesquisas têm como foco estudar os mecanismos biológicos de interação osso-implante. A nanotopografia de superfície de implantes osseointegráveis apresenta efeito direto sobre a resposta biológica óssea. No entanto a maneira como afeta a osseointegração in vivo ainda não está totalmente elucidada. O objetivo neste estudo foi comparar in vivo a influência da superfície em nanoescala (nano) confeccionada em implantes de titânio comercialmente puro (Ticp), comparado-a a superfície lisa (controle) em modelo experimental de camundongos osterix-mcherry (Osx-mcherry), os quais expressam proteína fluorescente concomitante com a expressão do gene osterix (Osx). Os animais receberam implantes de superfície lisa no fêmur direito e com nanoescala no fêmur esquerdo. Após diferentes períodos de eutanásia baseados na metodologia empregada foram realizados nas peças e nas células os seguintes testes biológicos: microscopia eletrônica de varredura (MEV) para avaliação da adesão celular e da superfície do implante; histologia e nanotomografia (nanoCT) para observação e quantificação de osso neoformado na interface osso/implante; citometria de fluxo para quantificação de células marcadas pelo gene osterix; PCR em tempo real (qPCR) para avaliação da expressão gênica; coloração fosfatase ácida resistente ao tartarato (TRAP) para contagem de osteoclastos. Nossos resultados mostraram que a maioria dos genes estudados estavam superexpressos nas amostras com superfície em nanoescala sendo que alguns deles apresentaram diferenças estatísticas (Teste t, p < 0.05), tais como: Osx (osterix), Alp (fosfatase alcalina), Prx1(homeobox relacionado emparelhado -1), Dmp1 (Dolicol-fosfatase mannosiltransferase subunidade 1), Bsp (sialoproteína óssea) e Ocn (osteocalcina). Os testes estatísticos ANOVA two way seguido do Teste de Tukey quando necessário, foram utilizados para os demais experimentos e o nível de significância foi estabelecido em p < 0.05. Diferenças estatísticas foram encontradas para o nanoCT e histologia entre as superfícies e períodos avaliados e os melhores resultados foram observados para a nanoescala. A coloração TRAP também mostrou diferenças estatísticas entre as superfícies e períodos estudados, com a superfície lisa mostrando melhores resultados aos 3 dias e a nano aos 5 e 7 dias. Não houve diferença estatística para a citometria de fluxo, porém a superfície em nanoescala mostrou melhores resultados que a lisa em todos os períodos analisados. Concluímos que a superfície em nanoescala possui propriedades osteocondutivas e favorece os eventos biológicos que ocorrem na superfície do implante melhorando o processo de osseointegração.

Though the concept of junctionless field effect transistor (JLFET) is old, it was not possible to fabricate a useful JLFET device, as it requires a very shallow channel region. Very recently, the emergence of new and advanced technologies has made it possible to create viable JLFET devices using nanowires. This work aims to computationally investigate the interplay of quantum size-quantization and random dopant fluctuations (RDF) effects in nanoscale JLFETs. For this purpose, a 3-D fully atomistic quantum-corrected Monte Carlo device simulator has been integrated and used in this work. The size-quantiza¬tion effect has been accounted for via a param¬eter-free effec¬tive potential scheme and benchmarked against the NEGF approach in the ballistic limit. To study the RDF effects and treat full Coulomb (electron-ion and electron-electron) interactions in the real-space and beyond the Poisson picture, the simulator implements a corrected-Coulomb electron dynamics (QC-ED) approach. The essential bandstructure and scattering parameters (energy bandgap, effective masses, and the density-of-states) have been computed using an atomistic 20-band nearest-neighbour sp3d5s* tight-binding scheme. First, an experimental device was simulated to evaluate the validity of the simulator. Because of the small dimension, quantum mechanical confinement was found to be the dominant mechanism that significantly degrades the current drive capability of nanoscale JLFETs. Surface roughness scattering is not as prominent as observed in conventional MOSFETs. Also, because of its small size, the performance of the device is prone to the effect of variability, for which a discrete doping model was proved essential. Finally, a new JLFET was designed and optimized in this work. The proposed device is based on a gate-all-around silicon nanowire. Source/drain length is 32.5 nm and channel length is 14 nm. Gate contact length is 9 nm. The EOT (equivalent oxide thickness) is 1 nm. It has a metal gate with a workfunction of 4.55 eV. The source, channel and drain regions are n-type with a doping density of 1.5×1019 cm-3. Detailed simulation shows that the two most influential mechanisms that degrade the drive capability are quantum mechanical confinement and Coulomb scattering. Surface roughness scattering is found to be very weak. In addition, thinner nanowire is more prone to Coulomb scattering exhibiting a reduced ON-current (ION). Simulation results show that silicon nanowires with a side length (width and depth) of 3 nm and a doping density of 1.5×1019 cm-3 produce satisfactory drive current.

Dual gate MOSFET structures such as FinFETs are widely regarded as the most promising option for continued scaling of silicon based transistors after 2010. This work examines key process modules that enable reduction of both device area and fin width beyond requirements for the 16nm node. Because aggressively scaled FinFET structures suffer significantly degraded device performance due to large source/drain series resistance (RS/D), several methods to mitigate RS/D such as maximizing contact area, silicide engineering, and epitaxially raised S/D have been evaluated.

Oxide heterostructures are attracting huge interest in recent years due to the special functionalities of quasi two-dimensional quantum gases. In this thesis, the electronic states at the interface between perovskite oxides and pyrite compounds have been studied by first-principles calculations based on density functional theory. Optimization of the atomic positions are taken into account, which is considered very important at interfaces, as observed in the case of LaAlO3/SrTiO3. The creation of metallic states at the interfaces thus is explained in terms of charge transfer between the transition metal and oxygen atoms near the interface. It is observed that with typical thicknesses of at least 10-12 °A the gases still extend considerably in the third dimension, which essentially determines the magnitude of quantum mechanical effects. To overcome this problem, we propose incorporation of highly electronegative cations (such as Ag) in the oxides. A fundamental interest is also the thermodynamic stability of the interfaces due to the possibility of atomic intermixing in the interface region. Therefore, different cation intermixed configurations are taken into account for the interfaces aiming at the energetically stable state. The effect of O vacancies is also discussed for both polar and non-polar heterostructures. The interface metallicity is enhanced for the polar system with the creation of O vacancies, while the clean interface at the non-polar heterostructure exhibits an insulating state and becomes metallic in presence of O vacancy. The O vacancy formation energies are calculated and explained in terms of the increasing electronegativity and effective volume of A the side cation. Along with these, the electronic and magnetic properties of an interface between the ferromagnetic metal CoS2 and the non-magnetic semiconductor FeS2 is investigated. We find that this contact shows a metallic character. The CoS2 stays quasi half metallic at the interface, while the FeS2 becomes metallic. At the interface, ferromagnetic ordering is found to be energetically favorable as compared to antiferromagnetic ordering. Furthermore, tensile strain is shown to strongly enhance the spin polarization so that a virtually half-metallic interface can be achieved, for comparably moderate strain. Our detailed study is aimed at complementing experiments on various oxide interfaces and obtaining a general picture how factors like cations, anions, their atomic weights and elecronegativities, O vacancies, lattice mismatch, lattice relaxation, magnetism etc play a combined role in device design.

No description available.

Une précision à l’échelle de la milliseconde dans le transfert d'informations entre les neurones est essentielle pour la synchronisation et la plasticité des circuits neuronaux dans le cerveau. Les axones sont des prolongements neuronaux qui assurent la communication via des impulsions électriques ou des potentiels d’action (PA). A cause du manque de myéline et de leur diamètre très fin, les axones de l'hippocampe propagent les PA lentement et ainsi générer des délais de conduction très long (jusqu’à 100 ms) qui sont traditionnellement considérés comme invariants. Cependant, plusieurs études ont montré que l'activité change la morphologie des axones et module le temps de latence de la transmission. Il convient donc de se demander si le diamètre des axones varie en fonction de l'activité pouvant influencer lapropagation des PA.Les diamètres des axones non-myélinisés de l’hippocampe (compris entre 100-350 nm) sont généralement trop petits pour être résolu par la microscopie photonique conventionnelle. Le développement récent de l’imagerie super résolution STED permet désormais l'observation de la dynamique de leur morphologie détaillée dans le tissu vivant. En combinant la microscopie STED, l’électrophysiologie avec enregistrements en champs et patch-clamp dans des tranches de cerveau de souris et des simulations informatiques, nous avons découvert que les axones du CA3 subissent un élargissement de leur diamètre après l'induction de la potentialisation à long terme (PLT). Nous démontrons que cet élargissementde diamètre augmente la vitesse de conduction des PA. Dans l'ensemble, nos résultats indiquent que les axones peuvent réguler leur diamètre de manière dynamique changeant le délai de conduction des PA, ce qui modifie le timing du transfert d’information dans les circuits neuronaux. Cette étude suggère l’existence d’un nouveau type de mécanisme structurel dans le compartiment axonal jouant un rôle pour la plasticité neuronale. / Millisecond timing precision in the transfer of information between neurons is essential for the synchrony and plasticity of neural circuits in the brain. Axons are neuronal extensions that ensure the communication via brief electrical impulses called action potentials (AP). Because they are unmyelinated and are extremely thin, hippocampal axons propagate APsslowly and thus generate long delays of conduction (up to 100 ms) that are traditionally considered invariant. However, recent studies have shown that activity changes the morphology of axons and modulate the latency of transmission, thus raising the question whether axons undergo activity-dependent structural changes that could influence the propagation of APs. The diameter of hippocampal axons (ranging between 100-350 nm) are usually too thin to be properly resolved by conventional light microscopy. However, the development of super resolution STED imaging now enables the observation of their detailed morphological dynamics in living tissue. Using a novel combination of STED microscopy, field recordings, patch-clamp electrophysiology in mouse brain slices and computer simulations we discovered that CA3 axons undergo long-lasting enlargement in their diameter after the induction of long term potentiation (LTP). We provide strong evidence that this diameter enlargement increases AP conduction velocity. Taken together, our findings indicate that axons can dynamically tune AP propagation delays by changing their diameters, thereby altering the timing of information transfer in neural circuits. This study suggests a novel and powerful structural mechanism for neural plasticity.

Thermal transport performance at the nanoscale and/or of biomaterials is essential to the success of many new technologies including nanoelectronics, biomedical devices, and various nanocomposites. Due to complicated microstructures and chemical bonding, thermal transport process in these materials has not been well understood yet. In terms of chemical bonding, it is well known that the strength of atomic bonding can significantly affect thermal transport across materials or across interfaces between materials. Given the intrinsic high strength of hydrogen bonds, this dissertation explores the role of hydrogen bonds in nanoscale thermal transport in various materials, and investigates novel material designs incorporating hydrogen bonds for drastically enhanced thermal conduction. Molecular dynamics simulation is employed to study thermal transport processes in three representative hydrogen-bonded materials: (1) crystalline motifs of the spider silk, silkworm silk and synthetic silk, (2) crystalline polymer nanofibers, and (3) polymer nanocomposites incorporating graphene or functionalized graphene. Computational and theoretical investigations demonstrate that hydrogen bonds significantly facilitate thermal transport in all three material systems. The underlying molecular mechanisms are systematically investigated. The results will not only contribute new physical insights, but also provide novel concepts of materials design to improve thermal properties towards a wide range of applications.

Memristor-based nano-crossbar computing is a revolutionary computing paradigm that does away with the traditional Von Neumann architectural separation of memory and computation units. The computation of Boolean formulas using memristor circuits has been a subject of several recent investigations. Crossbar computing, in general, has also been a topic of active interest, but sneak paths have posed a hurdle in the design of pervasive general-purpose crossbar computing paradigms. In this paper, we demonstrate that sneak paths in nano-crossbar computing can be exploited to design a Boolean-formula evaluation strategy. We demonstrate our approach on a simple Boolean formula and a 1-bit addition circuit. We also conjecture that our nano-crossbar design will be an effective approach for synthesizing high-performance customized arithmetic and logic circuits.

No description available.

No description available.