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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.
1

Quantum drude oscillators for accurate many-body intermolecular forces

Jones, Andrew January 2010 (has links)
One of the important early applications of Quantum Mechanics was to explain the Van-der-Waal’s 1/R6 potential that is observed experimentally between two neutral species, such as noble gas atoms, in terms of correlated uncertainty between interacting dipoles, an effect that does not occur in the classical limit [London-Eisenschitz,1930]. When many-body correlations and higher-multipole interactions are taken into account they yield additional many-body and higher-multipole dispersion terms. Dispersion energies are closely related to electrostatic interactions and polarisation [Hirschfelder-Curtiss-Bird,1954]. Hydrogen bonding, the dominant force in water, is an example of an electrostatic effect, which is also strongly modified by polarisation effects. The behaviour of ions is also strongly influenced by polarisation. Where hydrogen bonding is disrupted, dispersion tends to act as a more constant cohesive force. It is the only attractive force that exists between hydrophobes, for example. Thus all three are important for understanding the detailed behaviour of water, and effects that happen in water, such as the solvation of ions, hydrophobic de-wetting, and thus biological nano-structures. Current molecular simulation methods rarely go beyond pair-wise potentials, and so lose the rich detail of many-body polarisation and dispersion that would permit a force field to be transferable between different environments. Empirical force-fields fitted in the gas phase, which is dominated by two-body interactions, generally do not perform well in the condensed (many-body) phases. The leading omitted dispersion term is the Axilrod-Teller-Muto 3-body potential, which does not feature in standard biophysical force-fields. Polarization is also usually ommitted, but it is sometimes included in next-generation force-fields following seminal work by Cochran [1971]. In practice, many-body forces are approximated using two-body potentials fitted to reflect bulk behaviour, but these are not transferable because they do not reproduce detailed behaviour well, resulting in spurious results near inhomogeneities, such as solvated hydrophobes and ions, surfaces and interfaces. The Quantum Drude Oscillator model (QDO) unifies many-body, multipole polarisation and dispersion, intrinsically treating them on an equal footing, potentially leading to simpler, more accurate, and more transferable force fields when it is applied in molecular simulations. The Drude Oscillator is simply a model atom wherein a single pseudoelectron is bound harmonically to a single pseudonucleus, that interacts via damped coulomb interactions [Drude,1900]. Path Integral [Feynman-Hibbs,1965] Molecular Dynamics (PIMD) can, in principle, provide an exact treatment for moving molecules at finite temperature on the Born- Oppenheimer surface due to their pseudo-electrons. PIMD can be applied to large systems, as it scales like N log(N), with multiplicative prefactor P that can be effectively parallelized away on modern supercomputers. There are other ways to treat dispersion, but all are computationally intensive and cannot be applied to large systems. These include, for example, Density Functional Theory provides an existence proof that a functional exists to include dispersion, but we dont know the functional. We outline the existing methods, and then present new density matrices to improve the discretisation of the path integral. Diffusion Monte Carlo (DMC), first proposed by Fermi, allows the fast computation of high-accuracy energies for static nuclear configurations, making it a useful method for model development, such as fitting repulsion potentials, but there is no straightforward way to generate forces. We derived new methods and trial wavefunctions for DMC, allowing the computation of energies for much larger systems to high accuracy. A Quantum Drude model of Xenon, fit in the gas-phase, was simulated in the condensed-phase using both DMC and PIMD. The new DMC methods allowed for calculation of the bulk modulus and lattice constant of FCC-solid Xenon. Both were in excellent agreement with experiment even though this model was fitted in the gasphase, demonstrating the power of Quantum Drudes to build transferable models by capturing many-body effects. We also used the Xenon model to test the new PIMD methods. Finally, we present the outline of a new QDO model of water, including QDO parameters fitted to the polarisabilities and dispersion coefficients of water.
2

Étude théorique et modélisation par la méthode FDTD de nanostructures plasmoniques : application à la conception de biocapteurs / Theoretical study of plasmonic nanostructures and numerical simulation by FDTD method : application to biosensors design

Saison-Francioso, Ophélie 25 June 2014 (has links)
Ce travail de thèse est une contribution à l’étude des propriétés optiques de structures plasmoniques composées de nanoparticules métalliques. Il s’appuie sur diverses simulations numériques réalisées à l’aide de la méthode des différences finies dans le domaine temporel ou FDTD (Finite-Difference Time-Domain). La première partie de ce travail concerne l’étude d’un réseau périodique de nanofils d’or, de section droite rectangulaire, situé au sein d’un environnement diélectrique multi-couches. L’influence des paramètres géométriques des nanofils, de la période du réseau et de l’épaisseur de diélectrique recouvrant les nanofils sur la position spectrale de la résonance plasmonique a été explorée. Cette étude a démontré que la longueur d’onde de résonance oscille quand l’épaisseur du diélectrique recouvrant les nanofils varie. Un modèle analytique simple a été développé afin de mieux appréhender l’origine de ces oscillations. L’influence des indices de réfraction de la matrice diélectrique sur les paramètres de l’oscillation a également été analysée. La deuxième partie de ce travail a été consacrée à la détermination et à l’étude de facteurs contrôlant la sensibilité des capteurs à résonance de plasmons de surface localisés. Différentes formes de nanoparticules et différents types de nanofils ont été analysés. De plus, trois grands thèmes ont été abordés :- l’influence sur la sensibilité du substrat sur lequel sont déposées les nanoparticules,- l’influence sur la sensibilité du matériau recouvrant les nanoparticules et,- l’origine du lien existant entre la longueur d’onde de résonance plasmonique et la sensibilité des nanoparticules à un changement d’indice de réfraction. / This thesis is a contribution to the optical properties study of plasmonic structures composed by metallic nanoparticles. This study is based on numerical simulation results obtained by the Finite-Difference Time-Domain method (FDTD).The first part of this work is related to the analysis of gold nanowires periodic arrays, which section is rectangular, placed in a multi-layered dielectric environment. The influence of the nanowires geometrical parameters, of the array period and of the dielectric thickness covering the nanowires on the Localized Surface Plasmon Resonance (LSPR) spectral position has been explored. This study especially demonstrated that the resonance wavelength oscillates when the dielectric thickness covering the nanowires is varying. A simple analytical model has been developed in order to better understand the oscillations origin. The influence of the refractive indexes of the dielectric matrix on the oscillation parameters has been analyzed too.The second part of this work concerns the determination and the study of factors controlling LSPR sensors sensitivity. Different shapes of nanoparticles and different kinds of nanowires have been considered. Moreover, three wide topics have been approached in this part:- the influence of the nanoparticles substrate on the sensitivity,- the influence of the material covering the nanoparticles on the sensitivity and,- the origin of the relationship between the LSPR wavelentgh and the refractive index sensitivity of the nanoparticles.
3

FDTD Algorithm for Plasmonic Nanoparticles with Spatial Dispersion

Zhang, Li 09 June 2016 (has links)
No description available.
4

Sammlung Matthias Drude (*1960): Bestandsverzeichnis

Roner, Miriam 17 June 2020 (has links)
Sammlung Matthias Drude (1960): Bestandsverzeichnis Zusammengestellt von Miriam Roner, Mai 2019
5

Polarizable Simulations of the bcl-2 DNA G-Quadruplex and FMRP RNA G-Quadruplex:Duplex Junction Binding Protein

Ratnasinghe, Brian Damith 03 June 2021 (has links)
A G-quadruplex (GQ) is a type of noncanonical nucleic acid structure that can form in regions of nucleic acids rich in guanine nucleotides. The guanine bases form a square planar conformation via Hoogsteen hydrogen bonding. These stacked tetrads have inward-facing carbonyl oxygens, facilitating the coordination of ions. Improper GQ conformations can lead to improper regulation of gene expression, potentially resulting in genetic diseases or cancer. Here, we performed molecular dynamics simulations using the Drude polarizable force field (FF) to gain insight into factors contributing to the stability of two GQs. One is the bcl-2 promoter region GQ, which is implicated in several types of cancer including B-cell lymphoma, and the second is the sc1 RNA GQ, which binds to the Fragile-X Mental Retardation Protein (FMRP) and is implicated in the development of Fragile X Syndrome (FXS). Aberrant bcl-2 GQ conformations result in increased production of the BCL2 protein, which is an apoptosis inhibitor. As such, we aim to characterize the factors stabilizing the GQ for future small-molecule development to prevent apoptosis inhibition and therefore cancer. The FMRP protein functions as a regulator of sc1 conformation to control the translation of proteins required for frontal lobe development. FXS arises from a nonsense mutation that causes the deletion of the C-terminal region of FMRP, rendering it non-function. Therefore, we aim to simulate sc1 when FMRP is bound as well as unbound to provide insight into the types of interactions that must be maintained and therefore mimicked by a small molecule drug. / Master of Science in Life Sciences / DNA is commonly represented as a double helix and RNA is thought of as a simple single stranded, disordered molecule, but DNA and RNA can both adopt more complicated structures. An example of this is the G-quadruplex (GQ), a structure that can form in regions of DNA and RNA that are rich in guanine. These guanine bases form a stable core structure that can act as an "on-off" switch for different processes in the cell. Alterations to GQ structure can lead to dysfunction and different types of disease. Here, we perform atomistic computer simulations to further understand factors that contribute to GQ stability, focusing on two different GQs, one of plays a role in several types of cancer, and the other whose regulation is in Fragile X Syndrome (FXS). Furthermore, we study the Fragile X Mental Retardation Protein, which is what brain cells normally use to regulate expression of proteins needed for frontal lobe development by modulating specific GQ structure. The information from these simulations can be used to potentially develop drugs for these conditions.
6

Developing Fast and Accurate Water Models for Atomistic Molecular Dynamics Simulations

Xiong, Yeyue 15 September 2021 (has links)
Water models are of great importance for different fields of studies such as fluid mechanics, nano materials, and biomolecule simulations. In this dissertation, we focus on the water models applied in atomistic simulations, including those of biomolecules such as proteins and DNA. Despite water's simple structure and countless studies carried out over the decades, the best water models are still far from perfect. Water models are normally divided into two types--explicit model and implicit model. Here my research is mainly focused on explicit models. In explicit water models, fixed charge n-point models are most widely used in atomistic simulations, but have known accuracy drawbacks. Increasing the number of point charges, as well as adding electronic polarizability, are two common strategies for accuracy improvements. Both strategies come at considerable computational cost, which weighs heavily against modest possible accuracy improvements in practical simulations. With a careful comparison between the two strategies, results show that adding polarizability is a more favorable path to take. Optimal point charge approximation (OPCA) method is then applied along with a novel global optimization process, leading to a new polarizable water model OPC3-pol that can reproduce bulk liquid properties of water accurately and run at a speed comparable to 3- and 4-point non-polarizable water models. For practical use, OPC3-pol works with existing non-polarizable AMBER force fields for simulations of globular protein or DNA. In addition, for intrinsically disordered protein simulations, OPC3-pol fixes the over-compactness problem of the previous generation non-polarizable water models. / Doctor of Philosophy / With the rapid advancements of computer technologies, computer simulation has become increasingly popular in biochemistry research fields. Simulations of microscopic substances that are vital for living creatures such as proteins and DNAs have brought us more and more insights into their structures and functions. Because of the fact that almost all the microscopic substances are immersed in water no matter they are in a human body, a plant, or in bacteria, accurately simulating water is crucial for the success of such simulations. My research is focused on developing accurate and fast water models that can be used by researchers in their biochemical simulations. One particular challenge is that water in nature is very flexible and properties of water can change drastically when its surroundings change. Many classical water models cannot correctly mimic this flexibility, and some more advanced water models that are able to mimic it can cost several times more computing resources. Our latest water model OPC3-pol, benefited from a new design, accurately mimics the flexibility and runs as fast as a traditional rigid water model.
7

Formação e viabilidade das sementes da palmeira real australiana / Australian palm seed formation and viability

Silva, Sibelle Santanna da 06 December 2016 (has links)
A palmeira real australiana (Archontophoenix cunninghamiana H. Wendl. & Drude) é uma espécie nativa das florestas tropicais da Austrália que se adaptou ao cultivo no Brasil e é utilizada para o paisagismo e também para a extração do palmito. A determinação da maturidade fisiológica das sementes e da época ideal para a colheita é essencial para preservar a qualidade das sementes e para a formação das mudas. No entanto, existe restrição de métodos disponíveis para avaliar a qualidade das sementes da palmeira real australiana e, além disso, para o teste de germinação são necessários, pelo menos, 70 dias para obter os resultados. Dessa forma, o teste de tetrazólio é uma alternativa para estimar a viabilidade das sementes, em função da rapidez de obtenção dos resultados. Assim, um dos objetivos dessa pesquisa foi estudar o preparo das sementes da palmeira real australiana para o teste de tetrazólio; para tanto, foram avaliadas sementes de diferentes plantas matrizes quanto à hidratação das sementes e à coloração dos tecidos, utilizando as soluções 0,075%, 0,1% e 0,2% de tetrazólio, durante 60, 120, 240 e 360 minutos no escuro, a 40°C. O estudo relacionado à formação das sementes incluiu avaliações dos frutos e das sementes. Assim, os frutos foram avaliados quanto à cor, utilizando a colorimetria digital e a carta de Munsell para tecidos vegetais, e às características morfométricas, tais como o diâmetro, o comprimento e a massa. Para a determinação do parâmetro fisiológico das sementes foram avaliados a germinação (total, o índice de velocidade de germinação e o tempo médio de germinação), a viabilidade (teste de tetrazólio) e o teor de água das sementes. Além disso, foi determinada também a composição química das sementes nos diferentes estádios de maturação em função da peroxidação de lipídeos e do peróxido de hidrogênio. Para complementar o estudo da formação das sementes foi avaliada também a desidratação das mesmas, no ponto de maturidade fisiológica, para determinar se são recalcitrantes, ou seja, avaliar qual é o limite da redução de água dos tecidos que interfere negativamente na viabilidade. Essas sementes, com diferentes teores de água, foram também radiografadas para verificação dos tecidos internos das sementes. A avaliação da formação das sementes foi complementada com o estudo do armazenamento; para isso, as sementes em dois estádios de maturação (76 e 85 dias após a antese) foram colocadas em sacos de polietileno, com 0,20mm de espessura, e, em seguida, mantidas em ambiente não controlado e em ambiente controlado, com temperatura de 10°C e umidade relativa do ar de 80%, por 5 meses; a cada 30 dias foram retiradas amostras para as seguintes análises: teor de água, teste de germinação (total, índice de velocidade de germinação e tempo médio de germinação), teste de tetrazólio e imagens por meio dos raios X. Há a possibilidade de utilizar o teste de tetrazólio para estimar a viabilidade das sementes de palmeira real australiana. É recomendado o seccionamento longitudinal a partir do opérculo e a coloração do embrião em soluções 0,1% por 360 minutos, no escuro e a 40°C e 0,2% por 120 minutos ou por 240 minutos. A maturidade fisiológica das sementes é atingida quando têm 41% de água, aos 76 dias após a antese, 2,49g de massa seca e germinação máxima; nesse momento os frutos têm coloração caracterizada como 10.R 6/8 vermelha amarela-avermelhada. Com relação à quantidade de água para o armazenamento, a secagem até 25% de água não tem efeitos negativos imediatos na qualidade das sementes da palmeira real australiana; contudo a partir de 20% de água há redução da qualidade das sementes e com 10% de água não há germinação. As condições adequadas para o armazenamento das sementes da palmeira real australiana, que têm inicialmente 48% de água, são a embalagem de polietileno (0,20mm de espessura) e o ambiente com temperatura de 10°C e 80% de umidade relativa do ar; essas condições são favoráveis para manter a qualidade das sementes por até 150 dias. / The Archontophoenix cunninghamiana H. Wendl. & Drude is a native specie from tropical forests in Australia, is used in brazilian environment to landscaping and the heart palm extraction. The knowledge about physiological maturity and harvest time are essential to preserve the quality of seeds and seedling production. However, there are few methods availably to evaluate these seeds quality, once the germination test needs, at least 70 days, for results. Thus, the tetrazolium test is one option to estimate the seeds viability, as it allows faster results. Then, the aim of this research was adapt the tetrazolium test to evaluate the quality of royal palm seeds, for this it were evaluated seeds from different plants, and the moisture content of the embryo and the color of tissues, using the tetrazolium solutions 0.075%, 0.1% and 0.2%, during 1, 2, 4 e 6h in the dark at 40 °C. Additionally, in this research were determinate the physical and physiological characteristics of the fruits and the seeds to characterize the seed maturity, then were evaluated the color, using digital colorimetry, and the morphometric characteristics, diameter, length and weight. To determine the physiological parameters were evaluated the germination, germination speed and average germination time, the viability (tetrazolium test) and the seed moisture content. The evaluation of seeds formation was completed with storage study once that seeds are classified as recalcitrant. For this, the seeds from two stages of maturation (color of pericarp red and dark red) were packed in polyethylene bags, with 0.20mm thickness and, then, were kept in uncontrolled environment and in controlled temperature (10 °C and 80% RH), per 5 months; each 30 days the samples were removed for analyses: moisture content, germination test, germination speed, average germination time, tetrazolium test and X-ray images. In the storage study also was evaluated dehydration of those seeds to determine the better moisture content for storage those seeds, without seed viability interference. There is the possibility of using tetrazolium test to assess the viability of Australian royal palm seeds. It is recommended to longitudinal sectioning from the operculum and staining of the embryo in 0.1% solutions for 360 minutes in the dark and at 40 ° C and 0.2% for 120 minutes or for 240 minutes in the dark and at 40 ° C . The physiological maturity of seeds is achieved when they have 41% water, 76 days after anthesis, 2,49g of dry mass and maximum germination; at that time the fruits were characterized as coloring 10.R 6/8 yellow-red red. With respect to the amount of water for storage, drying to 25% of water has no immediate negative effects on the quality of the seeds of Australian royal palm; however from 20% of water is reduced seed quality and 10% water no germination. Suitable conditions for the storage of seeds of the Australian royal palm, which initially have 48% water, are the polyethylene bags (0.20mm thick) and the ambient temperature of 10° C and 80% relative humidity; these are favorable conditions to maintain seed quality for up to 150 days.
8

Formação e viabilidade das sementes da palmeira real australiana / Australian palm seed formation and viability

Sibelle Santanna da Silva 06 December 2016 (has links)
A palmeira real australiana (Archontophoenix cunninghamiana H. Wendl. & Drude) é uma espécie nativa das florestas tropicais da Austrália que se adaptou ao cultivo no Brasil e é utilizada para o paisagismo e também para a extração do palmito. A determinação da maturidade fisiológica das sementes e da época ideal para a colheita é essencial para preservar a qualidade das sementes e para a formação das mudas. No entanto, existe restrição de métodos disponíveis para avaliar a qualidade das sementes da palmeira real australiana e, além disso, para o teste de germinação são necessários, pelo menos, 70 dias para obter os resultados. Dessa forma, o teste de tetrazólio é uma alternativa para estimar a viabilidade das sementes, em função da rapidez de obtenção dos resultados. Assim, um dos objetivos dessa pesquisa foi estudar o preparo das sementes da palmeira real australiana para o teste de tetrazólio; para tanto, foram avaliadas sementes de diferentes plantas matrizes quanto à hidratação das sementes e à coloração dos tecidos, utilizando as soluções 0,075%, 0,1% e 0,2% de tetrazólio, durante 60, 120, 240 e 360 minutos no escuro, a 40°C. O estudo relacionado à formação das sementes incluiu avaliações dos frutos e das sementes. Assim, os frutos foram avaliados quanto à cor, utilizando a colorimetria digital e a carta de Munsell para tecidos vegetais, e às características morfométricas, tais como o diâmetro, o comprimento e a massa. Para a determinação do parâmetro fisiológico das sementes foram avaliados a germinação (total, o índice de velocidade de germinação e o tempo médio de germinação), a viabilidade (teste de tetrazólio) e o teor de água das sementes. Além disso, foi determinada também a composição química das sementes nos diferentes estádios de maturação em função da peroxidação de lipídeos e do peróxido de hidrogênio. Para complementar o estudo da formação das sementes foi avaliada também a desidratação das mesmas, no ponto de maturidade fisiológica, para determinar se são recalcitrantes, ou seja, avaliar qual é o limite da redução de água dos tecidos que interfere negativamente na viabilidade. Essas sementes, com diferentes teores de água, foram também radiografadas para verificação dos tecidos internos das sementes. A avaliação da formação das sementes foi complementada com o estudo do armazenamento; para isso, as sementes em dois estádios de maturação (76 e 85 dias após a antese) foram colocadas em sacos de polietileno, com 0,20mm de espessura, e, em seguida, mantidas em ambiente não controlado e em ambiente controlado, com temperatura de 10°C e umidade relativa do ar de 80%, por 5 meses; a cada 30 dias foram retiradas amostras para as seguintes análises: teor de água, teste de germinação (total, índice de velocidade de germinação e tempo médio de germinação), teste de tetrazólio e imagens por meio dos raios X. Há a possibilidade de utilizar o teste de tetrazólio para estimar a viabilidade das sementes de palmeira real australiana. É recomendado o seccionamento longitudinal a partir do opérculo e a coloração do embrião em soluções 0,1% por 360 minutos, no escuro e a 40°C e 0,2% por 120 minutos ou por 240 minutos. A maturidade fisiológica das sementes é atingida quando têm 41% de água, aos 76 dias após a antese, 2,49g de massa seca e germinação máxima; nesse momento os frutos têm coloração caracterizada como 10.R 6/8 vermelha amarela-avermelhada. Com relação à quantidade de água para o armazenamento, a secagem até 25% de água não tem efeitos negativos imediatos na qualidade das sementes da palmeira real australiana; contudo a partir de 20% de água há redução da qualidade das sementes e com 10% de água não há germinação. As condições adequadas para o armazenamento das sementes da palmeira real australiana, que têm inicialmente 48% de água, são a embalagem de polietileno (0,20mm de espessura) e o ambiente com temperatura de 10°C e 80% de umidade relativa do ar; essas condições são favoráveis para manter a qualidade das sementes por até 150 dias. / The Archontophoenix cunninghamiana H. Wendl. & Drude is a native specie from tropical forests in Australia, is used in brazilian environment to landscaping and the heart palm extraction. The knowledge about physiological maturity and harvest time are essential to preserve the quality of seeds and seedling production. However, there are few methods availably to evaluate these seeds quality, once the germination test needs, at least 70 days, for results. Thus, the tetrazolium test is one option to estimate the seeds viability, as it allows faster results. Then, the aim of this research was adapt the tetrazolium test to evaluate the quality of royal palm seeds, for this it were evaluated seeds from different plants, and the moisture content of the embryo and the color of tissues, using the tetrazolium solutions 0.075%, 0.1% and 0.2%, during 1, 2, 4 e 6h in the dark at 40 °C. Additionally, in this research were determinate the physical and physiological characteristics of the fruits and the seeds to characterize the seed maturity, then were evaluated the color, using digital colorimetry, and the morphometric characteristics, diameter, length and weight. To determine the physiological parameters were evaluated the germination, germination speed and average germination time, the viability (tetrazolium test) and the seed moisture content. The evaluation of seeds formation was completed with storage study once that seeds are classified as recalcitrant. For this, the seeds from two stages of maturation (color of pericarp red and dark red) were packed in polyethylene bags, with 0.20mm thickness and, then, were kept in uncontrolled environment and in controlled temperature (10 °C and 80% RH), per 5 months; each 30 days the samples were removed for analyses: moisture content, germination test, germination speed, average germination time, tetrazolium test and X-ray images. In the storage study also was evaluated dehydration of those seeds to determine the better moisture content for storage those seeds, without seed viability interference. There is the possibility of using tetrazolium test to assess the viability of Australian royal palm seeds. It is recommended to longitudinal sectioning from the operculum and staining of the embryo in 0.1% solutions for 360 minutes in the dark and at 40 ° C and 0.2% for 120 minutes or for 240 minutes in the dark and at 40 ° C . The physiological maturity of seeds is achieved when they have 41% water, 76 days after anthesis, 2,49g of dry mass and maximum germination; at that time the fruits were characterized as coloring 10.R 6/8 yellow-red red. With respect to the amount of water for storage, drying to 25% of water has no immediate negative effects on the quality of the seeds of Australian royal palm; however from 20% of water is reduced seed quality and 10% water no germination. Suitable conditions for the storage of seeds of the Australian royal palm, which initially have 48% water, are the polyethylene bags (0.20mm thick) and the ambient temperature of 10° C and 80% relative humidity; these are favorable conditions to maintain seed quality for up to 150 days.
9

Zero-Group-Velocity Propagation Of Electromagnetic Wave Through Nanomaterial

Fan, Taian 01 January 2016 (has links)
This research will investigate the problem on the propagation of electromagnetic wave through a specific nanomaterial. The nanomaterial analyzed is a material consisting of a field of Pt nanorods. This field of Pt nanorods are deposited on a substrate which consists of a RuO2 nano structure. When the nanorod is exposed to an electron beam emitted by a TEM (Transmission electron microscopy). A wave disturbance has been observed. A video taken within the chamber shows a wave with a speed in the scale of um/s (Á?10Á?^(-6) m/s), which is 14 orders of magnitude lower than speed of light in free space (approximate 3ÁÁ?10Á?^8 m/s ). A physical and mathematical model is developed to explain this phenomenon. Due to the process of fabrication, the geometry of the decorated Pt nanorod field is assumed to be approximately periodic. The nanomaterials possess properties similar to a photonic crystal. Pt, as a noble metal, shows dispersive behaviours that is different from those ones of a perfect or good conductors. A FDTD algorithm is implemented to calculate the band diagram of the nanomaterials. To explore the dispersive properties of the Pt nanorod field, the FDTD algorithm is corrected with a Drude Model. The analysis of the corrected band diagram illustrates that the group velocity of the wave packet propagating through the nanomaterial can be positive, negative or zero. The possible zero-group velocity is therefore used to explain the extremely low velocity of wave (wave envelope) detected in the TEM.
10

Study of m-plane ZnO Grown by Radio Frequency Magnetron Sputtering

Hsieh, Ming-fong 05 August 2010 (has links)
M-plane (101 ¡Â0) ZnO thin films were grown on m-plane sapphire (101 ¡Â0) substrates by RF magnetron sputtering. We varied the RF power, working pressure, and O2/Ar ratio to obtain the best growth conditions. Structural properties were investigated by X-ray diffraction(XRD). XRD measurements showed that the crystal orientation of ZnO films was non-polar m-plane (101 ¡Â0). In addition, photoluminescence (PL) spectrum showed the bandgap energy of ZnO films was about 3.24 eV. PL spectrum showed zinc vacancy signal for films grown in oxygen rich condition. Carrier concentration was measured by hall measurement as well as FTIR spectrometry. The results showed the carrier concentration calculated by optical measurements was higher than hall measurements. One possibility for this could be the band tail at the bottom of conduction band. This band tail can make the effective mass larger and thus influencing the optical carrier concentration.

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