Dissertations / Theses on the topic 'Polarization phenomena'

The demonstration of an electrically pumped organic laser remains a major issue of organic optoelectronics for several decades. This goal requires an improved device configuration so as to reduce losses which are intrinsically higher under electrical excitation compared to optical pumping. Moreover a systematic investigation of the material properties is still missing and should lead to a reliable estimate of the lasing threshold under optical pumping, and then to a lower limit for electrical pumping. In this thesis we addressed the issue of gain and polarization properties of organic materials in the case of dye-doped polymer thin films. The originality of this work lies in the study of materials via the features of dielectric micro-lasers, allowing to investigate the issues of gain and mode coupling and the physics of open systems. We propose a quantitative description of amplification in organic materials. The "gain-loss-threshold" relation was developed and demonstrated for a Fabry-Perot type cavity, opening the way to study both amplification in organic materials and light out-coupling in dielectric micro-cavities via the lasing threshold. Within this context, different cavity shapes were studied, for instance squares, where light out-coupling takes place by diffraction at dielectric corners. We evidence that polarization properties of such lasing system originate from the intrinsic fluorescence anisotropy of dyes, which required to develop a specific anisotropic model going beyond the existing theory. We also investigated the role of the cavity geometry on the polarization states of the micro-lasers and proposed different ways to influence these features.

An advanced femtosecond laser micropolarimeter has been developed for transient pump-probe polarization measurements in opaque and semitransparent samples. The polarimeter has been used with femtoecond Kerr modelocked Ti:sapphire (810nm) and Cr:forsterite (1260nm) lasers, and in both reflective and transmissive configurations. A time resolution of 32fs was achieved with the Ti:sapphire laser, in a reflective configuration, and a time resolution of 90fs was achieved with the Cr:forsterite laser. In both cases a resolution to polarization azimuth rotation better than 10^-6 radians was achieved. A double pass polarimeter, based on a polarization modulation technique, has been developed for the study of nonreciprocal polarization occurring on the background of strong natural polarization rotation. A sensitivity to nonreciprocal polarization rotation better than 5 x 10^-4 radians has been achieved at several wavelengths of an argon ion laser: 514.5, 501.7, 496.5, 476.5 and 457.9 nm. The degenerate cubic optical nonlinearity in bulk gold was measured for the first time, at wavelengths of 1260nm and 810 nm, using a technique based on the pump-probe specular inverse Faraday effect. A reflected probe polarization azimuth rotation of ~1 x 10^-14 rad cm^2/W of pump power was seen in gold at 1260 nm, this corresponds to a considerable nonlinearity of |chi xxyy(3)(w,w,w,-w) - chi xyyx(3)(w,w,w,-w)| ~ 10^-9 esu (gaussian), 10^-16 m2 Volt^-2 (SI). The nonlinear response was found to be faster than 40fs at 810nm, and faster than 90fs at 1260nm. The nonlinearity is attributed predominantly to a spin-flipping mechanism. The frequency degenerate nonlinear optical response has been measured for the first time in opaque and semitransparent nickel films, of ~3-30nm thickness, at a wavelength of 810nm. Simultaneous measurements of the pump induced polarization azimuth rotation in reflective and transmissive configurations, at both the air and glass interfaces of the nickel films, indicated the importance of the surface in determining the nonlinear response. It has been established that the surface layer significantly influences the nonlinearity to a depth of about 4-5nm into the bulk. The nonlinear polarization rotation appears on the background, but is independent of, the linear polarization rotation due to the Kerr effect. From the large specular inverse Faraday effect observed, nickel films have been shown to be suitable for use in broadband femtosecond autocorrelation pulse duration measurements. A nonlinearity of liquefying gallium has been used to achieve broadband light by light modulation, at milliwatt operating power levels, with a frequency band spanning up to several hundred kilohertz, in a fibrized all-optical switch. For the first time nonreciprocity of natural polarization rotation has been seen in the optically active crystal, Bi12SiO20. A nonreciprocal component of the polarization rotation of ~2 x 10^-3 radians was observed on the background of the polarization rotation due to conventional optical activity. The nonreciprocal rotation has been attributed to the presence of the symmetric part of the nonlocality tensor Re{gamma xyz + gamma xyz} ~ 5 x 10^-12 cm (gaussian), 6 x 10^-9m (SI), at 457.9nm. [note that "w" represents l.c. omega].

Phénomènes de spintronique dans les jonctions tunnel magnétiques et des films minces sont très prometteurs des deux points fondamentaux et l'application de vue. Elles sont basées sur l'exploration de spin d'électron en plus de sa charge et comprennent intercalaire couplage d'échange (CEI), l'anisotropie magnétique perpendiculaire (PMA), géante (GMR) et magnétorésistance tunnel (TMR), Couple de transfert de spin (STT), Spin effet Hall (SHE) et même induire du magnétisme dans les éléments non compris d graphène. Cette thèse comprendra premiers principes des études de phénomènes spintronique qui ont été d'un grand intérêt récemment. La première partie est consacrée à intercalaire couplage d'échange à travers les matériaux isolants dont le MgO, SrTiO3, GaAs et ZnSe. La deuxième partie comprendra des études ab initio d'anisotropie magnétique perpendiculaire au Fe | interfaces MgO et MTJ y compris le mécanisme et sa corrélation avec le spin Bloch symétrie Etat fondé de filtrage. Dans les enquêtes troisième partie de l'anisotropie magnétique et la fonction de travail dans les Co | interfaces graphène seront présentés. Ensuite, il sera montré possibilité d'induire et d'optimiser le magnétisme intrinsèque dans nanomeshes graphène. Dernière partie sera consacrée à l'induction de polarisation de spin et le réglage de Dirac point et ordre magnétique dans le graphène à l'aide d'effets de proximité magnétiques substrat
Spintronic phenomena in magnetic tunnel junctions and thin films are very promising from both fundamental and application points of view. They are based on exploring spin of electron in addition to its charge and include interlayer exchange coupling (IEC), perpendicular magnetic anisotropy (PMA), giant (GMR) and tunnel magnetoresistance (TMR), Spin Transfer Torque (STT), Spin Hall Effect (SHE) and even inducing magnetism in non d elements including graphene. This thesis will include first-principles studies of spintronic phenomena which have been of high interest recently. First part is devoted to interlayer exchange coupling across insulating materials including MgO, SrTiO3, GaAs and ZnSe. The second part will include ab initio studies of perpendicular magnetic anisotropy at Fe|MgO interfaces and MTJs including the mechanism and its correlation to the Bloch state symmetry based spin filtering. In third part investigations of magnetic anisotropy and work function in Co|graphene interfaces will be presented. Next, it will be shown possibility of inducing and optimizing intrinsic magnetism in graphene nanomeshes. Final part will be devoted to inducing spin polarization and tuning Dirac point and magnetic order in graphene by means of magnetic substrate proximity effects

Significant advances in the efficacy of cancer therapy have been accompanied by an escalation of side effects that result from therapy-induced injury to normal tissues. Patients with high grade cancer or metastasis are often treated with chemotherapy, 50% of which are associated with reactive oxygen species generation and cellular oxidative stress. Heart is the normal tissue most susceptible to chemotherapy-induced oxidative stress and heart disease is the most common leading cause of death in cancer survivors. However, early and sensitive biomarkers to identify heart disease are still lacking. Extracellular vesicles (EVs) are released from cells during oxidative stress and send oxidized proteins into the circulation as a compensatory mechanism that prevents cellular proteotoxicity. Thus, the protein contents of EVs released during the pre-degeneration stage reveal that oxidative stress is occurring early in the damaged tissue. Using a mouse model of doxorubicin (DOX)-induced cardiac injury, we demonstrated that EVs can be used as an early diagnostic tool for tissue injury as they are oxidatively modified with 4-hydroxynonenal and contain tissue specific proteins—glycogen phosphorylase brain/heart, muscle, and liver isoforms—that indicate their origins. These biomarkers increased early, before the changes of conventional biomarkers occurred. EVs also mediate intercellular communication by transferring bioactive molecules between cells. In the cell culture system, EVs play an important role in oxidative stress response by inducing macrophage polarization. EVs from cardiomyocytes promoted both proinflammatory (M1) and anti-inflammatory (M2) macrophage polarization evidenced by higher pro- and anti-inflammatory cytokines and nitric oxide generation, as well as mitochondrial oxidative phosphorylation suppression and glycolysis enhancement. In contrast, EVs from the hepatocytes supported anti-inflammatory macrophage (M2) by enhancing oxidative phosphorylation and anti-oxidant proteins. DOX promoted the immunostimulatory effects of cardiomyocyte EVs but not hepatocyte EVs. The differential functions of EVs on macrophage phenotype switching are due to their different effects on Thioredoxin 1 redox state, which regulates activities of redox sensitive transcription factors NFκB and Nrf-2. Our findings shed light on the role of EVs as a redox active mediator of immune response during chemotherapy.

Geophysical methods are essential for exploration and monitoring of subsurface formations, e.g. in carbon dioxide sequestration or enhanced geothermal energy. One of the keys to their successful application is the knowledge of how the measured physical quantities are related to the desired reservoir parameters. The work presented in this thesis shows that the presence of carbon dioxide (CO2) in pore space gives rise to multiple processes all of which contribute to the electrical rock conductivity variation. Basically, three mechanisms take place: (1) CO2 partially replaces the pore water, which is equivalent to a decrease in water saturation. (2) CO2 chemically interacts with the pore water by dissolution and dissociation. These processes change both the chemical composition and the pH of the pore filling fluid. (3) The low-pH environment can give rise to mineral dissolution and/or precipitation processes and changes the properties of the grain-water interface. Investigations on the pore water phase show that the reactive nature of CO2 in all physical states significantly acts on the electrical conductivity of saline pore waters. The physico-chemical interaction appears in different manifestations depending mainly on the pore water composition (salinity, ion types) but also on both temperature and pressure. The complex behaviour includes a low- and a high-salinity regime originating from the conductivity increasing effect of CO2 dissociation, which is opposed by the conductivity decreasing effect of reduced ion activity caused by the enhanced mutual impediment of all solutes. These results are fundamental since the properties of the water phase significantly act on all conduction mechanisms in porous media. In order to predict the variation of pore water conductivity, both a semi-analytical formulation and an empirical relationship for correcting the pore water conductivity, which depends on salinity, pressure and temperature, are derived. The central part of the laboratory experiments covers the spectral complex conductivity of water-bearing sand during exposure to and flow-through by CO2 at pressures up to 30MPa and temperatures up to 80°C. It is shown that the impact of CO2 on the real part of conductivity of a clean quartz sand is dominated by the low- and high-salinity regime of the pore water. The obtained data further show that chemical interaction causes a reduction of interface conductivity, which could be related to the low pH in the acidic environment. This effect is described by a correction term, which is a constant value as a first approximation. When the impact of CO2 is taken into account, a correct reconstruction of fluid saturation from electrical measurements is possible. In addition, changes of the inner surface area, which are related to mineral dissolution or precipitation processes, can be quantified. Both the knowledge gained from the laboratory experiments and a new workflow for the description and incorporation of geological geometry models enable realistic finite element simulations. Those were conducted for three different electromagnetic methods applied in the geological scenario of a fictitious carbon dioxide sequestration site. The results show that electromagnetic methods can play an important role in monitoring CO2 sequestration. Compared to other geophysical methods, electromagnetic techniques are generally very sensitive to pore fluids. The proper configuration of sources and receivers for a suitable electromagnetic method that generates the appropriate current systems is essential. Its reactive nature causes CO2 to interact with a water-bearing porous rock in a much more complex manner than non-reactive gases. Without knowledge of the specific interactions between CO2 and rock, a determination of saturation and, consequently, a successful monitoring are possible only to a limited extend. The presented work provides fundamental laboratory investigations for the understanding of the electrical properties of rocks when the reactive gas CO2 enters the rock-water system. All laboratory results are put in the context of potential monitoring applications. The transfer from petrophysical investigations to the planning of an operational monitoring design by means of close-to-reality 3D FE simulations is accomplished.

The principle element of a democratic society is the belief held by its citizens that governance institutions are transparent, accountable and are influenced through stakeholder interests. In particular, confidence resides in a belief that representation models based on democratic elections have the capacity to aggregate the singular voices of the electorate into a colleCtive endeavour. The advancement of Democratic Dialogue Practices (OOPs) represents a move away from the exclusiveness of this electoral model through offering governments new opportuniti~s to engage with citizens through multiple forms of· facilitated dialogue. DDP specifically targets those least likely to engage within governance strategies aiming to ensure the inclusion of participants in a wide variety of transparent, accountable and inclusive dialogue practices. Central to the focus of this thesis is the facilitated practice of DDP and therein the dialogue of the small group discussion. The aim is to explore the existence of the 'Group Polarization Phenomenon' (GPP) and its implications for DDP and the promotion of a 'culture of democracy'.

Thesis (Honors)--Ohio State University, 2007.
Title from first page of PDF file. Document formatted into pages: contains 35 p. Includes bibliographical references (p. 22-23). Available online via Ohio State University's Knowledge Bank.

Le présent travail de thèse met l'accent sur divers aspects de la distillation membranaire dans l'objectif de concevoir des procédés de dessalement proches du " zéro effluent liquide ". De manière générale, deux sujets sont discutés en détail: (i) la corrélation entre les caractéristiques de la membrane et les performances du procédé de distillation membranaire (ii) la compréhension et le contrôle de la polarisation thermique en DM. L'analyse de l'état de l'art en distillation membranaire porte notamment sur les progrès dans le développement des membranes, dans la compréhension des phénomènes de transport, les récents développements dans la conception des modules et le colmatage. Des phénomènes annexes et les applications innovantes sont également discutés dans la partie introductive de la thèse. L'effet des conditions de fabrication et de la composition des collodions sur les caractéristiques des membranes et la corrélation entre ces dernières et leurs performances a été discuté dans la section suivante. Il est établi que la morphologie de la membrane joue un rôle crucial dans ses performances pour des applications sur des fluides réels. En outre, on met en évidence que l'impact de la morphologie de la membrane est différente selon que la procédé fonctionne avec une phase liquide froide du côté distillat (Direct Contact Membrane Distillation - DCMD)) ou avec un courant d'air sec ou le vide (Air Gap ou Vacuum Membrane Distillation). Dans une deuxième partie, les aspects théoriques et expérimentaux de la polarisation thermique en distillation membranaire (DCMD) ont également été étudiés. Les phénomènes de polarisation thermique sur une membrane plane ont été étudiés en utilisant une cellule spécialement conçue. L'effet des conditions de fonctionnement et de la concentration de la solution sur la polarisation thermique a été étudié expérimentalement. Nous avons observé que l'augmentation de concentration de la solution favorise la polarisation thermique à cause d'une détérioration de l'hydrodynamique résultante à la surface de la membrane. Certaines techniques actives et passives pour réduire la polarisation thermique et le colmatage en distillation membranaire ont également été examinées dans l'étude cette étude. Nous avons montré que la polarisation thermique peut être considérablement réduite en générant des écoulements secondaires dans le fluide circulant à l'intérieur du canal d'alimentation, donc à l'intérieur de la fibre creuse si c'est cette configuration qui est retenue. Dans la présente étude, l'induction d'un écoulement secondaire a été réalisée en utilisant les fibres torsadées en hélice et une configuration ondulée. En raison de l'amélioration du niveau de polarisation thermique du côté de l'alimentation et du distillat, les géométries de fibres ondulées fournissent des flux et des taux de rendement supérieurs à ceux des autres configurations. La mise en œuvre d'un écoulement pulsé et intermittent pour contrôler la polarisation en distillation membranaire a également été examinée. Notre étude permet de conclure que ces types d'écoulements ont un impact positif sur les taux de rendement et le facteur d'amélioration volumique (gain en flux ramené par rapport à l'augmentation du volume de l'équipement) sans compromis sur le taux de remplissage des carters de fibres creuses
The current PhD work emphasizes on various aspects of membrane distillation for approaching zero liquid discharge in seawater desalination. In broader sense, two themes have been discussed in detail: (i) correlation between membrane features and their performance in MD (ii) understanding and control of thermal polarization in MD. Introduction and state-of-the-art studies of MD including progress in membrane development, understanding the transport phenomenon, recent developments in module fabrication, fouling and related phenomenon and innovative applications have been discussed in introductory part of the thesis. The effect of operating conditions and dope compositions on membrane characteristics and correlation between membrane features and their performance has been discussed in subsequent section. It has been established that membrane morphology plays a crucial role in performance of the membrane for real applications. Furthermore, it has been demonstrated that the effect of membrane morphology is different for direct contact and vacuum configurations. Theoretical and experimental aspects of thermal polarization in direct contact membrane distillation have also been investigated. Thermal polarization phenomenon in a flat sheet membrane has been studied by using a specifically designed cell. The effect of operating conditions and solution concentration on thermal polarization has been explored experimentally. It has been observed that increased solution concentration favors the thermal polarization due to resulting poor hydrodynamic at the membrane surface and increase in diffusion resistance to the water vapors migrating from bulk feed phase to the membrane surface. Some active and passive techniques to decrease thermal polarization and possible fouling in membrane distillation have also been discussed in the current study. Thermal polarization can be greatly reduced by inducing secondary flows in the fluid flowing inside the fiber. The induction of secondary flows in the current study has been realized by using the fibers twisted in helical and wavy configurations. Due to improvement of thermal polarization coefficient on up and downstream, the undulating fiber geometries provide high flux and superior performance ratio. Application of intermittent and pulsatile flow to control thermal polarization in MD has also been discussed. It has been inferred that these flows have positive impact on performance ratio and volume based enhancement factors without compromising on packing density of the system. The application of MD for treatment of produced water has also been studied

The proton is a bound state of quarks which are held together by the strong force, mediated by gluons. The understanding of the proton structure is presently one of the central issues in hadron physics. The present work reports on phenomenological and experimental studies related to the possibilities offered by the future antiproton beam at the FAIR facility at Darmstadt, in the momentum range between 1.5 and 15 GeV/c. After a classification of the reaction channels which are accessible in antiproton-proton annihilation, the main features of the PANDA detector are described. A chapter of this thesis is dedicated to the study of the optical coupling between crystals and photodiodes in the electromagnetic calorimeter, which will be operated at low temperature (-25° C). Mechanical, thermal, optical properties and radiation hardness of two commercial glues are quantified.Feasibility studies of the reaction barp → e+e− for the Time-Like proton form factor measurements at PANDA are presented. The electromagnetic structure of the proton is parametrized in terms of electric GE and magnetic GM form factors. The electromagnetic interaction is well described by the theory of quantum electrodynamics. The traditional tool to determine proton electromagnetic form factors is polarized and unpolarized electron-proton elastic scattering, assuming that the interaction occurs through the exchange of one virtual photon. The crossed symmetry channels pbarp ↔ e+e− allowto access the Time-Like region. The background reactions are also studied, in particular the pbarp → π+π− channel. The results obtained from a realistic Monte Carlo simulation using PANDARoot show that the proton form factor ratio can be measured at PANDA with unprecedented accuracy. The effects of radiative corrections due to real and virtual photon emission are considered.Based on a model independent formalism, the calculation of the experimental observables for the pbarp → e+e− reaction is extended to the annihilation into a heavy lepton pair which carries the same physical information on the proton structure as the electrons. In this case, the lepton mass can not be neglected. The same formalism is also applied in Space-Like region to the elastic scattering of protons from electrons at rest (pe-inverse kinematics). We suggest that the elastic pe scattering can be used to polarize and/or to measure the polarization of high energy proton (antiproton) beams, and allows a precise measurement of the proton charge radius.

Le phénomène d'émission électronique est étudié dans de nombreux domaines fondamentaux de la physique et pose le principe de fonctionnement d'un grand nombre de dispositifs tels que les écrans à émission de champ, les propulseurs Hall, etc. Il est mieux compris pour les métaux. Cependant pour les matériaux isolants, il constitue un phénomène critique limitant la fiabilité des composants dans les applications spatiales où les phénomènes de décharge et de claquage sont entièrement contrôlés par l'émission électronique. Selon l'énergie des électrons incidents et les propriétés des diélectriques, les électrons peuvent être piégés au sein du matériau, et/ou être à l'origine de phénomènes d'émission électronique. Ce travail de thèse se situe à l'interface de trois domaines de recherche : le dépôt par plasma de couches minces nanocomposites, le piégeage et le transport de charges électriques dans les diélectriques, et la caractérisation des matériaux sous irradiation en milieu spatial. Il explore l'effet des nanoparticules d'argent (AgNPs) enterrées dans des couches minces de silice, sur les mécanismes physiques (injection, piégeage, transport de charges et émission électronique secondaire) responsables du chargement diélectrique et des émissions d'électrons, afin de moduler ces phénomènes. Les couches minces nanostructurées de silice contenant un plan d'AgNPs ont été élaborées par procédé plasma combinant dans un même réacteur la pulvérisation d'une cible métallique et le dépôt chimique en phase vapeur activé par plasma (PECVD). La caractérisation structurale des échantillons a permis de déterminer la composition chimique de la matrice de silice plasma, la taille, la forme, la densité et la distribution des AgNPs ainsi que l'épaisseur totale de la structure. Ces analyses ont permis de corréler les paramètres structurels avec la réponse des couches diélectriques nanostructurées réalisées sous contrainte électrique et irradiation électronique. Il a été constaté que pour des électrons primaires de faible énergie (< 2keV), le rendement total d'émission d'électrons (TEEY) des couches minces de silice sans AgNPs présente une forme atypique avec un minimum local situé à environ 1 keV. Afin de mieux comprendre ce comportement, un modèle de TEEY a été développé. Il est basé sur le modèle de Dionne, et adapté aux diélectriques. Il considère le champ électrique interne résultant de l'accumulation de charges électriques dans la couche diélectrique. [...]
Electron emission phenomenon is intensively studied in many fundamental areas in physics and lays down the principle of operation of a large number of devices such as field emission display devices, Hall thrusters, etc. It is better described for metals. However, when originating from insulating materials it becomes a critical phenomenon involved in reliability issues of components in space applications where surface flashover phenomena and vacuum breakdown are entirely controlled by the electron emission from solids. Depending on the energy of impinging electrons and the dielectric properties, the electrons can be trapped within the dielectric bulk, and/or be responsible of electron emission phenomena. This PhD work, carried out at the interface of three research domains: plasma deposition of thin nanocomposite layers, dielectric charging and charge transport in thin dielectrics, and characterization of materials under irradiation in space environment, aims to explore the effect of metal inclusions (silver nanoparticles, AgNPs), embedded in thin dielectric silica layers, on the physical mechanisms (charge injection, trapping, transport and secondary electron emission from the surface) responsible of the dielectric charging and electron emission from dielectrics, in order to modulate them. Nanostructured thin dielectric silica layers containing a single plan of AgNPs have been elaborated by plasma process successfully combining in the same reactor sputtering of a metallic target and plasma enhanced chemical vapor deposition (PECVD). Structural characterization of the resulting samples has been performed to determine the chemical composition of the plasma silica matrix as well as to obtain the AgNPs size, shape, density and distribution and the total thickness of the structure. These analyses allowed correlation of the structural parameters with the response of the obtained nanostructured dielectric layers under electrical stress and electronic irradiation. It was found that for low energy of the incident electrons (< 2keV) the total electron emission yield (TEEY) from thin silica layers without AgNPs presents an atypical shape with local minimum situated at around 1keV. To get closer to the description of this behavior a model for the TEEY was developed. It is based on Dionne's model, but adapted to dielectrics. It considers the internal electric field resulting from dielectric charging phenomenon.[...]

博士
國立成功大學
工程科學系碩博士班
96
Microfluidics with the effect of electrokinetic phenomena is replete with many potential possibilities for the development of convenient devices for chemical and biological analyses. Accordingly, Lab-on-Chip (LOC) has been proposed integrate multiple microfluidic systems into a single chip that includes several benefits, such as the pocket sized chip, easy integration into electrical circuitry, low sample consumption, and high-speed analysis. The concept of Lab-on-Chip has been attracted by many researchers and has prompted rapid development of science and technology. Given this, this thesis is focused on microfluidics and associated electrokinetic phenomena. The scope of this thesis, which is classified according to the channel dimension: micro- and nano- sized channels, covers the fluidic behavior, ionic transport, and its applications, respectively. In the first part of this thesis, we concentrate on the fluidic behavior in microchannel and perform a series of numerical simulations to investigate both the influence of the Joule-heating effect and the interaction between the electrostatic force and hydrodynamic pressure force. In studying the former effect, we simulate the variation of a flow field by including temperature dependent fluidic parameters, such as thermal conductivity, electrical conductivity, and viscosity of fluid. Results show that a convex velocity profile is induced in a relative high temperature region, whereas a concave velocity profile appears in a relative low temperature region. The latter effect is investigated in a basic model to analyze the formation of flow recirculation and a nozzle-like acceleration effect under the interaction between two kinds of driving forces in a straight microchannel. The existence of the recirculation structure is also validated by experiments where the hydrodynamic force is counterbalanced by the electrostatic force generated from a pair of plated electrodes onto the surface of the microchannel. The second part of this thesis focuses on distinguishing the difference between ionic transport observed in nanochannels and that observed in microchannel. First, this study focuses on experimental mesaurements regarding streaming current. Several studies in literature have pointed out that the streaming current has different tendencies in nanochannels when the concentration of buffer solution is dense and in a diluted concentration. In this thesis, by using a modified concentration approach, the results reveal that the surface charge density is insensitive to the buffer concentration as the electrical double layer is overlapped and a nearly constant streaming current is predicted. Secondly, the development of a hybrid micro-/nano-channel is utilized to investigate the concentration polarization effect which contains the ionic depletion and ionic enrichment effect. Results show that the low conductivity within the depletion zone induces a rapid electroosmotic flow, which in turn prompts the generation of vortex flow structures within the depletion zone. Both the lengthening of the depletion bulk charge layer and decrease in length of the diffusion layer, as the applied voltage is increased, are shown in this study. Finally, these results are utilized to design a novel fluidic concentrator via an ionic depletion effect and the field-amplified effect. Using Rhodamine 6G dye for visualization purposes, we show that an ionic depletion region can be induced on the anodic side of the nano-channel. It is seen that the electrical conductivity of this region is around 60 times lower than that of the buffer through an appropriate manipulation of the external potentials applied to the reservoirs of the device. Furthermore, via an appropriate time-based switching of the external electrical potentials, the sample species can be concentrated with a concentration factor close to the conductivity ratio within one minute.

碩士
國立臺南大學
電機工程學系碩博士班
107
In this paper, we propose a novel polarization beam splitter (PBS) based on symmetric directional coupler (DC) by utilizing decoupling of rib waveguide in silicon on insulator (SOI), thus the TM mode is ill coupled in the PBS. However, the TE mode can couple by satisfy the phase matching condition at an appropriate coupling length due to the same refractive index of symmertrical waveguides；hence the TE and TM modes can achieve separation effect. In order to analysis the PBS, we utilize finite element method (FEM) to perform the simulation and improve the extinction ratio of the component in the range of 1500 nm to 1600 nm as the main research direction. First, we explore the height of the slab waveguide and invent that the extinction ratio is increased as the height of the slab waveguide increases. Nevertheless, the TM mode at the long wavelength range will be cut of and the component will be fail when the height of the slab waveguide becomes too high. Under the premise, we shall select the height of slab waveguide that the TM mode isn’t cut off at the wavelength of 1600 nm, and explore the performance of different component sizes. Finally, the two sets of parameters with ER greater than 10 dB and 15 dB at a bandwidth of 100 nm are selected, and the fabrication tolerance is probed and optimized. Numerical simulations show that the present PBS has a high extinction ratio of more than 60 dB, and the device length is 109.43 µm

碩士
國立臺灣大學
物理學研究所
107
Dielectric heating by microwave has been studied for a long period and its applications are widely used in a variety of research fields. There are a plenty of papers discussing about the uniformity of heating, heating rate, hotspot, microwave synthesis, pest control, etc. However, best to our knowledge, it seems that the shielding effect of polarization charges have been overlooked. In this thesis, we first introduce the shielding effect of polarization charges by reviewing the problem of dielectric objects immersed in static uniform E-field. Next, we focus on the problem of dielectric objects hit by uniform plane waves which serves as a simplified model of microwave dielectric heating; solve the Helmholtz equations with separation of variables in spherical and cylindrical coordinates. The procedure of solving the Helmholtz equations is standard, but for completeness we point out the steps. We find out that when the wavelength is much longer than the geometry size of the object, shielding effects take place. And for elongate objects, orientations of objects have a great influence on polarization charge shielding. When wavelength has the same order as the size of the object, microwave resonance phenomenon will occur.

碩士
國立臺南大學
電機工程學系碩博士班
107
In this paper, a novel polarization splitter is proposed based on the CMOS structure in the TSRI U18 process technology. The symmetrical waveguide directional coupler (DC) is designed by utilizing the decoupling of rib waveguide , so that the TM mode is decoupling , the TE mode can couple by satisfy the phase matching condition at an appropriate waveguide gap due to the same refractive index of symmertrical waveguides；hence the TE and TM modes can achieve separation effect. In order to simulate the designed polarization separator, this paper uses the finite element method to perform the simulation. First, we follow the TSRI U18 process technology. In the etch depth of only two options, in order to ensure the existence of fundamental mode, a poly-Si is selectively deposited, and the polarization separator is designed by changing the width of the waveguide core and the spacing of the waveguide core. So that improve the light transmittance and reduce the bending loss, we use the general waveguide structure at the output and reduce the bending loss by the plate structure, and use the gradual structure to improve the light transmittance. Finally, we fixed the size of the waveguide core by the waveguide core spacing is changed to optimize the processing of the overall component extinction ratio. Numerical simulations show that the present PBS has a high extinction ratio of more than 60 dB, and the device length is 109.43

This work focuses on high-capacity spectral-efficient Earth-space microwave communication links, supporting the access to wider and less congested bandwidths and providing the required technological advances on radiowave propagation for the design and operation of system-technologies improving the spectral efficiency, proposing the operation of frequency-reuse schemes and polarization diversity techniques at Ka- and Q/V-bands. Because the suitable planning, successful deployment and effective, spectralefficient and interference-free, operation of all space-borne systems and services is necessarily related and directly dependent, although not exclusively, on the propagation channel conditions, this work provides a comprehensive and systematic approach intending the relevant propagation phenomena characterization and understanding, modelling and mitigation. It is proved that there is a bigger operational margin for the operation of the abovementioned system-technologies than what may be believed by considering the international recommended models. Major challenges are envisaged, specially in what concerns the ice-induced depolarization that is more persistent and takes longer than the corresponding rain-induced effects. Nevertheless, their mitigation is possible for which the depolarization shall be the controlling variable. The time lag of 15 minutes is identified as the best trade-off between affordable time and achievable gain in the framework of a time diversity scheme.
Este trabalho foca-se em links de comunicação Terra-espaço em microondas espectralmente eficientes e de elevada capacidade, suportando o acesso a larguras de banda maiores e menos congestionadas e ofereçendo os avanços tecnológicos necessários em termos de propagação de ondas de rádio para o projeto e operação de tecnologias de sistema que visam o uso otimizado do espectro, propondo a operação de esquemas de reuso de frequência e de técnicas de diversidade de polarização nas bandas Ka e Q/V. Porque o adequado planeamento, a implementação bem sucedida, bem como a efetiva operação, espectralmente eficiente e livre de interferências, de todos os sistemas e serviços espaciais está necessariamente relacionada e diretamente dependente, ainda que não exclusivamente, das condições do canal de propagação, este trabalho oferece uma abordagem completa e sistemática pretendendo a caracterização, compreensão, modelação e mitigação dos fenómenos de propagação relevantes. É provado existir uma maior margem operacional para a operação das tecnologias acima mencionadas do que aquela que se acredita existir considerando os modelos internacionais recomendados. São previstos maiores desafios, especialmente no que concerne à despolarização causada por gelo que é mais persistente e que dura mais tempo do que os correspondentes efeitos causados por chuva. De qualquer forma, a sua mitigação é possível e para a qual a despolarização deverá ser a variável de controlo. O intervalo de tempo de 15 minutos é identificado como o melhor compromisso entre tempo acessível e ganho alcançável no contexto de um esquema de diversidade temporal.
Programa Doutoral em Engenharia Eletrotécnica