No description available.

Abstract Epidemiological studies on malocclusions in Finland have so far concentrated on children and adolescents. Regarding the Finnish adult population, there is scarce epidemiological knowledge available on malocclusions even though the number of adults seeking orthodontic treatment has increased during the last decades. Occlusion is an important factor in the function of the masticatory system, and its role in the aetiology of temporomandibular disorders (TMD) is one of the most disputed topics in dentistry. Malocclusions can affect the characteristics of the facial soft tissue profile. The aim of the study was to investigate the prevalence of malocclusions and the role of occlusion in TMD as well as the association of facial characteristics with malocclusions and facial aesthetics. The study population consisted of subjects from the Northern Finland Birth Cohort 1966 (NFBC1966). Data were collected using questionnaires, standardized clinical examination and facial photos. The profile photographs were analysed using linear and angular soft tissue cephalometric measurements. The most common malocclusion in the NFBC1966 subjects was lateral crossbite. This study showed a significant association between asymmetric malocclusions and TMD. TMD signs associated significantly with lateral crossbite, scissors bite, negative overjet, and the length and lateral deviation in slide between retruded contact position and intercuspal position (RCP-ICP). Soft tissue profile characteristics were highly correlated with negative overjet. The ANB-angle was significantly associated with the perception of facial attractiveness. In conclusion, malocclusions were associated with signs and symptoms of TMD in the Finnish adult population. Overjet appeared to affect the facial profile more than overbite. Facial convexity seemed to be a more important determinant of facial aesthetics for orthodontists than for dentists and laypersons. / Tiivistelmä Suomalaiset epidemiologiset tutkimukset purennan poikkeamista ovat tähän asti keskittyneet tarkastelemaan lapsia ja nuoria. Tarkkaa epidemiologista tietoa suomalaisen aikuisväestön purennan poikkeamista on tällä hetkellä saatavilla vain niukasti, vaikka oikomishoitoon hakeutuvien aikuispotilaiden määrä on Suomessa viime vuosina lisääntynyt. Purennalla on tärkeä merkitys purentaelimistön toiminnassa ja sen rooli purentaelimistön toimintahäiriöiden (TMD) etiologiassa on yksi kiistanalaisimpia aiheita hammaslääketieteessä. Purennan poikkeamat voivat vaikuttaa myös kasvojen pehmytkudosprofiilin piirteisiin. Tutkimuksen tarkoituksena oli selvittää purennan poikkeamien esiintyvyyttä ja tutkia kasvojen piirteiden yhteyttä purennan poikkeamiin sekä kasvojen estetiikkaan. Lisäksi tutkittiin purennan poikkeamien yhteyttä TMD:hen. Tutkimusjoukko koostui Pohjois-Suomen syntymäkohortti 1966 -tutkimukseen osallistuneista. Tutkimuksen aineisto kerättiin kyselomakkeiden, standardoidun kliinisen tutkimuksen ja kasvovalokuvien avulla. Profiilivalokuvien analysointi perustui pehmytkudoksen kefalometrisiin lineaari- ja kulmamittauksiin. Tässä tutkimuksessa yleisin purennan poikkeama oli sivualueen ristipurenta. Asymmetriset purennan poikkeamat olivat merkittävästi yhteydessä TMD:hen; erityisesti sivualueen ristipurenta, saksipurenta, negatiivinen horisontaalinen ylipurenta sekä nivelaseman ja keskipurennan (RCP-ICP) välisen liu’un pituus ja sivuttainen deviaatio. Negatiivisen horisontaalisen ylipurennan todettiin vaikuttavan voimakkaasti kasvojen profiiliin. ANB-kulma oli merkitsevästi yhteydessä kasvojen arvioituun viehättävyyteen. Purennan poikkeamilla näyttää olevan yhteys TMD:n oireisiin ja kliinisiin löydöksiin suomalaisessa aikuisväestössä. Horisontaalinen ylipurenta näyttää vaikuttavan kasvojen profiiliin enemmän kuin vertikaalinen ylipurenta. Kasvojen kuperuus painottuu enemmän oikomishoidon erikoishammaslääkärien näkemyksessä kasvojen estetiikasta hammaslääkäreihin ja maallikoihin verrattuna.

There has been growing interest in two-dimensional (2-D) crystals beyond graphene for next-generation nano-electronics. Transition metal dichalcogenides have been most widely studied, for their semiconducting characteristics and hence, potential applications. This interest has fueled many efforts to establish methods for synthesis of MoS2 layers, a most promising candidate, in controlled numbers over large areas. One of the most scalable methods is chemical vapor deposition (CVD). The current approaches to growth from the vapor phase are by and large very empirical. This thesis is hence concerned with the predictive synthesis of n-layered MoS2 using CVD uniformly over large areas and the correlation of growth parameters with the structural and electronic properties of the deposited films. A simple, relatively non-toxic and non-pyrophoric chemistry, consisting of Mo(CO)6 and H2S was first chosen for vapor phase synthesis. This chemistry allowed synthesis of MoS2 from precursors located outside of the growth reactor, a necessary condition for electronics device technology. Iterative thermodynamic modeling of the Mo-S-C-O-H system and growth was then done to identify the appropriate CVD process windows for the growth of pure MoS2, departures from stoichiometry, contamination and breakdown of equilibrium modelling. Remarkable agreement between theoretical modelling and actual growth has been observed leading to predictable deposition. Within these thermodynamic windows, the gas phase supersaturation were then reduced to obtain better kinetic control over crystal growth. It is shown that control of supersaturation at the very initial stages of growth is critical to reduce the nucleation density and hence obtain monolayers with small defect densities. In addition, it is shown that at higher temperatures the kinetics of nucleation and growth are determined by the supersaturation on the growth surface. Physico-chemical modelling reveals that this steady state supersaturation is determined by the kinetics of adsorption and desorption. All of this understanding has been used to realize a variety of structures from discrete crystalline islands- 30 nm to 150 microns- to deposits with controlled number of layers – n =1 to 6 or greater- uniformly over large areas on quartz and sapphire. Gas phase chemistry also affects the electrical characteristics of the as deposited layers. It is shown, for the first time, that by changing gas phase Mo to S ratios the stoichiometry of the deposited layers MoS2 can be made metal or chalcogen deficient. This yields MoS2 that can be either p-type or n-type. p-type and n-type MoS2 with mobilities up to 7.4 cm2/Vs and 40 cm2/Vs respectively are demonstrated. FETs fabricated on MoS(2-x) samples (increasing x) with varying stoichiometry showed a maximum on-current of 18 μA (4.5 μA/μm) in vacuum and 0.6 μA (0.15 μA/μm) in air for a drain bias Vds = 1 V. Sulphur deficiency also affect reliability. While samples with a higher concentration of sulphur vacancies have higher mobility in vacuum, the mobility degrades significantly in air and gets reversed on annealing in H2S. The details of such correlation between growth and electrical characteristics are discussed in this thesis.

No description available.

Técnicas e dispositivos para controlar vibrações em estruturas vêm sendo desenvolvidos e aprimorados para garantir segurança a estruturas sujeitas a carregamentos dinâmicos de grande magnitude, como o caso de tufões e terremotos. Neste sentido, o controle passivo de vibrações por meio de amortecedores de massa sintonizados, TMDs (Tuned Mass Dampers), é utilizado com muita eficiência no controle de vibrações induzidas por carregamentos externos de baixas frequências, como ventos. Porém, terremotos possuem um amplo espectro de frequências e por isso não há um acordo sobre a eficácia dos TMDs ao mitigar vibrações induzidas por sismos. Neste trabalho, estudou-se a sensibilidade dos parâmetros de frequência de sintonização e razão de massa dos TMDs que influenciam seu desempenho para controlar vibrações em edifícios sob carregamentos de terremotos. Para isso utilizou-se um modelo mais preciso em elementos finitos de pórtico plano não linear geométricos para obtenção do comportamento estrutural de um edifício de 20 pavimentos. Na simulação dos terremotos, desenvolveu-se um código para geração de processos estocásticos totalmente não estacionários e espectro-compatíveis, simulados para três diferentes configurações de solo. Descobriu-se que TMDs sintonizados para altas frequências têm melhor desempenho na minimização de deslocamentos e frequências de oscilação da estrutura. Esta conclusão é contrastante com o que se encontra na literatura, de que dispositivos sintonizados para a primeira frequências natural da estrutura são mais eficientes. Também se observou que TMDs com altas razões de massa (i.e. maiores que 10%) têm melhor performance. O melhor desempenho dos TMDs foi observado em dispositivos com altas razões de massa e moderadas a altas frequências de sintonização. Este trabalho mostra que o desempenho de sistemas de controle de vibrações passivos como TMDs depende do tipo de solo, do projeto dos dispositivos, da correta avaliação da resposta estrutural e da adequada representação do fenômeno que excita a estrutura. / Techniques and devices for vibration control have been developed to ensure safety of structures subjected to relevant dinamic loads, as hurricanes and earthquakes. In this way, the passive control with TMDs (Tuned Mass Dampers) has been used with efficiency to suppress vibrations in structures subjected to low-frequency wind loads, for instance. However, for earthquakes that have a broad-banded frequency contend, there is no general agreement about the performance of TMDs. In this thesis, the sensitivity of TMD parameters that influence the performance of the devices is evaluated. An accutare non-linear plane frame finite element (FE) formulation is employed to estimate the structural behaviour of a 20-storey building under earthquake loads. For the representation of earthquakes, a code was developed for the generation of fully non-stationary spectrum-compatible stochastic process, for three types of soil. It was found that TMDs tuned to higher frequencies perform better at minimizing displacements and vibration frequencies, in contrast to what is commonly believed (e.g., that devices tuned to the building\'s fundamental natural frequency present ideal performance). Further, a compounding effect is also observed, with the best performance being obtained by TMDs of large mass tuned to moderate to high frequencies. The thesis shows that the performance of passive systems like TMDs depend on the type os soil, the design of the absorbers, the correct evaluation of structural behaviour and the right representation of the phenomenon that excitates the structure.

Técnicas e dispositivos para controlar vibrações em estruturas vêm sendo desenvolvidos e aprimorados para garantir segurança a estruturas sujeitas a carregamentos dinâmicos de grande magnitude, como o caso de tufões e terremotos. Neste sentido, o controle passivo de vibrações por meio de amortecedores de massa sintonizados, TMDs (Tuned Mass Dampers), é utilizado com muita eficiência no controle de vibrações induzidas por carregamentos externos de baixas frequências, como ventos. Porém, terremotos possuem um amplo espectro de frequências e por isso não há um acordo sobre a eficácia dos TMDs ao mitigar vibrações induzidas por sismos. Neste trabalho, estudou-se a sensibilidade dos parâmetros de frequência de sintonização e razão de massa dos TMDs que influenciam seu desempenho para controlar vibrações em edifícios sob carregamentos de terremotos. Para isso utilizou-se um modelo mais preciso em elementos finitos de pórtico plano não linear geométricos para obtenção do comportamento estrutural de um edifício de 20 pavimentos. Na simulação dos terremotos, desenvolveu-se um código para geração de processos estocásticos totalmente não estacionários e espectro-compatíveis, simulados para três diferentes configurações de solo. Descobriu-se que TMDs sintonizados para altas frequências têm melhor desempenho na minimização de deslocamentos e frequências de oscilação da estrutura. Esta conclusão é contrastante com o que se encontra na literatura, de que dispositivos sintonizados para a primeira frequências natural da estrutura são mais eficientes. Também se observou que TMDs com altas razões de massa (i.e. maiores que 10%) têm melhor performance. O melhor desempenho dos TMDs foi observado em dispositivos com altas razões de massa e moderadas a altas frequências de sintonização. Este trabalho mostra que o desempenho de sistemas de controle de vibrações passivos como TMDs depende do tipo de solo, do projeto dos dispositivos, da correta avaliação da resposta estrutural e da adequada representação do fenômeno que excita a estrutura. / Techniques and devices for vibration control have been developed to ensure safety of structures subjected to relevant dinamic loads, as hurricanes and earthquakes. In this way, the passive control with TMDs (Tuned Mass Dampers) has been used with efficiency to suppress vibrations in structures subjected to low-frequency wind loads, for instance. However, for earthquakes that have a broad-banded frequency contend, there is no general agreement about the performance of TMDs. In this thesis, the sensitivity of TMD parameters that influence the performance of the devices is evaluated. An accutare non-linear plane frame finite element (FE) formulation is employed to estimate the structural behaviour of a 20-storey building under earthquake loads. For the representation of earthquakes, a code was developed for the generation of fully non-stationary spectrum-compatible stochastic process, for three types of soil. It was found that TMDs tuned to higher frequencies perform better at minimizing displacements and vibration frequencies, in contrast to what is commonly believed (e.g., that devices tuned to the building\'s fundamental natural frequency present ideal performance). Further, a compounding effect is also observed, with the best performance being obtained by TMDs of large mass tuned to moderate to high frequencies. The thesis shows that the performance of passive systems like TMDs depend on the type os soil, the design of the absorbers, the correct evaluation of structural behaviour and the right representation of the phenomenon that excitates the structure.

Discovery of grapheme has paved way for experimental realization of many physical phenomena such as massless Dirac fermions, quantum hall effect and zero-field conductivity. Search for other two dimensional (2D) materials led to the discovery of boron nitride, transition metal dichalcogenides(TMDs),transition metal oxides(MO2)and silicene. All of these materials exhibit different electronic and transport properties and are very promising for nanodevices such as nano-electromechanical-systems(NEMS), field effect transistors(FETs),sensors, hydrogen storage, nano photonics and many more. For practical utility of these materials in electronic and photonic applications, varying the band gap is very essential. Tuning of band gap has been achieved by doping, functionalization, lateral confinement, formation of hybrid structures and application of electric field. However, most of these techniques have limitations in practical applications. While, there is a lack of effective method of doping or functionalization in a controlled fashion, growth of specific sized nanostructures (e.g., nanoribbons and quantum dots),freestanding or embedded is yet to be achieved experimentally. The requirement of high electric field as well as the need for an extra electrode is another disadvantage in electric field induced tuning of band gap in low dimensional materials. Development of simpler yet effective methods is thus necessary to achieve this goal experimentally for potential application of these materials in various nano-devices. In this thesis, novel methods for tuning band gap of few 2D materials, based on strain and stacking, have been proposed theoretically using first principles based density functional theory(DFT) calculations. Electronic properties of few layered nanomaterials are studied subjected to mechanical and chemical strain of various kinds along with the effect of stacking pattern. These methods offer promising ways for controlled tuning of band gap in low dimensional materials. Detailed methodology of these proposed methods and their effect on electronic, structural or vibrational properties have also been studied. The thesis has been organized as follows: Chapter1 provides a general introduction to the low dimensional materials: their importance and potential application. An overview of the systems studied here is also given along with the traditional methods followed in the literature to tune their electronic properties. The motivation of the current research work has also been highlighted in this chapter. Chapter 2 describes the theoretical methodology adopted in this work. It gives brief understanding of first principles based Density Functional Theory(DFT) and various exchange and correlation energy functionals used here to obtain electronic, structural, vibrational and magnetic properties of the concerned materials. Chapter 3 deals with finding the origin of a novel experimental phenomenon, where electromechanical oscillations were observed on an array of buckled multiwalled carbon nanotubes (MWCNTs)subjected to axial compression. The effect of structural changes in CNTs in terms of buckling on electronic properties was studied. Contribution from intra-as well as inter-wall interactions was investigated separately by using single-and double-walled CNTs. Chapter 4 presents a method to manipulate electronic and transport properties of graphene bilayer by sliding one of the layers. Sliding caused breaking of symmetry in the graphene bilayer, which resulted in change in dispersion in the low energy bands. A transition from linear dispersion in AA stacking to parabolic dispersion in AB stacking is discussed in details. This shows a possibility to use these slid bilayers to tailor graphene based devices. Chapter 5 develops a method to tune band gap of bilayers of semiconducting transition metal dichalcogenides(TMDs) by the application of normal compressive strain. A reversible semiconductor to metal(S-M) transition was reported in this chapter for bilayers of TMDs. Chapter 6 shows the evolution of S-M transition from few layers to the bulk MoS2 under various in-plane and out of plane strains. S-M transition as a function of layer number has been studied for different strain types. A comparison between the in-plan and normal strain on modifying electronic properties is also presented. Chapter 7 discusses the electronic phase transition of bulk MoS2 under hydrostatic pressure. A hydrostatic pressure includes a combined effect of both in-plane and normal strain on the structure. The origin of metallic transition under pressure has been studied here in terms of electronic structure, density of states and charge analysis. Chapter 8 studies the chemical strain present in boron nitride nanoribbons and its effect on structural, electronic and magnetic properties of these ribbons. Properties of two achiral (armchair and zig-zag) edges have been analyzed in terms of edge energy and edge stress to predict stability of the edges. Chapter9 summarizes and concludes the work presented in this thesis.

Recent advances in atomically thin two-dimensional materials have led to various promising technologies such as nanoelectronics, sensing, energy storage, and optoelectronics applications. Graphene with sp2-bonded carbon atoms densely packed in a honeycomb crystal lattice has attracted tremendous interest with excellent electrical, optical, mechanical, and chemical properties. In this work, graphene’s mechanical properties, chemical properties, and piezoelectric properties are explored as graphene is implemented in the automotive electrical distribution system. Graphene is useful in friction reduction, corrosion protection, and piezoelectric energy harvesting cell improvement. Besides graphene, transition metal dichalcogenides (TMDs), which are the metal atoms sandwiched between two chalcogen atoms, have also attracted much attention. Unlike graphene, many TMDs are semiconductors in nature and possess enormous potential to be used as a potential channel material in ultra-scaled field-effect transistors (FETs). In this work, chemical doping strategies are explored for the tunnel FETs applications using different metal phthalocyanines and polyethyleneimines as dopants. TMDs FETs can also be used as a selective NO₂ gas sensor with a polydimethylsiloxane filter and a highly sensitive photo-interfacial gated photodetector application.

This thesis describes the fabrication and characterization of two-dimensional transition dichalcogenides (2D TMDs) nanolayers for various applications in electronic and opto-electronic devices applications. In Chapter 1, crystal and optical structure of TMDs materials are introduced. Many TMDs materials reveal three structure polytypes (1T, 2H, and 3R). The important electronic properties are determined by the crystal structure of TMDs; thus, the information of crystal structure is explained. In addition, the detailed information of photon vibration and optical band gap structure from single-layer to bulk TMDs materials are introduced in this chapter. In Chapter 2, detailed information of physical properties and synthesis techniques for molybdenum disulfide (MoS2), tungsten disulfide (WS2), and molybdenum ditelluride (MoTe2) nanolayers are explained. The three representative crystal structures are trigonal prismatic (hexagonal, H), octahedral (tetragonal, T), and distorted structure (Tʹ). At room temperature, the stable structure of MoS2 and WS2 is semiconducting 2H phase, and MoTe2 can reveal both 2H (semiconducting phase) and 1Tʹ (semi-metallic phase) phases determined by the existence of strains. In addition, the pros and cons of the synthesis techniques for nanolayers are discussed. In Chapter 3, the topic of synthesized large-scale MoS2, WS2, and MoTe2 films is considered. For MoS2 and WS2 films, the layer thickness is modulated from single-layer to multi-layers. The few-layer MoTe2 film is synthesized with two different phases (2H or 1Tʹ). The all TMDs films are fabricated using two-step chemical vapor deposition (CVD) method. The analyses of atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy confirm that the synthesis of high crystalline MoS2, WS2, and MoTe2 films are successful. The electronic properties of both MoS2 and WS2 exhibit a p-type conduction with relatively high field effect mobility and current on/off ratio. In Chapter 4, vertically-stacked few-layer MoS2/WS2 heterostructures on SiO2/Si and flexible polyethylene terephthalate (PET) substrates is presented. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) show the structural integrity of two distinct 2D TMD layers with atomically sharp van der Waals (vdW) heterointerfaces. Electrical transport measurements of the MoS2/WS2 heterostructure reveal diode-like behavior with current on/off ratio of ~ 104. In Chapter 5, optically uniform and scalable single-layer Mo1-xWxS2 alloys are synthesized by a two-step CVD method followed by a laser thinning. Post laser treatment is presented for etching of few-layer Mo1-xWxS2 alloys down to single-layer alloys. The optical band gap is controlled from 1.871 to 1.971 eV with the variation in the tungsten (W) content, x = 0 to 1. PL and Raman mapping analyses confirm that the laser-thinning of the Mo1-xWxS2 alloys is a self-limiting process caused via heat dissipation to SiO2/Si substrate, resulting in fabrication of spatially uniform single-layer Mo1-xWxS2 alloy films.

No description available.