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Stellar bars are the most important internal drivers of the evolution of disk galaxies because they efficiently redistribute mass and angular momentum in the baryonic and dark matter components of galaxies. Mounting evidence suggests that mechanisms other than major mergers of galaxies, such as minor mergers, gas accretion, and bar-driven secular processes, play an important role in galaxy evolution since a redshift z~2. In order to characterize the evolution of barred disks, this thesis presents one of the most comprehensive studies of barred galaxies in the field at low redshifts, and also as a function of environment across galaxy clusters of different densities. This work improves significantly on earlier studies by using quantitative methods to characterize bars, analyzing high-quality data from some of the largest disk galaxy samples to date, and using results across a range of Hubble types and environments to test different theoretical models for the evolution of disk galaxies. Our main results are summarized below: (1) Studies done as a part of this thesis have quantitatively shown for the first time that the optical bar fraction in z~ 0 field galaxies is a sensitive and non-monotonic function of host galaxy properties, such as the luminosity, stellar mass, and bulge-to-disk ratio. We find that at z~0, the bar fraction increases significantly from galaxies of intermediate mass and Hubble types (Sb) toward those of lower mass and late Hubble types (Sd-Sm). The behavior from intermediate to early Hubble types is more uncertain. These results, which have been subsequently confirmed by independent studies, set constraints for theoretical models and in particular underline the importance for bar growth of angular momentum exchange between the bar, disk, bulge, and dark matter halo, as well as the possible triggering of bars by external satellites and interactions with the dark matter. Furthermore, our results at optical and near-infrared wavelengths on the fraction and sizes of bars at z~0 provide the zero-redshift anchor point for studies of bars at higher redshifts with current and future space missions (e.g., ACS, WFC3, JWST), and allow us to assess the systematic effects in such studies. (2) Although cluster environments are unique laboratories for investigating the evolution of barred disks, only sparse and disparate results have emerged from early studies. In this thesis, we study barred disks in clusters using high-quality data from the Hubble Space Telescope Advanced Camera for Surveys for the moderately-rich cluster Abell 901/902 (characterized by a galaxy number density n~1,000 gal Mpc⁻³) at z~0.165, and of the Coma cluster at z~0.02, the densest cluster (n~10,000 gal Mpc⁻³) in the nearby Universe. We find that the optical bar fraction for bright, early Hubble type disk galaxies does not show a statistically significant variation (within the error bars of ± 10 to 12%) as a function of galaxy environment within the Abell 901/902 cluster, as well as between the Abell 901/902 cluster and the field. Similarly, the optical bar fraction for bright S0 galaxies shows no statistically significant variation (within the error bars of ±10%) between the Virgo, Abell 901/902, and core of the Coma clusters, even though these environments span over an order of magnitude in galaxy number density (n~300 to 10,000 gal Mpc⁻³). We suggest that the S0 bar fraction is not greatly enhanced in denser environments, such as the core of Coma, due to the predominance of high speed encounters over slow ones, the tidal heating of S0 disks, and the low gas content of S0s in rich clusters. / text

Gedvilas R. Determination of fatigue curves parameters and lifetime at low cycle straining for stainless steels: Master thesis of mechanical engineer / research advisor associate professor dr. R. Šniuolis; Šiauliai University, Technological Faculty, Mechanical Engineering Department. – Šiauliai, 2006. - 58 p. Cycle fracture parameters of structural materials at low cycle straining are understood as lifetime or low cycle fatigue curves that are constructed in coordinates or according to the number of loading cycles N. The lifetime of material at low cycle straining in elastic plastic area is expressed by Coffin’s equation. Parameter of Coffin’s equation C markedly differs from the experimental, therefore high errors occur in evaluating lifetime of the material. It is noticed in many works that parameter proposed by Coffin is close to experimental. Parameter m=0,5, proposed by Coffin, is determined according the low cycle fatigue curves in coordinates for structural materials. Parameters of low cycle fatigue curves mp, Cp for stainless steels according to Coffin were specified and parameters me, Ce according to elastic strain at low cycle straining at room and elevated temperature were determined. Analytic dependences of low cycle fatigue curve parameters on modified plasticity (su/sy)y were proposed, lifetime for stainless steels at room and elevated temperature was calculated in this work. Statistical analysis of results of low cycle fatigue fracture parameters and... [to full text]

Pilotuojamiems orlaiviams keliami vienodi skrydžio saugumo reikalavimai nepriklausomai nuo jų dydžio ir skrydžio greičio. Sparčiai vystantis mažų greičių aviacijai aktualu mažinti tokių orlaivių projektavimo, gamybos ir bandymų išlaidas, išlaikant tą patį skrydžio saugumo lygį. Kadangi orlaivio skrydžio savybes daugiausia nulemia sparno aerodinaminės savybės, ypač aktualu pigiai ir greitai kurti sparnus mažų greičių orlaiviui. Tam reikalingas patikimas, sąlyginai paprastas sparno projektavimo metodas, kurio tikslumas būtų pagrindžiamas sparno profilių matavimo rezultatais aerodinaminiame vamzdyje. Mažų grei��ių orlaivio projektavimo procese tiesioginių sparno matavimų rezultatų aerodinaminiame vamzdyje panaudojimas yra apribotas, nes dėl didelės sparnų įvairovės kiekvieno sparno atveju būtina atlikti unikalius kompleksinius matavimus. Čia išvardintos aplinkybės sudarė sąlygas pradėti tyrimus, skirtus pritaikyti matavimų inžinerijoje naudojamus matavimų metodus matematiškai modeliuojant orlaivio sparno aerodinamines jėgas. / Dissertation presents a method of aircraft wing modeling. The method combines wing modeling by means of flat elements and horseshoe-shaped vortices with an algorithm what takes into consideration non-linear characteristics of wing airfoils. This algorithm provides for a possibility of using the results of both numerical and measurement results in calculation of aerodynamic forces of a wing. A methodology is included to evaluate convergence of the calculation process and to establish conditions of reliability of the results. Calculation results are presented for lift and drag force coefficients of 24 different wings. These results are compared with the results obtained by other authors and measurement results in wind tunnel. Dissertation consists of Introduction, 4 chapters, Conclusions, List of Literature, List of Publications and Addendum. The total scope of the dissertation - 90 pages, 96 pictures, 1 table and 1 addendum.

The aim of this research is to develop and examine a method for analysis of aerodynamic parameters of the aircraft wing based on the airfoil measurement results and mathematical simulation using non-linear characteristics of airfoils constituting the wing. / Pilotuojamiems orlaiviams keliami vienodi skrydžio saugumo reikalavimai nepriklausomai nuo jų dydžio ir skrydžio greičio. Sparčiai vystantis mažų greičių aviacijai aktualu mažinti tokių orlaivių projektavimo, gamybos ir bandymų išlaidas išlaikant tą patį skrydžio saugumo lygį. Kadangi orlaivio skrydžio savybes daugiausia nulemia sparno aerodinaminės savybės, ypač aktualu pigiai ir greitai kurti sparnus mažų greičių orlaiviui. Tam reikalingas patikimas, sąlyginai paprastas sparno projektavimo metodas, kurio tikslumas būtų pagrindžiamas sparno profilių matavimo rezultatais aerodinaminiame vamzdyje. Mažų greičių orlaivio projektavimo procese tiesioginių sparno matavimų rezultatų aerodinaminiame vamzdyje panaudojimas ribotas, nes dėl didelės sparnų įvairovės kiekvieno sparno atveju būtina atlikti unikalius kompleksinius matavimus. Čia išvardintos aplinkybės sudarė sąlygas pradėti tyrimus, skirtus pritaikyti matavimų inžinerijoje naudojamus matavimų metodus matematiškai modeliuojant orlaivio sparno aerodinamines jėgas.

No description available.

The development of an experimental synchrophasors network and application of synchrophasors for real-time transmission line parameter monitoring are presented in this thesis. In the laboratory setup, a power system is simulated in a RTDS real-time digital simulator, and the simulated voltages and currents are input to hardware phasor measurement units (PMUs) through the analog outputs of the simulator. Time synchronizing signals for the PMU devices are supplied from a common GPS clock. The real time data collected from PMUs are sent to a phasor data concentrator (PDC) through Ethernet using the TCP/IP protocol. A real-time transmission line parameter monitoring application program that uses the synchrophasor data provided by the PDC is implemented and validated. The experimental synchrophasor network developed in this thesis is expected to be used in research on synchrophasor applications as well as in graduate and undergraduate teaching.

Accurate predictions of the annual energy yield from wave energy converters are essential to the development of the wave industry. The current method based on power matrices uses only a small part of the data available from sea state estimations and it is consequently prone to inaccuracies. The research presented in this work investigates the issue of energy yield prediction and questions the power matrix method. This is accomplished by quantifying the influence of several directional sea states parameters on the performances of wave energy converters. The approach taken was to test several wave energy converters in the Edinburgh Curved tank with a large set of sea states. The selected wave energy converters are a fix OWC, a set of two OWCs acting as a weak directional device and the desalination duck model. Uni-modal and bi-modal sea states were used. For the uni-modal sea states, parameters related to the wave system shape were considered. For the bi-modal sea states, the relative position of the wave system peaks was investigated and the uni-modality index was introduced to quantify the degree to which sea states could be considered bi-modal. For all sea states, the significant wave height was kept constant. The experimental work required good spectral estimates. The MLM and MMLM were adapted to deterministic waves to improve their stability and accuracy. A routine to isolate wave systems was also developed in order to estimate parameters with respect to each wave systems. For uni-modal spectra, parametric models of the observed performances of the devices could be devised. The frequency spreading and its interaction with the energy period proved to be as important as the energy period itself, which suggests that the frequency spreading should be used for energy production prediction. For bi-modal spectra, evidence of the duck sensitivity to directionality was found while the OWCs were not affected.

The purpose of this study is to gain an understanding of an agile way of working at an IT organization in a context of a surrounding and otherwise manufacturing industrial organization, when it comes to software development projects. Thus the study aims to answer whether to what extent agile methodologies are manifested at an IT organization, what is demanded of the IT organization in order to follow agile values and principles, and whether it is possible to develop software according to agile values and principles in an IT organization in the above mentioned context. The study has been carried out as a case study at a case company where an IT organization, within a larger organization, was investigated. The study consisted of a pre-study, a literature review and an empirical study followed by analysis of the gathered data. The pre-study aimed to give the authors relevant insights into the case company as well as to the available academic literature. During the pre-study eight initial interviews were conducted, at the case company, among project managers, methodology experts and group managers. The pre-study was used in order to define and refine the scope of this study. From this the authors investigated literature relevant to their findings in the pre-study and to the scope. The literature review was used to formulate the theoretical framework of this study. The theoretical framework is mainly based on academic journals complemented by various publications and books. The empirical study was conducted by investigations of four software development projects, at the case company. Here nine interviews were conducted among the project managers, customers of the projects, and with managers of the IT organization. The empirical study have then been analyzed using the theoretical framework in order to form the conclusions of this report. The theory presents benefits, drawbacks and demands when it comes to agile methodologies in software development. The importance of support from the IT department, and from the customer, to a project is especially highlighted in literature. The empirical study presents findings of both agile and non-agile projects operating in the above mentioned organization. Several advantages and drawbacks have been identified regarding agile projects in the organization. Also hinders for an agile way of working, in the form or organizational demands, extensive processes, limited support and customer commitment have also been seen. While benefits regarding agile projects can be identified, in the context of an IT organization functioning within a larger industrial manufacturing organization, several drawbacks and hinders are also prominent. The analysis show agile values and principles manifested in the IT organization agile practices are harder to identify. It is also seen that an organization should strive for agility on several organizational levels in order to support an agile way of working. Regarding the surrounding organization an agile way of working is seen to be possible. Furthermore several benefits are identified, for a customer, when it comes to agile projects. However agile methodologies are also seen to be demanding when it comes to time, commitment and external support. Putting this in the context of an IT organization developing business support systems for a surrounding organization the benefits, while still prominent, can be further discussed.

An empirically-based classification of lower Paleozoic carbonate-bearing rocks was created for field-based geotechnical applications. Geotechnical parameters were subsequently correlated to that classification. Seven hundred seventy-seven samples were used as the basis for the classification. Thirteen categories based on visual and tactile properties and a hydrochloric acid test were created. Samples were from central, north-central, and south-central Kentucky and represented the majority of Ordovician exposures in the state, and some Mississippian exposures. Few Silurian and Devonian units were included in the sample set. Geotechnical parameters, including density as well as elastic constants (shear and compression wave velocities, Poisson’s ratio, Young’s modulus, and shear modulus), were calculated for 113 representative samples from the classification. Compression strength testing was completed on 29 samples and the slake durability index was calculated for 18 samples. Testing values were correlated to the classification system in an attempt to use the classification as a predictive and comparative tool for geotechnical applications. Despite samples being heterogeneous and isotropic, each of the 13 categories behaved differently and predictably, with the sharpest contrast in siliciclastic and carbonate rocks.