• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 357
  • 178
  • 92
  • 46
  • 43
  • 24
  • 17
  • 10
  • 6
  • 5
  • 4
  • 3
  • 3
  • 3
  • 3
  • Tagged with
  • 952
  • 139
  • 117
  • 96
  • 62
  • 61
  • 61
  • 58
  • 57
  • 53
  • 51
  • 48
  • 47
  • 47
  • 44
  • 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.
411

Dopravní projekty mikroregionu Orlickoústecka / Transport projects in Orlickoústecko region

Kaplan, Ondřej January 2009 (has links)
This master thesis describes transport projects in Orlikoústecko region. At the first part it concerns on the general history of transport and actual trends in road, railway and cycle transport in European Union and Czech republic. In next part it characterizes Pardubice region and describes chosen transport projects in Orlickoustecko region. It focuses especially on legislation, financing methods and complete description of each project.
412

Analýza cyklistické dopravy v mikroregionu Lipensko / Analysis of cycling in Lipno region

Jelínková, Petra January 2013 (has links)
The aim of diploma thesis is to analyze actual condition and development of cycling transport in the Lipno region. There is a description of cycling and the explanation of basic terms and types of cycling transport in the first part of diploma thesis. Next part is focused on National strategy of cycling in the Czech Republic and other projects of cycling. There is the description of the Lipno region, current conditions of cycling, density, quality and connectivity to other regions and other services in the following text. SWOT analysis defines strengths, weaknesses, opportunities and threats of the whole Lipno region in context with cycling. In the text, there are mentioned actual projects, ideas for progress, opportunities and reduction of threats. The SWOT analysis shows, that the Lipno region is a popular location for cyclists with many strong aspects and with great potential for development.
413

Preference šikmosti / Skewness Preference

Kvapil, Mikuláš January 2013 (has links)
The diploma thesis is concerned with analysis of behavior of bettors on horse races. The aim is to test the hypothesis that bettors prefer skewness and they are risk averse. In the thesis is used the method of empirical data collection of horse racing in the Czech Republic and their subsequent testing using a regression model. The testing of the presented model did not confirm the hypothesis of skewness preference in the case of betting on horse races in the Czech Republic.
414

Nutzung von Gleismessdaten für die Überwachung von Verformungen an Erdkörpern von Schienenfahrwegen

Kipper, René 12 October 2016 (has links) (PDF)
In der Dissertation ist eine Methodik beschrieben, die es ermöglicht, mittel- und langwellige Gradientenänderungen auf Grundlage der Rohdaten des bei der DB AG zur Gleisgeometrieprüfung gemäß RIL 821.2001 eingesetzten Messfahrzeuges RAILab zu detektieren. Weil mittel- und langwellige Längshöhenfehler eines Gleises die Verschlechterung der Tragfähigkeitseigenschaften von Bettung/Unterbau/Untergrund anzeigen, können mit der Methodik Zustandsänderungen von Erdkörpern kontrolliert werden. Dabei ist eine geodätische Aufnahme von Verformungen, wie sie derzeit beim Monitoring von Erdkörpern im Allgemeinen angewendet wird, nicht erforderlich. Die Methodik wurde an einem Streckenabschnitt, in welchem infolge von verformungsempfindlichen Böden im Untergrund erhebliche Gleisverformungen eingetreten waren, erprobt und durch Vergleich mit geodätischen Messdaten verifiziert. Weiterhin wurde ein Vorschlag zur Festlegung von Aufmerksamkeitswerten für mittel- und langwellige Höhenänderungen unterbreitet. Die vorgeschlagenen Aufmerksamkeitswerte wurden wirkungsbezogen auf Grundlage der Vertikalbeschleunigung abgeleitet, die ein Feder-Dämpfer-Modell bei der Überfahrt über einen aus den RAILab-Gleismessdaten rekonstruierten Höhenverlauf eines Gleises erfährt. Über zwei Beispiele der Anwendung der Methodik bei der Sonderinspektion von Erdkörpern wird berichtet.
415

Index Tracking com controle do número de ativos e aplicação com uso de algoritmos genéticos

Sant'anna, Leonardo Riegel January 2014 (has links)
Nesta dissertação, discute-se o problema de otimização de carteiras de investimento para estratégia passiva de Index Tracking. Os objetivos principais são (i) apresentar um modelo de otimização de Index Tracking e (ii) a solucionar esse modelo com uso do método heurístico de Algoritmos Genéticos (AG) para formação de carteiras com número reduzido de ativos. O índice de referência utilizado é o Ibovespa, para o período de Janeiro/2009 a Julho/2012, com um total de 890 observações diárias de preços. A partir de uma amostra de 67 ativos, são formadas carteiras sem limite de ativos e limitadas a 40, 30, 20, 10 e 05 ativos; os intervalos de rebalanceamento das carteiras são 20, 40 e 60 períodos (dias úteis), ou seja, rebalanceamento mensal, bimestral e trimestral. É verificado que, para essa amostra, não é possível formar carteiras de 20 ou menos ativos via otimização direta com o solver Cplex com menos de 1 hora de processamento e gap abaixo de 5%. Com uso da heurística de Algoritmos Genéticos, são formadas carteiras de 10 e 05 ativos com tempo de processamento em torno de 5 minutos; nesse caso, o gap médio fica abaixo de 10% para ambos os tipos de carteira. E, com tempo de processamento do AG um pouco maior, em torno de 8 minutos, o algoritmo fornece soluções para carteiras de 10 e 05 ativos com gap médio abaixo de 5%. / In this master’s thesis it is discussed the portfolio optimization problem using the passive investment strategy of Index Tracking. The main goals are (i) to present an optimization model for the Index Tracking problem and (ii) to solve this model using the heuristic approach of Genetic Algorithms (GA) to create portfolios with reduced amount of stocks. The benchmark used is the Ibovespa Index (main reference for the Brazilian Stock Market), during the period from January/2009 to July/2012 (using a total of 890 daily stock prices). The sample contains 67 assets, and the model is used to build portfolios without limit in the amount of assets and portfolios limited to 40, 30, 20, 10 and 05 assets; the ranges of time to rebalance the portfolios are 20, 40, and 60 trading days, which means to rebalance monthly, bimonthly and quarterly. The results show that, considering this sample, it is not possible to build portfolios with 20 stocks (or less than 20) through direct optimization using the solver Cplex with computational processing time less than 1 hour and results with gap below 5%. On the other hand, using the Genetic Algorithms heuristic approach, portfolios limited to 10 and 05 stocks are built with computational time close to 5 minutes; for both types of portfolio, the solutions provided by the GA have average gap below 10%. Also, with a computational time slightly bigger, close to 8 minutes, the algorithm provides solutions with average gap below 5% for portfolios limited to 10 and 05 stocks.
416

Swift heavy ion irradiation of polyester and polyolefin polymeric film for gas separation application

Adeniyi, Olushola Rotimi January 2015 (has links)
Philosophiae Doctor - PhD / The combination of ion track technology and chemical etching as a tool to enhance polymer gas properties such as permeability and selectivity is regarded as an avenue to establish technology commercialization and enhance applicability. Traditionally, permeability and selectivity of polymers have been major challenges especially for gas applications. However, it is important to understand the intrinsic polymer properties in order to be able to predict or identify their possible ion-polymer interactions thus facilitate the reorientation of existing polymer structural configurations. This in turn can enhance the gas permeability and selectivity properties of the polymers. Therefore, the choice of polymer is an important prerequisite. Polyethylene terephthalate (PET) belongs to the polyester group of polymers and has been extensively studied within the context of post-synthesis modification techniques using swift heavy ion irradiation and chemical treatment which is generally referred to as ‘track-etching’. The use of track-etched polymers in the form of symmetrical membranes structures to investigate gas permeability and selectivity properties has proved successful. However, the previous studies on track-etched polymers films have been mainly focused on the preparation of symmetrical membrane structure, especially in the case of polyesters such as PET polymer films. Also, polyolefins such as polymethyl pentene (PMP) have not been investigated using swift heavy ions and chemical etching procedures. In addition, the use of ‘shielded’ material on PET and PMP polymer films prior to swift heavy ion irradiation and chemical etching to prepare asymmetrical membrane structure have not been investigated. The gas permeability and selectivity of the asymmetrical membrane prepared from swift heavy ion irradiated etched 'shielded' PET and PMP polymer films have not been determined. These highlighted limitations will be addressed in this study. The overall objective of this study was to prepare asymmetric polymeric membranes with porous surface on dense layer from two classes of polymers; (PET and PMP) in order to improve their gas permeability and selectivity properties. The research approach in this study was to use a simple and novel method to prepare an asymmetric PET and PMP polymer membrane with porous surface and dense layer by mechanical attachment of ‘shielded’ material on the polymer film before swift heavy ion irradiation. This irradiation approach allowed for the control of swift heavy ion penetration depth into the PET and PMP polymer film during irradiation. The procedure used in this study is briefly described. Commercial PET and PMP polymer films were mechanically ‘shielded’ with aluminium and PET foils respectively. The ‘shielded’ PET polymer films were then irradiated with swift heavy ions of Xe source while ‘shielded’ PMP polymer films were irradiated with swift heavy ions Kr. The ion energy and fluence of Xe ions was 1.3 MeV and 106 respectively while the Kr ion energy was 3.57 MeV and ion fluence of 109. After swift heavy ion irradiation of ‘shielded’ PET and PMP polymer films, the attached ‘shielded’ materials were removed from PET and PMP polymer film and the irradiated PET and PMP polymer films were chemically etched in sodium hydroxide (NaOH) and acidified chromium trioxide (H2SO4 + CrO3) respectively. The chemical etching conditions of swift heavy ion irradiated ‘shielded’ PET was performed with 1 M NaOH at 80 ˚C under various etching times of 3, 6, 9 and 12 minutes. As for the swift heavy ion irradiated ‘shielded’ PMP polymer film, the chemical etching was performed with 7 M H2SO4 + 3 M CrO3 solution, etching temperature was varied between 40 ˚C and 80 ˚C while the etching time was between 40 minutes to 150 minutes. The SEM (surface and cross-section micrograph) morphology results of the swift heavy ion irradiated ‘shielded’ etched PET and PMP films showed that asymmetric membranes with a single-sided porous surface and dense layer was prepared and remained unchanged even after 12 minutes of etching with 1 M NaOH solution as in the case of PET and 2 hours 30 minutes of etching with 7 M H2SO4 + 3 M CrO3 as observed for PMP polymer film. Also, the swift heavy ion irradiated ‘shielded’ etched PET polymer film showed the presence of pores on the polymer film surface within 3 minutes of etching. After 12 minutes chemical etching with 1 M NaOH solution, the dense layer of swift heavy ion irradiated ‘shielded’ etched PET polymer film experienced significant reduction in thickness of about 40 % of the original thickness of as-received PET polymer film. The surface morphology of swift heavy ion irradiated ‘shielded’ etched PET polymer film by SEM analysis revealed finely distributed pores with spherical shapes for the swift heavy ion irradiated ‘shielded’ etched PET polymer film within 6 minutes of etching with 1 M NaOH solution. Also, after 9 minutes and 12 minutes of etching with 1 M NaOH solution of the swift heavy ion irradiated ‘shielded’ etched PET polymer film, the pore walls experienced complete collapse with intense surface roughness. Interestingly, the 12 minutes etched swift heavy ion ‘shielded’ irradiated PET did not lose its asymmetrical membrane structure despite the collapse of the pore walls. In the case of swift heavy ion irradiated ‘shielded’ etched PMP polymer film, SEM morphology analysis showed that the pores retained their shape with the presence of defined pores without intense surface roughness even after extended etching with 7 M H2SO4 + 3 M CrO3 for 2 hours 30 minutes. Also, the pores of swift heavy ion irradiated ‘shielded’ etched PMP polymer films were observed to be mono dispersed and not agglomerated or overlapped. The SEM cross-section morphology of the swift heavy ion irradiated ‘shielded’ etched PMP polymer film showed radially oriented pores with increased pore diameters in the PMP polymer film which indicated that etching was radial instead of lateral, and no through pores were observed showing that the dense asymmetrical structure was retained. The SEM results revealed that the pore morphology i.e. size and shape could be accurately controlled during chemical etching of swift heavy ion ‘shielded’ irradiated PET and PMP polymer films. The XRD results of swift heavy ion irradiated ‘shielded’ etched PET revealed a single diffraction peak for various times of chemical etching in 1 M NaOH solution at 3, 6, 9 and 12 minutes. The diffraction peak of swift heavy ion irradiated ‘shielded’ etched PET was observed to reduce in intensity and marginally shifted to lower angles from 25.95˚ 2 theta to 25.89˚ 2 theta and also became broad in shape. It was considered that the continuous broadening of diffraction peaks due to an increase in etching times could be attributed to disorderliness of the ordered region within the polymer matrix and thus decreases in crystallinity of the swift heavy ion irradiated ‘shielded’ etched PET polymer film. The XRD analysis of swift heavy ion irradiated ‘shielded’ etched PMP polymer films indicated the presence of the diffraction peak at 9.75˚ 2 theta with decrease in intensity while the diffraction peaks located at 13.34˚, 16.42˚, 18.54˚ and 21.46˚ 2 theta disappeared after chemical etching in acidified chromium trioxide (H2SO4 + CrO3) after 2 hours 30 minutes. The TGA thermal profile analysis of swift heavy ion irradiated ‘shielded’ etched PET did not show the evolution of volatile species or moisture at lower temperatures even after 12 minutes of etching in 1 M NaOH solution in comparison with commercial PET polymer film. Also, it was observed that the swift heavy ion irradiated layered’ etched PET polymer film started to undergo degradation at a higher temperature than untreated PET which resulted in an approximate increase of 50 ˚C in comparison with the commercial PET polymer film. The TGA results of swift heavy ion irradiated ‘shielded’ etched PMP polymer film revealed an improvement of about 50 ˚C in thermal stability before thermal degradation even after etching in acidified chromium trioxide for 2 hours 30 minutes at 80 ˚C. Spectroscopy (IR) analysis of the swift heavy ion irradiated ‘shielded’ etched PET and PMP polymer films showed the presence of characteristic functional groups associated with either PET or PMP structures. The variations of irradiation and chemical etching conditions revealed that the swift heavy ion ‘shielded’ irradiated etched PET polymer film experienced continuous degradation of available functional groups as a function of etching time and also with complete disappearance of some functional groups such as 1105 cm-1 and 1129 cm-1 compared with the as-received PET polymer film which are both associated with the para-substituted position of benzene rings. In the case of swift heavy ion irradiated ‘shielded’ etched PMP polymer film, spectroscopic (IR) analysis showed significant variations in the susceptibility of associated functional groups within the PMP polymer film with selective attack and emergence of some specific functional groups such as at 1478 cm-1, 1810 cm-1 and 2115 cm-1 which were assigned to methylene, CH3 (asymmetry deformation), CH3 and CH2 respectively Also, the IR results for swift heavy ion irradiated ‘shielded’ etched PMP polymer showed that unsaturated olefinic groups were the dominant functional groups that were being attacked by during etching with acidified chromium trioxide (H2SO4+CrO3) which is an aggressive chemical etchant. The gas permeability analysis of swift heavy ion irradiated ‘shielded’ etched PET and PMP polymer films showed that the gas permeability was improved in comparison with the as-received PET and as-received PMP polymer films. The gas permeability of swift heavy ion irradiated ‘shielded’ etched PET increased as a function of etching time and was found to be highest after 12 minutes of chemical etching in 1 M NaOH at 80 ˚C. In the case of swift heavy ion irradiated ‘shielded’ etched PMP, the gas permeability was observed to show the highest gas permeability after 2 hours 30 minutes of etching in H2SO4 + CrO3 solution. The gas permeability analysis for swift heavy ion irradiated ‘shielded’ PET and PMP polymer films was tested for He, CO2 and CH4 and the permeability results showed that helium was most permeable compared with CO2 and CH4 gases. In comparison, the selectivity analysis was performed for He/CO2 and CH4/He and the results showed that the selectivity decreased with increasing in etching time as expected. This study identified some important findings. Firstly, it was observed that the use of ‘shielded’ material on PET and PMP polymer films prior to swift heavy ion irradiation proved successful in the creation of asymmetrical polymer membrane structure. Also, it was also observed that the chemical etching of the ‘shielded’ swift heavy ion irradiated PET and PMP polymer films resulted in the presence of pores on the swift heavy ion irradiated side while the unirradiated sides of the PET and PMP polymer films were unaffected during chemical etching hence the pore depth could be controlled. In addition, the etching experiment showed that the pores geometry can be controlled as well as the gas permeability and selectivity properties of swift heavy ion ‘shielded’ irradiated etched PET and PMP polymer films. The process of polymer bulk and surface properties modification using ion-track technology i.e. swift heavy ion irradiation and subsequent chemical treatment of the irradiated polymer serves to reveal characteristic pore profiles unique to the prevailing ion-polymer interaction and ultimately results in alteration of the polymer characteristics.
417

Design and testing of a NITPC X-ray polarimeter with applications for the measurement of SGR burst polarization

Prieskorn, Zachary Ryan 01 May 2011 (has links)
Soft gamma repeaters (SGRs) are neutron stars with ultra-strong magnetic fields, on the order of 1014 G. As the source of the strongest magnetic fields in the universe, they are ideal objects to study the behavior of matter and light in this extreme environment. SGRs emit recurrent short duration, 0.1s, bursts of soft gamma-rays/hard X-rays that are expected to be highly polarized in the 2-10 keV energy range. By measuring the polarization of these bursts we can learn about the strength and configuration of the magnetic fields, the geometry of the emission region and the mass/radius relationship of the neutron star. Using the archival RXTE/PCA data we analyzed ~3 Ms of observations for SGR1806-20 and SGR1900+14. Over 5000 bursts were detected from the sources and each distribution of burst fluence was found to be well fit by a power law with an exponent of 1.60±0.02 for SGR1806-20 and 1.64±0.03 for SGR1900+14. The power law form holds over 4 magnitudes of fluence and the exponents were found to be independent of the level of burst activity. The exponent values suggest that SGR bursts are associated with a self-organized critical system, similar to earthquakes. To measure the polarization of SGR bursts a wide-field-of-view, large area detector is needed. To accomplish this we designed and tested a negative ion time projection chamber (NITPC) X-ray polarimeter which uses nitromethane (CH3NO¬2) as an electronegative gas additive. Utilizing a double gas electron multiplier (GEM) NITPC with CO2+CH3NO2 as a gas mixture we successfully measured gas gains, imaged photoelectron tracks and measured distributions of their length, measured drift velocity of negative ions in various electric fields, and measured modulation from polarized and unpolarized X-ray sources between 3 and 8 keV. Based on the lab instrument results and our SGR burst fluence analysis we propose an instrument appropriately sized for a NASA Small Mission Explorer Mission (SMEX) that would be capable of measuring the polarization of hundreds of bursts from an SGR in a state of high burst activity.
418

Changes in Muscle Architecture, Explosive Ability, and Track and Field Throwing Performance Throughout a Competitive Season and Following a Taper

Bazyler, Caleb D., Mizuguchi, Satoshi, Harrison, Alex P., Sato, Kimitake, Kavanaugh, Ashley A., DeWeese, Brad H., Stone, Michael H. 01 January 2016 (has links)
The purpose of this study was to examine the effects of an overreach and taper on measures of muscle architecture, jumping, and throwing performance in Division I collegiate throwers preparing for conference championships. Six collegiate track and field throwers (3 hammer, 2 discus, 1 javelin) trained for 12 weeks using a block-periodization model culminating with a 1-week overreach followed by a 3-week taper (ORT). Session rating of perceived exertion training load (RPETL) and strength training volume-load times bar displacement (VLd) were recorded weekly. Athletes were tested pre-ORT and post-ORT on measures of vastus lateralis architecture, unloaded and loaded squat and countermovement jump performance, underhand and overhead throwing performance, and competition throwing performance. There was a statistical reduction in weight training VLd/session (d = 1.21, p ≤ 0.05) and RPETL/session (d = 0.9, p ≤ 0.05) between the in-season and ORT training phases. Five of 6 athletes improved overhead throw and competition throwing performance after the ORT (d = 0.50, p ≤ 0.05). Vastus lateralis muscle thickness statistically increased after the in-season training phase (d = 0.28, p ≤ 0.05) but did not change after the ORT. Unloaded countermovement jump peak force and relative peak power improved significantly after the ORT (d = 0.59, p ≤ 0.05, d = 0.31, p ≤ 0.05, respectively). These findings demonstrate that an overreaching week followed by a 3-week taper is an effective means of improving explosive ability and throwing performance in collegiate track and field throwers despite the absence of detectable changes in muscle architecture.
419

The Sport Education Model: A Track and Field Unit Application

O’Neil, Kason M., Krause, Jennifer M. 26 October 2016 (has links)
Track and field is a traditional instructional unit often taught in secondary physical education settings due to its history, variety of events, and potential for student interest. This article provides an approach to teaching this unit using the sport education model (SEM) of instruction, which has traditionally been presented as a model for team and dual sports. The application of the SEM to this individual sport provides teachers with an opportunity to provide their students with an authentic, engaging and festive environment in which to learn a sport that has been around for centuries.
420

Comparison Of Block Versus Dup Training Among Division-1 (D-1) Collegiate Track And Field Athletes: An Exploratory Study

Haff, G. Gregory, Painter, Keith B., Ramsey, Michael W., Triplett, N. Travis, McBride, Jeff, Stuart, Charles, Sands, William A., Stone, Margaret E., Stone, Michael H. 01 June 2010 (has links)
No description available.

Page generated in 0.0454 seconds