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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Quantification of acoustic emission from soils for predicting landslide failure

Spriggs, M. P. January 2005 (has links)
Acoustic emission (AE) is a natural phenomenon that occurs when a solid is subjected to stress. These emissions are produced by all materials during pre failure. In soil, AE results from the release of energy as particles undergo small strains. If these emissions can be detected, then it becomes possible to develop an early warning system to predict slope failure. International research has shown that AE can be used to detect ground deformations earlier than traditional techniques, and thus it has a role to play in reducing risk to humans, property and in mitigating such risks. This thesis researches the design of a system to quantify the AE and calculate the distance to the deformation zone, and hence information on the mechanism of movement. The quantification of AE is derived from measuring the AE event rate, the output of which takes the form of a displacement rate. This is accurate to an order of magnitude, in line with current standards for classifying slope movements The system also demonstrates great sensitivity to changes within the displacement rate by an order of magnitude, making the technique suitable to remediation monitoring. Knowledge of the position of the shear surface is critical to the planning of cost effective stabllisation measures. This thesis details the development of a single sensor source location technique used to obtain the depth of a developing or existing shear surface within a slope. The active waveguide is used to reduce attenuation by taking advantage of the relatively low attenuation of metals such as steel. A method of source location based on the analysis of Lamb wave mode arrival times at a smgle sensor is summansed. An automatic approach to source location is demonstrated to locate a regular AE source to within one metre. Overall consideration is also given to field trials and towards the production of monitoring protocols for data analysis, and the implementation of necessary emergency/remediation plans.
32

PHOTO-REVERBERATION MAPPING OF A PROTOPLANETARY ACCRETION DISK AROUND A T TAURI STAR

Meng, Huan Y. A., Plavchan, Peter, Rieke, George H., Cody, Ann Marie, Güth, Tina, Stauffer, John, Covey, Kevin, Carey, Sean, Ciardi, David, Duran-Rojas, Maria C., Gutermuth, Robert A., Morales-Calderón, María, Rebull, Luisa M., Watson, Alan M. 23 May 2016 (has links)
Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner "wall" at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the rho Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 mu m) and K (2.2 mu m) bands were synchronized while the 4.5 mu m emission lagged by 74.5 +/- 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at similar to 1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.
33

The Shadow Knows: Using Shadows to Investigate the Structure of the Pretransitional Disk of HD 100453

Long, Zachary C., Fernandes, Rachel B., Sitko, Michael, Wagner, Kevin, Muto, Takayuki, Hashimoto, Jun, Follette, Katherine, Grady, Carol A., Fukagawa, Misato, Hasegawa, Yasuhiro, Kluska, Jacques, Kraus, Stefan, Mayama, Satoshi, McElwain, Michael W., Oh, Daehyon, Tamura, Motohide, Uyama, Taichi, Wisniewski, John P., Yang, Yi 24 March 2017 (has links)
We present Gemini Planet Imager polarized intensity imagery of HD 100453 in Y, J, and K1 bands that reveals an inner gap (9-18 au), an outer disk (18-39 au) with two prominent spiral arms, and two azimuthally localized dark features that are also present in Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) total intensity images. Spectral energy distribution fitting further suggests that the radial gap extends to 1 au. The narrow, wedge-like shape of the dark features appears similar to predictions of shadows cast by an inner disk that is misaligned with respect to the outer disk. Using the Monte Carlo radiative transfer code HOCHUNCK3D, we construct a model of the disk that allows us to determine its physical properties in more detail. From the angular separation of the features, we measure the difference in inclination between the disks (45 degrees) and their major axes, PA = 140 degrees east of north for the outer disk, and 100 degrees for the inner disk. We find an outer-disk inclination of 25 degrees +/- 10 degrees from face-on, in broad agreement with the Wagner et al. measurement of 34 degrees. SPHERE data in J and H bands indicate a reddish disk, which indicates that HD 100453 is evolving into a young debris disk.
34

Quantification of slope deformation behaviour using acoustic emission monitoring

Smith, Alister January 2015 (has links)
Early warning of slope instability will enable evacuation of vulnerable people and timely repair and maintenance of critical infrastructure. However, currently available warning systems are too expensive for wide-scale use or have technical limitations. The acoustic emission (AE) monitoring approach using active waveguides (i.e. a steel tube with granular backfill surround installed in a borehole through a slope), in conjunction with the Slope ALARMS AE measurement system, has the potential to be an affordable early warning system for slope instability. However, the challenge has been to develop strategies to interpret and quantify deformation behaviour from measured AE. The development of an approach to quantify slope deformation behaviour from measured AE will enable the AE monitoring system to provide early warning of slope instability through detecting, quantifying and communicating accelerations in slope movement. Field monitoring and full-scale physical modelling have been conducted to characterise the AE response from the system to both reactivated slope movements and first-time slope failure. Definitive field evidence has been obtained showing AE monitoring can measure slope movements and generated AE rates are proportional to slope displacement rates, which was confirmed through comparisons with both conventional inclinometer and continuous ShapeAccelArray deformation measurements. A field monitoring case study demonstrated that the AE approach can detect very slow slope movements of 0.075 mm/day. In addition, the concept of retrofitting inclinometer casings with active waveguides to convert the manually read instrument to a real-time monitoring system has been demonstrated using a field trial. Dynamic strain-controlled shear tests on active waveguide physical models demonstrated that AE monitoring can be used to quantify slope displacement rates, continuously and in real-time, with accuracy to within an order of magnitude. Large-scale first-time slope failure experiments allowed the AE response to slope failure to be characterised. AE was detected after shear deformations of less than a millimetre in previously un-sheared material, and AE rates increased proportionally with displacement rates as failure occurred. The AE rate-displacement rate relationship can be approximated as linear up to 100 mm/hour and shear surface deformations less than 10-20 mm. At greater velocities and larger deformations the gradient of the relationship progressively increases and is best represented using a polynomial. This is because complex pressure distributions develop along the active waveguide analogous to a laterally loaded pile, and the confining pressures increase. Variables that influence the AE rate-displacement rate relationship have been quantified using physical model experiments and empirical relationships. A framework has been developed to allow AE rate-displacement rate calibration relationships to be determined for any AE system installation. This provides a universal method that can be used by practitioners when installing AE systems, to calibrate them to deliver alarm statuses/warning levels that are related to slope displacement rates. Use of this framework has been demonstrated using a case study example, and decision making protocols have been suggested that use trends in alarms with time to trigger decisions, which could be to send an engineer to inspect the slope, manage traffic, or evacuate people.
35

Uma abordagem multinível para a obtenção de alinhamento estratégico no gerenciamento de processos de negócio / Making the link between strategy and process model collections: a multilayered approach

Dallilo, Felipe Diniz 11 April 2014 (has links)
Teoricamente, o Alinhamento Estratégico pode ser obtido com um bom Gerenciamento de Processos de Negócio (BPM na sigla em inglês), porém a relação entre esses temas é, na maioria das vezes, assumida implicitamente e pouco elaborada, tornando-se difícil a visualização e vínculo entre as estratégias e os modelos de processos detalhados, sendo necessário empreender pesquisas na direção de uma união efetiva dos dois temas. O presente trabalho desenvolveu um metamodelo multinível, para ligar os objetivos estratégicos com os processos de negócio da organização através da modelagem de processos de negócio. O trabalho conceitual foi acrescido por uma ferramenta de suporte à modelagem que permite a geração de modelos com base no metamodelo multinível e também a representação dos modelos em diferentes formas de abstração. A abordagem foi aplicada em uma grande multinacional e posteriormente foi conduzida uma avaliação experimental no qual foram realizadas entrevistas com funcionários de diferentes níveis hierárquicos para validar a eficiência e eficácia do trabalho desenvolvido. Como resultado foi possível constatar não apenas a efetividade em alcançar os objetivos propostos como também a facilidade na utilização e compreensão da abordagem em níveis devido a simplicidade na representação dos elementos e seus possíveis relacionamentos / Theoretically, the Strategic Alignment can be accomplished with a good Business Process Management, but the relationship between these themes is, most often, implicitly assumed and little developed, making it difficult to visualize and link between the strategies and the models of detailed processes, being necessary to undertake research towards an effective union of the two themes. This study developed a multilevel metamodel for connecting strategic objectives with organizational business processes through modeling of business processes. The conceptual work was increased by a support tool for modeling that allows the generation of models based on multilevel metamodel and also the representation of models in different forms of abstraction. The approach was applied in a large multinational and was subsequently conducted an experimental evaluation in which interviews with employees from different hierarchical levels were performed to validate the efficiency and effectiveness of their work. As a result it was possible to not only the effectiveness in achieving the proposed objectives as well as the ease of use and understanding of the tiered approach because of the simplicity in the representation of the elements and their possible relationships
36

Using Advanced PSF Subtraction Techniques on Archival Data of Herbig Ae/Be Stars to Search for New Candidate Companions

Safsten, Emily Diane 01 July 2017 (has links)
Herbig Ae/Be (HAeBe) stars are intermediate mass (2-10 solar mass) pre-main sequence stars with circumstellar disks. Observing planets within these young disks would greatly aid in understanding planet formation processes and timescales particularly around massive stars. So far, only one planet, HD 100546 b, has been confirmed to orbit a HAeBe star. With over 250 HAeBe stars known, and several observed to have disks with structures thought to be related to planet formation, it seems likely that there are as yet undiscovered planetary companions within the circumstellar disks of some of these young stars. Direct detection of a low-luminosity companion near a star requires high contrast imaging, often with the use of a coronagraph, and the subtraction of the central star's point spread function (PSF). Several processing algorithms have been developed in recent years to improve PSF subtraction and enhance the signal-to-noise of sources close to the star. However, many HAeBe stars were observed via direct imaging before these algorithms came out. We used the PSF subtraction program PynPoint to reprocess archival images of HAeBe stars from the Advanced Camera for Surveys on the Hubble Space Telescope to increase the likelihood of detecting a planet in their disks. We believe we have recovered the known planet around HD 100546 and possibly its candidate second companion. We also detect new candidate sources in the vicinities of HD 141569 and HD 163296. Further observations are needed to confirm the reality of these detections and also establish their association with the host stars.
37

Quality Of Working Life, Posture Analysis Of Upper Extremity Musculoskeletal Complaints Among Office Workers

Akyildiz, Ayca 01 February 2013 (has links) (PDF)
This thesis analyzes the relationship between upper extremity musculoskeletal disorders and longtime computer usage. Firstly / maastricht upper extremity questionnaire is applied to Financial Control and Information Technology Departments of Turk Telekom. Results are analyzed by using spss 16.0 tool by conduction of ordinal logistic regression analysis to determine the significance between work environment and postural information and upper extremity musculoskeletal complaints. Then / development of a new tool, namely PACU (postural analysis of computer users), takes place aiming to determine the factors of disorders, by mainly focusing on work-related neck and upper limb disorders, for long time computer users of Financial Control and Information Technology Departments of Turk Telekom. Results of the PACU are analyzed by using the methods of correlation, chi square goodness of fit test, factor analysis, and ordinal logistic regression.
38

Research for polyethylene fibers Reinforced Concrete

Chen, Yan-Shuo 24 May 2012 (has links)
In this study, Dyneema fiber can bear tension and not easy to react with the chemicals characteristics, to explore for the resistance to bending moment and compressive strength of concrete. To compare with different rate of Dyneema fiber added at different ratio of AE water-reducing in the condition of concrete slump test and slump flow test. We planning in different water-cement ratio 0.48(non AE water-reducing)¡B0.4(add AE water-reducing), to test for its fresh properties and hardened properties, and discussion the effect by AE water-reducing and Dyneema fiber on the marine engineering. According to this study, adding Dyneema fiber will make the slump and slump flow value dropped, and affecting the workability. Because of Dyneema fiber will tangle when add too much Dyneema fiber in concrete. So in mixing time, the Dyneema fiber and concrete will form clumps, in this study, we add the AE water-reducing to improve. After we add AE water-reducing, the slump, slump flow, compressive strength, are increase, but we still had to pay attention to the ratio between Dyneema fiber and AE water-reducing, the strength of structure perhaps decrease if added too much Dyneema fiber or AE water-reducing. This study can get the best positive effect when added 1.5% volume volume of Dyneema fiber.
39

Bounds On The Anisotropic Elastic Constants

Dinckal, Cigdem 01 February 2008 (has links) (PDF)
In this thesis, mechanical and elastic behaviour of anisotropic materials are inves- tigated in order to understand the optimum mechanical behaviour of them in selected directions. For an anisotropic material with known elastic constants, it is possible to choose the best set of e&curren / ective elastic constants and e&curren / ective eigen- values which determine the optimum mechanical and elastic properties of it and also represent the material in a speci.ed greater material symmetry. For this reason, bounds on the e&curren / ective elastic constants which are the best set of elastic constants and e&curren / ective eigenvalues of materials have been constructed symbollicaly for all anisotropic elastic symmetries by using Hill [4,13] approach. Anisotropic Hooke.s law and its Kelvin inspired formulation are described and generalized Hill inequalities are explained in detail. For di&curren / erent types of sym- metries, materials were selected randomly and data of elastic constants for them were collected. These data have been used to calculate bounds on the e&curren / ective elastic constants and e&curren / ective eigenvalues. Finally, by examining numerical results of bounds given in tables, it is seen that the materials selected from the same symmetry type which have larger interval between the bounds, are more anisotropic, whereas some materials which have smaller interval between the bounds, are closer to isotropy.
40

Structural Properties Of Defected Graphene Nanoribbons Under Tension: Molecular-dynamics Simulations

Tuzun, Burcu 01 February 2012 (has links) (PDF)
Structural properties of pristine and defected graphene nanoribbons have been investigated by stretching them under 5 percent and 10 percent uniaxial strain until fragmentation. The stretching process has been carried out by performing molecular dynamics simulations (MDS) at 1 K and 300 K to determine the temperature effect on the structure of the graphene nanoribbons. Results of the simulations indicated that temperature, edge shape of graphene nanoribbons and stretching speed have a considerable effect on structural properties, however they have a slight effect on the strain value. The maximum strain at which fracture occurs is found to be 46.41 percent whereas minimum strain value is calculated as 21.00 percent. On the other hand, the defect formation energy is strongly affected from temperature and edge shape of graphene nanoribbons. Stone-Wales formation energy is calculated as -1.60 eV at 1 K whereas -30.13 eV at 300 K for armchair graphene nanoribbon.

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