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FRUSTAGLI, GIUSEPPE. "Exoplanets Characterization: from Ultra-short Period Planets to Ultra-hot Jupiters Atmospheres." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/311363.
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La scoperta di pianeti che orbitano intorno ad altre stelle è uno degli eventi più importanti nell'astrofisica galattica degli ultimi due decenni. Dalla scoperta del primo esopianeta nel 1995, il numero di esopianeti scoperti è cresciuto sempre più in fretta e attualmente conosciamo più di 4,000 pianeti, molto diversi per dimensioni e distanza dalla stella ospite e anche in fattori come temperatura, massa, densità.
La diversità degli esopianeti è un fattore chiave per comprendere la formazione dei sistemi planetari e in particolare la formazione del Sistema Solare e del nostro pianeta, la Terra. Questo è il motivo per cui la scienza osservativa degli esopianeti si sta concentrando su due diversi obiettivi: i) la caratterizzazione degli esopianeti, nel tentativo di determinare il raggio, la massa, la densità e la composizione degli oggetti osservati e ii) la caratterizzazione delle loro atmosfere, stabilendo gli elementi che l'atmosfera di un pianeta può supportare e i meccanismi che guidano i processi atmosferici.
Caratterizzazione degli Esopianeti
La fotometria, con il metodo dei transiti si è rivelato senza dubbio il metodo di scoperta di esopianeti con il maggior successo. La forza di questo metodo è il numero di parametri che possono essere ottenuti osservando il transito dei pianeti, soprattutto in combinazione con le osservazioni di velocità radiale (VR).
In questo contesto, uno dei gruppi più prolifici è il Consorzio GTO di HARPS-N, che sfrutta l'alta risoluzione e l'estrema stabilità dello spettrografo HARPS-N, installato al Telescopio Nazionale Galileo, per caratterizzare e scoprire esopianeti combinando il metodo dei transiti e quello delle velocità radiali. Come collaboratore di questo gruppo, ho studiato un pianeta candidato scoperto dalla Campagna 16 della missione K2, HD 80653 b, una super-Terra che transita davanti alla sua stella con un periodo orbitale molto breve, e ho usato le VR HARPS-N per caratterizzarlo, ottenendo la sua massa e definendone la densità. Il pianeta appartiene ad una particolare classe di esopianeti: i pianeti a periodo ultra-corto, oggetti che orbitano intorno alle loro stelle con periodi estremamente brevi, più piccoli di due raggi terrestri e con composizioni simili a quella terrestre.
Caratterizzazione di Atmosfere
I gioviani ultra-caldi sono laboratori eccellenti per lo studio delle atmosfere esoplanetarie. Il sodio, per la sua grande sezione d'urto e per il fatto che le sue righe spettrali principali si trovano nel range spettrale della maggior parte degli spettrografi, è l'elemento più studiato, ma lo studio di nuove righe spettrali è cominciato. Righe del ferro, del titanio, del magnesio, ma anche tracce di cromo, scandio e ittrio sono state trovate negli spettri di trasmissione ad alta risoluzione dei pianeti più caldi.
I due gioviani ultra-caldi KELT-9 b e KELT-20 b sono stati osservati dal programma atmosfere del gruppo italiano Global architecture of Planetary Systems (GAPS).
Come membro del gruppo ho potuto esplorare più in dettaglio il metodo della spettroscopia in transito, creando due diverse routine per la caratterizzazione delle atmosfere. Il primo metodo segue approcci già utilizzati in precedenza, ma è in grado di rilevare righe spettrali deboli come quelle del magnesio, sommandole nello spazio delle velocità. Usando questo approccio ho analizzato gli spettri ad alta risoluzione di KELT-9 b e KELT-20 b e ho ottenuto i loro spettri di trasmissione, rilevando un assorbimento significativo per Na, H, Fe e Mg I.
Il secondo metodo estrae gli spettri di trasmissione ad alta risoluzione e li cross-correla con modelli teorici di spettri di trasmissione. Analizzando gli spettri di KELT-20 b e utilizzando la cross-correlazione ho potuto confermare la presenza di Fe I, Fe II e Na I, trovate da analisi precedenti di altri gruppi di ricerca.<br>The discovery of planets orbiting around stars other than the Sun is by far the most relevant event in the galactic astrophysics of the last two decades. Since the discovery of the first exoplanet in 1995, the number of exoplanets discovered grew fast and we currently know more than 4,000 exoplanets, very diverse in dimension and distance from parent stars and also in factors as temperature, mass, density.
The diversity of exoplanets is a key factor to understand more about the formation of planetary systems and in particular the formation of the Solar System and our planet, the Earth. This is the reason why observational exoplanetary science is currently focusing on two different fields: i) the characterization of exoplanets, trying to determine the radius, the mass, the density and the bulk composition of the objects observed, and ii) the characterization of their atmospheres, establishing the elements that the atmosphere of a planet supports and the mechanisms that drive the atmospheric processes.
Characterization of Exoplanets
Photometry with the transit method has arguably been the most successful exoplanet discovery method to date. The method’s strength is the rich set of parameters that can be obtained from transiting planets, in particular in combination with RV observations.
In this framework, one of the most prolific groups is the HARPS-N Guaranteed Time Observations (GTO) Consortium, that makes use of the high resolution (R = 115,000) and extreme stability of the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo (TNG), to characterize and discover exoplanets by combining transits and RV methods. As a collaborator of this group, I studied a candidate planet discovered by K2 Campaign 16, HD 80653 b, a super-Earth planet transiting the star on a short period orbit, and used HARPS-N RV data to characterize it, finding its mass and defining its bulk density. It belongs to a peculiar class of exoplanets: the Ultra-Short Period (USP) planets, objects that orbit their stars with extremely short periods, smaller than about 2 Earth Radii and compositions similar to that of the Earth.
Characterization of Atmospheres
Ultra-hot Jupiters are excellent laboratories for the study of exoplanetary atmospheres. Sodium, due to its large cross-section and to the fact it is in the wavelength range of most optical spectrographs, is the most studied element, but new interesting features begin to be analyzed. Lines of iron, titanium, magnesium, but also chromium, scandium and yttrium have been found in the high resolution transmission spectra of the hottest planets.
The two ultra-hot Jupiters KELT-9 b and KELT-20 b were observed in the framework of the Global architecture of Planetary Systems (GAPS) Atmosphere program. I explored more in detail the transit spectroscopy method, creating two different routines for atmosphere characterization.
The first routine follows previous approaches for high-resolution spectroscopy, but is able to detect weak spectral lines such as those of magnesium, by co-adding the lines in the velocities space.
Using this procedure, I analyzed the high-resolution spectra of KELT-9 b and KELT-20 b, obtaining their transmission spectra and detecting significant absorption for Na, H, Fe and Mg I.
The second routine extracts the high-resolution transmission spectra of exoplanets and cross-correlates them with theoretical transmission spectra models. I analyzed the high-resolution spectra of KELT-20 b and with the cross-correlation technique I confirmed previous detections of Fe I, Fe II, and Na I.
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Kennedy, Michael David Joseph. "A comparison of critical velocity estimates to actual velocities in predicting simulated rowing performance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq22611.pdf.
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Hashim, Muazzam Ali. "Investigating subsurface heterogeneities and its impact on the variation in interval velocities : implications to velocity modelling in the Bredasdorp basin." Thesis, University of the Western Cape, 2015. http://hdl.handle.net/11394/5328.
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>Magister Scientiae - MSc<br>Velocity modelling forms an integral part of the seismic interpretation process initially completed in two-way time. In order for a representative depth conversion, it is obligatory to construct a velocity model that serves the bridge between velocity and respective two-way time. This study deals with the investigation of subsurface heterogeneities and its impact on the variation of velocities. Interpretation of time domain reflection data results in one or more seismic horizons, however these horizons should represent the variation in subsurface geology as a result of acoustically different layers displaying varying reflection amplitudes. The purpose of this study was fulfilled by examining the variation of these velocities in relation to the geology and its significance towards building a velocity model. It is evident that complexities, such as an existing heterogeneous subsurface is present in the study area. Using velocities only considered at formation well tops, as a result, does not completely honour the variation in these velocities. The velocity profile as calculated from the sonic log was characterized into zones representing unique velocity trends. The analyses to understand the impact of subsurface heterogeneities on the velocities was completed by the application of seismic facies analysis which entailed the study of the seismic reflector patterns and amplitudes; a study of the lithologies present and the generation of mineral plots using available wireline logs, all of which in close relation to the variation in velocities. The characterized zones, as a result have shown that shaly sediments are typically associated with higher velocities (~2800 – 4600m/s) compared to sandstones of lower densities. Mineral plots
however, have also indicated that where quartz minerals were present (specifically zone L), sandstones as a result have shown higher velocities (~4800m/s) as compared to the shales (~3600m/s). These higher velocities are also associated with more organised seismic reflectors with brighter amplitudes and strong contrasts in acoustic impedance as shown by the seismic. Uniform velocities were observed in zones such as zone Ia, typically associated with a low acoustic impedance contrast and minimal variation in its lithological make-up. The integrated investigation of subsurface heterogeneities has shown that velocities vary to a substantial degree as a result of existing subsurface heterogeneities. The variation of these velocities are hence significant enough that it should be considered when constructing a velocity model which aims to respect the geology of the study area. The result of understanding the relation between the geology and resultant velocities may prove to advance the results of the velocity model in a manner that it is more complete and representative of the subsurface.
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Van, Riper Steven G. "Investigation of increased forward flight velocities of helicopters using second harmonic control and reverse velocity rotor concept." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FVanRiper.pdf.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, December 2003.<br>Thesis advisor(s): E. Roberts Wood, Raymond Shreeve. Includes bibliographical references (p. 145-146). Also available online.
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Allen, G. F. "Interval velocities from moveout velocities over a seismic reflection survey area." Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/33751.
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Moveout velocities sampled frequently along seismic horizons on a selection of seismic lines are used to derive interval velocities in an 'inversion' algorithm developed from work published by Hubral. This inversion is based on zero-offset raytrace modelling in a simplistic local ground model. The 'Hubral algorithm' is incorporated into a database which allows spatial smoothing of velocities. The spatial consistency of derived interval velocities can then be assessed by reference to mis-ties at line intersections, while interval velocities from well data can be used to check their validity. These principles have been used to derive interval velocities both from real data and from 'synthetic' data generated by common mid-point raytracing over schematic ground models. The latter study reveals that the procedure performs well if the local subsurface sampled by the CMP gather conforms approximately to the simplistic ground model assumed by the Hubral algorithm. The method is unsuitable in areas of faulting and interval velocity heterogeneity, and may yield spurious results over fold axes. Application of the procedure to real data indicates that it is generally desirable to smooth both moveout velocities before inversion and interval velocities after inversion. Comparison with well information shows that interval velocities derived by the Hubral algorithm are consistently higher than those measured from calibrated velocity logs. This observation is disturbing, since the derived interval velocities require a correction if they are to be used for depth conversions, but the discrepancy cannot be explained by ray theoretical considerations. No advantage appears to be gained by the 'layer-by-layer' mode of inversion over the 'direct' inversion, despite the greater potential for error propagation anticipated in the latter. Further work on different data sets is required to justify general use of the layer-by-layer mode of inversion.
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Marshall, Stephen P. "Measuring laminar burning velocities." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:81ea0ed8-3abd-4192-86ef-67bd5581c325.
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The laminar burning velocity of a fuel is the rate of normal propagation of a 1D flame front relative to the movement of the unburned gas. This is a fundamental property of a fuel that affects many aspects of its combustion behaviour. Experimental values are required to validate kinetic simulations, and also to provide input for models of flashback, minimum ignition energy and turbulent combustion. Burning velocity affects burn duration and consequently power output in spark ignition engines. Burning velocities are affected by pressure, temperature, equivalence ratio, residuals, additives, and stretch rates. The constant volume vessel has been used as it is considered both the most versatile and accurate method of measuring laminar burning velocities. An existing combustion vessel and oven were refurbished and new systems built for fuel injection, ignition, experiment control, data acquisition and high speed schlieren photography. An existing multi-zone model was used to allow calculation of burning velocity from pressure and schlieren data, allowing the user to select data uncorrupted by heat transfer or cellularity. A twelve term correlation for burning velocity was validated using methane modelling data. The chosen data from all the experiments was then fitted to the correlation. Methane, n-butane, n-heptane, iso-octane, toluene, ethylbenzene and ethanol were tested over a wide range of initial pressures (0.5, 1, 2 and 4 barA), temperatures (289-450 K) and equivalence ratios (0.7-1.4). For liquid fuels, tests with real residuals at mole fractions of up to 0.3 were also conducted. Stoichiometric mixture tests were performed at two initial temperatures (380 and 450 K) and the same four initial pressures. For mixtures of iso-octane and ethylbenzene, percentage volumes of 12.5, 25, 50 and 75% iso-octane were tested. It was found that the the percentage of iso-octane affected burning velocity non-linearly. For iso-octane/ethanol, a single 50:50% mixture was tested.
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Kratochvíl, Pavel. "Analýza seismického rychlostního pole." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220661.
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Seismic velocities are an important prerequisite for seismic processing as a method for hydrocarbons accumulations detection. Seismic velocities are often displayed for mutual comparing, improvement checking, they are filtrated and recalculated for its different characteristic determination. This work deals with basic seismic propagation laws, the meaning of velocities in different stages of seismic processing and this theoretical background is followed by a proposition of method for calculating and displaying of stack velocities.
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Lewis, Braxton V. "Effects of 0[degree] cross draft velocity and the presence of a table and manikin on midline velocities in front of a rectangular capture hood." Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/11147.
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Thesis (M.S.)--West Virginia University, 2010.<br>Title from document title page. Document formatted into pages; contains ix, 74 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 53-55).
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Seabroke, George Michael. "Probing the Milky Way galaxy through thick and thin (discs and halo) with the CORrelation RAdial VELocities (CORAVEL) and the RAdial velocity experiment (RAVE) surveys." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612308.
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Ehwald, Lena Elisa. "Seasonal Velocities on Nordenskiöldbreen, Svalbard." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-296682.
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Global warming leads to increased precipitation in the Arctic, as warmer air can carry more moisture. The consequence is that many arctic glaciers get steeper slopes over time as increased melt at their lower part causes thinning and increased solid precipitation in their upper regions leads to thickening of the glacier. Ice flow of glaciers is strongly controlled by the surface slope, where steeper slopes leads to increased ice flow. An altered flow regime of the glaciers can lead to unpredicted contributions to sea-level changes as more glacier ice is delivered to lower regions and eventually to the sea through calving of melt- runoff. Long-term measurements of ice-flow velocities are therefore crucial to receive a better understanding of how glaciers respond to climate changes in a temporal and spatial scale. This study investigates ice flow velocities measured over a period of 10 years between 2006 and 2015 on Nordenskiöldbreen, Svalbard. The poly-thermal outlet glacier is centrally located on Spitsbergen; the main island of the Svalbard archipelago (74N°,10°E /81N°,35°E). Ice-flow velocities are measured continuously using stand-alone single-frequency GPS receivers attached to 8 metal stakes along the central flow line of Nordenskiöldbreen. The Institute for Marine and Atmospheric research in Utrecht, the Netherlands (IMAU) has developed such GPS units to measure ice-flow velocities at low costs and all year-round. Ice flow velocities at the central-flow line of Nordenskiöldbreen for the period 2006-2016 are estimated to be between 40 and 60 m a-1. Results show that maximum ice flow velocities can reach up to 80 m a-1 and occur mainly in the beginning of July. The highest annual averaged velocity of 53.88 m a-1 was measured during summer 2014. Averaged ice-flow velocities show an increasing trend of about 1.78 m a-1 during summer seasons. Results are further compared with mass balance observations and temperature records to analyze how glacier systems respond to climate changes.<br>Klimatuppvärmningen bidrar till att glaciärer blir tunnare och smälter snabbare. Ett varmare klimat är också orsaken till att snöfall ökar då varmare luft kan transportera mer fuktighet. Konsekvensen blir att glaciärer i arktiska områden får brantare sluttningar. Brantare sluttningar leder sedan till att glaciärer rör sig snabbare. Om glaciärer plötsligt rör sig snabbare uppstår möjligheten att havsnivån också stiger snabbare. Uppsatsen undersöker is-hastigheten från Nordenskiöldbreen. Nordenskiöldbreen är en glaciär på Spetsbergen, Svalbard som går ut i Adolfbukta innerst Billesjorden. Hastigheten uppmättes med hjälp av 13 GPS-stationer på glaciärens yta, placerade mellan 800 och 1200 meter över havsnivån. GPS-stationerna är utvecklade av Institut för Marin- och Atmosfär-undersökningar i Utrecht, Holland (IMAU) för att mäta glaciärens hastighet året runt till låga kostnader. Sedan 1997 har Institutionen för geovetenskaper vid Uppsala Universitet utfört flera mätningar på Nordenskiöldbreen för att mäta massbalans, isrörelse och miljöförändringar. Massbalans mätningar har visat att glaciären fick brantare sluttningar över den senaste tio-års perioden. Uppsatsen analyserar trenden för isrörelse vid Nordenskiöldbreen över de senaste tio åren. Dessutom är resultanterna jämförda med massbalans-analyser och temperaturmätningar från Svalbard Flygplats. Jämförelsen hjälper att förstå hur glaciärens system reagerar på klimatförändringar. De uppskattade hastighetsresultaten visar att Nordenskiöldbreen rör sig med en medelhastighet av 45-53 meter per år. Isrörelse kan nå upp till 80 meter per år och är främst förekommande under juli månad när temperaturen är hög. Detta producerar då mer smältvatten vilket driver upp vattentrycket vid glaciärens botten och leder till basal glidning.
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Galaitsis, George Stergios. "Extraction of drilling-angular velocities using a nodal-spatial array of in-plane translational velocities." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-05042010-020305/.
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Makin, Alexis David James. "Velocity memory." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/velocity-memory(c5c1c28d-0a23-44a5-93bc-21f993d2e7ad).html.
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It is known that primates are sensitive to the velocity of moving objects. We can also remember velocity information after moving objects disappear. This cognitive faculty has been investigated before, however, the literature on velocity memory to date has been fragmented. For example, velocity memory has been disparately described as a system that controls eye movements and delayed discrimination. Furthermore, velocity memory may have a role in motion extrapolation, i.e. the ability to judge the position of a moving target after it becomes occluded. This thesis provides a unifying account of velocity memory, and uses electroencephalography (EEG) to explore its neural basis. In Chapter 2, the relationship between oculomotor control and motion extrapolation was investigated. Two forms of motion extrapolation task were presented. In the first, participants observed a moving target disappear then reappear further along its path. Reappearance could be at the correct time, too early or too late. Participants discriminated reappearance error with a two-alternative forced choice button press. In the second task, participants saw identical targets travel behind a visible occluder, and they attempted to press a button at the exact time that it reached the other side. Tasks were completed under fixation and free viewing conditions. The accuracy of participant's judgments was reduced by fixation in both tasks. In addition, eye movements were systematically related to behavioural responses, and small eye movements during fixation were affected by occluded motion. These three results imply that common velocity memory and pre-motor systems mediate eye movements and motion extrapolation. In Chapter 3, different types of velocity representation were explored. Another motion extrapolation task was presented, and targets of a particular colour were associated with fast or slow motion. On identical-velocity probe trials, colour still influenced response times. This indicates that long-term colour-velocity associations influence motion extrapolation. In Chapter 4, interference between subsequently encoded velocities was explored. There was robust interference between motion extrapolation and delayed discrimination tasks, suggesting that common processes are involved in both. In Chapter 5, EEG was used to investigate when memory-guided tracking begins during motion extrapolation. This study compared conditions where participants covertly tracked visible and occluded targets. It was found that a specific event related potential (ERP) appeared around 200 ms post occlusion, irrespective of target location or velocity. This component could delineate the onset of memory guided tracking during occlusion. Finally, Chapter 6 presents evidence that a change in alpha band activity is associated with information processing during motion extrapolation tasks. In light of these results, it is concluded that a common velocity memory system is involved a variety of tasks. In the general discussion (Chapter 7), a new account of velocity memory is proposed. It is suggested that a velocity memory reflects persistent synchronization across several velocity sensitive neural populations after stimulus offset. This distributed network is involved in sensory-motor integration, and can remain active without visual input. Theoretical work on eye movements, delayed discrimination and motion extrapolation could benefit from this account of velocity memory.
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Seligman, Joshua R. "Power development through low velocity isotonic, or combined low velocity isotonic-high velocity isokinetic training /." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/7046.
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Ardha, Vishwanath Reddy. "Laminar burning velocities of gas mixtures." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Eiesland, Ole Wostryck. "Estimating seabed velocities from normal modes." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for petroleumsteknologi og anvendt geofysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18514.
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In this Master Thesis a method for estimating seabed p-wave velocities from normal mode seismic data is developed. This is done through forward modeling using two dimensional finite difference modeling to generate synthetic data based on a given parallel two layered laterally varying seabed velocity model and a constant two layered density model, with a common fixed water depth. A semblance inversion technique is developed in MATLAB using the period equation eqref{eq:period} and the resulting velocity profiles is plotted against the exact velocity model to check the validity of the estimates. The same method is extended to estimations of seabed densities. For analysis of the robustness of the method, analysis with added pseudo random noise is preformed.The results shows a good performance of the semblance method to reproduce the model velocity parameters. The introduction of noise is handled well and decent results are obtained for significantly low signal to noise ratios.It suggests that the semblance method is applicable to use for determination of other parameters influencing the normal mode response signal.
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Ortiz, Mauricio, Sabine Reffert, Trifon Trifonov, et al. "Precise radial velocities of giant stars." EDP SCIENCES S A, 2016. http://hdl.handle.net/10150/622444.
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Context. For over 12 yr, we have carried out a precise radial velocity (RV) survey of a sample of 373 G- and K-giant stars using the Hamilton Echelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims. We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods. We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope. Results. We report the probable discovery of a giant planet with a mass of m(p) sin i = 6.92(-0.24)(+0.18) M-Jup orbiting at a(p) = 1.0860(-0.0007)(+0.0006) aufrom the giant star HD 59686 A. In addition to the planetary signal, we discovered an eccentric (e(B) = 0.729(-0.003)(+0.004)) binary companionwith a mass of m(B) sin i = 0.5296(-0.0008)(+0.0011) M-circle dot orbiting at a close separation from the giant primary with a semi-major axis of a(B) = 13.56(-0.14)(+0.18) au. Conclusions. The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second-generation planets or dynamical interactions in an early phase of the system's lifetime need to be seriously considered to better understand the origin of this enigmatic planet.
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Barnhart, Gregory J. "Predicting hail size using model vertical velocities." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://bosun.nps.edu/uhtbin/hyperion-image.exe/08Mar%5FBarnhart.pdf.
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Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2008.<br>Thesis Advisor(s): Nuss, Wendell. "March 2008." Description based on title screen as viewed on April 25, 2008. Includes bibliographical references (p. 47-49). Also available in print.
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Bunkute, Birute. "Burning Velocities of Coal-derived Syngas Mixtures." Thesis, Cranfield University, 2008. http://hdl.handle.net/1826/3135.
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Summary
Integrated gasification combined cycle (IGCC) systems, which utilize coal,
petroleum coke, heavy oil, biomass and waste materials as a feedstock,
continue to enter the power generation market. The gasification products
from gasifiers using these feedstocks are mixtures of hydrogen, carbon
monoxide and inerts like nitrogen, carbon dioxide and water. These
mixtures are then used as a fuel in low-emission power generation
applications. Unlike natural gas or methane, which has been widely used
and researched for many years, these mixtures have not been widely
investigated. Thus the aim of this study is to provide data on the
combustion properties of syngas mixtures, mainly focusing on laminar
burning velocities and critical strain rates to extinction. These combustion
properties data are essential for gas turbine combustor modelling using
turbulent burning velocity closure models.
The establishment of such a database in this study mainly relies on
numerical computations. Therefore, the experimental campaign was
limited to investigation of several CO/H2/N2 fuel mixtures fuel mixtures at
different equivalence ratios and operating conditions. The laminar burning
velocity values, obtained from the experimental campaign were used
mainly for validation of the chemical kinetics model and reaction
mechanism.
The principal outcome from this study is that at ambient conditions and
reactant preheat temperatures up to 400K experimental laminar burning
velocity values compare well with numerical predictions. The laminar
burning velocity tests at high pressure presented a number of
complications due to the formation of cellular flames and the flow in theburner tube entering the transitional laminar to turbulent regime. As a
result the numerical model could not be fully validated experimentally for
high pressure conditions.
A comprehensive combustion properties database has been created using
numerical simulations, based on comprehensive descriptions of the
chemical kinetics and extensions using neural networks.
CFD simulations of reacting flows in a practical combustor geometry
demonstrated the importance of obtaining accurate laminar burning
velocities and critical strain rates to extinction data.
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Shen, Gang 1953. "Bubble swarm velocities in a flotation column." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28529.
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A new fast response conductivity meter was developed and tested. The "five time constant" of the meter is 0.08 s which meets the requirement for measurements under the dynamic conditions relevant to this work.<br>In a laboratory column, a bubble interface was created by introducing a step change of gas flow, and the rising velocity of this interface, $u sb{in},$ was measured using a conductivity method with the new conductivity meter. A measurement of the three-dimensional bubble swarm velocity in the column was obtained by interpolation from the $u sb{in}$ measured as a function of $J sb{g2} vert J sb{g} sb1 ,$ where $J sb{g} sb1$ and $J sb{g} sb2$ are the superficial gas velocities before and after a step change of gas flowrate, respectively. This velocity was referred to as the hindered velocity, $u sb{h}.$ The buoyancy velocity, $u sb0 ,$ was readily determined by switching off the gas, i.e. $u sb0 = u sb{in}$ at $J sb{g} sb2 = 0.$<br>The average gas velocity, $u sb{g},$ was corrected to the local average gas velocity, $u sb{g,loc},$ to obtain the average gas velocity under the local pressure conditions at a given vertical position in the column. The experimental results showed that $u sb{h}$ was significantly less than $u sb{g,loc}$ (and $u sb{g}).$ This is because the $u sb{h}$ is the three-dimensional bubble swarm velocity and $u sb{g,loc}$ is the one-dimensional bubble swarm velocity. Unlike $u sb{g,loc},$ the $u sb{h}$ was constant along the column, which was supported by theoretical momentum analysis. The $u sb{h}$ is proposed as the key characteristic swarm velocity of the system.<br>For the air-water only system in the two-dimensional domain, using parabolic models for gas holdup and liquid circulation velocity profiles over the cross section of the column, the $u sb{h}$ could be fitted to the experimental data. For the air-water-frother system, the $u sb{h}$ could not be fitted to the experimental data which is attributed to the air bubbles adopting a circulatory flow pattern.<br>In the air-water only system under batch operation, Nicklin's derivation (1962), i.e. $u sb{g} = u sb0 + J sb{g},$ was supported only under restrictive conditions, namely $u sb{g}$ and $J sb{g}$ must be measured at atmospheric pressure. Considering the local values, the experiments showed that $u sb{g,loc}$ was not equal to $u sb0 + J sb{g,loc}.$ In the presence of frothers under batch or countercurrent operation, the experiments showed that Nicklin's derivation was not applicable even if atmospheric values of $u sb{g}$ and $J sb{g}$ were used.
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Werthmüller, Dieter. "Bayesian estimation of resistivities from seismic velocities." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8932.
Full textAbstract:
I address the problem of finding a background model for the estimation of resistivities in the earth from controlled-source electromagnetic (CSEM) data by using seismic data and well logs as constraints. Estimation of resistivities is normally done by trial-and-error, in a process called “inversion”, by finding a model of the earth whose responses match the data to within an acceptable error; what comes out of the inversion is what is put into the model by the geophysicist: it does not come out of the data directly. The premise underlying this thesis is that an earth model can be found that satisfies not only the CSEM data but also the seismic data and any well logs. I present a methodology to determine background resistivities from seismic velocities using rock physics, structural constraints, and depth trends. The physical parameters of the seismic wave equation are different from those in the electromagnetic diffusion equation, so there is no direct link between the governing equations. I therefore use a Bayesian framework to incorporate not only the errors in the data and our limited knowledge of the rock parameters, but also the uncertainty of our chosen and calibrated velocity-to-resistivity transform. To test the methodology I use a well log from the North Sea Harding South oil and gas field to calibrate the transform, and apply it to seismic velocities of the nearby Harding Central oil and gas field. I also use short-offset CSEM inversions to estimate the electric anisotropy and to improve the shallow part of the resistivity model, where there is no well control. Three-dimensional modelling of this resistivity model predicts the acquired CSEM data within the estimated uncertainty. This methodology makes it possible to estimate background resistivities from seismic velocities, well logs, and other available geophysical and geological data. Subsequent CSEM surveys can then focus on finding resistive anomalies relative to this background model; these are, potentially, hydrocarbon-bearing formations.
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Cox, Isaiah. "Monte Carlo Simulations of Ultracold Neutron Velocities." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/honors/588.
Full textAbstract:
An electric dipole moment (EDM) in the neutron would indicate a source of CP-violation that is needed to explain the dominance of matter over antimatter in the universe. Several experiments are currently looking for a neutron EDM and so far, the value has been constrained to dn 1.8 x10 26 ecm. Presented here is work supporting the nEDM experiment at Los Alamos National Laboratory which utilizes ultracold neutrons (UCNs) and Ramsey’s separated oscillating fields method. In such an experiment, it is important to understand the velocity of the neutrons due to false EDM signals that can be pro- duced by the presence of a magnetic field. Monte Carlo simulations were used to study the optimal design parameters of a chopper system that would reproduce a given velocity spectrum of a population of neutrons by measuring the time of flight to a detector.
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El, Borgi Mouna, and Mårten Norman. "Estimation of Velocities in Ice Hockey Collisions." Thesis, KTH, Medicinteknik och hälsosystem, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297592.
Full textAbstract:
Concussions occur frequently as a result of tackles in ice hockey. Analysis of video material may provide an understanding of the relationship between the kinematics of collisions and the risk for injury. In this thesis, two video analysis methods were used to estimate the impact velocities of 22 ice hockey tackles that resulted in concussions. The Point tracking method uses tracking of user-defined object points on the players and ice to estimate the velocities. It was used in an earlier thesis. A deep learning-based method was implemented in this thesis. It uses a pre-trained deep learning model to detect the players in each frame of the video. Both methods were validated in this thesis using soccer videos containing accelerometer data from the players. The mean error was 25.6 % for the Point tracking method and 43.1 % for the Deep learning method. The difference was not significant. Both methods calculate the player velocity as a mean from a given number of video frames before impact. The choice of the number of frames did not significantly affect the difference in estimated velocities between the Point tracking method and the Deep learning method. The Point tracking method succeeded in estimating velocities in 17 cases. The mean velocities for the attacking and injured players were 10.5 m/s and 9.3 m/s, respectively. The Deep learning method succeeded in 9 cases, and the mean velocities were 9.7 m/s and 9.5 m/s. The velocities are higher than what has been found in earlier research, suggesting that both methods may be biased towards estimating too high velocities. More investigation needs to be done to evaluate the methods’ performance, possibly by comparing with accelerometer data from ice hockey.
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Carleo, Ilaria. "High precision radial velocities with giano spectra." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7388/.
Full textAbstract:
Radial velocities measured from near-infrared (NIR) spectra are a potential tool to search for extrasolar planets around cool stars. High resolution infrared spectrographs now available reach the high precision of visible instruments, with a constant improvement over time. GIANO is an infrared echelle spectrograph and it is a powerful tool to provide high resolution spectra for accurate radial velocity measurements of exo-planets and for chemical and dynamical studies of stellar or extragalactic objects. No other IR instruments have the GIANO's capability to cover the entire NIR wavelength range.
In this work we develop an ensemble of IDL procedures to measure high precision radial velocities on a few GIANO spectra acquired during the commissioning run, using the telluric lines as wevelength reference.
In Section 1.1 various exoplanet search methods are described. They exploit different properties of the planetary system. In Section 1.2 we describe the exoplanet population discovered trough the different methods. In Section 1.3 we explain motivations for NIR radial velocities and the challenges related the main issue that has limited the pursuit of high-precision NIR radial velocity, that is, the lack of a suitable calibration method. We briefly describe calibration methods in the visible and the solutions for IR calibration, for instance, the use of telluric lines. The latter has advantages and problems, described in detail. In this work we use telluric lines as wavelength reference.
In Section 1.4 the Cross Correlation Function (CCF) method is described. This method is widely used to measure the radial velocities.In Section 1.5 we describe GIANO and its main science targets.
In Chapter 2 observational data obtained with GIANO spectrograph are presented and the choice criteria are reported.
In Chapter 3 we describe the detail of the analysis and examine in depth the flow chart reported in Section 3.1.
In Chapter 4 we give the radial velocities measured with our IDL procedure for all available targets. We obtain an rms scatter in radial velocities of about 7 m/s.
Finally, we conclude that GIANO can be used to measure radial velocities of late type stars with an accuracy close to or better than 10 m/s, using telluric lines as wevelength reference.
In 2014 September GIANO is being operative at TNG for Science Verification and more observational data will allow to further refine this analysis.
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Brandås, Linn Tove. "Relating acoustic wave velocities to formation mechanical properties." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for petroleumsteknologi og anvendt geofysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18408.
Full textAbstract:
Proper correlation between formation mechanical properties and acoustic data is essential for acquiring field rock mechanical data for analysis, and it has thereby a great significance to oilfield development.This thesis presents results from a correlation study between formation mechanical properties and acoustic wave velocities from a set of unpublished rock mechanical experiments on sandstone samples from the Norwegian shelf. The core samples from the Norwegian shelf were subjected to triaxial compression tests performed at various confining pressures with simultaneous measurements of acoustic velocities. Correlations between formation compressive strength, elastic stiffness and Poisson's ratio and compressional and shear transit time have been established.The results obtained in this study confirm that the stress level and the stress configuration affect the acoustic velocities, and this should be accounted for when using generalized empirical correlations to estimate formation strength, elastic stiffness and Poisson's ratio from acoustic logs in field studies. The empirical correlations established through this work are found to match reasonable well with other published relations. By acoustic logs from field studies, it is found that the empirical correlations overestimate the formation strength and the elastic stiffness.
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Doumler, Timur. "Constrained local universe simulations from galaxy peculiar velocities." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10076/document.
Full textAbstract:
Les vitesses particulières de galaxies fournissent des informations importantes sur notre mouvement par rapport aux grandes structures observées et peuvent être utilisées afin de contraindre la distribution de matière noire sous-jacente. En ce basant sur cette approche, la technique des réalisations contraintes permet de calculer des simulations numériques qui ressemblent à l'Univers Local observé. Ceci fourni un laboratoire numérique puissant pour étudier la dynamique, la formation et l' évolution des structures bien connues de l'Univers Local. L' étape cruciale est de générer, à partir des données observationnelles, des conditions initiales appropriées. Nous présentons ici des améliorations de la technique des simulations contraintes, accompagnées d'un code numérique nouvellement développé et hautement optimisé, qui peut ingérer les énormes ensemble de données observationnelles. Les galaxies évoluent à partir du collapse gravitationnel des surdensités primordiales de l'univers très jeune; leurs mouvements créent un champ de déplacement à grande échelle. Une source majeure d'erreurs systématiques dans les simulations contraintes est produite si l'on ne tient pas compte de cet effet. Afin de dépasser cette limitation, nous avons développé la méthode de reconstruction par approximation inverse de Zeldovich (RZA). La RZA permet de reconstruire les déplacements et les positions initiales des galaxies observées et de générer une estimation significativement meilleure des conditions initiales de l'Univers Local. Cette méthode est intensivement testée sur des données de simulations. Nous étudions aussi l'influence de la qualité des données et de diverses erreurs observationnelles et/ou systématiques. Nous démontrons qu'avec la technique RZA, la qualité de la reconstruction des champs de densité et de vitesse est drastiquement améliorée. La position des objets dans les simulations contraintes évoluées sont retrouvées plus précisément et sur un plus grand intervalle de masses<br>Galaxy peculiar velocities provide valuable information about our motion with respect to theobserved large-scale structure and can be used to constrain the underlying dark matter distribution.Based on this approach, the technique of constrained realisations allows us to run numericalsimulations that resemble the observed Local Universe. This provides a powerful numerical laboratoryto study the dynamics, formation and evolution of structure in the Local Universe. Thecrucial step is to generate appropriate initial conditions from the observational data.We present here improvements on the technique of constrained simulations, along with anewly developed highly optimised numerical code that can handle the upcoming large observationaldatasets. Galaxies evolve from the gravitational collapse of primordial overdensities in theearly Universe; their motion leads to a large-scale displacement field. A major source of systematicerrors in constrained simulations arises by not accounting for this effect. To overcome thislimitation, we develop the Reverse Zeldovich Approximation (RZA) reconstruction method. TheRZA allows to reconstruct displacements and initial positions of observed galaxies and generatea significantly better estimate of the initial conditions of the Local Universe. This method isextensively tested on simulation data. We also study the influence of data quality and variousobservational and systematic errors. We show that with the RZA technique, the reconstructionquality of the density and velocity fields improves significantly. The positions of objects in theevolved constrained simulations are recovered more accurately and over a wider range of masses<br>Die Pekuliargeschwindigkeiten von Galaxien liefern wertvolle Informationen über ihre Bewegungrelativ zu den beobachteten großräumigen Strukturen und können verwendet werden, um diezugrundeliegende Verteilung der dunklen Materie abzuschätzen. Auf dieser Grundlage könnenmit der Methode der “Constrained Realisations” numerische Simulationen durchgeführt werden,die die Materieverteilung im Lokalen Universum widerspiegeln und somit leistungsfähige numerischeExperimente ermoeglichen, um die Dynamik, Entstehung und Evolution von Strukturenim lokalen Universum zu untersuchen. Eine wichtige Voraussetzung für diese Experimente ist es,korrekte Anfangsbedingungen aus den Beobachtungsdaten abzuleiten.In dieser Arbeit werden Verbesserungen der “Constrained Simulations”-Technik sowie ein fürdiesen Zweck neu entwickelter, hochgradig optimierter numerischer Code vorgestellt, welcheres ermöglicht, die kommenden, sehr umfangreichen Beobachtungsdaten zu verarbeiten. Galaxienentwickeln sich aus dem Gravitationskollaps von primordialen Überdichten im frühen Universum.Deren Bewegung führt zu einer großräumigen Dislokation, deren Vernachlässigung die größtesystematische Fehlerquelle für “Constrained Simulations” darstellt. An dieser Stelle knüpft dieReverse-Zeldovich-Näherung (RZA) an, die hier vorgestellt wird. Mithilfe der RZA können wirdiese Dislokation abschätzen und somit die ursprünglichen Positionen der beobachteten Galaxienrekonstruieren. Dadurch erhält man wesentlich genauere Anfangsbedingungen fuer die Entwicklungdes Lokalen Universums. Diese Methode wird ausführlich an Simulationsdaten getestet.Der Einfluß der Datenqualität und verschiedener Beobachtungs- und systematischer Fehler wirdeingehend untersucht. Die Rekonstruktionsgenauigkeit der Dichte- und Geschwindigkeitsfelderkann durch den Einsatz der RZA signifikant erhöht werden. In unseren Tests stimmen die Positionenvon Objekten in den mit RZA erzeugten “Constrained Simulations” wesentlich besser mitden ursprünglichen überein, als ohne die RZA, und das für einen deutlich größeren Bereich vonMassen
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Postlethwaite, Benjamin. "Seismic velocities and composition of the Canadian crust." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46687.
Full textAbstract:
It has been suggested that processes driving crustal formation in the Archean and Proterozoic
were dissimilar and produced crusts with unique bulk properties and average thicknesses.
The calibration of models based on evolving mantle fractionation or mantle convection style
require accurate estimates of the geological and geophysical properties of crustal provinces
to better constrain the details of crustal formation. Fifteen years of publicly accessible
teleseismic data from all available Canadian seismic stations are binned in horizontal slowness
and deconvolved into receiver functions. We apply a stacking method to retrieve estimates of
the bulk crustal velocity ratio V P /V S and thickness H from these data under the assumption
of locally 1-D structure. We also investigate modifications to this approach that can allow
discrimination of V S and V P under certain conditions. Bootstrap error analysis is performed
for each station dataset and subsets of these measurements are compared with results for
matching stations from previous studies. Analysis of results in conjunction with additional
velocity estimates from active source seismic studies and a seismic property database affords
improved constraints on bulk geological composition of the Canadian landmass that are used
to evaluate competing models of crustal formation.
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Brooks, S. G. "Seismic velocities from crustal sections in Northern Scandinavia." Thesis, University of East Anglia, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372358.
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Wittels, Kelsey Lynn. "Influence of extreme velocities on dynamic cavity expansion." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111533.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 35-36).<br>Cavitation can broadly be described as the unstable expansion of an empty void in a body, usually occurring when loads on the body reach a critical level. In this thesis, dynamic cavity expansion (DCE) in solids is of particular interest. Cavity expansion has been studied extensively under quasi-static and dynamic loading conditions. However, the behavior of cavitation fields with extreme dynamic expansion velocities have little been studied, especially in materials without a definite yield point. In this thesis, DCE in a hardening elastoplastic medium is considered under extreme velocities. Two nonlinear differential equations are used to describe the steady-state expansion. Using numerical integration, this system is solved to explore the behavior under extreme expansion velocities. By gradually increasing the expansion velocities, we find that a singularity occurs in the governing system, indicating a shock wave emerging and propagating through the material. With this limit velocity of the material known, further characteristics of the material can be described and investigated.<br>by Kelsey Lynn Wittels.<br>M. Eng.
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Leigh, Nathan D. "On the velocities of ions produced at surfaces /." free to MU campus, to others for purchase, 2001. http://wwwlib.umi.com/cr/mo/fullcit?p3012996.
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Morgan, Thomas. "Measurement of MAST edge ion temperatures and velocities." Thesis, University of York, 2011. http://etheses.whiterose.ac.uk/2098/.
Full textAbstract:
A novel experimental method using gas puffing of neutrals to stimulate charge exchange emission has been developed to measure ion temperatures and toroidal rotation velocities in the edge of MAST. This uses cold deuterium gas puffing as the source of neutrals in place of the more usual method of donation from neutral beams. A pre-existing spectroscopy system with 60 toroidal chords with spatial resolution of 1.5 mm and temporal resolution of 10 ms was adopted for this purpose. The C6+(n = 8 → 7) transition at 5290.5 A was identified as the optimal emission line, while a resonance in the cross section between the D0(n = 2) and C6+(n = 8) energy levels makes the measurement feasible. In order to assess the potential of this measurement method a model of the expected performance of the system was created. All important processes in the edge regime were identified and density profiles of electrons, carbon ions and deuterium neutrals were modelled. These were combined to produce a prediction of performance. The spectrum observed was complicated by molecular deuterium emission and a fitting routine to this complex data was developed and benchmarked. Correction factors were also identified and calculated for the emission line. System improvements were made including a new bandpass filter, gas valve and camera. Analysis of the measured intensity profiles showed a good response to gas puffing and toroidal velocity and ion temperature results are presented. A large reverse shear in the toroidal rotation is observed close to the separatrix in normal operation, but not in counter-rotation experiments. This is attributed to parallel Pfirsch-Schluter flow. The ion temperature results display a large difference between ion and electron temperature in the pedestal region in many H-mode discharges. This is linked to the collisionality of the ions such that flux surface coupling in the banana regime leads to small ion gradients.
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Zhu, Weijia. "A new instrumentation for particle velocity and velocity related measurements under water /." View online ; access limited to URI, 2006. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/fullcit/3239913.
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Beg, Sarena. "The determinants of velocity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20781.pdf.
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Saeed, Khizer. "Laminar burning velocity measurements." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270733.
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Kopp, Robert William. "Determination of the velocity." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25837.
Full textAbstract:
Hypervelocity flows for velocities is excess of 1.4 km/sec (Mach 5) require very high stagnation temperature to avoid liquefaction. The arc heater wind tunnel has been designed to provide such flows. The electric-are driven wind tunnel can develop stagnation temperatures up to 13,000 K which will produce hypervelocity flows up to 7 km/sec (earth orbital speed). The nature of the flow, however, is such that the high temperature source flow may cause severe gradients at the nozzle exit. In order to perform aero-thermodynamic tests the characterization of the flow in the test section is required. This paper experimentally determines the stream profiles for an arcjet wind tunnel conical nozzle directly from calorimetry and pitot probe surveys. Keywords: Arcjet flow; Hypervelocity flow; High enthalpy flow; Flow characteristics; Characteristic profile of the flow;
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Teng, Xiaoqing. "High velocity impact fracture." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32118.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Includes bibliographical references (p. 315-330).<br>An in-depth understanding of dynamic ductile fracture is one of the most important steps to improve the survivability of critical structures such as the lost Twin Towers. In the present thesis, the macroscopic fracture modes and the fracture mechanisms of ductile structural components under high velocity impact are investigated numerically and theoretically. Attention is focused on the formation and propagation of through-thickness cracks, which is difficult to experimentally track down using currently available instruments. Studied are three typical and challenging types of impact problems: (i) rigid mass-to beam impact, (ii) the Taylor test, and (iii) dynamic compression tests on an axisymmetric hat specimen. Using an existing finite element code (ABAQUS/Explicit) implemented with the newly developed Bao-Wierzbicki's (BW) fracture criterion, a number of distinct failure modes including fragmentation, shear plugging, tensile tearing in rigid mass-to-beam impact, confined fracture, petalling, and shear cracking in the Taylor test, are successfully recreated for the first time in the open literature. All of the present predictions are in qualitative agreement with experimental observations.<br>(cont.) This investigation convincingly demonstrates the applicability of the BW's fracture criterion to high velocity impact problems and at the same time provides an insight into deficiencies of existing fracture loci. Besides void growth, the adiabatic shear banding is another basic failure mechanism often encountered in high velocity impact. This failure mechanism and subsequent fracture is studied through numerical simulation of a recently conducted compression test on a hat specimen. The periodical occurrence of hot spots in the propagating adiabatic shear bands is successfully captured. The relation between hot spots and crack formation is revealed. The numerical predictions correlate well with experimental results. An explicit expression controlling through-thickness crack growth is proposed and verified by performing an extensive parametric study in a wide range of input variables. Using this expression, a two-stage analytical model is formulated for shear plugging of a beam/plate impacted by a flat-nosed projectile. Obtained theoretical solutions are compared with experimental results published in the literature showing very good agreement.<br>(cont.) Three theoretical models for rigid mass-to-beam impact, the single, double, and multiple impact of beam-to-beam are derived from the momentum conservation principle. The obtained closed-form solutions, which are applicable to the axial stretching dominated case, are validated by finite element analysis.<br>by Xiaoqing Teng.<br>Ph.D.
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Johansson, Torneus Daniel, and Alexander Kotoglou. "Velocity of plasma flow." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199363.
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Stober, Gunter, and Christoph Jacobi. "Meteor head velocity determination." Universität Leipzig, 2007. https://ul.qucosa.de/id/qucosa%3A15571.
Full textAbstract:
Meteore, die in die Atmosphäre eindringen, bilden bei hohen Oberflächentemperaturen, die durch Kollisionen mit der umgebenden Luft hervorgerufen werden, einen mehrere Kilometer langen Plasmaschweif aus. An diesem Schweif werden ausgesandte Radarwellen reflektiert und zurückgestreut. Dies führt zu einem charakteristischen Schwingungsverhalten, auch Fresnel Zonen genannt, am Empfänger. Die Überlagerung dieser Wellen ist verantwortlich für die typische Signalform eines Meteors, mit dem abrupten Anstieg und dem exponentiellen Abfall für \'underdense\' Meteore. Mit Hilfe einer Simulation wird der theoretische Zusammenhang zwischen Geschwindigkeit und Signalverlauf demonstriert. Des weiteren wird gezeigt, das die Methode von Baggaley et al. [1997] zur Bestimmung von Meteoreintrittsgeschwindigkeiten auch auf ein Radarinterferometer (SKiYMET) anwendbar ist. Abschliessend werden die gewonnen Ergebnisse mit einem anderen Verfahren sowie der Literatur verglichen.<br>Meteors, penetrating the earths atmosphere, creating at high surface temperatures, which are caused by collisions with the surrounding air molecules, a several kilometer long plasma trail. The ionized plasma backscatters transmitted radar waves. This leads to characteristic oscillations, called Fresnel zones, at the receiver. The interference of these waves entails the typical signal shape of a underdense meteor with the sudden rise of the signal and the exponential decay. By means of a simulation the theoretical connection between velocity and signal shape is demonstrated. Furthermore it is presented, that the method from Baggaley et al. [1997] for determination of meteor entry velocities is applicable for a radar interferometer (SKiYMET). Finally the results are compared to other radar methods on similar equipment and to other experiments.
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Stober, Gunter, and Christoph Jacobi. "Meteor head velocity determination." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-223206.
Full textAbstract:
Meteore, die in die Atmosphäre eindringen, bilden bei hohen Oberflächentemperaturen, die durch Kollisionen mit der umgebenden Luft hervorgerufen werden, einen mehrere Kilometer langen Plasmaschweif aus. An diesem Schweif werden ausgesandte Radarwellen reflektiert und zurückgestreut. Dies führt zu einem charakteristischen Schwingungsverhalten, auch Fresnel Zonen genannt, am Empfänger. Die Überlagerung dieser Wellen ist verantwortlich für die typische Signalform eines Meteors, mit dem abrupten Anstieg und dem exponentiellen Abfall für \"underdense\" Meteore. Mit Hilfe einer Simulation wird der theoretische Zusammenhang zwischen Geschwindigkeit und Signalverlauf demonstriert. Des weiteren wird gezeigt, das die Methode von Baggaley et al. [1997] zur Bestimmung von Meteoreintrittsgeschwindigkeiten auch auf ein Radarinterferometer (SKiYMET) anwendbar ist. Abschliessend werden die gewonnen Ergebnisse mit einem anderen Verfahren sowie der Literatur verglichen<br>Meteors, penetrating the earths atmosphere, creating at high surface temperatures, which are caused by collisions with the surrounding air molecules, a several kilometer long plasma trail. The ionized plasma backscatters transmitted radar waves. This leads to characteristic oscillations, called Fresnel zones, at the receiver. The interference of these waves entails the typical signal shape of a underdense meteor with the sudden rise of the signal and the exponential decay. By means of a simulation the theoretical connection between velocity and signal shape is demonstrated. Furthermore it is presented, that the method from Baggaley et al. [1997] for determination of meteor entry velocities is applicable for a radar interferometer (SKiYMET). Finally the results are compared to other radar methods on similar equipment and to other experiments
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Hu, Yezheng. "Internal velocity estimation in laterally inhomogeneous areas by deconvolution of stacking velocity profiles." Thesis, University of London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296900.
Full textAbstract:
The problem of inferring the velocity field is central to exploration seismology. Conventional velocity analysis is based on the hypothesis that reflection traveltime is a hyperbolic function of the distance between the source and the receiver. This is basis upon which interval velocities are obtained using Dix's equation for a horizontally layered model and Shah's equation for a dipping layered structure. However, in laterally inhomogeneous areas, traveltimes do not follow hyperbolae, hence, hyperbola based velocity estimation techniques fail in such areas. Although many sophisticated techniques, such as tomography, migration and model based velocity analysis can be used to obtain accurate velocity fields from seismic data in such areas, these methods are very computationally expensive. In this thesis, a simple, quicker and accurate velocity estimation technique is proposed. This technique does not abandon conventional velocity analysis, but gives further processing to stacking velocity data provided by conventional techniques. The new technique is based on the hypothesis that stacking slowness variations due to lateral interval slowness anomalies can be represented by the outputs of a linear impulse response system. The inputs of the system are the interval slowness anomalies. The system is space invariant for a horizontally layered model, but is space variant for a dipping layered model. A pre-determined background model is required to compute the linear system. Since the linear system is space invariant for a horizontally layered model and space variant for a dipping layered model, there are two schemes for velocity estimation for these two cases. In horizontal geology, the relationship between stacking slowness variations and interval slowness anomalies can be expressed by a set of linear equations in the wavenumber domain. The singular value decomposition method is used to solve the set of linear equations to obtain interval slowness anomalies from stacking slowness variations. In dipping geology, the relationship between stacking slowness variations and interval slowness anomalies cannot be written as a set of linear equations in the wavenumber domain. Interval slownesses must in this case be derived in the least square sense. Basis functions are introduced to construct interval slowness anomalies. Once the interval slowness anomalies have been estimated, interval slownesses (and hence velocities) are obtained by adding these to the background interval slownesses. Finally, the sensitivity of the linear system to data errors and model errors is investigated through a series of synthetic examples, the applications of these velocity estimation techniques and suggestions for further studies of the linear system are discussed
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Håkman, Olof. "Boltzmann Equation and Discrete Velocity Models : A discrete velocity model for polyatomic molecules." Thesis, Karlstads universitet, Institutionen för matematik och datavetenskap (from 2013), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-76143.
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In the study of kinetic theory and especially in the study of rarefied gas dynamics one often turns to the Boltzmann equation. The mathematical theory developed by Ludwig Boltzmann was at first sight applicable in aerospace engineering and fluid mechanics. As of today, the methods in kinetic theory are extended to other fields, for instance, molecular biology and socioeconomics, which makes the need of finding efficient solution methods still important. In this thesis, we study the underlying theory of the continuous and discrete Boltzmann equation for monatomic gases. We extend the theory where needed, such that, we cover the case of colliding molecules that possess different levels of internal energy. Mainly, we discuss discrete velocity models and present explicit calculations for a model of a gas consisting of polyatomic molecules modelled with two levels of internal energy.<br>I studiet av kinetisk teori och speciellt i studiet av dynamik för tunna gaser vänder man sig ofta till Boltzmannekvationen. Den matematiska teorien utvecklad av Ludwig Boltzmann var vid första anblicken tillämpbar i flyg- och rymdteknik och strömningsmekanik. Idag generaliseras metoder i kinetisk teori till andra områden, till exempel inom molekylärbiologi och socioekonomi, vilket gör att vi har ett fortsatt behov av att finna effektiva lösningsmetoder. Vi studerar i denna uppsats den underliggande teorin av den kontinuerliga och diskreta Boltzmannekvationen för monatomiska gaser. Vi utvidgar teorin där det behövs för att täcka fallet då kolliderande molekyler innehar olika nivåer av intern energi. Vi diskuterar huvudsakligen diskreta hastighetsmodeller och presenterar explicita beräkningar för en modell av en gas bestående av polyatomiska molekyler modellerad med två lägen av intern energi.
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Duffaut, Kenneth. "Stress sensitivity of elastic wave velocities in granular media." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for petroleumsteknologi og anvendt geofysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16174.
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Knowledge of the stress sensitivity of elastic-wave velocities in sedimentary rocks with different consolidation is important for several geophysical applications such as seismic pore pressure prediction, time-lapse seismic analysis and not least in seismic exploration. Since clays or shales are more compactable than sand or sandstones they often experience large plastic deformation causing both clay platelet orientation and porosity reduction of the order of 50% or more. The interplay between stress and porosity effects may mask the stress sensitivity of velocities in clays or shales. The porosity loss occurring in sandstones during mechanical compaction is generally slower and hence the stressinduced velocity changes are better preserved at least prior to the onset of grain cementation. Small amounts of contact cement, 1 to 2% of the total rock volume, can have a dramatic effect on velocities and their corresponding stress dependence. We demonstrate this reduction in stress sensitivity of elastic-wave velocity between sandstones of different consolidation through comparison of rock physics contact model-predictions of compressional to shear velocity ratio (Vp/Vs), with similar estimates obtained from time-lapse seismic amplitude versus offset (AVO) data from two oil producing fields. Furthermore, modified contact models are proposed to investigate the role of the combined effects of intergrain contact friction, increasing differential stress and stress ratio in relation to the propagation direction of the elasticwaves in granular media. Model-predictions are compared with ultrasonic measurements obtained from experimental compression tests on unconsolidated sands.
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Baggley, Glenn. "Peculiar velocities of clusters determined from early-type galaxies." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360018.
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Al-Barwani, Hamdi. "Propagation of fronts with gradient and curvature dependent velocities." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/10341.
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The thesis considers and examines methods of surface propagation, where the normal velocity of the surface depends on the local curvature and the gradient of the surface. Such fronts occur in many different physical situations from the growth of crystals to the spreading of flames. A number of different methods are considered to find solutions to these physical problems. First the motion is modelled by partial differential equations and numerical methods are developed for solving these equations. The numerical methods involve characteristic, finite differences and transformation of the equations. Stability of the solutions is also briefly considered. Secondly the fronts are modelled by using a cellular approach which subdivides space into regions of small cells. The fronts are assumed to propagate through the region according to stochastic rules. Monte-Carlo simulations are carried out using this approach. Results of the simulations are carried out in two-dimensions and three-dimensions for a number of interesting physical examples.
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Totterdell, Ian John. "Lower-crustal velocities from long-offset seismic reflection data." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259655.
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Prosper, David 1970. "Automated detection of wave velocities in concrete bridge decks." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/46142.
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Ridler, Emma Louise. "Wave-current interactions and drift velocities over rippled beds." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624706.
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Чужа, Олексій Олександрович, Ганна Андріївна Положевець, and Донченко І. "INFORMATIONAL SERVICES FOR CREW ABOUT MINIMAL CRITICAL FLIGHT VELOCITIES." Thesis, Національний авіаційний університет, 2014. http://er.nau.edu.ua/handle/NAU/11067.
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For determining of approaching of critical flight modes, warning systems are installed. However, signalizing about minimal indicated speed is neglected, it is controlled by auto throttle. Therefore, it is necessary to include Informational services for crew about minimal critical flight velocities into warning system.
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Kotani, Yosuke. "Factors related to creating force-velocity and load-velocity profiles with the squat jump." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2021. https://ro.ecu.edu.au/theses/2487.
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It is well recognized that the ability to rapidly generate high levels of force is an important factor underpinning vertical jump performance. Recently, it has become popular to use forcevelocity (FV) and load-velocity (LV) profiles created from progressively loaded squat jumps (SJs) to guide the resistance training process. By creating FV profiles, the coach can determine if the athlete has a force or velocity deficit and then create an individualized training program based upon the determined deficit. Alternatively, the LV profile can be used to monitor performance and as a method for prescribing training load. While several recent studies have explored the efficacy of the use of training methods based on the FV or LV profile, there is limited research examining the various methodologies and technologies that are commonly used to create these profiles with SJs. Therefore, the primary purpose of this thesis project was to investigate the reliability and validity of various methods for assessing the FV and LV profile during the SJ. In Study 1, progressively loaded SJs were performed on a force plate in order to determine the overall reliability of the FV and LV profiles. After this was completed, Study 2 was used to compare three methods of determining the FV and LV profiles. Specifically, the FV and LV profiles created from data collected with the PUSH BandTM 2.0 (PUSH) and GymAware (GYM) were compared with the profiles created from data collected with a force plate in order to determine if the velocities determined with these methods agreed. In Study 3, the FV and LV profiles created with two accelerometers (Bar Sensei [BS] and Beast Sensor [BEAST]) were compared with a laboratory based four-linear position transducer system (4- LPT) in order to determine if the velocities measured with these devices agreed and were reliable. In Study 4, the mode of exercise (free-weight or Smith Machine) was compared to determine if there was agreement between the FV and LV profiles created with each mode. Finally, in Study 5, SJs that were performed with free-weights and the Smith Machine were compared in order to determine if there was agreement between the FV and LV profiles created with a force plate, the PUSH, and GYM. The primary finding of this thesis was that the FV and LV profiles created from SJs with a force plate were unreliable regardless of which mode of exercise was utilized. Additionally, the PV quantified with the GYM agreed with the PV determined with the force plate regardless of whether the SJ was performed with free-weights or a Smith Machine. Conversely, the PV determined with the PUSH did not agree with the force plate regardless of which mode of exercise was performed. Finally, the PVs determined with the BEAST agreed with the 4-LPT system, whilst the BS did not. Based upon these findings, it is important that coaches are aware that there is a lack of reliability with these profiles and that velocities measured by different devices do not always agree.
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Törnquist, Martin. "Investigation of rotational velocity sensors." Thesis, Linköping University, Department of Electrical Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15904.
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<p><p>To improve the speed measurement of construction equipment, different sensor technologies have been investigated. Many of these sensor technologies are very interesting but to keep the extent of the thesis only two was chosen for testing, magnetic absolute angle sensors using Hall and GMR technology, to investigate if those are a valid replacement for the current measurement system that is using a passive sensor. Tests show that these sensors are capable of speed measurement, but because of noisy angle estimates they need filtering for good speed computation. This filtering introduces a large time delay that is of significance for the quality of the estimate. A Kalman filter has been implemented in an attempt to lower the time delays but since only a very simple model has been used it does not give any improvements over ordinary low pass filtering. For these sensors the mounting tolerance is of great interest. For best performance the offset between the sensor and magnet centres need to be kept small for both sensors. This is due to a non-linearity effect this causes. The distance between the sensors and the magnet is not critical for linearity issues, but only for the quality of the signal, where it might drop out when the distance is too large. This is where the sensor using GMR technology stands out. Compared to the Hall technology sensor, the GMR sensor can handle distances that are more than 10 times larger. The conclusion is that these sensors can be a valid replacement of the current measurement system. They will introduce more functionality with the capability of detecting rotational direction and zero velocity. In an application with more than one sensor they can also be used for more purposes, like detecting slip in clutches etc. Depending on the application, the time delays may not be critical, else more work need to be done to improve the estimate, e.g. with a more advanced model for the Kalman filter.</p></p><p> </p>
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Brown, Ian David. "The velocity of molecular clouds." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293612.
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