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Darling, Samantha. "Velocity Variations of the Kaskawulsh Glacier, Yukon Territory, 2009-2011." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23511.
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Laser altimetry and satellite gravity surveys indicate that the St Elias Icefields are currently losing mass and are among the largest non-polar sea level contributors in the world. However, a poor understanding of glacier dynamics in the region is a major hurdle in evaluating regional variations in ice motion and the relationship between changing surface conditions and ice flux. This study combines in-situ dGPS measurements and advanced Radarsat-2 (RS-2) processing techniques to determine daily and seasonal ice velocities for the Kaskawulsh Glacier from summer 2009 to summer 2011. Three permanent dGPS stations were installed along the centreline of the glacier in 2009, with an additional permanent station on the South Arm in 2010. The Precise Point Positioning (PPP) method is used to process the dGPS data using high accuracy orbital reconstruction. RS-2 imagery was acquired on a 24-day cycle from January to March 2010, and from October to March 2010-2011 in a combination of ultra-fine and fine beam modes.
Seasonal velocity regimes are readily identifiable in the dGPS results, with distinct variations in both horizontal velocity and vertical motion. The Spring Regime consists of an annual peak in horizontal velocity that corresponds closely with the onset of the melt season and progresses up-glacier, following the onset of melt at each station. The Summer Regime sees variable horizontal velocity and vertical uplift, superimposed on a long-term decline in motion. The Fall Regime sees a gradual slowing at all stations with little variation in horizontal velocity or vertical position. Rapid but short accelerations lasting up to 10 days were seen in the Winter regimes in both 2010 and 2011, occurring at various times throughout each regime. These events initiated at the Upper Station and progress down-glacier at propagation speeds up to 16,380 m day-1 and were accompanied by vertical uplift lasting for similar periods. Three velocity maps, one from the winter of 2010 and two from the fall/winter of 2011, produced from speckle tracking were validated by comparison with dGPS velocity, surface flow direction, and bedrock areas of zero motion, with an average velocity error of 2.0% and average difference in orientation of 4.3º.
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Unwin, Beverley Victoria. "Arctic ice cap velocity variations revealed using ERS SAR interferometry." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287749.
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This thesis will examine the velocity structure of Austfonna, a large ice cap in the Svalbard archipelago. The remoteness of its location had previously hindered detailed observation by traditional methods, but indirect evidence suggested that it had the potential to be dynamically interesting. A recently developed remote sensing technique, SAR interferometry (inSAR), has allowed us to obtain the most detailed map of Austfonna's topography to date, plus unprecedented synoptic measurements of its velocity field. A four year time series of data acquired by the European Remote Sensing satellites ERS-1 and ERS-2 has been used to delineate active and inactive areas of the ice cap, which suggest that past ideas about Austfonna's thermal structure may need to be re-examined. It has also revealed large temporal velocity variations in one of its major drainage basins. These are difficult to classify because intermittent sampling has prevented us from determining their temporal wavelength, and also because globally the database of observed glacier velocity variations is so sparse that the range of possible variable flow scenarios is unknown. The work here demonstrates the huge potential for inSAR in helping to resolve such issues, and in providing an invaluable resource for scientists monitoring the stability of the world's ice fields.
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Smith, Saskia. "Seismic wave phase-velocity variations in the state of Ohio /." Connect to resource, 2010. http://hdl.handle.net/1811/45057.
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Bertrand, Alexandre. "The impact of seawater velocity variations on time-lapse seismic monitoring." Thesis, Heriot-Watt University, 2005. http://hdl.handle.net/10399/274.
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Tziranis, Alexander Konstantinos 1968. "Temperature, heat flux, and velocity measurements in oscillating flows with pressure variations." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12790.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1992.Vita.
Includes bibliographical references (leaves 99-101).
by Alexander Konstantinos Tziranis.
M.S.
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Ghaychi, Afrouz Setareh. "Seismic Wave Velocity Variations in Deep Hard Rock Underground Mines by Passive Seismic Tomography." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97890.
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Mining engineers are tasked with ensuring that underground mining operations be both safe and efficiently productive. Induced stress in deep mines has a significant role in the stability of the underground mines and hence the safety of the mining workplace because the behavior of the rock mass associated with mining-induced seismicity is poorly-understood. Passive seismic tomography is a tool with which the performance of a rock mass can be monitored in a timely manner. Using the tool of passive seismic tomography, the advance rate of operation and mining designs can be updated considering the induced stress level in the abutting rock. Most of our current understanding of rock mass behavior associated with mining-induced seismicity comes from numerical modeling and a limited set of case studies. Therefore, it is critical to continuously monitor the rock mass performance under induced stress. Underground stress changes directly influence the seismic wave velocity of the rock mass, which can be measured by passive seismic tomography. The precise rock mass seismicity can be modeled based on the data recorded by seismic sensors such as geophones of an in-mine microseismic system. The seismic velocity of rock mass, which refers to the propagated P-wave velocity, varies associated with the occurrence of major seismic events (defined as having a local moment magnitude between 2 to 4). Seismic velocity changes in affected areas can be measured before and after a major seismic event in order to determine the highly stressed zones. This study evaluates the seismic velocity trends associated with five major seismic events with moment magnitude of 1.4 at a deep narrow-vein mine in order to recognize reasonable patterns correlated to induced stress redistribution. This pattern may allow recognizing areas and times which are prone to occurrence of a major seismic event and helpful in taking appropriate actions in order to mitigate the risk such as evacuation of the area in abrupt cases and changing the aggressive mine plans in gradual cases. In other words, the high stress zones can be distinguished at their early stage and correspondingly optimizing the mining practices to prevent progression of high stress zones which can be ended to a rock failure. For this purpose a block cave mine was synthetically modeled and numerically analyzed in order to evaluate the capability of the passive seismic tomography in determining the induced stress changes through seismic velocity measurement in block cave mines. Next the same method is used for a narrow vein mine as a case study to determine the velocity patterns corresponding to each major seismic event.Doctor of Philosophy
Mining activities unbalance the stress distribution underground, which is called mining induced stress. The stability of the underground mines is jeopardized due to accumulation of induced stress thus it is critical for the safety of the miners to prevent excessive induced stress accumulation. Hence it is important to continuously monitor the rock mass performance under the induced stress which can form cracks or slide along the existing discontinuities in rock mass. Cracking or sliding releases energy as the source of the seismic wave propagation in underground rocks, known as a seismic event. The velocity of seismic wave propagation can be recorded and monitored by installing seismic sensors such as geophones underground. The seismic events are similar to earthquakes but on a much smaller scale. The strength of seismic events is measured on a scale of moment magnitude. The strongest earthquakes in the world are around magnitude 9, most destructive earthquakes are magnitude 7 or higher, and earthquakes below magnitude 5 generally do not cause significant damage. The moment magnitude of mining induced seismic events is typically less than 3. In order to monitor mining induced stress variations, the propagated seismic wave velocity in rock mass is measured by a series of mathematical computations on recorded seismic waves called passive seismic tomography, which is similar to the medical CT-scan machine. Seismic wave velocity is like the velocity of the vibrating particles of rock due to the released energy from a seismic event. This study proposes to investigate trends of seismic velocity variations before and after each seismic event. The areas which are highly stressed have higher seismic velocities compared to the average seismic velocity of the entire area. Therefore, early recognition of highly stressed zones, based on the seismic velocity amount prior the occurrence of major seismic events, will be helpful to apply optimization of mining practices to prevent progression of high stress zones which can be ended to rock failures. For this purpose, time-dependent seismic velocity of a synthetic mine was compared to its stress numerically. Then, the seismic data of a narrow vein mine is evaluated to determine the seismic velocity trends prior to the occurrence of at least five major seismic events as the case study.
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Bastien, Fabienne Anne. "Empirically Interrelating Stellar Chromospheric Activity, Photometric Variability and Radial Velocity Variations to Enhance Planet Discovery." Thesis, Vanderbilt University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3584409.
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H, Purdie. "Intra-annual variations in abaltion and surface velocity on the lower Fox Glacier, South Westland, New Zealand." Thesis, University of Canterbury. Geography, 2005. http://hdl.handle.net/10092/10451.
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Magoba, Moses. "Investigation of the acoustic impedance variations of the upper shallow marine sandstone reservoirs in the Bredasdorp basin, offshore South Africa." University of the Western Cape, 2019. http://hdl.handle.net/11394/7028.
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Philosophiae Doctor - PhDInvestigation of the acoustic impedance variations in the upper shallow marine sandstone reservoirs was extensively studied from 10 selected wells, namely: F-O1, F-O2, E-M4, E-CN1, E-G1, E-W1, F-A10, F-A11, F-A13, and F-L1 in the Bredasdorp Basin, offshore, South Africa. The studied wells were selected randomly across the upper shallow marine interval with the purpose of conducting a regional study to assess the variations in the acoustic impedance across the reservoirs using wireline log and core data. The datasets used in this study were geophysical wireline logs, conventional core analysis, geological well completion reports, core plugs, and core samples. The physical rock properties such as lithology, fluid type, and hydrocarbon bearing zone were identified while different parameters like the volume of clay, porosity, and water saturation were quantitatively estimated. The reservoirs were penetrated at a different depth ranging from a shallow depth of 2442m at well F-L1 to a deeper depth of 4256.7m at well E-CN1. The average volume of clay, average effective porosity from wireline log, and average water saturation ranged from 8.6%- 43%, 9%- 16% and 12%- 68%, respectively. Porosity distribution was fairly equal across the field from east to west except in well F-A10, F-A13, and F-A11 where a much higher porosity was shown with F-A13 showing the highest average value of 16%. Wells E-CN1, E-W1, F-O1, F-L1 and E-G1 had lower porosity with E-CN1 showing the lowest average value of 9%. The acoustic properties of the reservoirs were determined from geophysical wireline logs in order to calculate acoustic impedance and also investigate factors controlling density and acoustic velocities of these sediments. The acoustic impedance proved to be highest on the central to the western side of the field at E-CN1 with an average value of 11832 g/cm3s whereas, well F-A13 reservoir in the eastern side of the field proved to have the lowest average acoustic impedance of 9821 g/cm3s. There was a good linear negative relationship between acoustic impedance and porosity, compressional velocity vs porosity and porosity vs bulk density. A good linear negative relationship between acoustic impedance and porosity was obtained where the reservoir was homogenous, thick sandstone. However, interbedded shale units within the reservoir appeared to hinder a reliable correlation between acoustic impedance and porosity. The cross-plots results showed that porosity was one of the major factors controlling bulk density, compressional velocity (Vp) and acoustic impedance. The Gassmann equation was used for the determination of the effects of fluid substitution on acoustic properties using rock frame properties. Three fluid substitution models (brine, oil, and gas) were determined for pure sandstones and were used to measure the behaviour of the different sandstone saturations. A significant decrease was observed in Vp when the initial water saturation was substituted with a hydrocarbon (oil or gas) in all the wells. The value of density decreased quite visibly in all the wells when the brine (100% water saturation) was substituted with gas or oil. The fluid substitution affected the rock property significantly. The Vp slightly decreases when brine was substituted with water in wells F-A13, F-A10, F-O2, F-O1 F-A11, F-L1, and E-CN1. Wells E-G1, E-W1, and E-M4 contain oil and gas and therefore showed a notable decrease from brine to oil and from oil to gas respectively. Shear velocity (Vs) remained unaffected in all the wells. The acoustic impedance logs showed a decrease when 100% water saturation was replaced with a hydrocarbon (oil or gas) in all the wells. Clay presence significantly affects the behaviour of the acoustic properties of the reservoir rocks as a function of mineral type, volume, and distribution. The presence of glauconite mineral was observed in all the wells. Thirty-two thin sections, XRD and SEM/EDS from eight out of ten wells were studied to investigate lithology, diagenesis and the effect of mineralogy on porosity and acoustic properties (Compressional velocity and bulk density) within the studied reservoir units. Cementation (calcite and quartz), dissolution, compaction, clay mineral authigenesis, and stylolitization were the most significant diagenetic processes affecting porosity, velocity, and density.Well E-CN1 reservoir quality was very poor due to the destruction of intergranular porosity by extensive quartz and illite cementation, and compaction whereas well F-A13 show a highly porous sandstone reservoir with rounded monocrystalline quartz grain and only clusters of elongate to disc-like, authigenic chlorite crystals partly filling a depression within altered detrital grains. Overall, the results show that the porosity, lithology mineralogy, compaction and pore fluid were the major factors causing the acoustic impedance variations in the upper shallow marine sandstone reservoirs.
2021-09-01
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Balise, Michael John. "The relation between surface and basal velocity variations in glacier, with application to the mini-surges of variegated glacier /." Thesis, Connect to this title online; UW restricted, 1988. http://hdl.handle.net/1773/6846.
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Raub, Christina [Verfasser]. "Characterizing Near-Surface Velocity and Attenuation Structures and Evaluating Spatiotemporal b-Value Variations in the Marmara Sea Region / Christina Raub." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1133074723/34.
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Fallahi, Mohammad Javad. "Surface wave tomography and monitoring of time variations with ambient noise in NW-Bohemia/Vogtland." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-191196.
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In this study, ambient noise wavefield was used for the first time to image spatial and temporal upper crustal seismic structures in NW-Bohemia/Vogtland region. The data come from 111 stations and were collected from continuous recordings of the permanent station networks of Germany and Czech Academy of Sciences as well as temporary stations of the BOHEMA and PASSEQ experiments. Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions between 0.1 and 1 Hz, and are tomographically inverted to provide 2-D group velocity maps. At shorter periods Rayleigh wave group velocity maps are in good agreement with surface geology where low velocity anomalies appear along Mariánské Lázně Fault and Eger rift. A low velocity zone is observed at the northern edge of Mariánské Lázně Fault which shifts slightly to the south with increasing period and correlates well with the main focal zone of the earthquake swarms at 5 s period. We invert the 2-D group velocity maps into a 3-D shear wave velocity model. In this step Love waves were excluded from further analysis because of their high level of misfit to modelled dispersion curves. Horizontal and vertical sections through the model reveal a clear low velocity zone above the Nový Kostel seismic focal zone which narrows towards the top of the seismic activity and ends above the shallowest hypocenters at 7 km depth.
We investigate temporal variation of seismic velocity within and around the Nový Kostel associated with 2008 and 2011 earthquake swarms by employing Passive Image Interferometry method using 7 continuous seismograms recorded by the WEBNET network. The results reveals stable seismic velocities without a clear post seismic velocity change during earthquake swarms in the Nový Kostel area.
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Jonsdottir, Frida. "Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619.
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Relative seismic velocity variations in the Earth’s crust can be estimated by using ambient seismic noise records from a pair of stations. Velocity variations can be caused by stress perturbations in the subsurface. Therefore, information on stress changes in the crust can possibly be retrieved from measured velocity variations in the medium. The measurement is done by comparing the coda part of two cross-correlation functions (CCFs) obtained from ambient noise recordings at two seismic stations; a current CCF that is considered to represent the actual state in the study medium at a specific time and a reference CCF that is considered to represent its average state. Here, the method is applied to the area around Katla volcano in southern Iceland. Katla is an active subglacial volcano and therefore frequent stress changes can be expected to take place there. Long-term changes (of the order of 1-2 months) in relative seismic velocity were estimated over a period of 7 months in 2011. These changes were of the order of about 0.1% for a frequency range of 0.2-1.0 Hz. For this frequency range, surface waves around Katla have been estimated to be most sensitive to velocity changes taking place at depths of about 1-5 km but the sensitivity kernels also have a peak at the surface. The scattering volume (in this case area since we are working with surface waves) depends on both the inter-station distance and how far into the coda the measurements are made. The inter-station distances vary between 5.8 and 23.4 km. Measurements are made 30 s into the coda. This results in scattering areas on the order of 100 km2. The velocity variations have a negative trend over July and over a two month period from the end of August until early November, and a positive trend in August and from early November until the end of the study period in late December. These variations are possibly the results of a combination of changes in the ground water level beneath the glacier, surface load changes and possibly hydrothermal and magmatic pressurization changes. No significant velocity change was estimated in the area associated with the tremor event that took place in early July in 2011.Seismiska vågor är vibrationer i jordytan som genereras av jordbävningar, explosioner eller andra processer som skakar jorden. Seismiska vågor färdas genom jordens lager och innehåller därför information om jordens inre struktur. Dessa vibrationer kan hämtas med ett känsligt instrument som kallas seismometer. Seismiska vågor färdas med en viss hastighet som beror på hur hård och tung berggrunden är. Förändringar av dessa egenskaper kan därför resultera i förändringar av hastigheten. Dessa förändringar kan orsakas av spänningsförändringar under marken, till exempel trycket i porer eller variationer i vikten ovanför marken, exempelvis från en glaciär. I denna uppsats studeras förändringar av seismiska vågors hastighet kring vulkanen Katla på Island under 7 månader, 2011. Katla är en av Islands mest aktiva vulkaner och är belägen under en glaciär, Mýrdalsjökull. Detta görs genom att använda omgivande seismiskt brus, som består av seismiska vågor. Bruset genereras av tryckvariationer i samband med havsvågor. Bruset analyseras med en korrelationsanalys som bland annat isolerar spridda vågor från detaljer i strukturen och variationer av dessa med tid kan användas til mätningar av hastighets förändringar. Resultaten tyder på förändringar i relativ seismik hastighet avstorleken 0.1% som varar i en till två månader. Hastigheten minskar i juli och över en tvåmånadersperiod från slutet av augusti till början av november, men ökar i augusti och från början av november till slutet av december. Dessa variationer kan ha orsakats av en kombination av förändringar i grundvattennivån under glaciären, förändringar i glaciärens vikt och magmatiska processer. Inga tydliga förändringar i samband med sekvenser av små jordbävningar som ägde rum i början av juli 2011 kunde observeras frånförändringar i relativ seismisk hastighet runt Katla.
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Olivier, Gerrit. "Seismic imaging and monitoring in mines with ambient seismic noise correlations." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAU018/document.
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Cette thèse s'intéresse au développement des méthodes d'auscultation sismique passive pour l'imagerie et la surveillance des mines profondes. Les résultats marquants sont 1/ la possibilité d'imager en profondeur les structures géologiques d'intérêt et 2/ la possibilité de suivre dans le temps les propriétés mécaniques des roches qui subissent les sollicitation associés à l'exploitation minière. Ce travail ouvre des perspectives quant à l'amélioration de la sécurité dans les mines profondesThis work focus on using passive noise-based seismic methods to image and monitor the rock mass in underground mines. The main results show that it is possible to gain benefit from the diffuse ambient seismic field in mines to 1/ image the rock mass and 2/ monitor its mechanical property changes over time. This work opens a way to improve safety in deep underground mines
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Clarke, Daniel. "The measurement of temporal seismic velocity variations on Piton de la Fournaise volcano, La Réunion, from cross-correlations of mbient seismic noise." Paris, Institut de physique du globe, 2011. http://www.theses.fr/2011GLOB0010.
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Ravenna, Matteo. "A reversible jump markov chain Monte Carlo inversion method for layering and amplitude of seismic velocity variations : an application to 1-D structure of the lower mantle." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510764.
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Propes, Russell Lee. "Crustal velocity variation in the southern Appalachians." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/25744.
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Bezodis, Ian Nicholas. "Biomechanical performance variation in maximum velocity sprinting." Thesis, University of Bath, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432390.
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Cros, Estelle. "Etude de la dynamique du Geyser Old Faithful, USA, à partir de méthodes de sismique passive." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00765878.
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Le geyser d'Old Faithful dans le Parc National de Yellowstone, aux États-Unis, est l'undes geysers les plus connus au monde. La cyclicité de ses éruptions est étudiée depuis lesannées 60 a_n de comprendre sa dynamique. En e_et, le caractère bimodal de la fréquencede ses éruptions intriguent les scienti_ques qui cherchent à en connaître les causes.Les enregistrements sismiques réalisés à la surface du geyser démontrent des signauximpulsionnels dont l'origine fut identi_ée par Sharon Kedar. Ainsi, en 1992, S. Kedar etses collègues ont déployé plusieurs capteurs sismiques dans le but d'étudier la source dessignaux sismiques de type tremor enregistrés à la surface du dôme. Ils ont ainsi identi_éla source du signal sismique enregistré à la surface du geyser comme étant des signauxde cavitation de bulles. La cavitation se produisant à la surface du niveau de l'eau dansle conduit, les localisations des sources sismiques réalisées à partir des enregistrements desurface peuvent être reliées au niveau de l'eau dans le conduit.Dans un premier temps nous avons proposé de localiser les sources sismiques desenregistrements à partir de la méthode du Matched Field Processing (MFP) provenantde l'acoustique sous-marine. Plusieurs algorithmes du MFP ont été testés pour pouvoirlocaliser au mieux les sources sismiques. La bonne concordance des résultats obtenus avecchacun des algorithmes a permis d'obtenir un grand nombre de localisations des sourcesau cours du cycle. Les positions déterminées avec les di_érents algorithmes du MFP ontpermis de mettre en évidence deux zones d'activité hydrothermale du geyser associéesà di_érentes périodes du cycle éruptif, telles que le remplissage du conduit avant leséruptions et l'alimentation du geyser en eau une fois la vidange du conduit e_ectuée.Dans un second temps, l'analyse des variations de vitesse des signaux sismiques estproposée pour suivre des changements des propriétés du dôme du geyser, comme des variationsde pression avant l'éruption. Pour cela, une nouvelle méthode basée sur les mesuresde phases instantanées est suggérée. Les résultats obtenus montrent des faibles changementsde vitesse, pouvant être associés à la mise en pression du dôme ou à l'augmentationde la température du milieu avant l'éruption en surface.
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Wigö, Hans. "Technique and human perception of intermittent air velocity variation." Doctoral thesis, KTH, Civil and Architectural Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-423.
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Objectives. The main objective of the present thesis was to evolve a controlled intermittent velocity field and to examine the impact of this type of dynamic indoor climate on human’s psychology and physiology. The prediction was that intermittent velocity variation could provide occupants with the desired cooling without causing draught and that this intermittent change of the indoor climate would influence peoples’ affect and cognitive performance.
Methods. All experiments were performed in a classroom-like environment where groups of subjects were exposed to a temperature increase and step changes in air velocity. The changes or intermittent variations in air velocity consisted of elevated speed during five minutes, which were repeated three times. To reduce the influence of individual thermal preferences all measures were collected twice and the statistical analyses were based on the change scores in these measures.
Results. The obtained results showed that, intermittent velocity variation may provide occupants with the desired cooling without causing draught. Subjects exposed to velocity variations were significantly less affected by the temperature rise in the room, compared to the control group. Moreover, the method reduced the expected increase of occupants who perceived the temperature condition as uncomfortable. The findings concerning air movements demonstrate that very few perceived the condition as draughty, after being exposed to the three high velocity pulses.
The results concerning affect showed a significant effect on high activation, in the temperature range 21 - 24oC when the velocity variations made the subjects rate the temperature as slightly lowered over time, they kept their level of activation. In the higher temperature interval, 25 - 27oC, unactivated unpleasantness increased and activated pleasantness decreased significantly more in subjects in the constant velocity condition than it did for subjects in the velocity variation condition. In sum, all results concerning affect, the significant ones and tendencies point in the same direction. Subjects exposed to velocity variation report changes, over time, indicating higher activation and more positive feelings.
No differences in cognitive performances were shown between the air velocity conditions. However, a tendency to a significant result (p = 0.10) in an attention task was shown, indicating that subjects in the velocity variation condition increased their speed in a short-term memory search, compared to subjects in the constant velocity condition.
In the temperature range 21- 24oC, where the perception of the room temperature was measured at 0, 5 and 10 minutes respectively after the last high velocity period, the difference in MTV scores between the two groups, did decrease over time. Ten minutes after the last pulse the difference in MTV scores between the two groups was not significant. This suggests that the high velocity period should be repeated every10 to 15 minutes to keep the expected rise in subjects who judged the thermal conditions as uncomfortable down.
The skin temperature was not affected neither by the rise in ambient temperature (from 21 to 24oC over 80 minutes) nor the periods (3 x 5 minutes) of high velocity. A consequence of this result is that the human temperature regulation system permitted an increased heat loss during the high velocity pulse, and hence a reduction of the body’s internal stored heat. For uncovered body parts the increase in heat loss was 20 % during the high velocity pulse. Summarised over the whole exposure time the three pulses produced a total energy loss that was only 2 % higher compared to constant low velocity.
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Wigö, Hans. "Technique and human perception of intermittent air velocity variation /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-423.
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Panagos, Adam G., and Kurt Kosbar. "MIMO CHANNEL TIME VARIATION AS A FUNCTION OF MOBILE USER VELOCITY." International Foundation for Telemetering, 2004. http://hdl.handle.net/10150/605780.
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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, CaliforniaThe analysis of multiple-input multiple-output (MIMO) communication systems often assumes a static, or quasi-static, environment. Platform motion and changes in the environment makes this an unreasonable assumption for many telemetry applications. This paper uses computer simulations to characterize the time variation of MIMO channel parameters when there is relative motion between the transmitter and receiver. These simulation results yield explicit time intervals over which a MIMO channel can be considered static for a given relative velocity and propagation environment. These results can be used to predict the practical limitations of proposed MIMO system algorithms.
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Budi, Santoso Agus. "The seismic activity associated with the large 2010 eruption of Merapi volcano, Java : source location, velocity variation, and forecasting." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU003/document.
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L'éruption de 2010 du Merapi est la première grande éruption explosive du volcan qui a été observée instrumentalement. Dans ce travail, nous étudions les précurseurs de l'éruption et le comportement du volcan avant l'éruption en reliant les caractéristiques sismiques avec d'autres observations disponibles. Nous présentons les principaux aspects de l'activité sismique au cours de la crise de 2010, tels que la chronologie de la sismicité, l'évolution spatio-temporelle des positions de source de séisme et les changements de vitesse sismique. En effectuant des localisations absolues et relatives, nous obtenons des preuves de l'existence de zones asismiques, concordant avec des études antérieures, que nous interprétons comme des zones plus ductiles. La migration du magma de la partie profonde à la partie superficielle du conduit à travers la zone asismique supérieure est mise en évidence par un déplacement vers le haut des hypocentres. Nous analysons l'énergie sismique quantifiée par le RSAM calculé pour plusieurs bandes de fréquences. Ces fonctions affichent des accélérations claires dans les dernières semaines avant l'éruption. Ce comportement est utilisé pour effectuer des prévisions d'éruption volcanique rétrospective avec la méthode « Material Failure Forecast » ou FFM. Le début de la première éruption est estimé avec une bonne précision. Nous proposons une méthode originale de détection d'événement basée sur un rapport d'énergie. En utilisant cette méthode et la corrélation de la forme d'onde, nous identifions 10 familles de séismes similaires. Ces multiplets sismiques sont situés en dessous ou au -dessus de la zone asismique supérieure et sont composés soit d'événements volcano-tectoniques soit d'événements basse fréquence. Certains de ces groupes ont été actifs pendant plusieurs mois avant la crise éruptive alors qu'une famille qui comprend 119 événements répétitifs est apparue 20 heures avant le début de l'éruption. Nous estimons des variations de vitesse sismique, liées principalement à l'activité magmatique, en utilisant la coda des multiplets et les fonctions d'intercorrélation du bruit sismique. Ces variations montrent une forte variabilité spatiale et temporelle de leur amplitude et de leur signe. Bien qu'elles ne puissent pas être décrites par une simple tendance unique, ces variations de vitesse peuvent être considérées comme un précurseur de l'éruption. En utilisant les résultats précédents ainsi que d'autres observations, nous déterminons les particularités associées à la grande éruption explosive de 2010. En outre, nous proposons un scénario chronologique de l'activité pré- éruptive du MerapiThe 2010 eruption of Merapi is the first large explosive eruption of the volcano that has been instrumentally observed. In this work, we study the eruption precursors and the pre-eruptive volcano behaviour by linking seismic features with other available observations. The main characteristics of the seismic activity during the 2010 crisis, including the chronology of seismicity, the spatio-temporal evolution of earthquake source positions and the seismic velocity changes, are presented. By performing absolute and relative locations, we obtain evidences of aseismic zones which are consistent with earlier studies and are interpreted as more ductile zones. Magma migration from the deep to the shallow part of the conduit through the upper aseismic zone is revealed by an upward shift of the hypocenters. We analyse the seismic energy quantified by RSAM calculated for several frequency bands. These functions display clear accelerations in the last few weeks before the eruption. This behaviour is used to perform hindsight eruption forecasting with the Material Failure Forecast method (FFM). The onset of the first eruption is estimated with a good precision. We propose an original method of event detection based on energy ratio. Using this method and waveform correlation, we identify 10 families of similar earthquakes. The seismic multiplets are located either below or above the upper aseismic zone and are composed of either volcano-tectonic or low-frequency events. Some of the clusters were active during several months before the eruptive crisis while a family that includes 119 repeating events appeared 20 hours before the eruption onset. Seismic velocity variations associated mainly with magmatic activity are estimated using the coda of both multiplets and noise cross correlation functions. These variations display strong temporal and spatial variability of their amplitude and sign. Although they cannot be described by a unique simple trend, these velocity variations can be considered as an eruption precursor. Using the preceding results together with other observations, we determine the specific features associated with the large explosive eruption of 2010. Furthermore, we propose a chronological scenario of the pre-eruptive activity of Merapi 2010 unrest
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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 - MScVelocity 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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Genova, Barazarte Ezequiel. "Stochastic modeling of the variation of velocity and permeability as a function of effective pressure using the Bed-of-Nails asperity-deformation model." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1525.
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Goodin, Jacob. "Comparison of External Kinetic and Kinematic Variables between High Barbell Back Squats and Low Barbell Back Squats across a Range of Loads." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etd/2539.
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This study compared peak force, peak power, peak velocity, impulse, work, and vertical displacement between the high bar back squat (HBBS) and low bar back squat (LBBS). Six trained males performed each using 20, 30, 40, 50, 60, 70, 80, and 90% of their recent training 1 repetition maximum. Dual force plates recorded force-time curve characteristics of ground reaction forces and four potentiometers tracked vertical and horizontal barbell displacement. Repeated–measures analysis of variance revealed a significant main effect for load (p<0.01) across all variables, but no significant effects for condition or interaction. The HBBS generated higher peak force in loads 20%–80%, higher peak power in loads 20%–60% and 80%–90%, higher peak velocity at every load, and greater vertical displacement at every load. The LBBS generated a larger impulse at loads 30%-90% and the HBBS generated more work at loads 20%, 40%, and 60%–90%.
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Nayak, Soumya Sambit. "Continuum Analytical Shape Sensitivity Analysis of 1-D Elastic Bar." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101764.
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In this thesis, a continuum sensitivity analysis method is presented for calculation of shape sensitivities of an elastic bar. The governing differential equations and boundary conditions for the elastic bar are differentiated with respect to the shape design parameter to derive the continuum sensitivity equations. The continuum sensitivity equations are linear ordinary differential equations in terms of local or material shape design derivatives, otherwise known as shape sensitivities. One of the novelties of this work is the derivation of three variational formulations for obtaining shape sensitivities, one in terms of the local sensitivity and two in terms of the material sensitivity. These derivations involve evaluating (a) the variational form of the continuum sensitivity equations, or (b) the sensitivity of the variational form of the analysis equations. We demonstrate their implementation for various combinations of design velocity and global basis functions. These variational formulations are further solved using finite element analysis. The order of convergence of each variational formulation is determined by comparing the sensitivity solutions with the exact solutions for analytical test cases. This research focusses on 1-D structural equations. In future work, the three variational formulations can be derived for 2-D and 3-D structural and fluid domains.Master of Science
When solving an optimization problem, the extreme value of the performance metric of interest is calculated by tuning the values of the design variables. Some optimization problems involve shape change as one of the design variables. Change in shape leads to change in the boundary locations. This leads to a change in the domain definition and the boundary conditions. We consider a 1-D structural element, an elastic bar, for this study. Subsequently, we demonstrate a method for calculating the sensitivity of solution (e.g. displacement at a point) to change in the shape (length for 1-D case) of the elastic bar. These sensitivities, known as shape sensitivities, are critical for design optimization problems. We make use of continuum analytical shape sensitivity analysis to derive three variational formulations to compute these shape sensitivities. The accuracy and convergence of solutions is verified using a finite element analysis code. In future, the approach can be extended to multi-dimensional structural and fluid domain problems.
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Carroll, Kevin M., Kimitake Sato, Caleb D. Bazyler, N. Travis Triplett, and Michael H. Stone. "Increases in Variation of Barbell Kinematics Are Observed with Increasing Intensity in a Graded Back Squat Test." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/3779.
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The purpose of the current study was two-fold: (1) To examine the variation in velocity and power with increasing intensity in the back squat among subjects; and (2) To explore individual subject characteristics as possible explanations for variations of velocity in the back squat. Fourteen recreationally trained male subjects with experience in the back squat agreed to participate in the study (age = 25.0 ± 2.6 years, height = 178.9 ± 8.1 cm, body mass = 88.2 ± 15.8 kg). One-repetition maximums (1RM) were performed for each subject on force platforms with four linear position transducers attached to the barbell. The 1RM assessment was immediately preceded by warm-up sets at 65%, 75%, 85%, and 95% of estimated 1RM for 5, 3, 2, and 1 repetitions, respectively. Mean concentric velocity (MCV) and mean power were recorded for each intensity condition and were analyzed using Pearson correlation to determine the relationship between each variable and relative intensity (%1RM). Statistically significant negative relationships existed between %1RM and MCV (r = −0.892) and mean power (r = −0.604). Between-subject coefficient of variation tended to increase as %1RM increased for both MCV and mean power. These results suggest that MCV is superior to mean power as an indicator of relative intensity in the back squat. Additionally, the between-subject variation observed at higher intensities for MCV and mean power support the use of velocity ranges by strength and conditioning coaches.
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Mainsant, Guenolé. "Variation de la vitesse des ondes de cisaillement lors de la transition solide-liquide au sein des argiles. Application aux glissements de terrain." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENU005/document.
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Les glissements de terrain argileux affectent de nombreux versants à travers le monde et menacent régulièrement les activités humaines dans les zones urbanisées montagneuses. Ces glissements sont caractérisés par des cinématiques souvent lentes mais ils peuvent brutalement se liquéfier et accélérer de manière imprévisible. Cette transition solide-liquide a été étudiée sur les argiles de la région du Trièves (Alpes Françaises) à l'aide d'études rhéologiques. Elles ont montré le caractère de fluide à seuil thixotrope avec une bifurcation de viscosité importante lors de la fluidification pouvant expliquer le caractère catastrophique de l'accélération observée sur le terrain. Cette perte de rigidité du matériau peut être observée par une chute de la vitesse des ondes de cisaillement (Vs). Des études réalisées en parallèle à la fois sur un modèle analogique de plan incliné et sur le terrain (glissement de Pont-Bourquin, Suisse) ont permis d'observer une chute de Vs précédent à cette fluidification montrant ainsi que Vs pourrait être un bon proxy pour la surveillance des instabilités de terrain argileuxLandslides affect many clay slopes in the world and regularly threaten people in urban areas mountainous. These landslides are characterized by a slow velocity but they may suddenly liquefy and accelerate unexpectedly. The solid-liquid transition on the clay has been studied of Trièves region (French Alps) using rheological experiments. They have shown the yield stress thixotropic behavior with a viscosity bifurcation which can explain the catastrophic fluidization observed in the field. This loss of material stiffness can be followed by a drop in the shear wave velocity (Vs). Inclined plane test and field experiments (Pont-Bourquin landslides in Switzerland) have both shown a precursor drop of Vs indicating that it could be a good proxy for monitoring unstable clay slope
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Simba, Kudakwashe. "The impact of vascular calcification among dialysis dependent South African CKD patients. A five year follow up study. Cardiovascular mortality and morbidity, ethnic variation and hemodynamic correlates." Master's thesis, Faculty of Health Sciences, 2019. http://hdl.handle.net/11427/31257.
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BACKGROUND
Vascular calcification is a major risk factor for cardiovascular morbidity and mortality in patients with end stage renal disease (ESRD). In Western countries, Blacks with ESRD appear to have lesser degrees of vascular calcification compared to non-Blacks. However, there is no published data on the association of ethnic differences in vascular calcification and survival in ESRD from Sub-Saharan Africa.
METHODS
This study assessed the 5-year change in vascular calcification and mortality in a previously published cohort of patients with ESRD. Vascular calcification was assessed by abdominal aortic calcification score (lateral abdominal radiograph) and vascular stiffness by pulse wave velocity.
RESULTS
Sixty-six of the original 74 participants, studied a baseline, were identified. The median age was 46.6 years (37.6-59.2) and 57.6% were women. Abdominal aortic calcification showed no progression among Blacks [baseline range 0-5, follow up range 0-8 (p=1.00)], but a nonsignificant trend to progression among non-Blacks [baseline range 0-19, follow up range 0-22 (p=0.066)]. Black participants did not display a survival advantage (p=0.870). Overall, sepsis was the most common cause of mortality (64% of those with an identifiable cause of death). Non-Blacks had higher parathyroidectomy rates than Blacks with 9/30 cases compared to 2/36 (p=0.036). After adjustment for parathyroidectomy at follow up, the odds ratio of having abdominal vascular calcification score of ≥1 amongst non-Blacks was 8.6-fold greater compared to Blacks (p= 0.03). Central aortic systolic pressures (CASP) and pulse wave velocities (PWV) were higher in the study population than age matched normative values. At follow up, a positive correlation (r=0.3) was observed between PWV and abdominal aortic calcification (p=0.04). Elevated baseline coronary artery calcification score and FGF-23 level at baseline were not associated with a difference in mortality.
CONCLUSION
There was no significant progression in vascular calcification among Blacks. After adjusting for increased parathyroidectomy rates, there was a greater progression of vascular calcification amongst non-Blacks compared to Blacks highlighting possible ethnic differences in calcium phosphate metabolism in patients with ESRD. The lack of vascular calcification progression in Blacks was not however associated with improved survival, but the sample size was small.
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Page, Jennifer Lynn. "The effects of plume property variation on odor plume navigation in turbulent boundary layer flows." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29752.
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Thesis (Ph.D)--Biology, Georgia Institute of Technology, 2009.Committee Chair: Weissburg, Marc; Committee Member: Hay, Mark; Committee Member: Kubanek, Julia; Committee Member: Webster, Donald; Committee Member: Yen, Jeannette. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Makarynska, Dina. "Theoretical and numerical modelling of the effect of viscous and viscoelastic fluids on elastic properties of saturated rocks." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/289.
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Rock physics is an essential link connecting seismic data to the properties of rocks and fluids in the subsurface. One of the most fundamental questions of rock physics is how to model the effects of pore fluids on rock velocity and density. Contemporary scientific computing allows geophysicists to conduct extremely complex virtual (computational) experiments on realistic digital representations of complex porous media, and thus directly relate the measurable properties of the media to their microstructure and saturation. Computational (digital) rock physics can also serve as an effective tool in examining new and existing rock physics models. The finite element method (FEM) has been proved effective in simulations of the linear elastic properties of porous rock under static conditions. In this thesis, FEM is used to study the effect of patchy saturation on elastic velocities of digital images of rocks. However, FEM belongs to a group of grid methods, and its accuracy is limited by discretization errors. This can cause errors in rock property predictions and needs to be thoroughly examined. In this thesis, a test scenario based on rigorous theories for grid-based methods such as FEM is developed, which allows establishing optimal computational parameters in terms of accuracy of the results and time cost of computations.Gassmann’s equations are the most widely used relations to predict velocity changes resulting from different pore fluid saturations. This problem is also known as fluid substitution. Despite the popularity of Gassmann’s equations and their incorporation in most software packages for seismic reservoir interpretation, important aspects of these equations such as sensitivity to microheterogeneity has not been thoroughly examined. In this thesis, the sensitivity of Gassmann’s equations to microheterogeneity is estimated for different quartz/clay porous mixtures using computational (FEM) simulations. The results of this study suggest that the accuracy of Gassmann’s fluid substitution remains adequate for a wide variety of highly porous rocks even if the contrast between the elastic properties of mineral constituents is large.While Gassmann’s fluid substitution is robust for rocks saturated with Newtonian fluids (brine, gas, light oil), it breaks down for viscoelastic fluids such as heavy oils. An alternative fluid substitution scheme for rocks saturated with viscoelastic fluids based on self-consistent effective medium theory is proposed in this thesis. Comparison with laboratory measurements shows that the scheme realistically estimates the frequency- and temperature dependent properties of heavyoil rocks and can be used for practical applications.A useful tool for modelling and estimation of properties of rocks with arbitrary or unknown microstructure are rigorous bounds on elastic moduli. The common elastic bounding methods such as Hashin-Shtrikman bounds are not applicable for heavy-oil rocks because of viscoelastic rheology of heavy oils. In this work, it is demonstrated that the viscoelastic bounding method of Milton and Berryman for the effective shear modulus of a two phase three-dimensional isotropic composite provides rigorous bounds for dispersion and attenuation of elastic waves in heavy-oil rocks. In particular, computation of these bounds shows that dispersion and attenuation in a rock saturated with a fluid (viscous or viscoelastic) can be much stronger than in the free fluid. This phenomenon is caused by wave-induced fluid flow relative to the solid. At sonic and ultrasonic frequencies, dispersion and attenuation appears to be dominated by the local (pore-scale) flow between pores of different shapes and orientations. The Mavko and Jizba expressions for the so-called unrelaxed frame bulk and shear moduli are one of the most popular quantitative models of squirt dispersion. However, these expressions are limited to liquidsaturated rocks and high frequency. In this thesis, The Mavko-Jizba relations are generalized to gas-saturated rocks. Furthermore, dispersion and attenuation is computed using a new squirt flow model, presented in this thesis. All the parameters in this model can be independently measured or estimated from measurements. The model gives complex frequency- and pressure-dependent effective bulk and shear moduli of a rock consistent with laboratory measurements.Variation of elastic properties of rocks with pressure is often modelled using penny-shaped or spheroidal cracks as idealization of real crack/pore geometry. In this doctorate, the validity of this approach is analysed by extracting the ratios of shear to bulk stress sensitivity coefficients, and normal to tangential compliances from ultrasonic measurements on a number of dry sandstone samples. The ratios show large scatter and, for a large number of dry sandstone samples, are not consistent with spheroidal crack theory. This inconsistency results in significantly different estimates of crack density from bulk and shear moduli, and in deviation of predicted pressure variation of Poisson’s ratio from the measured data.
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Ricci, Monia. "Analisi del segnale elettroencefalografico acquisito durante movimenti lenti e veloci dell'arto superiore." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19910/.
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Questo lavoro di tesi ha riguardato l’acquisizione e l’elaborazione di segnali elettroencefalografici (EEG) registrati su 18 volontari mentre veniva loro chiesto di eseguire uno specifico task motorio, ovvero flesso-estensione dell’arto superiore destro a due diverse velocità, per indagare possibili differenze nei segnali EEG associate alla velocità di esecuzione del movimento. Il protocollo sperimentale è stato strutturato in tre blocchi intervallati da una breve pausa di riposo. Ogni blocco consta di 90 trial: si susseguono in maniera random 30 comandi ‘slow’ (il soggetto deve muoversi lentamente), 30 comandi ‘fast’ (il soggetto deve muoversi velocemente), 30 comandi ‘rest’ (il soggetto deve restare fermo). Ogni trial inizia con 1 s di rilassamento; segue il primo segnale (‘cue’ una scritta con l’indicazione del task da eseguire); in corrispondenza alla sua scomparsa si presenta il secondo segnale (‘go’ un beep di 10 ms che indica al soggetto di eseguire il task); infine sono concessi al soggetto 5 s durante i quali eseguire il task. Le elaborazioni sono state condotte sui 16 segnali EEG e su un segnale accelerometrico, acquisiti rispettivamente mediante elettrodi premontati su cuffia e sensore inerziale fissato sul dorso della mano destra. Sono stati analizzati i seguenti correlati neurali del movimento: contingent negative variation, un potenziale di anticipazione motoria identificato nel dominio del tempo tra ‘cue’ e ‘go’; event-related de/synchronization, un incremento/decremento di potenza, osservabile in specifiche bande di frequenza (alpha e beta) e in specifici intervalli nelle mappe tempo-frequenza. Per valutare infine la significatività dei risultati ottenuti si è condotta un’analisi statistica (t-test). Sebbene i risultati ottenuti non evidenzino differenze significative nelle caratteristiche del segnale EEG tra i movimenti ‘slow’ e i movimenti ‘fast’, lo studio si pone come importante punto di partenza per investigazioni future.
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Natchimuthu, Sivakiruthika. "Freshwater methane and carbon dioxide fluxes : Spatio-temporal variability and an integrated assessment of lake and stream emissions in a catchment." Doctoral thesis, Linköpings universitet, Tema Miljöförändring, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-126779.
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Freshwater bodies such as lakes and streams release the greenhouse gases methane (CH4) and carbon dioxide (CO2) into the atmosphere. Global freshwater CH4 and CO2 emissions have been estimated to be of a similar magnitude to the global land or ocean carbon sink, and are thus significant components of global carbon budgets. However, the data supporting global estimates frequently lacks information regarding spatial and temporal variability and are thus highly inaccurate. In this thesis, detailed studies of the spatio-temporal variability of CH4 and CO2 fluxes were conducted in the open water areas of lakes and streams within a whole catchment in Sweden. One aim was also to evaluate the importance of spatio-temporal variability in lake and stream fluxes when making whole catchment aquatic or large scale assessments. Apart from the expected large spatio-temporal variability in lake fluxes, interactions between spatial and temporal variability in CH4 fluxes were found. Shallow lakes and shallow areas of lakes were observed to emit more CH4 as compared to their deeper counterparts. This spatial variability interacted with the temporal variability driven by an exponential temperature response of the fluxes, which meant that shallow waters were more sensitive to warming than deeper ones. Such interactions may be important for climate feedbacks. Surface water CO2 in lakes showed significant spatio-temporal variability and, when considering variability in both space and time, CO2 fluxes were largely controlled by concentrations, rather than gas transfer velocities. Stream fluxes were also highly variable in space and time and in particular, stream CH4 fluxes were surprisingly large and more variable than CO2 fluxes. Fluxes were large from stream areas with steep slopes and periods of high discharge which occupied a small fraction of the total stream area and the total measurement period, respectively, and a failure to account for these spatially distinct or episodic high fluxes could lead to underestimates. The total aquatic fluxes from the whole catchment were estimated by combining the measurements in open waters of lakes and streams. Using our data, recommendations on improved study designs for representative measurements in lakes and streams were provided for future studies. Thus, this thesis presents findings relating to flux regulation in lakes and streams, and urges forthcoming studies to better consider spatio-temporal variability so as to achieve unbiased large-scale estimates.Sötvatten som sjöar och vattendrag är källor till växthusgaserna metan (CH4) och koldioxid (CO2) i atmosfären. De globala utsläppen av CH4 och CO2 från sötvatten har uppskattats vara av samma storleksordning som den globala land- eller havskolsänkan och är därmed viktiga delar av jordens växthusgasbudget. De globala uppskattningarna saknar ofta information om variation i tid och rum och är därmed mycket osäkra. Denna avhandling behandlar hur CH4- och CO2-flöden från öppet vatten i sjöar och vattendrag i ett avrinningsområde varierar rumsligt och tidsmässigt. Ett syfte var också att utvärdera betydelsen av dessa variationer när data extrapoleras för att göra storskaliga uppskattningar av växthusgasflöden från vattenmiljöer. Förutom de förväntade stora rumsliga och tidsmässiga variationerna i sjöars gasflöden identifierades interaktioner mellan rumsliga och tidsmässiga variation för CH4-flöden. Den rumsliga variabiliteten med högre CH4-flöden från grunda vatten interagerade med tidsvariationen, som i sin tur drevs av en exponentiell temperaturrespons av gasflödena. Det betyder att grunda vattenområden var mer känsliga för uppvärmning än djupare vatten och därmed att vattendjupet har betydelse för hur sjöars CH4-utsläpp påverkas av klimatet. Koncentrationer av CO2 i sjöars ytvatten uppvisade också en betydande rumslig och tidsmässig variation som tillsammans visar att CO2-flöden över längre perioder till stor del styrs av koncentrationer snarare än av gasutbyteshastigheter. Vattendragens gasflöden varierade också mycket i tid och rum. Detta gällde i synnerhet CH4-flödena vilka var förvånansvärt stora och mer varierande än CO2-flödena. Gasflödena var höga från områden i vattendrag med högre lutning och då det var höga vattenflöden, trots att dessa områden och tidsperioder utgjorde en bråkdel av den totala arean och mätperioden. Att inte räkna med dessa gasflöden från bäcksektioner med höga vattenhastigheter eller korta perioder med höga flöden, leder till underskattningar. De totala CH4- och CO2-flödena från öppet vatten i hela avrinningsområdet uppskattades genom att kombinera mätningar i sjöar och vattendrag. Denna avhandling visar att rumslig och tidsmässig variabilitet har stor betydelse, och den ger information om hur denna variation kan beaktas för bättre framtida mätningar och storskaliga uppskattningar av växthusgasflöden från sjöar och vattendrag.
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Dey, Subhash Chandra. "Lateral variations in the upper mantle velocity structure under Northern Australia." Phd thesis, 1989. http://hdl.handle.net/1885/140379.
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WANG, MIN-HUA, and 王民華. "The variations of velocity and temperature profiles of jets with a power-law fluid." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/68200737326145327916.
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Yeh, Ren-jie, and 葉仁傑. "Probing the Lateral Velocity Variations along the Manila Trench by Analysis of Surface Wave Dispersion." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/54621494925095429684.
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碩士國立中央大學
地球物理研究所
99
The Eurasian Plate subducts to the east beneath the Philippine Sea Plate along the Manila Trench. While the subducting slab is relatively cold and seismically fast as compared to ambient mantle, those of the mantle wedge often exhibit opposite characters resulting from partial melting of wet peridotite. As a result, we expect the existence of lateral velocity variations in slab-normal direction along the Manila trench corresponding to different depths of subducting slab. The objective of this study is thus to test the expectation by analyzing surface wave dispersions as observed by Broadband Array in Taiwan for Seismology (BATS). The fact that earthquake sources distribute on both sides of the Philippine archipelago makes the test feasible with distinct ray coverages to BATS’s stations. Surface wave dispersion refers to the different velocities of waves with different frequencies (periods), which can be explained by the longer period wave sampling deeper structures. In this study, we applied the Multiple Filter Technique (MFT) to analyze the Rayleigh wave dispersion curves. Results thus analyzed are then used for inversion of 1-D velocity model with the AK135 model as the initial, using the damped least-square inversion scheme. We determine the optimal damping factors by grid searching on the inversion results of synthetic waveforms, which are synthesized by FK method. The velocity inversion is done with the conventional surf96 codes. While velocities are overall fast for ray paths to the east of the Manila trench relative to those to the west, explained by the sampling of oceanic lithosphere versus continental one, there are indeed paths of low velocity anomalies corresponding to surface volcanic chains suggesting the effects of magma chambers. Future works include 2-D tomography studies to better resolve the velocity anomalies.
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King, SGK. "Haemodynamic responses to climate variations in healthy individuals and those with Type 2 diabetes mellitus." Thesis, 2013. https://eprints.utas.edu.au/17170/2/Whole-King-thesis-2013.pdf.
Full textAbstract:
Background and aims
Environmental cold and heat exposure are linked to increased cardiovascular (CV) morbidity and mortality. People with impaired vascular function and thermoregulation, such as individuals with type 2 diabetes mellitus (T2DM) are at higher risk of heat or cold-related illness. To date, very few studies on whole-body cold or heat exposure have included individuals with T2DM. Even fewer have used central haemodynamic indicators of CV risk such as aortic pulse wave velocity (PWV), which is a marker of aortic stiffness, or augmentation index (AIx), which signifies left ventricular (LV) load. Moreover, there are no data available of the effects of high humidity, with or without heat, on resting central hemodynamic measures in any population. The studies that comprise this thesis aimed to determine the effects of whole-body exposure to differing air temperature (cold and heat) and relative humidity (RH) on measures of central haemodynamics and arterial stiffness in resting healthy individuals, and those with T2DM.
Methods
Five climate trials were undertaken in two participant groups; a Healthy and a T2DM group. The Healthy group comprised 16 adults (10 men), aged 43±19 years, and the T2DM group included 14 participants with T2DM (8 men), aged 63 ± 7 years. Supine, resting measures included aortic and brachial PWV, aortic AIx, brachial and aortic blood pressures (BPs), and measures of aortic reservoir function including reservoir pressure (`P_(res`), excess pressure (`P_(ex)`), and timing of `P_(ex)`. The five climate conditions were 21˚C with 40% RH (control), 21˚C with 80% RH (humid), 12˚C with 40% RH (mild-cold), 36˚C with 40% RH (hot-dry), and 36˚C with 80% RH (hot-humid). Every participant in both groups completed all five climate trials on separate days, with a washout of at least 7 days between each trial. Time points for data collection were ambient baseline, then at 5 (T2DM group only), 10, 30, 60, and 90 minutes while in each climate condition. 300mL (Healthy group) and 250mL (T2DM group) of water was consumed following the 60 minute measures in each climate condition in every participant. For analysis and presentation of results, data were split into mild-cold vs. control, and heat and humidity vs. control results. Data from baseline to 60 minutes were used for main analyses, and data from 60 to 90 minutes for heat and humidity results were analysed separately in order to account for any possible effect of dehydration and rehydration in the hot conditions.
Results
Results indicate that in the Healthy group, a change from a comfortable ambient climate to a mild-cold climate, as commonly happens in day-to-day life, significantly increased augmentation pressure (AP; P = 0.01) and AIx (P = 0.01), and reduced time to `P_(ex)` (P = 0.01) compared to control, without significantly altering aortic PWV (P = 0.87). Conversely, in the T2DM group, mild-cold exposure significantly increased aortic PWV (P = 0.03) but elicited a smaller pressor response compared to that observed in healthy individuals; brachial and aortic systolic BPs, and mean BP increased within condition in mild-cold (all P < 0.05) in T2DM participants, but these measures did not change compared to control (all P > 0.24).
In the heat and humidity trials, it was observed that humidity at 80% significantly reduced aortic PWV during heating at 36°C in both healthy individuals and those with T2DM (both groups P < 0.05); a result that was not apparent when each group was exposed to hot-dry conditions (each group P > 0.06). In healthy individuals, hot-humid conditions did not significantly change measures of LV load (mean BP and AIx both P > 0.05). However, in T2DM, mean BP was reduced similarly in all hot comparisons (all P < 0.005) and AIx was reduced by hot-humid (P = 0.03) but not hot-dry (P = 0.31) conditions. In the Healthy group, `P_(res)` was reduced only in hot-dry (P = 0.03) but not hothumid conditions. However, in the T2DM group `P_(res)` was reduced in all hot conditions (all P < 0.006). The only instance where `P_(ex)` was significantly affected during any climate trial was during humid-heating in T2DM participants, where `P_(ex)` was reduced (P < 0.05). Finally, the studies into heat and humidity demonstrated that compared to control, exposure to high humidity at room temperature (i.e. independently of heat) significantly reduced aortic systolic BP (P = 0.02), rate pressure product (P = 0.02) and aortic `P_(res)` (P = 0.03) in healthy individuals, and reduced AIx in people with T2DM (P = 0.04).
Discussion and Conclusions
The results from the mild-cold studies suggest that even a brief exposure to a mild-cold temperature can increase aortic stiffness (aortic PWV) in people with T2DM and increase haemodynamic stress and LV load (AP and AIx) in apparently healthy individuals. In healthy individuals, increased AP and AIx during mild-cold exposure were potentially the result of peripheral vasoconstriction causing reduced peripheral blood run-off and increased impedance to aortic outflow. This may create a transient situation in which aortic in-flow exceeds aortic out-flow volume for the duration of the cold exposure, and this imbalance may have increased AIx and altered timing of `P_(ex)` in this study. However, in a T2DM population, a greater aortic stiffness and smaller pressor response than observed in healthy individuals during cold exposure is potentially a normal response. This is because of the higher likelihood of autonomic dysfunction in individuals with T2DM which impairs normal vascular reactivity and pressor responses to cold exposure. Such acute increases in these indicators of CV risk during cold exposure may add to explanations of cold-associated morbidity and mortality in people with T2DM.
The findings of the heat and humidity studies show that in healthy individuals, aortic PWV was reduced by humid-heat without affecting brachial or aortic systolic or mean BPs. In T2DM individuals, aortic PWV was similarly reduced by humid-heat, but pressor responses were more variable in the heat and humidity trials than were observed for healthy people. Reductions in aortic PWV in healthy individuals and those with T2DM during humid-heating are potentially due to the increased heat load which accompanies increasing humidity, which in turn may produce a passive relaxation of the elastic aorta. This reduction in aortic stiffness may occur via flow-mediated increases in shear stress which triggers release of nitric oxide and other endogenous vasodilators that decrease large artery stiffness, and can work independently of changes in BP. The more variable pressor responses observed in the T2DM group may be due to impaired vascular reactivity which accompanies T2DM and is due to the toxic effects of chronic hyperglycaemia.
The T2DM heat and humidity data in this thesis are the first available that show `P_(ex)`, a measure of wave-related pressure and longitudinal wave reflections, was reduced only in response to whole-body humid-heat exposure in adults with T2DM. Aortic PWV is thought to be dependent on changes in mean BP, heart rate and AIx, and wave reflections. Given that in the T2DM group, mean BP was reduced and heart rates were increased similarly across all hot comparisons but aortic PWV was only reduced in hot-humid conditions, it is possible that the decreased aortic PWV in hot-humid conditions may be related to reduced wave motion, (i.e. `P_(ex)`), `P_(res)` and AIx in patients with T2DM.
Findings from the heat and humidity studies in healthy individuals and those with T2DM suggest that high humidity, with and without heat, can reduce measures of aortic stiffness and LV load, which may be beneficial to the CV system. The lowering effect of high humidity on arterial stiffness and haemodynamics may have particular clinical relevance for reduction of CV risk in T2DM individuals.
In conclusion, the results from this thesis show divergent haemodynamic responses between cooling and heating in people with T2DM and healthy individuals. During cooling, some haemodynamic responses to mild-cold were exaggerated in T2DM (i.e. increased aortic stiffness), and some were attenuated (i.e. pressor responses) compared to responses of healthy individuals. Conversely, during humid-heating, people with T2DM had greater pressor reductions yet similar magnitude reductions in aortic stiffness compared to healthy individuals. Results of this thesis highlight the similarities and differences between responses of healthy individuals and people with T2DM during sudden climate changes. The findings demonstrate that cold exposure is potentially detrimental to haemodynamic function, while short-term humid-heating is potentially beneficial to haemodynamic function in healthy individuals, but more particularly in individuals with T2DM.
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Pittard, ML. "The dynamics of the Lambert-Amery glacial system and its response to climatic variations." Thesis, 2016. https://eprints.utas.edu.au/23487/1/Pittard_whole_thesis_ex_pub-mat.pdf.
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Antarctica's current and future contribution to sea level rise is uncertain, with changes in ice dynamics along the coast leading to mass loss while increasing precipitation in the interior is leading to mass gain. The Lambert-Amery glacial system drains a large region of East Antarctica, with the two largest glaciers within the glacial system, the Lambert and Mellor glaciers, having a substantial volume of ice grounded below sea level, suggesting a risk of marine ice sheet instability. The velocities of Lambert-Amery glacial system have been observed to be stable between 1968 and 1999, albeit with limited sampling. Recent mass balance and gravimetry studies also suggest a system in near balance. Here, visible spectrum satellite images between 2004 to 2012 have been used to compute surface ice velocities using a feature tracking approach. No significant changes in velocity were observed over the study region that included the Amery Ice Shelf adjacent to the grounding line and its three main tributary glaciers, the Lambert, Mellor and Fisher Glaciers. The stability of the Lambert-Amery glacial system allows for the initialisation of an ice sheet model by minimising the misfit between the simulate and observed system.
A regional domain of the Lambert-Amery glacial system is simulated with the Parallel Ice Sheet Model. The control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. We investigate the importance of a primary boundary condition, geothermal heat flux to ice flow. Existing broad scale geothermal heat flux datasets fail to capture small scale localised variations in geothermal heat flux, such as estimates of geothermal heat flux in Prydz Bay suggesting that radiogenic crustal heat production can locally elevate geothermal heat flux by at least 100% compared to the background field. We insert high heat flow regions into a broad scale background geothermal heat flux field, and find that the presence of a high heat flow region can change the flow behaviour in regions from slow sheet flow to stream-like flow, while making no difference to regions of fast flow. This mechanism may contribute to the long term organisation of ice flow. Additionally, we use a range of different geothermal heat flux datasets, and compare simulation using them in place of our control geothermal heat flux. The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value as the control dataset. These scaled geothermal heat flux simulations showed that the ice flow was most sensitive to the spatial variation in the underlying geothermal heat flux near the ice divides and on the edges of the ice streams.
The Lambert-Amery glacial system is evidenced to change significantly during glacial cycles, with the grounding line advancing and retreating up to 700 km. This contrasts with the current stability of the glacial system. The Antarctic Ice Sheet responds to climate through several factors, including the temperature at the surface of the ice, the accumulation on the surface, the oceanic forcing at the base of the floating ice, and sea level change. We test the response of the Lambert-Amery glacial system to climatic variations by simulating the effects of a global air temperature change of ± 3°C. Each climate variable is simulated in isolation to test the sensitivity to each climatic variation, before a combined simulation. We find that the Lambert-Amery glacial system responds most rapidly to accumulation on the surface and the oceanic forcing at the base of the floating ice, while surface temperature eventually lead to the largest change, but on time scales longer than the recent glacial-inter-glacial cycles. The advance of the grounding line moves rapidly between negative sloping beds, where it then stabilises on a positive bed slope, with the ice sheet growing until a threshold is reached and the grounding line advances again. The model simulations are unable to recreate an advance simulation which was similar to the last glacial maximum, with the grounding line either not advancing to the continental shelf, or the ice sheet growing rapidly when the grounding line does advance.
The contribution of Lambert-Amery glacial system to future sea level change is investigated through a range of future scenarios. Within our simulations, we find that under a range of plausible and extreme scenarios, the grounding line is unlikely to become unstable and retreat into the deep marine basins. This causes increases in precipitation to exceed mass loss through ice discharge within our simulations as long as a minimal ice shelf remains. This suggests that the Lambert-Amery glacial system has the potential to gain mass and mitigate the severity of sea level rise from Antarctica for the next 500 years.
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Fallahi, Mohammad Javad. "Surface wave tomography and monitoring of time variations with ambient noise in NW-Bohemia/Vogtland." Doctoral thesis, 2015. https://ul.qucosa.de/id/qucosa%3A14060.
Full textAbstract:
In this study, ambient noise wavefield was used for the first time to image spatial and temporal upper crustal seismic structures in NW-Bohemia/Vogtland region. The data come from 111 stations and were collected from continuous recordings of the permanent station networks of Germany and Czech Academy of Sciences as well as temporary stations of the BOHEMA and PASSEQ experiments. Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions between 0.1 and 1 Hz, and are tomographically inverted to provide 2-D group velocity maps. At shorter periods Rayleigh wave group velocity maps are in good agreement with surface geology where low velocity anomalies appear along Mariánské Lázně Fault and Eger rift. A low velocity zone is observed at the northern edge of Mariánské Lázně Fault which shifts slightly to the south with increasing period and correlates well with the main focal zone of the earthquake swarms at 5 s period. We invert the 2-D group velocity maps into a 3-D shear wave velocity model. In this step Love waves were excluded from further analysis because of their high level of misfit to modelled dispersion curves. Horizontal and vertical sections through the model reveal a clear low velocity zone above the Nový Kostel seismic focal zone which narrows towards the top of the seismic activity and ends above the shallowest hypocenters at 7 km depth.
We investigate temporal variation of seismic velocity within and around the Nový Kostel associated with 2008 and 2011 earthquake swarms by employing Passive Image Interferometry method using 7 continuous seismograms recorded by the WEBNET network. The results reveals stable seismic velocities without a clear post seismic velocity change during earthquake swarms in the Nový Kostel area.
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Panepinto, Stefano. "Time and space domain analysis of gravimetric data." Thesis, 2010. http://hdl.handle.net/2122/6166.
Full textAbstract:
The goal of this PhD thesis is to provide an overview on the very different aspects of modern gravimetric research. In particular, this geophysical method is applied here on the one hand as volcano monitoring tool essentially by continuous gravity observations while, on the other hand, for the construction of density-velocity 3D regional models by an integrated inversion procedure of gravimetric and seismic data.
The first section concentrates on continuous gravity observation performed at different sites of both Etna and Stromboli volcanoes. The gravity studies allow investigation of mass displacements (magma) and density variations (deep structures) under volcano edifices. Results are presented from high precision gravity measurements fully corrected using tidal and drift optimization programs and having a standard error of few μgal. Tidal analyses results of the treated data sets are also shown and discussed in the first section. Moreover, the simultaneous recording of external parameters (atmospheric pressure, temperature and humidity) is essential as their effects must be removed from the gravity records. The analyses carried out with different processing techniques on several data sets led us to point out the temperature as the responsible parameter for the annual drift present in the records of spring gravimeters. During the end of 2002 one of the gravimetric signals acquired on Mt. Etna showed, in its final residuals reaching a 5 μgal precision, a strong decrease of about 400 μgal in few hours. Correlation between this gravity decrease, on the one hand, and the other geophysical and geochemical signals – in particular the seismic and ground deformation data – as well as the observed summit activities, on the other hand, enable us to qualify the recorded gravity variation as a precursor of the 2002 eruption period. By comparison with simultaneous ground deformation data it is shown that the observed gravity changes are not in general caused by elevation changes but are due to the direct gravitational effect of subsurface movements of matter. Residual gravity changes are interpretable entirely in terms of mass changes in crater conduits and in near-surface dykes lying along know fissure system. Furthermore, the summit activity is consistent with a source at greater depth. Gravity measurements may thus not only contribute to a better understanding of some important features of geodynamics in volcanoes but may also be used directly for the monitoring and the prediction of the eruptions.
Section two addresses the unresolved question of the possible interference between tidal forces and volcanism. After the discussion of gravimetric tide results and the determination of tidal parameters, this section is completely devoted to “tidal modulation” of thermometric data acquired at sites very close to the summit active craters of Mt Etna. The intuition that these types of data may contain some geophysical signals related to the tidal stress-strain action, as an evidence of the tidal influence on volcanic processes, comes from the following boundary consideration: since the volcanic areas are characterised by high heat fluxes due to the presence of magma bodies near the surface, taking into account that convection is the major heat transfer mechanism, the tidal strain field within the volcanic edifice could affect this convective process. Some time variations of the efficiency of the convective process should produce corresponding temperature changes observable at shallow depth. The aim of the study is thus to investigate about the presence of a periodic variation due to the main lunar tidal component (M2, tidal period of 12.421 hours). This component is chosen in order to rule out the solar radiation effects. The data set at hand was thus processed with a stacking technique coupled with a wavelet analysis for a preliminary denoising. Through the proposed procedure an anomalous amplitude of the spectral component with a period equal to that of the M2 tidal wave was found. This evidence opens a scientific speculative argument about the interaction between tidal forces and volcanic processes highlighting the possibility, under some particular conditions, of dynamic triggering.
The last section deals with a seismo-gravity integrated inversion procedure for the construction of reliable 3D models of the Sicilian area and its surrounding basins. The proposed procedure allows inverting seismic and gravimetric data with a sequential technique to avoid the problematic optimization of assigning relative weights to the different types of data. The proposed procedure underlined the necessity of the different data integration although the seismic problem seemed to be a priori well constrained. Furthermore, it allowed highlighting some velocity and density features that could play a crucial rule for the reconstruction of the geodynamic evolution of the study area.Università degli studi di Palermo, I.N.G.V. sezione di Catania, International Center for Earth Tides (Royal Observatory of Belgium)
Unpublished
2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
open
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Hou, Ting-Yi, and 侯廷易. "Variation of Submergence Velocity and Impact Pressure of ies." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/96043317990815495195.
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Wu, Kuan-Yi, and 吳冠儀. "Large scale lateral variation of shear wave velocity in D"." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/43770812279618514312.
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Chi, Tsai Yu, and 蔡育奇. "Intra-seasonal Variation of Current Velocity West of Luzon Strait." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/61904737688685966075.
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Fang, Yung-Shun, and 方詠舜. "The Study on Variation of Groundwater Velocity on Wells and Aquifer." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/28610980826280099162.
Full textAbstract:
碩士國立成功大學
資源工程學系碩博士班
94
The purpose of this study is to identify the variation of groundwater velocity on wells and aquifer. A self-designed sand tank is utilized to observe the difference between velocitys in the wells and darcy’s velocity in the aquifers. The experiments in the sand tank are also considered with different independent variables of the measurement such as the structure of the wells (size of wells、size of well′s screens、shape of well′s screens、density of well′s screens)、hydraulic head、the size of sands. A computer code MODFLOW was then performed to modify above-mentioned experiments in order to compare the variation of groundwater velocity around the wells and groundwater velocity in the aquifer. The relations between the experiments and the result of simulation were discussed. The results show that when the structure of the wells is considered as the independent variable, the ratio between velocity in the wells and darcy’s velocity in the aquifers is given in the range from four to six times. Meanwhile, as the hydraulic head and the size of sands are. considered as the independent variables, the ratio between velocity of observation in the wells and darcy’s velocity in the aquifers is given in the range from 4 to 10 times. The result also indicated that the groundwater direction of observation of each independent variables is matching with real direction in the aquifer. On the other hand, simulation results indicated that the ratio of groundwater velocity between surrounding of wells and aquifers is approximately two times. All flow directions of simulation results are matching with real direction in the aquifer .
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Yang, Ching-Wei, and 楊謦維. "Seafloor pressure variation of internal solitary wave estimated from current velocity." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/98953398701041457276.
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碩士國立臺灣大學
海洋研究所
99
The internal solitary waves (ISWs) are active and have large amplitude in the northern South China Sea. Two mooring sets, each set contains an Acoustic Doppler Current Profiler (ADCP) and a bottom-mounted pressure gauge, were deployed on the continental slope of the northern South China Sea. The mode-1 depression ISWs were clearly seen in the observed current velocity. The ISWs could induce 0.05-0.35 dbar of pressure fluctuation while the tides caused around 0.5-2 dbar of pressure fluctuations. 38 ISWs, caused pressure fluctuations larger than 0.05 dbar, were chosen to study the wave properties. The near bottom pressure disturbances which estimated from current velocity data are compared with the observation. The non-hydrostatic pressure disturbances are also calculated and discussed. The ISW vertical displacement was estimated from the time integration of vertical velocity with the correction of heave motion of background flow. The ISW propagation speed was estimated from the continuity equation. The wave propagation direction was the same as the direction of upper ocean current caused by ISW. These wave properties were used to estimate the current velocities of ISW by calibrating the beam-spreading effect of ADCP measurement. The non-hydrostatic and near bottom pressure disturbances of ISW were estimated from the calibrated current velocities by using the vertical momentum and Bernoulli equations, respectively. The result indicates that the estimated ISW bottom pressure variation could represent the observed pressure variation at bottom. The estimated ISW non-hydrostatic pressure variation and the ISW maximum vertical displacement were proportional to the bottom pressure perturbation. A conclusion is obtained that both the maximum vertical displacement and non-hydrostatic pressure variation caused by the mode-1 depression ISW in the northern SCS could be estimated from the bottom pressure gauge.
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Wilder, John D. "An Analysis of sound velocity variation in an estuary for NOS standards." Thesis, 1985. http://hdl.handle.net/10945/21156.
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Chen, Jong-Ren, and 陳仲仁. "The Study of Variation on Baseballs'' COR Curves in Different Velocity Impact." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/73388296837978340076.
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碩士國立體育學院
教練研究所
89
Although baseball is a very popular source of recreational activity throughout the world, safety of baseball exercise is still a concern. Results of previous studies showed that the properties of baseball were highly correlated with safety of baseball. The objective of this study was to investigate baseball’s coefficient of restitution (COR) in different impacting velocities. Another purpose was to find the relation between peak force, impulse of impact, and COR while baseball hitting the wall. In this study, the subjects were 20 trademarks baseballs, 16 trademarks were traditional baseballs and 4 trademarks were modified baseballs. Fourteen testing velocities were used in the experiment. JVC high speed video camera was used to film the ball’s impact process. In order to measure the peak force and impulse while impacting, force plant was fixed on the wall to be hit by the baseballs. The results showed that the peak force and impulse of impact were positively significantly correlated with the impact velocity, but COR was negatively significantly correlated with the impact velocity. In testing velocities 62∼80 mph, the curve of peak force, impulse, and COR curves of traditional baseballs were nonlinear and unstable. COR curves of traditional baseball were increasing in this interval, differing from decreasing in another intervals. In addition, the traditional baseballs’ COR didn’t correlate with the peak force and impulse of impact in all testing velocities. Most of the modified baseballs’ COR significantly correlated with the peak force and impulse of impact in testing velocities 71∼89 mph. Based on the results of this study, in different impact velocities, traditional baseballs’ COR curves were nonlinear and unstable. To make conjectures, this result was caused of change on the rebound model while ball impacting in high speed. Because of low correlation between impulse of impact and COR, it was difficult to find an effective method to project traditional baseballs’ COR. Modified baseball had a more simple structure, therefore each curve of parameter was relatively stable.
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Chuang, Wei-Hung, and 莊瑋宏. "The Study Of Removed Rate Of Micro-Cavity Including Geometry And Velocity Variation." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/22014430518724819716.
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Runge, Roberta M. "Variation of friction velocity across the surface marginal ice zone in the East Greenland Sea." Thesis, 1985. http://hdl.handle.net/10945/21617.
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