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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Evaluation of reanalysis precipitation estimates in the Canadian precipitation analysis (CaPA)

Choi, Hyaesun 04 January 2017 (has links)
Canadian Precipitation Analysis (CaPA) has been developed by Environment Canada to produce the most accurate near-real-time gridded precipitation estimates. It uses the Global Environmental Multiscale model (GEM) as a background and assimilates the synoptic network of weather stations through Optimal Interpolation. Accurate estimation of gridded precipitation is useful for hydrological modeling, stream ow forecasting, and climate change studies. However, the calibration and validation of hydrologic models requires long temporal coverage of data for a better performance. Since GEM/CaPA data are available only for the recent past (2002-present), the development of historical data sets starting earlier than 2002 becomes important. Using alternative models for producing the atmospheric gridded background is one solution to overcome the short temporal coverage of archived GEM data. This thesis evaluates and analyzes two candidate data sets. ERA-Interim and NARR were selected as potential alternatives to GEM background. The general conclusion of the study is that the use of ERA-Interim and NARR as background elds leads to performance results that are not signi cantly inferior to GEM after assimilation with stations in the CaPA framework. While result with the GEM background remains the best, one can cautiously conclude that for most practical applications, ERA-Interim and/or NARR may be used for the period that predates archived GEM data. The thesis presents a more detailed evaluation of ERA-Interim and NARR for di erent seasons and di erent regions of Canada. / February 2017
2

Validation of the Canadian Precipitation Analysis (CaPA) for Hydrological Modelling in the Canadian Prairies

Zhao, KuangYin 27 November 2013 (has links)
Traditional hydrological model inputs are often deemed inadequate in areas where stations are sparse, such as the northern extents of the Canadian Prairie basins. The Canadian Precipitation Analysis (CaPA) combines GEM (Global Environmental Multi-scale model) data and available observation data to provide enhanced precipitation estimates. The CaPA analysis has recently been extended to produce high-resolution precipitation data over the Canadian Prairies, encompassing the Nelson-Churchill River Basin. Manitoba Hydro and other water practitioners in Manitoba have expressed interest in potentially using CaPA precipitation as hydrological model forcing for Prairie watersheds. A three step validation approach was designed and applied to assess CaPA for hydrologic modelling applications in the Nelson-Churchill River basin. Results of validation show that the quality of CaPA data varies among regions and seasons, with CaPA proving beneficial in both data-sparse regions and winter seasons most prominently. Overall, CaPA shows promise for water resource application in the Canadian Prairies.
3

Short To Medium Range Hydrometeorological Forecasting In The Rio Grijalva Basin, Mexico

Uribe, Edgar M January 2007 (has links)
The Rio Grijalva basin is the most important basin in Mexico in terms of hydropower production and damages related to extreme rainfall events. This study investigates establishing a short- to medium-range hydrometeorological forecasting system for this basin which comprises a hydrological model and a regional Numerical Weather Prediction Model (NWPM). A physical, distributed, hydrological model (MMS-PRMS) is implemented through the following steps: (1) basin parameterization; (2) interfacing to observed meteorological fields, and (3) parameter optimization. The datasets normally used to parameterize the MMS-PRMS are only available in the US so an alternative methodology for deriving parameters from globally available public datasets was devised. Modeled streamflow calculated by model with the initial parameters was in good agreement with observed streamflow, and optimization yielded even better agreement. The predictive capabilities of the hydrological model was then tested by implementing modeled rainfall and temperature from the North American Regional Reanalysis (NARR), these data being used as a surrogate for those that would be available from a regional NWPM. A significant bias in NARR-rainfall was identified and a novel probabilistic correction procedure devised. This procedure was then extended to provide estimates of uncertainty in the modeled streamflow. Within the calculated uncertainty, the modeled streamflow calculated with these corrected NARR data is in good agreement with modeled streamflow calculated using local meteorological data.
4

The Rise of New Copulas in Arabic

January 2015 (has links)
abstract: Arabic is widely known for the lack of copulas in nominal sentences in the present tense. Arabic employs a copula ‘kana’ in the past and future tenses. However, in some constructions the presence of a third person pronoun is necessary for the purpose of emphasis or ambiguity reduction. The data investigated in this thesis was from Classical Arabic, Standard Arabic, and the Western Saudi ‘Hijazi’ dialect. The thesis briefly discussed the grammaticalization of a transitive verb to a non-present tense copula in Classical Arabic. In addition, the thesis discussed the process of copularization that was a result of grammaticalization of the demonstrative third person pronoun ‘huwa’ to a present tense copula in Standard Arabic. It was shown that the pronoun went through a process of reanalysis from the specifier to the head position of PredP driven by Feature Economy and the Head Preference Principle. The result was the loss of the person feature. The new copula developed and attached to the negative particle ‘ma’ in the Hijazi dialect losing all its phi-features. These phenomena are known as the copula and negative cycles, respectively. The analysis was based on the Generative Grammar framework and the Minimalist program. This study attempted to shed light on Arabic copulas and contribute to more understanding of the use of these copulas in question and negative constructions. It may also help in typological studies, which may lead to a better understanding of the linguistic theory and the language faculty. / Dissertation/Thesis / Masters Thesis English 2015
5

Involvement of the Intraparietal Sulcus in Sentence Comprehension - An rTMS investigation

Sabnis, Prerana Ajit 30 March 2020 (has links)
Semantically reversible sentences, i.e., sentences wherein both characters can potentially perform the given action, have long been used to understand the various mechanisms involved in successful sentence comprehension. Over the decades, studies have established that sentences with non-canonical word-orders such as passive voice sentences are more difficult to process than canonical counterparts such as active voice sentences using psycholinguistic, neuroimaging, lesion-based, and more recently transcranial brain stimulation methods such as transcranial magnetic stimulation (TMS). In addition to understanding the cognitive processes involved, these studies have also attempted to uncover the underlying neural correlates. Various parts of the frontal, temporal, and parietal lobes have been thought to be critical for different functions. In the recent years, the parietal regions have garnered considerable attention. In particular, various studies have found the intraparietal sulcus (IPS) to be involved in the comprehension of semantically reversible sentences, particularly when they have non-canonical word-orders. In this thesis, I attempted to build on this literature and further understand the role of the IPS in sentence comprehension. More specifically I followed-up on two TMS studies by Finocchiaro and colleagues that looked at reversible Italian active and passive sentences. Online repetitive TMS (rTMS) to the posterior portion of the left IPS (henceforth, l-pIPS) affected only the processing of passive sentences in both experiments. In fact, one of the studies also found an effect on ‘passive’ pseudosentences, thus, prompting the authors to suggest that the l-pIPS affects passive sentences irrespective of semantic meaningfulness. The authors concluded that this region is likely to be involved in sentence comprehension, particularly at the stage where thematic reanalysis, i.e., a revision of the initially ascribed thematic roles, occurs. However, these studies were unable to discern if these effects were seen on reversible passives due to their reversibility, passive voice, or the non-canonical word-order seen in passive sentences. They also raised questions regarding whether the region is important in processing only thematic reversibility or is also involved in comprehending reversible sentences without thematic roles (e.g., comparative sentences). I ran three experiments to better understand these factors. In Chapter 1 I summarise the literature on the comprehension of reversible sentences. I discuss findings from behavioural, lesion-based, neuroimaging, and TMS studies that have formed the basis of the current thesis. I conclude by bringing to attention some of the questions raised by these studies that I have attempted to answer in the subsequent chapters. In Chapter 2 I attempted to understand the role of passive voice and reversibility in reanalysis and sentence comprehension. To do this I used a sentence comprehension task while administering online rTMS to the l-pIPS. Participants performed a forced-choice task where they were required to read reversible and irreversible Italian active and passive voice sentences and identify either the agent or the theme in alternate blocks. The experiment showed an effect of rTMS only on reversible passive sentences. While these results are in line with the previous studies, they also draw attention to a critical aspect of comprehension of passive voice sentences. They suggest that passive voice in itself may be insufficient to trigger reanalysis. Instead, it is likely that reanalysis is triggered by the co-occurrence of numerous factors such as voice and reversibility. However, as with the previous studies, this study still does not clarify the role of non-canonical word-order or passive voice per se. In an attempt to distinguish between the two, I ran an rTMS experiment with a sentence-picture verification task in Chapter 3. The experiment used reversible active and passive voice sentences in Hindi. The advantage that Hindi offers in this regard is that both actives and passives are typically presented in the agent-theme-action order. Consequently, such passives may not require the reassigning of originally established thematic roles. Stimulation to the l-pIPS showed no effects on these actives or passives. Interestingly, these null results serve as supporting evidence (albeit, weak) that non-canonical word-order may be essential for thematic reanalysis. If passive voice alone, or even a combination of passive voice and reversibility were sufficient to engender reanalysis, stimulation should have had effects on the passives even in the absence of a non-canonical word-order (as seen in the stimuli of this experiment). Finally, I attempted to understand if the region was involved only in comprehending reversible sentences with thematic role assignment, or also played a role in reversible sentences without thematic role assignment such as comparative sentences (where one of the two characters is the owner of a given property/feature). To do this, I ran the final rTMS experiment reported in Chapter 4. Participants received online stimulation to the l-pIPS while performing a sentence-picture verification task. The stimuli sentences consisted of reversible Italian declarative active and passive sentences, and comparative of majority or minority sentences. Comparatives were used because unlike Italian actives and passives, both types of comparatives are identical in word-order and other morphosyntactic features. In an attempt to maintain the visual complexity across stimuli pictures, same pictures were used to depict the relationships in both declarative and comparative sentences. The results of this study are rather puzzling. Unlike previous studies no effects were found on passive sentences. In terms of the comparative sentences, a selective effect was seen on the ‘easier’ comparatives of majority. These results call into question previous findings which have found an effect on the more ‘difficult’ sentence type, i.e., the passives. The effect of TMS on the comparatives of majority indicates the involvement of the l-pIPS in sentence comprehension yet again. However, these results to do not clarify what specific features of a sentence the l-pIPS helps comprehend. Moreover, given the consistent effect of rTMS on reversible Italian passives in the previous experiments, and the effect on comparatives of majority, it is possible that the current results may have been confounded by the use of complex stimuli. Coupled with the findings from the Finocchiaro studies, this thesis establishes the role of the l-pIPS in sentence comprehension. In particular, the results of the two Finocchiaro studies and Chapter 2 suggest that the co-occurrence of passive voice and reversibility is essential for reanalysis. While the results of Chapter 3 concur with these findings, they also strongly indicate that these features must co-occur with a third factor, namely a non-canonical word-order, to trigger reanalysis. Lastly, the results of Chapter 4 clarify the l-pIPS’ involvement in sentence comprehension. However, it leaves the exact role of the l-pIPS unclear in comprehending reversible sentences without thematic role assignment. The current thesis has advanced our understanding of some key factors responsible for reanalysis, and its neural correlates. Future studies can aim to understand these factors better by exploiting parallel versions of the same sentence type, and by studying different sentence types in isolation. For example, Hindi passives can be presented in both agent-theme-action and theme-agent-action word-orders. Contrasting such versions may help answer questions pertaining to word-order. On the other hand, studying sentences like declaratives and comparatives in separate experiments or even separate sessions may help simplify stimuli, thereby giving us clearer results.
6

Graphically Driven Interactive Stress Reanalysis for Machine Elements in the Early Design Stage

Terdalkar, Sachin Sharad 18 August 2003 (has links)
"In this work a new graphically driven interactive stress reanalysis finite element technique has been developed so that an engineer can easily carry out manual geometric changes in a machine element during the early design stage. The interface allow an engineer to model a machine element in the commercial finite element code ANSYS® and then modify part geometry graphically to see instantaneous graphical changes in the stress and displacement contour plots. A reanalysis technique is used to enhance the computational performance for solving the modified problem; with the aim of obtaining results of acceptable accuracy in as short a period of time in order to emphasize the interactive nature of the design process. Three case studies are considered to demonstrate the effectiveness of the prototype graphically driven reanalysis finite element technique. The finite element type considered is a plane stress four-node quadrilateral based on a homogenous, isotropic, linear elastic material. The first two problems consider a plate with hole and plate with fillets. These two examples demonstrate that by changing the hole and fillet size/shape, an engineer can manually obtain an optimum design based on the stress concentration factor, i.e. engineer-driven optimization process. Each case study considered multiple redesigns. A combined approximation reanalysis method is used to solve each redesigned problem. The third case study considers a support bracket. The goal is to design the cantilever portion of the bracket to have uniform strength and to minimize the stress concentration at the fillet. The major beneficiaries of the work will be engineers working in product development and validation of components and structures, which are subjected to mechanical loads. The scientific and technological relevance of this work applies not only to the early stage of design, but to a number of other applications areas in which benefits may accrue. A company may have needs for a rapid analysis and re-analysis tool for fatigue assessment of components manufactured slightly out of tolerance. Typically this needs to be carried out under a very restrictive time scale."
7

Coupled Evaluation of Below- and Above-Ground Energy and Water Cycle Variables from Reanalysis Products Over Five Flux Tower Sites in the U.S.

Lytle, William January 2015 (has links)
Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes, and have been evaluated using in situ data above or below ground. Here measurements for several years at five flux tower sites in the U.S. (with a total of 315,576 hours of data) are used for the coupled evaluation of both below- and above-ground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2 meter air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net shortwave and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely-used products, and helps understand the connection of their errors in above- versus below-ground quantities.
8

Downscaling of Wind Fields Using NCEP-NCAR-Reanalysis Data and the Mesoscale MIUU-Model / Nedskalning av storskaliga vindfält genom användande av återanalys data från ncep-ncar och den mesoskaliga miuu-modellen

Larsson, Mattias January 2006 (has links)
The profitability from the production wind power energy is related to the quality of the wind speed forecasts. All wind predicting methods needs meteorological data, for the prevailing synoptic situation, as input. High quality input is wanted for a better result. In this study a new idea of a method for estimation of high resolution wind fields is examined. The idea is to use an existing database, containing simulations of high resolution wind fields, to estimate the actual wind by combining the simulations in a way fitting actual synoptic data. The simulations in the database have been produced by the mesoscale MIUU-model, which has been developed by Leif Enger at Uppsala University. The database contains simulations characterized by different geostrophic wind speeds and directions. There is also a separation into four seasons, where values which are typical for each season is put on meteorological parameters. Reanalysis data from NCEP-NCAR, containing 850 hPa geopotential heights describing actual synoptic situations, is used to calculate geostrophic wind speeds and directions. Three different geostrophic wind calculation methods, the triangle method, the small cross-method and the large cross-method, are tested. The calculated geostrophic wind is compared between the methods. The small cross-method is chosen and the main reason for that is the large amount of reanalysis information considered by this method and the use of a small calculation area. Measurements of the wind speed and direction are available from the tower at Utgrunden. The geostrophic wind speeds and directions are therefore calculated especially for the position of Utgrunden. This is done by a linear weighting of data, from several grid points close to Utgrunden, with respect to the distance to Utgrunden. Linear weighting is also used when estimating the wind speed for Utgrunden. The wind speed is estimated by weighting together MIUU-model simulations, for different geostrophic wind speeds and directions, so that they fit the geostrophic wind values calculated for Utgrunden. The calculated wind speed, measured wind speed and calculated geostrophic wind speed, for Utgrunden, are compared. The correspondence, between the calculated and measured wind speed, turns out to be quite good for many time periods. The diurnal variations in the measured wind speed are partly captured by calculated wind speed, but the diurnal variations tend to be larger in the measured wind speed then in the calculated. There are also cases where there are large differences between the measured and estimated wind speed. Many of these cases are probably cased by unusual weather situations. By considering additional parameters, as the temperature field, it is likely that these wind estimations can be improved. With more research it may be possible to produce high resolution wind fields with enough accuracy to be useful as inputs in wind prognostic systems. The advantage with such a method would be that accurate high resolution wind fields could be produced without the use of a time consuming numerical high resolution model. / Lönsamheten för produktion av vindkraft elektricitet bestäms delvis av förmågan att göra bra vindprognoser för nästkommande dygn. Alla metoder för vindprognostisering behöver meteorologisk indata som beskriver den rådande synoptiska situationen. Kvaliteten och upplösningen på dessa indata har stor betydelse för metodens resultat. I denna studie undersöks en alternativ metod för bestämning av högupplösta vind fält. Idén är att man ska försöka utnyttja en tillgänglig databas av högupplösta vindfält, producerade av den mesoskaliga MIUU – modellen som är utvecklad av Leif Enger på meteorologiska institutionen vid Uppsala Universitet. Tanken är att dessa vindfält ska kunna kombineras på ett sådant sätt att de överensstämmer med en given synoptisk situation. MIUU – modell körningarna, i databasen, är indelade i situationer karaktäriserade av olika värden på den geostrofiska vindstyrkan och vindriktningen. Körningarna är gjorda för fyra säsonger, för vilka typiska värden för säsongen är satta på styrande parametrar. För att kunna kombinera MIUU - modell körningarna beräknas den geostrofiska vinden från 850 hPa geopotential höjd återanalys data tillgänglig från NCEP-NCAR. Tre olika beräkningsmetoder för geostrofisk vind testas och jämförs. Den ”lilla korsmetoden” väljs för uppgiften beroende på att den utnyttjar en förhållandevis stor mängd återanalys data, för beräkning av geostrofisk vind, samt använder litet beräkningsområde. Automatiskt uppmätta värden över vindhastighet och vindriktning finns tillgängliga från en mast positionerad vid Utgrunden i Kalmar sund. Den geostrofiska vinden beräknas därför i Utgrundens position. Beräkningen utförs genom linjär viktning av data från de från Utgrunden sett fem närmaste gridpunkterna (i lilla korsmetodens gridfält). En linjär viktning används sedan även för att vikta ihop de MIUU – modell simulerade vindfälten så att de passar de beräknade värdena på geostrofisk vindhastighet och vindriktning. Jämförelser görs mellan den beräknade vinden, den uppmätta vinden samt den geostrofiska vinden, för Utgrunden. Korrelationen, mellan uppmätt och beräknad vind, visar sig vara ganska god periodvis. Den dagliga variationen i den uppmätta vindhastigheten fångas delvis av beräkningsmetoden, men dygnsvariationen är betydligt större i den uppmätta vinden än i den beräknade. Det noteras även att det finns situationer då det är stora skillnader mellan beräknad och uppmätt vind. Dessa situationer beror i många fall troligen på onormala vädersituationer. Studium av ytterliggare parametrar, som t.ex. temperaturfältet, skulle troligen leda till betydande förbättringar i vinduppskattningen. Ytterligare forskning och förbättring av metoden skulle kunna leda till produktion av högupplösta vindfält med tillräcklig kvalitet för användning i vindprognostiseringsmodeller. Fördelen skulle i så fall vara möjligheten att kunna producera högupplösta vindfält utan användning av tidskrävande numerisk modeller.
9

The July Arctic Front in North America from ECMWF ERA-40 and NCEP/NCAR Reanalysis Products

Ladd, Matthew Jared 26 August 2010 (has links)
Boundaries between air masses, called frontal zones, have been associated with vegetation boundaries (Bryson, 1966; Hare and Ritchie, 1972). Using gridded climate reanalysis data, we analyze the air masses and frontal zones of North America. The position of the July Arctic front varies significantly through the period 1948-2007, with a mean position similar to that found by Bryson (1966). The variability of the front position can be associated with changes in the general circulation; when the AO and SOI are positive (negative), the position of the July Arctic front is further north (south). There is also more variability in the July Arctic front position in Eastern versus Western Canada. When the July Arctic front is north (south) of the mean position, the boreal forest and tundra vegetation is more (less) productive. There is some evidence that climate warming is only starting to shift the July Arctic front to the north. / This study was funded by the Natural Sciences and Engineering Research Council (NSERC) and the Polar Climate Stability Network (PCSN) project funded by the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS).
10

The July Arctic Front in North America from ECMWF ERA-40 and NCEP/NCAR Reanalysis Products

Ladd, Matthew Jared 26 August 2010 (has links)
Boundaries between air masses, called frontal zones, have been associated with vegetation boundaries (Bryson, 1966; Hare and Ritchie, 1972). Using gridded climate reanalysis data, we analyze the air masses and frontal zones of North America. The position of the July Arctic front varies significantly through the period 1948-2007, with a mean position similar to that found by Bryson (1966). The variability of the front position can be associated with changes in the general circulation; when the AO and SOI are positive (negative), the position of the July Arctic front is further north (south). There is also more variability in the July Arctic front position in Eastern versus Western Canada. When the July Arctic front is north (south) of the mean position, the boreal forest and tundra vegetation is more (less) productive. There is some evidence that climate warming is only starting to shift the July Arctic front to the north. / This study was funded by the Natural Sciences and Engineering Research Council (NSERC) and the Polar Climate Stability Network (PCSN) project funded by the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS).

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