• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 41
  • 4
  • 3
  • 3
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 67
  • 67
  • 11
  • 10
  • 9
  • 9
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Four essays in dynamic macroeconomics

Sun, Qi January 2010 (has links)
The dissertation contains essays concerning the linkages between macroeconomy and financial market or the conduct of monetary policy via DSGE modelling. The dissertation contributes to the questions of fitting macroeconomic models to the data, and so contributes to our understanding of the driving forces of fluctuations in macroeconomic and financial variables. Chapter one offers an introduction to my thesis and outlines in detail the main results and methodologies. In Chapter two I introduce a statistical measure for model evaluation and selection based on the full information of sample second moments in data. A model is said to outperform its counterpart if it produces closer similarity in simulated data variance-covariance matrix when compared with the actual data. The "distance method" is generally feasible and simple to conduct. A flexible price two-sector open economy model is studied to match the observed puzzles of international finance data. The statistical distance approach favours a model with dominant role played by the expectational errors in foreign exchange market which breaks the international interest rate parity. Chapter three applies the distance approach to a New Keynesian model augmented with habit formation and backward-looking component of pricing behaviour. A macro-finance model of yield curve is developed to showcase the dynamics of implied forward yields. This exercise, with the distance approach, reiterate the inability of macro model in explaining yield curve dynamics. The method also reveals remarkable interconnection between real quantity and bond yield slope. In Chapter four I study a general equilibrium business cycle model with sticky prices and labour market rigidities. With costly matching on labour market, output responds in a hump-shaped and persistent manner to monetary shocks and the resulting Phillips curve seems to radically change the scope for monetary policy because (i) there are speed limit effects for policy and (ii) there is a cost channel for monetary policy. Labour reforms such as in mid-1980s UK can trigger more effective monetary policy. Research on monetary policy shall pay greater attention to output when labour market adjustments are persistent. Chapter five analyzes the link between money and financial spread, which is oft missed in specification of monetary policy making analysis. When liquidity provision by banks dominates the demand for money from the real economy, money may contain information of future output and inflation due to its impact on financial spreads. I use a sign-restriction Bayesian VAR estimation to separate the liquidity provision impact from money market equilibrium. The decomposition exercise shows supply shocks dominate the money-price nexus in the short to medium term. It also uncovers distinctive policy stance of two central banks. Finally Chapter six concludes, providing a brief summary of the research work as well as a discussion of potential limitations and possible directions for future research.
32

Evaluating enhanced hydrological representations in Noah LSM over transition zones : an ensemble-based approach to model diagnostics

Rosero Ramirez, Enrique Xavier 03 June 2010 (has links)
This work introduces diagnostic methods for land surface model (LSM) evaluation that enable developers to identify structural shortcomings in model parameterizations by evaluating model 'signatures' (characteristic temporal and spatial patterns of behavior) in feature, cost-function, and parameter spaces. The ensemble-based methods allow researchers to draw conclusions about hypotheses and model realism that are independent of parameter choice. I compare the performance and physical realism of three versions of Noah LSM (a benchmark standard version [STD], a dynamic-vegetation enhanced version [DV], and a groundwater-enabled one [GW]) in simulating high-frequency near-surface states and land-to-atmosphere fluxes in-situ and over a catchment at high-resolution in the U.S. Southern Great Plains, a transition zone between humid and arid climates. Only at more humid sites do the more conceptually realistic, hydrologically enhanced LSMs (DV and GW) ameliorate biases in the estimation of root-zone moisture change and evaporative fraction. Although the improved simulations support the hypothesis that groundwater and vegetation processes shape fluxes in transition zones, further assessment of the timing and partitioning of the energy and water cycles indicates improvements to the movement of water within the soil column are needed. Distributed STD and GW underestimate the contribution of baseflow and simulate too-flashy streamflow. This work challenges common practices and assumptions in LSM development and offers researchers more stringent model evaluation methods. I show that, because of equifinality, ad-hoc evaluation using single parameter sets provides insufficient information for choosing among competing parameterizations, for addressing hypotheses under uncertainty, or for guiding model development. Posterior distributions of physically meaningful parameters differ between models and sites, and relationships between parameters themselves change. 'Plug and play' of modules and partial calibration likely introduce error and should be re-examined. Even though LSMs are 'physically based,' model parameters are effective and scale-, site- and model-dependent. Parameters are not functions of soil or vegetation type alone: they likely depend in part on climate and cannot be assumed to be transferable between sites with similar physical characteristics. By helping bridge the gap between the model identification and model development, this research contributes to the continued improvement of our understanding and modeling of environmental processes. / text
33

The Vertical Route Forecast : an Evaluation of a New Flight Path Based Weather Forecast Product with HARMONIE-AROME High Resolution Forecasts over Scandinavia / Vertikal ruttprognos : En utvärdering av en ny flygvägsbaserad väderprognosprodukt med högupplösta prognoser från HARMONIE-AROME över Skandinavien

Leffler, Ingela January 2017 (has links)
As a complement to existing weather forecast products for aviation, a prototype of a new product is presented and evaluated. It shows the atmosphere in a vertical cross section along the intended route. This Vertical Route Forecast introduces the possibility to examine the vertical distribution of cloud layers, wind, precipitation, turbulence and more along the flight path. Through a market research with 166 participating Swedish pilots it was found that the demand for the product is high and that 90 % of the participants would use it if available. The Vertical Route Forecast is inspired by the existing product GRAMET by Ogimet (Ballester Valor, n.d) but instead of using forecasts from the weather prediction model GFS (Global Forecast System) at 0.5° (56 km) resolution it uses data from the 2.5 km resolution model HARMONIE-AROME. The latter is operational at SMHI (Swedish Meteor-ological and Hydrological Institute) and because of its high resolution it enables more detailed structures of the weather to be presented. The product differs further from GRAMET by showing only the lower parts of the atmosphere so as to be of more use to small aircraft pilots flying at low levels. To assess the accuracy of the forecasts, a model evaluation of HARMONIE-AROME has been conducted through a case study in which the model was verified and compared to GFS over Sweden. The two models were verified against their own analyses at four different atmospheric pressure levels in terms of bias, root mean square error, standard deviation and correlation. HARMONIE-AROME performed best for temperature while GFS had the best forecasts of relative humidity. Wind speed and direction were also evaluated with insignificantly better results for GFS. However, the weather did not vary very much during the study as the two weeks were dominated by high pressure systems. Other evaluations made of HARMONIE-AROME by e.g. the HIRLAM consortium (2016a) have shown good or adequate performance of the model. It was concluded that HARMONIE-AROME would be well suited as the forecast producing model for this Vertical Route Forecast. / För att piloter ska kunna planera en säker flygning behöver de tillgång till bra och användbara väderprognoser. Med de prognosprodukter som finns tillgängliga idag kan det dock vara svårt att få en detaljerad uppfattning om hur vädret kommer vara längs med vägen. Här presenteras och utvärderas därför ett förslag till en ny prognosprodukt som visar atmosfären i en sidovy längs en valfri sträcka. Med den kan piloten granska utbredningen av bland annat molntäcken, vind, nederbörd och turbulens i höjdled längs den planerade färdvägen. Denna vertikala ruttprognos är inspirerad av den redan befintliga produkten GRAMET från Ogimet (Ballester Valor, n.d) men visar mer detaljerade prognoser som är bättre anpassade till flygningar på låga höjder. Vid en marknadsundersökning utförd med 166 medverkande svenska piloter stod det klart att efterfrågan på produkten är hög och 90 % av de medverkande påstod att de skulle använda den om den fanns tillgänglig. För att bedöma prognosernas precision har en utvärdering gjorts av den prognosmodell som använts till produkten. Modellen används annars hos SMHI (Sveriges Meteorologiska och Hydrologiska Institut) och kallas HARMONIE-AROME. I en fallstudie jämfördes den med modellen GFS som skapar prognoserna för GRAMET. Studien täckte Sverige och sträckte sig över 14 dagar i början av februari, 2017. HARMONIE-AROME visade bäst resultat för temperatur medan GFS gjorde de bästa fuktighetsprognoserna. Vindhastighet och vindriktning undersöktes också och för dem var modellerna ungefär lika bra. Vädret varierade dock inte så mycket under tvåveckorsperioden som dominerades av högtryck. Andra utvärderingar som gjorts av HARMONIE-AROME togs också i beaktande och modellen verkar generellt sett göra bra prognoser. Från samtliga resultat drogs slutsatsen att prognos-produkten skulle underlätta för småplanspiloter samt att HARMONIE-AROME är en lämplig modell att använda för att skapa dess prognoser.
34

Estudo dos Mecanismos Vinculados ao Estabelecimento de um Evento de ZCAS Através de Simulações com o Modelo WRF / Study of Mechanisms Associated to the Establishment of a SACZ Event by Simulations with the WRF Model

Natália Pillar da Silva 30 May 2018 (has links)
No presente estudo, os mecanismos vinculados à formação de um intenso evento de Zona de Convergência do Atlântico Sul (ZCAS) foram investigados. Para isso, uma análise observacional foi realizada para identificação desse sistema e seguinte implementação de um estudo numérico em uma escala sub-sazonal. Uma vez que a atividade da ZCAS é predominantemente concentrada em uma das regiões de maior importância socioeconômica da América do Sul, os estudos de previsibilidade dessa feição são extremamente importantes. O evento escolhido pela análise observacional foi caracterizado pelo suporte de uma estrutura em larga escala para seu desenvolvimento e persistência, através da presença de um vórtice ciclônico na região costeira do sudeste do Brasil. A representação numérica desse caso de ZCAS foi particularmente desafiadora, uma vez que trata-se de um sistema complexo, cujo desenvolvimento e evolução conectam-se a características atmosféricas de grande escala. Para aprimorar a representação numérica desse evento, várias aplicações utilizando-se nudging espectral foram testadas, para garantir que as características de grande escala que suportam o sistema fossem bem representadas pelo modelo numérico. Os resultados mostram que a alternativa menos restritiva para a aplicação do nudging espectral mostrou-se ideal para manter suas características importantes, e ainda permitindo que os componentes físicos do modelo contribuam com a representação da atmosfera em escalas menores. A partir disso, novos experimentos numéricos foram conduzidos para uma avaliação de como diferentes parametrizações convectivas e microfísica representam a banda de precipitação associada ao sistema. Os resultados mostram que, quando usados juntos, tanto a opção de microfísica WRF Single Moment 6-Class (WSM6) quanto a opção cumulus de Kain-Fritsch (KF) contribuíram para a formação da banda convectiva associada à ZCAS. Os resultados também mostram que é possível usar um esquema de microfísica mais simples (WSM3) para a representação do sistema, uma vez que os desempenhos entre os diferentes testes em microfísica foram semelhantes. / In the present study, the mechanisms and formation of an intense South Atlantic Convergence Zone (SACZ) event were investigated. For this, an observational analysis was performed to identify this system for the implementation of a numerical study on a sub-seasonal scale. Since the SACZ activity is predominantly concentrated over one of the most socioeconomically important regions of South America, predictability studies for this system are extremely valuable. The SACZ event chosen by the observational analysis was supported by a large-scale structure that featured a cyclonic vortex in the coastal region of southeastern Brazil. The numerical representation of a SACZ case in this context was particularly challenging since the SACZ is a very complex system and its development and evolution are closely linked to large-scale atmospheric features. To improve the numerical representation of such event, several spectral nudging applications were tested to ensure the large scale features that support the systems are well represented by the numerical model. Results show that the less restrictive alternative for the spectral nudging application was ideal for maintaining important features in large scales while still allowing the physical components of the model to contribute the representation of the atmosphere on smaller scales. From this, numerical experiments were conducted for an evaluation of how different convective parametrizations and microphysics represent the precipitation band associated to the system. The results show that, when used together, both WRF Single Moment 6-Class (WSM6) microphysics option and Kain-Fritsch (KF) cumulus option contributed to the formation of convective band associated with the SACZ. Results also show that it is possible to use a simpler microphysics scheme (WSM3) for the representation of the system, since the performances between different tests in microphysics were similar.
35

Estudo dos Mecanismos Vinculados ao Estabelecimento de um Evento de ZCAS Através de Simulações com o Modelo WRF / Study of Mechanisms Associated to the Establishment of a SACZ Event by Simulations with the WRF Model

Silva, Natália Pillar da 30 May 2018 (has links)
No presente estudo, os mecanismos vinculados à formação de um intenso evento de Zona de Convergência do Atlântico Sul (ZCAS) foram investigados. Para isso, uma análise observacional foi realizada para identificação desse sistema e seguinte implementação de um estudo numérico em uma escala sub-sazonal. Uma vez que a atividade da ZCAS é predominantemente concentrada em uma das regiões de maior importância socioeconômica da América do Sul, os estudos de previsibilidade dessa feição são extremamente importantes. O evento escolhido pela análise observacional foi caracterizado pelo suporte de uma estrutura em larga escala para seu desenvolvimento e persistência, através da presença de um vórtice ciclônico na região costeira do sudeste do Brasil. A representação numérica desse caso de ZCAS foi particularmente desafiadora, uma vez que trata-se de um sistema complexo, cujo desenvolvimento e evolução conectam-se a características atmosféricas de grande escala. Para aprimorar a representação numérica desse evento, várias aplicações utilizando-se nudging espectral foram testadas, para garantir que as características de grande escala que suportam o sistema fossem bem representadas pelo modelo numérico. Os resultados mostram que a alternativa menos restritiva para a aplicação do nudging espectral mostrou-se ideal para manter suas características importantes, e ainda permitindo que os componentes físicos do modelo contribuam com a representação da atmosfera em escalas menores. A partir disso, novos experimentos numéricos foram conduzidos para uma avaliação de como diferentes parametrizações convectivas e microfísica representam a banda de precipitação associada ao sistema. Os resultados mostram que, quando usados juntos, tanto a opção de microfísica WRF Single Moment 6-Class (WSM6) quanto a opção cumulus de Kain-Fritsch (KF) contribuíram para a formação da banda convectiva associada à ZCAS. Os resultados também mostram que é possível usar um esquema de microfísica mais simples (WSM3) para a representação do sistema, uma vez que os desempenhos entre os diferentes testes em microfísica foram semelhantes. / In the present study, the mechanisms and formation of an intense South Atlantic Convergence Zone (SACZ) event were investigated. For this, an observational analysis was performed to identify this system for the implementation of a numerical study on a sub-seasonal scale. Since the SACZ activity is predominantly concentrated over one of the most socioeconomically important regions of South America, predictability studies for this system are extremely valuable. The SACZ event chosen by the observational analysis was supported by a large-scale structure that featured a cyclonic vortex in the coastal region of southeastern Brazil. The numerical representation of a SACZ case in this context was particularly challenging since the SACZ is a very complex system and its development and evolution are closely linked to large-scale atmospheric features. To improve the numerical representation of such event, several spectral nudging applications were tested to ensure the large scale features that support the systems are well represented by the numerical model. Results show that the less restrictive alternative for the spectral nudging application was ideal for maintaining important features in large scales while still allowing the physical components of the model to contribute the representation of the atmosphere on smaller scales. From this, numerical experiments were conducted for an evaluation of how different convective parametrizations and microphysics represent the precipitation band associated to the system. The results show that, when used together, both WRF Single Moment 6-Class (WSM6) microphysics option and Kain-Fritsch (KF) cumulus option contributed to the formation of convective band associated with the SACZ. Results also show that it is possible to use a simpler microphysics scheme (WSM3) for the representation of the system, since the performances between different tests in microphysics were similar.
36

Marketing Mix Modelling: A comparative study of statistical models / En jämförelsestudie av statistiska modeller i en Marketing Mix Modelling-kontext

Wigren, Richard, Cornell, Filip January 2019 (has links)
Deciding the optimal media advertisement spending is a complex issue that many companies today are facing. With the rise of new ways to market products, the choices can appear infinite. One methodical way to do this is to use Marketing Mix Modelling (MMM), in which statistical modelling is used to attribute sales to media spendings. However, many problems arise during the modelling. Modelling and mitigation of uncertainty, time-dependencies of sales, incorporation of expert information and interpretation of models are all issues that need to be addressed. This thesis aims to investigate the effectiveness of eight different statistical and machine learning methods in terms of prediction accuracy and certainty, each one addressing one of the previously mentioned issues. It is concluded that while Shapley Value Regression has the highest certainty in terms of coefficient estimation, it sacrifices some prediction accuracy. The overall highest performing model is the Bayesian hierarchical model, achieving both high prediction accuracy and high certainty.
37

Assessment of Control Charts for Evaluating Dynamic Accuracy of Forest Growth Models

Cristan, Richard Raymond 01 December 2010 (has links)
The purpose of this study was to determine if control charts are an effective tool to identify trends in forest growth and yield model accuracy. Accurate forest growth and yield models are important for projecting future forest composition. However, environmental factors have the potential to make forest growth models created from historic data inaccurate. Control charts in this study determine if forest growth predictions fall within confidence limits established for historic growth at a number of points in time. Two data sets were used in this study: the first was a Continuous Forest Inventory (CFI) from three tracts at the University of Tennessee Cumberland Research Station and the second data set was Forest Inventory and Analysis data collected by the U.S. Forest Service. The CFI plots represented a stand level data set measured every 5 years from 1962-1977 and revisited for a re-measurement in 2009. The FIA plots were a regional data with subsets of plots measured annually from 1999-2008. The FIA data set was limited to plots of the oak/hickory forest type from Tennessee, Alabama, and Georgia. Two forest growth and yield models were used to predict growth: (1) WinYield and (2) Forest Vegetation Simulator (FVS). The two different data sets were used with both FVS and WinYield to evaluate control charts using different models ad at different spatial and temporal scales. The data sets were also subset by site index, stand age, stocking percent, aspect, and species composition to determine if control charts could identify changes in model accuracy for forests subjected to different growing conditions. The CFI and FIA data had short growth predictions and control charts indicated that there were no trends affecting accuracy. The CFI data also had a long growth prediction of 32 years and the control charts found that the predictions using WinYield and FVS were inaccurate, indicating that there may be a trend causing inaccuracy in the model.
38

Essays on autoregressive conditional heteroskedasticity

Silvennoinen, Annastiina January 2006 (has links)
Diss. Stockholm : Handelshögskolan, 2006 S. 1-9: introduction, s. 11-170: 5 research papers
39

The Design, Development And Evaluation Of An Electronic Performance Support System (epss) For The Crime Scene Investigation Unit

Yakin, Ilker 01 December 2012 (has links) (PDF)
The purpose of this study is to design, develop and evaluate an electronic performance support system (EPSS) for the crime scene investigation unit (CSI). For this purpose, a sequential explanatory strategy as a procedure of the mixed method design was used in analysis and evaluation of the EPSS. The research was composed of three main phases: analysis / design, development and implementation, and evaluation of the EPSS. In first phase composed of performance and cause analyses, the CSI Unit&rsquo / s existing information, and contributing causal performance factors based on Gilbert&rsquo / Behavior Engineering Model were explored. In performance analysis phase, official documentation of the CSI Unit was reviewed. As for cause analysis, the survey and focus group interviews were conducted to 1176 and 22 CSI officers, respectively. These data were analyzed using with both quantitative and qualitative methods to facilitate the selection of the most appropriate intervention and its components. Analyses results revealed that 14 basic influences grouped under the workplace and competency on human behavior impacted performance of the officers. Based on these results, an EPSS composed of intrinsic, extrinsic and external levels, and support components was designed and developed in the second phase. Having been implemented, the evaluation of the EPSS based on the Kirkpatrick&rsquo / Four Levels of Evaluation Model was conducted v to determine the overall impact, perceived benefits, and effectiveness of the intervention in third phase. In this phase, a survey, interviews, computer logs and a checklist were used so as to assess the accomplishment of the EPSS. While the survey and the checklist were administered to the 191 officers and 2 experts from the field, the interviews were conducted with 12 officers. Evaluation results admitted that the CSI officers&rsquo / reactions were very positive to the EPSS. While, an intrinsic support made a major contribution to their productivity, establishing standardization would be perceived as the major impact of the EPSS. Lastly, increasing identity and simplifying criminal justice system were the two main impact factors on the society that the system would influence positively.
40

Modellering av vattenflöden samt kväve- och fosforkoncentrationer från Krycklans avrinningsområde med HYPE-modellen

Sandqvist, Elin January 2012 (has links)
HYPE-modellen utvecklades som ett hjälpmedel för att uppfylla målet om att alla svenska vattendrag ska ha uppnått åtminstone god ekologisk status år 2015, enligt EU:s ramdirektiv för vatten. I HYPE-modellen delas avrinningsområdet in i markklasser, som definieras utifrån kombinationen av jordart och markanvändning/marktäckeklass. I modellen finns det många parametrar. Vissa av dem är generella för ett större område eller kan hämtas ifrån tidigare forskning, medan andra måste kalibreras för varje avrinningsområde. De parametrar som kalibreras beror i de flesta fall antingen av jordart eller av markanvändning eller marktäckeklass. Syftet i den här undersökningen var att kalibrera HYPE-modellen för ett mindre avrinningsområde samt undersöka avrinningsvägar och utvärdera den utförda kalibreringen. Det undersökta avrinningsområdet kallas Krycklan och ligger i Vindeln kommun i Västerbottens län. Det är ett avrinningsområde som huvudsakligen består av skog, men även innehåller inslag av jordbruksmark och myrmark. Kalibreringen gjordes i två steg, först för ett mindre delavrinningsområde och sedan för hela avrinningsområdet. Två avrinningskalibreringar gjordes för det mindre delavrinningsområdet. Kalibrering A utfördes med ansatsen att få en så hög anpassning som möjligt, med utgångspunkt i det statistiska måttet NSE, vilket är kvadratsumman av residualerna dividerat i den totala kvadratsumman. Kalibrering B gjordes i samråd med SMHI om rimlig storlek på parametervärdena, men gav ett sämre värde på NSE. För hela avrinningsområdet utfördes endast en kalibrering. Ett försök till modellering av kväve- och fosforhalter i avrinnande vatten gjordes även. Resultatet visade att det gick att få en kalibrering av modellen att följa uppmätt flöde väl, även på mikroskala. Skillnaden mellan kalibrering A och kalibrering B var att den första bättre fångade uppmätta flödestoppar, men gav ett för högt basflöde. För både blöta och torra år gick det att få en hög anpassning, men kalibreringen fungerade generellt sätt bättre för blöta år. Det var betydligt svårare för modellen att fånga variationen i kväve- och fosforkoncentrationer, men samband mellan modell och mätvärdena kunde ändå ses. / The HYPE-model was developed as an aid of achieving the goal of all Swedish watercourses should have reached at least well ecological status by the year of 2015, according to the EU Water Framework Directive. In the HYPE model, the catchment is divided into soil classes which are a combination of soil and land use. In the model, there are many parameters. Some of them are general for a larger area or can be obtained from previous research, while others must be calibrated for each catchment. The parameters to be calibrated depend in the most cases either on soil or land uses. The aim of this study was to calibrate and evaluate the HYPE model for a small catchment. The investigated catchment is called Krycklan and is located in the municipality of Vindeln in the province Västerbotten. The catchment consists mostly of forest, but there are also some agriculture and mire. The calibration was made in two steps, first on a small sub-basin and then to the entire basin. Two runoff calibrations were made for the smaller sub-basin. Calibration A was performed with the approach to obtain as high fit as possible, on the basis of the statistical measure NSE, which is the quadrate of the residuals divided in the quadrate of the total quadrate sum. Calibration B was made after consultation with SMHI (The Swedish Meteorological and Hydrological Institute) of the adequate size of the parameter values. For the entire basin only one calibration was performed. An attempt at modelling of nitrogen and phosphorus concentration in runoff was also made. The results showed that it was possible to get the model to follow the measured flow well, even at the micro scale. The difference between calibration A and calibration B was that the first one was better to catch the measured flow peaks, but resulted in too high base flow. For both wet and dry years it was possible to obtain a high fit, but the model generally got better for the wet years. There was much more difficult for the model to capture variation in nitrogen and phosphorus, but the connection between the model and the measurements could still be seen.

Page generated in 0.0592 seconds