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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.
391

Improved quantitative estimation of rainfall by radar

Islam, Md Rashedul 06 January 2006 (has links)
Although higher correlation between gauge and radar at hourly or daily accumulations are reported, it is rarely observed at higher time resolution (e.g. 10 -minute). This study investigates six major rainfall events in year 2000 in the greater Winnipeg area with durations varying from four to nine hours. The correlation between gauge and radar measurements of precipitation is found to be only 0.3 at 10-minute resolution and 0.55 at hourly resolution using Marshall-Palmer’s Z-R relationship (Z=200R1.6). The rainfalls are classified into convective and stratiform regions using Steiner et al. (1995)’s algorithm and two different Z-R relationships are tested to minimize the error associated with the variability of drop-size-distribution, however no improvement is observed. The performance of the artificial neural network is explored as a reflectivity-rainfall mapping function. Three different types of neural networks are explored: the back propagation network, the radial basis function network, and the generalized regression neural network. It is observed that the neural network’s performance is better than the Z-R relationship to estimate the rainfall events which was used for training and validation (correlation 0.67). When this network is tested on a new rainfall its performance is found quite similar to that obtained from the Z-R relationship (correlation 0.33). Based on this observation neural network may be recommended as a post-processing tool but may not be very useful for operational purposes - at least as used in this study. Variability in weather and precipitation scenarios affects the radar measurements which apparently makes it impossible for the neural network or the Z-R relationship to show consistent performance at every rainfall event. To account for variability in weather and rainfall scenarios conventional correction schemes for attenuation and hail contamination are applied and a trajectory model is developed to account for rainfall advection due to wind drift. The trajectory model uses velocity obtained from the single-doppler observation. A space-time interpolation technique is applied to generate reflectivity maps at one-minute resolution based on the direction obtained from the correlation based tracking algorithm. The trajectory model uses the generated reflectivity maps having one-minute resolution which help to account for the travel time by the rainfall mass to reach to the ground. It was found that the attenuation correction algorithm adversely increases the reflectivity. This study assumes that the higher reflectivity caused by hail contaminated regions is one reason for the overestimation in the attenuation correction process. It was observed that the hail capping method applied prior to the attenuation correction algorithm helps to improve the situation. A statistical expression to account for radome attenuation is also developed. It is observed that the correlation between the gauge and the radar measurement is 0.81 after applying the various algorithms. Although Marshall-Palmer’s relationship is recommended for stratiform precipitation only, this study found it suitable for both convective and stratiform precipitation when attenuation is properly taken into account. The precipitation processing model developed in this study generates more accurate rainfall estimates at the surface from radar observations and may be a better choice for rainfall-runoff modellers.
392

Approaching Concept Drift by Context Feature Partitioning

Hoffmann, Nico, Kirmse, Matthias, Petersohn, Uwe 20 February 2012 (has links) (PDF)
In this paper we present a new approach to handle concept drift using domain-specific knowledge. More precisely, we capitalize known context features to partition a domain into subdomains featuring static class distributions. Subsequently, we learn separate classifiers for each sub domain and classify new instances accordingly. To determine the optimal partitioning for a domain we apply a search algorithm aiming to maximize the resulting accuracy. In practical domains like fault detection concept drift often occurs in combination with imbalances data. As this issue gets more important learning models on smaller subdomains we additionally use sampling methods to handle it. Comparative experiments with artificial data sets showed that our approach outperforms a plain SVM regarding different performance measures. Summarized, the partitioning concept drift approach (PCD) is a possible way to handle concept drift in domains where the causing context features are at least partly known.
393

共同基金風格飄移分析 / Style drift of mutual funds

陳沛鈞 Unknown Date (has links)
我們利用Sharpe(1992)所提出的return-based模型來分析台灣經理人的風格遷移狀況。基金經理人的投資風格在分析面上,通常假設是定態不變的,意即不隨時間改變而變化。但是事實上,這是一個動態改變的過程。基金投資說明書上常常明定此基金經理人限制投資在哪類型的股票,但是基金經理人有可能依照不同的市場情況以及時機,從原先偏向小型股的經理人,轉而變成投資大型股的經理人。我們用rolling-window迴歸式的係數結果來估計風格以及計算參考Idzorek & Bertsch (2004)的風格遷移分數來為台灣一般共同基金經理人締訂一個比較指標,我們也利用計算出的風格係數畫出資產權數分配圖,經由此圖,我們亦可以觀察到基金經理人投資風格隨著時間經過的整個改變過程。風格遷移分數提供我們一個量化的方法來衡量風格遷移的現象,因為較早的研究文獻只有提供一個質化的圖型做大約的估計,因此這個風格分數提供了我們一個很好的輔助工具,將質化的圖形輔以量化的分數做整合搭配比較。 根據Brown and Harlow (2002)的結論,基金經理人投資風格的一致性以及基金表現績效有正相關的關係,意即當基金經理人的投資風格越一致,基金的表現就會越好,但是在我們的數據裡面這個關係並不顯著。 / We provide an introduction to utilize the return based style model of Sharpe (1992) to analyze the style drift of mutual fund managers in Taiwan in practice. Often the investment style is assumed to be constant through time but it actually is dynamic. We use rolling regressions to estimate the style exposures and calculate style drift score (Idzorek & Bertsch 2004) to produce the allocated maps. We can clearly see the changing process over time by the maps. SDS provides a single quantitative measure of style drift over the sample period because earlier research has only provided a qualitative method to approximately estimate. Brown and Harlow (2002) conclude that there is a positive relationship between investment style consistency and performance but in our sample the relation between score and fund performance is not obvious.
394

Seismic response of building façade system with energy absorbing connections

Hareer, Rahila Wardak January 2007 (has links)
Facades are popular in modern buildings and are made of different materials such as pre-cast concrete, glass, aluminium, granite or marble and steel. During recent times seismic activity in densely populated areas has resulted in damage and a consequent loss of life. There were many types of building failure, including failure of building facade systems. Facade systems are highly vulnerable and fail more frequently than the buildings themselves with significant devastating effects. During an earthquake building frames suffer large interstorey drifts, causing racking of the building facade systems. The facade systems may not be able to cater for such large deformations and this can result in either functional or total failure at the facade connections or damage by pounding (impact) with adjacent facade panels. Façade failure and collapse can cause serious damage to buildings and injury to people in the vicinity. Moreover, facade represent between 10- 20 % or more of the total building cost depending on the size and importance of the facility and facade material (Facades1980). Considering the cost and safety issues, the importance of a well designed facade system on a building needs to be emphasised. In modern buildings, energy absorbing passive damping devices are very commonly used for energy absorption in order to manage the vibration response of multistorey buildings in an earthquake event. A number of manufactured dampers such as Viscoelastic and viscous, friction and yielding dampers are available. These dampers use a range of materials and designs in order to achieve diverse levels of damping and stiffness. This thesis is an investigation of the seismic behaviour of building facade systems and studies the effects of facade and connection properties on this response. The objectives with energy absorbing connections of the study are to determine and control facade distortions and to establish the required connection properties. Finite Element techniques have been used for modelling and analysis of the building frame, facade and connections. Time history analyses under earthquake loadings were carried out to determine the system response in terms of inter-storey drifts, facade distortions, differential displacement between facades and frames and the axial force in horizontal connections. Connection properties with respect to stiffness and energy absorption capability (or damping) have been modelled and varied to obtain the desired response. Findings illustrate the influence of these connection properties on system response and show that it is possible to control facade distortions to within acceptable limits. They also demonstrate that energy absorbing connections are able to reduce inter-storey drifts and mitigate the detrimental seismic effects on the entire building facade system.
395

Seismic performance of reinforced concrete frames.

Kashyap, Jaya January 2009 (has links)
Many intra-tectonic plate regions are considered to have low to moderate seismic risk. However, devastating earthquakes can occur in these regions and result in high consequences in terms of casualties and damage. Non-ductile detailing practice employed in these structures make them prone to potential damage and failure during an earthquake. Furthermore, the use of infill walls is a divisive issue as on positive side dual wall-frame systems have beneficial effects related to strength, stiffness, and ductility. However, if not designed properly infill wall can also lead to undesirable structural failures of complete wall frame system. Although, there has been significant amount of international research in this area, it is worth noting that very little research exists for Australian frames. This thesis presents the experimental and analytical research conducted at The University of Adelaide to gain some insight into the behaviour of typically detailed Australian reinforced concrete frames subjected to ground motions. The main objectives of this research were (1) to investigate the behaviour of non-seismically designed reinforced concrete frames under a 500-YRP earthquake; (2) to determine the different magnitudes of earthquake (YRP) that are likely to cause excessive drifts in or collapse of gravity-load-designed reinforced concrete frames and (3) to investigate the effect of infill walls on the moment-resisting frames subjected to seismic loads. The experimental program consisted of earthquake simulation tests on a 1/5 scale model of a 3-storey reinforced concrete frame and four ½-scale reinforced concrete brick infilled frame specimens subjected to quasi-static cyclic loading. The analytical study included static pushover and non-linear dynamic analyses of the 3-, 5- and 12-storey reinforced concrete frames. From the overall performance of gravity-load-designed bare reinforced concrete frames considered in this study, it was concluded that the non-seismically designed frames appear to be capable of resisting a “design magnitude earthquake” (i.e., 500- YRP) in low earthquake hazard regions. However, their behaviour under more severe earthquakes (e.g. a 2500-YRP earthquake) is questionable. Perhaps the earthquake design requirements should consider as an alternative the ‘collapse prevention’ limit state for longer return period earthquakes, of the order of 2000–2500-YRP. The experimental research on reinforced concrete infilled frame indicated that the infill wall does not adversely effect the in plane ultimate strength, stiffness, and ductility of the bare reinforced concrete frame. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1372229 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009
396

Nearshore Dispersal and Reproductive Viability of Intertidal Fucoid Algae : how effective is drift in local to regional dispersal?

Hawes, Nicola Ann January 2008 (has links)
The ecological importance of drifting will depend on the abundance of drifting algae and whether it is reproductively viable. However, the ability of adult plants to successfully disperse long-distances by drifting is largely unknown, particularly for fucoids. The abundance, species composition, and reproductive status of drifting algae was examined by transect surveys around Kaikoura and Banks Peninsula. Abundance and species composition varied between sites, but all drifting algae that were in reproductive season, and had reproductive structures intact, were reproductively active. The reproductive longevity and viability of drifting and beach-cast Hormosira banksii, Durvillaea antarctica and Cytophora torulosa was compared with attached populations. Drifting algae remained reproductively viable, and fecundity did not differ from that of attached algae. Viable propagules were released from drifting algae for the duration of the experiments (H. banksii 57 days, D. antarctica 62 days, and C. torulosa 43 days). In contrast, beach-cast algae ceased to release propagules after 14 days. Dispersal by drifting relies on offshore transport after detachment. To determine the influence of wind and tidal currents on the nearshore transport of drifting algae, tagged H. banksii, D. antarctica, C. torulosa and GPS-tracked drifters were released from shore. Drifters generally moved in the direction of the prevailing wind, but some influence of tidal direction and bathymetry was detected. Offshore winds and outgoing tides were favourable for the offshore transport of surface drifting algae. Following dispersal and arrival at new locations, the distance between gametes may be important in determining the fertilisation success of dioecious species. Experiments testing the fertilisation success of H. banksii and D. antarctica, over increasing distances, showed that fertilisation success decreased with increasing distance between male and female gametes. Despite this, eggs were fertilised when male and female gametes were up to 2m apart, and sperm remained viable for 2 hours.
397

Prestige as the Highest Ambition: Emerging Research Universities and the National Research University Fund

Ryan, Sean Alan 05 1900 (has links)
In 2009 the Texas legislature created the National Research University Fund (NRUF), intended to encourage a select group of public doctoral universities in the state, known as emerging research universities (ERUs), to increase their institutional status related to academic research by awarding supplemental financial support for meeting specific policy metrics. Efforts to increase the research status of these universities occurred at a time when public financial support remained stagnate and overall institutional costs increased within the higher education sector. This study utilizes a theoretical approach grounded in strategic action fields and employs panel data and a difference in differences statistical technique to analyze the impact that NRUF policy has in assisting ERUs in achieving R1 status, and how this organizational change impacted access to, and the quality of, undergraduate education. Results indicate that the NRUF policy intervention was not statistically significant for any part of the study. These findings suggest that policy interventions do not matter as much as specific institutional characteristics and the overall policy environment. Enrollment and tuition revenue predicted institutional performance related to academic research and graduate education, while also assisting these institutions in maintaining undergraduate academic quality and access. These cultural and material resources at the institutional level matter, as does how the overall state field prioritizes various aspects of higher education. Given the amount of resources required of the policy, and the general lack of evidence of its positive or negative effects, these indicate that those resources would be more wisely targeted elsewhere.
398

Continental tectonics and landscape evolution in south-central Australia and southern Tibet /

Quigley, Mark Cameron. January 2006 (has links)
Thesis (Ph.D.)--University of Melbourne, School of Earth Sciences, 2007. / Typescript. Includes bibliographical references (leaves 211-240).
399

Surface exposure dating of glacial deposits from the last glacial cycle : evidence from the Eastern Alps, the Bavarian Forest, the Southern Carpathians and the Altai Mountains /

Reuther, Anne U. January 2007 (has links) (PDF)
Univ., Diss.--Regensburg, 2005.
400

Optimierung der elektrischen Eigenschaften von lateralen Superjunction-Bauelementen

Komet Permthammasin January 2008 (has links)
Zugl.: München, Techn. Univ., Diss., 2008

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