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- Browsing Fakultet for naturvitenskap og teknologi by Title
Browsing Fakultet for naturvitenskap og teknologi by Title
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Hattermann, Tore (Doctoral thesis; Doktorgradsavhandling, 10-Dec-2012)[+][-]
Abstract: This thesis investigates the interaction of the Antarctic ice shelves along the coast of Dronning Maud Land with the ocean circulation in the Eastern Weddell Sea. A set of direct oceanic observations below the Fimbul Ice Shelf, which were acquired during three Antarctic field seasons in the austral summers 2009/10, 2010/11 and 2011/12, is a central element of the presented work. This new oceanographic dataset is complemented by a high-resolution state-of-the-art ice shelf - ocean circulation model. The results provide an estimate of the amount of basal melting at the Fimbul Ice Shelf, and revise the physical processes that determine the ocean heat fluxes over the East Antarctic continental slope. A major finding is that deep-ocean heat fluxes towards the ice are much more constrained than predicted by previous ocean models, causing substantially lower rates of basal melting than earlier suggested. The predicted basal melting is consistent with mass balance estimates from satellite data and implicates that the Fimbul Ice Shelf is currently not subject to rapid basal mass loss. Furthermore, the complex interplay of the processes within the coastal, frontal system, and their respective role in transporting heat for melting towards the ice is examined. The results emphasize the importance of oceanic eddies within the coastal circulation for controlling the inflow of Warm Deep Water into the ice shelf cavities. A realistic representation of the effect of the mesoscale eddy overturning is thus a crucial requirement in order to simulate basal melting along the Weddell Sea coast in the present and future climate. The results also imply that fresh, and solar-heated Antarctic Surface Water plays a central role for the ice shelf cavity exchange. Being produced by sea ice melting at the ocean surface, this water mass directly enters the cavity and increases the melting of shallow ice. Due to its buoyancy, the presence of Antarctic Surface Water also alters the coastal dynamics and regulates the inflow of warm water at depth, thus showing that a more detailed understanding of the role of this water mass for basal melting around Antarctica will need further attention. Finally, the results suggest a direct relationship between the simulated basal melting and only a few deterministic parameters of the coastal circulation, which is used to derive a simple parameterization of for basal melting at the Fimbul Ice Shelf. Description: Papers 3 and 4 are not available in Munin:
3. T. Hattermann, L. H. Smedsrud, O. A. Nøst, J. M. Lilly, and B. Galton-Fenzi: 'Modeling basal melting below the Fimbul Ice Shelf, Antarctica' (manuscript)
4. Q. Zhou, T. Hattermann and O. A. Nøst: 'Wind-driven spreading of fresh Antarctica Surface Water below ice shelves in the Eastern Weddell Sea' (manuscript)URI: http://hdl.handle.net/10037/5147 File(s) in this item: 3
paper_1.pdf (3.982Mb)paper_2.pdf (1.604Mb)thesis.pdf (22.16Mb) -
Lanes, Børge (Master thesis; Mastergradsoppgave, May-2010)[+][-]
Abstract: Graphic Processing Units have during the recent years evolved into inexpensive high-performance many-core computing units. Earlier being accessible only by graphic APIs, new hardware architectures and programming tools have made it possible to program these devices using arbitrary data types and standard languages like C. This thesis investigates the development process and performance of image and video processing algorithms on graphic processing units, regardless of vendors. The tool used for programming the graphic processing units is OpenCL, a rela- tively new specification for heterogenous computing. Two image algorithms are investigated, bilateral filter and histogram. In addition, an attempt have been tried to make a template-based solution for generation and auto-optimalization of device code, but this approach seemed to have some shortcomings to be usable enough at this time. URI: http://hdl.handle.net/10037/4346 File(s) in this item: 1
thesis.pdf (9.241Mb) -
Tobiassen, Alexander (Master thesis; Mastergradsoppgave, 27-Oct-2010)[+][-]
Abstract: Breast cancer is one of the most frequent types of cancer in the female population today. Modern diagnostic modalities, while proven to be helpful within large scale screening programs, are inherently limited with regards to specificity and sensitivity, and use active methods for acquisition of information. A passive and non-invasive method for detection and diagnostic purposes could therefore be a valuable asset to the existing technology. One such method is microwave radiometry. A microwave radiometer is an instrument for non-invasive thermography of subcutaneous temperatures. Recent advances within the field has demonstrated that this technology could be helpful in conjunction with existing methods. This thesis presents the design, implementation and experimental verification of a miniaturized medical microwave radiometer. The design is based on the Switch-Circulator Dicke-configuration to minimize effects of gain variations and mismatch at the antenna input. The performance of the radiometric system is verified through phantom experiments with a hot object embedded at various depths in a homogeneous, lossy medium. Results display a good coherence with regards to linearity, temperature sensitivity and repeatability. For an integration time constant of 2s, the temperature resolution is found to be approximately 0.07C, which is comparable with similar instruments as reported in literature. URI: http://hdl.handle.net/10037/2958 File(s) in this item: 1
thesis.pdf (4.112Mb) -
Frøisland, Dag Helge; Årsand, Eirik; Skårderud, Finn (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Background: Only 17% of Norwegian children and adolescents with diabetes achieve international treatment goals measured by glycated hemoglobin (HbA1c). Classic patient–physician consultations seem to be poorly adapted to young children. New strategies that are better attuned to young people to improve support of adolescents’ self-management of diabetes need to be tested and evaluated. Objective: (1) To explore how applications for mobile phones can be used in follow-up of adolescents with type 1 diabetes, and (2) to use the findings to guide further development of the applications and as a basis for future studies. Method: We pilot tested two mobile phone applications: (1) an application that contained a picture-based diabetes diary to record physical activity and photos taken with the phone camera of food eaten, where the phone also communicated with the glucometer by Bluetooth technology to capture blood glucose values, and (2) a Web-based, password-secured and encrypted short message service (SMS), based on access using login passwords received via SMS to be used by participants to send messages to their providers when they faced obstacles in everyday life, and to send educational messages to the participants. At the end of the 3-month pilot study, 12 participants (7 girls and 5 boys ) aged 13–19 years completed semistructured interviews. The participants had a mean HbA1c value of 8.3 (SD 0.3), mean age of 16.2 (SD 1.7) years, mean body mass index of 23.3 (SD 3.2) kg/m2, and mean diabetes duration of 7.5 (SD 4.6) years. We applied three additional measurements: change in metabolic control as measured by HbA1c, the System Usability Scale, and diabetes knowledge. Results: From the interviews, three main categories emerged: visualization, access, and software changes. Participants appreciated the picture-based diary more than the SMS solution. Visualization of cornerstones in diabetes self-care (ie, diet, insulin dosage, physical activity, and pre- and postprandial glucose measurements all transformed into one picture) in the mobile diary was found to be an important educational tool through reflections in action. This led to a change in participants’ applied knowledge about the management of their disease. Additional measurements supplemented and supported the qualitative findings. However, changes in HbA1c and participants’ theoretical knowledge as tested by a 27-item questionnaire, based on a national health informatics’ diabetes quiz, before and after the intervention were not statistically significant (P = .38 and P = .82, respectively, paired-samples t test). Participants suggested additional functionality, and we will implement this in the design of the next software generation. Conclusion: Participants reported an increased understanding of applied knowledge, which seem to positively affect diabetes self-care. Visual impressions seem well adapted to the maturation of the adolescent brain, facilitating the link between theoretical knowledge and executive functions. SMS gave the adolescents a feeling of increased access and security. Participants gave valuable input for further development of these applications. URI: http://hdl.handle.net/10037/5056 File(s) in this item: 1
article.pdf (378.0Kb) -
Heimdal, Tord-Arne (Master thesis; Mastergradsoppgave, 18-Dec-2009)[+][-]
Abstract: Live video search is emerging as a platform for multimedia production and entertainment service. Such systems rely on a stream of live video and metadata describing the video content. A high quality source for such metadata can be found on the web. Identifying and extracting metadata from web pages can be done by crawling and scraping. However, general crawler politeness rules limit per-site polling frequency, and therefore the freshness of the retrieved data is also limited. % our solution In this thesis we present a metadata extraction system capable of combining high metadata freshness, while at the same time adhering to polling politeness rules. To achieve this, the proposed solution uses a pool of web sources containing overlapping information scheduled in a round-robin fashion. % evaluation Our experiments and analysis show that our system is capable of keeping the average metadata freshness higher than any single-source solution, while at the same time adhere to polling politeness rules. URI: http://hdl.handle.net/10037/2400 File(s) in this item: 1
thesis.pdf (915.6Kb) -
Orlin, Karsten (Master thesis; Mastergradsoppgave, 24-Sep-2009)[+][-]
Abstract: In looking at the XMPP protocol as an alternative to the ordinary way of transferring files within a health network setting, namely e-mail, performance and security are important factors to consider. For security reasons we preferred to use in-band over out-of-band file transfer. The tradeoff is that this method puts a higher strain on the XMPP server and is significantly slower than its counterpart, out-of-band. In researching a specific XMPP implementation, the Openfire XMPP server, and looking into how it deals with in-band file transfers, we have found some ways to increase in-band file transfer performance, but not in the originally intended way, which would be through improvements in the Openfire source code concerning in-band file transfers. URI: http://hdl.handle.net/10037/2243 File(s) in this item: 1
thesis.pdf (1.171Mb) -
Aarflot, Tjalve (Master thesis; Mastergradsoppgave, 05-Feb-2009)[+][-]
Abstract: In recent years, an increasing amount of personal images, video, sound and text data are captured and stored in a digital format. Increased storage capacity at lower cost entice us to attempt to store everything, but without effective information retrieval techniques, the usefulness of the data becomes limited. Some people have taken personal data capture to extremes and have begun to capture digitally all aspects of their life, which creates enormous archives of multimedia data. This is not a new idea: in 1945 Vannevar Bush wrote his visionary article “As We May Think” where he described Memex, the first Human Digital Memory (HDM). Today we have projects like Microsoft MyLifeBits building on the Memex vision, however there has been little focus on organizing this kind of data effectively. By applying data reduction, we show the benefits of removing redundancy from HDMs, and illustrate how the same data reduction framework can be used to effectively support information access from HDMs. URI: http://hdl.handle.net/10037/1825 File(s) in this item: 1
thesis.pdf (2.313Mb) -
Wong, Aaron K.; Park, Christopher Y.; Greene, Casey S.; Bongo, Lars Ailo; Guan, Yuanfang; Troyanskaya, Olga (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Integrative multi-species prediction (IMP) is an interactive web server that enables molecular biologists to interpret experimental results and to generate hypotheses in the context of a large cross-organism compendium of functional predictions and networks. The system provides a framework for biologists to analyze their candidate gene sets in the context of functional networks, as they expand or focus these sets by mining functional relationships predicted from integrated high-throughput data. IMP integrates prior knowledge and data collections from multiple organisms in its analyses. Through flexible and interactive visualizations, researchers can compare functional contexts and interpret the behavior of their gene sets across organisms. Additionally, IMP identifies homologs with conserved functional roles for knowledge transfer, allowing for accurate function predictions even for biological processes that have very few experimental annotations in a given organism. IMP currently supports seven organisms (Homo sapiens, Mus musculus, Rattus novegicus, Drosophila melanogaster, Danio rerio, Caenorhabditis elegans and Saccharomyces cerevisiae), does not require any registration or installation and is freely available for use at http://imp.princeton.edu. URI: http://hdl.handle.net/10037/4962 File(s) in this item: 1
article.pdf (9.089Mb) -
Farsi, V. (Research report; Forskningsrapport, Sep-1994)[+][-]
Abstract: Scaling is recognized as a primary concern in developing distributed applications. Scaling problems occur when an application reach its upper boundary in some way or another. This paper describes the considerations made in the redesign of the StormCast distributed application to achieve more scalability. Naturally, there can be many factors that restrict a system's scalability. The challenge meeting the designers of distributed applications is to limit the influence of such factors. In this paper we focus on modularity, decentralized approach to design of application, transparent naming, caching of information, replicated data and services in order to enhance scalability. URI: http://hdl.handle.net/10037/397 File(s) in this item: 1
report.pdf (164.6Kb) -
Simonsson, Carl Erik Joakim (Master thesis; Mastergradsoppgave, 01-Jun-2010)[+][-]
Abstract: This thesis investigates how head tracking can be implemented by using inexpensive off-the-shelf hardware for a 6 x 3 meter high-resolution display wall. The tracking system has been integrated into to an existing event system, Shout, that allows for inter-program communication. An application called htsim has been developed that is used for testing different head tracking configurations in a virtual environment. Developing in a virtual environment does not require access to head tracking hardware. Tracking algorithms developed in the virtual environment can directly be used for head tracking in a physical environment. The tracking system is able to track a user's head with cameras that are placed behind the user. htsim is also used for configuring the head tracking system used in the physical environment. Experiments detail out the overall latency in the system and sources of jitter. URI: http://hdl.handle.net/10037/2634 File(s) in this item: 1
thesis.pdf (7.226Mb) -
Thorvaldsen, Idar (Master thesis; Mastergradsoppgave, 06-Feb-2009)[+][-]
Abstract: There is a continuing desire and need for improving the processes of describing and searching for digital images. While good progress has been made adapting traditional information retrieval techniques to perform these tasks, processing images still presents a number of challenges not encountered when working with just text. This project implements a system allowing for the indexing and searching of collections of images where images are not individually described. Such collections are typically largely unsuitable data material for traditional text-based image search systems. The basic idea underlying this system is to not search for images directly, but instead first search for the collections they are part of. When a set of relevant collections have been found, one can then apply the collection-level semantics to the images belonging to these collections. An important concept in this project is that one image can be a part of several collections. Such images can be identified when collection information is added to the system, allowing one to link the same image to several collections before searches are run. Semantic information from several different collections can then be applied to the same image, potentially giving a better idea of what the image actually depicts. URI: http://hdl.handle.net/10037/1881 File(s) in this item: 2
CD.zip (372.7Mb)thesis.pdf (1.826Mb) -
Svendsen, Åse (Master thesis; Mastergradsoppgave, 15-Dec-2011)[+][-]
Abstract: This work is focused on the three sounding rocket launches during the ECOMA Geminids campaign in December 2010: One before the Geminids meteor shower, one at its peak and one some days after the peak. In this work, the main emphasis is on analyzing the results from electron and ion probes on the rockets, obtaining electron and ion density profiles, and comparing them with the measurements of meteoric smoke particles. Aerosol particles originating from meteors may be the condensation nuclei for ice particles that form phenomena such as NLC ad PMSE. This work concludes that there are strong indications of the existence of negatively charged smoke particles in the height region between 80-95km. It describes how these parameters were measured, and how to get from raw data to the end results. URI: http://hdl.handle.net/10037/3996 File(s) in this item: 1
thesis.pdf (5.068Mb) -
Kvisle Storås, Ola (Master thesis; Mastergradsoppgave, 17-Dec-2007)[+][-]
Abstract: This thesis is a study of pattern classification based on information theoretic criteria. Information theoretic criteria are important measures based on entropy and divergence between data distributions. First, the basic concepts of pattern classification with the well known Bayes classification rule as a starting point is discussed. We discuss how the Parzen window estimator may be used to find good density estimates. The Parzen window density estimator can be used to estimate cost functions based on information theoretic criteria. Furthermore, we explain a model of an information theoretic learning machine. With cost functions based on information theoretic criteria, we argue that a learning machine potentially captures much more information about a data set than the traditional mean squared error cost (MSE) function. We find that there is a geometric link between information theoretic cost functions estimated using Parzen windowing, and mean vectors in a Mercer kernel feature space. This link is used to propose and implement different classifiers based on the integrated squared error (ISE) divergence measure, operating implicitly in a Mercer kernel feature space. We also apply spectral methods to implement the same ISE classifiers working in approximations of Mercer kernel feature spaces. We investigate the performance of the classifiers when we weight each data point with the the inverse of the probability density function at that point. We find that the ISE classifiers working implicitly in the Mercer kernel feature space performs similar to a Parzen window based Bayes classifier. Using a weighted inner-product definition gives slightly better results for some data sets, while for other data sets the classification rates are slightly worse. When comparing the results between the implicit ISE classifier using unweighted data points and the Parzen window Bayes classifier, some of the results indicate that the ISE classifier favor the classes with highest entropy. URI: http://hdl.handle.net/10037/1773 File(s) in this item: 1
thesis.pdf (1.092Mb) -
Vikjord, Vidar Vangen (Master thesis; Mastergradsoppgave, 01-Jun-2012)[+][-]
Abstract: The machine learning field based on information theory has received a lot of attention in recent years. Through kernel estimation of the probability density functions, methods developed with information theoretic measures are able to use all the statistical information available in the data, not just a finite number of moments. However, by using kernel estimation, the methods are dependent on choosing a suitable bandwidth parameter and have trouble dealing with data which vary on different scales. In this thesis, the field of information theoretic learning has been explored using k-nearest neighbor estimates for the probability density functions instead. The developed estimators of the information theoretic measures was used in a clustering routine and compared with the traditional kernel estimators.Performing clustering on a range of datasets and comparing the performance, the new method proved to provide superior results without the need of tuning any parameters. The performance difference was found to be especially large when clustering datasets where groups were on different scales. URI: http://hdl.handle.net/10037/4608 File(s) in this item: 1
thesis.pdf (7.115Mb) -
Rietveld, Michael T.; Kirkwood, S.; Chilson, P.; Belova, E.; Häggström, I.; Singer, W.; Dalin, P. (Journal article; Peer reviewed, 23-Mar-2006)[+][-]
Abstract: The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE) during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here. URI: http://hdl.handle.net/10037/613 File(s) in this item: 1
article.pdf (16.53Mb) -
Sivertsen, Annfrid (Master thesis; Mastergradsoppgave, 15-May-2008)[+][-]
Abstract: The Vibrio cholerae bacteria resistance against introduction of new genetic material through transformation is caused mainly by a small extracellular or periplasmic endonuclease of type I, the VcEndA of 24.7 kDa coded by the dns gene, (Focareta et al, 1987; Focareta et al, 1991; Altermark et al, 2007b). The VcEndA homologues in other bacteria, Serratia marcescens (Timmins et al, 1973), Erwinia chrysanthemi (Moulard et al, 1993), Aeromonas hydrophila (Chang et al, 1992), Vibrio vulnificus (Wu et al, 2001) and Vibrio salmonicida (Altermark et al, 2007b), are identified as the main mechanisms of preventing a successful transformation in these organisms. Of a broader commercial interest is the identification of the EndoI in Esterichia coli, that shares 60 % sequence identity with VcEndA (Jekel et al, 1995). This project aims to find a lead compound for an inhibitor that is commercially exploitable, and will be applied as an additive in a transformation kit that prevents nuclease activity. An inhibitior would increase the yield in transformation procedures, and delete the step of creating endonuclease type I negative strains prior to transformation experiments. As a starting point, the Hepes molecule known to decrease the activity of VcEndA and the homologues VsEndA from Vibrio salmonicida (Altermark, Ph.D thesis 2006), was used as a template to find more active compounds. In this thesis I report the work and results from an in vitro screening of selected compounds with similar structural features as the Hepes molecule, and their activity measured by IC50 values. I also report an X-ray crystallography study with both soaked and co-crystallized approaches, and observed changes in the active site of the catalytic important residues Arg99 and Glu113 upon binding of an inactive compound. Computational modeling experiments with molecular docking, and comparison of the performance of three different docking programs, GOLD, AutoDock and Glide are carried out. To find more novel active compounds, a virtual screening by the program GOLD was performed with two libraries of small molecules. By the activity measurements, three compounds with the consensus feature of an aminoethanesulfonic acid group followed by a hetero- or homo cyclohexane ring were identified. In the structures from data sets collected from soaked crystals, the inactive molecule cacodylate was found bound in the active site. Observation of a change in the conformations of residue Arg99 and the nearby Glu113 is shown for two data sets compared to an empty site. The formation of a salt bridge between Arg99 and Glu113 shows similarity to the findings of Arg99 conformations in dsDNA-VVn complexes of the close homologous endonuclease type I, Vvn in Vibrio vulnificus (Wu et al, 2001; Li et al, 2003). The comparison of the molecular modeling programs GOLD, AutoDock and Glide indicate that GOLD is most suited to perform modeling experiments of the VcEndA system. This program is able to differentiate between active and inactive compounds upon assigning fitness scores, as well as consistently treat active compounds by assigning similar docking poses. The program AutoDock is also considered to give satisfactory docking poses, but are penalized for not consistently differentiate between active and inactive compounds when assigning fitness scores. The results from the docking experiments and the virtual screening strengthen the interpretation of the IC50 values, the consensus structural features and the changes in Arg99 upon binding of the inactive compound cacodylate. URI: http://hdl.handle.net/10037/4908 File(s) in this item: 1
thesis.pdf (1.725Mb) -
Jakobsen, Oleg (Master thesis; Mastergradsoppgave, 15-Jun-2007)[+][-]
Abstract: Subversion, an open-source centralized version control system, developed by CoallabNet, is currently the second most popular version control system, after the ever popular CVS. Like CVS, Subversion uses a client-server architecture, but has a cleaner, modular architecture. One set of subversion modules, are the filesystem backends modules of subversion. Two ``official'' backends are currently supplied with subversion, a berkleyDB based backend(bdb), and a custom filebased filesystem implementation (fsfs). At least another un-official backend module using an SQL-database exists. Pesto is a secure, decentralized, distributed peer-to-peer storage system, implemented both as a NetBSD filesystem, and as middelware, a portable C-library (libpesto). Currently two applications using libpesto have been written, a C\#\/.Net windows client, and a highly scalable serverfarm for Pesto, written in Java. In this project we integrate subversion with pesto, by creating a new filesystem backend for subversion using libpesto. The result is a version-control system, that works like a centralized version-control system, but has decentralized storage. We show that this system can be used for backup, mirroring of repositories, and as a decentralized version-control system. URI: http://hdl.handle.net/10037/1174 File(s) in this item: 2
CD.zip (25.75Mb)thesis.pdf (719.5Kb) -
Hagen, Tor-Magne Stien (Doctoral thesis; Doktorgradsavhandling, 26-Sep-2011)[+][-]
Abstract: The vast volume of scientific data produced today requires tools that can enable scientists to explore large amounts of data to extract meaningful information. One such tool is interactive visualization. The amount of data that can be simultaneously visualized on a computer display is proportional to the display’s resolution. While computer systems in general have seen a remarkable increase in performance the last decades, display resolution has not evolved at the same rate. Increased resolution can be provided by tiling several displays in a grid. A system comprised of multiple displays tiled in such a grid is referred to as a display wall. Display walls provide orders of magnitude more resolution than typical desktop displays, and can provide insight into problems not possible to visualize on desktop displays. However, their distributed and parallel architecture creates several challenges for designing systems that can support interactive visualization. One challenge is compatibility issues with existing software designed for personal desktop computers. Another set of challenges include identifying characteristics of visualization systems that can: (i) Maintain synchronous state and display-output when executed over multiple display nodes; (ii) scale to multiple display nodes without being limited by shared interconnect bottlenecks; (iii) utilize additional computational resources such as desktop computers, clusters and supercomputers for workload distribution; and (iv) use data from local and remote compute- and data-resources with interactive performance. This dissertation presents Network Accessible Compute (NAC) resources and Network Accessible Display (NAD) resources for interactive visualization of data on displays ranging from laptops to high-resolution tiled display walls. A NAD is a display having functionality that enables usage over a network connection. A NAC is a computational resource that can produce content for network accessible displays. A system consisting of NACs and NADs is either push-based (NACs provide NADs with content) or pull-based (NADs request content from NACs). To attack the compatibility challenge, a push-based system was developed. The system enables several simultaneous users to mirror multiple regions from the desktop of their computers (NACs) onto nearby NADs (among others a 22 megapixel display wall) without requiring usage of separate DVI/VGA cables, permanent installation of third party software or opening firewall ports. The system has lower performance than that of a DVI/VGA cable approach, but increases flexibility such as the possibility to share network accessible displays from multiple computers. At a resolution of 800 by 600 pixels, the system can mirror dynamic content between a NAC and a NAD at 38.6 frames per second (FPS). At 1600x1200 pixels, the refresh rate is 12.85 FPS. The bottleneck of the system is frame buffer capturing and encoding/decoding of pixels. These two functional parts are executed in sequence, limiting the usage of additional CPU cores. By pipelining and executing these parts on separate CPU cores, higher frame rates can be expected and by a factor of two in the best case. To attack all presented challenges, a pull-based system, WallScope, was developed. WallScope enables interactive visualization of local and remote data sets on high-resolution tiled display walls. The WallScope architecture comprises a compute-side and a display-side. The compute-side comprises a set of static and dynamic NACs. Static NACs are considered permanent to the system once added. This type of NAC typically has strict underlying security and access policies. Examples of such NACs are clusters, grids and supercomputers. Dynamic NACs are compute resources that can register on-the-fly to become compute nodes in the system. Examples of this type of NAC are laptops and desktop computers. The display-side comprises of a set of NADs and a data set containing data customized for the particular application domain of the NADs. NADs are based on a sort-first rendering approach where a visualization client is executed on each display-node. The state of these visualization clients is provided by a separate state server, enabling central control of load and refresh-rate. Based on the state received from the state server, the visualization clients request content from the data set. The data set is live in that it translates these requests into compute messages and forwards them to available NACs. Results of the computations are returned to the NADs for the final rendering. The live data set is close to the NADs, both in terms of bandwidth and latency, to enable interactive visualization. WallScope can visualize the Earth, gigapixel images, and other data available through the live data set. When visualizing the Earth on a 28-node display wall by combining the Blue Marble data set with the Landsat data set using a set of static NACs, the bottleneck of WallScope is the computation involved in combining the data sets. However, the time used to combine data sets on the NACs decreases by a factor of 23 when going from 1 to 26 compute nodes. The display-side can decode 414.2 megapixels of images per second (19 frames per second) when visualizing the Earth. The decoding process is multi-threaded and higher frame rates are expected using multi-core CPUs. WallScope can rasterize a 350-page PDF document into 550 megapixels of image-tiles and display these image-tiles on a 28-node display wall in 74.66 seconds (PNG) and 20.66 seconds (JPG) using a single quad-core desktop computer as a dynamic NAC. This time is reduced to 4.20 seconds (PNG) and 2.40 seconds (JPG) using 28 quad-core NACs. This shows that the application output from personal desktop computers can be decoupled from the resolution of the local desktop and display for usage on high-resolution tiled display walls. It also shows that the performance can be increased by adding computational resources giving a resulting speedup of 17.77 (PNG) and 8.59 (JPG) using 28 compute nodes. Three principles are formulated based on the concepts and systems researched and developed: (i) Establishing the end-to-end principle through customization, is a principle stating that the setup and interaction between a display-side and a compute-side in a visualization context can be performed by customizing one or both sides; (ii) Personal Computer (PC) – Personal Compute Resource (PCR) duality states that a user’s computer is both a PC and a PCR, implying that desktop applications can be utilized locally using attached interaction devices and display(s), or remotely by other visualization systems for domain specific production of data based on a user’s personal desktop install; and (iii) domain specific best-effort synchronization stating that for distributed visualization systems running on tiled display walls, state handling can be performed using a best-effort synchronization approach, where visualization clients eventually will get the correct state after a given period of time. Compared to state-of-the-art systems presented in the literature, the contributions of this dissertation enable utilization of a broader range of compute resources from a display wall, while at the same time providing better control over where to provide functionality and where to distribute workload between compute-nodes and display-nodes in a visualization context. Description: Papers number 2-7 and appendix B and C of this thesis are not available in Munin:
2. Hagen, T-M.S., Johnsen, E.S., Stødle, D., Bjorndalen, J.M. and Anshus, O.: 'Liberating the Desktop', First International Conference on Advances in Computer-Human Interaction (2008), pp 89-94. Available at http://dx.doi.org/10.1109/ACHI.2008.20
3. Tor-Magne Stien Hagen, Oleg Jakobsen, Phuong Hoai Ha, and Otto J. Anshus: 'Comparing the Performance of Multiple Single-Cores versus a Single Multi-Core' (manuscript)
4. Tor-Magne Stien Hagen, Phuong Hoai Ha, and Otto J. Anshus: 'Experimental Fault-Tolerant Synchronization for Reliable Computation on Graphics Processors' (manuscript)
5. Tor-Magne Stien Hagen, Daniel Stødle and Otto J. Anshus: 'On-Demand High-Performance Visualization of Spatial Data on High-Resolution Tiled Display Walls', Proceedings of the International Conference on Imaging Theory and Applications and International Conference on Information Visualization Theory and Applications (2010), pages 112-119. Available at http://dx.doi.org/10.5220/0002849601120119
6. Bård Fjukstad, Tor-Magne Stien Hagen, Daniel Stødle, Phuong Hoai Ha, John Markus Bjørndalen and Otto Anshus: 'Interactive Weather Simulation and Visualization on a Display Wall with Many-Core Compute Nodes', Para 2010 – State of the Art in Scientific and Parallel Computing. Available at http://vefir.hi.is/para10/extab/para10-paper-60
7. Tor-Magne Stien Hagen, Daniel Stødle, John Markus Bjørndalen, and Otto Anshus: 'A Step towards Making Local and Remote Desktop Applications Interoperable with High-Resolution Tiled Display Walls', Lecture Notes in Computer Science (2011), Volume 6723/2011, 194-207. Available at http://dx.doi.org/10.1007/978-3-642-21387-8_15URI: http://hdl.handle.net/10037/3672 File(s) in this item: 2
paper_1.pdf (2.029Mb)thesis.pdf (8.025Mb) -
Grydeland, Tom (Doctoral thesis; Doktorgradsavhandling, 24-Jun-2003)[+][-]
Abstract: We know that the visible Aurora Borealis is structured on many different scales, down to a few tens of metres. By using the EISCAT radars on Svalbard as an interferometer, we have found structures in the radio echoes from the auroral ionosphere on a scale approaching that of the visible aurora, and simultaneously with it, but at far greater ranges. In this thesis we discuss how these radar observations were made, what they imply for theoretical explanations, as well as a new framework for the design and implementation of software-defined radar and other radio science instrumentation, in particular the signal processing which made these observations possible. URI: http://hdl.handle.net/10037/282 File(s) in this item: 1
thesis.pdf (5.154Mb) -
Grydeland, Tom; Hagfors, T.; Trondsen, T.S.; Blixt, Erik Mårten; Løvhaug, Unni Pia; La Hoz, Cesar (Journal article; Peer reviewed, 02-Apr-2004)[+][-]
Abstract: Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at midand high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations is whether or not simultaneously observed up- and downshifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging. The EISCAT Svalbard Radar has two antennas in the same radar system, which can be used as an interferometer when pointed parallel. In observations from 17 January 2002, between 06:46:10 and 06:46:30 UT, we used this possibility, in combination with direct sampling of the received signals, to yield measurements of “naturally enhanced ion-acoustic echoes” with sufficiently high resolution to resolve such averaging, if any. For the first time, radar interferometry has been employed to estimate the sizes of coherent structures. The observations were coordinated with an image intensified video camera with a narrow field of view. Together, this forms the initial study on the causal relationships between enhanced echoes and fine structure in the auroral activity on sub-kilometer, sub-second scales. The results confirm that the enhanced echoes originate from very localised regions ( 300m perpendicular to the magnetic field at 500 km altitude) with varying range distribution, and with high time variability ( 200 ms). The corresponding increase in scattering cross section, up to 50 dB above incoherent scattering, eliminates theoretical explanations based on marginal stability. The simultaneously observed up- and down-shifted enhanced shoulders, when caused by sufficiently narrow structures to be detected by the interferometer technique, originate predominantly from the same volume. These results have significant impact on theories attempting to explain the enhancements, in particular it is found that the ion-electron two-stream mechanism favoured by many authors is an unlikely candidate to explain the observations. The video data has helped establish a clear correlation between the enhanced echoes and auroral activity, on sub-second time scales, showing a threshold connection between the auroral intensity and the triggering of the radar enhancements. It appears that the up- and down-shifted enhanced echoes correlate with fine auroral structures in different ways. URI: http://hdl.handle.net/10037/546 File(s) in this item: 1
article.pdf (906.7Kb)
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