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Capillary suction model as pipes of different sizes: flow conditions and comparison with experimentsNguyen, Hung Thanh; Jacobsen, Stefan; Melandsø, Frank (Conference object; Konferansebidrag, 2012)[+][-]
Abstract: ABSTRACT Absorption of water in concrete is often described by the simple linear water uptake vs. square-root-of-time law. However, a deviation from this behaviour is frequently seen depending on factors such as initial water content, water/binder ratio and specimen thickness. The deviation increases with thickness (typically from 25 to 100 mm) and is seen even for very dry specimens with capillary pores. We have applied Laplaces law for suction created under a curved meniscus between air and water to series of pipes with different lengths and radii. The resulting analytical model was first compared with numerical simulations at abrupt reduction or increase of pipe radius showing good agreement. Then a complete second order equation describing the relation between the capillary suction and the suction time was developed. Varying geometries of the pipes of the capillary system were investigated including the effects on the flow rate of varying combination of lengths, radii and sequence. The results showed that largest flow reductions occurred with very narrow sections causing a blocking, reducing the capillary flow rate vs. square root of time in the same manner as in concrete. The often observed phenomenon of reduced flow below the straight line water uptake vs. square root of time could be simulated with the multiple diameter pipe models, as seen by comparing simulations with experiments with varying concrete qualities and sample thicknesses in simple capillary absorption tests. Key-words: capillary suction, pipe geometry, model URI: http://hdl.handle.net/10037/5114 File(s) in this item: 1
article.pdf (394.7Kb) -
Uldal, Siri Birgitte (Master thesis; Mastergradsoppgave, 15-Jun-2007)[+][-]
Abstract: Proliferation of wireless networks has been a major trigger behind increased mobility of computing devices. Along with increased mobility come requests for ad-hoc exchange of resources between computing devices as an extension of humans interacting. We termed it casual resource sharing where resources in this thesis have been narrowed down to files only. We have named our casual resource sharing model for shared virtual folders (SVF). SVFs can be looked upon as a common repository much in the same way as the tuplespace model. The SVF members perceive the repository similarly to a common file directory on a server, while in reality all participating devices stores their own contribution of files. All types of files could be added to the repository and shared. To become a SVF member one needs to be invited by another member or initiate a SVF oneself. All members are free to withdraw their SVF membership whenever they wish. They are also free to log on to the SVF and log out as they please. The SVF cease to exist when the last member has drawn his membership. The SVF implements a simple versioning detection system to alert members when a file has been modified by another member. Feasibility of the model is demonstrated in a prototype implementation based on Java and the JXTA middleware, a peer-to-peer (P2P) infrastructure middleware supporting the Internet protocol. The implementation functions with any underlying network supporting the IP protocol, both LAN or WAN. The interacting devices could be running on any operating system. The SVF itself is created with focus on simplicity and requires no more than software installation before use. The model and implementation is discussed and contrasted with other existing approaches to casual resource sharing. URI: http://hdl.handle.net/10037/1076 File(s) in this item: 2
thesis.pdf (909.1Kb)thesis.zip (11.09Mb) -
Skrøvseth, Stein Olav; Godtliebsen, Fred; Bellika, Johan Gustav (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Kernel density estimation and kernel regression are useful ways to visualize and assess the structure of data. Using these techniques we define a temporal scale space as the vector space spanned by bandwidth and a temporal variable. In this space significance regions that reflect a significant derivative in the kernel smooth similar to those of SiZer (Significant Zero-crossings of derivatives) are indicated. Significance regions are established by hypothesis tests for significant gradient at every point in scale space. Causality is imposed onto the space by restricting to kernels with left-bounded or finite support and shifting kernels forward. We show that these adjustments to the methodology enable early detection of changes in time series constituting live surveillance systems of either count data or unevenly sampled measurements. Warning delays are comparable to standard techniques though comparison shows that other techniques may be better suited for single-scale problems. Our method reliably detects change points even with little to no knowledge about the relevant scale of the problem. Hence the technique will be applicable for a large variety of sources without tailoring. Furthermore this technique enables us to obtain a retrospective reliable interval estimate of the time of a change point rather than a point estimate. We apply the technique to disease outbreak detection based on laboratory confirmed cases for pertussis and influenza as well as blood glucose concentration obtained from patients with diabetes type 1. URI: http://hdl.handle.net/10037/4961 File(s) in this item: 1
article.pdf (775.5Kb) -
Henden, John-André (Doctoral thesis; Doktorgradsavhandling, 16-Mar-2009)[+][-]
Abstract: A special case of population fluctuation is multi-annual population cycles. While such population cycles exist in several ecosystems, they are more prominent in northern (e.g.tundra) ecosystems, especially among key stone herbivore species. These herbivores providean important ecosystem function in the sense of pulsed flows of resources (i.e. for predators) and disturbances (i.e. for vegetation) throughout the ecosystem. However, the circumstances on the tundra are changing. For instance, large scale collapse of population cycles of many herbivors has been reported, as well as northward expansion of novel predators (e.g. red fox). These changes, heavily connected to climate changes, are capable of disrupting the function and structure of such systems. Overall this thesis aims to outline and evaluate the recent dramatic changes in multi-annual population cycles of many herbivores and the possible implications of such changes on the trophic dynamics and species conservation in the Fennoscandinavian tundra ecosystem. First I show that the recent collapse of multi-annual population cyclles are now a widespread phenomenon, extending several species and ecosystem barriers. Next I show, based on long time series of fox bounty data, that these recent changes have some historical analogies. Specifically, I show that the highly publicized patterns (e.g. geographic gradients, large scale synchrony) in Fennoscandian small rodent cycle have been buject to large spatio-temporal trensitions in their patterns, being highly non-stationary. I also demonstrate that collapse of cycles similar to the recent events, though on a smaller spatial extent, have occurred earlier and that these incidents seem to concur with shifts between cold and warm climatic periods. Then I demonstrate wich aspects of the recent changes in the dynamics of key prey species is likely to heavily affect the viability and existence of tundra predatirs strongly adapted to the pulsed flow of resources provided bycyclically fluctuating prey populations. Furthermore, the effect of recent and future projections of climate change may facilitate the establishment of novel predator species, which may act as dominant competitors for native species for habitat and prey. I here show that increased competition with red fox may be detrimental to arctic fox viability, especially if subsidies (e.g. reindeer carcasses) are available to the dominant competitor. Finally, I show that attempts to conserve native predators, such as the arctic fox, should take into account the factors that govern their demography and thus population dynamics. I show thet the effect of management action is highly dependent onthe phase of the demographic cycle of arctic fox. This means that management intervantion should be continous, but most focused to moments in time where the effect is expected to be most pronounced. Description: Papers number 1,2 and 3 of the thesis are not available in Munin due to publishers' restrictions.
1.Rolf A. Ims, John-André Henden, Siw T. Killengreen.: "Collapsing population cycles." Trends in Ecology & Evolution; 23(2): 79-86 (Science Direct). Available at http://dx.doi.org/10.1016/j.tree.2007.10.010
2.John-André Henden, Rolf A. Ims, Nigel G. Yoccoz.: "Nonstationary spatio-temporal small rodent dynamics: evidence from long-term Norwegian fox bounty data." Journal of Animal Ecology; 78(3): 636-645 (Wiley). Available at http://dx.doi.org/10.1111/j.1365-2656.2008.01510.x
3.John-André Henden , Bård-Jørgen Bårdsen, Nigel G. Yoccoz, Rolf A. Ims.: " Impacts of differential prey dynamics on the potential recovery of endangered arctic fox populations." Journal of Applied Ecology Journal of Applied Ecology; 45(4): 1086-1093 (Wiley). Available at http://dx.doi.org/10.1111/j.1365-2664.2008.01515.xURI: http://hdl.handle.net/10037/2585 File(s) in this item: 3
paper-4.pdf (624.5Kb)paper-5.pdf (324.9Kb)thesis.pdf (5.725Mb) -
Manson, Alan; Meek, Chris; Xu, X.; Aso, Takehiko; Drummond, J. R.; Hall, Chris; Hocking, W. K.; Tsutsumi, Masaki; Ward, W. E. (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: Operation of a Meteor Radar (MWR) at Eureka, Ellesmere Island (80° N, 86° W) began in February 2006: this is the location of the Polar Environmental and Atmospheric Research Laboratory (PEARL), operated by the "Canadian Network for the Detection of Atmospheric Change" (CANDAC). The first 36 months of tidal wind data (82–97 km) are here combined with contemporaneous tides from the Meteor Radar (MWR) at Adventdalen, Svalbard (78° N, 16° E), to provide the first significant evidence for interannual variability (IAV) of the High Arctic's diurnal and semidiurnal migrating (MT) and non-migrating tides (NMT). The three-year monthly means for both diurnal (DT) and semi-diurnal (SDT) winds demonstrate significantly different amplitudes and phases at Eureka and Svalbard. Typically the summer-maximizing DT is much larger (~24 m s−1 at 97 km) at Eureka, while the Svalbard tide (5–24 m s−1 at 97 km)) is almost linear (north-south) rather than circular. Interannual variations are smallest in the summer and autumn months. The High Arctic SDT has maxima centred on August/September, followed in size by the winter features; and is much larger at Svalbard (24 m s−1 at 97 km, versus 14–18 m s−1 in central Canada). Depending on the location, the IAV are largest in spring/winter (Eureka) and summer/autumn (Svalbard). Fitting of wave-numbers for the migrating and non-migrating tides (MT, NMT) determines dominant tides for each month and height. Existence of NMT is consistent with nonlinear interactions between migrating tides and (quasi) stationary planetary wave (SPW) S=1 (SPW1). For the diurnal oscillation, NMT s=0 for the east-west (EW) wind component dominates (largest tide) in the late autumn and winter (November–February); and s=+2 is frequently seen in the north-south (NS) wind component for the same months. The semi-diurnal oscillation's NMT s=+1 dominates from March to June/July. There are patches of s=+3 and +1, in the late fall-winter. These wave numbers are also consistent with SPW1-MT interactions. Comparisons for 2007 of the observed DT and SDT at 78–80° N, with those within the Canadian Middle Atmosphere Model Data Assimilation System CMAM-DAS, are a major feature of this paper. The diurnal tides for the two locations have important similarities as observed and modeled, with seasonal maxima in the mesosphere from April to October, and similar phases with long/evanescent wavelengths. However, differences are also significant: observed Eureka amplitudes are generally larger than the model; and at Svalbard the modeled tide is classically circular, rather than anomalous. For the semi-diurnal tide, the amplitudes and phases differ markedly between Eureka and Svalbard for both MWR-radar data and CMAM-DAS data. The seasonal variations from observed and modeled archives also differ at each location. Tidal NMT-amplitudes and wave-numbers for the model differ substantially from observations. URI: http://hdl.handle.net/10037/3943 File(s) in this item: 1
article.pdf (832.9Kb) -
Hall, Chris (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: Operation of a Meteor Wind Radar (MWR) at Eureka, Ellesmere Island (80° N, 86° W) began in February 2006; this is the location of the Polar Environmental and Atmospheric Research Laboratory (PEARL), operated by the "Canadian Network for the Detection of Atmospheric Change" (CANDAC). The first 36 months of wind data (82–97 km) are here combined with contemporaneous winds from the Meteor Wind Radar at Adventdalen, Svalbard (78° N, 16° E), to provide the first evidence for substantial interannual variability (IAV) of longitudinally spaced observations of mean/background winds and waves at such High Arctic latitudes. The influences of "Sudden Stratospheric Warmings" (SSW) are also apparent. Monthly meridional (north-south, NS) 3-year means for each location/radar demonstrate that winds (82–97 km) differ significantly between Canada and Norway, with winter-equinox values generally northward over Eureka and southward over Svalbard. Using January 2008 as case study, these oppositely directed meridional winds are related to mean positions of the Arctic mesospheric vortex. The vortex is from the Canadian Middle Atmosphere Model, with its Data Assimilation System (CMAM-DAS). The characteristics of "Sudden stratospheric Warmings" SSW in each of the three winters are noted, as well as their uniquely distinctive short-term mesospheric wind disturbances. Comparisons of the mean winds over 36 months at 78 and 80° N, with those within CMAM-DAS, are featured. E.g. for 2007, while both monthly mean EW and NS winds from CMAM/radar are quite similar over Eureka (82–88 km), the modeled autumn-winter NS winds over Svalbard (73–88 km) differ significantly from observations. The latter are southward, and the modeled winds over Svalbard are predominately northward. The mean positions of the winter polar vortex are related to these differences. URI: http://hdl.handle.net/10037/4085 File(s) in this item: 1
article.pdf (744.6Kb) -
Tribulato, Giulio (Master thesis; Mastergradsoppgave, Jun-2007)[+][-]
Abstract: Njord is a novel plasma device in which a low-temperature plasma is produced by RF waves inductively coupled into a cylindrical, magnetized vacuum. The main part of this project is to carry out an experimental characterization of the plasma in this device. The plasma expansion and acceleration of the source plasma into the main chamber will be of specific interest. The ultimate aim will then be to find operational regimes of the controlled parameters (e.g. magnetic field configuration and pressure), for which a so-called current-free double layer may be set up spontaneously and an ion beam formed. Such double layers have earlier been demonstrated in devices with a similar plasma source, and the formation of such double layers in Njord will be of importance for the feasibility of studying instabilities and turbulence set up by ion beams in this particular configuration. We performed this characterization using RF-compensated Langmuir and double probes. In particular, we investigated the region between the RF source and the expansion chamber, performing measurements along axial and radial positions. The results of the two probes were in agreements with what we were expecting, except for an unexpected behaviour of plasma density as a function of the magnetic field. We also found evidence of a large potential drop (40V) inside the source, which is a primary element in the formation of double layers. URI: http://hdl.handle.net/10037/1202 File(s) in this item: 1
G_Tribulato_Master_Thesis.pdf (1.751Mb) -
Plaza-Faverola, Andreia Aletia (Doctoral thesis; Doktorgradsavhandling, 12-Nov-2010)[+][-]
Abstract: What causes the escape of natural gases to the seafloor and how significant this escape has been along the mid-Norwegian continental margin? These are questions that guided the doctoral thesis. The thesis is part of a research project supported by the European Commission and the Norwegian Research Council, which aims at quantifying geological processes that control fluid flow and gas hydrate formation along the Norwegian-Barents-Svalbard margin. The thesis was divided in three stages according to the following three main objectives: (1) to assess the distribution of shallow gas reservoirs and paths for fluid migration from deep sources; (2) to investigate the internal structure of a vertical fluid escape feature (chimney) through implementation of high resolution travel-time reflection tomography modeling; and (3) to infer a time scale for fluid escape in the region through detailed seismic characterization of depositional settings and sediment deformation of sediments deposited during the last three major glaciations and their inter-glacial cycles. The methodology implemented consists in the integration of velocity analysis techniques and seismic imagine applied to different resolution seismic data sets. The thesis presents results from four articles that together bring us closer to the overall understanding of fluid flow related systems in Nyegga, offshore mid-Norway. While each article has separate and specific aims, the problems and results covered by the four articles are nevertheless guided by a single motive: to access geophysical and geological indications of sub-seabed fluid flow processes by the implementation of non-invasive methods. Two of the most important results encountered are first, that gas hydrates are at present hindering catastrophic escapes of fluids towards the seafloor; and second that fluid escape in the margin has seemingly been episodically. Fluid escape periods seem to be related to overpressure generation during the last three glaciations. Description: Paper number 1 and 2 of the thesis are not available in Munin due to publishers' restrictions:
1. Plaza-Faverola, A., S. Bünz, and J. Mienert (2010). "Fluid distributions inferred from Pwave velocity and reflection seismic amplitude anomalies beneath the Nyegga pockmark field of the mid-Norwegian margin", Marine and Petroleum Geology, 27(1): 46-60
2. Plaza-Faverola, A., G. K. Westbrook, K. Stephan, R. Exley, A. Gailler, T. Minshull and K. Broto, (2010). "Evidence from tomographic investigation of Vp variation for accumulation of substantial methane hydrate in a fluid-escape chimney in the Nyegga pockmark field, offshore Norway". JGR solid earth. v. doi:10.1029/2009JB007078, in press.URI: http://hdl.handle.net/10037/2812 File(s) in this item: 3
paper-3.pdf (1.402Mb)paper-4.pdf (1.854Mb)thesis.pdf (1.368Mb) -
Cannon, P. S.; Hall, Chris; Brekke, Asgeir (Journal article; Tidsskriftartikkel; Peer reviewed, 29-Nov-2007)[+][-]
Abstract: We have examined the long time series of observations of E-region virtual height (1948–2006) and critical frequency (1935-2006) hitherto made by the Tromsø ionosonde at 70 degrees N, 19 degrees E. Combining a simplistic trend analysis with a rigorous treatment of errors we identify a negative trend in critical frequency. While a similar analysis of the virtual height h'E also suggests a negative trend, a closer examination reveals a possible weak positive trend prior to ~1975 and a strong negative trend from ~1975 to present. These two metrics of essentially the same feature of the ionosphere do not exhibit the same signature since critical frequency is controlled by photochemistry within the E-layer while height is controlled by pressure level. We further find that the trend in critical frequency is a daylight/summer phenomenon, no significant trend being evident in the winter subset of the data. On the other hand, the trends in virtual height are independent of season/daylight. Description: This is the publishers version/PDF (published in Annales Geophysicae, an open access journal of the European Geosciences Union) URI: http://hdl.handle.net/10037/2385 File(s) in this item: 1
article.pdf (481.8Kb) -
Sydnes, Are K. (Conference object; Konferansebidrag, 2012)[+][-]
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Viken Valvåg, Steffen (Doctoral thesis; Doktorgradsavhandling, 30-Jan-2012)[+][-]
Abstract: MapReduce has become a widely employed programming model for large-scale data-intensive computations. Traditional MapReduce engines employ dynamic routing of data as a core mechanism for fault tolerance and load balancing. An alternative mechanism is static routing, which reduces the need to store temporary copies of intermediate data, but requires a tighter coupling between the components for storage and processing. The initial intuition motivating our work is that reading and writing less temporary data could improve performance, while the tight coupling of storage and processing could be leveraged to improve data locality. We therefore conjecture that a high-performance MapReduce engine can be based on static routing, while preserving the non-functional properties associated with traditional engines. To investigate this thesis, we design, implement, and experiment with Cogset, a distributed MapReduce engine that deviates considerably from the traditional design. We evaluate the performance of Cogset by comparing it to a widely used traditional MapReduce engine using a previously established benchmark. The results confirm our thesis that a high-performance MapReduce engine can be based on static routing, although analysis indicates that the reasons for Cogset's performance improvements are more subtle than expected. Through our work we develop a better understanding of static routing, its benefits and limitations, and its ramifications for a MapReduce engine. A secondary goal of our work is to explore how higher-level abstractions that are commonly built on top of MapReduce will interact with an execution engine based on static routing. Cogset is therefore designed with a generic, low-level core interface, upon which MapReduce is implemented as a relatively thin layer, as one of several supported programming interfaces. At its core, Cogset provides a few fundamental mechanisms for reliable and distributed storage of data, and parallel processing of statically partitioned data. While this dissertation mainly focuses on how these capabilities are leveraged to implement a distributed MapReduce engine, we also demonstrate how two other higher-level abstractions were built on top of Cogset. These may serve as alternative access points for data-intensive applications, and illustrate how some of the lessons learned from Cogset can be applicable in a broader context. Description: The papers of this thesis are not available in Munin:
1. Steffen Viken Valvåg and Dag Johansen: 'Oivos : simple and efficient distributed data processing' (2008). In Proceedings of the 2008 Tenth IEEE International Conference on High Performance Computing and Communications (HPCC 2008), pages 113– 122. IEEE Computer Society. Available at http://dx.doi.org/10.1109/HPCC.2008.105
2. Steffen Viken Valvåg and Dag Johansen: 'Update Maps : a new abstraction for High-Throughput Batch processing' (2009). In Proceedings of the 2009 IEEE International Conference on Networking, Architecture, and Storage (NAS 2009), pages 431–438. IEEE Computer Society. Available at http://dx.doi.org/10.1109/NAS.2009.73
3. Steffen Viken Valvåg and Dag Johansen: 'Cogset : a unified engine for reliable storage and parallel processing' (2009). In Proceedings of the 2009 Sixth IFIP International Conference on Network and Parallel Computing (NPC 2009), pages 174– 181. IEEE Computer Society. Available at http://dx.doi.org/10.1109/NPC.2009.23
4. Steffen Viken Valvåg, Dag Johansen, and Åge Kvalnes: 'Cogset vs. Hadoop : measurements and analysis', (2010). In Proceedings of the 2010 Second IEEE International Conference on Cloud Computing Technology and Science (CloudCom 2010), pages 768–775. IEEE Computer Society. Available at http://dx.doi.org/10.1109/CloudCom.2010.103URI: http://hdl.handle.net/10037/3817 File(s) in this item: 1
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Mortensen, Mats (Master thesis; Mastergradsoppgave, 15-Jun-2007)[+][-]
Abstract: Applications that adapt to environmental and situational changes are difficult to build because computers cannot capture, represent or process context information as easily as human beings. Nevertheless, context information is very valuable because it allows applications to be made more user-friendly, flexible, and adaptable. This realization has spawned a multitude of research efforts to simplify development of context-sensitive applications. A result of one of these research efforts is the Argos middleware platform, which is an application server created specifically for personal applications that can adapt to changes in their environment. Applications that rely on context information must often collect this information from external measurement devices, commonly known as sensors. These devices respond directly to physical stimulus to produce meaningful information about their surroundings. Typical examples are sensors that produce location, temperature or motion information, but they can also, for instance, be devices that monitors the physical condition of a person. The goal of this thesis has been to design, develop and evaluate functionality for the Argos middleware platform that makes it easier for Argos applications to collect and use sensor measurements. The functionality has been developed in collaboration with the National Center for Telemedicine (NST) who wants to use Argos for monitoring patients. They intend to develop a system that can give patients semi-automatic feedback and advice on how to maintain and improve their lifestyle. To do this they want to use personal sensors that monitor attributes relevant to a patient's condition. The functionality developed in this thesis has provided a starting point for NST to develop their system and contributed lots of technical information that will prove useful for their project. URI: http://hdl.handle.net/10037/1137 File(s) in this item: 2
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Jakobsen, Børge (Master thesis; Mastergradsoppgave, 08-Jan-2010)[+][-]
Abstract: Digital photographing has become more and more popular as cameras and mobile phones get more advanced and have newer technology embedded. Manually searching in these growing image collections is problematic because of missing context information related to the image itself. If related context information could be added as an automated process, it could help the user view and locate images and information about the image. In this thesis I purpose a system that tries to collect relevant context information connected to an image using time and date, gps location and a user given image category taken with a Nokia N95 using mobile image capturing software like described in [1]. URI: http://hdl.handle.net/10037/2443 File(s) in this item: 1
thesis.pdf (2.295Mb) -
Mjøen, Håvard Uv (Master thesis; Mastergradsoppgave, Jun-2008)[+][-]
Abstract: Information about snow covered area is important for several purposes, and this information can be found by detecting reflection of optical waves using optical sensors or by using active radars such as SAR. This thesis is explaining how information from the measurements are used to make snow maps. Optival sensors cannot detect snow when the area is covered by clouds, and this is a problem in the melting season in Norway. Microwaves can penetrate clouds, and detect wet snow. It cannot detect dry snow, but we will make snow maps based on the probability of dry snow. When we combine snow maps made from an optical instrument (MODIS) and a SAR (ENVISAT ASAR) we are able to get improved snow cover maps in times when the optical instrument cannot see the surface because of clouds. We will study a moving average filter and the Kalman filter. These filters are used to be able to filter the information about the snow cover to get an estimate of the snow covered area for each day. When comparing the results from the moving average filter with the Kalman filter, the results indicate that the Kalman filter gives a better estimation based on the measurements. We will also study relation between measured snow cover and the topography, and also if there are any relation between land cover and snow cover. The results indicate that the data from the optical sensors is underestimating the snow cover in northern slopes. The results also indicates that the melting of snow is correlated to the elevation. URI: http://hdl.handle.net/10037/1869 File(s) in this item: 1
thesis.pdf (2.200Mb) -
Stolle, C.; Rietveld, Michael T.; Jakowski, N.; Schlegel, K: (Journal article; Peer reviewed, 2004)[+][-]
Abstract: To obtain a comprehensive view on high latitude processes by applying different observation techniques, the SIRCUS campaign was initiated in 2001/2002. This paper compares electron density profiles derived from CHAMP radio occultation data and those measured with the EISCAT facility. Since ionospheric profiling with the help of space-based received GPS is a relatively new technique, validations with established independent instruments are of crucial need. We present 28 profiling events for quasi-statistical analyses, which occurred during the SIRCUS campaigns and describe some of them in more detail. We found out that the majority of profile comparisons in electron density peak value and height, as well as in TEC, lie within the error ranges of the two methods. Differences in the ionospheric quantities do not necessarily occur when the locations of the occultation and of the radar site show considerable distances. Differences are more pronounced when the ionosphere is remarkably structured. URI: http://hdl.handle.net/10037/611 File(s) in this item: 1
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Rietveld, Michael T.; Tereshchenko, E.D.; Brekke, Asgeir; Khudukon, B.Z.; Kozlova, M.O.; Evstafiev, O.V.; Nygren, T. (Journal article; Peer reviewed, 2000)[+][-]
Abstract: Results are shown from an experimental campaign where satellite scintillation was observed at three sites at high latitudes and, simultaneously, the F region plasma flow was measured by the nearby EISCAT incoherent scatter radar. The anisotropy parameters of field-aligned irregularities are determined from amplitude scintillation using a method based on the variance of the relative logarithmic amplitude. The orientation of the anisotropy in a plane perpendicular to the geomagnetic field is compared with the direction of F region plasma flow. The results indicate that in most cases a good agreement between the two directions is obtained. URI: http://hdl.handle.net/10037/559 File(s) in this item: 1
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Kruglikov, Boris; Lychagin, Valentin V. (Journal article; Tidsskriftartikkel; Peer reviewed, 20-Feb-2008)[+][-]
Abstract: We establish an efficient compatibility criterion for a system of generalized complete intersection type in terms of certain multi-brackets of differential operators. These multi-brackets generalize the higher Jacobi- Mayer brackets, important in the study of evolutionary equations and the integrability problem. We also calculate Spencer δ-cohomology of generalized complete intersections and evaluate the formal functional dimension of the solutions space. The results are applied to establish new integration methods and solve several differential-geometric problems. Description: Dette er forfatternes aksepterte versjon URI: http://hdl.handle.net/10037/2048 File(s) in this item: 1
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Živkovic, Tatjana (Doctoral thesis; Doktorgradsavhandling, 10-May-2011)[+][-]
Abstract: The subject of this thesis is self-organization, chaos and stochastic dynamics in laboratory plasmas, the magnetosphere, and in the Earth's climate system. For each of these systems we pose the question whether the global dynamics can be described by a set of a few variables governed by the same small number of deterministic equations. This problem is not trivial, because low-dimensional deterministic systems may exhibit chaotic dynamics where the solutions are sensitive to the initial conditions, and in most respects are indistinguishable from stochastic, noise-like dynamics. A number of data analysis methods for time series are employed and adapted to the problems at hand. Among these methods are time-delay phase space reconstruction, correlation-dimension estimation of strange attractors, recurrence plots, empirical mode decomposition, wavelet decomposition, estimation of predictability and long-range memory, estimation of low-dimensional determinism of the dynamics, and principal value decomposition. The analysis is complemented by numerical simulations of simple dynamic-stochastic model systems. Some of these have solutions with known properties, some low-dimensional and chaotic, and some are realizations of well-known stochastic processes. These are used to benchmark the analysis methods. Other models are designed to provide solutions with statistical properties very similar to those of the observational signals, and hence can be considered as minimal models for the phenomenon at hand. The thesis consists of an introductory part and four journal papers. The former briefly reviews the basics of low-dimensional dynamical systems and the reconstruction of the phase-space attractor from experimental time series, long-memory stochastic processes, and critical phenomena with emphasis on self-organized critical dynamics. We also review the data analysis methods employed in this work, and finally we give an introduction to, and some examples from, the particular plasma laboratory and geospace systems which are studied in more detail in the papers. This part ends with a section where some of the analysis methods are employed to climate data. This section has been included because climate dynamics appears to be a promising field for application of these concepts and methods, although this author has not published or submittet journal papers on this application yet. Paper 1 and Paper 2 deal with the detection of low-dimensional chaotic dynamics on time scales longer than those of the turbulent plasma dynamics in the laboratory Helimak configuration, and estimation of the largest Lyapunov exponent and the fractal dimension of the phase-space attractor. These estimates give us the degree of unpredictability and indicate how many equations we need to describe the chaotic dynamics. In Paper 3 and Paper 4 we estimate the degree of predictability and the organization of a deterministic component in the global magnetosphere during magnetic storms and substorms, respectively. These are accompanied by simultaneous estimations of solar wind parameters which are known to influence magnetospheric dynamics. From these results one may draw conclusions about the causal relationship between perturbations in the solar wind and in the magnetosphere, and infer that the organization of the magnetosphere during these events are internal processes and not imposed by an organization of the solar wind. Description: Paper 1 in the thesis is not available in Munin:
1. T. Živković and K. Rypdal:'Evidence of low-dimensional chaos in magnetized plasma turbulence', Eur. Phys. J. Special Topics 164, 157–164 (2008). Available at http://dx.doi.org/10.1140/epjst/e2008-00841-5URI: http://hdl.handle.net/10037/3231 File(s) in this item: 4
Paper_2.pdf (286.2Kb)Paper_3.pdf (2.968Mb)paper_4.pdf (1.351Mb)thesis.pdf (4.529Mb) -
Larsen, Jelena N (Master thesis; Mastergradsoppgave, Feb-2011)[+][-]
Abstract: The Internet has become a natural medium for finding information and resources, and has probably become the most important tool in education and e-learning as well. Many educational institutions use on-line systems for uploading, creating and publishing educational content to students and pupils. Extended use of multimedia files, video, audio and image, as a part of the content is a growing trend and there is ever more a need to search for desired multimedia content. This causing challenges to both the on-line systems and its users. To make multimedia content suited for search and retrieval it is imperative to organize and describe content well. Normally, users do not spend much of their time annotating and organizing content. Text-based search engines that are integrated into the educational on-line systems are normally not very suitable for search of multimedia content. The specific concern of this project is to investigate and suggest solutions to how image context information can be collected and then used in image annotation and retrieval within educational content. The image context in this setting is defined as the image environment in which the image is used. For example it can be a collection of images or documents, the course(s), subtopic(s) and/or assignments where images are used as illustrations. The system that is designed and implemented in this thesis will use image context to describe the images content and its semantics and use this in its image retrieval. If there are multiple versions of an image it will also be used in the description and retrieval processes. The evaluation of the system indicates that usage of the image context is very useful in describing the image content and its semantics. The system finds and retrieves more relevant images to the search than the integrated search engine in on-line educational portal. It has also good retrieval performance compared to the integrated one. URI: http://hdl.handle.net/10037/3030 File(s) in this item: 1
thesis.pdf (5.278Mb) -
Weihei, Yu; Yang, Jie (Research report; Forskningsrapport, 2006)[+][-]
Abstract: Scalability, reliability and adaptability are among the key requirements for the enactment of distributed workflows. In addition, system resources should be efficiently utilized. Central workflow engines and static analysis of workflow specifications are some of the important obstacles to meeting these requirements. We propose a fully decentralized approach to workflow enactment that is not subject to these obstacles. In addition, it supports automatic recovery. The approach is of continuation-passing style, where continuations, or the reminder of the executions, are passed along with asynchronous messages for workflow enactment. Two continuations are associated to an execution: a success continuation and a failure continuation. Recovery plans for workflows are automatically generated at runtime and included in failure continuations. A prototype is implemented. URI: http://hdl.handle.net/10037/398 File(s) in this item: 1
report.pdf (229.2Kb)
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