| 1. |
- Ahmed, Jawwad, et al.
(författare)
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Online approach to performance fault localization for cloud and datacenter services
- 2017
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Ingår i: Proceedings of the IM 2017 - 2017 IFIP/IEEE International Symposium on Integrated Network and Service Management. - : Institute of Electrical and Electronics Engineers Inc.. - 9783901882890 ; , s. 873-874
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Konferensbidrag (refereegranskat)abstract
- Automated detection and diagnosis of the performance faults in cloud and datacenter environments is a crucial task to maintain smooth operation of different services and minimize downtime. We demonstrate an effective machine learning approach based on detecting metric correlation stability violations (CSV) for automated localization of performance faults for datacenter services running under dynamic load conditions.
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| 2. |
- Bernhardt, H., et al.
(författare)
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Debris flow recurrence periods and multi-temporal observations of colluvial fan evolution in central Spitsbergen (Svalbard)
- 2017
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X. ; 296, s. 132-141
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Tidskriftsartikel (refereegranskat)abstract
- Fan-shaped accumulations of debris flow deposits are common landforms in polar regions such as Svalbard. Although depositional processes in these environments are of high interest to climate as well as Mars-analog research, several parameters, e.g., debris flow recurrence periods, remain poorly constrained. Here, we present an investigation based on remote sensing as well as in situ data of a similar to 0.4 km(2) large colluvial fan in Hanaskogdalen, central Spitsbergen. We analyzed high resolution satellite and aerial images covering five decades from 1961 to 2014 and correlated them with lichenometric dating as well as meteorological data. Image analyses and lichenometry deliver consistent results and show that the recurrence period of large debris flows (>= 400 m(3)) is about 5 to 10 years, with smaller flows averaging at two per year in the period from 2008 to 2013. While this is up to two orders of magnitude shorter than previous estimates for Svalbard (80 to 500 years), we found the average volume of -220 m(3) per individual flow to be similar to previous estimates for the region. Image data also reveal that an avulsion took place between 1961 and 1976, when the active part of the fan moved from its eastern to its western portion. A case study of the effects of a light rain event (similar to 5 mm/day) in the rainy summer of 2013, which triggered a large debris flow, further shows that even light precipitation can trigger major flows. This is made possible by multiple light rain events or gradual snow melt pre-saturating the permafrost ground and has to be taken into account when predicting the likelihood of potentially hazardous mass wasting in polar regions. Furthermore, our findings imply a current net deposition rate on the colluvial fan of similar to 480 m(3)/year, which is slightly less than the integrated net deposition rate of 576 to 720 m(3)/year resulting from the current fan volume divided by the 12,500 to 10,000 years since the onset of fan build-up after the area's deglaciation. However, the actual deposition rate, which should increase in a warmer climate including more rain, cannot be constrained due to effects like ongoing toe-cutting of the debris fan and some flows only causing internal redistributions.
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| 3. |
- Blidberg, Andreas, 1987-
(författare)
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Iron based Li-ion insertion materials for battery applications
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Li-ion batteries are currently the most efficient technology available for electrochemical energy storage. The technology has revolutionized the portable electronics market and is becoming a corner stone for large scale applications, such as electric vehicles. It is therefore important to develop materials in which the energy storage relies on abundant redox active species, such as iron. In this thesis, new iron based electrode materials for positive electrodes in Li-ion batteries were investigated. Lithium iron pyrophosphate (Li2FeP2O7) and two polymorphs of lithium iron sulphate fluoride (LiFeSO4F) were studied.For Li2FeP2O7, preferred oxidation of iron with different coordination numbers within the crystal structure was studied, and six-coordinated iron was found to be oxidized preferentially at lower potentials compared to five‑coordinated iron. Electrochemical cycling resulted in structural changes of Li2FeP2O7 through an increased Li-Fe mixing in the compound, forming a metastable state during battery operation.For tavorite LiFeSO4F, the influence of the amount of a conductive polymer (poly(3,4-ethylenedioxythiophene), or PEDOT) was studied. All the different amounts of PEDOT coating reduced the polarization significantly, but the trade-off between functionality and weight added also has to be considered. Additionally, the effect of densifying the electrodes to different degrees is reported, and was found to have a significant influence on the battery performance. Also triplite LiFeSO4F was coated with PEODT, and it was found that the electrochemical performance improved, but not to the same extent as for tavorite LiFeSO4F. The faster solid state transport of Li-ions in tavorite type LiFeSO4F possibly accounts for the difference in electrochemical performance.Together, the results presented herein should be of importance for developing new iron based materials for Li-ion batteries.
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| 4. |
- Carlsson, Ella, et al.
(författare)
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An evaluation of models for Martian gully formation using remote sensing and in situ measurments of Svalbard analogs.
- 2008
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Ingår i: Lunar and Planetary Science Conference 39. ; XXXIX:1852
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The newly discovered gully systems on Mars have been found on rather young geologi-cal surfaces such as dunes and polygons. This in combination with the general absence of superimposed impact craters suggests that the gullies are relatively young geological features. Their morphology indicates that they have been eroded by a liquid fluid, most probably water. A recent discovery suggests that gully formation is an ongoing process, which appears to occur even today. This is a paradox since water in current Martian atmospheric conditions cannot be found in a stable form on the surface due to the low pressure and temperature during normal conditions. Several formation mechanisms have been proposed for the Martian gullies such as liquid carbon dioxide reservoirs, shallow liquid water aquifer, melting ground ice, dry landslide, snow melt and deep liquid water aquifer. However, none of these models can alone explain all the gullies discovered on Mars. So far Martian gullies have only been studied from high orbit via satellites. Gullies found in Arctic climates on Earth could be an equitable analog for the Martian gullies and a com-parative analysis could help disclose the formation mechanisms of the Martian gullies as well as their eroding agent.
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| 5. |
- Carlsson, Ella, et al.
(författare)
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FIELD STUDIES OF GULLIES AND PINGOS ON SVALBARD – A MARTIAN ANALOG.
- 2008
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Ingår i: European Planetary Science Congress, 21-26 September 2008. ; 3
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Konferensbidrag (refereegranskat)abstract
- The gully systems on Mars have been found to superpose young geological surfaces such as dunes and thermal contraction polygons. This in combination with the general absence of superimposed impact craters suggest that the gullies are relatively recent geological formations. The observed gullies display a wide set of morphologies ranging from features seemingly formed by fluvial erosion to others pointing to dry landslide processes. A recent discovery suggests that this is an ongoing process, which appears to occur even today. Several formation mechanisms have been proposed for the Martian gullies, such as liquid carbon dioxide reservoirs, shallow liquid water aquifer, melting ground ice, dry landslide, snow melt and deep liquid water aquifer. However, none of these models can alone explain all the gullies discovered on Mars. So far Martian gullies have been studied only from orbit via remote sensing data. Hydrostatic pingos are perennial ice-cored mounds that may reach an elongated or circular radius of approximately 150 m. They are found in periglacial environments where they are formed by freezing processes in the continuous permafrost. The pingos go through different evolutionary stages as they mature, where the final stage leaves an annular rim left by the collapse of the summit. Images from the High Resolution Imaging Science Experiment (HiRISE) show small fractured mounds in the Martian mid-latitudes. Even though some differences are observed, the best terrestrial analogues for the observed mound morphology are pingos. Gullies and pingos found in Arctic climates on Earth could be an analog for the Martian ones. A comparative analysis might help to understand the formation mechanisms of the Martian pingos and gullies and their possible eroding agent.
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| 6. |
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| 7. |
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| 8. |
- de Vera, Jean Paul, et al.
(författare)
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EUROX (Europa Explorer): An astrobiology mission concept to the Jovian icy moon Europa.
- 2008
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Ingår i: Geophysical Research Abstracts. ; 10, EGU2008-A-01483, 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The discovery of so-called extremophiles indicates how robust life is. That microbial life can resist extreme and harsh environmental conditions as e.g. very high and cold temperatures, desiccation, acidity, salinity and wide ranges of radiation spectra including UV and X-rays, suggests that micro organisms are capable of surviving and maintaining essential living functions, or often thriving, in conditions previously thought impossible. Recently it seems that only liquid water and an energy source are the core prerequisites for the development of life, greatly expanding the range of potential habitats for life both on Earth and in the solar system. In light of these discoveries, the definition of the “Habitable Zone” as the region where liquid water can exist at a planetary surface may need revision. Energy in the form of heat may be found on several volcanic worlds in our solar system, and subsurface liquid water may exist there, too. One likely candidate for such a reserve of water is the jovian icy moon Europa. Imaged by the Voyager and Galileo probes, this icy body appears to have a geologically young outer surface. Spectroscopic studies from Earth have confirmed that the European crust is composed of water ice. Long cracks across its surface may be suggestive of huge ice blocks rafting upon an underlying liquid layer. Darker non ice material also covers much of the surface and is spatially associated with the cracks. Recent modeling suggests that tidal forces imparted upon the moon by Jupiter may cause heating in the depth – raising the possibility of a liquid water ocean beneath Europa’s icy crust. Further on it is supposed that a weak induced magnetic field is present on the moon. This classifies Europa as an object of great scientific interest, warranting investigation for habitability and even the presence of life within the supposed ocean of the moon. The Europa Explorer (EUROX) mission complements other proposed missions to study Europa. EUROX will characterize the habitability potential of Europa, with the aim of understanding whether life could exist there or not. The mission will address the following key questions: (i) existence or non- existence of a liquid ocean beneath the surface, (ii) the nature of the non icy material visible upon the surface cracks, (iii) the physical characteristics of the ice crust, (iv) effects by local radiation on the surface chemistry, (v) the depth of radiation penetration in the ice and probably shielding effects by a magnetic field and (vi) the presence of organic compounds on or in the Europan ice crust. Our proposed mission will operate as a fully European and further on international mission, with the aim of providing the initial information required for later, larger missions to visit Europa. EUROX will involve both remote-sensing and in-situ research. Its mission architecture sees a single space craft deployed to Europa, launched by an Ariane 5. This vehicle will use conventional propulsion and a Venus-Earth-Earth flight path to travel to the jovian system in six years. Upon arrival at Europa, the space craft will commence remote observations of the icy moon, to determine the physical nature of the ice crust, and to investigate the presence of a subsurface liquid ocean. The orbiter will carry two independent vehicles (two penetrators) that will then separate, de-orbit, and penetrate the crust nearby or in the cracks to a depth of several meters. A suite of compact instruments will address the physical and chemical properties of the crust, as well as seeking organic compounds and pre-biotic material in the ice. The use of a laser communication system removes the need for a relay spacecraft in orbit around Jupiter, decreasing overall mission cost. Expected orbiter mission duration is on the order of two months, with each penetrator functioning for approximately 24 hours.
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| 9. |
- Ekelin, Svante, et al.
(författare)
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Real-Time Measurement of End-to-End Available Bandwidth using Kalman Filtering
- 2006
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Ingår i: 10th IEEE/IFIP Network Operations and Management Symposium, 2006. NOMS 2006.. - Piscataway, New Jersey, USA : IEEE Computer Society. - 1424401429 - 9781424401420 ; , s. 73-84
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new method, BART (bandwidth available in real-time), for estimating the end-to-end available bandwidth over a network path. It estimates bandwidth quasi-continuously, in real-time. The method has also been implemented as a tool. It relies on self-induced congestion, and repeatedly samples the available bandwidth of the network path with sequences of probe packet pairs, sent at randomized rates. BART requires little computation in each iteration, is lightweight with respect to memory requirements, and adds only a small amount of probe traffic. The BART method uses Kalman filtering, which enables real-time estimation (a.k.a. tracking). It maintains a current estimate, which is incrementally improved with each new measurement of the inter-packet time separations in a sequence of probe packet pairs. The measurement model has a strong non-linearity, and would not at first sight be considered suitable for Kalman filtering, but we show how this non-linearity can be handled. BART may be tuned according to the specific needs of the measurement application, such as agility vs. stability of the estimate. We have tested an implementation of BART in a physical test network with carefully controlled cross traffic, with good accuracy and agreement. Test measurements have also been performed over the Internet. We compare the performance of BART with that of pathChirp, a state-of-the-art tool for measuring end-to-end available bandwidth in real-time
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