3,276 research outputs found
Jet Formation at the Sea Ice Edge
No full textMesoscale jet formation due to the Coriolis Effect is well understood over sharp changes in surface roughness such as coastlines. This sharp change in surface roughness is experienced by the atmosphere flowing over, and ocean flowing under, a compacted sea ice edge. Sea ice edge jets have been observed. This thesis presents a study of a dynamic sea ice edge responding to atmospheric and oceanic jet formation during various wind and ocean current conditions. An idealised analytical model of sea ice drift is created using a momentum balance and the viscous plastic rheology. This is compared to an ice edge in the Los Alamos sea ice climate model (CICE) run on an idealised domain. A scheme has been developed which analyses sea ice concentration and adds jets to the CICE model forcing data. The response of the model to jet formation is tested at various resolutions. The formation of atmospheric jets at the sea ice edge is shown to increase the wind speed parallel to the sea ice edge and results in the formation of a sea ice edge jet. The increase is dependent upon the angle between the ice and wind and results in an increase in ice transport along the sea ice edge of 40%. Observa- tions and climate model data of the polar oceans has been analysed to show areas of likely atmospheric jet formation with the Fram Strait being of particular interest. The possibility of oceanic jet formation and the resultant effect upon the sea ice edge is less conclusive. The coupling between the components of climate models is currently crude and does not allow for jet formation. Most climate model also misrepresent the ice drift through the Fram Strait leading to errors in the prediction of Arctic sea ice extent
Observations of Radar Penetration into Snow on Sea Ice
No full textSea ice is an important indicator of climate change. The ability to measure sea ice thickness is essential for monitoring trends in the volume of Arctic and Antarctic sea ice. Several methods of determining sea ice thickness are presented and it is concluded that the most appropriate for studying sea ice thickness trends on long time- and length-scales is satellite radar altimetry. One key uncertainty associated with determining sea ice thickness using satellite radar altimetry is the penetration of the radar into the snow cover. We discuss the dielectric theory related to penetration into snow. The bandwidth of satellite radar altimeters is not sufficient to resolve the air/snow and snow/ice interfaces, or layers within the snow pack. For these reasons we investigate the radar penetration into snow on sea ice using sled- and air-borne radars with wide bandwidths so that the interfaces are resolved. Coincident field measurements of the physical snow characteristics were also gathered. Data from three studies are presented. The first study is an analysis of data from the UCL Ground Penetrating Radar (GPR) deployed from an icebreaker ship off the coast of Antarctica. The radar dominant scattering surface was the snow/ice interface for 30% of the snow pits. The second is an analysis of data from the Airborne Synthetic aperture and Interferometric Altimeter System (ASIRAS) off the coast of Arctic Canada. In 2006 the radar dominant scattering surface was closer to the snow/ice than air/snow interface for 25% of the echoes; in 2008, this was 60%. The third is an analysis of coincident GPR and ASIRAS data over Arctic sea ice. We found average radar penetration (P) of 0.29 for GPR and ASIRAS data at the South site. Retrieved sea ice thickness would increase by a factor of two with P=0.29 compared with P=1
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Frazil dynamics and precipitation in a water column with depth-dependent supercooling
No full textWhen seawater becomes supercooled, collections of small ice crystals, known as frazil ice, form and grow. A model of frazil ice dynamics is presented that deals explicitly with the buoyant settling of frazil crystals onto an overlying surface. This yields further insight into transport associated with the ice pump mechanism, whereby ice is melted at depth and transferred to a shallower location as a result of the pressure variation of seawater's freezing temperature. The model is applied to a vertical cross-section through an Ice Shelf Water plume beneath Filchner-Ronne Ice Shelf, Antarctica, and helps to elucidate the depth-variation in its properties for the first time, as well as predicting the precipitation rate of frazil crystals. The model predicts that frazil ice should be preferentially located in a narrow layer near the ice shelf base as a result of the maximum supercooling there and an influx of crystals rising under their own buoyancy. The deposition of these crystals onto the ice shelf is governed by the balance between crystal rising and turbulent transfer of frazil away from the shelf, which is investigated in some detail
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Improving the spatial distribution of modeled Arctic sea ice thickness
No full textThe spatial distribution of ice thickness/draft in the Arctic Ocean is examined using a sea ice model. A comparison of model predictions with submarine observations of sea ice draft made during cruises between 1987 and 1997 reveals that the model has the same deficiencies found in previous studies, namely ice that is too thick in the Beaufort Sea and too thin near the North Pole. We find that increasing the large scale shear strength of the sea ice leads to substantial improvements in the model's spatial distribution of sea ice thickness, and simultaneously improves the agreement between modeled and ERS-derived 1993-2001 mean winter ice thickness
Utilising Deep Learning Models for the Surface Registration Problem in HoloNav
No full textSurface Registration is a registration problem that handles the registration of two similar surfaces. In most research that utilises Deep Learning (DL) models to handle surface registration two theories are investigated; the first being whether surfaces sampled from the same origin can be registered together, and the second theory being whether the models can register Point Clouds with low overlapping data for utilisation in Simultaneous Localisation and Mapping (SLAM) applications. However, the surface registration to be utilised in the HoloNav Augmented Reality (AR) navigation system will utilise Point Clouds sampled from different origins with a high overlap ratio. This research, therefore, aims to determine the viability of DL methods for surface registration in HoloNav data. To determine the viability, rotation and translation errors in the match were used, with the aforementioned metrics later being evaluated manually with the utilisation of a visualiser. The results indicate that the models can generalise on the navigator data for an initial Euler angle difference of 45 degrees, but due to the difference in sampling density on the utilised point clouds can not provide accurate matches. Therefore, the utilisation of DL models can be considered to be viable if the navigator data has a sampling density similar to the pre-operative model.https://github.com/alpcicimen/holonav-dl-registration The link to the github repository containing the utilised dataset, scripts, as well as the modified DL models RPMNet and PREDATOR.CSE3000 Research ProjectComputer Science and Engineerin
The Scent of a Smell: An Extensive Comparison between Textual and Structural Smells
No full textCode smells are symptoms of poor design or implementation choices that have a negative effect on several aspects of software maintenance and evolution, such as program comprehension or change- and fault-proneness. This is why researchers have spent a lot of effort on devising methods that help developers to automatically detect them in source code. Almost all the techniques presented in literature are based on the analysis of structural properties extracted from source code, although alternative sources of information (e.g., textual analysis) for code smell detection have also been recently investigated. Nevertheless, some studies have indicated that code smells detected by existing tools based on the analysis of structural properties are generally ignored (and thus not refactored) by the developers. In this paper, we aim at understanding whether code smells detected using textual analysis are perceived and refactored by developers in the same or different way than code smells detected through structural analysis. To this aim, we set up two different experiments. We have first carried out a software repository mining study to analyze how developers act on textually or structurally detected code smells. Subsequently, we have conducted a user study with industrial developers and quality experts in order to qualitatively analyze how they perceive code smells identified using the two different sources of information. Results indicate that textually detected code smells are easier to identify and for this reason they are considered easier to refactor with respect to code smells detected using structural properties. On the other hand, the latter are often perceived as more severe, but more difficult to exactly identify and remove.Accepted Author ManuscriptSoftware Engineerin
March dl: Adding Adaptive Heuristics and a New Branching Strategy
No full textWe introduce the march dl satisability (SAT) solver, a successor of march eq. The latter was awarded state-of-the-art in two categories during the Sat 2004 competition. The focus lies on presenting those features that are new in march dl. Besides a description, each of these features is illustrated with some experimental results. By extending the pre-processor, using adaptive heuristics, and by using a new branching strategy, march dl is able to solve nearly all benchmarks faster than its predecessor. Moreover, various instances which were beyond the reach of march eq, can now be solved - relatively easily - due to these new features.Software TechnologyElectrical Engineering, Mathematics and Computer Scienc
Crash Reproduction Using Helper Objectives
No full textEvolutionary-based crash reproduction techniques aid developers in their debugging practices by generating a test case that reproduces a crash given its stack trace. In these techniques, the search process is typically guided by a single search objective called Crash Distance. Previous studies have shown that current approaches could only reproduce a limited number of crashes due to a lack of diversity in the population during the search. In this study, we address this issue by applying Multi-Objectivization using Helper-Objectives (MO-HO) on crash reproduction. In particular, we add two helper-objectives to the Crash Distance to improve the diversity of the generated test cases and consequently enhance the guidance of the search process. We assessed MO-HO against the single-objective crash reproduction. Our results show that MO-HO can reproduce two additional crashes that were not previously reproducible by the single-objective approach.Virtual/online event due to COVID-19 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Software EngineeringSoftware Technolog
A General Formulation to Describe Empirical Rainfall Thresholds for Landslides
No full textAbstractIn this paper, a brief description of the Generalized FLaIR Model (GFM, De Luca and Versace, 2016) is provided, that is able to reproduce all the empirical thresholds proposed in literature, aimed to forecast landslides triggered by rainfall. In particular, this paper focuses on Antecedent Precipitation (AP) schemes. The paper demonstrates that these are particular solutions of the GFM and will exemplify this using AP schemes for NE Italy1, Seattle2 and Nicaragua - El Salvador3
Releasing Fast and Slow: An Exploratory Case Study at ING
No full textThe appeal of delivering new features faster has led many software projects to adopt rapid releases. However, it is not well understood what the effects of this practice are. This paper presents an exploratory case study of rapid releases at ING, a large banking company that develops software solutions in-house, to characterize rapid releases. Since 2011, ING has shifted to a rapid release model. This switch has resulted in a mixed environment of 611 teams releasing relatively fast and slow. We followed a mixed-methods approach in which we conducted a survey with 461 participants and corroborated their perceptions with 2 years of code quality data and 1 year of release delay data. Our research shows that: rapid releases are more commonly delayed than their non-rapid counterparts, however, rapid releases have shorter delays; rapid releases can be beneficial in terms of reviewing and user-perceived quality; rapidly released software tends to have a higher code churn, a higher test coverage and a lower average complexity; challenges in rapid releases are related to managing dependencies and certain code aspects, e.g. design debt.Software EngineeringSoftware Technolog
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