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Publications

2014

A Time-Frequency Analysis on the Impact of Climate Variability on Semi-Natural Mountain Meadows

Authors
Cunha, M; Richter, C;

Publication
IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING

Abstract
This paper analyzes the impact of climate dynamics on vegetation growth for a rural mountainous region in northeastern Portugal. As a measure of vegetation growth, we use the normalized difference vegetation index (NDVI), which is based on the ten-day synthesis data set (S10) from Satellite Pour l'Observation de la Terre (SPOT-VEGETATION) imagery from 1998 to 2011. We test whether the dynamic growth pattern of the NDVI has changed due to climate variability, and we test the relationship of NDVI with temperature and available soil water (ASW). In order to do so, we use a time-frequency approach based on Kalman filter regressions in the time domain. The advantage of our approach is that it can be used even in the case where the sample size is relatively small. By estimating the important relationships in the time domain first and transferring them into the frequency domain, we are still able to derive a complete spectrum over all frequencies. In our example, we find a change of the cyclical pattern for the spring season and different changes if we take into account all seasons. In other words, we can distinguish between deterministic changes of the vegetation cycles and stochastic changes that only occur randomly. Deterministic changes imply that the data-generating process has changed (such as climate), whereas stochastic changes imply only temporary changes. We find that individual seasons undergo cyclical changes that are different from other seasons. Moreover, our analysis shows that temperature and ASW are the main drivers of vegetation growth. We can also recognize a shift of the relative importance away from temperature to soil water.

2014

Integration and testing of the GRAVITY infrared camera for multiple telescope optical beam analysis

Authors
Gordo, P; Amorim, A; Abreu, J; Eisenhauer, F; Anugu, N; Garcia, P; Pfuhl, O; Haug, M; Sturm, E; Wieprecht, E; Perrin, G; Brandner, W; Straubmeier, C; Perraut, K; Duarte Naia, MD; Guimaraes, M;

Publication
OPTICAL AND INFRARED INTERFEROMETRY IV

Abstract
The GRAVITY Acquisition Camera was designed to monitor and evaluate the optical beam properties of the four ESO/VLT telescopes simultaneously. The data is used as part of the GRAVITY beam stabilization strategy. Internally the Acquisition Camera has four channels each with: several relay mirrors, imaging lens, H-band filter, a single custom made silica bulk optics (i.e. Beam Analyzer) and an IR detector (HAWAII2-RG). The camera operates in vacuum with operational temperature of: 240k for the folding optics and enclosure, 100K for the Beam Analyzer optics and 80K for the detector. The beam analysis is carried out by the Beam Analyzer, which is a compact assembly of fused silica prisms and lenses that are glued together into a single optical block. The beam analyzer handles the four telescope beams and splits the light from the field mode into the pupil imager, the aberration sensor and the pupil tracker modes. The complex optical alignment and focusing was carried out first at room temperature with visible light, using an optical theodolite/alignment telescope, cross hairs, beam splitter mirrors and optical path compensator. The alignment was validated at cryogenic temperatures. High Strehl ratios were achieved at the first cooldown. In the paper we present the Acquisition Camera as manufactured, focusing key sub-systems and key technical challenges, the room temperature (with visible light) alignment and first IR images acquired in cryogenic operation.

2014

Unified overhead-aware schedulability analysis for slot-based task-splitting

Authors
Sousa, PB; Bletsas, K; Tovar, E; Souto, P; Akesson, B;

Publication
REAL-TIME SYSTEMS

Abstract
Hard real- time multiprocessor scheduling has seen, in recent years, the flourishing of semi-partitioned scheduling algorithms. This category of scheduling schemes combines elements of partitioned and global scheduling for the purposes of achieving efficient utilization of the system's processing resources with strong schedulability guarantees and with low dispatching overheads. The sub-class of slot-based "task-splitting" scheduling algorithms, in particular, offers very good trade-offs between schedulability guarantees (in the form of high utilization bounds) and the number of preemptions/migrations involved. However, so far there did not exist unified scheduling theory for such algorithms; each one was formulated in its own accompanying analysis. This article changes this fragmented landscape by formulating a more unified schedulability theory covering the two state-of-the-art slot-based semi-partitioned algorithms, S-EKG and NPS-F (both fixed job-priority based). This new theory is based on exact schedulability tests, thus also overcoming many sources of pessimism in existing analysis. In turn, since schedulability testing guides the task assignment under the schemes in consideration, we also formulate an improved task assignment procedure. As the other main contribution of this article, and as a response to the fact that many unrealistic assumptions, present in the original theory, tend to undermine the theoretical potential of such scheduling schemes, we identified and modelled into the new analysis all overheads incurred by the algorithms in consideration. The outcome is a new overhead-aware schedulability analysis that permits increased efficiency and reliability. The merits of this new theory are evaluated by an extensive set of experiments.

2014

Building an Extended Ontological Perspective on Service Science

Authors
Dragoicea, M; Borangiu, T; Falcao e Cunha, JFE; Oltean, VE; Faria, J; Radulescu, S;

Publication
EXPLORING SERVICES SCIENCE, IESS 2014

Abstract
This paper presents an approach accounting for the classification of the main knowledge resources related to the new Science of Service. The main knowledge categories are defined as concepts integrated in an extended Service Science ontology. The ontology derived from several sources was captured using UML and Protege, and then, through a RDF/OWL transformation, a semantically annotated wiki has been directly implemented offering an execution of the ontology together with implemented use cases. Further, a dedicated application was developed - the Service Science Knowledge Environment (SSKE) in order to grant user access to different knowledge categories created along with the proposed ontology. The SSKE is a cloud based collaborative software service, aiming at providing co-created knowledge resources shared by academia, industry and government organizations. This application can be accessed through the Web (http://sske.cloud.upb.ro/) and it can be used for managing service related knowledge.

2014

An Approach of an Idea Management Platform to Improve the Innovation Process

Authors
Marcelo, P; Monteiro, J; Almeida, F;

Publication
International Journal of Computer Applications

Abstract

2014

Modelling operational expenditure savings for the implementation of autonomous networks

Authors
Spek, S; Gonçalves, V; Rits, O; Altman, Z; Destré, C;

Publication
IEEE Wireless Communications and Networking Conference, WCNC

Abstract
Developments in autonomic network management offer many promises, but its economic benefits are hard to assess. This paper proposes a method to calculate the OPEX gains of a typical network on the basis of a scenario, for which a management framework and autonomous mechanisms have been developed. It makes use of a novel approach, a Toy model, taking into account expert opinions as well as simulation results. The new approach allows assessment of the OPEX impact of both individual mechanisms as well as the overall impact, which, in the present scenario results in an expected OPEX saving of 11 to 13 per cent. © 2014 IEEE.

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