| 1. |
- Sherratt, K., et al.
(författare)
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Predictive performance of multi-model ensemble forecasts of COVID-19 across European nations
- 2023
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Methods: We used open-source tools to develop a public European COVID-19 Forecast Hub. We invited groups globally to contribute weekly forecasts for COVID-19 cases and deaths reported by a standardised source for 32 countries over the next 1–4 weeks. Teams submitted forecasts from March 2021 using standardised quantiles of the predictive distribution. Each week we created an ensemble forecast, where each predictive quantile was calculated as the equally-weighted average (initially the mean and then from 26th July the median) of all individual models’ predictive quantiles. We measured the performance of each model using the relative Weighted Interval Score (WIS), comparing models’ forecast accuracy relative to all other models. We retrospectively explored alternative methods for ensemble forecasts, including weighted averages based on models’ past predictive performance.Results: Over 52 weeks, we collected forecasts from 48 unique models. We evaluated 29 models’ forecast scores in comparison to the ensemble model. We found a weekly ensemble had a consistently strong performance across countries over time. Across all horizons and locations, the ensemble performed better on relative WIS than 83% of participating models’ forecasts of incident cases (with a total N=886 predictions from 23 unique models), and 91% of participating models’ forecasts of deaths (N=763 predictions from 20 models). Across a 1–4 week time horizon, ensemble performance declined with longer forecast periods when forecasting cases, but remained stable over 4 weeks for incident death forecasts. In every forecast across 32 countries, the ensemble outperformed most contributing models when forecasting either cases or deaths, frequently outperforming all of its individual component models. Among several choices of ensemble methods we found that the most influential and best choice was to use a median average of models instead of using the mean, regardless of methods of weighting component forecast models.Conclusions: Our results support the use of combining forecasts from individual models into an ensemble in order to improve predictive performance across epidemiological targets and populations during infectious disease epidemics. Our findings further suggest that median ensemble methods yield better predictive performance more than ones based on means. Our findings also highlight that forecast consumers should place more weight on incident death forecasts than incident case forecasts at forecast horizons greater than 2 weeks.
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| 2. |
- Chiaraviglio, L., et al.
(författare)
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Impact of energy-efficient techniques on a device lifetime
- 2014
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Ingår i: 2014 IEEE Online Conference on Green Communications, OnlineGreenComm 2014. - : IEEE conference proceedings. - 9781479973842
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Konferensbidrag (refereegranskat)abstract
- This paper focuses on the impact that energyefficient techniques have on the component lifetime in optical backbone networks. The study presented in the paper considers in particular the influence that green routing strategies have on the failure rate of Erbium Doped Fiber Amplifiers (EDFAs), i.e., if their lifetime is positively or negatively impacted when putting them into sleep mode in order to reduce their energy consumption. To this end, the paper proposes a model that estimates the failure rate acceleration factor as a function of: (i) for how long and how frequently a device is switched into sleep mode, and (ii) hardware parameters that characterize the device. The proposed model is then evaluated by considering an energyefficient Routing and Wavelength Assignment (RWA) strategy that targets saving energy by putting EDFAs into sleep mode. The results presented in the paper show that energy-efficient techniques may have the potential to lower the failure rate of EDFAs. However, this is true only under specific conditions, i.e., an energy-efficient strategy needs to be carefully planned in order to avoid frequent power state transitions, which result in shortening the lifetime of an EDFA.
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| 3. |
- Natalino, Carlos, Dr. 1987-, et al.
(författare)
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EFAH : An energy and fatigue aware heuristic for provisioning highly available connections in optical backbone networks
- 2017
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Ingår i: Proceedings of 2017 9th International Workshop on Resilient Networks Design and Modeling, RNDM 2017. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538606711
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Konferensbidrag (refereegranskat)abstract
- Optical backbone operators need to meet the availability requirements specified in the Service Level Agreements (SLAs). While less stringent availability constraints, i.e., less than three 9's might be met by provisioning connections without any protection, more stringent requirements, i.e., five 9's, force operator to use proactive protection strategies. The connection provisioning process becomes more cost-efficient when green aspects are considered. On the other hand, energy awareness introduces thermal fatigue effects, which may in turn lower the lifetime of devices that undergo frequent power state transitions, i.e., between Active Mode (AM) and Sleep Mode (SM). As a result the availability level experienced by the unprotected connections may decrease. At the same time, with devices failing more frequently the protection level chosen for a given connection might not be enough to guarantee the required average connection availability performance. This work tackles the problem of managing an optical back-bone network when green and thermal fatigue aspects are introduced. We propose an Energy and Fatigue Aware Heuristic (EFAH) that is able to balance between thermal fatigue effects and energy saving performance. When compared to the pure Energy-Aware (EA) strategies, EFAH manages to significantly improve the value of the average connection availability of both unprotected and protected connections. On the other hand, there is a price to pay in terms of lower energy saving performance.
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| 4. |
- Natalino, Carlos, et al.
(författare)
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Optimal lifetime-aware operation of green optical backbone networks
- 2016
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Ingår i: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 34:12, s. 3915-3926
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Tidskriftsartikel (refereegranskat)abstract
- This paper targets the lifetime-aware management of a set of optical line amplifiers (OLAs) in an optical network exploiting sleep mode (SM) in order to save energy. We first present a simple model to predict the OLA lifetime. We then provide different mixed-integer linear programming (MILP) formulations, which jointly consider energy saving and lifetime. The proposed MILP formulations are then solved on different realistic scenarios, by taking into account the spatial and temporal variations of traffic demands. Results show that our lifetime-aware approach outperforms classical energy saving ILP formulations, which instead tend to notably decrease the OLA lifetime. More important, the proposed approaches can achieve a good lifetime performance without consuming significantly more energy than purely energy-aware strategies.
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