| 1. |
- Aad, G., et al.
(författare)
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- 2014
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Mirzaeifard, Reza, et al.
(författare)
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Smoothing ADMM for Sparse-Penalized Quantile Regression With Non-Convex Penalties
- 2024
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Ingår i: IEEE Open Journal of Signal Processing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2644-1322. ; 5, s. 213-228
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates quantile regression in the presence of non-convex and non-smooth sparse penalties, such as the minimax concave penalty (MCP) and smoothly clipped absolute deviation (SCAD). The non-smooth and non-convex nature of these problems often leads to convergence difficulties for many algorithms. While iterative techniques such as coordinate descent and local linear approximation can facilitate convergence, the process is often slow. This sluggish pace is primarily due to the need to run these approximation techniques until full convergence at each step, a requirement we term as a secondary convergence iteration. To accelerate the convergence speed, we employ the alternating direction method of multipliers (ADMM) and introduce a novel single-loop smoothing ADMM algorithm with an increasing penalty parameter, named SIAD, specifically tailored for sparse-penalized quantile regression. We first delve into the convergence properties of the proposed SIAD algorithm and establish the necessary conditions for convergence. Theoretically, we confirm a convergence rate of o(k(-1/4)) for the sub-gradient bound of the augmented Lagrangian, where k denotes the number of iterations. Subsequently, we provide numerical results to showcase the effectiveness of the SIAD algorithm. Our findings highlight that the SIAD method outperforms existing approaches, providing a faster and more stable solution for sparse-penalized quantile regression.
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| 3. |
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| 4. |
- Aguilar, J. A., et al.
(författare)
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In situ, broadband measurement of the radio frequency attenuation length at Summit Station, Greenland
- 2022
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 68:272, s. 1234-1242
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Tidskriftsartikel (refereegranskat)abstract
- Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 10(17) electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length L-alpha. We find an approximately linear dependence of L-alpha on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: < L-alpha > = ((1154 +/- 121) - (0.81 +/- 0.14) (v/MHz)) m for frequencies v is an element of [145 - 3501 MHz.
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| 5. |
- Wamsler, Christine
(författare)
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Stakeholder involvement in strategic adaptation planning : Transdisciplinarity and co-production at stake?
- 2017
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Ingår i: Environmental Science and Policy. - : Elsevier BV. - 1462-9011 .- 1873-6416. ; 75, s. 148-157
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Tidskriftsartikel (refereegranskat)abstract
- To address increasing climatic variability and extremes, cities are gradually forced to develop climate change adaptation strategies that can ensure a continuous and transformative adaptation process. There is widespread consensus that the sustainable establishment of such strategies requires transdisciplinary approaches, that is, the involvement of internal and external stakeholders (state, civil society and market actors) to become part of the change and find innovative ways to unite their efforts and capacities. However, there is little research and hardly any empirical evidence on the process of stakeholder involvement and co-production in the development of municipal adaptation strategies. Against this background, this paper examines the factors that influence how and why different stakeholders are involved (or excluded) during the processes of developing adaptation strategies, and how this gets reflected in process outcomes. Based on applied participatory analysis of two pioneering municipalities in Germany and Sweden, the paper identifies and contrasts existing patterns to feed back into both theory and practice. Synergies, mismatches, barriers and driving forces for adaptation co-production are identified and contrasted with current adaptation discourses. The results highlight how the level of internal and external stakeholder involvement is conditional on (changes in) the broader governance context, and the associated power constellations in which stakeholders act (e.g., standing of departments, proximity to the decision making body, changes in [or constellations of) political parties, contractual arrangements for staff, individual champions, progress in mainstreaming). On this basis, conclusions are drawn regarding how to foster sustainable and transformative adaptation through increased stakeholder involvement. The results and conclusions are crucial to advance theory on adaptation co-production, providing a basis for further analyses, research and action. They inform how existing theory, policies and/or guidelines for strategic adaptation planning need to be revisited to support change across current risk governance.
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| 6. |
- Graham, Angus, 1968-, et al.
(författare)
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Theban Harbours And Waterscapes Survey, Spring 2016
- 2016
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Ingår i: Journal of Egyptian Archaeology. - : Sage Publications. - 0307-5133. ; 102:1, s. 13-21
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Tidskriftsartikel (refereegranskat)abstract
- Report on the 2016 spring season of the Theban Harbours and Waterscapes Survey (THaWS). The article discusses the geoarchaeological and geophysical survey along a 3.2 km-long transect starting close to the front of the Temple of Millions of Years of Ay and Horemheb and stretching to the village of Geziret el-Bairat on the West Bank of the Nile.
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| 7. |
- Fernandez Lacruz, Raul
(författare)
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Improving supply chains for logging residues and small-diameter trees in Sweden
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Forestry is expected to play a key enabling role in the transition towards a low-carbon, sustainable, and circular biomass-based economy in Europe. This will increase demand for forest biomass as a source of energy and traditional and new wood-based products. Consequently, it will be necessary to increase the mobilization of underutilized residual woody biomass such as logging residues (LR) and small-diameter trees (ST). While much residual biomass exists in forest land, significant quantities also exist in other lands such as overgrown agricultural land, power line corridors, and roadsides. However, high supply costs make it difficult to bring LR and ST to the market at a competitive price, which limits their utilization. Managing LR and ST supply chains is complex because it involves interconnected upstream and downstream operations performed by several contractors. This thesis aims to measure and analyse characteristics of LR and ST in Sweden, and the efficiency and costs of their supply systems, considering both current (heat and power plants, pulpmills) and future end-users (biorefineries). The main methods used for this purpose in this thesis are GIS analysis, time study, fuel-chip quality assessment, and discrete-event simulation. LR and ST were assessed along different supply chain operations in different operational environments, from the site to the enduser, and potential improvements leading to cost savings were identified. Large quantities of underutilized ST were identified across Sweden. It was also shown that using machines to extract overgrown vegetation along power line corridors could be more cost-efficient than current motor-manual (brush saw) clearing practices: even if this did not provide a net income, it could partially or fully offset maintenance costs. Models for predicting the dry mass content of windrows could improve logistics, and a holistic, supply chain management approach, is crucial for cost-effective delivery of high-quality residual biomass. The use of terminals increases supply costs but helps to secure supply during peak demand and cope with operational problems in the supply fleet that would prevent demand from being met on time in a direct supply system. Further development of supply systems (working methods and technology) is needed to realize the sustainable potential of LR and ST. These results offer policymakers, researchers, and industrial developers and practitioners new knowledge that could improve supply chains and increase the cost-competitiveness and utilization of LR and ST.
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| 8. |
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| 9. |
- Fernandez Lacruz, Raul, et al.
(författare)
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Productivity and profitability of harvesting overgrown roadside verges – a Swedish case study
- 2021
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Ingår i: International Journal of Forest Engineering. - : Informa UK Limited. - 1494-2119 .- 1913-2220. ; 32, s. 19-28
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Tidskriftsartikel (refereegranskat)abstract
- Despite the large biomass potential, current management practices for roadside verges (ditch backslopes,foreslopes and bottoms, possible parking lots and other lateral land) consist of regularly cutting the vegetation manually with motorized brush saws or flail mowers and leaving it to rot in situ. Regular vegetation clearing is crucial for safety reasons and to maintain road functionality. This study considered the cost-efficiency of a mechanized harvesting system, using a harvester and a forwarder (as an alternative to current clearing practices), to maintain the verges of a forest road in northern Sweden. Cutting a 2.5-m wide swath on each verge removed between 32 and 112 dry t ha−1 (16–56 dry t km−1 of road) of biomass. Analyses showed that the use of forest machinery to cut and extract biomass from roadside verges can be cost-competitive compared with motor-manual clearing when the average tree height is above 7 m (~26-year-old trees), and profitable for average heights above 8 m (~29-year-old trees). As the overgrown biomass has to be cleared anyway, a mechanized harvest could partially or fully offset maintenance costs. When setting cutting intervals, a trade-off needs to be made between larger biomass production and maintaining a clear and safe road. Future research needs to investigate how size, density of vegetation and width of the cleared swath affects the long-term quality and safety of roads.
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| 10. |
- Wesslander, Karin, 1976, et al.
(författare)
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On the carbon dioxide air-sea flux balance in the Baltic Sea.
- 2010
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Ingår i: Continental Shelf Research. - 0278-4343. ; 30:14, s. 1511-1521
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Tidskriftsartikel (refereegranskat)abstract
- We estimated the net annual air–sea exchange of carbondioxide (CO2) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO2 (pCO2w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (-) and sources (+) of CO2 within the -4.2 to+5.2molm-2 y-1 range. On average,forthe1994–2008 period, the East Gotland Sea was a source of CO2 (1.64molm-2 yr-1), the Bornholm Sea was a source (2.34 molm-2 yr-1), and the Kattegat was a sink (-1.16 molm-2 yr-1). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity (k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO2w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO2 flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth.
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