| 1. |
- Berg, Sofia, et al.
(författare)
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Ekologisk funktionalitet av värdekärnor för barrskogar inom Västra Götalands län : Ett strategiskt underlag för planering av förändrad skogsskötsel av barrskogsområden inom Västra Götalands län i syfte att stärka skogarnas förutsättningar att stödja biologisk mångfald och skogens klimatnytta
- 2022
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Rapport (populärvet., debatt m.m.)abstract
- Skogsstyrelsen redovisar i sin utvärdering av miljömålet Levande skogar 2019 att centrala hinder för uppfyllelse av miljömålet är minskande och fragmenterade livsmiljöer och minskande och/eller små populationer av ett antal hotade arter knutna till skogsekosystemet. En väg framåt för att vända denna trend är att framtidens skogsbruk bland annat bör utvecklas utifrån ett landskapsperspektiv och där hyggesfria skogsbruksmetoder ökar i omfattning.Länsstyrelserna i Sverige har genom sitt arbete med regionala handlingsplaner för grön infrastruktur identifierat så kallade värdekärnor – områden av stor betydelse för skogsarternas överlevnad. I denna studie har Västra Götalands läns värdekärnor analyserats med avseende på deras förmåga att stödja biologisk mångfald i ett landskapsperspektiv. Arbetet har gjorts i samverkan med Länsstyrelsen för Västra götalands län.Metoden som använts är Biotope Biodiversity Capacity Indicator (BBCI). Metoden har utvecklats inom forskningsprojektet “Landscape biodiversity capacity: a tool for measuring, monitoring and managing” finansierat av Naturvårdsverkets miljöforskningsanslag (2019-2022).Resultaten visar vilka geografiskt avgränsade värdekärnor som idag har hög ekologisk funktionalitet och som utgör biologiska överlevnads- och spridningshotspots för arter knutna till barrskogar. Vidare visar resultaten att endast sju kommuner har BBCI-värden över 1, det vill säga, ett hållbart skogslandskap som kan hålla fokusarten i ett 100-årsperspektiv.För att nå de svenska miljömålen Levande skogar och Ett rikt växt- och djurliv samt skapa bättre förutsättningar för skogens biologiska mångfald att fortleva behöver nuvarande skogsmetoder med trakthyggesbruk anpassas till brukningsformer som tar större hänsyn till skogens ekosystem. Resultaten från denna studie kan ge prioriteringsunderlag för inom vilka produktionsskogar en så kallad återvildning genom förändrad brukningsmetod skulle kunna resultera i betydelsefull ökad ekologisk funktionalitet på landskapsnivå för de västgötska barrskogarna.
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| 2. |
- Curtsdotter, Alva, et al.
(författare)
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Ecosystem function in predator-prey food webs : confronting dynamic models with empirical data
- 2019
-
Ingår i: Journal of Animal Ecology. - : John Wiley & Sons. - 0021-8790 .- 1365-2656. ; 88:2, s. 196-210
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Tidskriftsartikel (refereegranskat)abstract
- Most ecosystem functions and related services involve species interactions across trophic levels, for example, pollination and biological pest control. Despite this, our understanding of ecosystem function in multitrophic communities is poor, and research has been limited to either manipulation in small communities or statistical descriptions in larger ones. Recent advances in food web ecology may allow us to overcome the trade-off between mechanistic insight and ecological realism. Molecular tools now simplify the detection of feeding interactions, and trait-based approaches allow the application of dynamic food web models to real ecosystems. We performed the first test of an allometric food web model's ability to replicate temporally nonaggregated abundance data from the field and to provide mechanistic insight into the function of predation. We aimed to reproduce and explore the drivers of the population dynamics of the aphid herbivore Rhopalosiphum padi observed in ten Swedish barley fields. We used a dynamic food web model, taking observed interactions and abundances of predators and alternative prey as input data, allowing us to examine the role of predation in aphid population control. The inverse problem methods were used for simultaneous model fit optimization and model parameterization. The model captured >70% of the variation in aphid abundance in five of ten fields, supporting the model-embodied hypothesis that body size can be an important determinant of predation in the arthropod community. We further demonstrate how in-depth model analysis can disentangle the likely drivers of function, such as the community's abundance and trait composition. Analysing the variability in model performance revealed knowledge gaps, such as the source of episodic aphid mortality, and general method development needs that, if addressed, would further increase model success and enable stronger inference about ecosystem function. The results demonstrate that confronting dynamic food web models with abundance data from the field is a viable approach to evaluate ecological theory and to aid our understanding of function in real ecosystems. However, to realize the full potential of food web models, in ecosystem function research and beyond, trait-based parameterization must be refined and extended to include more traits than body size. © 2018 The Authors. Journal of Animal Ecology © 2018 British Ecological Society
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| 3. |
- Fick, Jerker, et al.
(författare)
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Screening of benzodiazepines in thirty European rivers
- 2017
-
Ingår i: Chemosphere. - : Elsevier BV. - 0045-6535 .- 1879-1298. ; 176, s. 324-332
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Tidskriftsartikel (refereegranskat)abstract
- Pharmaceuticals as environmental contaminants have received a lot of interest over the past decade but, for several pharmaceuticals, relatively little is known about their occurrence in European surface waters. Benzodiazepines, a class of pharmaceuticals with anxiolytic properties, have received interest due to their behavioral modifying effect on exposed biota. In this study, our results show the presence of one or more benzodiazepine(s) in 86% of the analyzed surface water samples (n = 138) from 30 rivers, representing seven larger European catchments. Of the 13 benzodiazepines included in the study, we detected 9, which together showed median and mean concentrations (of the results above limit of quantification) of 5.4 and 9.6 ng L-1, respectively. Four benzodiazepines (oxazepam, temazepam, clobazam, and bromazepam) were the most commonly detected. In particular, oxazepam had the highest frequency of detection (85%) and a maximum concentration of 61 ng L-1. Temazepam and clobazam were found in 26% (maximum concentration of 39 ng L-1) and 14% (maximum concentration of 11 ng L-1) of the samples analyzed, respectively. Finally, bromazepam was found only in Germany and in 16 out of total 138 samples (12%), with a maximum concentration of 320 ng L-1. This study clearly shows that benzodiazepines are common micro-contaminants of the largest European river systems at ng L-1 levels. Although these concentrations are more than a magnitude lower than those reported to have effective effects on exposed biota, environmental effects cannot be excluded considering the possibility of additive and sub-lethal effects.
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| 4. |
- Grut, Viktor, et al.
(författare)
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Cytomegalovirus seropositivity is associated with reduced risk of multiple sclerosis : a presymptomatic case-control study
- 2021
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Ingår i: European Journal of Neurology. - : Blackwell Publishing. - 1351-5101 .- 1468-1331. ; 28:9, s. 3072-3079
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Epstein-Barr virus (EBV) and Human herpesvirus 6A (HHV-6A) are associated with increased risk of multiple sclerosis (MS). Conversely, infection with Cytomegalovirus (CMV) has been suggested to reduce the risk of MS but supporting data from presymptomatic studies are lacking. Here, we sought to increase the understanding of CMV in MS aetiology.METHODS: We performed a nested case-control study with presymptomatically collected blood samples identified through cross-linkage of MS registries and Swedish biobanks. Serological antibody response against CMV, EBV and HHV-6A was determined using a bead-based multiplex assay. Odds ratio (OR) with 95 % confidence intervals (CI) for CMV seropositivity as risk factor for MS was calculated by conditional logistic regression and adjusted for EBV and HHV-6A seropositivity. Potential interactions on the additive scale were analysed by calculating attributable proportion due to interaction (AP).RESULTS: Serum samples from 670 pairs of matched cases and controls were included. CMV seropositivity was associated with a reduced risk for MS (OR = 0.70, 95% CI 0.56-0.88, p = 0.003). Statistical interactions on the additive scale were observed between seronegativity for CMV and seropositivity against HHV-6A (AP 0.34, 95% CI 0.06-0.61) and EBV antigen EBNA-1 (amino acid 385-420) at age 20-39 years (AP 0.37, 95% CI 0.09-0.65).CONCLUSIONS: CMV seropositivity is associated with a decreased risk for MS. The protective role for CMV infection in MS aetiology is further supported by the interactions between CMV seronegativity and EBV and HHV-6A seropositivity.
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| 5. |
- Heuvelmans, Matthijs, 1982-, et al.
(författare)
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Power Semiconductors for Voltage Source Converters in HVDC and STATCOM Applications
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With a steady increase in electricity consumption in both developed and developing regions combined with demand for sustainable energy infrastructure, trends towards more renewable energy sources and more open electricity markets are becoming more prominent. High Voltage DC (HVDC) connections and Static Synchronous Compensators (STATCOM) are two technologies that play a part in fulfilling this increasing demand. HVDC is beneficial in cases where production and consumption are geographically separated or for sub-sea cable transmissions. STATCOM helps to increase the capacity of AC transmission in addition to enhancing ac-grid voltage quality. A key component in both HVDC and STATCOM converters are the semiconductor switching devices. Switching devices have a fundamental impact on performance levels that can be obtained in terms of efficiency, reliability and functionality. This paper serves two purposes. The first is to give a historical overview of switching devices employed in HVDC transmission systems and STATCOMs. This starts with the use of mercury arc valves some 100 years ago and it continues with the semiconductor switching devices that are currently being employed in HVDC and STATCOM applications. A second purpose of this paper is to indicate developments in switching technology that are of interest for HVDC and STATCOM. In order to do this in a structured manner, the technologies are compared in terms of efficiency, reliability and functionality. Developments that are discussed in this paper are the emergence of Silicon Carbide (SiC) devices and the improvement of Insulated Gate Bipolar Transistor (IGBT) and Integrated Gate Commutated Thyristor (IGCT) devices in silicon. Currently, applications are based on silicon based thyristors or IGBT technology. Line commutated converters based on thyristors are cost-effective and efficient; however, due to lack of controlled turn-off capability, functionality is limited. Using voltage source converter technology with semiconductors having turn-off capability, such as the IGBT, increased functionality is obtained. The IGCT, a gate controlled thyristor with turn-off capability, has lower conduction losses compared to an IGBT with the same active area. In case a modular multilevel converter is used, the switching frequency of the individual switches can be reduced for the same performance. This leads to a shift towards the importance of having low conduction losses as opposed to low switching losses. A further shift can be achieved by using soft-switching techniques. Regarding SiC devices, different maturity is reached for unipolar and bipolar devices. Unipolar devices in SiC have been marketed successfully at low voltages (≤ 1700V). An example is SiC Schottky diodes for power factor correctors. For the voltages typically applied in HVDC and STATCOM, the drift region resistance would impose serious limitations on efficiency (if high current densities are used). Bipolar devices such as SiC IGBTs and IGCTs have been demonstrated in laboratory setups and results have been published; however, reliable operation is currently impeded due to the propagation of crystal lattice defects which causes rapid degradation of such devices.
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| 6. |
- Jonsson, Annie, et al.
(författare)
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Landskapets förmåga att hålla biologisk mångfald : – en indikator för biologisk mångfald och ett planeringsverktyg för prioritering av markanvändning
- 2022
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten beskriver ett nytt verktyg framtaget för att underlätta planering av grön infrastruktur på landskapsnivå och ger via fallstudier exempel på hur verktyget kan användas. Projektet har utförts i ett samarbete med expertis inom teoretisk ekologi, ekologi, biodiversitetsinformatik och tillämpad matematik.Forskningsprojektet har utvecklat en modell för att uppskatta ett landskaps för-måga att hålla biologisk mångfald i dess olika biotoper (Biotope Biodiversity Capacity Indicator, BBCI). Ett teoretiskt ramverk baserat på ekologisk kunskap har tagits fram som grund för modellen.Syftet med BBCI är att modellen ska kunna användas som ett planeringsverktyg för att:stärka biologisk mångfald i ett landskap,förbättra förutsättningarna för arter att använda hela landskapet ochskapa bättre förutsättningar för hänsyn till biologisk mångfald i samband med samhällsutveckling.För att testa och beskriva verktygets användbarhet har fyra fallstudier genomförts med olika fokus:Analys av fragmenteringen i ett barrskogslandskap som sköts med särskild naturhänsyn i Västernorrlands län.Analys av barrskogsvärdekärnors kapacitet för biologisk mångfald inom Västra Götalands län som synliggör vikten av kommunöverskridande samverkan.Analys av potentiella målkonflikter mellan två biotoper, ädellövskog och öppen mark med skyddsvärda träd i Valle.Analys av kapacitet för biologisk mångfald hos äldre ädellövträd i ett landskap mixat med urbana miljöer och landsbygd, Mjölby kommun.Parallellt med utvcklingen av BBCI har en tät dialog och samverkan skett med olika intressenter och slutanvändare. Den breda dialogen har medfört ett effektivt kun-skapsutbyte mellan olika parter.Rapporten avslutas med att beskriva utmaningar och verktygets utvecklings-potential både avseende pedagogik och teknik men även hur modellen kan byggas på och utvecklas med ytterligare funktioner för en breddad tillämpning.
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| 7. |
- Jonsson, Anders, et al.
(författare)
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Limitations of acyclic causal graphs for planning
- 2014
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Ingår i: Artificial Intelligence. - : Elsevier. - 0004-3702 .- 1872-7921. ; 210, s. 36-55
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Tidskriftsartikel (refereegranskat)abstract
- Causal graphs are widely used in planning to capture the internal structure of planning instances. Researchers have paid special attention to the subclass of planning instances with acyclic causal graphs, which in the past have been exploited to generate hierarchical plans, to compute heuristics, and to identify classes of planning instances that are easy to solve. This naturally raises the question of whether planning is easier when the causal graph is acyclic. In this article we show that the answer to this question is no, proving that in the worst case, the problem of plan existence is PSPACE-complete even when the causal graph is acyclic. Since the variables of the planning instances in our reduction are propositional, this result applies to STRIPS planning with negative preconditions. We show that the reduction still holds if we restrict actions to have at most two preconditions. Having established that planning is hard for acyclic causal graphs, we study two subclasses of planning instances with acyclic causal graphs. One such subclass is described by propositional variables that are either irreversible or symmetrically reversible. Another subclass is described by variables with strongly connected domain transition graphs. In both cases, plan existence is bounded away from PSPACE, but in the latter case, the problem of bounded plan existence is hard, implying that optimal planning is significantly harder than satisficing planning for this class.
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| 8. |
- Jonsson, Annie, et al.
(författare)
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Utvärdering av Hornborgasjöns restaurering : måluppfyllelse och effekter på biologisk mångfald med fokus på vegetation och fågelfauna
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Hornborgasjön räknas idag som en av Sveriges rikaste fågelsjöar och är internationellt utpekad som en av Sveriges värdefullaste våtmarker. Sjön har stor betydelse som både rast- och häckplats för en mängd fågelarter. Området är också av stort intresse för friluftslivet och som ett levande kulturlandskap. Under de senaste 150 åren har Hornborgasjön genomgått stora förändringar. En serie av sjösänkningar under 1800 och 1900-talen ledde till kraftig igenväxning och följdes av ett storskaligt restaureringsprojekt i senare tid. Syftet med Hornborgasjöns restaurering var att säkerställa Hornborgasjöns framtid som fågelsjö. Restaureringen är ett av Sveriges största naturvårdsprojekt. I denna rapport har vi utvärderat hur Hornborgasjöns restaurering påverkat vegetation och fågelfauna. Syftet var att analysera om och till vilken grad de biologiska målen med restaureringen uppnåtts.För att utvärdera måluppfyllelsen har vi i första hand jämfört olika naturtypers utbredning mellan åren 1905 och 2010 samt förändringar i fågelfaunan under flera tidsperioder. Analyser av vegetationskartor visar att vass- och buskområden kraftigt reducerats och att en stor öppen vattenspegel och omgivande mader återskapats. Våtmarksfåglarnas numerär har generellt sett återhämtat sig från igenväxningsperioden och är för vissa arter till och med större än vid förra sekelskiftet. För vissa naturtyper och fågelarter, som till exempel vassområden och häckande vadare, är dagens situation dock inte i linje med målen. Det står ändå klart att det övergripande målet och många av de mer specifika delmålen har uppfyllts så att Hornborgasjön idag är en levande våtmark med stort antal häckande och rastande fågelarter.I analyser av fågeldata från senare tid finns indikationer på negativa trender som man behöver vara observant på för att för framtiden säkra en biologiskt rik Hornborgasjö. En utmaning för denna utvärdering har dock varit bristen på högkvalitativa och jämförbara data att basera analyserna på. Vi belyser därför vikten av att ha ett fungerande övervakningssystem som kontinuerligt följer upp statusen i ekosystemet.
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| 9. |
- Jonsson, Anders, et al.
(författare)
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When Acyclicity is not Enough: Limitations of the Causal Graph
- 2013
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Ingår i: Proceedings of the Twenty-Third International Conference on Automated Planning and Scheduling. - : AAAI Press. - 9781577356097 ; , s. 117-125
-
Konferensbidrag (refereegranskat)abstract
- Causal graphs are widely used in planning to capture the internal structure of planning instances. In the past, causal graphs have been exploited to generate hierarchical plans, to compute heuristics, and to identify classes of planning instances that are easy to solve. It is generally believed that planning is easier when the causal graph is acyclic. In this paper we show that this is not true in the worst case, proving that the problem of plan existence is PSPACE-complete even when the causal graph is acyclic. Since the variables of the planning instances in our reduction are propositional, this result applies to STRIPS planning with negative pre-conditions. Having established that planning is hard for acyclic causal graphs, we study a subclass of planning instances with acyclic causal graphs whose variables have strongly connected domain transition graphs. For this class, we show that plan existence is easy, but that bounded plan existence is hard, implying that optimal planning is significantly harder than satisficing planning for this class.
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| 10. |
- Jonsson, Tomas, et al.
(författare)
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Food web structure affects the extinction risk of species in ecological communities
- 2006
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Ingår i: Ecological Modelling. - : Elsevier. - 0304-3800 .- 1872-7026. ; 199:1, s. 93-106
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the effect of food web structure on the extinction risk of species. We examine 793 different six-species food web structures with different number, position and strength of trophic links and expose them to stochasticity in a model with Lotka–Volterra predator–prey dynamics. The characteristics of species (intrinsic rates of increase as well as intraspecific density dependence) are held constant, but the interactions with other species and characteristics of the food web are varied.Extinctions of producer species occurred but were rare. Species at all trophic levels went extinct in communities with strong interactions as compared to communities with no strong interactions where only the secondary consumer went extinct. Extinction of a species directly involved in a strong interaction was more frequent than extinctions of species not directly involved in strong interactions (here termed direct and indirect extinctions, respectively). In model webs where both direct and indirect extinctions occurred, roughly 20% were indirect extinctions. The probability of indirect extinctions decreased with number of links. It is concluded that not just the presence of strong interactions but also their position and direction can have profound effects on extinction risk of species.Three principal components, based on 11 different food web metrics, explained 76.6% of the variation in trophic structure among food webs that differed in the number and position, but not strength, of trophic links. The extinction risk of consumer species was closely correlated to at least two of the three principal components, indicating that extinction risk of consumer species were affected by food web structure. The existence of a relationship between food web structure and extinction risk of a species was confirmed by a regression tree analysis and a complementary log-linear analysis. These analyses showed that extinction of consumer species were affected by the position of strong interactions and a varying number of other food web metrics, different for intermediate and top species. Furthermore, the degree to which the equilibrium abundance of a species is affected by a press perturbation is an indication of the risk of extinction that this species faces when exposed to environmental stochasticity. It is concluded that extinction risk of a species is determined in a complicated way by an interaction among species characteristics, food web structure and the type of disturbance.
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| 11. |
- Jonsson, Tomas, et al.
(författare)
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Predictive power of food web models based on body size decreases with trophic complexity
- 2018
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Ingår i: Ecology Letters. - : Wiley-Blackwell Publishing Inc.. - 1461-023X .- 1461-0248. ; 21:5, s. 702-712
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Tidskriftsartikel (refereegranskat)abstract
- Food web models parameterised using body size show promise to predict trophic interaction strengths (IS) and abundance dynamics. However, this remains to be rigorously tested in food webs beyond simple trophic modules, where indirect and intraguild interactions could be important and driven by traits other than body size. We systematically varied predator body size, guild composition and richness in microcosm insect webs and compared experimental outcomes with predictions of IS from models with allometrically scaled parameters. Body size was a strong predictor of IS in simple modules (r(2)=0.92), but with increasing complexity the predictive power decreased, with model IS being consistently overestimated. We quantify the strength of observed trophic interaction modifications, partition this into density-mediated vs. behaviour-mediated indirect effects and show that model shortcomings in predicting IS is related to the size of behaviour-mediated effects. Our findings encourage development of dynamical food web models explicitly including and exploring indirect mechanisms.
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| 12. |
- Jonsson, Tomas, et al.
(författare)
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Trophic interactions affect the population dynamics and risk of extinction of basal species in food webs
- 2010
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Ingår i: Ecological Complexity. - : Elsevier. - 1476-945X .- 1476-9840. ; 7:1, s. 60-68
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses effects of trophic complexity on basal species, in a Lotka–Volterra model with stochasticity. We use simple food web modules, with three trophic levels, and expose every species to random environmental stochasticity and analyze (1) the effect of the position of strong trophic interactions on temporal fluctuations in basal species’ abundances and (2) the relationship between fluctuation patterns and extinction risk. First, the numerical simulations showed that basal species do not simply track the environment, i.e. species dynamics do not simply mirror the characteristics of the applied environmental stochasticity. Second, the extinction risk of species was related to the fluctuation patterns of the species.More specifically, we show (i) that despite being forced by random stochasticity without temporal autocorrelation (i.e. white noise), there is significant temporal autocorrelation in the time series of all basal species’ abundances (i.e. the spectra of basal species are red-shifted), (ii) the degree of temporal autocorrelation in basal species time series is affected by food web structure and (iii) the degree of temporal autocorrelation tend to be correlated to the extinction risks of basal species.Our results emphasize the role of food web structure and species interactions in modifying the response of species to environmental variability. To shed some light on the mechanisms we compare the observed pattern in abundances of basal species with analytically predicted patterns and show that the change in the predicted pattern due to the addition of strong trophic interactions is correlated to the extinction risk of the basal species. We conclude that much remain to be understood about the mechanisms behind the interaction among environmental variability, species interactions, population dynamics and vulnerability before we quantitatively can predict, for example, effects of climate change on species and ecological communities. Here, however, we point out a new possible approach for identifying species that are vulnerable to environmental stochasticity by checking the degree of temporal autocorrelation in the time series of species. Increased autocorrelation in population fluctuations can be an indication of increased extinction risk.
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| 13. |
- Karlsson, Patrik, et al.
(författare)
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Food web structure and interaction strength pave the way for vulnerability to extinction
- 2007
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Ingår i: Journal of Theoretical Biology. - : Elsevier. - 0022-5193 .- 1095-8541. ; 249:1, s. 77-92
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on how food web structure and interactions among species affects the vulnerability, due to environmental variability, to extinction of species at different positions in model food webs. Vulnerability is here not measured by a traditional extinction threshold but is instead inspired by the IUCN criteria for endangered species: an observed rapid decline in population abundance. Using model webs influenced by stochasticity with zero autocorrelation, we investigate the ecological determinants of species vulnerability, i.e. the trophic interactions between species and food web structure and how these interact with the risk of sudden drops in abundance of species. We find that (i) producers fulfil the criterion of vulnerable species more frequently than other species, (ii) food web structure is related to vulnerability, and (iii) the vulnerability of species is greater when involved in a strong trophic interaction than when not. We note that our result on the relationship between extinction risk and trophic position of species contradict previous suggestions and argue that the main reason for the discrepancy probably is due to the fact that we study the vulnerability to environmental stochasticity and not extinction risk due to overexploitation, habitat destruction or interactions with introduced species. Thus, we suggest that the vulnerability of species to environmental stochasticity may be differently related to trophic position than the vulnerability of species to other factors.Earlier research on species extinctions has looked for intrinsic traits of species that correlate with increased vulnerability to extinction. However, to fully understand the extinction process we must also consider that species interactions may affect vulnerability and that not all extinctions are the result of long, gradual reductions in species abundances. Under environmental stochasticity (which importance frequently is assumed to increase as a result of climate change) and direct and indirect interactions with other species some extinctions may occur rapidly and apparently unexpectedly. To identify the first declines of population abundances that may escalate and lead to extinctions as early as possible, we need to recognize which species are at greatest risk of entering such dangerous routes and under what circumstances. This new perspective may contribute to our understanding of the processes leading to extinction of populations and eventually species. This is especially urgent in the light of the current biodiversity crisis where a large fraction of the world's biodiversity is threatened.
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| 14. |
- Laubmeier, A. N., et al.
(författare)
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From theory to experimental design : Quantifying a trait-based theory of predator-prey dynamics
- 2018
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 13:4
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Tidskriftsartikel (refereegranskat)abstract
- Successfully applying theoretical models to natural communities and predicting ecosystem behavior under changing conditions is the backbone of predictive ecology. However, the experiments required to test these models are dictated by practical constraints, and models are often opportunistically validated against data for which they were never intended. Alternatively, we can inform and improve experimental design by an in-depth pre-experimental analysis of the model, generating experiments better targeted at testing the validity of a theory. Here, we describe this process for a specific experiment. Starting from food web ecological theory, we formulate a model and design an experiment to optimally test the validity of the theory, supplementing traditional design considerations with model analysis. The experiment itself will be run and described in a separate paper. The theory we test is that trophic population dynamics are dictated by species traits, and we study this in a community of terrestrial arthropods. We depart from the Allometric Trophic Network (ATN) model and hypothesize that including habitat use, in addition to body mass, is necessary to better model trophic interactions. We therefore formulate new terms which account for micro-habitat use as well as intra-and interspecific interference in the ATN model. We design an experiment and an effective sampling regime to test this model and the underlying assumptions about the traits dominating trophic interactions. We arrive at a detailed sampling protocol to maximize information content in the empirical data obtained from the experiment and, relying on theoretical analysis of the proposed model, explore potential shortcomings of our design. Consequently, since this is a "pre-experimental" exercise aimed at improving the links between hypothesis formulation, model construction, experimental design and data collection, we hasten to publish our findings before analyzing data from the actual experiment, thus setting the stage for strong inference.
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| 15. |
- Lövdén, Martin, et al.
(författare)
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The dimensionality of between-person differences in white matter microstructure in old age
- 2013
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Ingår i: Human Brain Mapping. - : Wiley. - 1065-9471 .- 1097-0193. ; 34:6, s. 1386-1398
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Tidskriftsartikel (refereegranskat)abstract
- Between-person differences in white matter microstructure may partly generalize across the brain and partly play out differently for distinct tracts. We used diffusion-tensor imaging and structural equation modeling to investigate this issue in a sample of 260 adults aged 60–87 years. Mean fractional anisotropy and mean diffusivity of seven white matter tracts in each hemisphere were quantified. Results showed good fit of a model positing that individual differences in white matter microstructure are structured according to tracts. A general factor, although accounting for variance in the measures, did not adequately represent the individual differences. This indicates the presence of a substantial amount of tract-specific individual differences in white matter microstructure. In addition, individual differences are to a varying degree shared between tracts, indicating that general factors also affect white matter microstructure. Age-related differences in white matter microstructure were present for all tracts. Correlations among tract factors did not generally increase as a function of age, suggesting that aging is not a process with homogenous effects on white matter microstructure across the brain. These findings highlight the need for future research to examine whether relations between white matter microstructure and diverse outcomes are specific or general. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.
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| 16. |
- Moberg, Christina, et al.
(författare)
-
De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 17. |
- Roos, Henrik, et al.
(författare)
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Identification of patches with high ecological importance of broadleaved forests and open lands with valuable trees in Valle : Using a biodiversity capacity landscape metric, combining area and connectivity, to examining management options
- 2021
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This study is a complement to previous studies of regional action plans of green infrastructure in Valle (County Administrative Board 2016; County Administrative Board 2019). The aim was to identify the relative importance of biotope patches of broadleaved forest and open lands with valuable trees, respectively, in Valle for the maintenance and enhancement of biodiversity. A testversion of the method Biotope Biodiversity Capacity Indicator (BBCI) was applied on the two biotopes of broadleaved forest and open lands with valuable trees in Valle. BBCI was developed within the project “Landscape biodiversity capacity: a tool for measuring, monitoring and managing” financed by the Swedish Environmental Protection Agency, Miljövårdsanslaget (2019-2021).The results of the BBCI-analysis identified hotspots areas for the two studied biotopes in Valle, that is, areas with important patches for the sustainability of BBCI. For broadleaved forest, the northern part of Valle stands out as highly importantand for open lands with valuable trees the south-southwest parts of Valle stands out as the most important area. In this study, effects on BBCI from restauration of broadleaved forests to open land with valuable trees was evaluated. Calculations of BBCI shows encouraging results of an increased capacity for biodiversity of the biotope with open lands with valuable trees but not a significant decrease in biodiversity capacity of broadleaved forest, despite the area losses and fragmentation caused from the restauration. Both biotopes have BBCI values above one, showing that they are sustainable within a 100 year period. The result can be used as support to management plans of nature reserves in a landscape setting and as recommendations or advice to private land owners. Moreover, the study was produced within the work of BIOGOV, where regional action plans for nature, tourisms, culture and small enterprises were under development.
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| 18. |
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| 19. |
- Roubinet, Eve, et al.
(författare)
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High Redundancy as well as Complementary Prey Choice Characterize Generalist Predator Food Webs in Agroecosystems
- 2018
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Food web structure influences ecosystem functioning and the strength and stability of associated ecosystem services. With their broad diet, generalist predators represent key nodes in the structure of many food webs and they contribute substantially to ecosystem services such as biological pest control. However, until recently it has been difficult to empirically assess food web structure with generalist predators. We utilized DNA-based molecular gut-content analyses to assess the prey use of a set of generalist invertebrate predator species common in temperate agricultural fields. We investigated the degree of specialization of predator-prey food webs at two key stages of the cropping season and analysed the link temperature of different trophic links, to identify non-random predation. We found a low level of specialization in our food webs, and identified warm and cool links which may result from active prey choice or avoidance. We also found a within-season variation in interaction strength between predators and aphid pests which differed among predator species. Our results show a high time-specific functional redundancy of the predator community, but also suggest temporally complementary prey choice due to within-season succession of some predator species.
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| 20. |
- Thorgeirsson, Thorgeir E, et al.
(författare)
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A variant associated with nicotine dependence, lung cancer and peripheral arterial disease
- 2008
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 452:7187, s. 9-638
-
Tidskriftsartikel (refereegranskat)abstract
- Smoking is a leading cause of preventable death, causing about 5 million premature deaths worldwide each year(1,2). Evidence for genetic influence on smoking behaviour and nicotine dependence (ND)(3-8) has prompted a search for susceptibility genes. Furthermore, assessing the impact of sequence variants on smoking-related diseases is important to public health(9,10). Smoking is the major risk factor for lung cancer (LC)(11-14) and is one of the main risk factors for peripheral arterial disease (PAD)(15-17). Here we identify a common variant in the nicotinic acetylcholine receptor gene cluster on chromosome 15q24 with an effect on smoking quantity, ND and the risk of two smoking- related diseases in populations of European descent. The variant has an effect on the number of cigarettes smoked per day in our sample of smokers. The same variant was associated with ND in a previous genomewide association study that used low- quantity smokers as controls(18,19), and with a similar approach we observe a highly significant association with ND. A comparison of cases of LC and PAD with population controls each showed that the variant confers risk of LC and PAD. The findings provide a case study of a gene - environment interaction(20), highlighting the role of nicotine addiction in the pathology of other serious diseases.
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| 21. |
- Wootton, Kate, et al.
(författare)
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Beyond body size-new traits for new heights in trait-based modelling of predator-prey dynamics
- 2022
-
Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 17:7 July
-
Tidskriftsartikel (refereegranskat)abstract
- Food webs map feeding interactions among species, providing a valuable tool for understanding and predicting community dynamics. Using species' body sizes is a promising avenue for parameterizing food-web models, but such approaches have not yet been able to fully recover observed community dynamics. Such discrepancies suggest that traits other than body size also play important roles. For example, differences in species' use of microhabitat or non-consumptive effects of intraguild predators may affect dynamics in ways not captured by body size. In Laubmeier et al. (2018), we developed a dynamic food-web model incorporating microhabitat and non-consumptive predator effects in addition to body size, and used simulations to suggest an optimal sampling design of a mesocosm experiment to test the model. Here, we perform the mesocosm experiment to generate empirical timeseries of insect herbivore and predator abundance dynamics. We minimize least squares error between the model and time-series to determine parameter values of four alternative models, which differ in terms of including vs excluding microhabitat use and non-consumptive predator-predator effects. We use both statistical and expert-knowledge criteria to compare the models and find including both microhabitat use and non-consumptive predatorpredator effects best explains observed aphid and predator population dynamics, followed by the model including microhabitat alone. This ranking suggests that microhabitat plays a larger role in driving population dynamics than non-consumptive predator-predator effects, although both are clearly important. Our results illustrate the importance of additional traits alongside body size in driving trophic interactions. They also point to the need to consider trophic interactions and population dynamics in a wider community context, where non-trophic impacts can dramatically modify the interplay between multiple predators and prey. Overall, we demonstrate the potential for utilizing traits beyond body size to improve traitbased models and the value of iterative cycling between theory, data and experiment to hone current insights into how traits affect food-web dynamics. © 2022 Wootton et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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| 22. |
- Wootton, Kate L., et al.
(författare)
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Food webs coupled in space : Consumer foraging movement affects both stocks and fluxes
- 2023
-
Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 104:8
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Tidskriftsartikel (refereegranskat)abstract
- The exchange of material and individuals between neighboring food webs is ubiquitous and affects ecosystem functioning. Here, we explore animal foraging movement between adjacent, heterogeneous habitats and its effect on a suite of interconnected ecosystem functions. Combining dynamic food web models with nutrient-recycling models, we study foraging across habitats that differ in fertility and plant diversity. We found that net foraging movement flowed from high to low fertility or high to low diversity and boosted stocks and flows across the whole loop of ecosystem functions, including biomass, detritus, and nutrients, in the recipient habitat. Contrary to common assumptions, however, the largest flows were often between the highest and intermediate fertility habitats rather than highest and lowest. The effect of consumer influx on ecosystem functions was similar to the effect of increasing fertility. Unlike fertility, however, consumer influx caused a shift toward highly predator-dominated biomass distributions, especially in habitats that were unable to support predators in the absence of consumer foraging. This shift resulted from both direct and indirect effects propagated through the interconnected ecosystem functions. Only by considering both stocks and fluxes across the whole loop of ecosystem functions do we uncover the mechanisms driving our results. In conclusion, the outcome of animal foraging movements will differ from that of dispersal and diffusion. Together we show how considering active types of animal movement and the interconnectedness of ecosystem functions can aid our understanding of the patchy landscapes of the Anthropocene.
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| 23. |
- Wootton, Kate, et al.
(författare)
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Towards a modular theory of trophic interactions
- 2023
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Ingår i: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 37:1, s. 26-43
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Tidskriftsartikel (refereegranskat)abstract
- Species traits and environmental conditions determine the occurrence and strength of trophic interactions. If we understand the relationship between these factors and trophic interactions, we can make more accurate predictions and build better trophic-interaction models. We can compare traits and conditions by considering their effect on different parts (steps) of a trophic interaction, such as the steps search and pursuit. By linking traits to relevant steps, we can use these relationships to build trophic-interaction models. Currently, this is done ad hoc, defining steps based on the species and traits of interest. This makes it difficult to compare across traits and species and gain an overarching understanding of how traits and the environment drive trophic interactions. We present a comprehensive approach for the explicit choice of interaction steps and species traits or environmental conditions, which is readily integrated into existing models. The core of this framework is that it is modular; we present eight steps that occur in all trophic interactions and use them to build a modular, general dynamic model. When applying the framework, one explicitly selects only the most relevant steps and uses those to build a specific model. To build our modular framework, we revisit and expand the functional and numerical response functions, dividing the trophic interaction into eight steps: (1) search, (2) prey detection, (3) attack decision, (4) pursuit, (5) subjugation, (6) ingestion, (7) digestion and (8) nutrient allocation. Together these steps form a general dynamical model where trophic interactions can be explicitly parameterized for multiple traits and environmental factors. We then concretize this approach by outlining how a specific community can be modelled by selecting key modules (steps) and parameterizing them for relevant factors. This we exemplify for a community of terrestrial arthropods using empirical data on body size and temperature responses. With species interactions at the core of community dynamics, our modular approach allows for quantification and comparisons of the importance of different steps, traits, and abiotic factors across ecosystems and trophic-interaction types, and provides a powerful tool for trait-based prediction of food-web structure and dynamics. A free Plain Language Summary can be found within the Supporting Information of this article.
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| 24. |
- Abdulla, Parosh Aziz, et al.
(författare)
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Verification of heap manipulating programs with ordered data by extended forest automata
- 2016
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Ingår i: Acta Informatica. - : Springer Science and Business Media LLC. - 0001-5903 .- 1432-0525. ; 53:4, s. 357-385
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Tidskriftsartikel (refereegranskat)abstract
- We present a general framework for verifying programs with complex dynamic linked data structures whose correctness depends on ordering relations between stored data values. The underlying formalism of our framework is that of forest automata (FA), which has previously been developed for verification of heap-manipulating programs. We extend FA with constraints between data elements associated with nodes of the heaps represented by FA, and we present extended versions of all operations needed for using the extended FA in a fully-automated verification approach, based on abstract interpretation. We have implemented our approach as an extension of the Forester tool and successfully applied it to a number of programs dealing with data structures such as various forms of singly- and doubly-linked lists, binary search trees, as well as skip lists.
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| 25. |
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| 26. |
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| 27. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Preliminary Analysis of Compression System Integrated Heat Management Concepts Using LH 2 -Based Parametric Gas Turbine Model
- 2022
-
Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:4
-
Tidskriftsartikel (refereegranskat)abstract
- The investigation of the various heat management concepts using LH2 requires the development of a modeling environment coupling the cryogenic hydrogen fuel system with turbofan performance. This paper presents a numerical framework to model hydrogen-fueled gas turbine engines with a dedicated heat-management system, complemented by an introductory analysis of the impact of using LH2 to precool and intercool in the compression system. The propulsion installations comprise Brayton cycle-based turbofans and first assessments are made on how to use the hydrogen as a heat sink integrated into the compression system. Conceptual tubular compact heat exchanger designs are explored to either precool or intercool the compression system and preheat the fuel to improve the installed performance of the propulsion cycles. The precooler and the intercooler show up to 0.3% improved specific fuel consumption for heat exchanger effectiveness in the range 0.5–0.6, but higher effectiveness designs incur disproportionately higher pressure losses that cancel-out the benefits.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Almgren, Magnus, 1972, et al.
(författare)
-
Mapping Systems Security Research at Chalmers
- 2011
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Ingår i: First SysSec Workshop (SysSec 2011). - 9780769545301 ; , s. 67-70
-
Konferensbidrag (refereegranskat)abstract
- The department of Computer Science and Engineering at Chalmers University has a long tradition of research in systems security, including security metrics, attack detection, and mitigation. We focus on security issues arising in four specific environments: (1) backbone links, (2) sensor networks, (3) the connected car, and (4) the smart grid. In this short summary we describe recent results as well as open research questions we are exploring.
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| 32. |
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| 33. |
- Andreou, Dimitrios, et al.
(författare)
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Associations between a locus downstream DRD1 gene and cerebrospinal fluid dopamine metabolite concentrations in psychosis
- 2016
-
Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 619, s. 126-130
-
Tidskriftsartikel (refereegranskat)abstract
- Dopamine activity, mediated by the catecholaminergic neurotransmitter dopamine, is prominent in the human brain and has been implicated in schizophrenia. Dopamine targets five different receptors and is then degraded to its major metabolite homovanillic acid (HVA). We hypothesized that genes encoding dopamine receptors may be associated with cerebrospinal fluid (CSF) HVA concentrations in patients with psychotic disorder. We searched for association between 67 single nucleotide polymorphisms (SNPs) in the five dopamine receptor genes i.e., DRD1, DRD2, DRD3, DRD4 and DRD5, and the CSF HVA concentrations in 74 patients with psychotic disorder. Nominally associated SNPs were also tested in 111 healthy controls. We identified a locus, located downstream DRD1 gene, where four SNPs, rs11747728, rs11742274, rs265974 and rs11747886, showed association with CSF HVA concentrations in psychotic patients. The associations between rs11747728, which is a regulatory region variant, and rs11742274 with HVA remained significant after correction for multiple testing. These associations were restricted to psychotic patients and were absent in healthy controls. The results suggest that the DRD1 gene is implicated in the pathophysiology of psychosis and support the dopamine hypothesis of schizophrenia.
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| 34. |
- Andreou, Dimitrios, et al.
(författare)
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Cerebrospinal fluid monoamine metabolite concentrations as intermediate phenotypes between glutamate-related genes and psychosis
- 2015
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Ingår i: Psychiatry Research. - : Elsevier BV. - 0165-1781 .- 1872-7123. ; 229:1-2, s. 497-504
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Tidskriftsartikel (refereegranskat)abstract
- Glutamate-related genes have been associated with schizophrenia, but the results have been ambiguous and difficult to replicate. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major degradation products of the monoamines dopamine, serotonin and noradrenaline, respectively, and their concentrations in the cerebrospinal fluid (CSF), mainly HVA, have been associated with schizophrenia. In the present study, we hypothesized that CSF HVA, 5-HIAA and MHPG concentrations represent intermediate phenotypes in the association between glutamate-related genes and psychosis. To test this hypothesis, we searched for association between 238 single nucleotide polymorphisms (SNPs) in ten genes shown to be directly or indirectly implicated in glutamate transmission and CSF HVA, 5-HIAA and MHPG concentrations in 74 patients with psychotic disease. Thirty-eight nominally significant associations were found. Further analyses in 111 healthy controls showed that 87% of the nominal associations were restricted to the patients with psychosis. Some of the psychosis-only-associated SNPs found in the D-amino acid oxidase activator (DADA) and the kynurenine 3-monooxygenase (KMO) genes have previously been reported to be associated with schizophrenia. The present results suggest that CSF monoamine metabolite concentrations may represent intermediate phenotypes in the association between glutamate-related genes and psychosis.
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| 35. |
- ANGHOLT, JONAS, et al.
(författare)
-
A First Security Analysis of a Secure Intermodal Goods Transport System
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The goods transport business involves a lot of money and is a big part of the infrastructure of any European country. There are often many different actors involved in each transport and the communication network is rather complex due to the point-topoint communication structure. It is easy to understand why there is a high demand for increased simplicity and effectiveness. With this in mind, the e-Freight project which is based on PEPPOL has moved towards a standardized solution by developing a communication system based on access points (APs). These APs act as the interface to the system and makes it easy to establish communication between any two connected actors.With PEPPOL and e-Freight as a foundation, VOLVO leads the SITS project in close cooperation with Stena Line and DSV. The goal is to develop a harmonized communication framework that promotes increased sharing of information between actors and enable new applications to increase effectiveness and security in the chain of transportation. This leads to simplified accessibility for actors to a set of services by being connected to an AP. At the same time service providers benefit from being able to easily set up cloud services available for all actors. In addition to the back-office communication between APs, external devices such as cellphones, in-vehicle computers and check-in terminals can communicate directly with each other over short distances. This type of communication is only partially specified and a mutual standard is yet to be decided upon.In this report we have analyzed the SITS project from an IT-security perspective. The back-end system derived from e-Freight is looked into and communication links, access points, protocols, certificate handling etc., are examined. Another concern in the SITS project is the short-range communication between trucks and terminals. Since RFID is a highly potential candidate for use in this area, we have studied the technology by categorizing a typical RFID system into three distinct layers and researched important security threats with the classic CIA approach. Based on the security issues found, countermeasures such as encryption, authentication and protection against man-in-themiddle attacks are reviewed.
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| 36. |
- Ankel, Martin, 1996, et al.
(författare)
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Bistatic noise radar: Demonstration of correlation noise suppression
- 2023
-
Ingår i: IET Radar, Sonar and Navigation. - : Institution of Engineering and Technology (IET). - 1751-8792 .- 1751-8784. ; 17:3, s. 351-361
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudo-random noise, generated digitally at the receiver and transmitter units. Correlation losses, due to non-linearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.
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| 37. |
- Ankel, Martin, 1996, et al.
(författare)
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Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
-
Ingår i: 20th European Radar Conference, EuRAD 2023. ; , s. 213-216
-
Konferensbidrag (refereegranskat)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
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| 38. |
- Ankel, Martin, et al.
(författare)
-
Experimental Evaluation of Moving Target Compensation in High Time-Bandwidth Noise Radar
- 2023
-
Ingår i: Proceedings 20th European Radar Conference (EuRAD). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 213-216
-
Konferensbidrag (refereegranskat)abstract
- In this article, the effect a moving target has on the signal-to-interference-plus-noise-ratio (SINR) for high time-bandwidth noise radars is investigated. To compensate for cell migration we apply a computationally efficient stretch processing algorithm that is tailored for batched processing and suitable for implementation onto a real-time radar processor. The performance of the algorithm is studied using experimental data. In the experiment, pseudorandom noise, with a bandwidth of 100 MHz, is generated and transmitted in real-time. An unmanned aerial vehicle (UAV), flown at a speed of 11.5 m/s, is acting as a target. For an integration time of 1 s, the algorithm is shown to yield an increase in SINR of roughly 13 dB, compared to no compensation. It is also shown that coherent integration times of 2.5 s can be achieved.
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| 39. |
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| 40. |
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| 41. |
- Balachandran, Arvind, 1994-
(författare)
-
Battery Integrated Modular Multilevel Converter Topologies for Automotive Applications
- 2023
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electric vehicles are rapidly developing in response to the need for increasing sustainable energy sources. The range and lifetime of an electric vehicle are limited by the battery pack. A pack comprises modules with several parallel and/or series-connected cells. Differences in leakage currents and cell in-homogeneities cause individual cell voltage and state-of-charge distribution among the cells to be non-homogeneous. As a result, over time, some cells discharge faster than other cells, thus limiting the total energy delivered by the pack. In order to maximize the energy delivered by the pack, individual cell control is desirable. As a solution, battery-integrated modular multi-level converter (BI-MMC) topologies are proposed, presented, and evaluated. BI-MMC topology consists of either one or two arms per phase, and each arm comprises several cascaded stages of DC–AC converters and is commonly referred to as submodules. BI-MMCs provide increased controllability and potential improvement in the lifetime of the battery pack. Furthermore, BI-MMCs have low output total harmonic distortion, further improving the powertrain efficiency.The first contribution is the design and evaluation of 3-phase and 6-phase BI-MMCs; comparisons are made against a conventional 2-level inverter for a 40-ton 400 kW commercial vehicle. The evaluation considers the total number of submodules, energy rating of the DC-link capacitors, battery losses, capacitor losses, and semiconductor losses. The evaluation showed that the BI-MMCs have lower semiconductor losses than the conventional 2-level inverter. However, the BI-MMCs have higher capacitor and battery losses. The second contribution is the investigation of the impact that the number of series connected cells per submodule has on the total losses of the BI-MMC. The study showed that 5- to 6-series connected cells have the lowest losses. The third contribution is the design principles for optimization of the DC-link capacitors and the MOSFET switching frequency; this is supported by experimental validation for the loss distribution within a submodule. The fourth contribution is a methodology for determining the battery impedance using the full-load converter current. In a conventional battery pack, the battery is connected directly to the fast charger’s DC supply. However, in a BI-MMC, the battery and the inverter are integrated, potentially increasing the DC charging capabilities because higher voltages can be achieved during charging than during operation. The fifth contribution is thus the derivation and investigation of the maximum DC charging power of BI-MMCs assuming the same submodule semiconductor losses during traction. The analysis showed that most BI-MMCs have a maximum DC charging power of about 1MW.
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| 42. |
- Balachandran, Arvind, 1994-, et al.
(författare)
-
DC Charging Capabilities of Battery-Integrated Modular Multilevel Converters Based on Maximum Tractive Power
- 2023
-
Ingår i: Electricity. - : MDPI. - 2673-4826. ; 4:1, s. 62-77
-
Tidskriftsartikel (refereegranskat)abstract
- The increase in the average global temperature is a consequence of high greenhouse gas emissions. Therefore, using alternative energy carriers that can replace fossil fuels, especially for automotive applications, is of high importance. Introducing more electronics into an automotive battery pack provides more precise control and increases the available energy from the pack. Battery-integrated modular multilevel converters (BI-MMCs) have high efficiency, improved controllability, and better fault isolation capability. However, integrating the battery and inverter influences the maximum DC charging power. Therefore, the DC charging capabilities of 5 3-phase BI-MMCs for a 40-ton commercial vehicle designed for a maximum tractive power of 400 kW was investigated. Two continuous DC charging scenarios are considered for two cases: the first considers the total number of submodules during traction, and the second increases the total number of submodules to ensure a maximum DC charging voltage of 1250 V. The investigation shows that both DC charging scenarios have similar maximum power between 1 and 3 MW. Altering the number of submodules increases the maximum DC charging power at the cost of increased losses.
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| 43. |
- Balachandran, Arvind, 1994-, et al.
(författare)
-
Design and Analysis of Battery-Integrated Modular Multilevel Converters for Automotive Powertrain Applications
- 2021
-
Ingår i: 2021 23RD EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE21 ECCE EUROPE). - : IEEE. - 9789075815375 - 9781665433846
-
Konferensbidrag (refereegranskat)abstract
- The automotive industry has grown considerably over the last century consequently increasing green-house gas emissions and thus contributing towards increase in the average global temperature. It is thus of paramount importance to increase the use of alternative energy sources. Electric vehicles have gained popularity over the last decade. However, a major concern with electric vehicles is their range. The range of an electric vehicle is limited by the battery pack, in particular, the weakest cell of the pack. One method of increasing the available energy from the battery pack is by introducing more electronics. Modular multilevel converters, with their modular concept, could be a viable solution. The concept of battery-integrated modular multilevel converters (BI-MMC) for automotive applications is explored. In particular, the impact of the number of cascaded cells per submodule is investigated, considering battery losses, DC-link capacitor losses, and the converter losses. Furthermore, an optimization of the DC-link capacitors and the selection of MOSFET switching frequency is presented in order to minimize the total losses.
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| 44. |
- Balachandran, Arvind, 1994-, et al.
(författare)
-
Experimental Evaluation of Battery Impedance and Submodule Loss Distribution for Battery Integrated Modular Multilevel Converters
- 2022
-
Ingår i: 2022 24TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE22 ECCE EUROPE). - : Institute of Electrical and Electronics Engineers (IEEE). - 9789075815399 - 9781665487009
-
Konferensbidrag (refereegranskat)abstract
- Greenhouse gas emissions and the increase in average global temperature are growing concerns now more so than ever. Therefore it is of importance to increase the use of alternative energy sources, especially in the automotive industry. Battery electric vehicles (BEV) have gained popularity over the past several years. However, the performance of a BEV is limited by the battery pack, in particular, the weakest cell in the pack. Therefore, improved cell controllability and high efficiency are seen as important directions for research and development and one direction where it can be achieved is through using battery-integrated modular multilevel converters (BI-MMC). The battery current in BI-MMCs contains additional harmonics and the frequency dependent losses of these harmonics are determined by the resonance between the battery and the DC-link capacitor bank. The paper presents an experimental validation of previously published theoretical results for both harmonic allocations and loss distribution at the switching frequency within the BI-MMC submodule. Furthermore, a methodology for measuring the battery impedance using the full-load converter switching currents is presented.
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| 45. |
- Balachandran, Arvind, 1994-, et al.
(författare)
-
Experimental Evaluation of Submodule Losses in Battery-Integrated MMCs with NLM and PSPWM
- 2024
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Konferensbidrag (refereegranskat)abstract
- Electric vehicle (EV) battery packs contain several parallel and series-connected cells and variations in leakage currents and cell characteristics result in heterogeneous discharge rates among cells, thus limiting the total energy delivery of the pack. Battery-integrated modular multilevel converters (BI-MMCs) increase the controllability of cells thereby improving the energy utilization of the battery pack. Design optimization for BI-MMC with phase-shifted modulation (PSPWM) showed that submodule (SM) DC-link capacitors designed to bypass the switching frequency components result in minimum total losses. However, this requires a large DC-link capacitor bank, which increases the system cost. An alternative modulation technique, nearest level modulation (NLM), characterized by low semiconductor switching frequency, is often preferred for MMCs with many SMs. The first contribution is an experimental loss comparison in an SM of a BI-MMC with PSPWM and NLM. The second contribution is investigating the impact of the size of DC-link capacitors on battery and capacitor losses for NLM. The experiments showed that the battery and capacitor losses are independent of the DC-link capacitor size when using NLM. Furthermore, NLM has lower total losses but higher battery losses than PSPWM. A single-phase 4-SM BI-MMC is used as the experimental platform for the comparison.
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| 46. |
- Balk, Lennart, et al.
(författare)
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Biomarkers in Natural Fish Populations Indicate Adverse Biological Effects of Offshore Oil Production
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:5, s. e19735-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Despite the growing awareness of the necessity of a sustainable development, the global economy continues to depend largely on the consumption of non-renewable energy resources. One such energy resource is fossil oil extracted from the seabed at offshore oil platforms. This type of oil production causes continuous environmental pollution from drilling waste, discharge of large amounts of produced water, and accidental spills. Methods and principal findings: Samples from natural populations of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) in two North Sea areas with extensive oil production were investigated. Exposure to and uptake of polycyclic aromatic hydrocarbons (PAHs) were demonstrated, and biomarker analyses revealed adverse biological effects, including induction of biotransformation enzymes, oxidative stress, altered fatty acid composition, and genotoxicity. Genotoxicity was reflected by a hepatic DNA adduct pattern typical for exposure to a mixture of PAHs. Control material was collected from a North Sea area without oil production and from remote Icelandic waters. The difference between the two control areas indicates significant background pollution in the North Sea. Conclusion: It is most remarkable to obtain biomarker responses in natural fish populations in the open sea that are similar to the biomarker responses in fish from highly polluted areas close to a point source. Risk assessment of various threats to the marine fish populations in the North Sea, such as overfishing, global warming, and eutrophication, should also take into account the ecologically relevant impact of offshore oil production.
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| 47. |
- Banerjee, Debashree, et al.
(författare)
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Electrical tuning of radiative cooling at ambient conditions
- 2023
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Ingår i: Cell Reports Physical Science. - : ELSEVIER. - 2666-3864. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Passive radiative cooling forms a sustainable means for cooling of objects through thermal radiation. Along with progress on static cooling systems, there is an emerging need for dynamic control to enable thermoregulation. Here, we demonstrate temperature regu-lation of devices at ambient pressure and temperature by electri-cally tuning their radiative cooling power. Our concept exploits the possibility to electrochemically tune the thermal emissivity and thereby cooling power of a conducting polymer, which enabled reversible control of device temperatures of around 0.25 degrees C at ambient conditions in a sky simulator. Besides tuneable radiative cooling by exposure to the sky, the concept could also contribute to reduced needs for indoor climate control by enabling dynamic control of thermal energy flows between indoor objects, such as be-tween people and walls.
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| 48. |
- Banks, H. T., et al.
(författare)
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Parameter estimation for an allometric food web model
- 2017
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Ingår i: International journal of pure and applied mathematics. - : Academic Publications. - 1311-8080 .- 1314-3395. ; 114:1, s. 143-160
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Tidskriftsartikel (refereegranskat)abstract
- The application of mechanistic models to natural systems is of interest to ecological researchers. We use the mechanistic Allometric Trophic Network (ATN) model, whichis well-studied for controlled and theoretical systems, to describe the dynamics of the aphidRhopalosiphum padi in an agricultural field. We diagnose problems that arise in a first attemptat a least squares parameter estimation on this system, including formulation of the modelfor the inverse problem and information content present in the data. We seek to establishwhether the field data, as it is currently collected, can support parameter estimation for theATN model.
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| 49. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 50. |
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