| 1. |
- Rosén, Christoffer, 1986, et al.
(författare)
-
Discriminatory analysis of biochip-derived protein patterns in CSF and plasma in neurodegenerative diseases
- 2011
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Ingår i: Frontiers in Aging Neuroscience. - : Frontiers Media SA. - 1663-4365. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- The role of biomarkers in neurodegenerative diseases has been emphasized by recent research. Future clinical demands for identifying diseases at an early stage may render them essential. The aim of this pilot study was to test the analytical performance of two multiplex assays of cerebral markers on a well-defined clinical material consisting of patients with various neurodegenerative diseases. We measured 10 analytes in plasma and cerebrospinal fluid (CSF) from 60 patients suffering from Alzheimer's disease (AD), vascular dementia, frontotemporal dementia, dementia with Lewy bodies, or mild cognitive impairment, as well as 20 cognitively healthy controls. We used the Randox biochip-based Evidence Investigator™ system to measure the analytes. We found it possible to measure most analytes in both plasma and CSF, and there were some interesting differences between the diagnostic groups, although with large overlaps. CSF heart-type fatty acid-binding protein was increased in AD. Glial fibrillary acidic protein and neutrophil gelatinase-associated lipocalin in CSF and D-dimer in plasma were elevated in patients with cerebrovascular disease. A multivariate statistical analysis revealed that the pattern of analytes could help to differentiate the conditions, although more studies are required to verify this.
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| 2. |
- Abrahamsson, Christoffer, et al.
(författare)
-
Comparison of different variable selection methods conducted on NIR transmission measurements on intact tablets
- 2003
-
Ingår i: Chemometrics and Intelligent Laboratory Systems. - 0169-7439. ; 69:1-2, s. 3-12
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Tidskriftsartikel (refereegranskat)abstract
- Near infrared (NIR) transmission spectroscopy is a promising method for fast quantitative measurements on pharmaceutical tablets, but there are still some problems to overcome in order to incorporate the technique as a control tool in tablet production. The main problem is the limited precision for multivariate calibrations based on NIR transmission data. The precision is affected by several factors, where one of the most important is which variable to include in the multivariate calibration model. In this work, four different methods for variable selection in partial least square (PLS) regression were studied and compared to a calibration made with manually selected wavelengths. The methods used were genetic algorithm (GA), iterative PLS (IPLS), uninformative variable elimination by PLS (UVE-PLS) and interactive variable selection for PLS (IVS-PLS). All methods improved the predictive abilities of the model compared to the model where the wavelengths were selected manually. For the data set used in this work, IVS-PLS and GA achieved the best results with improvements in prediction error by 20%, but further measurements and investigations have to be made before any general conclusion can be drawn.
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| 3. |
- Abrahamsson, Christoffer, et al.
(författare)
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Scatter correction of transmission near-infrared spectra by photon migration data: Quantitative analysis of solids
- 2005
-
Ingår i: Applied Spectroscopy. - 1943-3530. ; 59:11, s. 1381-1387
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Tidskriftsartikel (refereegranskat)abstract
- The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model.
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| 4. |
- Abrahamsson, Christoffer, et al.
(författare)
-
Scatter correction of transmission NIR spectra by photon migration data - Quantitative analysis of solids
- 2005
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6009, s. 60090-60090
-
Konferensbidrag (refereegranskat)abstract
- The scope of this presentation is a new methodology to correct conventional NIR data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation, measured by conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample, and therefore independent of the scattering effects. The measurements in this work were made using a novel system for time-resolved measurements, based on short light continuum pulses generated in an index-guided crystal fibre and a spectrometer-equipped streak camera. The system enables spectral recordings in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The evaluation scheme is based on modeling of light transport by diffusion theory, that provides an independent measure of the scattering properties of the samples, that later is used to correct conventional NIR data. This yields a clear advantage over other pre-processing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. PLS calibration models shows that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to models based on conventional NIR data. The method also makes it possible to predict the concentration of active substance in samples with physical properties different from those of the samples included in the calibration model.
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| 5. |
- Abrahamsson, Christoffer, et al.
(författare)
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Time and wavelength resolved spectroscopy of turbid media using light continuum generated in a crystal fiber
- 2004
-
Ingår i: Optics Express. - 1094-4087. ; 12:17, s. 4103-4112
-
Tidskriftsartikel (refereegranskat)abstract
- We report a novel system for time-resolved diffuse remission spectral measurements, based on short light continuum pulses generated in an index-guided crystal fiber, and a spectrometer-equipped streak camera. The system enables spectral recordings of absorption and reduced scattering coefficients of turbid media in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The optical properties are calculated by fitting the solution of the diffusion equation to the time-dispersion curve at each wavelength. Example measurements are presented from an apple, a finger and a pharmaceutical tablet. (C) 2004 Optical Society of America.
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| 6. |
- Abrahamsson, Christoffer, et al.
(författare)
-
Time-resolved NIR spectroscopy for quantitative analysis of intact pharmaceutical tablets
- 2005
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 77:4, s. 1055-1059
-
Tidskriftsartikel (refereegranskat)abstract
- Near-infrared (NIR) spectroscopy is a useful technique for quantitative measurements of intact tablets, but it suffers from limitations due to the fact that changes in the physical properties of a sample strongly affect the recorded spectrum. In this work, time-resolved transmission NIR spectroscopy was utilized to conduct quantitative measurements of intact tablets. The technique enables separation of the absorption properties of the sample from the scattering properties and can therefore handle changes of the physical parameters of the samples in a better way than conventional NIR transmission spectroscopy. The experiments were conducted using a pulsed Ti:sapphire laser coupled into a nonlinear photonic crystal fiber as light source. The light transmitted through the sample was measured by a time-resolving streak camera. A comparison of the results from the time-resolved technique with the results from conventional transmission NIR spectroscopy was made using tablets containing different concentrations of iron oxide and manufactured with different thicknesses. A PLS model made with data from the time-resolved technique predicted samples 5 times better than a PLS model made data from the conventional NIR transmission technique. Furthermore, an improvement to predict samples with physical properties outside those included in the calibration set was demonstrated.
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| 7. |
- Berner, Christoffer, et al.
(författare)
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Long-term effect of apatite on ectomycorrhizal growth and community structure.
- 2012
-
Ingår i: Mycorrhiza. - : Springer Science and Business Media LLC. - 1432-1890 .- 0940-6360. ; 22:8, s. 615-621
-
Tidskriftsartikel (refereegranskat)abstract
- Ectomycorrhizal (ECM) fungi are efficient at taking up phosphorus (P) from mineral sources, such as apatite, which are not easily available to the host trees. Since ECM fungal species differ in P uptake rates, it can be expected that the composition of the ECM fungal community will change upon exposure to apatite, provided that the P transfer is rewarded by more carbon being transferred to the fungal symbiont. Control and apatite-amended mesh bags were buried in pairs in the humus layer of a P-poor Norway spruce forest. The ECM fungal community that colonized these bags was analyzed by DNA extraction, PCR amplification of the internal transcribed spacer (ITS) region, cloning, and random sequencing. Fungal biomass was estimated by ergosterol analysis. No change in the ECM fungal community structure was seen after 5 years of apatite exposure, although the fungal biomass increased threefold upon apatite amendment. Our results indicate that host trees enhance carbon allocation to ECM fungi colonizing P sources in P-poor forests but the lack of change in the composition of the ECM fungal community suggests that P transfer rates were similar among the species. Alternatively, higher P transfer among certain species was not rewarded with higher carbon transfer from the host.
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| 8. |
- Berntsson, Shala Ghaderi, et al.
(författare)
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Analysis of DNA repair gene polymorphisms and survival in low-grade and anaplastic gliomas
- 2011
-
Ingår i: Journal of Neuro-Oncology. - : Springer Science and Business Media LLC. - 0167-594X .- 1573-7373. ; 105:3, s. 531-538
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to explore the variation in DNA repair genes in adults with WHO grade II and III gliomas and their relationship to patient survival. We analysed a total of 1,458 tagging single-nucleotide polymorphisms (SNPs) that were selected to cover DNA repair genes, in 81 grade II and grade III gliomas samples, collected in Sweden and Denmark. The statistically significant genetic variants from the first dataset (P < 0.05) were taken forward for confirmation in a second dataset of 72 grade II and III gliomas from northern UK. In this dataset, eight gene variants mapping to five different DNA repair genes (ATM, NEIL1, NEIL2, ERCC6 and RPA4) which were associated with survival. Finally, these eight genetic variants were adjusted for treatment, malignancy grade, patient age and gender, leaving one variant, rs4253079, mapped to ERCC6, with a significant association to survival (OR 0.184, 95% CI 0.054-0.63, P = 0.007). We suggest a possible novel association between rs4253079 and survival in this group of patients with low-grade and anaplastic gliomas that needs confirmation in larger datasets.
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| 9. |
- Biswas, Rahul, et al.
(författare)
-
Two c's in a pod : cosmology-independent measurement of the Type Ia supernova colour-luminosity relation with a sibling pair
- 2022
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 509:4, s. 5340-5356
-
Tidskriftsartikel (refereegranskat)abstract
- Using Zwicky Transient Facility (ZTF) observations, we identify a pair of ‘sibling’ Type Ia supernovae (SNe Ia), i.e. hosted by the same galaxy at z = 0.0541. They exploded within 200 d from each other at a separation of 0.6arcsec0.6arcsec corresponding to a projected distance of only 0.6 kpc. Performing SALT2 light-curve fits to the gri ZTF photometry, we show that for these equally distant ‘standardizable candles’, there is a difference of 2 mag in their rest-frame B-band peaks, and the fainter supernova (SN) has a significantly red SALT2 colour c = 0.57 ± 0.04, while the stretch values x1 of the two SNe are similar, suggesting that the fainter SN is attenuated by dust in the interstellar medium of the host galaxy. We use these measurements to infer the SALT2 colour standardization parameter, β = 3.5 ± 0.3, independent of the underlying cosmology and Malmquist bias. Assuming the colour excess is entirely due to dust, the result differs by 2σ from the average Milky Way total-to-selective extinction ratio, but is in good agreement with the colour–brightness corrections empirically derived from the most recent SN Ia Hubble–Lemaitre diagram fits. Thus we suggest that SN ‘siblings’, which will increasingly be discovered in the coming years, can be used to probe the validity of the colour and light-curve shape corrections using in SN Ia cosmology while avoiding important systematic effects in their inference from global multiparameter fits to inhomogeneous data sets, and also help constrain the role of interstellar dust in SN Ia cosmology.
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| 10. |
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| 11. |
- Bowlin, Melissa, et al.
(författare)
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Aerodynamic costs of flying with holey wings
- 2009
-
Ingår i: Comparative Biochemistry and Physiology. Part A: Molecular & Integrative Physiology. - : Elsevier BV. - 1095-6433. ; 153A:2, suppl. 1, s. 122-122
-
Konferensbidrag (refereegranskat)
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| 12. |
- Bowlin, M. S., et al.
(författare)
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The aerodynamic consequences of molt
- 2011
-
Ingår i: Integrative and Comparative Biology. - : Oxford University Press (OUP). - 1557-7023 .- 1540-7063. ; 51, s. 14-14
-
Konferensbidrag (refereegranskat)
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| 13. |
- Brax, Christoffer, et al.
(författare)
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Evaluating Precise and Imprecise State-Based Anomaly Detectors for Maritime Surveillance
- 2010
-
Ingår i: Proceedings of the 13th International Conference on Information Fusion. - : IEEE. - 9780982443811 ; , s. Article number 5711997-
-
Konferensbidrag (refereegranskat)abstract
- We extend the State-Based Anomaly Detection approach by introducing precise and imprecise anomaly detectors using the Bayesian and credal combination operators, where evidences over time are combined into a joint evidence. We use imprecision in order to represent the sensitivity of the classification regarding an object being normal or anomalous. We evaluate the detectors on a real-world maritime dataset containing recorded AIS data and show that the anomaly detectors outperform previously proposed detectors based on Gaussian mixture models and kernel density estimators. We also show that our introduced anomaly detectors perform slightly better than the State-Based Anomaly Detection approach with a sliding window.
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| 14. |
- Cao, Yi, et al.
(författare)
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ABSENCE OF FAST-MOVING IRON IN AN INTERMEDIATE TYPE Ia SUPERNOVA BETWEEN NORMAL AND SUPER-CHANDRASEKHAR
- 2016
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 823:2
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report observations of a peculiar SN Ia iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show an absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv's light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band Delta m(15)=1.03 +/- 0.01) and overall spectral features resemble those of normal SNe Ia. On the other hand, its large peak optical and UV luminosity (M-B = -19.84 mag, M-uvm2 = -15.5 mag) and its low but almost constant Si II velocities of about 10,000 km s (1) are similar to those in super-Chandrasekhar events, and its persistent carbon signatures in the spectra are weaker than those seen commonly in super-Chandrasekhar events. We estimate a Ni-56 mass of 0.81(-0.18)(+0.10) M-circle dot and a total ejecta mass of 1.59(-0.12)(+0.45) M-circle dot. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.
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| 15. |
- Chorell, Erik, et al.
(författare)
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Design and Synthesis of Fluorescent Pilicides and Curlicides : Bioactive Tools to Study Bacterial Virulence Mechanisms
- 2012
-
Ingår i: Chemistry - A European Journal. - Berlin : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 18:15, s. 4522-4532
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Tidskriftsartikel (refereegranskat)abstract
- Pilicides and curlicides are compounds that block the formation of the virulence factors pili and curli, respectively. To facilitate studies of the interaction between these compounds and the pili and curli assembly systems, fluorescent pilicides and curlicides have been synthesized. This was achieved by using a strategy based on structure-activity knowledge, in which key pilicide and curlicide substituents on the ring-fused dihydrothiazolo 2-pyridone central fragment were replaced by fluorophores. Several of the resulting fluorescent compounds had improved activities as measured in pili- and curli-dependent biofilm assays. We created fluorescent pilicides and curlicides by introducing coumarin and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores at two positions on the peptidomimetic pilicide and curlicide central fragment. Fluorescence images of the uropathogenic Escherichia coli (UPEC) strain UTI89 grown in the presence of these compounds shows that the compounds are strongly associated with the bacteria with a heterogeneous distribution.
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| 16. |
- Chorell, Erik, 1980-, et al.
(författare)
-
Design and synthesis of fluorescently labeled pilicides and curlicides: bioactive tools to study bacterial virulence mechanisms
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Pilicides and curlicides block formation of the E. coli virulence factors pili and curli. To facilitate studies of the interaction between these compounds and the pili and curli assembly systems, fluorescent pilicides and curlicides have been synthesized. This was achieved using a strategy where key pilicide and curlicide substituents were replaced by fluorophores having similar physicochemical properties. The resulting fluorescent compounds had improved anti-virulence activities as measured in pili- and curli-dependent biofilm assays. We created fluorescent pilicides and curlicides by introducing both coumarin and 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores at two positions on the peptidomimetic pilicide and curlicide scaffold. Fluorescence images of the uropathogenic Escherichia coli (UPEC) strain UTI89 grown in the presence of these compounds shows that the compounds are strongly associated to the bacteria and seem to discriminate between different bacteria in a population.
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| 17. |
- Christoffer Johansson, L., et al.
(författare)
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Mechanical power curve measured in the wake of pied flycatchers indicates modulation of parasite power across flight speeds
- 2018
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 15:138
-
Tidskriftsartikel (refereegranskat)abstract
- How aerodynamic power required for animal flight varies with flight speed determines optimal speeds during foraging and migratory flight. Despite its relevance, aerodynamic power provides an elusive quantity to measure directly in animal flight. Here, we determine the aerodynamic power from wake velocity fields, measured using tomographical particle image velocimetry, of pied flycatchers flying freely in a wind tunnel. We find a shallow U-shaped power curve, which is flatter than expected by theory. Based on how the birds vary body angle with speed, we speculate that the shallow curve results from increased body drag coefficient and body frontal area at lower flight speeds. Including modulation of body drag in the model results in a more reasonable fit with data than the traditional model. From the wake structure, we also find a single starting vortex generated from the two wings during the downstroke across flight speeds (1–9 m s21). This is accomplished by the arm wings interacting at the beginning of the downstroke, generating a unified starting vortex above the body of the bird. We interpret this as a mechanism resulting in a rather uniform downwash and low induced power, which can help explain the higher aerodynamic performance in birds compared with bats.
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| 18. |
- Currie, Shannon E., et al.
(författare)
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Conversion efficiency of flight power is low, but increases with flight speed in the migratory bat Pipistrellus nathusii
- 2023
-
Ingår i: Proceedings of the Royal Society B: Biological Sciences. - 0962-8452. ; 290:1998
-
Tidskriftsartikel (refereegranskat)abstract
- The efficiency with which flying animals convert metabolic power to mechanical power dictates an individual's flight behaviour and energy requirements. Despite the significance of this parameter, we lack empirical data on conversion efficiency for most species as in vivo measurements are notoriously difficult to obtain. Furthermore, conversion efficiency is often assumed to be constant across flight speeds, even though the components driving flight power are speed-dependent. We show, through direct measurements of metabolic and aerodynamic power, that conversion efficiency in the migratory bat (Pipistrellus nathusii) increases from 7.0 to 10.4% with flight speed. Our findings suggest that peak conversion efficiency in this species occurs near maximum range speed, where the cost of transport is minimized. A meta-analysis of 16 bird and 8 bat species revealed a positive scaling relationship between estimated conversion efficiency and body mass, with no discernible differences between bats and birds. This has profound consequences for modelling flight behaviour as estimates assuming 23% efficiency underestimate metabolic costs for P. nathusii by almost 50% on average (36-62%). Our findings suggest that conversion efficiency may vary around an ecologically relevant optimum speed and provide a crucial baseline for investigating whether this drives variation in conversion efficiency between species.
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| 19. |
- Dreij, Kristian, et al.
(författare)
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Cancer Risk Assessment of Airborne PAHs Based on in Vitro Mixture Potency Factors
- 2017
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 51:15, s. 8805-8814
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Tidskriftsartikel (refereegranskat)abstract
- Complex mixtures of polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants associated with adverse human health effects including cancer. However, the risk of exposure to mixtures is difficult to estimate, and risk assessment by whole mixture potency evaluations has been suggested. To facilitate this, reliable in vitro based testing systems are necessary. Here, we investigated if activation of DNA damage signaling in vitro could be an endpoint for developing whole mixture potency factors (MPFs) for airborne PAHs. Activation of DNA damage signaling was assessed by phosphorylation of Chid and H2AX using Western blotting. To validate the in vitro approach, potency factors were determined for seven individual PAHs which were in very good agreement with established potency factors based on cancer data in vivo. Applying the method using Stockholm air PAH samples indicated MPFs with orders of magnitude higher carcinogenic potency than predicted by established in vivo-based potency factors. Applying the MPFs in cancer risk assessment suggested that 45.4 (6% of all) cancer cases per year in Stockholm are due to airborne PAHs. Applying established models resulted in <1 cancer case per year, which is far from expected levels. We conclude that our in vitro based approach for establishing MPFs could be a novel method to assess whole mixture samples of airborne PAHs to improve health risk assessment.
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| 20. |
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| 21. |
- Falck-Ytter, Terje, et al.
(författare)
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Eye Contact Modulates Cognitive Processing Differently in Children With Autism
- 2015
-
Ingår i: Child Development. - : Wiley. - 0009-3920 .- 1467-8624. ; 86:1, s. 37-47
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Tidskriftsartikel (refereegranskat)abstract
- In humans, effortful cognitive processing frequently takes place during social interaction, with eye contact being an important component. This study shows that the effect of eye contact on memory for nonsocial information is different in children with typical development than in children with autism, a disorder of social communication. Direct gaze facilitated memory performance in children with typical development (n = 25, 6 years old), but no such facilitation was seen in the clinical group (n = 10, 6 years old). Eye tracking conducted during the cognitive test revealed strikingly similar patterns of eye movements, indicating that the results cannot be explained by differences in overt attention. Collectively, these findings have theoretical significance and practical implications for testing practices in children.
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| 22. |
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| 23. |
- Goobar, Ariel, et al.
(författare)
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iPTF16geu : A multiply imaged, gravitationally lensed type Ia supernova
- 2017
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 356:6335, s. 291-295
-
Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because the light from the stellar explosion was magnified more than 50 times by the curvature of space around matter in an intervening galaxy. We used high-spatial-resolution observations to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec, smaller than is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration imply close alignment between the lines of sight to the supernova and to the lens. The relative magnifications of the four images provide evidence for substructures in the lensing galaxy.
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| 24. |
- Goobar, Ariel, et al.
(författare)
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THE RISE OF SN 2014J IN THE NEARBY GALAXY M82
- 2014
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 784:1
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Tidskriftsartikel (refereegranskat)abstract
- We report on the discovery of SN 2014J in the nearby galaxy M82. Given its proximity, it offers the best opportunity to date to study a thermonuclear supernova (SN) over a wide range of the electromagnetic spectrum. Optical, near-IR, and mid-IR observations on the rising light curve, orchestrated by the intermediate Palomar Transient Factory, show that SN 2014J is a spectroscopically normal Type Ia supernova (SN Ia), albeit exhibiting high-velocity features in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and do not detect any evolution in the resolved absorption features during the light curve rise. Similar to other highly reddened SNe Ia, a low value of total-to-selective extinction, R-V less than or similar to 2, provides the best match to our observations. We also study pre-explosion optical and near-IR images from Hubble Space Telescope with special emphasis on the sources nearest to the SN location.
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| 25. |
- Goobar, Ariel, 1962-, et al.
(författare)
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Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky
- 2023
-
Ingår i: Nature Astronomy. - 2397-3366. ; 7:9, s. 1098-1107
-
Tidskriftsartikel (refereegranskat)abstract
- Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. Here we describe how high-cadence optical observations with the Zwicky Transient Facility, with its unparalleled large field of view, led to the detection of a multiply imaged type Ia supernova, SN Zwicky, also known as SN 2022qmx. Magnified nearly 25-fold, the system was found thanks to the standard candle nature of type Ia supernovae. High-spatial-resolution imaging with the Keck telescope resolved four images of the supernova with very small angular separation, corresponding to an Einstein radius of only θE = 0.167″ and almost identical arrival times. The small θE and faintness of the lensing galaxy are very unusual, highlighting the importance of supernovae to fully characterize the properties of galaxy-scale gravitational lenses, including the impact of galaxy substructures.
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| 26. |
- Hakansson, Jonas, et al.
(författare)
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Body lift, drag and power are relatively higher in large-eared than in small-eared bat species
- 2017
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 14:135
-
Tidskriftsartikel (refereegranskat)abstract
- Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing aerodynamic lift. Here we compare quantitative aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body lift than the small-eared species, in line with prior studies on model bats. The measured aerodynamic power of P. auritus was higher than predicted from the aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and aerodynamic performance. The result of this trade-off would be the ecomorphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies.
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| 27. |
- Hansson, L-A, et al.
(författare)
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A synthesis of animal movement across scales
- 2014
-
Ingår i: Animal Movement Across Scales. - : Oxford University Press. - 9780199677184 ; , s. 259-267
-
Bokkapitel (refereegranskat)abstract
- This chapter aims at synthesizing the knowledge presented in the chapters of the book’s three sections by addressing evolutionary compromises, dispersal, gene flow, and assisted movements. How climate change and other environmental changes at different scales may affect animal movement, migration, and dispersal in the future are also summarized here. Moreover, how the different senses are utilized for navigation and orientation and how these may lead to different movement and migration patterns are also discussed. Finally, how the recent technical revolution has affected animal movement research is addressed and the view on future perspectives of animal movement research is also provided.
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| 28. |
- Hedenström, Anders, et al.
(författare)
-
Bat flight.
- 2015
-
Ingår i: Current Biology. - : Elsevier BV. - 1879-0445 .- 0960-9822. ; 25:10, s. 399-402
-
Tidskriftsartikel (refereegranskat)abstract
- Bats are unique among extant flying animals, as they have compliant wings and an echolocation sensory system that distinguish them from birds and insects. Flying in the dark, guided by echolocation, has influenced the aerodynamics of bat flight perhaps more than previously realized and resulted in a characteristic flight that is now being revealed.
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| 29. |
- Hedenström, Anders, et al.
(författare)
-
Bat flight: aerodynamics, kinematics and flight morphology.
- 2015
-
Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 218:5, s. 653-663
-
Forskningsöversikt (refereegranskat)abstract
- Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and time-history of aerodynamic forces can be estimated. At most speeds the downstroke generates both lift and thrust, whereas the function of the upstroke changes with forward flight speed. At hovering and slow speed bats use a leading edge vortex to enhance the lift beyond that allowed by steady aerodynamics and an inverted wing during the upstroke to further aid weight support. The bat wing and its skeleton exhibit many features and control mechanisms that are presumed to improve flight performance. Whereas bats appear aerodynamically less efficient than birds when it comes to cruising flight, they have the edge over birds when it comes to manoeuvring. There is a direct relationship between kinematics and the aerodynamic performance, but there is still a lack of knowledge about how (and if) the bat controls the movements and shape (planform and camber) of the wing. Considering the relatively few bat species whose aerodynamic tracks have been characterized, there is scope for new discoveries and a need to study species representing more extreme positions in the bat morphospace.
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| 30. |
- Hedenström, Anders, et al.
(författare)
-
Bat flight generates complex aerodynamic tracks
- 2007
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 316:5826, s. 894-897
-
Tidskriftsartikel (refereegranskat)abstract
- The flapping flight of animals generates an aerodynamic footprint as a time-varying vortex wake in which the rate of momentum change represents the aerodynamic force. We showed that the wakes of a small bat species differ from those of birds in some important respects. In our bats, each wing generated its own vortex loop. Also, at moderate and high flight speeds, the circulation on the outer ( hand) wing and the arm wing differed in sign during the upstroke, resulting in negative lift on the hand wing and positive lift on the arm wing. Our interpretations of the unsteady aerodynamic performance and function of membranous-winged, flapping flight should change modeling strategies for the study of equivalent natural and engineered flying devices.
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| 31. |
- Hedenström, Anders, et al.
(författare)
-
Bird or bat: comparing airframe design and flight performance.
- 2009
-
Ingår i: Bioinspiration & Biomimetics. - : IOP Publishing. - 1748-3190 .- 1748-3182. ; 4:1
-
Tidskriftsartikel (refereegranskat)abstract
- Birds and bats have evolved powered flight independently, which makes a comparison of evolutionary 'design' solutions potentially interesting. In this paper we highlight similarities and differences with respect to flight characteristics, including morphology, flight kinematics, aerodynamics, energetics and flight performance. Birds' size range is 0.002-15 kg and bats' size range is 0.002-1.5 kg. The wingbeat kinematics differ between birds and bats, which is mainly due to the different flexing of the wing during the upstroke and constraints by having a wing of feathers and a skin membrane, respectively. Aerodynamically, bats appear to generate a more complex wake than birds. Bats may be more closely adapted for slow maneuvering flight than birds, as required by their aerial hawking foraging habits. The metabolic rate and power required to fly are similar among birds and bats. Both groups share many characteristics associated with flight, such as for example low amounts of DNA in cells, the ability to accumulate fat as fuel for hibernation and migration, and parallel habitat-related wing shape adaptations.
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| 32. |
- Hedh, Linus, et al.
(författare)
-
Measuring power input, power output and energy conversion efficiency in un-instrumented flying birds
- 2020
-
Ingår i: The Journal of experimental biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 223
-
Tidskriftsartikel (refereegranskat)abstract
- Cost of flight at various speeds is a crucial determinant of flight behaviour in birds. Aerodynamic models, predicting that mechanical power (Pmech) varies with flight speed in a U-shaped manner, have been used together with an energy conversion factor (efficiency) to estimate metabolic power (Pmet). Despite few empirical studies, efficiency has been assumed constant across flight speeds at 23%. Ideally, efficiency should be estimated from measurements of both Pmech and Pmet in un-instrumented flight. Until recently, progress has been hampered by methodological constraints. The main aim of this study was to evaluate recently developed techniques and estimate flight efficiency across flight speeds. We used the 13C-labelled sodium bicarbonate method (NaBi) and particle image velocimetry (PIV) to measure Pmet and Pmech in blackcaps flying in a wind tunnel. We also cross-validated measurements made by NaBi with quantitative magnetic resonance (QMR) body composition analysis in yellow-rumped warblers. We found that Pmet estimated by NaBi was ∼12% lower than corresponding values estimated by QMR. Pmet varied in a U-shaped manner across flight speeds in blackcaps, but the pattern was not statistically significant. Pmech could only be reliably measured for two intermediate speeds and estimated efficiency ranged between 14% and 22% (combining the two speeds for raw and weight/lift-specific power, with and without correction for the ∼12% difference between NaBi and QMR), which were close to the currently used default value. We conclude that NaBi and PIV are viable techniques, allowing researchers to address some of the outstanding questions regarding bird flight energetics.
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| 33. |
- Henningsson, Per, et al.
(författare)
-
How swift are swifts Apus apus?
- 2010
-
Ingår i: Journal of Avian Biology. - 0908-8857. ; 41:1, s. 94-98
-
Tidskriftsartikel (refereegranskat)abstract
- Swifts Apus apus are renowned for their fast flight manner which has fascinated people in all times. However, previous studies of swifts in flight during migration and roosting flights have shown that the birds operate over a narrow range of flight speeds compared with most other birds studied. In this study we have focused on the special flight behavior often called 'screaming parties'. During these flights the birds appear to reach very high speeds and therefore we used a stereo high speed camera setup to measure the flight speeds of the birds during this behavior with high accuracy. The birds were found to fly at much higher speeds during 'screaming parties' than during migration or roosting, on average twice as fast, 20.9 ms-1 (+/- 5.1 ms-1) in horizontal speed. The highest record was 31.1 ms-1 which is the highest measured yet for a swift in self powered flight. Furthermore, the birds were performing steep climbing flights, on average 4.0 ms-1 (+/- 2.8 ms-1) in vertical velocity. A clear trade-off between horizontal speed and vertical speed was found, suggesting that the birds are operating at their maximum.
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| 34. |
- Holmgren, Sara, et al.
(författare)
-
Whose transformation is this? Unpacking the ‘apparatus of capture’ in Sweden's bioeconomy
- 2022
-
Ingår i: Environmental Innovation and Societal Transitions. - : Elsevier. - 2210-4224 .- 2210-4232. ; 42, s. 44-57
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates how and by whom the Swedish (forest) bioeconomy has been shaped so far. We unpack emerging bioeconomies as discursive constructs and use the ‘apparatus of capture’ as a conceptual framework to understand and rethink the Swedish bioeconomy. Based on analysis of empirical data from multiple sources (e.g., online surveys, in-depth interviews, participatory observations), we identify a closed bioeconomy network structure that includes forest industries, major forest owner associations, regional councils and research institutes/universities. The network (re)produces three key storylines that appeal to the majority of parties in the national parliament, defines the boundaries of relevant expertise, and discredits environmental regulation and expertise. Through these storylines the Swedish bioeconomy is turned into an issue of innovation governance, which blurs the boundaries between public and private interests in forests. To counteract future capture, different types of knowledges and forest perspectives need further exploration in Swedish bioeconomy and forest governance.
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| 35. |
- Hosseinzadeh, Griffin, et al.
(författare)
-
Type Ibn Supernovae Show Photometric Homogeneity and Spectral Diversity at Maximum Light
- 2017
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 836:2
-
Tidskriftsartikel (refereegranskat)abstract
- Type Ibn supernovae (SNe) are a small yet intriguing class of explosions whose spectra are characterized by low-velocity helium emission lines with little to no evidence for hydrogen. The prevailing theory has been that these are the core-collapse explosions of very massive stars embedded in helium-rich circumstellar material (CSM). We report optical observations of six new SNe Ibn: PTF11rfh, PTF12ldy, iPTF14aki, iPTF15ul, SN 2015G, and iPTF15akq. This brings the sample size of such objects in the literature to 22. We also report new data, including a near-infrared spectrum, on the Type Ibn SN 2015U. In order to characterize the class as a whole, we analyze the photometric and spectroscopic properties of the full Type Ibn sample. We find that, despite the expectation that CSM interaction would generate a heterogeneous set of light curves, as seen in SNe IIn, most Type Ibn light curves are quite similar in shape, declining at rates around 0.1 mag day(-1) during the first month after maximum light, with a few significant exceptions. Early spectra of SNe Ibn come in at least two varieties, one that shows narrow P Cygni lines and another dominated by broader emission lines, both around maximum light, which may be an indication of differences in the state of the progenitor system at the time of explosion. Alternatively, the spectral diversity could arise from viewing-angle effects or merely from a lack of early spectroscopic coverage. Together, the relative light curve homogeneity and narrow spectral features suggest that the CSM consists of a spatially confined shell of helium surrounded by a less dense extended wind.
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| 36. |
- Håkansson, Jonas, et al.
(författare)
-
The wake of hovering flight in bats.
- 2015
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5662 .- 1742-5689. ; 12:109
-
Tidskriftsartikel (refereegranskat)abstract
- Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.
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| 37. |
- Isaksson, Ola, 1969, et al.
(författare)
-
Virtual Contextual Validation of technologies and methods for Product Development
- 2016
-
Ingår i: 14th International Design Conference, DESIGN 2016, Cavtat, Dubrovnik, Croatia, 16-19 May 2016. - 1847-9073. ; DS 84, s. 669-678
-
Konferensbidrag (refereegranskat)abstract
- In this paper the use of virtual demonstrators as means to contextually validate both design methods and novel Technologies in advance of industrial Product development. Since maturity requirements are high, and pure technology and methods development Projects typically result in promising, but not validated, methods and Technologies and full scale hardware demonstration initiatives are costly, there is a gap to fill.Functional Modeling and Value Driven design methods are used with Ceramic Metallic Composites technologies in a virtual demonstrator.
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| 38. |
- Jencson, Jacob E., et al.
(författare)
-
The SPIRITS Sample of Luminous Infrared Transients : Uncovering Hidden Supernovae and Dusty Stellar Outbursts in Nearby Galaxies
- 2019
-
Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 886:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of the most luminous (M-IR [Vega magnitudes] brighter than ?14) infrared (IR) transients discovered by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) between 2014 and 2018 in nearby galaxies (D < 35 Mpc). The sample consists of nine events that span peak IR luminosities of M-[4.5],M-peak between ?14 and ?18.2, show IR colors between 0.2;<;([3.6]?[4.5]);<;3.0, and fade on timescales between 55 days;t(fade);<;480 days. The two reddest events (A(V) > 12) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type;Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of 2;A(V);<;8. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as
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| 39. |
- Johansson, Christoffer, et al.
(författare)
-
A methodology for the preliminary assessment of existing railway bridges for high-speed traffic
- 2014
-
Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 58, s. 25-35
-
Tidskriftsartikel (refereegranskat)abstract
- The Swedish government is considering upgrading the train speed along three railway lines in the Southern part of Sweden from 200 km/h to 250 km/h. According to the current design code, this requires that the bridges be examined with dynamic simulations to avoid excessive vibrations. This paper employs a method that can be used at an early stage to estimate the expected cost of upgrading a bridge network. The results revealed that 70% of the plate/beam bridges, 64% of the closed slab-frame bridges, and 41% of the open slab-frame bridges are expected to not fulfill the requirement on the maximum bridge deck acceleration for ballasted tracks.
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| 40. |
- Johansson, Christoffer, et al.
(författare)
-
A quantitative comparison of bird and bat wakes.
- 2010
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5662 .- 1742-5689. ; 7, s. 61-66
-
Tidskriftsartikel (refereegranskat)abstract
- Qualitative comparison of bird and bat wakes has demonstrated significant differences in the structure of the far wake. Birds have been found to have a unified vortex wake of the two wings, while bats have a more complex wake with gradients in the circulation along the wingspan, and with each wing generating its own vortex structure. Here, we compare quantitative measures of the circulation in the far wake of three bird and one bat species. We find that bats have a significantly stronger normalized circulation of the start vortex than birds. We also find differences in how the circulation develops during the wingbeat as demonstrated by the ratio of the circulation of the dominant start vortex and the total circulation of the same sense. Birds show a more prominent change with changing flight speed and a relatively weaker start vortex at minimum power speed than bats. We also find that bats have a higher normalized wake loading based on the start vortex, indicating higher relative induced drag and therefore less efficient lift generation than birds. Our results thus indicate fundamental differences in the aerodynamics of bird and bat flight that will further our understanding of the evolution of vertebrate flight.
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| 41. |
- Johansson, christoffer, et al.
(författare)
-
Closed-form solution for the mode superposition analysis of the vibration in multi-span beam bridges caused by concentrated moving loads
- 2013
-
Ingår i: Computers & structures. - : Elsevier BV. - 0045-7949 .- 1879-2243. ; 119, s. 85-94
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a closed-form solution for evaluating the dynamical behavior of a general multi-span Bernoulli-Euler beam is derived. The natural frequencies of vibration and corresponding mode shapes are obtained by applying the boundary conditions to the characteristic function of a beam. A Laplace transformation is applied to the governing differential equation which is then solved for each normal mode in the frequency domain. The main contribution of this paper is to provide a closed-form solution for the vibration of continuous stepped beams under constant moving loads. Several numerical examples are included.
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| 42. |
- Johansson, Christoffer, 1985-, et al.
(författare)
-
Development of design curves for preliminary dynamic assessment of railway bridges to higher speeds
-
Ingår i: The International Journal of Railway Technology. - 2049-5358.
-
Tidskriftsartikel (refereegranskat)abstract
- Resonance vibrations of railway bridges have become an important design issue during the last decade due to the development of new high–speed lines. From a designers point of view, this often requires that the bridge is analysed with a finite element software, resulting in long runtimes. The present paper presents design curves to calculate the maximum acceleration, displacement and angular rotation in multi-span bridges, during passages of high-speed trains. The design curves can preferably be used for conceptual design or to evaluate an existing network of bridges. Two numerical examples are included to validate the method and to show possible applications
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| 43. |
- Johansson, Christoffer, et al.
(författare)
-
Ear-body lift and a novel thrust generating mechanism revealed by the complex wake of brown long-eared bats (Plecotus auritus)
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Large ears enhance perception of echolocation and prey generated sounds in bats. However, external ears likely impair aerodynamic performance of bats compared to birds. But large ears may generate lift on their own, mitigating the negative effects. We studied flying brown long-eared bats, using high resolution, time resolved particle image velocimetry, to determine the aerodynamics of flying with large ears. We show that the ears and body generate lift at medium to cruising speeds (3-5 m/s), but at the cost of an interaction with the wing root vortices, likely reducing inner wing performance. We also propose that the bats use a novel wing pitch mechanism at the end of the upstroke generating thrust at low speeds, which should provide effective pitch and yaw control. In addition, the wing tip vortices show a distinct spiraling pattern. The tip vortex of the previous wingbeat remains into the next wingbeat and rotates together with a newly formed tip vortex. Several smaller vortices, related to changes in circulation around the wing also spiral the tip vortex. Our results thus show a new level of complexity in bat wakes and suggest large eared bats are less aerodynamically limited than previous wake studies have suggested.
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| 44. |
- Johansson, Christoffer, et al.
(författare)
-
Elytra boost lift, but reduce aerodynamic efficiency in flying beetles.
- 2012
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5662 .- 1742-5689. ; 9:75, s. 2745-2748
-
Tidskriftsartikel (refereegranskat)abstract
- Flying insects typically possess two pairs of wings. In beetles, the front pair has evolved into short, hardened structures, the elytra, which protect the second pair of wings and the abdomen. This allows beetles to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with the elytra extended, suggesting that they influence aerodynamic performance, but little is known about their role in flight. Using quantitative measurements of the beetle's wake, we show that the presence of the elytra increases vertical force production by approximately 40 per cent, indicating that they contribute to weight support. The wing-elytra combination creates a complex wake compared with previously studied animal wakes. At mid-downstroke, multiple vortices are visible behind each wing. These include a wingtip and an elytron vortex with the same sense of rotation, a body vortex and an additional vortex of the opposite sense of rotation. This latter vortex reflects a negative interaction between the wing and the elytron, resulting in a single wing span efficiency of approximately 0.77 at mid downstroke. This is lower than that found in birds and bats, suggesting that the extra weight support of the elytra comes at the price of reduced efficiency.
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| 45. |
- Johansson, Christoffer, et al.
(författare)
-
Hydrodynamics of surface swimming in leopard frogs (Rana pipiens)
- 2004
-
Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 207:22, s. 3945-3958
-
Tidskriftsartikel (refereegranskat)abstract
- The kinematics of swimming frogs have been studied extensively in the past and, based on these results, hypotheses regarding the hydrodynamics of frog swimming can be generated. To test these hypotheses we used digital particle image velocimetry (DPIV) to quantify the flow structure of the wake produced by the feet during the propulsion phase of the kick of surface swimming frogs (Rana pipiens). These frogs use two different gaits, asynchronous and synchronous kicking, and the magnitude of the thrust produced by the feet differs between asynchronous (34±5.4 mN foot–1) and synchronous kicking (71±13.3 mN foot–1), as does maximum swimming speed, with higher swimming speed and forces produced during the synchronous kicks. Previous studies have suggested that an interaction between the feet, resulting in a single posteriorly directed fluid jet, as the feet come together at the end of synchronous kicks, may augment force production. Our results show, however, that each foot produces its own distinct vortex ring, in both asynchronous and synchronous kicking of the feet. There is no evidence of a central jet being produced even during powerful synchronous kicks (maximum thrust calculated was 264 mN foot–1). An alternative mechanism of force production could be the lift-based paddling recently suggested for delta-shaped feet of swimming birds. However, the orientation of the vortex rings generated by the feet is almost perpendicular to the swimming direction for both gaits and there is only a slight asynchrony of the shedding of the distal (start) and proximal (stop) vortex rings, which is different from what would be expected by a dominantly lift-based mechanism. Thus, our results do not support lift as a major mechanism contributing to thrust. Instead, our data support the hypothesis that propulsion is based on drag and acceleration reaction forces where the thrust is generated by separated, but attached, vortex rings on the suction side of the feet, resulting in vortices that are shed behind the frogs during both asynchronous and synchronous kicking.
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| 46. |
|
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| 47. |
- Johansson, Christoffer, et al.
(författare)
-
Höghastighetsprojekt - Bro : Inventering av järnvägsbroar för ökad hastighet på befintliga banor
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I föreliggande rapport har omfattande dynamiska analyser av järnvägbroar utförts, i syfte att ge en översiktlig uppskattning av möjligheten att tillåta höghastighetståg på befintliga banor. Aktuella sträckor som studerats är Västra stambanan mellan Stockholm och Göteborg, Södra stambanan mellan Stockholm och Malmö samt Västkustbanan mellan Göteborg och Malmö. Totalt omfattar detta mer än 1000 broar. Eftersom detaljerade analyser av samtliga broar ej varit möjlig med givna resurser och tid, har en kombination av detaljstudier och sannolikhetsbaserade metoder valts. Analyserna har begränsats till balk- och plattbroar samt plattrambroar, vilka utgör ca. 90 % av tillgängligt underlag. Förutsättningarna för de dynamiska kontrollerna baseras på kraven enligt Eurokod EN-1990 samt EN-1991-2 och utgör främst vertikal acceleration av brokonstruktionen, begränsad till 3.5 m/s2. Förutsättningarna inom utredningen har varit att undersöka tåghastigheter upp till 250 km/h (sth). Baserat på omfattande parameteranalyser har ett antal faktorer identifierats som viktiga för en bros dynamiska respons. Många av dessa parametrar är svåra att entydigt bestämma och påverkar ofta strukturresponsen på ett oregelbundet sätt. Omfattande Monte-Carlo simulering har utförts baserat på förenklade 2D-modeller. Resultaten visar att ca. 70 % av balk- och plattbroarna samt ca. 50 % av plattrambroarna förväntas överskrida de dynamiska kraven enligt Eurokod, baserat på sth 250 km/h. Även om tillåten hastighet sänks till sth 150 km/h ger detta ett förväntat värde på 15 % för balk- och plattbroar samt 30 % för plattrambroar. Förväntat värde för varje bro redovisas i Bilaga F, vilket kan användas som underlag för kostnadskalkyl. Resultaten är en konsekvens av de höga krav som ställs i Eurokod, vilka är samma som vid dimensionering av nya broar. Andra förutsättningar avseende t.ex. lastmodell eller frekvensband för utvärdering av accelerationer är helt avgörande för resultaten. En av de största kvarstående frågeställningarna är det dynamiska verkningssättet för korta broar med höga egenfrekvenser. Den dynamiska responsen från dessa broar utgörs ofta av stötvis belastning istället för resonans. Enligt tidigare BV-Bro begränsades frekvensbandet till 30 Hz, i Eurokod anges att de 3 första egenmoderna ska medräknas, vilket ofta resulterar i betydligt högre frekvensband. Giltigheten av dessa krav måste utredas.
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| 48. |
- Johansson, Christoffer, et al.
(författare)
-
Improving the Control Design of the KNATTE Platform with Flexible Panels
- 2022
-
Ingår i: IAC 2022 Congress Proceedings, 73rd International Astronautical Congress (IAC), Paris, France. - : International Astronautical Federation.
-
Konferensbidrag (refereegranskat)abstract
- The effect of flexible structures such as solar panels or long booms on the dynamics of a spacecraft of any size can become a problem for the stability of its control subsystem. That said, proper control algorithms can be designed to reduce the vibrations of such appendages. The Kinesthetic Node and Autonomous Table-Top Emulator (KNATTE), developed at Luleå University of Technology in collaboration with the University of Rome “La Sapienza”, is a frictionless vehicle that has been conceived as a multipurpose platform to perform hardware-in-the-loop simulation experiments with real and analogous small-satellite components. The platform can emulate spacecraft behavior in orbit for validating various guidance, navigation and control algorithms.The object of this study is the KNATTE platform carrying a pair of flexible mock-up solar panels. In such circumstances, the steering system of the vehicle is not able to maneuver by applying a conventional Proportional-Integral-Derivative control algorithm. However, a Linear-Quadratic-Gaussian (LQG) algorithm has been proven effective to control the vehicle with the appendages in former simulations. The purpose of this work is to validate the performance of the previously developed LQGalgorithm in a hardware-in-the-loop simulation experiment and compare its results to those of applying a Sliding Mode Control (SMC) algorithm to the same scenario.This article presents a comparative study of the LQG and SMCalgorithms. For that, both algorithms have been developed in Simulink and tested in equivalent modeled environments. Next, the algorithms have been adapted to the operation of KNATTE for their validation on hardware, includingadditional modifications to the experiment setup when necessary. The tracking data coming from a computer vision system has been filtered to improve the accuracy of the navigation block. The signal conditioning circuit has also been upgraded to improve the reliability of panel deflection measurements given by piezoelectric sensors.Both the LQG and SMC algorithms proved to be effective to reduce the destabilizing vibrations of the flexible panels and their suitability for controlling the KNATTE platform with such panels despite their dependency on an accurate model of the plant. The SMC algorithm showed less error than the LQG algorithm in the tested scenario. Additionally, the implementations in this work can be used for future educational and research experiments with frictionless platforms.
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| 49. |
- Johansson, Christoffer, et al.
(författare)
-
Järnvägsbroar på Botniabanan : Dynamiska kontroller för framtida höghastighetståg - Steg 1
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I föreliggande rapport har inventering och dynamiska kontroller utförts på 76 järnvägsbroar längs Botniabanan. Samtliga broar är byggda under perioden 1999 – 2009 och dimensionerade statiskt för tåglast BV2000. Broarna kan indelas i tre grupper; balk- och plattbroar, plattrambroar och samverkansbroar.Baserat på förenklade dynamiska analyser erhålls ett överskridande av den vertikala accelerationen för 75 % av alla plattrambroar och 40 % av alla balk- och plattbroar. Överskridande erhålls även för 4 av 9 samverkansbroar. Av totalt 76 analyserade broar motsvarar detta 41 broar som inte uppfyller kravet på sth 250 km/h. En sänkning till sth 200 km/h ger att 26 broar inte klarar de dynamiska kraven. Fyra broar har en nominell kritisk hastighet under 120 km/h.För plattrambroarna är accelerationsnivån i hög grad beroende på grundläggningsförhållandena. Enligt tidigare BV Bro medräknades endast frekvenser upp till 30 Hz, vilket i kombination med antagande om oeftergivliga stöd ofta resulterade i att dynamiska kontroller inte utfördes för plattrambroar. Eftergivlighet hos grundläggningen resulterar i vertikala stelkroppsmoder som i kombination med medsvängande massa av angränsande fyllning ger låga egenfrekvenser och därmed låga resonanshastigheter.För balkbroar beräknas mycket höga accelerationsnivåer då dessa är utformade med ändskärmar. Orsaken är att tåglasten inducerar en stötbelastning då den passerar änden på ändskärmen. Detta ger höga accelerationsnivåer även i angränsande spann, även utanför ett resonanstillstånd. Plattbroar ger ofta högre accelerationsnivåer jämfört med motsvarande balkbroar, beroende på att en lägre böjstyvhet ger lägre resonanshastighet. Detta förvärras kraftigt för plattbroar utformade med ändskärmar, vilket identifierats för t.ex. bro över Sidensjövägen.För samverkansbroarna beror de höga accelerationsnivåerna på en kombination av låg böjstyvhet och låg massa, vilket ger en låg resonanshastighet och hög accelerationsnivå. Problemet är störst för två fritt upplagda broar, Banafjälsån och Bryngeån.Förslag på fortsatta utredningar i syfte att påvisa att fler broar klarar de dynamiska kraven inkluderar mer avancerade analysmetoder i kombination med fältmätningar och kontrollerad excitering. Det bedöms i nuläget finnas stor potential att påvisa lägre accelerationsnivåer baserat på mindre konservativa antaganden om t.ex. dämpning och samverkan mellan bro och omgivande fyllning.
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- Johansson, Christoffer, et al.
(författare)
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Multiple leading edge vortices of unexpected strength in freely flying hawkmoth.
- 2013
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The Leading Edge Vortex (LEV) is a universal mechanism enhancing lift in flying organisms. LEVs, generally illustrated as a single vortex attached to the wing throughout the downstroke, have not been studied quantitatively in freely flying insects. Previous findings are either qualitative or from flappers and tethered insects. We measure the flow above the wing of freely flying hawkmoths and find multiple simultaneous LEVs of varying strength and structure along the wingspan. At the inner wing there is a single, attached LEV, while at mid wing there are multiple LEVs, and towards the wingtip flow separates. At mid wing the LEV circulation is ~40% higher than in the wake, implying that the circulation unrelated to the LEV may reduce lift. The strong and complex LEV suggests relatively high flight power in hawmoths. The variable LEV structure may result in variable force production, influencing flight control in the animals.
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