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Draft:L Christoffer Johansson

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L Christoffer Johansson is a zoologist working as a lecturer at Lund University in Sweden (Personal webpage). His research focuses on fluid dynamics of animal locomotion and to understand morphological adaptations, with a current focus on animal flight. He is member of the Animal flight lab at Lund University (AFL page), working mainly with quantitative flow measurements (using PIV) of animals flying freely in a wind tunnel.

Christoffer earned his PhD in 2002 at Göteborg University, Sweden, with a thesis focused on functional morphology and hydrodynamics of swimming birds. In 2003, he did a postdoc at Harvard University, USA. As part of the Lauder lab, he studied the hydrodynamics of swimming in frogs. Since returning to Sweden in 2004, Christoffer has been working with animal flight at Lund University, becoming a Lecturer/Associate professor in 2010.

Research focus

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Flight

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Birds

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Christoffer’s work on bird flight covers both studies of the aerodynamic mechanism involved in generating the forces and how the cost of flight varies across speed. He has been part of showing that birds can use leading-edge vortices (LEVs) to boost their force production when flying slowly[1] and that the split feathers at the wing tip of many species work as individual airfoils.[2] He has also been part of showing that birds tend to be more efficient fliers than bats[3] and that the cost of flight varies with speed in a manner different from predicted by traditional models. The latter probably due to how drag changes across speed due to the birds tilting their bodies when flying slowly.[4] The work has also involved studies where cost of flight has been modelled, creating an updated and more accurate model of flight costs in flapping flight than the one that has been dominating for decades.[5]

Hybrid robotic wing in Lund University wind tunnel.
Hybrid robotic wing in Lund University wind tunnel.

Notably, Christoffer has also studied bird flight using an advanced flapping robot, where he and the coauthors where able to show the benefits of folding the wing during the upstroke and that the most efficient use of the upstroke was to generate some lift, just like many bird species do (but opposite to what bats do).[6]

Bats

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A merge of a photo of a bat and a snapshot of the aerodynamic wake generated during flight.
Bat wake

Animal flight lab in Lund was the first to measure and describe the wake left behind bats flying freely in their wind tunnel.[7] In addition, they performed the first on wing measurements, showing that the bats used leading-edge vortices (LEVs) to boost their force production when flying slowly.[8] These papers have been highly influential on our understanding of bat flight.

In addition, Christoffer’s work has also involved studying how flying close to a surface influences the cost of flight. Flight close to a surface generates what is known as ground effect and by comparing the aerodynamic cost for Daubentons’ bats flying in or out of ground effect they could show that the bats saved more energy than predicted by models.[9] Additional work has concerned comparing the cost of flight in bats with different sized ears[10] and the efficiency of converting physiological to mechanical power.[11]

Insects

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Christoffer has worked on several species and aspects of insect flight, including to understand how the elytra, the hard cover wings of beetles, affects the flight performance. Despite being evolved as a protection for the beetles, the elytra flap and add to the lift production. However, at the same time the reduce the efficiency of the flight.[12]

Artistic merging of photo of a butterfly during flight and the measured aerodynamic footprint of a butterfly during take off.
Butterfly take off

Insects use unsteady aerodynamic mechanisms to generate enough force to stay aloft. Christoffer’s work has focused on two of them, the leading edge vortex (LEV) and the clap and fling. He has performed the first quantitative measurements of the strength of the LEV in a freely flying insect, showing that it is stronger and more unstable than previously thought.[13] His work on wing clap in butterflies has showed that the butterflies use the upstroke to clap their wings together and due to the flexibility of the wings the clap is more effective and more efficient than if the wings had been stiff.[14][15]

Swimming

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Christoffer’s work on swimming has focused on secondary swimmers, animals that have returned to a life in water after their ancestors lived on land. Through studies of the motion pattern of swimming and diving birds and physical models of bird feet he has discovered and described novel ways of swimming. Foot propulsion has traditionally been considered to be based on the drag the feet generate as they are pushed in the opposite direction to swimming, but Christoffer have described two separate mechanisms that allows foot propelled birds to instead use lift, which makes their swimming more efficient and allows for faster swimming. One example is found in grebes, which have lobed toes resembling feathers, where the feet are swept sideways from underneath the body to a position above and behind the body. Almost like a propeller turning a third of a full turn.[16][17] The other example applies to birds with triangular feet and where he has shown that the feet can work as delta wings.[18] Unlike the bird examples, Christoffer has also worked with swimming in frogs showing that they use the expected drag-based paddling.[19]

For a complete list of publications see Google scholar profile

References

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  1. ^ Muijres, Florian T.; Johansson, L. Christoffer; Hedenström, Anders (23 August 2012). "Leading edge vortex in a slow-flying passerine". Biology Letters. 8 (4): 554–557. doi:10.1098/rsbl.2012.0130. PMC 3391469. PMID 22417792.
  2. ^ KleinHeerenbrink, Marco; Johansson, L. Christoffer; Hedenström, Anders (May 2017). "Multi-cored vortices support function of slotted wing tips of birds in gliding and flapping flight". Journal of the Royal Society Interface. 14 (130): 20170099. doi:10.1098/rsif.2017.0099. PMC 5454299. PMID 28539482.
  3. ^ Muijres, Florian T.; Johansson, L. Christoffer; Bowlin, Melissa S.; Winter, York; Hedenström, Anders (18 May 2012). "Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds". PLOS ONE. 7 (5): e37335. Bibcode:2012PLoSO...737335M. doi:10.1371/journal.pone.0037335. PMC 3356262. PMID 22624018.
  4. ^ Johansson, L. Christoffer; Maeda, Masateru; Henningsson, Per; Hedenström, Anders (January 2018). "Mechanical power curve measured in the wake of pied flycatchers indicates modulation of parasite power across flight speeds". Journal of the Royal Society Interface. 15 (138): 20170814. doi:10.1098/rsif.2017.0814. PMC 5805985. PMID 29386402.
  5. ^ Klein Heerenbrink, M.; Johansson, L. C.; Hedenström, A. (May 2015). "Power of the wingbeat: modelling the effects of flapping wings in vertebrate flight". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 471 (2177): 20140952. Bibcode:2015RSPSA.47140952H. doi:10.1098/rspa.2014.0952. PMC 4985036. PMID 27547098.
  6. ^ Ajanic, Enrico; Paolini, Adrien; Coster, Charles; Floreano, Dario; Johansson, Christoffer (February 2023). "Robotic Avian Wing Explains Aerodynamic Advantages of Wing Folding and Stroke Tilting in Flapping Flight". Advanced Intelligent Systems. 5 (2). doi:10.1002/aisy.202200148.
  7. ^ Hedenström, A.; Johansson, L. C.; Wolf, M.; von Busse, R.; Winter, Y.; Spedding, G. R. (11 May 2007). "Bat Flight Generates Complex Aerodynamic Tracks". Science. 316 (5826): 894–897. Bibcode:2007Sci...316..894H. doi:10.1126/science.1142281. PMID 17495171.
  8. ^ Muijres, F. T.; Johansson, L. C.; Barfield, R.; Wolf, M.; Spedding, G. R.; Hedenström, A. (29 February 2008). "Leading-Edge Vortex Improves Lift in Slow-Flying Bats". Science. 319 (5867): 1250–1253. Bibcode:2008Sci...319.1250M. doi:10.1126/science.1153019. PMID 18309085.
  9. ^ Johansson, L. Christoffer; Jakobsen, Lasse; Hedenström, Anders (November 2018). "Flight in Ground Effect Dramatically Reduces Aerodynamic Costs in Bats". Current Biology. 28 (21): 3502–3507.e4. Bibcode:2018CBio...28E3502J. doi:10.1016/j.cub.2018.09.011. PMID 30344122.
  10. ^ Håkansson, Jonas; Jakobsen, Lasse; Hedenström, Anders; Johansson, L. Christoffer (October 2017). "Body lift, drag and power are relatively higher in large-eared than in small-eared bat species". Journal of the Royal Society Interface. 14 (135): 20170455. doi:10.1098/rsif.2017.0455. PMC 5665827. PMID 29070593.
  11. ^ Currie, Shannon E.; Johansson, L. Christoffer; Aumont, Cedric; Voigt, Christian C.; Hedenström, Anders (10 May 2023). "Conversion efficiency of flight power is low, but increases with flight speed in the migratory bat Pipistrellus nathusii". Proceedings of the Royal Society B: Biological Sciences. 290 (1998). doi:10.1098/rspb.2023.0045. PMC 10154928. PMID 37132234.
  12. ^ Johansson, L. Christoffer; Engel, Sophia; Baird, Emily; Dacke, Marie; Muijres, Florian T.; Hedenström, Anders (7 October 2012). "Elytra boost lift, but reduce aerodynamic efficiency in flying beetles". Journal of the Royal Society Interface. 9 (75): 2745–2748. doi:10.1098/rsif.2012.0053. PMC 3427496. PMID 22593097.
  13. ^ Johansson, L. Christoffer; Engel, Sophia; Kelber, Almut; Klein Heerenbrink, Marco; Hedenström, Anders (20 November 2013). "Multiple leading edge vortices of unexpected strength in freely flying hawkmoth". Scientific Reports. 3 (1): 3264. Bibcode:2013NatSR...3E3264J. doi:10.1038/srep03264. PMC 3834544. PMID 24253180.
  14. ^ Johansson, L. C.; Henningsson, P. (January 2021). "Butterflies fly using efficient propulsive clap mechanism owing to flexible wings". Journal of the Royal Society Interface. 18 (174): 20200854. doi:10.1098/rsif.2020.0854. PMC 7879755. PMID 33468023.
  15. ^ Henningsson, P.; Johansson, L. C. (December 2021). "Downstroke and upstroke conflict during banked turns in butterflies". Journal of the Royal Society Interface. 18 (185). doi:10.1098/rsif.2021.0779. PMC 8633796. PMID 34847788.
  16. ^ Johansson, L. Christoffer; Lindhe Norberg, Ulla M. (October 2000). "Asymmetric toes aid underwater swimming". Nature. 407 (6804): 582–583. doi:10.1038/35036689. ISSN 1476-4687. PMID 11034197.
  17. ^ Johansson, L. Christoffer; Norberg, Ulla M. Lindhe (15 May 2001). "Lift-Based Paddling in Diving Grebe". Journal of Experimental Biology. 204 (10): 1687–1696. doi:10.1242/jeb.204.10.1687. PMID 11316488.
  18. ^ Johansson, L. Christoffer; Norberg, R. Åke (July 2003). "Delta-wing function of webbed feet gives hydrodynamic lift for swimming propulsion in birds". Nature. 424 (6944): 65–68. Bibcode:2003Natur.424...65J. doi:10.1038/nature01695. PMID 12840759.
  19. ^ Johansson, L. Christoffer; Lauder, George V. (15 October 2004). "Hydrodynamics of surface swimming in leopard frogs ( Rana pipiens )". Journal of Experimental Biology. 207 (22): 3945–3958. doi:10.1242/jeb.01258. PMID 15472025.