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  • 1
    Publication Date: 2014-04-15
    Description: Important processes of living cells, including intracellular transport, cell crawling, contraction, division, and mechanochemical signal transduction, are controlled by cytoskeletal (CSK) dynamics. CSK dynamics can be measured by tracking the motion of CSK-bound particles. Particle motion has been reported to follow a superdiffusive behavior that is believed to arise from ATP-driven intracellular stress fluctuations generated by polymerization processes and motor proteins. The power spectrum of intracellular stress fluctuations has been suggested to decay with 1/2 (Lau et al, Phys Rev Lett 91:198101). Here we report direct measurements of cellular force fluctuations that are transmitted to the extracellular matrix, and compared them with the spontaneous motion of CSK-bound beads. Fibronectin coated fluorescent beads (Ø 1 m) were bound to the CSK of confluent human vascular endothelial cells. Forces transmitted to the extracellular matrix (ECM) were quantified by plating these cells onto a collagen coated elastic polyacrylamide hydrogel, and measuring the gel deformation from the displacement of embedded fluorescent beads (Ø 0.5 m). Bead motion of both CSK-bound and ECM-bound beads were measured with nanometer-resolution and expressed as mean square displacement (MSD). The MSD of both CSK-bound and ECM-bound beads displayed a superdiffusive behavior that was well described by a power law: MSD = a*t^b. Surprisingly, we found an identical power law exponent for both CSK-bound and ECM-bound beads of b = 1.6. This finding suggests that the spontaneous motion of CSK-bound beads is driven by stress fluctuations with a 1/ b+1 power spectrum. This result is consistent with the notion that CSK dynamics and CSK stress fluctuations are closely coupled.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
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  • 2
    Publication Date: 2014-04-15
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
    Format: application/pdf
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  • 3
    Publication Date: 2017-01-25
    Description: Loud hydroacoustic sources, such as naval mid-frequency sonars or airguns for marine geophysical prospecting, have been increasingly criticized for their possible negative effects on marine mammals and were implicated in several whale stranding events. Competent authorities now regularly request the implementation of mitigation measures, including the shut-down of acoustic sources when marine mammals are sighted within a predefined exclusion zone. Commonly, ship-based marine mammal observers (MMOs) are employed to visually monitor this zone. This approach is personnel-intensive and not applicable during night time, even though most hydroacoustic activities run day and night. This study describes and evaluates an automatic, ship-based, thermographic whale detection system that continuously scans the ship’s environs for whale blows. Its performance is independent of daylight and exhibits an almost uniform, omnidirectional detection probability within a radius of 5 km. It outperforms alerted observers in terms of number of detected blows and ship-whale encounters. Our results demonstrate that thermal imaging can be used for reliable and continuous marine mammal protection.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
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    Journal of Biomechanics Vol. 39Supplement 1, Page S231
    Publication Date: 2014-04-15
    Description: Important processes of living cells, including intracellular transport, cell crawling, contraction, division and mechanochemical signal transduction, are controlled by cytoskeletal (CSK) dynamics. Some aspects of CSK dynamics have been studied by following the spontaneous motion of CSK-bound particles. Such particle exhibit a superdiffusive behavior that is believed to arise from random local ATP-driven intracellular force fluctuations generated by polymerization processes and motor proteins. (Lau et al, Phys Rev Lett 91:198101). Here we report simultaneous measurements of spontaneous particle motions and cellular force fluctuations. Human vascular endothelial cells were plated onto collagen coated elastic polyacrylamide hydrogels. Force fluctuations at the basal cell membrane(cell tractions) were computed from the displacements of gel-embedded fluorescent beads. Spontaneous particle motion was measured using fibronectin coated fluorescent beads that were bound to the apicell cell membrane via integrin receptors. Bead motion of both CSK-bound and ECM-bound beads were measured with nanometer-resolution and expressed as mean square displacement (MSD). The MSD of both CSK-bound and ECM-bound beads displayed a superdiffusive behavior that was well described by a power law: MSD = a*t^b. In contradiction to existing theories of stress dissipation within the CSK, we found an identical power law exponent for both CSK-bound and ECM-bound beads of b = 1.6. This finding suggests that the spontaneous motion of CSK-bound beads is driven not by random, local stress fluctuations within a viscoelastic continuum, but rather by large scale stress fluctuations within a CSK network that transmits these stresses with little or no dissipation to the ECM.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , NonPeerReviewed
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  • 5
    Publication Date: 2014-08-18
    Description: Seismic surveys are frequently a matter of concern regarding their potentially negative impacts on marine mammals. In the Southern Ocean, which provides a critical habitat for several endangered cetacean species, seismic research activities are undertaken at a circumpolar scale. In order to minimize impacts of these surveys, pre-cruise planning requires detailed, spatio-temporally resolved knowledge on the likelihood of encountering these species in the survey area. In this publication we present predictive habitat modelling as a potential tool to support decisions for survey planning. We associated opportunistic sightings (2005–2011) of humpback (Megaptera novaeangliae, N=93) and Antarctic minke whales (Balaenoptera bonaerensis, N=139) with a range of static and dynamic environmental variables. A maximum entropy algorithm (Maxent) was used to develop habitat models and to calculate daily basinwide/circumpolar prediction maps to evaluate how species-specific habitat conditions evolved throughout the spring and summer months. For both species, prediction maps revealed considerable changes in habitat suitability throughout the season. Suitable humpback whale habitat occurred predominantly in ice-free areas, expanding southwards with the retreating sea ice edge, whereas suitable Antarctic minke whale habitat was consistently predicted within sea ice covered areas. Daily, large-scale prediction maps provide a valuable tool to design layout and timing of seismic surveys as they allow the identification and consideration of potential spatio-temporal hotspots to minimize potential impacts of seismic surveys on Antarctic cetacean species.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Publication Date: 2014-04-15
    Description: Journal of Biomechanics Vol. 39Supplement 1, Page S238
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
    Publication Date: 2016-12-08
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS 11 (2016): e0150660, doi:10.1371/journal.pone.0150660.
    Description: Sperm whales are present in the Canary Islands year-round, suggesting that the archipelago is an important area for this species in the North Atlantic. However, the area experiences one of the highest reported rates of sperm whale ship-strike in the world. Here we investigate if the number of sperm whales found in the archipelago can sustain the current rate of ship-strike mortality. The results of this study may also have implications for offshore areas where concentrations of sperm whales may coincide with high densities of ship traffic, but where ship-strikes may be undocumented. The absolute abundance of sperm whales in an area of 52933 km2, covering the territorial waters of the Canary Islands, was estimated from 2668 km of acoustic line-transect survey using Distance sampling analysis. Data on sperm whale diving and acoustic behaviour, obtained from bio-logging, were used to calculate g(0) = 0.92, this is less than one because of occasional extended periods when whales do not echolocate. This resulted in an absolute abundance estimate of 224 sperm whales (95% log-normal CI 120–418) within the survey area. The recruitment capability of this number of whales, some 2.5 whales per year, is likely to be exceeded by the current ship-strike mortality rate. Furthermore, we found areas of higher whale density within the archipelago, many coincident with those previously described, suggesting that these are important habitats for females and immature animals inhabiting the archipelago. Some of these areas are crossed by active shipping lanes increasing the risk of ship-strikes. Given the philopatry in female sperm whales, replacement of impacted whales might be limited. Therefore, the application of mitigation measures to reduce the ship-strike mortality rate seems essential for the conservation of sperm whales in the Canary Islands.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
    Publication Date: 2019-07-17
    Description: Several countries require monitoring to be conducted near activities that have the potential to disturb or harm marine mammals in order to estimate the possible impacts and/or to trigger appropriate mitigations measures. Monitoring typically involves the use of trained personnel to conduct visual observations. However, visual observations are limited to animals at the surface and further by periods of darkness and inclement weather conditions. Various technologies for improving the effectiveness of monitoring continue to be developed, including passive and active acoustics and low-light and infrared (IR) imaging devices. The use of IR imaging technology may allow the detection of marine mammals at night and improve the detection during all periods through the use of automated detection algorithms. An advanced IR camera system capable of simultaneously monitoring 360° around a vessel was tested during a two month seismic operation in the Alaskan Chukchi Sea. This particular installation allowed monitoring of 270° ahead and to the sides of the vessel with a picture refresh rate of 5 Hz. The IR pictures were displayed in real-time on two monitors and visual observers recorded video during marine mammal sightings for retrospective analyses. Approximately 180 whale blows were detect-able in the recorded IR imagery. Smaller whales (Dall’s porpoise) were detectable at distances of several hundred meters, while blows from large baleen whales were seen at distances up to 7 km. The IR camera was also able to detect the majority of walrus that surfaced within 1 km of the vessel, with some detection out to a maximum distance of 1.5 km. Detection and tracking software recorded the swimming path of some Pacific walrus as the seismic vessel passed the animals. The IR camera system showed substantial promise for improving the effectiveness of detecting marine mammals at the surface, although improvements to auto-detection software are necessary.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 9
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
    Publication Date: 2019-07-17
    Description: For most cell types, adhesion, spreading and tension generation are crucial for cell survival. These processes are strongly influenced by the rigidity of the extracellular matrix: Cells spread more and faster, and generate higher tension on more rigid substrates. We report simulta- neous measurements of cell spreading and traction generation during adhesion of MDA-MB-231 breast carcinoma cells onto collagen coated polyacrylamid gels. The Youngs modulus of the gels was tuned between 1500 (’soft’) and 6000 (’hard’) Pa. The evolution of cell tractions was computed from the gel deformation measured every 30 sec by tracking the displacements of fluorescent beads (ø0.5µm) embedded at the gel surface. As a robust estimate of total force generation, we computed for each cell the elastic strain energy U stored within the gel. As ex- pected, cells generated a higher maximum strain energy U = 1.01pJ) and spread more (A = 6002 ± 961µm2) on harder gels compared to softer gels (U = 0.20pJ, A = 3012 ± 492µm2). When the strain energy vs. time data of individual cells were normalized by spreading area, they collapsed onto a single relationship, regardless of gel stiff- ness. These data extend earlier findings of a proportionality between cell spreading and tension generation (Reinhard-King, Biophys J 2005) and show that individual cells exhibit a constant rate of stress increase during early adhesion events regardless of the substrate rigidity.
    Repository Name: EPIC Alfred Wegener Institut
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