| 561. |
- Raff, Elizabeth C., et al.
(författare)
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Doushantuo fossils are not giant bacteria, but bacterial pseudomorphs of animal embryos
- 2008
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Ingår i: The Palaeontological Association.
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Konferensbidrag (refereegranskat)abstract
- Embryos from the Ediacaran Doushantuo Formation are among the most astonishing examples of exceptional fossilization. However, the mechanism of fossilization ispoorly understood, leading directly to debate over the interpretation of the fossils, someauthors even questioning their interpretation as embryos. It has been hypothesized thatmicrobial processes are responsible for preservation and mineralization of organic tissues.However, the actions of microbes in preservation of embryos have not been demonstratedexperimentally. We show that bacterial biofilms assemble rapidly in marine embryos,forming detailed pseudomorphs of cellular organization and structure. We define threeessential steps in embryo preservation: 1) blockage of autolysis by reducing or anaerobic conditions; 2) rapid formation of microbial biofilms that consume the embryo butform a replica that retains cell organization and morphology; 3) bacterially-catalyzedmineralization. We identified major bacterial taxa in embryo decay biofilms using16S rDNA sequencing. Decay processes were similar in different taphonomic conditions,but bacterial populations depended on specific conditions. Experimental taphonomyresembles preservation states of fossils. Our data show how fossilization of soft tissues insediments is mediated by bacterial replacement and mineralization, providing a foundationfor experimentally creating biofilms from defined microbial species to model fossilization asa biological process.
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| 562. |
- Raff, Elizabeth C., et al.
(författare)
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Embryo fossilization is a biological process mediated by microbial biofilms
- 2008
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Ingår i: Proceedings of the National Academy of Sciences. ; 105:49, s. 19360-19365
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Tidskriftsartikel (refereegranskat)abstract
- Fossilized embryos with extraordinary cellular preservation appear in the Late Neoproterozoic and Cambrian, coincident with the appearance of animal body fossils. It has been hypothesized that microbial processes are responsible for preservation and mineralization of organic tissues. However, the actions of microbes in preservation of embryos have not been demonstrated experimentally. Here, we show that bacterial biofilms assemble rapidly in dead marine embryos and form remarkable pseudomorphs in which the bacterial biofilm replaces and exquisitely models details of cellular organization and structure. The experimental model was the decay of cleavage stage embryos similar in size and morphology to fossil embryos. The data show that embryo preservation takes place in 3 distinct steps: (i) blockage of autolysis by reducing or anaerobic conditions, (ii) rapid formation of microbial biofilms that consume the embryo but form a replica that retains cell organization and morphology, and (iii) bacterially catalyzed mineralization. Major bacterial taxa in embryo decay biofilms were identified by using 16S rDNA sequencing. Decay processes were similar in different taphonomic conditions, but the composition of bacterial populations depended on specific conditions. Experimental taphonomy generates preservation states similar to those in fossil embryos. The data show how fossilization of soft tissues in sediments can be mediated by bacterial replacement and mineralization, providing a foundation for experimentally creating biofilms from defined microbial species to model fossilization as a biological process.
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| 563. |
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| 564. |
- Richard, Louis, et al.
(författare)
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Proton and Helium Ion Acceleration at Magnetotail Plasma Jets
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:8
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Tidskriftsartikel (refereegranskat)abstract
- We investigate two flow bursts in a series of Earthward bursty bulk flows (BBFs) observed by the Magnetospheric Multiscale spacecraft in Earth's magnetotail at (-24, 7, 4) R-E in Geocentric Solar Magnetospheric coordinates. At the leading edges of the BBFs, we observe complex magnetic field structures. In particular, we focus on one BBF which contains large-amplitude magnetic field fluctuations on the time scale of the proton gyroperiod, and another with a large scale dipolarization. For both events, the magnetic field structures are associated with flux increases of supra-thermal ions with energies greater than or similar to 100 keV. We observe that helium ions dominate the ion flux at energies greater than or similar to 150 keV. We investigate the ion acceleration mechanism and its dependence on the mass and charge state of H+ and He2+ ions. We show that for both events, the ions with gyroradii smaller than the dawn-dusk scale of the structure are accelerated by the ion bulk flow. For ions with larger gyroradii, the acceleration is likely due to a localized spatially limited electric field for the event with a large-scale dipolarization. For the event with fluctuating magnetic field, the acceleration of ions with gyroradii comparable with the scale of the magnetic fluctuations can be explained by resonance acceleration.
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| 565. |
- Sandström, K. J. Mattias, et al.
(författare)
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A gas-phase biosensor for environmental monitoring of formic acid: laboratory and field validation
- 2003
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Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry. - 1464-0325 .- 1464-0333. ; 5:3, s. 477-482
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Tidskriftsartikel (refereegranskat)abstract
- In order to encourage more exposure measurements to be performed, a formic acid gas-phase biosensor has been developed for this purpose. In the present paper, an enzyme based biosensor has been validated with respect to analyte selectivity and on-site use. To ensure that the sampler developed measures the compound of interest the biosensor was exposed to three near structural homologues to formic acid, i.e. acetic acid, methanol and formaldehyde. These vapours were generated with and without formic acid and the only compound that was found to have an effect on the performance of the biosensor, albeit a small one, was acetic acid. The field test was performed in a factory using formic acid-containing glue for glulam products. In parallel to the measurements with the biosensor a well defined reference method was used for sampling and analysing formic acid. It was found that the biosensor worked satisfactorily in this environment when used in a stationary position. It was also shown that the biosensor could determine formic acid vapour concentrations down to 0.03 mg m(-3).
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| 566. |
- Sandström, K. J. Mattias, et al.
(författare)
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Amperometric biosensor for formic acid in air
- 2000
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 70:1–3, s. 182-187
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of developing a simple, inexpensive and specific personal passive “real-time” air sampler incorporating a biosensor for formic acid was investigated. The sensor is based on the enzymatic reaction between formic acid and formate dehydrogenase (FDH) with nicotinamide adenine dinucleotide (NAD+) as a co-factor and Meldola's blue as mediator. An effective way to immobilise the enzyme, co-factor and Meldola's blue on screen-printed, disposable, electrodes was found to be in a mixture of glycerol and phosphate buffer covered with a gas-permeable membrane. Steady-state current was reached after 4–15 min and the limit of detection was calculated to be below 1 mg/m3. However, the response decreased by 50% after storage at −15°C for 1 day.
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| 567. |
- Sandström, K. J. Mattias, et al.
(författare)
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Biosensors in air monitoring
- 1999
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Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry. - 1464-0325 .- 1464-0333. ; 1:4, s. 293-298
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Forskningsöversikt (refereegranskat)
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| 568. |
- Sandström, K. J. Mattias, et al.
(författare)
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Multivariate evaluation of factors influencing the performance of a formic acid biosensor for use in air monitoring
- 2001
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Ingår i: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 126:11, s. 2008-2014
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Tidskriftsartikel (refereegranskat)abstract
- A formic acid biosensor for air monitoring has been evaluated using chemometric methods. Using experimental design eleven factors that could influence the performance of the biosensor were examined. The response matrices consisted of six parameters (steady state currents at three different formic acid concentrations and response rates during changes in formic acid concentrations) describing the performance of the biosensor. The data were evaluated using a combination of principal component analysis (PCA) and multiple linear regression (MLR). To confirm the conclusions from the PCA-MLR partial least squares (PLS) was also used. The most important factor for the biosensor performance was found to be the enzyme concentration. Using the information from the chemometric analyses the optimum operation conditions for the biosensor were determined. The steady state currents were increased by 18-30% and the initial two response rates increased by 47-89% compared with a biosensor that had not been optimised.
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| 569. |
- Sarkar, P., et al.
(författare)
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Electrochemical immunoassay for free prostate specific antigen (f-PSA) using magnetic beads
- 2008
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Ingår i: Electroanalysis. - : John Wiley andamp;amp; Sons, Ltd. - 1040-0397 .- 1521-4109. ; 20:13, s. 1414-1420
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Tidskriftsartikel (refereegranskat)abstract
- Prostate specific antigen (PSA) is a prominent marker for the prostate carcinoma. It is found in human blood in free (f-PSA) and complex forms. These two forms together are called total PSA (t-PSA). Estimation of both forms is essential to predict malignancy. In this study we report a unique and effective technique of electrochemical detection of f-PSA using magnetic beads on a three-electrode screen-printed sensor. A magnetic bead enzyme linked immunosorbent assay (ELISA) was performed in a cuvette. Following the immunoassay, magnetic beads were recovered by a magnetic concentrator and transferred on the working electrode of the 3-electrode assembly. The amperometric response, a measure of the amount of residual enzyme activity on the beads and hence the concentration of analyte in solution, was determined by addition of enzyme substrate. The device has a detection limit of less than0.1 ng mL(-1) f-PSA and a linear range of 0 to 1 ng mL(-1) f-PSA.
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| 570. |
- Schitter, Georg, et al.
(författare)
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Design and Modeling of a High-Speed AFM-Scanner
- 2007
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Ingår i: IEEE Transactions on Control Systems Technology. - 1558-0865. ; 15:5, s. 906-915
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Tidskriftsartikel (refereegranskat)abstract
- A new mechanical scanner design for a high-speed atomic force microscope (AFM) is presented and discussed in terms of modeling and control. The positioning range of this scanner is 13 mum in the X- and Y-directions and 4.3 mum in the vertical direction. The lowest resonance frequency of this scanner is above 22 kHz. This paper is focused on the vertical direction of the scanner, being the crucial axis of motion with the highest precision and bandwidth requirements for gentle imaging with the AFM. A second- and a fourth-order mathematical model of the scanner are derived that allow new insights into important design parameters. Proportional-integral (Pl)-feedback control of the high-speed scanner is discussed and the performance of the new AFM is demonstrated by imaging a calibration grating and a biological sample at 8 frames/s.
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