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Träfflista för sökning "WFRF:(Goetz Walter) "

Sökning: WFRF:(Goetz Walter)

  • Resultat 1-7 av 7
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  • Falk, Sven, et al. (författare)
  • Brain area-specific effect of TGF-beta signaling on Wnt-dependent neural stem cell expansion
  • 2008
  • Ingår i: Cell Stem Cell. - : Cell Press. - 1934-5909. ; 2:5, s. 472-483
  • Tidskriftsartikel (refereegranskat)abstract
    • Regulating the choice between neural stem cell maintenance versus differentiation determines growth and size of the developing brain. Here we identify TGF-beta signaling as a crucial factor controlling these processes. At early developmental stages, TGF-beta signal activity is localized close to the ventricular surface of the neuroepithelium. In the midbrain, but not in the forebrain, Tgfbr2 ablation results in ectopic expression of Wnt1/beta-catenin and FGF8, activation of Wnt target genes, and increased proliferation and horizontal expansion of neuroepithelial cells due to shortened cell-cycle length and decreased cell-cycle exit. Consistent with this phenotype, self-renewal of mutant neuroepithelial stem cells is enhanced in the presence of FGF and requires Wnt signaling. Moreover, TGF-beta signal activation counteracts Wnt-incluced proliferation of midbrain neuroepithelial cells. Thus, TGF-beta signaling controls the size of a specific brain area, the dorsal midbrain, by antagonizing canonical Wnt signaling and negatively regulating self-renewal of neuroepithelial stem cells.
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  • Goesmann, Fred, et al. (författare)
  • The Mars Organic Molecule Analyzer (MOMA) Instrument : Characterization of Organic Material in Martian Sediments
  • 2017
  • Ingår i: Astrobiology. - : Mary Ann Liebert Inc.. - 1531-1074 .- 1557-8070. ; 17:6-7, s. 655-685
  • Tidskriftsartikel (refereegranskat)abstract
    • The Mars Organic Molecule Analyzer (MOMA) instrument onboard the ESA/Roscosmos ExoMars rover (to launch in July, 2020) will analyze volatile and refractory organic compounds in martian surface and subsurface sediments. In this study, we describe the design, current status of development, and analytical capabilities of the instrument. Data acquired on preliminary MOMA flight-like hardware and experimental setups are also presented, illustrating their contribution to the overall science return of the mission..
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  • Hamilton, Victoria E., et al. (författare)
  • Observations and preliminary science results from the first 100 sols of MSL Rover Environmental Monitoring Station ground temperature sensor measurements at Gale Crater
  • 2014
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 119:4, s. 745-770
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe preliminary results from the first 100 sols of ground temperature measurements along the Mars Science Laboratory's traverse from Bradbury Landing to Rocknest in Gale. The ground temperature data show long-term increases in mean temperature that are consistent with seasonal evolution. Deviations from expected temperature trends within the diurnal cycle are observed and may be attributed to rover and environmental effects. Fits to measured diurnal temperature amplitudes using a thermal model suggest that the observed surfaces have thermal inertias in the range of 265-375?J m-2 K-1 s-1/2, which are within the range of values determined from orbital measurements and are consistent with the inertias predicted from the observed particle sizes on the uppermost surface near the rover. Ground temperatures at Gale Crater appear to warm earlier and cool later than predicted by the model, suggesting that there are multiple unaccounted for physical conditions or processes in our models. Where the Mars Science Laboratory (MSL) descent engines removed a mobile layer of dust and fine sediments from over rockier material, the diurnal temperature profile is closer to that expected for a homogeneous surface, suggesting that the mobile materials on the uppermost surface may be partially responsible for the mismatch between observed temperatures and those predicted for materials having a single thermal inertia. Models of local stratigraphy also implicate thermophysical heterogeneity at the uppermost surface as a potential contributor to the observed diurnal temperature cycle. Key Points Diurnal ground temperatures vary with location Diurnal temperature curves are not well matched by a homogeneous thermal model GTS data are consistent with a varied stratigraphy and thermophysical properties.
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  • Martin-Torres, Javier, et al. (författare)
  • Transient liquid water and water activity at Gale crater on Mars
  • 2015
  • Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 8:5, s. 357-361
  • Tidskriftsartikel (refereegranskat)abstract
    • Water is a requirement for life as we know it1. Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars2, in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover3, 4, lowers the freezing temperature of water5. Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence6, 7. Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere–soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms8. Perchlorates are widespread on the surface of Mars9 and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.
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7.
  • Rennó, Nilton O., et al. (författare)
  • Possible physical and thermodynamical evidence for liquid water at the Phoenix landing site
  • 2009
  • Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 114:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze-thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this article provide significant new insights into the behavior of water on Mars.
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