4,412 research outputs found
Habitability of the Goldilocks Planet Gliese 581g: Results from Geodynamic Models
Aims: In 2010, detailed observations have been published that seem to
indicate another super-Earth planet in the system of Gliese 581 located in the
midst of the stellar climatological habitable zone. The mass of the planet,
known as Gl 581g, has been estimated to be between 3.1 and 4.3 Earth masses. In
this study, we investigate the habitability of Gl 581g based on a previously
used concept that explores its long-term possibility of photosynthetic biomass
production, which has already been used to gauge the principal possibility of
life regarding the super-Earths Gl 581c and Gl 581d. Methods: A thermal
evolution model for super-Earths is used to calculate the sources and sinks of
atmospheric carbon dioxide. The habitable zone is determined by the limits of
photosynthetic biological productivity on the planetary surface. Models with
different ratios of land / ocean coverage are pursued. Results: The maximum
time span for habitable conditions is attained for water worlds at a position
of about 0.14+/-0.015 AU, which deviates by just a few percent (depending on
the adopted stellar luminosity) from the actual position of Gl 581g, an
estimate that does however not reflect systematic uncertainties inherent in our
model. Therefore, in the framework of our model an almost perfect Goldilock
position is realized. The existence of habitability is found to critically
depend on the relative planetary continental area, lending a considerable
advantage to the possibility of life if Gl 581g's ocean coverage is relatively
high. Conclusions: Our results are a further step toward identifying the
possibility of life beyond the Solar System, especially concerning super-Earth
planets, which appear to be more abundant than previously surmised.Comment: 5 pages, 3 figures, 1 table; in pres
Genetic control of sensory neuron diversification
The somatosensory system of vertebrates transmits information from external and
internal environments to the brain. This information relates to various modalities such
as touch, temperature, itch and pain. The different modalities require a variety of
subtypes of sensory neurons, tuned to detect and transmit specific stimuli. Each of these
subtypes expresses a specific set of proteins to serve this highly specialized function
and to control the cell type specific gene expression. This thesis explores the
development and diversity of sensory neuronal subtypes in the dorsal root ganglion
(DRG) of the mouse.
In the five studies included in this thesis, we have investigated the roles of several
genes in the development and function of sensory neurons. In Paper I, the focus is on a
transcription factor, Cux2. We described that its expression is limited to large, early
born neurons, which are mainly mechanosensitive, including a lineage of poorly
characterized large TrkA+ neurons. We found no evidence that Cux2 would affect
neuronal subtype specification, but instead we showed that it contributes to regulation
of mechanosensation.
Transcription factors themselves are closely regulated in order to be expressed at the
right time and place in development. In Paper II we identified that FGF signaling from
earlier-born neurons triggers the upregulation of the transcription factor Runx1 early in
the development of the thermo-nociceptive lineage. Signaling by soluble factors is also
involved in the late stages of maturation of neuronal identity, as we demonstrated in
Paper IV for the Ret receptor. We reported that the loss of Ret expression caused a
hypersensitivity to several sensory modalities and showed that Ret is necessary for the
expression of a large number of ion channels and receptors. One of the Ret-regulated
genes was the cold receptor TrpM8. In Paper III we showed that TrpM8 expression was
confined to a small population of neurons lacking coexpression with most subtype
markers. We also characterized the developmental expression of all members of the
TrpM family in the DRG and showed that most of them were expressed with individual
temporal patterns.
Finally, in Paper V, we characterized the expression pattern of the enzyme Tyrosine
hydroxylase (TH), the function of which is unknown in the DRG. TH is central in the
catecholamine synthesis pathway, but whether or not that pathway is active in the DRG
is uncertain. We showed that neurons expressing TH belong to the Ret+ population and
that the expression of TH depends on Runx1 but not Ret.
In summary, we have described a number of novel sensory neuron populations as well
as genetic mechanisms governing development and diversification of specific
populations. These results lead to a better understanding of the somatosensory system
and hopefully in extension to better treatments for patients with somatosensory
disturbances such as chronic pain conditions
The habitability of super-Earths in Gliese 581
Aims: The planetary system around the M star Gliese 581 consists of a hot
Neptune (Gl 581b) and two super-Earths (Gl 581c and Gl 581d). The habitability
of this system with respect to the super-Earths is investigated following a
concept that studies the long-term possibility of photosynthetic biomass
production on a dynamically active planet. Methods: A thermal evolution model
for a super-Earth is used to calculate the sources and sinks of atmospheric
carbon dioxide. The habitable zone is determined by the limits of biological
productivity on the planetary surface. Models with different ratios of land /
ocean coverage are investigated. Results: The super-Earth Gl 581c is clearly
outside the habitable zone, since it is too close to the star. In contrast, Gl
581d is a tidally locked habitable super-Earth near the outer edge of the
habitable zone. Despite the adverse conditions on this planet, at least some
primitive forms of life may be able to exist on its surface.Therefore, Gl 581d
is an interesting target for the planned TPF/Darwin missions to search for
biomarkers in planetary atmospheres.Comment: 6 pages, 4 figures, 2 table
Habitability of Super-Earths: Gliese 581c and 581d
The unexpected diversity of exoplanets includes a growing number of
super-Earth planets, i.e., exoplanets with masses smaller than 10 Earth masses.
Unlike the larger exoplanets previously found, these smaller planets are more
likely to have a similar chemical and mineralogical composition to the Earth.
We present a thermal evolution model for super-Earth planets to identify the
sources and sinks of atmospheric carbon dioxide. The photosynthesis-sustaining
habitable zone (pHZ) is determined by the limits of biological productivity on
the planetary surface. We apply our model to calculate the habitability of the
two super-Earths in the Gliese 581 system. The super-Earth Gl 581c is clearly
outside the pHZ, while Gl 581d is at the outer edge of the pHZ. Therefore it
could at least harbor some primitive forms of life.Comment: 3 pages, 1 figure; submitted to: Exoplanets: Detection, Formation and
Dynamics, IAU Symposium 249, eds. Y.-S. Sun, S. Ferraz-Mello, and J.-L. Zhou
(Cambridge: Cambridge University Press
Origin and roles of a strong electron-phonon interaction in cuprate oxide superconductors
A strong electron-phonon interaction arises from the modulation of the
superexchange interaction by phonons. As is studied in Phys. Rev. B 70, 184514
(2004), Cu-O bond stretching modes can be soft around (pm pi/a, 0) and (0, pm
pi/a), with a the lattice constant of CuO_2 planes. In the critical region of
SDW, where antiferromagnetic spin fluctuations are developed around nesting
wave numbers Q of the Fermi surface, the stretching modes can also be soft
around 2Q. Almost symmetric energy dependences of the 2Q component of the
density of states, which are observed in the so called stripe and checker-board
states, cannot be explained by CDW with 2Q following the complete softening of
the 2Q modes, but they can be explained by a second-harmonic effect of SDW with
Q. The strong electron-phonon interaction can play no or only a minor role in
the occurrence of superconductivity.Comment: 5 pages, 1 fugur
Intrinsic and structural isotope effects in Fe-based superconductors
The currently available results of the isotope effect on the superconducting
transition temperature T_c in Fe-based high-temperature superconductors (HTS)
are highly controversial. The values of the Fe isotope effect (Fe-IE) exponent
\alpha_Fe for various families of Fe-based HTS were found to be as well
positive, as negative, or even be exceedingly larger than the BCS value
\alpha_BCS=0.5. Here we demonstrate that the Fe isotope substitution causes
small structural modifications which, in turn, affect T_c. Upon correcting the
isotope effect exponent for these structural effects, an almost unique value of
\alpha~0.35-0.4 is observed for at least three different families of Fe-based
HTS.Comment: 4 pages, 2 figure
Habitability of Super-Earth Planets around Main-Sequence Stars including Red Giant Branch Evolution: Models based on the Integrated System Approach
In a previous study published in Astrobiology, we focused on the evolution of
habitability of a 10 M_E super-Earth planet orbiting a star akin to the Sun.
This study was based on a concept of planetary habitability in accordance to
the integrated system approach that describes the photosynthetic biomass
production taking into account a variety of climatological, biogeochemical, and
geodynamical processes. In the present study, we pursue a significant
augmentation of our previous work by considering stars with zero-age main
sequence masses between 0.5 and 2.0 M_sun with special emphasis on models of
0.8, 0.9, 1.2 and 1.5 M_sun. Our models of habitability consider again
geodynamical processes during the main-sequence stage of these stars as well as
during their red giant branch evolution. Pertaining to the different types of
stars, we identify so-called photosynthesis-sustaining habitable zones (pHZ)
determined by the limits of biological productivity on the planetary surface.
We obtain various sets of solutions consistent with the principal possibility
of life. Considering that stars of relatively high masses depart from the
main-sequence much earlier than low-mass stars, it is found that the biospheric
life-span of super-Earth planets of stars with masses above approximately 1.5
M_sun is always limited by the increase in stellar luminosity. However, for
stars with masses below 0.9 M_sun, the life-span of super-Earths is solely
determined by the geodynamic time-scale. For central star masses between 0.9
and 1.5 M_sun, the possibility of life in the framework of our models depends
on the relative continental area of the super-Earth planet.Comment: 25 pages, 6 figures, 2 tables; submitted to: International Journal of
Astrobiolog
Theories of developmental dyslexia: Insights from a multiple case study of dyslexic adults
A multiple case study was conducted in order to assess three leading theories of developmental dyslexia: the phonological, the magnocellular (auditory and visual) and the cerebellar theories. Sixteen dyslexic and 16 control university students were administered a full battery of psychometric, phonological, auditory, visual and cerebellar tests. Individual data reveal that all 16 dyslexics suffer from a phonological deficit, 10 from an auditory deficit, 4 from a motor deficit, and 2 from a visual magnocellular deficit. Results suggest that a phonological deficit can appear in the absence of any other sensory or motor disorder, and is sufficient to cause a literacy impairment, as demonstrated by 5 of the dyslexics. Auditory disorders, when present, aggravate the phonological deficit, hence the literacy impairment. However, auditory deficits cannot be characterised simply as rapid auditory processing problems, as would be predicted by the magnocellular theory. Nor are they restricted to speech. Contrary to the cerebellar theory, we find little support for the notion that motor impairments, when found, have a cerebellar origin, or reflect an automaticity deficit. Overall, the present data support the phonological theory of dyslexia, while acknowledging the presence of additional sensory and motor disorders in certain individuals
γ-H2AX foci as in vivo effect biomarker in children emphasize the importance to minimize x-ray doses in paediatric CT imaging
Objectives: Investigation of DNA damage induced by CT x-rays in paediatric patients versus patient dose in a multicentre setting.
Methods: From 51 paediatric patients (median age, 3.8 years) who underwent an abdomen or chest CT examination in one of the five participating radiology departments, blood samples were taken before and shortly after the examination. DNA damage was estimated by scoring gamma-H2AX foci in peripheral blood T lymphocytes. Patient-specific organ and tissue doses were calculated with a validated Monte Carlo program. Individual lifetime attributable risks (LAR) for cancer incidence and mortality were estimated according to the BEIR VII risk models.
Results: Despite the low CT doses, a median increase of 0.13 gamma-H2AX foci/cell was observed. Plotting the induced gamma-H2AX foci versus blood dose indicated a low-dose hypersensitivity, supported also by an in vitro dose-response study. Differences in dose levels between radiology centres were reflected in differences in DNA damage. LAR of cancer mortality for the paediatric chest CT and abdomen CT cohort was 0.08 and 0.13% respectively.
Conclusion: CT x-rays induce DNA damage in paediatric patients even at low doses and the level of DNA damage is reduced by application of more effective CT dose reduction techniques and paediatric protocols
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