6,490 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
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
The Makeenko-Migdal equation for Yang-Mills theory on compact surfaces
We prove the Makeenko-Migdal equation for two-dimensional Euclidean
Yang-Mills theory on an arbitrary compact surface, possibly with boundary. In
particular, we show that two of the proofs given by the first, third, and
fourth authors for the plane case extend essentially without change to compact
surfaces.Comment: Final version, minor typographical corrections. To appear in Comm.
Math. Phy
Atomic data from the Iron Project.XLIII. Transition probabilities for Fe V
An extensive set of dipole-allowed, intercombination, and forbidden
transition probabilities for Fe V is presented. The Breit-Pauli R-matrix (BPRM)
method is used to calculate 1.46 x 10^6 oscillator strengths for the allowed
and intercombination E1 transitions among 3,865 fine-structure levels dominated
by configuration complexes with n <= 10 and l <= 9. These data are complemented
by an atomic structure configuration interaction (CI) calculation using the
SUPERSTRUCTURE program for 362 relativistic quadrupole (E2) and magnetic dipole
(M1) transitions among 65 low-lying levels dominated by the 3d^4 and 3d^ 4s
configurations. Procedures have been developed for the identification of the
large number of fine-structure levels and transitions obtained through the BPRM
calculations. The target ion Fe VI is represented by an eigenfunction expansion
of 19 fine-structure levels of 3d^3 and a set of correlation configurations. Fe
V bound levels are obtained with angular and spin symmetries SL\pi and J\pi of
the (e + Fe VI) system such that 2S+1 = 5,3,1, L <= 10, J <= 8 of even and odd
parities. The completeness of the calculated dataset is verified in terms of
all possible bound levels belonging to relevant LS terms and transitions in
correspondence with the LS terms. The fine-structure averaged relativistic
values are compared with previous Opacity Project LS coupling data and other
works. The 362 forbidden transition probabilities considerably extend the
available data for the E2 and M1 transtions, and are in good agreement with
those computed by Garstang for the 3d^4 transitions.Comment: 19 pages, 1 figure. This paper marks the beginning of a large-scale
effort of ab initio atomic calculations that should eventually lead to
re-calculation of accurate iron opacities. Astron. Astrophys. Suppl. Ser. (in
press
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
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
Informe de investigacion 1997
Les activités du Département de recherches de la Gremial de Huleros ont été menées dans les domaines suivants : ressources génétiques, pratiques culturales, phytopathologie et exploitation de l'hévéa. L'acquisition de la plantation Santa Ana Mixpiya a permis d'établir un centre d'expérimentation. Les principaux résultats obtenus en 1997 dans les différentes stations sont présentés dans ce rapport annuel. Des jardins clonaux ont été établis pour l'évaluation du matériel génétique et pour la multiplication du matériel végétal. La collection de matériel génétique s'est également agrandie. L'évaluation des clones a été faite dans des champs à grande et à petite échelle. Les observations ont porté sur leurs caractéristiques morphologiques et leur sensibilité à #Microcyclus ulei#. Pour étudier l'exploitation de l'hévéa, différents systÚmes de saignée avec ou sans stimulation ont été étudiés. En phytopathologie, on a expérimenté plusieurs traitements contre l'encoche sÚche. Pour la production de plants greffés, on a évalué les caractéristiques agronomiques de semences d'origine différente, ainsi que leur sensibilité à #Microcyclus ulei# afin de les utiliser comme porte-greffes. Des essais de fertilisation (azote, phosphore et potassium) ont été menés sur plusieurs plantations. Tous les protocoles expérimentaux sont donnés en annexes
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