Atmospheric studies of habitability in the Gliese 581 system

The M-type star Gliese 581 is orbited by at least one terrestrial planet candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown that additional planets inside the habitable zone of GL 581 would be dynamically stable. Recently, two further planet candidates have been claimed, one of them in the habitable zone. In view of the ongoing search for planets around M stars which is expected to result in numerous detections of potentially habitable Super-Earths, we take the GL 581 system as an example to investigate such planets. In contrast to previous studies of habitability in the GL 581 system, we use a consistent atmospheric model to assess surface conditions and habitability. Furthermore, we perform detailed atmospheric simulations for a much larger subset of potential planetary and atmospheric scenarios than previously considered. A 1D radiative-convective atmosphere model is used to calculate temperature and pressure profiles of model atmospheres, which we assumed to be composed of molecular nitrogen, water, and carbon dioxide. In these calculations, key parameters such as surface pressure and CO2 concentration as well as orbital distance and planetary mass are varied. Results imply that surface temperatures above freezing could be obtained, independent of the here considered atmospheric scenarios, at an orbital distance of 0.117 AU. For an orbital distance of 0.146 AU, CO2 concentrations as low as 10 times the present Earth's value are sufficient to warm the surface above the freezing point of water. At 0.175 AU, only scenarios with CO2 concentrations of 5% and 95% were found to be habitable. Hence, an additional Super-Earth planet in the GL 581 system in the previously determined dynamical stability range would be considered a potentially habitable planet.Comment: 5 pages, 4 figures, accepted in Astronomy&Astrophysic

A Quantum Lovasz Local Lemma

The Lovasz Local Lemma (LLL) is a powerful tool in probability theory to show the existence of combinatorial objects meeting a prescribed collection of "weakly dependent" criteria. We show that the LLL extends to a much more general geometric setting, where events are replaced with subspaces and probability is replaced with relative dimension, which allows to lower bound the dimension of the intersection of vector spaces under certain independence conditions. Our result immediately applies to the k-QSAT problem: For instance we show that any collection of rank 1 projectors with the property that each qubit appears in at most $2^k/(e \cdot k)$ of them, has a joint satisfiable state. We then apply our results to the recently studied model of random k-QSAT. Recent works have shown that the satisfiable region extends up to a density of 1 in the large k limit, where the density is the ratio of projectors to qubits. Using a hybrid approach building on work by Laumann et al. we greatly extend the known satisfiable region for random k-QSAT to a density of $\Omega(2^k/k^2)$. Since our tool allows us to show the existence of joint satisfying states without the need to construct them, we are able to penetrate into regions where the satisfying states are conjectured to be entangled, avoiding the need to construct them, which has limited previous approaches to product states.Comment: 19 page

The extrasolar planet Gliese 581 d: a potentially habitable planet? (Corrigendum to arXiv:1009.5814)

We report here that the equation for H2O Rayleigh scattering was incorrectly stated in the original paper [arXiv:1009.5814]. Instead of a quadratic dependence on refractivity r, we accidentally quoted an r^4 dependence. Since the correct form of the equation was implemented into the model, scientific results are not affected.Comment: accepted to Astronomy&Astrophysic

Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

We investigate the detectability of atmospheric spectral features of Earth-like planets in the habitable zone (HZ) around M dwarfs with the future James Webb Space Telescope (JWST). We use a coupled 1D climate-chemistry-model to simulate the influence of a range of observed and modelled M-dwarf spectra on Earth-like planets. The simulated atmospheres served as input for the calculation of the transmission spectra of the hypothetical planets, using a line-by-line spectral radiative transfer model. To investigate the spectroscopic detectability of absorption bands with JWST we further developed a signal-to-noise ratio (S/N) model and applied it to our transmission spectra. High abundances of CH$_4$ and H$_2$O in the atmosphere of Earth-like planets around mid to late M dwarfs increase the detectability of the corresponding spectral features compared to early M-dwarf planets. Increased temperatures in the middle atmosphere of mid- to late-type M-dwarf planets expand the atmosphere and further increase the detectability of absorption bands. To detect CH$_4$, H$_2$O, and CO$_2$ in the atmosphere of an Earth-like planet around a mid to late M dwarf observing only one transit with JWST could be enough up to a distance of 4 pc and less than ten transits up to a distance of 10 pc. As a consequence of saturation limits of JWST and less pronounced absorption bands, the detection of spectral features of hypothetical Earth-like planets around most early M dwarfs would require more than ten transits. We identify 276 existing M dwarfs (including GJ 1132, TRAPPIST-1, GJ 1214, and LHS 1140) around which atmospheric absorption features of hypothetical Earth-like planets could be detected by co-adding just a few transits. We show that using transmission spectroscopy, JWST could provide enough precision to be able to partly characterise the atmosphere of Earth-like TESS planets around mid to late M dwarfs.Comment: 18 pages, 10 figure

Magnons in real materials from density-functional theory

We present an implementation of the adiabatic spin-wave dynamics of Niu and Kleinman. This technique allows to decouple the spin and charge excitations of a many-electron system using a generalization of the adiabatic approximation. The only input for the spin-wave equations of motion are the energies and Berry curvatures of many-electron states describing frozen spin spirals. The latter are computed using a newly developed technique based on constrained density-functional theory, within the local spin density approximation and the pseudo-potential plane-wave method. Calculations for iron show an excellent agreement with experiments.Comment: 1 LaTeX file and 1 postscript figur

Current in open quantum systems

We show that a dissipative current component is present in the dynamics generated by a Liouville-master equation, in addition to the usual component associated with Hamiltonian evolution. The dissipative component originates from coarse graining in time, implicit in a master equation, and needs to be included to preserve current continuity. We derive an explicit expression for the dissipative current in the context of the Markov approximation. Finally, we illustrate our approach with a simple numerical example, in which a quantum particle is coupled to a harmonic phonon bath and dissipation is described by the Pauli master equation.Comment: To appear in Phys. Rev. Let

Religious people only live longer in religious cultural contexts: A gravestone analysis.

Religious people live longer than non-religious people according to a staple of social science research. Yet, are those longevity benefits an inherent feature of religiosity? To find out, we coded gravestone inscriptions and imagery in order to assess the religiosity and longevity of 6,400 deceased people from religious and non-religious U.S. counties. We show that in religious cultural contexts, religious people lived 2.2 years longer than did non-religious people. In non-religious cultural contexts, however, religiosity conferred no such longevity benefits. Evidently, a longer life is not an inherent feature of religiosity. Instead, religious people only live longer in religious cultural contexts where religiosity is valued. Our study answers a fundamental question on the nature of religiosity and showcases the scientific potential of gravestone analyses

The role of a circumferential septal fiberotomy (CSF) in enhancing orthodontic stability- a randomized controlled clinical trial

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenInngangur: Mælt hefur verið með að gera fiberotomiu eftir tannréttingameðferð til að auka stöðugleika. Sú kenning var prófuð í þessari rannsókn. Efni og aðferðir: Níu einstaklingar sem voru að ljúka tannréttingameðferð voru valdir til að taka þátt. Neðri boginn var fjarlægður úr sporum, fiberotomia var framkvæmd í annarri hlið frá augntönn til miðframtannar en hin hliðin þjónaði hlutverki viðmiðunarhóps. Í byrjun og á 4 vikna fresti í allt að 6 mánuði voru tekin mát og ljósmyndir. Irregularity Index Little var notaður til að mæla þrengsli á módelum, en ljósmyndir af módelum voru skannaðar inn og tölvuforrit greindi allar breytingar sem urðu á tönnum á tímabilinu. Hliðrunarhreyfingar sem og snúningshreyfingar sem og breytingar á tannholdsindexum voru skráðar. Hvorug mælingaraðferðin sýndi marktækan mun á stöðugleika í þeirri hlið sem var skorin miðað við viðmiðunarhóp. Tannhold skaðaðist ekki við fiberotomiuna. Niðurstöður: Þar sem fiberotomia virðist ekki auka stöðugleika tanna eftir tannréttingameðferð, er ekki hægt að mæla með aðferðinni.Introduction: Circumferential septal fiberotomy (CSF) following orthodontic treatment has been propagated to improve stability and prevent relapse of tooth alignment. The hypothesis of no difference of performed CSF and controls was tested. Material and Methods: In 9 consecutively admitted patients at the end of orthodontic tooth alignment the lower archwire was removed. CSF was performed from canine to the central incisor on a randomly chosen side, while the contralateral side served as unsurgerized control. At baseline and every 4 weeks up to 6 months, study casts were taken and 1) analyzed using the Irregularity Index of Little and 2) photographed, traced and superimposed digitally. The translational and rotational movements of teeth as well as gingival parameters were analyzed as well. By using the II and by superimposing the tracings, no statistically significant differences were found between test (CSF) and control sides for any parameters. Moreover, CSF did not impinge on the gingival tissues. Conclusion: Since CSF did not improve stability of orthodontically aligned teeth nor prevent relapse during the healing phase of up to 6 months, CSF should not be recommended following orthodontic therapy. Key words: Fiberotomy, orthodontic treatment, stability, rotational relapse, gingival recession

Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy.

We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (Te-As), Ga vacancies (V-Ga), and Ga vacancy-donor complexes (V-Ga-Te-As). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy-donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a -3e charge state of V-Ga in bulk GaAs. (C) 2003 American Institute of Physics

Nitrogen use of a mixed tree crop plantation with a leguminous cover crop.

Study on two associated frut tree crops take up their N in comparison to a leguminous cover crop in an agroforestry system. Preliminar results showed the pueraria had the highest foliar N content followed by pupunha; cupuacu having less than the other two. One year after application, cupuacu took up more of the applied N in comparison to the total N uptake than pueraria and pupunha as seen from the high &15N values. The amount of 15N taken up in relation to dry matter equaled between the three species, since pueraria had a lot higher N contents. The other sampling dates showed the same tendency.bitstream/item/181065/1/ID-2600-2-45-52.pd