53 research outputs found
Tidal Constraints on Planetary Habitability
We review how tides may impact the habitability of terrestrial-like planets.
If such planets form around low-mass stars, then planets in the circumstellar
habitable zone will be close enough to their host stars to experience strong
tidal forces. We discuss 1) decay of semi-major axis, 2) circularization of
eccentric orbits, 3) evolution toward zero obliquity, 4) fixed rotation rates
(not necessarily synchronous), and 5) internal heating. We briefly describe
these effects using the example of a 0.25 solar mass star with a 10 Earth-mass
companion. We suggest that the concept of a habitable zone should be modified
to include the effects of tides.Comment: 6 pages, 3 figures. Proceedings submitted to "Pathways Towards
Habitable Planets" Symposium (eds.: D. Gelino, V. Coude du Foresto, I. Ribas
RoSETZ: Roman Survey of the Earth Transit Zone -- a SETI-optimized survey for habitable-zone exoplanets
In this White Paper for Nancy Grace Roman Space Telescope (Roman) science, we
propose the Roman Survey of the Earth Transit Zone (RoSETZ), a transit search
for rocky planets within the habitable zones (HZs) of stars located within the
Earth Transit Zone (ETZ). The ETZ holds special interest in the search for
extra-terrestrial intelligence (SETI) - observers on planets within the ETZ can
see Earth as a transiting planet. RoSETZ would augment the Roman Galactic Bulge
Time Domain Survey (GBTDS) as an additional field located ~degrees away
from other GBTDS fields. Our simulations show that RoSETZ alone can find from
120 to 630 Earth-sized HZ planets around K- and M-type hosts, with the range
reflecting different survey design assumptions. These yields are 5-20 times the
number currently known. Such a sample will transform our knowledge of
``Eta-Earth'' () -- the occurrence of Earth-sized HZ planets --
and would be the first catalogue of exoplanets selected in a manner optimized
according to the Mutual Detectability targetted-SETI strategy. If it can be
accommodated alongside the existing GBTDS design, we favour a RoSETZ-Max design
that is observed for the duration of the GBTDS. If not, we show that a
slimmed-down RoSETZ-Lite design, occupying two GBTDS seasons, would not
significantly impact overall GBTDS exoplanet yields, even if time allocated to
it had to come from time allocations to other fields. We argue that the angular
separation of RoSETZ from other GBTDS fields permits self-calibration of
systematic uncertainties that would otherwise hamper exoplanet demographic
modelling of both microlensing and transit datasets. Other science possible
with RoSETZ data include studies of small solar system bodies and high
resolution 3D extinction mapping.Comment: 20 pages. Submission to the NASA Roman Core Community Surveys White
Paper Cal
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Is green infrastructure an effective climate adaptation strategy for conserving biodiversity? A case study with the great crested newt
Electrical and Optical Properties of Amorphous SnO2:Ta Films, Prepared by DC and RF Magnetron Sputtering: A Systematic Study of the Influence of the Type of the Reactive Gas
By reactive magnetron sputtering from a ceramic SnO2:Ta target onto unheated substrates, X-ray amorphous SnO:Ta films were prepared in gas mixtures of Ar/O2(N2O, H2O). The process windows, where the films exhibit the lowest resistivity values, were investigated as a function of the partial pressure of the reactive gases O2, N2O and H2O. We found that all three gases lead to the same minimum resistivity, while the width of the process window is broadest for the reactive gas H2O. While the amorphous films were remarkably conductive (ρ ≈ 5 × 10−3 Ωcm), the films crystallized by annealing at 500 °C exhibit higher resistivities due to grain boundary limited conduction. For larger film thicknesses (d ≳ 150 nm), crystallization occurs already during the deposition, caused by the substrate temperature increase due to the energy influx from the condensing film species and from the plasma (ions, electrons), leading to higher resistivities of these films. The best amorphous SnO2:Ta films had a resistivity of lower than 4 × 10−3 Ωcm, with a carrier concentration of 1.1 × 1020 cm−3, and a Hall mobility of 16 cm2/Vs. The sheet resistance was about 400 Ω/â–¡ for 100 nm films and 80 Ω/â–¡ for 500 nm thick films. The average optical transmittance from 500 to 1000 nm is greater than 76% for 100 nm films, where the films, deposited with H2O as reactive gas, exhibit even a slightly higher transmittance of 80%. These X-ray amorpous SnO2:Ta films can be used as low-temperature prepared transparent and conductive protection layers, for instance, to protect semiconducting photoelectrodes for water splitting, and also, where appropriate, in combination with more conductive TCO films (ITO or ZnO)
Interaction of hydrogen with hafnium dioxide grown on silicon dioxide by the atomic layer deposition technique
The electrical and structural properties of thin hafnia films grown by the atomic layer deposition technique were investigated before and after different annealing steps as well as after a dc H plasma treatment. By using the nuclear reaction analysis, the authors demonstrated that high concentrations of hydrogen (about 1–2 at. %) could be observed even in as-grown hafnia layers. An additional hydrogenation of the samples with atomic H led to a significant shift of the flatband voltage. This shift could be explained by the introduction of positively charged H-related defects which were found to be stable at room temperature. By comparing the experimental findings with the theory and the data from muon spin spectroscopy, they tentatively ascribed these defects to interstitial H in HfO2
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