535 research outputs found
Entanglement and methods for its quantification
Abstract. The aim of this thesis is to introduce the quantum phenomena called entanglement and theoretical models for quantifying it in the context of mainly bipartite systems. The approach taken is in terms of quantum information and the thesis discusses the uses of entanglement in this field
Suomen metsät 2011 - Kestävän metsätalouden kriteereihin ja indikaattoreihin perustuen
Julkaisu on päivitetty ja uudelleen muokattu versio aiemmin julkaistuista Suomen metsät raporteista. Maa- ja metsätalousministeriön asettama kansainvälisen metsäpolitiikan neuvottelukunta on käsitellyt julkaisun sisältöä
Diffusion bonding of Cu atoms with molecular dynamics simulations
Diffusion bonding of copper disks is an important step during the assembly of accelerating structures -the main components of power radio-frequency linear accelerators-. During the diffusion bonding copper disks are subjected to pressure at high temperatures. Finding the optimal combination of pressure and temperature will enable an accurate design of manufacturing workflow and machining tolerances. However, required optimization is not possible without good understanding of physical processes developed in copper under pressure and high temperature. In this work, the combined effect of temperature and pressure on closing time of inter-granular voids is examined by means of molecular dynamics simulations. In particular, a nano-void of 3.5–5.5 nm in diameter representing a peak and a valley of surface roughness facing each other was inserted between identical copper grains. The simulations performed at T = 1250 K, the temperature used in experimental condition, and the 300–800 MPa pressure range indicated the dislocation-mediated enhancement of atomic diffusion leading to full void closure.Peer reviewe
The GTC exoplanet transit spectroscopy survey. VI. A spectrally-resolved Rayleigh scattering slope in GJ 3470b
Aims. As a sub-Uranus-mass low-density planet, GJ 3470b has been found to
show a flat featureless transmission spectrum in the infrared and a tentative
Rayleigh scattering slope in the optical. We conducted an optical transmission
spectroscopy project to assess the impacts of stellar activity and to determine
whether or not GJ 3470b hosts a hydrogen-rich gas envelop. Methods. We observed
three transits with the low-resolution OSIRIS spectrograph at the 10.4 m Gran
Telescopio Canarias, and one transit with the high-resolution UVES spectrograph
at the 8.2 m Very Large Telescope. Results. From the high-resolution data, we
find that the difference of the Ca II H+K lines in- and out-of-transit is only
0.67 +/- 0.22%, and determine a magnetic filling factor of about 10-15%. From
the low-resolution data, we present the first optical transmission spectrum in
the 435-755 nm band, which shows a slope consistent with Rayleigh scattering.
Conclusions. After exploring the potential impacts of stellar activity in our
observations, we confirm that Rayleigh scattering in an extended
hydrogen/helium atmosphere is currently the best explanation. Further
high-precision observations that simultaneously cover optical and infrared
bands are required to answer whether or not clouds and hazes exist at
high-altitude.Comment: 12 pages, 11 figures, accepted for publication in A&
Monitoring young associations and open clusters with Kepler in two-wheel mode
We outline a proposal to use the Kepler spacecraft in two-wheel mode to
monitor a handful of young associations and open clusters, for a few weeks
each. Judging from the experience of similar projects using ground-based
telescopes and the CoRoT spacecraft, this program would transform our
understanding of early stellar evolution through the study of pulsations,
rotation, activity, the detection and characterisation of eclipsing binaries,
and the possible detection of transiting exoplanets. Importantly, Kepler's wide
field-of-view would enable key spatially extended, nearby regions to be
monitored in their entirety for the first time, and the proposed observations
would exploit unique synergies with the GAIA ESO spectroscopic survey and, in
the longer term, the GAIA mission itself. We also outline possible strategies
for optimising the photometric performance of Kepler in two-wheel mode by
modelling pixel sensitivity variations and other systematics.Comment: 10 pages, 6 figures, white paper submitted in response to NASA call
for community input for alternative science investigations for the Kepler
spacecraf
Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry
The study of young Sun-like stars is of fundamental importance to understand
the magnetic activity and rotational evolution of the Sun. Space-borne
photometry by the Kepler telescope provides unprecedented datasets to
investigate these phenomena in Sun-like stars. We present a new analysis of the
entire Kepler photometric time series of the moderately young Sun-like star
Kepler-17 that is accompanied by a transiting hot Jupiter. We applied a
maximum-entropy spot model to the long-cadence out-of-transit photometry of the
target to derive maps of the starspot filling factor versus the longitude and
the time. These maps are compared to the spots occulted during transits to
validate our reconstruction and derive information on the latitudes of the
starspots. We find two main active longitudes on the photosphere of Kepler-17,
one of which has a lifetime of at least days, although with a
varying level of activity. The latitudinal differential rotation is of solar
type, that is, with the equator rotating faster than the poles. We estimate a
minimum relative amplitude between
and , our determination being affected by the finite lifetime of
individual starspots and depending on the adopted spot model parameters. We
find marginal evidence of a short-term intermittent activity cycle of
days and an indication of a longer cycle of days characterized by an
equatorward migration of the mean latitude of the spots as in the Sun. The
rotation of Kepler-17 is likely to be significantly affected by the tides
raised by its massive close-by planet. We confirm the reliability of
maximum-entropy spot models to map starspots in young active stars and
characterize the activity and differential rotation of this young Sun-like
planetary host.Comment: Accepted by Astronomy and Astrophysics - 22 pages, 29 figure, 1
table, 2 appendixe
Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star
We report the spectroscopic confirmation of the Kepler object of interest
KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old
solar-like star every 2.7 days. Our analysis is the first to combine the full
Kepler photometry (quarters 1-17) with high-precision radial velocity
measurements taken with the FIES spectrograph at the Nordic Optical Telescope.
We simultaneously modelled the photometric and spectroscopic data-sets using
Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that
the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits
quarter-to-quarter systematic variations of the transit depth, with a
peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every
four quarters. We attributed these systematics to an incorrect assessment of
the quarterly variation of the crowding metric. The host star KOI-183 is a G4
dwarf with M_\rm{Sun},
R_\rm{Sun}, K, dex, and with
an age of Gyr. The planet KOI-183b has a mass of
M and a radius of
R, yielding a planetary bulk
density of g/cm. The radius of KOI-183b
is consistent with both theoretical models for irradiated coreless giant
planets and expectations based on empirical laws. The inclination of the
stellar spin axis suggests that the system is aligned along the line of sight.
We detected a tentative secondary eclipse of the planet at a 2-
confidence level ( ppm) and found that the
orbit might have a small non-zero eccentricity of .
With a Bond albedo of , KOI-183b is one of the
gas-giant planets with the lowest albedo known so far.Comment: 13 pages, 13 figures, 5 tables. Accepted for publication in A&A.
Planet designation changed from KOI-183b to Kepler-423
Sustainability of cellulose dissolution and regeneration in 1,5-diazabicyclo[4.3.0]non-5-enium acetate : a batch simulation of the IONCELL-F process
The recyclability of 1,5-diazabicyclo[4.3.0] non-5-enium acetate ([DBNH][OAc]), as a direct dissolution solvent for cellulose, was evaluated during laboratory scale recycling trials. The main objective was to simulate the conditions of a spinning bath from a Lyocell-type air-gap spinning process, called the IONCELL-F process. The saline solution was then concentrated, recycled and reused as many times as possible before cellulose dissolution was no longer possible. The chemical compositions of the ionic liquid and pulp were recorded throughout the experiments. The results of the experiments showed that [DBNH][OAc] can be recycled from aqueous media with an average recovery rate of 95.6 wt% using basic laboratory equipment, without any further process intensification or optimisation. The recycling of the ionic liquid did not change the chemical composition or degree of polymerisation of the recovered pulp but the colour of the regenerated pulps gradually darkened as the recycling times increased. The ionic liquid was found to hydrolyse 6.0-13.6 mol% per cycle, under these conditions. The build-up of the hydrolysis product, 3-( aminopropyl)-2-pyrrolidonium acetate, killed the dissolution feature at between 30.6-45.6 wt% hydrolysis product. The enzymatic digestibility of the regenerated pulp samples was studied with both a monocomponent endoglucanase and a cellulase mixture. The amount of residual [DBNH][OAc] in the regenerated pulps was determined, by both NMR and capillary electrophoresis. Although hydrolysis of the ionic liquid occurs, this study clearly shows potential for industrial application, with appropriate process equipment and recycling conditions.Peer reviewe
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