2,448 research outputs found
Electron impact excitations of S2 molecules
Low-energy electron impact excitations of S_2 molecules are studied using the
fixed-bond R-matrix method based on state-averaged complete active space SCF
orbitals. Integral cross sections are calculated for elastic electron collision
as well as impact excitation of the 7 lowest excited electronic states. Also,
differential cross sections are obtained for elastic collision and excitation
of the a^1 Delta_g, b^1 Sigma_g^+ and B^3 Sigma_u^- states. The integrated
cross section of optically allowed excitation of the B^3 Sigma_u^- state agrees
reasonably well with the available theoretical result.Comment: 12 pages, 3 figures. Chemical Physics Letters, in pres
Digital Literacy Key Performance Indicators for Sustainable Development
The concept of digital literacy has been defined in numerous ways over the last two decades to incorporate rapid technological changes, its versatility, and to bridge the global digital divide. Most approaches have been technology-centric with an inherent assumption of cultural and political neutrality of new media technologies. There are multiple hurdles in every stage of digital literacy implementation. The lack of solutions such as local language digital interfaces, locally relevant content, digital literacy training, the use of icons and audio excludes a large fraction of illiterate people. In this article, we analyse case studies targeted at under-connected people in sub-Saharan Africa and India that use digital literacy programmes to build knowledge and health literacy, solve societal problems and foster development. In India, we focus on notable initiatives undertaken in the domain of digital literacy for rural populations. In Sub-Saharan Africa, we draw from an original project in Kenya aiming at developing digital literacy for youth from low-income backgrounds. We further focus on Senegal, Mali, Burkina Faso and Tanzania, where field studies have been conducted on the use of digital technologies by low-literacy people and on how audio and icon-based interfaces and Internet lite standard could help them overcome their limitations. The main objective of this article is to identify key performance indicators (KPIs) in the context of digital literacy skills as one of the pillars for digital inclusion. We will learn how digital literacy programmes can be used to build digital literacy and how KPIs for sustainable development can be established. In the final discussion, we offer lessons learned from the case studies and further recommendation for stakeholders and decision-makers in the field of digital health literacy
Characterizing the Adaptive Optics Off-Axis Point-Spread Function - I: A Semi-Empirical Method for Use in Natural-Guide-Star Observations
Even though the technology of adaptive optics (AO) is rapidly maturing,
calibration of the resulting images remains a major challenge. The AO
point-spread function (PSF) changes quickly both in time and position on the
sky. In a typical observation the star used for guiding will be separated from
the scientific target by 10" to 30". This is sufficient separation to render
images of the guide star by themselves nearly useless in characterizing the PSF
at the off-axis target position. A semi-empirical technique is described that
improves the determination of the AO off-axis PSF. The method uses calibration
images of dense star fields to determine the change in PSF with field position.
It then uses this information to correct contemporaneous images of the guide
star to produce a PSF that is more accurate for both the target position and
the time of a scientific observation. We report on tests of the method using
natural-guide-star AO systems on the Canada-France-Hawaii Telescope and Lick
Observatory Shane Telescope, augmented by simple atmospheric computer
simulations. At 25" off-axis, predicting the PSF full width at half maximum
using only information about the guide star results in an error of 60%. Using
an image of a dense star field lowers this error to 33%, and our method, which
also folds in information about the on-axis PSF, further decreases the error to
19%.Comment: 29 pages, 9 figures, accepted for publication in the PAS
The evolution of the luminosity functions in the FORS Deep Field from low to high redshift: I. The blue bands
We use the very deep and homogeneous I-band selected dataset of the FORS Deep
Field (FDF) to trace the evolution of the luminosity function over the redshift
range 0.5 < z < 5.0. We show that the FDF I-band selection down to I(AB)=26.8
misses of the order of 10 % of the galaxies that would be detected in a K-band
selected survey with magnitude limit K(AB)=26.3 (like FIRES). Photometric
redshifts for 5558 galaxies are estimated based on the photometry in 9 filters
(U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A
comparison with 362 spectroscopic redshifts shows that the achieved accuracy of
the photometric redshifts is (Delta z / (z_spec+1)) < 0.03 with only ~ 1 %
outliers. This allows us to derive luminosity functions with a reliability
similar to spectroscopic surveys. In addition, the luminosity functions can be
traced to objects of lower luminosity which generally are not accessible to
spectroscopy. We investigate the evolution of the luminosity functions
evaluated in the restframe UV (1500 Angstroem and 2800 Angstroem), u', B, and
g' bands. Comparison with results from the literature shows the reliability of
the derived luminosity functions. Out to redshifts of z ~ 2.5 the data are
consistent with a slope of the luminosity function approximately constant with
redshift, at a value of -1.07 +- 0.04 in the UV (1500 Angstroem, 2800
Angstroem) as well as u', and -1.25 +- 0.03 in the blue (g', B). We do not see
evidence for a very steep slope (alpha < -1.6) in the UV at z ~ 3.0 and z ~ 4.0
favoured by other authors. There may be a tendency for the faint-end slope to
become shallower with increasing redshift but the effect is marginal. We find a
brightening of M_star and a decrease of Phi_star with redshift for all analyzed
wavelengths. [abridged]Comment: 30 pages, re-submitted to A&A after referee comments have been taken
into account, full-resolution version available at
http://www.usm.uni-muenchen.de/people/gabasch/publications/gabasch_lfblue.p
Lyman alpha emission in high-redshift galaxies
A significant fraction of the high-redshift galaxies show strong Lyman
emission lines. For redshifts z>5, most known galaxies belong to this class.
However, so far not much is known about the physical structure and nature of
these objects. Our aim is to analyse the Lyman alpha emission in a sample of
high-redshift UV-continuum selected galaxies and to derive the physical
conditions that determine the Lyman alpha profile and the line strength.
VLT/FORS spectra with a resolution of R ~ 2000 of 16 galaxies in the redshift
range of z = 2.7 to 5 are presented. The observed Lyman alpha profiles are
compared with theoretical models. The Lyman alpha lines range from pure
absorption (EW = -17 Angstroem) to strong emission (EW = 153 Angstroem). Most
Lyman alpha emission lines show an asymmetric profile, and three galaxies have
a double-peaked profile. Both types of profiles can be explained by a uniform
model consisting of an expanding shell of neutral and ionised hydrogen around a
compact starburst region. The broad, blueshifted, low-ionisation interstellar
absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of
these lines are found to be determined in part by the velocity dispersion of
the outflowing medium. We find star-formation rates of these galaxies ranging
from SFR(UV) = 1.2 to 63.2 Msun uncorrected for dust absorption. The Lyman
alpha emission strength of our target galaxies is found to be determined by the
amount of dust and the kinematics of the outflowing material.Comment: 11 pages, 6 figures. A&A accepte
Satellite content and quenching of star formation in galaxy groups at z ~ 1.8
We study the properties of satellites in the environment of massive star-forming galaxies at z ~ 1.8 in the COSMOS field, using a sample of 215 galaxies on the main sequence of star formation with an average mass of ~1011Mâ. At z> 1.5, these galaxies typically trace halos of mass âł1013Mâ. We use optical-near-infrared photometry to estimate stellar masses and star formation rates (SFR) of centrals and satellites down to ~ 6 Ă 109Mâ. We stack data around 215 central galaxies to statistically detect their satellite halos, finding an average of ~3 galaxies in excess of the background density. We fit the radial profiles of satellites with simple ÎČ-models, and compare their integrated properties to model predictions. We find that the total stellar mass of satellites amounts to ~68% of the central galaxy, while spectral energy distribution modeling and far-infrared photometry consistently show their total SFR to be 25-35% of the central's rate. We also see significant variation in the specific SFR of satellites within the halo with, in particular, a sharp decrease at <100 kpc. After considering different potential explanations, we conclude that this is likely an environmental signature of the hot inner halo. This effect can be explained in the first order by a simple free-fall scenario, suggesting that these low-mass environments can shut down star formation in satellites on relatively short timescales of ~0.3 Gyr
The Evolution of Field Early-Type Galaxies in the FDF and WHDF
We explore the properties of 24 field early-type galaxies at 0.20<z<0.75 down
to M_B<=-19.30 in a sample extracted from the FORS Deep Field and the William
Herschel Deep Field. High S/N intermediate-resolution VLT spectroscopy was
complemented by deep high-resolution HST/ACS imaging and additional
ground-based multi-band photometry. To clarify the low level of star formation
(SF) detected in some galaxies, we identify the amount of AGN activity in our
sample using archive data of Chandra and XMM-Newton X-ray surveys. The B and
K-band Faber-Jackson relations and the Fundamental Plane display a moderate
evolution for the field early-type galaxies. Lenticular (S0) galaxies feature
on average a stronger luminosity evolution and bluer rest-frame colours which
can be explained that they comprise more diverse stellar populations compared
to elliptical galaxies. The evolution of the FP can be interpreted as an
average change in the dynamical mass-to-light ratio of our galaxies as <\Delta
\log{(M/L_B)}/z>=-0.74\pm0.08. The M/L evolution of these field galaxies
suggests a continuous mass assembly of field early-type galaxies during the
last 5 Gyr, that gets support by recent studies of field galaxies up to z~1.
Independent evidence for recent SF activity is provided by spectroscopic (OII
em., Hdelta) and photometric (rest-frame colors) diagnostics. Based on the
Hdelta absorption feature we detect a weak residual SF for galaxies that
accounts for 5%-10% in the total stellar mass of these galaxies. The
co-evolution in the luminosity and mass of our galaxies favours a downsizing
formation process. We find some evidence that our galaxies experienced a period
of SF quenching, possible triggered by AGN activity that is in good agreement
with recent results on both observational and theoretical side. (abridged)Comment: 26 pages, 23 figures, accepted for publication in MNRA
SL-COMP: Competition of Solvers for Separation Logic
International audienceSL-COMP aims at bringing together researchers interested on improving the state of the art of the automated deduction methods for Separation Logic (SL). The event took place twice until now and collected more than 1K problems for different fragments of SL. The input format of problems is based on the SMT-LIB format and therefore fully typed; only one new command is added to SMT-LIB's list, the command for the declaration of the heap's type. The SMT-LIB theory of SL comes with ten logics, some of them being combinations of SL with linear arithmetics. The competition's divisions are defined by the logic fragment, the kind of decision problem (satisfiability or entailment) and the presence of quantifiers. Until now, SL-COMP has been run on the StarExec platform, where the benchmark set and the binaries of participant solvers are freely available. The benchmark set is also available with the competition's documentation on a public repository in GitHub
Clustering of the AKARI NEP deep field 24<i>Ό</i>m selected galaxies
Aims. We present a method of selection of 24 ÎŒm galaxies from the AKARI north ecliptic pole (NEP) deep field down to 150 ÎŒJy and measurements of their two-point correlation function. We aim to associate various 24 ÎŒm selected galaxy populations with present day galaxies and to investigate the impact of their environment on the direction of their subsequent evolution.
Methods. We discuss using of Support Vector Machines (SVM) algorithm applied to infrared photometric data to perform star-galaxy separation, in which we achieve an accuracy higher than 80%. The photometric redshift information, obtained through the CIGALE code, is used to explore the redshift dependence of the correlation function parameter (r0) as well as the linear bias evolution. This parameter relates galaxy distribution to the one of the underlying dark matter. We connect the investigated sources to their potential local descendants through a simplified model of the clustering evolution without interactions.
Results. We observe two different populations of star-forming galaxies, at zmed ⌠0.25, zmed ⌠0.9. Measurements of total infrared luminosities (LTIR) show that the sample at zmed ⌠0.25 is composed mostly of local star-forming galaxies, while the sample at zmed ⌠0.9 is composed of luminous infrared galaxies (LIRGs) with LTIR ⌠1011.62 Lâš. We find that dark halo mass is not necessarily correlated with the LTIR: for subsamples with LTIR = 1011.15 Lâš at zmed ⌠0.7 we observe a higher clustering length (r0 = 6.21 ± 0.78 [hâ1Mpc]) than for a subsample with mean LTIR = 1011.84 Lâš at zmed ⌠1.1 (r0 = 5.86 ± 0.69 hâ1Mpc). We find that galaxies at zmed ⌠0.9 can be ancestors of present day Lâ early type galaxies, which exhibit a very high r0 ⌠8hâ1 Mpc.</p
GMASS ultradeep spectroscopy of galaxies at z~2 - VII. Sample selection and spectroscopy
The populations of both quiescent and actively star-forming galaxies at 1<z<2
are still under-represented in our spectroscopic census of galaxies throughout
the history of the Universe. In the light of galaxy formation models, however,
the evolution of galaxies at these redshifts is of pivotal importance and
merits further investigation. We therefore designed a spectroscopic observing
campaign of a sample of both massive, quiescent and star-forming galaxies at
z>1.4, called Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). To
determine redshifts and physical properties, such as metallicity, dust content,
dynamical masses, and star formation history, we performed ultra-deep
spectroscopy with the red-sensitive optical spectrograph FORS2 at the VLT. Our
sample consists of objects, within the CDFS/GOODS area, detected at 4.5 micron,
to be sensitive to stellar mass rather than star formation intensity. The
spectroscopic targets were selected with a photometric redshift constraint
(z>1.4) and magnitude constraints (B(AB)<26, I(AB)<26.5), which should ensure
that these are faint, distant, and fairly massive galaxies. We present the
sample selection, survey design, observations, data reduction, and
spectroscopic redshifts. Up to 30 hours of spectroscopy of 174 spectroscopic
targets and 70 additional objects enabled us to determine 210 redshifts, of
which 145 are at z>1.4. From the redshifts and photometry, we deduce that the
BzK selection criteria are efficient (82%) and suffer low contamination (11%).
Several papers based on the GMASS survey show its value for studies of galaxy
formation and evolution. We publicly release the redshifts and reduced spectra.
In combination with existing and on-going additional observations in
CDFS/GOODS, this data set provides a legacy for future studies of distant
galaxies.Comment: Accepted by A&A in August 2012, 45 pages, public release of reduced
spectra currently on www.mpe.mpg.de/~kurk/gmas
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