8,711 research outputs found
Theory of PbTiO3, BaTiO3, and SrTiO3 Surfaces
First-principles total-energy calculations are carried out for (001) surfaces
of the cubic perovskite ATiO3 compounds PbTiO3, BaTiO3, and SrTiO3. Both
AO-terminated and TiO2-terminated surfaces are considered, and fully-relaxed
atomic configurations are determined. In general, BaTiO3 and SrTiO3 are found
to have a rather similar behavior, while PbTiO3 is different in many respects
because of the partially covalent character of the Pb-O bonds. PbTiO3 and
BaTiO3 are ferroelectrics, and the influence of the surface upon the
ferroelectric distortions is studied for the case of a tetragonal ferroelectric
distortion parallel to the surface. The surface relaxation energies are found
to be substantial, i.e., many times larger than the bulk ferroelectric well
depth. Nevertheless, the influence of the surface upon the ferroelectric order
parameter is modest, and is qualitatively as well as quantitatively different
for the two materials. Surface energies and electronic properties are also
computed. It is found that for BaTiO3 and SrTiO3 surfaces, both AO-terminated
and TiO2-terminated surfaces can be thermodynamically stable, whereas for
PbTiO3 only the PbO surface termination is stable.Comment: 13 pages with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#bm_pbsur
New Geometric Algorithms for Fully Connected Staged Self-Assembly
We consider staged self-assembly systems, in which square-shaped tiles can be
added to bins in several stages. Within these bins, the tiles may connect to
each other, depending on the glue types of their edges. Previous work by
Demaine et al. showed that a relatively small number of tile types suffices to
produce arbitrary shapes in this model. However, these constructions were only
based on a spanning tree of the geometric shape, so they did not produce full
connectivity of the underlying grid graph in the case of shapes with holes;
designing fully connected assemblies with a polylogarithmic number of stages
was left as a major open problem. We resolve this challenge by presenting new
systems for staged assembly that produce fully connected polyominoes in O(log^2
n) stages, for various scale factors and temperature {\tau} = 2 as well as
{\tau} = 1. Our constructions work even for shapes with holes and uses only a
constant number of glues and tiles. Moreover, the underlying approach is more
geometric in nature, implying that it promised to be more feasible for shapes
with compact geometric description.Comment: 21 pages, 14 figures; full version of conference paper in DNA2
An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region
Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201
Multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean Region [Poster]
Poster presented at Tropentag 2013. International Research on Food Security, Natural Resource Management and Rural Development. "Agricultural development within the rural-urban continuum". Stuttgart-Hohenheim (Germany), Sep 17-19 2013
An approach to the multidimensional assessment of food security and environmental sustainability: a vulnerability framework for the Mediterranean region
Poster presented at First International Conference on Global Food Security. Noordwijkerhout (The Netherlands), 29 Sep - 2 Oct 201
How Much Water Do Households Require?
What is the basic water requirement per month of a Philippine household consisting of six members? This study provides an estimate based on various household activities dovetailed to local practices and situation which may serve as a valuable input in water sector planning, water supply allocation, and water pricing determination.water sector, water demand
The very faint hard state of the persistent neutron star X-ray binary SLX 1737-282 near the Galactic centre
We report on a detailed study of the spectral and temporal properties of the
neutron star low mass X-ray binary SLX 1737-282, which is located only ~1degr
away from Sgr A. The system is expected to have a short orbital period, even
within the ultra-compact regime, given its persistent nature at low X-ray
luminosities and the long duration thermonuclear burst that it has displayed.
We have analysed a Suzaku (18 ks) observation and an XMM-Newton (39 ks)
observation taken 7 years apart. We infer (0.5-10 keV) X-ray luminosities in
the range 3-6 x10^35erg s-1, in agreement with previous findings. The spectra
are well described by a relatively cool (kTbb = 0.5 keV) black body component
plus a Comptonized emission component with {\Gamma} ~1.5-1.7. These values are
consistent with the source being in a faint hard state, as confirmed by the ~
20 per cent fractional root mean square amplitude of the fast variability (0.1
- 7 Hz) inferred from the XMM-Newton data. The electron temperature of the
corona is >7 keV for the Suzaku observation, but it is measured to be as low as
~2 keV in the XMM-Newton data at higher flux. The latter is significantly lower
than expected for systems in the hard state. We searched for X-ray pulsations
and imposed an upper limit to their semi-amplitude of 2 per cent (0.001 - 7
Hz). Finally, we investigated the origin of the low frequency variability
emission present in the XMM-Newton data and ruled out an absorption dip origin.
This constraint the orbital inclination of the system to 65 degr unless the
orbital period is longer than 11 hr (i.e. the length of the XMM-Newton
observation).Comment: 7 pages, 4 figures, 1 table. Accepted for publication in MNRA
South–South student mobility: International students from Portuguese-speaking Africa in Brazil
As a complex and multi-faceted phenomenon, student mobility involves diverse actors, interests and rationalities. With the globalization of education, universities and other higher education providers have implemented strategies to recruit and attract international students, not least to increase their revenues and levels of internationalization (Findlay et al. 2017). Likewise, destination countries have acknowledged the advantages of hosting international students: financial benefits, an increase in the skilled worker pool and improvements in diplomatic relations (Riaño et al. 2018). Origin countries meanwhile identify student mobility as a means through which talented individuals can become qualified via moving to countries with well-developed higher education system (Findlay 2010). And students themselves, and their families, recognize the potential impact of an international diploma on employability, making them instrumental in establishing educational mobility imperatives at tertiary level (Alberts and Hazen 2005; Holloway et al. 2012).info:eu-repo/semantics/acceptedVersio
Portuguese migrations to South America after world war II: Extending citizenship abroad
info:eu-repo/semantics/publishedVersio
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