12,466 research outputs found
Non-hermitian approach to decaying ultracold bosonic systems
A paradigm model of modern atom optics is studied, strongly interacting
ultracold bosons in an optical lattice. This many-body system can be
artificially opened in a controlled manner by modern experimental techniques.
We present results based on a non-hermitian effective Hamiltonian whose quantum
spectrum is analyzed. The direct access to the spectrum of the metastable
many-body system allows us to easily identify relatively stable quantum states,
corresponding to previously predicted solitonic many-body structures
Exact numerical methods for a many-body Wannier Stark system
We present exact methods for the numerical integration of the Wannier-Stark
system in a many-body scenario including two Bloch bands. Our ab initio
approaches allow for the treatment of a few-body problem with bosonic
statistics and strong interparticle interaction. The numerical implementation
is based on the Lanczos algorithm for the diagonalization of large, but sparse
symmetric Floquet matrices. We analyze the scheme efficiency in terms of the
computational time, which is shown to scale polynomially with the size of the
system. The numerically computed eigensystem is applied to the analysis of the
Floquet Hamiltonian describing our problem. We show that this allows, for
instance, for the efficient detection and characterization of avoided crossings
and their statistical analysis. We finally compare the efficiency of our
Lanczos diagonalization for computing the temporal evolution of our many-body
system with an explicit fourth order Runge-Kutta integration. Both
implementations heavily exploit efficient matrix-vector multiplication schemes.
Our results should permit an extrapolation of the applicability of exact
methods to increasing sizes of generic many-body quantum problems with bosonic
statistics
Assessing the potential for reopening a building stone quarry : Newbigging Sandstone Quarry, Fife
Newbigging Sandstone Quarry in Fife is one of a number of former quarries in the Burntisland-
Aberdour district which exploited the pale-coloured Grange Sandstone from Lower
Carboniferous rocks. The quarry supplied building stone from the late 19th century, working
intermittently from 1914 until closure in 1937, and again when reopened in the 1970s to the
1990s. The stone was primarily used locally and to supply the nearby markets in the Scottish
Central Belt.
Historical evidence indicates that prior to sandstone extraction, the area was dominated by largescale
quarrying and mining of limestone, and substantial sandstone quarrying is likely to have
begun after the arrival of the main railway line in 1890. It is probable that removal of the
sandstone was directly associated with limestone exploitation, and that the quarried sandstone
was effectively a by-product of limestone production. Sandstone extraction was probably viable
due to the existing limestone quarry infrastructure (workforce, equipment, transportation) and the
high demand for building stone in Central Scotland in the late 19th century.
The geology within Newbigging Sandstone Quarry is dominated by thick-bedded uniform
sandstone with a wide joint spacing, well-suited for obtaining large blocks. However, a
mudstone (shale) band is likely to be present within a few metres of the principal (north) face of
the quarry, around which the sandstone bed thickness and quality is likely to decrease. The
mudstone bed forms a plane sloping at a shallow angle to the north, so that expansion of the
quarry in this direction is likely to encounter a considerable volume of poor quality stone.
Additionally, an east-west trending fault is present approximately 100 metres north of the quarry
face, which is also likely to be associated with poor quality (fractured) stone
Revisión tecnológica del aprendizaje de idiomas asistido por ordenador: una perspectiva cronológica
El presente artículo aborda la evolución y el
avance de las tecnologías del aprendizaje de
lenguas asistido por ordenador (CALL por sus
siglas en inglés, que corresponden a Computer-
Assisted Language Learning) desde una perspectiva
histórica. Esta revisión de la literatura sobre
tecnologías del aprendizaje de lenguas asistido
por ordenador comienza con la definición del
concepto de CALL y otros términos relacionados,
entre los que podemos destacar CAI, CAL,
CALI, CALICO, CALT, CAT, CBT, CMC o
CMI, para posteriormente analizar las primeras
iniciativas de implementación del aprendizaje
de lenguas asistido por ordenador en las décadas
de 1950 y 1960, avanzando posteriormente a
las décadas de las computadoras centrales y las
microcomputadoras. En última instancia, se
revisan las tecnologías emergentes en el siglo XXI,
especialmente tras la irrupción de Internet, donde
se presentan el impacto del e-learning, b-learning,
las tecnologías de la Web 2.0, las redes sociales
e incluso el aprendizaje de lenguas asistido por
robots.The main focus of this paper is on the advancement
of technologies in Computer-Assisted Language
Learning (CALL) from a historical perspective.
The review starts by defining CALL and its related
terminology, highlighting the first CALL attempts
in 1950s and 1960s, and then moving to other
decades of mainframes and microcomputers.
At the final step, emerging technologies in 21st
century will be reviewed
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