15,880 research outputs found
A Fourier-Mukai Transform for Stable Bundles on K3 Surfaces
We define a Fourier-Mukai transform for sheaves on K3 surfaces over \C, and
show that it maps polystable bundles to polystable ones. The role of ``dual''
variety to the given K3 surface is here played by a suitable component
of the moduli space of stable sheaves on . For a wide class of K3
surfaces can be chosen to be isomorphic to ; then the Fourier-Mukai
transform is invertible, and the image of a zero-degree stable bundle is
stable and has the same Euler characteristic as .Comment: Revised version, 15 pages AMSTeX with AMSppt.sty v. 2.1
The Orion constellation as an installation - An innovative three dimensional teaching and learning environment
Visualising the three dimensional distribution of stars within a
constellation is highly challenging for both students and educators, but when
carried out in an interactive collaborative way it can create an ideal
environment to explore common misconceptions about size and scale within
astronomy. We present how the common table top activities based upon the Orion
constellation miss out on this opportunity. Transformed into a walk-through
Orion installation that includes the position of our Solar system, it allows
the students to fully immerse themselves within the model and experience
parallax. It enables participants to explore within the installation many other
aspects of astronomy relating to sky culture, stellar evolution, and stellar
timescales establishing an innovative learning and teaching environment.Comment: 2 pages, submitted to The Physics Teacher - Colum
Plankton blooms in vortices: The role of biological and hydrodynamic time scales
We study the interplay of hydrodynamic mesoscale structures and the growth of
plankton in the wake of an island, and its interaction with a coastal
upwelling. Our focus is on a mechanism for the emergence of localized plankton
blooms in vortices. Using a coupled system of a kinematic flow mimicking the
mesoscale structures behind the island and a simple three component model for
the marine ecosystem, we show that the long residence times of nutrients and
plankton in the vicinity of the island and the confinement of plankton within
vortices are key factors for the appearance of localized plankton bloomsComment: 29 pages, 9 figure
Biological activity in the wake of an island close to a coastal upwelling
Hydrodynamic forcing plays an important role in shaping the dynamics of
marine organisms, in particular of plankton. In this work we study the
planktonic biological activity in the wake of an island which is close to an
upwelling region. Our research is based on numerical analysis of a kinematic
flow mimicking the hydrodynamics in the wake, coupled to a three-component
plankton model. Depending on model parameters different phenomena are
described: a) The lack of transport of nutrients and plankton across the wake,
so that the influence of upwelling on primary production on the other side of
the wake is blocked. b) For sufficiently high vorticity, the role of the wake
in facilitating this transport and leading to an enhancement of primary
production. Finally c) we show that under certain conditions the interplay
between wake structures and biological growth leads to plankton blooms inside
mesoscale hydrodynamic vortices that act as incubators of primary production.Comment: 42 pages, 9 figure
Fractional Newton-Raphson Method Accelerated with Aitken's Method
The Newton-Raphson (N-R) method is characterized by the fact that generating
a divergent sequence can lead to the creation of a fractal, on the other hand
the order of the fractional derivatives seems to be closely related to the
fractal dimension, based on the above, a method was developed that makes use of
the N-R method and the fractional derivative of Riemann-Liouville (R-L) that
has been named as the Fractional Newton-Raphson (F N-R) method.
In the following work we present a way to obtain the convergence of the F N-R
method, which seems to be at least linearly convergent for the case where the
order of the derivative is different from one, a simplified way to
construct the fractional derivative and fractional integral operators of R-L is
presented, an introduction to the Aitken's method is made and it is explained
why it has the capacity to accelerate the convergence of iterative methods to
finally present the results that were obtained when implementing the Aitken's
method in F N-R method.Comment: Newton-Raphson Method, Fractional Calculus, Fractional Derivative of
Riemann-Liouville, Method of Aitken. arXiv admin note: substantial text
overlap with arXiv:1710.0763
Expressive touch: Control of robot emotional expression by touch
In this paper, we present a work on control of robot emotional expression using touch sensing. A tactile Bayesian framework is proposed for recognition of different types of touch gestures. We include a sequential analysis method that, based on the accumulation of evidence from tactile interaction, allows to achieve accurate results for recognition of touch. Input data to our method is obtained from touch sensing, which is an important modality for social robotics. Here, emotion in the robot platform are represented by facial expressions, that are handled by a developed control architecture. We validate our method with experiments on tactile interaction in simulated and real robot environments. Results demonstrate that our proposed method is suitable and accurate for control of robot emotions through interaction with humans using touch sensing. Furthermore, it is demonstrated the potential that touch provides as a non-verbal communication channel for the development of social robots capable to interact with humans
Adaptive perception: learning from sensory predictions to extract object shape with a biomimetic fingertip
In this work, we present an adaptive perception method to improve the performance in accuracy and speed of a tactile exploration task. This work extends our previous studies on sensorimotor control strategies for active tactile perception in robotics. First, we present the active Bayesian perception method to actively reposition a robot to accumulate evidence from better locations to reduce uncertainty. Second, we describe the adaptive perception method that, based on a forward model and a predicted information gain approach, allows to the robot to analyse `what would have happened' if a different decision `would have been made' at previous decision time. This approach permits to adapt the active Bayesian perception process to improve the performance in accuracy and reaction time of an exploration task. Our methods are validated with a contour following exploratory procedure with a touch sensor. The results show that the adaptive perception method allows the robot to make sensory predictions and autonomously adapt, improving the performance of the exploration task
Collins functions for pions from SIDIS and new e+e- data: a first glance at their transverse momentum dependence
New data from Belle and BaBar Collaborations on azimuthal asymmetries,
measured in e+e- annihilations into pion pairs at Q^2=112 GeV^2, allow to take
the first, direct glance at the transverse momentum dependence of the Collins
functions, in addition to their z dependence. These data, together with
available Semi-Inclusive Deep Inelastic Scattering (SIDIS) data on the Collins
asymmetry, are simultaneously analysed in the framework of the generalised
parton model assuming two alternative Q^2 evolution schemes and exploiting two
different parameterisations for the Collins functions. The corresponding
results for the transversity distributions are presented. Analogous data, newly
released by the BESIII Collaboration, on e+e- annihilations into pion pairs at
the lower Q^2 of 13 GeV^2, offer the possibility to explore the sensitivity of
these azimuthal correlations on transverse momentum dependent evolution
effects.Comment: 20 pages, 15 figures, 4 table
HERA-B Framework for Online Calibration and Alignment
This paper describes the architecture and implementation of the HERA-B
framework for online calibration and alignment. At HERA-B the performance of
all trigger levels, including the online reconstruction, strongly depends on
using the appropriate calibration and alignment constants, which might change
during data taking. A system to monitor, recompute and distribute those
constants to online processes has been integrated in the data acquisition and
trigger systems.Comment: Submitted to NIM A. 4 figures, 15 page
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