900 research outputs found
Robust Simulation of a TaO Memristor Model
This work presents a continuous and differentiable approximation of a Tantalum oxide memristor model which is suited for robust numerical simulations in software. The original model was recently developed at Hewlett Packard labs on the basis of experiments carried out on a memristor manufactured in house. The Hewlett Packard model of the nano-scale device is accurate and may be taken as reference for a deep investigation of the capabilities of the memristor based on Tantalum oxide. However, the model contains discontinuous and piecewise differentiable functions respectively in state equation and Ohm's based law. Numerical integration of the differential algebraic equation set may be significantly facilitated under substitution of these functions with appropriate continuous and differentiable approximations. A detailed investigation of classes of possible continuous and differentiable kernels for the approximation of the discontinuous and piecewise differentiable functions in the original model led to the choice of near optimal candidates. The resulting continuous and differentiable DAE set captures accurately the dynamics of the original model, delivers well-behaved numerical solutions in software, and may be integrated into a commercially-available circuit simulator
Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream : Combining hydraulic and tracer methods
Acknowledgements. We would like to thank members of the Northern Rivers Institute, Aberdeen University, for helpful discussions of data. We also thank Lars Rasmussen, Jolanta Kazmierczak and Charlotte Ditlevsen for help in the field. This study is part of the Hydrology Observatory, HOBE (http://www.hobe.dk), funded by the Villum Foundation and was as well funded by the Aarhus University Research Foundation.Peer reviewedPublisher PD
On identifying the neutron star that was born in the supernova that placed 60Fe onto the Earth
Recently, 60Fe was found in the Earth crust formed in a nearby recent
supernova (SN). If the distance to the SN and mass of the progenitor of that SN
was known, then one could constrain SN models. Knowing the positions, proper
motions, and distances of dozens of young nearby neutron stars, we can
determine their past flight paths and possible kinematic origin. Once the birth
place of a neutron star in a SN is found, we would have determined the distance
of the SN and the mass of the SN progenitor star.Comment: refereed NPA5 conference proceedings, in pres
Neutron stars from young nearby associations the origin of RXJ1605.3+3249
Many neutron stars (NSs) and runaway stars apparently come from the same
regions on the sky. This suggests that they share the same birth places, namely
associations and clusters of young massive stars. To identify NS birth places,
we attempt to and NS-runaway pairs that could be former companions that were
disrupted in a supernova (SN). The remains of recent (<few Myr) nearby (< 150
pc) SNe should still be identifiable by observing the emission of rare
radioisotopes such as 26Al and 60Fe that can also be used as additional
indicators to confirm a possible SN event. We investigated the origin of the
isolated NS RXJ1605.3+3249 and found that it was probably born ~100 pc far from
Earth 0.45 Myr ago in the extended Corona-Australis or Octans associations, or
in Sco OB4 ~1 kpc 3.5 Myr ago. A SN in Octans is supported by the
identification of one to two possible former companions the runaway stars HIP
68228 and HIP 89394, as well as the appearance of a feature in the gamma ray
emission from 26Al decay at the predicted SN place. Both, the progenitor masses
estimated by comparison with theoretical 26Al yields as well as derived from
the life time of the progenitor star, are found to be ~11MSun.Comment: accepted for publication in PASA, special volume Astronomy with
Radioactivities; 10 pages, 4 figures, 5 table
Determination and ranking of target areas in catchments for the implementation of nitrogen reduction measures
International audienceThe implementation of the EU Water Framework Directive (EU-WFD) forms the background of the WAgriCo-project (Water Resources Management in Cooperation with Agriculture). WagriCo concentrates on the development of nitrogen management options adapted to hydrological and agro-economic site conditions and at demonstrating new participation approaches and technologies suitable for setting-up programmes of measures. The article outlines the conceptual model approach and its application in the pilot region "Große Aue" (Northern Germany). Furthermore the process of delineating priority areas is described, which act as spatial targets for the adaptation of regionally differentiated nutrient reduction measures
The origin of the Guitar pulsar
Among a sample of 140 OB associations and clusters, we want to identify
probable parent associations for the Guitar pulsar (PSR B2224+65) which would
then also constrain its age. For this purpose, we are using an Euler-Cauchy
technique treating the vertical component of the galactic potential to
calculate the trajectories of the pulsar and each association into the past. To
include errors we use Monte-Carlo simulations varying the initial parameters
within their error intervals. The whole range of possible pulsar radial
velocities is taken into account during the simulations. We find that the
Guitar pulsar most probably originated from the Cygnus OB3 association ~0.8 Myr
ago inferring a current radial velocity of v_r~-30 km/s, consistent with the
inclination of its bow shock.Comment: 4 pages, 1 figure, 3 table
Real time control of curved laser welding processes by cellular neural networks (CNN): first results
In the last decades the laser beam welding (LBW) has outclassed older welding
techniques in the industrial scenario. Despite the improvement in welding
technology, sophisticated methods of fault detection are not commonly used in
commercially available equipments yet. A recent analysis of process images
have revealed the possibility to build up a real time closed loop control
system. By the use of image based quality features, a feedback signal can be
provided to maintain the process in the desired state. The development of the
presented visual control system has been focused on the adjustment of the
laser power according to the detection of the so called full penetration
hole. Due to the high dynamics of the laser welding, a fast real time image
processing with controlling rates in the multi kilo Hertz range is necessary
to have a robust feedback control. In this paper an algorithm for the real
time control of welding processes is described. It has been implemented on
the Eye-RIS v1.2, a visual system which mounts a cellular structure. By
applying this algorithm in real time applications, controlling rates of about
7 kHz can be reached. In the following some real time control results are
also described
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